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Temperature Handbook Contents A - Z
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Technical Reference Section
Table of Contents
Z-3
Temperature Measurement
Z-4
Thermocouples
Z-16
Probe Response Times
Z-51
Resistance Temperature Measurement
Z-53
Infrared Temperature Measurement
Z-57
Cryogenic Temperature Measurement
Z-94
Humidity & Dewpoint
Z-100
Electrical Noise Reduction
Z-104
Temperature Control
Z-110
Safety
Z-128
Data Storage and Transmission
Z-149
ITS-90
Z-158
Standards
Z-194
Non-Electric Temperature Measurement
Z-197
Thermocouple Reference Data
Z-198
RTD & Thermistor Reference Data
Z-250
Conversion Charts
Z-259
Z Section Table of Contents Technical Reference Section......Z-2 Z Section Table of Contents .......Z-3 Frequently Asked Temperature Questions............Z-4 Temperature Measurement and Control Glossary................Z-5 Practical Guidelines for Temperature Measurement....Z-13 Physical Properties of Thermoelement Materials.......Z-16 OMEGACLAD® Sheath Selection Guide ......................Z-17 Introduction to Practical Temperature Measurements ...Z-19 Using Thermocouples.............Z-21 Using RTD’s............................Z-33 Using Thermistors ..................Z-36 Nicrosil/Nisil Type N Thermocouple ........................Z-41 The Choice of Sheathing for Mineral Insulated Thermocouples.......................Z-45 Temperature Properties of Some Metals, Elements and Compounds .....................Z-48 Thermocouple Properties .........Z-49 Metal Sheathed and Exposed Thermocouple Response Times in Air ............................Z-51 Metal Sheathed and Exposed Thermocouple Response Times in Water .......................Z-52 OMEGA® Interchangeable Thermistor Applications..........Z-53 Resistance Elements and RTD’s ..............................Z-54 Introduction to Infrared Pyrometers .............................Z-57 Principles of Infrared Thermometry ..........................Z-59 Infrared Temperature Measurement: Theory and Application.......................Z-63 Noncontact Temperature Measurement: Theory and Application.......................Z-67 Fiber Optics ..............................Z-70 Handheld Infrared Thermometers for All Applications .......................Z-74 Principles of Infrared Thermocouples.......................Z-76 Microcomputer-Based Infrared Temperature Transducers......Z-81 Infrared Thermocouples Extended Temperature Ranges ...................................Z-84
Infrared Window Data...............Z-86 IR Quick Help ...........................Z-87 Table of Total Infrared Emissivity ...............................Z-88 Cryogenic Temperature Sensors: CY7 Series Silicon Diodes .....Z-90 Resolution and Accuracy of Cryogenic Temperature Measurements........................Z-94 Heat Wave: A National Problem ..............Z-100 Dewpoint.................................Z-102 Equilibrium Relative Humidity: Saturated Salt Solutions.......Z-103 Two-Wire Transmitters For Temperature Applications ..........................Z-104 How to Use Ferrite Cores With Instrumentation ............Z-105 “Electromagnetic Compatibility” and CE Conformity ...............Z-106 Low Noise Thermocouple System .................................Z-108 Introduction to Temperature Controllers and Selection Considerations .....................Z-110 Temperature Control: Tuning a PID Controller........Z-115 Controller Operation ...............Z-118 SSR Thermal Considerations..Z-119 OMEGA PT41 Precision Clock/Timer/Controller Functions..............................Z-122 Solid State Relays ..................Z-124 Intrinsic Safety ........................Z-128 Intrinsic Safety Circuit Design ..................................Z-131 Selecting a Recorder ..............Z-149 Overview of IEEE-488 ............Z-151 ASCII Code Values and Hexadecimal Conversion Chart .................Z-154 The RS-232 Standard.............Z-157 Guidelines for Realizing the ITS-90...................................Z-158 The International Temperature Scale of 1990 .......................Z-186 International Standard Codes ...................................Z-194 Application Notes: Low-Cost Non-Electric Temperature Gauges ...........Z-197 ITS-90 Thermocouple Direct and Inverse Polynomials ......Z-198 Tungsten-Rhenium Thermocouples: Calibration Equivalents.........Z-202 Z-3
Thermocouple Reference Tables Revised to ITS-90 Type J, Deg. C .....................Z-203 Type K, Deg. C.....................Z-204 Type E, Deg. C.....................Z-207 Type S, Deg. C.....................Z-208 Type R, Deg. C.....................Z-210 Type B, Deg. C.....................Z-212 Type N, Deg. C.....................Z-214 Type J, Deg. F......................Z-216 Type K, Deg. F .....................Z-218 Type E, Deg. F .....................Z-221 Type T, Deg. F .....................Z-225 Type S, Deg. F .....................Z-225 Type R, Deg. F .....................Z-228 Type B, Deg. F .....................Z-231 Type N, Deg. F .....................Z-237 Type C, Deg. C.....................Z-239 Type C, Deg. F .....................Z-241 Tungsten and Tungsten/ Rhenium: Thermocouple Tables...........Z-246 CHROMEGA® vs. Gold-0.07 Atomic Percent Iron Thermocouple Table of Temp. vs.Thermoelectric Voltage .................................Z-247 Space for Transmitters in Probe Assembly Heads ....Z-249 Platinum Resistance Temp. Detector: Interchangability Tolerance Chart.....................................Z-250 ITS-90 Polynomial for RTD Temperature vs. Resistance ..Z-251 RTD Temp. vs. Resistance Table For European Curve, Alpha = .00385 .....................Z-252 RTD Temp. vs. Resistance Table For American Curve, Alpha = .00392 .....................Z-255 Thermistor Resistance vs. Temp............Z-256 Resistance vs. Temperature for Series “700” Linear Thermistor Pairs ........Z-258 Temperature Conversion Chart Between C and F........Z-259 Conversion Factors for Physical Units of Measure....Z-261 Ohm’s Law, Summary ............Z-263 Conversion Factors for Electrical Units of Measure...Z-264
Frequently Asked Questions Q. How many feet of T/C wire can I run? A. For a specific instrument, check its specifications to see if there are any limits to the input impedance. However as a rule of thumb, limit the resistance to 100 Ohms resistance maximum, and this depends on the gage of the wire; the larger the diameter, the less resistance/foot, the longer the run can be. However, if the environment is electrically noisy, then a transmitter may be required which transmits a 4-20 mA signal that can be run longer distances and is more resistant to noise. Q. Should I use a grounded or ungrounded probe? A. It depends on the instrumentation. If there is any chance that there may be a reference to ground (common in controllers with nonisolated inputs), then an ungrounded probe is required. If the instrument is a handheld meter, then a grounded probe can almost always be used. Q. What size relay do I need to control my heaters? A. This must be calculated from known parameters. Take the total wattage of heaters and divide this value in watts by the voltage rating of the heaters in volts. The answer will be in amperes, and solid state and mechanical relays are rated by “current rating” in amperes. Q. Can I send my 4-20 mA control output to a chart recorder to monitor a process input? A. No. A control output is designed to control a valve or some equivalent control device. If you need to send an analog signal to a recording device, then choose a controller that has a “retransmission or recorder output” option. Q. Can I split my one T/C signal to two separate instruments? A. No. The T/C signal is a very lowlevel millivolt signal, and should only be connected to one device. Splitting to two devices may result in bad readings or loss of signal. The solution is to use a “dual” T/C probe, or convert one T/C output to a 4-20 mA signal by using a transmitter or signal conditioner; then the new signal can be sent to more than one instrument. Q. What are the accuracies and temperature ranges of the various thermocouples?
A. They are summarized in the tables on the first few pages of Section H. It is important to know that both accuracy and range depend on such things as the thermocouple alloys, the temperature being measured, the construction of the sensor, the material of the sheath, the media being measured, the state of the media (liquid, solid, or gas) and the diameter of either the thermocouple wire (if it is exposed) or the sheath diameter (if the thermocouple wire is not exposed but is sheathed). Q. Why can't I use ANY multimeter for measuring temperature with thermocouples? What errors will result if I don't use a thermocouple temperature meter? A. The magnitude of the thermoelectric voltage depends on the closed (sensing) end as well as the open (measuring) end of the particular thermocouple alloy leads. Temperature sensing instruments that use thermocouples take into account the temperature of the measuring end to determine the temperature at the sensing end. Most millivoltmeters do not have this capability, nor do they have the ability to do non-linear scaling to convert a millivoltage measurement to a temperature value. It is possible to use lookup tables to correct a particular millivoltage reading and calculate the temperature being sensed. However, the correction value needs to be continuously recalculated, as it is generally not constant over time. Small changes in temperature at the measuring instrument and the sensing end will change the correction value. Q. How can I choose between thermocouples, resistance temperature detectors (RTD’s), thermistors and infrared devices when measuring temperature? A. You have to consider the characteristics and costs of the various sensors as well as the available instrumentation. In addition: THERMOCOUPLES generally can measure temperatures over wide temperature ranges, inexpensively, and are very rugged, but they are not as accurate or stable as RTD’s and thermistors. RTD’s are stable and have a fairly wide temperature range, but are not as rugged and inexpensive as thermocouples. Since they require the use of
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electric current to make measurements, RTD’s are subject to inaccuracies from self-heating. THERMISTORS tend to be more accurate than RTD’s or thermocouples, but they have a much more limited temperature range. They are also subject to selfheating. INFRARED SENSORS can be used to measure temperatures higher than any of the other devices and do so without direct contact with the surfaces being measured. However, they are generally not as accurate and are sensitive to surface radiation efficiency (or more precisely, surface emissivity). Using fiber optic cables, they can measure surfaces that are not within a direct line of sight. Q. What are the two most often overlooked considerations in selecting an infrared temperature measuring device? A. The surface being measured must fill the field of view, and the surface emissivity must be taken into account. Q. What are the best ways of overcoming electrical noise problems? A. 1) Use low noise, shielded leads, connectors and probes. 2) Use instruments and connectors that suppress EMI and RF radiation. 3) Consider using analog signal transmitters, especially current transmitters. 4) Evaluate the possibility of using digitized signals. Q. If a part is moving, can I still measure temperature? A. Yes. Use infrared devices or direct contacting sensors plus a slip ring assembly. Q. Can a two-color infrared system be used to measure low emissivity surfaces? A. Only if at high temperature, say, above 700°C (1300°F). Q. What error will result if the spot size of the infrared pyrometer is larger than the target size? A. It would be indeterminate. The value would be a weighted average that wouldn’t necessarily be repeatable. Q. What readout should be used with the OS36, OS37 and OS38 units? A. Using the DP5000, BS6000, or the HH-200 would be best.
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Presenting . . . OMEGA’s Temperature Measurement and Control Glossary A comprehensive glossary of terms used in the field of temperature measurement and control. A helpful reference tool for scientists, engineers, and technicians!
Absolute Zero: Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin, calculated to be –273.15°C or –459.67°F. AC: Alternating current; an electric current that reverses its direction at regularly recurring intervals. Accuracy: The closeness of an indication or reading of a measurement device to the actual value of the quantity being measured. Usually expressed as ± percent of full scale output or reading. Adaptor: A mechanism or device for attaching non-mating parts. ADC: Analog-to-Digital Converter: an electronic device which converts analog signals to an equivalent digital form, in either a binary code or a binary-coded decimal code. When used for dynamic waveforms, the sampling rate must be high to prevent aliasing errors from occurring. Address: The label or number identifying the memory location where a unit of information is stored. Aliasing: If the sample rate of a function (fs) is less than two times the highest frequency value of the function, the frequency is ambiguously presented. The frequencies above (fs/2) will be folded back into the lower frequencies producing erroneous data. Alloy 11: A compensating alloy used in conjunction with pure copper as the negative leg to form extension wire for platinum—platinumrhodium thermocouples Types R and S. Alloy 200/226: The combination of compensating alloys used with tungsten vs. tungsten/26%-rhenium thermocouples as extension cable for applications under 200°C. Alloy 203/225: The combination of compensating alloys used with tungsten/3%-rhenium vs. tungsten/25%-rhenium thermocouples as extension cable for applications under 200°C. Alloy 405/426: The combination of compensating alloys used with tungsten/5%-rhenium vs. tungsten/26%-rhenium thermocouples as extension cable for applications under 870°C. ALOMEGA®: An aluminum nickel alloy used in the negative leg of a type K thermocouple (registered trademark of OMEGA ENGINEERING, INC.). Alphanumeric: A character set that contains both letters and digits. Alumel: An aluminum nickel alloy used in the negative leg of a Type K thermocouple (Trade name of Hoskins Manufacturing Company). Ambient Compensation: The design of an instrument such that changes in ambient temperature do not affect the readings of the instrument. Ambient Conditions: The conditions around the transducer (pressure, temperature, etc.). Ambient Temperature: The average or mean temperature of the surrounding air which comes in contact with the equipment and instruments under test. Ammeter: An instrument used to measure current. Ampere (amp): A unit used to define the rate of flow of electricity (current) in a circuit; units are one coulomb (6.25 x 108 electrons) per second. Amplifier: A device which draws power from a source other than the input signal and which produces as an output an enlarged reproduction of the essential features of its input. Amplitude: A measurement of the distance from the highest to the lowest excursion of motion, as in the case of mechanical body in oscillation or the peak-to-peak swing of an electrical waveform. Analog Output: A voltage or current signal that is a continuous function of the measured parameter. Analog-to-Digital Converter (A/D or ADC): A device or circuit that outputs a binary number corresponding to an analog signal level at the input. Angstrom: Ten to the minus tenth (10–10) meters or one millimicron, a unit used to define the wavelength of light. Designated by the symbol Å. ANSI: American National Standards Institute. Anti-Reset Windup: This is a feature in a three-mode PID controller which prevents the integral (auto reset) circuit from functioning when the temperature is outside the proportional band. Application Program: A computer program that accomplishes specific tasks, such as word processing.
ASCII: American Standard Code for Information Interchange. A seven or eight bit code used to represent alphanumeric characters. It is the standard code used for communications between data processing systems and associated equipment. ASME: American Society of Mechanical Engineers. Assembler: A program that translates assembly language instructions into machine language instructions. ASTM: American Society for Testing and Materials. Asynchronous: A communication method where data is sent when it is ready without being referenced to a timing clock, rather than waiting until the receiver signals that it is ready to receive. ATC: Automatic temperature compensation. Auto-Zero: An automatic internal correction for offsets and/or drift at zero voltage input. Automatic Reset: 1. A feature on a limit controller that automatically resets the controller when the controlled temperature returns to within the limit bandwidth set. 2. The integral function on a PID controller which adjusts the proportional bandwidth with respect to the set point to compensate for droop in the circuit, i.e., adjusts the controlled temperature to a set point after the system stabilizes. AWG: American Wire Gage. Background Noise: The total noise floor from all sources of interference in a measurement system, independent of the presence of a data signal. Backup: A system, device, file or facility that can be used as an alternative in case of a malfunction or loss of data. Bandwidth: A symmetrical region around the set point in which proportional control occurs. Basic: A high-level programming language designed at Dartmouth College as a learning tool. Acronym for Beginner’s All-purpose Symbolic Instruction Code. Baud: A unit of data transmission speed equal to the number of bits (or signal events) per second; 300 baud = 300 bits per second. BCD, Buffered: Binary-coded decimal output with output drivers, to increase line-drive capability. BCD, Parallel: A digital data output format where every decimal digit is represented by binary signals on four lines and all digits are presented in parallel. The total number of lines is 4 times the number of decimal digits. BCD, Serial: A digital data output format where every decimal digit is represented by binary signals on four lines and up to five decimal digits are presented sequentially. The total number of lines is four data lines plus one strobe line per digit. BCD, Three-State: An implementation of parallel BCD, which has 0, 1 and high-impedance output states. The high-impedance state is used when the BCD output is not addressed in parallel connect applications. Beryllia: BeO (Beryllium Oxide), a high-temperature mineral insulation material; toxic when in powder form. BIAS Current: A very low-level DC current generated by a panel meter and superimposed on a signal. This current may introduce a measurable offset across a very high source impedance. Binary Coded Decimal (BCD): The representation of a decimal number (base 10, 0 through 9) by means of a 4-bit binary nibble. Binary: Refers to the base 2 numbering system, in which the only allowable digits are 0 and 1. Pertaining to a condition that has only two possible values or states. Bipolar: The ability of a panel meter to display both positive and negative readings. Bit: Acronym for binary digit. The smallest unit of computer information, it is either 0 or 1. Blackbody: A theoretical object that radiates the maximum amount of energy at a given temperature, and absorbs all the energy incident upon it. A blackbody is not necessarily black. (The name blackbody was chosen because the color black is defined as the total absorption of light energy.) BNC: A quick disconnect electrical connector used to interconnect and/or terminate coaxial cables.
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Temperature Measurement and Control Glossary Boiling Point: The temperature at which a substance in the liquid phase transforms to the gaseous phase; commonly refers to the boiling point of water which is 100°C (212°F) at sea level. BPS: Bits per second. Breakdown Voltage Rating: The dc or ac voltage which can be applied across insulation portions of a transducer without arcing or conduction above a specific current value. BTU: British thermal unit. The quantity of thermal energy required to raise one pound of water at its maximum density, 1 degree F. One BTU is equivalent to .293 watt hours, or 252 calories. One kilowatt hour is equivalent to 3412 BTU. Bulb (Liquid-in-Glass Thermometer): The area at the tip of a liquid-inglass thermometer containing the liquid reservoir. Burn-In: A long term screening test (either vibration, temperature or combined test) that is effective in weeding out premature failures because it simulates actual or worst case operation of the device, accelerated through a time, power, and temperature relationship. Burst Proportioning: A fast-cycling output form on a time proportioning controller (typically adjustable from 2 to 4 seconds) used in conjunction with a solid state relay to prolong the life of heaters by minimizing thermal stress. Bus: Parallel lines used to transfer signals between devices or components. Computers are often described by their bus structure (i.e., S-100, IBM PC). Byte: The representation of a character in binary. Eight bits.
CMV (Common-Mode Voltage): The AC or DC voltage which is tolerable between signal and ground. One type of CMV is specified between SIG LO and PWR GND. In differential meters, a second type of CMV is specified between SIG HI or LO and ANA GND (METER GND). Color Code: The ANSI established color code for thermocouple wires in the negative lead is always red. Color Code for base metal thermocouples is yellow for Type K, black for Type J, purple for Type E and blue for Type T. Common Mode: The output form or type of control action used by a temperature controller to control temperature, i.e. on/off, time proportioning, PID. Common-Mode Rejection Ratio: The ability of an instrument to reject interference from a common voltage at it’s input terminals with relation to ground, usually expressed in dB (decibels). Communication: Transmission and reception of data among data processing equipment and related peripherals. Compensated Connector: A connector made of thermocouple alloys used to connect thermocouple probes and wires. Compensating Alloys: Alloys used to connect thermocouples to instrumentation. These alloys are selected to have similar thermal electric properties as the thermocouple alloys (however, only over a very limited temperature range). Compensating Loop: Lead wire resistance compensation for RTD elements where an extra length of wire is run from the instrument to the RTD and back to the instrument, with no connection to the RTD. Compensation: An addition of specific materials or devices to counteract a known error. Compiler: A program that translates a high-level language, such as Basic, into machine language. Conductance: The measure of the ability of a solution to carry an electrical current. (See Equivalent Conductance) Conduction: The conveying of electrical energy or heat through or by means of a conductor. Confidence Level: The range (with a specified value of uncertainty, usually expressed in percent) within which the true value of a measured quantity exists. Conformity Error: For thermocouples and RTD’s, the difference between the actual reading and the temperature shown in published tables for a specific voltage input. Connection Head: An enclosure attached to the end of a thermocouple which can be cast iron, aluminum or plastic within which the electrical connections are made. Constantan: A copper-nickel alloy used as the negative lead in Type E, Type J, and Type T thermocouples. Continuous Spectrum: A frequency spectrum that is characterized by non-periodic data. The spectrum is continuous in the frequency domain and is characterized by an infinite number of frequency components. Control Character: A character whose occurrence in a particular context starts, modifies or stops an operation that affects the recording, processing, transmission or interpretation of data. Control Mode: The output form or type of control action used by a temperature controller to control temperature, i.e., on/off, time proportioning, PID. Control Point: The temperature at which a system is to be maintained. Convection: 1. The circulatory motion that occurs in a fluid at a nonuniform temperature owing to the variation of its density and the action of gravity. 2. The transfer of heat by this automatic circulation of fluid. Counts: The number of time intervals counted by the dual-slope A/D converter and displayed as the reading of the panel meter, before addition of the decimal point. CPS: Cycles per second; the rate or number of periodic events in one second, expressed in Hertz (Hz). CPU: Central processing unit. The part of the computer that contains the circuits that control and perform the execution of computer instructions. Critical Damping: Critical damping is the smallest amount of damping at which a given system is able to respond to a step function without overshoot. Cryogenics: Measurement of temperature at extremely low values, i.e., below –200°C. CSA: Canadian Standards Administration. Current Proportioning: An output form of a temperature controller which provides a current proportional to the amount of control required. Normally, a 4 to 20 milliamp current proportioning band.
Calender-van Dusen Equation: An equation that defines the resistance-temperature value of any pure metal that takes the form of (RT = RO) (1 + AT + BT2) for values between the ice point (0°C) and the freezing point of antimony (630.7°C) and the form RT = RO [1 + AT + BT2 + C (T–100)T2] between the oxygen point (–183.0°C) and the ice point (0°C). Calibration: The process of adjusting an instrument or compiling a deviation chart so that its reading can be correlated to the actual value being measured. Calorie: The quantity of thermal energy required to raise one gram of water 1°C at 15°C. Cavitation: The boiling of a liquid caused by a decrease in pressure rather than an increase in temperature. Celsius (Centigrade): A temperature scale defined by 0°C at the ice point and 100°C at the boiling point of water at sea level. Ceramic Insulation: High-temperature compositions of metal oxides used to insulate a pair of thermocouple wires. The most common are Alumina (Al2O3), Beryllia (BeO), and Magnesia (MgO). Their application depends upon temperature and type of thermocouple. High-purity alumina is required for platinum alloy thermocouples. Ceramic insulators are available as single and multihole tubes or as beads. Ceramic: Polycrystalline ferroelectric materials which are used as the sensing units in piezoelectric accelerometers. There are many different grades, all of which can be made in various configurations to satisfy different design requirements. Character: A letter, digit or other symbol that is used as the representation of data. A connected sequence of characters is called a character string. Chatter: The rapid cycling on and off of a relay in a control process due to insufficient bandwidth in the controller. CHROMEGA®: A chromium-nickel alloy which makes up the positive leg of type K and type E thermocouples (registered trademark of OMEGA ENGINEERING, INC.). Clear: To restore a device to a prescribed initial state, usually the zero state. Clipping: The term applied to the phenomenon which occurs when an output signal is limited in some way by the full range of an amplifier, ADC or other device. When this occurs, the signal is flattened at the peak values, the signal approaches the shape of a square wave, and high frequency components are introduced. Clipping may be hard, as is the case when the signal is strictly limited at some level, or it may be soft, in which case the clipping signal continues to follow the input at some reduced gain. Clock: The device that generates periodic signals for synchronization. Closeness of Control: Total temperature variation from a desired set point of system. Expressed as “closeness of control” is ±2°C or a system bandwidth with 4°C, also referred to as “amplitude of deviation.” CMR (Common-Mode Rejection): The ability of a panel meter to eliminate the effect of AC or DC noise between signal and ground. Normally expressed in dB at dc to 60 Hz. One type of CMR is specified between SIG LO and PWR GND. In differential meters, a second type of CMR is specified between SIG LO and ANA GND (METER GND).
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Temperature Measurement and Control Glossary Current: The rate of flow of electricity. The unit is the ampere (a) defined as 1 ampere = 1 coulomb per second. Curve Fitting: Curve fitting is the process of computing the coefficients of a function to approximate the values of a given data set within that function. The approximation is called a “fit”. A mathematical function, such as a least squares regression, is used to judge the accuracy of the fit. Cycle Time: The time, usually expressed in seconds, for a controller to complete one on/off cycle.
Drift: A change of a reading or a set point value over long periods due to several factors including change in ambient temperature, time, and line voltage. Droop: A common occurrence in time-proportional controllers. It refers to the difference in temperature between the set point and where the system temperature actually stabilizes due to the timeproportioning action of the controller. Dual Element Sensor: A sensor assembly with two independent sensing elements. Dual-Slope A/D Converter: An analog-to-digital converter which integrates the signal for a specific time, then counts time intervals for a reference voltage to bring the integrated signal back to zero. Such converters provide high resolution at low cost, excellent normal-mode noise rejection, and minimal dependence on circuit elements. Duplex: Pertaining to simultaneous two-way independent data communication transmission in both directions. Same as “full duplex”. Duplex Wire: A pair of wires insulated from each other and with an outer jacket of insulation around the inner insulated pair. Duty Cycle: The total time to one on/off cycle. Usually refers to the on/off cycle time of a temperature controller. Dynamic Calibration: Calibration in which the input varies over a specific length of time and the output is recorded vs. time.
Damping: The reduction of vibratory movement through dissipation of energy. Types include viscous, coulomb, and solid. Data Base: A large amount of data stored in a well-organized manner. A data base management system (DBMS) is a program that allows access to the information. dB (Decibel): 20 times the log to the base 10 of the ratio of two voltages. Every 20 dB’s correspond to a voltage ratio of 10, every 10 dB’s to a voltage ratio of 3.162. For instance, a CMR of 120 dB provides voltage noise rejection of 1,000,000/1. An NMR of 70 dB provides voltage noise rejection of 3,162/1. DC: Direct current; an electric current flowing in one direction only and substantially constant in value. Deadband: 1. For chart records: the minimum change of input signal required to cause a deflection in the pen position. 2. For temperature controllers: the temperature band where heat is turned off upon rising temperature and turned on upon falling temperature expressed in degrees. The area where no heating (or cooling) takes place. Debug: To find and correct mistakes in a program. Decimal: Refers to a base ten number system using the characters 0 through 9 to represent values. Default: The value(s) or option(s) that are assumed during operation when not specified. Degree: An incremental value in the temperature scale, i.e., there are 100 degrees between the ice point and the boiling point of water in the Celsius scale and 180°F between the same two points in the Fahrenheit scale. Density: Mass per unit of volume of a substance, i.e.: grams/cu.cm. or pounds/cu.ft. Deviation: The difference between the value of the controlled variable and the value at which it is being controlled. Differential Input: A signal-input circuit where SIG LO and SIG HI are electrically floating with respect to ANALOG GND (METER GND, which is normally tied to DIG GND). This allows the measurement of the voltage difference between two signals tied to the same ground and provides superior common-mode noise rejection. Differential: For an on/off controller, it refers to the temperature difference between the temperature at which the controller turns heat off and the temperature at which the heat is turned back on. It is expressed in degrees. Digit: A measure of the display span of a panel meter. By convention, a full digit can assume any value from 0 through 9, a 1⁄2-digit will display a 1 and overload at 2, a 3⁄4-digit will display digits up to 3 and overload at 4, etc. For example, a meter with a display span of ±3999 counts is said to be a 3 3⁄4 digit meter. Digital Output: An output signal which represents the size of an input in the form of a series of discrete quantities. Digital-to-Analog Converter (D/A or DAC): A device or circuit to convert a digital value to an analog signal level. DIN (Deutsche Industrial Norm): A set of German standards recognized throughout the world. The 1⁄8 DIN standard for panel meters specifies an outer bezel dimension of 96 x 48 mm and a panel cutout of 92 x 45 mm. DIN 43760: The standard that defines the characteristics of a 100 ohm platinum RTD having a resistance vs. temperature curve specified by a = 0.00385 ohms per degree. Discharge Time Constant: The time required for the output-voltage from a sensor or system to discharge 37% of its original value in response to a zero rise time step function input. This parameter determines a low frequency response. Disk Operating System (DOS): Program used to control the transfer of information to and from a disk, such as MS DOS. Displacement: The measured distance traveled by a point from its position at rest. Peak to peak displacement is the total measured movement of a vibrating point between its positive and negative extremes. Measurement units expressed as inches or milli-inches. Dissipation Constant: The ratio for a thermistor which relates a change in internal power dissipation to a resultant change of body temperature.
Echo: To reflect received data to the sender. For example, keys depressed on a keyboard are usually echoed as characters displayed on the screen. Electrical Interference: Electrical noise induced upon the signal wires that obscures the wanted information signal. Electromotive Force (emf): The potential difference between the two electrodes in a cell. The cell emf is the cell voltage measured when no current is flowing through the cell. It can be measured by means of a pH meter with high input impedance. Electronic Industries Association (EIA): A standards organization specializing in the electrical and functional characteristics of interface equipment. EMF: Electromotive force. A rise in (electrical) potential energy. The principal unit is the volt. EMI: Electromagnetic interference. Emissivity: The ratio of energy emitted by an object to the energy emitted by a blackbody at the same temperature. The emissivity of an object depends upon its material and surface texture; a polished metal surface can have an emissivity around 0.2 and a piece of wood can have an emissivity around 0.95. Endothermic: A process is said to be endothermic when it absorbs heat. End Point (Potentiometric): The apparent equivalence point of a titration at which a relatively large potential change is observed. Enthalpy: The sum of the internal energy of a body and the product of its volume multiplied by the pressure. Environmental Conditions: All conditions to which a transducer may be exposed during shipping, storage, handling, and operation. Eprom: Erasable Programmable Read-Only Memory. The PROM can be erased by ultraviolet light or electricity. Error: The difference between the value indicated by the transducer and the true value of the measured value being sensed. Usually expressed in percent of full scale output. Error Band: The allowable deviations to output from a specific reference norm. Usually expressed as a percentage of full scale. Eutectic Temperature: The lowest possible melting point of a mixture of alloys. Excitation: The external application of electrical voltage current applied to a transducer for normal operation. Exothermic: A process is said to be exothermic when it releases heat. Expansion Factor: Correction factor for the change in density between two pressure measurement areas in a constricted flow. Explosion-Proof Enclosure: An enclosure that can withstand an explosion of gases within it and prevent the explosion of gases surrounding it due to sparks, flashes or the explosion of the container itself, and maintain an external temperature which will not ignite the surrounding gases. Exposed Junction: A form of construction of a thermocouple probe where the hot or measuring junction protrudes beyond the sheath material so as to be fully exposed to the medium being measured. This form of construction usually gives the fastest response time.
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Temperature Measurement and Control Glossary Host: The primary or controlling computer in a multiple part system. Hysteresis: The difference in output when the measurand value is first approached with increasing and then with decreasing values. Expressed in percent of full scale during any one calibration cycle. See Deadband
Fahrenheit: A temperature scale defined by 32° at the ice point and 212° at the boiling point of water at sea level. Ferrule: A compressible tubular fitting that is compressed onto a probe inside a compression fitting to form a gas-tight seal. Field of View: A volume in space defined by an angular cone extending from the focal plane of an instrument. File: A set of related records or data treated as a unit. Firmware: Programs stored in PROM’s. Flag: Any of various types of indicators used for identification of a condition or event, for example, a character that signals the termination of a transmission. Floppy Disk: A small, flexible disk carrying a magnetic medium in which digital data is stored for later retrieval and use. FM: Factory Mutual Research Corporation. An organization which sets industrial safety standards. FM Approved: An instrument that meets a specific set of specifications established by Factory Mutual Research Corporation. FORTRAN: Formula Translation language. A widely used high-level programming language well suited to problems that can be expressed in terms of algebraic formulas. It is generally used in scientific applications. Freezing Point: The temperature at which a substance goes from the liquid phase to the solid phase. Frequency: The number of cycles over a specified time period over which an event occurs. The reciprocal is called the period. Frequency Modulated Output: A transducer output which is obtained in the form of a deviation from a center frequency, where the deviation is proportional to the applied stimulus. Frequency, Natural: The frequency of free (not forced) oscillations of the sensing element of a fully assembled transducer. Frequency Output: An output in the form of frequency which varies as a function of the applied input. Full Scale Output: The algebraic difference between the minimum output and maximum output.
Impedance: The total opposition to electrical flow (resistive plus reactive). Infrared: an area in the electromagnetic spectrum extending beyond red light from 760 nanometers to 1000 microns (106 nm). It is the form of radiation used for making non-contact temperature measurements. Input Impedance: The resistance of a panel meter as seen from the source. In the case of a voltmeter, this resistance has to be taken into account when the source impedance is high; in the case of an ammeter, when the source impedance is low. Insulated Junction: See Ungrounded Junction Insulation Resistance: The resistance measured between two insulated points on a transducer when a specific dc voltage is applied at room temperature. Integral: A form of temperature control. See Automatic Reset (2) Interchangeability Error: A measurement error that can occur if two or more probes are used to make the same measurement. It is caused by a slight variation in characteristics of different probes. Interface: The means by which two systems or devices are connected and interact with each other. Interrupt: To stop a process in such a way that it can be resumed. Intrinsically Safe: An instrument which will not produce any spark or thermal effects under normal or abnormal conditions that will ignite a specified gas mixture. IPTS-48: International Practical Temperature Scale of 1948. Fixed points in thermometry as specified by the Ninth General Conference of Weights and Measures which was held in 1948. IPTS-68: International Practical Temperature Scale of 1968. Fixed points in thermometry set by the 1968 General Conference of Weights and Measures. ISA: Instrument Society of America. Isolation: The reduction of the capacity of a system to respond to an external force by use of resilient isolating materials. Isothermal: A process or area that is a constant temperature.
Gain: The amount of amplification used in an electrical circuit. Galvanometer: An instrument that measures small electrical currents by means of deflecting magnetic coils. Ground: 1. The electrical neutral line having the same potential as the surrounding earth. 2. The negative side of DC power supply. 3. Reference point for an electrical system. Grounded Junction: A form of construction of a thermocouple probe where the hot or measuring junction is in electrical contact with the sheath material so that the sheath and thermocouple will have the same electrical potential.
Joule: The basic unit of thermal energy. Junction: The point in a thermocouple where the two dissimilar metals are joined. K: When referring to memory capacity, two to the tenth power (1024 in decimal notation). Kelvin: Symbol K. The unit of absolute or thermodynamic temperature scale based upon the Celsius scale with 100 units between the ice point and boiling point of water. 0°C = 273.15K (there is no degree (°) symbol used with the Kelvin scale). Kilowatt (kw): Equivalent to 1000 watts. Kilowatt Hour (kwh): 1000 watthours. Kilovolt amperes (kva): 1000 volt amps. KVA: Kilovolt amperes (1000 volt amps).
Half-Duplex: One way at a time data communication; both devices can transmit and receive data, but only one at a time. Handshake: An interface procedure that is based on status/data signals that assure orderly data transfer as opposed to asynchronous exchange. Hardcopy: Output in a permanent form (usually a printout) rather than in temporary form, as on disk or terminal display. Hardware: The electrical, mechanical and electromechanical equipment and parts associated with a computing system, as opposed to its firmware or software. Heat: Thermal energy. Heat is expressed in units of calories or BTU’s. Heat Sink: 1. Thermodynamic. A body which can absorb thermal energy. 2. Practical. A finned piece of metal used to dissipate the heat of solid state components mounted on it. Heat Transfer: The process of thermal energy flowing from a body of high energy to a body of low energy. Means of transfer are: conduction; the two bodies contact. Convection; a form of conduction where the two bodies in contact are of different phases, i.e. solid and gas. Radiation: all bodies emit infrared radiation. Heat Treating: A process for treating metals where heating to a specific temperature and cooling at a specific rate changes the properties of the metal. Hertz (Hz): Units in which frequency is expressed. Synonymous with cycles per second. Hexadecimal: Refers to a base sixteen number system using the characters 0 through 9 and A through F to represent the values. Machine language programs are often written in hexadecimal notation. Hold: Meter HOLD is an external input which is used to stop the A/D process and freeze the display. BCD HOLD is an external input used to freeze the BCD output while allowing the A/D process to continue operation.
Lag: 1. A time delay between the output of a signal and the response of the instrument to which the signal is sent. 2. A time relationship between two waveforms where a fixed reference point on one wave occurs after the same point of the reference wave. Latent Heat: Expressed in BTU per pound. The amount of heat needed (absorbed) to convert a pound of boiling water to a pound of steam. Leakage Rate: The maximum rate at which a fluid is permitted or determined to leak through a seal. Limits of Error: A tolerance band for the thermal electric response of thermocouple wire expressed in degrees or percentage defined by ANSI specification MC-96.1 (1975). Linearity: The closeness of a calibration curve to a specified straight line. Linearity is expressed as the maximum deviation of any calibration point on a specified straight line during any one calibration cycle. Load: The electrical demand of a process expressed as power (watts), current (amps) or resistance (ohms). Load Impedance: The impedance presented to the output terminals of a transducer by the associated external circuitry. Logarithmic Scale: A method of displaying data (in powers of ten) to yield maximum range while keeping resolution at the low end of the scale.
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Temperature Measurement and Control Glossary Loop Resistance: The total resistance of a thermocouple circuit caused by the resistance of the thermocouple wire. Usually used in reference to analog pyrometers which have typical loop resistance requirements of 10 ohms. LSD (Least-Significant Digit): The rightmost active (non-dummy) digit of the display. LS-TTL Compatible: For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which can source 20 µA, and a logic 0 is obtained for inputs of 0 to 0.8 V which can sink 400 µA. For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 µA, and a logic 0 is represented by 0 to 0.6 V with a current sink capability of at least 16 MA. “LS” stands for Low-power Schottky. LS-TTL Unit Load: A load with LS-TTL voltage levels, which will draw 20 µA for a logic 1 and –400 µA for a logic 0.
NEMA-4: A standard from the National Electrical Manufacturers Association, which defines enclosures intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose-directed water. NEMA-7: A standard from the National Electrical Manufacturers Association, which defines explosion-proof enclosures for use in locations classified as Class I, Groups A, B, C or D, as specified in the National Electrical Code. NEMA-12: A standard from the National Electrical Manufacturers Association, which defines enclosures with protection against dirt, dust, splashes by non-corrosive liquids, and salt spray. NEMA-Size Case: An older US case standard for panel meters, which requires a panel cutout of 3.93 x 1.69 inches. Network: A group of computers that are connected to each other by communications lines to share information and resources. Nibble: One half of a byte. Nicrosil/Nisil: A nickel-chrome/nickel-silicone thermal alloy used to measure high temperatures. Inconsistencies in thermoelectric voltages exist in these alloys with respect to the wire gage. NMR (Normal-Mode Rejection): The ability of a panel meter to filter out noise superimposed on the signal and applied across the SIG HI to SIG LO input terminals. Normally expressed in dB at 50/60 Hz. Noise: An unwanted electrical interference on the signal wires. Normal-Mode Rejection Ratio: The ability of an instrument to reject interference usually of line frequency (50–60 Hz) across its input terminals. NPT: National Pipe Thread. Null: A condition, such as balance, which results in a minimum absolute value of output.
M: Mega; one million. When referring to memory capacity, two to the twentieth power (1,048,576 in decimal notation). Manual Reset (Adjustment): The adjustment on a proportioning controller which shifts the proportioning band in relationship to the set point to eliminate droop or offset errors. Manual Reset (Switch): The switch in a limit controller that manually resets the controller after the limit has been exceeded. Maximum Operating Temperature: The maximum temperature at which an instrument or sensor can be safely operated. Maximum Power Rating: The maximum power in watts that a device can safely handle. Mean Temperature: The average of the maximum and minimum temperature of a process equilibrium. Measurand: A physical quantity, property, or condition which is measured. Measuring Junction: The thermocouple junction referred to as the hot junction that is used to measure an unknown temperature. Melting Point: The temperature at which a substance transforms from a solid phase to a liquid phase. Mica: A transparent mineral used as window material in hightemperature ovens. Microamp: One millionth of an ampere, 10–6 amps. Microcomputer: A computer which is physically small. It can fit on top of or under a desk; based on LSI circuitry, computers of this type are now available with much of the power currently associated with minicomputer systems. Micron: One millionth of a meter, 10–6 meters. Microvolt: One millionth of a volt, 10–6 volts. Mil: One thousandth of an inch (.001≤). Milliamp: One thousandth of an amp, 10–3 amps, symbol mA. Millimeter: One thousandth of a meter, symbol mm. Millivolt: Unit of electromotive force. It is the difference in potential required to make a current of 1 millampere flow through a resistance of 1 ohm; one thousandth of a volt, symbol mV. Mineral-insulated Thermocouple: A type of thermocouple cable which has an outer metal sheath and mineral (magnesium oxide) insulation inside separating a pair of thermocouple wires from themselves and from the outer sheath. This cable is usually drawn down to compact the mineral insulation and is available in diameters from .375 to .010 inches. It is ideally suited for hightemperature and severe-duty applications. Minor Scale Division: On an analog scale, the smallest indicated division of units on the scale. Modem: Modulator/Demodulator. A device that transforms digital signals into audio tones for transmission over telephone lines, and does the reverse for reception. MSD (Most-Significant Digit): The leftmost digit of the display. Mueller Bridge: A high-accuracy bridge configuration used to measure three-wire RTD thermometers. Multiplex: A technique which allows different input (or output) signals to use the same lines at different times, controlled by an external signal. Multiplexing is used to save on wiring and I/O ports.
Octal: Pertaining to a base 8 number system. O.D.: Outside diameter. Offset: The difference in temperature between the set point and the actual process temperature. Also referred to as droop. Ohmmeter: An instrument used to measure electrical resistance. On/off Controller: A controller whose action is fully on or fully off. Open Circuit: The lack of electrical contact in any part of the measuring circuit. An open circuit is usually characterized by rapid large jumps in displayed potential, followed by an off-scale reading. Operating System: A collection of programs that controls the overall operation of a computer and performs such tasks as assigning places in memory to programs and data, processing interrupts, scheduling jobs and controlling the overall input/output of the system. Optical Isolation: Two networks which are connected only through an LED transmitter and photoelectric receiver with no electrical continuity between the two networks. Output: The electrical signal which is produced by an applied input to the transducer. Output Impedance: The resistance as measured on the output terminals of a pressure transducer. Output Noise: The RMS, peak-to-peak (as specified) ac component of a transducer’s dc output in the absence of a measurand variation. Overshoot: The number of degrees by which a process exceeds the set point temperature when coming up to the set point temperature. Parallax: An optical illusion which occurs in analog meters and causes reading errors. It occurs when the viewing eye is not in the same plane, perpendicular to the meter face, as the indicating needle. Parallel Transmission: Sending all data bits simultaneously. Commonly used for communications between computers and printer devices. Parity: A technique for testing transmitting data. Typically, a binary digit is added to the data to make the sum of all the digits of the binary data either always even (even parity) or always odd (odd parity). Peltier Effect: When a current flows through a thermocouple junction, heat will either be absorbed or evolved depending on the direction of current flow. This effect is independent of joule I2 R heating. Peripheral: A device that is external to the CPU and main memory, i.e., printer, modem or terminal, but is connected by the appropriate electrical connections. Phase: A time-based relationship between a periodic function and a reference. In electricity, it is expressed in angular degrees to describe the voltage or current relationship of two alternating waveforms. Phase Difference: The time expressed in degrees between the same reference point on two periodic waveforms.
N/C (No Connection): A connector point for which there is no internal connection. NBS: National Bureau of Standards. NEC: National Electric Codes. Negative Temperature Coefficient: A decrease in resistance with an increase in temperature.
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Temperature Measurement and Control Glossary Proportioning Control with Integral and Derivative Functions: Three mode PID controller. A time-proportioning controller with integral and derivative functions. The integral function automatically adjusts the system temperature to the set point temperature to eliminate droop due to the time proportioning function. The derivative function senses the rate of rise or fall of the system temperature and automatically adjusts the cycle time of the controller to minimize overshoot or undershoot. Protection Head: An enclosure usually made out of metal at the end of a heater or probe where connections are made. Protection Tube: A metal or ceramic tube, closed at one end, into which a temperature sensor is inserted. The tube protects the sensor from the medium into which it is inserted. Protocol: A formal definition that describes how data is to be exchanged. PSIA: Pounds per square inch absolute. Pressure referenced to a vacuum. PSID: Pounds per square inch differential. Pressure difference between two points. PSIG: Pound per square inch gage. Pressure referenced to ambient air pressure. PSIS: Pounds per square inch standard. Pressure referenced to a standard atmosphere. Pulse Width Modulation: An output in the form of duty cycle which varies as a function of the applied measurand.
Phase Proportioning: A form of temperature control where the power supplied to the process is controlled by limiting the phase angle of the line voltage. PID: Proportional, integral, derivative. A three-mode control action where the controller has time proportioning, integral (auto reset) and derivative rate action. Piezoresistance: Resistance that changes with stress. Pixel: Picture element. Definable locations on a display screen that are used to form images on the screen. For graphic displays, screens with more pixels provide higher resolution. Platinel: A non-standard, high temperature platinum thermocouple alloy whose thermoelectric voltage nearly matches a Type K thermocouple (Trademark of Englehard Industries). Platinum: A noble metal which in its pure form is the negative wire of Type R and Type S thermocouples. Platinum 6% Rhodium: The platinum-rhodium alloy used as the negative wire in conjunction with platinum-30% rhodium to form a Type B thermocouple. Platinum 10% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with pure platinum to form a Type S thermocouple. Platinum 13% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with pure platinum to form a Type R thermocouple. Platinum 30% Rhodium: The platinum-rhodium alloy used as the positive wire in conjunction with platinum 6% rhodium to form a Type B thermocouple. Platinum 67: To develop thermal emf tables for thermocouples, the National Bureau of Standards paired each thermocouple alloy against a pure platinum wire (designated Platinum 2 prior to 1973, and currently Platinum 67). The thermal emf’s of any alloy combination can be determined by summing the “vs. Pt-67” emf’s of the alloys, i.e., the emf table for a Type K thermocouple is derived from the Chromel vs. Pt-67 and the Alumel vs .Pt-67 values. Polarity: In electricity, the quality of having two oppositely charged poles, one positive, one negative. Port: A signal input (access) or output point on a computer. Positive Temperature Coefficient: An increase in resistance due to an increase in temperature. Potential Energy: Energy related to the position or height above a place to which fluid could possibly flow. Potentiometer: 1. A variable resistor often used to control a circuit. 2. A balancing bridge used to measure voltage. Power Supply: A separate unit or part of a circuit that supplies power to the rest of the circuit or to a system. PPM: Abbreviation for “parts per million,” sometimes used to express temperature coefficients. For instance, 100 ppm is identical to 0.01%. Primary Standard (NBS): The standard reference units and physical constants maintained by the National Bureau of Standards upon which all measurement units in the United States are based. Probe: A generic term that is used to describe many types of temperature sensor. Process Meter: A panel meter with sizeable zero and span adjustment capabilities, which can be scaled for readout in engineering units for signals such as 4–20 mA, 10–50 mA and 1–5 V. Program: A list of instructions that a computer follows to perform a task. Prom: Programmable read-only memory. A semiconductor memory whose contents cannot be changed by the computer after it has been programmed. Proportioning Band: A temperature band expressed in degrees within which a temperature controller’s time proportioning function is active. Proportioning Control Mode: A time proportioning controller where the amount of time that the relay is energized is dependent upon the system’s temperature. Proportioning Control plus Derivative Function: A time proportioning controller with a derivative function. The derivative function senses the rate at which a system’s temperature is either increasing or decreasing and adjusts the cycle time of the controller to minimize overshoot or undershoot. Proportioning Control plus Integral: A two-mode controller with time proportioning and integral (auto reset) action. The integral function automatically adjusts the temperature at which a system has stabilized back to the set point temperature, thereby eliminating droop in the system.
Radiation: See Infrared Random Access Memory (RAM): Memory that can be both read and changed during computer operation. Unlike other semi-conductor memories, RAM is volatile—if power to the RAM is disrupted or lost, all the data stored is lost. Range: Those values which a transducer is intended to measure, specified by upper and lower limits. Rangeability: The ratio of the maximum flowrate to the minimum flowrate of a meter. Rankine (°R): An absolute temperature scale based upon the Fahrenheit scale with 180° between the ice point and boiling point of water. 459.67°R = 0°F. Rate Action: The derivative function of a temperature controller. Rate Time: The time interval over which the system temperature is sampled for the derivative function. Ratiometric Measurement: A measurement technique where an external signal is used to provide the voltage reference for the dualslope A/D converter. The external signal can be derived from the voltage excitation applied to a bridge circuit or pick-off supply, thereby eliminating errors due to power supply fluctuations. Read Only Memory (ROM): Memory that contains fixed data. The computer can read the data, but cannot change it in any way. Real Time: The time interval over which the system temperature is sampled for the derivative function. Record: A collection of unrelated information that is treated as a single unit. Recovery Time: The length of time which it takes a transducer to return to normal after applying a proof pressure. Reference Junction: The cold junction in a thermocouple circuit which is held at a stable, known temperature. The standard reference temperature is 0°C (32°F). However, other temperatures can be used. Refractory Metal Thermocouple: A class of thermocouples with melting points above 3600°F. The most common are made from tungsten and tungsten/rhenium alloys, Types G and C. They can be used for measuring high temperatures up to 4000°F (2200°C) in non-oxidizing, inert, or vacuum environments. Relay (Mechanical): An electromechanical device that completes or interrupts a circuit by physically moving electrical contacts into contact with each other. Relay (Solid State): A solid state switching device which completes or interrupts a circuit electrically with no moving parts. Remote: Not hard-wired; communicating via switched lines, such as telephone lines. Usually refers to peripheral devices that are located at a site away from the CPU. Repeatability: The ability of a transducer to reproduce output readings when the same measurand value is applied to it consecutively, under the same conditions, and in the same direction. Repeatability is expressed as the maximum difference between output readings. Resistance: The resistance to the flow of electric current measured in ohms (Ω). For a conductor, resistance is a function of diameter, resistivity (an intrinsic property of the material) and length.
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Temperature Measurement and Control Glossary Resistance Ratio Characteristic: For thermistors, the ratio of the resistance of the thermistor at 25°C to the resistance at 125°C. Resistance Temperature Characteristic: A relationship between a thermistor’s resistance and the temperature. Resolution: The smallest detectable increment of measurement. Resolution is usually limited by the number of bits used to quantize the input signal. For example, a 12-bit A/D can resolve to one part in 4096 (2 to the 12 power equals 4096). Resonant Frequency: The measurand frequency at which a transducer responds with maximum amplitude. Response Time: The length of time required for the output of a transducer to rise to a specified percentage of its final value as a result of a step change of input. Response Time (time constant): The time required by a sensor to reach 63.2% of a step change in temperature under a specified set of conditions. Five time constants are required for the sensor to stabilize at 100% of the step change value. RFI: Radio frequency interference. Rheostat: A variable resistor. Rise Time: The time required for a sensor or system to respond to an instantaneous step function, measured from the 10% to 90% points on the response waveforms. Room Conditions: Ambient environmental conditions under which transducers must commonly operate. Root Mean Square (RMS): Square root of the mean of the square of the signal taken during one full cycle. RTD: Resistance temperature detector.
Single Precision: The degree of numeric accuracy that requires the use of one computer word. In single precision, seven digits are stored, and up to seven digits are printed. Contrast with Double Precision. Software: Generally, programs loaded into a computer from external mass storage but also extended to include operating systems and documentation. Source Code: A non-executable program written in a high-level language. A compiler or assembler must translate the source code into object code (machine language) that the computer can understand and process. Span: The difference between the upper and lower limits of a range expressed in the same units as the range. Span Adjustment: The ability to adjust the gain of a process or strain meter so that a specified display span in engineering units corresponds to a specified signal span. For instance, a display span of 200°F may correspond to the 16 mA span of a 4–20 mA transmitter signal. Spare: A connector point reserved for options, specials, or other configurations. The point is identified by an (E#) for location on the electrical schematic. Specific Gravity: The ratio of mass of any material to the mass of the same volume of pure water at 4°C. Specific Heat: The ratio of thermal energy required to raise the temperature of a body 1° to the thermal energy required to raise an equal mass of water 1°. Spectral Filter: A filter which allows only a specific band width of the electromagnetic spectrum to pass, i.e., 4 to 8 micron infrared radiation. Spectrum: The resolving of overall vibration into amplitude components as a function of frequency. Spectrum Analysis: Utilizing frequency components of a vibration signal to determine the source and cause of vibration. Spot Size: The diameter of the circle formed by the cross section of the field of view of an optical instrument at a given distance. Spurious Error: Random or erratic malfunction. SSR: Solid state relay. See Relay, Solid State Stability: The ability of an instrument or sensor to maintain a consistent output when a constant input is applied. Stop Bit: A signal following a character or block that prepares the receiving device to receive the next character or block. String: A sequence of characters. Super Cooling: The cooling of a liquid below its freezing temperature without the formation of the solid phase. Super Heating: 1. The heating of a liquid above its boiling temperature without the formation of the gaseous phase. 2. The heating of the gaseous phase considerably above the boiling-point temperature to improve the thermodynamic efficiency of a system. Surge Current: A current of short duration that occurs when power is first applied to capacitive loads or temperature dependent resistive loads such as tungsten or molybdenum heaters—usually lasting not more than several cycles. Syntax: The rules governing the structure of a language.
SAMA: Scientific Apparatus Makers Association. An association that has issued standards covering platinum, nickel, and copper resistance elements (RTD’s). SCR: Silicon controlled rectifier. Scroll: To move all or part of the screen material up or down, left or right, to allow new information to appear. Seebeck Coefficient: The derivative (rate of change) of thermal EMF with respect to temperature, normally expressed as millivolts per degree. Seebeck Effect: When a circuit is formed by a junction of two dissimilar metals and the junctions are held at different temperatures, a current will flow in the circuit caused by the difference in temperature between the two junctions. Seebeck EMF: The open circuit voltage caused by the difference in temperature between the hot and cold junctions of a circuit made from two dissimilar metals. Self-Heating: Internal heating of a transducer as a result of power dissipation. Sensing Element: That part of a transducer which reacts directly in response to input. Sensitivity: The minimum change in input signal to which an instrument can respond. Sensitivity Shift: A change in slope of the calibration curve due to a change in sensitivity. Sequential Access: An access mode in which records are retrieved in the same order in which they were written. Each successive access to the file refers to the next record in the file. Serial Transmission: Sending one bit at a time on a single transmission line. Compare with Parallel Transmission. Set Point: The temperature at which a controller is set to control a system. Settling Time: The time taken for the display to settle within one digit final value when a step is applied to the meter input. SI: System Internationale. The name given to the standard metric system of units. Signal: An electrical transmittance (either input or output) that conveys information. Signal Conditioner: A circuit module which offsets, attenuates, amplifies, linearizes and/or filters the signal for input to the A/D converter. The typical output signal conditioner is +2 V dc. Signal Conditioning: To process the form or mode of a signal so as to make it intelligible to, or compatible with, a given device, including such manipulation as pulse shaping, pulse clipping, compensating, digitizing, and linearizing. Single-Ended Input: A signal-input circuit where SIG LO (or sometimes SIG HI) is tied to METER GND. Ground loops are normally not a problem in AC-powered meters, since METER GND is transformer-isolated from AC GND.
Tape: A recording medium for data or computer programs. Tape can be in permanent form, such as perforated paper tape, or erasable, such as magnetic tape. Generally, tape is used as a mass storage medium, in magnetic form, and has a much higher storage capacity than disk storage, but it takes much longer to write or recover data from tape than from a disk. Teflon: A fluorocarbon polymer used for insulation of electrical wires (trademark of DuPont). Telecommunication: Synonym for data communication. The transmission of information from one point to another. TEMPCO: Abbreviation for “temperature coefficient”: the error introduced by a change in temperature. Normally expressed in %/°C or ppm/°C. Temperature Error: The maximum change in output, at any measurand value within a specified range, when the transducer temperature is changed from room temperature to specified temperature extremes. Temperature Range, Compensated: The range of ambient temperatures within which all tolerances specified for Thermal Zero Shift and Thermal Sensitivity Shift are applicable (temperature error). Temperature Range, Operable: The range of ambient temperatures, given by their extremes, within which a transducer may be operated. Exceeding compensated range may require recalibration.
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Temperature Measurement and Control Glossary Terminal: An input/output device used to enter data into a computer and record the output. Thermal Coefficient of Resistance: The change in resistance of a semiconductor per unit change in temperature over a specific range of temperature. Thermal Conductivity: The ability of a material to conduct heat in the form of thermal energy. Thermal emf: See Seebeck emf Thermal Expansion: An increase in size due to an increase in temperature expressed in units of an increase in length or increase in size per degree, i.e. inches/inch/degree C. Thermal Gradient: The distribution of a differential temperature through a body or across a surface. Thermal Sensitivity Shift: The sensitivity shift due to changes of the ambient temperature from room temperature to the specified limits of the compensated temperature range. Thermal Zero Shift: An error due to changes in ambient temperature in which the zero pressure output shifts. Thus, the entire calibration curve moves in a parallel displacement. Thermistor: A temperature-sensing element composed of sintered semiconductor material which exhibits a large change in resistance proportional to a small change in temperature. Thermistors usually have negative temperature coefficients. Thermocouple: The junction of two dissimilar metals which has a voltage output proportional to the difference in temperature between the hot junction and the lead wires (cold junction) (refer to Seebeck emf). Thermocouple Type Material (ANSI Symbol) J Iron/Constantan K CHROMEGA®/ALOMEGA® T Copper/Constantan E CHROMEGA/Constantan R Platinum/Platinum 13% Rhodium S Platinum/Platinum 10% Rhodium B Platinum 6% Rhodium/Platinum 30% Rhodium G* Tungsten/Tungsten 26% Rhenium C* Tungsten 5% Rhenium/Tungsten 26% Rhenium D* Tungsten 3% Rhenium/Tungsten 25% Rhenium *Not ANSI symbols Thermopile: An arrangement of thermocouples in series such that alternate junctions are at the measuring temperature and the reference temperature. This arrangement amplifies the thermoelectric voltage. Thermopiles are usually used as infrared detectors in radiation pyrometry. Thermowell: A closed-end tube designed to protect temperature sensors from harsh environments, high pressure, and flows. They can be installed into a system by pipe thread or welded flange and are usually made of corrosion-resistant metal or ceramic material, depending upon the application. Thomson Effect: When current flows through a conductor within a thermal gradient, a reversible absorption or evolution of heat will occur in the conductor at the gradient boundaries. Transducer: A device (or medium) that converts energy from one form to another. The term is generally applied to devices that take physical phenomena (pressure, temperature, humidity, flow, etc.) and convert them to electrical signals. Transmitter (Two-Wire): A device which is used to transmit temperature data from either a thermocouple or RTD via a two-wire current loop. The loop has an external power supply and the transmitter acts as a variable resistor with respect to its input signal. Triac: A solid state switching device used to switch alternating current wave forms. Triple Point: The temperature and pressure at which solid, liquid, and gas phases of a given substance are all present simultaneously in varying amounts. Triple Point (Water): The thermodynamic state where all three phases, solid, liquid, and gas, may all be present in equilibrium. The triple point of water is .01°C. True RMS: The true root-mean-square value of an AC or AC-plus-DC signal, often used to determine power of a signal. For a perfect sine wave, the RMS value is 1.11072 times the rectified average value, which is utilized for low-cost metering. For significantly nonsinusoidal signals, a true RMS converter is required. TTL: Transistor-to-transistor logic. A form of solid state logic which uses only transistors to form the logic gates.
TTL-Compatible: For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which can source 40 µA, and a logic 0 is obtained for inputs of 0 to 0.8 V which can sink 1.6 mA. For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 µA, and a logic 0 is represented by 0 to 0.6 V with a current sink capability of at least 16 mA. TTL Unit Load: A load with TTL voltage levels, which will draw 40 µA for a logic 1 and –1.6 mA for a logic 0. Typical: Error within plus or minus one standard deviation (±1%) of the nominal specified value, as computed from the total population. UL: Underwriters Laboratories, Inc. An independent laboratory that establishes standards for commercial and industrial products. Ultraviolet: That portion of the electromagnetic spectrum below blue light (380 nanometers). Undershoot: The difference in temperature between the temperature a process goes to, below the set point, after the cooling cycle is turned off and the set point temperature. Ungrounded Junction: A form of construction of a thermocouple probe where the hot or measuring junction is fully enclosed by and insulated from the sheath material. Union: A form of pipe fitting where two extension pipes are joined at a separable coupling. Vacuum: A pressure less than atmospheric pressure. Velocity: The time rate of change of displacement; dx/dt. Vibration Transducer: Generally, any device which converts movement, either shock or steady state vibration, into an electrical signal proportional to the movement; a sensor. Volt: The (electrical) potential difference between two points in a circuit. The fundamental unit is derived as work per unit charge— (V = W/Q). One volt is the potential difference required to move one coulomb of charge between two points in a circuit using one joule of energy. Voltage: An electrical potential which can be measured in volts. Voltmeter: An instrument used to measure voltage. Watt Density: The watts emanating from each square inch of heated surface area of a heater. Expressed in units of watts per square inch. Wheatstone Bridge: A network of four resistances, an emf source, and a galvanometer connected such that when the four resistances are matched, the galvanometer will show a zero deflection or “null” reading. Window: In computer graphics, a defined area in a system not bounded by any limits; unlimited “space” in graphics. Word: Number of bits treated as a single unit by the CPU. In an 8-bit machine, the word length is 8 bits; in a sixteen-bit machine, it is 16 bits. Working Standard: A standard of unit measurement calibrated from either a primary or secondary standard which is used to calibrate other devices or make comparison measurements. Zero Adjustment: The ability to adjust the display of a process or strain meter so that zero on the display corresponds to a non-zero signal, such as 4 mA, 10 mA, or 1 V dc. The adjustment range is normally expressed in counts. Zero Offset: 1. The difference expressed in degrees between true zero and an indication given by a measuring instrument. 2. See Zero Suppression Zero Power Resistance: The resistance of a thermistor or RTD element with no power being dissipated. Zero Suppression: The span of an indicator or chart recorder may be offset from zero (zero suppressed) such that neither limit of the span will be zero. For example, a temperature recorder which records a 100° span from 400° to 500° is said to have 400° zero suppression. Zero Voltage Switching: The making or breaking of circuit timed such that the transition occurs when the voltage wave form crosses zero voltage; typically only found in solid state switching devices.
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Practical Guidelines for Temperature Measurement Temperature can be measured via a diverse array of sensors. All of them infer temperature by sensing some change in a physical characteristic. Six types with which the engineer is likely to come into contact are: thermocouples, resistance temperature devices (RTD’s and thermistors), infrared radiators, bimetallic devices, liquid expansion devices, and change-of-state devices. It is well to begin with a brief review of each. Thermocouples consist essentially of two strips or wires made of different metals and joined at one end. As discussed later, changes in the temperature at that juncture induce a change in electromotive force (emf) between the other ends. As temperature goes up, this output emf of the thermocouple rises, though not necessarily linearly. Resistance temperature devices capitalize on the fact that the electrical resistance of a material changes as its temperature changes. Two key types are the metallic devices (commonly referred to as RTD’s), and thermistors. As their name indicates, RTD’s rely on resistance change in a metal, with the resistance rising more or less linearly with temperature. Thermistors are based on resistance change in a ceramic semiconductor; the resistance drops nonlinearly with temperature rise. Infrared sensors are noncontacting devices. As discussed later, they infer temperature by measuring the thermal radiation emitted by a material. Bimetallic devices take advantage of the difference in rate of thermal expansion between different metals. Strips of two metals are bonded together. When heated, one side will expand more than the other, and the resulting bending is translated into a temperature reading by mechanical linkage to a pointer. These devices are portable and they do not require a power supply, but they are usually not as accurate as thermocouples or RTD’s and they do not readily lend themselves to temperature recording. Fluid-expansion devices, typified by the household thermometer, generally come in two main
classifications: the mercury type and the organic-liquid type. Versions employing gas instead of liquid are also available. Mercury is considered an environmental hazard, so there are regulations governing the shipment of devices that contain it. Fluid-expansion sensors do not require electric power, do not pose explosion hazards, and are stable even after repeated cycling. On the other hand, they do not generate data that are easily recorded or transmitted, and they cannot make spot or point measurements. Change-of-state temperature sensors consist of labels, pellets, crayons, lacquers or liquid crystals whose appearance changes when a certain temperature is reached. They are used, for instance, with steam traps – when a trap exceeds a certain temperature, a white dot on a sensor label attached to the trap will turn black. Response time typically takes minutes, so these devices often do not respond to transient temperature changes, and accuracy is lower than with other types of sensors. Furthermore, the change in state is irreversible, except in the case of liquid-crystal displays. Even so, change-of-state sensors can be handy when one needs confirmation that the temperature of a piece of equipment or a material has not exceeded a certain level, for instance for technical or legal reasons, during product shipment.
The workhorses In the chemical process industries, the most commonly used temperature sensors are thermocouples, resistive devices and infrared devices. There is widespread misunderstanding as to how these devices work and how they should be used. Thermocouples: Consider first the thermocouple, probably the mostoften-used and least-understood of the three. Essentially, a thermocouple consists of two alloys joined together at one end and open at the other. The emf at the output end (the open end; V1 in Figure 1a) is a function of the temperature T1 at the closed end. As the temperature rises, the emf goes up. Z-13
Often the thermocouple is located inside a metal or ceramic shield that protects it from a variety of environments. Metal-sheathed thermocouples are also available with many types of outer coatings, such as polytetrafluoroethylene, for trouble-free use in corrosive solutions. The open-end emf is a function of not only the closed-end temperature (i.e., the temperature at the point of measurement) but also the temperature at the open end (T2 in Figure 1a). Only by holding T2 at a standard temperature can the measured emf be considered a direct function of the change in T1. The industrially accepted standard for T2 is 0°C; therefore, most tables and charts make the assumption that T2 is at that level. In industrial instrumentation, the difference between the actual temperature at T2 and 0°C is usually corrected for electronically, within the instrumentation. This emf adjustment is referred to as the cold-junction, or CJ, correction. Temperature changes in the wiring between the input and output ends do not affect the output voltage, provided that the wiring is of thermocouple alloy or a thermoelectric equivalent (Figure 1a). For example, if a thermocouple is measuring temperature in a furnace and the instrument that shows the reading is some distance away, the wiring between the two could pass near another furnace and not be affected by its temperature, unless it becomes hot enough to melt the wire or permanently change its electrothermal behavior. The composition of the junction itself does not affect the thermocouple action in any way, so long as the temperature, T1, is kept constant throughout the junction and the junction material is electrically conductive (Figure 1b). Similarly, the reading is not affected by insertion of non-thermocouple alloys in either or both leads, provided that the temperature at the ends of the “spurious” material is the same (Figure 1c).
A V1 B
T1
T2 T3
(a)
Figure 1a
T1
D
F V1
T1
G T1
E T2
(b)
Figure 1b
A V1 B B
T1 T3
C
T2
C T3
(c)
This ability of the thermocouple to work with a spurious metal in the transmission path enables the use of a number of specialized devices, such as thermocouple switches. Whereas the transmission wiring itself is normally the thermoelectrical equivalent of the thermocouple alloy, properly operating thermocouple switches must be made of goldplated or silver-plated copper alloy elements with appropriate steel springs to ensure good contact. So long as the temperatures at the input and output junctions of the switch are equal, this change in composition makes no difference. It is important to be aware of what might be called the Law of Successive Thermocouples. Of the two elements that are shown in the upper portion of Figure 1d, one thermocouple has T1 at the hot end and T2 at the open end. The second thermocouple has its hot end at T2 and its open end at T3. The emf level for the thermocouple that is measuring T1 is V1; that for the other thermocouple is V2. The sum of the two emfs, V1 plus V2, equals the emf V3 that would be generated by the combined thermocouple operating between T1 and T3. By virtue of this law, a thermocouple designated for one open-end reference temperature can be used with a different open-end temperature. RTD’s: A typical RTD consists of a fine platinum wire wrapped around a mandrel and covered with a
Figure 1c
A
D V1
V2
B
T1
E
T2 T2
T3 D
A V1
Figure 1. Assuming that certain conditions are met (text), thermocouple performance is not affected by temperature changes in wiring (a), the composition of the junction (b), nor the insertion of non-thermocouple alloys in the leads (c). As also discussed in text, thermocouple readings can be additive (d).
T3 = V1+ V2
B T1 (d)
T2
E T3
Figure 1d
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protective coating. Usually, the mandrel and coating are glass or ceramic. The mean slope of the resistance vs. temperature plot for the RTD is often referred to as the alpha value (Figure 2), alpha standing for the temperature coefficient. The slope of the curve for a given sensor depends somewhat on the purity of the platinum in it. The most commonly used standard slope, pertaining to platinum of a particular purity and composition, has a value of 0.00385 (assuming that the resistance is measured in ohms and the temperature in degrees Celsius). A resistance vs. temperature curve drawn with this slope is a so-called European curve, because RTD’s of this composition were first used extensively on that continent. Complicating the picture, there is also another standard slope, pertaining to a slightly different platinum composition. Having a slightly higher alpha value of 0.00392, it follows what is known as the American curve. If the alpha value for a given RTD is not specified, it is usually 0.00385. However, it is prudent to make sure of this, especially if the temperatures to be measured are high. This point is brought out in Figure 2, which shows both the European and American curves for the most widely used RTD, namely one that exhibits 100 ohms resistance at 0°C. Thermistors: The resistancetemperature relationship of a thermistor is negative and highly nonlinear. This poses a serious problem for engineers who must design their own circuitry. However, the difficulty can be eased by using thermistors in matched pairs, in such a way that the nonlinearities offset each other. Furthermore, vendors offer panel meters and controllers that compensate internally for thermistors’ lack of linearity. Thermistors are usually designated in accordance with their resistance at 25°C. The most common of these ratings is 2252 ohms; among the others are 5,000 and 10,000 ohms. If not specified to the contrary, most instruments will accept the 2252 type of thermistor.
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Resistance
Practical Guidelines for Temperature Measurement Cont'd a surface, be sure that the surface completely fills the field of view. If the target surface does not at first fill the field of view, move closer, or use an instrument with a more narrow field of view. Or, simply take the background temperature into account (i.e., adjust for it) when reading the instrument.
α = .00392 (American Curve)
α = .00385 (European Curve)
100 ohms
0°C
Temperature
Figure 2. A given RTD embodies either of two standard resistance-vs.-temperature relationships, often referred to as alpha values. The wise engineer will not use an RTD, especially for high-temperature measurements, without being aware of its alpha value
Infrared sensors: These measure the amount of radiation emitted by a surface. Electromagnetic energy radiates from all matter regardless of its temperature. In many process situations, the energy is in the infrared region. As the temperature goes up, the amount of infrared radiation and its average frequency go up. Different materials radiate at different levels of efficiency. This efficiency is quantified as emissivity, a decimal number or percentage ranging between 0 and 1 or 0% and 100%. Most organic materials, including skin, are very efficient, frequently exhibiting emissivities of 0.95. Most polished metals, on the other hand, tend to be inefficient radiators at room temperature, with emissivity or efficiency often 20% or less. To function properly, an infrared measurement device must take into account the emissivity of the surface being measured. This can often be looked up in a reference table. However, bear in mind that tables cannot account for localized conditions such as oxidation and surface roughness. A sometimes practical way to measure temperature with infrared when the emissivity level is not known is to
“force” the emissivity to a known level, by covering the surface with masking tape (emissivity of 95%) or a highly emissive paint. Some of the sensor input may well consist of energy that is not emitted by the equipment or material whose surface is being targeted, but instead is being reflected by that surface from other equipment or materials. Emissivity pertains to energy radiating from a surface, whereas “reflection” pertains to energy reflected from another source. Emissivity of an opaque material is an inverse indicator of its reflectivity – substances that are good emitters do not reflect much incident energy, and thus do not pose much of a problem to the sensor in determining surface temperatures. Conversely, when one measures a target surface with only, say, 20% emissivity, much of the energy reaching the sensor might be due to reflection from, e.g., a nearby furnace at some other temperature. In short, be wary of hot, spurious reflected targets. An infrared device is like a camera, and thus covers a certain field of view. It might, for instance, be able to “see” a 1-degree visual cone or a 100-degree cone. When measuring Z-15
Selection guides RTD’s are more stable than thermocouples. On the other hand, as a class, their temperature range is not as broad: RTD’s operate from about -250 to 850°C, whereas thermocouples range from about -270 to 2,300°C. Thermistors have a more restrictive span, being commonly used between -40 and 150°C, but offer high accuracy in that range. Thermistors and RTD’s share a very important limitation. They are resistive devices, and accordingly they function by passing a current through a sensor. Even though only a very small current is generally employed, it creates a certain amount of heat and thus can throw off the temperature reading. This selfheating in resistive sensors can be significant when dealing with a still fluid (i.e., one that is neither flowing nor agitated), because there is less carry-off of the heat generated. This problem does not arise with thermocouples, which are essentially zero-current devices. Infrared sensors, though relatively expensive, are appropriate when the temperatures are extremely high. They are available for up to 3,000°C (5,400°F), far exceeding the range of thermocouples or other contact devices. The infrared approach is also attractive when one does not wish to make contact with the surface whose temperature is to be measured. Thus, fragile or wet surfaces, such as painted surfaces coming out of a drying oven, can be monitored in this way. Substances that are chemically reactive or electrically noisy are ideal candidates for infrared measurement. The approach is likewise advantageous in measuring temperature of very large surfaces, such as walls, that would require a large array of thermocouples or RTD’s for measurement. ®
Physical Properties of Thermoelement Materials Thermoelement Material Property Melting point (solidus temp.) °C °F Resistivity µΩ·cm at 0°C at 20°C Ω cmil/ft at 0°C at 20°C Temperature coefficient of resistance, Ω/Ω· °C (0 to 100°C)
J Iron
J, C, T Constantan
T Copper
K, E Chromel
K Alumel
N Nicrosil
N Nisil
1490 2715
1220 2228
1083 1981
1427 2600
1399 2550
1420 2590
1330 2425
1860 3380
1850 3362
1769 3216
1927 3501
1826 3319
8.57 9.67 51.5 58.2
48.9 48.9 294.2 294
1.56 1.724 9.38 10.37
70 70.6 421 425
28.1 29.4 169 177
97.4 97.8
32.5 34.6
19.0 19.6 114.3 117.7
18.4 18.9 110.7 114.0
9.83 10.4 59.1 62.4
19.0
17.5
114.5
106
65 x 10-4
-0.1 x 10-4
Coefficient of thermal expansion 11.7 x 10-6 14.9 x 10-6 in./in. °C (20 to 100°C) Thermal conductivity at 100°C Cal·cm/s·cm2·°C BTU·ft/h·ft2·°F
4.3 x 10-4 4.1 x 10-4
23.9 x 10-4
13.3 x 10-4 12.1 x 10-4
16.6 x 10-6 13.1 x 10-6 12.0 x 10-6
0.162 39.2
0.0506 12.2
0.901 218
0.046 11.1
0.071 17.2
0.0358 8.67
0.0664 16.07
Specific heat at 20°C, cal/ g·°C
0.107
0.094
0.092
0.107
0.125
0.11 8.52
0.12 8.70
Density g/cm3 lb/in3
7.86 0.284
8.92 0.322
8.92 0.322
Tensile strength (annealed) MPa psi
345 50,000
552 80,000
241 35,000
Magnetic attraction
strong
none
none
8.73 0.315
8.60 0.311
0.3078
655 95,000
586 85,000
none
moderate
R J Pt13% Rh Pt10% Rh
R,E B Platinum Pt30% Rh
15.6 x 10-4 16.6 x 10-4 39.2 x 10-4 13.3 x 10-4
9.0 x 10-6
9.0 x 10-6
9.0 x 10-6
0.088 21.3
0.090 21.8
0.171 41.4
B Pt6% Rh
20.6 x 10-4
0.032
0.3143
19.61 0.708
19.97 0.721
21.45 0.775
17.60 0.636
20.55 0.743
690 100,000
621 90,000
317 46,000
310 45,000
138 20,000
483 70,000
276 40,000
none
none
none
none
none
none
none
Omegalloy® Nicrosil
Omegalloy® Nisil
Platinum 13% Rhodium
Platinum 10% Rhodium
Pure Platinum
Platinum 30% Rhodium
Platinum 6% Rhodium
N=Neg JN,TN KP, P=Pos JP ENa TP EP ElementNominal Chemical Composition, % Iron 99.5 … … … b Carbon … … … b … … … Manganese b Sulfur … … … b … … … Phosphorus b Silicon … … … b Nickel 45 … 90 b Copper 55 100 … b Chromium … … 10 Aluminum … … … … Platinum … … … … Rhodium … … … … Magnesium … … … …
ALOMEGA®
CHROMEGA®
Copper
Constantan
Iron
Nominal Chemical Composition of Thermoelements
KN
NP
NN
RP
SP
RN, SN
BP
BN
… … 2 … … 1 95 … … 2 … … …
… … … … … 1.4 84.4 … 14.2 … … … …
… … … … … 4.4 95.5 … … … … … 0.15
… … … … … … … … … … 87 13 …
… … … … … … … … … … 90 10 …
… … … … … … … … … … 100 … …
… … … … … … … … … … 70.4 29.6 …
… … … … … … … … … … 93.9 6.1 …
aTypes JN, TN and EN thermoelements usually contain small amounts of various elements for control of thermal emf, with corresponding reductions in the nickel or copper content, or both. bThemoelectric iron ((JP) contains small but varying amounts of these elements.
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OMEGACLAD® SHEATH SELECTION GUIDE APPLICATIONS U Heat Treating Metal Parts U Gas or Oil Fired Furnaces U Fuel Fired Heat Exchangers U Ceramic Materials Firing U Powder Metal Sintering U Steel Carburizing Furnaces U Vacuum/Atmosphere Melting & Annealing U Solid Waste Incinerators U Heat Process Fluidized Beds U R&D Tube or Box Furnaces
The metallic sheath on the outside of an OMEGACLAD® probe is used to protect the internal thermocouple wires from chemically active atmospheres. In some cases, even hot air can damage thermocouple wires and cause them to permanently lose calibration. Selection of the best type of metal sheath to employ is based on our customers’ intended use, the industry in which they work, and the country where they are located. For instance, the most common OMEGA® metal sheaths are 304 stainless steel and Inconel 600. These are accepted in most industries, including food processing. Stainless steel 304 is a common alloy, readily available and low in the cost of both materials and manufacture. Some industries, however, such as petroleum, medical, nuclear, aircraft, and power generation, have their own standards and may require more complicated and expensive alloys. Listed below are the sheath materials that OMEGA Engineering uses to make OMEGACLAD®. Any materials not on this list must be customized; direct inquiries will have to made to OMEGA South for pricing, availability and size limitations.
304 Stainless Steel
OMEGA SUPERCLAD™
OMEGA Engineering uses a lowcarbon version of 304 stainless, called 304L, mainly because it is easier to weld. In general, it is interchangeable with plain 304.
This alloy has excellent resistance to air at high temperatures. It has an aluminum oxide layer on the surface that prevents further oxidation. This oxidation resistance allows thermocouple probes to operate for extended periods before EMF drift “decalibrates” the thermocouple. It is also popular for its resistance to hydrogen gas and its high strength at high temperatures. Because of form limitations and difficulty in processing, it is more expensive than any of the alloys discussed above.
Applications: Food & beverage processing Chemical processing Dairy Hospital equipment Pharmaceutical equipment Nuclear reactor equipment Containers for mild corrosives Temperature limitations: up to 1,600°F for cyclic processes. Use Inconel 600 for extended use around or above 1,650°F
Inconel 600 This high nickel and chromium content alloy is more expensive than most stainless steels. It is good for extended use at high temperatures and resists corrosion by most simple acids and very pure water. Applications: Furnace components Chemical & food processing Nuclear power generation Caustic chemicals Temperature limitations: up to 2,100°F
Z-17
Applications: Furnace components Gas turbine industry Catalytic converter components Aerospace jet & rocket engines Refractory anchors Waste incinerators Temperature limitations: Approx. 2,220°F Also is acceptable in heated hydrogen, ≈ 2000°F
SUPER OMEGACLAD® SHEATH
THERMOCOUPLE WIRE
Z
CERAMIC INSULATION
310 Stainless Steel
321 Stainless Steel
Hastelloy-X
This is commonly used at higher temperatures because it resists scaling up to 1,900°F. It is stronger and resists air attack better than 304SS at these higher temperatures. Also good in fossil fuel gases at elevated temperatures.
This alloy is similar to 304 stainless except that it incorporates titanium. It is intended for welded components that are exposed to high temperatures, and is especially well suited to long exposure to air and combustion atmospheres of around 800°F.
This alloy is expensive due to the addition of iron, chromium and molybdenum. It has very good high temperature strength and good oxidation resistance. It is a relatively old alloy, less costly and with better performance than some newer alloys.
Applications: (Higher temperatures) Air heaters Baking equipment Chemical processing equipment Furnace parts Heat exchangers and electric power equipment (that does not come in contact with sulphur) Petroleum refining
Applications: Aircraft exhausts & manifolds Jet engine parts Stack liners Welded equipment Chemical processing equipment
Applications: Gas Turbines for power generation Aerospace applications Industrial furnaces Boiler & pressure vessels
Temperature limitations: up to 1,600°F
Temperature limitations: up to 2,150°F
Temperature limitations: up to 1,900°F
316 (& 316L) Stainless Steel Better corrosion resistance to most chemicals, salts, and acids than most stainless steels due to the addition of molybdenum. It has good resistance to sulphur- or chlorinebearing liquids. Applications: Marine trim exteriors Chemical and food processing Petroleum refining equipment Pharmaceutical equipment Paper & pulp Textile finishing Temperature limitations: up to 1,600°F continuously in air or in cyclic corrosive environments, slightly higher in air. Thermocouple Wire Stripper for OMEGACLAD® wire. See PST Series Strippers in Section H.
Z-18
Practical Temperature Measurements*
T
I. C. Sensor V or I
R RESISTANCE
RESISTANCE
VOLTAGE TEMPERATURE
Advantages
Thermistor
R
V
Disadvantages
RTD
TEMPERATURE
T
VOLTAGE or CURRENT
Thermocouple
TEMPERATURE
T TEMPERATURE
T
□ Self-powered □ Simple □ Rugged □ Inexpensive □ Wide variety □ Wide temperature range
□ Most stable □ Most accurate □ More linear than thermocouple
□ High output □ Fast □ Two-wire ohms measurement
□ Most linear □ Highest output □ Inexpensive
□ Non-linear □ Low voltage □ Reference required □ Least stable □ Least sensitive
□ Expensive □ Current source required □ Small ∆ R □ Low absolute resistance □ Self-heating
□ Non-linear □ Limited temperature range □ Fragile □ Current source required □ Self-heating
□ T<200°C □ Power supply required □ Slow □ Self-heating □ Limited configurations
Figure 1
TABLE OF CONTENTS APPLICATION NOTES-PRACTICAL TEMPERATURE MEASUREMENTS Page Common Temperature Transducers ....................................................................................Z-19 Introduction ...........................................................................................................................Z-20 Reference Temperatures ...................................................................................................Z-21 The Thermocouple ................................................................................................................Z-21 Reference Junction............................................................................................................Z-22 Reference Circuit...............................................................................................................Z-23 Hardware Compensation...................................................................................................Z-24 Voltage-to-Temperature Conversion ..................................................................................Z-25 Practical Thermocouple Measurement ...............................................................................Z-27 Noise Rejection .................................................................................................................Z-27 Poor Junction Connection..................................................................................................Z-29 Decalibration......................................................................................................................Z-29 Shunt Impedance ..............................................................................................................Z-29 Galvanic Action..................................................................................................................Z-30 Thermal Shunting ..............................................................................................................Z-30 Wire Calibration .................................................................................................................Z-30 Diagnostics ........................................................................................................................Z-31 Summary ...........................................................................................................................Z-32 The RTD .................................................................................................................................Z-33 History ...............................................................................................................................Z-33 Metal Film RTD's ...............................................................................................................Z-33 Resistance Measurement..................................................................................................Z-34 3-Wire Bridge Measurement Errors...................................................................................Z-35 Resistance to Temperature Conversion.............................................................................Z-35 Practical Precautions.........................................................................................................Z-36 *Courtesy Hewlett Packard Company
Z-19
TABLE OF CONTENTS APPLICATION NOTES-PRACTICAL TEMPERATURE MEASUREMENTS The Thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-36 Linear Thermistors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-37 Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-37 Monolithic Linear Temperature Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-37 Appendix A-The Empirical Laws of Thermocouples . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-37 Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-38 Thermocouple Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-38 Base Metal Thermocouples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-38 Standard Wire Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-39 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z-40
INTRODUCTION Synthetic fuel research, solar energy conversion and new engine development are but a few of the burgeoning disciplines responding to the state of our dwindling natural resources. As all industries place new emphasis on energy efficiency, the fundamental measurement of temperature assumes new importance. The purpose of this application note is to explore the more common temperature monitoring techniques and introduce pro cedures for improving their accuracy. We will focus on the four most common temperature transducers: the thermocouple, the RTD, the thermistor and the integrated circuit sensor. Despite the widespread popularity of the thermocouple, it is frequently misused. For this reason, we will concentrate primarily on thermocouple measurement techniques. Appendix A contains the empirical laws of thermocouples which are the basis for all derivations used herein. Readers wishing a more thorough discussion of thermocouple theory are invited to read REFERENCE 17 in the Bibliography. For those with a specific thermocouple application, Appendix B may aid in choosing the best type of thermocouple. Throughout this application note, we will emphasize the practical considerations of transducer placement, signal conditioning and instrumentation. Early Measuring Devices - Galileo is credited with inventing the thermometer, circa 1592.1 In an open container filled with colored alcohol he suspended a long narrow-throated glass tube, at the upper end of which was a hollow sphere. When heated, the air in the sphere expanded and bubbled through the liquid. Cooling the sphere caused the liquid to move up the tube1 Fluctuations in the temperature of the sphere could then be observed by noting the position of the liquid inside the tube. This "upside-down" thermometer was a poor indicator since the level changed with barometric pressure and the tube had no scale. Vast improvements were made in temperature measurement accuracy with the development of the 1
Refer to Bibliography 1,2,3.
Florentine thermometer, which incorporated sealed construction and a graduated scale. In the ensuing decades, many thermometric scales were conceived, all based on two or more fixed points One scale, however, wasn't universally recognized until the early 1700's, when Gabriel Fahrenheit, a Dutch instrument maker, produced accurate and repeatable mercury thermometers. For the fixed point on the low end of his temperature scale, Fahrenheit used a mixture of ice water and salt (or ammonium chloride). This was the lowest temperature he could reproduce, and he labeled it "zero degrees". For the high end of his scale, he chose human blood temperature and called it 96 degrees. Why 96 and not 100 degrees? Earlier scales had been divided into twelve parts. Fahrenheit, in an apparent quest for more resolution divided his scale into 24, then 48 and eventually 96 parts. The Fahrenheit scale gained popularity primarily because of the repeatability and quality of the thermometers that Fahrenheit built. Around 1742, Anders Celsius proposed that the melting point of ice and the boiling point of water be used for the two benchmarks. Celsius selected zero degrees as the boiling point and 100 degrees as the melting point. Later, the end points were reversed and the centigrade scale was born. In 1948 the name was officially changed to the Celsius scale. In the early 1800's William Thomson (Lord Kelvin), developed a universal thermodynamic scale based upon the coefficient of expansion of an ideal gas. Kelvin established the concept of absolute zero and his scale remains the standard for modern thermometry. The conversion equations for the four modern temperature scales are: °C = 5/9 (°F - 32) °F= 9/5 °C + 32 K = °C + 273.15 °R= °F + 459.67 The Rankine Scale (ºR) is simply the Fahrenheit equivalent of the Kelvin scale, and was named after an early pioneer in the field of thermodynamics, W.J.M. Rankine.
Z-20
Z
Reference Temperatures We cannot build a temperature divider as we can a voltage divider, nor can we add temperatures as we would add lengths to measure distance. We must rely upon temperatures established by physical phenomena which are easily observed and consistent in nature. The International Practical Temperature Scale (IPTS) is based on such phenomena. Revised in 1968, it establishes eleven reference temperatures. Since we have only these fixed temperatures to use as a reference, we must use instruments to interpolate between them. But accurately interpolating between these temperatures can require some fairly exotic transducers, many of which are too complicated or expensive to use in a practical situation. We shall limit our discussion to the four most common temperature transducers: thermocouples, resistance-temperature
Metal A
+ eAB –
eAB = SEEBECK VOLTAGE Figure 3 All dissimilar metals exhibit this effect. The most common combinations of two metals are listed in Appendix B of this application note, along with their important characteristics. For small changes in temperature the Seebeck voltage is linearly proportional to temperature: ∆eAB = α∆T Where α, the Seebeck coefficient, is the constant of proportionality.
detector’s (RTD’s), thermistors, and integrated circuit sensors.
IPTS-68 REFERENCE TEMPERATURES EQUILIBRIUM POINT
K
Triple Point of Hydrogen Liquid/Vapor Phase of Hydrogen
13.81 17.042
-259.34 -256.108
at 25/76 Std. Atmosphere Boiling Point of Hydrogen
20.28
-252.87
Boiling Point of Neon Triple Point of Oxygen
27.102 54.361
-246.048 -218.789
Boiling Point of Oxygen Triple Point of Water
90.188 273.16
-182.962 .01
C
0
Boiling Point of Water Freezing Point of Zinc
373.15 692.73
100 419.58
Freezing Point of Silver Freezing Point of Gold
1235.08 1337.58
961.93 1064.43
Measuring Thermocouple Voltage - We can’t measure the Seebeck voltage directly because we must first connect a voltmeter to the thermocouple, and the voltmeter leads themselves create a new thermoelectric circuit. Let’s connect a voltmeter across a copper-constantan (Type T) thermocouple and look at the voltage output: J3 Fe
Cu + –
Cu +
v
C
Cu
V1 –
J1
Fe J2 EQUIVALENT CIRCUITS
Table 1
Cu
–
+
Cu
Cu
V3
THE THERMOCOUPLE When two wires composed of dissimilar metals are
+ V1 –
J3
Cu
J1
+ V1 –
–
+
joined at both ends and one of the ends is heated, there is a continuous current which flows in the thermoelectric circuit. Thomas Seebeck made this discovery in 1821.
Metal A
Metal B
V2 J2
C
–
+ Cu
J1
V2
C
J2
V3 = 0 MEASURING JUNCTION VOLTAGE WITH A DVM Figure 4
Metal C
Metal B THE SEEBECK EFFECT Figure 2 If this circuit is broken at the center, the net open circuit voltage (the Seebeck voltage) is a function of the junction temperature and the composition of the two metals.
We would like the voltmeter to read only V1, but by connecting the voltmeter in an attempt to measure the output of Junction J1, we have created two more metallic junctions: J2 and J3. Since J3 is a copper-tocopper junction, it creates no thermal EMF (V3 = 0), but J2 is a copper-to-constantan junction which will add an EMF (V2) in opposition to V1. The resultant voltmeter reading V will be proportional to the temperature difference between J1 and J2. This says that we can’t find the temperature at J1 unless we first find the temperature of J2.
Z-21
The Reference Junction
Cu + –
+
Cu
v
+
Cu
Cu
V2
+ V1 –
–
+ V1 –
v
J1
C
J1
–
+
–
T
V2
Voltmeter J2
J2 T=0°C
Z
Ice Bath
EXTERNAL REFERENCE JUNCTION Figure 5
The copper-constantan thermocouple shown in Figure 5 is a unique example because the copper wire is the same metal as the voltmeter terminals. Let’s use an iron-constantan (Type J) thermocouple instead of the copper-constantan. The iron wire (Figure 6) increases the number of dissimilar metal junctions in the circuit, as both voltmeter terminals become Cu-Fe thermocouple junctions.
One way to determine the temperature of J2 is to physically put the junction into an ice bath, forcing its temperature to be 0ºC and establishing J2 as the Reference Junction. Since both voltmeter terminal junctions are now copper-copper, they create no thermal emf and the reading V on the voltmeter is proportional to the temperature difference between J1 and J2.
V3 -+
Now the voltmeter reading is (see Figure 5): V = (V1 - V2) ≅ α(tJ1 - tJ2) If we specify TJ1 in degrees Celsius: TJ1 (ºC) + 273.15 = tJ1
+
+ –
V1 = V if V3 = V4
J4
i.e., if TJ3 = TJ4
JUNCTION VOLTAGE CANCELLATION Figure 7 If both front panel terminals are not at the same temperature, there will be an error. For a more precise measurement, the copper voltmeter leads should be extended so the copper-to-iron junctions are made on an isothermal (same temperature) block:
Cu
Isothermal Block
J3
Cu + –
Fe
v
Fe V2
Cu Voltmeter
Fe
v
V1
-+ Voltmeter V4
We use this protracted derivation to emphasize that the ice bath junction output, V2, is not zero volts. It is a function of absolute temperature. By adding the voltage of the ice point reference junction, we have now referenced the reading V to 0ºC. This method is very accurate because the ice point temperature can be precisely controlled. The ice point is used by the National Bureau of Standards (NBS) as the fundamental reference point for their thermocouple tables, so we can now look at the NBS tables and directly convert from voltage V to Temperature TJ1.
Cu
v
–
then V becomes: V = V1 - V2 = α [(TJ1 + 273.15) - (TJ2+ 273.15)] = α (TJ1 - TJ2) = α (TJ1 - 0) V = αTJ1
J3
J3
Cu
J4
C
T1
TREF
J1
Cu
Ice Bath
C
REMOVING JUNCTIONS FROM DVM TERMINALS Figure 8
Fe J4
J2
Ice Bath
IRON-CONSTANTAN COUPLE Figure 6
The isothermal block is an electrical insulator but a good heat conductor, and it serves to hold J3 and J4 at the same temperature. The absolute block temperature is unimportant because the two Cu-Fe junctions act in opposition. We still have V = α (T1 - TREF) Z-22
Reference Circuit Let’s replace the ice bath with another isothermal block
This is a useful conclusion, as it completely eliminates the need for the iron (Fe) wire in the LO lead:
Isothermal Block Cu
HI
LO
Cu
v
J1
J3 J4
–
C
Fe
Voltmeter
Cu
+
Fe
Cu
Fe J3 J4
J REF TREF Isothermal Block
TREF
ELIMINATING THE ICE BATH Figure 9a
EQUIVALENT CIRCUIT Figure 11
The new block is at Reference Temperature TREF, and because J3 and J4 are still at the same temperature, we can again show that V = α (T1-TREF) This is still a rather inconvenient circuit because we have to connect two thermocouples. Let’s eliminate the extra Fe wire in the negative (LO) lead by combining the Cu-Fe junction (J4) and the Fe-C junction (JREF). We can do this by first joining the two isothermal blocks (Figure 9b). Cu
HI
Again, V = α (TJ1 - TREF), where α is the Seebeck coefficient for an Fe-C thermocouple.| Junctions J3 and J4, take the place of the ice bath. These two junctions now become the Reference Junction. Now we can proceed to the next logical step: Directly measure the temperature of the isothermal block (the Reference Junction) and use that information to compute the unknown temperature, TJ1. Block Temperature = TREF
Fe Cu
J1
J3 LO
Cu J4
+
C
Fe
–
J REF
V = α (TJ1 - TJREF ) Now we call upon the law of intermediate metals (see Appendix A) to eliminate the extra junction. This empirical “law” states that a third metal (in this case, iron) inserted between the two dissimilar metals of a thermocouple junction will have no effect upon the output voltage as long as the two junctions formed by the additional metal are at the same temperature: =
Metal A
Metal C
Isothermal Connection Thus the low lead in Fig. 9b:
Cu
Becomes:
C
Fe
=
C
Cu
TREF TREF
LAW OF INTERMEDIATE METALS Figure 10
+ V1 –
J1
C
Cu RT
EXTERNAL REFERENCE JUNCTION-NO ICE BATH Figure 12
We haven’t changed the output voltage V. It is still
Metal C
Fe
v
Voltmeter
Isothermal Bloc k @ TREF
Metal B
J3
J4
JOINING THE ISOTHERMAL BLOCKS Figure 9b
Metal A
J1
C
A thermistor, whose resistance RT is a function of temperature, provides us with a way to measure the absolute temperature of the reference junction. Junctions J3 and J4 and the thermistor are all assumed to be at the same temperature, due to the design of the isothermal block. Using a digital multimeter under computer control, we simply: 1) Measure RT to find TREF and convert TREF to its equivalent reference junction voltage, VREF , then 2) Measure V and subtract VREF to find V1, and convert V1 to temperature TJ1. This procedure is known as Software Compensation because it relies upon the software of a computer to compensate for the effect of the reference junction. The isothermal terminal block temperature sensor can be any device which has a characteristic proportional to absolute temperature: an RTD, a thermistor, or an integrated circuit sensor. It seems logical to ask: If we already have a device that will measure absolute temperature (like an RTD or thermistor), why do we even bother with a thermocouple that requires reference junction compensation? The
Z-23
single most important answer to this question is that the thermistor, the RTD, and the integrated circuit transducer are only useful over a certain temperature range. Thermocouples, on the other hand, can be used over a range of temperatures, and optimized for various atmospheres. They are much more rugged than thermistors, as evidenced by the fact that thermocouples are often welded to a metal part or clamped under a screw. They can be manufactured on the spot, either by soldering or welding. In short, thermocouples are the most versatile temperature transducers available and, since the measurement system performs the entire task of reference compensation and software voltage to-temperature conversion, using a thermocouple becomes as easy as connecting a pair of wires. Thermocouple measurement becomes especially convenient when we are required to monitor a large number of data points. This is accomplished by using the isothermal reference junction for more than one thermocouple element (see Figure 13). A reed relay scanner connects the voltmeter to the various thermocouples in sequence. All of the voltmeter and scanner wires are copper, independent of the type of thermocouple chosen. In fact, as long as we know what each thermocouple is, we can mix thermocouple types on the same isothermal junction block (often called a zone box) and make the appropriate modifications in software. The junction block temperature sensor RT is located at the center of the block to minimize errors due to thermal gradients. Software compensation is the most versatile technique we have for measuring thermocouples. Many thermocouples are connected on the same block, copper leads are used throughout the scanner, and the technique is independent of the types of thermocouples chosen. In addition, when using a data acquisition system with a built-in zone box, we simply connect the thermocouple as we would a pair of test leads. All of the conversions are performed by the computer. The one disadvantage is that the computer requires a small amount of additional time to calculate the reference junction temperature. For maximum speed we can use hardware compensation.
Fe
Cu
+
Fe
C
+
HI
–
LO
Voltmeter
Pt - 10% Rh
Isothermal Block (Zone Box)
ZONE BOX SWITCHING Figure 13
Hardware Compensation Rather than measuring the temperature of the reference junction and computing its equivalent voltage as we did with software compensation, we could insert a battery to cancel the offset voltage of the reference junction. The combination of this hardware compensation voltage and the reference junction voltage is equal to that of a 0ºC junction. The compensation voltage, e, is a function of the temperature sensing resistor, RT. The voltage V is now referenced to 0ºC, and may be read directly and converted to temperature by using the NBS tables. Another 2name for this circuit is the electronic ice point reference. These circuits are commercially available for use with any voltmeter and with a wide variety of thermocouples. The major drawback is that a unique ice point reference circuit is usually needed for each individual thermocouple type. Figure 15 shows a practical ice point reference circuit that can be used in conjunction with a reed relay scanner to compensate an entire block of thermocouple inputs. All the thermocouples in the block must be of the same type, but each block of inputs can accommodate a different thermocouple type by simply changing gain resistors. Fe
C
Fe –
Cu
Fe –
+
C
v
= –
Cu
Cu
+
T
T v
Pt All Copper Wires
Cu
+
RT
Fe T
=
C
Fe –
Cu
Cu +
RT Cu e
0°C
2
Refer to Bibliography 6.
HARDWARE COMPENSATION CIRCUIT Figure 14 Z-24
Z
OMEGA TAC-Electronic Ice Point and Thermocouple Preamplifier/Linearizer Plugs into Standard Connector OMEGA Electronic Ice Point Built into Thermocouple Connector -”MCJ”
Cu
Fe
Cu
OMEGA Ice Point Reference Chamber. Electronic Refigeration Eliminates Ice Bath C
RH
PRACTICAL HARDWARE COMPENSATION Figure 15 The advantage of the hardware compensation circuit or electronic ice point reference is that we eliminate the need to compute the reference temperature. This saves us two computation steps and makes a hardware compensation temperature measurement somewhat faster than a software compensation measurement. HARDWARE COMPENSATION
SOFTWARE COMPENSATION
Fast Restricted to one thermocouple type per card
Requires more computer manipulation time Versatile - accepts any thermocouple
TABLE 2
Voltage-To-Temperature Conversion We have used hardware and software compensation to synthesize an ice-point reference. Now all we have to do is to read the digital voltmeter and convert the voltage reading to a temperature. Unfortunately, the temperature-versus-voltage relationship of a thermocouple is not linear. Output voltages for the more common thermocouples are plotted as a function of temperature in Figure 16. If the slope of the curve (the Seebeck coefficient) is plotted vs. temperature, as in Figure 17, it becomes quite obvious that the thermocouple is a non-linear device. A horizontal line in Figure 17 would indicate a constant α, in other words, a linear device. We notice that the slope of the type K thermocouple approaches a constant over a temperature range from 0ºC to 1000ºC. Consequently, the type K can be used with a multiplying voltmeter and an external ice point reference to obtain a moderately accurate direct readout of temperature. That is, the temperature display involves only a scale factor. This procedure works with voltmeters. By examining the variations in Seebeck coefficient, 3
Refer to Bibliography 4.
Z-25
80
E Type
Metals +
60 Millivolts
Integrated Temperature Sensor
we can easily see that using one constant scale factor would limit the temperature range of the system and restrict the system accuracy. Better conversion accuracy can be obtained by reading the voltmeter and consulting the National Bureau of Standards Thermocouple Tables3 in Section T of the OMEGA TEMPERATURE MEASUREMENT HANDBOOK - see Table 3. T = a0 +a1 x + a2x2 + a3x3 . . . +anxn where T = Temperature x = Thermocouple EMF in Volts a = Polynomial coefficients unique to each thermocouple n = Maximum order of the polynomial As n increases, the accuracy of the polynomial improves. A representative number is n = 9 for ± 1ºC accuracy. Lower order polynomials may be used over a narrow temperature range to obtain higher system speed. Table 4 is an example of the polynomials used to convert voltage to temperature. Data may be utilized in packages for a data acquisition system. Rather than directly calculating the exponentials, the computer is programmed to use the nested polynomial form to save execution time. The polynomial fit rapidly degrades outside the temperature range shown in Table 4 and should not be extrapolated outside those limits.
–
K E J K R
J
40
R
20
S
S T
0°
500°
Chromel vs. Constantan Iron vs. Constantan Chromel vs. Alumel Platinum vs. Platinum 13% Rhodium Platinum vs. Platinum 10% Rhodium Copper vs. Constantan
1000° 1500° 2000°
Temperature °C
THERMOCOUPLE TEMPERATURE vs. VOLTAGE GRAPH Figure 16
mV
Seebeck Coefficient mV/°C
100
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40
80 E J
T
60
Linear Region (SeeText) 40 K
20 R S
–500°
0°
500°
1000°
Temperature °C
1500°
.00
.01
.02
0.00 1.70 3.40 5.09 6.78 8.47 10.15 11.82 13.49 15.16 16.83 18.48 20.14 21.79 23.44
0.17 1.87 3.57 5.26 6.95 8.63 10.31 11.99 13.66 15.33 16.99 18.65 20.31 21.96 23.60
0.34 2.04 3.74 5.43 7.12 8.80 10.48 12.16 13.83 15.49 17.16 18.82 20.47 22.12 23.77
.03 .04 .05 .06 .07 .08 TEMPERATURES IN DEGREES C (IPTS 1968) 0.51 2.21 3.91 5.60 7.29 8.97 10.65 12.32 13.99 15.66 17.32 18.98 20.64 22.29 23.93
TYPE J
Nickel-10% Chromium(+)
TYPE R
Nickel-10% Chromium(+)
Versus
Constantan(-)
1.02 2.72 4.42 6.11 7.79 9.47 11.15 12.83 14.49 16.16 17.82 19.48 21.13 22.78 24.42
1.19 2.89 4.58 6.27 7.96 9.64 11.32 12.99 14.66 16.33 17.99 19.64 21.30 22.94 24.59
1.36 3.06 4.75 6.44 8.13 9.81 11.49 13.16 14.83 16.49 18.15 19.81 21.46 23.11 24.75
1.53 3.23 4.92 6.61 8.30 9.98 11.65 13.33 14.99 16.66 18.32 19.97 21.63 23.27 24.92
1.70 3.40 5.09 6.78 8.47 10.15 11.82 13.49 15.16 16.83 18.48 20.14 21.79 23.44 25.08
TYPE E THERMOCOUPLE Table 3
TYPE K
Iron(+)
Versus
0.85 2.55 4.25 5.94 7.62 9.31 10.98 12.66 14.33 15.99 17.66 19.31 20.97 22.62 24.26
.10
Constantan(-)
TYPE S
TYPE T
Platinum-13% Rhodium(+) Platinum-10% Rhodium(+)
Copper(+)
Versus
Versus
Versus
Versus
Nickel-5%(-) (Aluminum Silicon) 0ºC to 1370ºC ± 0.7ºC 8th order
Platinum(-)
Platinum(-)
Constantan(-)
0ºC to 1750ºC ± 1ºC 9th order
-160ºC to 400ºC ±0.5ºC 7th order
-100ºC to 1000ºC ± 0.5ºC 9th order
0ºC to 760ºC ± 0.1ºC 5th order
a1
0.104967248
-0.048868252
0.226584602
0.263632917
0.927763167
0.100860910
a2
17189.45282
19873.14503
24152.10900
179075.491
169526.5150
25727.94369
a3
-282639. 0850
-218614.5353
67233.4248
-48840341.37
-31568363.94
-767345.8295
a4
12695339.5
11569199.78
2210340.682
1.90002E + 10
8990730663
78025595.81
a5
-448703084.6
-264917531.4
-860963914.9
-4.82704E + 12
-1.63565E + 12
-9247486589
a6
1.10866E + 10
2018441314
a7
-1. 76807E + 11
a0
0ºC to 1000ºC ± 0.5ºC 8th order
4.83506E + 10
7.62091E + 14
1.88027E + 14
6.97688E + 11
-1. 18452E + 12
-7.20026E + 16
-1.37241E + 16
-2.66192E + 13 3.94078E + 14
a8
1.71842E + 12
1.38690E + 13
3.71496E + 18
6.17501E + 17
a9
-9.19278E + 12
-6.33708E + 13
-8.03104E + 19
-1.56105E + 19
2.06132E + 13
1.69535E + 20
TEMPERATURE CONVERSION EQUATION: T = a0 +a1 x + a2x2 + . . . +anxn NESTED POLYNOMIAL FORM: T = a0 + x(a1 + x(a2 + x (a3 + x(a4 + a5x)))) (5th order) where x is in Volts, T is in °C NBS POLYNOMIAL COEFFICIENTS Table 4 The calculation of high-order polynomials is a timeAll the foregoing procedures assume the consuming task for a computer. As we mentioned thermocouple voltage can be measured accurately and before, we can save time by using a lower order easily; however, a quick glance at Table 3 shows us that polynomial for a smaller temperature range. In the thermocouple output voltages are very small indeed. software for one data acquisition system, the Examine the requirements of the system voltmeter: thermocouple characteristic curve is divided into eight THERMOCOUPLE SEEBECK DVM SENSITIVITY sectors, and each sector is approximated by a thirdTYPE COEFFICIENT FOR 0.1ºC order polynomial.* (µV/ºC) @ 20ºC (µV)
{
Temp.
E J K R S T
a
2
3
CURVE DIVIDED INTO SECTORS Figure 18
62 51 40 7 7 40
6.2 5.1 4.0 0.7 0.7 4.0
REQUIRED DVM SENSITIVITY
Voltage
Ta = bx + cx + dx
mV 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40
2000°
SEEBECK COEFFICIENT vs. TEMPERATURE Figure 17 TYPE E
0.68 2.38 4.08 5.77 7.46 9.14 10.82 12.49 14.16 15.83 17.49 19.15 20.80 22.45 24.10
.09
Table 5 Even for the common type K thermocouple, the voltmeter must be able to resolve 4 µV to detect a 0. 1ºC change. The magnitude of this signal is an open invitation for noise to creep into any system. For this reason, instrument designers utilize several fundamental noise rejection techniques, including tree switching, normal mode filtering, integration and guarding.
* HEWLETT PACKARD 3054A.
Z-26
Z
PRACTICAL THERMOCOUPLE MEASUREMENT Noise Rejection
C DVM
C + –
Signal
(20 Channels)
C Tree Switch1
HI
+
= Noise Sour ce
~
–
Signal
DVM 20 C
C
C
+ Signal
DVM
– C
HI
Noise ~ Source
HI
~ Stray capacitance to noise source is reduced nearly 20:1 by leaving Tree Switch 2 open.
Next 20 Channels C Tree Switch2
~ =
TREE SWITCHING Figure 19
Tree Switching - Tree switching is a method of organizing the channels of a scanner into groups, each with its own main switch.
Guarding - Guarding is a technique used to reduce interference from any noise source that is common to both high and low measurement leads, i.e., from common mode noise sources.
Without tree switching, every channel can contribute noise directly through its stray capacitance. With tree switching, groups of parallel channel capacitances are in series with a single tree switch capacitance. The result is greatly reduced crosstalk in a large data acquisition system, due to the reduced interchannel capacitance.
Let’s assume a thermocouple wire has been pulled through the same conduit as a 220 Vac supply line. The capacitance between the power lines and the thermocouple lines will create an AC signal of approximately equal magnitude on both thermocouple wires. This common mode signal is not a problem in an ideal circuit, but the voltmeter is not ideal. It has some capacitance between its low terminal and safety ground (chassis). Current flows through this capacitance and through the thermocouple lead resistance, creating a normal mode noise signal. The guard, physically a floating metal box surrounding the entire voltmeter circuit, is connected to a shield surrounding the thermocouple wire, and serves to shunt the interfering current.
Analog Filter - A filter may be used directly at the input of a voltmeter to reduce noise. It reduces interference dramatically, but causes the voltmeter to respond more slowly to step inputs. Integration - Integration is an A/D technique which essentially averages noise over a full line cycle; thus, power line related noise and its harmonics are virtually eliminated. If the integration period is chosen to be less than an integer line cycle, its noise rejection properties are essentially negated. Since thermocouple circuits that cover long distances are especially susceptible to power line related noise, it is advisable to use an integrating analog-to-digital converter to measure the thermocouple voltage. Integration is an especially attractive A/D technique in light of recent innovations which allow reading rates of 48 samples per second with full cycle integration.
VIN
Z-27
VOUT
t
t
ANALOG FILTER Figure 20
220 VAC Line
Distributed Capacitance
HI
LO Distributed Resistance
Without Guard DVM
HI
Z
LO Without Guard
Guard DVM
GUARD SHUNTS INTERFERING WITH CURRENT Figure 21 Each shielded thermocouple junction can directly HI contact an interfering source with no adverse effects, R since provision is made on the scanner to switch the LO guard terminal separately for each thermocouple Guard channel. This method of connecting the shield to guard serves to eliminate ground loops often created when Noise Current the shields are connected to earth ground. Figure 24 The dvm guard is especially useful in eliminating noise voltages created when the thermocouple junction Notice that we can also minimize the noise by comes into direct contact with a common mode noise minimizing Rs. We do this by using larger thermocouple source. wire that has a smaller series resistance. S
To reduce the possibility of magnetically induced noise, the thermocouple should be twisted in a uniform manner. Thermocouple extension wires are available commercially in a twisted pair configuration.
240 VRMS
Figure 22 In Figure 22 we want to measure the temperature at the center of a molten metal bath that is being heated by electric current. The potential at the center of the bath is 120 V RMS. The equivalent circuit is: HI RS LO
120VRMS
Noise Current
Figure 23
Practical Precautions - We have discussed the concepts of the reference junction, how to use a polynomial to extract absolute temperature data, and what to look for in a data acquisition system, to minimize the effects of noise. Now let’s look at the thermocouple wire itself. The polynomial curve fit relies upon the thermocouple wire’s being perfect; that is, it must not become decalibrated during the act of making a temperature measurement. We shall now discuss some of the pitfalls of thermocouple thermometry. Aside from the specified accuracies of the data acquisition system and its zone box, most measurement errors may be traced to one of these primary sources: 1. Poor junction connection 2. Decalibration of thermocouple wire 3. Shunt impedance and galvanic action 4. Thermal shunting 5. Noise and leakage currents 6. Thermocouple specifications 7. Documentation
The stray capacitance from the dvm Lo terminal to chassis causes a current to flow in the low lead, which in turn causes a noise voltage to be dropped across the series resistance of the thermocouple, Rs. This voltage appears directly across the dvm Hi to Lo terminals and causes a noisy measurement. If we use a guard lead connected directly to the thermocouple, we drastically reduce the current flowing in the Lo lead. The noise current now flows in the guard lead where it cannot affect the reading: Z-28
Poor Junction Connection There are a number of acceptable ways to connect two thermocouple wires: soldering, silver-soldering, welding, etc. When the thermocouple wires are soldered together, we introduce a third metal into the thermocouple circuit, but as long as the temperatures on both sides of the thermocouple are the same, the solder should not introduce any error. The solder does limit the maximum temperature to which we can subject this junction. To reach a higher measurement temperature, the joint must be welded. But welding is not a process to be taken lightly.3 Overheating can degrade the wire, and the welding gas and the atmosphere in which the wire is welded can both diffuse into the thermocouple metal, changing its characteristics. The difficulty is compounded by the very different nature of the two metals being joined. Commercial thermocouples are welded on expensive machinery using a capacitive-discharge technique to insure uniformity.
Robert Moffat in his Gradient Approach to Thermocouple Thermometry explains that the thermocouple voltage is actually generated by the section of wire that contains the temperature gradient, and not necessarily by the junction.4 For example, if we have a thermal probe located in a molten metal bath, there will be two regions that are virtually isothermal and one that has a large gradient. In Figure 26, the thermocouple junction will not produce any part of the output voltage. The shaded section will be the one producing virtually the entire thermocouple output voltage. If, due to aging or annealing, the output of this thermocouple were found 25˚C
200 300 400 500
500˚C Metal Bath
Fe C
Solder (Pb, Sn)
GRADIENT PRODUCES VOLTAGE Figure 26
Junction: Fe - Pb, Sn - C = Fe - C
SOLDERING A THERMOCOUPLE Figure 25
to be drifting, then replacing the thermocouple junction alone would not solve the problem. We would have to replace the entire shaded section, since it is the source of the thermocouple voltage.
A poor weld can, of course, result in an open connection, which can be detected in a measurement situation by performing an open thermocouple check. This is a common test function available with dataloggers. While the open thermocouple is the easiest malfunction to detect, it is not necessarily the most common mode of failure.
Decalibration Decalibration is a far more serious fault condition than the open thermocouple because it can result in a temperature reading that appears to be correct. Decalibration describes the process of unintentionally altering the physical makeup of the thermocouple wire so that it no longer conforms to the NBS polynomial within specified limits. Decalibration can result from diffusion of atmospheric particles into the metal caused by temperature extremes. It can be caused by high temperature annealing or by cold-working the metal, an effect that can occur when the wire is drawn through a conduit or strained by rough handling or vibration. Annealing can occur within the section of wire that undergoes a temperature gradient. 3 Refer
to Bibliography 5 Refer to Bibliography 9 5 Refer to Bibliography 7
100˚C
Thermocouple wire obviously can’t be manufactured perfectly; there will be some defects which will cause output voltage errors. These inhomogeneities can be especially disruptive if they occur in a region of steep temperature gradient. Since we don’t know where an imperfection will occur within a wire, the best thing we can do is to avoid creating a steep gradient. Gradients can be reduced by using metallic sleeving or by careful placement of the thermocouple wire.
Shunt Impedance High temperatures can also take their toll on thermocouple wire insulators. Insulation resistance decreases exponentially with increasing temperature, even to the point that it creates a virtual junction.5 Assume we have a completely open thermocouple operating at a high temperature. The leakage Resistance, RL, can be sufficiently low to complete the circuit path and give us an improper voltage reading. Now let’s assume the thermocouple is not open, but we are using a very long section of small diameter wire.
4
Z-29
(
)
RL
To DVM
LEAKAGE RESISTANCE Figure 27 RS
RS RL
To DVM RS
T1
T2 RS
VIRTUAL JUNCTION Figure 28
Z
If the thermocouple wire is small, its series resistance, RS, will be quite high and under extreme conditions RL < < RS. This means that the thermocouple junction will appear to be at RL and the output will be proportional to T1 not T2. High temperatures have other detrimental effects on thermocouple wire. The impurities and chemicals within the insulation can actually diffuse into the thermocouple metal causing the temperature-voltage dependence to deviate from published values. When using thermocouples at high temperatures, the insulation should be chosen carefully. Atmospheric effects can be minimized by choosing the proper protective metallic or ceramic sheath
Galvanic Action The dyes used in some thermocouple insulation will form an electrolyte in the presence of water. This creates a galvanic action, with a resultant output hundreds of times greater than the Seebeck effect. Precautions should be taken to shield thermocouple wires from all harsh atmospheres and liquids.
Thermal Shunting No thermocouple can be made without mass. Since it takes energy to heat any mass, the thermocouple will slightly alter the temperature it is meant to measure. If the mass to be measured is small, the thermocouple must naturally be small. But a thermocouple made with small wire is far more susceptible to the problems of contamination, annealing, strain, and shunt impedance. To minimize these effects, thermocouple extension wire can be used. Extension wire is commercially available wire primarily intended to cover long distances between the measuring thermocouple and the voltmeter. Extension wire is made of metals having Seebeck coefficients very similar to a particular thermocouple type. It is generally larger in size so that its series resistance does not become a factor when traversing long distances. It can also be pulled more readily through a conduit than can very small thermocouple
wire. It generally is specified over a much lower temperature range than premium grade thermocouple wire. In addition to offering a practical size advantage, extension wire is less expensive than standard thermocouple wire. This is especially true in the case of platinum-based thermocouples. Since the extension wire is specified over a narrower temperature range and it is more likely to receive mechanical stress, the temperature gradient across the extension wire should be kept to a minimum. This, according to the gradient theory, assures that virtually none of the output signal will be affected by the extension wire. Noise - We have already discussed line-related noise as it pertains to the data acquisition system. The techniques of integration, tree switching and guarding serve to cancel most line-related interference. Broadband noise can be rejected with the analog filter. The one type of noise the data acquisition system cannot reject is a dc offset caused by a dc leakage current in the system. While it is less common to see dc leakage currents of sufficient magnitude to cause appreciable error, the possibility of their presence should be noted and prevented, especially if the thermocouple wire is very small and the related series impedance is high.
Wire Calibration Thermocouple wire is manufactured to a certain specification, signifying its conformance with the NBS tables. The specification can sometimes be enhanced by calibrating the wire (testing it at known temperatures). Consecutive pieces of wire on a continuous spool will generally track each other more closely than the specified tolerance, although their output voltages may be slightly removed from the center of the absolute specification. If the wire is calibrated in an effort to improve its fundamental specifications, it becomes even more imperative that all of the aforementioned conditions be heeded in order to avoid decalibration.
Z-30
Documentation - It may seem incongruous to speak of documentation as being a source of voltage measurement error, but the fact is that thermocouple systems, by their very ease of use, invite a large number of data points. The sheer magnitude of the data can become quite unwieldy. When a large amount of data is taken, there is an increased probability of error due to mislabeling of lines, using the wrong NBS curve, etc. Since channel numbers invariably change, data should be categorized by measureand, not just channel number.6 Information about any given measureand, such as transducer type, output voltage, typical value and location, can be maintained in a data file. This can be done under computer control or simply by filling out a pre-printed form. No matter how the data is maintained, the importance of a concise system should not be underestimated, especially at the outset of a complex data gathering project.
Diagnostics Most of the sources of error that we have mentioned are aggravated by using the thermocouple near its temperature limits. These conditions will be encountered infrequently in most applications. But what about the situation where we are using small thermocouples in a harsh atmosphere at high temperatures? How can we tell when the thermocouple is producing erroneous results? We need to develop a reliable set of diagnostic procedures. Through the use of diagnostic techniques, R.P. Reed has developed an excellent system for detecting faulty thermocouples and data channels.6 Three components of this system are the event record, the zone box test, and the thermocouple resistance history.
MARCH 18 EVENT RECORD 10:43 Power failure 10:47 System power returned 11:05 Changed M821 to type K thermocouple 13:51 New data acquisition program 16:07 M821 appears to be bad reading
Figure 29 We look at our program listing and find that measurand #M821 uses a type J thermocouple and that our new data acquisition program interprets it as a type J. But from the event record, apparently thermocouple M821 was changed to a type K, and the change was not entered into the program. While most anomalies are not discovered this easily, the event record can provide valuable insight into the reason for an unexplained change in a system measurement. This is especially true in a system configured to measure hundreds of data points. Refer to Bibliography 10
If the thermocouple lead resistance is much greater than the shunting resistance, the copper wire shunt forces V = 0. In the normal unshorted case, we want to measure TJ, and the system reads: V ≅ α (TJ - TREF) But, for the functional test, we have shorted the terminals so that V=0. The indicated temperature T’J is thus: 0 = α (T’J - TREF) T’J = TREF Thus, for a dvm reading of V = 0, the system will indicate the zone box temperature. First we observe the temperature TJ (forced to be different from TREF), then we short the thermocouple with a copper wire and make sure that the system indicates the zone box temperature instead of TJ. TREF Cu Fe
Cu + v –
Copper Wire Short C
TJ
Cu
Voltmeter
Cu Zone Box Isothermal Block
SHORTING THE THERMOCOUPLE AT THE TERMINALS Figure 30
Event Record - The first diagnostic is not a test at all, but a recording of all pertinent events that could even remotely affect the measurements. An example would be:
6
Zone Box Test - A zone box is an isothermal terminal block of known temperature used in place of an ice bath reference. If we temporarily short-circuit the thermocouple directly at the zone box, the system should read a temperature very close to that of the zone box, i.e., close to room temperature.
This simple test verifies that the controller, scanner, voltmeter and zone box compensation are all operating correctly. In fact, this simple procedure tests everything but the thermocouple wire itself. Thermocouple Resistance - A sudden change in the resistance of a thermocouple circuit can act as a warning indicator. If we plot resistance vs. time for each set of thermocouple wires, we can immediately spot a sudden resistance change, which could be an indication of an open wire, a wire shorted due to insulation failure, changes due to vibration fatigue, or one of many failure mechanisms. For example, assume we have the thermocouple measurement shown in Figure 31. We want to measure the temperature profile of an underground seam of coal that has been ignited. The wire passes through a high temperature region, into a cooler region. Suddenly, the temperature we measure rises from 300°C to 1200°C. Has the burning section of the coal seam migrated to a different location, or has the thermocouple insulation failed, thus causing a short circuit between the two wires at the point of a hot spot?
Z-31
To Data Acquisition System
T1
T = 1200˚C
switched on and the voltage across the resistance is measured again. The voltmeter software compensates for the offset voltage of the thermocouple and calculates the actual thermocouple source resistance. Special Thermocouples - Under extreme conditions, we can even use diagnostic thermocouple circuit configurations. Tip-branched and leg-branched thermocouples are four-wire thermocouple circuits that allow redundant measurement of temperature, noise, voltage and resistance for checking wire integrity. Their respective merits are discussed in detail in REF. 8.
T = 300˚C
BURNING COAL SEAM Figure 31 If we have a continuous history of the thermocouple wire resistance, we can deduce what has actually happened.
Only severe thermocouple applications require such extensive diagnostics, but it is comforting to know that there are procedures that can be used to verify the integrity of an important thermocouple measurement.
R
Time
t1
Leg-Branched Thermocouple
THERMOCOUPLE RESISTANCE vs. TIME Figure 32 The resistance of a thermocouple will naturally change with time as the resistivity of the wire changes due to varying temperature. But a sudden change in resistance is an indication that something is wrong. In this case, the resistance has dropped abruptly, indicating that the insulation has failed, effectively shortening the thermocouple loop.
Tip-Branched Thermocouple
Figure 34
Summary
T1
TS Short
CAUSE OF THE RESISTANCE CHANGE Figure 33 The new junction will measure temperature Ts, not T1. The resistance measurement has given us additional information to help interpret the physical phenomenon detected by a standard open thermocouple check. Measuring Resistance - We have casually mentioned checking the resistance of the thermocouple wire as if it were a straightforward measurement. But keep in mind that when the thermocouple is producing a voltage, this voltage can cause a large resistance measurement error. Measuring the resistance of a thermocouple is akin to measuring the internal resistance of a battery. We can attack this problem with a technique known as offset compensated ohms measurement. As the name implies, the voltmeter first measures the thermocouple offset voltage without the ohms current source applied. Then the ohms current source is
In summary, the integrity of a thermocouple system can be improved by following these precautions: • Use the largest wire possible that will not shunt heat away from the measurement area. • If small wire is required, use it only in the region of the measurement and use extension wire for the region with no temperature gradient. • Avoid mechanical stress and vibration which could strain the wires. • When using long thermocouple wires, connect the wire shield to the dvm guard terminal and use twisted pair extension wire. • Avoid steep temperature gradients. • Try to use the thermocouple wire well within its temperature rating. • Use a guarded integrating A/D converter. • Use the proper sheathing material in hostile environments to protect the thermocouple wire. • Use extension wire only at low temperatures and only in regions of small gradients. • Keep an event log and a continuous record of thermocouple resistance.
Z-32
Z
THE RTD History The same year that Seebeck made his discovery about thermoelectricity, Sir Humphrey Davy announced that the resistivity of metals showed a marked temperature dependence. Fifty years later, Sir William Siemens proffered the use of platinum as the element in a resistance thermometer. His choice proved most propitious, as platinum is used to this day as the primary element in all high-accuracy resistance thermometers. In fact, the Platinum Resistance Temperature Detector, or PRTD, is used today as an interpolation standard from the oxygen point (-182.96°C) to the antimony point (630.74°C). Platinum is especially suited to this purpose, as it can withstand high temperatures while maintaining excellent stability. As a noble metal, it shows limited susceptibility to contamination. The classical resistance temperature detector (RTD) construction using platinum was proposed by C.H. Meyers in 1932.7 He wound a helical coil of platinum on a crossed mica web and mounted the assembly inside a glass tube. This construction minimized strain on the wire while maximizing resistance.
A more rugged construction technique is shown in Figure 37. The platinum wire is bifilar wound on a glass or ceramic bobbin. The bifilar winding reduces the effective enclosed area of the coil to minimize magnetic pickup and its related noise. Once the wire is wound onto the bobbin, the assembly is then sealed with a coating of molten glass. The sealing process assures that the RTD will maintain its integrity under extreme vibration, but it also limits the expansion of the platinum metal at high temperatures. Unless the coefficients of expansion of the platinum and the bobbin match perfectly, stress will be placed on the wire as the temperature changes, resulting in a strain-induced resistance change. This may result in a permanent change in the resistance of the wire. There are partially supported versions of the RTD which offer a compromise between the bird-cage approach and the sealed helix. One such approach uses a platinum helix threaded through a ceramic cylinder and affixed via glass-frit. These devices will maintain excellent stability in moderately rugged vibrational applications.
Typical RTD Probes
MYERS RTD CONSTRUCTION Figure 35
Thick Film Omega Film Element Thin Film Omega TFD Element
Although this construction produces a very stable element, the thermal contact between the platinum and the measured point is quite poor. This results in a slow thermal response time. The fragility of the structure limits its use today primarily to that of a laboratory standard. Another laboratory standard has taken the place of Meyers’ design. This is the bird-cage element proposed by Evans and Burns.8 The platinum element remains largely unsupported, which allows it to move freely when expanded or contracted by temperature variations. Strain-induced resistance changes over time and temperature are thus minimized, and the bird-cage becomes the ultimate laboratory standard. Due to the unsupported structure and subsequent susceptibility to vibration, this configuration is still a bit too fragile for industrial environments. 7 Refer 8
to Bibliography 12 Refer to Bibliography 16
Glass sealed Biflar Winding
TYPICAL RTD’s FIgures 36 and 37
Metal Film RTD’s In the newest construction technique, a platinum or metal-glass slurry film is deposited or screened onto a small flat ceramic substrate, etched with a lasertrimming system, and sealed. The film RTD offers substantial reduction in assembly time and has the further advantage of increased resistance for a given size. Due to the manufacturing technology, the device size itself is small, which means it can respond quickly to step changes in temperature. Film RTD’s are presently less stable than their hand-made counterparts, but they are becoming more popular because of their decided advantages in size and production cost. These advantages should provide the impetus for future research needed to improve stability. Z-33
Metals - All metals produce a positive change in resistance for a positive change in temperature. This, of course, is the main function of an RTD. As we shall soon see, system error is minimized when the nominal value of the RTD resistance is large. This implies a metal wire with a high resistivity. The lower the resistivity of the metal, the more material we will have to use.
temperature measurement. A ten ohm lead impedance implies 10/.385 ≅ 26ºC error in measurement. Even the temperature coefficient of the lead wire can contribute a measurable error. The classical method of avoiding this problem has been the use of a bridge.
Table 6 lists the resistivities of common RTD materials. METAL _________ Gold Silver Copper Platinum Tungsten Nickel
+
RESISTIVITY OHM/CMF (cmf = circular mil foot) ___________________
Au Ag Cu Pt w Ni
WHEATSTONE BRIDGE Figure 39
Table 6 Because of their lower resistivities, gold and silver are rarely used as RTD elements. Tungsten has a relatively high resistivity, but is reserved for very high temperature applications because it is extremely brittle and difficult to work. Copper is used occasionally as an RTD element. Its low resistivity forces the element to be longer than a platinum element, but its linearity and very low cost make it an economical alternative. Its upper temperature limit is only about 120ºC.
The common values of resistance for a platinum RTD range from 10 ohms for the bird-cage model to several thousand ohms for the film RTD. The single most common value is 100 ohms at 0ºC. The DIN 43760 standard temperature coefficient of platinum wire is α = .00385. For a 100 ohm wire, this corresponds to + 0.385 ohms/ºC at 0ºC. This value for α is actually the average slope from 0ºC to 100ºC. The more chemically pure platinum wire used in platinum resistance standards has an α of +.00392 ohms/ohm/ºC.
100 Ω RTD
Lead
R=5Ω
EFFECT OF LEAD RESISTANCE Figure 38
DVM
–
Resistance Measurement
R=5Ω
The bridge output voltage is an indirect indication of the RTD resistance. The bridge requires four connection wires, an external source, and three resistors that have a zero temperature coefficient. To avoid subjecting the three bridge-completion resistors to the same temperature as the RTD, the RTD is separated from the bridge by a pair of extension wires:
+
The most common RTD’s are made of either platinum, nickel, or nickel alloys. The economical nickel derivative wires are used over a limited temperature range. They are quite non-linear and tend to drift with time. For measurement integrity, platinum is the obvious choice.
Lead
Z RTD
13.00 8.8 9.26 59.00 30.00 36.00
Both the slope and the absolute value are small numbers, especially when we consider the fact that the measurement wires leading to the sensor may be several ohms or even tens of ohms. A small lead impedance can contribute a significant error to our
DVM
–
RTD
Figure 40 These extension wires recreate the problem that we had initially: The impedance of the extension wires affects the temperature reading. This effect can be minimized by using a three-wire bridge configuration:
DVM
A C
B
3-WIRE BRIDGE Figure 41 If wires A and B are perfectly matched in length, their impedance effects will cancel because each is in an opposite leg of the bridge. The third wire, C, acts as a sense lead and carries no current. The Wheatstone bridge shown in Figure 41 creates a non-linear relationship between resistance change and bridge output voltage change. This compounds the already non-linear temperature-resistance characteristic of the RTD by requiring an additional equation to convert bridge output voltage to equivalent RTD impedance.
Z-34
The error term will be small if Vo is small, i.e., the bridge is close to balance. This circuit works well with devices like strain gauges, which change resistance value by only a few percent, but an RTD changes resistance dramatically with temperature. Assume the RTD resistance is 200 ohms and the bridge is designed for 100 ohms:
4-Wire Ohms - The technique of using a current source along with a remotely sensed digital voltmeter alleviates many problems associated with the bridge. + i =0 i
100 W RTD
DVM
i =0 –
4-WIRE OHMS MEASUREMENT Figure 42 The output voltage read by the dvm is directly portional to RTD resistance, so only one conversion equation is necessary. The three bridge-completion resistors are replaced by one reference resistor. The digital voltmeter measures only the voltage dropped across the RTD and is insensitive to the length of the lead wires. The one disadvantage of using 4-wire ohms is that we need one more extension wire than the 3-wire bridge. This is a small price to pay if we are at all concerned with the accuracy of the temperature measurement. RTD = Rg R1 VS
-
+ -
+
VO R2
R3
Figure 43
3-Wire Bridge Measurement Errors If we know VS and VO, we can find Rg and then solve for temperature. The unbalance voltage Vo of a bridge built with R1 = R2 is: VO= VS
R3 ——— R3 + Rg
(
1 – VS — 2
)
()
If Rg = R3, VO= 0 and the bridge is balanced. This can be done manually, but if we don’t want to do a manual bridge balance, we can just solve for Rg in terms of VO: Rg = R3
S
O
-
Rg
+
VO RL
R3
Figure 44 Again we solve for Rg:
9 Refer
4Vo
- R ———— (———— V + 2V ) (Vs + 2V ) S
3V
200Ω
VO 2.0066V 100Ω
1Ω
Figure 45 Since we don’t know the value of RL, we must use equation (a), so we get:
(
)
6 - 1.9868 = 199.01 ohms Rg = 100 ————— 6 + 1.9868 The correct answer is of course 200 ohms. That’s a temperature error of about 2.5ºC. Unless you can actually measure the resistance of RL or balance the bridge, the basic 3-wire technique is not an accurate method for measuring absolute temperature with an RTD. A better approach is to use a 4-wire technique.
Resistance to Temperature Conversion The RTD is a more linear device than the thermocouple, but it still requires curve-fitting. The Callendar-Van Dusen equation has been used for years to approximate the RTD curve:9 T -β —— T -1 —— T )(—— 100) (100 )(100) ] 3
VS - 2VO
+ -
Vs - 2Vo
+ -
[ (
(———— V + 2V )
RL
Rg = R3
6V
+
T -1 RT=R0+R0 α T-δ- —— 100
This expression assumes the lead resistance is zero. If Rg is located some distance from the bridge in a 3-wire configuration, the lead resistance RL will appear in series with both Rg and R3:
V3 2
1Ω -
L
o
to Bibliography 11 and 13.
o
Where: RT = Resistance at Temperature T Ro = Resistance at T = 0ºC α = Temperature coefficient at T = 0ºC (typically +0.00392Ω/Ω/ºC) δ = 1.49 (typical value for .00392 platinum) β = 0 T>0 0. 11 (typical) T < 0 The exact values for coefficients α , β , and δ are determined by testing the RTD at four temperatures and solving the resultant equations. This familiar equation was replaced in 1968 by a 20th order polynomial in order to provide a more accurate curve fit. The plot of this equation shows the RTD to be a more linear device than the thermocouple:
Z-35
THE THERMISTOR
12 .390 .344 .293
8
Equivalent Linearities Type S Thermocouple vs. Platinum RTD
4
0
200
400
600
Like the RTD, the thermistor is also a temperature sensitive resistor. While the thermocouple is the most versatile temperature transducer and the PRTD is the most stable, the word that best describes the thermistor is sensitive. Of the three major categories of sensors, the thermistor exhibits by far the largest parameter change with temperature.
Resistance Temperature Coefficient - RTD
Type S µv/°C Seebeck Coefficient
16
Thermistors are generally composed of semiconductor materials. Although positive temperature coefficient units are available, most thermistors have a negative temperature coefficient (TC); that is, their resistance decreases with increasing temperature. The negative T.C. can be as large as several percent per degree Celsius, allowing the thermistor circuit to detect minute changes in temperature which could not be observed with an RTD or thermocouple circuit.
800
Temperature, °C
Figure 46
Practical Precautions
The price we pay for this increased sensitivity is loss of linearity. The thermistor is an extremely non-linear device which is highly dependent upon process parameters. Consequently, manufacturers have not standardized thermistor curves to the extent that RTD and thermocouple curves have been standardized.
The same practical precautions that apply to thermocouples also apply to RTD’s, i.e., use shields and twisted-pair wire, use proper sheathing, avoid stress and steep gradients, use large extension wire, keep good documentation and use a guarded integrating dvm. In addition, the following precautions should be observed.
An individual thermistor curve can be very closely approximated through use of the Steinhart-Hart equation:18
Construction - Due to its construction, the RTD is somewhat more fragile than the thermocouple, and precautions must be taken to protect it.
v or R
Self-Heating - Unlike the thermocouple, the RTD is not self-powered. A current must be passed through the device to provide a voltage that can be measured. The current causes Joule (I2R) heating within the RTD, changing its temperature. This self-heating appears as a measurement error. Consequently, attention must be paid to the magnitude of the measurement current supplied by the ohmmeter. A typical value for selfheating error is 12ºC per milliwatt in free air. Obviously, an RTD immersed in a thermally conductive medium will distribute its Joule heat to the medium, and the error due to self-heating will be smaller. The same RTD that rises 1ºC per milliwatt in free air will rise only 110 ºC per milliwatt in air which is flowing at the rate of one meter per second.10
RTD Thermocouple
T Figure 47 1 T = A + BlnR + C (In R)3
To reduce self-heating errors, use the minimum ohms measurement current that will still give the resolution you require, and use the largest RTD you can that will still give good response time. Obviously, there are compromises to be considered.
where: T = Degrees Kelvin
Thermal Shunting - Thermal shunting is the act of altering the measurement temperature by inserting a measurement transducer. Thermal shunting is more a problem with RTD’s than with thermocouples, as the physical bulk of an RTD is greater than that of a thermocouple.
Small RTD
Large RTD
Fast Response Time Low Thermal Shunting High Self-Heating Error
Slow Response Time Poor Thermal Shunting Low Self-Heating Error
R = Resistance of the thermistor A,B,C = Curve-fitting constants
Thermal EMF - The platinum-to-copper connection that is made when the RTD is measured can cause a thermal offset voltage. The offset-compensated ohms technique can be used to eliminate this effect. 10 Refer
Thermistor
to Bibliography 6.
Z-36
Z
A, B, and C are found by selecting three data points on the published data curve and solving the three simultaneous equations. When the data points are chosen to span no more than 100ºC within the nominal center of the thermistor’s temperature range, this equation approaches a rather remarkable ±.02°C curve fit. Somewhat faster computer execution time is achieved through a simpler equation: B T= ——— - C In R-A where A, B, and C are again found by selecting three (R,T) data points and solving the three resultant simultaneous equations. This equation must be applied over a narrower temperature range in order to approach the accuracy of the Steinhart-Hart equation.
Linear Thermistors
MONOLITHIC LINEAR TEMPERATURE SENSOR A recent innovation in thermometry is the integrated circuit temperature transducer. It is available in both voltage and current-output configurations. Both supply an output that is linearily proportional to absolute temperature. Typical values are 1 µA/K and 10 mV/K. Except for the fact that they offer a very linear output with temperature, these devices share all the disadvantages of thermistor devices and thus have a limited temperature range. The same problems of selfheating and fragility are evident, and they require an external power source. These devices provide a convenient way to produce an analog voltage proportional to temperature. Such a need arises in a hardware thermocouple reference junction compensation circuit (see Figure 15).
A great deal of effort has gone into the development of thermistors which approach a linear characteristic. These are typically 2- or 4-leaded devices requiring external matching resistors to linearize the characteristic curve. The modern data acquisition system with its computing controller has made this kind of hardware linearization unnecessary.
+
+ i = 1µ A/K 10mv/ K 10kΩ
Measurement The high resistivity of the thermistor affords it a distinct measurement advantage. The four-wire resistance measurement is not required as it is with RTD’s. For example, a common thermistor value is 5000 ohms at 25’C. With a typical T.C. of 4%/ºC, a measurement lead resistance of 100 produces only a .05°C error. This error is a factor of 500 times less than the equivalent RTD error.
To DVM
To DVM
B
A CURRENT SENSOR
VOLTAGE SENSOR Figure 48
Disadvantages - Because they are semiconductors, thermistors are more susceptible to permanent decalibration at high temperatures than are RTD’s or thermocouples. The use of thermistors is generally limited to a few hundred degrees Celsius and manufacturers warn that extended exposures even well below maximum operating limits will cause the thermistor to drift out of its specified tolerance.
APPENDIX A
Thermistors can be made very small which means they will respond quickly to temperature changes. It also means that their small thermal mass makes them especially susceptible to self-heating errors. Thermistors are a good deal more fragile than RTD’s or thermocouples and they must be carefully mounted to avoid crushing or bond separation.
11
The Empirical Laws of Thermocouples11 The following examples illustrate the empirically derived “laws” of thermocouples which are useful in understanding and diagnosing thermocouple circuits.
Refer to Bibliography 2.
Z-37
APPENDIX B +
Fe
Cu
C
Cu
T
v
--
Thermocouple Characteristics
Fe Tl
C
Over the years, specific pairs of thermocouple alloys have been developed to solve unique measurement problems. Idiosyncrasies of the more common thermocouples are discussed here.
Isother mal Block T1
THE LAW OF INTERMEDIATE METALS
We will use the term standard wire error to refer to the common commercial specifications published in the Annual Book of ASTM Standards. It represents the allowable deviation between the actual thermocouple output voltage and the voltage predicted by the tables in NBS Monograph 125.
Inserting the copper lead between the iron and constantan leads will not change the output voltage V, regardless of the temperature of the copper lead. The voltage V is that of an Fe-C thermocouple at temperature T1.
Fe
+
Noble Metal Thermocouples - The noble metal thermocouples, types B, R, and S, are all platinum or platinum-rhodium thermocouples and hence share many of the same characteristics.
Fe T
v C
--
T
Diffusion - Metallic vapor diffusion at high temperatures can readily change platinum wire calibration; therefore, platinum wires should only be used inside a non-metallic sheath such as high-purity alumina. The one exception to this rule is a sheath made of platinum, but this option is prohibitively expensive.
C
C Isother mal Block T1
Stability - The platinum-based couples are by far the most stable of all the common thermocouples. Type S is so stable that it is specified as the standard for temperature calibration between the antimony point (630.74°C) and the gold point (1064.43ºC).
THE LAW OF INTERIOR TEMPERATURES The output voltage V will be that of an Fe-C couple at Temperature T, regardless of the external heat source applied to either measurement lead.
Type B - The B couple is the only common thermocouple that exhibits a double-valued ambiguity. C
+
C T
v Fe
Fe
--
T Fe
Isother mal Block T1 Pt
Due to the double-valued curve and the extremely low Seebeck coefficient at low temperatures, Type B is virtually useless below 50°C. Since the output is nearly zero from 0°C to 42°C, Type B has the unique advantage that the reference junction temperature is almost immaterial, as long as it is between 0º and 40ºC. Of course, the measuring junction temperature is typically very high.
THE LAW OF INSERTED METALS
v
The voltage V will be that of an Fe-C thermocouple at temperature T, provided both ends of the platinum wire are at the same temperature. The two thermocouples created by the platinum wire (FePt and Pt -Fe) act in opposition.
Double-Value Region
0
All of the above examples assume the measurement wires are homogeneous; that is, free of defects and impurities.
12
Refer to Bibliography 3
42
T, ˚C
Base Metal Thermocouples Unlike the noble metal thermocouples, the base metal couples have no specified chemical composition. Any combination of metals can be used which results in a voltage vs. temperature curve fit that is within the standard wire errors. This leads to some rather interesting metal combinations. Constantan, for example, is not a specific metal alloy at all, but a generic name for a whole series of copper-nickel alloys. Incredibly, the Constantan used in a type T (copperConstantan) thermocouple is not the same as the Constantan used in the type J (iron -Constantan) couple.12 Z-38
Z
ASTM STANDARD WIRE ERRORS14
Type E - Although Type E standard wire errors are not specified below 0°C, the type E thermocouple is ideally suited for low temperature measurements because of its high Seebeck coefficient (58 µV/°C), low thermal conductivity and corrosion resistance. The Seebeck coefficient for Type E is greater than all other standard couples, which makes it useful for detecting small temperature changes. Type J - Iron, the positive element in a J couple, is an inexpensive metal rarely manufactured in pure form. J thermocouples are subject to poor conformance characteristics because of impurities in the iron. Even so, the J couple is popular because of its high Seebeck coefficient and low price. The J couple should never be used above 760°C due to an abrupt magnetic transformation that can cause decalibration even after the instrument cools.
170 °C
871
± 8.5 °C
± 4.4 1
/2 % Slope
TYPE B 24 AWG
0
v=
± 1.4
T1
Cu
1
/4 %
(T1 _ T2)
C
TYPE R,S 24 AWG
_ Cu Voltmeter
0
T2 (Ambient Reference)
871 °C
316
Cu
± 4.4 °C
TYPE T
Type T - This is the only couple with published standard wire errors for the temperature region below 0°C; however, type E is actually more suitable at very low temperatures because of its higher Seebeck coefficient and lower thermal conductivity. Type T has the unique distinction of having one copper lead. This can be an advantage in a specialized monitoring situation where a temperature difference is all that is desired. The advantage is that the copper thermocouple leads are the same metal as the dvm terminals, making lead compensation unnecessary. Types K & Nicrosil-Nisil - The Nicrosil-Nisil thermocouple, type N, is similar to type K, but it has been designed to minimize some of the instabilities in the conventional Chromel-Alumel combination. Changes in the alloy content have improved the order/disorder transformations occurring at 500˚C, and a higher silicon content in the positive element improves the oxidation resistance at elevated temperatures. A full description with characteristic curves is published in NBS Monograph 161.13 Tungsten - Tungsten-rhenium thermocouples are normally used at high temperature in reducing or vacuum environments, but never in an oxidizing atmosphere because of the high reaction rates. Pure tungsten becomes very brittle when heated above its recrystallization temperature (about 1200°C). To make the wire easier to handle, rhenium alloys are used in both thermocouple legs. Types G (tungsten vs. tungsten 26% rhenium), C (tungsten 5% rhenium vs. tungsten 26% rhenium) and D (tungsten 3% rhenium vs. tungsten 25% rhenium) thermocouples are available in bare wire forms as well as complete probe assemblies. All materials conform to published Limits of Error. ®
Refer to Bibliography 14. 14 Refer to Bibliography 3. 13
1482 °C
± 3.7 °C
Cu
+
538
± 1.7 1
/2 %
TYPE E 8 AWG
_
101
_
371 °C
59 93
2% ± 1.2
± 2.8 °C
± .8 3
/4 %
TYPE T 14 AWG
0
277
760 °C
± 5.7 °C ± 2.2 3
/4 %
TYPE J 8 AWG
0
At high temperatures, small thermocouple wire is affected by diffusion, impurities, and inhomogeneity more so than large wire. The standard wire errors reflect this relationship.
277
°C
1260
± 9.5 ± 2.2 3
/4 %
TYPE K 8 AWG
Note that each NBS wire error specification carries with it a wire size. The noble metal thermocouples (B, R, and S) are specified with small (24 ga.) wire for obvious cost reasons.
Z-39
1260 °C
1093
982
AWG DIA, MILS DIA, mm
±2.2°C
34 %
Wire Size AWG
24 or 28 20 14
8 10 12 14 16 18 20 22 24 26 28
Error
±9.5°C
0°C
277°C
871
TYPE K
8
TEMPERATURE RANGE vs. WIRE SIZE vs. ERROR
TYPE B E J K N (AWG 14) N (AWG 28) R S T W-Re
METAL + Platinum 6% Rhodium Nickel 10% Chromium Iron Nickel I0% Chromium Nicrosil Nicrosil Platinum13% Rhodium Platinum 10% Rhodium Copper Tungsten 5% Rheniurn
Platinum 30% Rhodium
STANDARD COLOR CODE + –
Ω/DOUBLE FOOT 20 AWG
128 102 81 64 51 40 32 25 20 16 13
SEEBECK COEFFICIENT S(µV/ºC) @ T (ºC)
°C STANDARD WIRE ERROR (SEE APPENDIX B)
0.2
6
600
4.4 to 8.6
3.3 2.6 2.1 1.6 1.3 1 0.8 0.6 0.5 0.4 0.3 NBS SPECIFIED † MATERIAL RANGE† (ºC) 0 to 1820*
Constantan Constantan
Violet White
Red Red
0.71 0.36
58.5 50.2
0 0
1.7 to 4.4 1.1 to 2.9
-270 to 1000 - 210 to 760
Nickel Nisil
Yellow Red –
0.59 –
39.4 39
0 600
1.1 to 2.9 –
-270 to 1372 0 to 1300
Nisil
–
–
26.2
0
–
-270 to 400
Platinum
–
0.19
11.5
600
1.4 to 3.8
-50 to 1768
Platinum Constantan Tungsten 26% Rhenium
–
0.19 0.30
10.3 38
600 0
1.4 to 3.8 0.8 to 2.9
-50 to 1768 -270 to 400
–
19.5
600
–
Blue
Red –
0 to 2320
* Type B double-valued below 42°C - curve fit specified only above 130°C † Material range is for 8 AWG wire; decreases with decreasing wire size
BIBLIOGRAPHY Thermocouple Well: Lower gradient, protects wire and allows user to change thermocouple without interrupting process.
1. 2. 3. 4.
5. 6. 7.
8. 9. 10. 11.
Connector: Composed of same metals as thermocouple, for minimum connection error.
12. 13. 14.
Exposed
Ungrounded
Grounded 15. 16.
Exposed Junction: Wires unprotected, faster response. Ungrounded Junction: Best protection, electronically isolated. Grounded Junction: WIres protected, faster response.
17. 18.
Thermocouple Washers: Couple built into washer; convenient mounting.
Charles Herzfeld, F.G. Brickwedde: Temperature - Its Measurement and Control in Science and Industry, Vol. 3, Part 1, Reinhold, New York, 1962. Robert P. Benedict: Fundamentals of Temperature, Pressure and Flow Measurements, John Wiley & Sons, Inc., New York, 1969. Manual on the Use of Thermocouples in Temperature Measurement, ASTM Special Publication 470A, Omega Press, Stamford, Connecticut 06907, 1974. Thermocouple Reference Tables, NBS Monograph 125, National Bureau of Standards, Washington, D.C., 1979. Also, TemperatureMillivolt Reference Tables-Section T, Omega Temperature Measurement Handbook, Omega Press, Stamford Connecticut 06907,1983. H. Dean Baker, E.A. Ryder, N.H. Baker: Temperature Measurement in Engineering, Omega Press, Stamford, Connecticut 06907, 1953. Temperature Measurement Handbook, Omega Engineering, Inc., Stamford, Connecticut. R.L. Anderson: Accuracy of Small Diameter Sheathed Thermocouples for the Core Flow Test Loop, Oak Ridge National Laboratories, ORNL-54011 (available from National Information Service), April, 1979. R. R Reed: Branched Thermocouple Circuits in Underground Coal Gasification Experiments, Proceedings of the 22nd ISA International Instrumentation Symposium, Instrument Society of America, 1976. R.J. Moffat: The Gradient Approach to Thermocouple Circuitry, from Temperature - Its Measurement and Control in Science and Industry, Reinhold, New York, 1962 R.P. Reed: A Diagnostics-Oriented System for Thermocouple Thermometry, Proceedings of 24th ISA International Instrumentation Symposium, Instrument Society of America, 1978. Harry R. Norton: Handbook of Transducers for Electronic Measuring Systems, Prentice-Hall, Englewood Cliffs, New Jersey. C.H. Meyers: Coiled Filament Resistance Thermometers, NBS Journal of Research, Vol. 9, 1932. Bulletin 9612, Rev. B: Platinum Resistance Temperature Sensors, Rosemount Engineering Co., 1962. Burley, Powell, Burns & Scroger: The Nicrosil vs. Nisil Thermocouple: Properties and Thermoelectric Reference Data, NBS Monograph 161, U.S. Dept. of Commerce, Washington, D.C., 1978 J.P Tavener: Platinum Resistance Temperature Detectors - State of the Art, Measurements & Control, Measurements & Data Corporation, Pittsburgh, PA., April, 1974. J.P. Evans and G.W. Burns: A Study of Stability of High Temperature Platinum Resistance Thermometers, in Temperature - Its Measurement and Control in Science and Industry, Reinhold, New York, 1962. D.D. Pollock: The Theory and Properties of Thermocouple Elements, ASTM STP 492, Omega Press, Stamford, Connecticut 06907, 1979. YSI Precision Thermistors, Yellow Springs Instruments, Yellow Springs, Ohio, 1977.
* Hewlett Packard Company makes no warranty as to the accuracy or completeness of the foregoing material and disclaims any responsibility therefor. (Editor’s Note: Thermocouple data which conform to ITS-90 are given in “ITS-90 Thermocouple Direct and Inverse Polynomials.”) OMEGA ENGINEERING, INC. gratefully acknowledges the HEWLETT PACKARD COMPANY for permission to reproduce Application Note 290-Practical Temperature Measurements.
Z-40
Z
Nicrosil/Nisil Type N Thermocouples The Nicrosil/Nisil Type N thermocouple offers better stability than existent base-metal Types E, J, K and T. It is now available and in widespread use worldwide.
DR. NOEL A. BURLEY
T he
ANSI standard base-metal ther mocouples, designated E, J, K and T (Ref. 1), show inherent ther moelectric instability related to time- and/or temperature-dependent instabilities in several of their physical, chemical, nuclear, structural and electronic properties. This paper reviews the major thermoelectric properties of the new nickel-base thermocouple system Nicrosil versus Nisil (designated type N), in which very high thermoelectric stability has been achieved by a judicious choice of elemental component concentrations.
INSTABILITY OF CONVENTIONAL BASE-METAL THERMOCOUPLES There are three principal characteristic types and causes of thermoelectric instability in the standard base-metal thermoelement materials: 1. A gradual and generally cumulative drift in thermal EMF on long exposure at elevated temperatures. This is observed in all base-metal thermoelement materials and is majnly due to compositional changes caused by oxidation, in particular internal oxidation (Figures 1 and 2), and to neutron irradiation which can produce transmutation in nuclear reactor environments. 2. A short-term cyclic change in thermal EMF on heating in the temperature range about 250º to 650ºC, which occurs in types KP (or EP) and JN (or TN and EN). This kind of EMF instability is thought to be due to some form of structural change like magnetic shortrange order (Figures 3 and 4). 3. A time-independent perturbation in thermal EMF in specific temperature ranges. This is due to compositiondependent magnetic transformations which perturb the thermal EMF’s in type KN in the range of about 25º to 225ºC (Figure 5), and in type JP above about 730ºC.
ULTRA-HIGH STABILITY OF NICROSILINISIL (TYPE N) THERMOCOUPLE Nicrosil and Nisil thermocouple alloys (Ref. 2) show greatly enhanced thermoelectric stability (Ref. 3) relative to the other standard base-metal thermocouple alloys because their compositions (Table 1) are such as to virtually eliminate or substantially reduce the causes of thermoelectric instability described above. This is achieved primarily by increasing component solute concentrations (chromium and silicon) in a base of nickel above those required to cause a transition from internal to external modes of oxidation, and by selecting solutes (silicon and magnesium) which preferentially oxidize to form a diffusion-barrier, and hence oxidation inhibiting films. The thermal EMF instabilities of the short-term cyclic kind occurring in KP and JN alloys have virtually been eliminated in nicrosil (NP) by setting the chromium content at 14.2 weight-%. The increase in the silicon content of nisil (NN) to 4.4 weight-% has suppressed the magnetic transformation of this new alloy to below room temperature. Virtual freedom from nuclear transmutation effects is achieved by eliminating such elements as manganese, cobalt and iron from the specified compositions of both alloys. The ver y high ther moelectric stability of the Nicrosil/Nisil (type N) thermocouple is illustrated in Figures 1 and 2. The influence of thermoelement conductor cross-sectional area upon the thermal-EMF constancy of Nicrosil/Nisil is shown in Figure 6.
Z-41
300 #8K (KP/KN) 100
#8K
6
Z
200
(KP/KN) #14K
4
0 #14 NIC/NIS (KP/JN) (KP/JN)
–200
100
2
#8 NIC/NIS
#14 E #8E
0
0 200
#8K 4
(JP/JN) #8J
THERMAL EMF DRIFT (uv)
–600
CALIBRATION TEMPERATURE 497°C
#14 J –800 250 #14 0 NIC/NIS
2
#10 NIC/NIS
#14 E #8 E
0 200
0 #8K 4
#12 NIC/NIS 100
2 0 200
0 #8K 4
100 2
#14 NIC/NIS
–500
0 300
0
6
#8J
–1000
#8K
200
4
CALIBRATION TEMPERATURE 777°C #16 NIC/NIS
100 –1500
2
#14 J
0
0 0
300
600
900
1200
DRIFT (°C)
(JP/JN)
100
THERMAL EMF DRIFT (uv)
–400
1500
0
200
EXPOSURE TIME AT 777°C (h) AT
600
800
1000
1200
EXPOSURE TIME (h) 1077°C, 1152°C, 1202°C
FIGURE 2. Long-term thermal-EMF drifts in air, at three constant aging (and calibration) temperatures for Nicrosil/Nisil T/Cs in five wire gauges (#). Corresponding thermal-EMF drifts for 8 AWG (#8) type K T/Cs at two of these temperatures are also given. The drifts are changes from EMF output values existent after 80 hours of exposure at the constant aging temperature (Ref. 3).
FIGURE 1. Long-term thermal-EMF drifts in air, at two calibration temperatures, for 14 AWG (#14) Nicrosil/Nisil (N) and E, J and K T/Cs. ThermalEMF drifts for 8 AWG (#8) E and J T/Cs are also given. The drifts are changes from EMF output values existent after 20 hrs of exposure at constant aging temperature of 777°C (Ref. 3).
As Figure 2 shows, 8 AWG type K thermocouples appear to be markedly more unstable as temperatures progressively exceed about 1050ºC. In contrast, it is clear from Figure 6 that type N thermocouples, in a range of wire sizes finer than 8 AWG, can be used reliably for extended periods of time at temperatures up to at least 1200ºC. Indeed, it has recently been
400
demonstrated (Ref. 4) that, in oxidizing atmospheres, the ther moelectric stability of the Nicrosil/Nisil thermocouple, in wire sizes not finer than 10 AWG, is about the same as that of the noble-metal thermocouples of ANSI types R and S up to about 1200ºC.
Z-42
Type N Thermocouples PROMULGATION AS A STANDARD No new ther mocouple will sur vive for universal adoption and use unless it is formally promulgated by national standards authorities around the world. It is for tunate that the Nicrosil/Nisil thermocouple system is in vigorous process of being so promulgated.
0.2
0.6
30 Days
0.5
0.1
∆S (uV/°C)
0.05 0.4
0 –0.05
0.3
The ASTM, through its Committee E-20 on Temperature Measurement, has shown considerable interest in Nicrosil versus Nisil, and has kept matters relating to the development, availability and use of the new thermocouple under continual review.
5 min
–0.1 45 min
3 Days
0.2
–0.2 7h
0.1
45 min
ground state 0 200
400
600
3 Days 30 Days
–0.3
800
200
400
600
TEMPERATURE (°C)
FIGURE 3 (Left). Changes in the Seebeck coefficient (∆S) of a typical type KP thermoelement vs. platinum on initial heating, as a function of constant aging temperature for the indicated times (Ref. 3). FIGURE 4 (Right). Similar changes of a type JN thermoelement (Ref. 3).
TABLE.1- NOMINAL COMPOSITIONS OF ANSI STANDARD BASE-METAL THERMOELEMENT ALLOYS, AND NICROSIL AND NISIL ALLOYS ALLOY CHEMICAL COMPOSITION (WEIGHT-%) ANSI (1) Cr Si Mn Al Co Mg Cu Ni Fe DESIGNATION (+)KP, EP 9.5 0.4 bal (-)KN 1.0 3.0 2.0 0.4 0.015 bal (+)JP 0.3 bal (-)JN, EN, TN 1.0 0.5 54 44 0.5 (+)TP (+)NP (nicrosil) (-)NN (nisil)
100 14.2 1.4 4.4
0.10
bal bal
TABLE 2-VARIANTS OF TYPE KN ALLOY CHEMICAL COMPOSITION (WEIGHT-%) Mn Al Si co Ni KN1 3.02 1.90 1.19 0.41 balance KN2 1.67 1.25 1.56 0.72 balance KN3 2.50 1.00 balance KN4 0.43 2.39 0.23 balance Z-43
Recently, relevant subcommittees of ASTM E-20 have produced several publications containing information on the properties and characteristics of the Nicrosil versus Nisil thermocouple. A document quoting several of the EMF-temperature tables from NBS Monograph 161 (Ref. 2) was published (Ref. 6) for information. A formal ASTM Standard (E1223) is promulgated, while Type N data is now included in ASTM Standard E230. Again, in the recently published third edition of the ASTM Manual on the Use of Thermocouples (Ref. 8), various properties and characteristics of Nicrosil versus Nisil are summarized. Based mainly on the above information, several crucial actions now have been taken by the supreme standardizing bodies in several important countries: 1. The Instrument Society of America (ISA), in October 1983, promulgated the Nicrosil/Nisil system as a U.S. Standard Ther mocouple bearing the letter-designation “type N.” 2. The British Standards Institute (BSI) has recently promulgated a standard on the type N thermocouple identified as B.S.4937: Part 8. 3. The Japan Society for the Promotion of Science, through its Committee TC19 (Temperature), is nearing the conclusion of its deliberation on type N, leading to the issue of a Japan Industrial Standard (JIS). These actions have ensured that the type N ther mocouple and its allied pyrometric instrumentation and ancillary circuitry elements are now commercially available in a number of major countries around the world.
DISCUSSION The various types of ther moelectric instability described in this paper can cause substantial changes in thermoelectromotive force and, hence, calibration in ANSI-standard letterdesignated base-metal thermocouples types E, J, K and T. In the case of Nicrosil/Nisil, however, thermoelectric instability due to these causes is
REFERENCES 1. American National Standards Institute (ANSI) Standard MC96.1-1975, Instrument Society of America (1976), pp. vi and 1. 2. N.A. Burley, et al., U.S. National Bureau of Standards Monograph 161, NBS* Washington (1978). 3. N.A. Burley, et al., Temperature, Its Measurement and Control in Science and Industry, vol. 5, part 2, Instrument Society of America (1982), p. 1159. 4. N.A. Burley, Proc. 11th IMEKO Conference (Sensors), Houston, TX, 1988, p. 155. 5. R.L. Powell, et al., U.S. National Bureau of Standards Monograph 125, NBS* Washington (1974). 6. American Society for Testing and Materials (ASTM), Annual Book of Standards, vol. 14.01 (1983), p. 859. 7. ASTM Standard E 1223-87. 8. Manual on the Use of Thermocouples in Temperature Measurement, ASTM Special Technical Publication 470 B (1981). 9. N.A. Burley, et al., “The Nicrosil versus Nisil Type N Thermocouple: A Commercial Reality,” Australian Department of Defence Report MRL-R-903 (1983).
360
400
440
480
DEVIATION (uV)
40
520
1
KN2
0
0 KN1 KN3
–40
–1
–2
–80
KN4
–120
0
40
120
80
160
TEMPERATUREDEVIATION (K)
60
320
–3
200
240
TEMPERATURE (°C)
FIGURE 5. Deviations of the measured values of the thermal EMFs of several type KN thermoelements vs. platinum from reference table values (Ref. 5). Variants of type KN are given in Table 2. WIRE GAUGE (A W G) 16
250
14
12
10
8 6
200
5 1202°C 4
150 1152°C
3 100
DRIFT (°C)
Use of type N thermocouples in several countries has already demonstrated a number of advantages: enhanced pyrometric accuracy, improved product quality and performance, lower reject rates, enhanced energy utilization, lower pyrometric maintenance costs, and improved productivity.
TEMPERATURE (K) 280
THERMAL EMF DRIFT (uv)
virtually eliminated or substantially attenuated over the entire temperature range up to 1230˚C. ANSI-standard base-metal thermocouples types E, J, K and T can, therefore, be regarded as obsolescent. Their replacement by Nicrosil/Nisil thermocouples would lead, in most cases, to demonstrable technological and economic advantages for science and industry at large. Indeed, the enhanced calibration stability and longevity of the type N thermocouple, taken into account with its ability to operate at considerably higher upper operating temperatures than conventional base-metal thermocouples, make it ideally suited to scientific, technological and industrial applications where temperature measurements are critical.
2
1077°C 50
1
0 0
0.2
0.4
0.6
0.8
0 1.0
LOG CROSS-SECTIONAL AREA
FIGURE 6. Relationship between total thermalEMF drift (after 1000 hrs of exposure in air at each of three test temperatures) and crosssectional area of Nicrosil/Nisil T/C wires. The drifts are changes from EMF output values existent after 80 hours of exposure (Ref. 3).
THE AUTHOR
*The NBS is now NIST (National Institute of Standards and Technology).
Reproduced with permission of H.L. Daneman, Box 31056, Sante Fe, NM 87594
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DR. NOEL A. BURLEY, D.App.Sc., C. Eng., F.I.M., F.A.I.M., is General Manager, Research and Development, for BellIRH Pty., Ltd., an Australian company specializing in the manufacture of electrical and electronic components, instruments and sensors. It has considerable expertise and established reputation in temperature control. Contact Dr. Burley at Bell-IRH Pty., Ltd., 32 Paramatta Rd., Lidcombe NSW 2141, Sydney, Australia, phone: 02 648 5455.
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The Choice Of Sheathing For MineraI Insulated Thermocouples H.L. Daneman, P.E.
• • • •
Chemical isolation of wires from the surrounding atmosphere. Shielding of thermoelements from sources of electrical interference. Protection of the wires and insulation from damage due to shock. Flexibility of the final assembly allowing bending.
For two decades, people have credited MIMS construction with a greater capability than deserved. Quite frequently, this form has shown less stability, less durability and lower temperature limits than corresponding unsheathed elements. The nickel bearing MIMS thermocouples used above 400ºC (750ºF) are especially vulnerable to calibration instability and shortened lifetime - factors which bear heavily on thermocouple use and selection. HYSTERESIS Thermoelectric hysteresis is one contributor toward calibration instability. Hysteresis is a form of short-range order/disorder phenomenon occurring between 200 and 600ºC (peaking at ≈ 400ºC) for Ni-Cr alloys such as Type K. It is evidenced by a calibration change of several degrees as the thermocouple temperature is cycled within this temperature band. Type N thermocouples exhibit hysteresis of up to 5ºC when heated and cooled between 200 and 1000ºC (peaking around 750ºC). At 900ºC hysteresis is 2 to 3ºC. If the type K thermocouple, for example, will be used below 500ºC, hysteresis can be reduced by annealing overnight at 450ºC. OXIDATION Another phenomenon affecting calibration is oxidation. Ni-Cr-AI alloys (e.g., Chromel*) have limited life in air above 500ºC because of oxidation. A special form of oxidation is so-called “green rot” which is preferential oxidation of Cr in atmospheres with low oxygen content (e.g., sheaths in which the volume of air is limited and stagnant). Nicrosil resists oxidation up to about 1,250ºC (2,300ºF) and does not exhibit green rot. Several new sheath materials called “Nicrobell” (**) consist of Nicrosil with 1.5% or 3.0% niobium. Nicrobell “A” is particularly formulated to be resistant to oxidation. Another new oxidation resistant sheath material called Nicrosil + (***)
consists of Nicrosil plus 0.15% magnesium. It is reported (ref. 4) to exhibit less spalling and probably have a longer life than some Nicrobell version(s) tested.
due to metal fatigue. On heating to 900ºC, the thermal expansion of Nisil differs from SS 304 by 0.4% of length. Nicrosil has only 0.05% difference in thermal expansion compared to Nisil (the leg most likely to fracture). A sheath of Nicrosil, Nicrosil + or Niobell would therefore induce less metal fatigue in either leg of the Type N thermocouple than would stainless steel.
Nicrosil, itself, does not have satisfactory resistance to reducing atmospheres, such as encountered in most combustion or many heat treating processes. Other adaptations of Nicrosil for use as sheath material (such as Nicrobells B, C and D) can be expected to deal with typical nonoxidizing atmospheres.
COMPOSITION Composition changes in SS sheathed couples are generally greater than in Inconel (****) sheathed couples. In tests performed by Anderson, et al., the KN leg showed an increase in chromium but a decrease in aluminum. These changes in composition contributed the major portion of the resulting change in calibration of the thermocouple. Most stainless steels have from 1 to 2% of manganese. Type 304 has ≈ 2% manganese. Others have manganese concentrations varying from 1% to 10%. Inconel has up to 1% Mn. As a rule of thumb, each 1% of Mn in the sheath material contributes -10ºC calibration shift for 1,000 hours at 1,100ºC. According to Bentley, at 1,200ºC, Type N in a 3 mm diameter SS sheath drifted -24ºC in 1,000 hours.
CONTAMINATION A third influence on calibration stability is contamination. The idea behind the mineral-insulated, integrally designed, metal-sheathed thermocouple is that the uniform compression of finely divided mineral oxides (typically MgO) insulation surrounding the wires and filling the sheath would seal the internal volume, thereby eliminating contamination. The volume of the insulation compressed by swaging, rolling or drawing is on the order of 85% of solid material. This is useful, permitting the tubing to be bent and also permitting the manufacture of smaller diameter assemblies. It does, however, permit the intrusion of gas such as water vapor or air. It also permits vapor diffusion of elements composing the wires or sheath. Bentley and Morgan determined that the vapor-phase diffusion of Mn (manganese) through the MgO insulation has the greatest influence on thermocouple decalibration.
HUMIDITY There is a multiple effect of water vapor within the sheath. It is rapidly absorbed in the MgO, reducing the insulation resistance. Humidity intrusion can ruin a MIMS thermocouple assembly in as short a time as a few minutes. In lesser amounts, it destroys a protective oxide coating on Nickel-Chromium alloys, subjecting them to more rapid deterioration. The changes due to water
METAL FATIGUE Metal fatigue is another cause of shortened thermocouple life. Differing temperature coefficients of linear expansion between sheaths and wires causes strain during heating or cooling. These strains result in eventual fracture
+25
Type K (Inconel) 0
DRIFT (°C)
INTRODUCTION The mineral-insulated integrally metalsheathed (MIMS) form of thermocouple consists of matched thermocouple wires surrounded by insulating material (typically MgO) compacted by rolling, drawing or swaging until the sheath is reduced in diameter. The advantages of MIMS thermocouples are:
Type N (310 SS)
Type N (Inconel)
Type K (310 SS)
–25
–50 0
200
400
600
800
1000
1200
ElapsedTime (h) Figure 1. Drift of 3 mm diameter stainless steel sheathed and Inconel 600 sheathed type K and Nicrosil vs. Nisil thermocouples in 1200°C in vacuum. The dips in the drift curve are the result of the "in-place inhomogeneity test" where the samples were extracted from the furnace by 5 cm.
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20
1.6 mm Bare Wire 3 mm OD Mineral Insulated Metal Sheathed Thermocouple 1100°C
Insitu Drift (°C)
10
NCR 0
SS -10
-20 0
1000
2000
3000
Time (h)
Figure 2. The insitu drift in type N thermocouples with tips held at 1100°C. Curves refer to mineral insulated metal sheathed thermocouples with 3mm OD sheaths of 310 stainless steel (SS) or Nicrosil (NCR) and 1.6mm bare wire thermocouples in air. The range in drift for the latter is also indicated.
vapor can be sufficiently severe as to make affected couples useless by reducing insulation resistance. This reduced resistance can result in misleading temperature readings, premature failure or even erroneous readings after open circuiting. Water vapor can be introduced during thermocouple fabrication or repair, or even by changes in atmospheric pressure during air shipment or during long periods of storage (e.g., six months) at construction sites. Care must be taken of hermetic seals during shipment and installation. RECOMMENDATIONS Although not mentioned above , there is some relationship between the diameter of these thermocouple materials and stability and longevity at elevated temperatures. The surface of the brickwork on which electrical heaters are supported becomes conductive at elevated temperatures. This leads to flow of electrical currents through thermocouple sheaths to ground, perhaps through the measuring instrument. The temptation to use the finest sheathed thermocouples (as fine as 1 mm) should be resisted for higher temperature or corrosive industrial environments. Stainless steel is a poorer sheath for mineral-insulated, metal-sheathed thermocouples than either Inconel 600 or modified Nicrosil when used with Ni-Cr thermocouples such as Type K or Type N. The modified Nicrosil sheathed thermocouples offer improved oxidation resistance up to 1,100ºC (1,200 to 1,250ºC for Type N), reduced failures due to differential thermal expansion, improved ductility and the elimination of the drift
problems caused by the vapor diffusion of manganese from stainless steels or Inconel. Considering the current state of supply of the newer materials, one could well choose a low manganese (0.3% or less) Inconel sheathed Type K MIMS thermocouple until such time as modified Nicrosil sheathed Type K or N and appropriate supporting data become readily available. (*) CHROMEL is a trademark of the Hoskins Manufacturing Co. (**) NICROBELL is a trademark of NICROBELL Pty. Ltd. NICROBELL sheath alloys are patented in a number of countries including the USA (***) NICROSIL + is a trademark of Pyrotenax Australia Pty. Ltd. (****) INCONEL is a trademark of the International Nickel Co. Reproduced with the permission of: H.L. Daneman P.O. Box 31056 Sante Fe, NM 87594
REFERENCES 1. Anderson, R. L., Ludwig, R.L.,FAILURE OF SHEATHED THERMOCOUPLES DUE TO THERMAL CYCLING, Temperature, (1982) pp 939-951 2. Anderson, R. L., Lyons, J. D., Kollie, T G., Christie, W. H., Eby, R., DECALIBRATION OF SHEATHED THERMOCOUPLES, Temperature, (1982) pp 977-1007 3. Bentley, R. E., NEW-GENERATION TEMPERATURE PROBES, Materials Australasia, April (1987), pp. 10-13 4. Bentley, R. E., THEORY AND PRACTICE OF THERMOELECTRIC THERMOMETERY, 2nd Edition, CSIRO Div. of Applied Physics, (1990) 152 pages.
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5. Bentley, R.E., private communication, 11/22/90 6. Burley, N. A., HIGHLY STABLE NICKEL-BASE ALLOYS FOR THERMOCOUPLES, J. of the Australian Institute of Metals, May (1972), pp 101-113 7. Burley, N. A., Burns, G. W., Powell, R. L., NICROSIL AND NISIL: THEIR DEVELOPMENT AND STANDARDIZATION, Inst. Physical Conf. Ser. No. 26, (1975), pp 162-171 8. Burley, N. A., Jones, T.P., PRACTICAL PERFORMANCE OF NICROSIL-NISIL THERMOCOUPLES, Inst. Physical Conf. Ser. No. 26, (1975), pp 172-180 9. Burley, N. A., Powell, R. L., Burns, G. W., Scroger, M. G., THE NICROSIL VS NISIL THERMOCOUPLE: PROPERTIES AND THERMOELECTRIC DATA, NBS Monograph 161, April (1978), pp 1-156 10.Burley, N. A., THE NICROSIL VS NISIL THERMOCOUPLE: THE FIRST TWO DECADES, (1986) private communication 11. Burley, N. A., N-CLAD-N: A NOVEL ADVANCED TYPE N INTEGRALLY-SHEATHED THERMOCOUPLE OF ULTRA-HIGH THERMOELECTRIC STABILITY, High Temperatures-High Pressures, (1986) pp 609-616 12.Burley, N. A., NICROSIL/NISIL TYPE N THERMOCOUPLE, Measurements & Control, April (1989), pp 130-133 13.Burley, N. A., ADVANCED INTEGRALLY SHEATHED TYPE N THERMOCOUPLE OF ULTRA-HIGH THERMOELECTRIC STABILITY, Measurement, Jan-Mar 1990, pp 3641 14.Daneman, H. L., THERMOCOUPLES, Measurements & Control, June (1988), pp 242-243 15.Frank, D.E., AS TEMPERATURES INCREASE, SO DO THE PROBLEMS!, Measurements & Control, June (1988), p 245 16.Hobson, J. W., THE INTRODUCTION OF THE NICROSIL/NISIL THERMOCOUPLES IN AUSTRALIA, Australian Journal of Instrumentation and Control, October (1982), pp 102104 17.Hobson, J. W., THE K TO N TRANSITION - BUILDING ON SUCCESS, Australian Journal of Instrumentation and Control, (1985) pp 12-15 18.Northover, E. W., Hitchcock, J. A., A NEW HIGH-STABILITY NICKEL ALLOY, Instrument Practice, September (1971), pp 529-531 19.Paine, A., TYPE N AND K MIMS T/C’S, fax LNA5195, 11/23/90 20.Wang, T P., Starr, C. D., NICROSILNISIL THERMOCOUPLES IN PRODUCTION FURNACES, ISA (1978) Annual conference, pp 235-254 21.Wang, T. P., Starr, C. D., EMF STABILITY OF NICROSIL-NISIL AT 500˚C, ISA (1978) Annual conference, pp 221-233
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Material Selection Guide This chart is a guide to selection of thermocouple sheath and thermowell materials according to process fluid. It includes factors such as catalytic reaction, contamination and electrolysis. However, there are many instances where factors other than these must be considered. It is recommended that such special applications be submitted to OMEGA ENGINEERING for recommendations. These recommendations are only guides based on the most economical material selection. OMEGA ENGINEERING cannot be held responsible if these recommendations are not satisfactory for specific applications. SUBSTANCE
CONDITIONS
Acetate Solvents Acetic Acid " " " " " " " " Acetic Anhydride Acetone Acetylene Alcohol Ethyl " " Alcohol Methyl " " Aluminum Aluminum Acetate Aluminum Sulphate " " " " " " Ammonia Ammonium Chloride Ammonium Nitrate " " Ammonium Sulphate " " " " Aniline Amylacetate Asphalt
Crude or Pure 10% - 70°F 50% - 70°F 50% - 212°F 99% - 70°F 99% - 212°F 212°F 70°F 212°F 70°F 212°F Molten Saturated 10% - 70°F Saturated 70°F 10% - 212°F Saturated 212°F All concentrations 70°F All concentrations 212°F All concentrations 70°F All concentrations 212°F 5% - 70°F 10% - 212°F Saturated 212°F All concentrations 70°F
Barium Carbonate Barium Chloride " " " " Barium Hydroxide Barium Sulphite Benzaldehyde Benzene Benzine
70°F 5% - 70°F Saturated 70°F Aqueous - Hot
Benzol Boracic Acid Bromine Butadiene Butane Butylacetate Butyl Alcohol Butylenes
Hot 5% Hot or Cold 70°F
Butyric Acid " " Calcium Bisulfite Calcium Chlorate " " Calcium Hydroxide " " " " Carbolic Acid Carbon Dioxide " " Carbon Tetrachloride Chlorex Caustic Chlorine Gas " " " " Chromic Acid " " " " Citric Acid " " " " Coal Tar Coke Oven Gas Copper Nitrate Copper Sulphate Core Oils Cottonseed Oil
5% - 70°F 5% - 150°F 70°F Dilute 70°F Dilute 150°F 10% - 212°F 20% - 212°F 50% - 212°F All 212°F Dry Wet 10% - 70°F
70°F
70°F
Dry 70°F Moist 70°F Moist 212°F 5% - 70°F 10% - 212°F 50% - 212°F 15% - 70°F 15% - 212°F Concentrated 212°F Hot
Creosols Creosote Crude Cyanogen Gas Dowtherm Epsom Salt Ether
Hot and Cold 70°F
RECOMMENDED METAL Monel or Nickel 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel 430 Stainless Steel 430 Stainless Steel Monel 304 Stainless Steel 304, Monel, Nickel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel Cast iron 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel 316 Stainless Steel 304 Stainless Steel 316 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel 316 Stainless Steel 304 Stainless Steel Monel Steel (C1018) Phosphor Bronze, Monel, Nickel 304 Stainless Steel Monel Monel 316 Stainless Steel Steel (C1018) Nichrome Steel (C1018) 304 Stainless Steel Steel (C1018), Monel, Inconel 304 Stainless Steel 304 Stainless Steel Tantalum Brass, 304 304 Stainless Steel Monel Copper Steel (C1018), Phosphor Bronze 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 317 Stainless Steel 316 Stainless Steel Steel (C1018), Monel Aluminum,Monel,Nickel Monel 316SS, 317SS 317 Stainless Steel Hastelloy C Hastelloy C 304 Stainless Steel 316 Stainless Steel 316 Stainless Steel 304 Stainless Steel 316 Stainless Steel 317 Stainless Steel 304 Stainless Steel Aluminum 304, 316 304, 316 316 Stainless Steel Steel (C1018), Monel, Nickel 304 Stainless Steel Steel (C 1018), Monel, Nickel 304 Stainless Steel Steel (C1018) 304 Stainless Steel 304 Stainless Steel
SUBSTANCE Ethyl Acetate Ethyl Chloride Ethylene Glycol Ethyl Sulphate Ferric Chloride " " " " Ferric Sulphate Ferrous Sulphate Formaldehyde Freon Formic Acid " " Gallic Acid " " Gasoline Glucose Glycerine Glycerol Heat Treating Hydrobromic Acid Hydrochloric Acid " " " " " " " " " " Hydrocyanic Acid Hydrofluoric Acid Hydrogen Peroxide " " Hydrogen Sulphide Iodine Kerosene Lactic Acid " " " " Lacquer Latex Lime Sulphur Linseed Oil Magnesium Chloride " " Magnesium Sulphate Malic Acid Mercury
RECOMMENDED METAL Monel 304 Stainless Steel Steel (C1018) Monel 316 Stainless Steel Tantalum Tantalum 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel Steel (C1018) 316 Stainless Steel 316 Stainless Steel Monel Monel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 446 Stainless Steel Hastelloy B Hastelloy C Hastelloy B Hastelloy C Hastelloy B Hastelloy B Hastelloy B 316 Stainless Steel Hastelloy C 316 Stainless Steel 316 Stainless Steel 316 Stainless Steel Tantalum 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel Tantalum 316 Stainless Steel Steel (C1018) Steel (C1018), 304, Monel 304 Stainless Steel Monel Nickel Monel 316 Stainless Steel Steel (C1018) , 304, Monel Steel (1020) 304, Nickel Carpenter #20
CONDITIONS 70°F 70°F 1% - 70°F 5% - 70°F 5% - Boiling 5% - 70°F Dilute 70°F 5% - 70°F 5% - 150°F 5% - 70°F 5% - 150°F 70°F 70°F 70°F 48% - 212°F 1% - 70°F 1% - 212°F 5% - 70°F 5% - 212°F 25% - 70°F 25% - 212°F 70°F 212°F Wet and dry 70°F 70°F 5% - 70°F 5% - 150°F 10% - 212°F 70°F
70°F 5% - 70°F 5% - 212°F Cold and Hot Cold and Hot
Methane 70°F Milk Mixed Acids (Sulphuric and Nitric - all temp. and %) Molasses Muriatic Acid Nap Natural Gas Neon Nickel Chloride Nickel Sulphate Nitric Acid " " " " " " " " " " " " Nitrobenzene Nitrous Acid Oleic Acid Oleum Oxalic Acid " " Oxygen " Palmitic Acid Petroleum Ether PhenoI Pentane Phosphoric Acid " " " " " " " "
70°F 70°F 70°F 70°F 70°F Hot and Cold 5% - 70°F 20% - 70°F 50% - 70°F 50% - 212°F 65% - 212°F Concentrated - 70°F Concentrated - 212°F 70°F 70°F 70°F 5% - Hot and Cold 10% - 212°F 70°F Liquid
Steel (C1018), 304, Monel, Nickel Tantalum 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel 304 Stainless Steel Tantalum 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel 316 Stainless Steel 304 Stainless Steel Monel Steel (C1018) 304 Stainless Steel 316 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel Hastelloy C Hastelloy B
1% - 70°F 5% - 70°F 10% - 70°F 10% - 212°F 30% - 70°F
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SUBSTANCE
CONDITIONS
Picric Acid Potassium Bromide Potassium Carbonate Potassium Chlorate Potassium Chloride " " Potassium Hydroxide " " " " Potassium Nitrate " " Potassium Permanganate Potassium Sulphate " " Potassium Sulphide Propane Pyrogallic Acid Quinine Bisulphate Quinine Sulphate Resin Rosin Sea Water Salommoniac Salicylic Acid Shellac Soap Sodium Bicarbonate " " Sodium Bisulphate Sodium Carbonate " " Sodium Chloride " " " " " " Sodium Fluoride Sodium Hydroxide Sodium Hypochlorite Sodium Nitrate Sodium Peroxide Sodium Phosphate Sodium Silicate Sodium Sulphate Sodium Sulphide Sodium Sulphite Steam Stearic Acid Sulphur Dioxide " " Sulphur " Sulphuric Acid " " " " " " " " " " " " " " Tannic Acid Tar
70°F 70°F 1% - 70°F 70°F 5% - 70°*F 5% - 212°F 5% - 70°F 25% - 212°F 50% - 212°F 5% - 70°F 5% - 212°F
Tartaric Acid " " Tin Tolvene Trichloroethylene Turpentine Varnish Vegetable Oils Vinegar Water " Whiskey, Wine Xylene Zinc Zinc Chloride Zinc Sulphate " " " "
5% - 70°F 5% - 70°F 5% - 212°F 70°F
RECOMMENDED METAL 304 Stainless Steel 316 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 316 Stainless Steel 304 Stainless Steel 304 Stainless Steel
304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel Dry 316 Stainless Steel Dry 304 Stainless Steel 304 Stainless Steel Molten 304 Stainless Steel Monel Monel Nickel 304 Stainless Steel 70°F 304 Stainless Steel All concentrations 70°F 304 Stainless Steel 5% - 150°F 304 Stainless Steel Monel 5% - 70°F 304 Stainless Steel 5% - 150°F 304 Stainless Steel 5% - 70°F 316 Stainless Steel 5% - 150°F 316 Stainless Steel Saturated - 70°F 316 Stainless Steel Saturated - 212°F 316 Stainless Steel 5% - 70°F Monel 304 Stainless Steel 5% still 316 Stainless Steel Fused 317 Stainless Steel 304 Stainless Steel Steel (C1018) Steel (C1018) 70°F 304 Stainless Steel 70°F 316 Stainless Steel 150°F 304 Stainless Steel 304 Stainless Steel 304 Stainless Steel Moist Gas - 70°F 316 Stainless Steel Gas - 575°F 304 Stainless Steel Dry - Molten 304 Stainless Steel Wet 316 Stainless Steel 5% - 70°F Carp. 20, Hastelloy B 5% - 212°F Carp. 20, Hastelloy B 10% - 70°F Carp. 20, Hastelloy B 10% - 212°F Carp. 20, Hastelloy B 50% - 70°F Carp. 20, Hastelloy B 50% - 212°F Carp. 20, Hastelloy B 90% - 70°F Carp. 20, Hastelloy B 90% - 212°F Hastelloy D 70˚F 304 Stainless Steel Steel (C1018), 304, Monel, Nickel 70°F 304 Stainless Steel 150°F 316 Stainless Steel Molten Cast Iron Aluminum, Phosphor Bronze, Monel Steel (C1018) 304 Stainless Steel 304 Stainless Steel Steel (C1018), 304, Monel 304 Stainless Steel Fresh Copper, Steel (C1018), Monel Salt Aluminum 304, Nickel Copper Molten Cast Iron Monel 5% - 70°F 304 Stainless Steel Saturated - 70°F 304 Stainless Steel 25% - 212°F 304 Stainless Steel
Melting Temperatures Very High Temperature of Some Important Metals Sheath Materials Approximate melting points are given only as a guide for material selection since many factors including atmosphere, type of process, mounting, etc., all affect the operating maximum.
Tungsten ............
°F
6000 ..................... Rhenium
Sheath Material
Molybdenum
Rec. Useful Temp.
Melting Point
Environmental Conditions
4000ºF
4730ºF
Not Rec.
Fair
Fair
Good
Oxidizing
Hydrogen
Inert
Vacuum
Tantalum
4500ºF
5425ºF
Not Rec.
Not Rec.
Not Rec.
Good
Platinum
3050ºF
3223ºF
Very Good
Poor
Poor
Poor
Tantalum............ Molybdenum ....... Niobium ........... . (Columbium) Chromium ....... ... Titanium ............ Zirconium ........... Iron................... Cobalt ............... Nickel ...............
5000 ..................... Osmium ..................... Iridium 4000 ..................... Rhodium ..................... Platinum ..................... Vanadium 3000 ..................... Palladium
Beryllium ........... Manganese .........
.................... Stainless ....................} Steels .................... .................... Cast Irons
Uranium ............ Copper ..............
2000 ................Gold (24 Karat)
Silver ................
{
Brasses
Magnesium......... Zinc................... Lead ................. Bismuth ............. Tin.................... Indium ..............
Thermometry Fixed Points THERMOELECTRIC FIXED POINT
}
}
18 Karat 12 Karat 10 Karat
Gold Alloys
}
.........Aluminum Silver Solders 1000 ........ Cadmium 500
Gallium .............
Common ...................... Solders
Mercury .............
0ºF
}
Boiling point of oxygen Sublimation point of carbon dioxide Freezing point of mercury Ice Point Triple point of water Boiling point of water Triple point of benzoic acid Boiling point of naphthalene Freezing point of tin Boiling point of benzophenone Freezing point of cadmium Freezing point of lead Freezing point of zinc Boiling point of sulfur Freezing point of antimony Freezing point of aluminum Freezing point of siIver Freezing point of gold Freezing point of copper Freezing point of palladium Freezing point of platinum
MELTING POINTS FROM THE PRACTICAL INTERNATIONAL TEMPERATURE SCALE IPTS-68 -183.0 ºC - 78.5 - 38.9 0 0.01 100.0 122.4 218 231.9 305.9 321.1 327.5 419.6 444.7 630.7 660.4 961.9 1064.4 1084.5 1554 1772
-297.3 ºF -109.2 - 38 32 32 212 252.3 424.4 449.4 582.6 610 621.5 787.2 832.4 1167.3 1220.7 1763.5 1948 1984.1 2829 3222
Extension Grade Wires for Platinum and Tungsten-Rhenium Alloys + Copper Compensating alloys made into extension wire for tungsten-rhenium thermocouples and platinum-rhodium thermocouples closely match the emf of the thermocouples over limited range
Pt/Rh Hot Junction
Lead Junctions – Alloy No. 11
Pt.
Z-48
• The alloy 405/426 combination is used with Tungsten 5% Re vs Tungsten 26% Re. • The alloy 200/226 combination is used with Tungsten vs Tungsten 26% Re. • The alloy 203/225 combination is used with Tungsten 3% Re vs Tungsten 25%. • The Combination copper/alloy #11 is used with platinum-rhodium alloys vs pure platinum.
Z
Thermoelectric Alloy Property Data
ALLOY or DESIGNATION Pure Metals Iron Nickel Molybdenum Aluminum (H-P) Copper Gold Silver Tungsten Rhenium Platium Ref Rhodium Platinum Pt- 6%Rh Pt-10%Rh Pt-13% Rh Pt-20% Rh Pt-30% Rh Pt-40% Rh Nickel Alloys Constantan CHROMEGA® P ALOMEGA®
Compensating Alloys Alloy #11 Alloy #200 Alloy #203 Alloy #205 Alloy #225 Alloy #226 Alloy #260
Changes in Thermocouple Resistance with Increasing Temperature
N=Neg, P=Pos
99.9+% 99.98% 99.9+% 99.99+% 99.98% 99.999% 99.99% 99.99% 99.99% 99.999+% 99.99%
66 39 42 17.4 9.44 13.4 9.3 42 61.2 33.0
60 .0062 37 .0064 31 .0036 15 .0038 9.24 .0041 13.17 .0039 8.83 .0038 33 .0036 117 59.13 .00386 25.8 .0029
.0065 .0068 .0047 .0044 .0043 .0040 .0041 .0048 .00393 .0046
90 100 250 16.3 76 46 52 285 360 60 275
34 48 120 6.8 32 19 24 80 170 24 120
2 2 2 5 1.5 1.5 1.5 2 2
40 36 16 60 46 36 46 3 10 38 16
1536 1452 2610 660 1083 1063 960.8 3410 3170 1769 1966
7.9 8.9 10.2 2.71 8.93 19.30 10.5 19.3 20.0 21.45 12.42
94%Pt- 6%Rh 90% Pt-10% Rh 87% Pt-13% Rh 80% Pt-20% Rh 70% Pt-30% Rh 60% Pt-40% Rh
101 114 119 124 116 108
95 111 114 116 112 101
.0020 .0017 .0016 .0014 .0014 .0014
85 95 105 140 160 190
37 46 48 72 74 78
1.5 1.5 1.5 1.5 1.5 1.5
34 32 32 32 26 26
1810 1830 1840 1870 1910 1920
20.51 19.95 19.55 18.65 17.52 16.54
150 80 165 95 170 85
2 32 2 27 2 32
1270 1430 1400
8.86 8.73 8.60
55% Cu-45% Ni 315 294 90% Ni-10% Cr - 425 95% Ni-2% Mn-2% Al - 177
Tungsten Alloys Tungsten-3% Re Tungsten-5% Re Tungsten-25% Re Tungsten-26% Re
1. “Percent purity or composition” column refers to matching thermocouple grade alloy.
RESISTIVITY TEMP COEEF. TENSILE Ω cmil/ft OF RESISTANCE STRENGTH ELONGATION Melting (at 0ºC) (0-100ºC) (psi x 1000) (percent) point Density 0 C (g/cm3) Hard Annld Hard Annld Hard Annld Hard Annld
PERCENT PURITY or Notes composition
(1)
.0019 .0016 .0015 .0013 .0013 .0013
.00003 .00002 .00032 .00032 .00188 .00188
97% W- 3% Re 95% W- 5% Re 75% W-25% Re 74% W-26% Re
-
55 70 165 170
-
-
320 320 300 300
180 200 210 200
-
10 10 10 10
3410 3350 3130 3120
Pt alloys Tungsten Tungsten- 3% Re Tungsten- 5% Re Tungsten-25% Re Tungsten-26% Re Tungsten-26% Re
-
30 470 470 510 180 160 750
-
.0014 .0003 .0012 -
105 -
50 -
2 -
30 -
1090 1430 1400 1410 1370 1450 1520
19.4 19.4 19.7 19.7
8.91 8.73 8.60 8.58 8.88 8.85 7.42
Ratio of Resistance at Temperature Indicated to Resistance at 0°C (32°F) N=Neg P=Pos 0°C 20°C 200°C 400°C 600°C 800°C 1000°C 1200°C 1400°C 1500°C Thermoelements (32°F) (68°F) (392°F) (752°F) (1112°F) (1472°F) (1832°F) (2192°F) (2552°F) (2732°F) JP JN, TN, EN TP KP, EP KN NP NN RP SP RN, SN BP BN
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
1.13 0.999 1.11 1.01 1.05 1.01 1.07 1.03 1.03 1.06 1.03 1.03
2.46 0.996 1.86 1.09 1.43 1.02 1.13 1.31 1.33 1.77 1.26 1.40
4.72 0.994 2.75 1.19 1.64 1.07 1.27 1.60 1.65 2.50 1.51 1.78
7.84 1.02 3.70 1.25 1.82 1.08 1.39 1.89 1.95 3.18 1.76 2.14
12.0 1.056 4.75 1.30 1.98 1.08 1.55 2.16 2.23 3.81 1.98 2.47
13.07 1.092 5.96 1.37 2.15 1.10 1.68 2.41 2.50 4.40 2.20 2.78
… … … 1.43 2.32 … … 2.66 2.76 4.94 2.41 3.08
… … … … … … … 2.90 3.01 5.42 2.62 3.37
… … … … … … … 3.01 3.13 5.66 2.73 3.51
Resistance of Thermocouples, ohms per foot at 20°C ( 68°F)
Awg. No.
Diameter in.
KN
KP,EP
TN,JN,EN
TP
JP
NP
NN
RN, SN
RP
SP
BP
BN
16 20 24 30 36
0.0508 0.0320 0.0201 0.0100 0.0050
0.0683 0.173 0.438 1.77 7.08
0.164 0.415 1.05 4.25 17.0
0.1113 0.287 0.728 2.94 11.8
0.00402 0.0102 0.0257 0.1032 0.4148
0.0276 0.0699 0.1767 0.710 2.86
.2230 .5664 1.436 5.800 23.20
.08458 .2148 .5445 2.20 8.800
0.0247 0.0624 0.1578 0.6344 2.550
0.0456 0.1149 0.4656 2.965 12.25
0.0445 0.1125 0.2847 1.144 4.600
0.0447 0.1130 0.2859 1.149 4.620
0.0414 0.1046 0.2647 1.064 4.277
Z-49
Thermocouple Types
Trade Names of Alloys ANSI DESIGNATION
Iron-Constantan (ANSI Symbol J) The Iron-Constantan “J” curve thermocouple with a positive iron wire and a negative Constantan wire is recommended for reducing atmospheres. The operating range for this alloy combination is 1600°F for the largest wire sizes. Smaller size wires should operate in correspondingly lower temperatures. Copper-Constantan (ANSI Symbol T) The CopperConstantan “T” curve thermocouple, with a positive copper wire and a negative Constantan wire, is recommended for use in mildly oxidizing and reducing atmospheres up to 750°F. They are suitable for applications where moisture is present. This alloy is recommended for low temperature work since the homogeneity of the component wires can be maintained better than with other base metal wires. Therefore, errors due to inhomogeneity of wires in zones of temperature gradients are greatly reduced. CHROMEGA -ALOMEGA (ANSI Symbol K) The CHROMEGA®-ALOMEGA® “K” curve thermocouple with a positive CHROMEGA® wire and a negative ALOMEGA® wire is recommended for use in clean oxidizing atmospheres, The operating range for this alloy is 2300°F for the largest wire sizes. Smaller wire sizes should operate in correspondingly lower temperatures. ®
ALLOY (Generic or Trade Names)
JP JN, EN, or TN KP or EP KN TP RN or SN RP SP
Iron Constantan, Cupron, Advance CHROMEGA®, Tophel, T1, Thermokanthal KP ALOMEGA®, Nial, T2, Thermokanthal KN Copper Pure Platinum Platinum 13% Rhodium Platinum 10% Rhodium
Trade Names: Advance T - Driver Harris Co., CHROMEGA® and ALOMEGA® - OMEGA Engineering, Inc., Cupron, Nial and Trophel -Wilbur B. Driver Co., Thermokanthal KP and Thermokanthal KN -The Kanthal Corporation.
®
ANSI LETTER DESIGNATIONS -Currently thermocouple and extension wire is ordered and specified by an ANSI letter designation. Popular generic and trade name examples are CHROMEGA®/ALOMEGA® -ANSI Type K: Iron/Constantan ANSI Type J: Copper/Constantan - ANSI Type T CHROMEGA®/Constantan -ANSI Type E: Platinum/Platinum 10% Rhodium - ANSI Type S: Platinum/Platinum 13% Rhodium -ANSI Type R. The positive and negative legs are identified by letter suffixes P and N, respectively, as listed in the tables.
CHROMEGA®-Constantan (ANSI Symbol E) The CHROMEGA®-Constantan thermocouple may be used for temperatures up to 1600°F in a vacuum or inert, mildly oxidizing or reducing atmosphere. At sub-zero temperatures, the thermocouple is not subject to corrosion. This thermocouple has the highest emf output of any standard metallic thermocouple.
ANSI Symbol
E
70
T E J K N*
60 K Millivolts
Platinum-Rhodium Alloys (ANSI Symbols S, R and B) Three types of “noble-metal” thermocouples are in common use; they are: 1) a positive wire of 90% platinum and 10% rhodium used with a negative wire of pure platinum, 2) a positive wire of 87% platinum and 13% rhodium used with a negative wire of pure platinum, and 3) a positive wire of 70% platinum and 30% rhodium used with a negative wire of 94% platinum and 6% rhodium. They have a high resistance to oxidation and corrosion. However, hydrogen, carbon and many metal vapors can contaminate a platinum-rhodium thermocouple. The recommended operating range for the platinum-rhodium alloys is 2800°F, although temperatures as high as 3270°F can be measured with the Pt-30% Rh vs. Pt-6% Rh alloy combination.
80
50
J
N*
40
G* C*
30 T
20
R S B
10 0 1000
2000
3000
4000
5000
Temperature (Fahrenheit)
Tungsten-Rhenlum Alloys Three types of tungstenrhenium thermocouples are in common use for measuring temperatures up to 5000°F. These alloys have inherently poor oxidation resistance and should be used in vacuum, hydrogen or inert atmospheres.
Copper vs. Constantan CHROMEGA® vs. Constantan Iron vs. Constantan CHROMEGA® vs. ALOMEGA® OMEGALLOY® Nicrosil-Nisil G* Tungsten vs. Tungsten 26% Rhenium C* Tungsten 5% Rhenium vs. Tungsten 26% Rhenium D* Tungsten 3% Rhenium vs. Tungsten 25% Rhenium R Platinum 13% Rhodium vs. Platinum S Platinum 10% Rhodium vs. Platinum B Platinum 30% Rhodium vs. Platinum 6% Rhodium *Not an ANSI Symbol
Resistance Vs. Wire Diameter AWG No. 6 8 10 12 14 16 18 20 24 26 30 32 34 36 38 40 44 50 56
Type K Type J Type T Type E Type S Iron/ Copper/ CHROMEGA® Pt/ Diameter CHROMEGA® inches ALOMEGA® Constantan Constantan Constantan PT110%Rh 0.162 0.023 0.014 0.012 0.027 0.007 0.128 0.037 0.022 0.019 0.044 0.011 0.102 0.058 0.034 0.029 0.069 0.018 0.081 0.091 0.054 0.046 0.109 0.028 0.064 0.146 0.087 0.074 0.175 0.045 0.051 0.230 0.137 0.117 0.276 0.071 0.040 0.374 0.222 0.190 0.448 0.116 0.032 0.586 0.357 0.298 0.707 0.185 0.0201 1.490 0.878 0.7526 1.78 0.464 0.0159 2.381 1.405 1.204 2.836 0.740 0.0100 5.984 3.551 3.043 7.169 1.85 0.0080 9.524 5.599 4.758 11.31 1.96 0.0063 15.17 8.946 7.66 18.09 4.66 0.0050 24.08 14.20 12.17 28.76 7.40 0.0039 38.20 23.35 19.99 45.41 11.6 0.00315 60.88 37.01 31.64 73.57 18.6 0.0020 149.6 88.78 76.09 179.20 74.0 0.0010 598.4 355.1 304.3 716.9 185 0.00049 2408 1420 1217 2816 740
*Increase the resistance by 19% for nickel plated, type RTD wire
Type R Type RX/SX Type C† Pt/ Copper W5%Re/ PT113%Rh Alloy11** W26%Re 0.007 0.003 0.009 0.011 0.004 0.015 0.018 0.007 0.023 0.029 0.011 0.037 0.047 0.018 0.058 0.073 0.028 0.092 0.119 0.045 0.148 0.190 0.071 0.235 0.478 0.180 0.594 0.760 0.288 0.945 1.91 0.727 2.38 3.04 1.136 3.8 4.82 1.832 6.04 7.64 2.908 9.6 11.95 4.780 15.3 19.3 7.327 24.4 76.5 18.18 60.2 191 72.7 240 764 302.8 1000
**Maximum Resistance of reviewed wire
Z-50
Type CX Alloy 405 Alloy 426 0.014 0.023 0.037 0.058 0.093 0.146 0.238 0.371 0.941 1.503 3.800 5.94 9.57 15.20 24.98 38.30 95.00 380.0 1583
Type G† W/ W26%Re 0.008 0.012 0.020 0.031 0.049 0.078 0.126 0.200 0.560 0.803 2.03 3.22 5.10 8.16 12.9 20.6 51.1 204 850
†Not ANSI symbol
Type D† W3%Re/ W25%Re 0.009 0.015 0.022 0.035 0.055 0.088 0.138 0.220 0.560 0.890 2.26 3.60 5.70 9.10 15.3 23.0 56.9 227 945
Type BX Copper/ Copper* 0.000790 0.001256 0.001998 0.00318 0.00505 0.00803 0.01277 0.02030 0.05134 0.08162 0.2064 0.3282 0.5218 0.8296 1.3192 2.098 5.134 20.64 86.38
Z
Comparison of Time Constant* vs. Overall Outside Diameter of Bare Thermocouple Wires or Grounded Junction Thermocouples In Air Time constants calculated for air at room temperature and atmospheric pressure moving with velocity of 65 feet per second for thermocouples shown in Figures #1 and #2.
* The “Time Constant” or “Response TIme” is defined as the time required to reach 63.2% of an instantaneous temperature change.
1.1
2.1
1.0
2.0
.9
1.9
.8
1.8
.7
1.7
.6
1.6
Time constant of thermocouple made with exposed, butt welded 0.001 in. dia. wire = .003 sec.
.5 .4 .3
1.5 1.4 1.3 1.2
.2
1.1
.1
1/64 in.
1/32 in. 1.0
0.0 .002 .004 .006 .008 .010 .012 .014 .016 .018 .020 .022 .024 .026 .028 .030 .032 .034 .001
WIRE OR SHEATH DIAMETER - INCHES “D”
D
D
D GROUNDED Junction Fig. #2
BARE WIRE Butt Welded Fig. #1
D
BEADED-TYPE UNGROUNDEDThermocouple TYPE Fig. #3 Thermocouple Fig. #4
Because of space limitations, time constant curve is divided into 4 separate curves.
11.0
110
10.0
100
9.0
90
8.0
80
7.0
70
6.0
60
5.0
50
4.0
40
3.0
30
20
2.0
1.8 sec. 10
1.0
.03125
.0625
.09375
.125
.15625
.1875
.21875
.250
.28125
.3125
.375
1/32
1/16
3/32
1/8
5/32
3/16
7/32
1/4
9/32
5/16
3/8
WIRE OR SHEATH DIAMETER - INCHES “D”
Note: These comparisons apply to either bare “butt-welded” or “grounded” junction thermocouples. If the thermocouples are the “beaded” type or “ungrounded,” the time constant is longer. These times are only approximate and are provided for comparison purposes only. Multiply values from Time Constants by 1.5 for junctions shown in Fig. #3 and Fig. #4.
Z-51
TIME CONSTANT - SECONDS
TIME CONSTANT - SECONDS
Figure M Sheath Diameter 1⁄32" to 3⁄8 "
TIME CONSTANT - SECONDS
Time constant of thermocouple made with exposed butt welded 0.001 inch dia. wire = .003 sec.
TIME CONSTANT - SECONDS
For beaded-type and ungrounded junctions (Figures #3 or #4), multiply time constants by 1.5.
1.2
Metal Sheathed Thermocouple Probe Time Response Study in Water 2.25 .250
Ungrounded
2.00
1.75
Time in Seconds
1.50
1.25 .188
1.00
Grounded
.75
.125 .50
.25
.040
.05
.062
Exposed
.15
.10
Probe Diameter in Inches
Z-52
.20
.25
Z
OMEGA® Interchangeable Thermistor Applications
variable resistor for battery control
thermistor
variable resistor for battery control
thermistor
variable resistor for setting desired temperature
relay high gain amplifier
thermistor thermistor
Fig. 1
Fig. 6
Fig. 4
room temperature
oven #1
variable resistor for battery control
variable resistor for battery control
reference thermistor
slave thermistor
selector switch
oven #2
variable resistor for adjusting slave temperature slightly above or below temperature
refrigerator chamber
difference #2
difference #1
relay high gain amplifier
master thermistor
pressure chamber
Fig. 5
Fig. 2
Fig. 7
thermistor 1000 ohms at 25°C
meter coil 2150 ohms at 25°C
resistor 1000 ohms at 25°C
Thermistors can be used in a variety of ways. Here are a few typical applications. If you have questions concerning these or other thermistor uses, we will be happy to discuss them. TEMPERATURE MEASUREMENT-A thermistor in one leg of a Wheatstone bridge circuit will provide precise temperature information. Accuracy is limited in most applications only by the readout device. See Figure 1. Since lead length between thermistor and bridge is not normally a limiting factor, this basic system can be expanded to measure temperature at several locations from a central point. Thermistor interchangeability and large resistance change eliminate any significant error from switches or lead length. See Figure 2. METER COMPENSATION - The coil resistance of a meter movement changes with temperature, making the meter temperature dependent. Using the thermistor’s property of a high negative temperature coefficient, the coil can be compensated so total resistance due to temperature rise is essentially constant, allowing the meter to be used over a wide temperature range with minimal error. See Figure 3. DIFFERENTIAL THERMOMETERS-For accurate indication of temperature differential, two thermistors can be used in a Wheatstone bridge circuit. Thermistor interchangeability simplifies circuit design and reduces the number of components. See Figure 4.
can be placed at various points and the difference between these temperatures and the original temperature monitored at a convenient location. Measuring air temperature at different elevations with reference to ground temperature is useful for temperature inversion data and geological studies. See Figure 5. TEMPERATURE CONTROL-A system can be designed using a thermistor with a known temperature/ resistance curve to form one leg of an AC bridge and a variable resistor calibrated in temperature to form another leg. When the resistor is set to a desired temperature, bridge unbalance occurs. This unbalance is fed into an amplifier which actuates a relay to provide a source of heat or cold. When the thermistor senses the desired temperature, the bridge is balanced, opening the relay and turning off the heat or cold. See Figure 6. MASTER-SLAVE CONTROL-Occasionally there is a need to control one temperature with respect to another, such as a product going through a series of baths. The first bath acts as a master and uses a thermistor to sense temperature. Succeeding baths, also using thermistors, are slaves. When these thermistors are placed in the controller bridge, the slave baths can be kept at a temperature relative to the master bath. The master bath can be controlled with the system described earlier. The master-slave controller can be used for as many baths as necessary. See Figure 7.
To measure heat loss in a piping network, thermistors Z-53
®
Resistance Elements and RTD’s David J. King INTRODUCTION Resistance elements come in many types conforming to different standards, capable of different temperature ranges, with various sizes and accuracies available. But they all function in the same manner: each has a pre-specified resistance value at a known temperature which changes in a predictable fashion. In this way, by measuring the resistance of the element, the temperature of the element can be determined from tables, calculations or instrumentation. These resistance elements are the heart of the RTD (Resistance Temperature Detector). Generally, a bare resistance element is too fragile and sensitive to be used in its raw form, so it must be protected by incorporating it into an RTD. A Resistance Temperature Detector is a general term for any device that senses temperature by measuring the change in resistance of a material. RTD’s come in many forms, but usually appear in sheathed form. An RTD probe is an assembly composed of a resistance element, a sheath, lead wire and a termination or connection. The sheath, a closed end tube, immobilizes the element, protecting it against moisture and the environment to be measured. The sheath also provides protection and stability to the transition lead wires from the fragile element wires.
Some RTD probes can be combined with thermowells for additional protection. In this type of application, the thermowell may not only add protection to the RTD, but will also seal whatever system the RTD is to measure (a tank or boiler for instance) from actual contact with the RTD. This becomes a great aid in replacing the RTD without draining the vessel or system. Thermocouples are the old tried and true method of electrical temperature measurement. They function very differently from RTD’s but generally appear in the same configuration: often sheathed and possibly in a thermowell.
Basically, they operate on the Seebeck effect, which results in a change in thermoelectric emf induced by a change in temperature. Many applications lend themselves to either RTD’s or thermocouples. Thermocouples tend to be more rugged, free of self-heating errors and they command a large assortment of instrumentation. However, RTD’s, especially platinum RTD’s, are more stable and accurate. RESISTANCE ELEMENT CHARACTERISTICS There are several very important details that must be specified in order to properly identify the characteristics of the RTD: 1. 2. 3. 4. 5. 6.
Material of Resistance Element (Platinum, Nickel, etc.) Temperature Coefficient Nominal Resistance Temperature Range of Application Physical Dimensions or Size Restrictions Accuracy
1. Material of Resistance Element Several metals are quite common for use in resistance elements and the purity of the metal affects its characteristics. Platinum is by far the most popular due to its linearity with temperature. Other common materials are nickel and copper, although most of these are being replaced by platinum elements. Other metals used, though rarely, are Balco (an iron-nickel alloy), tungsten and iridium. 2. Temperature Coefficient The temperature coefficient of an element is a physical and electrical property of the material. This is a term that describes the average resistance change per unit of temperature from ice point to the boiling point of water. Different organizations have adopted different temperature coefficients as their standard. In 1983, the IEC (International Electrotechnical Commission) adopted the DIN (Deutsche Institute for Normung) standard of Platinum 100 ohm at 0ºC with a temperature coefficient of 0.00385 ohms per ohm degree centigrade. This is now the accepted standard of the industry in most countries, although other units are widely used. A quick explanation of how the coefficient is derived is as follows: Resistance at the boiling point (100ºC) =138.50 ohms. Resistance at ice point (0ºC) = 100.00 ohms. Divide the difference (38.5) by 100 degrees and then divide by the 100 ohm Z-54
nominal value of the element. The result is the mean temperature coefficient (alpha) of 0.00385 ohms per ohm per ºC. Some of the less common materials and temperature coefficients are: Pt TC
=
Pt TC
=
Pt TC Pt TC Copper TC Nickel TC Nickel TC
= = = = =
Balco TC = Tungsten TC =
.003902 (U.S. Industrial Standard) .003920 (Old U.S. Standard) .003923 (SAMA) .003916 (JIS) .0042 0.00617 (DIN) .00672 (Growing Less Common in U.S.) .0052 0.0045
Please note that the temperature coefficients are the average values between 0 and 100ºC. This is not to say that the resistance vs. temperature curves are truly linear over the specified temperature range. 3. Nominal Resistance
Nominal Resistance is the prespecified resistance value at a given temperature. Most standards, including IEC-751, use 0ºC as their reference point. The IEC standard is 100 ohms at 0ºC, but other nominal resistances, such as 50, 200, 400, 500, 1000 and 2000 ohm, are available. 4. Temperature Range of Application Depending on the mechanical configuration and manufacturing methods, RTD’s may be used from -270ºC to 850ºC. Specifications for temperature range will be different, for thin film, wire wound and glass encapsulated types, for example. 5. Physical Dimensions or Size Restrictions The most critical dimension of the element is outside diameter (O.D.), because the element must often fit within a protective sheath. The film type elements have no O.D. dimension. To calculate an equivalent dimension, we need to find the diagonal of an end cross section (this will be the widest distance across the element as it is inserted into a sheath).
Z
Resistance Elements and RTD’s Cont’d FIGURE 1. LOCATION OF THIN FILM ELEMENT IN CYLINDRICAL SHEATH WALL THICKNESS
DIAGONAL OF ELEMENT
Vibration Resistance: 50 g @ 500ºC; 200 g @ 20ºC; at frequencies from 20 to 1000 cps. THICKNESS OF ELEMENT
W OD
Permissible deviations from basic values Temperature ºC -200 -100 0 100 200 300 400 500 600 650
Class A Deviation ohms ºC ±0.24 ±0.55 ±0.14 ±0.35 ±0.06 ±0.15 ±0.13 ±0.35 ±0.20 ±0.55 ±0.27 ±0.75 ±0.33 ±0.95 ±0.38 ±1.15 ±0.43 ±1.35 ±0.46 ±1.45
Class B Temperature Deviation ºC ohms ºC -200 ±056 ±1.3 -100 ±0.32 ±0.8 0 ±0.12 ±0.3 100 ±0.30 ±0.8 200 ±0.48 ±1.3 300 ±0.64 ±1.8 400 ±0.79 ±2.3 500 ±0.93 ±2.8 600 ±1.06 ±3.3 650 ±1.13 ±3.6 700 ±1.17 ±3.8 800 ±1.28 ±4.3 850 ±1.34 ±4.6 For example, using an element that is 10 x 2 x 1.5 mm, the diagonal can be found by taking the square root of (22 + 1.52). Thus, the element will fit into a 2.5 mm (0.98") inside diameter hole. For practical purposes, remember that any element 2 mm wide or less will fit into a
10,000 hours at maximum temperature (1 year, 51 days, 16 hours continuous).
W = WIDTH OF ELEMENT
1/ " O.D. sheath with 0.010" walls, 8 generally speaking. Elements which are 1.5 mm wide will typically fit into a sheath with 0.084" bore. Refer to Figure 1.
6. Accuracy IEC 751 specifications for Platinum Resistance Thermometers have adopted DIN 43760 requirements for accuracy. DIN-IEC Class A and Class B elements are shown in the chart on this page. 7. Response Time 50% Response is the time the thermometer element needs in order to reach 50% of its steady state value. 90% Response is defined in a similar manner. These response times of elements are given for water flowing with 0. 2 m/s velocity and air flowing at 1 m/s. They can be calculated for any other medium with known values of thermal conductivity. In a 1/4" diameter sheath immersed in water flowing at 3 feet per second, response time to 63% of a step change in temperature is less than 5.0 seconds. 8. Measurement Current and Self Heating Temperature measurement is carried out almost exclusively with direct current. Unavoidably, the measuring current generates heat in the RTD. The permissible measurement currents are determined by the location of the element, the medium which is to be measured, and the velocity of moving media. A self-heating factor, “S”, gives the measurement error for the element in ºC per milliwatt (mW). With a given value of measuring current, I, the milliwatt value P can be calculated from P = I2R, where R is the RTD’s resistance value. The temperature measurement error ∆T (ºC) can then be calculated from ∆T = P x S.
RESISTANCE ELEMENT SPECIFICATIONS Stability: Better than 0.2ºC after Z-55
Temperature Shock Resistance: In forced air: over entire temperature range. In a water quench: from 200 to 20ºC. Pressure Sensitivity: Less than 1.5 x 10-4 C/PSI, reversible. Self Heating Errors & Response Times: Refer to specific Temperature Handbook pages for the type of element selected. Self Inductance From Sensing Current: Can be considered negligible for thin film elements; typically less than 0.02 microhenry for wire wound elements. Capacitance: For wire wound elements: calculated to be less than 6 PicoFarads; for film-type elements: capacitance is too small to be measured and is affected by lead wire connection. Lead connections with element may indicate about 300 pF capacitance.
LEAD WIRE CONFIGURATIONS As stated previously, a Resistance Temperature Detector (RTD) element generally appears in a sheathed form. Obviously, all of the criteria applicable to resistance elements also apply here, but rather than element size, the construction and dimensions of the entire RTD assembly must be considered. Since the lead wire used between the resistance element and the measuring instrument has a resistance itself, we must also supply a means of compensating for this inaccuracy. Refer to Figure 2 for the 2-wire configuration. BLACK
R2
RE RED ELEMENT
R1
FIGURE 2. 2-WIRE CONFIGURATION (STYLE 1) The circle represents the resistance element boundaries to the point of calibration. 3- or 4-wire configuration must be extended from the point of calibration so that all uncalibrated resistances are compensated.
The resistance RE is taken from the resistance element and is the value that will supply us with an accurate temperature measurement. Unfortunately, when we take our resistance measurement, the instrument will indicate RTOTAL: Where RT = R1 + R2 + RE This will produce a temperature readout higher than that actually being measured. Many systems can be calibrated to eliminate this. Most RTD’s incorporate a third wire with resistance R3. This wire will be connected to one side of the resistance element along with lead 2 as shown in Figure 3. This configuration provides one connection to one end and two to the other end of the sensor. Connected to an instrument designed to accept 3-wire input, compensation is achieved for lead resistance and temperature change in lead resistance. This is the most commonly used configuration.
BLACK R 3 BLACK R2 RE RED ELEMENT
R1
provided to each end of the sensor. This construction is used for measurements of the highest precision.
BLACK R 4 BLACK R 3
case. Still another configuration, now rare, is a standard 2-wire configuration with a closed loop of wire alongside (Figure 5). This functions the same as the 3-wire configuration, but uses an extra wire to do so. A separate pair of wires is provided as a loop to provide compensation for lead resistance and ambient changes in lead resistance.
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RE RED R
BLACK R 4
2
RED R 1
ELEMENT
RE RED ELEMENT
FIGURE 4. 4-WIRE CONFIGURATION (STYLE 3) With the 4-wire configuration, the instrument will pass a constant current (I) through the outer leads, 1 and 4. The voltage drop is measured across the inner leads, 2 and 3. So from V = IR we learn the resistance of the element alone, with no effect from the lead wire resistance. This offers an advantage over 3-wire configurations only if dissimilar lead wires are used, and this is rarely the
FIGURE 3. 3-WIRE CONFIGURATION (STYLE 2) If three identical type wires are used and their lengths are equal, then R1 = R2 = R3. By measuring the resistance through leads 1, 2 and the resistance element, a total system resistance is measured (R1 + R2 + RE ). If the resistance is also measured through leads 2 and 3 (R2 + R3), we obtain the resistance of just the lead wires, and since all lead wire resistances are equal, subtracting this value (R2 + R3) from the total system resistance (R1 + R2 + RE) leaves us with just RE, and an accurate temperature measurement has been made. A 4-wire configuration is also used. (See Figure 4.) Two connections are Z-56
BLACK LEAD RESISTANCE LOOP
FIGURE 5. 2-WIRE CONFIGURATION PLUS LOOP (STYLE 4)
®
R3 R2 R1
Introduction to Infrared Pyrometers Why should I use an infrared pyrometer to measure temperature in my application? Infrared pyrometers allow users to measure temperature in applications where conventional sensors cannot be employed. Specifically, in cases dealing with moving objects (i.e., rollers, moving machinery, or a conveyer belt), or where non-contact measurements are required because of contamination or hazardous reasons (such as high voltage), where distances are too great, or where the temperatures to be measured are too high for thermocouples or other contact sensors.
Emissivity (ε), a major but not uncontrollable factor in IR temperature measurement, cannot be ignored. Related to emissivity are reflectivity (R), a measure of an object’s ability to reflect infrared energy, and transmissivity (T), a measure of an object’s ability to pass or transmit IR energy. All radiation energy must be either emitted (E) due to the temperature of the body, transmitted (T) or reflected (R). The total energy, the sum of emissivity, transmissivity and reflectivity is equal to 1: E + T + R = 1.0
What should I consider about my application when selecting an infrared pyrometer? The critical considerations for any infrared pyrometer include field of view (target size and distance), type of surface being measured (emissivity considerations), spectral response (for atmospheric effects or transmission through surfaces), temperature range and mounting (handheld portable or fixed mount). Other considerations include response time, environment, mounting limitations, viewing port or window applications, and desired signal processing.
R E
Hot Source
T Infrared Pyrometer
FIELD OF VIEW What is meant by Field of View, and why is it important? The field of view is the angle of vision at which the instrument operates, and is determined by the optics of the unit. To obtain an accurate temperature reading, the target being measured should completely fill the field of view of the instrument. Since the infrared device determines the average temperature of all surfaces within the field of view, if the background temperature is different from the object temperature, a measurement error can occur (figure 1). Object A
Object B
Total infrared radiation reaching pyrometers
The ideal surface for infrared measurements is a perfect radiator, or a blackbody with an emissivity of 1.0. Most objects, however, are not perfect radiators, but will reflect and/or transmit a portion of the energy. Most instruments have the ability to compensate for different emissivity values, for different materials. In general, the higher the emissivity of an object, the easier it is to obtain an accurate temperature measurement using infrared. Objects with very low emissivities (below 0.2) can be difficult applications. Some polished, shiny metallic surfaces, such as aluminum, are so reflective in the infrared that accurate temperature measurements are not always possible.
Wall
Figure 1: Field of view
Most general purpose indicators have a focal distance between 20 and 60". The focal distance is the point at which the minimum measurement spot occurs. For example, a unit with a distance-to-spot size ratio of 120:1, and a focal length of 60" will have a minimum spot size of 0.5" at 60" distance. Close-focus instruments have a typical 0.1 to 12" focal length, while long-range units can use focal distances on the order of 50'. Many instruments used for long distances or small spot sizes also include sighting scopes for improved focusing. Field of view diagrams are available for most instruments to help estimate spot size at specific distances.
EMISSIVITY What is emissivity, and how is it related to infrared temperature measurements? Emissivity is defined as the ratio of the energy radiated by an object at a given temperature to the energy emitted by a perfect radiator, or blackbody, at the same temperature. The emissivity of a blackbody is 1.0. All values of emissivity fall between 0.0 and 1.0.
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Reflectivity is usually a more important consideration than transmission except in a few special applications, such as thin film plastics. The emissivity of most organic substances (wood, cloth, plastics, etc.) is approximately 0.95. Most rough or painted surfaces also have fairly high emissivity values.
FIVE WAYS TO DETERMINE EMISSIVITY There are five ways to determine the emissivity of the material, to ensure accurate temperature measurements: 1. Heat a sample of the material to a known temperature, using a precise sensor, and measure the temperature using the IR instrument. Then adjust the emissivity value to force the indicator to display the correct temperature.
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2. For relatively low temperatures (up to 500°F), a piece of masking tape, with an emissivity of 0.95, can be measured. Then adjust the emissivity value to force the indicator to display the correct temperature of the material. 3. For high temperature measurements, a hole (depth of which is at least 6 times the diameter) can be drilled into the object. This hole acts as a blackbody with emissivity of 1.0. Measure the temperature in the hole, then adjust the emissivity to force the indicator to display the correct temperature of the material. 4. If the material, or a portion of it, can be coated, a dull black paint will have an emissivity of approx. 1.0. Measure the temperature of the paint, then adjust the emissivity to force the indicator to display the correct temperature. 5. Standardized emissivity values for most materials are available (see pages 114-115). These can be entered into the instrument to estimate the material’s emissivity value.
TEMPERATURE MEASUREMENT THROUGH GLASS I want to measure the temperature through a glass or quartz window; what special considerations are there? Transmission of the infrared energy through glass or quartz is an important factor to be considered. The pyrometer must have a wavelength where the glass is somewhat transparent, which means they can only be used for high temperature. Otherwise, the instrument will have measurement errors due to averaging of the glass temperature with the desired product temperature.
MOUNTING How can I mount the infrared pyrometer?
SPECTRAL RESPONSE What is spectral response, and how will it affect my readings? The spectral response of the unit is the width of the infrared spectrum covered. Most general purpose units (for temperatures below 1000°F) use a wideband filter in the 8 to 14 micron range. This range is preferred for most measurements, as it will allow measurements to be taken without the atmospheric interference (where the atmospheric temperature affects the readings of the instrument). Some units use wider filters such as 8 to 20 microns, which can be used for close measurements, but are ‘‘distance-sensitive’’ against longer distances. For special purposes, very narrow bands may be chosen. These can be used for higher temperatures, and for penetrations of atmosphere, flames, and gases. Typical low band filters are at 2.2 or 3.8 microns. High temperatures above 1500°F are usually measured with 2.1 to 2.3 micron filters. Other bandwidths that can be used are 0.78 to 1.06 for high temperatures, 7.9 or 3.43 for limited transmissions through thin film plastics, and 3.8 microns to penetrate through clean flames with minimum interference.
The pyrometer can be of two types, either fixed-mount or portable. Fixed mount units are generally installed in one location to continuously monitor a given process. They usually operate on line power, and are aimed at a single point. The output from this type of instrument can be a local or remote display, along with an analog output that can be used for another display or control loop. Battery powered, portable infrared ‘‘guns’’ are also available; these units have all the features of the fixed mount devices, usually without the analog output for control purposes. Generally these units are utilized in maintenance, diagnostics, quality control, and spot measurements of critical processes.
RESPONSE TIME What else should I take into account when selecting and installing my infrared measurement system? First, the instrument must respond quickly enough to process changes for accurate temperature recording or control. Typical response times for infrared thermometers are in the 0.1 to 1 second range. Next, the unit must be able to function within the environment, at the ambient temperature. Other considerations include physical mounting limitations, viewing port/window applications (measuring through glass), and the desired signal processing to produce the desired output for further analysis, display or control.
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Principles of Infrared Thermometry W. R. Barron, Williamson Corporation
Temperature measurement can be divided into two categories: contact and noncontact. Contact thermocouples, RTDs, and thermometers are the most prevalent in temperature measurement applications. They must contact the target as they measure their own temperature and they are relatively slow responding, but they are inexpensive. Noncontact temperature sensors measure IR energy emitted by the target, have fast response, and are commonly used to measure moving and intermittent targets, targets in a vacuum, and targets that are inaccessible due to hostile environments, geometry limitations, or safety hazards. The cost is relatively high, although in some cases is comparable to contact devices. Infrared radiation was discovered in 1666 by Sir Isaac Newton, when he separated the electromagnetic energy from sunlight by passing white light through a glass prism that broke up the beam into colors of the rainbow. In 1800, Sir William Herschel took the next step by measuring the relative energy of each color. He also discovered energy beyond the visible. In the early 1900s, Planck, Stefan, Boltzmann, Wien, and Kirchhoff further defined the activity of the electromagnetic spectrum and developed quantitative data and equations to identify IR energy. This research makes it possible to define IR energy using the basic blackbody emittance curves (See Figure 1). From this plot it can be seen that objects (of a temperature greater than -273°C) emit radiant energy in an amount proportional to the fourth power of their temperature. The concept of blackbody emittance is the foundation for IR thermometry. There is, however, the term “emissivity” that adds a variable to the basic laws of physics. Emissivity is a measure of the ratio of thermal radiation emitted by a
1200°F
0.8
El = 1 - tl - rl This emissivity coefficient fits into Planck’s equation as a variable describing the object surface characteristics relative to wavelength. The majority of targets measured are opaque and the emissivity coefficient can be simplified to:
0.7
0.6
0.5
El = 1 - rl
1000°F 0.4
Exceptions are materials like glass, plastics, and silicon, but through proper selective spectral filtering it is possible to measure these objects in their opaque IR region.
0.3
0.2 VISIBLE
THEORY AND FUNDAMENTALS
Therefore:
RADIATION EMITTANCE (W/cm2/mm-1)
The fundamentals of IR thermometry are an important prerequisite for specifying an accurate monitoring system. Unfortunately, many users do not take the time to understand the basic guidelines, and consequently reject the concept of noncontact temperature measurement as inaccurate.
0.1
600°F
0 0
1
2
3
4
5
6
7
8
9
10
WAVELENGTH (mm)
BLACKBODY RADIATION CHARACTERISTICS STEFAN-BOLTZMANN LAW Q = sT4 WIEN'S DISPLACEMENT LAW l M = K/T PLANCK'S LAW Ql = Cl -5 (ec2 / lT-1) -1
Figure 1: As shown in curves representing the distribution of energy emitted by blackbodies ranging in temperature from 600°F to 1200°F, the predominant radiation is in the IR region of 0.5-14 µm, well beyond the visible region.
graybody (non-blackbody) to that of a blackbody at the same temperature. (A graybody refers to an object that has the same spectral emissivity at every wavelength; a non-graybody is an object whose emissivity changes with wavelength, e.g. aluminum.) L E = GB LBB The law of conservation of energy states that the coefficient of transmission, reflection, and emission (absorption) of radiation must add up to 1: tl + rl + al = 1 and the emissivity equals absorptivity: El = al
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There is typically a lot of confusion regarding emissivity error, but the user need remember only four things: – IR sensors are inherently colorblind. – If the target is visually reflective (like a mirror), beware – you will measure not only the emitted radiation, as desired, but also reflected radiation. – If you can see through it, you need to select IR filtering (e.g., glass is opaque at 5µm). – Nine out of ten applications do not require absolute temperature measurement. Repeatability and drift-free operation yield close temperature control. If the surface is shiny, there is an emissivity adjustment that can be made either manually or automatically to correct for emissivity error. It is a simple fix for most applications. In cases where emissivity varies and creates processing problems, consider dual- or multiwavelength radiometry to eliminate the emissivity problem.
DESIGN ELEMENTS IR thermometers come in a wide variety of configurations pertaining to optics, electronics, technology, size, and protective enclosures. All, however, have a common chain of IR energy in and an electronic signal out. This basic chain consists of collecting optics, lenses, and/or fiber optics, spectral filtering, and a detector as the front end. Dynamic processing comes in many forms, but can be summarized as amplification, thermal stability, linearization, and signal conditioning. Normal window
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From an applications standpoint, the primary characteristic of the optics is the field of view (FOV), i.e., what is the target size at a prescribed distance? A very common lens system, for example, would be a 1 in. dia. target size at a 15 in. working distance. Using the inverse square law, by doubling the distance (30 in.) the target area theoretically doubles (2 in. dia.). The actual definition of target size (area measured) will vary depending upon the supplier, and it is price dependent. Other optical configurations vary from small spot (0.030 in dia.) for close-up pinpoint measurement, to distant optics (3 in. at 30 ft) for distant aiming. It is important to note that working distance should not affect the accuracy if the FOV is filled by the target. In one technique for measuring FOV, the variable is signal loss vs. diameter. A strict rule is a 1% energy reduction, although some data are presented at half power, or 63.2% Alignment (aiming) is another optical factor. Many sensors lack that capability; the lens is aligned to the surface and measures surface temperature. This works with sizable targets, e.g., paper web, where pinpoint accuracy is not required. For small targets that use small-spot optics, and for distant optics used in remote monitoring, there are options of visual aiming, aim lights, and laser alignment. Selective spectral filtering typically uses short-wavelength filters for hightemperature applications (>1000°F, and long-wavelength filters for low temperatures –50°F). This obviously fits the blackbody distribution curves, and there are some technological advantages. For example, high temperature/short wavelength uses a very thermally stable silicon detector, and the short-wavelength design minimizes temperature error due to emissivity variations. Other selective filtering is used for plastic films (3.43 µm and 7.9 µm), glass (5.1 µm), and flame insensitivity (3.8 µm).
A variety of detectors are used to maximize the sensitivity of the sensor. As shown in Figure 2, PbS has the greatest sensitivity, while the thermopile has the least sensitivity. Most detectors are either photovoltaic, putting out a voltage when energized, or photoconductive, changing resistance when excited. These fast-responding, high sensitive detectors have a tradeoff thermal drift that can be overcome in many ways, including temperature compensation (thermistors) circuitry, temperature regulation, auto null circuitry, chopping (AC vs. DC output), and isothermal protection. Drift-free operation is available in varying degrees and is price dependent. 106 PbS
105
RELATIVE SENSIVITY
glass is usable at the short wavelength, quartz for the midrange, and germanium or zinc sulfide for the 8-14 µm range. Fiber optics are available to cover the 0.5-5.0 µm region.
Ge 104
Si
InAs InSb
3
10
THERMISTOR BOLOMETER 102
(PYROELECTRIC DETECTOR)
THIN FILM THERMOPILE
101
METAL THERMOPILE
1 0.1
0.2 0.3 0.5 0.7 1.0
2
3
5 7 10
20
WAVELENGTH (mm) CHOPPED UNCHOPPED
Figure 2: To optimize the respone of IR sensing systems, the detector’s spectral response and modulation characteristics must be considered.
In the IR thermometer’s electronics package, the detector’s nonlinear output signal, on the order of 100-1000 µV, is processed. The signal is amplified 1000 x, regulated, and linearized, and the ultimate output is a linear mV or mA signal. The trend is toward 4-20 mA output to minimize environmental electrical noise interference. This signal can also be transposed to RS 232 or fed to a PID controller, remote display, or recorder. Additional signal conditioning options involve on/off alarms, adjustable peak hold for intermittent targets, adjustable response time, and/or sample-and-hold circuitry.
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On the average, IR thermometers have a response time on the order of 300 ms, although signal outputs on the order of 10 ms can be obtained with silicon detectors. In the real world, many instruments have an adjustable response capability that permits damping of noisy incoming signals and field adjustment on sensitivity. It is not always necessary to have the fastest response available. There are cases involving induction heating and other types of applications, however, where response times on the order of 10-50 ms are required, and they are attainable through IR thermometry.
SINGLE-WAVELENGTH THERMOMETRY The basic single-wavelength design measures total energy emitted from a surface at a prescribed wavelength. The configurations range from handheld probes with a simple remote meter to sophisticated portables with simultaneous viewing of target and temperature, plus memory and/or printout capabilities. On-line, fixed-mount sensors range from simple small detectors with remote electronics (OEM designs) to rugged devices with remote PID control. Fiber optics, laser aiming, water cooling, CRT display, and scanning systems are among the options for process monitoring and control applications. There are many variations in size, performance, ruggedness, adaptability, and signal conditioning. Process sensor configuration, IR spectral filtering, temperature range, optics, response time, and target emissivity are important engineering elements that affect performance and which must be given careful consideration during the selection process. The sensor configuration can be a portable, a simple two-wire transmitter, a sophisticated ruggedized sensing unit, or a scanning device. Visual aiming, laser alignment, non-aiming, fiber optics, water cooling, output signals, and remote displays represent an overview of the various options. These are somewhat subjective, but demand engineering review. In most cases, if it is a simple application, e.g., web temperature, a simple low-cost sensor would do the job; if the application is
Infrared Thermometry Principles Cont’d
complicated, e.g., vacuum chamber or small target, then a more sophisticated sensor is a better choice. The selection of IR spectral response and temperature range is related to a specific application. Short wavelengths are for high temperature and long wavelengths are for low temperature, to coincide with the blackbody distribution curves. If transparent-type targets are involved, e.g., plastics and glass, then selective narrow-band filtering is required. For example, polyethylene film has a CH absorption band of 3.43 µm, where it becomes opaque. By filtering in this region, the emissivity factor is simplified. Likewise, most glass-type materials become opaque at 4.6 µm and narrow-band filtering at 5.1 µm permits accurate measurement of glass surface temperature. On the other hand, to look through a glass window, a sensor filtered in the 1-4 µm region would allow easy access via viewing ports into vacuum and pressure chambers. Another option, in the case of chambers, is to use a fiber-optic cable with a vacuum or pressure bushing. Optics and response time are two sensor characteristics that are, in most applications, nonissues, in that the standard FOV of approximately 1 in. at 15 in. is acceptable, and response time of <1 s is adequate. If the application requires a small target or a fast-moving intermittent target, however, then small spot (0.125 in dia.) and very small spot (0.030 in. dia.) may be applicable at a premium. Likewise, distant sighting (10-1000 ft away from the target) will also require an optical adjustment, as the standard FOV will become very large. In some instances, dual-wavelength radiometry is used for these applications, .e.g., wire and distant sighting. The fiber-optic front-end offers engineering flexibility by remoting the electronics from hostile environments, eliminating electrical noise interference and resolving accessibility concerns. It is an intriguing engineering tool that helps solve some unique application problems. Most sensors have adjustable response in the 0.2-5.0 s range, and typical settings are in the midrange. Fast response can expose application noise, while slow response affects sensitivity. Induction heating requires fast response, while conveyor or web monitoring requires a slower response to reduce application noise. A fast-responding sensor requires a fast-responding controller, SCR power pack, and other regulators. Integrated system dynamics can be defined by the following equation:
T = 1.1 =+++++++ t12 + t22 ....tn2 where: T
= total response
t1,t2= individual elements of the loop Considering the element of time, there are two types of process dynamics: steady state variations, where there is a fast-moving product that requires close temperature control due to the dynamics of the process, e.g., induction heating of wire. Step changes or ramp response pertains to the very quick heating of a product in a batch process, e.g., rapid thermal annealing of silicon wafers. In these dynamic applications, system responsivity and sensor FOV are critical parameters. In many cases, target emissivity is not a significant factor. With the proper selection of narrow-band spectral filtering, most materials have a constant emissivity in the 0.90 ±0.05 range. Setting the emissivity at 0.9 µm, the sensor will tend to read within ±5° or 10° of absolute temperature. This application error represents an accuracy variation of about 1% or 2% but, in the real world of IR thermometry, repeatability is critical for control. If, for example, a product is heated to 410°F and the sensor reads 400°F, and you make quality product when the sensor indicates 390-410°F, use the 400 setpoint for control. Most applications do not require NIST calibration standards to produce quality product. If an application requires accurate, absolute temperature measurement and documentation, the instruments can be calibrated and certified to referenced NIST standards. In addition, there is the need to fully define the application error due to surface emissivity. If a shiny roll must be measured, e.g., the first recommendation is to measure the product passing on the shiny roll. Second, the emissivity adjustment can be made on the sensor using static testing conditions to determine the proper setting. Third, dual-wavelength radiometry may be a viable option. Single-wavelength IR thermometry represents a very diversified, yet simple, selection technique used in thousands of applications where product temperature control is vital for consistent, high-quality products.
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DUAL-WAVELENGTH THERMOMETRY For more sophisticated applications where absolute accuracy is critical, and where the product is undergoing a physical or chemical change, dual- and multi-wavelength radiometry should be considered. The concept of the ratioing radiometer has been around since the early 1950s, but recent design and hardware changes are yielding higher performance, low-temperature capabilities, and reduced cost. Dual-wavelength (ratio) thermometry involves measuring the spectral energy at two different wavelengths (spectral bands). The target temperature can be read directly from the instrument if the emissivity has the same value at both wavelengths. This type of instrument can also indicate the correct temperature of a target when the FOV is partially occluded by relatively cold materials such as dust, wire screens, and gray translucent windows in the sight path. The theory of this design is quite simple and straightforward, and is illustrated by the following equations, where we take Planck’s equation for one wavelength and ratio it to the energy at a second wavelength. L e • C1 • l1 -5 • e-C2 / l1T R = l1 = l1 Ll2 el2 • C1 • l2 -5 • e-C2 / l2T
R=
e el2
l1 —– •
-5
[ ll21] —–
-5
R=
[ ll21] —–
•
e
•
e
[-—C2–(1–-1)] T
l1 l2
[-—C2–(1–-1)] Tr
l1 l2
1 = 1 + 1n (el1/el2)
—
—
T
Tr
——————–
C2
1
1
(l–1 - l–2 )
If el1 = el2, then T = Tr where: R = spectral radiance ratio Tr = ratio temperature of the surface el = spectral emissivity In this process, if the emissivity at both wavelengths is equal (graybody condition), the emissivity factor cancels out of the equation and we find the ratio is directly proportional to temperature.
RELATIVE RADIANT ENERGY
The same concept can be viewed also in a graphic presentation by taking a small segment of the blackbody distribution curve and measuring some ratios at various emissivities (see Figure 3). Using 0.7 µm and 0.8 µm as the narrowband filters, the ratio factor remains constant at 1.428 for the range of emissivities down to 0.1. 8 e = 1.0
7 6
e = 0.7
5 4
e = 0.5
3
Dual-wavelength thermometers have many applications throughout industry and research as simple, unique sensor that can reduce application error involving graybody surfaces. Figure 4 illustrates examples of total emissivity for a variety of products that have temperature-related varying emissivity. For example, most users would consider graphite to have a high constant emissivity. The fact is, however, that graphite’s emissivity varies from 0.4 to 0.65 over the temperature range of ambient to 2000°F. For accurate product temperature measurement and control, dual-wavelength thermometers should be used when these types of graybody materials are being processed at high temperatures.
2
0
0.5
0.6
0.7
0.8
0.9
A review of the basic application elements is outlined in Figure 5. The surface of a target to be measured is the prime concern. When selecting the instrument, the user must take into account target size, temperature limits, emissivity, and process dynamics as they relate to FOV, spectral response, and response time. It is also essential to characterize the surroundings, e.g., flames, IR heaters, induction coils, and the atmosphere (dust, dirty windows, flames, excessive heat) in order to select the optimum instrument for SURROUNDINGS, Tsur
0.9
e = 0.1
1
SUMMARY
RADIATION THERMOMETER 1.0
0.8
1.1
IRON OXIDIZED
WAVELENGTH, mm
Similarly, any other changes that are gray in nature will not affect the temperature determined by the dualwavelength thermometer. These variations include changes in target size such as a wire or a stream of molten glass whose diameters vary during measurement, even in the case of targets smaller than the thermometer’s FOV. For instance, suppose that a blackbody target fills only half the thermometer’s FOV; instead of a 50% reduction in emittance, this analysis is unchanged. Another example is a case where a target is obscured with smoke or dust, or where an intervening window (e.g., of a vacuum chamber) becomes clouded. As long as the obscured medium is not spectrally selective in its attenuation of radiation, at least in the wavelength region used by the thermometer, the analysis remains the same. The temperature inferred by the dual-wavelength radiometer remains unaffected. Nonetheless, there are always limits that must be recognized. The dualwavelength does not perform on non-graybodies, e.g., aluminum; it has difficulty looking through non-gray windows or heated Pyrex; and it tends to measure background temperatures where the background is hotter than the target.
S.T l TARGET, TS, el
ATMOSPHERE EMISSION AND ABSORPTION
0.6 TOTAL EMITTANCE
Figure 3: The dual-wavelength system automatically eliminates measurement errors by computing the ratio of the radiant energies emitted by the target in two adjacent wavebands, e.g., 0.7 µm and 0.8 µm.
COPPER OXIDIZED
0.7
Figure 5: When selecting noncontact temperature measurement instruments, it is necessary to take into account not only the target and its emissivity, but also the surroundings and the invtervening atmosphere.
0.5 GRAPHITE INCONEL X POLISHED 0.4
this application.
IRON, ARMCO POLISHED 0.3
0.2
0.1
COBALT ALLOY N-155 POLISHED
DOW METAL POLISHED
COPPER POLISHED LEAD GOLD POLISHED POLISHED
0 0
500 1000 1500 TEMPERATURE. F
2000
2500
Figure 4: Many materials have emissivity levels that vary with temperature. Several of the most commonly used are compared here.
There are also multi-wavelength thermometers available for non-graybody materials where the emissivity varies with wavelength. In these applications there is a detailed analysis of the product’s surface characteristics regarding emissivity vs. wavelength vs. temperature vs. surface chemistry. With these data, algorithms can be generated relating spectral emittance at various wavelengths to temperature.
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With regard to performance specifications, calibration accuracy will typically be in the 0.5-0.1% range, while the repeatability of most sensors will be in the 0.25-0.75% range. Pricing on the basic sensor will start at $500 and could go as high as $5000-$6000. In the majority of the applications, price is not an issue; when the sensor is properly installed and used, payback typically is on the order of one or two months.
Reproduced from Sensors Magazine with permission of HELMERS PUBLISHING, INC. 174 Concord St. Peterborough, NH 03458
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Infrared Temperature
Measurement Theory and Application Author and Presenter: John Merchant, Sales Manager, Mikron Instrument Company Inc. ABSTRACT
emission
absorption
Infrared thermometers for non-contact temperature measurement are highly developed sensors which have wide-spread application in industrial processing and research. This paper describes, in non-mathematical terms, the theory upon which the measurement technology is based, and how this is used to deal with the variety of application parameters which confront the intending user.
Designs for an infrared thermometer (IRT), have existed since at least the late nineteenth century, and various concepts by Féry were featured by Charles A. Darling (1) in his book “Pyrometry,” published in 1911.
incident
hot
cold reflected RADIATIVE HEAT EXCHANGE
Figure 2
However it was not until the 1930’s that the technology was available to turn these concepts into practical measuring instruments. Since that time there has been considerable evolution in the design and a large amount of measurement and application expertise has accrued. At the present time, the technique is well accepted and is widely used in industry and in research.
MEASUREMENT PRINCIPLES As previously stated IR energy is emitted by all materials above 0°K. Infrared radiation is part of the Electromagnetic Spectrum and occupies frequencies between visible light and radio waves. The IR part of the spectrum spans wavelengths from 0.7 micrometers to 1000 micrometers (microns). Figure 1. Within this wave band, only frequencies of 0.7 microns to 20 microns are used for practical, everyday temperature measurement. This is because the IR detectors currently available to industry are not sensitive enough to detect the very small amounts of energy available at wavelengths beyond 20 microns.
Wavelength (meters) 10
–12
10
–10
10
–8
10 –6
transmission
emitted
INTRODUCTION An infrared thermometer measures temperature by detecting the infrared energy emitted by all materials which are at temperatures above absolute zero, (0°Kelvin). The most basic design consists of a lens to focus the infrared (IR) energy on to a detector, which converts the energy to an electrical signal that can be displayed in units of temperature after being compensated for ambient temperature variation. This configuration facilitates temperature measurement from a distance without contact with the object to be measured. As such, the infrared thermometer is useful for measuring temperature under circumstances where thermocouples or other probe type sensors cannot be used or do not produce accurate data for a variety of reasons. Some typical circumstances are where the object to be measured is moving; where the object is surrounded by an EM field, as in induction heating; where the object is contained in a vacuum or other controlled atmosphere; or in applications where a fast response is required.
reflection
10 –4
10 –2
102
1
radio
infrared
visible
ultraviolet
x-ray
gamma rays
Infrared spectrum 0.7 to 1000 micrometers (microns) ELECTROMAGNETIC SPECTRUM
Figure 1
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104
Though IR radiation is not visible to the human eye, it is helpful to imagine it as being visible when dealing with the principles of measurement and when considering applications, because in many respects it behaves in the same way as visible light. IR energy travels in straight lines from the source and can be reflected and absorbed by material surfaces in its path. In the case of most solid objects which are opaque to the human eye, part of the IR energy striking the object’s surface will be absorbed and part will be reflected. Of the energy absorbed by the object, a proportion will be re-emitted and part will be reflected internally. This will also apply to materials which are transparent to the eye, such as glass, gases and thin, clear plastics, but in addition, some of the IR energy will also pass through the object. The foregoing is illustrated in Figure 2. These phenomena collectively contribute to what is referred to as the Emissivity of the object or material. Materials which do not reflect or transmit any IR energy are know as Blackbodies and are not known to exist naturally. However, for the purpose of theoretical calculation, a true blackbody is given a value of 1.0. The closest approximation to a blackbody emissivity of 1.0, which can be achieved in real life is an IR opaque, spherical cavity with a small tubular entry as shown in Figure 3. The inner surface of such a sphere will have an emissivity of 0.998. Different kinds of materials and gases have different emissivities, and will therefore emit IR at different intensities for a given temperature. The emissivity of a material or gas is a function of its molecular structure and surface characteristics. It is not generally a function of color unless the source of
the color is a radically different substance to the main body of material. A practical example of this is metallic paints which incorporate significant amounts of aluminum. Most paints have the same emissivity irrespective of color, but aluminum has a very different emissivity which will therefore modify the emissivity of metallized paints.
1. Kirchoff’s Law When an object is at thermal equilibrium, the amount of absorption will equal the amount of emission. a=e 2. Stephan Boltzmann Law The hotter an object becomes the more infrared energy it emits. W = eoT4 3. Wien’s Displacement Law The wavelength at which the maximum amount of energy is emitted becomes shorter as the temperature increases. lmax = 2.89 x 103mmK/T
1
1 0 theoretical blackbody
practical blackbody
EMISSIVITY
Figure 3
Just as is the case with visible light, the more highly polished some surfaces are, the more IR energy the surface will reflect. The surface characteristics of a material will therefore also influence its emissivity. In temperature measurement this is most significant in the case of infrared opaque materials which have an inherently low emissivity. Thus a highly polished piece of stainless steel will have a much lower emissivity than the same piece with a rough, machined surface. This is because the grooves created by the machining prevent as much of the IR energy from being reflected. In addition to molecular structure and surface condition, a third factor affecting the apparent emissivity of a material or gas is the wavelength sensitivity of the sensor, known as the sensor’s spectral response. As stated earlier, only IR wavelengths between 0.7 microns and 20 microns are used for practical temperature measurement. Within this overall band, individual sensors may operate in only a narrow part of the band, such as 0.78 to 1.06, or 4.8 to 5.2 microns, for reasons which will be explained later.
4. Planck’s Equation Describes the relationship between spectral emissivity, temperature and radiant energy. C2 Wl = C1el[l5(elT-1)]-1
INFRARED THERMOMETER DESIGN AND CONSTRUCTION A basic infrared thermometer (IRT) design, comprises a lens to collect the energy emitted by the target; a detector to convert the energy to an electrical signal; an emissivity adjustment to match the IRT calibration to the emitting characteristics of the object being measured; and an ambient temperature compensation circuit to ensure that temperature variations within the IRT, due to ambient changes, are not transferred to the final output. For many years, the majority of commercially available IRT’s followed this concept. They were extremely limited in application, and in retrospect did not measure satisfactorily in most
circumstances, though they were very durable and were adequate for the standards of the time. Such a concept is illustrated in Figure 4. The modern IRT is founded on this concept, but is more technologically sophisticated to widen the scope of its application. The major differences are found in the use of a greater variety of detectors; selective filtering of the IR signal; linearization and amplification of the detector output; and provision of standard, final outputs such as 4-20mA, 0-10Vdc, etc. Figure 5 shows a schematic representation of a typical contemporary IRT. Probably the most important advance in infrared thermometry has been the introduction of selective filtering of the incoming IR signal, which has been made possible by the availability of more sensitive detectors and more stable signal amplifiers. Whereas the early IRT’s required a broad spectral band of IR to obtain a workable detector output, modern IRT’s routinely have spectral responses of only 1 micron. The need to have selected and narrow spectral responses arises because it is often necessary to either see through some form of atmospheric or other interference in the sight path, or in fact to obtain a measurement of a gas or other substance which is transparent to a broad band of IR energy. Some common examples of selective spectral responses are 8-14 microns, which avoids interference from atmospheric moisture over long path measurements; 7.9 microns which is used for the measurement of some thin film plastics; and 3.86 microns which avoids interference from CO2 and H2O
DET
THEORETICAL BASIS FOR IR TEMPERATURE MEASUREMENT The formulas upon which infrared temperature measurement is based are old, established and well proven. It is unlikely that most IRT users will need to make use of the formulas, but a knowledge of them will provide an appreciation of the interdependency of certain variables, and serve to clarify the foregoing text. The important formulas are as follows:
A.T.C.
E
INFRARED TEMPERATURE MEASUREMENT
Figure 4
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Z
Infrared Temperature Cont’d
a.t.c. amp thermistor
lens
chopper
prw. amp
filter
signal amp
prw. amp
for the above stated reasons may often benefit from a narrow spectral response as close to 0.7 microns as possible. This is because the effective emissivity of a material is highest at shorter wavelengths and the accuracy of sensors with narrow spectral responses is less affected by changes in target surface emissivity.
signal ground motor control
d.c. motor led optical interrupter
power supply ±12 vdc
phase control
±15 vdc
MODERN INFRARED THERMOMETER
Figure 5
Spectral radiant emittance (W cm–2 m–1)
1
900°K
0.75
While it is almost always possible to establish the emissivity of the basic material being measured, a complication arises in the case of materials which have emissivities that change with temperature such as most metals, and other materials such as silicon and high purity, single crystal ceramics. Some applications which exhibit this phenomena can be solved using the two color, ratio method.
0.50 800°K
700°K
0.25
TWO COLOR-RATIO THERMOMETRY
600°K 500°K 0
2
4
6 8 10 12 14 16 18 Wavelength (microns)
Blackbody Spectral Distribution Curves Figure 6
vapor in flames and combustion gases. The choice between a shorter, or longer wavelength spectral response is also dictated by the temperature range because, as Planck’s Equation shows,
It will be apparent from the foregoing information that emissivity is a very important factor in infrared temperature measurement. Unless the emissivity of the material being measured is known, and incorporated into the measurement, it is unlikely that accurate data will be obtained. There are two methods for obtaining the emissivity of a material: a) by referring to published tables and b) by comparing the IRT measurement with a simultaneous measurement obtained by a thermocouple or resistance thermometer and adjusting the emissivity setting until the IRT reads the same. Fortunately, the published data available from the IRT manufacturers and some research organizations is extensive, so it is seldom necessary to experiment. As a rule of thumb, most opaque, non-metallic materials have a high and stable emissivity in the 0.85 to 9.0 range; and most un-oxidized, metallic materials have a low to medium emissivity from 0.2 to 0.5, with the exception of gold, silver and aluminum which have emissivities in the order of 0.02 to 0.04 and are, as a result, very difficult to measure with an IRT.
the peak energy shifts towards shorter wavelengths as the temperature increases. The graph in Figure 6 illustrates this phenomenon. Applications which do not demand selective filtering
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Given that emissivity plays such a vital role in obtaining accurate temperature data from infrared thermometers, it is not surprising that attempts have been made to design sensors which would measure independently of this variable. The best known and most commonly applied of these designs is the Two Color-Ratio Thermometer. This technique is not dissimilar to the infrared thermometers described so far, but measures the ratio of infrared energy emitted from the material at two wavelengths, rather than the absolute energy at one wavelength or wave band. The use of the word “color” in this
ratio
O/P
Z target Dl1
Dl2
beam splitter
colimator
TWO COLOR THERMOMETRY (ratio thermometry)
Figure 7
context is somewhat outdated, but nevertheless has not been superseded. It originates in the old practice of relating visible color to temperature, hence “color temperature.”
of all materials does not change equally at two different wavelengths. Those materials that do are called “Greybodies.” The ones that do not are called “Non-Greybodies.”
The basis for the effectiveness of twocolor thermometry is that any changes in either the emitting property of the material surface being measured, or in the sight path between the sensor and the material, will be “seen” identically by the two detectors, and thus the ratio and therefore the sensor output will not change as a result. Figure 7 shows a schematic representation of a simplified two-color thermometer.
Not all forms of sight path obscuration attenuate the ratio wavelengths equally either. The predominance of particulates in the sight path which are the same micron size as one of the wavelengths being used will obviously unbalance the ratio. Phenomena which are non-dynamic in nature, such as the “non-greybodyness” of a material, can be dealt with by biassing the ratio, an adjustment referred to as “Slope.” However, the appropriate slope setting must generally be arrived at experimentally. Despite these limitations, the ratio method works well in a number of well established applications, and in others is the best, if not the most preferred solution.
Because the ratio method will, under prescribed circumstances, avoid inaccuracies resulting from changing or unknown emissivity, obscuration in the sight path and the measurement of objects which do not fill the field of view, it is very useful for solving some difficult application problems. Among these are the rapid induction heating of metals, cement kiln burning zone temperature and measurements through windows which become progressively obscured, such as vacuum melting of metals. It should be noted however, that these dynamic changes must be “seen” identically by the sensor at the two wavelengths used for the ratio, and this is not always the case. The emissivity
SUMMARY Infrared thermometry is a mature but dynamic technology that has gained the respect of many industries and institutions. It is an indispensable technique for many temperature measurement applications, and the preferred method for some others. When the technology is adequately understood by the user, and all the relevant application parameters are properly considered, a successful
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application will usually result, providing the equipment is carefully installed. Careful installation means ensuring that the sensor is operated within its specified environmental limits, and that adequate measures are taken to keep the optics clean and free from obstructions. A factor in the selection process, when choosing a manufacturer, should be the availability of protective and installation accessories, and also the extent to which these accessories allow rapid removal and replacement of the sensor for maintenance. If these guidelines are followed, the modern infrared thermometer will operate more reliably than thermocouples or resistance thermometers in many cases.
REFERENCES 1. Darling, Charles R.; “Pyrometry. A Practical Treatise on the Measurement of High Temperatures.” Published by E.&F.N. Spon Ltd. London. 1911.
Reproduced with permission of the author, John Merchant, Sales Manager, MIKRON INSTRUMENT COMPANY, INC.
Noncontact Temperature Measurement Theory and Application Walter Glockmann, Capintec Instruments, Inc.
temperature of an object by intercepting and measuring the thermal radiation it emits.
Noncontact temperature measurement is the preferred technique for small, moving, or inaccessible objects; dynamic processes that require fast response; and temperatures <1000°C (1832°F). To select the best noncontact temperature measurement device for a particular application, it is essential to understand the basics of temperature measurement technology, temperature measurement parameters, and the features offered by the various measurement systems currently available.
Emissivity. This quality defines the fraction of radiation emitted by an object as compared to that emitted by a perfect radiator (blackbody) at the same temperature. Emissivity is determined in part by the type of material and its surface condition, and may vary from close to zero (for a highly reflective mirror) to almost 1 (for a blackbody simulator). Emissivity is used to calculate the true temperature of an object from the measured brightness or spectral radiance. Because an object’s emissivity may also vary with wavelength, a radiation thermometer with spectral response matching regions of high emissivity should be selected for
DEFINING THE TERMS Temperature. Temperature is one expression for the kinetic energy of the vibrating atoms and molecules of matter. This energy can be measured by various secondary phenomena, e.g., change of volume or pressure, electrical resistance, electromagnetic force, electron surface charge, or emission of electromagnetic radiation. The most frequently used temperature scales are Celsius and Fahrenheit, which divide the difference between the freezing and boiling points of water into 100° and 180°, respectively. The thermodynamic scale begins at absolute zero, or 0 Kelvin, the point at which all atoms cease vibrating and no kinetic energy is dissipated. 0 K = –273.15°C = –459.67°F IR Radiation. Infrared is that portion of the electromagnetic spectrum beyond the visible (blue to red, 0.4-0.75 µm) response of the human eye. IR wavelengths extend from 0.75 µm to 1000 µm, where the shortest microwaves (radar) begin. Because IR radiation is predominantly generated by heat, it is called thermal radiation. For the purpose of radiation thermometry, only portions of the IR spectrum are important. The spectrum is frequently divided into “atmospheric windows” that provide maximum loss-free transmission through water vapor in air: 0.7-1.3 µm; 1.4-1.8 µm; 2.0-2.5 µm; 3.2-4.3 µm; 4.8-5.3 µm; 8-14 µm Thermometer. Most of the well-known thermometers, e.g., glass bulb mercury or alcohol, thermocouple, or resistance thermometer, must be placed in direct contact with the temperature source. Their useful measurement range is –100°C to 1500°C. Radiation Thermometer. This noncontact thermometer determines the surface
a specific application. Emissivity values are listed in the literature for a variety of materials and spectral bands, or these values can be determined empirically. Brightness/Single-Color Pyrometer. These devices measure and evaluate the intensity, or brightness, of the intercepted thermal radiation. Intensity, or, more generally, spectral radiance, is measured in a narrow wavelength band of the thermal spectrum. Band selection is dictated by the temperature range and the type of material to be measured. The oldest brightness pyrometers compared optical brightness in the visible (red) spectrum at 0.65 µm by matching the glowing object to a hot “disappearing” filament. The term “single-color” derives from the single
Table 1: On-Line Temperature Measurement Instruments LOW TEMPERATURE
HIGH TEMPERATURE
General Purpose 0 to 500°C (30 to 1000°F) 8-14 mm wide band radiation thermometers • thermopile detector • optical resolution: 4 mm target (15:1 D-ratio) • response time: 0.5 sec • emissivity adjustment • analog output (mv/°C, mV/°F)
General Purpose 400 to 2000°C (750 to 3600°F) narrow spectral band radiation thermometers (0.7-1.1 µm; 0.9-1.9 µm) • solid-state photoelectric detectors (Si, Ge) • optical resolution 1 mm target (60:1 D-ratio) • response time 3 msec • emissivity adjustment • analog output (mV°C, mV/°F)
Extended Temperature Ranges – 30°C to 800°C (–20°F to 1500°F) high-stability, 8-14 µm thermometers • pyroelectric detector • chopper stabilized to compensate for rapid changes in ambient temperature • optical resolution: 3 mm dia. (30:1 D-ratio) • response time: 50 msec • analog output 4-20 mA
High-Stability/Complex Applications 300 to 2500°C (600 to 4500°F) narrow spectral band radiation thermometers • for glass and/or through hot gas (3.9 µm) • for glass surfaces (5.0 µm) • for combustion gases (4.2, 4.5, 5.3 µm) • pyroelectric detector • chopper stabilized • optical resolution: 1 mm target (100:1 D-ratio) • response time: 30 msec • analog output 4-20 mA
High-Precision/Complex Applications 50°C to 800°C (–60°F to 1500°F) narrow spectral band radiation thermometers • for thin plastic films with CH absorption bands (3.4 µm; 6.8 µm) • for polyester/fluorocarbon films (8.0 µm) • for thin glass and ceramics (7.8 µm) • optical resolution: 1.5 mm dia. (100:1 D-ratio)
High-Speed, Two-Color Ratio 150 to 2500°C (300 to 4500°F) narrow spectral bands (0.8/0.9 µm; 2.1/2.4 µm) • greatly independent of emissivity fluctuations and/or sight path disturbances • automatic compensation for moving targets • internal calibration check
Programmable/High-Performance –100°C to 2500°C (–150°F to 4500°F) with built-in signal conditioning and digital computing, spectral band choices in wide or narrow bands between 2 µm and 20 µm • digital RS 232 bidirectional interface • max./min./differential/hold functions • programmable ambient temperatures • choice of through-lens-sighting, LED, or laser
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narrow wavelength band of red seen by the user. Instruments sensitized to measure in the IR region are also called spectral radiation pyrometers or spectral radiation thermometers. Ratio/Two-Color Pyrometer. This radiation thermometer measures temperatures on the basis of two (or more) discrete wavelengths. The ratio of the brightnesses in separate wavelengths corresponds to color in the visible spectrum. The use of two distinct, visible colors – typically red and green – has long been popular to infer color temperatures. More recently, the term has broadened from its initial usage to include wavelengths in the infrared. The advantage of ratio measuring is that temperature readings are greatly independent of emissivity fluctuations and/or sight path obscurations. The technique is generally used for temperatures above incandescence (700°C,1300°F ), but measurements down to 200°C (400°F) are also possible.
MEASUREMENT PARAMETERS Advanced optical and electronic signal processing modules greatly extend the accuracy and performance capabilities of noncontact temperature measuring. For process control, standardized interfaces are available that provide conditioned signal outputs optimized for specific applications.
RADIATION DETECTION Emissivity Adjustment. Temperature reading accuracy depends on the correct adjustment of the instrument to the target emissivity. Preset emissivity values can be used for on-line sensors to monitor targets of constant emissivity. Measurements on those materials with changing emissivities require an accurate and reproducible emissivity adjustment. Surrounding Area Temperature. Thermal target radiation always contains stray radiation emitted by the environment surrounding the target area and reflected by the target’s surface. In practice, the ambient temperature is frequently presumed to be the same as the temperature of the sensor. If the target is exposed to a different thermal environment, e.g., inside a heated furnace, inside a cooled chamber, or outdoors facing the open sky, adjustments are necessary for accurate measurement. Separate sensors for the area surrounding the target may be used for automatic temperature calculation. Sight Path Obscuration. Gases, water vapor, dust, and other aerosols in the sight path of a sensor may affect the temperature reading. Using one of the “atmospheric windows” in the IR region greatly reduces measurement errors. Since both optical channels are equally
attenuated, ratio pyrometers are generally immune to sight path obscuration, and the signal color ratio remains unaffected. Ambient Temperature Drift. By the nature of their design, radiation detectors are strongly affected by ambient temperature changes. To maintain high measurement accuracy, precise compensation of this temperature drift is required. Temperature drift is specified in error/°C or error/°F of ambient temperature change.
OPTICAL SYSTEMS Optics. Reflective (mirror) and refractive (lens) optics are used in noncontact temperature sensors to isolate and define radiation from the measured target. Field of View. The field of view (FOV) is expressed in degrees solid angle or in radians. The FOV allows easy calculation of the minimum target size for each working distance. A convenient measure is the distance-to-target ratio, e.g., 20:1, indicating a minimum target of 1 in. at a 20 in. measuring distance. Focusing on Target. Optics in noncontact temperature sensors are generally of the fixed-focus type. Focusing at longer measuring distances is not required if the target area is smaller than the entrance aperture (lens diameter) of the instrument. Small Targets. For miniature objects, fixed-focus close-up optics are used, and the minimum target size is
specified. Targets as small as 0.5 mm can be isolated. Fiber Optics. Fiber optics permits a physical separation of the lens assembly from the detector and signal processing electronics in restricted spaces or hostile environments. The useful measuring range of fiber optics starts at 400°C (750°F). Minimum target areas are as defined above. Target Scanning. Reflective surface mirrors are used to change the viewing angle of the measuring sensor if direct viewing is difficult or impractical. An oscillating mirror can be employed to deflect the intercepted radiation and to scan a predetermined temperature profile across a target area. A sequence of scanned temperature profiles taken at preset spatial intervals over the target can be displayed as a thermal image or in the form of a thermal map. Aiming on Target. A variety of optical aiming techniques are used with noncontact temperature sensors: • Simple bead-and-groove gun sights • Integrated or detachable optical view finders • Through-the-lens sighting • Integrated or detachable light beam markers
SIGNAL PROCESSING Direct Output. Noncontact temperature sensors convert the intercepted thermal radiation into an electrical signal
Table 2: On-Line Temperature Measurement Instruments LOW TEMPERATURE General Purpose Extended Temperature Ranges 0 to 500°C (30 to 1000°F) 8-14 µm wide band –50 to 1400°C (–60 to 2550°F) 8-14µm with built-in signal conditioning • thermopile detector • optical resolution: 32 mm target • optical resolution: 4 mm dia. (30:1 D-ratio) (15:1 D-ratio) • data collection • emissivity adjustment • peak/valley/averaging functions • max./min. value • digital RS-232 output High Stability – 30 to 800°C (–30 to 1500°F) 8-14 µm • pyroelectric detector • chopper stabilized • choice of optics
Miniature Probe –50 to 500°C (–60 to 1000°F) 8-14 µm with interchangeable probes for long distance or small target applications • large LCD information display • max./min./differential/hold signal conditioning • optical resolution: 2.5 mm dia. (7:1 D-ratio) • LED or laser aided target aiming
HIGH TEMPERATURE General Purpose High-Precision, Two-Color Ratio Pyrometer 250 to 2500°C (500 to 4500°F) narrow spectral band radiation thermometers 650 to 2500°C (1200 to 4500°F) spectral (0.65 µm; 0.7-1.1 µm; 0.9-1.9 µm) bands 0.8/0.9 µm • solid-state photoelectric detectors (Si, Ge) • greatly independent of emissivity fluctuations and/or sight path • optical resolution 0.9 mm dia. (250:1 disturbances D-ratio) • automatic compensation for moving targets
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Noncontact Temperature Measurement Cont’d proportional to the spectral radiance emitted from the target surface. Linearized Output. An electronic network converts the thermal radiance signal into an electrical current/voltage proportional to temperature. Sample and Hold. The momentary temperature reading, selected by an external trigger is held (frozen) until replaced by a new value in the next sampling cycle. Maximum Value or Peak Hold. The highest temperature reading over the specific measuring period is displayed. Reset is triggered by an external signal. Minimum Value or Valley Hold. The lowest temperature reading during a specific measurement period is displayed. Rest is triggered by an external signal. Peak to Peak. The difference between the maximum and the minimum temperature readings during a specific measurement period is displayed. Speed of Response. Short response time is needed to follow rapidly changing dynamic temperature processes. Long response time integrates all signal variations during a specific measurement period and enhances temperature resolution in order to average changing values or to improve measurement precision. Automatic Trigger (Wave Function). The highest temperature reading is detected and displayed. Reset is triggered automatically when the signal reaches an adjustable threshold, but the last peak value is held on display until it is replaced by the following peak value. This technique is appropriate for rapid sampling and analysis of intermittent target values, without the use of external trigger signals. Alarms. An output signal (relay) is activated when the signal reaches a preset temperature value. Two independent set points – HI/LO – are generally provided.
ACCESSORIES Water Coolable Jackets. Water cooling extends the sensor’s ambient temperature range up to 400°C (752°F) or beyond. Air Purge Fittings. Lens barrels or attachments with fittings for compressed air are designed to direct a clean air flow across the lens surface. They keep the optical sight paths free of vapors, fumes, and dust.
BLACKBODY CALIBRATORS Deep cavities controlled at a homogeneously distributed temperature serve as blackbody simulators for the calibration of radiation thermometers. To accommodate the variety of instruments, they provide an effective aperture of ~ 1 in. (25 mm) and are
optimized for their operating temperature range: • Stirred water bath: 30-100°C (86-212°F) • Aluminum core: 50-400°C (122-752°F) • Stainless steel core: 350-1000°C (662-1832°F ) • Portable, battery operated field calibrator: fixed temperature choices from 40°C-100°C (104-212°F)
ON-LINE OR PORTABLE? On-Line Instruments. These devices are generally used for continuous process monitoring and control. They are available in low- and hightemperature models, each with its own operating specs (see Table 1).
Portable Instruments. Portables are typically favored for process checks, preventive/predictive maintenance, thermal surveys, R&D, and temporary temperature monitoring. The low- and high-temperature versions differ in performance, as shown in Table 2.
APPLICATIONS Successful applications of both on-line and portable noncontact temperature measurement instruments are summarized in Table 3. Reproduced with permission of Capintec, Inc.
Table 3: Temperature Measurement in Process Control SUCCESSFUL APPLICATIONS
ON-LINE PORTABLES R H
Cement kiln burning zones, preheaters
X
L
X
Energy conservation insulation and heat flow studies, thermal mapping
R
H
X
X
X
Filaments annealing, drawing, heat treating
X
L
X X
Food baking, candy-chocolate processing, canning, freezing, frying, mixing, packing, roasting
X
X
Furnaces flames, boiler tubes, catalytic crackers
X
X
X
X
Glass drawing, manufacturing/processing bulbs, containers, TV tubes, fibers
X
X X
X
X
Maintenance appliances, bearings, current overloads, driving shafts, insulation, power lines, thermal leakage detection
X
X
X
Metals (ferrous and nonferrous) annealing, billet extrusion, brazing, carbonizing, casting, forging, heat treating, inductive heating, rolling/strip mills, sintering, smelting
X
X
X
X
Quality control printed circuit boards, soldering, universal joints, welding, metrology
X
X X
X
X
X
Paint curing, drying
X
Paper coating, ink drying, printing photographic emulsions, web profiles
X
X
Plastic blow-molding, RIM, film extrusion, sheet thermoforming, casting
X
X
Remote sensing (thermal mapping) clouds, earth surfaces, lakes, rivers, roads, volcanic surveys
X
Rubber calendering, casting, molding, profile extrusion tires, latex gloves
X
Silicon crystal growing, strand/fiber, wafer annealing, epitaxial deposition
X
Textile curing, drying, fibers, spinning X R=Ratio/Two-Color
H=High-Temperature
X X
X
X
Vacuum chambers refining, processing, deposition
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X
X
X
X X
L=Low Temperature
Fiber Optics A New Approach to Monitor and Control Process Temperature The coupling of optical fibers to infrared detectors and signal processing electronics represents the latest progress in the field of non-contact temperature measurement and control.
All fibers used in infrared instrumentation are made of glasses especially chosen for their ability to transmit the radiation comprised in the chosen spectral region. All rays entering the front surface that acquire an inclination smaller than the critical angle are totally reflected inside the fiber core, and keep propagating in this fashion until they reach the opposite end or are totally absorbed, whichever comes first. For a fiber having a critical angle of X° means that all rays incident onto the fiber's front surface at the same angle or less with its axis are trapped inside the fiber by total internal reflection.
Only recently have fiber optics become the object of widespread interest thanks mainly to their ability to carry optical information signals over long distances and around unavoidable obstructions. For years infrared detectors have been used in conjunction with conventional optical elements (lenses, mirrors, prisms). Fiber optics were excluded from consideration since they are made of either glass or plastics, both of which are opaque throughout most of the infrared spectral region. Thus, according to fundamental laws of physics, their marriage to infrared detectors could never work.
On the other hand, all incident rays entering the fiber with an inclination larger than the same angle will leave the first contact with its internal surface. This behavior is commonly called “spilling” (See Figure 1).
Months of painstaking development proved the reality and practicality of transmitting IR with fiber optics. And thus it happened that coupling fiber optics with infrared detectors resulted in several new families of instrumentation and control systems endowed with superior performance characteristics.
The value of the critical angle is a function of the ratio between the refractive indexes of the glass of which the core is made and of the medium surrounding it. By controlling the ratio we can increase or decrease the acceptance angle of fiber optics, thus obtaining special performance characteristics.
Since most if not all of you are currently familiar with the theory of infrared radiation and the variety of methods for monitoring IR this discussion will deal mainly with the application of fiber optics in conjunction with IR detectors, i.e. their construction, advantages, disadvantages and applications.
For most IR monitoring applications, optical fibers are assembled into fiber bundles consisting of many hundreds of individual fibers contained within a flexible or rigid sheathing of either metallic or nonmetallic material. Each end of the bundle is held in place using a high temperature epoxy. The end surface is then highly polished to assure a clearly defined angle of acceptance and diminish reflectance losses due to irregular surfaces. Using such a large number of narrow fibers in a bundle allows us to gather and transmit more signal to the detector while retaining mechanical flexibility. Typically, the outside diameter of a single fiber is 25m.
A typical optical fiber is usually constructed of a silicon (glass) material, however, plastic and quartz are also available but normally for data transmission. Today most of all optical fibers manufactured consist of a lightconducting glass core surrounded by a thin layer of glass cladding with a lower refractive index. This cladding serves to protect the core finish.
Cladding Acceptance angle (72°) Light A ray
B 23°
A
67°
S "spilled" ray
A
A
35° Opaque coating B
Figure 1
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Generally speaking, in the majority of applications where optical fibers are used with infrared radiometers, the lengths are 1 or 2 meters long. On occasion fibers will be made up to approximately 10 meters in length. The determining factors in using fiber bundles to transmit IR, are MMT (minimum measurable temperature), target distance and spot size. The higher the temperature the longer the fiber, conversely low temperatures require a shorter fiber due to the glass attenuation. Unfocused fibers (those without a viewing lens) have a field of view or angle of acceptance of 60°. This is the target area viewed by the detector which is slightly larger than the distance between the front end of the fiber and the target surface. This can be easily verified by backlighting the target with visible light which will project onto the target surface. Unfocused fibers are used when the target area is large and it is desirable to measure its average temperature. Focused fibers (those with a viewing lens assembly attached to the front end) are used to measure targets as small as .01 cm from as far away as 4.5 meters or further. The determining factor as with fiber length is the amount of energy being collected. By backlighting we can be assured the lens is properly focused and aligned on the target. In some applications, where vibration or other type movement may alter the lens's alignment, a bifurcated fiber is preferable. One branch of the fiber is connected to a high intensity light source and activated by a momentaryon switch which will verify to the operator the correct alignment of the fiber. The other branch will allow the infrared detector to “see” the target at exactly the same spot that was illuminated.
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Fiber Optics Cont'd
FIBER ASSEMBLY VARIETIES The wide selection of fibers and lens configurations available allows for a satisfying and endless number of applications. Following are some of the many components that make up a fiber optic system and allow for such versatility. Sheathing – Single, bifurcated or trifurcated fiber optic systems – Flexible stainless steel (standard) – Heavy duty S.S. wire braid – Heavy duty braided fiber Imperial Eastman – Teflon (for use in high RF fields) – Protective tubing Lenses – 1.27 cm, 1.90 cm, 2.54 cm x 8.59 cm to 27.7 cm max. – Natural - black anodized aluminum – Angular lens configurations available Replaceable Tips – Glass or quartz, 7.62 cm, 15.24 cm & 22.86 cm long – Ceramic or stainless steel jacket Optical Rods – Glass, 15.24 cm, 30.48 cm & 60.96 cm long – Ceramic or stainless steel jacket Specials – Right angle prisms, high speed scanners, angled bundle configurations
APPLICATIONS Since virtually every manufactured product – from automobiles to the safety pin – requires the application of heat treatment in some form, the use for noncontact temperature monitoring and control is virtually limitless.
INDUCTION HEATING Because of the strong RF inductive energy field needed to heat the metal parts being treated, conventional measuring devices are of little value since they will be heated directly by the induction coil. Figures 2 and 3 show typical applications of fiber optic systems used to monitor and control induction treatment of metal objects either stationary in, or moving through induction furnaces.
Precise control of the temperature needed for perfect heat treatment of metal parts is essential to produce the crystal structure that will ensure meeting or exceeding the mechanical characteristic specifications. This control function is achieved either by on/off or high speed proportional control incorporated in the fiber optic Figure 2: Monitoring steel rod continues induction heating. Figure 4: Five-channel multiplexing, signal-processing and display system.
Figure 3: Controlling induction treating of automotive crankshafts.
and Thermal Monitoring System. Using fiber optics vs. the conventional direct line of sight infrared detection systems allows placing the viewing end of the fiber optic in close proximity of the target. The tip of the fiber in many cases may be positioned between the induction coils to view the processed material. To eliminate the adverse effects of the RF field a ceramic replaceable tip is utilized. In those instances where the design of the system won't allow room for the fibers, a lens system will then be provided to view and monitor targets from a distance. The fiber and electronics normally are not affected by induction energy fields, however, in unusual circumstances when the electrical noise environment is excessively high, a synchronous demodulation system is specified. The sync. demod, converts the 400 Hz AC signal from the detector head to DC. This conversion differs from conventional AC to DC converters in that it selects only the signal component at 400 Hz and discriminates against noise components of other frequencies.
CONTINUOUS CASTING These operations utilize fiber optic
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assemblies up to thirty feet in length that are installed between the rollers themselves to within one or two inches of the slab surface. A remotely located automatic multiplexing chassis monitors several points on a time shared basis, achieving significant savings in terms of cost and space. Due to the shielded path of constant transmissivity provided by the optical fibers and the short wave length 0.8 to 1 silicon detector, the system “watches” the target through smoke, fumes, vapors and water. (See Figure 4.) Quite often in this type of application the fibers are exposed to substantially elevated temperatures and mechanical abuse necessitating the need for air purging and special heavy duty protective sheathing. The purge tube is designed to allow the air flow to exit the front end of the fibers at a right angle thus preventing the build up of contaminants.
METAL FORGING, HOT STAMPING, PIPE BENDING Forging of metal parts includes both rough shape as well as precision forging, which requires less material removal and waste. Pipe bending and shaping is also included in this application. These operations are carried out by heating the parts to be worked upon to the optimum temperature with any of the several means available (ovens, flame, induction field, etc.) If the part temperature is below the optimum, cracks and internal tensions will develop, while if it is above the optimum, drooping will take place. The precise temperature control afforded by the use of infrared fiber optic controllers will: – Avoid the formation of defective parts (from cracks or drooping), thus eliminating rejects and waste due to these defects; – Save thermal energy by ensuring that no heat is wasted by heating the parts
Z Figure 5
beyond the optimum level; – Speed up production by allowing a faster rate of heating the parts without danger of temperature overshoot.
METAL DIE CASTING The die temperature is of critical importance in die casting of metals. Thermal cycling of aluminum products, with reference to die temperature has been successfully implemented with the help of optical fibers. Figure 5 shows schematically and in detail how the front end of the fiber is inserted through the mold frame and held in a corner of the runner plate, in contact with the aluminum flowing through it. The major advantages offered by this solution are: – Substantial savings of thermal energy, by eliminating overheating and drastically reducing production rejects. – Increased production due to the speedup of the casting cycle. The operation is automatically controlled by the temperature of the casting material and not solely by time, resulting in faster operation. – Improvement in the quality of the casting due to the control of the process as a function of temperature, results in simpler operation and automatic compensation for a cold die start-up or interrupted cycles.
Figure 6
the emissivity variations of the target surface. These variations, in turn, affect the amount of laser power absorbed by the target, and consequently the target's temperature, which is of paramount importance for good operating performance.
Among the advantages offered by the fiber optics infrared approach are the following:
This difficulty is overcome by the use of an emissivity-independent infrared fiber Cutting Oxygen
Preheating Gas
Cutting Nozzle Cutting Direction
Direct indication of the die and furnace pot temperature of the metal. Low level and blocked water lines are easily indicated several shots before the casting can display conditions visibly.
Lens Assembly
150 °
CONTROL OF METAL-WORKING LASER Lasers, generally high-power CO2 lasers, are used for welding, surface treating and finishing metals of various types. The conventional approach is to periodically sample the beam to keep its power at the desired level. This approach, however, cannot automatically take into account
optics system (EITM) aimed at the spot of laser beam impact. (See Figure 6.) The infrared system is made blind to the laser wavelength, and in this way it measures precisely the target temperature at the same spot and, via a feedback loop, it controls the laser power to ensure that the operation is carried out at the optimum temperature.
Pre-heating Flame Cutting Oxygen Jet
Reaction Zone Base Metal
Figure 7
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Fiber Optics Cont'd
– Non-contact temperature measurement in real time. – Fiber optics allow easy access to view the laser heating area because of their relatively small size. – EITM compensates for variations in emissivity as the part is being heated. – EITM response can be matched to the response speed of the laser. Additional applications of interest:
Substantial savings are realized by eliminating a previous costly process of destructive testing.
Flame Heads
Lens Assembly
FLAME CUTTING Automated flame cutting involves either pattern tracing or computer control to repetitively cut steel plates into a variety of shapes. (See Figure 7.) During start-up, a natural gas or propane flame heats the metal plate until a “puddle” of molten metal is detected by the operator; on multiple heat cutters the time may vary between torches. The puddle having been formed, oxygen is injected into the gas stream and blows the molten metal through the plate at which time the cutting cycle begins.
FLAME HARDENING OF STEEL WHEELS Hardening the surfaces of steel wheels used on heavy construction equipment such as drive & idler wheels for bulldozers, backhoes, and other track type equipment is presently being accomplished by flame hardening.
Figure 8
Flame
Quench
The above are but a few of the many and varied uses of fiber optics. The range and applications for these systems is only limited by one's imagination. The technology is expanding exponentially. Fiber optics are no longer viewed with doubts and misgivings. Like IC's, chips, bubble memories, RAM's, ROM's and PROM's, they are here to stay, they are the future.
Reproduced with permission of Vanzetti Instruments. Figure 9
By optically looking through the “clean” natural gas flame at the optimum point on the wheel, Figure 10, the variations in the temperature determined by the Thermal Monitor provide a proportional signal which is fed to a pneumatic transducer which pneumo/mechanically moves the head to the correct position. Optimum Measuring Point
A flame head is positioned on either side of the wheel (Figure 8). As the wheel is rotated the flame impinges on the surface elevating the temperature to approximately 976°C. Within close proximity to the flame the surface is rapidly quenched with cooling water (Figure 9). Because of the variations in the wheels, both in roundness and lateral distortions, if the flame head were fixed the hardening process would not be uniform throughout the critical areas.
By monitoring both level and temperature, the Coke Guide Pyrometer assures the optimum efficiency in the manufacture of coke. The multiplexing of several detectors on a vertical plane allows the operator to measure both height and temperature of the coke in the processing oven. When desired parameters are met, a controller signal activates the pusher to dump the processed coke into an awaiting transfer car, thus assuring a quality product and energy conservation.
If the oxygen is injected prematurely a defective cut is made leaving an objectionable rough and wide pitlike depression in the plate. By positioning a fiber optic bundle with lens assembly to look through the “clean” flame at the plate surface, the temperature is monitored and controlled to maintain the necessary temperature. By multiplexing and using hi-lo logic with relays tied in series, the oxygen is not turned on until all setpoints and associated relays are closed, insuring high quality cuts.
COKE GUIDE PYROMETER
Figure 10
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Handheld Infrared Thermometers for All Applications The new OS520/OS530 series handheld infrared thermometers from OMEGA Engineering adapt to virtually all remote temperature measurement applications. These universal instruments combine the features found in many specialized units into one high performance design. Rugged assembly and state-of-the-art measurement techniques are an integral part of these dependable and portable temperature measuring tools.
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IMPROVED MEASUREMENT ACCURACY Select from models of the OS520/OS530 series with temperature ranges from –18 to 2482°C (0 to 4500°F). Temperature readings are switchable from °F to °C via the keypad. Reading accuracy is to 1%. This accuracy is obtained through a unique keypad emissivity adjustment. The operator sets the infrared gun to match target material emissivity (0.10 to 1.00 in 0.01 increments) thus eliminating target emissivity error. Units have standard “V” groove gun sights for proper aiming accuracy. Laser sighting is an available option. Measurable target distances are from a few inches to approximately 200 feet (limited by line of sight and target size). To assure the operator that the target fills the field of view, near and far field-of-view diagrams are supplied with each unit and all instruments are labeled with a distance versus spot size chart. The distance to spot size ratio is from 10:1 to 110:1 depending on the model.
VERSATILE DISPLAY AND PROGRAMMING FEATURES The Custom backlit LCD display provides a dual parameter presentation. When the unit is turned on, the emissivity setting is displayed. Target temperature is then displayed simultaneously with either minimum, maximum, differential, or average temperature as selected by the operator. Non-volatile memory assures that all set parameters, such as target material emissivity, alarm setpoints, etc., remain in memory until reset. An electronic lock feature on the control panel keypad sets a trigger mechanism for continuous measurements. With the trigger programmed in the lock position, the instrument reads and displays temperature data up to 4 times per second. The electronic trigger is also used to enable/disable special functions like the audible/visual alarms. PATENT NOTICE
ANALOG AND DIGITAL OUTPUTS FOR DATA PROCESSING
This product may be protected by one or more of the following patents:
Analog and digital outputs are available for data recording and processing. The analog output is 1 mV/°C or °F (0.5mV/degree for OS524); the digital output interface is RS-232. High and low audible and visible alarms indicate preset temperature setpoints.
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U.S. PAT. D357, 194, 5,368,392, 5,524,984, 5,527,880, 5,465,838/Canada D 75811VOMEGA ENGINEERING, INC./Czech Republic 25372/France 0378411 to 0378446/Germany M 94 06 478.4/Italy RM9400000913/Japan 988.378/Netherlands 25009-00/Spain med. ut. 133292/Slovak Republic 24565/U.K. Registered 2041153 Other U.S. and Foreign Patents Pending.
THERMOCOUPLE INPUT FEATURE The OS530 Series thermometers offer thermocouple input. This allows measurement of target temperatures either by contact or non-contact means.
RUGGED AND FUNCTIONAL DESIGN EASES HANDLING For safety and ease of carrying, a soft holster and wrist strap are supplied with each infrared thermometer. Rubber boots encapsulate the lens and the display to ensure mechanical integrity during rough handling or mechanical shock. The OS520/OS530 series features a sealed keypad display. Unique packaging and styled design provide ease of handling and convenient trigger operation. The laser sighting option ensures added accuracy for target acquisition and definition.
UNIVERSAL PROBLEM SOLVER Handheld infrared thermometers are ideal for applications where noncontact temperature measurements are required. Typical examples include moving objects, materials in contaminated or hazardous areas, and locations of high voltage or very high temperature. In each of these environments, accurate and repeatable measurements are obtained at a safe distance using the OS520/OS530 infrared thermometers.
DIVERSE APPLICATION EXAMPLES Example 1: Predict and Prevent Process Failure Manufacturing and processing facilities, such as chemical and petrochemical plants, utilize solenoid valves to control critical functions. The solenoids are often inaccessible and difficult to test. Process engineers know that an upward shift in solenoid temperature is indicative of a pending malfunction. The portable OS520/OS530 thermometers are used to remotely sense the temperature of the solenoid housings. Utilizing the instrument’s audible and visual alarm system, a temperature shift from a pre-set norm signals the operator. The suspect solenoid valve is identified and replaced before a critical process failure occurs.
Example 2: Perform Energy Auditing Plant and maintenance engineering are required to reduce building heating costs by locating wall insulation voids. Variations in wall temperatures indicate areas of improper insulation. The OS520/OS530 series measures wall temperatures to identify areas of heat leakage. A unique target ambient temperature compensation feature allows precise target (wall) temperature measurement. Data is downloaded to a computer for mapping of wall temperature gradients. Example 3: Identify Permanent Test Sights Engineering must determine if a process warrants permanent temperature monitoring. Wide variations in process temperature indicate the need for tighter controls. The OS520/OS530 series mounts on a tripod for preliminary evaluation of that process (integral tripod mount is standard). Temperatures are measured and updated automatically using a unique trigger lock feature. Data can be transmitted to a recorder or a computer for evaluation. The need for permanent temperature monitoring is evaluated using the analyzed data. Example 4: Prevent Contamination Many processes in the food industry are sensitive to temperature limits and variations. Maintaining tight temperature controls of the processing, canning, packaging or freezing of food is critical to prevent spoilage and to ensure elimination of contaminant’s. Placement of temperature measuring devices within the food is discouraged due to possible introduction of impurities and contaminant’s. A remote temperature indicating instrument is required. The OS520/OS530 handheld infrared thermometers take accurate temperature readings without direct contact to food or packaging material. The instrument is adaptable to either a temporary or permanent installation. Intermittent measurements are performed utilizing the handheld configuration. A permanent setup is established using the tripod mount and the data downloading/ recording capabilities.
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ENGINEERING SUPPORT Unlimited applications and system support are provided by the full resources of OMEGA Engineering. Petrochemicals, pharmaceuticals, steel production, food processing, paper manufacturing and laboratory testing are just a few of the industries where OMEGA applications and systems personnel are currently providing close customer support.
ALL-IN-ONE INDUSTRY LEADER The OMEGA Engineering OS520/OS530 series handheld infrared thermometers respond to the need for a comprehensive remote temperature measuring instrument. Unique features such as ambient target temperature compensation, electronic trigger lock, adjustable emissivity set, themocouple input and audible/visual alarms ensure accurate and dependable readings. The OS520/OS530 series are competitively priced, are manufactured and tested in the United States and are CE approved for the European Market.
COMMON SPECIFICATIONS Repeatability: ±(1% of reading + 1 digit) Resolution: 1°F or 1°C Response Time: 250 to 500 msec Display: Backlit LCD, displays current and min., max., diff., or average temperature simultaneously Spectral Response: 8 to 14 microns Emissivity: 0.10 to 1.00 in 0.01 increments Distance to Spot Size Ratio: From 10:1 to 110:1 depending on the model Temperature Range: –18 to 2482°C (0 to 4500°F) Operating Ambient: 0 to 50°C (32 to 122°F) Power: 4 “AA” size batteries or AC adaptor Battery Life: 60 hrs., alkaline; 10 days, lithium under normal operation
Principles of Infrared Thermocouples INTRODUCTION IRt/c INFRARED THERMOCOUPLES – A REVOLUTIONARY NEW TEMPERATURE SENSING TECHNOLOGY The IRt/c product line represents a dramatic breakthrough in temperature sensing technology. The IRt/c sensors are unpowered, low cost, and can measure surface temperatures of materials without touching. They can be directly installed on conventional thermocouple controllers, PLCs, transmitters, and other readout devices.
Actual IR/tc Signal millivolt output
Target Temperature The actual signal generated by the IRt/c can be approximated with a fourth order polynomial function of target temperature. This fourth power dependence is due to radiation physics, and not a limitation of the IRt/c.
How do they measure temperature? All IRt/c’s have a proprietary infrared detection system which receives the heat energy radiated from objects the sensor is aimed at, and converts the heat passively to an electrical potential. A millivolt signal is produced, which is scaled to the desired thermocouple characteristics. Since all IRt/c’s are self-powered devices, and rely only on the incoming infrared radiation to produce the signal through thermoelectric effects, the signal will follow the rules of radiation thermal physics, and be subject to the non-linearities inherent in the process. However, over a range of temperatures, the IRt/c output is sufficiently linear to produce a signal which can be interchanged directly for a conventional t/c signal. For example, specifying a 2% match to t/c linearity results in a temperature range in which the IRt/c will produce a signal within 2% of the conventional t/c operating over that range. Specifying 5% will produce a somewhat wider range, etc.
OS36 Series
yy , , ,y y , Linear Range ***
2%
Conventional thermocouple millivolt output
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Linear region
millivolt output
5% > 5%
Actual IR/tc Signal
Target Temperature The linear region matches the conventional t/c to a specified tolerance.
Target Temperature
,, y y , y , y yy ,, yy ,,, yy yyy, ,,, yy, ,, , y ,, y yy , yyyy ,, yy , , Temperature Selection Guide
90.00
2%
millivolts of signal output
80.00
> 5%
70.00
Sensor - Type - Temperature
60.00
* * * * * * * * *
50.00 40.00 30.00 20.00 10.00 0.00
–10.00 –50
Linear Range *** 5%
50
150 250 350 450 550 650 Actual Temperature (C)
The OS36-K-80 has its 2% linear range centered at 80°F (27°C), but produces a repeatable signal to 1200°F (650°C).
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** ** ** ** ** ** ** ** **
-
220C/440F 170C/340F 140C/280F 120C/240F 90C/180F 60C/140F 27C/80F 10C/50F 37C/98.6F
0°
50°
100°
150°
200°
300° C
Special Biomedical Calibration ±0.2 C (35.5-39.4), ±0.3 C (25-40C)
0° 100° 200° 300° 400° Target Temperature * Select OS36, OS36-2, or OS36-5 ** Select Type J, K, E, T *** Temperature Range in which IRt/c output is linear compared to conventional t/c, within stated % (of reading).
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250°
500°
600° F
Principles of Infrared Thermocouples Cont'd Each IRt/c model is specifically designed for optimum performance in the region of best linear fit with conventional t/c’s, but can be used outside of those ranges by simply calibrating the readout device appropriately. The output signal is smooth and continuous over its entire rated temperature range, and maintains 1% repeatability over its entire range. The Temperature Selection Guide is a summary of the linear range performance of each IRt/c model. The user selects the IRt/c model and type, and the target temperature range for the application. The normal offset adjustments on the thermocouple readout device are used to calibrate the installation for emissivity and background effects.
Long term accuracy is influenced by the same things that influence repeatability: mechanical changes and metallurgical changes. It is well known that thermocouples can change calibration over time due to these effects. Mechanical changes occur because conventional thermocouples are constructed generally as small and light as possible to enhance response time, thus making them vulnerable to deformations that can change the thermoelectric properties. More importantly, the conventional thermocouple must operate at elevated temperature since it merely measures its own temperature.
percentage of failure, the IRt/c has essentially unlimited long term calibration accuracy.
QUICK INSTALLATION GUIDE All infrared-based sensing systems must be calibrated for specific material surface properties (for example, the amount of heat radiated from the target surface, environmental heat reflections, etc.). This calibration is performed by measuring the target surface temperature with a reliable independent surface temperature probe. The easiest and fastest method of accurately calibrating out these effects is to use an OMEGA OS91 hand-held Infrared Thermometer with a patented Automatic Emissivity Compensation System to give a true reading regardless of emissivity.
How reliable are these new devices?
The following procedure is recommended:
Of fundamental interest in temperature control is the ability of the measuring device to maintain its calibration under service conditions, and over a long period of time. The IRt/c is rated at 1% (of reading) repeatability and to have no measurable long term calibration change, which makes it well suited for reliable temperature control. These attributes are inherent in the basic design and construction of each IRt/c.
1. Install IRt/c as close as practical to view the target material to be measured.
IRt/c at Room Temperature Thermocouple Probe at Product Temperature Conventional thermocouple operating at elevated temperature is subject to long-term drift, while the IRt/c operating at room temperature is stable.
Repeatability is defined as the ability of a measuring device to reproduce its calibration under identical conditions. The IRt/c is a solid, hermetically sealed, fully potted system that does not change either mechanically or metallurgically during service. There are no active electronic components and no power source to produce the signal – only the thermoelectric effects that produce a thermocouple signal. The 1% rating is a conservative value based on the practical difficulty of demonstrating tighter tolerances under test conditions, rather than a true limitation of the device.
The IRt/c gives repeatable static and dynamic readings.
The metallurgical changes which affect thermoelectric properties are a strong function of temperature, being negligible at room temperature, and of serious concern at high temperature. The IRt/c solves both problems by its design and basic operation. Its solid fully potted construction in a mechanically rigid stainless steel housing, and operation at near room temperature conditions, essentially eliminates the classical drift problems of conventional thermocouples. Every IRt/c is double annealed at temperatures above 100° C to ensure long term stability, and tested 5 times prior to packaging. Barring a very small
2. Wire IRt/c to controller, PLC Transmitter, etc. in standard fashion (including shield). As in conventional t/c’s, red wire is always (–). 3. Bring process up to normal operating temperature and measure actual temperature of target material with OS90 Series Infrared Thermometer. 4. Adjust “input offset,” “zero,” “low cal,” on the readout device to match the OS91 reading. Installation complete.
Quick Installation Guide
2 + –
3
1
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IRt/c SETUP WITH AUTO-TUNE TEMPERATURE CONTROLLERS 10,000 V 60 Hz
In many applications, heating elements are employed to heat a product in an oven, furnace, or with jets of hot air. Conventional control devices using contact thermocouples measure and control the oven air temperature, IR heating element temperature, or air jet temperature in an effort to maintain product temperature and therefore, quality; often with less than satisfactory results.
IRt/c
Fast Meter
Heat Input
Product Temperature
Time
Replacing the contact thermocouple, (for example measuring oven temperature) with a non-contact IRt/c measuring product temperature directly, will insure that product temperature is maintained. Some readjustment of the controller parameters is required because of differences in sensor response times (an IRt/c is much faster), and time required to heat the product compared to the original sensor (slower). After installing the IRt/c and calibrating the controller reading using an OS91 Infrared Scanner (see Quick Installation Guide below), initiate the self-tuning cycle of the controller and check to see that the control is stable and accurate. If it will not self tune properly, manually adjust the control coefficients to achieve stable control. Because the product temperature is likely to change temperature more slowly than the original sensor, start with slowly increasing the “D” of the PID coefficients.
1000 ft (300 m) Twisted Shield Pair t/c Wire
IRt/c CAN BE USED WITH UP TO 1,000 FT (300 M) OF THERMOCOUPLE EXTENSION WIRE With twisted shielded pair thermocouple extension wire, an IRt/c can be mounted as far as 300 meters (1,000 ft) from the readout device, even in a very fierce electrical noise environment. A demonstration test was performed with a 300 m (1000 ft) coil of twisted shielded pair of extension wire, with 30 m (100 ft) unwound, connecting an IRt/c to a fast (100 msec. response) A/D conversion module to a computer. As a noise generator, a 60 Hz 10,000 volt transformer and spark generator was set up to spark within 15 cm (6 inches) of the wire. The test results showed less than 0.1°C of noise at any relative position of the wire, spark, and transformer. The extraordinary noise suppression characteristics designed into the IRt/c make it possible to locate it at very long distances, without the necessity of a transmitter. The IRt/c housing is electrically isolated from the signal leads and is connected to the shielded ground of the extension cable. For long distances, twisted shielded extension cable should be used, and the shield connected to a good electrical ground.
IRt/c’s are intrinsically safe when used with barriers
IRt/c’S ARE INTRINSICALLY SAFE WHEN USED WITH BARRIERS “Field Apparatus having energy storing or generating characteristics of <1.2V, 0.1A, 25 mW or 25 microJ shall be considered Simple Apparatus (nonenergy storing). These general purpose devices may be used in a hazardous (classified) location without further approval when connected to a certified intrinsically safe circuit.” – Quote from R. Stahl, Inc. Comprehensive Product Manual On Intrinsic Safety Barrier and Repeater Relays. Examples of non-energy storing Intrinsically Safe Apparatus are: • Thermocouples • RTD’s • LED’s • Dry Switch Contacts • NAMUR Inductive Proximity Switches • Non-inductive Strain Gage Devices and Resistors The IRt/c falls into the category of thermocouples, since it generates its signal by converting the radiated heat energy to an electrical signal via Seebeck effects, the basic driving force of thermocouples. Like all thermocouples, it requires no power source and generates signals measured in millivolts of voltage, microamps of current and nanowatts of power. IRt/c’s have a small capacitance, but at one microFarad, the energy storage is measured in nanojoules and is a thousand times lower than the 25 microjoule criterion. Accordingly, the IRt/c qualifies as a Simple Apparatus for use in hazardous locations, and with the appropriate barrier, qualifies as Intrinsically Safe.
IRt/c Barrier
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Principles of Infrared Thermocouples Cont'd IRt/c APPLICATION NOTES IRt/c MONITORS TIRE TEMPERATURES FOR RACING PERFORMANCE
Tire temperature is of critical concern in automotive racing for two reasons: the tire temperature directly affects its adhesion and its wear characteristics; and tire temperature patterns provide valuable information on the set-up and performance of the suspension. For example, excessive loading of a tire caused by out-of-tune suspension will cause that tire to become considerably warmer than the others. The IRt/c is an ideal measuring device for on-board data acquisition, due to its small size, ruggedness, and low cost. It may be connected to standard thermocouple read-out systems. Installation should include connecting the shield to a suitable ground in order to avoid interference from the electrically harsh environment of a racing automobile. Mechanical installation should include attention to air flow patterns to minimize dirt building on the lens. The OS36-2 or OS36-5 are recommended due to their narrower field of view, thus allowing you to position it further away.
IRt/c RELATIVE HUMIDITY MEASUREMENT
CONTROLLING WEB ROLLER TEMPERATURE
IRt/c’s can be used to measure actual relative humidity in many situations where there is a convenient source of water and flowing air, and measure it accurately and reliably.
The IRt/c infrared thermocouples have quickly become the sensors of choice for monitoring and controlling both web and roller temperatures. Tips on accurate roller temperature measurement:
An IRt/c aimed at a wet porous surface with ambient air blowing across the wet surface, can actually measure what is called “wet bulb” temperature for that ambient area. (More precisely, wet bulb temperature is the equilibrium temperature of the air-water interface when a water film is evaporated. When air is moved over a wet surface, the water cools by evaporation until it reaches wet-bulb temperature, then the cooling stops, no matter how much more air is moved over the surface. The temperature at which the cooling stops is the wet bulb temperature.)
1. Uncoated Metal or Chrome Rolls – Shiny, uncoated metal rolls are difficult for any infrared sensor to properly sense the true temperature (the sensor will see too many environmental reflections). The solution to the problem is to simply: paint a small black stripe on an unused end of the roller. Aim the IRt/c sensor at the black paint stripe. It will then measure the temperature accurately and reliably regardless of changes in the surface conditions of the rest of the roller.
The IRt/c measures the temperature of the air-water interface on a surface directly. The quality of the water or of the absorbing material does not affect the reading, since the IRt/c can directly view the air-water interface, and the wet bulb equilibrium temperature is not materially affected by impurities. The highest precision method is to employ an IRt/c wired differentially with a conventional thermocouple to measure the quantity “wet bulb depression”. The differential pair arrangement guarantees high accuracy, since RH is a strong function of wet bulb depression and a weak function of dry bulb temperature. Standard psychrometric tables, charts, and software algorithms can be used with the data to obtain accurate relative humidity for your environmental measurements.
+
If there is very little space on the edge of the roller, move the sensor closer and paint a very small black stripe. The minimum spot size of the IRt/c is 8 mm (0.3 inches) and for the OS36-2 it is 4 mm (0.16 inches) when the sensor is brought close to the surface. 2. Dull Metal Rollers – Dull metal rollers can provide a reliable signal. It is best to test the surface for reliability, though, as the surface emissive properties may shift via dirt, moisture, cleaning, etc. It is best, if in doubt, to simply paint a stripe to eliminate these variations.
Relative Humidity Measurement
+ – – Air Flow
+
+ –
Wet Bulb Depression Temperature
+ Dry Bulb Temperature
–
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3. Non-metallic Surfaced Rollers – These will provide a reliable IR signal at any point the IRt/c is aimed. No painted stripe is required.
CONTROLLING VACUUM FORMING AND THERMOFORMING PROCESSES
IRt/c CONTROLS PRINTED CIRCUIT BOARD PREHEAT DURING WAVE SOLDERING
For forming plastics, an excellent combination of heating method and control is radiant heat with an IRt/c for control. They work extraordinarily well together, since both the heating and measuring occur right at the surface – where the plastic is located. The IRt/c reading is unaffected by reflections from the heater, since the spectral response of the 6-14 micron IRt/c lens filters out the shorter wavelengths of the radiant heater energy.
An excellent solution to the problem of proper heater control for PC board preheat is an IRt/c. They work extraordinarily well together, since both the heating and measuring occur right at the surface – where the solder must flow. The IRt/c reading is unaffected by reflections from the heater, since the spectral response of the 6-14 micron IRt/c lens filters out any shorter wavelengths of the radiant heater energy.
,yy,y,y , y,y,y,y ,
Air
OS36-2 Air
The IRt/c may be mounted in between ceramic heaters, or in the shroud or reflector of the radiant heater, such that it can see in between the elements. Select the IRt/c standard, OS36-2 or OS36-5 model, depending on the field-of-view required to see past the elements to the painted surface. Care should be taken in mounting the IRt/c in such a way as to keep its temperature below 93°C (200°F) and to keep the lens clean. The OS36-2 is the preferred model for this application because of its small physical size with built-in air purge. It can be used in temperatures to 121°C (250°F) environments when the air purge system is used. Its narrower field-of-view allows more leeway in positioning, and thus more flexibility in installation. For still narrower fields of view, use the OS36-5 with its 5:1 FOV.
OS36-2 Ceramic Heaters
2. The field-of-view: the preferred method is to view the part between the coil turns or from the end. Select the IRt/c model that best suits the requirements. 3. Part temperature: both the OS36-2 and OS36-5 models can be used to target temperatures of 1100°C (2000°F), and have linear ranges to 260°C (500°F).
ASPHALT TEMPERATURE MONITORING Asphalt properties are particularly sensitive to temperature, and it is important that the asphalt is applied at the correct temperature in order to perform to its specifications. Accordingly, temperature monitoring is a common requirement, but the thermocouples normally used have severe breakage problems due to the harsh abrasiveness of the material, and must constantly be replaced at high cost and interruption of production.
For this application, the IRt/c may be mounted identically to Vacuum Forming/Thermoforming (above).
INDUCTION HEATER CONTROL The induction heating process can be readily controlled by the temperature of the part as measured by an IRt/c non-contact infrared thermocouple. Several issues should be considered in an installation.
IRt/c Cooling Water OS36-5 OS36-2
1. The effect of the field on the IRt/c: since the measuring signal is electrically isolated from the housing, the IRt/c will operate in even a very strong field. The shield wire should be attached to a proper signal ground. If there is excessive heating from the field, consider using the optional cooling jacket kit, with the same water source as is used to cool the coil. OS36-2 and OS36-5 models feature built-in air purge to keep these quality thermocouples functioning efficiently and accurately, even in dirty environments
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yyy ,,, ,,, yyy
Air
OS36-2
Air
OS36-5
The IRt/c solves this problem directly, since the temperature is monitored without contact. The normal thermocouple controller can be used – simply calibrate offset if necessary. The OS36-2 and OS36-5 models are recommended due to their built-in air purge, which will keep the lens clean by preventing vapors from condensing on the lens. The OS36-2 can be mounted in the chute to view the asphalt through a small hole, while the OS36-5 can be mounted some distance away due to its narrow 5:1 field of view.
Reproduced with permission of Exergen Corp.
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Microcomputer Based IR Temperature Transducers Charles E. Everest, Everest Interscience, Inc.
systems, an increment of radiant power dWD is transmitted from the detector’s sensitive area to the target spot according to the equation: eDC1f dWD = dl 5 l (eC2 / lTD-1)
Microcomputer based IR temperature transducers are superior to the readily available analog types because in situ computing can be used to correct detector imperfections, provide threefigure emissivity compensation settings (including real-time control of emissivity compensation during individual measurements), and process transducer data, transmitting only salient information and thereby reducing data load on the data acquisition system (DAS) (see Figure 1).
The net incremental radiant power flow from the target spot to the sensitive area is: dWnet = dWT - dWD
The µC makes it possible also to calibrate the transducer in real time without bothering the DAS unless a failure mode is detected. In situ data logging and buffering for asynchronous polling by the DAS is available. The data rate of the transducer can be matched to the data rate of the DAS.
or: dWnet= -
CORRECTING DETECTOR IMPERFECTIONS
A
eD ] dl eC2/lTD-1
C1, C2 = absolute constants f = optical gain of the IR focusing optics l = wavelength in microns eT = emissivity of the target surface eD = emissivity of the detector surface then: Wnet =
C1f l5
*
l = l1
From this basic energy balance equation, the target temperature is an exponential function of the detector temperature TD.
A N A L O G
ASCII
ADC
MICRO– COMPUTER
BCD RS232-C RS232-C
MUX
OUTPUT CONNECTOR
REFERENCE THERMISTOR
OPTICAL CHOPPER
l = l2
eD T [ eC2e/lT ] dl T-1 eC2 /lTD-1
Furthermore, since the optical system and its media are linear, bilateral
LOW NOISE IR REAMP SENSOR
[
where:
The thermal-type IR detectors used in moderate-temperature IR thermometers all suffer from shortcomings, but these can be corrected by sophisticated data processing techniques available with digital computers. The sensitive area of the detector and its image spot on the target are conjugate images of each other formed by the optics. Also, since Planck’s equation defines a spectral quantity, an increment of radiant power, dWT, for each micron of spectral bandwidth in the IR spectrum is radiated from the target spot to the IR detector according to the equation: eTC1f dWT = dl 5 l (eC2/lTT-1)
OPTICAL ASSY.
eT eC2/lTT-1
C1f l5
+9 VDC
Figure 1
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The output signal from the IR detector is a minute voltage proportional to the difference in temperature between the target and the detector body itself. To obtain an accurate measurement of the target temperature, it is therefore necessary to accurately measure the detector body temperature and add the processed difference temperature provided by the IR detector. If our embedded computer can improve the accuracy of either of these component temperature measurements, the overall target temperature measurement is enhanced. In fact, the accuracy of both of these component temperature measurements is significantly improved using computer enhancements, as explained later. Another troublesome detector error source that can be completely corrected with the computer is DC drift caused by ambient temperature variations. The detector body temperature TD is probably the most important variable the computer uses to improve overall system accuracy. The techniques by which the computer obtains this variable with greatly enhanced accuracy are outlined below. TD spans the range of the natural environment, from roughly -50 to 100°C. Over this range, the most precise and accurate temperature measuring transducer is the thermistor. It is rarely used as the temperature reference element for IR thermometers, however, because its output signal is highly nonlinear, and, although extremely stable, its as-manufactured nominal values vary widely from unit to unit (production spread). Most IR thermometer manufacturers are limited to simple analog correction techniques for their detector reference elements and so must abandon the more accurate and stable thermistor for a less accurate but easier to use element such as an integrated circuit, which outputs a linear current with temperature. Highly nonlinear transducer responses are no problem for a computer, however, because they can be characterized with a Taylor series polynomial of the form shown in Equation 6 with an order, n, high
enough to give arbitrarily perfect linearization correction for any transducer’s curve: A + BX + CX2 + DX3 + ... ZXn An algorithm for a general solution of the equation is held as a subroutine in program memory, while the transducerspecific coefficients A,B,D,C ... Z are held in firmware (EEPROM). Given the power of modern µC’s, complex mathematical operations like this are practically free of hardware costs and can be performed in real time quickly enough not to affect the overall reading speed. The bottom line is that actual detector case temperature measurements of 0.05°C absolute accuracy are routine. The IR detector itself is another temperature transducer with a highly nonlinear and temperature-dependent response: E0 = R • W where: E0 = detector output in volts W = IR electromagnetic radiant power in W/m2 R = responsivity (constant of proportionality) Responsivity is also a nonlinear function of TD. It is typically grossly corrected in the industry with a simple linear gain correction produced by a temperature sensitive resistor in the preamplifier feedback network. With an embedded µC, a third-order Taylor series correction using the real-time values computed for TD will effect a complete error correction for less cost than the temperature sensitive feedback resistor. These techniques allow the price of new computer based digital IR temperature transducers to be no greater than that of their analog predecessors, even with greatly enhanced performance and accuracy. WT, the net radiant target signal power impinging on the detector, is highly nonlinear with target temperature TT; for low-temperature targets (TT<1000°F), it is also highly dependent on the detector temperature itself (TD). WT is a spectral quantity that depends on the spectral window it passes through, as calculated from Planck’s equation. For very wide
band IR thermometers measuring hightemperature targets, this characteristic approaches the fourth order of the Stefan-Boltzmann law: ; KoTT4 W; where: TT = absolute target temperature o = Stefan-Boltzmann constant K = a nonlinear function of TD In present-day IR thermometers, K is usually combined with R of Equation 7 and a single linear compensation correction is applied, even though they have differing slopes in TD. With Taylor series digital corrections, only three or four coefficients need to be stored for use with the general purpose Taylor series algorithm to effect nearly perfect corrections of both coefficients independently. The critical linearization of the TT4 term (in the equation above) is usually left to linear approximation techniques. The instrument’s entire scale span is divided into a convenient number of curved sections, usually between 6 and 12, and each section is approximated by a straight line that can be easily handled by analog techniques. Unfortunately, each section is accurately corrected at only two temperatures; other temperatures in the section can be read out in error by as much as the entire accuracy specification of the instrument, which was fixed at one of the accurate points of the highest section. Thus the ± linearity error specification is usually equal to, and in addition to, the span accuracy specification of the instrument. In digital IR thermometers with embedded µC’s, a Taylor series polynomial with as many as 7 terms, solved in real time, can effectively solve the fourth-power relationship between detector output voltage and target temperature. Detector zero (or DC) drift is another imperfection that can be effectively corrected with an embedded µC. Thermal detectors usually have negligible long-term zero drift under stable ambient conditions but are quite susceptible to thermal transients. Errors of several degrees are common when taking an instrument with a simple thermal detector from one room to another with a different ambient temperature.
Z-82
An effective way to correct this error is periodically to completely block the incoming IR radiation signal from the target with an optical chopper, while measuring the remaining error signal and storing its value in computer memory for later subtraction from the measured composite signal. This procedure can be performed as often as necessary or convenient under adaptive computer control. Whenever an inactive time interval can be identified by the computer, the procedure can be cycled without interrupting the useful flow of information. If this asynchronous chopping is done frequently as compared to the drift rate of the detector, nearly perfect DC zero restoration can be achieved.
DIGITAL TARGET EMISSIVITY COMPENSATION Extremely precise (three-figure) emissivity corrections can be called up either from as many as 10 values stored in resident EEPROM, or from complex, real-time programs dependent on target timetemperature relationships. An example of the latter is a program for compensation of the emissivity of an induction heated steel part, which oxidized as it heats to higher temperatures. The emissivity may be quite low (;0.1) at low temperatures, but as it is rapidly heated, an oxide film forms on its surface, which raises the emissivity according to its time-temperature history. This timetemperature integral can be easily calculated by the computer and the corresponding emissivity value applied to the temperature readout in real time.
EMBEDDED DATA PROCESSING CHORES Transducer data can be preprocessed at the point of measurement to extract the pertinent information for transmission to the mainframe data processing system. For instance, only excess limit or out-of-range data may be desired. In this case, set point values can be programmed into the embedded computer firmware so that only data above (or below) the set point will be transmitted, perhaps on a priority interrupt basis. On a serial digital interface bus, a priority interrupt hierarchy can be defined that will maximize the number of drops (transducers) a single wire will accommodate.
Z
Microcomputer Based IR Temperature Transducers Cont'd A smart transducer can be programmed to identify windows in data flow patterns where a preprogrammed calibration procedure can be performed without affecting useful data flow. For instance, if the IR thermometer is measuring the temperature of cans proceeding down a conveyor belt, a gap between successive cans is sensed and the dead time during the gap is used to cycle the calibration procedure. The master DAS need not be aware of the individual transducer’s calibration details unless an out-of-limits condition occurs and the affected transducer initiates a priority interrupt alarm.
There are also four precision, low-level analog inputs available that can accept auxiliary inputs from thermocouples, RTDs, or other IR detectors for support functions. The simplest of these might be detection of temperatures above or below a preset threshold that has been programmed into EEPROM. This set point could even be automatically programmed by the computer in response to input variable history. As many as four set points can be monitored and controlled simultaneously. Among the more complex control functions are complete local closed-loop PID control of a process temperature entirely by the transducer with no external help from other control electronics.
INTEGRAL DATA LOGGING AND BUFFERING
INTERFACE MANAGEMENT
AUTOMATIC CALIBRATION
Both volatile and nonvolatile data logging are built into the transducer. Volatile data logging with the resident RAM is used to assemble and temporarily store on-line data either for use in computations or to wait for bus polling. This ability to locally process and format data reduces the data transfer time to the processor. Furthermore, because even fast IR thermometers are relatively slow (;ms) compared to electronic DASs (;µs), very little time is needed to service an individual digital IR thermometer on a data bus. The data can often be compressed into 50 µs/s, allowing dozens of drops (transducers) on a single-wire pair (see section on Interface Management). Nonvolatile data logging, via the embedded EEPROM, is used to store significant historical data such as maximum, minimum, average, mean, and out-oflimit values for indefinite times.
IN SITU DIGITAL CONTROL INTELLIGENCE The powerful integral microcontroller can also be programmed to act on the incoming temperature data to perform external control functions. There are 16 multipurpose µC control ports available for command inputs from external signals such as simple switch closures or photo-detector signals, or for control outputs such as power relays. Each port can directly drive an optically isolated solid-state relay capable of controlling a 10 kW load operating at 1600 V differential from the transducer.
The computer’s data processing power minimizes the hardware complexity of the transmission lines by managing both electrical power and data transmission flow for the transducer. For example, the computer can function as a traffic cop to time share a single line among several dozen transducers for both power and two-way data transmission. In addition, when the line is used for power transmission, other transducers can be connected to it and powered up at the same time. When the computer disconnects line power, data can be transmitted so quickly that many connected transducers can be polled before the next power up. The bottom line is that inexpensive BNCs can be used with the transducers and a simple 2-wire party line can service up to 16 transducers over a distance of 1000 ft. Another performance advantage accrues from the all-digital data transmission, which is far less susceptible to RFI/EMI than is analog data transmission. Because the binary data transmission is serial in nature and is formatted for bilateral transmission on a single line, a single fiber-optic line can be substituted to provide complete immunity from RFI/EMI, up to and including lightning strikes. Finally, the savings on multipin connectors and individual multiconductor cables is enough to pay for the µC, not to mention the greatly enhanced reliability from a single line system vs. six conductors.
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SUMMARY The superiority of µC based IR temperature sensing instruments over present generation analog IR thermometers is apparent. This statement is supported by the enhanced accuracy of temperature measurements of the difference between the target and detector body, and the measurement of the detector body itself. Also to be noted is the ability of the microcomputer based instrumentation to replace the linear approximation techniques. Extremely precise emissivity correction is another plus, as are the automatic calibration, integral data logging, and in situ digital control intelligence capabilities. The reduction in the cost of the interface between the host computer and the transducers can be substantial. An extremely sophisticated IR temperature measurement system can be provided at a cost that is equal to or less than previously available analog systems with limited capabilities.
Reproduced with permission of EVEREST INTERSCIENCE, INC.
Infrared Thermocouples, Extended Temperature Ranges Z
Infrared thermocouples can be used with most thermocouple meters or controller over a specified temperature range. For example, the OS36-J-50F would have a 2% accuracy over the range of -18 to 27°C (0 to 80°F). The following table shows the series of equations that permit a determination of measured temperature by measuring the IR-TC’s output voltage. If desired, the cold junction (CJ) correction can be set at any known constant temperature, e.g., 25°C. If the CJ temperature is not known and constant, it is suggested you use an OMEGA CJ connection device like a TRC IIIA or CJ-K. This will correct to 0°C and allow use of a standard voltmeter without other cold junction compensation. The CJT term can then be dropped in the following polynomial table.
Z-84
Polynomial Table for OS36, 37 and 38 Signal Output TT = A·(mV)6 + B·(mV)5 + C·(mV)4 + D·(mV)3 + E·(mV)2 + F·(mV) + CJT OS36-J-50F/10C OS36-J-80F/27C OS36-J-140F/60C OS36-J-180F/90C OS36-J-240F/120C OS36-J-280F/140C OS36-J-340F/170C OS36-J-440F/220C OS36-K-50F/10C OS36-K-80F/27C OS36-K-140F/60C OS36-K-180F/90C OS36-K-240F/120C OS36-K-280F/140C OS36-K-340F/170C OS36-K-440F/220C OS37-K OS38-K OS38-K OS38-K
A
B
C
D
-6.14473E-09 -2.83996E-08 -4.31591E-08 -7.03138E-08 -1.05707E-07 -1.89514E-07 -2.99852E-07 -5.20472E-07 -1.59875E-08 -6.09875E-08 -1.42546E-07 -3.22615E-07 -5.08511E-07 -9.34497E-07 -1.62369E-06 -2.90564E-06 -7.13085E-08 -2.17588E+04 -3.01228E-08
2.08199E-06 7.41635E-06 1.06077E-05 1.59337E-05 2.23776E-05 3.63996E-05 5.33519E-05 8.44263E-05 4.63673E-06 1.41502E-05 2.87094E-05 5.67063E-05 8.28536E-05 1.37576E-04 2.18012E-04 3.54076E-04 2.30925E-05 7.42505E+04 9.50466E-06
-2.72953E-04 -7.54046E-04 -1.01002E-03 -1.39844E-03 -1.83521E-03 -2.70839E-03 -3.67751E-03 -5.30444E-03 -5.20959E-04 -1.27187E-03 -2.24003E-03 -3.86135E-03 -5.22978E-03 -7.84637E-03 -1.13401E-02 -1.67152E-02 -2.88585E-03 -9.73319E+04 -1.17636E-03
1.75317E-02 3.79224E-02 4.72155E-02 6.02655E-02 7.38926E-02 9.89395E-02 1.24452E-01 1.63572E-01 2.87368E-02 5.61266E-02 8.58077E-02 1.29089E-01 1.62069E-01 2.19704E-01 2.89601E-01 3.87409E-01 1.75033E-01 6.14482E+04 7.27752E-02
E -5.84883E-01 -1.00406E+00 -1.14872E+00 -1.35167E+00 -1.54843E+00 -1.88106E+00 -2.19192E+00 -2.62438E+00 -8.24991E-01 -1.28905E+00 -1.71070E+00 -2.24604E+00 -2.61390E+00 -3.20171E+00 -3.84908E+00 -4.67308E+00 -5.35670E+00 -1.92711E+04 -2.41603E+00
Alternative: Power Law Fit=298.0514(mV)0 2864
Maximum Range mV TT
Minimum Range mV TT
Test Conditions TT
CJT
OS36-J-50F/10C OS36-J-80F/27C OS36-J-140F/60C OS36-J-180F/90C OS36-J-240F/120C OS36-J-280F/140C OS36-J-340F/170C OS36-J-440F/220C OS36-K-50F/10C OS36-K-80F/27C OS36-K-140F/60C OS36-K-180F/90C OS36-K-240F/120C OS36-K-280F/140C OS36-K-340F/170C OS36-K-440F/220C OS37-K OS38-K OS38-K
70 70 70 70 65 60 55 50 70 70 65 55 50 45 45 40 70 1 80
466 577 634 674 671 678 674 667 551 664 685 678 671 670 681 685 957 334 1035
-4 -3 -3 -3 -2 -2 -2 -2 -3 -3 -2 -2 -2 -2 -2 -1 0 0 1
-47 -47 -47 -47 -46 -47 -46 -49 -47 -45 -47 -47 -49 -48 -45 -48 0 0 309
mV 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 1 80
89 107 112 117 122 130 136 143 101 116 126 137 143 152 160 169 341 334 1035
25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 262
OS38xxx-K Power Law
80
1046
0
0
5
473
25
Notes: TT = Target Temperature CJT = Cold junction temperature at input added via the input Device (controller, indicator, PLC, etc.). A controlled constant 25°C is assumed here for most polynomials. It can be changed. mV = Signal produced by infrared thermocouple in millivolts. All temperatures in °C. Assumed target emissivity is 0.9 for all models except OS38 which has assumed emissivity 0.2.
Z-85
F 1.53003E+01 2.06592E+01 2.20397E+01 2.39075E+01 2.55885E+01 2.82034E+01 3.04447E+01 3.31770E+01 1.86777E+01 2.33472E+01 2.68960E+01 3.08183E+01 3.32464E+01 3.67952E+01 4.03439E+01 4.44530E+01 8.58605E+01 2.97242E+03 4.88735E+01
Infrared Window Transmission Refractive Indexes for IR Windows Material Barium Fluoride Cesium Bromide Cesium Iodide Calcium Fluoride Germanium Lithium Fluoride Magnesium Fluoride Potassium Bromide Potassium Chloride Sapphire Silicon Silver Bromide Silver Chloride Sodium Chloride Sodium Fluoride Strontium Fluoride Thallium Bromide Thallium Bromide-Chloride KRS6 Thallium Bromide-Iodide KRS5 Thallium Chloride Zinc Selenide Zinc Sulphide
n
at wavelength µm
1.45 1.66251 1.73916 1.399 4.003 1.39 No = 1.379 Ne = 1.391 1.526 1.454 1.755 3.4179 2.31 1.980 1.49482 1.238 1.439 2.338 2.1767 2.37069 2.193 2.40 2.2
5 10 10 5 10 0.5 0.5 10 10 1 10 0.5 10 10 10 0.5 10 10 10 10 10 10
Transmission Range
Wavelength (µm) Reproduced with permission of Optovac Corporaton
Z-86
Z
Infrared Quick Help When to Use Infrared Temperature Measurement: Surface Is:
OS520 Series Handheld Infrared Thermometer
U Too Hot to Be Measured With Thermocouples U Too Large to Be Measured Without a Very Large Number of Thermocouples U Moving Too Much for Thermocouple Lead Wire to Accept Without Breaking U At So High an Electrical Potential That Use of a Thermocouple Would Be Dangerous U So Low in Mass That The Thermocouple Itself Will Affect the Unknown Surface Temperature
U Too Fragile or Wet to Accommodate Thermocouple Contact U Too Active (Chemically) to Accept a Thermocouple or Its Probe U In an Atmosphere That Is Hostile to a Thermocouple U Inaccessible to a Thermocouple or Its Instrumentation U Near Noise Producing Electric or Magnetic Fields
Key Infrared Application Factors U Target Spot Size and Distance U Target Material (for Emissivity) U Fixed or Handheld Unit U Temperature Range
OS550 Sensor Head Industrial Noncontact Infrared Thermometer/Transmitter and OS550-MB Mounting Bracket
U U U U U
Response Time Sighting System Environment Viewing Port Options Needed
Determination of Infrared Emissivity U Measure Surface Temperature by Some Other Means (After Stopping Motion) U Place Masking Tape on Surface (Emissivity 0.95) U Drill Hole in Surface At Least Six Times as Deep as It Is Wide (Emissivity 0.95)
BB704 Series Blackbody Calibration Source with Portable Design
Z-87
U Paint Surface Dull Black (M IR Region) U Look up Emissivity in Table (Last Resort)
Table of Total Emissivity These tables are presented for use as a guide when making infrared temperature measurements with the OMEGASCOPE® or other infrared pyrometers. The total emissivity (ε) for Metals, Non-metals and Common Building Materials are given.
Material
Temp °F (°C)
Alloys 20-Ni, 24-CR, 55-FE, Oxid. 392 (200) 20-Ni, 24-CR, 55-FE, Oxid. 932 (500) 60-Ni , 12-CR, 28-FE, Oxid. 518 (270) 60-Ni , 12-CR, 28-FE, Oxid. 1040 (560) 80-Ni, 20-CR, Oxidized 212 (100) 80-Ni, 20-CR, Oxidized 1112 (600) 80-Ni, 20-CR, Oxidized 2372 (1300) Aluminium Unoxidized 77 (25) Unoxidized 212 (100) Unoxidized 932 (500) Oxidized 390 (199) Oxidized 1110 (599) Oxidized at 599°C (1110°F) 390 (199) Oxidized at 599°C (1110°F) 1110 (599) Heavily Oxidized 200 (93) Heavily Oxidized 940 (504) Highly Polished 212 (100) Roughly Polished 212 (100) Commercial Sheet 212 (100) Highly Polished Plate 440 (227) Highly Polished Plate 1070 (577) Bright Rolled Plate 338 (170) Bright Rolled Plate 932 (500) Alloy A3003, Oxidized 600 (316) Alloy A3003, Oxidized 900 (482) Alloy 1100-0 200-800 (93-427) Alloy 24ST 75 (24) Alloy 24ST, Polished 75 (24) Alloy 75ST 75 (24) Alloy 75ST, Polished 75 (24) Bismuth, Bright 176 (80) Bismuth, Unoxidized 77 (25) Bismuth, Unoxidized 212 (100) Brass 73% Cu, 27% Zn, Polished 476 (247) 73% Cu, 27% Zn, Polished 674 (357) 62% Cu, 37% Zn, Polished 494 (257) 62% Cu, 37% Zn, Polished 710 (377) 83% Cu, 17% Zn, Polished 530 (277) Matte 68 (20) Burnished to Brown Colour 68 (20) Cu-Zn, Brass Oxidized 392 (200) Cu-Zn, Brass Oxidized 752 (400) Cu-Zn, Brass Oxidized 1112 (600) Unoxidized 77 (25) Unoxidized 212 (100) Cadmium 77 (25) Carbon Lampblack 77 (25) Unoxidized 77 (25) Unoxidized 212 (100) Unoxidized 932 (500) Candle Soot 250 (121) Filament 500 (260) Graphitized 212 (100) Graphitized 572 (300) Graphitized 932 (500) Chromium 100 (38) Chromium 1000 (538) Chromium, Polished 302 (150) Cobalt, Unoxidized 932 (500) Cobalt, Unoxidized 1832 (1000) Columbium, Unoxidized 1500 (816) Columbium, Unoxidized 2000 (1093) Copper Cuprous Oxide 100 (38) Cuprous Oxide 500 (260) Cuprous Oxide 1000 (538) Black, Oxidized 100 (38) Etched 100 (38) Matte 100 (38) Roughly Polished 100 (38)
ε–Emissivity .90 .97 .89 .82 .87 .87 .89 .02 .03 .06 .11 .19 .11 .19 .20 .31 .09 .18 .09 .04 .06 .04 .05 .40 .40 .05 .09 .09 .11 .08 .34 .05 .06 .03 .03 .03 .04 .03 .07 .40 .61 .60 .61 .04 .04 .02 .95 .81 .81 .79 .95 .95 .76 .75 .71 .08 .26 .06 .13 .23 .19 .24 .87 .83 .77 .78 .09 .22 .07
Material
Since the emissivity of a material will vary as a function of temperature and surface finish, the values in these tables should be used only as a guide for relative or delta measurements. The exact emissivity of a material should be determined when absolute measurements are required. Temp °F (°C)
Polished 100 (38) Highly Polished 100 (38) Rolled 100 (38) Rough 100 (38) Molten 1000 (538) Molten 1970 (1077) Molten 2230 (1221) Nickel Plated 100-500 (38-260) Dow Metal 0.4-600 (–18-316) Gold Enamel 212 (100) Plate (.0001) Plate on .0005 Silver 200-750 (93-399) Plate on .0005 Nickel 200-750 (93-399) Polished 100-500 (38-260) Polished 1000-2000 (538-1093) Haynes Alloy C, Oxidized 600-2000 (316-1093) Haynes Alloy 25, Oxidized 600-2000 (316-1093) Haynes Alloy X, Oxidized 600-2000 (316-1093) Inconel Sheet 1000 (538) Inconel Sheet 1200 (649) Inconel Sheet 1400 (760) Inconel X, Polished 75 (24) Inconel B, Polished 75 (24) Iron Oxidized 212 (100) Oxidized 930 (499) Oxidized 2190 (1199) Unoxidized 212 (100) Red Rust 77 (25) Rusted 77 (25) Liquid 2760-3220 (1516-1771) Cast Iron Oxidized 390 (199) Oxidized 1110 (599) Unoxidized 212 (100) Strong Oxidation 40 (104) Strong Oxidation 482 (250) Liquid 2795 (1535) Wrought Iron Dull 77 (25) Dull 660 (349) Smooth 100 (38) Polished 100 (38) Lead Polished 100-500 (38-260) Rough 100 (38) Oxidized 100 (38) Oxidized at 1100°F 100 (38) Gray Oxidized 100 (38) Magnesium 100-500 (38-260) Magnesium Oxide1880-3140 (1027-1727) Mercury 32 (0) " 77 (25) " 100 (38) " 212 (100) Molybdenum 100 (38) " 500 (260) " 1000 (538) " 2000 (1093) " Oxidized at 1000°F 600 (316) " Oxidized at 1000°F 700 (371) " Oxidized at 1000°F 800 (427) " Oxidized at 1000°F 900 (482) " Oxidized at 1000°F 1000 (538) Monel, Ni-Cu 392 (200) Monel, Ni-Cu 752 (400) Monel, Ni-Cu 1112 (600) Monel, Ni-Cu Oxidized 68 (20)
Z-88
ε–Emissivity .03 .02 .64 .74 .15 .16 .13 .37 .15 .37 .11-.14 .07-.09 .02 .03 .90-.96 .86-.89 .85-.88 .28 .42 .58 .19 .21 .74 .84 .89 .05 .70 .65 .42-.45 .64 .78 .21 .95 .95 .29 .94 .94 .35 .28 .06-.08 .43 .43 .63 .28 .07-.13 .16-.20 .09 .10 .10 .12 .06 .08 .11 .18 .80 .84 .84 .83 .82 .41 .44 .46 .43
METALS
Material
Temp °F (°C)
Monel, Ni-Cu Oxid. at 1110°F 1110 (599) Nickel Polished 100 (38) Oxidized 100-500 (38-260) Unoxidized 77 (25) Unoxidized 212 (100) Unoxidized 932 (500) Unoxidized 1832 (1000) Electrolytic 100 (38) Electrolytic 500 (260) Electrolytic 1000 (538) Electrolytic 2000 (1093) Nickel Oxide 1000-2000 (538-1093) Palladium Plate (.00005 on .0005 silver) 200-750 (93-399) Platinum 100 (38) " 500 (260) " 1000 (538) Platinum, Black 100 (38) " 500 (260) " 2000 (1093) " Oxidized at 1100°F 500 (260) " 1000 (538) Rhodium Flash (0.0002 on 0.0005 Ni) 200-700 (93-371) Silver Plate (0.0005 on Ni) 200-700 (93-371) Polished 100 (38) " 500 (260) " 1000 (538) " 2000 (1093) Steel Cold Rolled 200 (93) Ground Sheet 1720-2010 (938-1099) Polished Sheet 100 (38) " 500 (260) " 1000 (538) Mild Steel, Polished 75 (24) Mild Steel, Smooth 75 (24) Mild Steel, Liquid 2910-3270 (1599-1793) Steel, Unoxidized 212 (100) Steel, Oxidized 77 (25) Steel Alloys Type 301, Polished 75 (24) Type 301, Polished 450 (232) Type 301, Polished 1740 (949) Type 303, Oxidized 600-2000 (316-1093) Type 310, Rolled 1500-2100 (816-1149) Type 316, Polished 75 (24) Type 316, Polished 450 (232) Type 316, Polished 1740 (949) Type 321 200-800 (93-427) Type 321 Polished 300-1500 (149-815) Type 321 w/BK Oxide 200-800 (93-427) Type 347, Oxidized 600-2000 (316-1093) Type 350 200-800 (93-427) Type 350 Polished 300-1800 (149-982) Type 446, Polished 300-1500 (149-815) Type 17-7 PH 200-600 (93-316) Type 17-7 PH Polished 300-1500 (149-815) Type C1020, Oxidized 600-2000 (316-1093) Type PH-15-7 MO 300-1200 (149-649) Stellite, Polished 68 (20) Tantalum, Unoxidized 1340 (727) " 2000 (1093) " 3600 (1982) " 5306 (2930) Tin, Unoxidized 77 (25) " 212 (100) Tinned Iron, Bright 76 (24) " 212 (100)
ε–Emissivity .46 .05 .31-.46 .05 .06 .12 .19 .04 .06 .10 .16 .59-.86 .16-.17 .05 .05 .10 .93 .96 .97 .07 .11 .10-.18 .06-.07 .01 .02 .03 .03 .75-.85 .55-.61 .07 .10 .14 .10 .12 .28 .08 .80 .27 .57 .55 .74-.87 .56-.81 .28 .57 .66 .27-.32 .18-.49 .66-.76 .87-.91 .18-.27 .11-.35 .15-.37 .44-.51 .09-.16 .87-.91 .07-.19 .18 .14 .19 .26 .30 .04 .05 .05 .08
Z
Table of Total Emissivity Cont’d Material
Temp °F (°C)
Titanium Alloy C110M, Polished 300-1200 (149-649) " Oxidized at 538°C (1000°F) 200-800 (93-427) Alloy Ti-95A, Oxid. at 538°C (1000°F) 200-800 (93-427) Anodized onto SS 200-600 (93-316)
Material Adobe
ε–Emissivity .08-.19 .51-.61
.35-.48 .96-.82
Temp °F (°C)
ε–Emissivity
68 (20)
.90
Asbestos Board 100 (38) Cement 32-392 (0-200) Cement, Red 2500 (1371) Cement, White 2500 (1371) Cloth 199 (93) Paper 100-700 (38-371) Slate 68 (20) Asphalt, pavement 100 (38) Asphalt, tar paper 68 (20) Basalt 68 (20) Brick Red, rough 70 (21) Gault Cream 2500-5000 (1371-2760) Fire Clay 2500 (1371) Light Buff 1000 (538) Lime Clay 2500 (1371) Fire Brick 1832 (1000) Magnesite, Refractory 1832 (1000) Gray Brick 2012 (1100) Silica, Glazed 2000 (1093) Silica, Unglazed 2000 (1093) Sandlime 2500-5000 (1371-2760) Carborundum 1850 (1010) Ceramic Alumina on Inconel 800-2000 (427-1093) Earthenware, Glazed 70 (21) Earthenware, Matte 70 (21) Greens No. 5210-2C 200-750 (93-399) Coating No. C20A 200-750 (93-399) Porcelain 72 (22) White Al2O3 200 (93) Zirconia on Inconel 800-2000 (427-1093) Clay 68 (20) " Fired 158 (70) " Shale 68 (20) " Tiles, Light Red 2500-5000 (1371-2760) " Tiles, Red 2500-5000 (1371-2760) " Tiles, Dark Purple 2500-5000 (1371-2760) Concrete Rough 32-2000 (0-1093) Tiles, Natural 2500-5000 (1371-2760) " Brown 2500-5000 (1371-2760) " Black 2500-5000 (1371-2760) Cotton Cloth 68 (20) Dolomite Lime 68 (20) Emery Corundum 176 (80) Glass Convex D 212 (100) Convex D 600 (316) Convex D 932 (500) Nonex 212 (100) Nonex 600 (316) Nonex 932 (500) Smooth 32-200 (0-93)
.96 .96 .67 .65 .90 .93 .97 .93 .93 .72 .93 .26-.30 .75 .80 .43 .75-.80 .38 .75 .88 .80 .59-.63 .92 .69-.45 .90 .93 .89-.82 .73-.67 .92 .90 .62-.45 .39 .91 .69 .32-.34 .40-.51 .78 .94 .63-.62 .87-.83 .94-.91 .77 .41 .86 .80 .80 .76 .82 .82 .78 .92-.94
Material Tungsten Unoxidized Unoxidized Unoxidized Unoxidized Unoxidized Unoxidized Filament (Aged) Filament (Aged) Filament (Aged)
Temp °F (°C)
ε–Emissivity
Uranium Oxide 77 (25) 212 (100) 932 (500) 1832 (1000) 2732 (1500) 3632 (2000) 100 (38) 1000 (538) 5000 (2760)
.02 .03 .07 .15 .23 .28 .03 .11 .35
Temp °F (°C)
ε–Emissivity
Granite
70 (21)
.45
Gravel
100 (38)
.28
68 (20) 32 (0)
.80-.90 .97
Ice, Rough 32 (0) Lacquer Black 200 (93) Blue, on Al Foil 100 (38) Clear, on Al Foil (2 coats) 200 (93) Clear, on Bright Cu 200 (93) Clear, on Tarnished Cu 200 (93) Red, on Al Foil (2 coats) 100 (38) White 200 (93) White, on Al Foil (2 coats) 100 (38) Yellow, on Al Foil (2 coats) 100 (38) Lime Mortar 100-500 (38-260) Limestone 100 (38) Marble, White 100 (38) " Smooth, White 100 (38) " Polished Gray 100 (38) Mica 100 (38) Oil on Nickel 0.001 Film 72 (22) 0.002 " 72 (22) 0.005 " 72 (22) Thick " 72 (22) Oil, Linseed On Al Foil, uncoated 250 (121) On Al Foil, 1 coat 250 (121) On Al Foil, 2 coats 250 (121) On Polished Iron, .001 Film 100 (38) On Polished Iron, .002 Film 100 (38) On Polished Iron, .004 Film 100 (38) On Polished Iron, Thick Film 100 (38) Paints Blue, Cu2O3 75 (24) Black, CuO 75 (24) Green, Cu2O3 75 (24) Red, Fe2O3 75 (24) White, Al2O3 75 (24) White, Y2O3 75 (24) White, ZnO 75 (24) White, MgCO3 75 (24) White, ZrO2 75 (24) White, ThO2 75 (24) White, MgO 75 (24) White, PbCO3 75 (24) Yellow, PbO 75 (24) Yellow, PbCrO4 75 (24) Paints, Aluminium 100 (38) 10% Al 100 (38) 26% Al 100 (38) Dow XP-310 200 (93) Paints, Bronze Low Gum Varnish (2 coats) 70 (21) Gum Varnish (3 coats) 70 (21) Cellulose Binder (2 coats) 70 (21)
.98
Material
METALS Material
Gypsum Ice, Smooth
Z-89
.96 .78 .08 (.09) .66 .64 .61 (.74) .95 .69 (.88) .57 (.79) .90-.92 .95 .95 .56 .75 .75 .27 .46 .72 .82 .09 .56 .51 .22 .45 .65 .83 .94 .96 .92 .91 .94 .90 .95 .91 .95 .90 .91 .93 .90 .93 .27-.67 .52 .30 .22 .34-.80 .53 .50 .34
Temp °F (°C)
ε–Emissivity
1880 (1027)
.79
Zinc Bright, Galvanized 100 (38) Commercial 99.1% 500 (260) Galvanized 100 (38) Oxidized 500-1000 (260-538) Polished 100 (38) Polished 500 (260) Polished 1000 (538) Polished 2000 (1093)
.23 .05 .28 .11 .02 .03 .04 .06
NON-METALS Material
Temp °F (°C)
Paints, Oil All colors 200 (93) Black 200 (93) Black Gloss 70 (21) Camouflage Green 125 (52) Flat Black 80 (27) Flat White 80 (27) Gray-Green 70 (21) Green 200 (93) Lamp Black 209 (98) Red 200 (93) White 200 (93) Quartz, Rough, Fused 70 (21) Glass, 1.98 mm 540 (282) Glass, 1.98 mm 1540 (838) Glass, 6.88 mm 540 (282) Glass, 6.88 mm 1540 (838) Opaque 570 (299) Opaque 1540 (838) Red Lead 212 (100) Rubber, Hard 74 (23) Rubber, Soft, Gray 76 (24) Sand 68 (20) Sandstone 100 (38) Sandstone, Red 100 (38) Sawdust 68 (20) Shale 68 (20) Silica,Glazed 1832 (1000) Silica, Unglazed 2012 (1100) Silicon Carbide 300-1200 (149-649) Silk Cloth 68 (20) Slate 100 (38) Snow, Fine Particles 20 (–7) Snow, Granular 18 (–8) Soil Surface 100 (38) Black Loam 68 (20) Plowed Field 68 (20) Soot Acetylene 75 (24) Camphor 75 (24) Candle 250 (121) Coal 68 (20) Stonework 100 (38) Water 100 (38) Waterglass 68 (20) Wood Beech P!aned Oak, Planed Spruce, Sanded
Low 158 (70) 100 (38) 100 (38)
ε–Emissivity .92-.96 .92 .90 .85 .88 .91 .95 .95 .96 .95 .94 .93 .90 .41 .93 .47 .92 .68 .93 .94 .86 .76 .67 .60-.83 .75 .69 .85 .75 .83-.96 .78 .67-.80 .82 .89 .38 .66 .38 .97 .94 .95 .95 .93 .67 .96 .80-.90 .94 .91 .89
Cryogenic Temperature Sensors CY7 Series Silicon Diodes
Z
MADE IN
USA The new CY7 Series Sensors from OMEGA represent the first truly new cryogenic sensor technology introduced in the last decade. The sensors incorporate uniform sensing elements that exhibit precise, repeatable, monotonic temperature response over a wide range. The elements are mounted into rugged, hermetically sealed packages that have been specifically designed for proper behavior in a cryogenic environment. The result is a family of sensors with temperature responses so predictable, tightly grouped, and stable that the sensors can be routinely interchanged with one another. A New Proprietary Silicon Diode Chip The key to the sensor’s temperature response lies with the basic sensing element itself. The small silicon chip in each sensor has a temperature characteristic that is so stable, so predictable, and conforms so well from chip to chip, that the CY7’s sensors are the first massproduced, interchangeable cryogenic sensors.
Precise thermal response of the sensing element itself is of little benefit if thermal errors generated in installing and using the sensor swamp out its capability. It is in minimizing these frequently unsuspected errors that the CY7 excels. A Sensor Package Designed for Cryogenics
As shown on the graph on page Z-93, the temperature response profile of a CY7 is comprised of two distinct elements. With their inherent dual sensitivity, CY7 sensors can cover a wide temperature range (up to 475 Kelvin) and at the same time exhibit high sensitivity for critical low temperature measurement.
Sensors for higher temperatures fall far short for cryogenic use. The complex thermal link between the sensing element and its entire environment must be taken into account, as must the effect of any measurement-induced self-heating of the sensor, if one is to achieve accurate results. In addition, the package must also withstand repeated cycling to low temperatures without mechanical failure.
Z-90
Cryogenic Temperature Sensors CY7 Series The development of the CY7 Series has included the design of unique sensor packages to solve many of the problems encountered in low temperature thermometry. For example, the CY7 hermetic package incorporates a sapphire substrate for high electrical isolation yet good thermal conductivity. The base bottom is metallized for easy anchoring to a sample. Large strong leads form an integral part of the package and are thermally sunk into the substrate. This simplifies making connections to the sensor and at the same time helps reduce measurement errors that could be caused by heat conduction along the leads.
10 Microampere Excitation Current Key to the achievement of error-free measurement is low excitation current. The lower the current, the less power is dissipated in the sensor and the less self-heating occurs.
Tolerance, K (kelvin)
2.0 1.5 BAND 4
1.0 BAND 2
0.5 BAND 1
0.0
0
50
100
150
200
250
One measure of the effectiveness of a cryogenic sensor’s thermal design is the variation in reading obtained between operation in a vacuum at liquid helium temperature and immersion directly in the liquid. In a field where discrepancies of a degree or more have been reported, OMEGA® CY7 sensors exhibit variations as low as 5 millikelvin.
Tolerance Bands for CY7 Series Sensors allow selection of appropriate (and economical) accuracy levels for a given application.
1.8
1.6 Average Slope -26mV/K
Forward Voltage –– Vf (volts)
1.4
1.2
1.0
10
0
20
30
40
60
50
0.8
0.6
Average Slope -2.3mV/K
0.4
0.2
0.0 0
20 40 60 80 100
300
Temperature, K (kelvin)
300
200
400
Temperature, K (kelvin)
Standard Temperature Response (Curve 10) for CY7 Series Sensors. All Sensors Track this Curve Within Specified Tolerance Bands. Z-91
70
Select the Sensor Configuration Best Suited to Your Application CY7-SD
The SD configuration is the smallest package in this series, and is designed primarily for bonding or clamping to a flat surface. Since the sensing element is in best thermal contact with the base (largest surface) of the package, the package should be mounted with that same surface in good contact with the sample. Mounting materials and methods which will not expose the sensor to temperatures above 200ºC are required. Low temperature indium-lead-tin based solder or low temperature epoxy is recommended. The SD package style is usable at temperatures up to 475 K.
CY7-LR With a CY7-SD sensor mounted on a slightly more than halfround cylinder, this package is designed to be inserted into a 1/8 inch (3.2 mm) diameter hole. Low temperature epoxy can also be used to install the sensor, although the mounting is much more permanent in that case. As with other soldered down sensors, the temperature range of the CY7-LR extends to 325 K.
Z
CY7-ET
This convenient screw-in package is formed by soldering a basic SD configuration into a recess in one flat of a hexagonal cylinder. The cylinder terminates in a standard 6-32 SAE thread. Thus the sensor can be threaded (finger tight only) into a mounting hole in the sample. A light coating of vacuum grease on the threads further enhances the thermal contact between the sensor package and the sample. The solder used in mounting the SD package to this adaptor constrains the upper useful temperature of this configuration to 325 K.
CY7-MT The MT package is similar to the ET version except the SD package is mounted in a slot in the center of the cylinder and the stud is a 3 mm x 0.5 metric thread. CY7-CO
A spring-loaded clamp holds a standard SD sensor in contact with the surface of the sample in this configuration. This allows the sensor to be easily changed or replaced. It also enables the sensor to be used over its full operational temperature range of 1.4 to 475 K. Extra clamps are available to accommodate applications where frequent relocation of the sensor is desirable. The 4-40 brass screw used with this clamp has a formed shoulder so that, once the screw is properly seated, the spring applies correct pressure to the clamp.
CY7-CU In this configuration, the SD sensor is epoxied into a flat cylindrical disk and the sensor leads are thermally anchored to that same disk. The unit can be mounted to any flat surface with a 4-40 brass screw (not supplied). The CU style sensor is wired in a fourlead configuration with the leads comprised of a 36-inch length of OMEGA’s color coded cryogenic wire. Temperature range is 1.4 to 325 K.
CY7-D1 This is a two-lead version of the the CY7-CU.
CY7-CY
Some applications are best served by a relatively large, robust sensor, and the CY7-CY fills that bill. It is very similar to the CU style except that the disk has a larger center diameter with the mounting hole directly in the center. The CY sensor has 36-inch heavy duty (30 AWG, PTFE coated) leads. Special attention must be paid to thermally anchoring the leads to prevent heat leak induced measurement error.
CY7-BO
In addition to being soldered to the mounting block, the SD sensor in this design has its leads thermally anchored (without epoxy) to the block via a beryllium oxide insert. Since leads can be a significant heat path to the sensing element, and can lead to measurement errors when incorrectly anchored, this configuration helps maintain the leads at the same temperature as the sensor. Mounting of this block is accomplished with a 4-40 screw (not supplied). Usable temperature range of the CY7-BO sensor is 1.4 to 325 K.
Probes
The flexibility of the CY7 series sensors makes them ideal candidates for incorporation into various probes and thermowells. However, the individualized nature of these applications usually demands customized designs. ®
Z-92
Cryogenic Temperature Sensors CY7 Series
TABLE 1. Chebychev fit coefficients
Polynomial Representation
Curve #10 can be represented by a polynomial equation based on the Chebychev polynomials which are described below. Four separate ranges are required to accurately describe the curve, with the parameters for these ranges given in Table 1. The polynomials represent Curve #10 on the preceding page with RMS deviations on the order of 10 mK. The Chebychev equation is of the form T(x) =
Σn=0a
t (x)
n n
(1)
where T(x) represents the temperature in kelvin, tn(x) is a Chebychev polynomial, and a n represents the Chebychev coefficients. The parameter x is a normalized variable given by x=
(V-VL)-(VU-V) (VU-VL)
(2)
where V is the voltage and VL and VU designate the lower and upper limits of the voltage over the fit range. The Chebychev polynomials can be generated from the recursion relation tn+1 (x)=2xtn(x)-tn-1(x), to(x)=1, t1(x)=x.
(3)
Alternately, these polynomials are given by tn(x)=cos[n*arccos(x)]. (4) The use of Chebychev polynomials is no more complicated than the use of the regular power series, and they offer significant advantages in the actual fitting process. The first step is to transform the measured voltage into the normalized variable using equation (2). Equation (1) is then used in combination with equation (3) or (4) to calculate the temperature. Programs 1 and 2 give sample BASIC subroutines which will take the voltage and return the temperature T calculated from Chebychev fits.The subroutines assume that the values VL and VU have been input along with the degree of the fit, Ndegree. The Chebychev coefficients are also assumed to be in an array A(0), A(1), ...,A(Ndegree). An interesting property of the Chebychev fits is evident in the form of the Chebychev polynomial given in equation (4). No term in equation (1) will be greater than the absolute value of the coefficient. This property makes it easy to determine the contribution of each term to the temperature calculation and where to truncate the series if the full accuracy is not required. ®
PROGRAM 1. BASIC subroutine for evaluating the temperature T from the Chebychev series using equations (1) and (3). An array Tc(Ndegree) should be dimensioned. 100 REM Evaluation of Chebychev series 110 X= ((V-VL)-(VU-V))/(VU-VL) 120 Tc(0) = 1 130 Tc(1) = X 140 T = A(0) + A(1) *X 150 FOR I = 2 to Ndegree 160 Tc(l) = 2*X*Tc(l-1)-Tc(l-2) 170 T = T + A(l) *Tc(l) 180 NEXT 1 190 RETURN
2.0 to 12.0 K A(0) = 7.556358 A(1) = -5.917261 A(2) = 0.237238 A(3) = 0.334636 A(4) = -0.058642 A(5) = -0.019929 A(6) = -0.020715 A(7) = -0.014814 A(8) = -0.008789 A(9) = -0.008554 12.0 to 24.5 K A(0) = 17.304227 A(1) = -7.894688 A(2) = 0.453442 A(3) = 0.002243 A(4) = 0.158036 A(5) = -0.193093 A(6) = 0.155717 A(7) = -0.085185 A(8) = 0.078550 A(9) = -0.018312 A(10) = 0.039255 24.5 to 100.0 K A(0) = 71.818025 A(1) = -53.799888 A(2) = 1.669931 A(3) = 2.314228 A(4) = 1.566635 A(5) = 0.723026 A(6) = -0.149503 A(7) = 0.046876 A(8) = -0.388555 A(9) = 0.056889 A(10) = -0.116823 A(11) = 0.058580 100 to 475 K A(0) = 287.756797 A(1) = -194.144823 A(2) = -3.837903 A(3) = -1.318325 A(4) = -0.109120 A(5) = -0.393265 A(6) = 0.146911 A(7) = -0.111192 A(8) = 0.028877 A(9) = -0.029286 A(10) = 0.015619
VL = 1.32412 VU = 1.69812
VL = 1. 11732 VU = 1.42013
VL = 0.923174 VU = 1.13935
VL = 0.079767 VU = 0.999614
PROGRAM 2. BASIC subroutine for evaluating the temperature T from the Chebychev series equations (1) and (4). ACS is used to represent the arccosine function. 100 110 120 130 140 150 160
Z-93
REM Evaluation of Chebychev series X = ((V-VL)-(VU-V))/(VU-VL) T=0 FOR I = 0 to Ndegree T = T + A(I)*COS(I*ACS(X)) NEXT I RETURN
Resolution and Accuracy of Cryogenic Temperature Measurements D. Scott Holmes and S. Scott Courts Lake Shore Cryotronics, Inc., Westerville, Ohio 43081-2399 A procedure is outlined and typical data provided for calculation of achievable resolutions and accuracies using commercially available cryogenic temperature sensors suitable for use as secondary or tertiary standards. Differences between resolutions achievable in absolute temperature measurements as opposed to measurements of temperature changes are discussed. Methods for estimating or determining errors are discussed and typical sensor calibration errors are given.
ε εV / V εrel —T = ——————— [ — T (T / V) (dV /dT) S
INTRODUCTION Temperature resolution and accuracy are important, but are not the only, considerations when choosing a temperature sensor and its associated measurement system. Other considerations include: sensor size or thermal mass, stability over time, response time, mechanical shock resistance, interchangeability, measurement system simplicity, cost, magnetic field effects, and resistance to ionizing radiation. The scope of this paper is limited to the estimation of resolutions and accuracies possible when making cryogenic temperature measurements with commercially available temperature sensors. Cryogenic temperature sensors have been developed based on a variety of temperature-dependent properties (1). Common, commercially available sensors include resistors, capacitors, thermocouples, and semiconductor junction devices such as diodes or transistors. The temperaturedependent characteristics of such sensors are published elsewhere (2,3). Such sensors, suitable for use as a secondary or tertiary temperature standards, are of primary concern in this paper. Primary standards-grade sensors are very sensitive to thermal and mechanical shock and are therefore not suitable for ordinary laboratory or industrial temperature measurements. Other temperature measurement techniques such as gas, vapor pressure, acoustic, noise, and magnetic susceptibility thermometry, are not covered by this paper as they require much greater effort to implement or they severely constrain system design. Temperature resolution is the smallest temperature change that can be detected. The precision (or reproducibility or stability) is a measure of how closely the measured values are grouped. Accuracy is indicated by the difference between measured and true values of a parameter. The accuracy of a single measurement can be no better than the resolution, but is degraded by calibration and measurement errors. The relevant equations for determining resolution and accuracy depend on whether the measurement is of the absolute temperature or of a temperature change. In either case, the achievable resolution depends on 1) the sensor characteristics and 2) the measurement system resolution. The accuracy of a temperature measurement can be evaluated using error analysis.
ABSOLUTE TEMPERATURE RESOLUTION
The temperature resolution εT of a thermometer measuring a temperature T is limited by the measurement system resolution εv according to the expression
εV εT = ———— dV / dT
(1)
when the sensitivity dV/dT of the thermometer does not change significantly within εT of the temperature, T. The measured parameter and the system resolution, V, are assumed to be voltages in Equation 1. The sensitivity dV/dT can be written as I(dR/dT) in the case of a ohmic resistance thermometer excited with a constant current, I. Equation 1 can be put in dimensionless form by dividing both sides by T and dividing the numerator and denominator of the right hand side by V, yielding
(2)
The dimensionless group in the numerator is the relative measurement system resolution, εrel, consisting of the measurement system resolution, εV, divided by the voltage measured. The denominator consists of S [ (T/V)(dV/dT), known as the specific sensitivity, giving the relative temperature sensitivity of the thermometer at temperature T. The specific sensitivity is also equal to (d InV/d InT), the slope of the parameter versus temperature on a log-log plot. Note that equations 1 and 2 can be made to apply to thermometers based on other temperature-dependent properties (e.g., capacitance, resistance or pressure) by replacing V with C, R or P. The dimensionless nature of Equation 2 makes somewhat easier the comparison of thermometers based on different temperature-dependent properties. Specific sensitivities of some representative cryogenic temperature sensors are plotted in Figure 1. Sensors of the same type made by different manufacturers may have similar characteristics. Nonmetallic sensors of the same type but different nominal resistances usually have different S versus T characteristics. Metallic resistance thermometers should all fall on the same line with some exceptions: variations in residual resistance cause differences in specific sensitivity at lower temperatures, and the sensitivity of alloys such as Rh-Fe also depends on the concentration of the active impurity. A specific sensitivity in the 0.1 to 10 range is usually best for temperature measurements over a wide range, although other factors can be much more important. A large specific sensitivity allows the resolution of small temperatures relative to the temperature measured, but the temperature range becomes limited if the value of the property measured becomes too large or small to be determined accurately with the measurement system. The relative absolute temperature resolution is also a function of the relative measurement system resolution, εrel = εv /V (εc/C for capacitance measurements). As an example, a germanium resistance sensor with a specific sensitivity of -2.14 and resistance of 1000 Ω at a temperature of 4.2 K, 1 µA excitation current, and a measurement system with 1 µV resolution would provide an absolute temperature resolution of about 2 mK. Note that the sensor excitation current affects the output voltage (V = IR), and thus the relative measurement system resolution, so the sensor and the measurement system are not independent. Absolute temperature resolutions calculated using Equation 2, the specific sensitivities plotted in Figure 1, and sample excitations and system resolutions are plotted in Figure 2. The temperature resolutions plotted in Figure 2 were calculated only as a demonstration of how to calculate temperature resolutions for a variety of different sensors; different operating conditions, sensor models, or measurement equipment can greatly affect the achievable resolution. Optimization of the temperature resolution is dependent on both the sensor properties and the measurement system. The minimum resolvable temperature is not merely a matter of finding a sensor with the highest specific sensitivity. Some examples of interactions between sensor properties and measurement system resolution follow.
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15 10 CGR
Absolute Temperature Resolution, T (K)
YSI CS-501
Specific Sensitivity (S)
GR
1
Au-Fe Thermocouple Rh-Fe
0.1 GaAlAs Diode Si Diode RO
Pt CLTS
0.01 1
10 100 500 Temperature (K) Figure 1. Absolute values of specific sensitivities of representative commercial cryogenic temperature sensors. Model numbers refer to Lake Shore sensors except where noted. Au-Fe thermocouple: KP chromel vs. Au-0.07%Fe, CGR: CGR-1-1000 carbon-glass resistor, CLTS: Vishay Micro-Measurements CLTS-2 metal foil gauge, CS-501: CS501 capacitor, GaAlAs diode: TG-120P gallium-aluminumarsenide @ 10 µA, GR: GR-200A-1000 germanium resistor, Pt: Pt-103 platinum resistor, Rh-Fe: RF-800-4 rhodium-iron resistor, RO: Scientific Instruments RO-600 ruthenium oxide sensor, Si diode: DT-470 @ 10 µA, YSI: Yellow Springs Instruments 44003A thermistor.
Temperature (K) Figure 2. Absolute temperature resolutions of representative commercial cryogenic temperature sensors under the following operating conditions: Au-Fe thermocouple: versus KP chromel, CGR: 1-3 mV or I = 0.1 µA minimum, CLTS: 10 µA, CS-501: 5 kHz charging current, GaAlAs diode: 10 µA, GR: 1-3 mV or I = 0.1 µA minimum, Pt: 100 µA, Rh-Fe: 300 µA, RO: 10 µA, Si diode: 10 µA, YSI: 1 µW. Relative measurement system resolution: capacitance: εrel = 0.1 pF/C; voltage: εrel = 0.1 µV/V or 10-5, whichever is larger. Refer to Figure 1 for sensor identification.
As a first example, gold-iron versus chromel thermocouples have what appears to be a nearly ideal specific sensitivity near unity across the entire 1 to 300 K temperature range. Unfortunately, thermocouples suffer from very small signal output, which can decrease the temperature resolution possible from a given measurement system. Thermocouples are also affected by nonuniformities in the wire and require a good understanding of thermocouple physics for proper installation and operation (4). A sensor with large specific sensitivity, such as a germanium resistor near 1 K, can be limited in resolution by power dissipation constraints. The germanium crystal requires strain-free mounting for accurate temperature readings and long term stability, but the strain-free mounting reduces the thermal contact between the sensor and the body whose temperature is to be measured, making the sensor more susceptible to self heating. The excitation current for germanium and carbon-glass sensors is typically adjusted to produce an output voltage in the 1 to 3 mV range, thereby maintaining a balance between signal level and power dissipation. Other sensors such as platinum or thick film resistors do not require strain-free mounting, so signal levels of thin film or encapsulated platinum sensors can be increased by operating with higher power dissipation. The trade off is that strain-free mounted platinum sensors are more stable over time. A diode is an example of a sensor that can have relatively low specific sensitivity, but large signal level, typically on the order of a volt. Potentials on the order of one volt can be measured with great resolution. Diodes, however, are nonohmic and thus constrained to constant current operation, which can lead to self-heating problems at low temperatures.
RELATIVE TEMPERATURE RESOLUTION Better resolution is possible with the same measurement system when measuring temperature changes (relative temperatures) smaller than the absolute temperature. The reason for this fact is that only the change in the value, and not the entire value, must be measured. In this case, Equation 2 is not valid since the specific sensitivity is defined using the full parameter value (e.g., V) whereas the relative system response requires the change in the measured value (e.g., ∆V). Equation 1 is valid, but provides little guidance for optimizing the resolution of relative temperature measurements. Equation 2 can be modified to apply to relative temperature measurements by multiplying the right hand side by (∆V/∆V), yielding the expression
εT = ∆ V εV / ∆V ∆V εrel ––– –– –––––––––– [ –– —– T V (T/V)(dV/dT) V S
(3)
The resolvable temperature is seen to be reduced by a factor of (∆V/V) if εrel remains the same as for an absolute temperature measurement. In practice, the system resolution, εV, is ordinarily not reduced in proportion to the ratio (∆V/V) so less resolution gain is realized. Note that both equations 1 and 3 implicitly or explicitly require knowledge of the absolute temperature, T (the sensitivity dV/dT at temperature T is required in Equation 1). This problem can be avoided by using a thermometer with a linear response to temperature. Alternately, the relative temperature can be measured with one thermometer while the absolute temperature is measured with a second thermometer, but the accuracy of the absolute temperature measurement will affect the accuracy of the relative temperature measurement.
Optimization of the absolute temperature resolution can require complex tradeoffs between sensor and measurement system costs and capabilities.
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SOURCES OF MEASUREMENT ERROR Equations 1 - 3 can be used to calculate the temperature resolution (or error) once the measurement system resolution (or error) is specified. This section discusses the sources of the errors and how to determine their magnitudes. Error sources include the sensor calibration, the applied excitation, measurement system calibration, thermal voltages, noise, sensor self-heating and poor thermal grounding of the sensor. The total error arising from several independent error sources is usually calculated in one of two ways. The worstcase error, εWC, can be estimated by direct summation of all errors
εWC = ε1 + ε2 +···+ εi +···+ εn
(4)
where εi is the i th of n total errors.
The most probable error, εMP, can be estimated by assuming a statistical distribution of errors, in which case the errors are summed in quadrature according to
ß ß ßεß εMP = œ ßε1ß +ß ßε2ß+···+ +···εn2 i ß 2
2
2
(5)
The worst-case and most probable errors must be computed from errors of the same dimensions. Dimensionless relative system errors can be summed using either Equations 4 or 5 and then translated to temperature errors using Equations 2 or 3. Getting statistical data suitable for addition by quadrature can be a problem; instrument and sensor specifications commonly give maximum rather than most probable or typical values for errors. Two approaches may be taken to dealing with maximum error specifications. The conservative approach is to use the specification limit value in worst case or most probable error calculations. The less conservative approach is to assume a statistical distribution within the specification limits and assume the limit is roughly three standard deviations, in which case one-third of the specification limit is used in error calculations. The manufacturer may be able to supply additional information to help improve error estimates.
Thermoelectric Voltages and Zero Offsets Voltages develop in electrical conductors with temperature gradients when no current is allowed to flow (thermal EMF’s). Thermoelectric voltages appear when dissimilar metals are joined and joints are held at different temperatures. Typical thermoelectric voltages in cryogenic measurement systems are on the order of microvolts. A zero offset is the signal value measured with no input to the measuring instrument. The zero offset can drift with time or temperature and is usually included in the instrument specifications. Thermoelectric voltages and zero offsets can be eliminated from voltage measurements on ohmic resistors by reversal of the excitation current and use of the formula:
V = (V+ - V_)/2
(7)
where V+ and V_ are the voltages with respectively positive and negative excitation currents. Alternating current (ac) excitation can also be used with ohmic sensors to eliminate zero offsets. Measurements made in rapid succession might not allow time for current switching and the required settling times. The error can be reduced by measuring the offset before and after a series of rapid measurements and subtracting the offset voltage from the measured voltages. The sum of the thermoelectric voltages and zero offset can be calculated as
Vo = (V+ + V_)/2
Voltage or Frequency Measurement Errors
(8)
Note that the resolution of Vo is practically limited by the resolution of the measurement system. The value of Vo can be expected to vary little in a static system, but may change during a thermal transient under study. The value of Vo should be rechecked as often as is practical.
The accuracy of instrumentation such as voltmeters and frequency counters is subject to calibration uncertainty and drift with time and operating temperature. Accuracies of such instruments should be available from the manufacturer.
Excitation Current Error The temperature measurement error due to an error in the excitation current can be calculated from Equation 2 by replacing the quantity εV /V by the relative voltage change due to the current error. The resulting expression is
ε (εI /I)(Rd /Rs) —T = ————— T S
• π/2 times the upper 3 db frequency limit of the analog dc measuring circuitry, given as approximately 1/(4 Reff Cin) where Reff is the effective resistance across the measuring instrument (including the instrument’s input impedance in parallel with the sensor resistance and wiring) and Cin is the total capacitance shunting the input; • 0.55/tr where tr is the instrument’s 10-90% rise time; • one Hz if an analog panel meter is used for readout; or • one-half the conversion rate (readings per second) of an integrating digital voltmeter.
(6)
where Rd and Rs are the dynamic and static resistances of the sensor. Note that the dynamic and static resistances of an ohmic sensor are equal. Typical dynamic resistances of a Lake Shore DT-470 silicon diode are 3000 Ω at 300 K, 1000 Ω at 77 K, and 2800 Ω at 4.2 K, while the static resistances are respectively 51.9 kΩ, 102 kΩ and 163 kΩ.
Thermal (Johnson) Noise Thermal energy produces random motions of the charged particles within a body, giving rise to electrical noise. The minimum rms noise power available is given by Pn = 4kT∆fn, where k is the Boltzmann constant and ∆fn is the noise bandwidth. Peak-to-peak noise is approximately five times greater than the rms noise. Metallic resistors approach this fundamental minimum, but other materials produce somewhat greater thermal noise. The noise power is related to current or voltage noise by the relations: I = [Pn /R]1/2 and V = [PnR]1/2. The noise bandwidth is not necessarily the same as the signal bandwidth, but is approximately equal to the smallest of (5):
The offset voltage Vo is best measured by reversing the current through a resistor. Measurement of Vo with zero excitation current is also possible, but large resistances can produce excessive time constants for discharge of any capacitances in the circuit, requiring long waiting times before Vo can be measured accurately. Measurements on diodes do not allow current reversal. The value of Vo can be estimated by shorting the leads at the diode and measuring the offset voltage with zero excitation current at operating temperature.
Ground Loops and Electromagnetic Noise Improper grounding of instruments or grounding at multiple points can allow current flows which result in small voltage offsets. One common problem is the grounding of cable shields at both ends. The current flow through ground loops is not necessarily constant, resulting in a fluctuating error voltage. Electromagnetic pickup is a source of additional noise. Alternating current noise is a serious problem in sensors with nonlinear current-voltage characteristics (6). Measurement of the ac noise across the terminals of the reading instrument can give a quick indication of the magnitude of this noise source (thermal noise will be included in this measurement). Books on grounding and shielding can help to identify and eliminate both ground loops and electromagnetic noise (7,8).
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Self Heating Heat dissipated within a temperature sensor causes its temperature to rise, resulting in an error relative to the sensor’s surroundings. Self heating errors might not affect relative temperature measurements. Attempting to correct for self heating errors by calculation or extrapolation is not considered good practice. An estimate of the self heating error should be included in the total error calculation instead. An easy way to check for self heating is to increase the power dissipation and check for an indicated temperature rise. Unfortunately, this procedure will not work with diodes. An indication of the self heating error can be made by reading the diode temperature in both a liquid bath and in a vacuum at the same temperature, as measured by a second thermometer not dissipating enough power to self heat significantly.
Calibration Uncertainty Commercially calibrated temperature sensors should have calibrations traceable to international standards. Calibration uncertainties for sensors calibrated by Lake Shore are provided later in this paper. The calibration uncertainty of the temperature sensor must be included in accuracy calculations.
Interpolation Errors Once a calibration has been performed, an interpolation function is required for temperatures which lie between calibration points. The interpolation method must be chosen with care since some fitting functions can be much worse than others. Common interpolation methods include linear interpolation, cubic splines and Chebychev polynomials. Formulas based on the physics of the sensor material may give the best fits when few fit parameters are used. Use of an interpolation function adds to the temperature measurement uncertainty. The additional uncertainty due to an interpolation function can be gauged by the ability of the interpolation function to reproduce the calibration point temperatures from the calibration point resistances. Lake Shore calibration reports include the mean and largest deviations. Fitting with Chebychev polynomials is standard practice. Each calibration can be broken up into several ranges to decrease the fitting errors. Typical errors introduced by the interpolation function are on the order of one-tenth the calibration uncertainty.
CALIBRATION SYSTEM EXAMPLE
Figure 3. Calibration cryostat schematic block and surrounding chamber cool to a nominal temperature of 4.2 K. The transfer gas is then pumped out. To obtain temperatures below 4.2 K, the subpot is filled with liquid helium and vacuum pumped. As the vapor pressure of the helium liquid in the subpot decreases, the temperature decreases. The pumping is controlled by a high resolution pumping valve. The subpot bath temperature is not actively controlled. Depending on the pumping speed and base pressure, temperatures as low as 1.05 K can be reached. To obtain temperatures above 4.2 K, the subpot is pumped dry and the heater is energized by the temperature controller. A diode monitors the nominal temperature of the isothermal shield and calibration block and the temperature is read by the temperature controller. The heater is used to bring the temperature to a point just below the desired temperature. The heater power is then reduced so that the temperature is increasing on the order of a millikelvin per minute. Data are taken when the drift rate is sufficiently small (typically about 10 minutes).
Electronic Equipment
The example to be discussed in detail is the cryogenic temperature calibration facility operated by Lake Shore. This facility is designed to calibrate a variety of resistance and diode temperature sensors over the temperature range of 1.2 to 330 K.
Physical Construction Calibrations are performed by mounting sensors on a probe to be inserted in a liquid helium cryostat (see Figure 3). The sensors are mounted in a gold-plated OFHC copper calibration block which provides an isothermal environment. Special adapters and a variety of calibration blocks allow calibration of sensors with varying shapes and sizes. The electrical leads from the sensors are soldered to contacts thermally anchored to a second gold-plated OFHC copper block directly above the calibration block. The thermal anchoring block is attached to a flange, on top of which is a liquid helium subpot. Surrounding the thermal anchoring and calibration blocks is an isothermal OFHC copper shield. The shield has a resistance wire heater wound around the outside with several layers of super-insulation overwrap to reduce thermal radiation to or from the vacuum can. Thermoelectric voltages are minimized by using continuous wire from the thermal anchoring block to the low thermal EMF connectors at the top of the probe which is at room temperature.
The electronic equipment used in this facility consists of a HP3456A voltmeter, a Keithley model 224 variable current source, five Lake Shore model 8085 scanners, a Lake Shore DRC-82C temperature controller, five Guildline 9330 standard resistors (10 Ω, 100 Ω, 1 kΩ, 10 kΩ and 100 kΩ values), a 1000 Ω germanium standard thermometer and a 100 Ω platinum standard thermometer. Other electronic equipment such as the computer used for system control has no effect on the accuracy of the system. A block diagram of the equipment connection scheme is shown in Figure 4. Data acquisition is computer controlled. Two scanners are used to switch between each of twenty unknown sensors, one scanner is used to place one of the standard resistors into the circuit, one scanner chooses between the germanium and platinum standard, and the last scanner chooses whether the voltmeter measures the voltage drop across the unknown sensor or the standard resistor. current source computer
standard resistors
scanners temperature sensors
Operation
voltmeter
During cooldown, a small amount of helium gas is introduced into the vacuum chamber to act as a transfer medium. The cryostat is then filled with liquid helium and the calibration
Figure 4. Thermometer calibration facility instrumentation block diagram
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Resistance Measurements The resistance of a sensor is measured by comparison with a standard resistor. Long term stability of resistor standards tends to be somewhat better than the long term stability of current sources, so overall accuracy is improved over methods relying on a calibrated current source. The normal operating procedure is to place a resistor standard in series with the sensor whose resistance is to be measured. A voltmeter reading is taken with current in both the forward and reverse directions across the sensor. Voltmeter readings are then taken with current in both the forward and reverse directions across the standard resistor. The resistance of the sensor can be calculated using the relation
Rsensor =
(V+ - V_)sensor —————————— (V+ - V_)standard
x Rstandard
Nominal Value of Working Standard Resistor R (Ω)
1 Year Base Uncertainty of Primary Standard Resistor A
Voltmeter Transfer Accuracy B
Error From Possible Room Temperature Fluctuations C
15 15 20
6 6 6
5 5 5
100 1000 10000
(9)
17 17 22
26 26 31
Table I. Uncertainty estimates for calibrations of working standard resistors. Errors and uncertainties are expressed in parts per million (±ppm). Typical values are calculated by quadrature (MP) and worst case (WC) values by direct summation.
where V+ and V_ are the voltages measured with current in the forward and reverse directions respectively. Measuring and averaging voltage for current in both forward and reverse directions serves two purposes: errors due to thermoelectric voltages are eliminated and voltmeter offsets are canceled out. In this situation, the voltmeter transfer specification, rather than the absolute measurement specification, applies. The gain in accuracy is about a factor of ten over using the voltmeter as an absolute measurement device.
T (K) 1.5 4.2 10. 20. 30. 50. 100. 300.
Diode Measurements Diode measurements are no more difficult to perform but typically less accurate. The reduced accuracy is a consequence of the nonlinear current-voltage characteristic of diodes. The voltage across the diode can be measured only in the forward direction, so the voltmeter must now make an absolute measurement. Without current reversal, thermoelectric voltages and voltmeter offsets may be present and these directly affect the achievable accuracy. The longterm accuracy and stability of the current source is also a factor. Fortunately, the small dynamic resistance reduces the error due to small current errors by a factor of 100 to 1000 (6).
Total Uncertainty for Working Standard Resistor MP WC
CGR-1-1000 (mK) 1 1 3 10 19 41 110 425
GR-200A-1000 (mK) 1 1 2 6 10 20 76 -
PT-103 (mK) 14 5 3 6 16
Table II. Temperature measurement uncertainties in millikelvin for carbon glass (CGR), germanium (GR) and platinum (PT) sensors.
Calibration Calibration is accomplished by comparison calibration against standard thermometers. Two standard thermometers are used: a germanium resistance thermometer for the 1 to 28 K range and a platinum resistance thermometer for the 28 to 330 K range. A standard sensor reading is taken before and after every unknown sensor reading. The initial and final readings are averaged to compensate for temperature drifts between the time the standard and unknown are read.
Total System Accuracy Calculation
T [K] εT [mK]:
20 10
30 15
50 15
100 15
300 20
Table III. Uncertainties in realizing the ITS-90 temperature scale at the Lake Shore calibration facility.
The attainable accuracy for a temperature measurement system depends on a number of variables. Lake Shore bases its calibrations on a calibrated voltmeter and calibrated working resistance standards to transfer a temperature scale from working temperature standards to unknown resistance temperature sensors. Calculating the total system accuracy requires information such as absolute and transfer specifications for equipment being used and a derating schedule for the calibration of the equipment. Some of this information is normally supplied with the equipment, but other parts are not. The manufacturer is the best source for this information. Keep in mind, however, that the degradation of the equipment is directly dependent upon its use and treatment. Our voltmeters are calibrated every six months to ensure they meet their transfer specifications. Primary standard resistors are calibrated once per year. The working resistance standards are calibrated every six months against the primary standard resistors.The following table lists typical uncertainties for the 10 Ω, 100 Ω, 1000 Ω and 10 kΩ working standard
<10 5
T (K) 1.5 4.2 10. 20. 30. 50. 100. 300.
CGR-1-1000 [mK]
GR-200A-1000 [mK]
MP
WC
MP
WC
5 5 5 20 35 55 125 450
4 4 4 8 12 20 45 -
5 5 5 15 25 35 90 -
4 4 4 10 20 30 65 250
PT-103 [mK] MP
WC
15 10 10 10 20
Table IV. Total temperature measurement uncertainties relative to ITS-90 in millikelvin for carbon glass (CGR), germanium (GR) and platinum (PT) sensors.
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25 20 20 20 35
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resistors. Uncertainties arise from shifts in the primary standard resistances, limitations of the voltmeter as a transfer device, and dependence of the voltmeter and standard resistors on variations in room temperature. The total errors from the standard resistors due to calibration shifts and operating temperature variations are listed in Table I in terms of parts per million (ppm). The uncertainty estimates can be converted into equivalent temperature uncertainties given the temperature and specific sensitivity of the sensor measured using Equation 2. Using the voltmeter as a transfer standard gives an improved accuracy over using it to make absolute measurements. The transfer accuracy of the voltmeter is roughly ±10 counts which translates to about ±1 µV on an absolute scale in the millivolt range. Signals for carbon glass and germanium sensors are kept between 1 and 3 mV so this is equivalent to a relative accuracy, εrel, of about 0.05%. Platinum sensors are read at a power somewhat less than 10 µW and produce voltage signals ranging from 3.5 mV at 30 K (1 mA current) to 27.5 mV at 300 K (0.25 mA). The voltmeter relative accuracy for 100 Ω platinum sensors ranges from 0.03% at 30 K to about 0.0036% at 300 K. Higher accuracy at higher temperatures is also observed in rhodiumiron sensors. Equivalent temperature uncertainties are given in Table II for a typical carbon glass resistor (model CGR-11000), germanium resistor (model GR-200A-1000) and a platinum resistor (model PT-103). The uncertainties due to calibration transfer of the resistance standards and that of the voltmeter transfer accuracies have been added together in this table.
REFERENCES 1. L.G. Rubin, B.L. Brandt and H.H. Sample, “Cryogenic thermometry: a review of recent progress, II,” Cryogenics 22 (1982) 491-503. 2. L.L. Sparks, “Temperature, strain and magnetic field measurements,” in Materials at Low Temperatures, R.P. Reed and A.F. Clark, eds., American Society for Metals, Ohio (1983) 515-571. 3. S.S. Courts, D.S. Holmes, P.R. Swinehart and B.C. Dodrill, “Cryogenic thermometry—an overview,” Applications of Cryogenic Technology, Vol. 10, Plenum Press, New York (1991) 55-69. 4. P.L. Walstrom, Spatial dependence of thermoelectric voltages and reversible heats, Am. J. Phys. 56 (1988) 890-894. 5. Low Level Measurements , Keithly Instruments, Inc., Cleveland, Ohio, U.S.A. (1984). 6. J.K. Krause and B.C. Dodrill, “Measurement system induced errors in diode thermometry, Rev. Sci. Instrum. 57 (1986) 661-665. 7. H.W. Ott, Noise Reduction Techniques in Electronic Systems, John Wiley & Sons, New York (1976). 8. R. Morrison, Grounding and Sheilding Techniques in Instrumentation, John Wiley & Sons, New York (1977).
Another important source of error comes from the error limits assigned to the secondary temperature standards calibrated by national standards laboratories. Based on estimates given in NBS Monograph 126 concerning the accuracy of the fixed points maintained at NIST (National Institute for Standards and Technology, formerly NBS) and the variations observed in platinum thermometers, an uncertainty estimate of ±5 mK can be made. Added to this uncertainty is the measurement uncertainty from Table II. Germanium standards (1000 Ω) are used below 28 K and platinum standards (100 Ω) are used above 30 K. The measurement uncertainty added to the calibration uncertainty of the secondary temperature standards gives the overall uncertainty in realizing the ITS-90 temperature scale. The uncertainty of Lake Shore calibrations relative to ITS-90 is given in Table III at several temperatures. The temperature resolution of the Lake Shore Calibration Facility is generally a factor of 10 or more better than our accuracy specification. The total error of a given calibration is the combination of the first three tables. The total error is given in Table IV for the same representative temperature sensors included in Table II. The total uncertainty is expressed as millikelvin deviation from ITS-90. Two columns are given for each sensor. The “MP” column is the estimated most probable error of a given calibration computed using summation by quadrature. The “WC” column is the unlikely worst case error computed by direct summation of all error sources.
CONCLUSION The accuracies stated apply only to the sensors as calibrated. An end user must be careful to distinguish between the desired measurement accuracy and the calibration accuracy of the sensor alone. Errors introduced by the user’s measurement system, rough handling and inadequate thermal contact will add to the calibration uncertainty. An estimate of the accuracy of a temperature sensor can be made by combining the errors due to calibration, interpolation and the measurement system. Errors can be added in quadrature to give the most probable error, or can be summed directly to give worst case error.
Reproduced with permission of the American Institute of Physics and Lake Shore Cryogenics.
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Heat Wave
A National Problem
Heat kills by taxing the human body beyond its abilities. In a normal year, about 175 Americans succumb to the demands of summer heat. Among the large continental family of natural hazards, only the cold of winter–not lightning, hurricanes, tornadoes, floods or earthquakes–takes a greater toll. In the 40-year period from 1936 through 1975, nearly 20,000 people were killed in the United States by the effects of heat and solar radiation. In the disastrous heat wave of 1980, more than 1,250 people died. And these are the direct casualties. No one can know how many more deaths are advanced by heat wave weather - how many diseased or aging hearts surrender that under better conditions would have continued functioning. North American summers are hot; most summers see heat waves in one section or another of the United States. East of the Rockies, they tend to combine both high temperature and high humidity although some of the worst have been catastrophically dry.
Heat Index/Heat Disorders Heat Index 130° or Higher 105° to 130°
90° to 105° 80° to 90°
Possible Heat Disorders for People in Higher Risk Groups Heatstroke/sunstroke highly likely with continued exposure Sunstroke, heat cramps or heat exhaustion likely, with heatstroke possible with prolonged exposure and / or physical activity Sunstroke, heat cramps and heat exhaustion possible with prolonged exposure and / or physical activity Fatigue possible with prolonged exposure and / or physical activity
Summary of NWS’s Alert Procedures
NOAA’S National Weather Service Heat Index Program Considering this tragic death toll, the National Weather Service (NWS) has stepped up its efforts to alert more effectively the general public and appropriate authorities to the hazards of heat waves - those prolonged excessive heat/humidity episodes. Based on the latest research findings, the NWS has devised the “Heat Index” (HI), (sometimes referred to as the “apparent temperature”). The HI, given in degrees F, is an accurate measure of how hot it really feels when relative humidity (RH) is added to the actual air temperature. To find the HI, look at the Heat Index Chart. As an example, if the air temperature is 95°F (found on the left side of the table) and the RH is 55% (found at the top of the table), the HI - or how hot it really feels - is 110°F. This is at the intersection of the 95° row and the 55% column. IMPORTANT: Since HI values were devised for shady, light wind conditions, EXPOSURE TO FULL SUNSHINE CAN INCREASE HI VALUES BY UP TO 15°F. ALSO, STRONG WINDS, PARTICULARLY WITH VERY HOT, DRY AIR, CAN BE EXTREMELY HAZARDOUS. Note on the HI chart the shaded zone above 105°F. This corresponds to a level of HI that may cause increasingly severe heat disorders with continued exposure and/or physical activity. The “Heat Index vs. Heat Disorder” table (next to the HI chart) relates ranges of HI with specific disorders, particularly for people in higher risk groups.
The NWS will initiate alert procedures when the HI is expected to exceed 105°-110°F (depending on local climate) for at least two consecutive days. The procedures are: • Include HI values in zone and city forecasts. • Issue Special Weather Statements and/or Public Information Statements presenting a detailed discussion of (1) the extent of the hazard including HI values, (2) who is most at risk, (3) safety rules for reducing the risk. • Assist state/local health officials in preparing Civil Emergency Messages in severe heat waves. Meteorological information from Special Weather Statements will be included as well as more detailed medical information, advice, and names and telephone numbers of health officials. • Release to the media and over NOAA’s own Weather Radio all of the above information.
How Heat Affects the Body Human bodies dissipate heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and - as the last extremity is reached - by panting, when blood is heated above 98.6 degrees. The heart begins to pump more blood, blood vessels dilate to accommodate the increased flow, and the bundles of tiny capillaries are threading through the upper layers of skin are put into operation. The body’s blood is circulated closer to the skin’s surface, and excess heat drains off into the cooler atmosphere. At the same time, water diffuses through the skin as perspiration. The skin handles about 90 percent of the body’s heat dissipating function.
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Z
Heat Wave Cont’d
AIR TEMPERATURE (°F)
RELATIVE HUMIDITY (%) 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70
0
5
125 120 117 111 107 103 99 95 91 87 83 78 73 69 64
128 122 116 111 107 102 97 93 88 84 79 74 69 64
10
131 123 116 111 105 100 95 90 85 80 75 70 65
15
131 123 115 108 102 97 91 86 81 76 71 65
20
141 130 120 112 105 99 93 87 82 77 72 66
25
139 127 117 109 101 94 88 83 77 72 66
30
148 135 123 113 104 96 90 84 78 73 67
35
40
45
50
55
60
65
70
75
80
85
90
95 100
Heat Index (or Apparent Temperature) 143 130 118 107 98 91 85 79 73 67
151 137 123 110 101 93 86 79 74 68
143 129 115 104 95 87 80 74 68
150 135 142 149 120 126 132 138 144 107 110 114 119 124 130 136 96 98 100 102 106 109 113 117 122 88 89 90 91 93 95 97 99 102 105 108 81 81 82 83 85 86 86 87 88 89 91 75 75 76 76 77 77 78 78 79 79 80 69 69 70 70 70 70 71 71 71 71 72
Heat Index Chart Air Temperature and Relative Humidity Versus Apparent Temperature
Sweating, by itself, does nothing to cool the body, unless the water is removed by evaporation–and high relative humidity retards evaporation. The evaporation process itself works this way: the heat energy required to evaporate the sweat is extracted from the body, thereby cooling it. Under conditions of high temperature (above 90 degrees) and high relative humidity, the body is doing everything it can to maintain 98.6 degrees inside. The heart is pumping a torrent of blood through dilated circulatory vessels; the sweat glands are pouring liquid–including essential dissolved chemicals, like sodium and chloride–onto the surface of the skin.
Ranging in severity, heat disorders share one common feature: the individual has overexposed or over exercised for his age and physical condition in the existing thermal environment.
Too Much Heat
Acclimatization has to do with adjusting sweat-salt concentrations, among other things. The idea is to lose enough water to regulate body temperature, with the least possible chemical disturbance.
Heat disorders generally have to do with a reduction or collapse of the body’s ability to shed heat by circulatory changes and sweating, or a chemical (salt) imbalance caused by too much sweating. When heat gain exceeds the level the body can remove, or when the body cannot compensate for fluids and salt lost through perspiration, the temperature of the body’s inner core begins to rise, and heat-related illness may develop.
Sunburn, with its ultraviolet radiation burns, can significantly retard the skin’s ability to shed excess heat. Studies indicate that, other things being equal, the severity of heat disorders tend to increase with age–heat cramps in a 17-year old may be heat exhaustion in someone 40, and heat stroke in a person over 60.
Reprinted with permission of National Weather Service.
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Dew Point
% HUMIDITY 2
10
5
30
20
40
50
60
70 90 80 100
70 65 60
Charts based on:
55
td - ta 17.5 ––––––––– td + 240.97
)
50 45 AIR TEMPERATURE (°C)
H =100«
(
where H = relative humidity (%) td = dewpoint temperature (°C) ta = air temperature (°C)
Z
40 35 30 25 20 15 10 5 0 -10
-5
0
5
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15
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35
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55
60
65
70
DEWPOINT TEMPERATURE (°C)
% HUMIDITY 2
5
10
20
30
40
50
70 90 60 80 100
160 150 140
To determine the dewpoint temperature: After measuring the air temperature and relative humidity, use the graph by drawing a horizontal line from the air temperature (Y-axis) to the appropriate relative humidity line. Then draw a vertical line from that intersection down to the dewpoint temperature (X-axis).
130
AIR TEMPERATURTE (°F)
120 110 100 90
®
80 70 60 50 40 32 10 20 30 40 50 60 70 80 90 100 110120 130 140 150 160 DEWPOINT TEMPERATURE (°F)
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Equilibrium ReIative Humidity Saturated SaIt Solutions Temperature °C 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Relative Humidity (%RH) Lithium Potassium Chloride Acetate 11.23 ± 0.54 11.26 ± 0.47 11.29 ± 0.41 11.30 ± 0.35 11.31 ± 0.31 11.30 ± 0.27 11.28 ± 0.24 11.25 ± 0.22 11.21 ± 0.21 11.16 ± 0.21 11.10 ± 0.22 11.03 ± 0.23 10.95 ± 0.26 10.86 ± 0.29 10.75 ± 0.33 10.64 ± 0.38 10.51 ± 0.44 10.38 ± 0.51 10.23 ± 0.59 10.07 ± 0.67 9.90 ± 0.77
23.28 ± 0.53 23.40 ± 0.32 23.11 ± 0.25 22.51 ± 0.32 21.61 ± 0.53
Magnesium Chloride 33.66 ± 0.33 33.60 ± 0.28 33.47 ± 0.24 33.30 ± 0.21 33.07 ± 0.18 32.78 ± 0.16 32.44 ± 0.14 32.05 ± 0.13 31.60 ± 0.13 31.10 ± 0.13 30.54 ± 0.13 29.93 ± 0.16 29.26 ± 0.18 28.54 ± 0.21 27.77 ± 0.25 26.94 ± 0.29 26.05 ± 0.34 25.11 ± 0.39 24.12 ± 0.46 23.07 ± 0.52 21.97 ± 0.60
Saturated Salt Solutions A very convenient method to calibrate humidity sensors is the use of saturated salt solutions. At any temperature, the concentration of a saturated solution is fixed and does not have to be determined. By providing excess solute, the solution will remain saturated even in the presence of modest moisture sources and sinks. When the solute is a solid in the pure phase, it is easy to determine that there is saturation. The saturated salt solution, made up as a slushy mixture with distilled water and chemically pure salt, is enclosed in a sealed metal or a glass chamber. Wexler and Hasegawa measured the humidity in the atmosphere above eight saturated salt solutions for ambient temperatures 0 to 50°C using a dewpoint hygrometer. Later, Greenspan compiled, from the literature, data on 28 saturated salt solutions to cover the entire range of relative humidity. Using a data base from 21 separate investigations comprising 1106 individual measurements, fits were made by the method of least squares to regular polynomial equations to obtain the “best” value of relative humidity in air as a function of temperature. These values are summarized in the table shown. ®
Relative Humidity (%RH) Temperature Potassium Magnesium Sodium Potassium °C Carbonate Nitrate Chloride Chloride 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
43.13 ± 0.66 43.13 ± 0.50 43.14 ± 0.39 43.15 ± 0.33 43.16 ± 0.33 43.16 ± 0.39 43.17 ± 0.50
60.35 ± 0.55 58.86 ± 0.43 57.36 ± 0.33 55.87 ± 0.27 54.38 ± 0.23 52.89 ± 0.22 51.40 ± 0.24 49.91 ± 0.29 48.42 ± 0.37 46.93 ± 0.47 45.44 ± 0.60
75.51 ± 0.34 75.65 ± 0.27 75.67 ± 0.22 75.61 ± 0.18 75.47 ± 0.14 75.29 ± 0.12 75.09 ± 0.11 74.87 ± 0.12 74.68 ± 0.13 74.52 ± 0.16 74.43 ± 0.19 74.41 ± 0.24 74.50 ± 0.30 74.71 ± 0.37 75.06 ± 0.45 75.58 ± 0.55 76.29 ± 0.65
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88.61 ± 0.53 87.67 ± 0.45 86.77 ± 0.39 85.92 ± 0.33 85.11 ± 0.29 84.34 ± 0.26 83.62 ± 0.25 82.95 ± 0.25 82.32 ± 0.25 81.74 ± 0.28 81.20 ± 0.31 80.70 ± 0.35 80.25 ± 0.41 79.85 ± 0.48 79.49 ± 0.57 79.17 ± 0.66 78.90 ± 0.77 78.68 ± 0.89 78.50 ± 1.0
Potassium Nitrate
Potassium Sulfate
96.33 ± 2.9 96.27 ± 2.1 95.96 ± 1.4 95.41 ± 0.96 94.62 ± 0.66 93.58 ± 0.55 92.31 ± 0.60 90.79 ± 0.83 89.03 ± 1.2 87.03 ± 1.8 84.78 ± 2.5
98.77 ± 1.1 98.48 ± 0.91 98.18 ± 0.76 97.89 ± 0.63 97.59 ± 0.53 97.30 ± 0.45 97.00 ± 0.40 96.71 ± 0.38 96.41 ± 0.38 96.12 ± 0.40 95.82 ± 0.45
Two-Wire Transmitters For Temperature Applications A two-wire transmitter is an ideal solution for many remote temperature measurement applications. Transmitters have definite advantages over conventional temperature measuring devices, but must be selected with caution in order to avoid “ground loop” problems. PURPOSE In many cases, the temperature of a remote process must be monitored. Common temperature sensing devices such as thermocouples and RTD’s produce very small “signals.” These sensors can be connected to a two-wire transmitter that will amplify and condition the small signal. Once conditioned to a usable level, this signal can be transmitted through ordinary copper wire and used to drive other equipment such as meters, dataloggers, chart recorders, computers or controllers. OPERATION A two-wire transmitter draws current from a remote dc power supply in proportion to its sensor input. The actual signal is transmitted as a change in the power supply current. Specifically, a thermocouple input transmitter will draw 4 mA of current from a dc power supply when measuring the lowest temperature of the process. Then, as the temperature rises, the two-wire transmitter will draw proportionally more current, until it reaches 20 mA. This 20 mA signal corresponds to the thermocouple’s highest sensed temperature. The transmitter’s internal signal-conditioning circuitry (powered by a portion of the 4-20 mA current) determines the temperature range that the output current signal will represent. Physically, only two copper wires are necessary to connect the transmitter output signal in a series circuit with the remote power supply and the process equipment. This is made possible since the signal and the power supply line are combined (one circuit serves a dual function). ADVANTAGES Two-wire transmitters offer numerous advantages over the more traditional ways of measuring temperature.
1.ac power is not needed at the remote location to operate a twowire transmitter. Since transmitters are powered by a low level 4-20 mA output current signal, no additional power has to be supplied at the remote location. In addition, the usual 24 Vdc signal necessary for operation is standard in plants that have large amounts of instrumentation. 2.Electrical noise and signal degradation are not a problem for two-wire transmitter users. The transmitter's current output signal lends itself to a high immunity when it comes to ambient electrical noise. Any noise that does appear in the output current is usually eliminated by the common-mode rejection of the receiving device. In addition, the current output signal will not change (diminish) with distance as most voltage signals do. 3.Wire costs drop significantly when using two-wire transmitters. Low voltage signals produced by thermocouples almost always require the use of shielded cable when they are sent any significant distance. Ambient electrical noise from arcing electrical relays, motors and ac power lines can raise havoc with these signals that are transmitted in an unshielded cable. In addition, expensive, heavy gage wire is often installed in applications that call for long cable runs (since it reduces errors from signal voltage drops caused by line resistance). Ordinary copper wire can be used to connect all the pertinent equipment in a two-wire transmitter system. The 4-20 mA current output signal is relatively immune to ambient electrical noise and is not degraded by long distance transmission, even over a small diameter wire. Adding a two-wire transmitter to a system eliminates the problem of having to provide long runs of costly wire and an extensive amount of shielding. GROUND LOOP PROBLEMS If a grounding rod was driven into the earth at two different points and a voltmeter was connected between them, a voltage difference would be detected between the two. This difference in potential exists between Z-104
practically any two points along the earth’s surface. When one tries to measure a process that is at a remote location, this voltage difference will induce an error current along the line, which is referred to as a “ground loop” signal. Its result will be an error at the display. To prevent “ground loop” errors of this type, select an isolating two-wire transmitter for your system. This type of transmitter will optoelectronically isolate the sensor signal from the output current loop. This will allow the user to ground both the sensor and one side of the current loop. TRANSMITTER FEATURES Transmitters provide a two-wire output with the same wiring used for power and output. The load resistance is connected in series with a dc power supply, and the current drawn from the supply is a 4-20 mA or output signal which is proportional to the input signal. Two-wire transmission permits remote mounting of the transmitter near the sensor to minimize the effects of noise and signal degradation to which low level sensor outputs are susceptible. A rugged metal enclosure, suitable for field mounting, offers environmental protection and screw terminal input and output connections. This enclosure may be either surface or standard relay track mounted. Most two-wire transmitters are linearized to the voltage signal produced by the thermocouple or RTD, although there are new models now available that are linearized to the actual temperature. The two-wire transmitters convert the thermocouple or RTD signal to a 4-20 mA output signal. Some models will convert to an RS-232C output. Transmitters are available with dip switch selection for several thermocouple types per model, as well as thermocouple and RTD selection on a single model. Two-wire transmitters are available in either isolating or non-isolating models, and they also feature output ranging adjustments with zero and span adjustments over 80 to 100% (depending on model) of the sensor range. ®
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Technical Information How to Use Ferrite Cores with Instrumentation OMEGA’s thermocouple and RTD connectors with built-in nickel-zinc ferrite cores are used where it is desired to suppress electro-magnetic, interference commonly known as EMI. Suppression of EMI has become a major concern in the instrumentation and control field. It is particularly important in handling and transmitting electronic data, as well as signals from transducers, such as thermocouples, thermistors and RTD’s. This is because lead wires, extension wires, and signal wires often act as antennae. OMEGA offers a family of nickel-zinc ferrites in our new OMEGA® ferrite connectors. This allows the user to reduce the “antenna effect”, which allows undesired signals to enter the instrumentation and controls. Ferrite Connectors The effectiveness of any ferrite core is based upon the material selection, number of wire turns around the core, and overall wire length. OMEGA’s ferrite connectors listed here have been developed for a multitude of general applications. The use of additional ferrite cores, as well as a specific selection of ferrite material, will provide a significant improvement in EMI suppression. While the OMEGA® ferrite connectors are designed for a multitude of applications, the amount of EMI suppression will vary from application to application. Please consult the factory for those applications where the standard OMEGA’s ferrite connectors may not be sufficient. Note: Built-in ferrite cores are available in male miniature connectors and both male and female standard size connectors.
OMEGA® Panel Meters and Controllers 1) OMEGA® Panel Meters and Controllers are intended for installation in metal panels which should be connected to Earth Ground. (Standard rack panels are available from OMEGA Engineering. In environments with extreme electromagnetic radiation, shielded EMI cabinets offer additional protection.) 2) NEVER run signal wires and power in the same conduit. 3) Whenever electromagnetic compatibility is an issue, always use SHIELDED CABLES for all inputs and outputs. (A vast selection of shielded signal cable is available from OMEGA Engineering.) Connect the shield to the analog signal ground if appropriate or to earth ground.
Patent applications pending in various countries
4) Install one (or more) FERRITE BEADS on each signal input wire close to the meter.
L
NA
SIG
R
WE
PO
HI LO GND
AC
N
Omega’s policy is to make running changes, not model changes, whenever an improvement is possible. This affords our customers the latest in technology and engineering.
Ferrite Beads supplied standard with all DP40 and DP25 meters.
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Electromagnetic Compatibility Electromagnetic Compatibility (EMC) may be a new term to some. However, it has been important for many years and actually predates World War II. For several decades, three agencies have been driving forces behind EMC: the U.S. Military; Europe’s Special International Committee on Radio Perturbations (Interference), CISPR; and the U.S. Federal Communications Commissions (F.C.C.).
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History EMC first began to be an issue in the military environment particularly on broad ships where many types of electronic equipment had to successfully operate in close proximity to each other. In such an environment, communication, navigation and data processing electronics all need to function simultaneously in the presence of strong radio frequency (RF) fields. Such RF fields are produced by two-way communications equipment, radar transmitters and microprocessor controlled devices. Added to this “mix,” on board a military ship is the presence of ordinance or explosives and aircraft fuel. In such an environment it becomes transparently clear that each device needs to be Electromagnetically Compatible with its environment and not be rendered inoperative or unsafe by this environment. Also each device added to this milieu must not unnecessarily or unintentionally contribute spurious emissions that do not perform any particular function. From the preceding, the origin of the two major aspects of EMC, emissions and immunity, can be seen. Due to the global proliferation of electronic devices in non-military living, it is becoming increasingly important that EMC be maintained in civilian settings as well. Residential and commercial environments may contain dozens of appliances that are controlled by microprocessors, i.e., kitchen stoves, video cassette recorders, TV’s, breadmakers, personal computers, etc. All electronic devices utilizing microprocessor technology generate radio frequencies.
Open Area Test Site (O.A.T.S.). Used for 3- and 10-meter testing. It is F.C.C. listed and NVLAP accredited. In addition, the site was assessed by ACEMARK Europe, LTD which is recognized by numerous European competent bodies.
For example, a 100 MHz computer contains an electronic clock that steps the microprocessor through its program. In this case, the clock frequency falls within the frequency spectrum allocated in the U.S. for FM radio broadcasting. If precautions were not taken by PC manufacturers, interference to nearby radio receivers would result. Harmonics or multiples of this frequency could, if not subdued, cause interference to other radio receivers; such as those used by emergency medical personnel and to television receivers. It is therefore incumbent upon manufacturers of digital electronic devices to guarantee their products will not be incompatible with or a nuisance to other electronic devices. EMC and the USA Because of the proliferation of Information Technology Equipment (ITE) and other microprocessorcontrolled electronic equipment, in the 1970’s the F.C.C. (as the authority having jurisdiction in the U.S.) implemented limits on RF emissions from digital devices. Digital devices that are intended to be used in residential environments are classified as Class “B” devices. All such Class “B” devices must comply with limits set forth in part 15 of the F.C.C. rules for radiated and
From analab1.com™ On-Line Publications
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conducted emissions. Before Class “B” devices may be sold in the U.S., it must conform to the requirements of the F.C.C. rules. Currently there are no U.S. requirements for immunity testing. Products destined for use in the U.S. industrial, scientific and medical fields have, to this point, been exempt from compliance with these limits. Such devices are classified as Class “A” devices and may not be used in residential environments. EMC and the European Union Products sold in the European Union must carry the “CE” mark that constitutes a declaration by the manufacturer of the products’ compliance with all applicable Harmonized Directives and Standards. Electronic devices are subject to EMC Directive, 89/392/EEC. Article 4 of this document states: “The apparatus...shall be so constructed that (a) the EMC disturbance it generates does not exceed a level allowing radio and telecommunications equipment and other apparatus to operate as intended; (b) the apparatus has an adequate level of intrinsic immunity of EMC disturbance to enable it to operate as intended.” Clearly, complying with the essential requirements of the European EMC
Directive requires evaluation of a product’s emission and immunity characteristics. Notably, products used in commercial, light industrial and heavy industrial environments are not exempt from compliance. The Intrinsic Immunity requirement dictates that an electronic apparatus be so constructed that its performance will not be degraded by its normal electromagnetic environment. For example, a consumer in Europe has a right to expect that the digital security system monitoring his home will not malfunction if a nearby ambulance crew talks to their local dispatcher via two-way radio communications equipment. The directive implies that manufacturers will design products to possess immunity not only to radiated RF fields, but to other electromagnetic phenomena as well. Specific immunity tests are itemized by generic and product-specific European norms or standards. Minimally, this means that a device’s performance will not be adversely effected by: (1) RF fields, such as radio and TV broadcast stations, and licensed two-way radio equipment; (2) Electrostatic Discharge events (ESD); (3) and Electrical Fast Transients (EFT). Testing of products for immunity in simulation of real-world environments allows manufacturers to demonstrate compliance with Article 4, clause (b) of the EMC Directive. Additional immunity testing is required by certain specific standards and the new 1997 generic immunity standard. These additional tests include: Conducted RF Immunity; Surge Immunity; Power Frequency Magnetic Fields Immunity; Voltage Dips and Interrupts Immunity; and Pulsed RF Fields Immunity.
maintain technical evidence supporting all claims of product “conformity”. This supporting evidence is assembled in a Technical Construction File (TCF). A TCF will exist for each product sold in the European Union. Verification of compliance (testing) may be performed by the manufacturer or a third-party test house. In all cases though, tests must be performed in harmony with International IEC Test Standards. Results of EMC testing, such as the Test Report issued by a testing laboratory, shall be included in the TCF. A product that meets the requirements of an appropriate “product specific standard,” or in lieu of a “product specific standard” the generic standard, is presumed to meet the essential requirements of the EMC Directive. In addition to the EMC Directive, other directives may be applicable to an electronic device. Conformity with all applicable directives must be verified and documented. Having
met all requirements, the “CE” mark may then be applied. For a period of ten years after being placed on the European Market, the supporting technical documentation (TCF) must be kept on file and be accessible by an authorized representative within the European Union. Benefits Compliance with the European Union’s EMC Directive leads to increasingly robust products, improvements in quality and increased customer satisfaction. For example, ESD (electrostatic discharge) Immunity Testing quickly reveals any latent vulnerability a product might have to such standards and promotes corrective measures that render the product immune to such real world occurrences. The result is improved customer satisfaction realized from reliable, solid products that provide years of trouble free service. C.R.S. 26-Jan-98
Biconical Antenna
CE Conformity Conformity to the essential requirements of the EMC Directive must be declared by the manufacturer or his authorized representative. This is done by issuing a document called a “Declaration of Conformity” (DOC). It is the manufacturer’s responsibility to procure and
Anechoic Chamber
Z-107
The “Noise Is Off” with This Thermocouple System OMEGA’s innovative Low Noise Thermocouple System provides stable and accurate temperature measurements by neutralizing the effects of ambient electrical noise. This low cost and versatile system is used for measuring temperatures of sensitive circuits and equipment where precise and stable readings are critical. It is also used throughout industry as a noise rejecting standard.
Low Noise Thermocouple System
The low noise thermocouple system consists of three interrelated elements: a probe assembly, a connector and thermocouple wire. Each of these three components has distinct and coordinated noise neutralizing features and together they provide a path for diverting electrical noise. The system, which uses universal two-terminal connections, shunts noise signals and preserves the integrity of the temperature-measuring circuit (see Figure 1).
ELECTRICAL NOISE NEUTRALIZED U.S. and Foreign Patents
Electrical noise, typically generated by power equipment, rotating machinery, line processing conveyors, mobile units, welding machines and cleaning appliances, introduces spurious signals that destabilize sensitive temperature measurements. The system’s unique positive ground path, from the thermocouple probe to the temperature indicating instrument, fully neutralizes the effects of electrical noise. Precise temperature control for data acquisition, data logging and computer interface circuits is now possible with the added assurance that noise is being rejected.
BALANCED SYSTEM ELEMENTS The thermocouple system’s three building blocks – probe, connector and wire – are integrated into a balanced and easily assembled unit. The probe and connector are available in both standard and miniature configurations (see Figure 2).
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(1) The thermocouple probe is shaped to ease handling and improve viewing of the test object. Probe types are interchangeable to suit many applications. The probe sheath (outer jacket) connects to a ground through an internal ground strap link. (2) The connector, which joins the probe and thermocouple wire, is a standard two-terminal quick disconnect type (miniature or standard size). The external metal ground strap, attached to the connector, provides the continued noise shunting circuit and adds mechanical strength to the assembly. (3) The twisted/shielded thermocouple wire contains an integral drain wire which provides the noise grounding link between the probe assembly and the measuring instrument.
CONVENIENT FEATURES The probe assembly is designed to ease handling, improve mechanical integrity and allow the user to view the subject under test without obstruction. A 30 degree profile, found only in OMEGA’s patented design, allows for improved user performance (see Figure 2). The probe assemblies are color coded to identify thermocouple materials and a full selection of probe sheath diameters and lengths are available. Probe lengths are 6", 12", 18", and 24"; diameters are from .040" to .250". The probe sheath is 304SS or Inconel. The connector provides continuity of ground from the probe to the thermocouple wire through an external ground strap. Polarized connector pins allow for quick connection or disconnection to the probe assembly. Connectors include removable write-on pads. This feature, unique in the industry, allows positive identification of thermocouple assemblies in multiple measurement applications.
PROBLEM SOLVER The user often cannot forecast what electrical noise sources will be present during temperature readings. Typical temperature measurements are performed in electrically noisy environments.
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Figure 2. Balanced system elements include: thermocouple probe, connector, and thermocouple wire. The thermocouple probe has a 30° profile, an exclusive OMEGA feature, and comes with the mating female connector and cable clamp
In a laboratory, where processes are being controlled at precise temperature transition points, electrical noise may be introduced from sources such as mixers, ovens, heating elements and power supplies. Grounding of this noise is essential for precise temperature sensing. This thermocouple system grounds the destabilizing noise signals. Precise control of solder bath temperatures, during an automated flow soldering process, is required to ensure that proper soldering takes place and that no damage occurs to sensitive components on a printed circuit board. Typically, the thermal sensing system is in the presence of equipment which generates electrical noise such as motors and welding equipment. The system’s unique and positive noise grounding path neutralizes the effects of generated noise.
In high noise applications such as environmental control, air conditioning, heat treating and foundry operations, noise neutralization during critical temperature measurements is required for accurate and stable control. By shunting electrical noise harmlessly to ground, the OMEGA® thermocouple system provides the required stable readings.
To order probes Standard quick disconnect probes and miniature quick disconnect probes are sold in Section A of this catalog.
The noisy environments encountered in industrial, mobile, field and laboratory applications are no match for this easily assembled and handy-to-use system.
To order connectors Standard connectors and miniature connectors are sold in Section G of this catalog.
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METAL STRAP DED SHIEL D E T TWIS T/C WIRE
CONNECTOR
INTERNAL DRAIN WIRE (3)
(2)
PROBE
(1)
Figure 1. Continuous ground from probe to test instrument
Z-109
Introduction To Temperature Controllers On/Off An on-off controller is the simplest form of temperature control device. The output from the device is either on or off, with no middle state. An on-off controller will switch the output only when the temperature crosses the setpoint. For heating control, the output is on when the temperature is below the setpoint, and off above setpoint. Since the temperature crosses the setpoint to change the output state, the process temperature will be cycling continually, going from below setpoint to above, and back below. In cases where this cycling occurs rapidly, and to prevent damage to contactors and valves, an onoff differential, or “hysteresis,“ is added to the controller operations. This differential requires that the temperature exceed setpoint by a certain amount before the output will turn off or on again. On-off differential prevents the output from “chattering” (that is, engaging in fast, continual switching if the temperature’s cycling above and below the setpoint occurs very rapidly). On-off control is usually used where a precise control is not necessary, in systems which cannot handle the energy’s being turned on and off frequently, where the mass of the system is so great that temperatures change extremely slowly, or for a temperature alarm.
The Miniature CN77000 is a full featured microprocessor-based controller in a 1/16 DIN package.
How Can I Control My Process Temperature Accurately and Reliably?
One special type of on-off control used for alarm is a limit controller. This controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached.
To accurately control process temperature without extensive operator involvement, a temperature control system relies upon a controller, which accepts a temperature sensor such as a thermocouple or RTD as input. It compares the actual temperature to the desired control temperature, or setpoint, and provides an output to a control element.
ON
2. 3 4
ON
ON
Heater OFF
The controller is one part of the entire control system, and the whole system should be analyzed in selecting the proper controller. The following items should be considered when selecting a controller: 1.
ON
OFF
OFF
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Temperature
Type of input sensor (thermocouple, RTD) and temperature range Type of output required (electromechanical relay, SSR, analog output) Control algorithm needed (on/off, proportional, PID) Number and type of outputs (heat, cool, alarm, limit)
Setpoint On-Off Differential (Deadband)
What Are the Different Types of Controllers, and How Do They Work? There are three basic types of controllers: on-off, proportional and PID. Depending upon the system to be controlled, the operator will be able to use one type or another to control the process.
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Time
ON/Off Temperature Control Action
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Introduction To Temperature Controllers Cont’d Proportional Proportional controls are designed to eliminate the cycling associated with on-off control. A proportional controller decreases the average power being supplied to the heater as the temperature approaches setpoint. This has the effect of slowing down the heater, so that it will not overshoot the setpoint but will approach the setpoint and maintain a stable temperature. This proportioning action can be accomplished by turning the output on and off for short intervals. This “time proportioning “ varies the ratio of ‘on’ time to ‘off‘ time to control the temperature. The proportioning action occurs within a “proportional band” around the setpoint temperature. Outside this band, the controller functions as an on-off unit, with the output either fully on (below the band) or fully off (above the band). However, within the band, the output is turned on and off in the ratio of the measurement difference from the setpoint. At the setpoint (the midpoint of the proportional band), the output on:off ratio is 1:1; that is, the on-time and off-time are equal. If the temperature is further from the setpoint, the on- and off-times vary in proportion to the
15 Sec. On
temperature difference. If the temperature is below setpoint, the output will be on longer; if the temperature is too high, the output will be off longer. The proportional band is usually expressed as a percent of full scale, or degrees. It may also be referred to as gain, which is the reciprocal of the band. Note, that in time proportioning control, full power is applied to the heater, but is cycled on and off, so the average time is varied. In most units, the cycle time and/or proportional band are adjustable, so that the controller may better match a particular process. In addition to electromechanical and solid state relay outputs, proportional controllers are also available with proportional analog outputs, such as 4 to 20 mA or 0 to 5 Vdc. With these outputs, the actual output level is varied, rather than the on and off times, as with a relay output controller. One of the advantages of proportional control is simplicity of operation. It may require an operator to make a small adjustment (manual reset) to bring the temperature to setpoint on initial startup, or if the process conditions change significantly.
5 Off
Time Proportional Percent On Time Off Time On Seconds Seconds 0.0 0.0 12.5 25.0 37.5 50.0 62.5 75.0 87.5 100.0 100.0
Repetitive 20 sec. Cycle Time
Time Proportioning at 75% Output Level
0.0 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 20.0
20.0 20.0 17.5 15.0 12.5 10.0 7.5 5.0 2.5 0.0 0.0
Temp (ºF) over 540 540.0 530.0 520.0 510.0 500.0 490.0 480.0 470.0 460.0 under 460
4-20 mA Proportional Output Percent Level Output 4 mA 4 mA 6 mA 8 mA 10 mA 12 mA 14 mA 16 mA 18 mA 20 mA 20 mA
0.0 0.0 12.5 25.0 37.5 50.0 62.5 75.0 87.5 100.0 100.0
Proportional Bandwith Example: heating Setpoint: 500˚F Proportional Band: 80˚F (±40˚F) Systems that are subject to wide temperature cycling will also need proportional controllers. Depending upon the process and the precision required, either a simple proportional control or one with PID may be required.
The CN2010 controller features ramp and soak, the ability to control temperature over time.
Processes with long time lags and large maximum rate of rise (e.g., a heat exchanger), require wide proportional bands to eliminate oscillation. The wide band can result in large offsets with changes in the load. To eliminate these offsets, automatic reset (integral) can be used. Derivative (rate) action can be used on processes with long time delays, to speed recovery after a process disturbance.
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There are also other features to consider when selecting a controller. These include auto- or selftuning, where the instrument will automatically calculate the proper proportional band, rate and reset values for precise control; serial communications, where the unit can “talk” to a host computer for data storage, analysis, and tuning; alarms, that can be latching (manual reset) or non-latching (automatic reset), set to trigger on high or low process temperatures or if a deviation from setpoint is observed; timers/event indicators which can mark elapsed time or the end/beginning of an event. In addition, relay or triac output units can be used with external switches, such as SSR solid state relays or magnetic contactors, in order to switch large loads up to 75 A. PID The third controller type provides proportional with integral and derivative control, or PID. This controller combines proportional control with two additional adjustments, which helps the unit automatically compensate for changes in the system. These adjustments, integral and derivative, are expressed in
Offset
Temp.
PB SP
Time Process with Temperature Offset
time-based units; they are also referred to by their reciprocals, RESET and RATE, respectively. The proportional, integral and derivative terms must be individually adjusted or “tuned” to a particular system, using a “trial and error” method. It provides the most accurate and stable control of the three controller types, and is best used in systems which have a relatively small mass, those which react quickly to changes in energy added to the process. It is recommended in systems where the load changes often, and the controller is expected to compensate automatically due to frequent changes in setpoint, the amount of energy available, or the mass to be controlled.
What Do Rate and Reset Do, and How Do They Work? Rate and reset are methods used by controllers to compensate for offsets and shifts in temperature. When using a proportional controller, it is very rare that the heat input to maintain the setpoint temperature will be 50%; the temperature will either increase or decrease from the setpoint, until a stable temperature is obtained. The difference between this stable temperature and the setpoint is called offset. This offset can be compensated for manually or automatically. Using manual reset, the user will shift the proportional band so that the process will stabilize at the setpoint temperature. Automatic reset, also known as integral, will integrate the deviation signal with respect to time, and the integral is summed with the deviation signal to shift the proportional band. The output power is thus automatically increased or decreased to bring the
process temperature back to setpoint, The rate or derivative function provides the controller with the ability to shift the proportional band, to compensate for rapidly changing temperature. The amount of shift is proportional to the rate of temperature change. A PID, or three-mode controller, combines the proportional, integral (reset) and derivative (rate) actions, and is usually required to control difficult processes. These controllers can also be made with two proportional outputs, one for heating and another for cooling. This type of controller is required for processes which may require heat to start up, but then generate excess heat at some time during operation. What are the Different Output Types That Are Available for Controllers? The output from the controller may take one of several forms. The most common forms are time proportional and analog proportional. A time proportional output applies power to the load for a percentage of a fixed cycle time. For example, with a 10 second cycle time, if the controller output were set for 60%, the relay would be energized (closed, power applied) for 6 seconds, and de-energized (open, no power applied) for 4 seconds. Time proportional outputs are available in three different forms: electromechanical relay, triac or ac solid state relay, or a dc voltage pulse (to drive an external solid state relay). The electromechanical relay is generally the most economical type, and is usually chosen on systems with cycle times greater than 10 seconds, and relatively small loads. An ac solid state relay or dc voltage pulse are chosen for reliability, since they contain no moving parts. Recommended for processes requiring short cycle times, they need an additional relay, external to the controller, to handle the typical load required by a heating element. These external solid state relays are usually used with an ac control signal for ac solid state relay output controllers, or with a dc control signal for dc voltage pulse output controllers. An analog proportional output is usually an analog voltage (0 to 5 Vdc) or current (4 to 20 mA). The output level from this output type is also set by the controller; if the output were set at 60%, the output level would be 60% of 5 V, or 3 V. With a 4 to 20 mA output (a 16 mA span), 60% is equal to (0.6 x 16) + 4, or 13.6 mA. These controllers are usually used with proportioning valves or power controllers.
What Should I Consider When Selecting a Controller for My Application? When you choose a controller, the main considerations include the precision of control that is necessary, and how difficult the process is to control. For easiest tuning and lowest initial cost, the simplest controller which will produce the desired results should be selected. Simple processes with a well matched heater (not overor undersized) and without rapid cycling can possibly use on-off controllers. For those systems subject to cycling, or with an unmatched heater (either over- or undersized), a proportional controller is needed. ®
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Temperature Controllers Selection Considerations CONTROLLABILITY OF ELECTRIC HEAT The basic function of a controller is to compare the actual temperature with its setpoint and produce an output which will maintain that setpoint. The controller is one part of the entire control system, and the whole system should be analyzed in selecting the proper controller. The following items should be considered when selecting a controller. 1. Type of input sensor (thermocouple, RTD, card and temperature range). 2. Placement of sensor 3. Control algorithm needed (on/off, proportional, PID, autotune PID) 4. Type of output hardware required (electromechanical relay, SSR, analog output signal) 5. Additional outputs or requirements of system (display required of temperature and/or setpoint, cooling outputs, alarms, limit, computer communication, etc.) TYPE OF INPUT The type of input sensor will depend on the temperature range required, the resolution and accuracy of the measurement required, and how and where the sensor is to be mounted. PLACEMENT OF THE SENSOR The correct placement of the sensing element with respect to the work and heat source is of the utmost importance for good control. If all three can be located in close proximity, a high degree of accuracy, up to the limit of the controller, is relatively easy to achieve. However, if the heat source is located some distance from the work, widely different accuracies can be obtained just by locating the sensing element at various places between the heater and the work. Before selecting the location for the sensing element, determine whether the heat demand will be predominantly steady or variable. If the heat demand is relatively steady, placement of the sensing element near the heat source will hold the temperature change at the work to a minimum. On the other hand, placing the sensing element near the work, when heat demand is variable, will enable it to more quickly sense a change in heat requirements. However, because of the increase in thermal lag between the heater and the sensing elements, more overshoot and undershoot can occur, causing a greater spread between maximum and minimum temperature. This spread can be reduced by selecting a PID controller.
CONTROL ALGORITHM (MODE) This refers to the method in which the controller attempts to restore system temperature to the desired level. The two most common methods are two-position (on-off) and proportioning (throttling) controls. ON/OFF CONTROL On/Off control has the simplest of control modes. It has a deadband (differential) expressed as a percentage of the input span. The setpoint is usually in the center of the deadband. Therefore, if the input is 0-1000°F, the deadband is 5% and the setpoint is set at 500°F, the output will be full on when the temperature is 495°F or below and will stay full on until the temperature reaches 505°F, at which time the output will be full off. It will stay full off until the temperature drops to 495°F. If the process has a fast rate of response, the cycling between 495 and 505°F will be fast. The faster the rate of response of the process, the greater the overshoot and undershoot and the faster the cycling of the contactor when used as a final control element. On-off control is usually used where a precise control is not necessary, for example, in systems which cannot handle having the energy turned on and off frequently, where the mass of the system is so great that the temperature changes extremely slowly, or for a temperature alarm. One special type of on-off control used for alarm is a limit controller. This controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached. PROPORTIONAL Proportional controls are designed to eliminate the cycling associated with onoff control. A proportional controller decreases the average power being supplied to the heater as the temperature approaches setpoint. This has the effect of slowing down the heater so that it will not overshoot the setpoint, but will approach the setpoint and maintain a stable temperature. This proportioning action can be accomplished by turning the output on and off for short intervals. This “time proportioning” varies the ratio of “on” time to “off ” time to control the temperature. The time period between two successive turn-ons is known as the “cycle time” or “duty cycle”. The proportioning action occurs within a “proportional band” around the setpoint temperature. Outside this band, the controller functions as an on-off unit, with the output either fully on (below the band) or fully off (above the band). However, within the band, the
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output is turned on and off in the ratio of the measurement difference from the setpoint. At the setpoint (the midpoint of the proportional band), the output on-off ratio is 1:1 that is, the on-time and offtime are equal. If the temperature is further from the setpoint, the on- and offtimes vary in proportion to the temperature difference. If the temperature is below setpoint, the output will be on longer. If the temperature is too high, the output will be off longer.
Above Temp.
On Time
Off Time
At Set Point Temp.
Below Temp.
Figure 1: Proportional control
The proportional band is usually expressed as a percentage of full input range scale, or in degrees. It may also be referred to as gain, which is the reciprocal of the band. In many units, the cycle time and/or proportional bandwidth are adjustable, so that the controller may be better matched to a particular process. Proportional controllers have a manual reset (trim) adjustment, which may be used to adjust for an offset between the steady state temperature and the setpoint. In addition to electromechanical and solid state relay outputs, proportional controllers are also available with proportional analog signal outputs, such as 4 to 20 mA or 0 to 5 Vdc. With these outputs, the actual output level amplitude is varied, rather than the proportion of on and off times. PROPORTIONAL PLUS INTEGRAL PLUS DERIVATIVE CONTROL MODE (PID): This controller operates the same way a proportional controller does, except that the function of the trim adjustment is performed automatically by the integral function (automatic reset). Thus, load changes are compensated for automatically and the temperature agrees with the setpoint under all operating conditions. Offset is eliminated.
Temperature Controllers Selection Considerations
Low Rate Setting
Set Point Rate Set Properly
Figure 2: Rate function compensates for rapid changes.
The derivative function (rate action) compensates for load changes which take place rapidly. An example is a traveling belt oven where the product is fed intermittently. When the product enters the oven, there is a sharp rise in the demand for heat, and when it stops, there is an excess of heat. Derivative action reduces the undershoot and overshoot of temperature under these conditions and prevents bad product due
Set Point
Offset
Figure 3: Reset fuction eliminates offset.
to over or under curing. PID control provides more accurate and stable control than on/off or proportional controller types. It is best used in systems that have a relatively small mass and which react quickly to changes in energy added to the process. It is recommended in systems where the load changes often. The controller is expected to automatically compensate the amount of energy available or the mass to be controlled, due to frequent changes in setpoint. The proportional, integral and derivative
terms must be “tuned,” i.e., adjusted to a particular process. This is done by trial and error. Some controllers called Autotune controllers attempt to adjust the PID parameters automatically. TYPE OF CONTROL OUTPUT HARDWARE The output hardware in a temperature controller may take one of several forms. Deciding on the type of control hardware to be used depends on the heater used and power available, the control algorithm chosen, and the hardware external to the controller available to handle the heater load. The most commonly used controller output hardware is as follows: Time Proportional or On/Off 1) Mechanical Relay 2) Triac (ac solid state relay) 3) dc Solid State Relay Driver (pulse) Analog Proportional 1) 4-20 mA dc 2) 0-5 Vdc or 0-10 Vdc A time proportional output applies power to the load for a percentage of a fixed cycle time. For example, with a 10 second cycle time, if the controller output were set for 60%, the relay would be energized (closed, power applied) for 6 seconds, and de-energized (open, no power applied) for 4 seconds. The electromechanical relay is generally the most economical output type, and is usually chosen on systems with cycle times greater than 10 seconds and relatively small loads. Choose an ac solid state relay or dc voltage pulse to drive an external SSR with reliability, since they contain no moving parts. They are also recommended for processes requiring short cycle times. External solid state relays may require an ac or dc control signal. An amplitude proportional output is usually an analog voltage (0 to 5 Vdc) or current (4 to 20 mA). The output level from this output type is also set by the controller. If the output were set at 60%, the output level would be 60% of 5 V, or 3 V. With a 4 to 20 mA output (a 16 mA span), 60% is equal to (0.6 x 16) + 4, or 13.6 mA. These controllers are usually used with SCR power controllers or proportioning valves. The power used by an electrical resistance heater will usually be given in watts. The capacity of a relay is given in amps. A common formula to determine the safe relay rating requirements is: W = V(A)(1.5) or A = W/(V)(1.5) Where A = relay rating in amps W = heater capacity in watts V = voltage used 1.5 = safety factor
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The types of hardware available, external to the controller, to allow it to handle the load, are as follows: 1) Mechanical Contactor 2) ac controlled solid state relay 3) dc controlled solid state relay 4) Zero crossover SCR power controller 5) Phase angle fired SCR power controller Mechanical contactors are external relays, which can be used when a higher amperage than can be handled by the relay in the controller is required, or for some three-phase systems. They are not recommended for cycle times shorter than 15 seconds. Solid state relays have the advantage over mechanical contactors, in that they have no moving parts, and thus can be used with short cycle times. The shorter the cycle time, the less dead lag and the better the control. The “switching” takes place at the zero voltage crossover point of the alternating current cycle; thus, no appreciable electrical noise is generated. An ac controlled solid state relay is used with either a mechanical relay or triac output from the controller, and is available for currents up to 90 amps at voltages of up to 480 Vac. DC solid state relays are used with dc solid state driver (pulse) outputs. The “turn on” signal can be from 3 to 32 Vdc and models are available to control up to 90 amps at up to 480 Vac. Zero crossover SCR power controllers are used to control single or three-phase power for even larger loads. They can be used for currents up to 200 amps at 480 volts. A 4-20 mA dc control signal is usually required from the controller. The zero crossover SCR power controllers convert the analog output signal to a time proportional signal with a cycle time of about two seconds or less, and also provide switching at the zero crossover point to avoid generating electrical noise. Phase angle SCR power controllers also are operated by a 4-20 mA dc controller output. Power to the load is controlled by governing the point of turn on (firing) of each half cycle of a full ac sine wave. This has the effect of varying the voltage within a single 0.0167 second period. By comparison, time proportional controllers vary the average power over the cycle time, usually more than 1 second, and often more than 15 seconds. Phase angle SCR’s are only recommended for low mass heating elements such as infrared lamps or hot wire heaters. ®
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Temperature Control
Tuning a PID (Three Mode) Controller Tuning a temperature controller involves setting the proportional, integral, and derivative values to get the best possible control for a particular process. If the controller does not include an autotune algorithm, or if the autotune algorithm does not provide adequate control for the particular application, then the unit must be tuned using trial and error.
After the controller is installed and wired: 1. Apply power to the controller. 2. Disable the control outputs if possible. 3. For time proportional primary output, set the cycle time. Enter the following value:
The following is a tuning procedure for the OMEGA CN2000 controller. It can be applied to other controllers as well. There are other tuning procedures which can also be used, but they all use a similar trial and error method. Note that if the controller uses a mechanical relay (rather than a solid state relay), a longer cycle time (20 seconds) should be used when starting out.
CYCLE TIME 1 5 SEC (Only appears if output is a time proportional output. A smaller cycle time may be required for systems with an extremely fast response time.)
The following definitions may be needed:
Then select the following parameters:
1) Cycle time - Also known as duty cycle; the total length of time for the controller to complete one on/off cycle. Example: with a 20 second cycle time, an on time of 10 seconds and an off time of 10 seconds represents a 50 percent power output. The controller will cycle on and off while within the proportional band.
PR BAND 1 _______5% (PB) RESET 1 _________0 R/M (TURNS OFF RESET FUNCTION) RESET 2 _________0 R/M RATE 1 __________0 MIN (TURNS OFF RATE FUNCTION) RATE 2 __________0 MIN
2) Proportional band - A temperature band expressed in % of full scale or degrees within which the controller‘s proportioning action takes place. The wider the proportional band, the greater the area around the setpoint in which the proportional action takes place. This is sometimes referred to as gain, which is the reciprocal of proportional band.
NOTE On units with dual three mode outputs, the primary and secondary tuning parameters are independently set and must be tuned separately. The procedure used in this section is for a HEATING primary output. A similar procedure may be used for a primary COOLING output or a secondary COOLING output.
3) Integral, also known as reset, is a function which adjusts the proportional bandwidth with respect to the setpoint to compensate for offset (droop) from setpoint; that is, it adjusts the controlled temperature to setpoint after the system stabilizes.
A. TUNING OUTPUTS FOR HEATING CONTROL 1. Enable the OUTPUT(S) and start the process. 2. The process should be run at a setpoint that will allow the temperature to stabilize with heat input required.
A PID (three mode) controller is capable of exceptional control stability when properly tuned and used. The operator can achieve the fastest response time and smallest overshoot by following these instructions carefully. The information for tuning this three mode controller may be different from other controller tuning procedures. Normally a SELF TUNE feature will eliminate the need to use this manual tuning procedure for the primary output; however, adjustments to the SELF TUNE values may be made if desired.
3. With RATE and RESET turned OFF, the temperature will stabilize with a steady state deviation, or droop, between the setpoint and the actual temperature. Carefully note whether or not there are regular cycles or oscillations in this temperature by observing the measurement on the display. (An oscillation may be as long as 30 minutes.) The tuning procedure is easier to follow if you use a recorder to monitor the process temperature.
PRIMARY SETPOINT
TEMP.
TEMP.
PRIMARY SETPOINT
TIME Divide PB by 2 if you observe this.
TIME This is close to perfect tuning.
Figure 1. Temperature Oscillations Z-115
PRIMARY SETPOINT TEMP.
4) Derivative, also known as rate, senses the rate of rise or fall of system temperature and automatically adjusts the proportional band to minimize overshoot or undershoot.
TIME Multiply PB by 2 if you observe this.
4. If there are no regular oscillations in the temperature, divide the PB by 2 (see Figure 1). Allow the process to stabilize and check for temperature oscillations. If there are still no oscillations, divide the PB by 2 again. Repeat until cycles or oscillations are obtained. Proceed to Step 5. If oscillations are observed immediately, multiply the PB by 2. Observe the resulting temperature for several minutes. If the oscillations continue, increase the PB by factors of 2 until the oscillations stop.
9. You have now completed all the measurements necessary to obtain optimum performance from the Controller. Only two more adjustments are required - RATE and RESET. 10.Using the oscillation time measured in Step 7, calculate the value for RESET in repeats per minutes as follows: RESET = 8 x __ 1 __ 5
Where TO = Oscillation Time in Minutes. OR Use Nomogram II (see Figure 5):
5. The PB is now very near its critical setting. Carefully increase or decrease the PB setting until cycles or oscillations just appear in the temperature recording.
TEMPERATURE CYCLE TIME IN MINUTES
0.1
If no oscillations occur in the process temperature even at the minimum PB setting of 1%, skip Steps 6 through 11 below and proceed to paragraph B.
0.2
2
1
0.3 5
10
20
3
2
3
10
0.50
1
20
0.30 0.20
0.10
100
30
0.03 0.02
0.05
CORRECT RESET SETTING IN REPEATS PER MINUTE
6. Read the steady-state deviation, or droop, between setpoint and actual temperature with the “critical” PB setting you have achieved. (Because the temperature is cycling a bit, use the average temperature.) 7 Measure the oscillation time, in minutes, between neighboring peaks or valleys (see Figure 2). This is most easily accomplished with a chart recorder, but a measurement can be read at one minute intervals to obtain the timing. TEMP.
TO
Figure 5. Nomogram II Enter the value for RESET 1. 11.Again using the oscillation time measured in Step 7, calculate the value for RATE in minutes as follows: RESET = T O __ 10 Where TO = Oscillation Time OR Use Nomogram III (see Figure 6)
PRIMARY SETPOINT MEASURE THIS TEMP TRMPERATURE CYCLE TIME IN MINUTES INCREASE PB CRITICAL PB
DECREASE PB
0.1
MEASURE THIS TIME
0.01
TIME
STARTUP
TEMP
10
20
0.3
1
2
30 40 50 3
4
5
6 x Reset Value
i.e., if reset = 2 R/M, the RATE = 0.08 min. 1.65 · TEMP DEVIATION WITH PB
DEVIATION TEMP WITH PB
CRITICAL PB TIME WITH PB
STARTUP
13.Several setpoint changes and consequent RESET and RATE time adjustments may be required to obtain the proper balance between “RESPONSE TIME” to a system upset and “SETTLING TIME.” In general, fast response is accompanied by larger overshoot and consequently shorter time for the process to “SETTLE OUT.” Conversely, if the response is slower, the process tends to slide into the final value with little or no overshoot. The requirements of the system dictate which action is desired.
TIME
Figure 3. Calculating Final Temperature Deviation
TEMPERATURE DEVIATION WITH CRITICAL PBC. SETTING
3
3
0.2
12.If overshoot occurred, it can be eliminated by decreasing the RESET time. When changes are made in the RESET value, a corresponding change should also be made in the RATE adjustment so that the RATE value is equal to: RATE = 1 ______________
PRIMARY SETPOINT
2
2
0.1
Enter this value for Rate 1.
The desired final temperature deviation can be calculated by multiplying the initial temperature deviation achieved with the CRITICAL PB setting by 1.65 (see Figure 3) or by use of the convenient Nomogram I (see Figure 4). Try several trialand-error settings of the PB control until the desired final temperature deviation is achieved.
2
0.02 0.03
1
Figure 6. Nomogram III
8. Now, increase the PB setting until the temperature deviation, or droop, increases 65%.
1
0.3
CORRECT RATE SETTING IN MINUTES
Figure 2. Oscillation Time
EXAMPLE 3° DEVIATION WITH PB SET PB TO OBTAIN 5° FINAL DEVIATION
0.2
3
5
4 5
10
10
15 20
15 20
30 40 50
30 40 50
70 100
100 150
FINAL TEMPERATURE DEVIATION = 1.65 DEVIATION WITH CRITICAL PBC. SETTING.
14.When satisfactory tuning has been achieved, the cycle time should be increased to save contactor life (applies to units with time proportioning outputs only (TPRI)). Increase the cycle time as much as possible without causing oscillations in the measurement due to load cycling. 15.Proceed to Section C.
Figure 4. Nomogram I
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Tuning a PID Controller Cont'd
B. TUNING PROCEDURE WHEN NO OSCILLATIONS ARE OBSERVED 1. Measure the steady-state deviation, or droop, between setpoint and actual temperature with minimum PB setting. 2. Increase the PB setting until the temperature deviation (droop) increases 65%. Nomogram I (see Figure 4) provides a convenient method of calculating the desired final temperature deviation. 3. Set the RESET 1 to a high value (10 R/M). Set the RATE 1 to a corresponding value (0.02 MIN). At this point, the measurement should stabilize at the setpoint temperature due to reset action. 4. Since we were not able to determine a critical oscillation time, the optimum settings of the reset and rate adjustments must be determined by trial and error. After the temperature has stabilized at setpoint, increase the setpoint temperature setting by 10 degrees. Observe the overshoot associated with the rise in actual temperature. Then return the setpoint setting to its original value and again observe the overshoot associated with the actual temperature change. Excessive overshoot implies that the RESET and/or RATE values are set too high. Overdamped response (no overshoot) implies that the RESET and/or RATE values are set too low. Refer to Figure 7. Where improved performance is required, change one tuning parameter at a time and observe its effect on performance when the setpoint is changed. Make incremental changes in the parameters until the performance is optimized.
2. After some delay (for heat to reach the sensor), the PV will start to rise. After more delay, the PV will reach a maximum rate of change (slope). Record the time at which this maximum slope occurs and the PV at which it occurs. Record the maximum slope in degrees per minute. Turn off system power. 3. Draw a line from the point of maximum slope back to the ambient temperature axis to obtain the lumped system time delay Td (see Figure 8). The time delay may also be obtained by the equation: Td = time to max. slope-(PV at max. slope - Ambient)/max. slope
4. Apply the following equations to yield the PID parameters: Pr. Band = Td x max. slope x 100/span = % of span Reset= 0.4 / Td = resets/minute Rate = 0.4 x Td = minutes 5. Restart the system and bring the process to setpoint with the controller in the loop and observe response. If the response has too much overshoot, or is oscillating, then the PID parameters can be changed (slightly, one at a time, and observing process response) in the following directions: Widen the proportional band, lower the Reset value, and increase the Rate value. Example: The chart recording in Figure 8 was obtained by applying full power to an oven. The chart scales are 10°F/cm, and 5 min/cm. The controller range is 100 to 600°F, or a span of 500°F.
5. When satisfactory tuning has been achieved, the cycle time should be increased to save contactor life (applies to units with time proportioning outputs only (TPRI)). Increase the cycle time as much as possible without causing oscillations in the measurement due to load cycling.
Maximum slope = 18°F/5 minutes = 3.6˚F/minute Time delay = Td = approximately 7 minutes. Proportional Band = 7 minutes x 3.6°F/minutes x 100/500°F = 5%. Reset = 0.4/7 minutes = 0.06 resets/minute Rate = 0.4 x 7 minutes = 2.8 minute
RESET OR RATE TOO HIGH
RESET OR RATE TOO LOW
Figure 7. Setting RESET and/or RATE
C. TUNING THE PRIMARY OUTPUT FOR COOLING CONTROL The same procedure is used as for heating. The process should be run at a setpoint that requires cooling control before the temperature will stabilize.
PV
D. SIMPLIFIED TUNING PROCEDURE FOR PID CONTROLLERS
18oF
The following procedure is a graphical technique of analyzing a process response curve to a step input. It is much easier with a strip chart recorder reading the process variable (PV).
5 mins Td TO
1. Starting from a cold start (PV at ambient), apply full power to the process without the controller in the loop, i.e., with an open loop. Record this starting time.
TIME
Figure 8. System Time Delay
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Controller Operation There are three basic types of controllers: on-off, proportional and PID. Depending upon the system to be controlled, the operator will be able to use one type or the other to control the process. On/Off An on-off controller is the simplest form of temperature control device. The output from the device is either on or off, with no middle state. An on-off controller will switch the output only when the temperature crosses the setpoint. For heating control, the output is on when the temperature is below the setpoint, and off above setpoint. Since the temperature crosses the setpoint to change the output state, the process temperature will be cycling continually, going from below setpoint to above, and back below. In cases where this cycling occurs rapidly, and to prevent damage to contactors and valves, an on-off differential, or “hysteresis,” is added to the controller operations. This differential requires that the temperature exceed setpoint by a certain amount before the output will turn off or on again. On-off differential prevents the output from “chattering” or making fast, continual switches if the cycling above and below the setpoint occurs very rapidly. On-off control is usually used where a precise control is not necessary, in systems which cannot handle having the energy turned on and off frequently, where the mass of the system is so great that temperatures change extremely slowly, or for a temperature alarm. One special type of on-off control used for alarm is a limit controller. This controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached. Proportional Proportional controls are designed to eliminate the cycling associated with on-off control. A proportional controller decreases the average power supplied to the heater as the temperature approaches setpoint. This has the effect of slowing down the heater so that it will not overshoot the setpoint, but will approach the setpoint and maintain a stable temperature. This proportioning action can be accomplished by turning the output on and off for short intervals. This “time proportioning” varies the ratio of “on” time to “off” time to control the temperature. The proportioning action occurs within a “proportional band” around the setpoint temperature. Outside this band, the controller functions as an on-off unit, with the output either fully on (below the band) or fully off (above the band). However, within the band, the output is turned on and off in the ratio of the measurement difference from the setpoint. At the setpoint (the midpoint of the proportional band), the output on:off ratio is 1:1; that is, the on-time and off-time are equal. if the temperature is further from the setpoint, the on- and off-times vary in proportion to the temperature difference. If the temperature is below setpoint, the output will be on longer; if the temperature is too high, the output will be off longer. The proportional band is usually expressed as a percentage of full scale, or degrees. It may also be referred to as gain, which is the reciprocal of the band. Note that in time proportioning control, full power is applied to the heater, but cycled on and off, so the average time is
varied. In most units, the cycle time and/or proportional band are adjustable, so that the controller may better match a particular process. In addition to electromechanical and solid state relay outputs, proportional controllers are also available with proportional analog outputs, such as 4 to 20 mA or 0 to 5 Vdc. With these outputs, the actual output level is varied, rather than the on and off times, as with a relay output controller. One of the advantages of proportional control is the simplicity of operation. It may require an operator to make a small adjustment (manual reset) to bring the temperature to setpoint on initial startup, or if the process conditions change significantly. Systems that are subject to wide temperature cycling will also need proportional controllers. Depending upon the process and the precision required, either a simple proportional control or one with PID may be required. Processes with long time lags and large maximum rates of rise (e.g., a heat exchanger), require wide proportional bands to eliminate oscillation. The wide band can result in large offsets with changes in the load. To eliminate these offsets, automatic reset (integral) can be used. Derivative (rate) action can be used on processes with long time delays, to speed recovery after a process disturbance. PID The third controller type provides proportional with integral and derivative control, or PID. This controller combines proportional control with two additional adjustments, which helps the unit automatically compensate for changes in the system. These adjustments, integral and derivative, are expressed in time-based units; they are also referred to by their reciprocals, RESET and RATE, respectively. The proportional, integral and derivative terms must be individually adjusted or “tuned” to a particular system using trial and error. It provides the most accurate and stable control of the three controller types, and is best used in systems which have a relatively small mass, those which react quickly to changes in the energy added to the process. It is recommended in systems where the load changes often and the controller is expected to compensate automatically due to frequent changes in setpoint, the amount of energy available, or the mass to be controlled. There are also other features to consider when selecting a controller. These include auto- or self-tuning, where the instrument will automatically calculate the proper proportional band, rate and reset values for precise control; serial communications, where the unit can “talk” to a host computer for data storage, analysis, and tuning; alarms, that can be latching (manual reset) or non-latching (automatic reset), set to trigger on high or low process temperatures or if a deviation from setpoint is observed; timers/event indicators which can mark elapsed time or the end/beginning of an event. In addition, relay or triac output units can be used with external switches, such as SSR solid state relays or magnetic contactors, in order to switch large loads up to 75 A.
Z-118
®
Z
SSR Thermal Considerations One of the major considerations when using a SSR, which cannot be stressed too strongly, is that an effective method of removing heat from the SSR package must be employed. The most common method is to employ a heat sink. SSR’s have a relatively high “contact” dissipation, in excess of 1 watt per amp. TC RΘCA
AMBIENT (AIR TEMPERATURE)
HEAT FLOW WITH HEAT SINK
TJ
TC RΘJC
CASE TEMPERATUE
TS RΘCS
= Junction temperature, °C
TA
= Ambient temperature, °C
P
= Power dissipation (ILOAD x EDROP) watts
RΘJC = Thermal resistance, junction to case °C/W
TJ - TA RΘSA = ––––– - (RΘJC + RΘCS) P 100 - 71.2 = –––––––– -(1.3 + 0.1) 12 = 1°C/W (c). To determine maximum load current, for 1°C/W heat sink and 71.2°C ambient temperature:
TA
RΘJC OUTPUT SEMICONDUCTOR (JUNCTION TEMPERATURE)
TJ
RΘCS = Thermal resistance, case to sink. °C/W
NO HEAT SINK
TJ
where
TA RΘSA
HEAT SINK TEMPERATUE
Fig. 18 A simplified thermal model
With loads of less than 5 amps, cooling by free flowing air or forced air current around the SSR is usually sufficient. At higher currents it will become necessary to make sure the radiating surface is in good contact with a heat sink. Essentially this involves mounting the base plate of the SSR onto a good heat conductor, usually aluminum. Good thermal transfer between the SSR and the heat sink can be achieved with thermal grease or heat sink compound. Using this technique, the SSR case to heat sink thermal resistance (RΘCS) is reduced to a negligible value of 0.1°C/W (celsius per watt) or less. This is usually presumed and included in the thermal data. The simplified thermal model in Fig. 18 indicates the basic elements to be considered in the thermal design. The values that are determinable by the user are the case to heat sink interface (RΘCS), as previously mentioned, and the heat sink to ambient interface (RΘSA).
Thermal Calculations Fig. 18 illustrates the thermal relationships between the output semiconductor junction and the surrounding ambient. TJ - TA is the temperature gradient or drop from junction to ambient, which is the sum of the thermal resistances multiplied by the junction power dissipation (P watts). Hence
RΘSA = Thermal resistance, sink to ambient °C/W To use the equation, the maximum junction temperature must be known, typically 125°C, together with the actual power dissipation, say 12 watts for a 10 amp SSR, assuming a 1.2 volt effective (not actual) voltage drop across the output semiconductor. The power dissipation (P watts) is determined by multiplying the effective voltage drop (EDROP) Assuming a thermal resistance from junction to case (RΘJC) of, say, 1.3°C/W and inserting the above typical values into the equation, solutions can be found for unknown parameters, such as maximum load current, maximum operating temperature, and the appropriate heat sink thermal resistance. Where two of these parameters are known the third can be found as shown in the following examples: (a) To determine the maximum allowable ambient temperature for 1°C/W heat sink and 10 amp load (12 watts) with a maximum allowable T3 of 100°C: TJ - TA = P(RΘJC + RΘCS + RΘSA) = 12 (1.3 + 0.1 + 1.0) = 28.8
TJ - TA P = –––––––––––––––– RΘJC + RΘCS + RΘSA 100 - 7.2 = –––––––––––– 1.3 + 0.1 + 1.0 =12 watts hence, P ILOAD = –––––– EDROP 12 = –– 1.2 = 10 amperes Regardless of whether the SSR is used on a heat sink or the case is cooled by other means, it is possible to confirm proper operating conditions by making a direct base plate temperature measurement when certain parameters are known. The same basic equation is used except that base plate temperature (TC) is substituted for ambient temperature (TA) and RΘCS and RΘSA are deleted. The temperature gradient now becomes TJ - TC that is the thermal resistance (RΘJC) multiplied by the junction power dissipation (P watts). Hence: TJ - TC = P(RΘJC)
hence, TA = TJ - 28.8 = 100 - 28.8 = 71.2°C (b) To determine required heat sink thermal resistance, for 71.2C maximum ambient temperature and a 10 amp load (12 watts):
Parameter relationships are similar in that solutions can be found for maximum allowable case temperature, maximum load current, and required junction to case (RΘJC) thermal resistance. Again, where two parameters are known, the third can be found as shown in the following examples (using previous values). (d). To determine maximum allowable case temperature, for
TJ - TA = P(RΘJC + RΘCS + RΘSA) Z-119
35
80
0.5C/W
RΘCS+ RΘSA=
1.0C/W
30 POWER DISSIPATION (W)
TJ - TC = P (RΘJC) = 12 x 1.3 = 15.6 hence,
85 E
3.0C/W
25 20
95 K
H
J
100
10
105
NO H
INK
5
= 84.4°C
= 12 watts
L
15
110 G
100 - 84.4 = –––––––– 1.3
90
B
EAT S
= 100 - 15.6
TJ - TC P = –––––– RΘJC
F
C
TC = TJ - 15.6
(e). To determine maximum load current for RΘJC = 1.3°C/W and 84.4°C case temperature:
2.0C/W
0
5
10
15
D 20
25/0
I 10
LOAD CURRENT (ARMS)
20
30
40
50
A 60
70
MAX ALLOWABLE CASE TEMPERATURE (°C)
RΘJC = 1.3°C/W and 10 amp load (12 watts):
80
MAX AMBIENT TEMPERATURE (°C)
Fig. 19 Thermal operating curves (25 A SSR)
and when it is, it is more commonly combined with (RΘJC) and stated as (RΘJA) The equation would appear as follows: TJ - TA = P(RΘJC + RΘCA ) Or TJ - TA = P(RΘJA)
Ratings The free air performance of lower powered SSR’s is usually defined in the catalogue by means of a single derating curve, current versus ambient temperature based on the foregoing formulas, which is adequate for most situations
Where SSR
hence, P ILOAD = –––––– EDROP 12 = –– 1.2 = 10 amperes (f). To determine required thermal resistance (RΘJC) for 84.4°C case temperature and 10 amp load (12 watts): RΘJC
TJ - TC = ––––– P 100 - 84.4 = –––––––– 12 = 1.3°C/W
In examples (a) through (c) SSR operating conditions are determined as they relate to ambient air temperature using a heat sink. Similarly, conditions can be determined for an SSR operating in free air without a heat sink, provided that a value is given for the radiating characteristics of the package (RΘCA). This value is rarely given
RΘCA = Thermal resistance, case to ambient, °C/W RΘJA = Thermal resistance, junction to ambient, °C/W The equation can be used to calculate maximum load current and maximum ambient temperature as before. However, the resultant values are inclined to be less precise due to the many variables that affect the case to air relationship (i.e... positioning, mounting, stacking, air movement, etc). Generally, free air performance is associated with PCB or plug-in SSR’s of 5 amps or less, which have no metallic base to measure. The question is often raised as to where the air temperature is measured. There is no clear-cut answer for this. Measurement is made more difficult when the SSR’s are closely stacked, each creating a false environment for its neighbor. One suggested approach is to place a temperature probe or thermocouple in the horizontal plane approximately 1 inch away from the subject SSR. This technique is reasonably accurate and permits repeatability. Z-120
0.15 INCH 1.5 INCHES
2.3 INCHES
Fig. 20 Typical light duty aluminum heat sink extrusion (end view)
Heat Sinking Under worst case conditions the SSR case temperature should not exceed the maximum allowable shown in the right hand vertical scales of Fig. 19. A typical finned section of extruded aluminum heat sink material is shown in outline form in Fig. 20. A 2 inch length of this material would approximate the same thermal characteristics as curve (a) in Fig. 21, likewise, a 4 inch length would approximate curve (b). This is assuming the heat sink is positioned with the fins in the vertical plane, with an unimpeded air flow. As a general rule, a heat sink with the proportions of the 2 inch length of extrusion (curve (a)) is suitable
Z
SSR Thermal Considerations Cont’d
TEMPERATURE RISE ABOVE AMBIENT (°C)
THERMAL RESISTANCE (RΘSA)°C/W
3.0
A 2.5
B 2.0
1.5
100 STILL AIR (NATURAL CONVECTION) FINS VERTICAL 80
60 300 LFM 500 LFM
40
1000 LFM 20
0
1.0 0
5
10
15
20
25
30
35
0
20
40
DISSIPATION (WATTS)
60
80
100
120
140
160
POWER DISSIPATED (WATTS)
Fig. 21 Typical heat sink characteristics
Fig. 23 Typical free-moving air characteristics of a heavy duty heat sink, temperature rise versus power dissipated
for SSR’s rated up to 10 amps, while the 4 inch length (curve (b)) will serve SSR’s rated up to 20 amps. For power SSR’s with ratings greater than 20 amps, heavy duty heat sink of the type shown in Fig. 22 become necessary. The performance of a 5.5 inch length of the extrusion would approximate the characteristics shown in Fig. 23.
Not all heat sink manufacturers show their characteristics in terms of degrees C per watt (°C/W). Some show them as a temperature rise above ambient as shown in Fig. 23. In this case, a value for RΘSA is found by dividing power dissipation (watts) into the temperature rise (°C). For example, taking the 60 watt point on the dissipation scale the free air curve would indicate a 40 degree rise. Hence:
SSR
TRISE RΘSA = –––– P
2.62 INCHES 1.44 INCHES
4.75 INCHES
Fig. 22 An end view of a typical heavy duty aluminum heat sink extrusion
40 = –– 60 = 0.66°C/W In many applications, the SSR is mounted to a panel or base plate which may also be more than
Z-121
adequate as a heat sink. By ensuring flatness, using thermal compound, and removing paint to maximize effectiveness, a base plate (SSR) temperature measurement at maximum ambient may be all that is necessary to confirm proper operation as previously mentioned. If an SSR installation does not provide an adequate heat sink, a selection is made from the wide variety of commercial heat sink types that are available. Each configuration has its own unique thermal characteristics and are usually well documented with manufacturers’ performance curves and application data.
No Time Out for This Programmable Timer/Controller Model PT41 a precision clock/timer, controller, combines the features of many dedicated meters into one multipurpose design. See Figure 1. Challenge this universal and economical, programmable timer/controller to any level task, from variable cycle timing in complex patterns to elementary stop watch and reset operations.
Z
Timing modes and patterns are virtually Figure 1 PT41 timer/controller unlimited and the four independently If power is interrupted, the microprocessor-based nonvolatile controlled outputs are easily memory retains all timer settings. If programmed using front panel retention of day and date is required, pushbuttons or remote serial link. a battery backup option is available. Connected by a common bus to other DP41 series test instruments, the PT41 timer/ controller is capable Programming Made Simple The PT41 is fully programmable of requesting readings from all from the front panel or remotely via meters and recording the data on an RS-232 or RS-485 serial link. a common printer. Front panel programming is Special Features accomplished with five pushbuttons. The programmer is prompted with The features of this precision key words (such as START, TIMSET, instrument allow variations of UNITS, ELAPSE) on the six position timing patterns through simplified alphanumeric LED display. programming and process monitoring. There are four The remote programming option independent outputs with eight has more than forty commands programmable setpoints and five which allows full control by a controlled output modes allowing personal computer or work station. for extensive combinations of load Programming and timing status is control patterns. For the often used fed back to the personal computer timing sequences, the instrument for program verification. The remote can store up to 64 preset patterns. programming feature comes with its Operations may be timed in own directive software. intervals as short as 0.01 second or as long as 24 hours and will repeat Automated Data Logging any cycle up to a million times. A unique feature of the PT41 is The meter may be configured to found in its controller mode. A use any one of eight built-in time maximum of 32 DP41 series bases (such as time-of-day or one instruments (such as voltmeters, hour resolution). temperature indicators, batch controllers) equipped with RS-485 The user can view the setup and serial interface boards, can be timing configuration any time the bussed together using this meter is functioning. Depress the instrument as a timer/controller. It front panel REVIEW button or can sequence through all meters on activate the remote serial link and the bus and request readings from this feature will display the timing all devices. An RS-485 printer, also sequence without disturbing the located on the bus, is then directed timing function. Z-122
to record the readings, with or without a time and date stamp. The PT41 can be programmed to monitor remote devices in intervals of up to eleven days. Figure 2 illustrates a typical configuration using the PT41 to connect three DP41 instruments and a printer.
Manages Any Time Problem The flexible timing and output load control of this meter provide the tools needed to manage any timing problem. Applications such as life testing, burn-in, reliability evaluation, process control, and repeat cycle timing are typical. Example 1 Time and control of intermittent burn-in, where a product is to be energized for ten seconds and deenergized for 50, with the process cycled 10,000 times; voltage readings logged every hour. Example 2 Time and control of four production processes running concurrently, each requiring different start-stop sequencing with an alarm to signal key steps in each process. Example 3 Control the opening and closing time periods for a set of doors in a facility for security reasons. Example 4 Record readings from five remote unattended test instruments once a day and repeat the process for ten days.
No Time Out for This Programmable Timer/Controller
U.S. and Int’l Patents. Used Under License.
+140°F (0°C to +60°C). The AC power is 115V or 230V ±10 % with power consumption 9 Watts maximum.
Adaptable Design The six position, 14 segment red or green LED display operates at 100% and 50% brightness levels. Additional indicator lights show alarm settings, AM/PM reference and timer status. The clock time base is derived from the 50 or 60 Hz line frequency and from an internal crystal oscillator with an accuracy of ±50 PPM over the full operating temperature range of +32°F to
Universal Instrument The PT41 is a full function instrument capable of timing, controlling and directing data logging. The functions and features included in this one low cost instrument are normally attained by combining several individual meters. PT41 functions in a panel mount or table configuration and is the “all in one” solution for automated test, operation and process control.
The UL-rated polycarbonate case is dimensioned 1.89" H x 3.78" W x 5.86" D (48 x 96 x 149 mm).
Controller Mode Operation RS-485
RS-485 1
2
SETPTS
3
STOP
4
MENU
RESET
PTC41 TIMER/ CONTROLLER
RS-485
RS-485
REVIEW
AB PQ CDEFGH AB RSTUVW IJKLMN PQ CDEFGH XYZ[/] O ABCD RSTUVWX IJKLMNO ^_ Y EFGH IJKLM Z[/]^_ NO 1
MAX
1
1
2
SETPTS
3
MIN
2
3
4
SETPTS MENU
RESET
DP41-E PROCESS METER
DISPLAY
2
SETPTS STOP
3
4
MENU
MAX
RESET
DPF400 RATE TOTALIZER
DEV
4
MENU
RESET
DP41-T TEMPERATURE INDICATOR
PRINTER
Figure 2 A typical configuration demonstrating the PT41 linked to three DP41 instruments and a printer.
Z-123
Solid State ReIays
ISOLATING TRANSFORMER CONTROL
DC-AC CONVERTER
TRIAC
LOAD
TRIGGER CIRCUIT
Figure 1. Hybrid SSR
Figure 2. Transformer-Coupled SSR
AC POWER
PHOTO-TRANSISTOR REED RELAY TRIAC
CONTROL SIGNAL OPTIONAL PREAMPLIFIER
LED
LOAD CONTROL SIGNAL
TRIGGER CIRCUIT
TRIAC
LOAD
TRIGGER CIRCUIT AC POWER
Figure 3. Photo-Coupled SSR
AC POWER
Defined and Described SSR Defined. A solid-state relay is an ON-OFF control device in which the load current is conducted by one or more semiconductors - e.g., a power transistor, an SCR, or a TRIAC. (The SCR and TRIAC are often called “thyristors,” a term derived by combining thyratron and transistor, since thyristors are triggered semiconductor switches.) Like all relays, the SSR requires relatively low controlcircuit energy to switch the output state from OFF to ON, or vice versa. Since this control energy is very much lower than the output power controllable by the relay at full load, "power gain" in an SSR is substantial--frequently much higher than in an electromagnetic relay of comparable output rating. To put it another way, the sensitivity of an SSR is often significantly higher than that of an EMR of comparable output rating. Types of SSR's. It is convenient to classify SSR's by the nature of the input circuit, with particular reference to the means by which input-output isolation is achieved. Three major categories are recognized: • Reed-Relay-Coupled SSR's (see figure 1), in which the control signal is applied (directly, or through a preamplifier) to the coil of a reed relay. The closure of the reed switch then activates appropriate circuitry that triggers the thyristor switch. Clearly, the input-output isolation achieved is that of the reed relay, which is usually excellent. • Transformer-Coupled SSR's (see figure 2), in which the control signal is applied (through a DC-AC converter, if it is DC, or directly, if It is AC) to the primary of a small, low-power transformer, and the secondary voltage that results from the primary excitation is used (with or without rectification, amplification, or other modification) to trigger the thyristor switch. In this type, the degree of input-output isolation depends on the design of the transformer.
• Photo-coupled SSR's (see figure 3), in which the control signal is applied to a light or infrared source (usually, a light-emitting diode, or LED), and the radiation from that source is detected in a photosensitive semi-conductor (i.e., a photosensitive diode, a photo-sensitive transistor, or a photo-sensitive thyristor). The output of the photo-sensitive device is then used to trigger (gate) the TRIAC or the SCR's that switch the load current. Clearly, the only significant “coupling path” between input and output is the beam of light or infrared radiation, and electrical isolation is excellent. These SSR's are also referred to as “optically coupled” or “photo-isolated”. In addition to the major types of SSR's described above, there are some special-purpose designs that should be mentioned: • Direct-control AC types (see figure 4), in which external contacts, operating in a circuit energized by the same AC power line as is used for the load circuit, trigger a TRIAC (or back-to-back-connected SCR's). This type is also referred to as having a “switch closure” input. Clearly, this type of relay, while simpler and inherently less expensive than more sophisticated designs, has the great disadvantage (for most applications) of having no isolation between the control and load circuits. • Direct-control DC types (see figure 5) in which external contacts, operating in a circuit energized by the same DC power line as is used for the load circuit, control the conduction of a transistor. This type of relay, which is perhaps the simplest of all, and inherently the least expensive, also has the great disadvantage (for most applications) of having no isolation between the control and load circuits. • SCR types designed for DC, in which the load-currentcarrying SCR is made to turn off by means of a second
Z-124
Z
Solid State Relays Cont’d CONTROL CONTACTS LOAD
DC POWER
Figure 5. Direct-Control DC SSR
COMMUTATING CAPACITOR
CONTROL CONTACTS TRIGGER CIRCUIT
LOAD
A CONTROL SIGNAL
ISOLATING CIRCUIT (SEE FIGS. 1-3) B
R
SCR-2
SCR-1 LOAD
AC POWER
Figure 4. Direct-Control AC SSR
Figure 6. SSR using SCR switch DC POWER
SCR, connected in a “commutating circuit” (such as that of figure 6), which is capable of turning off the first SCR by momentarily reducing its current to zero.
because all the input signal must do is to gate on the AC-DC converter (see figure 2) that drives the transformer, and that requires, typically, less than 10 milliwatts (e.g., 4.5 v dc at 2 mA) and rarely more than 50 milliwatts. This sensitivity is better than required by any single-TTL digital output, and a high-fan-out TTL output can drive from 3 to 10 such SSR’s in parallel.
• Designs using special isolating means, such as. . . ...the Hall effect in which the motion of a magnet external to, but in proximity to, the SSR causes a change in resistance in a field -sensitive material, thereby triggering on-off behavior. ...oscillator tuning, in which the external signal shifts the frequency of an oscillator, thereby causing a closely coupled resonant circuit to trigger on-off behavior. ...saturable reactors or magnetic amplifiers, in which a DC control current in one winding controls the induced voltage (from an AC source) in another winding. The induced voltage is then used to trigger on-off behavior. It is safe to say that well over 95% of all SSR requirements are best satisfied by one of the three major types described earlier (i.e., figures 1-3). Input Circuit Performance. The sensitivity of isolated SSR’s (that is, the minimum control voltage and current at which the SSR turns on) depends on the characteristics of the isolating component or circuit: • In hybrid (reed-relay isolated) designs, the SSR’s sensitivity is established by the operating-power requirement of the reed relay, which ranges from as low as 40 milliwatts (e.g., 5 volts dc at 8 mA) to as high as several hundred milliwatts. Note that the low-voltage, low-power designs are compatible with standard digitalcomputer “logic levels,” and that the standard “high-fanout” TTL logic-level output from a digital computer or digital controller can drive two or more hybrid SSR’s in parallel. • In transformer-coupled SSR’s, the sensitivity is usually considerably higher than that of the hybrid type,
• In optically coupled SSR’s, the sensitivity ranges from about 6 milliwatts (e.g., 3 volts dc at 2 mA) to 100 milliwatts. Using an appropriate series resistor or current regulator, this type of input circuit is also compatible with TTL logic levels, and several optically coupled SSR’s can be driven in parallel by high-fan-out logic lines. • The sensitivity of most “direct-control“ SSR’s (figures 4 and 5) is significantly lower than that of the isolated designs, but that fact is of little importance because the control power required is almost always well within the capability of even the smallest control contacts. The maximum turn-off level (voltage and/or current) of an SSR is about 50% of the minimum level at which it turns on. This characteristic provides an adequate margin of safety between the ON and OFF states, thereby eliminating erratic behavior due to small changes in the control signal. In many SSR designs, the control-voltage range is much greater than that implied by the minimum turn-on voltage. In designs optimized for wide input voltage range, it is not uncommon for the SSR to be rated for use over more than a 6-to-1 range of control voltages (e.g., 3.0 V to 32 V). In hybrid designs, the coil of the reed relay may be wound for almost any useful control voltage, from as low as 3 volts nominal, to 50 volts, or even higher, but the range of input voltage tolerated by a hybrid SSR is limited by dissipation in the relay coil. Generally, a range of 1.5 to 1 is acceptable. On the other hand, series resistance, or a “constant-current” active input circuit, may be used to accommodate a hybrid relay to higher input voltages.
Z-125
(a) V S U P P LY l LOAD
LOAD
l LEAKAGE TRIGGER CIRCUIT
V LOAD AC POWER
V OFF
R
R LEAKAGE
l LOAD
( ≈ V S U P P LY )
Z
(c)
R
Vd
L
VSSR (X50)
V S U P P LY L
(b)
Figure 7. Simplified Circuit of an SSR (a), and equivalent circuits for the ON state (b) and the OFF state. (c)
V S U P P LY
Input Characteristics. Beyond consideration of the sensitivity characteristics (page Z-120), we must also describe the input-circuit isolation characteristics of an SSR, which requires consideration of many different parameters, including:
Figure 8a. ON-Mode Waveforms (VSSR is greatly exaggerated)
Note that these parameters are (at least at first glance) analogous to the usual voltage and current ratings of the contacts on an electro-magnetic relay. There are, however, differences between EMR output ratings and SSR output ratings--differences that will be examined in detail as this exposition proceeds.
• Dielectric strength, rated in terms of minimum breakdown voltage from control circuit to both the SSR case and the output (load) circuit. A typical rating is 1500 volts ac (RMS), for either control to case or control to output. • Insulation Resistance, from control circuit to both the case and the output circuit. Typical ratings range from 10 megohms to 100,000 megohms for transformer and hybrid designs. For optically isolated SSR’s, typical insulation resistances range from 1000 to 1 million megohms. • Stray Capacitance from control circuit to both case and the output circuit. Capacitance to case is rarely significant, but capacitance to the output circuit may couple ac and transients back to the sensitive control circuit, and even further back, into the control-signal sources. Fortunately, in well designed SSR’s, this capacitance is rarely large enough to cause interaction. Typical stray capacitance ranges from 1 to 10 picofarads. The speed of response of the SSR to the application of control voltage is covered later in this section. Output Circuit Performance. Clearly, the most significant output-circuit parameters are the maximum load-circuit voltage that may be impressed across the relay output circuit in the OFF condition without causing it to break down into conduction or failure, and the maximum current that can flow through the output circuit and load in ON condition.
In the most general approach, one may say that the “contact ratings” of an SSR are determined almost entirely by the characteristics of the load-current switching device. Perhaps this fact is most apparent from an examination of the simplest type of ac SSR - a direct-control (non-isolated) design, such as that originally shown in figure 4, and redrawn above in figure 7, with its equivalent circuit for both the ON and OFF states. In the ON state (figure 7b), the TRIAC exhibits a nearly constant voltage drop (i.e., almost independent of load current) approximately equal to that of two silicon diodes - less than 2 volts. The passage of load current through this voltage drop causes power dissipation (Pd = Vd x Iload), and this power will cause a temperature rise in the TRIAC junction. If proper “heatsinking” is provided - i.e., thermal conduction from the TRIAC case to the outside air or to a heat-conductive metal structure that can in turn dissipate the power to the surrounding air without significant temperature rise then the TRIAC temperature will not rise above the rated maximum value for reliable operation (typically, 100°C). With generous heat sinking, the current rating of the SSR may be determined, not by power dissipation, but by the current rating of the TRIAC. Figure 7c shows the equivalent circuit of this very simple SSR in the OFF state. Note that even when the TRIAC is turned off, a very small amount of leakage current can flow. This current path, represented by a resistance in the equivalent circuit, is actually a non-linear function of the load-circuit voltage. The normal practice, in rating
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Solid State Relays Cont’d V S U P P LY
CURRENT STARTS AT NEXT CROSSING
V S U P P LY
V S S R ≈ V S U P P LY l
LEAKAGE
(≈
1/1000 X l L O A D ) l LOAD
Figure 8b. OFF-Mode Waveforms (Ileakage is greatly exaggerated)
l LOAD
TURN OFF HERE
ON OFF
START DELAY
CURRENT CONTINUES TO HERE
V S U P P LY
CONTROL SIGNAL
ON OFF
OFF
Figure 9a. Non-Synchronous SSR waveforms for resistive load
TRIAC’s, is to specify a worst case maximum value for this “OFF-state leakage” and a typical value is 0.001 A max. for a 5-ampere load-current rating. The load circuit voltage rating is simply that determined by the blocking voltage rating of the thyristor. The output-circuit ratings of the more common isolated SSR’s, most of which are designed to control ac load circuits, are very similar to those described above, except that OFF-state leakage is usually higher---on the order of 5 mA at 140 V for a 5-ampere device---still only about one-thousandth of the load current rating. Figure 7 shows the equivalent circuit of a TRIAC-switch SSR design, and figure 8 shows the voltage and current waveforms in the load circuit, for both OFF and ON states. Note that the ON-state voltage-drop curves are drawn to a much expanded scale compared with the OFF state and load voltage curves. Even at this early stage in our examination of SSR performance, it is necessary to consider the time relationships between the control signal and the ac load-circuit voltage and current. With respect to timing, there are two classes of switching SSR’s. In one, no particular effort is made to achieve synchronism between the alternations of the load circuit-power line and the turning on of the thyristor switch. In this “non-synchronous” class, then, the response delay between the application of control voltage and the beginning of load-circuit conduction is very short...typically from 20 to 200 microseconds in optically coupled and transformer types, and less than one millisecond in hybrids (longer due to the reed relay operation time). The current waveform on turn-on in non-synchronous designs is clearly a function of when in the ac cycle the control signal is applied, as illustrated in figure 9a.
CONTROL SIGNAL
OFF
Figure 9b. Synchronous SSR waveforms for resistive load
In synchronous (zero-voltage turn-on) designs, the effect of the application of a control signal is delayed (if necessary) until the power-line voltage is passing through zero (see figure 9b). (This is done by internal gating circuitry that senses the magnitude of the line voltage, and prevents triggering the thyristor until the next zero crossing occurs.) Thus, if the control signal happens to be applied immediately after a zero crossing, the SSR would not actually begin conducting until almost a full half-cycle later. On the other hand, if the control signal happens to be applied just before a zero-crossing is about to occur, the SSR would begin to conduct almost immediately, with only the very small turn-on delays described above for non-synchronous designs. Clearly, then, the turn-on delay of a synchronous SSR can have any value from less than a millisecond to a full half-cycle of the power line (about 8.3 milliseconds for a 60-Hz power line). Usually, for 60 Hz service, the rating is given as 8.3 milliseconds maximum for all-solid-state designs, and 1.5 milliseconds maximum for hybrid designs. The final major characteristic of the AC-switching SSR is its turn-off behavior. Because a thyristor, once triggered, will not stop conducting until the load current flowing through it falls to zero, there is a maximum possible turn-off delay (between the removal of the control signal and the cessation of load current) of one half cycle. As in the case of turn-on, the minimum turnoff delay is close to zero. Thus, a typical 60-Hz rating for turn-off time is 9 milliseconds maximum. ®
Reproduced with permission of Crydom Corporation
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Intrinsic Safety How are Hazardous Locations Defined? Answer: According to the National Electrical Code, Article 500, hazardous locations are defined by Class, Group and Division. Differentiation by Class and Group is in accordance with the laws of physics, while Division classification is based on environmental and physical plant conditions. Relative to the application of Intrinsic Safety, it is important to define the actual Class, Group and Division into which any proposed Intrinsically Safe electrical circuits are to be installed. As shown by the ignition curves, all flammable mixtures do not require the same energy levels to ignite. Because Intrinsic Safety requires maintaining an energy level lower than that required to ignite a specific hazardous mixture, it is important to know what the energy allowances are for operational and safety considerations.
The Definition of Intrinsic Safety Identifies Both Electrical and Thermal Energy as Potential Causes of Ignition. How Does Thermal Energy Relate to the Ignition of a Specific Flammable or Combustible Mixture? Answer: There are temperatures at which a flammable or combustible mixture will ignite. The minimum temperature at which ignition takes place is called the “Auto-Ignition Temperature.” Intrinsically Safe systems will not allow thermal energy to reach levels at which a specific flammable or combustible mixture will autoignite. Figure 1 identifies common hazardous mixtures and their auto-ignition temperatures. Hazardous Mixture
Typical Resistance Circuit Ignition Currents Identify Only Four Hazardous Substances: Hydrogen, Ethylene, Propane and Methane. Aren’t There More Flammable or Combustible Materials Than That? Answer: Yes, but those four hazardous mixtures represent the basis for all flammable or combustible mixtures subject to ignition from electrical sources. All are found, as shown in the Hazardous (Classified) Locations chart following, in Class I, with Hydrogen identified as Group B; Ethylene identified as Group C; Propane being Group D and, as a separate curve within Group D, Methane.
Acetone Acetylene Ammonia Benzene Benzol Butane Butylalchohol Carbon Disulphide Carbon Oxide Cyclohexane Diesel Fuel Ethane Ethylacetate Ethylalchohol Ethylchloride Ethylene Ethylether Ethyl Glycol Fuel Oil Hexane Hydrogen aeroxide Hydrogen disulphide Methane Methanol Methyl chloride Naphthalene Phenol Propane Tetraline Toluol
Acetylene: Group A and Hydrogen: Group B share the same required energy levels relative to ignition. They require less energy for ignition than does Group C, which requires less energy for ignition than Group D. Within Class II Group E, metal or electrically conductive dusts, Group F, Coal Dust and Group G, electrically nonconductive dusts, generally grain or agricultural dusts are identified. As Groups A and B share the same ignition curve, Group C, Ethylene, and Group E, metal or electrically conductive dusts, share the same ignition curve. Groups D, Propane, F, Coal Dust, and G, electrically nonconductive dusts, share the same ignition curve. A complete listing of hazardous mixtures defined by Group can be found in National Fire Protection Association document NFPA 497 M.
Autoignition Temperature °C °F 540 305 630 220 555 365 340 95 605 430 220 to 300 515 460 425 510 425 180 235 220 to 300 240 560 270 595 455 625 520 595 470 425 535
1004 581 1166 428 1031 689 644 203 1121 806 428 to 572 959 860 797 950 797 356 455 428 to 572 464 1040 518 1103 851 1157 968 1103 878 797 995
Figure 1: Autoignition temperatures of some hazardous mixtures.
Reproduced with permission of R. Stahl.
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Z
Intrinsic Safety Cont’d
Hazardous (Classified) Locations in Accordance with Article 500, National Electric Code-1990
Class I Flammable Gases or Vapors
Division 1 • Exists under normal conditions • May exist because of: - repair conditions - maintenance operations - leakage • Released concentration because of: - breakdown of equipment - breakdown of process - faulty operation of equipment - faulty operation of process which causes simultaneous failure of electrical equipment
Group A:
Division 2 • Liquids and gases in closed containers or the systems are: - handled - processed - used • Concentrations are normally prevented by positive mechanical ventilation. • Adjacent to a Class I, Division 1 location
Atmospheres containing Acetylene
Group B:
Atmospheres such as Butadiene, ethylene oxide, Propylene Oxide, Acrolein, or Hydrogen (or gases or vapors equivalent in hazard to hydrogen such as manufactured gas)
Group C:
Atmospheres such as Cyclopropane, Ethyl Ether, Ethylene, or gases or vapors equivalent in hazard
Group D:
Atmospheres such as Acetone, Alcohol, Ammonia, Benzene, Benzol, Butane, Gasoline, Hexane, Lacquer Solvent vapors, Naphtha, Natural Gas, Propane or gases or vapors equivalent in hazard
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Class II Combustible Dusts
Division 1 • Exists under normal conditions • Combustible mixture produced by: - mechanical failure of equipment or machinery - abnormal operation of equipment and provide source of ignition from: - simultaneous failure of electrical equipment - simultaneous failure of operation of protection devices - other causes • Electrically conductive dusts may be present
Division 2 • Not normally in the air • Accumulations normally sufficient to interfere with normal operation of electrical equipment or other apparatus. • In the air as a result of infrequent malfunctioning of: - handling equipment - process equipment • Accumulations are sufficient to interfere with the safe dissipation of heat from electrical equipment • Accumulations may be ignitible by abnormal or failure of electrical equipment
Group E:
Atmospheres containing combustible metal dusts (regardless of resistivity), dusts of similarly hazardous characteristics ( < 100 kΩ/cm) or electrically conductive dusts
Group F:
Atmospheres containing combustible Carbon Black, Charcoal or Coke Dusts which have > 8% total volatile material or if these dusts are sensitized so that they present an explosion hazard and having a resistivity > 100 kΩ/cm but ≤ 100 MΩ/cm
Group G:
Atmospheres containing combustible dusts having a resistivity > 100 kΩ/cm or electrically nonconductive dusts
Class III Ignitable Fibers or Flyings Division 1 • Fibers or materials producing combustible flyings are manufactured, stored or handled
Not Grouped • Manufacturers such as textile mills, cotton-related mills or clothing plants • Fibers and flyings including Rayon, Cotton, Sisal, Hemp, Jute and Spanish Moss Z-130
Division 2 • Fibers are handled except during the process of manufacture or are stored except during the process of manufacture
Z
Intrinsic Safety Circuit Design
Making instruments intrinsically safe need not seem like a nightmare. Here, the basics of intrinsic safety circuit design are discussed. Paul S. Babiarz
Intrinsically Safe Apparatus
Intrinsically Safe Applications(%)
Switching mechanical switches proximity switches
32.0% 85.0% 15.0%
2-wire transmitters Thermocouples & RTDs Load cells Solenoid valves Potentiometers LEDs I/P transducers Other devices
22.0% 13.0% 8.5% 4.5% 2.5% 2.0% 2.0% 13.5%
Total field devices
Intrinsic safety prevents instruments and other low-voltage circuits in hazardous areas from releasing sufficient energy to ignite volatile gases. Although it is used widely in Europe to safely install and operate instrumentation circuits in hazardous areas, it has caused much confusion in North American markets. Many users have heard of it and want to know more; however, most feel uncomfortable applying intrinsically safe products. One reason is that intrinsic safety has been a part of Section 504 of the National Electric Code only since 1990. In addition, the number of different products on the market and seemingly endless calculations make applying intrinsic safety seem like an engineer’s nightmare. This is the first of a series of short articles that explain how to make the most common field devices (thermocouples, RTDs, contacts, solenoid valves, transmitters, and displays) intrinsically safe. We will begin with an introduction to the practical side of intrinsic safety circuit design.
100.0%
Figure 1. Current use of intrinsically safe apparatus in hazardous areas.
device, also known as a barrier or intrinsically safe associated apparatus; and the field wiring. When designing an intrinsically safe circuit, begin the analysis with the field device. This will determine the type of barrier that can be used so that the circuit functions properly under normal operating conditions but still is safe under fault conditions. More than 85% of all intrinsically safe circuits involve commonly known instruments. Figure 1 shows the approximate use of intrinsically safe apparatus in hazardous areas. An intrinsically safe apparatus (field device) is classified either as a simple or nonsimple device. Simple apparatus is defined in paragraph Safe Area
A nonsimple device can create or store levels of energy that exceed those listed above. Typical examples are transmitters, transducers, solenoid valves, and relays. When these devices are approved as intrinsically safe, under the entity concept, they have the following entity parameters: Vmax (maximum voltage allowed); Imax (maximum current allowed); Ci (internal capacitance); and Li (internal inductance). The Vmax and Imax values are straightforward. Under a fault condition, excess voltage or current could be transferred to the intrinsically safe apparatus (field device). If the voltage or current exceeds the apparatus’ Vmax or Imax, the device can heat up or spark and ignite the gases in the hazardous area. The Ci and Li values describe the device‘s ability to store energy in the form of internal capacitance and internal inductance.
Intrinsically Safe Barrier
Fuse
Input Voltage
3.12 of the ANSI/ISA-RP 12.6-1987 as any device which will neither generate nor store more than 1.2 volts, 0.1 amps, 25 mW or 20 µJ. Examples are simple contacts, thermocouples, RTDs, LEDs, noninductive potentiometers, and resistors. These simple devices do not need to be approved as intrinsically safe. If they are connected to an approved intrinsically safe associated apparatus (barrier), the circuit is considered intrinsically safe.
Hazardous Area
Current Limiting Resistor
Zener Diodes
Start With The Field Device All intrinsically safe circuits have three components: the field device, referred to as the intrinsically safe apparatus; the energy-limiting
Instrinsically Safe Ground
Figure 2. Barrier circuit
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Field Device
5A
Limiting Energy To The Field Device
There are three components to a barrier that limit current and voltage: a resistor, at least two zener diodes, and a fuse. The resistor limits the current to a specific value known as the short circuit current, Isc. The zener diode limits the voltage to a value referred to as open circuit voltage, Voc. The fuse will blow when the diode conducts. This interrupts the circuit, which prevents the diode from burning and allowing excess voltage to reach the hazardous area. There always are at least two zener diodes in parallel in each intrinsically safe barrier. If one diode should fail, the other will operate providing complete protection. A simple analogy is a restriction in a water pipe with an overpressure shut-off valve. The restriction prevents too much water from flowing through the point, just like the resistor in the barrier limits current. If too much pressure builds up behind the restriction, the overpressure shutoff valve turns off all the flow in the pipe. This is similar to what the zener diode and fuse do with excess voltage. If the input voltage exceeds the allowable limit, the diode shorts the input voltage to Associated Apparatus Apparatus (barrier) (field device) Open circuit voltage Voc ≤ Vmax Short circuit current Isc ≤ Imax Allowed capacitance Ca ≥ Ci Allowed inductance La ≥ Li Figure 3. Comparison of the entity values of an intrinsically safe apparatus and associated apparatus
2A
1A
Z Ignition Current (A)
To protect the intrinsically safe apparatus in a hazardous area, an energy-limiting device must be installed. This is commonly referred to as an intrinsically safe associated apparatus or barrier. Under normal conditions, the device is passive and allows the intrinsically safe apparatus to function properly. Under fault conditions, it protects the field circuit by preventing excess voltage and current from reaching the hazardous area. The basic circuit diagram for an intrinsically safe barrier is shown in Figure 2.
500 mA
Groups C and D Methane Propane Ethylene
200 mA
100 mA
Groups A and B Hydrogen
50 mA
20 mA
10 mA 10
20
30
40
50
100
200
Open Circuit Voltage (V) Figure 4. Ignition curves – resistance
ground and the fuse blows, shutting off electrical power to the hazardous area. When conducting the safety analysis of the circuit, it is important to compare the entity values of the intrinsically safe apparatus against the associated apparatus. These parameters usually are found on the product or in the control wiring diagram from the manufacturer (see Figure 3).
Will The Circuit Work? It also is important to make sure that the intrinsically safe circuit will work under normal conditions. With the current-limiting resistor, a voltage drop will occur between the input and output of the barrier. This has to be accounted for in your circuit design. In the subsequent articles in this series, a step-by-step explanation will be given on how to calculate these voltage drops and make sure that the circuit is safe. Z-132
Determining Safe Energy Levels Voltage and current limitations are ascertained by ignition curves, as seen in Figure 4. A circuit with a combination of 30 V and 150 mA would fall on the ignition level of gases in Group A. This combination of voltage and current could create a spark large enough to ignite the mixture of gases and oxygen. Intrinsically safe applications always stay below these curves where the operating level of energy is about 1 watt or less. There are also capacitance and inductance curves which must be examined in intrinsically safe circuits. The purpose of this series of articles is to simplify the application of intrinsic safety. Consider the ignition curves to demonstrate a point about thermocouples.
Intrinsic Safety Circuit Design Cont’d NON-HAZARDOUS SIDE
HAZARDOUS SIDE
Recorder Maximum 0.1 volt produced by thermocouple
Figure 5. Thermocouple installed in a hazardous area
NON-HAZARDOUS SIDE
HAZARDOUS SIDE
Recorder
explosion possible
110 V FAULT
Figure 6. Thermocouple with fault
NON-HAZARDOUS SIDE
Recorder
HAZARDOUS SIDE
Instrinsically Safe Barrier
Figure 7. Thermocouple with barrier
A thermocouple is classified as a simple device. It will not create or store enough energy to ignite any mixture of volatile gases. If the energy level of a typical thermocouple circuit were plotted on the ignition curve in Figure 4, it would not be close to the ignition levels of the most volatile gases in Group A. Is the thermocouple which is installed in a hazardous area (Figure 5) intrinsically safe? The answer is no, because a fault could
occur on the recorder which could cause excess energy to reach the hazardous area, as seen in Figure 6. To make sure that the circuit remains intrinsically safe, a barrier to limit the energy must be inserted (Figure 7). The next installment in this series will explain how the selection is made for thermocouples and RTDs, which comprise about 13% of all intrinsically safe applications. Z-133
BEHIND THE BYLINE Paul B. Babiarz is marketing manager of intrinsically safe products for CrouseHinds. He holds a B.S. from the University of Rochester, an M.S. from the University of Michigan, and an M.B.A. from Syracuse University. He has more than 13 years of experience in working in hazardous areas and has specialized in intrinsic safety. Copyright Instrument Society of America. Intech, October, 1992. All Rights Reserved.
Intrinsic Safety Circuit Design–Part 2 Fault conditions in hazardous-area temperature sensors can be explosive without the proper protection. You can safeguard all of the devices in your application with one type of intrinsic safety barrier.
Z Paul S. Babiarz When thermocouples and RTD’s (resistance temperature devices) are installed in hazardous areas, barriers are required to make their circuits intrinsically safe. These intrinsic safety barriers prevent excess energy from possible faults on the safe side from reaching the hazardous area. Without the barriers, excessive heat or sparks produced by the fault condition could ignite volatile gases or combustible dusts. Hundreds of different barriers are available from North American suppliers. The multitude of products can give control engineers nightmares as they try to select the proper barrier for common instrumentation loops. The search can be simplified, however. One type of barrier can be selected to make all thermocouples and RTD’s intrinsically safe so that polarity problems are avoided and calculations are not necessary. Normally, the design of all intrinsically safe circuits centers on one of two approaches: the universal approach, which uses a universal device that often is isolated so that a ground for safety is not required; or the engineered approach, which uses grounded safety barriers. ■ Isolated temperature converters. These universal devices measure temperature in hazardous areas, but at a higher cost. (Dispensing with the need for a ground is a convenience that may cost two to three times as much as grounded safety barriers.) Isolated temperature converters accept a low-level DC signal from a thermocouple or 3-wire RTD and convert it into a proportional 4-20 mA signal in the safe area. •They also are available with set points that trip an on-off signal to
HAZARDOUS SIDE CLASS I,II, III DIVISION 1 GROUPS A-G
NON-HAZARDOUS SIDE
+
Control Room – GRD
Intrinsic Safety Barrier Use same type of wire
Thermocouples are simple devices. Do not need approval
Use same type of wire Safety Barrier Parameters VN: 2.5 V
Ri: 71 Ω
Note: Use consistent wiring
Figure 1. Current use of intrinsically safe apparatus in hazardous areas.
+ -
V
RTD
V Voltmeter
Figure 2. Typical values of barrier in thermocouple circuit.
the safe side when the temperature reaches a designated level. These units must be approved as intrinsically safe. Advantages of isolated temperature converters as compared to grounded safety barriers include: • Good signal response • No ground required for safety Z-134
• More versatile application • One product for all applications Disadvantages include: • Larger in size • Requires calibration • More expensive • May not work with all thermocouples and RTD’s
Intrinsic Safety Barrier A
A V
V
B
R1
B C R2
C V Voltmeter
V Voltmeter
Note: When R1 = R2, bridge remains balanced
Figure 3. 3-wire RTD bridge
■ Grounded safety barriers. These are passive devices that prevent all excess energy from a fault occurring on the safe side from reaching the hazardous area. Under normal conditions, the barriers allow the circuit to function properly by allowing the signals to pass between the field device and the control room. In a fault condition, the barriers limit voltage and current to levels that are not sufficient enough to ignite gases. For a more detailed explanation, refer to Part 1 of this series. Advantages of grounded safety barriers as compared to isolated temperature converters include: • Less expensive • Precise signal response • Very small (less than 1⁄2 in. wide) • Simple application • One barrier for all types of thermocouples and RTD’s Disadvantages include: • Requires ground • Requires some engineering
Examine The Barrier Parameters Articles in this series will focus on methods to select the proper grounded safety barriers. Before we analyze thermocouple and RTD circuits, we should examine the functional parameters necessary to select the proper barrier. These parameters are: polarity of circuit; rated voltage of barrier; and resistance of barrier. ■ Polarity. The circuit’s polarity must be known in order to choose the correct type of barrier. DC barriers are rated either as positive or negative. AC barriers can be connected to circuits with either a positive or negative supply. SIGNAL & RETURN barriers are used for transmitter and switching applications. All of these barriers are available in single- or double-channel versions. However, because double-channel barriers save space and money by being connected to two legs of a loop, they are becoming the standard.
Figure 4. 3-wire RTD bridge with barrier
■ Rated voltage. Like any electrical device, safety barriers have a rated nominal voltage, Vn, referred to as working voltage. The barrier’s Vn should be greater than or equal to the supply to the barrier, much like the rated voltage of a lamp must be equal to or greater than the supply to it. If the voltage supply to the barrier is much greater than its Vn, the barrier will sense a fault. The protective zener diodes will conduct, causing leakage currents and inaccurate signals on the loop. Most barriers have a rated working voltage that guarantees a minimal leakage current from 1 to 10 micro amps if it is not exceeded. If the supply voltage to the barrier becomes too high, the zener diode will conduct. The resulting high current through the fuse will cause the fuse to blow. Excess supply voltage is the main reason why grounded barriers fail. ■ Internal resistance. Every safety barrier has an internal resistance, Ri, that limits the current under fault conditions. Ri also creates a voltage drop across the barrier. This drop can be calculated by applying Ohm’s law, V=IR. Not accounting for the voltage drop produces the most problems in the proper functioning of intrinsically safe systems.
Thermocouple System Design Pointers ■ Polarity. A thermocouple has two wires, each with a positive and negative polarity. Two single-channel barriers, each with the proper polarity, could be used. Problems would occur if the positive leg to the thermocouple were connected to the negative terminal of the barrier or vice versa. There are two possible barrier choices for thermocouple circuits: Thermocouple circuit with one positive and one negative lead 1 standard DC barrier, positive polarity and 1 standard DC barrier, negative polarity OR 1 double AC barrier
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When barriers and thermocouples are being installed, the technician may forget which wire is positive and which is negative. To avoid polarity problems on the terminals, a double AC barrier should be used. The wires can be connected to either terminal and the circuit will function properly as long as thermocouple polarity is maintained throughout. ■ Rated voltage. A thermocouple produces a very small voltage (less than 0.1 V). It is connected to a voltmeter which has a high impedance and which requires a very small current. Since the thermocouple produces such a small voltage, choose a double AC barrier with a higher rated nominal voltage (Vn). A survey of most double AC barriers on the market shows that they are rated at low nominal voltages from 1 V and higher. Select one between 1 and 10 V. ■ Internal resistance. Since the mV signal has a very small current and is going to a high-impedance voltmeter, the resistance of the barrier will not influence circuit function. A simple rule of thumb is that when a signal is going to a high-impedance voltmeter, an internal barrier resistance of less than 1000 ohms will not affect the mV signal. It usually is good practice, however, to select a barrier with a low resistance in case the circuit is modified later. ■ Barrier selection. For proper operation of thermocouples in hazardous areas, select safety barriers based on the following parameters: • Barrier type: double-channel AC barrier to avoid polarity problems • Rated voltage: Barrier Vn > 1V • Internal resistance: barrier with lowest resistance (less than 110 ohms) ■ Safety and installation check. Since the thermocouple is a simple device, it does not need third-party approval. Make sure that the barrier has the proper approvals for hazardous area locations. The thermocouple wires will be different
from terminal connections on the barrier. Always use consistent wiring from the thermocouple to the barrier and then to the control room. This will cancel any thermocouple effect caused by the dissimilar metals on the barrier connection.
RTD System Design Pointers RTD’s come in 2-, 3-, and 4-wire versions. The 3-wire RTD is used in more than 80% of all applications. The 2-wire version is not as accurate and is used mostly in the heating, ventilation, and air conditioning industry for set-point temperature measurements. The 4-wire RTD provides the most accurate signal, but is more expensive and requires one more extension wire to the process area. Understanding RTD accuracy is essential in selecting the correct barrier. Many RTD measurements are in the form of a Wheatstone bridge, whose output voltage is a function of the RTD resistance. The bridge requires four connection wires, an external source, and three resistors that have a balanced temperature coefficient. The RTD normally is separated from the bridge by a pair of extension wires. With a 2-wire RTD, the impedance of the barrier in series with the RTD will cause an imbalance on the bridge and will affect the accuracy of the temperature reading. This
effect can be minimized by using a third wire to measure the voltage (refer to Figure 3 for this discussion). If wires A and B are perfectly matched and if the resistance in both channels of the barrier is the same, the impedance effects will cancel because each is in an opposite leg of the bridge. The third wire, C, acts as a sense lead to the voltmeter. ■ Current loop A & B: Polarity. The current loop to the RTD has a positive and a negative polarity. Possible solutions are similar to the thermocouple: 1 standard DC barrier, positive polarity and 1 standard DC barrier, negative polarity OR 1 double AC barrier
Select the double AC barrier to avoid polarity problems. Because it is smaller, it is also less expensive. ■ Current loop A & B: Rated voltage. The constant current amperage sent to the RTD typically is in the micro amp (10-6 ) level. The maximum resistance of the most commonly used RTD, Pt100 is 390 ohms at 1560°C. The voltage drop across the RTD will be in mV, so the Vn of the RTD loop is similar to the thermocouple. To be safe, select a barrier with a Vn greater than 1 V, similar to the Vn of the thermocouple barrier.
HAZARDOUS SIDE CLASS I,II, III DIVISION 1 GROUPS A-G
NON-HAZARDOUS SIDE Item 1
Current loop
RTD
GRD
Item 2
signal
RTD’s are simple devices. Do not need approval.
GRD
Safety Barrier Parameters VN: 2.5 V
This channel can be used to serve part of loop #2.
Rj: 71 Ω
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■ Current loop A & B: Internal resistance. The constant current source will have a rated maximum load or burden (resistance load it can drive). Assume that this maximum load is 500 ohms and the maximum resistance of the RTD at the highest temperature is 390 ohms. Knowing this information, the Ri of the barrier can be calculated: control room ≤ barrier
resistance 500 ohms Ri
+ RTD resistance resistance < Ri ohms + 390 ohms < 110 ohms
■ Current loop A & B: Barrier selection. Use the same barrier that was used for the thermocouple circuit. ■ Leg C to the voltmeter: Barrier selection. The RTD leg going to the voltmeter (C) is a millivolt signal similar to the thermocouple circuit. The rated voltage, Vn, and internal resistance, Ri, of the barrier will have the same parameters as the barriers used in the thermocouple and current loop of the RTD. Selecting the correct barrier to make all thermocouples and RTD’s intrinsically safe is not difficult. Use a double-channel AC barrier with a rated voltage greater than 1 volt with the lowest internal resistance. The double-channel barrier is the lowest cost solution. The AC version will avoid any polarity problems. A barrier with a rated voltage between 1 and 10 volts will provide a wide selection which have a low resistance and are approved for the hazardous areas where the temperature sensors are located. This single barrier can then be used to make all thermocouples and RTDs intrinsically safe. And don’t forget, all thermocouples and RTD’s are simple devices, so they do not need third party approval to be intrinsically safe. When they are connected to an approved intrinsically safe barrier, the circuits are intrinsically safe. Many temperature sensors are attached to 4-20 mA temperature transmitters, which comprise 22% of all intrinsically safe applications. The next article in this series will show how to make these transmitters intrinsically safe. Copyright Instrument Society of America. Intech, December, 1992. All Rights Reserved.
Z
Use The 80/20 Rule In Intrinsic Safety Circuit Design Part 3 of this series on intrinsic safety circuit design describes how to select barriers for intrinsically safe 4-20 mA transmitters. Use the 80/20 Rule to simplify this process.
Paul S. Babiarz
The 80/20 Rule actually is five rules that are based on the fact that certain practices prevail 80% of the time, and 20% of applications are more difficult. This article focuses on how to choose intrinsically safe barriers when the transmitters are installed in hazardous areas for both the 80% standard category and the remaining 20% more difficult applications. The most common way to process and send analog signals in the instrumentation industry is via 4-20 mA transmitters. Transmitters can be one of the simplest devices involving barriers. However, improper selection of intrinsically safe barriers in loops with 4-20 mA transmitters can introduce too much impedance on the circuit and cause the transmitters to function improperly at the high end near the 20 mA reading. Before selecting barriers, examine how 4-20 mA analog circuits function. Transmitters convert a physical measurement such as temperature or pressure into an electrical signal that can be sent without signal modification to a →
converted to mA signal
0°C (min)
→
100°C (max)
→
Temperature
+
+
+24V
4 – 20 mA 2-Wire Transmitter
Distributed Control System –
250 Ω
–
S E N S O R
4 – 20 mA
Conversion
Figure 1. 4-20 mA 2-wire transmitter.
control system over a long distance. The brains of the system, the DCS, interprets the electrical signal into the physical measurement. Because these analog signals are sent to a DCS, 4-20 mA circuits are called analog inputs or A/I. Using temperature as an example, examine the function of the transmitter (Fig. 1). A power source in the DCS usually supplies 24 VDC to the transmitter. The transmitter converts the physical measurement into an electrical current signal. Transmitter current ranging from 4-20 mA is sent back to the DCS. Current signals are used to avoid potential voltage drops or electrical interference associated with voltage signals. However, because the
x multiplied by ohm resistor
=
converted to a voltage reading in the DCS
4 mA (0.004 A)
x 250
=
1V
20 mA (0.020 A)
x 250
=
5V
Table 1. Conversion of physical measurement to electrical signals.
Z-137
controller reads a voltage signal, a conversion resistor (most commonly 250 ohms) converts the 4-20 mA current range into a voltage signal on the DCS input channel. Applying Ohm’s Law of V = IR, the controller has a 1-to-5 V signal (Table 1). Assume the temperature span to be measured is from 0°C to 100°C. The transmitter is calibrated so that a 4 mA signal equals the low reading of 0° and a 20 mA signal equals the high reading of 100°. The DCS then runs the signal through a conversion resistor which can be placed either on the supply (+) or return (-) lead of the circuit, converting the signal back to a voltage reading. There are three types of barriers for intrinsically safe transmitter applications: ungrounded repeaters, grounded repeaters, or grounded safety barriers. Each has its advantages and disadvantages (Table 2). Ungrounded repeater barriers, also known as galvanically isolated or transformer-isolated barriers, are used more frequently in Europe
Imax, Ci, and Li (see Part 1 of this series).
Advantages
Disadvantages
Grounded Safety
Least expensive
Requires ground
Barrier
Precise signal response Very small size (<1⁄2 in. wide)
Requires engineering
Grounded
One product can be used
More expensive
Repeater
Can use transmitters with higher operating voltage
Requires ground Larger in size Consumes more power
One product can be used No ground required Can use transmitters with
Most expensive Larger in size (1 in. wide) Possible radio frequency
higher operating voltage Isolation, if good ground
interference May not be compatible
Ungrounded Repeater
not available
with smart transmitters
Table 2. Advantages and disadvantages of grounded safety barriers, grounded and ungrounded repeaters.
than in North America. Repeaters suit most transmitter applications, but at a higher cost. Grounded or ungrounded repeaters supply a constant regulated voltage of 15 to 17 V to the transmitter from a 24 V source. The return channel is then run through the barrier, which repeats it without any appreciable loss in signal. For example, if a transmitter sends 19.6 mA through the barrier, it is repeated in the barrier without any loss so that 19.6 mA reaches the control room. Repeaters act like mirrors by retransmitting, or repeating, the analog signals. When budget constraints or control panel space are important considerations, grounded safety barriers may be a better choice. 80/20 Rule #1: In North America, most analog circuits are protected by grounded safety barriers because of lower costs. ■ Define the hazardous area where the transmitter is located. In North America, these areas are defined by the National Electric Code as classes, divisions, and groups. The class defines the type of materials that are in the hazardous area. Class I — flammable gases and vapors; Class II — combustible dusts; Class III — fibers and flyings. Hazardous areas are further broken down into two divisions. Division 1 means normally hazardous; Division 2 means not normally hazardous. The group
designates the type of vapor or dust in the area. Group A — acetylene; Group B — hydrogen; Group C — ethylene; Group D — propane; Group E — metal dust; Group F — coal dust; Group G — grain dust. ■ Complex devices. Because transmitters can store energy, they are considered complex devices, and must be approved as intrinsically safe. If they are third-party approved, they have entity parameters such as Vmax, Conversion Resistor +24V
+
250 Ω
■ Selection of safety barriers. The proper barrier must be selected by two separate evaluations: one to determine that the analog circuit functions properly at 20 mA, and one to determine that the circuit is safe under fault conditions. ■ Functional parameters: Type of safety barrier, voltage input (Vn), and internal resistance (Ri). The type of safety barrier is largely determined by the placement of the conversion resistor. If the resistor is placed on the supply leg of the circuit, a simple DC positive barrier can be used (Fig. 2). 80/20 Rule #2: Most transmitter circuits have the conversion resistor on the return channel. Use the double channel supply and return barrier. The supply channel is constructed like the positive DC barrier; it prevents a fault on the safe side from transferring excess energy to the transmitter. The return channel has two diodes in series which allow the signal to pass only in one direction back to the DCS, and prevent any excess fault energy from being transferred to the transmitter. These diodes and the supply channel have voltage drops which must be accounted for in the analog circuit (Fig. 3).
NON-HAZARDOUS SIDE
+
+
HAZARDOUS SIDE
+
+
Intrinsically Safe Transmitter
Distributed Control System –
Z
–
–
S E N S O R
–
GRD
Figure 2. Positive DC barrier. NON-HAZARDOUS SIDE
+24V
+
+
HAZARDOUS SIDE
+
+
Intrinsically Safe Transmitter
Distributed Control System –
–
250 Ω
– GRD
Conversion Resistor
Figure 3. Supply and return barrier.
Z-138
–
S E N S O R
80/20 Rule #3: The supply voltage normally is 24 VDC. ■ Select the voltage input, Vn. One of the reasons that barriers fail is because the voltage supply is too high. Use a regulated supply source with a high end of tolerance that does not exceed the barrier rating and a low end that is enough to drive the circuit. A 24 Vdc source ±1% usually is a good choice. ■ Determine the internal resistance, Ri (also referred to as end-to-end resistance) of the barrier best suited for your circuit. The most critical component of the barrier selection is the barrier’s internal resistance. If the resistance is too high, the transmitter will not work near 20 mA. As seen in Table 1 and the following discussion, at 20 mA the voltage drops across the barrier and the conversion resistor will be the highest. If the internal resistance is too low, the barrier’s short circuit current, Isc, may exceed the transmitter’s entity parameter, Imax. The easiest way to determine the barrier’s permitted resistance is to calculate the total voltage drop on the circuit. To select the proper transmitter barrier, determine the following: • Hazardous area Groups A-G or C-G • Placement of the conversion resistor on either the supply or return leg of the circuit • Size of the conversion resistor (250 ohms is most common) • Minimum operating voltage of the transmitter (This figure, also referred to as lift-off voltage, is in the transmitter data sheet. Most operate at a minimum of 12 V or lower.) • Entity parameters of approved transmitter ■ Case 1. Assume that conditions are as follows: • Groups A-G • Supply • 250 ohms • 12 V • Vmax = 30 V, Imax = 150 mA, Ci = 0 µF, Li = 0 mH Calculate the maximum allowable resistance of the barrier under worst-case conditions when the transmitter is sending a 20 mA signal. The supply is 24 Vdc; the transmitter requires a minimum of 12 V; and the 250 ohm conversion
24 Supply
+24V
NON-HAZARDOUS SIDE
+
+
HAZARDOUS SIDE
+
+
Intrinsically Safe Transmitter
Distributed Control System –
–
–
250 Ω
–
GRD
5 volt loss
maximum 7 volt loss
VOLTAGE BALANCE: Transmitter = 12 volts Resistor = 5 volts Barrier(+ line loss) = 7 volts Total Supply = 24 volts
12 volt loss
Figure 4. Voltage balance.
NON-HAZARDOUS SIDE
+24V
S E N S O R
+
+
Distributed Control System
HAZARDOUS SIDE
+
15 - 17V + Intrinsically Safe Transmitter
Repeater Barrier –
–
–
4 – 20 mA
–
S E N S O R
4 – 20 mA
Conversion Resistor 750 - 1000 Ω max
Repeated
Figure 5. Repeater barriers.
resistor requires 5 V at 20 mA. Simple subtraction leaves a maximum allowable voltage drop of 7 V. Using Ohm’s Law, this converts to an internal resistance of 350 ohms. Allow for a cable resistance of about 10 ohms. Thus, the circuit functions properly with a barrier having an internal resistance of 340 ohms.
supply and return side. Voltage drop on the return side diodes is about 0.7 V. This leaves a maximum drop of 6.3 V on the supply side or a maximum resistance of 305 ohms (allowing 10 ohms for cable resistance). Again, verify the entity parameters of the barrier and transmitter.
Next, to make sure the circuit is safe, verify that the barrier’s entity parameters match the transmitter’s entity parameters. This design offers the lowest cost solution where two transmitters can be connected to one double channel barrier. This circuit arrangement allows one common barrier to be used for most circuits (Fig. 4).
80/20 Rule #4: The two solutions above cover 80% of all transmitter applications.
■ Case 2. Use the same conditions as in Case 1, except change the placement of the conversion resistor to the return side, and use the supply and return barrier. Voltage drop on the barrier occurs on both the Z-139
But what happens if the circuit falls into the 20% category? Grounded safety barriers may not work in conditions where a loop-powered indicator is connected, or where the transmitter requires a minimum voltage greater than 12 V. In these cases, the easiest solution is to use a repeater barrier. Repeaters provide a regulated power supply of 15-17 V to the transmitters and can drive a conversion resistor load of 750 to 1000 ohms (Fig. 5)
Groups Internal Resistance Voltage Drop
Short Circuit Open Circuit
(Ri)
at 20 mA
Current, Isc
Voltage, Voc
A-G
340 ohms
6.8 V
93 mA
28 V
Barrier #2 C-G
140 ohms
2.8 V
213 mA
28 V
Barrier #1
Table 3. Typical values of barriers rated for different groups.
If repeaters still are not the best solution, there may be other ways to use grounded safety barriers. Either the impedance in the circuit must be reduced or the voltage must be increased. If these alternatives are used, recheck the barrier and transmitter entity parameters to make sure the circuit is safe.
Increasing Voltage Supply
Reducing Impedance
■ Case 1: Resistor on the supply side. When transmitters are first energized, they transmit 4 mA for calibrating zero readings. There always is at least a 1 V drop across the resistor before the supply reaches the barrier. The voltage supply could be increased to 25 to 26 V without the barrier sensing a fault condition. This would allow 1 to 2 additional volts on the circuit.
■ Case 1. Reduce the conversion resistor. As seen in Fig. 2, only two fixed sources of impedance can be reduced: the conversion resistor or the barrier. One solution is to reduce the conversion resistor to 100 or 50 ohms to obtain maximum voltage readings of 2.0 to 1.0 V respectively. (Example: 20 mA (0.02 A) x 100 ohms = 2 V.) This may be practical for new installations, but it may not be possible for cases where additions are being made to an existing control system.
If the voltage supply is increased too much, the barrier may sense a fault and the fuse could blow, interrupting the circuit. Some allowance can be tolerated for increasing the voltage supply on barriers with a nominal rated voltage of 24 VDC.
■ Case 2: Resistor on the return side. Since the resistor is on the return side, the barriers receive the total voltage supply. Since this circuit is more sensitive to voltage increases, be careful about increasing the supply above the barrier's nominal rated voltage, Vn. Before the zener diodes in the barriers reach their rated voltage, there may be some leakage current that could affect the transmitter signals. Diode leakage current values ranging from 1 to 10µA are listed by the barrier manufacturers. In Case 1, this could mean that the current signal could be deformed by a maximum of 0.025% at 4 mA (1 µA/4 mA). When the resistor is placed on the return side, leakage current is on the supply side and does not affect the transmitter’s 4-20 mA signal. Transmitters comprise 22% of all intrinsically safe circuits. The next article will feature discrete inputs, also referred to as switching. These represent 32% or almost one-third of all intrinsically safe circuits.
Copyright Instrument Society of America. Intech, March, 1993. All Rights Reserved.
■ Case 2. Select a barrier with lower resistance. 80/20 Rule #5: Many hazardous locations are classified as Groups C-G. Ignition curves in Groups C-G allow higher rated voltages and current before gases ignite (see Part 1 of this series, October 1992). Barriers designed for hydrogen and other gases classified as Group A or B require higher series resistance than barriers designed for only the more common gases in Groups C and D. Thus, most intrinsically safe instruments should have entity parameters (Imax, maximum short circuit current) that are higher for Groups C-G. (As a practical matter, most instrument manufacturers have not taken advantage of this fact.) With the Group C-G rating high-current barriers can be used, which have a lower internal resistance. These barriers have corresponding lower voltage drops but higher Isc (Table 3).
See SIB Series of Intrinsically Safe Transmitters
Z-140
Z
Making Digital Inputs Intrinsically Safe Part 4 of this series describes how to make a switch intrinsically safe by using a switch amplifier or a grounded safety barrier.
Digital inputs constitute almost onethird of all process signals. They also are known as binary, on-off, 0/1, or simple switching signals where a switch is either opened or closed. The most common examples of these are mechanical or reed contacts, transistors, limit, float, on-off, and pushbutton switches. As defined in paragraph 3.12 of the ANSI/ISA-RP12.6-1987, switches are simple devices that neither generate nor store more than 1.2 V, 0.1 A, 25 mW, or 20µJ. Since switches are simple devices, they do not have to be approved as intrinsically safe. If they are connected to an approved intrinsically safe associated apparatus (barrier), the circuit is deemed to be intrinsically safe.
To make a switch intrinsically safe, the user may select a switch amplifier or a safety barrier. A switch amplifier is an intrinsically safe relay that solves virtually all switching applications. However, if power is not available in the control panel or if panel space is an important consideration, a grounded safety barrier may be a better choice. There is not a significant cost savings of one alternative over the other. Each has its own advantages and disadvantages, as shown in Table 1.
Switch Amplifiers The most common application is switching through an intrinsically safe relay (Fig. 1). Relays, which normally are powered by 110 VAC or 24 VDC, have a low voltage and current which are safe at the contact in the hazardous area. When this contact is closed, the relay transfers the signal from the hazardous
Non-Intrinsically Safe Wiring
Paul S. Babiarz
Intrinsic Safety Barrier Intrinsic Safety Barrier Intrinsic Safety Barrier Intrinsic Safety Barrier
location to the non-hazardous side. A closed switch on the hazardous side operates a relay or optocoupler output on the non-hazardous side. The signals are electrically isolated so that grounding is not required. When proximity switches became a popular means of sensing the presence of objects and materials, the NAMUR-style sensor was developed. Contrary to popular opinion, NAMUR is not an approval standard. It was organized by the German chemical industry to develop operating standards for proximity switches. A NAMUR-style proximity switch is a 2-wire DC sensor that operates at 8.2 V with switch points operating between 1.2 to 2.1 mA. This NAMUR standard later was superseded by the German Standard DIN 199234, Measurement And Control:
Intrinsic Safety Barrier Intrinsic Safety Barrier Intrinsic Safety Barrier Intrinsic Safety Barrier
INTRINSICALLY SAFE WIRING
To Field Circuits Figure 1. Switch amplifier — 2 channels.
Z-141
NON-HAZARDOUS SIDE
NON-HAZARDOUS SIDE
HAZARDOUS SIDE
Distributed Control System
Intrinsic Safety Barrier
Electrical Sensors Used For Intrinsically Safe 2-Wire DC Systems. Because these switches required a remote amplifier for operation, most switch amplifiers standardized on an intrinsically safe voltage of 8.2 V and current of 8 mA at the contacts in hazardous areas. This provided enough power to operate NAMUR-style proximity switches safely. The amplifiers are sensitive enough to detect closed contacts in corrosive or abusive areas. Despite the fact that the intrinsically safe voltage and current at the contacts are very low, most modern switch amplifiers will detect a closed contact when the resistance of the circuit is less than 3000 ohms. Intrinsically safe switches can be located a long distance from the switch amplifiers and still function properly. Switch amplifiers are available with two different output contacts to the safe side, relays and optocouplers. The more commonly used relay versions are applied in slow speed switching to operate smaller pumps, motors, or other electrical devices. Optocouplers are transistors operated by photo diodes to close the output contacts. These outputs have lower contact ratings but an almost infinite switching capability. Optocouplers are used for switching back to a DCS or for high-speed counting operations up to thousands of times per second (KHz).
Intrinsically Safe Apparatus
Figure 3. Current sinking switching.
used for transmitters (see Part 3 of this series). The current sourcing method of switching in Fig. 2 could use the same signal and return barrier that was used for 4-20 mA transmitters. The voltage to the switch is supplied through the supply channel. The second channel is used for signal return. A closed switch will close the contact in the DCS. Most digital input signals operate with 24 V and 10 mA. If the same barrier is used for switching as 4-20 mA transmitters, there will be about a 3 to 4 V drop across the barrier. The barrier used for current sinking switching can be a single-channel DC barrier as seen in Fig. 3. When the switch is open, the DCS input will sense 24 V. When the switch is closed, the DCS will recognize a lower voltage. This lower voltage is calculated as a voltage divider circuit. Make sure the rated voltage of the barrier, Vn, is equal to or greater
than the voltage supply. Since most switching uses 24 VDC, select a barrier rated at 24 V. The internal resistance of the barrier is not as critical since the current in digital inputs usually is very small. However, it always is good practice to select a barrier with low resistance. Check the approvals of the barriers to make sure that they are rated for the proper hazardous area group location. Intrinsically safe relays, also referred to as switch amplifiers, can be applied universally for all digital inputs. However, if safety barriers are used, the same barriers used to make analog inputs intrinsically safe can be used for either current sourcing or current sinking switching. The next article in this series will explain how to make digital outputs intrinsically safe. Copyright Instrument Society of America. Intech, April, 1993. All Rights Reserved.
Switch Amplifiers Advantages
Disadvantages
Simple application No ground required No internal resistance LEDs to indicate power and monitor operations Sensitive to detect closed contacts in corrosive areas
Needs power supply Larger in size
Switching Through Safety Barriers When a 110 V supply is not available in the control panel, safety barriers frequently are used for digital inputs back to a DCS. There are two methods of switching: current sourcing or current sinking. Both of these methods can use the same types of barriers that were
Intrinsic Safety Barrier
Potential of Ground Loops
ONLY THESE WIRESARE INTRINSICALLYSAFE
Figure 2. Current sourcing switching.
HAZARDOUS SIDE
Safety Barriers Advantages
Disadvantages
Smaller size Does not require power supply
Requires grounding Has internal resistance
Table 1. Advantages and disadvantages of switch amplifiers and safety barriers.
Z-142
Z
Intrinsically Safe Outputs Made Easy Part 5 of this series explains how to make solenoid valves, LED’s, and I/P transducers intrinsically safe.
HAZARDOUS SIDE CLASS I, II, III DIVISION 1 GROUPS A-G
NON-HAZARDOUS SIDE
+ 24 V
+
+
+
Digital Output D/O
Solenoid Valve –
–
–
GRD
Solenoid valves need entity approval
Typical Safety Barrier Parameters VN: 24 V Ri::≤ ≤ 350 VN = Rated voltage Ri = Internal resistance
Paul S. Babiarz
Digital outputs refer to closed contacts in a distributed control system (DCS). They transfer a voltage to a process area to operate a field device. The two most commonly used digital output field devices, solenoid valves and LED displays, can easily be made intrinsically safe. For solenoid valves, the same types of barriers are used that make analog and digital inputs (transmitters and switch contacts) intrinsically safe. LED’s may require a different barrier.
There is good news and bad news for making circuits (or loops) containing solenoid valves intrinsically safe. The bad news is that unlike transmitters which have minimum operating voltages, valve manufacturers often describe their valves with a nominal operating current or voltage. To select the proper barrier one needs to know the minimum operating characteristics under the most extreme conditions. Without these characteristics it can be quite difficult to select a barrier that will allow the circuit to function properly and still meet the entity parameters of the valves. Conditions that may affect the operating characteristics are high ambient temperatures, position of the actuator, and length of cable runs. Z-143
The good news is that there are only a handful of approved intrinsically safe solenoid valves to choose from. For this article, manufacturers tested their intrinsically safe valves with the most common barrier used in analog and digital input circuits — the 24 Vdc barrier with a resistance equal to or less than 350 ohms (Fig. 1). To determine the correct barrier, start with the basics. Since most digital output circuits operate with 24 Vdc switched on the positive side, use a positive DC barrier rated at 24 Vdc. Knowing the minimum operating current of the valve and the internal impedance of the coil, you can calculate the maximum allowable impedance for the barrier and the cable.
Analog Outputs NON-HAZARDOUS SIDE
+24 V
+
HAZARDOUS SIDE CLASS I, II, III DIVISION 1 GROUPS A-G
Analog outputs refer to I/P transducers, also known as I/P’s (pronounced “Ida Pease”). An I/P transducer produces a pneumatic output proportional to the electrical current input that it receives. The more current that is applied to the transducer, the more air pressure is allowed into the system to drive a device. As opposed to a solenoid valve which is either in an opened or closed position, a transducer is a proportional valve. I/P transducers are referred to as analog outputs because a variable output, the current signal, is sent from the DCS to the transducer.
25 mA
+
Digital Output D/O
12 V –
– GRD
12 volt drop across barrier (480 x .025)
LED Pilot Light LED pilot light is a simple device; does not need approval
Typical Safety Barrier Parameters VN: 24 V Ri: 480 Ω VN = Rated voltage Ri = Internal resistance
Figure 2. LED pilot light.
For example, assume a valve has a minimum operating current of 28 mA and a coil impedance of 400 ohms. The maximum allowable impedance of the circuit is 857 ohms (24/.028 = 857). If the internal impedance of the solenoid coil is 400 ohms, the allowable impedance of the barrier and cable would be 457 ohms (857-400 = 457). The resistance of one mile of #18 AWG wire at 60°C is about 40 ohms (resistance of #18 AWG wire at 60°C is 0.00737 ohms/ft.). This makes the maximum resistance of the barrier 457-40 = 417 ohms. Selecting the barrier now is simple: 1. Select a simple DC positive barrier. (The rated voltage should be 24 V.) 2. Calculate the maximum allowable resistance of the barrier as in the example. 3.Confirm that the entity parameters of the solenoid valve match those of the barrier (refer to Part 1 of this series). Associated Apparatus (barrier)
Open circuit voltage Short circuit current Allowed capacitance Allowed inductance
Apparatus (field device)
Voc Isc Ca La
≤ ≤ ≥ ≥
Vmax Imax Ci Li
LED’s LED’s (light emitting diodes) are simple devices since they do not store energy (capacitance or inductance); therefore, they do not need to be approved. However, they still must be used with safety barriers to make circuits intrinsically safe. Typical LED’s are rated at 24, 18, 12, or 6 V and operate at about
25 mA. Since there will always be a voltage drop across the barrier, the best application is to choose an LED rated at less than 24 VDC. Use a barrier rated at 24 V, then subtract the rated voltage of the LED. This difference is the allowable voltage drop on the barrier at the rated current. Use Ohm’s Law (V = IR) to calculate the internal impedance of the barrier. Example: • LED rated at 12 V at 25 mA • Allowable voltage drop 12 V (24-12 = 12) • Internal impedance of the barrier = 480 ohms (12/.025 = 480) Choose a 24 V positive DC barrier with an internal impedance of about 480 ohms (Fig. 2).
+
The barrier must have an internal resistance less than 850 ohms (1000-150 = 850). Verify the rated voltage of the barrier by calculating the voltage drop of the circuit. For example, use the same barrier and cable values as in the solenoid valve example. The total impedance (impedance of barrier + transducer + cable) of the circuit would be
HAZARDOUS SIDE CLASS I, II, III DIVISION 1 GROUPS A-G
NON-HAZARDOUS SIDE
+ 4-20 mA
I/P transducers need entity approval. They act like resistors in the circuit, so three facts must be known to select the correct barrier: transducer impedance; maximum burden of the driver that sends the current signal; and transducer entity values. Burden, rated in ohms, measures the maximum load the DCS can drive. To select the barrier, use the following characteristics: • Transducer impedance is 150 ohms • Burden of the drive is 1000 ohms
+
+
Analog Output A/O
I/P Transducer –
–
–
GRD
Single Channel DC Barrier
Typical Safety Barrier Parameters VN ≥ 12 V Ri ≥150 ≥150 Ω VN = Rated voltage Ri= Internal resistance
Figure 3. 4-20 mA I/P transducer.
Z-144
I/P transducers need entity approval
Z
Device
*
Barrier Type
Rated Voltage
Internal Resistance
Notes (IT = INTECH)
Thermocouples
AC
>1 V
<1000*
Thermocouples are simple devices; do not need approval.
RTD’s
AC
>1 V
<1000*
RTD’s are simple devices; do not need approval.
Digital inputs
switch amplifiers
Dry contacts are simple devices; do not need approval.
D/I - current sourcing
supply & return
24
350**
Dry contacts are simple devices; do not need approval.
D/I - current sinking
DC
24
350**
Dry contacts are simple devices; do not need approval.
A/I transmitters
supply & return
24
350
Transmitters need approval. Check entity parameters. Conversion resistor of 250 ohms is on negative side. Minimum lift-off voltage of transmitter is 12 or less.
A/I transmitters
DC
24
350
Same, except conversion resistor is on + side.
D/O solenoid valves
DC
24
350
Solenoid valves need approval. Check entity parameters.
A/O transducers
DC
>12
>150
Transducers need approval. Check entity parameters and DCS burden.
Select a barrier with a low resistance.
** Other barriers with a different resistance can be used. However, these barriers match those of the analog inputs. Table 1. Guide to selecting grounded safety barriers.
540 ohms (350 + 150 + 40). At the maximum current of 20 mA, the voltage drop would be 10.8 V (540 x 0.20 = 10.8). Select a barrier rated equal to or higher than 10.8 V. A barrier rated at 12 V or higher with an internal resistance of 150 ohms also would be a good choice (Fig. 3). Confirm that the entity parameters of the barrier correspond with those of the transducer. This series of articles has shown how the most common applications of temperature measurements and analog or digital inputs/outputs can be made intrinsically safe with a few intrinsic safety barriers. Selection is simple: 1. Determine if the field device is a simple or nonsimple (energy
storing) device that needs approval and has entity parameters. 2. Select the type of barrier needed to protect the individual ungrounded lines of the circuit. Normally, temperature sensors use an AC barrier. For analog inputs and current sourcing switching, use the supply and return barrier. The remainder (analog and digital outputs and some switching circuits) require DC barriers.
5. Confirm that the entity parameters of the barrier match those of the field device. Use Table 1 as a guide in selecting grounded safety barriers. There will always be exceptions to these guidelines, so verify your selection with the manufacturer of the barriers or field devices. The last installment in this series will discuss the general rules of grounding, installation, and maintenance of intrinsically safe systems.
3. Select a barrier with a rated voltage equal to or greater than the voltage of the circuit. 4. Confirm that the internal resistance of the barrier will allow enough voltage for the field device to operate properly. Z-145
Copyright Instrument Society of America. Intech, September, 1993. All Rights Reserved.
Installing Intrinsically Safe Systems Part 6 of this series summarizes the major points of barrier replacement, wiring, installation, grounding, sealing, maintenance, and troubleshooting of intrinsically safe systems.
Z
Paul S. Babiarz We have shown how an intrinsically safe circuit is designed for most common applications. Now the intrinsically safe system must be properly installed and provisions must be made to maintain and troubleshoot it. These procedures are discussed in detail in Article 504 of the National Electrical Code (NEC) and the ANSI/ISA RP 12.6-1987 Recommended Practice — Installation of Intrinsically Safe Systems For Hazardous (Classified) Locations.
Intrinsic Safety Barrier Intrinsic Safety Barrier Intrinsic Safety Barrier Intrinsic Safety Barrier
Non-Intrinsically Safe Wiring
To Control Room Circuits
Intrinsic Safety Barrier Intrinsic Safety Barrier Intrinsic Safety Barrier Intrinsic Safety Barrier
INTRINSICALLY SAFE WIRING
Wiring Intrinsically safe circuits may be wired in the same manner as comparable circuits installed for unclassified locations with two exceptions summarized as separation and identification. These wiring practices are simple and clear; however, they often are overlooked and are the source of potential problems.
To Field Circuits Figure 1. Suggested panel arrangement using separate wireways.
NON-HAZARDOUS SIDE
The intrinsically safe conductors must be separated from all other wiring by placing them in separate conduits or by a separation of 2 inches of air space. Within an enclosure the conductors can be separated by a grounded metal or insulated partition (Fig. 1).
HAZARDOUS SIDE
Intrinsic Safety Barrier
ONLY THESE WIRESARE INTRINSICALLYSAFE Figure 2. Barrier installation.
Z-146
NON-HAZARDOUS SIDE
influence the function of the system by creating noise on the circuit or modifying the signals. Fig. 3 shows an improperly grounded system. The numerous grounding points create ground loops which can modify the signals and induce stray voltages into the intrinsically safe circuits. The correct method of grounding is shown in Fig. 4 where all the grounds are tied together at one single point in the system.
HAZARDOUS SIDE
Distributed Control System
Intrinsic Safety Barrier
Intrinsically Safe Apparatus
Sealing Potential of Ground Loops Main Earth Ground
Figure 3. Unacceptable grounding.
Intrinsically safe wiring may be light blue when no other conductors colored light blue are used. The raceways, cable trays, open wiring, and terminal boxes must be labeled Intrinsically Safe Wiring to prevent unintentional interference with the circuits. The spacing between the labels should not exceed 25 ft.
Barrier Installation The barriers normally are installed in a dust- and moisture-free NEMA 4 or 12 enclosure located in the nonhazardous area. Only the barrier outputs are intrinsically safe. Conductive dust or moisture could lessen the required distance of 2 in. between intrinsically safe and nonintrinsically safe conductors (Fig. 2). The enclosure should be as close as possible to the hazardous area to minimize cable runs and increased capacitance of the circuit. If they are installed in a hazardous area, they must be in the proper enclosure suited for that area.
• The grounding conductor must be a minimum 12 AWG.
• All ground path connections must
be secure, permanent, visible, and accessible for routine inspection. • A separate isolated ground conductor normally is required since the normal protective ground conductor (green or yellow/green wire) may not be at the same ground potential because of the voltage drop from fault currents in other equipment. • For installations designed to Canadian standards, the Canadian Electrical Code (Appendix F) recommends redundant grounding conductors. A poor grounding system can
HAZARDOUS SIDE
NON-HAZARDOUS SIDE
Distributed Control System
Grounding First determine if the intrinsically safe barriers used in the system are grounded or isolated. The isolated barriers normally are larger, more expensive, and do not require a ground for safety. The grounded safety barriers are smaller and less expensive, but require a ground to divert the excess energy. The main rules of grounding intrinsically safe systems are: • The ground path must have less than 1 ohm of resistance from the furthest barrier to the main grounding electrode.
The requirements for sealing intrinsically safe circuits have been discussed by a panel of experts and published in “Seals for Intrinsically Safe Circuits,” EC&M, September 1992, pp. 48-49. The panel’s conclusion is that seals are required to prevent the transmission of gases and vapors from the hazardous area to the nonhazardous area, not to prevent passage of flames from explosions. Explosion-proof seals are not required as long as there is some other mechanical means of preventing the passage of gases such as positive pressure in the control room and/or application of an approved mastic at cable terminations and between the cable and raceway. Many experts generally agree that a commercially available silicon caulk is a suitable mastic which would minimize the passage of gases. This must, however, be acceptable to the authority having jurisdiction.
Intrinsic Safety Barrier
Intrinsically Safe Apparatus
Single Ground Point
Main Earth Ground
Figure 4. Acceptable grounding.
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NON-HAZARDOUS SIDE
Explosion Proof Enclosure
HAZARDOUS SIDE
Intrinsically Safe Apparatus
Intrinsic Safety Barrier
Distributed Control System
Intrinsically Safe Seal
Explosion Proof Seal
Figure 5. Mounting in a hazardous area.
When barriers are installed in explosion-proof enclosures, which are located in the hazardous area, explosion-proof seals are required on the enclosure (Fig. 5). Since other conduits containing nonintrinsically safe conductors between the hazardous and nonhazardous areas require explosion-proof seals, it is good practice to maintain consistency and install explosion-proof seals on the conduits containing intrinsically safe conductors also. The exception to this would be where multiconductor shielded cable is used. This cable may be difficult to seal in some explosion-proof fittings. However, it will be necessary to seal both the cable terminations and between the cable and raceway to minimize the passage of gases, vapors, or dust.
Maintenance No special maintenance of intrinsically safe systems is
required. Once a year the barriers should be checked to ensure that the connections are tight, the ground wiring has less than one ohm of resistance, and the barriers are free from moisture and dirt. Check the panel and conduits for separation and identification of the intrinsically safe wiring. Never test the barrier with an ohmmeter or other test instrument while it is connected in the circuit (Fig. 6). This bypasses the barrier and could induce voltages into the intrinsically safe wiring.
Troubleshooting If the intrinsic safety circuit does not operate properly once it is completed and energized, follow these troubleshooting guidelines: • Make sure the connections are tight. • Check the wiring to the appropriate terminals against the control wiring diagram. A control
Testmeter
Intrinsic Safety Barrier
NEVER DO THIS!
wiring diagram is defined by the NEC as “a drawing or other document provided by the manufacturer of the intrinsically safe or associated apparatus that details the allowed interconnections between the intrinsically safe and associated apparatus.” These diagrams are easier to obtain than in the past. Make sure that one of the manufacturers provides not only diagrams which show the interconnections between the field device and barriers, but also wiring diagrams which demonstrate that the circuit functions properly and is safe by comparing the safety parameters of the field device and the barriers. • Make sure the circuit is powered. • Check to see if the resistance in the barrier is too high for the circuit. As stated in the previous articles in this series, circuits are analyzed for the proper loop resistance (barrier and cable) and supply voltages. If the circuit does not operate properly, check the circuit against the design in the control wiring diagram. • Check for a blown barrier fuse. This is accomplished by disconnecting the barrier from the circuit and measuring the end-to-end resistance of the barrier. If the ohmmeter registers an infinite resistance, the fuse in the barrier is blown. The fuse has opened because of a fault in the circuit, so reevaluate the entire circuit before reinstalling a new barrier.
Barrier Replacement If the barrier’s fuse has opened, it usually is the result of excessive voltage being applied to the barrier. This causes the diode to conduct, which results in high current in the fuse. After determining the cause of the excess voltage, the barrier must be replaced. The procedure is to disconnect the wiring from the safety barriers in the proper order of nonhazardous terminal first, hazardous terminals next, and the ground last. Cover the bare wire ends with tape, replace the barrier, and then reverse the procedure to mount the new barrier. Always install the ground first and disconnect the ground last. Copyright Instrument Society of America. Intech, October, 1993. All Rights Reserved.
Figure 6. The barrier should never be tested with an ohmmeter or other instrument while it is connected in circuit.
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Selecting A Recorder of/in addition to trend recording? Is color differentiation available for trend lines? Is message printing required? Is the recorder to perform alarm functions? How many setpoints per channel? What types of alarms: threshold, rate delta? Are physical relay contacts available for external alarm output? Number required
SIGNAL INPUTS GETTING STARTEDA CHECKLIST How many inputs need to be recorded? What types of inputs need to be recorded? Voltage and sensitivity Thermocouples RTD’s Do different input types need to be recorded in the same unit? What type of recording is required? Continuous Multiplex scanning (what minimum scan cycle is required?) Is a communciation interface required? To transmit measured data to a computer
Available input types Typical process recorders accept analog dc voltage inputs, thermocouple, or RTD temperature inputs or dry contact status input. Signal processing Linear scaling (conversion to engineering units) Thermocouple characterization Difference calculation Square root calculation
HIGHER-LEVEL FUNCTIONS Intelligence Math functions: +, -, x, ÷, square root, absolute value, logarithm, exponential functions, max, min, time average, group average, summantion, (maxmin), standard deviation, and integration.
For remote setup of recorder To connect to an external printer
Programming method Front panel Remote (downloaded)
Is recorder to be bench style or panel mounting? What type of instrument power is available? Is log-type recording desirable instead
Communications RS-232C: serial point to point, 50 feet cable length maximum at 9600 baud; GPIB (IEEE-488): parallel (20 meter system cable length maximum, 2 meter
Features Printing method Marking element
Continuous Writing Wet ink Thermal Felt-tip or capillary Thermal array with drag pen heat-sensitive paper
Multicolor trending
Multicolor trending enhances chart readability
Single color trending makes readability difficult when trend lines cross or are in close proximity
Ability to capture fastchanging signals Special chart paper required
Yes
Yes
No
Temperature-sensitive No nature of paper can cause problems in application of recorder and storage of charts
distance between devices, up to 14 devices per controller); RS-422A/RS-485: Balanced/unbalanced, serial, up to 32 devices per system, cable length can extend to 1.2 km at 9600 baud.
HARD COPY AND DISPLAY Recording method Galvanometer movement Servo Stepper-driven Fixed array Writing method Capillary ink Disposable felt-tip ink cartridges Dot printing: ink ribbon cassette or pressure-sensitive paper Thermal-moving head or stationary linear array Rotating ink wheel The most popular methods have become disposable ink cartridges for continuous (drag pen) recording, and multicolor ink ribbon cassette for dotprinting multipoint recording. These writing methods use an economical type of paper which is not sensitive to routine handling and does not require special storage considerations. Chart types For process recorders there are basically two types of charts, Z-fold or roll. Z-fold has become a predominant choice for process applications due to the ease of review of past traces without disrupting active recording. Chart speeds Fixed or programmable
Multipoint Mechanical High-speed wire Impact dot matrix dot with multicolor with pressureribbon sensitive paper Multicolor trending Single color enhances chart trending makes readability readability difficult when trend lines cross or are in close proximity No No
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Pressure-sensitive nature of paper can create problems in handling and storage of charts
Thermal Thermal matrix with heat-sensitive paper Single color trending makes readability difficult when trend lines cross or are in close proximity No Temperature-sensitive nature of paper can cause problems in application of recorder and storage of charts
Chart annotation Tag printing Digital printing List printing Alarm printing Prints in engineering units Message printing Scale printing Channel identifier (numeric or alphanumeric) Date and time Chart speed Snapshot digital measured values
internal when no alarm condition exists, automactically switching to alternate chart speed or log interval when an alarm condition exists
RECORDER DEFINITIONS Hybrid recorder: A recorder that combines analog trend representation and digital measured value printing on the same chart paper, without disruption of trend
For continuous writing recorders, the annotation is accomplished by a separate writing pen so that trace information is not lost. For dot-printing recorders, the annotation is done by the dot-printer, with either single-dot or full character printing with each traverse of the printhead, depending on whether the instrument is performing analog trending or log reporting. Chart widths 100 mm 180 mm 250 mm Visual indicators Analog bargraph indication (% of full scale) Analog scale indication (% of full scale) Digital channel number and measured value Alarm status Engineering units Recorder setup Until the advent of the microprocessor, recorders were dedicated to measuring only the type of input signal and only the span specified at the time of order. To change input signal type and/or measuring span, hardware changes were required. Presently, recorders are available in which input signal type, measuring span, tag and unit designators can conveniently be set in by the user. The recorder setup is done by a keypad or, if the instrument has a communication interface, by means of a computer keyboard or downloading of a computer file. Modes Normal: Monitoring at set scan interval and trending at set chart speed, or logging at set intervals Print on alarm: Monitoring at set scan interval but not trending or logging until an alarm condition occurs Change on alarm: Trending or logging at a base chart speed or log
printing. Servo balancing: A means of positioning the pen of a drag pen recorder. Null-balance operation has no current flow at balance, nullifying the effect of lead resistance. Conventional servo balancing recorders use contact mechanisms in the feedback loop and brushes in the servo motor. New technology allows the use of a noncontact pen positioning transducer and a brushless dc servo motor. Scanning recorder: A multi-point recorder that scans all of its inputs to obtain new measured data every set time period (usually 2 to 6 seconds). Printing for all points is often
Linear scaling: Recording of a voltage input in terms of the engineering variable, such as temperature, that the voltage represents. Transformation is Y (variable to be recorded) = mX (slope x input signal) + b (Y intercept). Pen offset compensation: In traditional multiple input drag pen recorders, each pen can travel the full width of the recording chart. In order to do so, the pens must be physically offset from one another. This puts the different pen traces on different time lines of the chart. By placing the measured data of the front-most pen(s) into a buffer and delaying their printing, the traces can be synchronized to the same time line, thereby compensating for their offset. Accuracy: The closeness to the actual signal that the measured value or trend position takes, stated as either a percentage of full scale or percent of reading. Separate accuracy statements are typically provided for measuring and recording functions. Tag ID: A means of designating a trace or digital measured value by an alphanumeric identifier instead of a numeric identifier. Typically available with up to seven characters. Digital printing: Printing of the precise measured numerical values for the various channels, along with their channel identifiers. Digital printing usually occurs in a margin of the chart so as not to interrupt trend recording. Log report: A printout of precise measured numerical values for the various channels, along with their channel identifiers. Typically prints in full character height per print cycle. During trending, prints on demand, resuming trending automatically. When trending is not being used,
performed during each cycle of the printing mechanism. Multi-color printing: A recorder that records trend traces in more than one color to make traces easier to differentiate. Drag pen recorders use a different color for each pen (usually four pens maximum). Mulit-point recorders typically record in six colors. Z-150
prints at a preselected time interval. May also include alarm status indication.
Courtesy of Johnson Yokogawa Corporation.
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Overview of IEEE-488 INTRODUCTION
Some of its key features are:
IEEE-488 refers to the Institute of Electrical and Electronics Engineers (IEEE) Standard number 488. This standard was first established in 1978, 13 years after Hewlett-Packard (HP) of Palo Alto, CA, began work to enable its broad range of instruments to communicate with one another and with “host” computers.
• •
At the time of its development, IEEE-488 was particularly well-suited for instrument applications when compared with the alternatives. In essence, IEEE-488 comprises a “bus on a cable,” providing both a parallel data transfer path on eight lines and eight dedicated control lines. Given the demands of the times, its nominal 1 Mbyte/sec maximum data transfer rate seemed quite adequate; even today, IEEE-488 is sufficiently powerful for many highly sophisticated and demanding applications.
Mechanical Specifications
• • •
However, IEEE-488, as originally defined, left some ambiguities in the specifics of controller-instrument interaction and communication. While these open issues were likely intended to give instrument and controller designers some latitude, the result was confusion and compatibility problems among instruments from different manufacturers. During the 1980’s, a new layer was added to the IEEE488 standard, IEEE-488.2. The original standard was re-designated IEEE-488.1. IEEE-488.2 provides for a minimum set of capabilities among “controllers” and “devices,” as well as for more specific content and structure of messages and communications protocols.
Up to 15 devices may be connected to one bus Total bus length may be up to 20 m and the distance between devices may be up to 2 m Communication is digital (as opposed to analog) and messages are sent one byte (8 bits) at a time Message transactions are hardware handshaked Data rates may be up to 1 Mbyte/sec
CONNECTOR The IEEE-488 connector is a 24-pin connector. Devices on the IEEE-488 bus have female receptacles; interconnecting cables have the mating male connectors. Connecting cables will typically have male and female receptacles wired in parallel at each connecting head to allow parallel connection of cables at a device and/or to allow daisychaining between devices. INTERCONNECTION CABLING Any individual IEEE-488 bus is limited to 15 devices including the controller. However, the IEEE-488 specification limits the total length of all cabling used to interconnect devices on a common bus to 20 m, or 2 m times the number of interconnected devices (up to 20 m). Cable lengths between devices may vary, as long as total cable length does not exceed these restrictions. Devices may be interconnected in a star or linear topology, or in a combination of the two, as long as the distance limits are observed. For maximum data transfer rates, the total cable length should be reduced to 15 m, with the average interdevice cable 1 m or less.
IEEE-488.2 is fully backward compatible with IEEE488.1; the use of a “488.2”-compliant controller affords the ability to use the new protocols available with “488.2” instruments while retaining the ability to communicate with and control “488.1”-compliant instruments and associated vendor idiosyncrasies.
Electrical Specifications
Today, IEEE-488 is the most widely recognized and used method for communication among scientific and engineering instruments. Major stand-alone general purpose instrument vendors include IEEE-488 interfaces in their products. Many vertical market instrument makers also rely on IEEE-488 for data communications and control.
• Data Lines - Eight lines (DIO1 through DIO8) used to transfer information (data and commands) between devices on the bus, one byte at a time. • Handshake Lines - Three lines used to handshake the transfer of information across the data lines: DAV: Data Valid NDAC: Not Data Accepted NRFD: Not Ready for Data • Bus Management Lines - Five lines used for general control and coordination of bus activities: ATN: Attention I FC: Interface Clear REN: Remote Enable SRQ: Service Request EOI: End or Identify • Ground Lines - Eight lines used for shielding and signal returns: One Shield One General Signal Ground Six logic ground lines paired off with ATN, SRQ, IFC, NDAC, NRFD and DAV
BUS LINES The IEEE-488 bus is a multidrop interface in which all connected devices have access to the bus lines. The 24 bus lines group into four categories:
IEEE-488 controllers support a variety of personal computers, from the IBM PC/XT/AT and PS/2 and compatibles to the multifaceted Macintosh family. Some of these controllers are plug-in cards; others are protocol converters (e.g., SCSI-to-IEEE-488). All provide at least IEEE-488.1 in compliance, and a growing number adhere to “488.2.”
GENERAL INFORMATION The IEEE-488 interface, sometimes called the General Purpose Interface Bus (GPIB), is a general purpose digital interface system that can be used to transfer data between two or more devices. It is particularly wellsuited for interconnecting computers and instruments.
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HANDSHAKING The IEEE-488 bus uses three handshake lines in a “We're ready - Here's the data - We've got it” sequence to transfer information across the data bus. The handshake protocol assures reliable data transfer at the rate determined by the slowest Listener. The handshake lines, like all other IEEE-488 lines, are active low. DAV is controlled by the Active Talker. Before sending any data, the Talker verifies that NDAC is asserted (low) which indicates that all Listeners have accepted the previous data byte. The Talker then places a byte onto the data lines and waits until NRFD is unasserted (high), indicating that all Addressed Listeners are ready to accept the information. When NRFD and NDAC are in the proper state, the Talker asserts DAV (active low) to indicate that the data on the bus is valid. NRFD is used by the Listeners to inform the Talker that they are ready to accept the new data. The Talker must wait for each Listener to unassert this line (high), which they do at their own rates when they are ready for more data. This assures that all devices accepting the information are ready to receive it. NDAC, also controlled by the Listeners, indicates to the Talker that each device addressed to listen has accepted the information. Each device releases NDAC (high) at its own rate, but NDAC does not go high until the slowest Listener has accepted the data byte. This type of handshaking permits multiple devices to receive data from a single data transmitter on the bus. All active receiving devices participate in the data handshaking on a byte-by-byte basis and operate the NDAC and NRFD lines in a “wired-or” scheme so that the slowest active device determines the rate at which the data transfers take place.
IEEE-488 FUNCTIONS When information is placed on the data lines, it can represent either a data byte or a command. If the Attention bus management line (ATN) is asserted while the data is transferred, then the data lines are carrying a multiline command to be received by every bus device. If ATN is not asserted, then a data byte is being transferred, and only the Active Listeners receive that byte. The IEEE-488 bus also has a number of uniline commands that are carried on a single bus management line. For example, the Interface Clear (IFC) line, when asserted, sends the Interface Clear command to every bus device, causing each to reset its IEEE-488 bus interface.
ADDRESSING The IEEE-488 standard normally permits up to 15 devices to be configured within one system. Each of these devices has a unique bus address, a number from 0 to 30. Address limits can be circumvented directly by the use of bus expanders or indirectly through the use of an isolator or an extender.
address from the Active Controller. Similarly, it becomes Addressed to Listen when it receives a Listen Address Group (LAG) multiline command. Other address commands include My Talk Address (MTA) and My Listen Address (MLA), which are the TAG and LAG commands of the Active Controller. The secondary Command Group (SCG) is used to refer to subaddresses or subfunctions within a particular device. This permits direct access and control of the subdevices or subinstruments embedded within complex devices or instruments.
THE SYSTEM CONTROLLER The System Controller, usually a computer with an IEEE488 board installed, always retains ultimate control of the bus. When the system is first powered up, the System Controller is the Active Controller and controls all bus transactions. The System Controller may Pass Control to a device, making it the New Active Controller, which may then Pass Control to yet another device. Even if it is not the Active Controller, the System Controller maintains exclusive control of the Interface Clear (IFC) and Remote Enable (REN) bus management lines and can take control of the bus whenever it desires.
IEEE-488.2 The IEEE-488.2 standard was developed to simplify the basic process of communicating with instruments. IEEE488.2 extends the 488 standard with code, format and protocol standardization and serves to resolve issues left open in 488.1. IEEE-488.2 details preferred implementation of many of the issues that were either optional or unspecified on the first standard. IEEE-488.1 covers the key physical issues (connector type, bus length, maximum number of instruments, etc.), electrical issues (open collector TTL, tristate) and low-level protocols (device addressing, control passing and data handshaking/timing). Four basic device functions (Talker, Listener, Controller and System Controller) are specified, as are capability subsets for each type of device. A number of items not covered by 488.1 can cause problems for the test engineer, particularly regarding equipment compatibility and data corruption. For example, 488.1 does not cover these specifications: • Minimum Device Capability Requirements No minimum set of requirements is mandated in IEEE488.1 for Talkers, Listeners, Controllers or System Controllers. Hence, a device may implement all, or only some, of the capability sets set forth in 488.1, giving rise to systems containing devices with varying levels of abilities. The Controller, in such a situation, has no guarantee of a basic communication subset among system devices. This can lead to confusion for the system operator and miscommunication between devices.
A device becomes Addressed to Talk when it receives a Talk Address Group (TAG) multiline command (a byte transferred with ATN asserted) specifying its own
• Data Coding, Formats and Message Protocol Under 488.1, the messages transferred between the Controller and a device are entirely at the discretion of
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Overview of IEEE-488 Cont’d
the device manufacturer. The use of ASCII, binary or some other form of data code and the choice of terminators such as carriage-return or EOI is arbitrary. Also, the sequence of the sending of commands and the reading of their responses is unspecified and varies from instrument to instrument. • Definition of the Status Byte 488.1 defines a status byte and one bit within, but the meaning of the other seven bits is at the discretion of the device designer. This forces the user to provide a unique interpretation of each bit of the status byte. Also, the relationship between the status byte and the device's other internal status registers is unspecified.
DRIVER SOFTWARE FOR IBM PC Great variety is found in the software required to complete the interface between the user's program and the IEEE instruments. Two fundamental techniques are used: the DOS device driver and the subroutine library. These are not mutually exclusive, as subroutine libraries can be implemented via a DOS device driver. DOS DEVICE DRIVER A popular form of device driver used by several IEEE488 controller providers is the Terminate and Stay Resident (TSR) DOS device driver approach. In this method, the driver code is stored in memory as a TSR and waits for access by an application program, much as Borland’s Sidekick waits for user “hot key” input. OMEGA’s 488 driver establishes a file I/O link with DOS, just as DOS provides file I/O links for system devices such as the keyboard/screen, printer or serial port. These DOS I/O files may be accessed directly from DOS, from programs with file I/O capability, including spreadsheets such as Lotus 1-2-3 and Borland's Quattro, and from most programming languages. These files provide a direct link to the IEEE-488 bus using HP-style English language commands. This style of Applications Program Interface (API) is often referred to as Character Command Language (CCL), as the IEEE commands are sent as ASCII strings to the driver via the API’s file I/O links through DOS. Controlling Instruments from Any Language Just as DOS and spreadsheets can access IEEE instruments directly using the file I/O services provided by DOS for device drivers, most programming languages also can use file I/O to quickly and easily access the IEEE-488 bus. SUBROUTINE IEEE-488 DRIVER INTERFACE An alternative means of controlling the IEEE-488 hardware is via subroutine calls from high level languages. This method has the advantage of minimizing the overhead of DOS device driver services and the ASCII message (CCL) parser and interpreter. Disadvantages include the loss of the convenience and effectiveness of accessing the IEEE-488 bus from a wide variety of applications programs, as well as from DOS. Also, the use of subroutines, even those with easy-to-use HP-style commands, typically requires compiling and linking to run even simple test codes.
Some IEEE controller implementations on the IBM PC give the user the choice of subroutine calls or CCL. IEEE-488 SUBROUTINE CONTROL LIBRARIES The logical complement to subroutine interfaces for a TSR DOS device driver are subroutine libraries that directly access the IEEE-488 hardware from a high-level language with code that is compiled and linked directly into the user’s program. This approach eliminates the DOS device driver, integrating the IEEE-488 control functions directly into the applications program code. This method has the potential for the highest performance, as it eliminates possible DOS effects on the speed of commands and data. MICROSOFT WINDOWS COMPATIBILITY The growing popularity of the Windows 3.0 Graphical User Interface (GUI) is rapidly spreading to test and measurement applications. Until 1991, few tools were available for the end user to build Windows applications. Now, tools such as Microsoft's Visual Basic and Borland’s C++ provide GUI development interfaces that allow users to draw windows and fill them with buttons, scroll bars and dialog boxes. Soon, these tools (and the tools, libraries and utilities that follow) will be widely used by developers of IEEE-488 test programs. IEEE-488 controller package vendors will adapt their offerings to be compatible with Windows, so users will be able to apply Windows solutions to their measurement problems. As these new Windows-oriented drivers and packages debut, there will undoubtedly be a broad range of solutions offered to the end user. It is important to know and understand what makes Windows and Windows applications different from DOS, and what features an IEEE-488 driver should have in order to make the most of the Windows environment. Users should keep the following issues in mind when reviewing new offerings: • Is the software written as a Windows application, or is it merely a port of DOS software? Windows performs its own memory management functions; typical DOS ports to Windows do not permit Windows to dynamically allocate memory use, which can lead to “Unrecoverable Application Errors.” As Windows is an event-based system, it provides extensive event handling facilities; Windows applications should take advantage of them. Windows has no equivalent of the TSR concept used with DOS. Although some DOS TSR’s will function while Windows is running, their operation can be erratic and unpredictable. • Will the driver support concurrent access of different peripherals on a single interface by multiple Windows applications? Windows’ pseudo muItitasking is one of its reasons for being. • Will the driver service multiple bus adaptor boards? • Is the driver IEEE-488.2 compliant?
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ASCII Code Values ASCII Value 000 001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 041 042 043 044 045 046 047 048 049
Hex Value 0 1 2 3 4 5 6 7 8 9 A B C D E F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31
Character (NUL) A B ♥ ♦ ♣ ♠ (BEEP) (TAB) (LF) (HOME) (FF) (CR)
-
I J K L M N O P Q R S (ESC) (RIGHT) (LEFT) (UP) (DOWN) (SPACE) ! “ # $ % & ‘ ( ) * + , . / 0 1
ASCII Value 050 051 052 053 054 055 056 057 058 059 060 061 062 063 064 065 066 067 068 069 070 071 072 073 074 075 076 077 078 079 080 081 082 083 084 085 086 087 088 089 090 091 092 093 094 095 096 097 098 099
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Hex Value 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F 50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5F 60 61 62 63
Character 2 3 4 5 6 7 8 9 : ; < = > ? @ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z [ \ ] ^ _ ` A B C
Z
ASCII Code Values Cont’d ASCII Value 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
Hex Value 64 65 66 67 68 69 6A 6B 6C 6D 6E 6F 70 71 72 73 74 75 76 77 78 79 7A 7B 7C 7D 7E 7F 80 81 82 83 84 85 86 87 88 89 8A 8B 8C 8D 8E 8F 90 91 92 93 94 95
Character D E F G H I J K L M N O P Q R S T U V W X Y Z { | } ~ T á ö E A é A è á E E E I I I é Å E í í O î O
ASCII Value 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199
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Hex Value 96 97 98 99 9A 9B 9C 9D 9E 9F A0 Al A2 A3 A4 A5 A6 A7 A8 A9 AA AB AC AD AE AF B0 Bl B2 B3 B4 B5 B6 B7 B8 B9 BA BB BC BD BE BF C0 C1 C2 C3 C4 C5 C6 C7
Character U U ò î ö õ ú õ û ü A I O U § § ¶ ß ® © ™ ´ ¨ ≠ Æ Ø ∞ ± ≤ | ¥ µ ∂ ∑ ∏ π ∫ ª º Ω æ ø ¿ ¡ ¬ Ô _ ± ∆ «
ASCII Value 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227
Hex Value C8 C9 CA CB CC CD CE CF D0 Dl D2 D3 D4 D5 D6 D7 D8 D9 DA DB DC DD DE DF E0 El E2 E3
Character » … G À Ã Õ Œ œ – — “ ” ‘ ’ ÷ ◊ ÿ Ÿ ⁄ ¤ ‹ › fi fl ‡ · ‚ „
ASCII Value 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255
Hex Value E4 E5 E6 E7 E8 E9 EA EB EC ED EE EF F0 Fl F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF
Character ‰ Â Ê Á Ë È Í Î Ï Ì Ó Ô Ò Ú Û Ù ı ˆ ˜ ¯ ˘ ˙
˚ ¸ ˝ ˛ (BLANK)
Hexadecimal Conversion Chart Hex Number
Binary Number
Decimal Digit 000X
Decimal Digit 00X0
Decimal Digit 0X00
Decimal Digit X000
0 1 2 3 4 5 6 7 8 9 A B C D E F
0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
0 256 512 768 1,024 1,280 1,536 1,792 2,048 2,304 2,560 2,816 3,072 3,328 3,584 3,840
0 4,098 8,192 12,288 16,384 20,480 24,576 28,672 32,768 36,864 40,960 45,056 49,152 53,248 57,344 61,440
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The RS-232 Standard Information being transferred between data processing equipment and peripherals is in the form of digital data which is transmitted in either a serial or parallel mode. Parallel communications are used mainly for connections between test instruments or computers and printers, while serial is often used between computers and other peripherals. Serial transmission involves the sending of data one bit at a time, over a single communications line. In contrast, parallel communications require at least as many lines as there are bits in a word being transmitted (for an 8-bit word, a minimum of 8 lines are needed). Serial transmission is beneficial for long distance communications, whereas parallel is designed for short distances or when very high transmission rates are required.
Standards
One of the advantages of a serial system is that it lends itself to transmission over telephone lines. The serial digital data can be converted by modem, placed onto a standard voice-grade telephone line, and converted back to serial digital data at the receiving end of the line by another modem. Officially, RS-232 is defined as the “Interface between data terminal equipment and data communications equipment using serial binary data exchange.” This definition defines data terminal equipment (DTE) as the computer, while data communications equipment (DCE) is the modem. A modem cable has pin-to-pin connections, and is designed to connect a DTE device to a DCE device.
Interfaces
In addition to communications between computer equipment over telephone lines, RS-232 is now widely used for connections between data acquisition devices and computer systems. As in the definition of RS232, the computer is data transmission equipment (DTE). However, many interface products are not data communications equipment (DCE). Null modem cables are designed for this situation; rather than having the pinto-pin connections of modem cables, null modem cables have different internal wiring to allow DTE devices to communicate with one another.
Cabling Options
RS-232 cables are commonly available with either 4, 9 or 25-pin wiring. The 25-pin cable connects every pin; the 9-pin cables do not include many of the uncommonly used connections; 4-pin cables provide the bare minimum connections, and have jumpers to provide “handshaking” for those devices that require it. These jumpers connect pins 4, 5 and 8, and also pins 6 and 20. The advent of the IBM PC AT has created a new wrinkle in RS-232 communications. Rather than having the standard 25-pin connector, this computer and many new expansion boards for pc’s feature a 9-pin serial port. To connect this port to a standard 25pin port, a 9- to 25-pin adaptor cable may be utilized, or the user may create his own cable specifically for that purpose.
2 Received Data Request to Send 7 3 Transmitted Data Clear to Send 8 4 Data Terminal Ready Ring Indicator 9 5 Signal Ground
®
RS-232 Specifications TRANSMITTED SIGNAL VOLTAGE LEVELS: Binary 0: +5 to +15 Vdc (called a “ space” or “on”) Binary 1: -5 to -15 Vdc (called a “mark” or “off”) RECEIVED SIGNAL VOLTAGE LEVELS: Binary 0: +3 to +13 Vdc Binary 1: -3 to -13 Vdc DATA FORMAT: Start bit: Binary 0 Data: 5, 6, 7 or 8 bits Parity: Odd, even, mark or space (not used with 8-bit data) Stop bit: Binary 1, one or two bits
Transmission Example 1111101100001011 1 1 CHARACTER “A”
TRAILING IDLE BITS STOP BIT
LEADING IDLE BITS START BIT
PARITY BIT
Pin Assignments 25-Pin Style PIN NUMBER
PIN NUMBER 1 Data Carrier Detect
The major considerations in choosing an RS-232 cable are based upon the devices to be connected. First, are you connecting two DTE devices (null modem cable) or a DTE device to a DCE device (modem cable)? Second, what connectors are required on each end, male or female, and 25 or 9-pin (AT style)? Usually, it is recommended that the user obtain the two devices to be connected, and then determine which cable is required.
Data Flow
9-Pin “AT” Style
Data Set Ready 6
Selecting a Cable
Secondary Transmitted Data DCE Transmitter Signal Element Timing Secondary Received Data Receiver Signal Element Timing
14 15 16 17 18 Secondary Request to Send 19 Data Terminal Ready 20 Signal Quality Detector 21 Ring Indicator 22 Data Signal Rate Selector 23 DTE Transmitter Signal Element Timing 24 25
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PIN NUMBER 1 Protective Ground 2 Transmitted Data 3 Received Data 4 Request to Send 5 Clear to Send 6 Data Set Ready 7 Signal Ground/Common Return 8 Received Line Signal Detector 9 +Voltage 10 -Voltage 11 12 Secondary Received Line Signal Detector 13 Secondary Clear to Send
Guidelines for Realizing the ITS-90 Guidelines for Realizing the
11.
International Temperature Scale of 1990 (ITS-90)
12. 13. 14. 15. 16. 17.
B. W. Mangum National Institute of Standards and Technology Gaithersburg, MD 20899
National Institute of Standards and Technology [NIST], Gaithersburg, MD, USA, National Physical Laboratory [NPLj, Teddington, UK, National Research Laboratory of Metrology [NRLM), Ibaraki, Japan, Physikalisch-Technische Bundesanstalt [PTB], Braunschweig, FRG, Van Swinden Laboratorium [VSL], Delft, The Netherlands, Iowa State University, Ames, Iowa, USA, and Bureau International des Poids et Mesures [BIPM], Sevres, France.
and G. T. Furukawa Guest Scientist National Institute of Standards and Technology Gaithersburg, MD 20899 1.
INTRODUCTION
The Comité Consultatif de Thermométrie (CCT) is one of eight specialized technical subcommittees of the Comité International des Poids et Mesures (CIPM). The CIPM is a committee of the Conférence Générale des Poids et Mesures (CGPM). These eight subcommittees are: 1 2 3. 4. 5. 6. 7. 8.
The Comité Consultatif d’Électricité (CCE), established in 1927, The Comité Consultatif de Photométrie et Radiométrie (CCPR), assigned this name in 1971; the previous name was the Comité Consultatif de Photométrie, established in 1933, The Comité Consultatif de Thermométrie (CCT), established in 1937, The Comité Consultatif pour la Définition du Métre (CCDM), established in 1952, The Comité Consultatif pour la Définition de la Seconde (CCDS), established in 1956, The Comité Consultatif pour les Étalons de Mesure des Rayonnements Ionisants (CCEMRI), established in 1958, The Comité Consultatif des Unités (CCU), established in 1964, and The Comité Consultatif pour la Masse et les grandeurs apparentées (CCM), established in 1980.
The CCT is composed presently of members from the following laboratories:
2. 3. 4. 5. 6. 7. 8. 9. 10.
Amt für Standardisierung, Messwesen und Warenprufung [ASMW], Berlin, DDR, Bureau National de Metrologie, Paris, France: Institut National de Metrologie [INM], du Conservatoire National des Arts et Métiers, Ceskoslovensky Metrologicky Ustav [CSMU], Bratislava Czechoslovakia, National Research Council [NRC], Ottawa, Canada, CSIRO, Division of Applied Physics [CSIRO], Lindfield, Australia, D.I. Mendeleyev Institute for Metrology [VNIIM), Leningrad, USSR; Physico-Technical and Radio-Technical Measurements Institute [PRMI], Moscow, USSR, National Institute of Metrology [NIM], Beijing, PRC, Istituto di Metrologia G. Colonnetti [IMGC], Turin, Italy, Kamerlingh Onnes Laboratorium [KOL], Leiden, The Netherlands, Korea Standards Research Institute [KSRI], Seoul, Korea,
The CCT met 12-14 September 1989 at the Bureau International des Poids et Mesures (BIPM) in its 17th Session [14] and completed the final details of the new temperature scale, the International Temperature Scale of 1990 (ITS-90) [66,83]. The CCT then recommended to the CIPM, which met [84] on 26-28 September 1989 at the BIPM, that the ITS-90 be adopted and made the official scale (see appendices). Upon considering this recommendation, the CIPM adopted the new temperature scale (see appendices), and the ITS-90 became the official international temperature scale on 1 January 1990, the same date on which changes affecting certain electrical reference standards were implemented [12]. The ITS-90 supersedes the IPTS-68, the International Practical Temperature Scale of 1968, Amended Edition of 1975 [IPTS - 68 (75)][101], and the 1976 Provisional 0.5 K to 30 K Temperature Scale (EPT-76) [99]. The ITS-90 was implemented at the NIST on 1 January 1990. The purpose of this document is to describe the new scale, to give some guidelines for its realization and use, to facilitate its implementation, to give the differences between temperatures on it and those on the IPTS-68(75) and on the EPT-76, and to describe how the NIST realizes the scale. The ITS-90 extends upward from 0.65 K and temperatures on this scale are in much better agreement with thermodynamic values than are those on the IPTS-68(75) and the EPT-76. The new scale has subranges and alternative definitions in certain ranges that greatly facilitate its use. Furthermore, its continuity, nonuniqueness and reproducibility throughout its ranges are much improved over the corresponding characteristics of the previous scales. The biggest improvement in reproducibility results from the replacement of thermocouple thermometry with platinum resistance thermometry in the range 630 ˚C to the freezing-point temperature of silver, and with radiation thermometry in the range from the freezing-point temperature of silver to that of gold. The change in the temperature scale affects not only technical interests involved directly in thermometry but also those involved with other reference standards,
* Reproduced with permission of National Institute of Standards and Technology
0.02 Temperature difference (t 90-t 68)/°C
1
Shortly after the adoption of the International Practical Temperature Scale of 1968 (IPTS-68) [100], it was realized that the scale had many deficiencies and limitations. These included its lower limit of 13.81 K, its inaccuracy relative to thermodynamic temperatures, and its non-uniqueness and irreproducibility, especially in the temperature region from T 68 - 903.89 K (630.74 ˚C) to T68 - 1337.58 K (1064.43 ˚C, the region in which the Pt-10%Rh/Pt thermocouple was the standard interpolating instrument. Consequently, the CCT undertook the development of a new scale, and completed it in accordance with Resolution 7 of the 18th Conference Generale des Poid et Mesures [29], which met in October 1987 (see appendices).
0
0.4
-0.02 -0.04
0.2 -200
0
200
400 0
0 0
-0.2
100
-0.01
-0.2
-0.02
-200
0
200
400
600
800
1000
t 90/°C Figure 1. The temperature difference (t90 - t68)/°C in the range between the triple point of equilibrium hydrogen (-259.3467 °C) and the freezing point of gold (1064.18°C) [83, 85].
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Guidelines for Realizing the ITS-90 Cont’d
such as electrical standards, that are sensitive to temperature. As examples, standard resistors and standard cells are sensitive to temperature and generally are maintained in constant-temperature environments, at least in national standards laboratories,. At the present time, the temperatures of those environments are normally determined with thermometers that were calibrated on the IPTS-68(75). A given thermodynamic temperature expressed on the ITS-90, however, has a value that is different from that expressed on the IPTS-68(75), except at absolute zero (0 K), at the triple-point temperature of water (273.16 K), and at a few other points at which the temperatures on the two scales are fortuitously the same . This difference is shown in figure 1 [83]. A table of differences between temperatures on the ITS-90, i.e., T90 or T90,and those on the IPTS-68(75), i.e. , T68 or t68 and those on the EPT-76, T76, is given in the text of the ITS-90 and is presented here in table 1. Although temperature values expressed on the two scales are different, the change is only in the expression of the value of temperature and not in the temperature itself. That is to say, the Kelvin thermodynamic temperature (the hotness) of a material at any given point is independent of the use of any of the ‘practical’ temperature scales. The better the ‘practical’ scale is, the closer the values of temperature on that scale are to the thermodynamic temperature values. Needless to say, the Kelvin thermodynamic temperature values are experimentally determined, and they may have significant error. Since temperature values expressed on the thermodynamic and ‘practical’ scales are different, if the temperature of the environment of a reference standard is adjusted so that its value when expressed on the ITS-90 has the same value as had been used on the IPTS-68(75), there will have been a change of the thermodynamic temperature and the value of the reference standard will usually change. Of course, one may not want to change the thermodynamic temperature of the reference standard. In that case, the thermodynamic temperature, as expressed an the IPTS-68(75), can simply be expressed on the ITS90 (a numerical value different from that on the IPTS-68(75)) and the reference standards will be unaffected. For more details on the effects of the change of the temperature scale on electrical standards, see National Institute of Standards and Technology (NIST) Technical Note 1263 [12]. In addition to the effect on reference standards for measurements, all temperature-sensitive properties, e.g., tables of thermodynamic properties, that are presently expressed on the IPTS-68(75) may require changes in values. 2. DEFINITION OF THE ITS-90 The ITS-90 was designed by the CCT in such a manner that temperature values obtained on it do not deviate from the Kelvin thermodynamic temperature values by more than the uncertainties of the latter values at the time the ITS-90 was adopted. Thermodynamic temperature is indicated by the symbol T and has the unit known as the kelvin, symbol K. The size of the kelvin is defined to be 1/273.16 of the thermodynamic temperature of the triple point of water. This definition of the Kelvin Thermodynamic Temperature Scale (KTTS) that is based on the value of a single finite temperature is not new; the CCT proposed it in 1954, the CIPM recommended it, and the Tenth CGPM adopted it that same year [30]. Because temperatures on previous temperature scales were expressed relative to the ice point (271.15 K), temperature, symbol t, on the Celsius Temperature Scale is defined by:
Table 1. Differences between T90 and T68 (and t90 and t68), and between T90 and T76
(T90 - T76) /mK T90 /K
(T90 -
1
-0.6 -2.2
2
3
4
5
6
7
8
9
-1.1 -3.2
-0.1 -1.3 -3.5
-0.2 -1.4 -3.8
-0.3 -1.6 -4.1
-0.4 -1.8
-0.5 -2.0
-0.7 -2.5
-0.8 -2.7
-1.0 -3.0
1
2
3
4
5
6
7
8
9
-0.007 -0.008 -0.006 -0.004 0.004 0.007 0.008 0.008
-0.006 -0.006 -0.008 -0.006 -0.003 0.005 0.007 0.008 0.008
-0.003 -0.005 -0.007 -0.007 -0.002 0.005 0.008 0.608 0.008
-0.004 -0.004 -0.007 -0.007 -0.001 0.006 0.008 0.008 0.008
-0.006 -0.004 -0.007 -0.007 0.000 0.006 0.008 0.008 0.009
-0.008 -0.005 -0.006 -0.006 0.001 0.007 0.008 0.008 0.009
-0.009 -0.006 -0.006 -0.006 0.002 0.007 0.008 0.008 0.009
T68) /K
T90 / K 10 20 30 40 50 60 70 80 90
0 -0.009 -0.006 -0.006 -0.006 0.003 0.007 0.008 0.008
-0.008 -0.007 -0.006 -0.005 0.003 0.007 0.008 0.008
-0.007 -0.008 -0.006 -0.005 0.004 0.007 0.008 0.008
T90 /K
0
10
20
30
40
50
60
70
80
90
100 200
0.009 0.011
0.011 0.010
0.013 0.009
0.014 0.008
0.014 0.007
0.014 0.005
0.014 0.003
0.013 0.001
0.012
0.012
(T90 - T68) / °C T90 / °C -100 0
T90 / °C 0 100 200 300 400 500 600 700 800 900 1000
T90 / ° C 1000 2000 3000
e-H2 TP e-H2 17K e-H2 20.3K
4He Point
0
0 10 20
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
0.013 0.000
0.013 0.002
0.014 0.004
0.014 0.006
0.014 0.008
0.013 0.009
0.012 0.010
0.010 0.011
0.008 0.012
0.008 0.012
0
10
20
30
40
50
60
70
80
90
0.000 -0.026 -0.040 -0.039 -0.048 -0.079 -0.115 0.20 0.34 -0.01 -0.19
-0.002 -0.028 -0.040 -0.039 -0.051 -0.083 -0.118 0.24 0.32 -0.03 -0.20
-0.005 -0.030 -0.040 -0.039 -0.053 - 0. 087 -0.122 0.28 0.29 -0.06 -0.21
-0.007 -0.032 -0.040 -0.040 -0.056 -0.090 -0.125 0.31 0.25 -0.08 -0.22
-0.010 -0.034 -0.040 -0.040 -0.059 -0.094 -0.08 0.33 0.22 -0.10 -0.23
-0.013 -0.036 -0.040 -0.041 -0.062 -0.098 -0.03 0.35 0.18 -0.12 -0.24
-0.016 -0.037 -0.040 -0.042 -0.065 -0.101 0.02 0.36 0.14 -0.14 -0.25
-0.018 -0.038 -0.039 -0.443 -0-068 -0.105 0.06 0.36 0.10 -0.16 -0.25
-0.021 -0.039 -0.039 -0.045 -0.072 -0.106 0.11 0.36 0.06 -0.17 -0.26
-0.024 -0.039 -0.039 -0.046 -0.075 -0.112 0.16 0.35 0.03 -0.18 -0.26
0 -0.72 -1.50
100
200
300
400
500
600
700
800
900
-0.26 -0.79 -1.59
-0.30 -0.85 -1.69
-0.35 -0.93 -1.78
-0.39 -1.00 -1.89
-0.44 -1.07 -1.99
-0.49 -1.15 -2.10
-0.54 -1.24 -2.21
-0.60 -1.32 -2.32
-0.66 -1.41 -2.43
H2O TP
Planck's Radiation Equation
SPRT
SPRT
e-H2TP, VP Ar TP
In FP
Hg TP
Ag FP
Zn FP
Au FP
3He CVGT
Ga MP
O2 TP
4He CVGT
Sn FP
Al FP
Cu FP
Calibration Points Bounds of Helium Vapor Pressure Calibration Bounds of Helium Vapor Pressure Thermometry
4He VP EQN
Ne TP
3He VP EQN
0.1
0.3
0.5
1
3
5
10
30
50
100
300
500
1000
3000
5000
10000
Temperature, K (ITS-90)
Figure 2. A schematic representation of the ITS-90 showing the temperatures of the defining fixed points (or phase equilibrium states) on the scale and temperature ranges defined by interpolation instruments and equations.
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t/˚C = T/K - 273.15.
(1)
The unit of temperature t is the degree Celsius, symbol ˚ C, and it is by definition the same size as the kelvin. A difference of temperature may be expressed either in kelvins or in degrees Celsius. Temperatures on the ITS-90 are expressed, in terms of the International Kelvin Temperatures, with the symbol, T90, or, in terms of the International Celsius Temperatures, with the symbol t90. The unit of the temperature T90 is the kelvin, symbol K, and the unit of the temperature t90 is the degree Celsius, symbol ˚C. The relation between T90 and t90 is:
t90/˚C = T90/K - 273.15.
(2)
The ITS-90 extends upward from 0.65 K. There are alternative definitions of T90 in certain temperature ranges and they have equal status. In measurements of the highest precision made at the same temperature, the alternative definitions will yield detectable temperature differences. Also, at any given temperature between defining fixed points, different interpolating thermometers that meet the specifications of the ITS-90 will indicate different temperature values. These latter differences are referred to as the non-uniqueness in the definition of the ITS-90, The magnitude of the differences that result from these two sources is sufficiently small to be negligible for all practical purposes. Temperatures on the ITS-90 are defined in terms of equilibrium phase states of pure substances (defining fixed points), interpolating instruments, and equations that relate the measured property of the instruments to T90. The equilibrium phase states of the pure substances and the assigned temperatures used as defining fixed points of the ITS-90 are listed in table 2. Figure 2 shows schematically the defining phase states and temperature ranges defined by the various interpolating instruments and equations. For comparison purposes, we give in table 3 the defining fixed points, and their assigned temperatures, of the ITS-90 and of all the previous internationally agreed-upon scales. 2.1 BETWEEN 0.65 K AND 5.0 K: 3He and 4He VAPOR PRESSURE THERMOMETRY The ITS-90 is defined between 0.65 K and 3.2 K by the vapor-pressure-temperature relation of 3He, and between 1.25 K and 2.1768 K (the λ point) and between 2.1768 K and 5.0 K by the vapor-pressure-temperature relations of 4He. T90 is defined by the vapor-pressure equations of the form: 9 T90/K = A0 + ∑ Ai{[ δn(p/Pa) - B] /C)1. i=1
Table 3. Comparison of temperatures of fixed points assigned on various scales. Temperatures are expressed in kelvins on the KTTS or eqviivalent scales Point
NHSa
ITS-27b
Au FPc Ag FP Al FP S BPd Zn FP Sn FP In FP H2O BP Ga TP H2O TPe H2O FP Hg TP 02 BPf Ar TP O2 TP Ne BP Ne TP H2 BP H2 BPg H2 TP Pb SPh 4He BP In SP 3He BP Al SP Zn SP Cd SP
373 273 -
1336.15 1336.15 1233.65 1233.95 717.75 717.75 373.15 373.15 273.15 273.15 90.18 90.18 -
a b
c d e f g h
Wr(T90)e
Temperature
He
VP TP VP (or CVGT) VP (or CVGT) TP TP TP TP TP MP FP FP FP FP FP FP FP
3 to 5 13.8033 ≈ 17 ≈ 20.3 24.5561 54.3584 83.8058 234.3156 273.16 302.9146 429.7485 505.078 692.677 933.473 1234.93 1337.33 1357.77
IPTS-68(75) EPT-76
ITS-90
21.102 24.5591 20.2734 17.0373 13.8044 7.1999 4.2221 3.4145 1.1796 0.851 0.519
1337.33 1234.93 933.473 692.677 505.078 429.7485 302.9146 273.16 234.3156 83.8058 54.3584 -24.5561 20.3 17.0 13.8033 4.2 3.2 -
NHS = Normal hydrogen scale [25]. For a time, the ice point Was taken to be 273.16 K. Here, the value 273.15 K was used to convert temperature values in degrees Centigrade or Celsius to kelvins in order to be as consistent as possible throughout the table. FP = Freezing point. BP = Boiling point at 101,325 Pa. TP = Triple point. Changed in 1975 to the condensation point. Reduced-pressure boiling point, at P = 33,330.6 Pa. SP = Superconductive transition point.
Coef. or Constant
t90 (˚C)
T90(K)
e-H2 e-H2 (or He) e-H2 (or He) Nec O2 Ard Hgc H2O Gac Inc Snd Zn Alc Ag Au Cuc
IPTS-68
1337.58 1337.58 1235.08 1235.08 692.73 692.73 (505.1181) (505.1181) 373.15 373.15 273.16 273.16 90.188 90.188 (83.798) 54.361 54.361 27.102 27.102 20.28 20.28 17.042 17.042 13.81 13.81 -
Table 4. Values of the coefficients A1 and of the constants B and C for the 3He and 4He vapor-pressure equations and the temperature range for which each equation is valid
Defining fixed points of the ITS-90
Materiala Equilibrium Stateb
IPTS-48b 1336.15 1233.95 717.75 (692.655) 373.15 (273.16) 90.18 -
(3)
The values of the coefficients Ai and of the constants A0, B and C of the vaporpressure equations for 3He and 4He are given in table 4.
Table 2.
ITS-48b
≈≈-
270.15 to 268.15 259.3467 256.15 252.85 248.5939 218.7916 189.3442 38.8344 0.01 29.7646 156.5985 231.928 419.527 660.323 961.78 1064.18 1084.62
A0 A1 A2
0.00119007
0.00844974 0.09171804 0.21585975 0.84414211 1.00000000 1.11813889 1.60980185 1.89279768 2.56891730 3.37600860 4.28642053
a e-H 2 indicates equilibrium hydrogen, that is, hydrogen with the equilibrium distribution of its ortho and para states at the corresponding temperatures. Normal hydrogen at room temperature contains 25% para and 75% ortho hydrogen. b VP indicates vapor pressure point or equation; CVGT indicates constant volume gas thermometer point; TP indicates triple point (equilibrium temperature at which the solid, liquid and vapor phases coexist); FP indicates freezing point and MP indicates melting point (the equilibrium temperatures at which the solid and liquid phases coexist under a pressure of 101,325 Pa, one standard atmosphere). The isotopic composition is that naturally occurring. c
Previously, these were secondary fixed points.
d
Previously, these were alternative fixed points.
e
From reference functions, equations (14) and (22).
3 He 0.65 K to 3.2 K
4 He 1.25 K to 2.1768 K
1.053 447 0.980 106 0.676 380
5 He 2.1768 K to 5.0 K
1.392 408 0.527 153 0.166 756
3.146 631 1.357 655 0.413 923
A3 A4 A5
0.372 692 0.151 656 -0.002 263
0.050 988 0.026 514 0.001 975
0.091 159 0.016 349 0.001 826
A6 A7 A8
0.006 596 0.088 966 -0.004 770
-0.017 976 0.005 409 0.013 259
-0.004 325 -0.004 973 0
A9 B C
-0.054 943 7.3 4.3
0 5.6 2.9
2.2 BETWEEN 3.0 K AND 24.5561 K (THE TRIPLE POINT OF Ne): VOLUME GAS THERMOMETRY
0 10.3 1.9
He and
3
He CONSTANT
4
Between 3.0 K and 24.5561 K, the ITS-90 is defined in terms of the 3He or 4He constant volume gas thermometer(CVGT). The thermometer is calibrated at three temperatures - at the triple point of neon (24.556,1 K), at the triple point of equilibrium hydrogen (13.8033 K), and at a temperature between 3.0 K and 5.0 K, the value of which is determined by using either a 3He or a 4He vapor-pressure thermometer as described in section 2.1. For a 4 He CVGT that is used between 4.2 K and the triple point of neon (24.5561 K), T90 is defined by the equation:
T90 = a + bp + cp2
(4)
where p is the CVGT pressure and a, b, and c are coefficients that are determined from calibrations at the three specified temperatures, but with the additional requirement that the calibration with the vapor-pressure thermometer be made at a temperature between 4.2 K and 5.0 K For a 4He CVGT that is used between 3.0 K and 4.2 K, and for a 3He CVGT that is used between 3.0 K and 24.5561 K, the non-ideality of the gas must be accounted for, using the respective second virial coefficients, B4(T90) or B3(T90). T90 is defined in this range by the equation:
T90
a + bp + cp2 =
1 + Bx (T90)N/V
Z-160
(5)
Z
Guidelines for Realizing the ITS-90 Cont’d
where p is the CVGT pressure; a, b, and c are coefficients that are determined from calibrations at the three defining temperatures; Bx(T90) refers to B3(T90) or B4(T90), and N/V is the gas density, in moles per cubic meter, in the CVGT bulb. The values of the second virial coefficients are given by the following equations: for
Note that in the earlier international scales, W(T) was defined with reference to the SPRT resistance 273.15K, not 273.16 K. There are two reference functions W r( T 90), one for the range 13.8033 K to 273.16 K and another for the range 273.15 K to 1234.93 K. These reference functions will be described in the discussion of the two ranges (secs. 2.3.3 and 2 3 4).
3He,
The deviation ∆W(T90) is obtained as a function of T90 for various ranges and subranges by calibration at specified fixed points. The form of the deviation function depends upon the temperature range of calibration.
B3(T90)/m3mol-1 = [16.69 - 336.98 (T90/K)-1 + 91.04 (T9O/K)-2 - 13.82 (T90/K)-3] 10-6, and for
(6)
A schematic representation of the ITS-90 in the range of temperature specified for SPRT’s is given in figure 3. Shown in figure 3 are the temperatures of the defining fixed points in this region of the scale and the various subranges specified by the scale.
4He,
B4(T90)/m3mol-1 = [16.708
-
374.05 (T90/K)-1 - 383.53 (T90/K)-2
+ 1799.2 (T90/K)-3 - 4033.2 (T90/K)-4 + 3252.8 (T90/K)-5] 10-6.
(7)
2.3.2
The accuracy of realization of T90 by using a CVGT is dependent upon the CVGT design and the gas density used.
SPRT SPECIFICATIONS
The SPRT sensing element must be made from pure platinum and be strain-free. finished SPRT must meet one of the following criteria:
2.3 BETWEEN 13.8033 K (THE TRIPLE POINT OF EQUILIBRIUM HYDROGEN) AND 1234.93 K (THE FREEZING POINT OF SILVER): PLATINUM RESISTANCE THERMOMETRY
W(302.9146 K) ≥ 1.118 07,
[dW(T90)/dT90] ≥ 3.986 x 10-3 K-1 at 273.16 K.
(12)
An SPRT that is acceptable for use to the freezing point of silver must meet the following additional criterion:
GENERAL RELATION BETWEEN RESISTANCE RATIOS AND T90
W(1234.93 K) ≥ 4.2844.
Temperatures on the ITS-90 in the above-indicated range are expressed in terms of the ratio of the resistance R ( T 90) at temperature T 90 and the resistance R (273.16 K) at the triple-point temperature of water. (Hereinafter, for convenience, the terms triple-point temperature, freezing-point temperature and melting-point temperature will be expressed as triple point, freezing point and melting point, respectively.) The resistance ratio W(T90) is:
W(T90) = R(T90)/R(273.16 K).
(8)
(9)
where W(T90) is the observed value, Wr(T90) is the value calculated from the reference functions, and ∆W(T90) is the deviation of the observed W(T90) value of the particular SPRT from the reference function value. The official version of the ITS-90 [83] does not indicate the difference [W(T90) - Wr(T90)] by ∆W(T90).
If the sheath of the long-stem type SPRT is borosilicate glass or stainless steel, the SPRT should not be used above the upper calibration temperature limit of 42˚C. If the sheath is Inconel, the upper temperature limit becomes about
273.16 H2O TP
Calibration Points
100
933.473, Al FP
1234.93, Ag FP
692.677, Zn FP
505.078, Sn FP
234.3156, Hg TP
302.9146, Ga MP
83.8058, Ar TP
54.3584, O2 TP
13.8033, e-H2 TP 17, e-H2 VP 20.3, e-H2 VP 24.5561, Ne TP
Interpolation Range
10
(13)
The temperature range over which an SPRT can be used depends upon the thermometer design, but no single design of SPRT can be used over the whole temperature range with high accuracy. For measurements at temperatures from 13.8033 K (-259.3467 ˚C) to 429.7485 K (156.5985 ˚C), or perhaps to as high as 505.078 K (231.928 ˚C) , capsule-type SPRT’s that have a nominal resistance of 25.5 Ω at 273.16 K may be used. Long-stem type SPRT’s of the same nominal resistance may be used in the range from about 77 K to 933.473 K (660.323 ˚C) . For temperatures above about 660 ˚C and to as high as 1234.93 K (961.78 ˚C), long-stem type SPRT’s having a nominal resistance of 0.25 Ω (or possibly 2.5 Ω) at 273.16 K should be used. When SPRT’s are used at the highest temperatures, leakage currents through the insulation supports of the platinum wire become significant and these result In shunting of the resistor. The effect of this shunting is reduced by using low voltages with low resistance SPRT’s.
The temperature T90 is calculated from the resistance ratio relation:
W(T90) - Wr(T90) = ∆W(T90)
(10) (11)
These criteria are equivalent to a requirement on the slope, namely,
429.7485, In FP
2.3.1
or
W(234.3156 K) ≤ 0.844 235.
Between 13.8033 K (-259.3467 ˚C) and l234.93 K (961.78 ˚C),the ITS-90 is defined in terms of specified fixed points to which temperature values have been assigned, by resistance ratios of platinum resistance thermometers obtained by calibration at specified sets of the fixed points, and by reference functions and deviation functions of resistance ratios which relate to T90 between the fixed points. (Henceforth, for convenience, the standards type platinum resistance thermometers will be referred to by the acronym SPRT.)
The
1000
10000
Temperature, K (ITS-90)
Figure 3. A schematic representation of the ITS-90 in the range specified for the platinum resistance thermometer, showing the various defined subranges and the temperatures of the defining
Z-161
660 ˚C. If the sheath is fused silica, temperature measurements can be made up to 962˚C. For measurements up to about 630˚C, mica is just barely adequate as an electrical insulator for the temperature sensing element and leads of SPRT’s. Starting at about 500˚C, muscovite mica begins to decompose, evolving water that electrically shunts the thermometer resistor, Phlogopite mica is adequately stable to 630˚C. For measurements up to 962˚C, refractory materials such as fused silica and sapphire are used for electrical insulation.
with n = 2. The coefficients a 1, b1, and the five c 1 ‘s are obtained by calibration at all eight of the above temperatures, including that at the triple point of water, The values of Wr,(T90) are obtained from the reference function [eq (14)]. The official version of the ITS-90 [83] does not indicate the difference [W(T90) - Wr(T90)] by ∆ W,(T90), does not use the subscript m, where in eq (18), m = 1, nor does it label the coefficients a and b with subscript m. However, we adopt this subscript notation to identify the subranges. Additionally, this notation is useful when reporting calibration results.
2.3.3 RANGE 13.8033 K TO 273.16 K If an SPRT is not to be used over the entire 13.8033 K to 273.16 K range, but its use restricted to one of the subranges, the deviation functions and the calibration points are as follows.
In the range 13.8033 K to 273.16 K, the reference function Wr(T90) is given by: 12 ,n[Wr(T90)] = A0 + ∑ Ai([,n(T90/273.16 K) + 1.5]/1.5)i i=I
(14)
A specified,, approximate inverse [83] of this equation, equivalent to within ± 0.000 1 K, is: 12 T90/273.16 K = B0 + ∑ Bi{([Wr(T90)]1/6 - 0.65)/0.35}i i=I
(15)
The values of the constants A0 and B0, and of the coefficients Ai and Bi of equations (14) and (15) are listed in table 5. If an SPRT is to be used throughout the range from 13.8033 K to 273.16 K, it must be calibrated at the triple points of equilibrium hydrogen (13.8033 K), neon (24.5561 K), oxygen (54.3584 K) argon (83.8058 K), mercury (234.3156 k), and water (273.16 K), and at two additional temperatures close to 17.0 K and 20.3 K. The temperatures of calibration near 17.0 K and 20.3 K maybe determined by using either a CVGT as defined in section 2.2 or the specified vapor - pressure temperature relation of equilibrium hydrogen. When the CVGT is used, the two temperatures must be within the ranges 16.9 K to 17.1 K and 20.2 K to 20.4 K, respectively. When the equilibrium hydrogen vaporpressure thermometer is used, the two temperatures must be within the ranges 17.025 K to 17.045 K and 20.26 K to 20.28 K, respectively. The temperatures of the equilibrium hydrogen vapor-pressure thermometer are determined from the values of the hydrogen vapor pressure, p, and the equations:
2.3.3.1
SUBRANGE 24.5561 K TO 273.16 K
The deviation function for calibration in the subrange 24.5561 K to 273.16 K is given by the relation: 3 ∆W2 (T90) a2[W(T90) - 1] + b2[W(T90) - 1]2 + ∑ ci[,n[W(T90)]i+n, (19) i=I with n = 0. The coefficients a 2 , b 2 , and the three, c 1 ’s are obtained by calibrating,the SPRT at the triple points of equilibrium hydrogen (13.8033 K), neon (24.5561 K), oxygen (54.35 84 K), argon (81.8058 K), mercury (234.3156 K) and water (273.16 K). The, values of Wr( T 90), are obtained from the reference function [eq (14)]. Note that for this subrange, temperatures are measured only down to the triple point of neon, although the-thermometer must be calibrated at the triple point of equilibrium hydrogen. 2.3.3.2 SUBRANGE 54.3584 K TO 273.16 K The deviation function for calibration in the subrange 54.3584 K to 273 16 K is given by the relation: ∆ W2 (T90) a3[W(T90) - 1] + b3[W(T90) - 1]2 + ci[,nW(T90)]i+n,
(20)
with n - 1. The coefficients a3, b3, and c1 are obtained by calibrating the SPRT at the triple points of oxygen (54.3584 K), argon (83.8058 K), mercury (234.3156 K), and water (273.16 K). The values of Wr(T90) are obtained from the reference function [eq (14)]. 2.3.3.3 SUBRANGE 83.8058 K TO 273.16 K
T90/K - 17.035 = (p/kPa - 33.3213)/13.32
(16)
T90/K - 20.27
(17)
= (p/kPa - 101.292)/30.
where 13.32 and 30 are, values of -(dp/dT90)/(kPa/K) at 17.035 K and 20.27 K, respectively.
The deviation function for calibration in the subrange 83.8058 K to 273.16 K is given-by the relation: ∆ W4 (T90) a4[W(T90) - 1] + b4[W(T90) - 1]lnW(T90).
(21)
Depending upon the’ temperature range of use, the SPRT may be calibrated from 273.16 K down to 13.8033 K (the triple point of equilibrium hydrogen), down to
The coefficients a4 and b4 are obtained by calibrating the SPRT at the triple points of argon (83.8058 K), mercury (234.3156 K), and water (273.16 K). The values of Wr(T90) are obtained from the reference function [eq (14)].
Table 5. Values of the coefficients, Ai, Bi, Ci and Di, and of the constants A0, B 0, C 0, and D 0 in the reference functions, eqs (14) and (22), and in the functions approximating them, given by eqs (15) and (23)
In the range 273.15. K. to 12341.93 K, the equation for the reference function Wr(T90) is given by:
2.3.4 RANGE 273.15 K (O˚C) TO 1234.93 K (961.78 ˚C)
Constant or Coefficient
Value
Constant or Coefficient
9 Wr(T90) = C0 + ∑ C1[(T90/K - 754.15)/481]i i=I
Value
A0 A1 A2 A3
-2.135 3.183 -1.801 0.717
347 247 435 272
29 20 97 04
B0 B1 B2 B3
0.183 0.240 0.209 0.190
324 975 108 439
722 303 771 972
A4 A5 A6 A7
0.503 -0.618 -0.053 0.280
440 993 323 213
27 95 22 62
B4 B5 B6 B7
0.142 0.077 0.012 -0.032
648 993 475 267
498 465 611 127
A8 A9 A10 A11
0.107 -0.293 0.044 0.118
152 028 598 686
24 65 72 32
B8 B9 B10 B11
-0.075 -0.056 0.076 0.123
291 470 201 893
522 670 285 204
A12
-0.052 481 34
B12 B13 B14 B15
-0.029 -0.091 0.001 0.026
201 173 317 025
193 542 696 526
C0 C1 C2 C3
2.781 1.646 -0.137 -0.006
572 509 143 497
54 16 90 67
D0 D1 D2 D3
439.932 472.418 37.684, 7.472
854 020 494 018
C4 C5 C6 C7
-0.002 0.005 0.001 -0.002
344 118 879 044
44 68 82 72
D4 D5 D6 D7
2.920 0.005, -0.963 -0.188
828 184 864 732
C8 C9
-0.000 461 22 0.000 457 24
D8 D9
0.191 0.049
203 025
A specified, approximate inverse [83] of this equation, equivalent to within ± 0.000 13 K, is: 9 T90/K - 273.15 = D0 + ∑ Di([Wr(T90) - 2.64]/1.64]i i=I
calibration
∆W1(T90) = a1[W(T90) - 1] +
If the SPRT is to be used over the entire range 273.15 K to 1234.93 K, it must be calibrated at the triple point of water (273.16 K) and at the freezing points of tin (505.078 K), zinc (692.677 K), aluminum (933.473 K), and silver, (1234.93 K). The deviation function is given by the relation: ∆ W6(T90) = a6[W(T90) - 1] + b6[W(T90) - 1]2 + c6[W(T90) - 1]3 + d[W(T90) - W(933.473 K)]2
5 1]2 + ∑ c1[,nW(T90)]i+n, i=I
(24)
The values of a6, b6, and c6 are determined from the measured deviations ∆ W(T90) of W ( T 90) from the reference values W, ( T 90) [obtained from eq (22)] at the freezing points :of tin (505.078 K), zinc (692.677 K), and aluminum, (933.473 K), ignoring the term involving d. Then, d is determined-from these values of a6, b 6, c 6 and the deviation ∆ W 6( T 90) of W ( T 90) from the reference value W i( T 90) at the freezing point of silver (1234.93 K). The coefficient d is, used only for temperature measurements in the range from the freezing point of aluminum to the freezing point of silver. For temperature measurements below the freezing point of aluminum, d = 0.
over the range 13,8033 K to 273.16 K is
b1[W(T90) -
(23)
The values of the constants C0 and D0 and of the coefficients Ci and Di of eqs (22) and (23) are, listed in table 5.
24.5561 K (the triple point of neon), down. to 54.3584 K (the triple point of oxygen), or down to 83.8058 K (the triple point of argon). The deviation function for given by the relation:
(22)
(18)
SPRT’s may be calibrated for use throughout the whole range 273.15 K to 1234.93 K or for shorter subranges by calibrations at fixed points between 273.15 K and the upper limit of 933.473 K (freezing point of aluminum,. 660.323 ˚C), of 692.677 K (freezing point of zinc, 419.527 °C), of 505.078 K (freezing point of tin, 231.928 ˚C) of 429.7485 K (freezing point of indium, 156.5985 °C), or of 302.9146 K (melting point of gallium, 29.7646 °C). The
Z-162
deviation
function
∆ W 5 ( T 90 )
will
be
discussed
liter
in
the
text.
Z
Guidelines for Realizing the ITS-90 Cont’d
If an SPRT is not to be used over the entire 273.15 K to 1234.93 K range, but its use restricted to one of the subranges, the deviation functions and the calibration points are as follows. 2.3.4.1 ALUMINUM)
SUBRANGE 273.15 K (0° C) TO 933.473 K (660.323 -C. FREEZING POINT OF
For an SPRT used throughout the subrange 273.15 K to 933.473 K, the thermometer is calibrated at the triple point of water (273.6 K) and at the freezing points of tin (505.078 K) zinc (692.677 K), and aluminum (9 33.473 K). The deviation function is given by the relation: ∆W7(T90) - a7[W(T90) - 1] + b7(W(T90) _ 1]2 + C7(WT90) - 1]3.
For an SPRT used throughout the subrange 273.15 K to 692.677 K, the thermometer is calibrated at the triple point of water (273.16 K); and at the freezing points of tin (505.078 K) and zinc (692.677 K). The deviation function is given by the relation: (26)
The coefficients a8 and ba are determined from the deviations ∆W(T90) of W(T90) from the reference values Wr(T90) [eq (22)] at the freezing points of tin (505.078 K) and zinc (692.677 K). 2.3.4.3 SUBRANGE 273.15 K (0 °C) TO 505.078 K (231.928 °C. FREEZING POINT OF TIN) to 505.078 K. the thermometer is , and at the freezing points of of the deviation function is the K, i.e.,
∆W9(T90) - a9[W(T90) - 1] + b9(W(T90) - 1]2.
(27)
The coefficients a8 and b8 are determined from the deviations ∆W(T90) of W(T90) from the reference values Wr(T90) [eq (22)] at the freezing points of indium (429.7485 K) and tin (505.078 K). 2.3.4.4 SUBRANGE 273.15 K (0 °C) To 429.7485 K (156.5985 °C, FREEZING POINT OF INDIUM) For an SPRT used throughout the subrange 273.15 K to 429.7485 K. the thermometer is calibrated at the triple point of water (273.16 K) and at the freezing point of indium (429.7485 K). The deviation function is: ∆W10(T90) - a9[W(T90) -1]
(28)
The coefficient a10 is determined from the deviation ∆W(T90) of W(T90) from the reference value Wr(T90) [eq (22)] at the freezing point of indium (429.7485 K).
2.3.4.5 SUBRANGE 273.15 K (0 °C) TO 302.9146 K (29.7646 °C. MELTING POINT OF GALLIUM) For an SPRT used throughout the subrange 273.15 K to 302.9146 K, the thermometer is calibrated at the triple point of water (273.16 K) and at the melting point of gallium (302.9146 K). The deviation function is: ∆W11(T90) - a11W(T90) - 1].
(29)
The coefficient a11 is determined from the deviation ∆W(T90) of W(T90) from the reference value Wr(T90) [eq (22)] at the melting point of gallium (302.9146 K)
2.3.5 SUBRANGE 234.3156 K (-38.8344 °C. TRIPLE POINT OF MERCURY) TO 302.9146 K (29.7646 THE MELTING POINT OF GALLIUM) For an SPRT used throughout the subrange 234. 3156 K to 302.9146 is calibrated at the triple points of mercury (234.3156 K) and and at the melting point of gallium (302.9146 K). The form function is the sameas that for the subrange 273.15 K to ∆W5(T90) - a5[W(T90) - 1] + b5[W(T90) -1.]
K, the thermometer water (273.16 K), of the deviation 692.677 K, i.e., (30)
The coefficients a5 and b5 are determined from the deviations ∆W(T90) of W(T90) from the reference values Wr(T90) at the triple point of mercury (234.3156 K) and at the melting point of gallium (302.9146 K) The reference values Wr(T90) must be calculated from the appropriate reference function [either eq (14) or eq (2 2 ) } both reference functions being required to cover this range.
2.4 ABOVE 1234.93 K (961.78 °C. FREEZING POINT OF SILVER): RADIATION THERMOMETRY RASED ON PLANCK’S LAW OF RADIATION At temperatures above 1234.93 K, T90 is defined by the relation: Lλ (T90) ——————————— Lλ [T90(X)]
-
3.1
VAPOR PRESSURE THERMOMETRY AND GAS THERMOMETRY REALIZATION OF THE ITS-90 BELOW 273.16 K
(25)
2.3.4.2 SUBRANGE 273.15 K (0 °C) TO 692.677 K (419.527 °C, FREEZING POINT OF ZINC)
For an SPRT used throughout the subrange 273.15 K calibrated at the triple point of.water)(273.16 K) indium (429.7485 K) and tin (505 078 K). The form same as that for the subrange 273.15 K to 692.677
3. REALIZATION OF THE ITS-90
3.1.1
The coefficients a7, b7, and C7, are identical to a6, b6, and C6, respectively, are determined from the deviations ∆W(T90) of W(T90) from the reference values WI,(T90) [eq (22)] at the freezing points of tin (505.078 K), zinc (692.677 K), and aluminum (933 . 473 K).
∆W8(T90) - a8[W(T90) - 1]+ b8[W(T90) - 1]2
temperature of silver is the Junction point of platinum resistance thermometry and radiation thermometry, it is believed that the T90 values of the freezing points of silver, gold and copper are sufficiently self-consistent that the use of any one of them as the reference temperature T90(X) will not result in any significant difference in the measured values of T90 from what would be obtained if only the silver freezing point were used.
exp[c2/λT90(X)]-1 ————————————————— exp[c2/λT90-1
in which Lλ(T90) and Lλ[T90(X)] are the spectral concentrations of the radiance of a blackbody at wavelength (in vacuum) at T90 and at T90(X), respectively. T90(X) refers to either the silver freezing point [T90(Ag) - 1234.93 K] , the gold freezing point (T 90 (Au) - 1337.33 K], or the copper freezing point [T90 (Cu) 1357.77 K]. The second radiation constant, C2 (-hc/k), of Planck’s radiation formula has the value C 2 - 0.0143 88 m-K. Although the freezing-point
The calibration of thermometers below the triple point of argon on the ITS-90, as defined, is relatively complex It is expected that capsule-type SPRT’s, rhodiumiron resistance thermometers (RIRT’s), and other stable encapsulated resistance thermometers will be calibrated in terms of the defined ITS-90 and then used as reference thermometers to maintain the ITS-90 below about 84 K and used to calibrate other resistance thermometers by the comparison method. The reference thermometers will be calibrated periodically in terms of the defined ITS-90. By use of the term "realization of the ITS-90," reference is made to obtaining the equilibrium states as defined by the scale, to having thermometers in thermal equilibrium with those equilibrium states, and to making accurate measurements and interpretations of the requisite properties of those thermometers in terms of the ITS-90. Considerable effort has been expended to develop and realize the EPT-76, a scale which covered the range 0.5 K to 30 K. This scale has been widely disseminated among low temperature scientists. At NIST, the EPT-76 has been maintained on referencestandard RIRT’s for use in calibrating customer thermometers. Upon introduction of the ITS-90, NIST converted the EPT-76 on the reference-standard RIRT’s to the ITS-90 using the specified differences [83] between T90 and T76, This converted scale is being used to calibrate other thermometers until such time that NIST realizes the ITS-90 in this temperature region directly as defined. It is recommended that those laboratories that have thermometers with calibrations on the EPT-76 adjust their T76 values to conform to T90 values. When NIST realizes the ITS-90 as defined in this range, the difference between the converted scale on the referencestandard RIRT’s (and, where appropriate, on capsule SPRT’s) and the realized scale will be determined. 3.1.2 VAPOR PRESSURE THERMOMETRY AND THE CVGT RANGE For most measurements below about 100 K, better precision can be obtained with capsule-type SPRT’s than with the long-stem type. In the calibration of SPRT’s, however, long-stem type SPRT’s (immersion-type SPRT’s) can be calibrated easily by a direct immersion process down to the triple point of argon (83.8058 K) by moving the SPRT’s from one fixed-point device to another. Unless capsule-type SPRT’s and other capsule-type thermometers are installed inside long stem-like holders, however, they will require re-installation, and re-wiring whenever different fixed-point apparatuses are used. (In this document, the phrase “capsule-type thermometers” means encapsulated resistance thermometers of small o v e r a l l dimensions.) It is desirable, therefore, to be able to calibrate capsule-type SPRT’s and other capsule-type thermometers at the argon triple point and below (or, if possible, even at the triple point of water and below since calibrations of SPRT’s require measurements at the triple point of water) in an integrated "multi-task" (multi- fixed-point) apparatus. Such a multi-task apparatus requires, in addition to wells for capsule thermometers (in thermal equilibrium in a "single cryostat block"), means for calibration using 3He, 4He, and e-H2 vapor pressure thermometry, 3He and 4He CVGT’s, and triple points of e-H2 Ne, O2, Ar, Hg, and H 2 O - A total of 11 chambers is required if all of the overlapping definitions of the ITS-90 are to be evaluated and if a "continuous calibration," without re-installation and re-wiring of the SPRT’s, is desired from 0.65 K to 273.16 K. In addition, unless high pressure sealed cells of the reference gases are used, tubes to each of the chambers, except those for Hg and H20, are required. Since 3He and 4He vapor-pressure and CVGT ranges overlap to a large extent chambers for 4He vapor-pressure measurements and for 4He CVGT measurements could be eliminated and the ITS-90 could still be realized. Also, chambers for e-H2 vaporpressure and the e-H2 triple-point realizations could be combined. The number of chambers could be reduced further if the cryostat block could be allowed to warm to ambient temperature or higher for exchanging certain of the fixed-point substances, or if it were permissible to perform the calibrations of the capsule thermometers at the triple points of argon, mercury, and water in other apparatuses, using a long-stem type holder. This procedure, however, would require a longer time for calibration. The number of chambers can also be reduced if suitable, highly stable capsule thermometers are available for correlating the scales; for this purpose, the capsule SPRT’s would be calibrated in another, simpler, fixed-point apparatus. It is expected that such a set of reference-standard resistance thermometers would be calibrated, and that routine calibrations of customer thermometers on the ITS-90 would be by comparison with these reference thermometers. The reference thermometers would be checked occasionally against the defined ITS-90. It is hoped that resistance thermometer devices will be more reproducible than the ability to realize the defined ITS-90. Depending upon the design of the cryostat, the defined ITS-90 may lack the desired reproducibility when realized in a multi-task apparatus of high complexity. In order to achieve the best realization of the ITS-90, it may be more practical to limit the number of defining fixed points in a single cryostat block. The greatest problem in realization of the fixed points and in calibrations of capsule thermometers is ensuring that the multi-task or a "single-task" cryostat block is isothermal. Depending upon the design, a thermal gradient can persist. The presence 3 He, 4 He, e-H 2 , Ne, 0 2 , and/or Ar gases in their respective chambers are expected to be beneficial in making the apparatus isothermal, but, the gases may be a source of thermal oscillation. (In designing an apparatus for low temperature gases, provisions should be made to avoid thermal oscillations in the gas.) The vapor pressures of Ne and Ar are high at their respective triplepoint temperatures so that thermal equilibrium should be easily attained at their triple points.
Z-163
For a practical cryostat block, the 3He and 4He CVGT’s must connect thermally the 3He and 4He vapor-pressure scales and the fixed points of e-H2 and Ne. Such a cryostat block will require six chambers (separate 3He and 4He vapor-pressure chambers, separate 3He and 4He CVGT chambers, e-H2 vapor-pressure and e-H2 triple-point chamber, and a Ne chamber) to realize the ITS-90 in the most satisfactory manner at and below the Ne triple point. This arrangement will permit a direct comparison of the different parts of the scale and/or calibration of thermometers. Since the combination of 4He vapor-pressure thermometry and 4He constant volume gas thermometry are redundant with 3He vapor-pressure thermometry and 3He constant volume gas thermometry, the 4He systems are not required. Hence, the number of chambers required could be reduced to four and the ITS-90 could still be realized. It should be noted, however, that, depending upon the CVGT filling pressure, the dp/dT of a 3He CVGT may be less sensitive than 4He vapor-pressure thermometry. Since SPRT’S can be calibrated only down to the argon triple-point temperature using the longstem SPRT apparatus, it would be most practical and useful to include an oxygen triple-point chamber in the low-temperature system, thereby increasing the number of chambers,to five. Also, since it is highly desirable to overlap calibrations obtained in a long-stem type SPRT apparatus with those obtained in a lowtemperature apparatus, an argon triple-point chamber should be included. This increases the number of chambers for the low temperature apparatus to six. Although it is desirable to have as few tubes as possible going to the cryostat block in order to minimize temperature gradients in the block, one must build into the system enough redundant components to be able to check the system for proper and accurate operation. For example, although the CVGT is calibrated at only the triple-point temperatures of neon and hydrogen and at one point in the 3He or 4He vapor pressure range between 3.0 K and 5.,0 K, the system should have the capability for the measurement of hydrogen vapor pressures at about 17 K and 20.3 K so that temperatures measured by means of vapor pressures and by the CVGT m a y b e compared. Of course, if the system is operating properly, the temperatures measured by the two techniques should agree. Similarly, there should be the capability to measure the vapor pressures of both 3He and 4He so that temperatures measured with the CVGT in the range from 3 K to 5 K and by means of 3He and 4He vapor pressures may be compared for agreement. Also, it is desirable to design the CVGT for absolute gas thermometry measurements; the CVGT can check the consistency of the ITS-90 from about 3 K to 90 K.
3.1.3.2
Since measurement of pressure is common to both vapor pressure and CVGT measurements, it will be discussed later in this section (see sec. 3.1.3.5). In vapor pressure measurements, it is important that cold spots be absent along the gas-pressure transmitting tube. If cold spots are present, the observed vapor pressure will reflect the temperature of the condensation at the cold spot instead of that of the bulk bath. A separate vacuum jacket around the tube will maintain a continuous heat flux to the sample bulb or bath and should free the tube of any condensation [24]. The vacuum jacket should also reduce the occurrence of thermal oscillation in the gas-pressure, sensing tube. If thermal oscillations do occur, they may be suppressed by either one or a combination of the following: increasing,the volume of the external gas-pressure space at the ambient temperature, or by inserting a wad of wool or glass fiber or a piece of yarn in the gas-pressure sensing tube. The thermal oscillations may be suppressed also by “tuning” a variable volume device [36]. Thermocouples should be placed along the gas-pressure sensing tube in order to determine temperatures along that tube, the distribution of those temperatures being required to determine the aerostatic head correction. The vapor pressure may be determined over the bath of bulk liquid 3He, 4He, or e-H2 with which the thermometer to be calibrated is in thermal equilibrium. The measurement can be made also by using a separate, small sample bulb with which the thermometer is in good thermal contact. The latter method is preferred with the rather expensive 3 He and with e-H 2 which requires a catalyst for the equilibrium ortho-para conversion of the sample [2,58,91]. 3.1.3.1 3He Vapor-Pressure Measurements Because of the relatively high cost of the sample, vapor-pressure measurements are made with 3He contained in a small volume of about 5 cm . Likewise, the gas pressure volume to the manometer should be kept relatively small, but large enough to avoid large thermomolecular pressure effects and thermal oscillations. Thermomolecular-pressure-effect corrections depend on the sensing tube diameter, surface condition of the tube, temperature difference, and pressure [49,71,102]. As mentioned above, thermal oscillations can be reduced by varying the gaspressure volume at the ambient temperature or by introducing a wad of fiber or yarn (cotton, wool, or glass) in the gas-pressure tube. In the past, 3He contained significant amounts of 4He and the observed vapor pressures of 3He required corrections for its presence. In recent years, however, 3He samples of 99.9995% purity have become available, eliminating the requirement for such corrections. At 0.65 K, the vapor pressure and the temperature derivative of the vapor pressure are 115.9 Pa and 1.08 Pa/mK, respectively. At the upper limit of 3.2 K, the vapor pressure and the temperature derivative of the vapor pressure are 101,662.1 Pa and 106.83 Pa/mK, respectively. The required pressure resolution that corresponds to 0.1 mK of vapor-pressure measurements varies from 0.108 Pa at 0.65 K to 10.7 Pa at 3.2 K. Since the amount of 3He in the cryostat is small, and since the amount of 4He used in cooling is relatively large, every effort should be made to avoid contamination of the sample of 3He by the 4He through diffusion, particularly through any glass parts of the apparatus. The sample bulb should contain enough 3He that the liquid surface temperature and the cryostat block temperature can be correlated with the observed vapor pressure. The temperature of the cryostat block must be checked for consistency with the observed dp/dT of the vapor pressure at the temperature of measurement. Aerostatic-head corrections depend upon the density of the gas in the pressuretransmitting gas tube. Thermocouples must be distributed along the tube in order to measure the temperatures required for calculation of these corrections.
Vapor-Pressure Measurements
At the lower temperature limit of 1.25 K, the vapor pressure of 4He is 114.7 Pa and the temperature derivative of the vapor pressure is 0.76 Pa/.K. At the upper limit of 5 K, the vapor pressure and, the temperature derivative of the vapor pressure of 4He are 1946.29.7 Pa and 146.53 Pa/mK, respectively. The required pressure resolutions of the vapor pressure that corresponds to 0.1 mK are 0.076 Pa at 1.25 K and 14.7 Pa at 5.0 K [37,38]. 3.1.3.3
e-H2. Vapor Pressure Measurements
The equilibrium composition of the two molecular states of hydrogen (ortho and para) is temperature dependent. The room temperature composition, about 75% ortho and 25% -para, is referred to as normal hydrogen (n-H2). On liquefaction, the composition slowly changes toward the equilibrium composition corresponding to its temperature. ~ In the process, the heat of transition is released, resulting in the evaporation of some hydrogen. A catalyst, such as activated ferric hydroxide, hastens the equilibration. The catalyst must be placed in the sample chamber in order to ensure that the hydrogen has the appropriate equilibrium composition. Most of the conversion must be made before collecting the liquid in the sample chamber since the heat of conversion (1664 J/mol) from the ortho to the -para,molecular state is larger than the heat of vaporization (900 J/mol) of normal hydrogen. The normal boiling point of e-H2 (equilibrium composition: 0.21% ortho and 99.79% -para) is about 0.12 K lower than that of n-H2. The temperatures near 17.035 K and 20.27 K are determined from vaporpressure measurements near 33,,321.3 Pa and 101,292 Pa, respectively [2,31,58]. 3.1.3.4
3.1.3 REALIZATION OF THE VAPOR PRESSURE AND CVGT SCALES AT TEMPERATURES BELOW THE NEON TRIPLE POINT
4He
Since liquid 4He can be obtained easily, the vapor pressure can be determined above a bath of the liquid in which an apparatus containing the thermometer is i m m e r s e d . o r a t e c h n i q u e u s i n g a s m a l l b u l b o f 4H e s a m p l e , w i t h t h e thermometer in good thermal contact, can be employed. The lower end of the gaspressure tube should have a small orifice in order to reduce superfluid 4He film flow at temperatures below 2.1768 K [61,91]. The 4He sample bulb must be in thermal equilibrium with the cryostat block. The cryostat block temperature should be checked for consistency with the observed dp/,dT of the vapor pressure at the temperature of measurement.
Constant Volume Gas Thermometry
Some of the following precautions and corrections that are applicable to absolute constant-volume gas thermometry should be included in the calibration of the CVGT at the three specified temperatures of calibration: 1. The volume of the gas bulb should be sufficiently large relative to the gaspressure-line volume to minimize the error in correcting for the "dead space." On the other hand, the diameter of the gas-pressure line should not be so small as to cause large thermomolecular pressure corrections. 2. The temperature coefficient of volume expansion and the pressure expansion of the gas bulb should be known accurately. (It is desirable to check the calibration by using the,CVGT ih the absolute mode.)
Table 6. The effect of pressure on the temperatures of the defining fixed points. The reference pressure for the equilibrium states of freezing and melting points is one standard atmosphere (101,325 Pa). Triple points have the vapor pressure of the material when the solid, liquid and vapor phases are present in equilibrium.
Material
T90
Pressure Effect of Fixed Point K Pa-1 x108*
e-H2 TP Ne TP O2 TP Ar TP Hg TP H2O TP Ga HP In FP Sn FP Zn FP Al FP Ag FP Au FP Cu FP
13.8033 24.5561 54.3584 83.8058 234.3156 273.16 302.9146 429.7485 505.078 692.677 933.473 1234.93 1337.33 1357.77
mK/(meter of liquid)
34 16 12 25 5.4 -7.5 -2.0 4.9 3.3 4.3 7.0 6.0 6.1 3.3
0.25 1.9 1.5 3.3 7.1 -0.73 -1.2 3.3 2.2 2.7 1.6 5.4 10. 2.6
*Equivalent to millikelvins per standard atmosphere.
3. In order to be able to calculate the aerostatic head correction, the temperature distribution along the connecting gas-presure transmitting tube (capillary) must be known. That temperature distribution may be determined by placing thermocouples along the tube. 4. The gas-bulb filling pressure should be sufficiently high to give an adequate dp/dT for measurement, but not so high as to require large corrections for non-ideality of the gas. 5. Higher pressures reduce the thermomolecular pressure gradients in the connecting gas-pressure tube. 6. The effect of adsorption can be reduced by designing the gas bulb so that the volume is large relative to the surface and by polishing the inside surface of the bulb. For optimizing the CVGT design, the Differentiating the ideal gas relation,
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pV = nRT,
(32)
yields dp/dT
Rn/V,
(33)
where p is the pressure of n moles of gas contained in a volume of V m3. Equation (33) shows that the dp/dT sensitivity of the CVGT is directly related to the gas density n/V. Expressing the gas constant R as 8.31441 Nm/mol • K or 8.31441 Nm3/(M2•mol•K), the sensitivity dp/dT can be expressed in the units Pa/K. Thus, dp/dT = 8.31441(n/V) Pa/K,
(34)
where n/V is given in mol/m3. If a gas bulb of 1000 cm3 is filled to four atmospheres at 273.16 K, n/V would be approximately 178 mol/m 3, and dp/dT becomes 1484 Pa/K. Since the resolution of many high quality mercury-manometer systems is about 0.03 Pa to 0.2 Pa, the temperature resolution is about 0.03 mK to 0.1 mK. It is to be noted that since
p/T = Rn/V,
(35)
the sensitivity dp/dT is “constant,: independent of the gas bulb volume, as long as the gas density at the filling temperature is constant. Hence, the gas-bulb volume and the gas filling pressure should be chosen so that errors from the effect of dead space, gas non-ideality effects and other effects are negligibly small. See references [6,13,49,60]. 3.1.3.5
Pressure Measurements
Efforts have been made to minimize the requirement of highly precise and accurate pressure measurements in the realization of the defining fixed points of the ITS-90 . The fixed points involving freezing and melting require knowledge of the pressure only within the significance of the relative ly small pressure effect ( cf. table 6). Accurate pressure measurements are required, however, to realize the vapor-pressure-temperature scales of 3He and 4He in the range 0.65 K to 5.0 K, and to realize the vapor-pressure-temperature scale of eH2 close to 17.035 K and 20.27 K. To realize the CVGT scale using 3He or 4He gas in the range 3.0 K to the triple point of neon (24.5561 K), only accurate pressure-ratio measurements are required.
3.1.3.5.5
Thermolecular Pressure Difference
Thermolecular pressure differences occur at low gas pressures in tubes with temperature gradients when the tube diameter is not much larger than the mean free path of the gas. The pressure difference depends upon the gas, the temperature of the gas, the diameter of the tube, the tube material, and the surface condition of the tube. The best procedure is either to use a sufficiently large tube to minimize the thermomolecular pressure difference or to experimentally determine the difference by comparing the pressures between the small diameter tube being used in the cryostat and a large diameter tube [49,71,102] 3.2
REALIZATION OF THE FIXED POINTS OF THE ITS-90
3.2.1
EFFECT OF IMPURITIES
Except for the vapor-pressure-temperature points of helium and equilibrium hydrogen, the fixed points of the ITS-90 are freezing points. melting points, or triple points. The vapor-pressure measurements with 3He, 4He, and e-Hz must be performed with sufficiently pure samples to minimize the effect of impurities. The principal components of air impurity would be frozen. Neon in hydrogen, however, causes positive deviations from ideal behavior [93,97). In the vapor pressure measurements of 4He, it is very likely that the He will be pure but 3He may contain some 4He. For such a circumstance, Roberts, Sherman and Sydoriak described a procedure for correcting for the presence of 4He in 3He [90]. The temperatures of freezing points (liquid-solid or liquid-solid-vapor equilibrium points) of substances are usually lowered by the presence of an impurity. This sometimes, however, is not the case when that impurity is soluble in both the liquid and the solid phases of the major component. If a given impurity is known to be present or is suspected, one must consult the literature on the heterogeneous phase data of metal and non-metal systems to estimate the possible effect of that impurity on the freezing point [39,51,88]. (Note: often in the analysis of the effect of impurities on freezing points, the impurity is assumed to be nonvolatile.) Assuming that the ideal solution law holds and that the impurities remain in liquid solution, with no concentration gradients, then as the major component slowly freezes, the depression in the freezing point, relative to the freezing point of the 100% pure material, is directly proportional to the overall impurity concentration divided by the "first cryoscopic constant." This is expressed as:
3.1.3.5.1 Mercury Manometry
T(pure) - T(obs) = x2/A.
Mercury manometry requires precise determination of the difference in height of the two mercury surfaces in a U-tube manometer. Traditionally, cathetometers have been used with a smallest imprecision of ab t 2 Pa. In recent years , the levels have been sensed, in conjunction with length standards, by capacitive and interferome tric. methods . The resolution of such mercury manometry systems is about 0.05 Pa [19,50, 5 2,81] . (Note : the NIST manometry resolution has been reported [50] to be about 0.0013 Pa.) For accurate pressure measurements, it is necessary to know the density of mercury (which is pressure and temperature dependent), the capillary depression at the mercury meniscus, the vapor pressure of mercury, the aerostatic head difference of the pressure transmitting gas or gases, and the local acceleration due to gravity. At one standard atmosphere, uncertainties as of absolute pressure measurements of about 3 ppm and pressure ratios of about 1 ppm have been reported. See references [19,50,52,81].
A = L/R[T(pure)]2,
Oil Manometry
The techniques and the requirements of oil manometry are similar to those of mercury manometry. 3.1.3.5.3
Piston Gauges (Pressure Balances)
The pressure balanced by a dead-weight piston gauge is obtained from the mass of the piston and the applied weights, and the effective area of the freely rotating piston inside a closely-fitting cylinder. For determination of the absolute pressure, the gauge must be enclosed and evacuated by a high capacity pumping system to minimize the back pressure from the gas leaking between the piston and the cylinder [13,60,81,96]. The local acceleration due to gravity must be known accurately. Corrections must be applied for the effect of the streaming gas and for any back pressure. It is advisable to check the readings of the piston gauge against a primary mercury manometer. Also, the variation of the effective area with pressure must be determined with a mercury manometer. The aerostatic head of the manometry system will change as gas leaks between the piston and the cylinder causing the piston to sink deeper into the cylinder. The position of the piston may be maintained by automatically pumping more gas into the system. A resolution of 1 ppm [13] and an certainty of about 15 ppm have been reported in the pressure range 2 kPa to 200 kPa [63,81]. 3.1.3.5.4
Diaphragm Pressure Detector
The diaphragm pressure detector consists of a thin metal disk clamped under tension between two flat electrodes which form two capacitors, with the disk common to both capacitors. Any pressure differential across the metal disk causes the disk to deflect , increasing the capacitance on one side while decreasing the capacitance on the other side. This change is detected by capacitance bridge techniques. Instruments for absolute pressure measurements are available; however, they require periodic recalibrations to achieve uncertainties of 1 to 5 parts in 104 of the readings. The diaphragm pressure detector is used in high precision manometry as pressure balance detectors, i.e. , with the pressures equal on both sides of the diaphragm. The diaphragm pressure balance detector separates the gas of the apparatus (vapor pressure apparatus or GVGT) from the counter-balancing gas of which the pressure is determined. The resolution of diaphragm gauges has been reported [13] to be about 0.002 Pa. Instability due to different pressures, hysteresis temperature effects,and other causes may decrease the resolution ion to 0.02 Pa in actual pressure measurements [13].
(37)
Table 7. Latent heats of fusion and first cryoscopic constants of defining fixed-point materials
Substance 3.1.3.5.2
(36)
In eq (36), T(obs) is the observed freezing point of the particular sample being investigated, T(pure) is the freezing point of the 100% pure material, x2 is the mole fraction impurity concentration, and A is the first cryoscopic constant. A is given by the relation:
e-H2 Ne O2 Ar Hg H2O Ga In Sn Zn Al Ag Au Cu
Fixed Point Temperature T/K 13.8033 24.5561 54.3584 83.8058 234.3156 273.16 302.9146 429.7485 505.078 692.677 933.473 1234.93 1337.33 1357.77
Latent Heat of Fusion
First Cryoscopic Constant
kJ/mole 0.117 0.335 0.444 1.188 2.292 6.008 5.585 3.264 6.987 7.385 10.79 11.30 12.364 13.14
K-1 0.0739 0.0668 0.0181 0.0203 0.00502 0.00968 0.00732 0.00213 0.00329 0.00185 0.00149 0.000891 0.000831 0.000857
where L is the molar heat of fusion and R is the molar gas constant. (Note: eq (36) is an approximation. A more complete expression includes secondary cryoscopic constants. The term "first cryoscopic constant" is used here for distinction. Also, in some cases, the term "cryoscopic constant" refers to the reciprocal of eq (37) and in other cases, to the effect of impurities per liter or kilogram of solvent.) The first cryoscopic constants of metals are relatively smaller than those of molecular substances and of the "cryogenic" gases (3He, 4 He, e-H , Ne, O , and Ar). Referring to eq (36), zinc, which has a first 2 2 cryoscopic constant of 0.0018/K, requires an overall impurity concentration of approximately 2 parts in 107 for the temperature of the halffrozen sample to be depressed by 0.0001 K, relative to the liquidus point. On the other hand, argon, with a first cryoscopic constant of 0.0203/K, requires an impurity concentration close to 2 parts in 106 for the same temperature depression. Table 7 lists the heats of fusion and the first cryoscopic constants of substances specified for the defining fixed points. It is the usual practice at NIST to calibrate SPRT’s during the first 50% of the freeze. 3.2.2 3.2.2.1
TRIPLE POINTS OF e-H2, Ne, O2. AND Ar GENERAL CONSIDERATION OF APPARATUS DESIGN
The cryogenic fixed points (triple-points of pure gases equilibrium hydrogen, natural neon, oxygen, and argon) are best real ed in a calorimetric type apparatus designed for calibrating capsule-type thermometer (SPRT’s, RIRT’s, germanium resistance thermometers (GRT’s), and others) [1, 2, 17, 18,20, 21,41,47, 58, 59, 78, 79, 80] . During calibration of the thermometers,
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LIQUID NITROGEN
LONG STEM SPRT WELLS (7) HE GAS MANIFOLD TO SPRT WELLS TEMPERATURE CONTROLLED SHIELD PASSIVE SHIELD SAMPLE CELL SHIELD
SAMPLE CELL
67 cm
BAFFLES CAPSULE SPRT WELLS (6) VACUUM CAN SUPER INSULATED DEWAR
56 cm
Figure 4. A schematic drawing of the NIST argon triple-point apparatus for calibrating seven long-stem SPRT’s and six capsule SPRT’s. Six long-stem SPRT wells surround a central SPRT well, which is large enough to accommodate a holder for calibrating a capsule SPRT. At the bottom of the sample cell, six capsule SPRT wells are circularly arranged between the long-stem SPRT wells.
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COPPER CAPILLARY AUXILIARY ISOTHERMAL SHELL, HELD WITH NUT
CELL HEATER
COPPER TEMPERING STRIPS
SAMPLE CELL
COPPER TUBES 94 mm
HELICALLY GROOVED COPPER SLEEVE
PLATINUM RESISTANCE THERMOMETER
THERMOCOUPLE CLIPS
25.4 mm
Figure 5. A sealed cell suitable for containing cryogenic gases at high pressures. This cell of 20 cm3 volume was filled to 100 atmospheres with pure oxygen and used to realize the triple point of oxygen. Another cell of the same outer dimensions, but of 16 cm3 volume and with wells for three capsule SPRT’s, was filled to 163 atmospheres with oxygen and also used to realize the triple point of oxygen [47].
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the calorimeter system thermally isolates the vessel containing the pure gas sample and the thermometers. The capsule thermometers should be installed in close-fitting wells of the sample vessel, using stopcock grease to enhance the thermal contact. The wells should be vented for easy installation and subsequent removal of the thermometers since such thermometers are sensitive to shock. The wells can be vented by designing the well tubes to extend completely through the sample cell or by machining a small groove along the length of the well wall. The number of wells in.the vessel is limited only by the practical size of the vessel and of the calorimeter system. On the other hand, for large vessels, larger temperature gradients should be expected. The leads to the thermometers should be tempered on the sample vessel. (Note: the term "temper" refers to a process whereby sections of the leads or of the protective sheaths of long-stem SPRT’s are placed in "steady-state thermal equilibrium" with selected parts of the apparatus.)
For calibration of SPRT’s, the sample should be completely frozen for the second time and the temperature set at about 1 K below the triple point, the sample thermally isolated, and the equilibrium temperature measured. From the knowledge of the previously determined heat capacity of the system below the triple point and of the heat of fusion, add enough electrical energy to melt about 10% of the sample. If T1 is the initial equilibrium temperature just below the triple point, the required amount of electrical energy Q, to melt 10% of the sample is:
Since the triple point of argon is about 6 K above the normal boiling point (NBP) of nitrogen and since liquid nitrogen is readily available in large quantities, long-stem type SPRT’s can be calibrated at the argon triple point in an apparatus cooled by liquid nitrogen. The apparatus should be designed to cool the upper part of the protective sheath of the long-stem SPRT’s to liquid nitrogen temperatures, and then to heat the intermediate section of the sheath above the sensing element to the argon triple point so that the sensing coil will be in thermal equilibrium with the argon at its triple point [42]. See figure 4 for a schematic of such an apparatus presently in use at the NIST.
In using a temperature fixed point, one must make corrections for the hydrostatic head of the liquid and for the gas pressure on the defined equilibrium state. Table 6 gives the dT/dp for the defining fixed points of the ITS-90, both in terms of the external gas pressure to which the fixed-point material is exposed and in terms of the column of liquid.
Sample vessels for the cryogenic fixed points could be ruggedly constructed for high pressures and sealed with a suitable amount of the pure gas [41,79]. These "sealed-sample vessels can be easily installed and removed from the calorimeter for replacement of thermometers and also to be transported to other laboratories for comparison (see fig.5).The amount of gas that can be sealed in such vessels however,is rather limited and, hence,the calorimetric system must be operated with sufficient adiabatic control that the small amount of heat of fusion of the sample is adequate to realize the triple point and then calibrate the thermometers. Also, since the amount of sample gas is small, extra care must be taken to clean the vessel thoroughly before filling. The recommended procedure is to bake the vessel at high vacuum and then purge many times with the sample gas before finally filling and sealing the cell [41,47,79]. The vessel for a cryogenic fixed point can be installed in the calorimeter and connected by a small diameter tube to a source of pure gas {1,2,31,32,44,58,59}. In this design, enough condensed liquid could be used to nearly fill the vessel and thus, to provide an abundant supply of heat of fusion for calibration of thermometers. The tube from the vessel must be connected to an "external expansion volume" of appropriate size so that when the system is at ambient temperature the pressure is not excessive. The vessel could also be connected to an external rugged container into which all or nearly all of the sample can be transferred by cooling, and then contained bye high-pressure valve. Since under these conditions the "sample vessel" would not be subjected to high pressures, it can be constructed of thin copper parts. With appropriate gas handling and cleaning provisions, the same vessel could be used with all of the reference gases, stored in separate external rugged containers, and the thermometers calibrated at the fixed points of the gases without the necessity of having to remove the thermometers from the vessel between fixed-point can have separate chambers for each of the gases. In the latter design, separate tubes for the gases must enter the calorimeter system. Although each of the chambers of a "multi-chamber sample vessel" would be relatively small, the amount of sample that could be condensed inside each chamber would still be more than that which is normally used with the high pressure "sealed-sample vessel" Similar to the procedure used in filling sealed-sample vessels, a thorough baking, pumping, and purging procedure before filling should be followed with permanently installed vessels.
where Cs and Ct are the mean heat capacities in the temperature intervals in the solid and liquid phases, respectively, and To is the triple-point temperature.
Q1= 0.1L. + C8(T0 - T1).
3.2.2.2.1 TRIPLE POINT OF EQUILIBRIUM HYDROGEN, 13,8033 K (-259.3467°C) Hydrogen gas samples of 99.9999% and higher purity are readily available. [The first cryoscopic constant of hydrogen is relatively high (0.040/K). Consequently, the liquidus point of an ideal hydrogen solution of 99.9999% purity would be approximately 0.01 mK lower than that of 100% pure hydrogen. Except for helium and deuterium, all other impurities would be either frozen or in solution in very small amounts.] The commonly used catalyst for converting ortho hydrogen to para hydrogen is hydrated ferric oxide (Fe 2 O 3 +H 2 O or FeO+OH) Other oxides of magnetic elements, either pure or mixed-metal, such as those of chromium, nickel, cobalt, and neodymium, also have been used as catalysts for ortho to para hydrogen conversion. The hydrated ferric oxide catalyst is prepared by mixing at about 30°C relatively dilute solutions (about 2 molal) of ferric chloride and sodium hydroxide, with only a slight excess of sodium hydroxide, washing the resulting gelatinous Fe(OH)3 precipitate thoroughly with distilled water, air drying at 140°C for 24 hours, vacuum baking at 110°C for 16 to 20 hours, and back-filling with hydrogen while the catalyst is still hot [7,104). The catalyst is activated by flowing hydrogen through it for about 4 hours while the catalyst is maintained at a temperature of about 150°C. The sample vessel and ancillary components should be designed to permit the whole of the hydrogen sample to come into contact with the catalyst at the equilibrium temperature. See references [2,31,58]. 3.2.2.2.2 TRIPLE POINT OF NATURAL NEON. 24,5561 K (-248,5939,˚C) Neon gas samples of 99.999% purity are commercially available. Samples of higher purity may be obtained by special arrangement with the supplier. The
yy ,, ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy
3.2.2.2 REALIZATIONS OF THE TRIPLE POINTS AND THEIR APPLICATION TO CALIBRATION The procedure for realizing a triple point of the cryogenic gases is to first completely freeze the sample. If the triple point is being realized for the first time with the apparatus, the sample should be cooled sufficiently below the triple point to determine the heat capacity of the system (sample, vessel, and thermometers) from about 5 K to 20 K below (depending on the gas) to about 20 K above the triple point, and to determine the heat of fusion of the sample during the same series of measurements [41,47]. (Note: check thermometers must be calibrated along with the test thermometers. The measurements on the check thermometers will serve to guide the heating process during the calibration, as well as to provide measurement statistics.) After cooling to the required low temperature the vessel should be thermally isolated by placing it under continuous adiabatic control. Then the following series of measurements should be performed: 1. the equilibrium temperature should be observed with the check thermometer, 2. a measured amount of electrical energy should be added to the system. 3. a new equilibrium temperature should be established and measured 4. steps 2 and 3 should be repeated until three heat capacity points are obtained below the triple point. 5. then,the sample should be completely melted by introducing a measured amount of heat, 6. next, the equilibrium temperature just above the triple point should be measured 7. then, three additional heat capacity points should be obtained above the triple point in accordance with steps 2 and 3. From the knowledge of the eight equilibrium temperatures (four below the triple point and four above the triple point) and the measured amounts of electrical energies added, the heat capacities of the system below and above the triple point, and the heat of fusion, are calculated. If Q joules are added to the system from an initial equilibrium temperature Ti just below the triple point to heat the system to a final equilibrium temperature Tf Just above the triple point, the heat of fusion L is: L=Q - CS(TO - T1) - C,(Tf - TO),
(38)
(39)
Once the system comes to equilibrium, measure the resistances of all of the thermometers. Repeat the measurements at 20%, 40%, 60%, 70%, and 80% melted. If the sample is about 99.9999% pure, all measurements on each thermometer throughout this melted range should agree to within 0.1 mK to 0.2 mK.
Type A
yyy ,,, ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,, yyy Type B
Figure 6. Two types of triple point of water cells with wells for platinum resistance thermometers. The cells contain pure air-free water. The thermometer wells are made of precision-bore tubing.
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Guidelines for Realizing the ITS-90 Cont’d
principal impurities are CO, H2, He, and N2. The CO and the N2 impurities can be frozen out by slowly flowing the sample through a coiled tube immersed in liquid neon; the H2 and the He impurities can be removed by freezing the neon sample in liquid hydrogen and pumping, with care so that the lighter isotopes of neon are not preferentially removed. [The first cryoscopic constant of neon is 0.0668/K. Consequently, the liquidus point of an ideal neon solution of 99.999% purity would be approximately 0.1 mK lower than that of 100% pure neon.] The purified sample should be collected in a clean stainless-steel cylinder by cooling the cylinder in liquid hydrogen (or cooled with liquid helium). If desired, the purified sample can be collected directly in the cooled sample vessel. See references [1,79].
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3.2.2.2.3 TRIPLE POINT OF OXYGEN. 54 .3584 K (-218,7916 ˚C) Oxygen gas samples of 99.999% purity are commercially available. Accurate chemical analysis of oxygen is difficult and, therefore, the claimed purity may not be correct. Unknown or undetected impurities are chemically less reactive than oxygen, e.g, the noble gases, and, in particular, argon, which forms a peritectic with oxygen. Samples of purity greater than 99.999% may be obtained by special arrangement with the supplier. [The first cryoscopic constant of oxygen is 0.0181/K. Consequently, the liquidus point of an ideal oxygen solution of 99.999% purity would be approximately 0.6 mK lower than that of 100% pure oxygen.] Careful preparation by thermal decomposition of potassium permanganate can yield samples of 99.99992% purity or better [47]. The oxygen sample should be stored in clean stainless-steel cylinders. See references [32,47,59,79,80].
,
3.2.2.2.4 TRIPLE POINT OF ARGON. 83,8058 K (-189.3442 ˚C) Argon gas samples of 99.9999% purity or better are readily available. The usual impurities are the components of air, moisture, and hydrocarbons. [The first cryoscopic constant of argon is 0.0203/K. Consequently, the liquidus point of an ideal argon solution of 99.9999% purity would be approximately 0.05 mK lower than that of 100% pure argon.] To fill the sample vessel, the gas may be used directly or it may be dried first by slowly passing it through a coiled tube immersed in either liquid oxygen or a Dry Ice/ethyl alcohol mixture. See references [17,41,42,59,79,80]. 3.2.3 TRIPLE POINT OF WATER. 273.16.K (0.01˚C) The triple-point temperature of water is assigned the value 273.16 K on the Kelvin Thermodynamic Temperature Scale and also on the ITS-90. It is the reference temperature for resistance ratios in platinum resistance thermometry. The water used in preparing triple point of water cells is pure water of naturally-occurring isotopic composition. Figure 6 shows two commonly used types of triple point of water cells. Triple point of water cells are usually prepared from river water that has been purified by chemical treatment and distillation. River water is expected to have concentrations of deuterium and the heavier isotopes of oxygen that are lower than that of ocean water. The extreme difference in the triple points of naturally occurring water, including polar water, is given as 0.25 mK [100]. It is expected that differences among water triple-point cells of river water would be much smaller than 0.25 mK. (The isotopic composition difference between river water and ocean water [100] has been estimated to cause no more than a 0.050 mK difference in the triple-point temperature.) While the basic material is plentifully available, preparation of water triple-point cells requires a special effort [5,40]. Although the effect on the triple-point temperature is negligible, a trace of air always remains in most sealed triple point of water cells. When a cell at room temperature is gently inverted from one end to the other and a sharp "click" is produced through the water hammer action, the amount of gas in the cell wi11 have negligible influence on the triple-point temperature. 3.2.3.1 REALIZATION AND APPLICATION OF THE TRIPLE POINT OF WATER In preparation for producing an ice mantle that is required for realizing the triple-point temperature of water, the thermometer well of the cell is wiped thoroughly dry, sealed with a rubber stopper, and the cell placed in an ice bath to cool to a few degrees above the ice point. When the cell has been cooled in this manner, an ice mantle of fairly uniform thickness can be obtained. Withdraw the cell from the ice bath, set it upright on a stand, and place one drop of ethyl alcohol at the bottom of the well. Introduce small amounts of crushed Dry Ice into the bottom of the well and continue to do so until a thick mantle is formed at the bottom. Then, fill the well with crushed Dry Ice to the water level of the cell. Continue to add crushed Dry Ice to the well so as to maintain the level of Dry Ice at the water level. If the Dry Ice level becomes low before more is added, the ice mantle may crack. If the cell were precooled as indicated above, a solid ice bridge may form at the water level. If such a bridge forms, melt it immediately with heat from the hands while gently shaking the cell. The solid ice bridge can completely seal the cell at the top and any subsequent formation of ice could produce enough pressure to rupture the glass c e l l . W h e n a m a n t l e o f approximately the desired thickness (4 to 8 mm) is formed, stop adding Dry Ice, replace the cell in the ice bath with the well opening slightly above the water surface of the ice bath, and leave the cell there until all of the Dry Ice evaporates. Then, fill the well with ice water and store the cell in an ice bath or ice pack for a day before using it. When the ice mantle is frozen by using Dry Ice, a process that usually requires less than one hour, the strains in the ice cause the "triple-point temperature" to be about 0.2 mK low. These are removed by letting the mantle anneal for one day. Other methods can be used also to prepare the ice mantle. With ethyl alcohol in the thermometer well, any "cold finger" technique can be used. This technique includes successively inserting liquid nitrogen cooled rods, using a closed-end tube containing crushed Dry Ice, or using a heat-pipe cooler. These methods require more time to freeze the mantle,,but the strain produced in the ice will be less than those produced by the Dry Ice technique. After the strains in the ice mantle have been relieved by storing the cell in an ice bath for at least one day, insert momentarily a glass rod into the well in order to melt a thin layer of ice next to the well. This forms an ice-water interface immediately adjacent to the thermometer well. The test for this "inner melt" is made by giving the cell a rotatory impulse to determine whether
A
B C
D E F G H I J K L
Figure 7. An SPRT in a Type A triple point of water cell immersed in an ice bath. A - platinum resistance thermometer, B - heavy black felt to shield against ambient radiation, C - polyethylene tube for guiding the SPRT into the thermometer well (the tube has a small hole near the top of the thermometer well to allow water, but not ice, to enter the tube.), D - water vapor, E borosilicate glass cell, F - water from the ice bath, G - thermometer well (precision bore glass), H – ice mantle I - air-free water, J - aluminum bushing with internal taper,at the upper end to guide the SPRT into its close fitting inner bore, K – polyurethane sponge for cushioning the SPRT, L – finely divided ice and water. the ice mantle rotates freely about the axis of the thermometer well. The outer ice water interface guards and thermally stabilizes the inner ice-water interface temperature that is measured with the SPRT. Figure 7 shows a triple point of water cell immersed in an ice bath with an SPRT inserted into the thermometer well. An SPRT should be precooled in a glass tube of water in an ice bath before it is inserted into the triple-point well so that the thickness of the water layer next to the thermometer well will not become excessive. Also, the time required for the SPRT to come into thermal equilibrium will be shortened. Heavy felt cloth should be used to cover the ice bath in order to prevent ambient radiation from entering the bath and reaching the thermometer element, which otherwise would cause the thermometer to give a slightly high (erroneous) reading. A plastic foam cushion should be placed at the bottom of the thermometer well to protect the well and the SPRT. Since water is a poor thermal conductor, a close fitting aluminum sleeve should be used to enhance the thermal conduction. The thermometer current should be imposed immediately after insertion of the SPRT into the cell so that readings can be made under conditions of steady-state self heating. Five to ten minutes or longer may be required before steady-state conditions are reached. To avoid errors due to variations in the self heating that arise from variations in the thermal contact of the thermometer with its surroundings, it is best to read the SPRT at two currents and extrapolate the readings to zero power in the SPRT. 3.2.4 FREEZING. MELTING. OR TRIPLE POINTS OF METALS: Hg Ga. In. Sn. Zn. Al. Ag Au. or Cu The realization of metal fixed points requires the continuous presence of liquid-solid or liquid-solid-vapor phases in thermal equilibrium. With SPRT’s, the liquid-solid interface, i.e., the equilibrium whose temperature is measured, must surround and must be as close to the temperature sensing element as possible. Since the first cryoscopic constants of metals are relatively low, the fixed-point metal samples should be at least 99.9999% pure. Figure 8 shows idealized liquid/solid equilibrium conditions inside fixed point cells used in freezing and melting experiments. Figure 9 shows a representative arrangement of an SPRT inserted inside a metal fixed point cell. Ideally, and similar to the water triple-point cell, an outer liquid-solid interface, which completely surrounds the inner interface, exists close to the container wall. This outer interface, which has a temperature very close to that of the inner interface, thermally protects and thermally stabilizes the inner interface. In freezing experiments, a layer of solid is first formed at the crucible wall, then a thin layer of solid is induced on the thermometer well by inserting cooling rods. As freezing advances, the outer interface approaches the inner interface until all of the material is solid. In melting experiments, a layer of liquid is first formed next to the crucible, then a thin layer of liquid is formed next to the thermometer well by inserting a warming rod or a long heater. As melting advances, the outer liquid/solid interface approaches the inner interface. Since different furnace or bath designs are required for fixed-point cells operated at different temperatures, they will1 be discussed along with each of the f i x e d p o i n t s , o r r e f e r e n c e s w i l l b e m a d e t o a p p r o p r i a t e s o u r c e s o f
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descriptions. A
In radiation thermometry, the liquid-solid phase of the metal fixed point must completely surround the blackbody radiator capacity 3.2.4.1 CONTAINER MATERIAL
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Containers for the fixed-point metals must not contaminate the metal sample, and the container material must be rugged enough to retain its integrity under thermal cycling between the temperature of use and ambient temperature. The container material preferably should be inert to air at temperatures of use;if not, e.g., graphite above about 200 °C, the container plus the fixed-point material must be protectively enclosed in an inert gas such as nitrogen, argon, or helium, using either a borosilicate or fused silica glass envelope. It should be assumed that the fixed-point material itself will react chemically with air and, thus, the material must be protected.*
76 cm
Figure 9 shows a representative fixed-point cell that can be used for calibrating long-stem type SPRT’s. In the following sections, individual types will be described.
46 cm
3.2.4.2.1.1 MERCURY SAMPLE
F
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H
25.2 cm
G
I
J
K
L
M
Figure 9. An SPRT in a metal freezing-point cell. A - platinum resistance thermometer, B - to helium gas supply and pressure gauge, C - thermometer gas seal with silicone rubber, D - silicone rubber stopper, E - thermal insulation (washed Fiberfrax),F - thermometer guide tube [precision bore tube, ground (matt finish) to uniform outside diameter], G heat shunt (graphite) in close contact with F and with H, H - borosilicate glass cell [precision bore tube ground (matt finish ) to uniform outside diameter], I - graphite cap (lid) for the graphite crucible, J - graphite thermometer well, K - metal sample, L - graphite crucible, M - thermal insulation (Fiberfrax paper) between the graphite crucible and the borosilicate glass cell.
9.5 O.D. x 0.9 Wall
Melting
Sample
Liquid Sample
Solid Sample
Thermometer Well
Resistance Thermometer
210
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10 O.D. x1 Wall
38 O.D . x2 Wall
Freezing
yy ,, ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy ,, yy Borosilicate Glass
Figure 8. Idealized liquid/solid equilibrium conditions inside fixed point cells used in freezing and melting experiments. In freezing experiments, a layer of solid is first formed at the crucible wall, then a thin layer of solid is induced on the thermometer well by inserting cooling rods. In melting experiments, a layer of liquid is first formed next to the crucible, then a thin layer of liquid is formed next to the thermometer well by inserting a warming rod or a long heater, As melting advances, the outer liquid/solid interface approaches the inner interface.
9.5 O.D. x0.13 Wall
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9.5 O.D. x0.9 Wall
38.1 O.D. x1.7 Wall
445
Sample Cell
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216
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Cell Holder
197
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Z
G
25
Any container material can be used with mercury that is sufficiently rigid and does not dissolve in, or chemically react with, mercury in the temperature range of storage and application. The choice will depend upon whether the mercury fixedpoint cell is to be used at its triple point, at its freezing point, or
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32 cm
3.2.4.2.1 MERCURY TRIPLE POINT
3.2.4.2.1.2 CONTAINERS FOR MERCURY
E
10 cm
3.2.4.2 METAL FIXED POINT DEVICES FOR CALIBRATING SPRT’s
On the ITS-90, the triple point of mercury (equilibrium phase state of mercury solid, liquid, and vapor phases) is assigned the value 234.3156 K (-38.8344°C). Depending upon the choice of container material and operating procedure, it may be more practical to realize the mercury freezing point at one standard atmosphere, the value being 234.3210 K (-38.8290 °C). Mercury samples with impurity content of 1 part in 108 or less can be prepared by potassium hydroxide and nitric acid washings, followed by triple distillation [48]. The alkali and acid washings can be carried out by vigorously bubbling clean filtered air, through the mixture of mercury and the alkali or the acid. To remove any remaining oxidizable impurities, the first two distillations should be carried out under reduced pressures with a fine stream of clean filtered air bubbling into the mercury in the distillation container. The third distillation should be done under high vacuum to remove the noble metals. With the high-purity mercury (99.999999%), both freezing and melting techniques give triple-point temperatures that agree to within ± 0.1 mK over most of the liquid-solid range. [The first cryoscopic constant of mercury is 0.00503/K. Consequently, the liquidus point of an ideal mercury solution of 99.999999% purity would be approximately 0.002 mK lower than that of 100% pure mercury.]
B C D
1.0 Thick
1.6 Thick
Type 304 Stainless Steel
Dimensions in mm
Figure 10. Two mercury triple-point cells, one constructed of borosilicate glass and one of Type 304 stainless steel. The two small-diameter tubes at the top facilitate the cleaning of the cells before filling and sealing. The glass cell is sealed by melting the small-diameter tubes, but the stainless steel cell is sealed by pinching flat the small-diameter tubes and electric-arc welding them, thereby serving them at the middle of the flat.
Z-170
Guidelines for Realizing the ITS-90 Cont’d
at either one.
A VALVE AND VACUUM
3.2.4.2.1.3 METAL CONTAINERS
B
Mercury is capable of dissolving most metals, at least at the low levels of impurity content (
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3.2.4.2.1.4 CONTAINERS OF GLASS It is expected that some metal impurities in glasses [single metal oxide (e.g.,fused silica glass) or mixed metal oxide (e.g., borosilicate glass)] or "ceramics" can be leached out by mercury when the mercury is stored in them for many years. Traditionally, "soft glass" has been considered suitable for storing mercury [48]; however, soft glass, without special treatment, may be susceptible to breakage when thermally shocked. Borosilicate glass and fused silica glass are more practical choices for mercury containers. Figure 11 shows a borosilicate glass mercury triple-point cell inside a stainless steel holder.
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3.2.4.2.1.5 CONTAINERS OF PLASTIC Organic plastics, such as polyethylene polytetrafluoroethylene (Teflon), or polytrifluorochloroethylene (Kel-F), all of which are free of metals, can be used to contain mercury and be used at the mercury freezing point. A stainless steel holder similar to that used for the glass mercury cell and for the stainless steel mercury cell (see fig.11) or similar to the holder used for the indium cell (see fig. 12) could be used as the external holder for a plastic mercury cell. Although plastic cells have not been used yet in preparing mercury fixed point cells, it would be practical and desirable to use plastic cells for realizing the mercury fixed point. Since the vapor pressure of mercury at room temperature is sufficiently high that mercury vapors can be transported u n d e r v a c u u m conditions, the vapors should be confined by an atmosphere of helium or other inert gases.
A ="O" ring tube seal B = Thermometer well C = Ethyl alcohol in well D = Indium gasket seal E = Insulation, rolled paper tissue F = Stainless steel jacket G = Tubular connection for cleaning and filling H = Insulation tissue paper rolled around (l) for centering I = Copper foil cylinder J = Borosilicate glass cell K = Mercury L = Thermometer cushion (fused quartz wool) M = Stand for mercury cell N = Inculation (Aluminum silicate wool)
3.2.4.2.1.6 ASSEMBLY OF MERCURY CELLS A purified mercury sample can be vacuum distilled into glass containers, with the glass filling tube then sealed under vacuum with a flame [43]. The mercury sample may be vacuum distilled into stainless steel containers and the filling tube pinched, and then cut and sealed using electric-arc welding techniques [43]. 3.2.4.2.1.7 REALIZATION AND APPLICATION When the total impurity content of a mercury sample is about one part in 108, both freezing and melting techniques yield triple-point temperatures agreeing to within ± 0.1 mK over most of the liquid-solid range. A dual-stage refrigerator can yield a temperature near -40°C and, hence, could be used for freezing mercury, but a much simpler stainless steel vacuum enclosure placed in a Dry Ice/ethyl alcohol mixture (-78 °C) can reduce the freezing rate of mercury to give a freeze duration of about 10 hours or more with 2.2 kg of mercury, and that is perfectly adequate. Figure 11 shows such a stainless steel enclosure that has been used with a borosilicate-glass mercury cell at the NIST.
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yy ,,
I J K
,,,
L
yyy ,,, ,,, yyy ,,, yyy ,,, yyy ,,, yyy ,,,,
,,,
,,,,
,,,
M
N
Figure 11. A borosilicate glass, mercury triple point cell in a stainless steel container. A stainless-steel, mercury triple-point cell may also be mounted inside the stainless steel container. With the high-purity mercury sample, both freezing and melting techniques yield triple-point values agreeing to within ±0.1 mK over most of the liquid-solid range.
To start a freeze, fill the stainless steel enclosure that contains the mercury triple-point cell with dry air and immerse it in a Dry Ice/ethyl alcohol bath. Fill the themometer well with ethyl alcohol and insert therein an SPRT for monitoring the temperature of the cell. Usually, mercury supercools about 6 °C in a borosilicate glass cell but only about 3 °C in a stainless steel cell. When recilescence is observed, evacuate the stainless steel holder. Remove the monitoring SPRT from the well and replace it with a thin-wall stainless steel tube that contains ethyl alcohol and that has been cooled in a tube of ethyl alcohol immersed in a Dry Ice/ethyl alcohol bath. Insert successively into the stainless steel tube two or three liquid-nitrogen cooled glass rods, for about 5 minutes each, in order to freeze a thin layer of mercury around the thermometer well. The purpose of the stainless steel tube is to collect the frost that forms on the rods when they are removed from the liquid nitrogen. Remove the stainless steel tube and replace it with the monitoring SPRT, which has been cooling in the tube of cold ethyl alcohol. Switch on the thermometer measuring current. (Note: it may be necessary to refill the thermometer well with a small amount of cold ethyl alcohol from the Dry-ice cooled tube before the monitoring SPRT is inserted into the well. The well should be completely filled with ethyl alcohol when the SPRT is in the well.) With the induced inner freeze around the thermometer well, temperature equilibrium is reached in about 5 minutes. After the resistance of the monitoring SPRT is read, other cooled SPRT’s are successively inserted into the mercury cell and calibrated. The final reading in a cell is made with the monitoring SPRT in order to check the extent of the freeze. This final reading of the monitoring SPRT must agree with the initial reading to within ± 0.1 mK. See reference {43} for more details on the calibration procedure at the mercury triple point.
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A B C D E F G H
20.5 cm
I
3.2.4.2.2 MELTING POINT OF GALLIUM The melting point of gallium is assigned a temperature of 302.9146 K (29.7646°C) on the ITS-90. Gallium of 99.99999% purity can be obtained commercially. At such high purity, both freezing and melting techniques should yield liquid-solid equilibrium temperatures that agree to within ± 0.1 mK. Since the metal expands about 3% on freezing, plastic containers, such as polyethylene, polypropylene, or polytetrafluoroethylene, are the most suitable. These are sufficiently flexible at around 30 °C to accommodate the volume change in the gallium. In assembling the gallium fixed-point cell, the supercooled metal can be poured directly into the container. A second more rugged container of Nylon, glass, or stainless steel should enclose the flexible container so that the pressure of the inert gas over the metal can be controlled at one atmosphere or be evacuated to observe the triple point. A gallium fixed-point cell, consisting of an all plastic container, that is used at the NIST is shown in figure 13. Since gallium supercools as much as 25 °C to 70 °C, depending upon the plastic material that is in contact with it, the most convenient method of observing its liquid-solid equilibrium temperature is the melting technique. [The first
4.5 cm
F J
Figure 13. An all-plastic gallium melting/triple-point cell. The triple-point is realized by using the melting technique. The cell is periodically evacuated through the valve. A - valve (Zytel), B - bath lid (Plexiglass), C - support rod (Nylon), D - pumping tube (polyethylene), E - cap (Nylon), F - sample container (Teflon), G - case (Nylon), H - thermometer well (Nylon), I - gallium metal, J - base of the case
Z-171
Z
Figure 12.
Photograph of an all-plastic indium cell and its stainless steel container
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Guidelines for Realizing the ITS-90 Cont’d
cryoscopic constant of gallium is 0.00732/K. Consequently, the liquidus point of an ideal gallium solution of 99.99999% purity would be approximately 0.01 mK lower than that of 100% pure gallium.] 3.2.4.2.2.1 REALIZATION AND APPLICATION In order to solidify the gallium metal in a fixed-point cell, initially in the supercooled state (e.g., at room temperature), first insert successively two or three liquid-nitrogen-cooled copper rods into the thermometer well of the cell to induce nucleation, and then place the cell in an ice bath for about one hour or longer. The cell with the solidified gallium may then be placed in an oil bath at a temperature of about 40 *C to partially melt the sample to form an outer liquid-solid interface. To form a liquid-solid interface next to the thermometer well (an inner melt), the bath oil may be circulated through the thermometer well by pumping the oil through a tube placed in the well. After about 20 minutes in the hot oil bath, about 25% of the gallium will be melted. The inner liquid-solid interface can also be prepared by using an electric heater in the well. The amount of electric energy required, e.g., to form about a 7 mm shell of liquid around the thermometer well, can be calculated from the outer dimensions of the thermometer well and the heat of fusion of gallium (see table 7). The gallium cell is then securely mounted, completely immersed so that the thermometer well will be filled with the bath oil, in a stirred oil bath, controlled at a temperature about 10 mK above the liquid-solid equilibrium temperature (melting point or the triple point). Also, the cell can immersed in a fairly close-fitting, oil-filled aluminum or copper block, controlled at a temperature about 10 mK above the equilibrium temperature. The monitoring PRT is heated and then inserted into the thermometer well of the gallium cell. Readings are taken after about 20 minutes of equilibration in the cell. The monitoring SPRT is replaced in the cell with a preheated test SPRT and measurements on it are made after about 20 minutes. A number of SPRT’s can be successively calibrated in the same "melt". When all of the test SPRT’s have been calibrated, a final measurement in the cell is made on the monitoring SPRT. This reading of the monitoring SPRT should agree with the initial reading to within ± 0.1 mK. Also, measurements with different melts should agree to within 0.1 mK. See references [16,26,65,68,94]. 3.2.4.2.3 FREEZING POINT OF INDIUM The freezing point of indium is assigned the value 429.7485 K (156.5985 ˚C) on the ITS-90. Metal samples of 99.9999% purity and higher are commercially available. The freezing point of indium is at a sufficiently low temperature to permit the use of containers of high temperature plastics [Polytetrafluoroethylene (Teflon), polyimide/amide, and others), borosilicate glass, and stainless steel (4,69,14,92). See figure 14 for an example of a Teflon container used for indium at the NIST. As used with metals that freeze at higher temperatures, graphite can also be used with indium. The metal is available in the form of small pellets, wire, and rods. Suitable amounts for a sample can be easily weighed into the container. (The first cryoscopic constant of indium is 0.00212/K. Consequently, the liquidus point of an ideal indium solution of 99.9999% purity would be approximately 0.5 mK lower than that of 100% pure indium.]
CAP (TEFLON)
9 mm 1 mm
5 mm DIA. HOLE THROUGH CAP 34.34 mm ID 44.34 mm OD
2 mm
18.70 mm OD
25 mm 15 mm
5 mm
3.2.4.2.3.1 REALIZATION AND APPLICATION A tube furnace containing the indium-point cell is controlled about 5 ˚C above the freezing point of indium until the metal is completely melted. (It is convenient to control the furnace temperature automatically and melt the metal sample overnight so that the freezing of the metal may be s started in the morning.) Insert the check SPRT into the cel1 well and when the SPRT indicates that the sample is about 5 above the freezing temperature, change the furnace temperature control settings to control at 5 ˚C below the freezing point. When the check SPRT indicate. recalescence, change the furnace temperature control settings to control at 1 ˚C to 0.5 ˚C below the freezing point. Withdraw the check SPRT from the cell well and insert successively in the well two fused silica glass rods, each initially at room temperature, for about 5 minutes each and then insert the cool check SPRT in order to freeze a thin mantle around the thermometer well. (To avoid the consequence of inserting borosilicate glass rods into the aluminum or silver point cell to form the mantle around the thermometer well, all glass rods used for this purpose in the laboratory should be fused silica glass.) Within 20 to 30 minutes, the readings on the check SPRT should indicate that the cell is at temperature equilibrium. After the readings on the check SPRT are completed, test SPRT’s, that have been heated in an auxiliary furnace, are successively inserted into the cell well and calibrated. After all of the test SPRT’s have been calibrated the preheated check SPRT is inserted again into the cell well and read. This second reading should agree with the first to within ± 0.1 mK. See references (4,69,74,92]. 3.2.4.2.4 FREEZING POINT OF TIN The freezing point of tin is assigned the value 505.078 K (231.928 ˚C) Metal samples of 99.9999% purity are commercially available. Graphite containers are commonly and successfully used for tin. Although the use of materials such as boron nitride (BN) has not been reported, it could be a suitable container for tin. High purity tin has been found to supercool 25 ˚C or more [73,76]; hence, the freeze is nucleated by rapid cooling outside the furnace. The metal is available in the form of small pellets and in rods suitable for filling the graphite container. A method for filling graphite containers and installing the graphite thermometer wells is described in reference [46]. [The first cryoscopic constant of tin is 0.00329/K. Consequently, the liquidus point of an ideal tin solution of 99.9999% purity would be approximately 0.3 mK lower than that of 100% pure tin.] 3.2.4.2.4.1 REALIZATION AND APPLICATION A tube furnace [46] containing the tin freezing-point cell is controlled about 5 ˚C above the freezing-point temperature until the metal is completely melted. (It is convenient to control the furnace temperature automatically and melt the metal overnight so that freezing of the metal can be started early in the morning.) Insert the check SPRT into the cell well and, when the SPRT indicates that the sample temperature is about 5 ˚C above the freezing point, change the furnace temperature control settings to control at 1 ˚C to 0.5 ˚C below the freezing point. When the check SPRT indicates that the cell temperature is close to the freezing-point value, withdraw the cell and the SPRT from the furnace. The cell will then cool rapidly and when the SPRT detects recalescence, replace the cell in the furnace. Withdraw the check SPRT from the cell well. Insert successively in the well two fused silica glass rods, each initially at room temperature, for about, 5 minutes each, and then the cool check SPRT in order to freeze a thin mantle around the thermometer well. Within about 20 to 30 minutes the readings on the check SPRT, should indicate that the cell is at temperature equilibrium. After the readings on the check SPRT are completed, test SPRT’s, that have been heated in an auxiliary furnace, are successively inserted into the cell well and calibrated. After all of the test SPRT’s have been calibrated, the check SPRT is heated and inserted again into the cell well and read. This reading should agree with the initial reading to within ±0.1 mK. See references [43,46,73,76]. 3.2.4.2.5 FREEZING POINT OF ZINC The freezing point of zinc is assigned the value 692.677 K (419.527 ˚C) Metal samples of 99.9999% purity are commercially available. High purity liquid zinc has been found to supercool about 0.02 ˚C to 0.06 ˚C; hence, unlike the freezing procedure used with the tin-point cell, its freeze can be initiated in the furnace without withdrawing the cell from the furnace. Graphite containers are commonly and successfully used for zinc. Although the use of materials such as boron nitride (BN) has not been reported, it could be a suitable container for zinc. The metal is available in the form of small pellets and in rods suitable for filling graphite containers. [The first cryoscopic constant of zinc is 0.00185/K. Consequently, the liquidus point of an ideal zinc solution of 99.9999% purity would be approximately 0.5 mK lower than that of 100% pure zinc.]
115 mm CONTAINER (TEFLON®) THERMOMETER WELL (TEFLON®) 240 mm
5 mm
0.005" SPIRAL GROOVE ALONG INSIDE OF THERMOMETER WELL (1 OR 2 THREADS/in.)
3.2.4.2.5.1 REALIZATION AND APPLICATION
36.34 mm ID 40.34 mm OD 111 mm
25 mm
12.70 mm (0.500in.) ID 14.70 mm OD
1 mm
10 mm
3 mm 5 mm 3 mm
10 mm ID 14 mm OD
30 mm OD FUSED SILICA TUBE
Figure 14. An all-plastic indium freezing-point cell to be used steel container, such as that shown in figure 12. The argon gas the stainless steel container is adjusted to one atmosphere at the A similar all-plastic cell and stainless steel container may be the mercury freezing point or meIting point at one atmosphere.
in a stainless pressure inside freezing point. used to realize
A tube furnace containing the zinc-point cell is controlled about 5 ˚C above the freezing point until the metal is completely melted. If the furnace temperature is maintained at a higher temperature, the zinc will melt faster, but the zinc should never be heated by more than about 5 ˚C above its melting point. (It is convenient to control the furnace temperature automatically and melt the zinc sample overnight so that the freezing of the metal can be started early in the morning and the calibration of six or more test SPRT’s can be completed during the same day.) Insert the zinc-point check SPRT into the cell well. When the SPRT indicates that the melt is about 5 ˚C above the freezing point, change the furnace temperature control settings to control at 5 ˚C below the freezing point in order to initiate rapid cooling for nucleation. When the check SPRT indicates recalescence, change the furnace temperature control settings to control at 1 ˚C to 0.5 ˚C below the freezing point. Withdraw the check SPRT from the cell well and insert successively into the well two fused silica glass rods, each initially at room temperature, for about 5 minutes each, and then insert again the cool check SPRT. This freezes a thin mantle around the thermometer well. Within about 20 to 30 minutes, the readings on the check SPRT should indicate that the cell is at temperature equilibrium. After the readings on the check SPRT are completed, test SPRT’s, that have been heated in an auxiliary furnace, are successively inserted into the cell well and calibrated. After all of the test SPRT’s are calibrated, the preheated check SPRT is inserted again into the cell well and measurements made on it. This second reading should agree with the first to within ± 0.1 mK. references [41,73,75].
Z-173
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TO PURIFIED ARGON SOURCE
TO HIGH VACUUM
A B
A
C
8.3 cm
D E
5.5 cm
5.5 cm
B
Z
E F E
3.5 cm
51.3 cm
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28 cm
E G H I J K L
M
C N D O
5.1 cm
Figure 15. A graphite freezing point cell enclosed inside a fused silica tube with tube connection to high vacuum, purified argon gas source, and pressure gauge. A - connection to high vacuum, purified argon source, and pressure gauge, B – fused-silica-to-Kovar graded seal, C - fused-silica connecting tube, outer surface matte finished to minimize radiation piping, D - thermometer guide tube, E - heat shunts (Inconel disks), F - thermal insulation (Fiberfrax), G fused-silica outer envelope, H - graphite lid, I - graphite thermometer well, J - fused-silica thermometer well, K - fused-silica fiber-woven tape for cushioning the graphite freezing-point cell inside the fused-silica enclosure, L - metal sample, M - graphite crucible, N - fused-silica fiber pad for cushioning the thermometer, 0 - Fiberfrax paper liner.
Figure 16. A method for filling a graphite freezing-point cell by melting the metal sample in the graphite crucible. The required amount of sample is placed in the graphite crucible and the crucible is inserted into the fused silica tube. To protect the sample, the fused silica tube is evacuated or filled with an inert gas (e.g., purified argon) before melting the metal in a tube furnace. Depending upon the geometry of the sample, the melting of two or more batches of sample may be required. A - Silicone rubber stopper, B - fused silica tube, C - graphite crucible, D - metal sample.
3.2.4.2.6 FREEZING POINT OF ALUMINUM A
The freezing point of aluminum is assigned the value 933.473 K (660.323 ˚C). Metal samples of 99.9999% purity are commercially available. High purity graphite containers have been used successfully with aluminum. High purity liquid aluminum has been found to supercool about 1 ˚C to 2 ˚C; hence, its freeze can be initiated in the furnace without withdrawing the cell from the furnace. Aluminum is highly reactive, particularly at elevated temperatures; liquid aluminum is capable of dissolving many metals. Liquid aluminum reacts with moisture, forming the oxide and dissolving the hydrogen. The compounds Al4C3 and aluminum oxycarbide have been found in aluminum samples cast in graphite at 1000 ˚C. Because of the high chemical reactivity of aluminum, the graphite cell containing the metal must be completely protected by enclosing the cell in a fused silica envelope (see fig. 15). The argon or helium gas that is used to pressurize the freezing metal at one atmosphere must be thoroughly devoid of moisture, hydrogen, oxygen, hydrocarbons, and other substances that would react with liquid aluminum. The cell must not be heated more than 5 ˚C above the aluminum freezing point. [The first cryoscopic constant of aluminum is 0.00149/K. Consequently, the liquidus point of an ideal aluminum solution of 99.9999% purity would be approximately 0.7 K lower than that of 100% pure aluminum.]
B 560 mm
C D
E F
153 mm
219 mm
G
H
I 560 mm
3.2.4.2.6.1 ASSEMBLY OF AN ALUMINUM-POINT CELL
J
High purity aluminum can be obtained in the form of shots or rods. Determine. the internal volume of the graphite container, taking into account the thermometer well. Determine the mass of liquid aluminum required to fill the cell to within 0.5 cm of the graphite lid. Weight out aluminum shots or cut and clean aluminum rods that correspond to this mass. The rods should be cut with a carbide tipped tool and cleaned by etching in a hot (about 200 ˚C) solution consisting (by volume) of reagent grade phosphoric acid (15 parts, sulfuric acid (5 parts), and nitric acid (7 part), and then carefully rinsing many times in distilled water. Load the graphite crucible with the aluminum sample and then slide it into an extra-long fused-silica test tube such as that shown in figure 16. Insert the test tube into the tube furnace and evacuate it. While continuing to evacuate the tube, set the furnace temperature to control at about 5 ˚C above the melting point of aluminum. When the sample has completely melted, cool it to room temperature, while continuing to pump the tube. If aluminum shot, or rods of odd sizes, are used, the graphite cell will require several loadings and meltings before the desired amount of total sample has been loaded into the cell. When the graphite crucible is appropriately loaded with the sample, replace the silicone rubber stopper at the mouth of the extra-long test tube of figure 16 with the device for inserting the graphite thermometer well and lid (see reference [45] or fig. 17). Insert the test tube into the tube furnace, evacuate it, and then fill it with high purity argon to a pressure slightly above ambient. Melt the aluminum sample and push the graphite well and lid into the cell. Cool the sample to room temperature, while maintaining the argon pressure in the test tube slightly above the ambient pressure. Finally, assemble the graphite cel1 containing the aluminum sample into the desired freezing - point cell configuration (see references [43,45,701] or fig. 15).
K
244 mm
L
Figure 17. An apparatus for installing a graphite thermometer well and lid in a graphite crucible containing a molten metal sample. A - stainless steel pusher rod, B - silicone rubber gas seal (permits linear motion of the pusher rod A), C - inlet for purified argon gas that is used in purging and maintaining positive pressure of the gas during the assembly process, D - silicone rubber stopper, E - stainless steel flange attached to the pusher rod for pressing against the graphite lid and thermometer well during assembly. F - graphite lid for the crucible, G - slit on the pusher rod (the two halves spring outward to hold the graphite thermometer well and lid while melting the metal sample), H - graphite thermometer well, I - fused-silica tube, J - a part of the fused-silica tube where its I.D. matches closely with the O.D. of the crucible and its lid so that the lid can be easily guided onto the opening of the crucible, K - graphite crucible, L - molten metal sample.
Z-174
Guidelines for Realizing the ITS-90 Cont’d
3.2.4.2.6.2 REALIZATION AND APPLICATION SPRT’s that are to be calibrated at the aluminum point and higher must have fused silica, sapphire, or ceramic insulation for the resistance element and its extension leads. Such high temperature SPRT’s should be handled by procedures that avoid thermally shocking them. A tube furnace containing the aluminum point cell is controlled about 5°C above the freezing point of aluminum until the metal is completely melted. It is convenient to control the furnace temperature automatically and melt the metal overnight so that the freezing of the metal can be started early in the morning and the calibration of two or three test SPRT’s completed during the same day. Insert the aluminum point check SPRT stepwise into the cell well. Since the SPRT will cool considerably between the time it is withdrawn from any auxiliary preheat furnace and inserted into the aluminum point cell, the SPRT is heated in the section of the thermometer guide tube that is maintained close to the furnace temperature. The SPRT is inserted initially to a location where its tip is about 3 cm above the graphite cell lid. After about 5 minutes, the SPRT is inserted an additional 5 cm and after another 5 minutes, another 5 cm, and so on until the tip of the SPRT is at the bottom of the thermometer well. When the SPRT indicates that the sample is about 5°C above the freezing point, change the furnace temperature control settings to control at 5°C below the freezing point in order to initiate rapid cooling for nucleation. When the check SPRT indicates recalescence, change the furnace temperature control settings to control at 1°C to 0.5°C below the freezing point. Withdraw the check SPRT stepwise from the cell, first to a location about 3 cm above the graphite cell lid. After about 5 minutes, withdraw the SPRT another 5 cm,and after another 5 minutes, another 5 cm, and so on until the SPRT is completely out of the thermometer guide tube. Next, insert successively into the cell well two fused silica glass rods, each initially at room temperature, for about 5 minutes each to freeze a thin mantle of solid aluminum around the thermometer well. Again insert the check SPRT stepwise, as described above, into the cell. Within 20 to 30 minutes, the readings on the check SPRT should indicate that the cell is at temperature equilibrium. After the readings on the check SPRT are completed, the SPRT is removed from the cell stepwise, as described above. The test SPRT’s are then successively inserted stepwise, calibrated, and removed stepwise as described for the check SPRT. After all of the test SPRT’S have been calibrated, the check SPRT is inserted again into the cell well and measurements made. This second reading at temperature equilibrium should agree with the first to within ± 0.1 mK. When SPRT’s are cooled rapidly from the aluminum point to ambient temperature, lattice vacancies are quenched in and these must be removed before the SPRT’s are calibrated at the triple point of water. To relieve any quenched in lattice vacancies, the SPRT’s that have been calibrated at the aluminum point should be heated in an auxiliary furnace at about 660°C for about 30 minutes and then gradually cooled to about 500°C over 3 hours or more before withdrawing from the furnace to cool at ambient temperature. See references (43, 45, 70). 3.2.4.2.7 FREEZING POINT OF SILVER The freezing point of silver is assigned the value 1234.93 K (961,78°C). Metal samples of 99.9999% purity are commercially available in the form of pellets. High purity graphite containers have been used successfully with silver. Liquid silver has been found to supercool not more than 0.5°C; hence, its freeze can be initiated in the furnace without withdrawing the cell from the furnace. See references [3,15,72,98]. Oxygen is known to “dissolve” in liquid silver and lower the freezing point. Although the dissociation pressure of Ag20 is expected to be quite high at the freezing point of silver, the lowering of the freezing point may be a combination of the solution of Ag20 and of oxygen in liquid silver. (The dissociation pressure of Ag20 is given as 414 atmospheres at 507°C.) In a graphite environment at the freezing point of silver, a small amount of the oxygen will eventually react with the graphite; however, a newly prepared cell should be pumped at high vacuum at about 1000°C for a week before back filling to one atmosphere with purified argon, nitrogen, or helium. [The first cryoscopic constant of silver is very small (0.000891/K). Consequently, the liquidus point of an ideal silver solution of 99.9999% purity would be approximately 1.1 mK lower than that of 100% pure silver.] 3.2.4.2.7.1 REALIZATION AND APPLICATION The freezing-point cell of silver may be assembled by a procedure similar to that used with aluminum. See section 3.2.4.2.6.1. SPRT’s that are to be calibrated at the silver freezing point must have fused silica, sapphire, or ceramic insulation for the resistance coil and its extension leads. Such high temperature SPRT’s should be handled by procedures that avoid thermally shocking them. A tube furnace containing the silver freezing point cell is controlled at about 5°C above the freezing point until the metal is completely melted. (It is convenient to control the furnace temperature automatically and melt the metal overnight so that the freezing of the metal can be started early in the morning and the calibration of two or three test SPRT’s completed during the same day.) Insert the silver point check SPRT stepwise into the cell well. Since the SPRT will cool considerably between the time it is withdrawn from any auxiliary preheat furnace and inserted into the silver point cell, the SPRT is heated in the section of the thermometer guide tube that is maintained close to the furnace temperature. The SPRT is inserted initially to a location where its tip is about 3 cm above the graphite cell lid. After about 5 minutes, the SPRT is inserted an additional 5 cm, and after another 5 minutes, another 5 cm, and so on until the tip of the SPRT is at the bottom of the thermometer well. When the SPRT indicates that the temperature of the sample is about 5°C above the freezing point, change the furnace temperature control settings to control at 5°C below the freezing point in order to initiate rapid cooling for nucleation. When the check SPRT indicates recalescence, change the furnace temperature control settings to control at 1°C to 0.5°C below the freezing point. Withdraw the check SPRT stepwise from the cell well, first to a location about 3 cm above the graphite cell lid. After about 5 minutes, withdraw the SPRT an additional 5 cm, and after another 5 minutes, another 5 cm, and so on until the SPRT is completely out of the thermometer guide tube. Next, insert successively into the cell well two fused-silica glass rods, each initially at room temperature, for about 5 minutes each in order to freeze a thin mantle of solid silver around the
thermometer well. Then, insert again the check SPRT stepwise, as described above, into the cell. Within about 20 to 30 minutes, the readings on the check SPRT should indicate that the cell is at temperature equilibrium. After the readings on the check SPRT are completed, it is removed from the cell stepwise, as described above. The test SPRT’s are then successively inserted stepwise, calibrated, and removed stepwise as described for thecheck SPRT. After all of the test SPRT’s have been calibrated, the check SPRT is inserted again into the cell well and read. This second reading should agree with the first to within ±0.2 mK. When SPRT’s are cooled rapidly from the silver point to ambient temperature, lattice vacancies are quenched in and these must be removed before the SPRT’s are measured at the triple point of water. To relieve any quenched in lattice vacancies, the SPRT’s that have been calibrated at the silver point are heated in an auxiliary furnace at about 960°C for 30 minutes or so and then gradually cooled to about 500 ˚C over 3.5 hours or more before withdrawing from the furnace to cool at ambient temperature. In order to protect the platinum of the SPRT from contamination by diffusion of metals at high temperatures (above 660°C, the SPRT’s should be enclosed in a platinum tube or other protective device. 3.2.5 CONTROL CHARTS OF CHECK THERMOMETERS Control charts should be kept for all of the check thermometers associated with the various fixed points. Each of these charts will usually consist of a chronological graph of the check thermometer resistance value, R(X), obtained from measurements in the fixed-point cell X, and of the ratio, W(X) = R(X)/R(TPW), of the resistance value R(X) to the resistance value, R(TPW), obtained from measurements in a triple point of water cell. Presumably, such charts have been kept by those involved in precision thermometry. Entries on such control charts are made each time the particular fixed point cell is used. Since those involved in precision thermometry would have used triple point of water cells for their work based on the IPTS-68 and they would have used W(X), the same control chart can be continued with the ITS-90. The reason, of course, is that the behavior of the fixed point cells is independent of the scale. Not all of the fixed points of the ITS-90, however, are the same as those of the IPTS-68. The ITS-90 uses some of the IPTS-68 fixed points but it also uses other fixed points. See reference (64). Some metrologists may not have used W(X) as defined above, but may have used the W(t) of the IPTS-68. In that case, there will be a discontinuity in their control charts involving W when they implement the ITS-90 and begin using W(X). The magnitude of the discontinuity will simply be the ratio R(273.16 K)/R(273.15 K). Control charts involving only R(X) as a function of time will not have any discontinuity due to the change in the scale. Depending on the temperature of interest, of course, there may be need to start additional control charts. 3.3 RADIATION THERMOMETRY Above the freezing point of silver (1234.93 K), the ITS-90 is defined in terms of Planck’s radiation law. The values of temperatures T90 on the ITS-90 are obtained from the observed ratios of the spectral concentrations of the radiance L λ of a blackbody at the wavelength (in vacuum) λ at T90 and at the reference temperature T90(X) according to eq. (31). Inside a closed cavity, the radiation densities at different wavelengths λ depend only upon the temperature of the cavity walls. When a practical radiator is designed with a small hole in the wall to observe the radiation density at λ, there arises the question of how much the observed radiation departs from the blackbody radiation for a radiator design of a given geometry and material of construction. There are numerous papers on the theoretical analysis of the emissivities, associated with cavity geometry and construction materials and descriptions of radiator designs that have been used in radiation thermometry (8, 9, 34, 35, 54, 77, 87, 89, 95). The emissivities of cavities constructed of specular reflectors and diffuse reflectors have been analyzed (87). It is expected that at high temperatures many materials become oxidized and, consequently, become diffuse reflectors. Although it is difficult to determine the actual temperature gradients in a cavity, the effect of temperature gradients has also been treated (10, 11). The effective emissivity of a graphite blackbody cavity has been computed to be 0.99997 ± 0.00003 (77). For radiation thermometer calibrations at the silver, gold, or copper fixed point, the blackbody cavity should be constructed of graphite and surrounded by the freezing or melting metal contained in graphite to retain the high purity of the metal that is used. [The first cryoscopic constants of all three of these metals are extremely low (silver: 0.000891/K; gold: 0.000831/K; Cu: 0.000857/K). Consequently, the idealsolution liquidus points of these metals of 99.9999% purity would be approximately 1.1 mK to 1.2 mK lower than that of 100% pure metals.] References [27, 55, 56, 57, 62, 77] give some details of construction of suitable graphite fixed point blackbody cavities. The metal should be protected from air using an inert gas, such as argon, nitrogen, or helium, at a pressure slightly above ambient. The graphite container or auxiliary graphite scavengers can remove small amounts of oxygen impurities. For the blackbody cavity at the platinum point, pure alumina has been used in an oxidizing atmosphere to avoid the reaction between platinum metal and alumina in which oxygen gas is formed and metallic aluminum is dissolved in the platinum [33,86]. Usually, optical pyrometers or photoelectric pyrometers are used to determine the ratio of the radiances of a source of unknown temperature with that of the reference source. The optical system of the instrument is designed to focus a nearly monochromatic image of the radiation source onto a photodetector, which until about the mid 1950’s was only the human eye; now the eye has been replaced in high precision measurements by photoelectric detectors because of their greater accuracy and their suitability for automation of the measurements. Two methods are commonly used to determine the ratios of spectral radiances. Either the photoelectric pyrometer is designed for comparing the two radiation sources by null detection operation, similar in principle to the disappearing filament
Z-175
optical pyrometers using suitable neutral filters or sectored discs for attenuating the radiation of one source, or for measuring directly the radiation density in terms of the detector output, e.g., photocell current. The latter requires high stability and linearity of signal processing [34,77). The optics of the system may comprise refracting components (lenses) or reflecting components (mirrors) [28,34,54,57,87]. Equation (31) requires the ratio of monochromatic radiances. Usually, interference filters are used for this purpose. The bandwidth should be narrow with high transmittance while completely blocking out wavelengths outside the desired band. The temperature error is smaller the narrower the bandwidth. The temperature of the filters should be controlled, since they are sensitive to temperature changes. The photoelectric detector should be protected from undesired radiations from outside the solid angle defined by the aperture of the blackbody cavity. Where the output of the photocell is used to determine the ratio of the radiances, the linearity of the detector should be carefully checked or calibrated. For details of optical pyrometer operation and attendant sources of error, see references [28,34,54,57,77,87]. 4. CALIBRATION OF THERMOMETERS ON THE ITS-90 AT VARIOUS LEVELS OF UNCERTAINTY AND SOME APPROXIMATIONS OF THE SCALE In a standards laboratory, the design of apparatus and equipment for calibration of thermometers on the ITS-90 should be based on the desired accuracy, the number of thermometers and thermometric instruments that must be calibrated per year, the cost of realizing the ITS-90 (the fixed points and the measurement equipment), the cost of applying and maintaining the ITS-90, and the cost of research to maintain and make necessary improvements on the realization of the ITS-90. In a national standards laboratory, the efforts are directed toward the accurate realization of the ITS-90. On 1 January 1990, no laboratory was able to calibrate thermometers over the complete range of the ITS-90 in accordance with the strict definition of the scale. Also, it is thought that on that date there was no immediate, widespread requirement for “experimental calibration conversion” from the IPTS-68(75) to ITS-90 over the complete range. Since the differences between IPTS-68(75) and ITS-90 were known, “arithmetical conversions” should have met most of the immediate requirements. Also, where stable thermometers have been used to maintain the EPT-76 or parts of the IPTS-68(75), the scales on those reference thermometers could be converted to ITS-90, using the published approximate differences between the scales, and then those thermometers can be used to calibrate other thermometers on the ITS-90. To realize the ITS-90 as defined and for international traceability, however, it is essential for the national calibration laboratory to have all of the fixed-point apparatus and measurement equipment. Furthermore, without continued research and comparison with other standards laboratories, the question regarding the accuracy of the realization of the scale will remain. The ITS-90 temperature calibrations are based on the thermal equilibrium states (vapor-liquid or liquid-solid equilibrium at known pressures, or vapor-liquid-solid triple points) of pure substances. Substances, however, have some impurity content; the amount must be small enough to have negligible effect on the measurement of temperature. Obviously, the fixed-point device and the experimental procedure must be designed so that during calibration, the thermometer will be in thermal equilibrium with the equilibrium state of the defining fixed point. A method for checking whether or not the thermometer is in thermal equilibrium with a metal fixed-point standard device is to reduce the immersion in the device a known amount or vary the experimental conditions. The observed temperature change of the thermometer must correspond with the hydrostatic head effect of the liquid metal in the device, or there must be no observed temperature change with experimental conditions (such as changing furnace temperatures of metal fixed-point cells). In order to determine the precision of the calibration process, it is essential to use check thermometers with every calibration. The results of the check thermometers will show whether the calibration process is “under statistical control” or not. The accumulated results show the precision of the “gross” calibration process. Since some parts of this section deal with approximations of the ITS-90, and will make reference to the scale differences given in table 1, the methods by which the table was constructed will be described. The differences (T90 - T76) between 5 K and 27 K were obtained using the same relation [99] as that used for (TNPL-75- T90). namely, (T90 - T76)/mK = - 0.00.56(T90/K)2.
(40)
The differences (T90 - T90) between 14 K and 100 K were obtained by Working Group 4 of the CCT by graphical interpolation of data from the published literature. The differences (T 90 - T 68 ), or (t 90 - t 68 ), between -200 ˚C and 630 ˚C were obtained by Working Group 4 of the CCT from published data on two SPRT’s, one SPRT covering the range, below 0 ˚C, and the other covering the range from 0 ˚C to 630 ˚C. A polynomial of the form: 8 (t90 - t68)/˚C = ∑ ai(t90/630)i i=1 was fitted to the data from a1 = -0.148759 a2 = -0.267408 a3 = 1.080760 a4 = 1.269056
(41)
-200 ˚C to 630 ˚C and the coefficients are: a5 = -4.089591 a6 = -1.871251 a7 = 7.438081 a8 = -3.536296
- 0.25 [(t90/˚C + 273.15)/(1337.33)]2.
The NIST offers calibration services for various thermometers and pyrometers covering the range from 0.65 K to 4200 ˚C (see NIST SP 250). Of this range, the Chemical Process Metrology Division offers calibrations for contact thermometers covering the range from 0.65 K to 2400 K, and the Radiometric Physics Division offers calibrations for non-contact thermometers (radiation pyrometers) covering the range from 1234.93 K (961.78 ˚Q to 4200 ˚C. Calibrations of only contacttype. thermometers will be discussed here. The types of contact thermometers calibrated include rhodium-iron resistance thermometers (RIRT’s), germanium resistance thermometers (GRT’s), standard platinum resistance thermometers (SPRT’S), thermocouples (t/c), liquid-in-glass thermometers, thermistor thermometers, industrial platinum resistance thermometers (IPRT’s), digital thermometers, and other special thermometers that are compatible with the NIST calibration equipment. 4.1 RHODIUM-IRON RESISTANCE THERMOMETERS At temperatures below 13.8033 K, RIRT’s and GRT’s are, at the present time, the only thermometers that are suitable for precision temperature measurements. Also, RIRT’s (and to a lesser extent GRT’s) are suitable for use at temperatures up to the triple point of neon (24.5561 K). In the range from 0.65 K to about 25 K, RIRTs have -reproducibilities of about ± 0.2 mK. Consequently, RIRT’s don’t degrade the realization of the ITS-90 significantly. When the ITS-90 is realized, as defined, at NIST, some NIST RIRT’s will be calibrated at many temperatures through the Use of vapor-pressure thermometry and gas thermometry to produce reference-standard RIRT’s, which will be periodically recalibrated. The resistance temperature data of these RIRT’s will be represented by a polynomial. Customer RIRT’s are calibrated by comparison with reference-standard RIRT’s. A polynomial is fitted by the method of least squares to the RIRT resistancetemperature data so obtained and the results are reported in terms of the polynomial that is selected. Until the NIST completes the development of the CVGT and vapor-pressure thermometry apparatus with which the reference-standard RIRT’s will be calibrated, calibrations of customer RIM are performed by comparison against referencestandard RIRT’s that have been calibrated on the NPL-75 Scale [13) or on the EPT-76 and converted to the ITS-90. To convert a calibration of an RIRT on the EPT-76 to an approximate calibration on the ITS-90, use the EPT-76 calibration res instance temperature data change the T76 values to T90 values Using the (T90 - T76) differences given in table 1, or calculated with eq (40), to produce a new set of. resistance-temperature values, and then fit a polynomial of the required degree to these data. Using the coefficients of the polynomial so determined, produce the desired calibration table. A typical calibration report on the EPT-76 and one on the ITS-90 are given in appendix 3, sections 6.3.6 and 6.3.7, respectively. 4.2 GERMANIUM RESISTANCE THERMOMETERS GRT’s are comparable with, but not quite as stable as RIRT’s. They are calibrated in a manner similar to that of the RIRT’s and their results similarly reported. At NIST, customer GRT’s are calibrated by comparison with reference to standard RIRT’s. Anyone with a calibration on the EPT-76 may convert it to an approximate ITS-90 calibration by the same procedure as just outlined for RIRT’s. 4.3 STANDARD PLATINUM RESISTANCE THERMOMETERS Both capsule and long-stem type SPRT’s are calibrated at the NIST. They will be discussed separately. 4.3.1 CAPSULE SPRT’S (13.8033 K TO 429.7485 K OR 505.078 K)
The polynomial with these coefficients reproduces the tabulated differences [83] to within 1 mK above 0˚C and to within 1.5 mK below 0˚C. The differences (T 90 - T 68 ) between 630˚C and 1064˚C were obtained by Working Group 4 by graphical interpolation from published data [14). The differences (T90 - T68) above 1064 ˚C were obtained from the equation: (t90 - t68)/˚C
For nonstandard types of thermometers used to approximate the ITS-90, the level of uncertainty is higher than the numbers just given because of the inherent instability of these thermometers. In all cases, these types of thermometers are calibrated by comparison with one or more standard instruments of the scale, e.g., vapor-pressure thermometry; vapor-pressure thermometry and gas thermometry; vaporpressure thermometry, gas thermometry, and platinum resistance thermometry; gas thermometry and platinum resistance :thermometry; platinum resistance thermometry; or pyrometers or spectral radiometers.
(42)
In section 3, we discussed the direct realization of the ITS-90, using the standard instruments of the scale, i.e. , the realization of the scale at the lowest level of uncertainty. Of course, even the standard interpolating instruments used at the same thermodynamic temperature will indicate temperatures that differ slightly due to the devices having nonideal behavior and the scale’s being expressed in as simple a form as possible. The differences in indicated temperatures, however, are negligible for all practical purposes, being of the order of ≤ ± 0.5 mK for temperatures above about 5 K (i.e., assuming no errors in calibration). The realization of the ITS-90 in the liquid helium range of temperatures (0.65 K to 5.0 K) through helium vapor pressure- temperature relations can be accurate to about ± 0.1 mK or ± 0.2 mK.
For temperatures in the range from 13.8033 K to 273.16 K, capsule SPRT’s are the most suitable thermometers. NIST has reference capsule SPRT’s that have been, or will have been, calibrated at the defining fixed points in this range. Those SPRT’s are used in calibrating customer thermometers by the comparison technique over the range from about 13 K to 84 K. The temperatures at which comparisons are made are at, or within a few mK of, the defining fixed-point temperatures of the ITS-90 and at temperatures approximately mid-way between the fixed-point, values. Data at the temperatures intermediate to the fixed-point values are incorporated as a check on the calibration process. At and above the argon triple point (83.8058 K), customer capsule SPRT’s are calibrated by the fixedpoint method. See section 6.3 for an example of how to calculate the coefficients of the deviation functions. 4.3.2 LONG-STEM TYPE SPRT’S (83.8058 TO 1234.93 K) Long-stem type SPRT’s are used in the range from 83.8058 K to 1234.93 K. Two different long-stem type SPRT’s are required to cover this whole range, one type being the customary SPRT having a nominal 25.5 0 resistance at 0 *C and used in
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Guidelines for Realizing the ITS-90 Cont’d
the range from 83.8058 K to 692.677 K or to 933.473 K, and the second type having a somewhat longer stem and having a nominal 0.25 Ω or 2.5 Ω resistance and used in the range from 273.15 K to 1234.93 K. Such thermometers are very stable if handled carefully, In this range of temperature, SPRT’s are calibrated by the fixed-point method, different sets of fixed points being required for different temperature subranges. The required fixed points for the different subranges were specified in section 2 of this document. In the fixed-point method, corrections for hydrostatic heads and gas pressure over the metals, of the freezing point and melting-point cells are made (see table 6). Similarly, corrections for hydrostatic heads present in metal and in gas triple-point cells are made. As a check on the accuracy of the calibration, measurements are made at one or more “redundant” defining fixed points lying within the temperature range of calibration or at a well characterized secondary fixed point, such as the cadmium freezing point, that lies within the temperature range of calibration. The value of the temperature of a check point calculated from the calibration constants should agree closely with the accepted value of that point. If not, then either an error was made in the calibration, one or more fixed point cells are defective, or the thermometer is defective. The procedures indicated in section 3.2 for realizing the various fixed-point temperatures and for handling SPRT’s are followed lowed care fully during calibration of platinum thermometers, especially so for calibration at the aluminum and silver freezing points (see sec. 3.2.4.2.7.1 for a discussion of lattice defects). See section 6.3 for an example of how the coefficients of the deviation functions are calculated from the data for the two sets of fixed points.
4.3.3 CONVERSION OF THE IPTS-68 CONSTANTS APPROXIMATE ITS - 90 CONSTANTS AND W ( T 90 ) TABLES For SPRT’s calibrations temperatures the freezing
AND
W ( T 68)
TABLES
that have been calibrated recently on the IPTS-68(75), their may be. converted to approximate, calibrations on the ITS-90 at between the triple point of equilibrium hydrogen (13.8033 K) and point of zinc (692.677 K).
To make the conversion, first obtain values of W(T68), i.e. R(T68)/R(O˚C), from the, IPTS-68(75) calibrations, at values of T68 corresponding to the temperatures of the relevant fixed points of the ITS-90 in the appropriate range in which the conversion is desired. [Note : for a fixed point, the temperature values T68 and T90 are different, but the “hotness“ is the same and so the resistance of a given SPRT remains unchanged. The temperature values on the two scales are defined to be the same only at the triple point of water and at the absolute zero of the temperature scales. Due to the nature of the scales, however., there are other temperature values of these scales that are also the same, which are fortuitous. See fig. 1, which shows the difference of t90 and t68 as a function of t90. ] Using these values of W ( T 68) at the appropriate ITS-90 fixed-point temperatures, calculate values of W(T90), i.e., R(T90)/R(273.16 K), by dividing the values of W(T68) at the appropriate fixed-point temperatures by the value of W(273.16 K), i.e., the, value of W(T68) at the triple point of water. Table 8 shows samples of such conversions for a capsule-type SPRT and for a long-stem type SPRT calibrated on the IPTS-68(75). The calibration constants of the IPTS-68(75) equations for the two SPRT’s are given also in table 8. The values of W(T90) so
Difference Between ITS-90 Calibration and IPTS-68 Calibration Converted to ITS-90, Chino RS8YA-5, 25.5 ohm
T90-T90(68) mK
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
0.0
-0.1
-0.1 50
100
150
200
250
300
TO
350
400
450
500
550
600
650
700
Temperature, K
Figure 18. Differences between T90 and (T90) as calculated from IPTS-68 calibration for the long-
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Table 8. Example of conversion of calibrations of SPRT’s on the IPTS-68 to approximate calibrations on the ITS-90 Capsule SPRT, S/N 1812284 : e-H2 TP to Sn FP IPTS-68 CALIBRATION CONSTANTS R(0 ˚C) = 25.4964808 A1 = 1.6314209x10-4 D1 = 1.4525327x10-4 A2 = 2.1616630x10-4 D2 = 2.2572375x10-10
a = 3.9262754x10-3 B1 = -8.7377446x10-7
d = 1.4964667 C1 = 4.0321350x10-7
B2 = -1.7113512x10-7
C2 = 6.6163769x10-8
A3 = 4.5449999x10-7 A4 = 3.0860000xl0-7
B3 = -7.7242433x10-6
C3 = 3.9028516x10-8 C4 = 1.0880791x10-4
4.3.4 UNCERTAINTIES OF CALIBRATIONS AND THEIR PROPAGATION Both systematic and random errors of measurements introduced in a calibration are propagated throughout the temperature range of the calibration. It is the total uncertainty arising from both of these types of errors, however, that is of interest to the customer and user of a calibrated thermometer. International comparisons of fixed-point cells below 90 K [79] and other data suggest that the uncertainties (at the 10 level) in the realizations of the defining fixed points of the ITS-90 are about ± 0.2 mK for the triple points 0f hydrogen and neon, ± 0.1 mK for the triple point of oxygen through the melting point of gallium, ± 0.7 K at the freezing point of indium, ± 1 mK from the freezing point of tin through the freezing point of aluminum, and ± 2 mK for the freezing point of silver. The uncertainty of temperature measurements in the liquid helium range (0.65 K to 5.0 K) results from the uncertainty of the helium vapor-pressure measurements. The uncertainty (at the 1 o level) throughout this range of temperature is estimated to be approximately ± 0.1 mK to ± 0.2 mK.
ITS-90 CALIBRATION CONSTANTS CONVERTED FROM THE IPTS-68 CONSTANTS R(273.16) = 25.4974973 a1 = -2.5239001x10-4
b1 = 1.2277862x10-4
C1 = -2.3783015x10-6
ag = -2.5287142x10-4
bg = 1.1130131x10-5
C2 = -4.3892024x10-6 C3 = -1.5608728x10-6 C4 = -2.1374663x10-7 C5 = -1.0344171x10-8
For the CVGT, the uncertainty in the measured temperature over its temperature range (3.0 K to 24. 5561 K) arises from uncertainties of realizations of the triple points of neon and of equilibrium hydrogen, of the measurement of the CVGT gas pressure and of the measurement of the vapor pressure of helium. The uncertainty (at the 1o level) throughout this range of temperature is estimated to be approximately ± 0.1 mK to ± 0.2 mK. Uncertainties introduced by a particular CVGT design may add to these uncertainties.
Long-Stem SPRT. SIN RS8YA-5 : Ar TP to Zn FP IPTS-68 CALIBRATION CONSTANTS R(0 ˚C) = 25.5086208 A4 =
A = 3.9856609x10-3 a = 3.9268986x10-3
B = -5.8762238x10-6 d = 1.49640322 C4 = 9.3183900x10-7
2.6581418x10-14
ITS-90 CALIBRATION CONSTANTS CONVERTED FROM THE IPTS-68 CONSTANTS R(273.16 K) = 25.5096386 a4 = -9.3225823x10-5 a8 = -9.1058813x10-5
b4 = -9.9914440x10-6 b8 = -7.6061559x10-6
obtained may then be used with the appropriate relations described in section 2 to obtain the constants of the ITS-90 deviation equations for the SPRT’s. In tab1e 8 we list the value of the deviation constants that were calculated from the sample data presented there. For comparison, values of the conversion from W(T68) to W(T90) as well as measured values of W(T90), for the various relevant fixed-point temperatures T68 and T90, respectively, are given in table 9. The deviations in the values of the last two columns of table 9 for the capsule SPRT reflect the inconsistency between the NBS-IPTS-68(75) wire scale and the difference between the IPTS-68(75) and the ITS-90 as given in table 1. Note that for the long-stem SPRT, the zero deviations for tin and zinc are a consequence of those fixed points having been used in both cases and the
Table 9. Values of W(T68) and W(T0) for various fixed-point temperatures T68 and
Capsule SPRT (S/N 1812284) Fixed Point
T68/K
W(T68) meas..
e-H2 e-H2 e-H2 Ne o2 Ar Hg H2O Ga In Sn
TP BP BP TP TP TP TP TP MP FP FP
13.81 17.04200 20.280 24.5616 54.361 83.79723 234.3086 273.16 302.9218 429.7848 505.1181
0.00119822** 0.00231120** 0.00425962** 0.00848337** 0.09182547** 0.21598575** 0.84421212** 1.00003987** 1.11815352** 1.60970773** 1.89263856**
Ar Hg H2O Ga In Sn Zn
TP TP TP MP FP FP FP
83.79723 234.3086 273.16 302.9218 429.7848 505.1181 692.73
0.21592943** 0.84418993** 1.00003976 1.11817175*** 1.60980450*** 1.89278557 2.56885786
T90/K 13.8033 17.0357 20.2711 24.5561 54.3584 83.8058 234.3156 273.16 302.9146 429.7485 505.078
W(T90) calc.*
W(T90) meas..
0.00119817 0.00231111 0.00425945 0.00848303 0.09182180 0.21597714 0.84417846 1.00000000 1.11810895 1.60964355 1.89256311
0.00119721 0.00231049 0.00425815 0.00848391 0.09182102 0.21597795 0.84417781 1.00000000 1.11810896 1.60964566 1.89256311
*
0.21592084 0.84415637 1.00000000 1.11812729 1.60974050 1.89271033 2.56875573
4.3.5 ESTIMATES OF POSSIBLE ERRORS INTRODUCED BY EXTRAPOLATIONS BEYOND THE RANGE OF CALIBRATION It is unwise and is poor practice to use any thermometer beyond the temperature range over which it was calibrated. Nevertheless, some users persist in doing just that. In some cases, especially if the extrapolation is for only a few kelvins, the error introduced may be rather small. The errors of some typical extrapolations calculated and depicted for NIST SPRT’s, are shown in figures 21, 22, 23, 24, and 25. The curve in figure 21 shows the error introduced for a NIST SPRT by extrapolating the deviation function, determined from calibration over the range from the triple point of argon to the triple point of water, downward from the argon triple point to 54 K. Extrapolating downward to about the boiling point of nitrogen (77 K) results in a fairly insignificant error in this case and, thus, can be done with the usual caution that some thermometers may not be as good as that of figure 21. Figure 22 depicts the results for another NIST SPRT. The curve shows the error introduced by extrapolating the deviation function, determined from calibration over the range from the triple point of mercury to the melting point of gallium, downward from the mercury triple point to 84 K.
Long-Stem SPRT (S/N RS8YA-5): 83.8058 234.3156 273.16 302.9146 429.7485 505.078 692.677
In the calibration of SPRT’s over any given subrange, the possible error in the realization of each of the fixed points and any error of measurement must be considered and they will be propagated independently of that incurred at the other fixed points involved. The total uncertainty of measurements at a given temperature is then the root-mean-square of the appropriate contributing uncertainties. Curve, showing the propagation of a ± (unit error ) incurred at each of the defining fixed points of the two major ranges are shown in figures 19 and 20. Figure 19 shows the propagation of errors associated with the fixed point, below 213.16 K; and figure 20 shows curves for the fixed points used in the calibration of SPRT’s in the range from 273.15 K to 1234.93 K. The labels on the various curves indicate the fixed-point in which there is the unit error in its temperature, and the other fixed points without error. As an example, consider the curve labelled Sn(Ag, Al, Zn) of figure 20. The symbol Sn indicates that the unit error occurs in the Sn freezing-point temperature; that is clearly indicated by a unit offset of the curve at that point. The symbols in parenthesis,i.e., (Ag, Al, Zn), indicate that the Ag, Al, and Zn freezing points were made at those fixed-point temperatures without error. Also, it is assumed that the measurements at the triple point of water were without error. The other labelled curves are similarly interpreted. The straight lines labelled TPW show the errors propagated for an error of ± 0.1 mK made by the user in the triple point of water.
Figure 23 displays the results for the same NIST SPRT as used for figure 22, but the curve in this case shows the error introduced by extrapolating the deviation function, determined from calibration over the range from the triple point of mercury to the melting point of gallium, downward from the mercury triple point to only 200 K. A sizable error is shown for observations that would be made at Dry Ice temperatures (-78 ˚C).
0.21592281 0.84415625 1.00000000 1.11812699 1.60974062 1.89271033 2.56875573
Values of W(T90) calc. were obtained by conversion of corresponding values of W(T68) meas.
These values were calculated from NBS-IPTS-68 calibration constants, based on the NBS wire scale and calibration at the triple point of water and the freezing point of tin (and the freezing point of zinc for the long-stem SPRT).
**
These values were calculated from IPTS-68 calibration constants determined from fixed points. ***
conversion process having been consistent. The deviations for the other fixed points (Ar, Hg, Ga, and In) reflect the non-uniqueness of this SPRT and possible errors incurred in measurements at those fixed points. The results of tables 8 and 9 for the long-stem SPRT, with regard to the differences between temperatures determined from an actual ITS-90 calibration and those deterimined from an IPTS-68 calibration but then calculated for approximate ITS-90 values, are shown in figure 18. Note that at temperatures above 273.16 K. the zero deviation of figure 18 is a consequence of the fact that the same fixed points (tin and zinc ) have been used in both cases and the conversion process having been consistent.
Figure 24 depicts the results for several NIST SPRT’s, but the curves in this case show the errors introduced by extrapolating their deviation functions, determined from calibration over the range from the triple point of water to the freezing point of zinc, downward from the triple point of water to -50 ˚C. Figure 25 displays the results for several NIST SPRT’s, but in this case the curves show the errors introduced by extrapolating their deviation functions, determined from calibration over the range from the triple point of water to the freezing point of zinc, upward from the freezing point of zinc to 934 K (660 ˚C). As a general rule and good practice, one should never extrapolate any of the ITS-90 deviation functions beyond their range of application. If however, the estimated uncertainty introduced by extrapolating a deviation function beyond the range of calibration is acceptable, then the user may do so, but with the knowledge that his thermometer may yield results with a larger uncertainty than that estimated. The user that makes such extrapolations should realize that not all SPRT’s wi1l behave as indicated in figures 21 through 25. The results depicted in these figures are examples only and are valid for only those SPRT’s indicated. Other SPRT’s may be better or worse.
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Guidelines for Realizing the ITS-90 Cont’d
ITS-90 Propagation of Calibration Errors in Platinum Resistance Thermometry 2.0
2.0
1.5
20.3(e-H2, 17, Ne, O2, Ar, Hg)
17(e-H2, 17, Ne, O2, Ar, Hg)
error in mK
1.5
Hg(e-H2, 17, 20.3, Ne, O2, Ar)
Ar(e-H2, 17, 20.3, Ne, O2, Hg)
1.0
1.0
0.5
0.5
0.0
0.0
-0.5
-0.5
e-H2(17, 20.3, Ne, O2, Ar, Hg)
-1.0
-1.0 O2(e-H2, 17, 20.3, Ne, Hg, Ar)
-1.5
-1.5 Ne(e-H2, 17, 20.3, O2, Ar, Hg)
-2.0
-2.0 0
25
50
75
100
125
150
200
175
225
275
250
Temperature, K
Figure 19. Propagation of errors from errors of calibration of SPRT’s between 13.8033 K and 273.16 K. The curves show the error in the temperature values caused by a unit positive or unit negative error of calibration at each of the fixed points in the range, namely, the triple points of equilibrium hydrogen, neon, oxygen, argon, and mercury. The calibration at the triple point of water is assumed to have been made without error. The curves are identified by the fixed point
ITS-90 Propagation of Calibration Errors in Platinum Resistance Thermometry 1.5
1.5 Sn(Ag,Al,Zn)
Al(Ag,Zn,Sn) Zn(Ag,Al,Sn) Ag(Al,Zn,Sn)
1.0
0.5
1.0
0.5 TPW
Error in degrees per degree error in calibration
0.0
0.0
-0.5
-0.5
-1.0
-1.0
-1.5
-1.5 250
350
450
550
650
750
850
950
1050
1150
1250
Temperature, K
Figure 20. Propagation of errors from errors of calibration of SPRT’s between 273.15 K and 1234.93 K. The curves show the error in the temperature values caused by a unit positive or unit negative error of calibration at each of the fixed points in the range, namely, gallium, indium, tin, zinc, aluminum, and silver points. The calibration at the triple point of water is assumed to have been made without error. The curves are identified by the fixed point with error outside the parenthesis and the three fixed points without error inside the parenthesis. Also included in this figure are error curves for errors made by the user at the triple point of water; these curves
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ITS-90, 25.2 ohm Capsule PRT 1812284 Oxygen Subrange - Extrapolated Argon Subrange 0.1
0.1
0.0
0.0
-0.1
-0.1
-0.2
-0.2
-0.3
-0.3
-0.4
-0.4
-0.5
-0.5
-0.6
-0.6
-0.7
-0.7
-0.8
-0.8
-0.9
-0.9
error in mK
-1.0
-1.0 50
75
100
125
175 150 Temperature, K
200
225
250
275
Figure 21. Error curve for a NIST SPRT; the curve shows the error introduced by extrapolating its deviation function, determined from calibration over the range from the triple point of argon to the triple point of water, downward from the triple point of argon to 54K.
ITS-90, Chino Model R800-2, RS8YA-5, 25.5 ohm Ar to T3 Subrange - Extrapolated Hg to Ga Subrange 20
50
15
15
10
10
error in mK 5
5
0
0
-5
-5 75
100
125
150
175
200
225
250
275
Temperature, K
Figure 22. Curve for a NIST SPRT that shows the error introduced by extrapolating its deviation function, determined from calibration over the range from the triple point of mercury to the melting point of gallium, downward from the triple point of mercury to 84K
Z-180
Z
Guidelines for Realizing the ITS-90 Cont’d
ITS-90, Chino Model R800-2, RS8YA-5, 25.5 ohm Ar to T3 Subrange - Extrapolated Hg to Ga Subrange 1.5
1.5
1.0
1.0
error in mK 0.5
0.5
0.0
0.0
-0.5
-0.5 205
200
210
215
220
225
230 235 240
245
250
255 260
265
270 275
Temperature, K Figure 23. Curve for the NIST SPRT of figure 22 that shows the error introduced by extrapolating its deviation function, determined from calibration over the range from the triple point of mercury to the melting point of gallium, downward from the triple point of mercury to only 200 K.
ITS-90, 25.5 ohm PRTs Ar Subrange - Extrapolated Zn Subrange 0.0
0.0
-0.5
-0.5
-1.0
-1.0
error in m°C -1.5
-1.5 35
32
-2.0
-2.0
34 31
30
-2.5
-2.5
-3.0
-3.0 -50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Temperature, °C
Figure 25. Curves for several NIST SPRT’s that show the errors introduced by extrapolating their deviation functions, determined from calibration over the range from the triple point of water to the freezing point of zinc, downward to the triple point of water to -50˚C.
Z-181
ITS-90, 25.5 ohm PRT’s Al Subrange - Extrapolated Zn Subrange 3.0
3.0
2.0
2.0 30
1.0
Z
1.0
31
33
0.0
0.0
error -1.0 in mK
-- 1 . 0
32
-- 2 . 0
-- 2 . 0
-- 3 . 0
-- 3 . 0 35
-- 4 . 0
-- 4 . 0 34
-- 5 . 0
-- 5 . 0 250
350
450
550
650
750
850
950
Temperature, K Figure 25. Curves for several NIST SPRT’s that show the errors introduced by extrapolating their deviation functions, determined from calibration over the range from the triple point of water to the freezing point of zinc, upward from the freezing point of zinc to 934 K (660˚C). Also shown are subrange inconsistencies for the subrange triple point of water to zinc, relative to the subrange
4.4 THERMOCOUPLES (77 K TO 2400 K)
Table 10. Example of a conversion of calibration values of a type K thermocouple on the IPTS-68 to an approximate calibration on the ITS-90
There are numerous letter-designated types of thermocouples. The Type S thermocouple was the standard instrument of the IPTS-68(75) in the range from 630.74 ˚C to 1064.43 ˚C, but it is not a standard instrument of the ITS-90. Customer thermocouples are calibrated at NIST by using a set of temperature fixed points, by comparison with SPRT’s, or by comparison with referencestandard thermocouples that have been calibrated either by comparison with an SPRT or a radiation pyrometer, or through the use of fixed points. For details of the calibration procedures and of the uncertainties involved, see NIST SP 250-35 [22] and NIST Monograph 175 (23] (or Monograph 125 (82]).
Calibration Values on IPTS-68
t68 (˚C) 0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.0 900.0 1000.0 1100.0
Usually, the calibration data for most types of thermocouples are analyzed relative to reference tables, such as those given in NBS Monograph 125 [82]. Monograph 125, of course, has reference tables for thermocouples based on the IPTS-68(75). This monograph has been revised and updated to give reference tables for all letter-designated thermocouples based on the ITS-90. The revised version of Monograph 125 is Monograph 175 (23) and it supersedes Monograph 125. The electromotive-force-temperature data for a thermocouple calibrated on the IPTS-68(75) can be converted to an approximate ITS-90 calibration through the use of the differences (t90 - t68,) given in table 1 of this document and the S values in mV/˚C for the relevant thermocouple given in Monograph 175 or Monograph 125. An example of this conversion is given in table 10. A typical calibration report is presented in appendix 3 (see sec. 6.3.8).
a
emf68 (mV) 0.000 4.092 8.130 12.195 16.383 20.633 24.904 29.136 33.288 37.338 41.281 45.118
Calibration Values on IPTS-90 S (mV/˚C) Monograph 125 0.0395 0.414 0.0400 0.0415 0.0422 0.0426 0.0425 0.0419 0.0410 0.0400 0.0389 0.0378
t90-t68 (˚C) Table 1 0.000 -0.026 -0.040 -0.039 -0.048 -0.079 -0.115 0.20 0.34 -0.01 -0.19 -0.26
∆ [-S•(t90-t68)] (mV) 0.000 -0.001 -0.002 -0.002 -0.002 -0.003 -0.005 0.008 0.014 0.000 -0.007 -0.010
t90 (˚C)
emf90a (mV)
0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.0 900.0 1000.0 1100.0
0.000 4.093 8.132 12.197 16.385 20.636 24.909 29.128 29.128 37.338 41.288 45.128
emf90 - emf68 -∆
4.5 LIQUID-IN-GLASS THERMOMETERS Liquid-in-glass thermometers have uncertainties of realization as small as ± 30 mK in the temperature range from 0˚C to about 100 ˚C, but deteriorates at lower and higher temperaures. Liquid-in-glass (primarily,Mercury-in-glass) thermometers are calibrated at NIST by comparison with SPRT’s in liquid baths of various kinds that cover different temperature ranges. For details of the calibration procedures and of the uncertainties involved, see NIST SP 250-23 (105]. An example of a calibration report, based on the IPTS-68(75), of a liquid-in-glass thermometer is given in appendix 3 (see sec. 6.3.9). A calibration report for the same thermometer, with the IPTS-68(75) calibration converted to an approximate ITS-90 calibration through the use of (t90 - t68) differences given in table 7 is given also in appendix 3 (see sec. 6.3.10). 4.6 INDUSTRIAL PLATINUM RESISTANCE THERMOMETERS Industrial platinum resistance thermometers (IPRT’s) are designed primarily for use in the temperature range from about 77 K (approximate liquid nitrogen boiling point) to 500 ˚C. Typically, the manufacturer of IPRT’s quotes minimum instabilities of the IPRTs at the ± 0. 1 K level over this range of temperatures. Some IPRT’s may be somewhat better than this but others may be considerably worse. As seen from table 1, the maximum difference of (T9o - T68) below 500˚C is about 0.08 K, and therefore the difference in temperature due to the change in temperature scales is within the instability of many IPRT’s. Continued use of the IPTS-68(75) and of equations and standards [American Society for Testing and Materials (ASTM) Standard,E1137,and International ElectrotechnicalCommission (IEC) Standard, Publication 751] referenced to the IPTS-68(75),therefore, would result in an increase in uncertainty of temperature of only about 0.1 K if the temperature
were expressed as being on the ITS-90. (Note: the ASTM and the IEC are converting their respective IPRT tables from the IPTS-68(75) to the ITS-90. ASTM Committee E-20 on Temperature Measurements is responsible for this conversion for the ASTM). When IPRT’s are calibrated on the ITS-90, of course, they may be calibrated in the same manner as is used for SPRT’s. A better method of calibrating IPRT’s, however, is to obtain resistance-temperature data by comparison with a calibrated SPRT at numerous temperatures the range of interest and then fit a p o l y n o m i a l i n t 9o t o R ( t 90) / R ( 0 ˚ C ) , o r t o R ( t 90) / R ( 0 . 0 l ˚ C ) d a t a b y a least squares technique. 4.7 THERMISTOR THERMOMETERS.
THERMOMETERS,
DIGITAL
THERMOMETERS,
AND
OTHER
TYPES
OF
Thermistor thermometers, digital thermometers (with resistance, thermocouple, or diode sensors), and other types of thermometers are calibrated at NIST by comparison with SPRT’s in liquid baths. The calibration procedures followed are similar to those used with liquid-in-glass thermometers. The uncertainties of calibration range from as small as ± 2 mk for thermistor thermometers to tenths
Z-182
Guidelines for Realizing the ITS-90 Cont’d
of kelvins for the others. The temperatures of calibration for these types ofthermometers usually lie somewhere within the range from about 77 K to 850 K Bead-in-glass probe type thermistors used in the moderate temperature range are quite stable and they may be used to approximate the ITS-90 at a level of about ± 1 . 5mK to ± 2.0 mK [67] . In their case , a polynomial, the degree of which depends on the temperature range of the calibration, is fitted to resistancetemperature data and the results reported in terms of that polynomial. A calibration on the IPTS-68 (75) may be converted to an approximate ITS-90 calibration by the same procedure as outlined for RIRT’s . 4.8 THE LOGO OF THE NATIONAL CONFERENCE OF STANDARDS LABORATORIES FOR THE ITS-90 The National Conference of Standards Laboratories (NCSL) formed an Ad Hoc Committee on the Change of the Temperature Scale at the beginning of l988 in order to publicize the new temperature scale (ITS-90) and to facilitate its implementation. At the NCSL meeting in July 1989, the Ad Hoc Committee adopted a logo available from the NCSL [1800 30th Street, Suite 305B , Boulder, CO 80301, Tel. (303) 440-3339 ] , that may be affixed to thermometers that have been calibrated on the ITS-90. The purpose of the logo, illustrated in figure 26, is to indicate at a glance, without having to refer to documentation, those thermometers in a laboratory that have been calibrated on the new scale. This is particularly useful for those laboratories that have their various thermometers calibrated on a prescribed schedule, with different thermometers being
5. REFERENCES [1] Ancsin, J., Vapour Pressures and Triple Point of Neon and the Influence of Impurities on these Properties, Metrologia 14, 1-7 (1978) [2] Ancsin, J., Thermometric Fixed Points of Hydrogen, Metrologia 13, 79-86 (1977) [3] Ancsin, J., A Study of the Realization of the Melting and Freezing Points of silver, Metrologia 26, 167-174 (1989). [4] Ancsin, J., Melting Curves and Heat of Fusion of Indium , Metrologia 21, 7-9 (19 85). [5] Barber, C. R., Handley, R. and Herington, E . F. G. The Preparation and Use of Cells for the Realization of the Triple Point of Water , Brit. J. Appl Phys. .2, 41-44 (1954). [6] Barber, C. R. , A Proposal for a Practical Scale of Temperature Below 20 K, Temperature, . Its Measurement and Control in Science and Industry, Edited by H. H. Plumb, Vol. 4, Part 1, pp. 99-103 (Instrument Society of America, Pittsburgh, 1972). [7] Barrick, P. L., Brown, L. F., Hutchinson, H. L., and Cruse, R. L.,Improved Ferric Oxide Gel Catalysts for Ortho-Parahydrogen Conversion, Edited by K. D. Timmerhaus, Vol. 10, paper D-1, 131-189 (Plenum Press, New York, NY, 1965). [8] Bauer, G., and Bischoff, K., Evaluation of the Emissivity of a Cavity Source by Reflection Measurements, Applied Optics 10, 2639-2643 (1971). [9] Bedford, R.E. , Effective Emissivities of Blackbod Cavities – A Review, Temperature, Its Measurement and Control in Science and Industry, Edited by H. H. Plumb, Vol. 4, Part 1, pp. 425-434 (Instrument Society of America, Pittsburgh, PA, 1972). [10] Bedford , R. E . and Ma, C. K., Emissivities of Diffuse Cavities, II: Isothermal and Nonisothermal Cylindro-cones, J. Opt. Soc. Am. 65, 565-572 (1974). [11] Bedford , R. E. and Ma, C. K., Emissivities of Diffuse Cavities: Isothermal and Nonisothermal Cones and Cylinders, J. Opt. Soc. Am. 64, 339-349 (1974). [12] Belecki, N. B., Dziuba R. F., Field, B.F., and Taylor, B. N., Guidelines for Implementing the New Representations of the Volt and Ohm Effective January 1, 1990, NIST Technical Note 1263 (June 1989). [13] Berry , K. H. NPL- 75: A Low Temperature Gas Thermometry Scale from 2. 6 K to 27 . 1 K, Metrologia 15 89 -115 (1979). [14] BIPM Com. Cons. Thermometrie, 17, 1989, in press. [15] Bongiovanni, G., Crovini, L. and Marcarino P., Effects of Dissolved Oxygen and Freezing Techniques on the Silver Point, Metrologia 11, 125-132 (1975). [16] Bonhoure, J. and Pello, R., Temperature du Point Triple du Gallium, Metrologia 19 15-20 (1983). [17] Bonhoure, J. and Pello, R. , Points Triples de l’Argon et du Methane: Utilisation de Cellules Scellees, Metrologia 16 95-99 (1980). [18] Bonhoure, J. and Pello, R., Temperature of the Triple Point of Methane, Metrologia 14 1 75-177 (1978).
Figure 26. The NCSL ITS-90 logo.
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[29] Comptes Rendus des Seances de la Dix-huitieme Conference Generale des Poids et Mesures, Resolution 7, p. 101 (1987). [30] Comptes Rendus des Seances de la Dixieme Conference Generale des Poids et Mesures, Resolution 3, p. 79 (1954). [31) Compton,J. P., The Realization of Low Temperature Fixed Points, Temperature, Its Measurement And Control in Science and Industry, Edited by H. H. Plumb, Vol. 4, Part 1, pp. 195-209 (Instrument Society of America, Pittsburgh, PA, 1972). [32] Compton,J. P. and Ward,S. D., Realization of the Boiling and Triple of Oxygen, Metrologia 12, 101-113 (1976).
Points
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Guidelines for Realizing the ITS-90 Cont’d
[80] Pavese.F., The Triple Points of Argon and Oxygen, Metrologia 14, 93-103, (1978).
[95] Sparrow, E. M., Albers, L. U., and Eckert, E. R. G., Thermal Radiation Characteristics of Cylindrical Enclosures, J. Heat Transfer 04, 73-81 (1962).
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[82] Powell, R. L., Hall, W. J., Hyink, H. Jr., Sparks, L. L., Burn., G. W., Scroger M. G., and Plumb, H. H., Thermocouple Reference Tables Based on the IPTS-68, NBS Monograph 125 (March 1974).
[97] Streett, W. B. and D. H. Jones, Liquid Phase Separation and Liquid-vapor Equilibrium in the System Neon-Hydrogen, J. Chem. Phys. 42, 3989-3994 (1965).
[83] Preston-Thomas, H., The International Temperature Scale of 1990 (ITS-90), Metrologia 27, 3-10 (1990).
[98] Takiya, M., Precise Measurement of the Freezing Point of Silver with a Platinum Resistance Thermometer, Comitee Consultatif de Thermometrie. 12th Session, Annexe T30, T154-T159 (1978).
[84] Proces-Verbaux des Seances du Comite International des Poid. et Mesures, (78• session, octobre 1989), in press.
[99] The 1976 Provisional 0.5.K to 30 K Temperature Scale, Metrologia 15, 65-68 (1979).
[85] Quinn, T. J., News from the BIPM, Metrologia 26, 69-74 (1989). [86] Quinn, T. J. and Chandler, T. R. D., The Freezing Point of Platinum Determined by the NPL Photoelectric Pyrometer, Temperature, Its Measurement and Control in Science and Industry. Edited by H. H . Plumb, Vol. 4, Part 1, pp. 295- 309 (Instrument Society of America, Pittsburgh, PA, 1972). 1871 Quinn, T. J., Temperature (Academic Press, Inc., New York, N. Y. (1983). [88] Ricci, J. E., The Phase Rule and Heterogeneous Equilibrium, (Dover Publications, Inc., New York, NY, 1966). [89] Righini, F., Rosso, A., and Ruffino, G., Temperature Dependence of Effective Wavelength in Optical Pyrometry, Temperature. Its, Measurement and Control in Science and Industry, Edited by H. H. Plumb, Vol. 4, Part 1, pp. 413421 (Instrument Society of America, Pittsburgh, PA, 1972). [90] Roberts, T. R., Sherman, R. H., and Sydoriak, S. G., The 1962 The Scale of Temperatures III. Evaluation and Status, J. Res. Natl. Bur. Stands. 68A, 567-578 (1964).
[100] The International Practical Temperature Scale of 1968, Metrologia 5, 35-44(1969). [101] The International Practical Temperature Scale of 1968, Amended Edition of1975, Metrologia 12, 7-17 (1976) [102] Weber,S. and Schmidt,G., Experimentelle Untersuchungen Ober Thermomolekulare Druckdifferenz in der Nahe der Grenzbedingung Pl/P2 = (T1/T2)1/2 und Vergleichung nit der Theorie, Leiden Communication 246C, 1-13 (1936).
die
[103] Weeks. J. R., Liquidus Curves and Corrosion of Fe, Cr , Ni, Co, V, Cb, Ta, Ti, Zr, in 500-750 ˚C Mercury, Corrosion 23, 98-106 (1967). [104] Weitzel, D. H. and Park, 0. E., Iron Catalyst for Production of Liquid para-Hydrogen, Rev. Sci. Instr. 27,57-58 (1956). [105] Wise, Jacquelyn, Liquid-In-Glass Thermometer Calibration Service, NIST Special Publication 250-23 (September 1988).
[91] Rusby, R. L. and Swenson, C. A., A New Determination of the Helium Vapour Pressure Scales Using a CMN Magnetic Thermometer and the NPL-75 Gas Thermometer Scale, Metrologia-16, 73-87 (1980). [92] Sawada, S., Realization of the triple point of Indium in a sealed glass cell, Temperature Its Measurement and Control in Science and Industry, Edited by J. F. Schooley, Vol. 5, Part 1, pp. 343-346 (American Institute of Physics, New York 1982). [93] . Simon,M ., On the Phase Separation in the Liquid System Ne-pH2, Phys. Letters, 5, 319 (1963). [94] Sostman, H. E., Melting point of gallium as a temperature calibration standard, Rev. Sci. Instrum . 41, 127-130 (1977).
Reproduced with permission of National Institute of Standards and Technology
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The International Temperature Scale of 1990 metrologia ©Springer-Verlag 1990
This copy incorporates textual corrections detailed in Metrologia 27, 107 (1990)
The International Temperature Scale of 1990 (ITS-90) H. Preston-Thomas
Introductory Note
President of the Comité Consultatif de Thermométrie and Vice-President of the Comité International des Poids et Mesures Division of Physics, National Research Council of Canada, Ottawa, K1A OS1 Canada Received: October 24, 1989
The official French text of the ITS-90 is published by the BIPM as part of the Prochès-verbaux of the Comité International des Poids et Mesures (CIPM). However, the English version of the text reproduced here has been authorized by the Comité Consultatif de Thermométrie (CCT) and approved by the CIPM.
The International Temperature Scale of 1990
2. Principles of the International Temperature Scale of 1990 (ITS-90)
The International Temperature Scale of 1990 was adopted by the International Committee of Weights and Measures at its meeting in 1989, in accordance with the request embodied in Resolution 7 of the 18th General Conference of Weights and Measures of 1987. This scale supersedes the International Practical Temperature Scale of 1968 (amended edition of 1975) and the 1976 Provisional 0.5 K to 30 K Temperature Scale.
The ITS-90 extends upwards from 0.65 K to the highest temperature practicably measurable in terms of the Planck radiation law using monochromatic radiation. The ITS-90 comprises a number of ranges and sub-ranges throughout each of which temperatures T90 are defined. Several of these ranges or sub-ranges overlap, and where such overlapping occurs, differing definitions of T90 exist: these differing definitions have equal status. For measurements of the very highest precision there may be detectable numerical differences between measurements made at the same temperature but in accordance with differing definitions. Similarly, even using one definition, at a temperature between defining fixed points two acceptable interpolating instruments (e.g. resistance thermometers) may give detectably differing numerical values of T90. In virtually all cases these differences are of negligible practical importance and are at the minimum level consistent with a scale of no more than reasonable complexity; for further information on this point see “Supplementary information for the ITS-90” (BIPM-1990). The ITS-90 has been constructed in such a way that, throughout its range, for any given temperature the numerical value of T90 is a close approximation to the numerical value of T according to best estimates at the time the scale was adopted. By comparison with direct measurements of thermodynamic temperatures, measurements of T90 are more easily made, are more precise and are highly reproducible. There are significant numerical differences between the values of T90 and the corresponding values of T90 measured on the International Practical Temperature Scale of 1968 (IPTS-68), see Fig. 1 and Table 6. Similarly there were differences between the IPTS-68 and the International Practical Temperature Scale of 1948 (IPTS-48), and between the International Temperature Scale of 1948 (ITS-48) and the International Temperature Scale of 1927 (ITS-27). See the Appendix, and, for more detailed information, “Supplementary Information for the ITS-90”.
1. Units of Temperature The unit of the fundamental physical quantity known as thermodynamic temperature, symbol T, is th kelvin symbol K, defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water 1. Because of the way earlier temperature scales were defined, it remains common practice to express a temperature in terms of its difference from 273.15 K, the ice point. A thermodynamic temperature, T, expressed in this way is known as a Celsius temperature, symbol t, defined by: t / °C=T/K —273.15 . (1) The unit of Celsius temperature is the degree Celsius, symbol °C, which is by definition equal in magnitude to the kelvin. A difference of temperature may be expressed in kelvins or degrees Celsius. The International Temperature Scale of 1990 (ITS-90) defines both International Kelvin Temperatures, symbol T90, and International Celsius Temperatures, symbol t 90. The relation between T90 and t 90 is the same as that between T and t, i.e.: t 90 /°C = T90 /K —273.15 . (2) The unit of the physical quantity T90 is the kelvin, symbol K, and the unit of the physical quantity t90 is the degree Celsius, symbol °C, as is the case for the thermodynamic temperature T and the Celsius temperature t. 1 Comptes Rendux des Séances de la Treizième Conférence Générale des Poids et Mesures (1967-1968). Resolutions 3 and 4, p. 104 Reprinted with permission of Bureau International des Poids et Mesures.
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The International Temperature Scale of 1990 Cont’d
Temperature difference (t 90-t 68)/°C
0.02 0
0.4
-0.02 -0.04
0.2 -200
0
200
400 0
0 0
-0.2
100
-0.01
-0.2
-0.02
-200
0
200
400
600
800
1000
t 90/°C FIG. 1. The differences (t 90 — t 68) as a function of Celsius temperatue t 90
3. Definition of the International Temperature Scale of 1990
3.1. From 0.65 K: Helium Vapour-Pressure Temperature Equations In this range T90 is defined in terms of the vapour pressure p of 3He and 4He using equations of the form:
Between 0.65 K and 5.0 K T90 is defined in terms of the vapour-pressure temperature relations 3He and 4He. 9 Between 3.0 K and the triple point of neon (24.5561 K) T90 /K = A0 + ∑ Ai [(ln (p /Pa) — B )/C ) i . (3) i=1 T90 is defined by means of a helium gas thermometer calibrated at three experimentally realizable temperatures The values of the constants A0, Ai, B and C are given having assigned numerical values (defining fixed points) in Table 3 for 3He in the range of 0.65 K to 3.2 K, and and using specified interpolation procedures. for 4He in the ranges 1.25 K to 2.1768 K (the l point) Between the triple point of equilibrium hydrogen and 2.1768 K to 5.0 K. (13.8033 K) and the freezing point of silver (961.78 °C) 3.2 From 3.0 K to the Triple Point of Neon (24.5561 K): T90 is defined by means of platinum resistance Gas Thermometer thermometers calibrated at specified sets of defining fixed points and using specified interpolation In this range T90 is defined in terms of a 3He or a 4He procedures. gas thermometer of the constant-volume type that has been calibrated at three temperatures. These are the Above the freezing point of silver (961.78°C) T90 is triple point of neon (24.5561 K), the triple point of defined in terms of a defining fixed point and the equilibrium hydrogen (13.8033 K), and a temperature Planck radiation law. is between 3.0 K and 5.0 K. This last temperature is The defining fixed points of the ITS-90 are listed in determined using a 3He or a 4He vapour pressure Table 1. The effects of pressure, arising from thermometer as specified in Sect. 3.1. significant depths of immersion of the sensor or from other causes, on the temperature of most of these points are given in Table 2. Z- 187
Table 1. Defining fixed points of the ITS-90 Number Temperature —————————— T90 /K t 90 /°C 1
He 0,65 K to 3,2 K 3
2 3
— 270.15 to — 268.15 13.8033 — 259.3467 ≈ 17 ≈ — 256.15
4
≈ 20.3
5 6 7 8
24.5561 — 248.5939 54.3584 — 218.7916 83.8058 — 189.3442 234.3156 — 38.8344
e-H2 e-H2 (or He) e-H2 (or He) Ne O2 Ar Hg
273.16 302.9146 429.7485 505.078
H2O Ga In Sn
T M F F
1.000 000 00 1.118 138 89 1.609 801 85 1.892 797 68
Zn Al Ag Au Cu
F F F F F
2.568 917 30 3.376 008 60 4.286 420 53
9 10 11 12 13 14 15 16 17
3 to 5
Table 3. Values of the constants for the helium vapour pressure Eqs. (3), and the temperature range for which each equation, identified by its set of constants, is valid
Sub- Stateb Wr(T90) stancea
≈ — 252.85
692.677 933.473 1234.93 1337.33 1357.77
0.01 29.7646 156.5985 231.928 419.527 660.323 961.78 1064.18 1084.62
He
V T V (or G) V (or G) T T T T
0.0001 190 07
0.008 449 74 0.091 718 04 0.215 859 75 0.844 142 11
All substances except 3He are of natural isotopic composition. e-H2 is hydrogen at the equilibrium concentration of the ortho- and paramolecular forms b For complete definitions and advice on the realization of these various states, see “Supplementary Information for the ITS-90”. The symbols have the following meanings: V: vapour pressure point; T: triple point (temperature at which the solid liquid and vapour phases are in equilibrium); G: gas thermometer point; M, F: melting point, freezing point (temperature, at a pressure of 101 325 Pa, at which the solid and liquid phases are in equilibrium) a
Table 2. Effect of pressure on the temperatures of some defining fixed points ‡ Substance
e-Hydrogen (T) Neon (T) Oxygen (T) Argon (T) Mercury (T) Water (T) Gallium Indium
Assignment value of equilibrium temperature T90 /K
Temperature with pressure, p (dT/dp)/ (10 -8 K · Pa -1)*
13.8033 24.5561 54.3584 83.8058
34 16 12 25
234.3156 273.16 302.9146 429.7485
5.4 — 7.5 — 2.0 4.9
Variation with depth, l (dT/dl)/ (10-3 K · m-1)** 0.25 1.9 1.5 3.3 7.1 — 0.73 — 1.2 3.3
Tin Zinc Aluminium Silver
505.078 692.677 933.473 1234.93
3.3 4.3 7.0 6.0
2.2 2.7 1.6 5.4
Gold Copper
1337.33 1357.77
6.1 3.3
10 2.6
* Equivalent to millikelvins per standard atmosphere ** Equivalent to millikelvins per metre of liquid ‡ The Reference pressure for melting and freezing points is the standard atmosphere (p0=101 325 Pa). For triple points (T) the pressure effect is a consequence only of the hydrostatic head of liquid in the cell
He 1,25 K to 2,1768 K
4
He 2,1768 K to 5,0 K
4
A0 A1 A2 A3 A4 A5
1.053 447 0.980 106 0.676 380 0.372 692 0.151 656 — 0.002 263
1.392 408 0.527 153 0.166 756 0.050 988 0.026 514 0.001 975
3.146 631 1.357 655 0.413 923 0.091 159 0.016 349 0.001 826
A6 A7 A8
0.006 596 0.088 966 — 0.004 770
— 0.017 976 0.005 409 0.013 259
— 0.00 4325 — 0.00 4973 0
A9 B C
— 0.054 943 7.3 4.3
0 5.6 2.9
0 10.3 1.9
3.2.1. From 4.2 K to the Triple Point of Neon (24.5561 K) with 4He as the Thermometric Gas. In this range T90 is defined by the relation: T90 = a + bp + cp 2 , (4) where p is the pressure in the gas thermometer and a, b and c are coefficients the numerical values of which are obtained from measurements made at the three defining fixed points given in Sect. 3.2. but with the further restriction that the lowest one of these points lies between 4.2 K and 5.0 K. 3.2.2. From 3.0 K to the Triple Point of Neon (24.5561 K) with 3He or 4He as the Thermometric Gas. For a 3He gas thermometer, and for a 4He gas thermometer used below 4.2 K, the non-ideality of the gas must be accounted for explicitly, using the appropriate second virial coefficient B3 (T90) or B4 (T90). In this range T90 is defined by the relation: a + bp + cp 2 T90 = ————————— , (5) 1 + BX (T90) N /V where p is the pressure in the gas thermometer, a, b and c are coefficients the numerical values of which are obtained from measurements at three defining temperatures as given in Sect. 3.2, N /V is the gas density with N being the quantity of gas and V the volume of the bulb, X is 3 or 4 according to the isotope used, and the values of the second virial coefficients are given by the relations: For 3He, B (T90)/m3 mol — 1 = {16.69 — 336.98 (T90 /K) — 1 (6a) + 91.04 (T90 /K) — 2 — 13.82 (T90 /K) — 3} 10 — 6 . For 4He, B4 (T90)/m3 mol-1 = {16.708 — 374.05 (T90 /K) — 1 (6b) — 383.53 (T90 /K) — 2 + 1799.2 (T90 /K) — 3 — 4033.2 (T90 /K) — 4 + 3252.8 (T90 /K) — 3} 10 — 6 .
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The International Temperature Scale of 1990 Cont’d
Table 4. The constants A 0, A i; B o, B i; C 0, C i; D 0 and D i in the reference functions of equations (9a); (9b); (10a); and (10b), respectively A0 — 2.135 347 29 A1 3.183 247 20 A2 — 1.801 435 97 A3 0.717 272 04
B0 B1 B2 B3
A4 0.503 440 27 A5 — 0.618 993 95 A6 — 0.053 323 22 A7 0.280 213 62
B4 0.142 648 498 B5 0.077 993 465 B6 0.012 475 611 B7 — 0.032 267 127
A8 0.107 152 24 A9 — 0.293 028 65 A10 0.044 598 72 A11 0.118 686 32 A12 — 0.052 481 34
B8 B9 B10 B11 B12
C0 2.781 572 54 C1 1.646 509 16 C2 — 0.137 143 90 C3 — 0.006 497 67
D0 439.932 854 D1 472.418 020 D2 37.684 494 D3 7.472 018
C4 — 0.002 344 44 C5 0.005 118 68 C6 0.001 879 82 C7 — 0.002 044 72
D4 2.920 828 D5 0.005 184 D6 — 0.963 864 D7 — 0.188 732
C8 — 0.000 461 22 D8 C9 0.000 457 24 D9
0.183 324 722 0.240 975 303 0.209 108 771 0.190 439 972
B13 — 0.091 173 542 B14 0.001 317 696 B15 0.026 025 526
— 0.075 291 522 — 0.056 470 670 0.076 201 285 — 0.123 893 204 — 0.029 201 193
0.191 203 0.049 025
Temperatures are determined in terms of the ratio of the resistance R (T90) at a temperature T90 and the resistance R (273.16 K) at the triple point of water. This ratio, W (T90), is 2: W (T90) = R (T90)/R (273.16 K) . (7) An acceptable platinum resistance thermometer must be made from pure, strain-free platinum, and it must satisfy at least one of the following two relations: W (29.7646 °C) ≥ 1.118 07 , (8a) W (— 38.8344 °C) ≥ 0.844 235 . (8b) An acceptable platinum resistance thermometer that is to be used up to the freezing point of silver must also satisfy the relation: W (961.78 °C) ≥ 4.2844 . (8c) In each of the resistance thermometer ranges, T90 is obtained from W (T90) as given by the appropriate reference function {Eqs. (9b) or (10b)}, and the deviation W (T90) — Wr (T90). At the defining fixed points this deviation is obtained directly from the calibration of the thermometer: at intermediate temperatures it is obtained by means of the appropriate deviation function {Eqs. (12), (13) and (14)}. (i) — For the range 13.8033 K to 273.16 K the following reference function is defined: 12 In (T90)/273.16 K) + 1,5 i In [Wr (T90)] = A0 + ∑ A i —————————— .(9a) i=1 1,5 An inverse function, equivalent to Eq. (9a) to within 0,1 mK, is: 15 i Wr (T90)1/6 — 0.65 T90 /273.16 K = B 0 + ∑ B i ———————— .(9b) i=1 0.35 The values of the constants A0, A i, B 0 and B i are given in Table 4. A thermometer may be calibrated for use throughout this range or, using progressively fewer calibration points, for ranges with low temperature limits of 24.5561 K, 54.3584 K and 83.8058 K, all having an upper limit of 273.16 K. (ii) — For the range 0 °C to 961.78 °C the following reference function is defined: 9 T90 /K — 754.15 i Wr (T90 ) = C 0 + ∑ C i ——————— . (10a) i=1 481 An inverse function, equivalent to equation (10a) to within 0,13 mK is: 9 Wr (T90) — 2.64 i T90 /K — 273.15 = D 0 + ∑ D i ——————— .(10b) i=1 1.64 The values of the constants C 0, C i, D 0 and D i are given in Table 4. —————
[
The accuracy with which T90 can be realized using Eqs. (4) and (5) depends on the design of the gas thermometer and the gas density used. Design criteria and current good practice required to achieve a selected accuracy are given in “Supplementary Information for the ITS-90”. 3.3. The Triple Point of Equilibrium Hydrogen (13.8033 K) to the Freezing Point of Silver (961.78 °C): Platinum Resistance Thermometer In this range T90 is defined by means of a platinum resistance thermometer calibrated at specified sets of defining fixed points, and using specified reference and deviation functions for interpolation at intervening temperatures. No single platinum resistance thermometer can provide high accuracy, or is even likely to be usable, over all of the temperature range 13.8033 K to 961.78 °C. The choice of temperature range, or ranges, from among those listed below for which a particular thermometer can be used is normally limited by its construction. For practical details and current good practice, in particular concerning types of thermometer available, their acceptable operating ranges, probable accuracies, permissible leakage resistance, resistance values, and thermal treatment, see “Supplementary Information for ITS-90”. It is particularly important to take account of the appropriate heat treatments that should be followed each time a platinum resistance thermometer is subjected to a temperature above about 420°C.
]
[
]
[
]
[
]
2 Note that this definition of W (T90) differs from the corresponding definition used in the ITS-27, ITS-48, IPTS-48, and IPTS-68: for all of these earlier scales W (T) was defined in terms of reference temperature of 0°C, which since 1954 has itself been defined as 273.15 K
Z- 189
A thermometer may be calibrated for use throughout this range or, using fewer calibration points, for ranges with upper limits of 660.323 °C, 419.527 °C, 231.928 °C, 156.5985 °C or 29.7646 °C, all having a lower limit of 0°C. (iii) — A thermometer may be calibrated for use in the range 234.3156 K ( — 38.8344 °C) to 29.7646 °C, the calibration being made at these temperatures and at the triple point of water. Both reference functions {Eqs. (9) and (10)} are required to cover this range. The defining fixed points and deviation functions for the various ranges are given below, and in summary from in Table 5. 3.3.1. The Triple Point of Equilibrium Hydrogen (13.8033 K) to the Triple Point of Water (273.16 K). The thermometer is calibrated at the triple points of equilibrium hydrogen (13.8033 K), neon (24.5561 K), oxygen (54.3584 K), argon (83.8058 K), mercury (234.3156 K), and water (273.16 K), and at two additional temperatures close to 17.0 K and 20.3 K. These last two may be determined either: by using a gas thermometer as described in Sect. 3.2, in which case the two temperatures must lie within the ranges 16.9 K to 17.1 K and 20.2 K to 20.4 K respectively; or by using the vapour pressure-temperature relation of equilibrium hydrogen, in which case the tow temperatures must lie within the ranges 17.025 K to 17.045 K and 20.26 K to 20.28 K respectively, with the precise values being determined from Eqs. (11a) and (11b) respectively: T90/K — 17.035 = (p/kPa — 33.3213)/13.32 (11a) T90/K — 20.27 = (p/kPa — 101.292)/30 . (11b) The deviation function is 3: W (T90) — Wr (T90) = a [W (T90)—1] + b [W (T90)—1] 2 5
+ ∑ c i [ln W (T90)]
i+n
(12)
i=1
with values for the coefficients a, b and ci being obtained from measurements at the defining fixed points and with n = 2. For this range and for the sub-ranges 3.3.1.1 to 3.3.1.3 the required values Wr (T90) are obtained from Eq. (9a) or from Table 1. 3.3.1.1. The Triple Point of Neon (24.5561 K) to the Triple Point of Water (273.16 K). The thermometer is calibrated at the triple points of equilibrium hydrogen (13.8033 K), neon (24.5561 K), oxygen (54.3584 K), argon (83.8058 K), mercury (234.3156 K) and water (273.16 K). The deviation function is given by Eq. (12) with values for the coefficients a, b, c1, c2 and c3 being obtained from measurements at the defining fixed points and with c4 = c5 = n = 0. 3.3.1.2 The Triple Point of Oxygen (54.3584 K) to the Triple Point of Water (273.16 K). The thermometer is 3 This deviation function {and also those of Eqs. (13) and (14)} may be expressed in terms of Wr rather than W; for this procedure see “Supplementary Information for ITS-90”
Table 5. Deviation functions and calibration points for platinum resistance thermometers in the various ranges in which they define T90 a Ranges with an upper limit of 273,16 K Section
Lower temperature limit T /K
3.3.1
13.8033
Deviation functions
Calibration points (see Table 1)
a [W (T90) — 1]+b [W (T90) — 1] 2 2-9 5
+ ∑ ci [ln W (T90)] i + n, n = 2 i=1
3.3.1.1 3.3.1.2
24.5561 54.3584
As for 3.3.1 with c4 = c5 = n = 0 As for 3.3.1 with c2 = c3 =c4 = c5 = 0, n = 1
2, 5-9 6-9
3.3.1.3
83.8058
a [W (T90) — 1] +b [W (T90) — 1] ln W (T90)
7-9
b Ranges with a lower limit of 0°C Section
Upper temperature limit t /°C
3.3.2* 961.78
3.3.2.1 3.3.2.2 3.3.2.3 3.3.2.4 3.3.2.5
660.323 419.527 231.928 156.5982 29.7646
Deviation functions
Calibration points (see Table 1)
a [W (T90) — 1]+b [W (T90) — 1] 2 + c [W (T90) — 1] 3, + d [W (T90) — W (660.323 °C)]2 As for 3.3.2 with d = 0 As for 3.3.2 with c = d = 0 As for 3.3.2 with c = d = 0 As for 3.3.2 with b = c = d = 0 As for 3.3.2 with b = c = d = 0
9, 12-15
9, 12 - 14 9, 12, 13 9, 11, 12 9, 11 9, 10
c Range from 234.3156 K ( — 38.8344 °C) to 29.7646°C 3.3.3
As for 3.3.2 with c = d = 0
8-10
* Calibration points 9, 12-14 are used with d = 0 for t 90 ≤ 660.323 °C; the values of a, b and c thus obtained are retained for t 90 > 660.323 °C with d being determined from calibration point 15
calibrated at the triple points of oxygen (54.3584 K), argon (83.8058 K), mercury (234.3156 K) and water (273.16 K). The deviation function is given by Eq. (12) with values for the coefficients a, b and c 1 being obtained from measurements at the defining fixed points, with c2 = c3 = c4 = c 5 = 0 and with n = 1. 3.3.1.3. The Triple Point of Argon (83.8058 K) to the Triple Point of Water (273.16 K). The thermometer is calibrated at the triple points of argon (83.8058 K), mercury (234.3156 K) and water (273.16 K). The deviation function is: W (T90) — Wr (T90) = a [W (T90)—1] + b [W (T90)—1] In W (T90) (13) with the values of a and b being obtained from measurements at the defining fixed points. 3.3.2. From 0 °C to the Freezing Point of Silver (961.78 °C). The thermometer is calibrated at the triple Z- 190
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The International Temperature Scale of 1990 Cont’d
point of water (0.01 °C), and at the freezing points of tin (231.928 °C), zinc (419.527 °C), aluminium (660.323 °C) and silver (961.78 °C). The deviation function is: W (T90) — Wr (T90) = a [W (T90)—1] + b [W (T90)—1] 2(14) + c [W (T90)—1] 3 + d [W (T90)—W (660.323 °C)] 2 . For temperatures below the freezing point of aluminium d = 0, with the values of a, b and c being determined from the measured deviations from Wr (T90) at the freezing points of tin, zinc and aluminium. From the freezing point of aluminium to the freezing point of silver the above values of a, b and c are retained and the value of d is determined from the measured deviation from Wr (T90) at the freezing point of silver. For this range and for the sub-ranges 3.3.2.1 to 3.3.2.5 the required values for Wr (T90) are obtained from Eq. (10a) or from Table 1. 3.3.2.1. From 0 °C to the Freezing Point of Aluminium (660.323 °C). The thermometer is calibrated at the triple point of water (0.01 °C), and at the freezing points of tin (231.928 °C), zinc (419.527 °C) and aluminium (660.323 °C). The deviation function is given by Eq. (14), with the values of a, b and c being determined from measurements at the defining fixed points and with d = 0. 3.3.2.2. From 0 °C to the Freezing Point of Zinc (419.527 °C). The thermometer is calibrated at the triple point of water (0.0 °C), and at the freezing points of tin (231.928 °C) and zinc (419.527 °C). The deviation function is given by Eq. (14), with the values of a and b being obtained from measurements at the defining fixed points and with c = d = 0. 3.3.2.3. From 0 °C to the Freezing Point of Tin (231.928 °C). The thermometer is calibrated at the triple point of water (0.01 °C), and at the freezing points of indium (156.5985 °C) and tin (231.928 °C). The deviation function is given by Eq. (14), with the values of a and b being obtained from measurements at the defining fixed points and with c = d = 0. 3.3.2.4.From 0 °C to the Freezing Point of Indium (156.5985 °C). The thermometer is calibrated at the triple point of water (0.01 °C), and at the freezing point of indium (156.5985 °C). The deviation function is given by Eq. (14) with the value of a being obtained from measurements at the defining fixed points and with b = c = d = 0. 3.3.2.5. From 0 °C to the Melting Point of Gallium (29.7646 °C). The thermometer is calibrated at the triple point of water (0.01 °C), and the melting point of gallium (29.7646 °C). The deviation function is given by Eq. (14) with the value of a being obtained from measurements at the defining fixed points and with b = c = d = 0.
3.3.3. The Triple Point of Mercury (—38.8344 °C) to the Melting Point of Gallium (29.7646 °C). The thermometer is calibrated at the triple points of mercury (— 38.8344 °C), and water (0.01 °C), and at the melting point of gallium (29.7646 °C). The deviation function is given by Eq. (14) with the values of a and b being obtained from measurements at the defining fixed points and with c = d = 0. The required values of Wr (T90) are obtained from Eqs. (9a) and (10a) for measurements below and above 273.16 K respectively, or from Table 1. 3.4. The Range Above the Freezing Point of Silver (961.78 °C): Planck Radiation Law Above the freezing point of silver the temperature T90 is defined by the equation: Ll(T90) exp (c 2 [lT90(X)] —1)—1 —————— = ——————————— . (15) Ll [(T90 (X)] exp (c 2 [lT90] —1)—1 where T90 (X) refers to any one of the silver {T90 (Ag) = 1234.93 K}, the gold {T90 (Au) = 1337.33 K} or the copper {T90(Cu) = 1357.77 K} freezing points4 and in which Ll(T90) and Ll[T90 (X)] are the spectral concentrations of the radiance of a blackbody at the wavelength (in vacuo) l at T90 and at T90 (X) respectively, and c 2 = 0.014388 m · K. For practical details and current good practice for optical pyrometry, see “Supplementary Information for the ITS-90” (BIPM-1990). 4. Supplementary Information and Differences from Earlier Scales The apparatus, methods and procedures that will serve to realize the ITS-90 are given in “Supplementary Information for the ITS-90”. This document also gives an account of the earlier International Temperature Scales and the numerical differences between successive scales that include, where practicable, mathematical functions for differences T90 — T68. A number of useful approximations to the ITS-90 are given in “Techniques for Approximating the ITS-90”. These two documents have been prepared by the Comité Consultatif de Thermométrie and are published by the BIPM; they are revised and updated periodically. The differences T90 — T68 are shown in Fig. 1 and Table 6. The number of significant figures given in Table 6 allows smooth interpolations to be made. However, the reproducibility of the IPTS-68 is, in many areas, substantially worse than is implied by this number. 4 The T90 values of the freezing points of silver, gold and copper are believed to be self consistent to such a degree that the substitution of any one of them in place of one of the other two as the reference temperature T90 (X) will not result in significant differences in the measured values of T90.
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Table 6. Differences between ITS-90 and EPT-76, and between ITS-90 and IPTS-68 for specified values of T90 and t 90
T90 /K 0 10 20 T90 /K 10 20 30 40 50 60 70 80 90 T90/K 100 200 t 90 /°C — 100 0 t 90 /°C 0 100 200 300 400 500 600 700 800 900 1000 t 90 /°C 1000 2000 3000
(T90 — T76)/mK 4 5 — 0.1 —1.1 —1.3 — 3.2 — 3.5
6 —0.2 — 1.4 — 3.8
7 — 0.3 — 1.6 — 4.1
8 — 0.4 — 1.8
9 — 0.5 — 2.0
— 0.007 — 0.008 — 0.006 — 0.004 0.004 0.007 0.008 0.008 30 0.014 0.008
(T90 — T68)/K 4 5 — 0.006 — 0.003 — 0.006 — 0.005 — 0.008 — 0.007 — 0.006 — 0.007 — 0.003 — 0.002 0.005 0.005 0.007 0.008 0.008 0.008 0.008 0.008 40 50 0.014 0.014 0.007 0.005
6 —0.004 —0.004 —0.007 —0.007 —0.001 0.006 0.008 0.008 0.008 60 0.014 0.003
7 — 0.006 — 0.004 — 0.007 — 0.007 0.000 0.006 0.008 0.008 0.009 70 0.013 0.001
8 — 0.008 — 0.005 — 0.006 — 0.006 0.001 0.007 0.008 0.008 0.009 80 0.012
9 — 0.009 — 0.006 — 0.006 — 0.006 0.002 0.007 0.008 0.008 0.009 90 0.012
— 30 0.014 0.006 30 — 0.007 — 0.032 — 0.040 — 0.040 — 0.056 — 0.090 — 0.125* 0.31 0.25 — 0.08 — 0.22 300 — 0.35 — 0.93 — 1.78
(t 90 — t 68)/°C — 40 — 50 0.014 0.013 0.008 0.009 40 50 — 0.010 — 0.013 — 0.034 — 0.036 — 0.040 — 0.040 — 0.040 — 0.041 — 0.059 — 0.062 — 0.094 — 0.098 — 0.08 — 0.03 0.33 0.35 0.22 0.18 — 0.10 — 0.12 — 0.23 — 0.24 400 500 — 0.39 — 0.44 — 1.00 — 1.07 — 1.89 — 1.99
— 60 0.012 0.010 60 — 0.016 — 0.037 — 0.040 — 0.042 — 0.065 — 0.101 0.02 0.36 0.14 — 0.14 — 0.25 600 — 0.49 — 1.15 — 2.10
— 70 0.010 0.011 70 — 0.018 — 0.038 — 0.039 — 0.043 — 0.068 — 0.105 0.06 0.36 0.10 — 0.16 — 0.25 700 — 0.54 — 1.24 — 2.21
— 80 0.008 0.012 80 — 0.021 — 0.039 — 0.039 — 0.045 — 0.072 — 0.108 0.11 0.36 0.06 — 0.17 — 0.26 800 — 0.60 — 1.32 — 2.32
— 90 0.008 0.012 90 — 0.024 — 0.039 — 0.039 — 0.046 — 0.075 — 0.112 0.16 0.35 0.03 — 0.18 — 0.26 900 — 0.66 — 1.41 — 2.43
0
1
2
3
— 0.6 — 2.2
— 0.7 — 2.5
— 0.8 — 2.7
— 1.0 — 3.0
0
1
2
3
— 0.009 — 0.006 — 0.006 — 0.006 0.003 0.007 0.008 0.008 0 0.009 0.011
— 0.008 — 0.007 — 0.006 — 0.005 0.003 0.007 0.008 0.008 10 0.011 0.010
0 — 10 0.013 0.013 0.000 0.002 0 10 0.000 — 0.002 — 0.026 — 0.028 — 0.040 — 0.040 — 0.039 — 0.039 — 0.048 — 0.051 — 0.079 — 0.083 — 0.115 — 0.118 0.20 0.24 0.34 0.32 — 0.01 — 0.03 — 0.19 — 0.20 0 100 — 0.26 — 0.72 — 0.79 — 1.50 — 1.59
—0.007 —0.008 —0.006 —0.004 0.004 0.007 0.008 0.008 20 0.013 0.009
— 20 0.014 0.004 20 — 0.005 — 0.030 — 0.040 — 0.039 — 0.053 — 0.087 — 0.122 0.28 0.29 — 0.06 — 0.21 200 — 0.30 — 0.85 — 1.69
* A discontinuity in the first derivative of (t 90 — t 68) occurs at a temperature of t 90 = 630.6 °C, at which (t 90 — t 68) = — 0.125 °C Appendix
The International Temperature Scale of 1927 (ITS-27) The International Temperature Scale of 1927 was adopted by the seventh General Conference of Weights and Measures to overcome the practical difficulties of the direct realization of thermodynamic temperatures by gas thermometry, and as a universally acceptable replacement for the differing existing national temperature scales. The ITS-27 was formulated so as to allow measurements of temperature to be made precisely and reproducibly, with as close an approximation to thermodynamic temperatures as could be determined at that time. Between the oxygen boiling point and the gold freezing point it was based upon a number of reproducible
temperatures, or fixed points, to which numerical values were assigned, and two standard interpolating instruments. Each of these interpolating instruments was calibrated at several of the fixed points, this giving the constants for the interpolating formula in the appropriate temperature range. A platinum resistance thermometer was used for the low part and a platinum rhodium/platinum thermocouple for temperatures above 660 °C. For the region above the gold freezing point, temperatures were defined in terms of the Wien radiation law: in practice, this invariably resulted in the selection of an optical pyrometer as the realizing instrument.
The International Temperature Scale of 1948 (ITS-48) The International Temperature Scale of 1948 was adopted by
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The International Temperature Scale of 1990 Cont’d
the ninth General Conference. Changes from the ITS-27 were: the lower limit of platinum resistance thermometer range was changed from —190 °C to the defined oxygen boiling point of —182.97 °C, and the junction of the platinum resistance thermometer range and the thermocouple range became the measured antimony freezing point (about 630 °C) in place 660 °C; the silver freezing point was defined as being 960.8 °C instead of 960.5 °C; the gold freezing point replaced the gold melting point (1063 °C); the Planck radiation law replaced the Wien law; the value assigned to the second radiation constant became 1.438 x 10 —2 m · K in place of 1.432 x 10 —2 m · K; the permitted ranges for the constants of the interpolation formula for the standard resistance thermometer and thermocouple were modified; the limitation on lT for optical pyrometry (lT<3x10 —3 m · K) was changed on the requirement that “visible” radiation be used.
(27.102 K), the triple point of oxygen (54.361 K), and the freezing point of tin (231.9681 °C) which became a permitted alternative to the boiling point of water; the boiling point of sulphur was deleted; the values assigned to four fixed points were changed — the boiling point of oxygen (90.188 K), the freezing point of zinc (419.58 °C), the freezing point of silver (961.93 °C), and the freezing point of gold (1064.43 °C): the interpolating formulae for the resistance thermometer range became much more complex; the value assigned to the second radiation constant c 2 became 1.4388 x 10 —2 m · K; the permitted ranges of the constants for the interpolation formulae for the resistance thermometer and thermocouple were again modified.
The International Practical Temperature Scale of 1948 (Amended Edition of 1960) (IPTS-48)
The International Practical Temperature Scale of 1968, amended edition of 1975, was adopted by the fifteenth General Conference in 1975. As was the case for the IPTS-48 with respect to the ITS-48, the IPTS-68 (75) introduced no numerical changes. Most of the extensive textural changes were; the oxygen point was defined as the condensation point rather than the boiling point; the triple point of argon (83.798 K) was introduced as a permitted alternative to the condensation point of oxygen; new values of the isotopic composition of naturally occurring neon were adopted; the recommendation to use values of T given by the 1958 4He and 1962 3He vaporpressure scales was rescinded.
The International Practical Temperature Scale of 1948, amended edition of 1960, was adopted by the eleventh General Conference: the tenth General Conference had already adopted the triple point of water as the sole point defining the kelvin, the unit of thermodynamic temperature. In addition to the introduction of the word “Practical”, the modifications to the ITS48 were: the triple point of water, defined as being 0,01 °C, replaced the freezing point of zinc, defined as being 419.505 °C, became a preferred alternative to the sulphur boiling point (444.6 °C) as a calibration point; the permitted ranges for the constants of the interpolation formulae for the standard resistance thermometer and the thermocouple were further modified; the restriction to “visible” radiation for optical pyrometry was removed. Inasmuch as the numerical values of temperature on the IPTS-48 were the same as on the ITS-48, the former was not a revision of the scale of 1948 but merely an amended form of it.
The International Practical Temperature Scale of 1968 (IPTS-68) In 1968 the International Committee of Weights and Measures promulgated the International Practical Temperature Scale of 1968, having been empowered to do so by the thirteenth General Conference of 1967 — 1968. The IPTS-68 incorporated very extensive changes from the IPTS-48. These included numerical changes, designed to bring to more nearly in accord with thermodynamic temperatures, that were sufficiently large to be apparent to many users. Other changes were as follows: the lower limit of the scale was extended down to 13.81 K; at even lower temperatures (0.5 K to 5.2 K), the use of two helium vapour pressure scales was recommended; six new defining fixed points were introduced — the triple point of equilibrium hydrogen (13.81 K), an intermediate equilibrium hydrogen point (17.042 K), the normal boiling point of equilibrium hydrogen (20.28 K), the boiling point of neon
The International Practical Temperature Scale of 1968 (Amended Edition of 1975) (IPTS-68)
The 1976 Provisional 0,5 K to 30 K Temperature Scale (EPT-76) The 1976 Provisional 0.5 K to 30 K Temperature Scale was introduced to meet two important requirements: these were to provide means of substantially reducing the errors (with respect to corresponding thermodynamic values) below 27 K that were then known to exist in the IPTS-68 and throughout the temperature ranges of the 4He and 3He vapour pressure scales of 1958 and 1962 respectively, and to bridge the gap between 5.2 K and 13.81 K in which there had not previously been an international scale. Other objectives in devising the ETP-76 were “that it should be thermodynamically smooth, that it should be continuous with the IPTS-68 at 27.1 K, and that is should agree with thermodynamic temperature T as closely as these two conditions allow”. In contrast with the IPTS-68, and to ensure its rapid adoption, several methods of realizing the ETP-76 were approved. These included: using a thermodynamic interpolation instrument and one or more of eleven assigned reference points; taking differences from the IPTS-68 above 13.81 K; taking differences from certain wellestablished laboratory scales. Because there was a certain “lack of internal consistency” it was admitted that “slight ambiguities between realizations” might be introduced. However the advantages gained by adopting the EPT-76 as a working scale until such time as the IPTS-68 should be revised and extended were considered to outweigh the disadvantages.
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International Standards International Standards Agencies Argentina
Germany
Mexico
South Africa
Australia
Hungary
Netherlands
Spain
Austria
India
New Zealand
Sweden
Belgium
Indonesia
Norway
Switzerland
Canada
Iran
Pakistan
United Kingdom
Denmark
Ireland
Poland
Egypt
Israel
Portugal
Finland
Italy
Romania
Venezuela
France
Japan
Singapore
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1st Digit
Protection from Solid Objects
0
No Protection
1
Protected against solid objects greater than 50 mm
2
Protected against solid objects greater than 12 mm
3
Protected against solid objects greater than 2.5 mm
4
Protected against solid objects greater than 1.0 mm
5
Dust Protected
6
Dust Tight
®
International Power Plugs and Sockets Continental Europe
IP Codes (Ingress Protection) IEC 529 outlines an international classification system for the sealing effectiveness of enclosures of electrical equipment against the intrusion into the equipment of foreign bodies (i.e., tools, dust, fingers) and moisture. This classification system utilises the letters ‘IP’ (Ingress Protection) followed by two digits. An ‘X’ is used for one of the digits if there is only one class of protection; i.e., IPX4, which addressed moisture resistance only.
Europlug (ungrounded) Australia Australia (ungrounded) United Kingdom
Degrees of Protection – First Digit
India
The first digit of the IP code indicates the degree that persons are protected against contact with moving parts (other than rotating shafts, etc.) and the degree that equipment is protected against solid bodies intruding into a enclosure.
Israel
Degrees of Protection – Second Digit
Denmark France
The second digit indicates the degree of protection of the equipment inside the enclosure against the harmful entry of various forms of moisture (e.g., dripping, spraying, submersion, etc.).
Italy Japan
North America
2nd Digit
Protection from Moisture
0
No Protection
1
Protected against vertically dripping water
2
Protected against dripping water when tilted up to 15°
3
Protected against spraying water @ up to 60° from vertical
4
Protected against splashing water from all directions
5
Protected against water jets
6
Protected against heavy seas & streaming water
7
Protected against effects of short-term immersion
8
Protected against submersion
Switzerland
Reproduced with permission of Panel Components Corp.
5
IEC 906-1
18.5 19
3
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Standards NEMA, UL and CSA Ratings What’s in a rating?
NEMA, UL and CSA Ratings
As a way of standardizing enclosure performance, organizations like NEMA, UL, CSA, IEC, VDE and TUV use rating systems to identify an enclosure’s ability to resist external environmental influences. Resistance to everything from dripping liquid to hose-down to total submersion is defined by the ratings systems. While these ratings systems are all intended to provide information to help you make a safer, more informed product choice, there are differences among them.
NEMA, UL and CSA are standard-writing organizations commonly recognized in North America. Their ratings are based on similar application descriptions and expected performance. UL and CSA both require enclosure testing by qualified evaluators. They also send site inspectors to make sure a manufacturer adheres to prescribed manufacturing methods and material specifications. NEMA, on the other hand, does not require independent testing and leaves compliance completely up to the manufacturer.
North American enclosure ratings systems also include a 4X rating that indicates resistance to corrosion. This rating is based on the enclosure’s ability to withstand prolonged exposure to salt water spray. While a 4X rating is a good indicator that an enclosure can resist corrosion, it does not provide information on how a specific corrosive agent will affect a given enclosure material. It is best to conduct a full analysis of the specific application and environment to determine the best enclosure choice.
Exposure type non-hazardous location NEMA
Enclosure Rating
National Electrical Manufacturers Association (NEMA Standard 250) and Electrical and Electronic Mfg. Association of Canada (EEMAC)
Underwriters Laboratories Inc. (UL 50 and UL508) ®
Canadian Standards Association (Standard C22.2 No.94)
LISTED
Enclosures are intended for indoor use primarily to provide a degree of protection against contact with the enclosed equipment or locations where unusual service conditions do not exist
Indoor use primarily to provide protection against contact with the enclosed equipment and against a limited amount of falling dirt.
General purpose enclosure. Protects against accidental contact with live parts.
Enclosures are intended for indoor use primarily to provide a degree of protection against limited amounts of falling water and dirt.
Indoor use to provide a degree of protection against limited amounts of falling water and dirt.
Indoor use to provide a degree of protection against dripping and light splashing of non-corrosive liquids and falling dirt.
Type 3
Enclosures are intended for outdoor use primarily to provide a degree of protection against windblown dust, rain and sleet; undamaged by the formation of ice on the enclosure.
Outdoor use to provide a degree of protection against windblown dust and windblown rain; undamaged by the formation of ice on the enclosure.
Indoor or outdoor use; provides a degree of protection against rain, snow, and windblown dust; undamaged by the external formation of ice on the enclosure.
Type 3R
Enclosures are intended for outdoor use primarily to provide a degree of protection against falling rain and sleet; undamaged by the formation of ice on the enclosure.
Outdoor use to provide a degree of protection against falling rain; undamaged by the formation of ice on the enclosure.
Indoor or outdoor use; provides a degree of protection against rain and snow; undamaged by the external formation of ice on the enclosure.
Type 4
Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain. splashing water, and hosedirected water; undamaged by the formation of ice on the enclosure.
Either indoor or outdoor use to provide a degree of protection against falling rain, splashing water, and hose-directed water; undamaged by the formation of ice on the enclosure.
Indoor or outdoor use; provides a degree of protection against rain, snow, windblown dust, splashing and hose-directed water; undamaged by the external formation of ice on the enclosure.
Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against corrosion,windblown dust and rain, splashing water, and hosedirected water; undamaged by the formation of ice on the enclosure.
Either indoor or outdoor use to provide a degree of protection against falling rain, splashing water, and hose-directed water; undamaged by the formation of ice on the enclosure; resists corrosion.
Indoor or outdoor use; provides a degree of protection against rain, snow, windblown dust, splashing and hose-directed water; undamaged by the external formation of ice on the enclosure; resists corrosion.
Type 6
Enclosures are intended for use indoors or outdoors where occasional submersion is encountered; limited depth; undamaged by the formation of ice on the enclosure; resists corrosion.
Indoor or outdoor use to provide a degree of protection against entry of water during temporary submersion at a limited depth; undamaged by the formation of ice on the enclosure.
Indoor or outdoor use; provides a degree of protection against the entry of water during temporary submersion.
Type 12
Enclosures are intended for indoor use primarily to provide a degree of protection against dust, falling dirt, and dripping non-corrosive liquids.
Indoor use to provide a degree of protection against dust, dirt, fiber flyings, dripping water, and external condensation of non-corrosive liquids.
Indoor use; provides a degree of protection against circulating dust, lint, fibers and flyings; dripping and light splashing of non-corrosive liquids; not provided with knockouts.
Type 13
Enclosures are intended for indoor use primarily to provide a degree of protection against dust, spraying of water, oil, and non-corrosive coolant.
Indoor use to provide a degree of protection against lint, dust seepage, external condensation and spraying of water, oil, and non-corrosive liquids.
Indoor use; provides a degree of protection against circulating dust, lint, fibers and flyings, seepage and spraying of non-corrosive liquids, including oils and coolants.
Type 1
Type 2
Type 4X
This material is reproduced with permission from NEMA. The preceding descriptions, however, are not intended to be complete representations of National Electrical Manufacturers Association standards for enclosures nor those of the Electrical and Electronic Manufacturers Association of Canada
This material is reproduced with permission from Underwriters Laboratories Inc. Enclosures for Electrical Equipment, UL 50.Copyright 1995; and Industrial Control Equipment, 508, Copyright 1996 by Underwriters Laboratories, Inc. Underwriters Laboratories Inc.(UL) shall not be responsible for the use of or reliance upon a UL Standard by anyone. UL shall not incur any obligation or liability for damages, including consequential damages, arising out of or in connection with, interpretation of, or reliance upon a UL Standard.
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This material is reproduced with permission from Canadian Standards Association.
Standards CE and IEC Classifications CE
Applicable European Directives
The CE Mark is a European Union (EU) compliance symbol and acronym for Conformité Européenne. The CE Mark indicates that a product complies with all European directives and essential Harmonized Standards for health, safety, environment, and consumer protection that may apply to that product. In addition, the CE Mark promotes free trade movement from outside and within the EU.
73/23/EEC Low Voltage Directive for Electrical Equipment within Certain Voltage Limits
For industrial control equipment, the CE Mark is not intended to be applied to empty enclosures because such enclosures are inactive components of a final assembly. The responsibility for insuring compliance to all applicable EU Directives and Harmonized Standards belongs with the final equipment manufacturer.
EN60204-1 (IEC204-1) Electrical Equipment of Industrial Machines
Hoffman enclosures are designed in compliance with European standards and are eligible to receive a Manufacturer’s Declaration of Conformity. The certificate assists the final equipment manufacturer in obtaining the CE Mark. Contact Applications Engineering at (612) 4222868 for further information. Hoffman enclosures meet the requirements of the applicable European standards specified below.
89/336/EEC EMC Directive Relating to Electromagnetic Compatibility Note: The EMC Directive is only secondarily applicable since an empty enclosure does not produce electromagnetic interference.
Applicable European Standards EN60529-1 (IEC529-1) Degrees of Protection Provided by Enclosures
International Standards’ IP Protection Classification IEC Publication 529, Classification of Degrees of Protection by Enclosures, provides a system for specifying enclosures of electrical equipment on the basis of the degree of protection required. IEC 529 does not specify degrees of protection against risk of explosions or conditions such as moisture (produced, for example, by condensation), corrosive vapors, fungus, or vermin. NEMA Standards Publication 250 does
not test for environmental conditions such as corrosion, rust, icing, oil, and coolants. For this reason, and because the tests and evaluations for other characteristics are not identical, the IEC enclosure classification designations cannot be exactly equated with NEMA enclosure Type numbers. The table on below provides a crossreference from NEMA enclosure Type numbers to IEC enclosure classification designations. This cross-reference is a Hoffman approximation based on the most current available information on enclosure test performance and is not sanctioned by NEMA, IEC, VDE, or any affiliated agency. To use the table, first find the appropriate NEMA rating along the vertical axis and then read across the horizontal axis for the corresponding IP rating. Do not use this table to convert IEC classification designations to NEMA Type numbers.
In Europe, IEC ratings are based on performance criteria similar to NEMA. Nevertheless, there are differences in how enclosure performance is interpreted. For example, UL and CSA test requirements specify that an enclosure fails the watertight test if even a single drop of water enters the enclosure. In the IEC standards for each protection level (IP), a certain amount of water is allowed to enter the enclosure. IEC does not specify degrees of protection against risk of explosions or conditions such as moisture or corrosive vapors. NEMA, on the other hand, does specify for most environmental conditions. For this reason, and because the tests and evaluations for other characteristics are not identical, the IEC enclosure classification designations cannot be exactly equated with NEMA enclosure Type numbers.
Cross Reference (Approximate) NEMA, UL, CSA, vs. IEC Enclosure Type (Cannot be used to convert IEC Classifications to NEMA Type numbers)
Enclosure Rating Type 1 Type 2 Type 3 Type 3R Type 3S Type 4 Type 4X Type 6 Type 12 Type 13
IP23
IP30
IP32
IP55
IP64
IP65
IP66
IP67
• • • • • • • • • •
IEC 529 has no equivalents to NEMA enclosure Types 7, 8, 9, 10, or 11. •Indicates compliance
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Application Notes Low Cost Non-Electronic Temperature Gages When the need arises for measuring temperatures in various industrial situations, most engineers think in terms of expensive electronic temperature measuring equipment. In many cases, though, you can do the job with less costly and much simpler methods. When the need is only for an indication that a pre-determined temperature has or has not been reached, heat-sensitive materials in the form of crayons, paints, pellets, or labels can do the job readily, inexpensively, and accurately enough for most industrial applications. WHAT ARE THESE NON-ELECTRONIC TEMPERATURE INDICATING DEVICES? These heat-sensitive, fusible materials consist of crystalline solids. When heated, a temperature will be reached in which the solids change sharply to a liquid. The melting point is reproducible and is virtually unaffected by ambient conditions that may cause errors with other temperature-sensing methods. For example, electrical means of measuring temperatures often function erratically in the presence of static electricity, electrical “noise” or ionized air near electrical equipment. ADVANTAGES OVER ELECTRONIC DEVICES This family of fusible temperature indicators has several advantages over other methods of determining surface temperature. First, the temperature indications obtained are unquestionably those of the surface being tested. The temperature sensitive material is applied directly to the surface, and therefore changes state in direct response to that surface, and only that surface. A second advantage of using fusible temperature indicators is the fact that there is no delay in obtaining a signal. Since a mark left by a crayon or a lacquer has an extremely small mass, it attains rapid equilibrium with the surface. The use of a “massive” probe tends to prolong response time and could result in an erroneously low reading. With the use of fusible temperature indicators, there is no conduction of heat away from the surface. Nor is there any dependence on the duration of heating. The third advantage of fusible indicators is that the technique for using them is simple and economical. Determining surface temperatures by most other means requires some technical competence and skill and, in many cases, sophisticated instrumentation. Surface temperature readings can be obtained from fusible indicators with little effort, training, and expense.
WHAT FORMS DO THESE TEMPERATURE INDICATORS TAKE? 1. Crayons: The most commonly used of all the fusible indicators is the temperature sensitive stick, or crayon. Each crayon has a calibrated melting point. These indicators are manufactured in 100 different temperature ratings and range from 100˚F to 2500˚F. Each has a temperature indicating accuracy within 1% of its temperature rating. Using the crayons is simple. The workpiece to be tested is marked with a crayon. When the pre-determined melting point of the crayon mark is attained, the mark instantly liquifies, notifying the observer that the workpiece has reached that temperature. However, under some circumstances, premarking with a crayon is not practical. This can be the case if a prolonged heating period is involved (the crayon mark may evaporate), if the surface is highly polished and does not readily accept a crayon mark, or if the material being marked is such that it absorbs the liquid phase of the crayon. In such instances, the operator can repeatedly stroke the workpiece with the crayon. The point at which the surface reaches the desired temperature is determined by noting when the crayon ceases to make dry marks and instead leaves a liquid smear. 2. Lacquers: Another form of heat sensitive material is a dull lacquer-type liquid that turns glossy and transparent at a predetermined temperature. This phase changing liquid is a fusible coating material that offers greater flexibility than crayons as to the types of surfaces on which it can be applied. Chemically, this lacquer-type fluid contains a solid material that has a calibrated melting point. These solids are suspended in an inert, volatile, but nonflammable vehicle. Upon reaching its rated temperature, the dull lacquer mark liquifies. On subsequent cooling, however, the fluid does not revert to its original dull appearance, but rather to a glossy or crystalline coating. This shiny state of appearance is evidence that the lacquer has reached the rated temperature. Due to their physical properties, these lacquers are often used instead of crayons on very smooth surfaces (glass, plastic film, laminated plastic), soft surfaces (paper, cloth), or on surfaces not readily accessible for application of a crayon mark during heating. Within seconds after application, the lacquer dries to a dull matte finish. Response is only a fraction of a second when the temperature to be indicated is reached. This time can be reduced to milliseconds by applying a mark of minimal thickness.
Z-197
These fluids are available in over 100 different temperature ratings, covering the range from 100˚F to 2500˚F. As with the crayon type indicators, accuracy is within ±1%. The temperature ratings available range from 100˚F to 350˚F in 6 increments, from 350˚F to 500˚F in 12 increments, from 500˚F to 750˚F in 25 increments, and from 750˚F to 2500˚F in 50 increments. The temperature-sensitive lacquers are supplied in the proper consistency for brushing. If spraying or dipping is preferred, a special thinner is added to alter the viscosity without impairing the temperature indicating performance. 3. Pellets: The first commercial form of the fusible indicator was the pellet, which continues to be useful in certain applications. Pellets are most frequently employed when extended heating periods are involved or when oxidation of a metal workpiece might obscure a crayon mark. Pellets are also ideal when a relatively large bulk of indicator material is necessary because observations must be made from a distance. Another major use of pellet-type indicators is for determining specific air-space temperatures. A typical application is the monitoring of heat zones in industrial ovens and furnaces. Phase change temperature indicating pellets are available in flat tablets, 7⁄16” in diameter and 1⁄8” thick. For special applications, smaller 1⁄8” by 1⁄8” thick pellets are also available. One application for these miniature pellets is that of thermal fuses. The solid pellet acts as a circuit breaker as it melts and releases tension on a spring which, in relaxing, opens a contact, in turn, cutting off electrical continuity. Pellets come in the extended range from 100˚F to 3000˚F. For temperature measurements in hydrogen, carbon monoxide, or other reducing environments, a special series of pellets is also available. 4. Labels: Another variation of the phase-change indicators is the temperature sensitive label. These adhesive backed monitors consist of one or more heat sensitive indicators sealed under transparent, heat-resistant windows. The centers of these indicators turn from white to black at the temperature ratings as shown on the label face. This color change, caused by the temperature-sensitive substance being absorbed into its backing material, is irreversible. After registering the temperature history of the workpiece, the exposed monitor label can then be removed and affixed to a service report to remain part of a permanent record. Reproduced with permision of Penton Publishing
ITS-90 Thermocouple Direct & Inverse Polynomials Direct Polynomials provide the thermoelectric voltage (µV) from a known temperature (°C); Inverse Polynomials provide the temperature (°C) from a known thermoelectric voltage (µV). Type J Thermocouples - coefficients, ci, of reference equations giving the thermoelectric voltage, E, as a function of temperature t90, for the indicated temperature ranges. The equations are of the form:
Type J Thermocouples - coefficients of approximate inverse functions giving temperature, t90 , as a function of the thermoelectric voltage, E, in selected temperature and voltage ranges. The functions are of the form:
n
E =
(
t90 = c0 + c1E + c2 E 2+…ci E i
ci (t90)i
where E is in microvolts and t90 is in degrees Celsius.
i=0
where E is in microvolts and t90 is in degrees Celsius. -210 to 760°C
Temperature Range: c0 c1 c2 c3 c4 c5 c6 c7 c8
= = = = = = = = =
760 to 1,200°C
0.000 000 000 0 .... 5.038 118 781 5 x101 3.047 583 693 0 x 10-2 -8.568 106 572 0 x 10-5 1.322 819 529 5 x 10-7 -1.705 295 833 7 x 10-10 2.094 809 069 7 x 10-13 -1.253 839 533 6 x 10-16 1.563 172 569 7 x 10-20
2.964 562 568 1 x 105 -1.497 612 778 6 x 103 3.178 710 392 4 -3.184 768 670 1 x 10-3 1.572 081 900 4 x 10-6 -3.069 136 905 6 x 10-10
Temperature Range: Voltage Range: c0 = c1 = c2 = c3 = c4 = c5 = c6 = c7 = c8 = Error Range:
Type K Thermocouples - coefficients α0, α1 and αi , of reference equations giving the thermoelectric voltage, E, as a function of temperature, t90 for the indicated temperature ranges. The equation below 0°C is of the form:
α0e α1 (t90 - 126.9686)2
i=0
where E is the natural logarithm constant, E is in microvolts and t90 is in degrees Celsius. Temperature Range:
270 to 0°C
0 to 1372°C
0.03 to -0.04°C
where E is in microvolts and t90 is in degrees Celsius.
i=0
E =( ci (t90) +
0.04 to -0.04°C
t90 = co + c1E + c2E2 ciE i
the equation above 0°C is of the form: i
0.03 to -0.05°C
760 to 1,200°C 42,919 to 69,553 µV -3.113 581 87 x 103 3.005 436 84 x 10-1 -9.947 732 30 x 10-6 1.702 766 30 x 10-10 -1.430 334 68 x 10-15 4.738 860 84 x 10-21
Type K Thermocouples - coefficients of approximate inverse functions giving temperature, t90, as a function of the thermoelectric voltage, E, in selected temperature and voltage ranges. The functions are of the form:
n
E = ( c1 (t90) i n
-210 0 to to 0°C 760°C -8,095 0 to to 0 µV 42,919 µV 0.000 000 0 .... 0.000 000 .... 1.952 826 8 x 10-2 1.978 425 x 10-2 -6 -1.228 618 5 x 10 -2.001 204 x 10-7 -1.075 217 8 x 10-9 1.036 969 x 10-11 -5.908 693 3 x 10-13 -2.549 687 x 10-16 -1.725 671 3 x 10-16 3.585 153 x 10-21 -2.813 151 3 x 10-20 -5.344 285 x 10-26 -2.396 337 0 x 10-24 5.099 890 x 10-31 -8.382 332 1 x 10-29
c0 = c1 = c2 = c3 = c4 = c5 = c6 = c7 = c8 = c9 = c10 = c0 = c1 = c2 = c3 = c4 = c5 = c6 = c7 = c8 = c9 = α0 = α1 =
Coefficients 0.000 000 000 0 .... 3.945 012 802 5 x 101 2.362 237 359 8 x 10-2 -3.285 890 678 4 x 10-4 -4.990 482 877 7 x 10-6 -6.750 905 917 3 x 10-8 -5.741 032 742 8 x 10-10 -3.108 887 289 4 x 10-12 -1.045 160 936 5 x 10-14 -1.988 926 687 8 x 10-17 -1.632 269 748 6 x 10-20 1.760 041 368 6 x 101 3.892 120 497 5 x 101 1.855 877 003 2 x 10-2 -9.945 759 287 4 x 10-5 3.184 094 571 9 x 10-7 -5.607 284 488 9 x 10-10 5.607 505 905 9 x 10-13 -3.202 072 000 3 x 10-16 9.715 114 715 2 x 10-20 -1.210 472 127 5 x 10-23 1.185 976 x 102 -1.183 432 x 10-4
Temperature Range: Voltage Range: c0 = c1 = c2 = c3 = c4 = c5 = c6 = c7 = c8 = c9 = Error Range:
Z-198
-200 0 to to 0°C 500°C -5891 0 to to 0 µV 20,644 µV 0.000 000 0 .... 0.000 000 .... 2.517 346 2 x 10-2 2.508 355 x 10-2 -6 -1.166 287 8 x 10 7.860 106 x 10-8 -9 -1.083 363 8 x 10 -2.503 131 x 10-10 -8.977 354 0 x 10-13 8.315 270 x 10-14 -3.734 237 7 x 10-16 -1.228 034 x 10-17 -8.663 264 3 x 10-20 9.804 036 x 10-22 -1.045 059 8 x 10-23 -4.413 030 x 10-26 -5.192 057 7 x 10-28 1.057 734 x 10-30 -1.052 755 x 10-35 0.04°C to -0.02°C
0.04°C to -0.05°C
500 to 1,372°C 20,644 to 54,886 µV -1.318 058 x 102 4.830 222 x 10-2 -1.646 031 x 10-6 5.464 731 x 10-11 -9.650 715 x 10-16 8.802 193 x 10-21 -3.110 810 x 10-26
0.06°C to -0.05°C
Z
ITS-90 Thermocouple Direct & Inverse Polynomials Cont’d Type T Thermocouples - coefficients, ci , of reference equations giving the thermoelectric voltage, E, as a function of temperature, t90, for the indicated temperature ranges. The equations are of the form:
Type T Thermocouples - coefficients of approximate inverse functions giving temperature, t90, as a function of the thermoelectric voltage, E, in selected temperature and voltage ranges. The functions are of the form:
t90 = c0 + c1E + c2 E 2+…ciE i
n
E =( ci (t90)i
where E is in microvolts and t90 is in degrees Celsius.
i=0
where E is in microvolts and t90 is in degrees Celsius. Temperature Range: c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13 c14
= = = = = = = = = = = = = = =
-270 to 0°C 0.000 000 000 0.... 3.874 810 636 4 x101 4.419 443 434 7 x 10-2 1.184 432 310 5 x 10-4 2.003 297 355 4 x 10-5 9.013 801 955 9 x 10-7 2.265 115 659 3 x 10-8 3.607 115 420 5 x 10-10 3.849 393 988 3 x 10-12 2.821 352 192 5 x 10-14 1.425 159 477 9 x 10-16 4.876 866 228 6 x 10-19 1.079 553 927 0 x 10-21 1.394 502 706 2 x 10-24 7.979 515 392 7 x 10-28
0 to 400°
Temperature Range:
0.000 000 000 0.... 3.874 810 636 4 x101 3.329 222 788 0 x10-2 2.061 824 340 4 x 10-4 -2.188 225 684 6 x 10-6 1.099 688 092 8 x 10-8 -3.081 575 877 2 x 10-11 4.547 913 529 0 x 10-14 -2.751 290 167 3 x 10-17
Voltage: Range:
n
E = ( ci (t90)i i=0
where E is in microvolts and t90 is in degrees Celsius.
c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13
= = = = = = = = = = = = = =
-270 to 0°C 0.000 000 000 0 .... 5.866 550 870 8 x101 4.541 097 712 4 x 10-2 -7.799 804 868 6 x 10-4 -2.580 016 084 3 x 10-5 -5.945 258 305 7 x 10-7 -9.321 405 866 7 x 10-9 -1.028 760 553 4 x 10-10 -8.037 012 362 1 x 10-13 -4.397 949 739 1 x 10-15 -1.641 477 635 5 x 10-17 -3.967 361 951 6 x 10-20 -5.582 732 872 1 x 10-23 -3.465 784 201 3 x 10-26
= = = = = = = =
Error Range:
Type E Thermocouples - coefficients, ci, of reference equations giving the thermoelectric voltage, E, as a function of temperature, t90, for the indicated temperature ranges. The equations are of the form:
Temperature Range:
c0 c1 c2 c3 c4 c5 c6 c7
-200 to 0°C -5,603 to 0 µV 0.000 000 0.... 2.592 919 2 x 10-2 -2.131 696 7 x 10-7 7.901 869 2 x 10-10 4.252 777 7 x 10-13 1.330 447 3 x 10-16 2.024 144 6 x 10-20 1.266 817 1 x 10-24
0 to 400°C 0 to 20,872 µV 0.000 000 .... -2 2.592 800 x 10 -7.602 961 x 10-7 4.637 791 x 10-11 -2.165 394 x 10-15 6.048 144 x 10-20 -7.293 422 x 10-25
0.04 to -0.02°C
0.03 to -0.03°C
Type E Thermocouples - coefficients of approximate inverse functions giving temperature, t90, as a function of the thermoelectric voltage, E, in selected temperature and voltage ranges. The functions are of the form: t90 = c0 + c1E + c2E 2+… ciE i where E is in microvolts and t90 is in degrees Celsius. Temperature Range:
0 to 400°C 0.000 000 000 0 .... 5.866 550 871 0 x101 4.503 227 558 2 x10-2 2.890 840 721 2 x 10-5 -3.305 689 665 2 x 10-7 6.502 440 327 0 x 10-10 -1.919 749 550 4 x 10-1 -1.253 660 049 7 x 10-15 2.148 921 756 9 x 10-18 -1.438 804 178 2 x 10-21 3.596 089 948 1 x 10-25
Voltage Range: c0 c1 c2 c3 c4 c5 c6 c7 c8 c9
= = = = = = = = = =
Error Range:
Z-199
-200 to 0°C -8,825 to 0 µV 0.000 000 0 .... 1.697 728 8 x 10-2 -4.351 497 0 x 10-7 -1.585 969 7 x 10-10 -9.250 287 1 x 10-14 -2.608 431 4 x 10-17 -4.136 019 9 x 10-21 -3.403 403 0 x 10-25 -1.156 489 0 x 10-29 0.03 to -0.01°C
0 to 1,000°C 0 to 76,373 µV 0.000 000 0 .... 1.705 703 5 x 10-2 -2.330 175 9 x 10-7 6.543 558 5 x 10-12 -7.356 274 9 x 10-17 -1.789 600 1 x 10-21 8.403 616 5 x 10-26 -1.373 587 9 x 10-30 1.062 982 3 x 10-35 -3.244 708 7 x 10-41 0.02 to -0.02°C
Type N Thermocouples - coefficients, ci , of reference equations giving the thermoelectric voltage, E, as a function of temperature, t90, for the indicated temperature ranges. The equations are of the form:
Temperature Range: c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 c10
n
E = ( ci (t90)i i=0
where E is in microvolts and t90 is in degrees Celsius.
Type N Thermocouples coefficients of approximate inverse functions giving temperature, t90, as a function of the thermoelectric voltage, E, in selected temperature and voltage ranges. The functions are of the form:
t90 = c0 + c1E + c2E 2+… ci E i where E is in microvolts and t90 is in degrees Celsius.
-200 to 0°C -3,990 to 0 µV
Temperature Range: Voltage Range: c0 = c1 = c2 = c3 = c4 = c5 = c6 = c7 = c8 = c9 = Error Range:
= = = = = = = = = = =
0 to 600°C 0 to 20,613 µV
0.000 000 0 .... 3.843 684 7 x 10-2 1.101 048 5 x 10-6 5.222 931 2 x 10-9 7.206 052 5 x 10-12 5.848 858 6 x 10-15 2.775 491 6 x 10-18 7.707.516 6 x 10-22 1.158 266 5 x 10-25 7.313 886 8 x 10-30
0.03 to -0.02°C
= = = = = = = = =
47,513 µV
0.02 to -0.04°C
0.06 to -0.06°C
where E is in microvolts and t90 is in degrees Celsius.
where E is in microvolts and t90 is in degrees Celsius.
c0 c1 c2 c3 c4 c5 c6 c7 c8
0 to 1,300°C 0
t90 = c0 + c1E + c2E 2+… ci E i
i=0
0 to 630.615°C 0.000 000 000 0 .... -2.465 081 834 6 x10-1 5.904 042 117 1 x 10-3 -1.325 793 163 6 x 10-6 1.566 829 190 1 x 10-9 -1.694 452 924 0 x 10-12 6.229 034 709 4 x 10-16
600 to 1,300°C 20,613 to 47,513 µV
Type B Thermocouples - coefficients of approximate inverse functions giving temperature, t90, as a function of the thermoelectric voltage, E, in selected temperature and voltage ranges. The functions are of the form:
n
E = ( ci (t90)i
Temperature Range:
0 to 1,300°C 0.000 000 000 0.... 2.592 939 460 1 x 101 1.571 014 188 0 x 10-2 4.382 562 723 7 x 10-5 -2.526 116 979 4 x 10-7 6.431 181 933 9 x 10-10 -1.006 347 151 9 x 10-12 9.974 533 899 2 x 10-16 -6.086 324 560 7 x 10-19 2.084 922 933 9 x 10-22 -3.068 219 615 1 x 10-26
0.000 00 .... 1.972 485 x 101 0.000 000 0 .... 3.868 96 x 10-2 3.300 943 x 10-2 3.878 327 7 x 10-2 -6 -7 -1.082 67 x 10 -3.915 159 x 10 -1.161 234 4 x 10-6 4.702 05 x 10-11 9.855 391 x 10-12 6.952 565 5 x 10-11 -2.121 69 x 10-18 -1.274 371 x 10-16 -3.009 007 7 x 10-15 -1.172 72 x 10-19 7.767 022 x 10-22 8.831 158 4 x 10-20 5.392 80 x 10-24 -1.621 383 9 x 10-24 -7.981 56 x 10-29 1.669 336 2 x 10-29 -7.311 754 0 x 10-35
0.03 to -0.02°C
Type B Thermocouples - coefficients, ci , of reference equations giving the thermoelectric voltage, E, as a function of temperature, t90, for the indicated temperature ranges. The equations are of the form:
-270 to 0°C 0.000 000 000 0.... 2.615 910 596 2 x101 1.095 748 422 8 x 10-2 -9.384 111 155 4 x 10-5 -4.641 203 975 9 x 10-8 -2.630 335 771 6 x 10-9 -2.265 343 800 3 x 10-11 -7.608 930 079 1 x 10-14 -9.341 966 783 5 x 10-17
Temperature Range:
630.615 to 1,820°C -3.893 816 862 1 x 103 2.857 174 747 0 x 101 -8.488 510 478 5 x 10-2 1.578 528 016 4 x 10-4 -1.683 534 486 4 x 10-7 1.110 979 401 3 x 10-10 -4.451 543 103 3 x 10-14 9.897 564 082 1 x 10-18 -9.379 133 028 9 x 10-22
Voltage Range: c0 c1 c2 c3 c4 c5 c6 c7 c8
= = = = = = = = =
Error Range:
Z-200
250 to 700°C 291 to 2,431 µV 9.842 332 1 x 101 6.997 150 0 x 10-1 -8.476 530 4 x 10-4 1.005 264 4 x 10-6 -8.334 595 2 x 10-10 4.550 854 2 x 10-13 -1.552 303 7 x 10-16 2.988 675 0 x 10-20 -2.474 286 0 x 10-24 0.03 to -0.02°C
700 to 1,820°C 2,431 to 13,820 µV -2.131 507 1 x 102 2.851 050 4 x 10-1 -5.274 288 7 x 10-5 9.916 080 4 x 10-9 -1.296 530 3 x 10-12 1.119 587 0 x 10-16 -6.062 519 9 x 10-21 1.866 169 6 x 10-25 -2.487 858 5 x 10-30 0.02 to -0.01°C
Z
ITS-90 Thermocouple Direct & Inverse Polynomials Cont’d Type R Thermocouples coefficients, ci , of reference equations giving the thermoelectric voltage, E, as a function of temperature, t90, for the indicated temperature ranges. The equations are of the for:
Temperature Range: c0 c1 c2 c3 c4 c5 c6 c7 c8 c9
n
E = ( ci (t90)i i=0
where E is in microvolts and t90 is in degrees Celsius. Type R Thermocouples coefficients of approximate inverse functions giving temperature, t90 , as a function of the thermoelectric voltage, E, in selected temperature and voltage ranges. The functions are of the form:
= = = = = = = = = =
-50°C to 250°C -226 to 1,923 µV
Temperature Range: Voltage Range: c0 c1 c3 c4 c5 c6 c7 c8 c9 c10
t90 = c0 + c1E + c2E2+…ciEi where E is in microvolts and t90 is in degrees Celsius.
= = = = = = = = = =
0.02 to -0.02°C
c0 c1 c2 c3 c4 c5 c6 c7 c8
n
i=0
where E is in microvolts and t90 is in degrees Celsius.
Type S Thermocouples coefficients of approximate inverse functions giving temperature, t90 , as a function of the thermoelectric voltage, E, in selected temperature and voltage ranges. The functions are of the form:
t90 = c0 + c1E + c2E 2+…ci E i where E is in microvolts and t90 is in degrees Celsius.
Temperature Range:
= = = = = = = = =
0.005 to -0.005°C
c0 = c1 = c2 = c3 = c4 = c5 = c6 = c7 = c8 = c9 = Error Range:
0.02 to -0.02°C
Voltage Range:
-8.199 599 416 x 101 1.553 962 042 x 10-1 4.279 433 549 x 10-10 -1.191 577 910 x 10-14 1.492 290 091 x 10-19
0.001 to -0.0005°C
1.329 004 450 85 x 103 3.345 093 113 44 .... 6.548 051 928 18 x 10-3 -1.648 562 592 09 x 10-6 1.299 896 051 74 x 10-11
0.0002 to -0.0002°C
3.406 177 836 x 104 -7.023 729 171 .... -5.582 903 813 x 10-4 -1.952 394 635 x 10-8 2.560 740 231 x 10-13
0.002 to -0.001°C
1,664.5 to 1,768.1°C 1.466 282 326 36 x 105 -2.584 305 167 52 x 102 1.636 935 746 41 x 10-1 -3.304 390 469 87 x 10-5 -9.432 236 906 12 x 10-12
250 1,064 to to 1,200°C 1,664.5°C 1,874 10,332 to to 11,950 µV 17,536 µV 1.291 507 177 x 101 -8.087 801 117 x 101 1.466 298 863 x 10-1 1.621 573 104 x 10-1 -5 -1.534 713 402 x 10 -8.536 869 453 x 10-6 3.145 945 973 x 10-9 4.719 686 976 x 10-10 -4.163 257 839 x 10-13 -1.441 693 666 x 10-14 -17 2.081 618 890 x 10-19 3.187 963 771 x 10 -1.291 637 500 x 10-21 2.183 475 087 x 10-26 -1.447 379 511 x 10-31 8.211 272 125 x 10-36 0.01 to -0.01°C
Z-201
1,664.5 to 1,768.1°C 19,739 to 21,103 µV
1,064.18 to 1,664.5°C
0.000 000 000 0 .... 5.403 133 086 31.... 1.259 342 897 40 x 10-2 -2.324 779 686 89 x 10-5 3.220 288 230 36 x 10-8 -3.314 651 963 89 x 10-11 2.557 442 517 86 x 10-14 -1.250 688 713 93 x 10-17 2.714 431 761 45 x 10-21
-50 to 250°C -235 to 1,874 µV 0.000 000 0 .... 1.849 494 60 x 10-1 -8.005 040 62 x 10-5 1.022 374 30 x 10-7 -1.522 485 92 x 10-10 1.888 213 43 x 10-13 -1.590 859 41 x 10-16 8.230 278 80 x 10-20 -2.341 819 44 x 10-23 2.797 862 60 x 10-27
1,064 to 1,664.5°C 11,361 to 19,739 µV
1.334 584 505 x 101 1.472 644 573 x 10-1 4.031 129 x 726 10-9 -6.249 428 360 x 10-13 6.468 412 046 x 10-17 -4.458 750 426 x 10-21 1.994 710 146 x 10-25 -5.313 401 790 x 10-30 6.481 976 217 x 10-35
-50 to 1,064.18°C
Temperature Range:
E = ( ci (t90)i
2,500 to 1,200°C 1,923 to 13,228 µV
0.000 000 0 .... 1.889 138 0 x 10-1 1.306 861 9 x 10-7 -2.270 358 0 x 10-10 3.514 565 9 x 10-13 -3.895 390 0 x 10-16 2.823.947 1 x 10-19 -1.260 728 1 x 10-22 3.135 361 1 x 10-26 -3.318 776 9 x 10-30
Error Range:
Type S Thermocouples coefficients, ci , of reference equations giving the thermoelectric voltage, E, as a function of temperature, t90, for the indicated temperature ranges. The equations are of the for:
-50 1,064.18 1,664.5 to to to 1,064.18°C 1,664.5°C 1,768.1°C 0.000 000 000 0 .... 2.951 579 253 16 x 103 1.522 321 182 09 x 105 5.289 617 297 65 .... -2.520 612 513 32 .... -2.688 198 885 45 x 102 1.391 665 897 82 x 10-2 1.595 645 018 65 x 10-2 1.712 802 804 71 x 10-1 -2.388 556 930 17 x 10-5 -7.640 859 475 76 x 10-6 -3.458 957 064 53 x 10-5 3.569 160 010 63 x 10-8 2.053 052 910 24 x 10-9 -9.346 339 710 46 x 10-12 -4.623 476 662 98 x 10-11 -2.933 596 681 73 x 10-13 5.007 774 410 34 x 10-14 -3.731 058 861 91 x 10-17 1.577 164 823 67 x 10-20 -2.810 386 252 51 x 10-24
1,664.5 to 1,768.1°C 17,536 to 18,693 µV 5.333 875 126 x 104 -1.235 892 298 x 101 1.092 657 613 x 10-3 -4.265 693 686 x 10-8 6.247 205 420 x 10-13
0.002 to -0.002°C
Tungsten-Rhenium Thermocouples Calibration Equivalents CALIBRATIONS G AND C
CALIBRATION D
The nominal emf versus temperature values for WM26Re (type G) and W5ReM26Re (type C) thermocouples are defined by fifth degree polynominals. The emf in absolute millivolts (IPTS68) is determined, using the equation and coefficients shown below, from the temperature in Fahrenheit degrees.
A similar equation is used to generate emf versus temperature values for W3ReM25Re thermocouples. For this combination, however, the curve is broken into two functions and the temperature is expressed in Celsius degrees.
Gen. Form: EMF = AT + BT2 + CT3 + DT4 + ET5 + K
Gen. Form: EMF = AT + BT2 + CT3 + DT4 + ET5
Temp. Range: 32˚F to 4200˚F (0 to 2315˚C)
Temp. Range: 32 to 4208˚F (0 to 2320˚C)
THERMOCOUPLE WIRE IDENTIFICATION GUIDE Coefficients W/W26Re A 0.2883146 x 10-3 B 0.6783829 x 10-5 C -0.1795965 x 10-8 D 0.2125270 x 10-12 E -0.1176051 x 10-16 K -0.1580014 x 10-1
W5Re/W26Re 0.7190027 x 10-2 0.3956443 x 10-5 -0.1842722 x 10-8 0.3471851 x 10-12 -0.2616792 x 10-16 -0.234471
Coefficients T<783˚C A 9.5685256 x 10-3 B 2.0592621 x 10-5 C -1.8464573 x 10-8 D 7.9498033 x 10-12 E -1.4240735 x 10-15
T≥ 783 ˚C 9.9109462 x 10-3 1.8666488 x 10-5 -1.4935266 x 10-8 5.3743821 x 10-12 -7.9026726 x 10-16
Reprinted with Permission, from the Annual Book of ASTM Standards, Copyright American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103
THERMOCOUPLE WIRE IDENTIFICATION GUIDE Letter Code
G C D
Alloy Combination +Lead -Lead
TUNGSTEN W
TUNGSTEN 26% RHENIUM W-26% Re
Color Coding Ext. Grade + WHITE + –
-RED WHITE BLUE TRACE
TUNGSTEN TUNGSTEN 5% RHENIUM 26% RHENIUM W-5% Re W-26% Re
+ WHITE + –
-RED WHITE RED TRACE
TUNGSTEN TUNGSTEN 3% RHENIUM 25% RHENIUM W-3% Re W-56% Re
+ WHITE + –
-RED WHITE YELLOW TRACE
Maximum Useful Temperature Range
EMF(mV) Over Useful Temperature Range
Standard Limits of Error
Comments Environment Bare WIre
32 TO 4208˚F 0 TO 2320˚C Thermocouple Grade 32 to 500˚F 0 to 260˚C Extension Grade
0 TO 38.564
4.5˚C TO 425˚C 1.0% TO 2320˚C
Vacuum Inert Hydrogen. Beware of Embrittlement. Not Practical Below 750˚F Not for Oxidizing Atmosphere
32 TO 4208˚F 0 TO 2320˚C Thermocouple Grade 32 to 1600˚F 0 to 870˚C Extension Grade
0 TO 37.066
4.5˚C TO 425˚C 1.0% TO 2320˚C
Vacuum Inert Hydrogen. Beware of Embrittlement. Not Practical Below 750˚F Not for Oxidizing Atmosphere
32 TO 4208˚F 0 TO 2320˚C Thermocouple Grade 32 to 5000˚F 0 to 260˚C Extension Grade
0 TO 39.506
4.5˚C TO 425˚C 1.0% TO 2320˚C
Vacuum Inert Hydrogen. Beware of Embrittlement. Not Practical Below 750˚F Not for Oxidizing Atmosphere
®
Z-202
+ –
Revised Thermocouple Reference Tables
J
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°C
-10
-9
-8
-7
-6
-5
-4
Thermocouple Grade
Iron vs. Copper-Nickel + – Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 1382°F 0 to 750°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Reducing, Vacuum, Inert; Limited Use in Oxidizing at High Temperatures; Not Recommended for Low Temperatures TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
Thermoelectric Voltage in Millivolts
-3
-2
-1
0
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
-190 -180 -170 -160 -150
500 510 520 530 540
27.393 27.953 28.516 29.080 29.647
27.449 28.010 28.572 29.137 29.704
27.505 28.066 28.629 29.194 29.761
27.561 28.122 28.685 29.250 29.818
27.617 28.178 28.741 29.307 29.874
27.673 28.234 28.798 29.363 29.931
27.729 28.291 28.854 29.420 29.988
27.785 28.347 28.911 29.477 30.045
27.841 28.403 28.967 29.534 30.102
27.897 28.460 29.024 29.590 30.159
27.953 28.516 29.080 29.647 30.216
500 510 520 530 540
-6.159 -5.801 -5.426 -5.037 -4.633
-140 -130 -120 -110 -100
550 560 570 580 590
30.216 30.788 31.362 31.939 32.519
30.273 30.845 31.419 31.997 32.577
30.330 30.902 31.477 32.055 32.636
30.387 30.960 31.535 32.113 32.694
30.444 31.017 31.592 32.171 32.752
30.502 31.074 31.650 32.229 32.810
30.559 31.132 31.708 32.287 32.869
30.616 31.189 31.766 32.345 32.927
30.673 31.247 31.823 32.403 32.985
30.730 31.304 31.881 32.461 33.044
30.788 31.362 31.939 32.519 33.102
550 560 570 580 590
-4.257 -3.829 -3.389 -2.938 -2.478
-4.215 -3.786 -3.344 -2.893 -2.431
-90 -80 -70 -60 -50
600 610 620 630 640
33.102 33.689 34.279 34.873 35.470
33.161 33.748 34.338 34.932 35.530
33.219 33.807 34.397 34.992 35.590
33.278 33.866 34.457 35.051 35.650
33.337 33.925 34.516 35.111 35.710
33.395 33.984 34.575 35.171 35.770
33.454 34.043 34.635 35.230 35.830
33.513 34.102 34.694 35.290 35.890
33.571 34.161 34.754 35.350 35.950
33.630 34.220 34.813 35.410 36.010
33.689 34.279 34.873 35.470 36.071
600 610 620 630 640
-2.055 -1.578 -1.093 -0.600 -0.101
-2.008 -1.530 -1.044 -0.550 -0.050
-1.961 -1.482 -0.995 -0.501 0.000
-40 -30 -20 -10 0
650 660 670 680 690
36.071 36.675 37.284 37.896 38.512
36.131 36.736 37.345 37.958 38.574
36.191 36.797 37.406 38.019 38.636
36.252 36.858 37.467 38.081 38.698
36.312 36.918 37.528 38.142 38.760
36.373 36.979 37.590 38.204 38.822
36.433 37.040 37.651 38.265 38.884
36.494 37.101 37.712 38.327 38.946
36.554 37.162 37.773 38.389 39.008
36.615 37.223 37.835 38.450 39.070
36.675 37.284 37.896 38.512 39.132
650 660 670 680 690
0.354 0.865 1.381 1.902 2.427
0.405 0.916 1.433 1.954 2.480
0.456 0.968 1.485 2.006 2.532
0.507 1.019 1.537 2.059 2.585
0 10 20 30 40
700 710 720 730 740
39.132 39.755 40.382 41.012 41.645
39.194 39.818 40.445 41.075 41.708
39.256 39.880 40.508 41.138 41.772
39.318 39.943 40.570 41.201 41.835
39.381 40.005 40.633 41.265 41.899
39.443 40.068 40.696 41.328 41.962
39.505 40.131 40.759 41.391 42.026
39.568 40.193 40.822 41.455 42.090
39.630 40.256 40.886 41.518 42.153
39.693 40.319 40.949 41.581 42.217
39.755 40.382 41.012 41.645 42.281
700 710 720 730 740
2.903 3.436 3.971 4.510 5.052
2.956 3.489 4.025 4.564 5.106
3.009 3.543 4.079 4.618 5.160
3.062 3.596 4.133 4.672 5.215
3.116 3.650 4.187 4.726 5.269
50 60 70 80 90
750 760 770 780 790
42.281 42.919 43.559 44.203 44.848
42.344 42.983 43.624 44.267 44.913
42.408 43.047 43.688 44.332 44.977
42.472 43.111 43.752 44.396 45.042
42.536 43.175 43.817 44.461 45.107
42.599 43.239 43.881 44.525 45.171
42.663 43.303 43.945 44.590 45.236
42.727 43.367 44.010 44.655 45.301
42.791 43.431 44.074 44.719 45.365
42.855 43.495 44.139 44.784 45.430
42.919 43.559 44.203 44.848 45.494
750 760 770 780 790
5.595 6.141 6.689 7.239 7.789
5.650 6.196 6.744 7.294 7.844
5.705 6.251 6.799 7.349 7.900
5.759 6.306 6.854 7.404 7.955
5.814 6.360 6.909 7.459 8.010
100 110 120 130 140
800 810 820 830 840
45.494 46.141 46.786 47.431 48.074
45.559 46.205 46.851 47.495 48.138
45.624 46.270 46.915 47.560 48.202
45.688 46.334 46.980 47.624 48.267
45.753 46.399 47.044 47.688 48.331
45.818 46.464 47.109 47.753 48.395
45.882 46.528 47.173 47.817 48.459
45.947 46.593 47.238 47.881 48.523
46.011 46.657 47.302 47.946 48.587
46.076 46.722 47.367 48.010 48.651
46.141 46.786 47.431 48.074 48.715
800 810 820 830 840
150 8.010 8.065 8.120 8.175 8.231 8.286 8.341 8.396 8.452 8.507 8.562 160 8.562 8.618 8.673 8.728 8.783 8.839 8.894 8.949 9.005 9.060 9.115 170 9.115 9.171 9.226 9.282 9.337 9.392 9.448 9.503 9.559 9.614 9.669 180 9.669 9.725 9.780 9.836 9.891 9.947 10.002 10.057 10.113 10.168 10.224 190 10.224 10.279 10.335 10.390 10.446 10.501 10.557 10.612 10.668 10.723 10.779
150 160 170 180 190
850 860 870 880 890
48.715 49.353 49.989 50.622 51.251
48.779 49.417 50.052 50.685 51.314
48.843 49.481 50.116 50.748 51.377
48.907 49.544 50.179 50.811 51.439
48.971 49.608 50.243 50.874 51.502
49.034 49.672 50.306 50.937 51.565
49.098 49.735 50.369 51.000 51.627
49.162 49.799 50.432 51.063 51.690
49.226 49.862 50.495 51.126 51.752
49.290 49.926 50.559 51.188 51.815
49.353 49.989 50.622 51.251 51.877
850 860 870 880 890
200 210 220 230 240
10.779 11.334 11.889 12.445 13.000
10.834 11.389 11.945 12.500 13.056
10.890 11.445 12.000 12.556 13.111
10.945 11.501 12.056 12.611 13.167
11.001 11.556 12.111 12.667 13.222
11.056 11.612 12.167 12.722 13.278
11.112 11.667 12.222 12.778 13.333
11.167 11.723 12.278 12.833 13.389
11.223 11.778 12.334 12.889 13.444
11.278 11.834 12.389 12.944 13.500
11.334 11.889 12.445 13.000 13.555
200 210 220 230 240
900 910 920 930 940
51.877 52.500 53.119 53.735 54.347
51.940 52.562 53.181 53.796 54.408
52.002 52.624 53.243 53.857 54.469
52.064 52.686 53.304 53.919 54.530
52.127 52.748 53.366 53.980 54.591
52.189 52.810 53.427 54.041 54.652
52.251 52.872 53.489 54.102 54.713
52.314 52.934 53.550 54.164 54.773
52.376 52.996 53.612 54.225 54.834
52.438 53.057 53.673 54.286 54.895
52.500 53.119 53.735 54.347 54.956
900 910 920 930 940
250 260 270 280 290
13.555 14.110 14.665 15.219 15.773
13.611 14.166 14.720 15.275 15.829
13.666 14.221 14.776 15.330 15.884
13.722 14.277 14.831 15.386 15.940
13.777 14.332 14.887 15.441 15.995
13.833 14.388 14.942 15.496 16.050
13.888 14.443 14.998 15.552 16.106
13.944 14.499 15.053 15.607 16.161
13.999 14.554 15.109 15.663 16.216
14.055 14.609 15.164 15.718 16.272
14.110 14.665 15.219 15.773 16.327
250 260 270 280 290
950 960 970 980 990
54.956 55.561 56.164 56.763 57.360
55.016 55.622 56.224 56.823 57.419
55.077 55.682 56.284 56.883 57.479
55.138 55.742 56.344 56.942 57.538
55.198 55.803 56.404 57.002 57.597
55.259 55.863 56.464 57.062 57.657
55.319 55.923 56.524 57.121 57.716
55.380 55.983 56.584 57.181 57.776
55.440 56.043 56.643 57.240 57.835
55.501 56.104 56.703 57.300 57.894
55.561 56.164 56.763 57.360 57.953
950 960 970 980 990
300 310 320 330 340
16.327 16.881 17.434 17.986 18.538
16.383 16.936 17.489 18.041 18.594
16.438 16.991 17.544 18.097 18.649
16.493 17.046 17.599 18.152 18.704
16.549 17.102 17.655 18.207 18.759
16.604 17.157 17.710 18.262 18.814
16.659 17.212 17.765 18.318 18.870
16.715 17.268 17.820 18.373 18.925
16.770 17.323 17.876 18.428 18.980
16.825 17.378 17.931 18.483 19.035
16.881 17.434 17.986 18.538 19.090
300 310 320 330 340
1000 1010 1020 1030 1040
57.953 58.545 59.134 59.721 60.307
58.013 58.604 59.193 59.780 60.365
58.072 58.663 59.252 59.838 60.423
58.131 58.722 59.310 59.897 60.482
58.190 58.781 59.369 59.956 60.540
58.249 58.840 59.428 60.014 60.599
58.309 58.899 59.487 60.073 60.657
58.368 58.957 59.545 60.131 60.715
58.427 59.016 59.604 60.190 60.774
58.486 59.075 59.663 60.248 60.832
58.545 59.134 59.721 60.307 60.890
1000 1010 1020 1030 1040
350 360 370 380 390
19.090 19.642 20.194 20.745 21.297
19.146 19.697 20.249 20.800 21.352
19.201 19.753 20.304 20.855 21.407
19.256 19.808 20.359 20.911 21.462
19.311 19.863 20.414 20.966 21.517
19.366 19.918 20.469 21.021 21.572
19.422 19.973 20.525 21.076 21.627
19.477 20.028 20.580 21.131 21.683
19.532 20.083 20.635 21.186 21.738
19.587 20.139 20.690 21.241 21.793
19.642 20.194 20.745 21.297 21.848
350 360 370 380 390
1050 1060 1070 1080 1090
60.890 61.473 62.054 62.634 63.214
60.949 61.531 62.112 62.692 63.271
61.007 61.589 62.170 62.750 63.329
61.065 61.647 62.228 62.808 63.387
61.123 61.705 62.286 62.866 63.445
61.182 61.763 62.344 62.924 63.503
61.240 61.822 62.402 62.982 63.561
61.298 61.880 62.460 63.040 63.619
61.356 61.938 62.518 63.098 63.677
61.415 61.996 62.576 63.156 63.734
61.473 62.054 62.634 63.214 63.792
1050 1060 1070 1080 1090
400 410 420 430 440
21.848 22.400 22.952 23.504 24.057
21.903 22.455 23.007 23.559 24.112
21.958 22.510 23.062 23.614 24.167
22.014 22.565 23.117 23.670 24.223
22.069 22.620 23.172 23.725 24.278
22.124 22.676 23.228 23.780 24.333
22.179 22.731 23.283 23.835 24.389
22.234 22.786 23.338 23.891 24.444
22.289 22.841 23.393 23.946 24.499
22.345 22.896 23.449 24.001 24.555
22.400 22.952 23.504 24.057 24.610
400 410 420 430 440
1100 1110 1120 1130 1140
63.792 64.370 64.948 65.525 66.102
63.850 64.428 65.006 65.583 66.160
63.908 64.486 65.064 65.641 66.218
63.966 64.544 65.121 65.699 66.275
64.024 64.602 65.179 65.756 66.333
64.081 64.659 65.237 65.814 66.391
64.139 64.717 65.295 65.872 66.448
64.197 64.775 65.352 65.929 66.506
64.255 64.833 65.410 65.987 66.564
64.313 64.890 65.468 66.045 66.621
64.370 64.948 65.525 66.102 66.679
1100 1110 1120 1130 1140
450 460 470 480 490
24.610 25.164 25.720 26.276 26.834
24.665 25.220 25.775 26.332 26.889
24.721 25.275 25.831 26.387 26.945
24.776 25.331 25.886 26.443 27.001
24.832 25.386 25.942 26.499 27.057
24.887 25.442 25.998 26.555 27.113
24.943 25.497 26.053 26.610 27.169
24.998 25.553 26.109 26.666 27.225
25.053 25.608 26.165 26.722 27.281
25.109 25.664 26.220 26.778 27.337
25.164 25.720 26.276 26.834 27.393
450 460 470 480 490
1150 1160 1170 1180 1190
66.679 67.255 67.831 68.406 68.980
66.737 67.313 67.888 68.463 69.037
66.794 67.370 67.946 68.521 69.095
66.852 67.428 68.003 68.578 69.152
66.910 67.486 68.061 68.636 69.209
66.967 67.543 68.119 68.693 69.267
67.025 67.601 68.176 68.751 69.324
67.082 67.658 68.234 68.808 69.381
67.140 67.716 68.291 68.865 69.439
67.198 67.773 68.348 68.923 69.496
67.255 67.831 68.406 68.980 69.553
1150 1160 1170 1180 1190
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
-200
-8.095 -8.076 -8.057 -8.037 -8.017 -7.996 -7.976 -7.955 -7.934 -7.912 -7.890 -200
-190 -180 -170 -160 -150
-7.890 -7.659 -7.403 -7.123 -6.821
-7.868 -7.634 -7.376 -7.094 -6.790
-7.846 -7.610 -7.348 -7.064 -6.759
-7.824 -7.585 -7.321 -7.035 -6.727
-7.801 -7.559 -7.293 -7.005 -6.695
-7.778 -7.534 -7.265 -6.975 -6.663
-7.755 -7.508 -7.237 -6.944 -6.631
-7.731 -7.482 -7.209 -6.914 -6.598
-7.707 -7.456 -7.181 -6.883 -6.566
-7.683 -7.429 -7.152 -6.853 -6.533
-7.659 -7.403 -7.123 -6.821 -6.500
-140 -130 -120 -110 -100
-6.500 -6.159 -5.801 -5.426 -5.037
-6.467 -6.124 -5.764 -5.388 -4.997
-6.433 -6.089 -5.727 -5.350 -4.957
-6.400 -6.054 -5.690 -5.311 -4.917
-6.366 -6.018 -5.653 -5.272 -4.877
-6.332 -5.982 -5.616 -5.233 -4.836
-6.298 -5.946 -5.578 -5.194 -4.796
-6.263 -5.910 -5.541 -5.155 -4.755
-6.229 -5.874 -5.503 -5.116 -4.714
-6.194 -5.838 -5.465 -5.076 -4.674
-90 -80 -70 -60 -50
-4.633 -4.215 -3.786 -3.344 -2.893
-4.591 -4.173 -3.742 -3.300 -2.847
-4.550 -4.130 -3.698 -3.255 -2.801
-4.509 -4.088 -3.654 -3.210 -2.755
-4.467 -4.045 -3.610 -3.165 -2.709
-4.425 -4.002 -3.566 -3.120 -2.663
-4.384 -3.959 -3.522 -3.075 -2.617
-4.342 -3.916 -3.478 -3.029 -2.571
-4.300 -3.872 -3.434 -2.984 -2.524
-40 -30 -20 -10 0
-2.431 -1.961 -1.482 -0.995 -0.501
-2.385 -1.913 -1.433 -0.946 -0.451
-2.338 -1.865 -1.385 -0.896 -0.401
-2.291 -1.818 -1.336 -0.847 -0.351
-2.244 -1.770 -1.288 -0.798 -0.301
-2.197 -1.722 -1.239 -0.749 -0.251
-2.150 -1.674 -1.190 -0.699 -0.201
-2.103 -1.626 -1.142 -0.650 -0.151
0 10 20 30 40
0.000 0.507 1.019 1.537 2.059
0.050 0.558 1.071 1.589 2.111
0.101 0.609 1.122 1.641 2.164
0.151 0.660 1.174 1.693 2.216
0.202 0.711 1.226 1.745 2.269
0.253 0.762 1.277 1.797 2.322
0.303 0.814 1.329 1.849 2.374
50 60 70 80 90
2.585 3.116 3.650 4.187 4.726
2.638 3.169 3.703 4.240 4.781
2.691 3.222 3.757 4.294 4.835
2.744 3.275 3.810 4.348 4.889
2.797 3.329 3.864 4.402 4.943
2.850 3.382 3.918 4.456 4.997
100 110 120 130 140
5.269 5.814 6.360 6.909 7.459
5.323 5.868 6.415 6.964 7.514
5.378 5.923 6.470 7.019 7.569
5.432 5.977 6.525 7.074 7.624
5.487 6.032 6.579 7.129 7.679
5.541 6.087 6.634 7.184 7.734
Z-203
°C
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 2282°F – 200 to 1250°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Clean Oxidizing and Inert; Limited Use in Vacuum or Reducing; Wide Temperature Range; Most Popular Calibration TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
+ –
Thermocouple Grade
Nickel-Chromium vs. Nickel-Aluminum
Revised Thermocouple Reference Tables
K
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °C
-10
-9
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
-260 -250
-6.458 -6.457 -6.456 -6.455 -6.453 -6.452 -6.450 -6.448 -6.446 -6.444 -6.441 -260 -6.441 -6.438 -6.435 -6.432 -6.429 -6.425 -6.421 -6.417 -6.413 -6.408 -6.404 -250
250 260 270 280 290
10.153 10.561 10.971 11.382 11.795
10.194 10.602 11.012 11.423 11.836
10.235 10.643 11.053 11.465 11.877
10.276 10.684 11.094 11.506 11.919
10.316 10.725 11.135 11.547 11.960
10.357 10.766 11.176 11.588 12.001
10.398 10.807 11.217 11.630 12.043
10.439 10.848 11.259 11.671 12.084
10.480 10.889 11.300 11.712 12.126
10.520 10.930 11.341 11.753 12.167
10.561 10.971 11.382 11.795 12.209
250 260 270 280 290
-240 -230 -220 -210 -200
-6.404 -6.344 -6.262 -6.158 -6.035
-6.399 -6.337 -6.252 -6.147 -6.021
-6.393 -6.329 -6.243 -6.135 -6.007
-6.388 -6.322 -6.233 -6.123 -5.994
-6.382 -6.314 -6.223 -6.111 -5.980
-6.377 -6.306 -6.213 -6.099 -5.965
-6.370 -6.297 -6.202 -6.087 -5.951
-6.364 -6.289 -6.192 -6.074 -5.936
-6.358 -6.280 -6.181 -6.061 -5.922
-6.351 -6.271 -6.170 -6.048 -5.907
-6.344 -6.262 -6.158 -6.035 -5.891
-240 -230 -220 -210 -200
300 310 320 330 340
12.209 12.624 13.040 13.457 13.874
12.250 12.665 13.081 13.498 13.916
12.291 12.707 13.123 13.540 13.958
12.333 12.748 13.165 13.582 14.000
12.374 12.790 13.206 13.624 14.042
12.416 12.831 13.248 13.665 14.084
12.457 12.873 13.290 13.707 14.126
12.499 12.915 13.331 13.749 14.167
12.540 12.956 13.373 13.791 14.209
12.582 12.998 13.415 13.833 14.251
12.624 13.040 13.457 13.874 14.293
300 310 320 330 340
-190 -180 -170 -160 -150
-5.891 -5.730 -5.550 -5.354 -5.141
-5.876 -5.713 -5.531 -5.333 -5.119
-5.861 -5.695 -5.512 -5.313 -5.097
-5.845 -5.678 -5.493 -5.292 -5.074
-5.829 -5.660 -5.474 -5.271 -5.052
-5.813 -5.642 -5.454 -5.250 -5.029
-5.797 -5.624 -5.435 -5.228 -5.006
-5.780 -5.606 -5.415 -5.207 -4.983
-5.763 -5.588 -5.395 -5.185 -4.960
-5.747 -5.569 -5.374 -5.163 -4.936
-5.730 -5.550 -5.354 -5.141 -4.913
-190 -180 -170 -160 -150
350 360 370 380 390
14.293 14.713 15.133 15.554 15.975
14.335 14.755 15.175 15.596 16.017
14.377 14.797 15.217 15.638 16.059
14.419 14.839 15.259 15.680 16.102
14.461 14.881 15.301 15.722 16.144
14.503 14.923 15.343 15.764 16.186
14.545 14.965 15.385 15.806 16.228
14.587 15.007 15.427 15.849 16.270
14.629 15.049 15.469 15.891 16.313
14.671 15.091 15.511 15.933 16.355
14.713 15.133 15.554 15.975 16.397
350 360 370 380 390
-140 -130 -120 -110 -100
-4.913 -4.669 -4.411 -4.138 -3.852
-4.889 -4.644 -4.384 -4.110 -3.823
-4.865 -4.618 -4.357 -4.082 -3.794
-4.841 -4.593 -4.330 -4.054 -3.764
-4.817 -4.567 -4.303 -4.025 -3.734
-4.793 -4.542 -4.276 -3.997 -3.705
-4.768 -4.516 -4.249 -3.968 -3.675
-4.744 -4.490 -4.221 -3.939 -3.645
-4.719 -4.463 -4.194 -3.911 -3.614
-4.694 -4.437 -4.166 -3.882 -3.584
-4.669 -4.411 -4.138 -3.852 -3.554
-140 -130 -120 -110 -100
400 410 420 430 440
16.397 16.820 17.243 17.667 18.091
16.439 16.862 17.285 17.709 18.134
16.482 16.904 17.328 17.752 18.176
16.524 16.947 17.370 17.794 18.218
16.566 16.989 17.413 17.837 18.261
16.608 17.031 17.455 17.879 18.303
16.651 17.074 17.497 17.921 18.346
16.693 17.116 17.540 17.964 18.388
16.735 17.158 17.582 18.006 18.431
16.778 17.201 17.624 18.049 18.473
16.820 17.243 17.667 18.091 18.516
400 410 420 430 440
-90 -80 -70 -60 -50
-3.554 -3.243 -2.920 -2.587 -2.243
-3.523 -3.211 -2.887 -2.553 -2.208
-3.492 -3.179 -2.854 -2.519 -2.173
-3.462 -3.147 -2.821 -2.485 -2.138
-3.431 -3.115 -2.788 -2.450 -2.103
-3.400 -3.083 -2.755 -2.416 -2.067
-3.368 -3.050 -2.721 -2.382 -2.032
-3.337 -3.018 -2.688 -2.347 -1.996
-3.306 -2.986 -2.654 -2.312 -1.961
-3.274 -2.953 -2.620 -2.278 -1.925
-3.243 -2.920 -2.587 -2.243 -1.889
-90 -80 -70 -60 -50
450 460 470 480 490
18.516 18.941 19.366 19.792 20.218
18.558 18.983 19.409 19.835 20.261
18.601 19.026 19.451 19.877 20.303
18.643 19.068 19.494 19.920 20.346
18.686 19.111 19.537 19.962 20.389
18.728 19.154 19.579 20.005 20.431
18.771 19.196 19.622 20.048 20.474
18.813 19.239 19.664 20.090 20.516
18.856 19.281 19.707 20.133 20.559
18.898 19.324 19.750 20.175 20.602
18.941 19.366 19.792 20.218 20.644
450 460 470 480 490
-40 -30 -20 -10 0
-1.889 -1.527 -1.156 -0.778 -0.392
-1.854 -1.490 -1.119 -0.739 -0.353
-1.818 -1.453 -1.081 -0.701 -0.314
-1.782 -1.417 -1.043 -0.663 -0.275
-1.745 -1.380 -1.006 -0.624 -0.236
-1.709 -1.343 -0.968 -0.586 -0.197
-1.673 -1.305 -0.930 -0.547 -0.157
-1.637 -1.268 -0.892 -0.508 -0.118
-1.600 -1.231 -0.854 -0.470 -0.079
-1.564 -1.194 -0.816 -0.431 -0.039
-1.527 -1.156 -0.778 -0.392 0.000
-40 -30 -20 -10 0
500 510 520 530 540
20.644 21.071 21.497 21.924 22.350
20.687 21.113 21.540 21.966 22.393
20.730 21.156 21.582 22.009 22.435
20.772 21.199 21.625 22.052 22.478
20.815 21.241 21.668 22.094 22.521
20.857 21.284 21.710 22.137 22.563
20.900 21.326 21.753 22.179 22.606
20.943 21.369 21.796 22.222 22.649
20.985 21.412 21.838 22.265 22.691
21.028 21.454 21.881 22.307 22.734
21.071 21.497 21.924 22.350 22.776
500 510 520 530 540
0 10 20 30 40
0.000 0.397 0.798 1.203 1.612
0.039 0.437 0.838 1.244 1.653
0.079 0.477 0.879 1.285 1.694
0.119 0.517 0.919 1.326 1.735
0.158 0.557 0.960 1.366 1.776
0.198 0.597 1.000 1.407 1.817
0.238 0.637 1.041 1.448 1.858
0.277 0.677 1.081 1.489 1.899
0.317 0.718 1.122 1.530 1.941
0.357 0.758 1.163 1.571 1.982
0.397 0.798 1.203 1.612 2.023
0 10 20 30 40
550 560 570 580 590
22.776 23.203 23.629 24.055 24.480
22.819 23.245 23.671 24.097 24.523
22.862 23.288 23.714 24.140 24.565
22.904 23.331 23.757 24.182 24.608
22.947 23.373 23.799 24.225 24.650
22.990 23.416 23.842 24.267 24.693
23.032 23.458 23.884 24.310 24.735
23.075 23.501 23.927 24.353 24.778
23.117 23.544 23.970 24.395 24.820
23.160 23.586 24.012 24.438 24.863
23.203 23.629 24.055 24.480 24.905
550 560 570 580 590
50 60 70 80 90
2.023 2.436 2.851 3.267 3.682
2.064 2.478 2.893 3.308 3.723
2.106 2.519 2.934 3.350 3.765
2.147 2.561 2.976 3.391 3.806
2.188 2.602 3.017 3.433 3.848
2.230 2.644 3.059 3.474 3.889
2.271 2.685 3.100 3.516 3.931
2.312 2.727 3.142 3.557 3.972
2.354 2.768 3.184 3.599 4.013
2.395 2.810 3.225 3.640 4.055
2.436 2.851 3.267 3.682 4.096
50 60 70 80 90
600 610 620 630 640
24.905 25.330 25.755 26.179 26.602
24.948 25.373 25.797 26.221 26.644
24.990 25.415 25.840 26.263 26.687
25.033 25.458 25.882 26.306 26.729
25.075 25.500 25.924 26.348 26.771
25.118 25.543 25.967 26.390 26.814
25.160 25.585 26.009 26.433 26.856
25.203 25.627 26.052 26.475 26.898
25.245 25.670 26.094 26.517 26.940
25.288 25.712 26.136 26.560 26.983
25.330 25.755 26.179 26.602 27.025
600 610 620 630 640
100 110 120 130 140
4.096 4.509 4.920 5.328 5.735
4.138 4.550 4.961 5.369 5.775
4.179 4.591 5.002 5.410 5.815
4.220 4.633 5.043 5.450 5.856
4.262 4.674 5.084 5.491 5.896
4.303 4.715 5.124 5.532 5.937
4.344 4.756 5.165 5.572 5.977
4.385 4.797 5.206 5.613 6.017
4.427 4.838 5.247 5.653 6.058
4.468 4.879 5.288 5.694 6.098
4.509 4.920 5.328 5.735 6.138
100 110 120 130 140
650 660 670 680 690
27.025 27.447 27.869 28.289 28.710
27.067 27.489 27.911 28.332 28.752
27.109 27.531 27.953 28.374 28.794
27.152 27.574 27.995 28.416 28.835
27.194 27.616 28.037 28.458 28.877
27.236 27.658 28.079 28.500 28.919
27.278 27.700 28.121 28.542 28.961
27.320 27.742 28.163 28.584 29.003
27.363 27.784 28.205 28.626 29.045
27.405 27.826 28.247 28.668 29.087
27.447 27.869 28.289 28.710 29.129
650 660 670 680 690
150 160 170 180 190
6.138 6.540 6.941 7.340 7.739
6.179 6.580 6.981 7.380 7.779
6.219 6.620 7.021 7.420 7.819
6.259 6.660 7.060 7.460 7.859
6.299 6.701 7.100 7.500 7.899
6.339 6.741 7.140 7.540 7.939
6.380 6.781 7.180 7.579 7.979
6.420 6.821 7.220 7.619 8.019
6.460 6.861 7.260 7.659 8.059
6.500 6.901 7.300 7.699 8.099
6.540 6.941 7.340 7.739 8.138
150 160 170 180 190
700 710 720 730 740
29.129 29.548 29.965 30.382 30.798
29.171 29.589 30.007 30.424 30.840
29.213 29.631 30.049 30.466 30.881
29.255 29.673 30.090 30.507 30.923
29.297 29.715 30.132 30.549 30.964
29.338 29.757 30.174 30.590 31.006
29.380 29.798 30.216 30.632 31.047
29.422 29.840 30.257 30.674 31.089
29.464 29.882 30.299 30.715 31.130
29.506 29.924 30.341 30.757 31.172
29.548 29.965 30.382 30.798 31.213
700 710 720 730 740
200 210 220 230 240
8.138 8.539 8.940 9.343 9.747
8.178 8.579 8.980 9.383 9.788
8.218 8.619 9.020 9.423 9.828
8.258 8.659 9.061 9.464 9.869
8.298 8.699 9.101 9.504 9.909
8.338 8.739 9.141 9.545 9.950
8.378 8.418 8.458 8.499 8.539 8.779 8.819 8.860 8.900 8.940 9.181 9.222 9.262 9.302 9.343 9.585 9.626 9.666 9.707 9.747 9.991 10.031 10.072 10.113 10.153
200 210 220 230 240
750 760 770 780 790
31.213 31.628 32.041 32.453 32.865
31.255 31.669 32.082 32.495 32.906
31.296 31.710 32.124 32.536 32.947
31.338 31.752 32.165 32.577 32.988
31.379 31.793 32.206 32.618 33.029
31.421 31.834 32.247 32.659 33.070
31.462 31.876 32.289 32.700 33.111
31.504 31.917 32.330 32.742 33.152
31.545 31.958 32.371 32.783 33.193
31.586 32.000 32.412 32.824 33.234
31.628 32.041 32.453 32.865 33.275
750 760 770 780 790
°C
0
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
1
-8
2
-7
3
-6
4
-5
5
-4
6
-3
7
-2
8
-1
9
0
10
Z-204
Z
+ –
Revised Thermocouple Reference Tables
TYPE
K
Thermocouple Grade
Nickel-Chromium vs. Nickel-Aluminum
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 2282°F – 200 to 1250°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Clean Oxidizing and Inert; Limited Use in Vacuum or Reducing; Wide Temperature Range; Most Popular Calibration TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
Thermoelectric Voltage in Millivolts
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
800 810 820 830 840
33.275 33.685 34.093 34.501 34.908
33.316 33.726 34.134 34.542 34.948
33.357 33.767 34.175 34.582 34.989
33.398 33.808 34.216 34.623 35.029
33.439 33.848 34.257 34.664 35.070
33.480 33.889 34.297 34.704 35.110
33.521 33.930 34.338 34.745 35.151
33.562 33.971 34.379 34.786 35.192
33.603 34.012 34.420 34.826 35.232
33.644 34.053 34.460 34.867 35.273
33.685 34.093 34.501 34.908 35.313
800 810 820 830 840
1100 1110 1120 1130 1140
45.119 45.497 45.873 46.249 46.623
45.157 45.534 45.911 46.286 46.660
45.194 45.572 45.948 46.324 46.697
45.232 45.610 45.986 46.361 46.735
45.270 45.647 46.024 46.398 46.772
45.308 45.685 46.061 46.436 46.809
45.346 45.723 46.099 46.473 46.847
45.383 45.760 46.136 46.511 46.884
45.421 45.798 46.174 46.548 46.921
45.459 45.836 46.211 46.585 46.958
45.497 45.873 46.249 46.623 46.995
1100 1110 1120 1130 1140
850 860 870 880 890
35.313 35.718 36.121 36.524 36.925
35.354 35.758 36.162 36.564 36.965
35.394 35.798 36.202 36.604 37.006
35.435 35.839 36.242 36.644 37.046
35.475 35.879 36.282 36.685 37.086
35.516 35.920 36.323 36.725 37.126
35.556 35.960 36.363 36.765 37.166
35.596 36.000 36.403 36.805 37.206
35.637 36.041 36.443 36.845 37.246
35.677 36.081 36.484 36.885 37.286
35.718 36.121 36.524 36.925 37.326
850 860 870 880 890
1150 1160 1170 1180 1190
46.995 47.367 47.737 48.105 48.473
47.033 47.404 47.774 48.142 48.509
47.070 47.441 47.811 48.179 48.546
47.107 47.478 47.848 48.216 48.582
47.144 47.515 47.884 48.252 48.619
47.181 47.552 47.921 48.289 48.656
47.218 47.589 47.958 48.326 48.692
47.256 47.626 47.995 48.363 48.729
47.293 47.663 48.032 48.399 48.765
47.330 47.700 48.069 48.436 48.802
47.367 47.737 48.105 48.473 48.838
1150 1160 1170 1180 1190
900 910 920 930 940
37.326 37.725 38.124 38.522 38.918
37.366 37.765 38.164 38.561 38.958
37.406 37.805 38.204 38.601 38.997
37.446 37.845 38.243 38.641 39.037
37.486 37.885 38.283 38.680 39.076
37.526 37.925 38.323 38.720 39.116
37.566 37.965 38.363 38.760 39.155
37.606 38.005 38.402 38.799 39.195
37.646 38.044 38.442 38.839 39.235
37.686 38.084 38.482 38.878 39.274
37.725 38.124 38.522 38.918 39.314
900 910 920 930 940
1200 1210 1220 1230 1240
48.838 49.202 49.565 49.926 50.286
48.875 49.239 49.601 49.962 50.322
48.911 49.275 49.637 49.998 50.358
48.948 49.311 49.674 50.034 50.393
48.984 49.348 49.710 50.070 50.429
49.021 49.384 49.746 50.106 50.465
49.057 49.420 49.782 50.142 50.501
49.093 49.456 49.818 50.178 50.537
49.130 49.493 49.854 50.214 50.572
49.166 49.529 49.890 50.250 50.608
49.202 49.565 49.926 50.286 50.644
1200 1210 1220 1230 1240
950 960 970 980 990
39.314 39.708 40.101 40.494 40.885
39.353 39.747 40.141 40.533 40.924
39.393 39.787 40.180 40.572 40.963
39.432 39.826 40.219 40.611 41.002
39.471 39.866 40.259 40.651 41.042
39.511 39.905 40.298 40.690 41.081
39.550 39.944 40.337 40.729 41.120
39.590 39.984 40.376 40.768 41.159
39.629 40.023 40.415 40.807 41.198
39.669 40.062 40.455 40.846 41.237
39.708 40.101 40.494 40.885 41.276
950 960 970 980 990
1250 1260 1270 1280 1290
50.644 51.000 51.355 51.708 52.060
50.680 51.036 51.391 51.744 52.095
50.715 51.071 51.426 51.779 52.130
50.751 51.107 51.461 51.814 52.165
50.787 51.142 51.497 51.849 52.200
50.822 51.178 51.532 51.885 52.235
50.858 51.213 51.567 51.920 52.270
50.894 51.249 51.603 51.955 52.305
50.929 51.284 51.638 51.990 52.340
50.965 51.320 51.673 52.025 52.375
51.000 51.355 51.708 52.060 52.410
1250 1260 1270 1280 1290
1000 1010 1020 1030 1040
41.276 41.665 42.053 42.440 42.826
41.315 41.704 42.092 42.479 42.865
41.354 41.743 42.131 42.518 42.903
41.393 41.781 42.169 42.556 42.942
41.431 41.820 42.208 42.595 42.980
41.470 41.859 42.247 42.633 43.019
41.509 41.898 42.286 42.672 43.057
41.548 41.937 42.324 42.711 43.096
41.587 41.976 42.363 42.749 43.134
41.626 42.014 42.402 42.788 43.173
41.665 42.053 42.440 42.826 43.211
1000 1010 1020 1030 1040
1300 1310 1320 1330 1340
52.410 52.759 53.106 53.451 53.795
52.445 52.794 53.140 53.486 53.830
52.480 52.828 53.175 53.520 53.864
52.515 52.863 53.210 53.555 53.898
52.550 52.898 53.244 53.589 53.932
52.585 52.932 53.279 53.623 53.967
52.620 52.967 53.313 53.658 54.001
52.654 53.002 53.348 53.692 54.035
52.689 53.037 53.382 53.727 54.069
52.724 53.071 53.417 53.761 54.104
52.759 53.106 53.451 53.795 54.138
1300 1310 1320 1330 1340
1050 1060 1070 1080 1090
43.211 43.595 43.978 44.359 44.740
43.250 43.633 44.016 44.397 44.778
43.288 43.672 44.054 44.435 44.816
43.327 43.710 44.092 44.473 44.853
43.365 43.748 44.130 44.512 44.891
43.403 43.787 44.169 44.550 44.929
43.442 43.825 44.207 44.588 44.967
43.480 43.863 44.245 44.626 45.005
43.518 43.901 44.283 44.664 45.043
43.557 43.940 44.321 44.702 45.081
43.595 43.978 44.359 44.740 45.119
1050 1060 1070 1080 1090
1350 54.138 54.172 54.206 54.240 54.274 54.308 54.343 54.377 54.411 54.445 54.479 1350 1360 54.479 54.513 54.547 54.581 54.615 54.649 54.683 54.717 54.751 54.785 54.819 1360 1370 54.819 54.852 54.886 1370
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
Z-205
0
1
2
3
4
5
6
7
8
9
10
°C
°C
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 1652°F – 200 to 900°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 1.7°C or 0.5% Above 0°C 1.7°C or 1.0% Below 0°C Special: 1.0°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Limited Use in Vacuum or Reducing; Highest EMF Change per Degree TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
+ –
Revised Thermocouple Reference Tables
Thermocouple Grade
TYPE
Nickel-Chromium vs. Copper-Nickel
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °C
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
E
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
-260 -250
-9.835 -9.833 -9.831 -9.828 -9.825 -9.821 -9.817 -9.813 -9.808 -9.802 -9.797 -260 -9.797 -9.790 -9.784 -9.777 -9.770 -9.762 -9.754 -9.746 -9.737 -9.728 -9.718 -250
350 360 370 380 390
24.964 25.757 26.552 27.348 28.146
25.044 25.836 26.631 27.428 28.226
25.123 25.916 26.711 27.507 28.306
25.202 25.995 26.790 27.587 28.386
25.281 26.075 26.870 27.667 28.466
25.360 26.154 26.950 27.747 28.546
25.440 26.233 27.029 27.827 28.626
25.519 26.313 27.109 27.907 28.706
25.598 26.392 27.189 27.986 28.786
25.678 26.472 27.268 28.066 28.866
25.757 26.552 27.348 28.146 28.946
350 360 370 380 390
-240 -230 -220 -210 -200
-9.718 -9.604 -9.455 -9.274 -9.063
-9.709 -9.591 -9.438 -9.254 -9.040
-9.698 -9.577 -9.421 -9.234 -9.017
-9.688 -9.563 -9.404 -9.214 -8.994
-9.677 -9.548 -9.386 -9.193 -8.971
-9.666 -9.534 -9.368 -9.172 -8.947
-9.654 -9.519 -9.350 -9.151 -8.923
-9.642 -9.503 -9.331 -9.129 -8.899
-9.630 -9.487 -9.313 -9.107 -8.874
-9.617 -9.471 -9.293 -9.085 -8.850
-9.604 -9.455 -9.274 -9.063 -8.825
-240 -230 -220 -210 -200
400 410 420 430 440
28.946 29.747 30.550 31.354 32.159
29.026 29.827 30.630 31.434 32.239
29.106 29.908 30.711 31.515 32.320
29.186 29.988 30.791 31.595 32.400
29.266 30.068 30.871 31.676 32.481
29.346 30.148 30.952 31.756 32.562
29.427 30.229 31.032 31.837 32.642
29.507 30.309 31.112 31.917 32.723
29.587 30.389 31.193 31.998 32.803
29.667 30.470 31.273 32.078 32.884
29.747 30.550 31.354 32.159 32.965
400 410 420 430 440
-190 -180 -170 -160 -150
-8.825 -8.561 -8.273 -7.963 -7.632
-8.799 -8.533 -8.243 -7.931 -7.597
-8.774 -8.505 -8.213 -7.899 -7.563
-8.748 -8.477 -8.183 -7.866 -7.528
-8.722 -8.449 -8.152 -7.833 -7.493
-8.696 -8.420 -8.121 -7.800 -7.458
-8.669 -8.391 -8.090 -7.767 -7.423
-8.643 -8.362 -8.059 -7.733 -7.387
-8.616 -8.333 -8.027 -7.700 -7.351
-8.588 -8.303 -7.995 -7.666 -7.315
-8.561 -8.273 -7.963 -7.632 -7.279
-190 -180 -170 -160 -150
450 460 470 480 490
32.965 33.772 34.579 35.387 36.196
33.045 33.852 34.660 35.468 36.277
33.126 33.933 34.741 35.549 36.358
33.207 34.014 34.822 35.630 36.439
33.287 34.095 34.902 35.711 36.520
33.368 34.175 34.983 35.792 36.601
33.449 34.256 35.064 35.873 36.682
33.529 34.337 35.145 35.954 36.763
33.610 34.418 35.226 36.034 36.843
33.691 34.498 35.307 36.115 36.924
33.772 34.579 35.387 36.196 37.005
450 460 470 480 490
-140 -130 -120 -110 -100
-7.279 -6.907 -6.516 -6.107 -5.681
-7.243 -6.869 -6.476 -6.065 -5.637
-7.206 -6.831 -6.436 -6.023 -5.593
-7.170 -6.792 -6.396 -5.981 -5.549
-7.133 -6.753 -6.355 -5.939 -5.505
-7.096 -6.714 -6.314 -5.896 -5.461
-7.058 -6.675 -6.273 -5.853 -5.417
-7.021 -6.636 -6.232 -5.810 -5.372
-6.983 -6.596 -6.191 -5.767 -5.327
-6.945 -6.556 -6.149 -5.724 -5.282
-6.907 -6.516 -6.107 -5.681 -5.237
-140 -130 -120 -110 -100
500 510 520 530 540
37.005 37.815 38.624 39.434 40.243
37.086 37.896 38.705 39.515 40.324
37.167 37.977 38.786 39.596 40.405
37.248 38.058 38.867 39.677 40.486
37.329 38.139 38.948 39.758 40.567
37.410 38.220 39.029 39.839 40.648
37.491 38.300 39.110 39.920 40.729
37.572 38.381 39.191 40.001 40.810
37.653 38.462 39.272 40.082 40.891
37.734 38.543 39.353 40.163 40.972
37.815 38.624 39.434 40.243 41.053
500 510 520 530 540
-90 -80 -70 -60 -50
-5.237 -4.777 -4.302 -3.811 -3.306
-5.192 -4.731 -4.254 -3.761 -3.255
-5.147 -4.684 -4.205 -3.711 -3.204
-5.101 -4.636 -4.156 -3.661 -3.152
-5.055 -4.589 -4.107 -3.611 -3.100
-5.009 -4.542 -4.058 -3.561 -3.048
-4.963 -4.494 -4.009 -3.510 -2.996
-4.917 -4.446 -3.960 -3.459 -2.944
-4.871 -4.398 -3.911 -3.408 -2.892
-4.824 -4.350 -3.861 -3.357 -2.840
-4.777 -4.302 -3.811 -3.306 -2.787
-90 -80 -70 -60 -50
550 560 570 580 590
41.053 41.862 42.671 43.479 44.286
41.134 41.943 42.751 43.560 44.367
41.215 42.024 42.832 43.640 44.448
41.296 42.105 42.913 43.721 44.529
41.377 42.185 42.994 43.802 44.609
41.457 42.266 43.075 43.883 44.690
41.538 42.347 43.156 43.963 44.771
41.619 42.428 43.236 44.044 44.851
41.700 42.509 43.317 44.125 44.932
41.781 42.590 43.398 44.206 45.013
41.862 42.671 43.479 44.286 45.093
550 560 570 580 590
-40 -30 -20 -10 0
-2.787 -2.255 -1.709 -1.152 -0.582
-2.735 -2.201 -1.654 -1.095 -0.524
-2.682 -2.147 -1.599 -1.039 -0.466
-2.629 -2.093 -1.543 -0.982 -0.408
-2.576 -2.038 -1.488 -0.925 -0.350
-2.523 -1.984 -1.432 -0.868 -0.292
-2.469 -1.929 -1.376 -0.811 -0.234
-2.416 -1.874 -1.320 -0.754 -0.176
-2.362 -1.820 -1.264 -0.697 -0.117
-2.309 -1.765 -1.208 -0.639 -0.059
-2.255 -1.709 -1.152 -0.582 0.000
-40 -30 -20 -10 0
600 610 620 630 640
45.093 45.900 46.705 47.509 48.313
45.174 45.980 46.785 47.590 48.393
45.255 46.061 46.866 47.670 48.474
45.335 46.141 46.946 47.751 48.554
45.416 46.222 47.027 47.831 48.634
45.497 46.302 47.107 47.911 48.715
45.577 46.383 47.188 47.992 48.795
45.658 46.463 47.268 48.072 48.875
45.738 46.544 47.349 48.152 48.955
45.819 46.624 47.429 48.233 49.035
45.900 46.705 47.509 48.313 49.116
600 610 620 630 640
0 10 20 30 40
0.000 0.591 1.192 1.801 2.420
0.059 0.651 1.252 1.862 2.482
0.118 0.711 1.313 1.924 2.545
0.176 0.770 1.373 1.986 2.607
0.235 0.830 1.434 2.047 2.670
0.294 0.890 1.495 2.109 2.733
0.354 0.950 1.556 2.171 2.795
0.413 1.010 1.617 2.233 2.858
0.472 1.071 1.678 2.295 2.921
0.532 1.131 1.740 2.357 2.984
0.591 1.192 1.801 2.420 3.048
0 10 20 30 40
650 660 670 680 690
49.116 49.917 50.718 51.517 52.315
49.196 49.997 50.798 51.597 52.395
49.276 50.077 50.878 51.677 52.475
49.356 50.157 50.958 51.757 52.555
49.436 50.238 51.038 51.837 52.634
49.517 50.318 51.118 51.916 52.714
49.597 50.398 51.197 51.996 52.794
49.677 50.478 51.277 52.076 52.873
49.757 50.558 51.357 52.156 52.953
49.837 50.638 51.437 52.236 53.033
49.917 50.718 51.517 52.315 53.112
650 660 670 680 690
50 60 70 80 90
3.048 3.685 4.330 4.985 5.648
3.111 3.749 4.395 5.051 5.714
3.174 3.813 4.460 5.117 5.781
3.238 3.877 4.526 5.183 5.848
3.301 3.942 4.591 5.249 5.915
3.365 4.006 4.656 5.315 5.982
3.429 4.071 4.722 5.382 6.049
3.492 4.136 4.788 5.448 6.117
3.556 4.200 4.853 5.514 6.184
3.620 4.265 4.919 5.581 6.251
3.685 4.330 4.985 5.648 6.319
50 60 70 80 90
700 710 720 730 740
53.112 53.908 54.703 55.497 56.289
53.192 53.988 54.782 55.576 56.368
53.272 54.067 54.862 55.655 56.447
53.351 54.147 54.941 55.734 56.526
53.431 54.226 55.021 55.814 56.606
53.510 54.306 55.100 55.893 56.685
53.590 54.385 55.179 55.972 56.764
53.670 54.465 55.259 56.051 56.843
53.749 54.544 55.338 56.131 56.922
53.829 54.624 55.417 56.210 57.001
53.908 54.703 55.497 56.289 57.080
700 710 720 730 740
100 110 120 130 140
6.319 6.998 7.685 8.379 9.081
6.386 7.066 7.754 8.449 9.151
6.454 7.135 7.823 8.519 9.222
6.522 7.203 7.892 8.589 9.292
6.590 7.272 7.962 8.659 9.363
6.658 7.341 8.031 8.729 9.434
6.725 7.409 8.101 8.799 9.505
6.794 7.478 8.170 8.869 9.576
6.862 7.547 8.240 8.940 9.647
6.930 7.616 8.309 9.010 9.718
6.998 7.685 8.379 9.081 9.789
100 110 120 130 140
750 760 770 780 790
57.080 57.870 58.659 59.446 60.232
57.159 57.949 58.738 59.525 60.311
57.238 58.028 58.816 59.604 60.390
57.317 58.107 58.895 59.682 60.468
57.396 58.186 58.974 59.761 60.547
57.475 58.265 59.053 59.839 60.625
57.554 58.343 59.131 59.918 60.704
57.633 58.422 59.210 59.997 60.782
57.712 58.501 59.289 60.075 60.860
57.791 58.580 59.367 60.154 60.939
57.870 58.659 59.446 60.232 61.017
750 760 770 780 790
150 160 170 180 190
9.789 10.503 11.224 11.951 12.684
9.860 10.575 11.297 12.024 12.757
9.931 10.647 11.369 12.097 12.831
10.003 10.719 11.442 12.170 12.904
10.074 10.791 11.514 12.243 12.978
10.145 10.863 11.587 12.317 13.052
10.217 10.935 11.660 12.390 13.126
10.288 11.007 11.733 12.463 13.199
10.360 11.080 11.805 12.537 13.273
10.432 11.152 11.878 12.610 13.347
10.503 11.224 11.951 12.684 13.421
150 160 170 180 190
800 810 820 830 840
61.017 61.801 62.583 63.364 64.144
61.096 61.879 62.662 63.442 64.222
61.174 61.958 62.740 63.520 64.300
61.253 62.036 62.818 63.598 64.377
61.331 62.114 62.896 63.676 64.455
61.409 62.192 62.974 63.754 64.533
61.488 62.271 63.052 63.832 64.611
61.566 62.349 63.130 63.910 64.689
61.644 62.427 63.208 63.988 64.766
61.723 62.505 63.286 64.066 64.844
61.801 62.583 63.364 64.144 64.922
800 810 820 830 840
200 210 220 230 240
13.421 14.164 14.912 15.664 16.420
13.495 14.239 14.987 15.739 16.496
13.569 14.313 15.062 15.815 16.572
13.644 14.388 15.137 15.890 16.648
13.718 14.463 15.212 15.966 16.724
13.792 14.537 15.287 16.041 16.800
13.866 14.612 15.362 16.117 16.876
13.941 14.687 15.438 16.193 16.952
14.015 14.762 15.513 16.269 17.028
14.090 14.837 15.588 16.344 17.104
14.164 14.912 15.664 16.420 17.181
200 210 220 230 240
850 860 870 880 890
64.922 65.698 66.473 67.246 68.017
65.000 65.776 66.550 67.323 68.094
65.077 65.853 66.628 67.400 68.171
65.155 65.931 66.705 67.478 68.248
65.233 66.008 66.782 67.555 68.325
65.310 66.086 66.860 67.632 68.402
65.388 66.163 66.937 67.709 68.479
65.465 66.241 67.014 67.786 68.556
65.543 66.318 67.092 67.863 68.633
65.621 66.396 67.169 67.940 68.710
65.698 66.473 67.246 68.017 68.787
850 860 870 880 890
250 260 270 280 290
17.181 17.945 18.713 19.484 20.259
17.257 18.021 18.790 19.561 20.336
17.333 18.098 18.867 19.639 20.414
17.409 18.175 18.944 19.716 20.492
17.486 18.252 19.021 19.794 20.569
17.562 18.328 19.098 19.871 20.647
17.639 18.405 19.175 19.948 20.725
17.715 18.482 19.252 20.026 20.803
17.792 18.559 19.330 20.103 20.880
17.868 18.636 19.407 20.181 20.958
17.945 18.713 19.484 20.259 21.036
250 260 270 280 290
900 910 920 930 940
68.787 69.554 70.319 71.082 71.844
68.863 69.631 70.396 71.159 71.920
68.940 69.707 70.472 71.235 71.996
69.017 69.784 70.548 71.311 72.072
69.094 69.860 70.625 71.387 72.147
69.171 69.937 70.701 71.463 72.223
69.247 70.013 70.777 71.539 72.299
69.324 70.090 70.854 71.615 72.375
69.401 70.166 70.930 71.692 72.451
69.477 70.243 71.006 71.768 72.527
69.554 70.319 71.082 71.844 72.603
900 910 920 930 940
300 310 320 330 340
21.036 21.817 22.600 23.386 24.174
21.114 21.895 22.678 23.464 24.253
21.192 21.973 22.757 23.543 24.332
21.270 22.051 22.835 23.622 24.411
21.348 22.130 22.914 23.701 24.490
21.426 22.208 22.993 23.780 24.569
21.504 22.286 23.071 23.858 24.648
21.582 22.365 23.150 23.937 24.727
21.660 22.443 23.228 24.016 24.806
21.739 22.522 23.307 24.095 24.885
21.817 22.600 23.386 24.174 24.964
300 310 320 330 340
950 960 970 980 990
72.603 73.360 74.115 74.869 75.621
72.678 73.435 74.190 74.944 75.696
72.754 73.511 74.266 75.019 75.771
72.830 73.586 74.341 75.095 75.847
72.906 73.662 74.417 75.170 75.922
72.981 73.738 74.492 75.245 75.997
73.057 73.813 74.567 75.320 76.072
73.133 73.889 74.643 75.395 76.147
73.208 73.964 74.718 75.471 76.223
73.284 74.040 74.793 75.546 76.298
73.360 74.115 74.869 75.621 76.373
950 960 970 980 990
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
Z-206
Z
+ –
Revised Thermocouple Reference Tables
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°C
-10
-9
0
6
7
8
10
°C
-260 -250
-6.258 -6.256 -6.255 -6.253 -6.251 -6.248 -6.245 -6.242 -6.239 -6.236 -6.232 -260 -6.232 -6.228 -6.223 -6.219 -6.214 -6.209 -6.204 -6.198 -6.193 -6.187 -6.180 -250
2.079 2.512 2.953 3.403 3.860
2.122 2.556 2.998 3.448 3.907
2.165 2.600 3.043 3.494 3.953
2.208 2.643 3.087 3.539 3.999
2.251 2.687 3.132 3.585 4.046
2.294 2.732 3.177 3.631 4.092
2.338 2.776 3.222 3.677 4.138
2.381 2.820 3.267 3.722 4.185
2.425 2.864 3.312 3.768 4.232
2.468 2.909 3.358 3.814 4.279
50 60 70 80 90
-240 -230 -220 -210 -200
-6.180 -6.105 -6.007 -5.888 -5.753
-6.174 -6.096 -5.996 -5.876 -5.739
-6.167 -6.087 -5.985 -5.863 -5.724
-6.160 -6.078 -5.973 -5.850 -5.710
-6.153 -6.068 -5.962 -5.836 -5.695
-6.146 -6.059 -5.950 -5.823 -5.680
-6.138 -6.049 -5.938 -5.809 -5.665
-6.130 -6.038 -5.926 -5.795 -5.650
-6.122 -6.028 -5.914 -5.782 -5.634
-6.114 -6.017 -5.901 -5.767 -5.619
-6.105 -6.007 -5.888 -5.753 -5.603
-240 -230 -220 -210 -200
100 110 120 130 140
4.279 4.750 5.228 5.714 6.206
4.325 4.798 5.277 5.763 6.255
4.372 4.845 5.325 5.812 6.305
4.419 4.893 5.373 5.861 6.355
4.466 4.941 5.422 5.910 6.404
4.513 4.988 5.470 5.959 6.454
4.561 5.036 5.519 6.008 6.504
4.608 5.084 5.567 6.057 6.554
4.655 5.132 5.616 6.107 6.604
4.702 5.180 5.665 6.156 6.654
4.750 5.228 5.714 6.206 6.704
100 110 120 130 140
-190 -180 -170 -160 -150
-5.603 -5.439 -5.261 -5.070 -4.865
-5.587 -5.421 -5.242 -5.050 -4.844
-5.571 -5.404 -5.224 -5.030 -4.823
-5.555 -5.387 -5.205 -5.010 -4.802
-5.539 -5.369 -5.186 -4.989 -4.780
-5.523 -5.351 -5.167 -4.969 -4.759
-5.506 -5.334 -5.148 -4.949 -4.737
-5.489 -5.316 -5.128 -4.928 -4.715
-5.473 -5.297 -5.109 -4.907 -4.693
-5.456 -5.279 -5.089 -4.886 -4.671
-5.439 -5.261 -5.070 -4.865 -4.648
-190 -180 -170 -160 -150
150 160 170 180 190
6.704 7.209 7.720 8.237 8.759
6.754 7.260 7.771 8.289 8.812
6.805 7.310 7.823 8.341 8.865
6.855 7.361 7.874 8.393 8.917
6.905 7.412 7.926 8.445 8.970
6.956 7.463 7.977 8.497 9.023
7.006 7.515 8.029 8.550 9.076
7.057 7.566 8.081 8.602 9.129
7.107 7.617 8.133 8.654 9.182
7.158 7.668 8.185 8.707 9.235
7.209 7.720 8.237 8.759 9.288
150 160 170 180 190
-140 -130 -120 -110 -100
-4.648 -4.419 -4.177 -3.923 -3.657
-4.626 -4.395 -4.152 -3.897 -3.629
-4.604 -4.372 -4.127 -3.871 -3.602
-4.581 -4.348 -4.102 -3.844 -3.574
-4.558 -4.324 -4.077 -3.818 -3.547
-4.535 -4.300 -4.052 -3.791 -3.519
-4.512 -4.275 -4.026 -3.765 -3.491
-4.489 -4.251 -4.000 -3.738 -3.463
-4.466 -4.226 -3.975 -3.711 -3.435
-4.443 -4.202 -3.949 -3.684 -3.407
-4.419 -4.177 -3.923 -3.657 -3.379
-140 -130 -120 -110 -100
200 9.288 9.341 9.395 9.448 9.501 9.555 210 9.822 9.876 9.930 9.984 10.038 10.092 220 10.362 10.417 10.471 10.525 10.580 10.634 230 10.907 10.962 11.017 11.072 11.127 11.182 240 11.458 11.513 11.569 11.624 11.680 11.735
9.608 10.146 10.689 11.237 11.791
9.662 10.200 10.743 11.292 11.846
9.715 10.254 10.798 11.347 11.902
9.769 10.308 10.853 11.403 11.958
9.822 10.362 10.907 11.458 12.013
200 210 220 230 240
-90 -80 -70 -60 -50
-3.379 -3.089 -2.788 -2.476 -2.153
-3.350 -3.059 -2.757 -2.444 -2.120
-3.322 -3.030 -2.726 -2.412 -2.087
-3.293 -3.000 -2.695 -2.380 -2.054
-3.264 -2.970 -2.664 -2.348 -2.021
-3.235 -2.940 -2.633 -2.316 -1.987
-3.206 -2.910 -2.602 -2.283 -1.954
-3.177 -2.879 -2.571 -2.251 -1.920
-3.148 -2.849 -2.539 -2.218 -1.887
-3.118 -2.818 -2.507 -2.186 -1.853
-3.089 -2.788 -2.476 -2.153 -1.819
-90 -80 -70 -60 -50
250 260 270 280 290
12.013 12.574 13.139 13.709 14.283
12.069 12.630 13.196 13.766 14.341
12.125 12.687 13.253 13.823 14.399
12.181 12.743 13.310 13.881 14.456
12.237 12.799 13.366 13.938 14.514
12.293 12.856 13.423 13.995 14.572
12.349 12.912 13.480 14.053 14.630
12.405 12.969 13.537 14.110 14.688
12.461 13.026 13.595 14.168 14.746
12.518 13.082 13.652 14.226 14.804
12.574 13.139 13.709 14.283 14.862
250 260 270 280 290
-40 -30 -20 -10 0
-1.819 -1.475 -1.121 -0.757 -0.383
-1.785 -1.440 -1.085 -0.720 -0.345
-1.751 -1.405 -1.049 -0.683 -0.307
-1.717 -1.370 -1.013 -0.646 -0.269
-1.683 -1.335 -0.976 -0.608 -0.231
-1.648 -1.299 -0.940 -0.571 -0.193
-1.614 -1.264 -0.904 -0.534 -0.154
-1.579 -1.228 -0.867 -0.496 -0.116
-1.545 -1.192 -0.830 -0.459 -0.077
-1.510 -1.157 -0.794 -0.421 -0.039
-1.475 -1.121 -0.757 -0.383 0.000
-40 -30 -20 -10 0
300 310 320 330 340
14.862 15.445 16.032 16.624 17.219
14.920 15.503 16.091 16.683 17.279
14.978 15.562 16.150 16.742 17.339
15.036 15.621 16.209 16.802 17.399
15.095 15.679 16.268 16.861 17.458
15.153 15.738 16.327 16.921 17.518
15.211 15.797 16.387 16.980 17.578
15.270 15.856 16.446 17.040 17.638
15.328 15.914 16.505 17.100 17.698
15.386 15.973 16.564 17.159 17.759
15.445 16.032 16.624 17.219 17.819
300 310 320 330 340
0 10 20 30 40
0.000 0.391 0.790 1.196 1.612
0.039 0.431 0.830 1.238 1.654
0.078 0.470 0.870 1.279 1.696
0.117 0.510 0.911 1.320 1.738
0.156 0.549 0.951 1.362 1.780
0.195 0.589 0.992 1.403 1.823
0.234 0.629 1.033 1.445 1.865
0.273 0.669 1.074 1.486 1.908
0.312 0.709 1.114 1.528 1.950
0.352 0.749 1.155 1.570 1.993
0.391 0.790 1.196 1.612 2.036
0 10 20 30 40
350 360 370 380 390
17.819 18.422 19.030 19.641 20.255
17.879 18.483 19.091 19.702 20.317
17.939 18.543 19.152 19.763 20.378
17.999 18.604 19.213 19.825 20.440
18.060 18.665 19.274 19.886 20.502
18.120 18.725 19.335 19.947 20.563
18.180 18.786 19.396 20.009 20.625
18.241 18.847 19.457 20.070 20.687
18.301 18.908 19.518 20.132 20.748
18.362 18.969 19.579 20.193 20.810
18.422 19.030 19.641 20.255 20.872
350 360 370 380 390
°C
0
6
7
8
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
5
-4
Thermoelectric Voltage in Millivolts 2.036 2.468 2.909 3.358 3.814
4
-5
Extension Grade
50 60 70 80 90
3
-6
+ –
°C
2
-7
Copper vs. Copper-Nickel
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 662°F – 200 to 350°C Extension Grade – 76 to 212°F – 60 to 100°C LIMITS OF ERROR (whichever is greater) Standard: 1.0°C or 0.75% Above 0°C 1.0°C or 1.5% Below 0°C Special: 0.5°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Mild Oxidizing, Reducing Vacuum or Inert; Good Where Moisture Is Present; Low Temperature and Cryogenic Applications TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
°C
1
-8
T
Thermocouple Grade
-3
-2
-1
9
0
Z-207
1
2
3
4
5
9
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °C Extension REFERENCE JUNCTION AT 0°C Grade
Thermocouple Grade
NONE ESTABLISHED
Platinum-10% Rhodium vs. Platinum
Revised Thermocouple Reference Tables
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts °C
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
°C
°C
0
6
7
8
10
°C
-40 -30 -20 -10 0
-0.236 -0.194 -0.150 -0.103 -0.053
-0.232 -0.190 -0.146 -0.098 -0.048
-0.228 -0.186 -0.141 -0.093 -0.042
-0.224 -0.181 -0.136 -0.088 -0.037
-0.219 -0.177 -0.132 -0.083 -0.032
-0.215 -0.173 -0.127 -0.078 -0.027
-0.211 -0.168 -0.122 -0.073 -0.021
-0.207 -0.164 -0.117 -0.068 -0.016
-0.203 -0.159 -0.113 -0.063 -0.011
-0.199 -0.155 -0.108 -0.058 -0.005
-0.194 -0.150 -0.103 -0.053 0.000
-40 -30 -20 -10 0
550 560 570 580 590
4.732 4.833 4.934 5.035 5.137
4.742 4.843 4.944 5.045 5.147
4.752 4.853 4.954 5.055 5.157
4.762 4.863 4.964 5.066 5.167
4.772 4.873 4.974 5.076 5.178
4.782 4.883 4.984 5.086 5.188
4.793 4.893 4.995 5.096 5.198
4.803 4.904 5.005 5.106 5.208
4.813 4.914 5.015 5.116 5.218
4.823 4.924 5.025 5.127 5.228
4.833 4.934 5.035 5.137 5.239
550 560 570 580 590
0 10 20 30 40
0.000 0.055 0.113 0.173 0.235
0.005 0.061 0.119 0.179 0.241
0.011 0.067 0.125 0.185 0.248
0.016 0.072 0.131 0.191 0.254
0.022 0.078 0.137 0.197 0.260
0.027 0.084 0.143 0.204 0.267
0.033 0.090 0.149 0.210 0.273
0.038 0.095 0.155 0.216 0.280
0.044 0.101 0.161 0.222 0.286
0.050 0.107 0.167 0.229 0.292
0.055 0.113 0.173 0.235 0.299
0 10 20 30 40
600 610 620 630 640
5.239 5.341 5.443 5.546 5.649
5.249 5.351 5.454 5.557 5.660
5.259 5.361 5.464 5.567 5.670
5.269 5.372 5.474 5.577 5.680
5.280 5.382 5.485 5.588 5.691
5.290 5.392 5.495 5.598 5.701
5.300 5.402 5.505 5.608 5.712
5.310 5.413 5.515 5.618 5.722
5.320 5.423 5.526 5.629 5.732
5.331 5.433 5.536 5.639 5.743
5.341 5.443 5.546 5.649 5.753
600 610 620 630 640
50 60 70 80 90
0.299 0.365 0.433 0.502 0.573
0.305 0.372 0.440 0.509 0.580
0.312 0.378 0.446 0.516 0.588
0.319 0.385 0.453 0.523 0.595
0.325 0.392 0.460 0.530 0.602
0.332 0.399 0.467 0.538 0.609
0.338 0.405 0.474 0.545 0.617
0.345 0.412 0.481 0.552 0.624
0.352 0.419 0.488 0.559 0.631
0.358 0.426 0.495 0.566 0.639
0.365 0.433 0.502 0.573 0.646
50 60 70 80 90
650 660 670 680 690
5.753 5.857 5.961 6.065 6.170
5.763 5.867 5.971 6.076 6.181
5.774 5.878 5.982 6.086 6.191
5.784 5.888 5.992 6.097 6.202
5.794 5.898 6.003 6.107 6.212
5.805 5.909 6.013 6.118 6.223
5.815 5.919 6.024 6.128 6.233
5.826 5.930 6.034 6.139 6.244
5.836 5.940 6.044 6.149 6.254
5.846 5.950 6.055 6.160 6.265
5.857 5.961 6.065 6.170 6.275
650 660 670 680 690
100 110 120 130 140
0.646 0.720 0.795 0.872 0.950
0.653 0.727 0.803 0.880 0.958
0.661 0.735 0.811 0.888 0.966
0.668 0.743 0.818 0.896 0.974
0.675 0.750 0.826 0.903 0.982
0.683 0.758 0.834 0.911 0.990
0.690 0.765 0.841 0.919 0.998
0.698 0.773 0.849 0.927 1.006
0.705 0.780 0.857 0.935 1.013
0.713 0.788 0.865 0.942 1.021
0.720 0.795 0.872 0.950 1.029
100 110 120 130 140
700 710 720 730 740
6.275 6.381 6.486 6.593 6.699
6.286 6.391 6.497 6.603 6.710
6.296 6.402 6.508 6.614 6.720
6.307 6.412 6.518 6.624 6.731
6.317 6.423 6.529 6.635 6.742
6.328 6.434 6.539 6.646 6.752
6.338 6.444 6.550 6.656 6.763
6.349 6.455 6.561 6.667 6.774
6.360 6.465 6.571 6.678 6.784
6.370 6.476 6.582 6.688 6.795
6.381 6.486 6.593 6.699 6.806
700 710 720 730 740
150 160 170 180 190
1.029 1.110 1.191 1.273 1.357
1.037 1.118 1.199 1.282 1.365
1.045 1.126 1.207 1.290 1.373
1.053 1.134 1.216 1.298 1.382
1.061 1.142 1.224 1.307 1.390
1.069 1.150 1.232 1.315 1.399
1.077 1.158 1.240 1.323 1.407
1.085 1.167 1.249 1.332 1.415
1.094 1.175 1.257 1.340 1.424
1.102 1.183 1.265 1.348 1.432
1.110 1.191 1.273 1.357 1.441
150 160 170 180 190
750 760 770 780 790
6.806 6.913 7.020 7.128 7.236
6.817 6.924 7.031 7.139 7.247
6.827 6.934 7.042 7.150 7.258
6.838 6.945 7.053 7.161 7.269
6.849 6.956 7.064 7.172 7.280
6.859 6.967 7.074 7.182 7.291
6.870 6.977 7.085 7.193 7.302
6.881 6.988 7.096 7.204 7.312
6.892 6.999 7.107 7.215 7.323
6.902 7.010 7.117 7.226 7.334
6.913 7.020 7.128 7.236 7.345
750 760 770 780 790
200 210 220 230 240
1.441 1.526 1.612 1.698 1.786
1.449 1.534 1.620 1.707 1.794
1.458 1.543 1.629 1.716 1.803
1.466 1.551 1.638 1.724 1.812
1.475 1.560 1.646 1.733 1.821
1.483 1.569 1.655 1.742 1.829
1.492 1.577 1.663 1.751 1.838
1.500 1.586 1.672 1.759 1.847
1.509 1.594 1.681 1.768 1.856
1.517 1.603 1.690 1.777 1.865
1.526 1.612 1.698 1.786 1.874
200 210 220 230 240
800 810 820 830 840
7.345 7.454 7.563 7.673 7.783
7.356 7.465 7.574 7.684 7.794
7.367 7.476 7.585 7.695 7.805
7.378 7.487 7.596 7.706 7.816
7.388 7.497 7.607 7.717 7.827
7.399 7.508 7.618 7.728 7.838
7.410 7.519 7.629 7.739 7.849
7.421 7.530 7.640 7.750 7.860
7.432 7.541 7.651 7.761 7.871
7.443 7.552 7.662 7.772 7.882
7.454 7.563 7.673 7.783 7.893
800 810 820 830 840
250 260 270 280 290
1.874 1.962 2.052 2.141 2.232
1.882 1.971 2.061 2.151 2.241
1.891 1.980 2.070 2.160 2.250
1.900 1.989 2.078 2.169 2.259
1.909 1.998 2.087 2.178 2.268
1.918 2.007 2.096 2.187 2.277
1.927 2.016 2.105 2.196 2.287
1.936 2.025 2.114 2.205 2.296
1.944 2.034 2.123 2.214 2.305
1.953 2.043 2.132 2.223 2.314
1.962 2.052 2.141 2.232 2.323
250 260 270 280 290
850 860 870 880 890
7.893 8.003 8.114 8.226 8.337
7.904 8.014 8.125 8.237 8.348
7.915 8.026 8.137 8.248 8.360
7.926 8.037 8.148 8.259 8.371
7.937 8.048 8.159 8.270 8.382
7.948 8.059 8.170 8.281 8.393
7.959 8.070 8.181 8.293 8.404
7.970 8.081 8.192 8.304 8.416
7.981 8.092 8.203 8.315 8.427
7.992 8.103 8.214 8.326 8.438
8.003 8.114 8.226 8.337 8.449
850 860 870 880 890
300 310 320 330 340
2.323 2.415 2.507 2.599 2.692
2.332 2.424 2.516 2.609 2.702
2.341 2.433 2.525 2.618 2.711
2.350 2.442 2.534 2.627 2.720
2.360 2.451 2.544 2.636 2.730
2.369 2.461 2.553 2.646 2.739
2.378 2.470 2.562 2.655 2.748
2.387 2.479 2.571 2.664 2.758
2.396 2.488 2.581 2.674 2.767
2.405 2.497 2.590 2.683 2.776
2.415 2.507 2.599 2.692 2.786
300 310 320 330 340
900 910 920 930 940
8.449 8.562 8.674 8.787 8.900
8.460 8.573 8.685 8.798 8.912
8.472 8.584 8.697 8.810 8.923
8.483 8.595 8.708 8.821 8.935
8.494 8.607 8.719 8.832 8.946
8.505 8.618 8.731 8.844 8.957
8.517 8.629 8.742 8.855 8.969
8.528 8.640 8.753 8.866 8.980
8.539 8.652 8.765 8.878 8.991
8.550 8.663 8.776 8.889 9.003
8.562 8.674 8.787 8.900 9.014
900 910 920 930 940
350 360 370 380 390
2.786 2.880 2.974 3.069 3.164
2.795 2.889 2.983 3.078 3.173
2.805 2.899 2.993 3.088 3.183
2.814 2.908 3.002 3.097 3.192
2.823 2.917 3.012 3.107 3.202
2.833 2.927 3.021 3.116 3.212
2.842 2.936 3.031 3.126 3.221
2.851 2.946 3.040 3.135 3.231
2.861 2.955 3.050 3.145 3.240
2.870 2.965 3.059 3.154 3.250
2.880 2.974 3.069 3.164 3.259
350 360 370 380 390
950 960 970 980 990
9.014 9.128 9.242 9.357 9.472
9.025 9.139 9.254 9.368 9.483
9.037 9.151 9.265 9.380 9.495
9.048 9.162 9.277 9.391 9.506
9.060 9.174 9.288 9.403 9.518
9.071 9.185 9.300 9.414 9.529
9.082 9.197 9.311 9.426 9.541
9.094 9.208 9.323 9.437 9.552
9.105 9.219 9.334 9.449 9.564
9.117 9.231 9.345 9.460 9.576
9.128 9.242 9.357 9.472 9.587
950 960 970 980 990
400 410 420 430 440
3.259 3.355 3.451 3.548 3.645
3.269 3.365 3.461 3.558 3.655
3.279 3.374 3.471 3.567 3.664
3.288 3.384 3.480 3.577 3.674
3.298 3.394 3.490 3.587 3.684
3.307 3.403 3.500 3.596 3.694
3.317 3.413 3.509 3.606 3.703
3.326 3.423 3.519 3.616 3.713
3.336 3.432 3.529 3.626 3.723
3.346 3.442 3.538 3.635 3.732
3.355 3.451 3.548 3.645 3.742
400 410 420 430 440
1000 9.587 9.599 9.610 9.622 9.633 9.645 9.656 9.668 9.680 9.691 9.703 1000 1010 9.703 9.714 9.726 9.737 9.749 9.761 9.772 9.784 9.795 9.807 9.819 1010 1020 9.819 9.830 9.842 9.853 9.865 9.877 9.888 9.900 9.911 9.923 9.935 1020 1030 9.935 9.946 9.958 9.970 9.981 9.993 10.005 10.016 10.028 10.040 10.051 1030 1040 10.051 10.063 10.075 10.086 10.098 10.110 10.121 10.133 10.145 10.156 10.168 1040
450 460 470 480 490
3.742 3.840 3.938 4.036 4.134
3.752 3.850 3.947 4.046 4.144
3.762 3.859 3.957 4.056 4.154
3.771 3.869 3.967 4.065 4.164
3.781 3.879 3.977 4.075 4.174
3.791 3.889 3.987 4.085 4.184
3.801 3.898 3.997 4.095 4.194
3.810 3.908 4.006 4.105 4.204
3.820 3.918 4.016 4.115 4.213
3.830 3.928 4.026 4.125 4.223
3.840 3.938 4.036 4.134 4.233
450 460 470 480 490
1050 1060 1070 1080 1090
10.168 10.285 10.403 10.520 10.638
10.180 10.297 10.414 10.532 10.650
10.191 10.309 10.426 10.544 10.662
10.203 10.320 10.438 10.556 10.674
10.215 10.332 10.450 10.567 10.686
10.227 10.344 10.461 10.579 10.697
10.238 10.356 10.473 10.591 10.709
10.250 10.367 10.485 10.603 10.721
10.262 10.379 10.497 10.615 10.733
10.273 10.391 10.509 10.626 10.745
10.285 10.403 10.520 10.638 10.757
1050 1060 1070 1080 1090
500 510 520 530 540
4.233 4.332 4.432 4.532 4.632
4.243 4.342 4.442 4.542 4.642
4.253 4.352 4.452 4.552 4.652
4.263 4.362 4.462 4.562 4.662
4.273 4.372 4.472 4.572 4.672
4.283 4.382 4.482 4.582 4.682
4.293 4.392 4.492 4.592 4.692
4.303 4.402 4.502 4.602 4.702
4.313 4.412 4.512 4.612 4.712
4.323 4.422 4.522 4.622 4.722
4.332 4.432 4.532 4.632 4.732
500 510 520 530 540
1100 1110 1120 1130 1140
10.757 10.875 10.994 11.113 11.232
10.768 10.887 11.006 11.125 11.244
10.780 10.899 11.017 11.136 11.256
10.792 10.911 11.029 11.148 11.268
10.804 10.922 11.041 11.160 11.280
10.816 10.934 11.053 11.172 11.291
10.828 10.946 11.065 11.184 11.303
10.839 10.958 11.077 11.196 11.315
10.851 10.970 11.089 11.208 11.327
10.863 10.982 11.101 11.220 11.339
10.875 10.994 11.113 11.232 11.351
1100 1110 1120 1130 1140
°C
0
6
7
8
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
9
Z-208
1
2
3
4
5
S 9
°C
Z
+ –
Revised Thermocouple Reference Tables
S
NONE ESTABLISHED
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
Platinum-10% Rhodium vs. Platinum + – Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
Thermoelectric Voltage in Millivolts
°C
0
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
8
9
10
1150 1160 1170 1180 1190
11.351 11.471 11.590 11.710 11.830
11.363 11.483 11.602 11.722 11.842
11.375 11.495 11.614 11.734 11.854
11.387 11.507 11.626 11.746 11.866
11.399 11.519 11.638 11.758 11.878
11.411 11.531 11.650 11.770 11.890
11.423 11.542 11.662 11.782 11.902
11.435 11.554 11.674 11.794 11.914
11.447 11.566 11.686 11.806 11.926
11.459 11.578 11.698 11.818 11.939
11.471 11.590 11.710 11.830 11.951
1150 1160 1170 1180 1190
°C
1500 1510 1520 1530 1540
15.582 15.702 15.822 15.942 16.062
15.594 15.714 15.834 15.954 16.074
15.606 15.726 15.846 15.966 16.086
15.618 15.738 15.858 15.978 16.098
15.630 15.750 15.870 15.990 16.110
15.642 15.762 15.882 16.002 16.122
15.654 15.774 15.894 16.014 16.134
15.666 15.786 15.906 16.026 16.146
15.678 15.798 15.918 16.038 16.158
15.690 15.810 15.930 16.050 16.170
15.702 15.822 15.942 16.062 16.182
1500 1510 1520 1530 1540
1200 1210 1220 1230 1240
11.951 12.071 12.191 12.312 12.433
11.963 12.083 12.203 12.324 12.445
11.975 12.095 12.216 12.336 12.457
11.987 12.107 12.228 12.348 12.469
11.999 12.119 12.240 12.360 12.481
12.011 12.131 12.252 12.372 12.493
12.023 12.143 12.264 12.384 12.505
12.035 12.155 12.276 12.397 12.517
12.047 12.167 12.288 12.409 12.529
12.059 12.179 12.300 12.421 12.542
12.071 12.191 12.312 12.433 12.554
1200 1210 1220 1230 1240
1550 1560 1570 1580 1590
16.182 16.301 16.420 16.539 16.658
16.194 16.313 16.432 16.551 16.670
16.205 16.325 16.444 16.563 16.682
16.217 16.337 16.456 16.575 16.694
16.229 16.349 16.468 16.587 16.706
16.241 16.361 16.480 16.599 16.718
16.253 16.373 16.492 16.611 16.729
16.265 16.385 16.504 16.623 16.741
16.277 16.396 16.516 16.634 16.753
16.289 16.408 16.527 16.646 16.765
16.301 16.420 16.539 16.658 16.777
1550 1560 1570 1580 1590
1250 1260 1270 1280 1290
12.554 12.675 12.796 12.917 13.038
12.566 12.687 12.808 12.929 13.050
12.578 12.699 12.820 12.941 13.062
12.590 12.711 12.832 12.953 13.074
12.602 12.723 12.844 12.965 13.086
12.614 12.735 12.856 12.977 13.098
12.626 12.747 12.868 12.989 13.111
12.638 12.759 12.880 13.001 13.123
12.650 12.771 12.892 13.014 13.135
12.662 12.783 12.905 13.026 13.147
12.675 12.796 12.917 13.038 13.159
1250 1260 1270 1280 1290
1600 1610 1620 1630 1640
16.777 16.895 17.013 17.131 17.249
16.789 16.907 17.025 17.143 17.261
16.801 16.919 17.037 17.155 17.272
16.812 16.931 17.049 17.167 17.284
16.824 16.943 17.061 17.178 17.296
16.836 16.954 17.072 17.190 17.308
16.848 16.966 17.084 17.202 17.319
16.860 16.978 17.096 17.214 17.331
16.872 16.990 17.108 17.225 17.343
16.883 17.002 17.120 17.237 17.355
16.895 17.013 17.131 17.249 17.366
1600 1610 1620 1630 1640
1300 1310 1320 1330 1340
13.159 13.280 13.402 13.523 13.644
13.171 13.292 13.414 13.535 13.657
13.183 13.305 13.426 13.547 13.669
13.195 13.317 13.438 13.559 13.681
13.208 13.329 13.450 13.572 13.693
13.220 13.341 13.462 13.584 13.705
13.232 13.353 13.474 13.596 13.717
13.244 13.365 13.487 13.608 13.729
13.256 13.377 13.499 13.620 13.742
13.268 13.390 13.511 13.632 13.754
13.280 13.402 13.523 13.644 13.766
1300 1310 1320 1330 1340
1650 1660 1670 1680 1690
17.366 17.483 17.600 17.717 17.832
17.378 17.495 17.612 17.728 17.844
17.390 17.507 17.623 17.740 17.855
17.401 17.518 17.635 17.751 17.867
17.413 17.530 17.647 17.763 17.878
17.425 17.542 17.658 17.775 17.890
17.437 17.553 17.670 17.786 17.901
17.448 17.565 17.682 17.798 17.913
17.460 17.577 17.693 17.809 17.924
17.472 17.588 17.705 17.821 17.936
17.483 17.600 17.717 17.832 17.947
1650 1660 1670 1680 1690
1350 1360 1370 1380 1390
13.766 13.887 14.009 14.130 14.251
13.778 13.899 14.021 14.142 14.263
13.790 13.911 14.033 14.154 14.276
13.802 13.924 14.045 14.166 14.288
13.814 13.936 14.057 14.178 14.300
13.826 13.948 14.069 14.191 14.312
13.839 13.960 14.081 14.203 14.324
13.851 13.972 14.094 14.215 14.336
13.863 13.984 14.106 14.227 14.348
13.875 13.996 14.118 14.239 14.360
13.887 14.009 14.130 14.251 14.373
1350 1360 1370 1380 1390
1700 1710 1720 1730 1740
17.947 18.061 18.174 18.285 18.395
17.959 18.073 18.185 18.297 18.406
17.970 18.084 18.196 18.308 18.417
17.982 18.095 18.208 18.319 18.428
17.993 18.107 18.219 18.330 18.439
18.004 18.118 18.230 18.341 18.449
18.016 18.129 18.241 18.352 18.460
18.027 18.140 18.252 18.362 18.471
18.039 18.152 18.263 18.373 18.482
18.050 18.163 18.274 18.384 18.493
18.061 18.174 18.285 18.395 18.503
1700 1710 1720 1730 1740
1400 1410 1420 1430 1440
14.373 14.494 14.615 14.736 14.857
14.385 14.506 14.627 14.748 14.869
14.397 14.518 14.639 14.760 14.881
14.409 14.530 14.651 14.773 14.894
14.421 14.542 14.664 14.785 14.906
14.433 14.554 14.676 14.797 14.918
14.445 14.567 14.688 14.809 14.930
14.457 14.579 14.700 14.821 14.942
14.470 14.591 14.712 14.833 14.954
14.482 14.603 14.724 14.845 14.966
14.494 14.615 14.736 14.857 14.978
1400 1410 1420 1430 1440
1750 18.503 18.514 18.525 18.535 18.546 18.557 18.567 18.578 18.588 18.599 18.609 1750 1760 18.609 18.620 18.630 18.641 18.651 18.661 18.672 18.682 18.693 1760
1450 1460 1470 1480 1490
14.978 15.099 15.220 15.341 15.461
14.990 15.111 15.232 15.353 15.473
15.002 15.123 15.244 15.365 15.485
15.015 15.135 15.256 15.377 15.497
15.027 15.148 15.268 15.389 15.509
15.039 15.160 15.280 15.401 15.521
15.051 15.172 15.292 15.413 15.534
15.063 15.184 15.304 15.425 15.546
15.075 15.196 15.317 15.437 15.558
15.087 15.208 15.329 15.449 15.570
15.099 15.220 15.341 15.461 15.582
1450 1460 1470 1480 1490
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
°C
Z-209
0
1
2
3
4
5
6
7
8
9
10
°C
°C
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °C Extension REFERENCE JUNCTION AT 0°C Grade
Revised Thermocouple Reference Tables
Thermocouple Grade
NONE ESTABLISHED
R
TYPE
Platinum-13% Rhodium vs. Platinum
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts °C
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
°C
°C
0
6
7
8
10
°C
-40 -30 -20 -10 0
-0.226 -0.188 -0.145 -0.100 -0.051
-0.223 -0.184 -0.141 -0.095 -0.046
-0.219 -0.180 -0.137 -0.091 -0.041
-0.215 -0.175 -0.132 -0.086 -0.036
-0.211 -0.171 -0.128 -0.081 -0.031
-0.208 -0.167 -0.123 -0.076 -0.026
-0.204 -0.163 -0.119 -0.071 -0.021
-0.200 -0.158 -0.114 -0.066 -0.016
-0.196 -0.154 -0.109 -0.061 -0.011
-0.192 -0.150 -0.105 -0.056 -0.005
-0.188 -0.145 -0.100 -0.051 0.000
-40 -30 -20 -10 0
550 560 570 580 590
5.021 5.133 5.245 5.357 5.470
5.033 5.144 5.256 5.369 5.481
5.044 5.155 5.267 5.380 5.493
5.055 5.166 5.279 5.391 5.504
5.066 5.178 5.290 5.402 5.515
5.077 5.189 5.301 5.414 5.527
5.088 5.200 5.312 5.425 5.538
5.099 5.211 5.323 5.436 5.549
5.111 5.222 5.335 5.448 5.561
5.122 5.234 5.346 5.459 5.572
5.133 5.245 5.357 5.470 5.583
550 560 570 580 590
0 10 20 30 40
0.000 0.054 0.111 0.171 0.232
0.005 0.060 0.117 0.177 0.239
0.011 0.065 0.123 0.183 0.245
0.016 0.071 0.129 0.189 0.251
0.021 0.077 0.135 0.195 0.258
0.027 0.082 0.141 0.201 0.264
0.032 0.088 0.147 0.207 0.271
0.038 0.094 0.153 0.214 0.277
0.043 0.100 0.159 0.220 0.284
0.049 0.105 0.165 0.226 0.290
0.054 0.111 0.171 0.232 0.296
0 10 20 30 40
600 610 620 630 640
5.583 5.697 5.812 5.926 6.041
5.595 5.709 5.823 5.938 6.053
5.606 5.720 5.834 5.949 6.065
5.618 5.731 5.846 5.961 6.076
5.629 5.743 5.857 5.972 6.088
5.640 5.754 5.869 5.984 6.099
5.652 5.766 5.880 5.995 6.111
5.663 5.777 5.892 6.007 6.122
5.674 5.789 5.903 6.018 6.134
5.686 5.800 5.915 6.030 6.146
5.697 5.812 5.926 6.041 6.157
600 610 620 630 640
50 60 70 80 90
0.296 0.363 0.431 0.501 0.573
0.303 0.369 0.438 0.508 0.581
0.310 0.376 0.445 0.516 0.588
0.316 0.383 0.452 0.523 0.595
0.323 0.390 0.459 0.530 0.603
0.329 0.397 0.466 0.537 0.610
0.336 0.403 0.473 0.544 0.618
0.343 0.410 0.480 0.552 0.625
0.349 0.417 0.487 0.559 0.632
0.356 0.424 0.494 0.566 0.640
0.363 0.431 0.501 0.573 0.647
50 60 70 80 90
650 660 670 680 690
6.157 6.273 6.390 6.507 6.625
6.169 6.285 6.402 6.519 6.636
6.180 6.297 6.413 6.531 6.648
6.192 6.308 6.425 6.542 6.660
6.204 6.320 6.437 6.554 6.672
6.215 6.332 6.448 6.566 6.684
6.227 6.343 6.460 6.578 6.695
6.238 6.355 6.472 6.589 6.707
6.250 6.367 6.484 6.601 6.719
6.262 6.378 6.495 6.613 6.731
6.273 6.390 6.507 6.625 6.743
650 660 670 680 690
100 110 120 130 140
0.647 0.723 0.800 0.879 0.959
0.655 0.731 0.808 0.887 0.967
0.662 0.738 0.816 0.895 0.976
0.670 0.746 0.824 0.903 0.984
0.677 0.754 0.832 0.911 0.992
0.685 0.761 0.839 0.919 1.000
0.693 0.769 0.847 0.927 1.008
0.700 0.777 0.855 0.935 1.016
0.708 0.785 0.863 0.943 1.025
0.715 0.792 0.871 0.951 1.033
0.723 0.800 0.879 0.959 1.041
100 110 120 130 140
700 710 720 730 740
6.743 6.861 6.980 7.100 7.220
6.755 6.873 6.992 7.112 7.232
6.766 6.885 7.004 7.124 7.244
6.778 6.897 7.016 7.136 7.256
6.790 6.909 7.028 7.148 7.268
6.802 6.921 7.040 7.160 7.280
6.814 6.933 7.052 7.172 7.292
6.826 6.945 7.064 7.184 7.304
6.838 6.956 7.076 7.196 7.316
6.849 6.968 7.088 7.208 7.328
6.861 6.980 7.100 7.220 7.340
700 710 720 730 740
150 160 170 180 190
1.041 1.124 1.208 1.294 1.381
1.049 1.132 1.217 1.303 1.389
1.058 1.141 1.225 1.311 1.398
1.066 1.149 1.234 1.320 1.407
1.074 1.158 1.242 1.329 1.416
1.082 1.166 1.251 1.337 1.425
1.091 1.175 1.260 1.346 1.433
1.099 1.183 1.268 1.355 1.442
1.107 1.191 1.277 1.363 1.451
1.116 1.200 1.285 1.372 1.460
1.124 1.208 1.294 1.381 1.469
150 160 170 180 190
750 760 770 780 790
7.340 7.461 7.583 7.705 7.827
7.352 7.473 7.595 7.717 7.839
7.364 7.485 7.607 7.729 7.851
7.376 7.498 7.619 7.741 7.864
7.389 7.510 7.631 7.753 7.876
7.401 7.522 7.644 7.766 7.888
7.413 7.534 7.656 7.778 7.901
7.425 7.546 7.668 7.790 7.913
7.437 7.558 7.680 7.802 7.925
7.449 7.570 7.692 7.815 7.938
7.461 7.583 7.705 7.827 7.950
750 760 770 780 790
200 210 220 230 240
1.469 1.558 1.648 1.739 1.831
1.477 1.567 1.657 1.748 1.840
1.486 1.575 1.666 1.757 1.849
1.495 1.584 1.675 1.766 1.858
1.504 1.593 1.684 1.775 1.868
1.513 1.602 1.693 1.784 1.877
1.522 1.611 1.702 1.794 1.886
1.531 1.620 1.711 1.803 1.895
1.540 1.629 1.720 1.812 1.905
1.549 1.639 1.729 1.821 1.914
1.558 1.648 1.739 1.831 1.923
200 210 220 230 240
800 810 820 830 840
7.950 8.073 8.197 8.321 8.446
7.962 8.086 8.209 8.334 8.459
7.974 8.098 8.222 8.346 8.471
7.987 8.110 8.234 8.359 8.484
7.999 8.123 8.247 8.371 8.496
8.011 8.135 8.259 8.384 8.509
8.024 8.147 8.272 8.396 8.521
8.036 8.160 8.284 8.409 8.534
8.048 8.172 8.296 8.421 8.546
8.061 8.185 8.309 8.434 8.559
8.073 8.197 8.321 8.446 8.571
800 810 820 830 840
250 260 270 280 290
1.923 2.017 2.112 2.207 2.304
1.933 2.027 2.121 2.217 2.313
1.942 2.036 2.131 2.226 2.323
1.951 2.046 2.140 2.236 2.333
1.961 2.055 2.150 2.246 2.342
1.970 2.064 2.159 2.255 2.352
1.980 2.074 2.169 2.265 2.362
1.989 2.083 2.179 2.275 2.371
1.998 2.093 2.188 2.284 2.381
2.008 2.102 2.198 2.294 2.391
2.017 2.112 2.207 2.304 2.401
250 260 270 280 290
850 860 870 880 890
8.571 8.697 8.823 8.950 9.077
8.584 8.710 8.836 8.963 9.090
8.597 8.722 8.849 8.975 9.103
8.609 8.735 8.861 8.988 9.115
8.622 8.748 8.874 9.001 9.128
8.634 8.760 8.887 9.014 9.141
8.647 8.773 8.899 9.026 9.154
8.659 8.785 8.912 9.039 9.167
8.672 8.798 8.925 9.052 9.179
8.685 8.811 8.937 9.065 9.192
8.697 8.823 8.950 9.077 9.205
850 860 870 880 890
300 310 320 330 340
2.401 2.498 2.597 2.696 2.796
2.410 2.508 2.607 2.706 2.806
2.420 2.518 2.617 2.716 2.816
2.430 2.528 2.626 2.726 2.826
2.440 2.538 2.636 2.736 2.836
2.449 2.547 2.646 2.746 2.846
2.459 2.557 2.656 2.756 2.856
2.469 2.567 2.666 2.766 2.866
2.479 2.577 2.676 2.776 2.876
2.488 2.587 2.686 2.786 2.886
2.498 2.597 2.696 2.796 2.896
300 310 320 330 340
900 910 920 930 940
9.205 9.333 9.461 9.590 9.720
9.218 9.346 9.474 9.603 9.733
9.230 9.359 9.487 9.616 9.746
9.243 9.371 9.500 9.629 9.759
9.256 9.384 9.513 9.642 9.772
9.269 9.397 9.526 9.655 9.785
9.282 9.410 9.539 9.668 9.798
9.294 9.423 9.552 9.681 9.811
9.307 9.436 9.565 9.694 9.824
9.320 9.449 9.578 9.707 9.837
9.333 9.461 9.590 9.720 9.850
900 910 920 930 940
350 360 370 380 390
2.896 2.997 3.099 3.201 3.304
2.906 3.007 3.109 3.212 3.315
2.916 3.018 3.119 3.222 3.325
2.926 3.028 3.130 3.232 3.335
2.937 3.038 3.140 3.242 3.346
2.947 3.048 3.150 3.253 3.356
2.957 3.058 3.160 3.263 3.366
2.967 3.068 3.171 3.273 3.377
2.977 3.079 3.181 3.284 3.387
2.987 3.089 3.191 3.294 3.397
2.997 3.099 3.201 3.304 3.408
350 360 370 380 390
950 9.850 9.863 9.876 960 9.980 9.993 10.006 970 10.111 10.124 10.137 980 10.242 10.255 10.268 990 10.374 10.387 10.400
9.889 10.019 10.150 10.282 10.413
9.902 10.032 10.163 10.295 10.427
9.915 10.046 10.177 10.308 10.440
9.928 10.059 10.190 10.321 10.453
9.941 10.072 10.203 10.334 10.466
9.954 10.085 10.216 10.347 10.480
9.967 10.098 10.229 10.361 10.493
9.980 10.111 10.242 10.374 10.506
950 960 970 980 990
400 410 420 430 440
3.408 3.512 3.616 3.721 3.827
3.418 3.522 3.627 3.732 3.838
3.428 3.533 3.637 3.742 3.848
3.439 3.543 3.648 3.753 3.859
3.449 3.553 3.658 3.764 3.869
3.460 3.564 3.669 3.774 3.880
3.470 3.574 3.679 3.785 3.891
3.480 3.585 3.690 3.795 3.901
3.491 3.595 3.700 3.806 3.912
3.501 3.606 3.711 3.816 3.922
3.512 3.616 3.721 3.827 3.933
400 410 420 430 440
1000 1010 1020 1030 1040
10.506 10.638 10.771 10.905 11.039
10.519 10.652 10.785 10.918 11.052
10.532 10.665 10.798 10.932 11.065
10.546 10.678 10.811 10.945 11.079
10.559 10.692 10.825 10.958 11.092
10.572 10.705 10.838 10.972 11.106
10.585 10.718 10.851 10.985 11.119
10.599 10.731 10.865 10.998 11.132
10.612 10.745 10.878 11.012 11.146
10.625 10.758 10.891 11.025 11.159
10.638 10.771 10.905 11.039 11.173
1000 1010 1020 1030 1040
450 460 470 480 490
3.933 4.040 4.147 4.255 4.363
3.944 4.050 4.158 4.265 4.373
3.954 4.061 4.168 4.276 4.384
3.965 4.072 4.179 4.287 4.395
3.976 4.083 4.190 4.298 4.406
3.986 4.093 4.201 4.309 4.417
3.997 4.104 4.211 4.319 4.428
4.008 4.115 4.222 4.330 4.439
4.018 4.125 4.233 4.341 4.449
4.029 4.136 4.244 4.352 4.460
4.040 4.147 4.255 4.363 4.471
450 460 470 480 490
1050 1060 1070 1080 1090
11.173 11.307 11.442 11.578 11.714
11.186 11.321 11.456 11.591 11.727
11.200 11.334 11.469 11.605 11.741
11.213 11.348 11.483 11.618 11.754
11.227 11.361 11.496 11.632 11.768
11.240 11.375 11.510 11.646 11.782
11.253 11.388 11.524 11.659 11.795
11.267 11.402 11.537 11.673 11.809
11.280 11.415 11.551 11.686 11.822
11.294 11.429 11.564 11.700 11.836
11.307 11.442 11.578 11.714 11.850
1050 1060 1070 1080 1090
500 510 520 530 540
4.471 4.580 4.690 4.800 4.910
4.482 4.591 4.701 4.811 4.922
4.493 4.602 4.712 4.822 4.933
4.504 4.613 4.723 4.833 4.944
4.515 4.624 4.734 4.844 4.955
4.526 4.635 4.745 4.855 4.966
4.537 4.646 4.756 4.866 4.977
4.548 4.657 4.767 4.877 4.988
4.558 4.668 4.778 4.888 4.999
4.569 4.679 4.789 4.899 5.010
4.580 4.690 4.800 4.910 5.021
500 510 520 530 540
1100 1110 1120 1130 1140
11.850 11.986 12.123 12.260 12.397
11.863 12.000 12.137 12.274 12.411
11.877 12.013 12.150 12.288 12.425
11.891 12.027 12.164 12.301 12.439
11.904 12.041 12.178 12.315 12.453
11.918 12.054 12.191 12.329 12.466
11.931 12.068 12.205 12.342 12.480
11.945 12.082 12.219 12.356 12.494
11.959 12.096 12.233 12.370 12.508
11.972 12.109 12.246 12.384 12.521
11.986 12.123 12.260 12.397 12.535
1100 1110 1120 1130 1140
°C
0
6
7
8
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
1
2
3
4
5
9
Z-210
1
2
3
4
5
9
Z
+ –
Revised Thermocouple Reference Tables
R
NONE ESTABLISHED
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
Platinum-13% Rhodium vs. Platinum + – Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
Thermoelectric Voltage in Millivolts
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
1150 1160 1170 1180 1190
12.535 12.673 12.812 12.950 13.089
12.549 12.687 12.825 12.964 13.103
12.563 12.701 12.839 12.978 13.117
12.577 12.715 12.853 12.992 13.131
12.590 12.729 12.867 13.006 13.145
12.604 12.742 12.881 13.019 13.158
12.618 12.756 12.895 13.033 13.172
12.632 12.770 12.909 13.047 13.186
12.646 12.784 12.922 13.061 13.200
12.659 12.798 12.936 13.075 13.214
12.673 12.812 12.950 13.089 13.228
1150 1160 1170 1180 1190
1500 1510 1520 1530 1540
17.451 17.591 17.732 17.872 18.012
17.465 17.605 17.746 17.886 18.026
17.479 17.619 17.760 17.900 18.040
17.493 17.633 17.774 17.914 18.054
17.507 17.647 17.788 17.928 18.068
17.521 17.661 17.802 17.942 18.082
17.535 17.676 17.816 17.956 18.096
17.549 17.690 17.830 17.970 18.110
17.563 17.704 17.844 17.984 18.124
17.577 17.718 17.858 17.998 18.138
17.591 17.732 17.872 18.012 18.152
1500 1510 1520 1530 1540
1200 1210 1220 1230 1240
13.228 13.367 13.507 13.646 13.786
13.242 13.381 13.521 13.660 13.800
13.256 13.395 13.535 13.674 13.814
13.270 13.409 13.549 13.688 13.828
13.284 13.423 13.563 13.702 13.842
13.298 13.437 13.577 13.716 13.856
13.311 13.451 13.590 13.730 13.870
13.325 13.465 13.604 13.744 13.884
13.339 13.479 13.618 13.758 13.898
13.353 13.493 13.632 13.772 13.912
13.367 13.507 13.646 13.786 13.926
1200 1210 1220 1230 1240
1550 1560 1570 1580 1590
18.152 18.292 18.431 18.571 18.710
18.166 18.306 18.445 18.585 18.724
18.180 18.320 18.459 18.599 18.738
18.194 18.334 18.473 18.613 18.752
18.208 18.348 18.487 18.627 18.766
18.222 18.362 18.501 18.640 18.779
18.236 18.376 18.515 18.654 18.793
18.250 18.390 18.529 18.668 18.807
18.264 18.404 18.543 18.682 18.821
18.278 18.417 18.557 18.696 18.835
18.292 18.431 18.571 18.710 18.849
1550 1560 1570 1580 1590
1250 1260 1270 1280 1290
13.926 14.066 14.207 14.347 14.488
13.940 14.081 14.221 14.361 14.502
13.954 14.095 14.235 14.375 14.516
13.968 14.109 14.249 14.390 14.530
13.982 14.123 14.263 14.404 14.544
13.996 14.137 14.277 14.418 14.558
14.010 14.151 14.291 14.432 14.572
14.024 14.165 14.305 14.446 14.586
14.038 14.179 14.319 14.460 14.601
14.052 14.193 14.333 14.474 14.615
14.066 14.207 14.347 14.488 14.629
1250 1260 1270 1280 1290
1600 1610 1620 1630 1640
18.849 18.988 19.126 19.264 19.402
18.863 19.002 19.140 19.278 19.416
18.877 19.015 19.154 19.292 19.430
18.891 19.029 19.168 19.306 19.444
18.904 19.043 19.181 19.319 19.457
18.918 19.057 19.195 19.333 19.471
18.932 19.071 19.209 19.347 19.485
18.946 19.085 19.223 19.361 19.499
18.960 19.098 19.237 19.375 19.512
18.974 19.112 19.250 19.388 19.526
18.988 19.126 19.264 19.402 19.540
1600 1610 1620 1630 1640
1300 1310 1320 1330 1340
14.629 14.770 14.911 15.052 15.193
14.643 14.784 14.925 15.066 15.207
14.657 14.798 14.939 15.080 15.221
14.671 14.812 14.953 15.094 15.235
14.685 14.826 14.967 15.108 15.249
14.699 14.840 14.981 15.122 15.263
14.713 14.854 14.995 15.136 15.277
14.727 14.868 15.009 15.150 15.291
14.741 14.882 15.023 15.164 15.306
14.755 14.896 15.037 15.179 15.320
14.770 14.911 15.052 15.193 15.334
1300 1310 1320 1330 1340
1650 1660 1670 1680 1690
19.540 19.677 19.814 19.951 20.087
19.554 19.691 19.828 19.964 20.100
19.567 19.705 19.841 19.978 20.114
19.581 19.718 19.855 19.992 20.127
19.595 19.732 19.869 20.005 20.141
19.609 19.746 19.882 20.019 20.154
19.622 19.759 19.896 20.032 20.168
19.636 19.773 19.910 20.046 20.181
19.650 19.787 19.923 20.060 20.195
19.663 19.800 19.937 20.073 20.208
19.677 19.814 19.951 20.087 20.222
1650 1660 1670 1680 1690
1350 1360 1370 1380 1390
15.334 15.475 15.616 15.758 15.899
15.348 15.489 15.630 15.772 15.913
15.362 15.503 15.645 15.786 15.927
15.376 15.517 15.659 15.800 15.941
15.390 15.531 15.673 15.814 15.955
15.404 15.546 15.687 15.828 15.969
15.419 15.560 15.701 15.842 15.984
15.433 15.574 15.715 15.856 15.998
15.447 15.588 15.729 15.871 16.012
15.461 15.602 15.743 15.885 16.026
15.475 15.616 15.758 15.899 16.040
1350 1360 1370 1380 1390
1700 1710 1720 1730 1740
20.222 20.356 20.488 20.620 20.749
20.235 20.369 20.502 20.633 20.762
20.249 20.382 20.515 20.646 20.775
20.262 20.396 20.528 20.659 20.788
20.275 20.409 20.541 20.672 20.801
20.289 20.422 20.554 20.685 20.813
20.302 20.436 20.567 20.698 20.826
20.316 20.449 20.581 20.711 20.839
20.329 20.462 20.594 20.724 20.852
20.342 20.475 20.607 20.736 20.864
20.356 20.488 20.620 20.749 20.877
1700 1710 1720 1730 1740
1400 1410 1420 1430 1440
16.040 16.181 16.323 16.464 16.605
16.054 16.196 16.337 16.478 16.619
16.068 16.210 16.351 16.492 16.633
16.082 16.224 16.365 16.506 16.647
16.097 16.238 16.379 16.520 16.662
16.111 16.252 16.393 16.534 16.676
16.125 16.266 16.407 16.549 16.690
16.139 16.280 16.422 16.563 16.704
16.153 16.294 16.436 16.577 16.718
16.167 16.309 16.450 16.591 16.732
16.181 16.323 16.464 16.605 16.746
1400 1410 1420 1430 1440
1750 20.877 20.890 20.902 20.915 20.928 20.940 20.953 20.965 20.978 20.990 21.003 1750 1760 21.003 21.015 21.027 21.040 21.052 21.065 21.077 21.089 21.101 1760
1450 1460 1470 1480 1490
16.746 16.887 17.028 17.169 17.310
16.760 16.901 17.042 17.183 17.324
16.774 16.915 17.056 17.197 17.338
16.789 16.930 17.071 17.211 17.352
16.803 16.944 17.085 17.225 17.366
16.817 16.958 17.099 17.240 17.380
16.831 16.972 17.113 17.254 17.394
16.845 16.986 17.127 17.268 17.408
16.859 17.000 17.141 17.282 17.423
16.873 17.014 17.155 17.296 17.437
16.887 17.028 17.169 17.310 17.451
1450 1460 1470 1480 1490
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
Z-211
0
1
2
3
4
5
6
7
8
9
10
°C
°C
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 3092°F 0 to 1700°C Extension Grade 32 to 212°F 0 to 100°C LIMITS OF ERROR (whichever is greater) Standard: 0.5°C over 800°C Special: NOT ESTABLISHED COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature; Common Use in Glass Industry Extension TEMPERATURE IN DEGREES °C Grade REFERENCE JUNCTION AT 0°C
Thermocouple Grade
NONE ESTABLISHED
Platinum-30% Rhodium vs. Platinum-6% Rhodium
Revised Thermocouple Reference Tables
B
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts °C 0 10 20 30 40
0
1
2
3
0.000 0.000 0.000 -0.001 -0.002 -0.002 -0.002 -0.002 -0.003 -0.003 -0.003 -0.003 -0.002 -0.002 -0.002 -0.002 0.000 0.000 0.000 0.000
4
5
6
7
8
-0.001 -0.002 -0.003 -0.002 0.000
-0.001 -0.002 -0.002 -0.001 0.001
-0.001 -0.002 -0.002 -0.001 0.001
-0.001 -0.002 -0.002 -0.001 0.001
-0.002 -0.003 -0.002 -0.001 0.002
9
10
-0.002 -0.002 -0.003 -0.003 -0.002 -0.002 -0.001 0.000 0.002 0.002
°C
°C
0
6
7
8
10
°C
0 10 20 30 40
600 610 620 630 640
1.792 1.852 1.913 1.975 2.037
1.798 1.858 1.919 1.981 2.043
1
1.804 1.864 1.925 1.987 2.050
2
1.810 1.870 1.931 1.993 2.056
3
1.816 1.876 1.937 1.999 2.062
4
1.822 1.882 1.944 2.006 2.069
5
1.828 1.888 1.950 2.012 2.075
1.834 1.894 1.956 2.018 2.082
1.840 1.901 1.962 2.025 2.088
1.846 1.907 1.968 2.031 2.094
9
1.852 1.913 1.975 2.037 2.101
600 610 620 630 640
50 60 70 80 90
0.002 0.006 0.011 0.017 0.025
0.003 0.007 0.012 0.018 0.026
0.003 0.007 0.012 0.019 0.026
0.003 0.008 0.013 0.020 0.027
0.004 0.008 0.014 0.020 0.028
0.004 0.009 0.014 0.021 0.029
0.004 0.009 0.015 0.022 0.030
0.005 0.010 0.015 0.022 0.031
0.005 0.010 0.016 0.023 0.031
0.006 0.011 0.017 0.024 0.032
0.006 0.011 0.017 0.025 0.033
50 60 70 80 90
650 660 670 680 690
2.101 2.165 2.230 2.296 2.363
2.107 2.171 2.237 2.303 2.370
2.113 2.178 2.243 2.309 2.376
2.120 2.184 2.250 2.316 2.383
2.126 2.191 2.256 2.323 2.390
2.133 2.197 2.263 2.329 2.397
2.139 2.204 2.270 2.336 2.403
2.146 2.210 2.276 2.343 2.410
2.152 2.217 2.283 2.350 2.417
2.158 2.224 2.289 2.356 2.424
2.165 2.230 2.296 2.363 2.431
650 660 670 680 690
100 110 120 130 140
0.033 0.043 0.053 0.065 0.078
0.034 0.044 0.055 0.066 0.079
0.035 0.045 0.056 0.068 0.081
0.036 0.046 0.057 0.069 0.082
0.037 0.047 0.058 0.070 0.084
0.038 0.048 0.059 0.072 0.085
0.039 0.049 0.060 0.073 0.086
0.040 0.050 0.062 0.074 0.088
0.041 0.051 0.063 0.075 0.089
0.042 0.052 0.064 0.077 0.091
0.043 0.053 0.065 0.078 0.092
100 110 120 130 140
700 710 720 730 740
2.431 2.499 2.569 2.639 2.710
2.437 2.506 2.576 2.646 2.717
2.444 2.513 2.583 2.653 2.724
2.451 2.520 2.590 2.660 2.731
2.458 2.527 2.597 2.667 2.738
2.465 2.534 2.604 2.674 2.746
2.472 2.541 2.611 2.681 2.753
2.479 2.548 2.618 2.688 2.760
2.485 2.555 2.625 2.696 2.767
2.492 2.562 2.632 2.703 2.775
2.499 2.569 2.639 2.710 2.782
700 710 720 730 740
150 160 170 180 190
0.092 0.107 0.123 0.141 0.159
0.094 0.109 0.125 0.142 0.161
0.095 0.110 0.127 0.144 0.163
0.096 0.112 0.128 0.146 0.165
0.098 0.113 0.130 0.148 0.166
0.099 0.115 0.132 0.150 0.168
0.101 0.117 0.134 0.151 0.170
0.102 0.118 0.135 0.153 0.172
0.104 0.120 0.137 0.155 0.174
0.106 0.122 0.139 0.157 0.176
0.107 0.123 0.141 0.159 0.178
150 160 170 180 190
750 760 770 780 790
2.782 2.854 2.928 3.002 3.078
2.789 2.862 2.935 3.010 3.085
2.796 2.869 2.943 3.017 3.093
2.803 2.876 2.950 3.025 3.100
2.811 2.884 2.958 3.032 3.108
2.818 2.891 2.965 3.040 3.116
2.825 2.898 2.973 3.047 3.123
2.833 2.906 2.980 3.055 3.131
2.840 2.913 2.987 3.062 3.138
2.847 2.921 2.995 3.070 3.146
2.854 2.928 3.002 3.078 3.154
750 760 770 780 790
200 210 220 230 240
0.178 0.199 0.220 0.243 0.267
0.180 0.201 0.222 0.245 0.269
0.182 0.203 0.225 0.248 0.271
0.184 0.205 0.227 0.250 0.274
0.186 0.207 0.229 0.252 0.276
0.188 0.209 0.231 0.255 0.279
0.190 0.212 0.234 0.257 0.281
0.192 0.214 0.236 0.259 0.284
0.195 0.216 0.238 0.262 0.286
0.197 0.218 0.241 0.264 0.289
0.199 0.220 0.243 0.267 0.291
200 210 220 230 240
800 810 820 830 840
3.154 3.230 3.308 3.386 3.466
3.161 3.238 3.316 3.394 3.474
3.169 3.246 3.324 3.402 3.482
3.177 3.254 3.331 3.410 3.490
3.184 3.261 3.339 3.418 3.498
3.192 3.269 3.347 3.426 3.506
3.200 3.277 3.355 3.434 3.514
3.207 3.285 3.363 3.442 3.522
3.215 3.292 3.371 3.450 3.530
3.223 3.300 3.379 3.458 3.538
3.230 3.308 3.386 3.466 3.546
800 810 820 830 840
250 260 270 280 290
0.291 0.317 0.344 0.372 0.401
0.294 0.320 0.347 0.375 0.404
0.296 0.322 0.349 0.377 0.407
0.299 0.325 0.352 0.380 0.410
0.301 0.328 0.355 0.383 0.413
0.304 0.330 0.358 0.386 0.416
0.307 0.333 0.360 0.389 0.419
0.309 0.336 0.363 0.392 0.422
0.312 0.338 0.366 0.395 0.425
0.314 0.341 0.369 0.398 0.428
0.317 0.344 0.372 0.401 0.431
250 260 270 280 290
850 860 870 880 890
3.546 3.626 3.708 3.790 3.873
3.554 3.634 3.716 3.798 3.882
3.562 3.643 3.724 3.807 3.890
3.570 3.651 3.732 3.815 3.898
3.578 3.659 3.741 3.823 3.907
3.586 3.667 3.749 3.832 3.915
3.594 3.675 3.757 3.840 3.923
3.602 3.683 3.765 3.848 3.932
3.610 3.692 3.774 3.857 3.940
3.618 3.700 3.782 3.865 3.949
3.626 3.708 3.790 3.873 3.957
850 860 870 880 890
300 310 320 330 340
0.431 0.462 0.494 0.527 0.561
0.434 0.465 0.497 0.530 0.564
0.437 0.468 0.500 0.533 0.568
0.440 0.471 0.503 0.537 0.571
0.443 0.474 0.507 0.540 0.575
0.446 0.478 0.510 0.544 0.578
0.449 0.481 0.513 0.547 0.582
0.452 0.484 0.517 0.550 0.585
0.455 0.487 0.520 0.554 0.589
0.458 0.490 0.523 0.557 0.592
0.462 0.494 0.527 0.561 0.596
300 310 320 330 340
900 910 920 930 940
3.957 4.041 4.127 4.213 4.299
3.965 4.050 4.135 4.221 4.308
3.974 4.058 4.144 4.230 4.317
3.982 4.067 4.152 4.239 4.326
3.991 4.075 4.161 4.247 4.334
3.999 4.084 4.170 4.256 4.343
4.008 4.093 4.178 4.265 4.352
4.016 4.101 4.187 4.273 4.360
4.024 4.110 4.195 4.282 4.369
4.033 4.118 4.204 4.291 4.378
4.041 4.127 4.213 4.299 4.387
900 910 920 930 940
350 360 370 380 390
0.596 0.632 0.669 0.707 0.746
0.599 0.636 0.673 0.711 0.750
0.603 0.639 0.677 0.715 0.754
0.607 0.643 0.680 0.719 0.758
0.610 0.647 0.684 0.723 0.762
0.614 0.650 0.688 0.727 0.766
0.617 0.654 0.692 0.731 0.770
0.621 0.658 0.696 0.735 0.774
0.625 0.662 0.700 0.738 0.778
0.628 0.665 0.703 0.742 0.782
0.632 0.669 0.707 0.746 0.787
350 360 370 380 390
950 960 970 980 990
4.387 4.475 4.564 4.653 4.743
4.396 4.484 4.573 4.662 4.753
4.404 4.493 4.582 4.671 4.762
4.413 4.501 4.591 4.680 4.771
4.422 4.510 4.599 4.689 4.780
4.431 4.519 4.608 4.698 4.789
4.440 4.528 4.617 4.707 4.798
4.448 4.537 4.626 4.716 4.807
4.457 4.546 4.635 4.725 4.816
4.466 4.555 4.644 4.734 4.825
4.475 4.564 4.653 4.743 4.834
950 960 970 980 990
400 410 420 430 440
0.787 0.828 0.870 0.913 0.957
0.791 0.832 0.874 0.917 0.961
0.795 0.836 0.878 0.922 0.966
0.799 0.840 0.883 0.926 0.970
0.803 0.844 0.887 0.930 0.975
0.807 0.849 0.891 0.935 0.979
0.811 0.853 0.896 0.939 0.984
0.815 0.857 0.900 0.944 0.988
0.819 0.861 0.904 0.948 0.993
0.824 0.866 0.909 0.953 0.997
0.828 0.870 0.913 0.957 1.002
400 410 420 430 440
1000 1010 1020 1030 1040
4.834 4.926 5.018 5.111 5.205
4.843 4.935 5.027 5.120 5.214
4.853 4.944 5.037 5.130 5.223
4.862 4.954 5.046 5.139 5.233
4.871 4.963 5.055 5.148 5.242
4.880 4.972 5.065 5.158 5.252
4.889 4.981 5.074 5.167 5.261
4.898 4.990 5.083 5.176 5.270
4.908 5.000 5.092 5.186 5.280
4.917 5.009 5.102 5.195 5.289
4.926 5.018 5.111 5.205 5.299
1000 1010 1020 1030 1040
450 460 470 480 490
1.002 1.048 1.095 1.143 1.192
1.007 1.053 1.100 1.148 1.197
1.011 1.057 1.105 1.153 1.202
1.016 1.062 1.109 1.158 1.207
1.020 1.067 1.114 1.163 1.212
1.025 1.071 1.119 1.167 1.217
1.030 1.076 1.124 1.172 1.222
1.034 1.081 1.129 1.177 1.227
1.039 1.086 1.133 1.182 1.232
1.043 1.090 1.138 1.187 1.237
1.048 1.095 1.143 1.192 1.242
450 460 470 480 490
1050 1060 1070 1080 1090
5.299 5.394 5.489 5.585 5.682
5.308 5.403 5.499 5.595 5.692
5.318 5.413 5.508 5.605 5.702
5.327 5.422 5.518 5.614 5.711
5.337 5.432 5.528 5.624 5.721
5.346 5.441 5.537 5.634 5.731
5.356 5.451 5.547 5.643 5.740
5.365 5.460 5.556 5.653 5.750
5.375 5.470 5.566 5.663 5.760
5.384 5.480 5.576 5.672 5.770
5.394 5.489 5.585 5.682 5.780
1050 1060 1070 1080 1090
500 510 520 530 540
1.242 1.293 1.344 1.397 1.451
1.247 1.298 1.350 1.402 1.456
1.252 1.303 1.355 1.408 1.462
1.257 1.308 1.360 1.413 1.467
1.262 1.313 1.365 1.418 1.472
1.267 1.318 1.371 1.424 1.478
1.272 1.324 1.376 1.429 1.483
1.277 1.329 1.381 1.435 1.489
1.282 1.334 1.387 1.440 1.494
1.288 1.339 1.392 1.445 1.500
1.293 1.344 1.397 1.451 1.505
500 510 520 530 540
1100 1110 1120 1130 1140
5.780 5.878 5.976 6.075 6.175
5.789 5.887 5.986 6.085 6.185
5.799 5.897 5.996 6.095 6.195
5.809 5.907 6.006 6.105 6.205
5.819 5.917 6.016 6.115 6.215
5.828 5.927 6.026 6.125 6.225
5.838 5.937 6.036 6.135 6.235
5.848 5.947 6.046 6.145 6.245
5.858 5.956 6.055 6.155 6.256
5.868 5.966 6.065 6.165 6.266
5.878 5.976 6.075 6.175 6.276
1100 1110 1120 1130 1140
550 560 570 580 590
1.505 1.561 1.617 1.675 1.733
1.511 1.566 1.623 1.680 1.739
1.516 1.572 1.629 1.686 1.745
1.522 1.578 1.634 1.692 1.750
1.527 1.583 1.640 1.698 1.756
1.533 1.589 1.646 1.704 1.762
1.539 1.595 1.652 1.709 1.768
1.544 1.600 1.657 1.715 1.774
1.550 1.606 1.663 1.721 1.780
1.555 1.612 1.669 1.727 1.786
1.561 1.617 1.675 1.733 1.792
550 560 570 580 590
1150 1160 1170 1180 1190
6.276 6.377 6.478 6.580 6.683
6.286 6.387 6.488 6.591 6.693
6.296 6.397 6.499 6.601 6.704
6.306 6.407 6.509 6.611 6.714
6.316 6.417 6.519 6.621 6.724
6.326 6.427 6.529 6.632 6.735
6.336 6.438 6.539 6.642 6.745
6.346 6.448 6.550 6.652 6.755
6.356 6.458 6.560 6.663 6.766
6.367 6.468 6.570 6.673 6.776
6.377 6.478 6.580 6.683 6.786
1150 1160 1170 1180 1190
°C
0
6
7
8
10
°C
°C
0
6
7
8
1
2
3
4
5
9
Z-212
1
2
3
4
5
9
10
°C
Z
+ –
Revised Thermocouple Reference Tables
B
NONE ESTABLISHED
TYPE
Platinum-30% Rhodium vs. Platinum-6% Rhodium
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
1
2
3
4
5
Thermocouple Grade
+ –
Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 3092°F 0 to 1700°C Extension Grade 32 to 212°F 0 to 100°C LIMITS OF ERROR (whichever is greater) Standard: 0.5°C over 800°C Special: NOT ESTABLISHED COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature; Common Use in Glass Industry TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
Thermoelectric Voltage in Millivolts
°C
0
6
7
8
1200 1210 1220 1230 1240
6.786 6.890 6.995 7.100 7.205
6.797 6.901 7.005 7.110 7.216
6.807 6.911 7.016 7.121 7.226
6.818 6.922 7.026 7.131 7.237
6.828 6.932 7.037 7.142 7.247
°C
°C
0
1
2
3
4
5
6
7
8
9
10
6.838 6.942 7.047 7.152 7.258
6.849 6.953 7.058 7.163 7.269
6.859 6.963 7.068 7.173 7.279
6.869 6.974 7.079 7.184 7.290
6.880 6.984 7.089 7.194 7.300
9
6.890 6.995 7.100 7.205 7.311
10
1200 1210 1220 1230 1240
1550 1560 1570 1580 1590
10.679 10.796 10.913 11.029 11.146
10.691 10.808 10.924 11.041 11.158
10.703 10.819 10.936 11.053 11.169
10.714 10.831 10.948 11.064 11.181
10.726 10.843 10.959 11.076 11.193
10.738 10.854 10.971 11.088 11.205
10.749 10.866 10.983 11.099 11.216
10.761 10.877 10.994 11.111 11.228
10.773 10.889 11.006 11.123 11.240
10.784 10.901 11.018 11.134 11.251
10.796 10.913 11.029 11.146 11.263
1550 1560 1570 1580 1590
1250 1260 1270 1280 1290
7.311 7.417 7.524 7.632 7.740
7.322 7.428 7.535 7.643 7.751
7.332 7.439 7.546 7.653 7.761
7.343 7.449 7.557 7.664 7.772
1300 1310 1320 1330 1340
7.848 7.957 8.066 8.176 8.286
7.859 7.968 8.077 8.187 8.298
7.870 7.979 8.088 8.198 8.309
1350 1360 1370 1380 1390
8.397 8.508 8.620 8.731 8.844
8.408 8.519 8.631 8.743 8.855
1400 1410 1420 1430 1440
8.956 9.069 9.182 9.296 9.410
8.967 9.080 9.194 9.307 9.421
1450 1460 1470 1480 1490
9.524 9.639 9.753 9.868 9.984
1500 1510 1520 1530 1540
10.099 10.215 10.331 10.447 10.563
10.111 10.226 10.342 10.458 10.575
10.122 10.238 10.354 10.470 10.586
10.134 10.249 10.365 10.482 10.598
10.145 10.261 10.377 10.493 10.609
10.157 10.273 10.389 10.505 10.621
10.168 10.284 10.400 10.516 10.633
10.180 10.296 10.412 10.528 10.644
10.192 10.307 10.423 10.540 10.656
10.203 10.319 10.435 10.551 10.668
10.215 10.331 10.447 10.563 10.679
°C
0
1
2
3
4
5
6
7
8
9
10
°C
7.353 7.460 7.567 7.675 7.783
7.364 7.471 7.578 7.686 7.794
7.375 7.482 7.589 7.697 7.805
7.385 7.492 7.600 7.707 7.816
7.396 7.503 7.610 7.718 7.827
7.407 7.514 7.621 7.729 7.837
7.417 7.524 7.632 7.740 7.848
1250 1260 1270 1280 1290
1600 1610 1620 1630 1640
11.263 11.380 11.497 11.614 11.731
11.275 11.392 11.509 11.626 11.743
11.286 11.403 11.520 11.637 11.754
11.298 11.415 11.532 11.649 11.766
11.310 11.427 11.544 11.661 11.778
11.321 11.438 11.555 11.673 11.790
11.333 11.450 11.567 11.684 11.801
11.345 11.462 11.579 11.696 11.813
11.357 11.474 11.591 11.708 11.825
11.368 11.485 11.602 11.719 11.836
11.380 11.497 11.614 11.731 11.848
1600 1610 1620 1630 1640
7.881 7.990 8.099 8.209 8.320
7.892 8.001 8.110 8.220 8.331
7.903 8.012 8.121 8.231 8.342
7.914 8.023 8.132 8.242 8.353
7.924 8.034 8.143 8.253 8.364
7.935 8.045 8.154 8.264 8.375
7.946 8.056 8.165 8.275 8.386
7.957 8.066 8.176 8.286 8.397
1300 1310 1320 1330 1340
1650 1660 1670 1680 1690
11.848 11.965 12.082 12.199 12.316
11.860 11.977 12.094 12.211 12.327
11.871 11.988 12.105 12.222 12.339
11.883 12.000 12.117 12.234 12.351
11.895 12.012 12.129 12.246 12.363
11.907 12.024 12.141 12.257 12.374
11.918 12.035 12.152 12.269 12.386
11.930 12.047 12.164 12.281 12.398
11.942 12.059 12.176 12.292 12.409
11.953 12.070 12.187 12.304 12.421
11.965 12.082 12.199 12.316 12.433
1650 1660 1670 1680 1690
8.419 8.530 8.642 8.754 8.866
8.430 8.542 8.653 8.765 8.877
8.441 8.553 8.664 8.776 8.889
8.453 8.564 8.675 8.787 8.900
8.464 8.575 8.687 8.799 8.911
8.475 8.586 8.698 8.810 8.922
8.486 8.597 8.709 8.821 8.934
8.497 8.608 8.720 8.832 8.945
8.508 8.620 8.731 8.844 8.956
1350 1360 1370 1380 1390
1700 1710 1720 1730 1740
12.433 12.549 12.666 12.782 12.898
12.444 12.561 12.677 12.794 12.910
12.456 12.572 12.689 12.805 12.921
12.468 12.584 12.701 12.817 12.933
12.479 12.596 12.712 12.829 12.945
12.491 12.607 12.724 12.840 12.956
12.503 12.619 12.736 12.852 12.968
12.514 12.631 12.747 12.863 12.980
12.526 12.642 12.759 12.875 12.991
12.538 12.654 12.770 12.887 13.003
12.549 12.666 12.782 12.898 13.014
1700 1710 1720 1730 1740
8.979 9.092 9.205 9.319 9.433
8.990 9.103 9.216 9.330 9.444
9.001 9.114 9.228 9.342 9.456
9.013 9.126 9.239 9.353 9.467
9.024 9.137 9.251 9.364 9.478
9.035 9.148 9.262 9.376 9.490
9.047 9.160 9.273 9.387 9.501
9.058 9.171 9.285 9.398 9.513
9.069 9.182 9.296 9.410 9.524
1400 1410 1420 1430 1440
1750 1760 1770 1780 1790
13.014 13.130 13.246 13.361 13.476
13.026 13.142 13.257 13.373 13.488
13.037 13.153 13.269 13.384 13.499
13.049 13.165 13.280 13.396 13.511
13.061 13.176 13.292 13.407 13.522
13.072 13.188 13.304 13.419 13.534
13.084 13.200 13.315 13.430 13.545
13.095 13.211 13.327 13.442 13.557
13.107 13.223 13.338 13.453 13.568
13.119 13.234 13.350 13.465 13.580
13.130 13.246 13.361 13.476 13.591
1750 1760 1770 1780 1790
9.536 9.547 9.558 9.570 9.581 9.593 9.604 9.616 9.627 9.639 9.650 9.662 9.673 9.684 9.696 9.707 9.719 9.730 9.742 9.753 9.765 9.776 9.788 9.799 9.811 9.822 9.834 9.845 9.857 9.868 9.880 9.891 9.903 9.914 9.926 9.937 9.949 9.961 9.972 9.984 9.995 10.007 10.018 10.030 10.041 10.053 10.064 10.076 10.088 10.099
1450 1460 1470 1480 1490
1800 13.591 13.603 13.614 13.626 13.637 13.649 13.660 13.672 13.683 13.694 13.706 1800 1810 13.706 13.717 13.729 13.740 13.752 13.763 13.775 13.786 13.797 13.809 13.820 1810
1500 1510 1520 1530 1540
°C
°C
Z-213
0
1
2
3
4
5
6
7
8
9
10
°C
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 450 to 2372°F – 270 to 1300°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Alternative to Type K; More Stable at High Temperatures TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
+ –
Thermocouple Grade
Revised Thermocouple Reference Tables
Nickel-14.2% Chromium-1.4% Silicon vs. Nickel-4.4% Silicon0.1% Magnesium +
N
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
– Extension Grade
Thermoelectric Voltage in Millivolts °C
-10
-9
9
10
°C
-260 - 4.345 - 4.345 - 4.344 - 4.344 - 4.343 - 4.342 - 4.341 - 4.340 - 4.339 - 4.337 -4.336 -260 -250 -4.338 -4.334 -4.332 -4.330 -4.328 -4.326 -4.324 -4.321 -4.319 -4.318 -4.313 -250
300 9.341 9.377 9.412 9.448 9.483 9.519 9.554 9.590 9.625 310 9.696 9.732 9.768 9.803 9.839 9.875 9.910 9.946 9.982 320 10.054 10.089 10.125 10.161 10.197 10.233 10.269 10.305 10.341 330 10.413 10.449 10.485 10.521 10.557 10.593 10.629 10.665 10.701 340 10.774 10.810 10.846 10.882 10.918 10.955 10.991 11.027 11.064
9.661 10.018 10.377 10.737 11.100
9.696 10.054 10.413 10.774 11.136
300 310 320 330 340
-240 -230 -220 -210 -200
-4.313 -4.277 -4.226 -4.162 -4.083
-4.310 -4.273 -4.221 -4.154 -4.074
-4.307 -4.268 -4.215 -4.147 -4.066
-4.304 -4.263 -4.209 -4.140 -4.057
-4.300 -4.258 -4.202 -4.132 -4.048
-4.297 -4.254 -4.196 -4.124 -4.038
-4.293 -4.248 -4.189 -4.116 -4.029
-4.289 -4.243 -4.183 -4.108 -4.020
-4.285 -4.238 -4.176 -4.100 -4.010
-4.281 -4.232 - 4.169 -4.091 -4.000
-4.277 -4.226 -4.162 -4.083 -3.990
-240 -230 -220 -210 -200
350 360 370 380 390
11.136 11.501 11.867 12.234 12.603
11.173 11.537 11.903 12.271 12.640
11.209 11.574 11.940 12.308 12.677
11.245 1.610 11.977 12.345 12.714
11.282 11.647 12.013 12.382 12.751
11.318 11.683 12.050 12.418 12.788
11.355 11.720 12.087 12.455 12.825
11.391 11.757 12.124 12.492 12.862
11.428 11.793 12.160 12.529 12.899
11.464 11.830 12.197 12.566 12.937
11.501 11.867 12.234 12.603 12.974
350 360 370 380 390
-190 -180 -170 -160 -150
-3.990 -3.884 -3.766 -3.634 -3.491
-3.980 -3.873 -3.753 -3.621 -3.476
-3.970 -3.862 -3.740 -3.607 -3.461
-3.960 -3.850 -3.728 -3.593 -3.446
-3.950 -3.838 -3.715 -3.578 -3.431
-3.939 -3.827 -3.702 -3.564 -3.415
-3.928 -3.815 -3.688 -3.550 -3.400
-3.918 -3.803 -3.675 -3.535 -3.384
-3.907 -3.790 -3.662 -3.521 -3.368
-3.898 -3.778 -3.648 -3.506 -3.352
-3.884 -3.786 -3.634 -3.491 -3.336
-190 -180 -170 -160 -150
400 410 420 430 440
12.974 13.346 13.719 14.094 14.469
13.011 13.383 13.756 14.131 14.507
13.048 13.420 13.794 14.169 14.545
13.085 13.457 13.831 14.206 14.582
13.122 13.495 13.869 14.244 14.620
13.159 13.532 13.906 14.281 14.658
13.197 13.569 13.944 14.319 14.695
13.234 13.607 13.981 14.356 14.733
13.271 13.644 14.019 14.394 14.771
13.308 13.682 14.056 14.432 14.809
13.346 13.719 14.094 14.469 14.846
400 410 420 430 440
-140 -130 -120 -110 -100
-3.336 -3.171 -2.994 -2.808 -2.612
-3.320 -3.153 -2.976 -2.789 -2.592
-3.304 -3.136 -2.958 -2.769 -2.571
-3.288 -3.119 -2.939 -2.750 -2.551
-3.271 -3.101 -2.921 -2.730 -2.531
-3.255 -3.084 -2.902 -2.711 -2.510
-3.238 -3.066 -2.883 -2.691 -2.490
-3.221 -3.048 -2.865 -2.672 -2.469
-3.205 -3.030 -2.846 -2.652 -2.448
-3.188 -3.012 -2.827 -2.632 -2.428
-3.171 -2.994 -2.808 -2.612 -2.407
-140 -130 -120 -110 -100
450 460 470 480 490
14.848 15.225 15.604 15.984 16.366
14.884 15.262 15.642 16.022 16.404
14.922 15.300 15.680 16.060 16.442
14.960 15.338 15.718 I 6.099 16.480
14.998 15.376 15.756 16.137 16.518
15.035 15.414 15.794 16.175 16.557
15.073 15.452 15.832 16.213 16.595
15.111 15.490 15.870 16.251 16.633
15.149 15.528 15.908 16.289 16.671
15.187 15.566 15.946 16.327 16.710
15.225 15.604 15.984 16.366 16.748
450 460 470 480 490
-90 -80 -70 -60 -50
-2.407 -2.193 -1.972 -1.744 -1.509
-2.386 -2.172 -1.950 -1.721 -1.485
-2.385 -2.150 -1.927 -1.698 -1.462
-2.344 -2.128 -1.905 -1.674 -1.438
-2.322 -2.106 -1.882 -1.651 -1.414
-2.301 -2.084 -1.859 -1.627 -1.390
-2.280 -2.082 -1.836 -1.604 -1.366
-2.258 -2. 039 -1.813 -1.580 -1.341
-2.237 -2.017 -1.790 -1.557 -1.317
-2.215 -1.995 -1.767 -1.533 -1.293
-2.193 -1.972 -1.744 -1.509 -1.269
-90 -80 -70 -60 -50
500 510 520 530 540
16.748 17.131 17.515 17.900 18.286
16.786 17.169 17.554 17.938 18.324
I 6.824 17.208 17.592 17.977 18.363
16.883 17.246 17.630 18.016 18.401
16.901 17.285 17.669 18.054 18.440
16.939 17.323 17.707 18.093 18.479
16.978 17.361 17.746 18.131 18.517
17.016 17.400 17.784 18.170 18.556
17.054 17.438 17.823 18.208 18.595
17.093 17.477 17.861 18.247 18.633
17.131 17.515 17.900 18.286 18.672
Soo 510 520 530 540
-40 -30 -20 -10 0
-1.269 -1.023 -0.772 -0.518 -0.260
-1.244 -0.998 -0.747 -0.492 -0.234
-1.220 -0.973 -0.722 -0.467 -0.209
-1.195 -0.948 -0.696 -0.441 -0.183
-1.171 -0.923 -0.671 -0.415 -0.157
-1.146 -0.898 -0.646 -0.390 -0.131
-1.122 -0.873 -0.620 -0.364 -0.104
-1.097 -0.848 -0.595 -0.338 -0.078
-1.072 -0.823 -0.589 -0.312 -0.052
-1.048 -0.798 -0.544 -0.286 -0.026
-1.023 -0.772 -0.518 -0.260 0.000
-40 -30 -20 -10 0
550 560 570 580 590
18.672 19.059 19.447 19.835 20.224
18.711 19.096 19.485 19.874 20.263
18.749 19.136 19.524 19.913 20.302
18.788 19.175 19.563 19.952 20.341
18.827 19.214 19.602 19.990 20.379
18.865 19.253 19.641 20.029 20.418
18.904 19.292 19.680 20.068 20.457
18.943 19.330 19.718 20.107 20.496
18.982 19.369 19.757 20.146 20.535
19.020 19.408 19.796 20.185 20.574
19.059 19.447 19.835 20.224 20.613
550 560 570 580 590
0 10 20 30 40
0.000 0.261 0.525 0.793 1.065
0.026 0.287 0.552 0.820 1.092
0.052 0.313 0.578 0.847 1.119
0.078 0.340 O.605 0.874 1.147
0.104 0.130 0.366 0.393 0.632 O.659 0.901 0.928 1.174 1.202
0.156 0.419 0.685 0.955 1.229
0.182 0.446 0.712 0.983 1.257
0.208 0.472 0.739 1.010 1.284
0.235 0.499 0.766 1.037 1.312
0.261 0.525 0.793 1.065 1.340
0 10 20 30 40
600 610 620 630 640
20.613 21.003 21.393 21.784 22.175
20.652 21.042 21.432 21.823 22.214
20.69l 21.081 21.471 21.862 22.253
20.730 21.120 21.510 21.901 22.292
20.769 21.159 21.549 21.940 22.331
20.808 21.198 21.588 21.979 22.370
20.847 21.237 21.628 22.018 22.410
20.886 21.276 21.667 22.058 22.449
20.925 21.315 21.706 22.097 22.488
20.964 21.354 21.745 22.136 22.527
21.003 21.393 21.784 22.175 22.566
600 610 620 630 640
50 60 70 80 90
1.340 1.619 1.902 2.189 2.480
1.368 1.647 1.930 2.218 2.509
1.395 1.675 1.959 2.247 2.538
1.423 1.703 1.988 2.276 2.568
1.451 1.732 2.016 2.305 2.597
1.479 1.760 2.045 2.334 2.826
1.507 1.788 2.074 2.363 2.656
1.535 1.817 2.102 2.392 2.685
1.563 1.845 2.131 2.421 2.715
1.501 1.873 2.160 2.450 2.744
1.619 1.902 2.189 2.480 2.774
50 60 70 80 90
650 660 670 680 690
22.556 22.958 23.350 23.742 24.134
22.605 22.997 23.389 23.781 24.173
22.644 23.036 23.428 23.820 24.213
22.684 23.075 23.467 23.860 24.252
22.723 23.115 23.507 23.899 24.291
22.762 23.154 23.546 23.938 24.330
22.801 23.193 23.585 23.977 24.370
22.840 23.232 23.624 24.016 24.409
22.879 23.271 23.663 24.056 24.448
22.919 23.311 23.703 24.095 24.487
22.958 23.350 23.742 24.134 24.527
650 660 670 680 690
100 110 120 130 140
2.774 3.072 3.374 3.680 3.989
2.804 3.102 3.405 3.711 4.020
2.833 3.133 3.435 3.742 4.051
2.863 3.163 3.466 3.772 4.083
2.893 3.193 3.496 3.803 4.114
2.923 3.223 3.527 3.834 4.145
2.953 3.253 3.557 3.865 4.176
2.983 3.283 3.588 3.896 4.208
3.012 3.314 3.619 3.927 4.239
3.042 3.344 3.649 3.958 4.270
3.072 3.374 3.680 3.989 4.302
100 110 120 130 140
700 710 720 730 740
24.527 24.919 25.312 25.705 26.098
24.566 24.959 25.351 25.744 26.137
24.605 24.998 25.391 25.783 26.176
24.644 25.037 25.430 25.823 26.216
24.684 25.076 25.469 25.862 26.255
24.723 25.116 25.508 25.901 26.294
24.762 25.155 25.548 25.941 26.333
24.801 25.194 25.587 25.980 26.373
24.841 25.233 25.626 26.019 26.412
24.880 25.273 25.666 26.058 26.451
24.919 25.312 25.705 26.098 26.491
700 710 720 730 740
150 160 170 180 190
4.302 4.618 4.937 5.259 5.585
4.333 4.650 4.969 5.292 5.618
4.365 4.681 5.001 5.324 5.650
4.396 4.713 5.033 5.357 5.683
4.428 4.745 5.066 5.389 5.716
4.459 4.777 5.098 5.422 5.749
4.491 4.809 5.130 5.454 5.782
4.523 4.841 5.162 5.487 5.815
4.554 4.873 5.195 5.520 5.847
4.586 4.905 5.227 5.552 5.880
4.618 4.937 5.259 5.585 5.913
I5O 160 170 ISO 190
750 760 770 780 790
26.491 26.883 27.276 27.669 28.062
26.530 26.923 27.316 27.708 28.101
26.569 26.962 27.355 27.748 28.140
26.608 27.001 27.394 27.787 28.180
26.648 27.041 27.433 27.826 28.219
26.687 27.080 27.473 27.866 28.258
26.726 27.119 27.512 27.905 28.297
26.766 27.158 27.551 27.944 28.337
26.805 27.198 27.591 27.983 28.376
26.844 27.237 27.630 28.023 28.415
26.883 27.276 27.669 28.062 28.455
75O 760 770 780 790
200 210 220 230 240
5.913 5.946 6.245 6.278 6.579 68.612 6.916 6.949 7.255 7.289
5.979 6.311 e.e" 6.983 7.323
6.013 6.345 6.680 7.017 7.357
6.046 6.079 6.378 6.411 8.713 15.747 7.051 7.085 7.392 7.426
6.112 6.445 6.781 7.119 7.460
6.145 6.478 6.814 7.153 7.494
6.178 6.512 6.848 7.187 7.528
6.211 6.545 6.882 7.221 7.583
6.245 6.579 6.918 7.255 7.597
200 210 220 230 240
800 810 820 830 840
28.455 28.847 29.239 29.632 30.024
28.494 28.886 29.279 29.671 30.063
28.533 28.926 29.318 29.710 30.102
28.572 28.965 29.357 29.749 30.141
28.612 29.004 29.396 29.789 30.181
28.651 29.043 29.436 29.828 30.220
28.690 29.083 29.475 29.867 30.259
28.729 29.122 29.514 29.906 30.298
28.769 29.161 29.553 29.945 30.337
28.808 29.200 29.592 29.985 30.376
28.847 29.239 29.632 30.024 30.416
800 810 820 830 840
250 260 270 280 290
7.597 7.941 8.288 8.637 8.988
7.666 8.010 8.358 8.707 9.058
7.700 8.045 8.392 8.742 9.094
7.734 8.080 8.427 8.777 9.129
7.803 8.149 8.497 8.847 9.200
7.838 8.184 8.532 8.882 9.235
7.872 8.218 8.567 8.918 9.270
7.907 8.253 8.602 8.953 9.306
7.941 8.288 8.637 8.988 9.341
250 260 270 280 290
850 860 870 880 890
30.416 30.807 31.199 31.590 31.981
30.455 30.846 31.238 31.629 32.020
30.494 30.886 31.277 31.668 32.059
30.533 30.925 31.316 31.707 32.098
30.572 30.964 31.355 31.746 32.137
30.611 31.003 31.394 31.785 32.176
30.651 31.042 31.433 31.824 32.215
30.690 31.081 31.473 31.863 32.254
30.729 31.120 31.512 31.903 32.293
30.768 31.160 31.551 31.942 32.332
30.807 31.199 31.590 31.981 32.371
850 860 870 880 890
°C
0
6
7
8
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
7.631 7.976 8.323 8.672 9.023
1
-8
2
-7
3
-6
4
-5
7.769 8.114 8.462 8.812 9.164
5
-4
-3
-2
-1
9
0
°C
°C
Z-214
0
1
2
3
4
5
6
7
8
Z
+ –
Revised Thermocouple Reference Tables
Nickel-14.2% Chromium-1.4% Silicon vs. Nickel-4.4% Silicon0.1% Magnesium +
N
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
– Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 450 to 2372°F – 270 to 1300°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Alternative to Type K; More Stable at High Temperatures TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
Thermoelectric Voltage in Millivolts
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
900 910 920 930 940
32.371 32.761 33.151 33.541 33.930
32.410 32.800 33.190 33.580 33.969
32.449 32.839 33.229 33.619 34.008
32.488 32.878 33.268 33.658 34.047
32.527 32.917 33.307 33.697 34.086
32.566 32.956 33.346 33.736 34.124
32.605 32.995 33.385 33.774 34.163
32.644 33.034 33.424 33.813 34.202
32.683 33.073 33.463 33.852 34.241
32.722 33.112 33.502 33.891 34.280
32.761 33.151 33.541 33.930 34.319
900 910 920 930 940
1150 1160 1170 1180 1190
41.976 42.352 42.727 43.101 43.474
42.014 42.390 42.764 43.138 43.511
42.052 42.427 42.802 43.176 43.549
42.089 42.465 42.839 43.213 43.586
42.127 42.502 42.877 43.250 43.623
42.164 42.540 42.914 43.288 43.660
42.202 42.577 42.951 43.325 43.698
42.239 42.614 42.989 43.362 43.735
42.277 42.652 43.026 43.399 43.772
42.314 42.689 43.064 43.437 43.809
42.352 42.727 43.101 43.474 43.846
1150 1160 1170 1190 1190
950 960 970 980 990
34.319 34.707 35.095 35.482 35.869
34.358 34.746 35.134 35.521 35.908
34.396 34.785 35.172 35.560 35.946
34.435 34.823 35.211 35.598 35.985
34.474 34.862 35.250 35.637 36.024
34.513 34.901 35.289 35.676 36.062
34.552 34.940 35.327 35.714 36.101
34.591 34.979 35.366 35.753 36.140
34.629 35.017 35.405 35.792 36.178
34.668 35.056 35.444 35.831 36.217
34.707 35.095 35.482 35.889 36.256
950 960 970 980 990
1200 1210 1220 1230 1240
43.846 44.218 44.588 44.958 45.326
43.884 44.255 44.625 44.995 45.363
43.921 44.292 44.662 45.032 45.400
43.958 44.329 44.699 45.069 45.437
43.995 44.366 44.736 45.105 45.474
44.032 44.403 44.773 45.142 45.510
44.069 44.440 44.810 45.179 45.547
44.106 44.477 44.847 45.216 45.584
44.144 44.514 44.884 45.253 45.621
44.181 44.551 44.921 45.290 45.657
44.218 44.551 44.958 45.326 45.694
1900 1210 1220 1230 1240
1000 1010 1020 1030 1040
36.256 36.841 37.027 37.411 37.795
38.294 36.680 37.065 37.450 37.834
36.333 36.718 37.104 37.488 37.872
36.371 38.757 37.142 37.527 37.911
36.410 38.796 37.181 37.565 37.949
36.449 38.834 37.219 37.603 37.987
36.487 36.873 37.258 37.642 38.026
36.526 36.911 37.296 37.680 38.064
36.564 36.950 37.334 37.719 38.102
36.603 36.988 37.373 37.757 38.141
36.641 37.027 37.411 37.795 38.179
1000 1010 1020 1030 1040
1250 1260 1270 1280 1290
45.694 46.060 46.425 46.789 47.152
45.731 46.097 46.462 46.826 47.188
45.767 46.133 46.498 46.862 47.224
45.804 46.170 46.535 46.898 47.260
45.841 46.207 46.571 46.935 47.296
45.877 46.243 46.608 46.971 47.333
45.914 46.280 46.844 47.007 47.369
45.951 46.316 46.880 47.043 47.405
45.987 46.353 46.717 47.079 47.441
46.024 46.389 46.753 47.116 47.477
46.080 46.425 46.789 47.152 47.513
1250 1260 1270 1280 1290
1050 1060 1070 1080 1090
38.179 38.562 38.944 39.326 39.708
38.217 38.600 38.982 39.364 39.744
38.256 38.638 39.020 39.402 39.783
38.294 38.677 39.059 39.440 39.821
38.332 38.715 39.097 39.478 39.859
38.370 38.753 39.135 39.516 39.897
38.409 38.791 39.173 30.554 39.935
38.447 38.829 39.211 39.592 39.973
38.485 38.868 39.249 39.630 40.011
38.524 38.906 39.287 39.668 40.049
38.562 38.944 39.326 39.706 40.087
1050 1060 1070 1000 1090
1100 1110 1120 1130 1140
40.087 40.466 40.845 41.223 41.600
40.125 40.504 40.883 41.260 41.638
40.163 40.542 40.920 41.298 41.675
40.201 40.580 40.958 41.336 41.713
40.238 40.818 40.996 41.374 41.751
40.276 40.655 41.034 41.411 41.788
40.314 40.693 41.072 41.449 41.826
40.352 40.731 41.109 41.487 41.864
40.390 40.769 41.147 41.525 41.901
40.428 40.807 41.185 41.562 41.939
40.466 40.845 41.223 41.6OO 41.976
1100 1110 1120 1130 1140
°C
0
1
2
3
4
5
6
7
8
9
10
°C
0
1
2
3
4
5
6
7
8
9
10
°C
Z-215
°C
°C
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 1382°F 0 to 750°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Reducing, Vacuum, Inert; Limited Use in Oxidizing at High Temperatures; Not Recommended for Low Temperatures TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermocouple Grade
+ –
Revised Thermocouple Reference Tables
TYPE
Iron vs. Copper-Nickel
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ – Extension Grade
Thermoelectric Voltage in Millivolts °F
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
°F
°F
0
-340 -330 -320 -310 -300
-8.030 -7.915 -7.791 -7.659
-8.019 -7.903 -7.778 -7.645
-8.008 -7.890 -7.765 -7.632
-7.996 -7.878 -7.752 -7.618
-8.095 -7.985 -7.866 -7.739 -7.604
-8.085 -7.973 -7.854 -7.726 -7.590
-8.074 -7.962 -7.841 -7.713 -7.576
-8.063 -7.950 -7.829 -7.699 -7.562
-8.052 -7.938 -7.816 -7.686 -7.548
-8.041 -7.927 -7.804 -7.672 -7.534
-8.030 -7.915 -7.791 -7.659 -7.519
-340 -330 -320 -310 -300
300 310 320 330 340
7.949 8.255 8.562 8.869 9.177
-290 -280 -270 -260 -250
-7.519 -7.373 -7.219 -7.058 -6.890
-7.505 -7.357 -7.203 -7.041 -6.873
-7.491 -7.342 -7.187 -7.025 -6.856
-7.476 -7.327 -7.171 -7.008 -6.839
-7.462 -7.312 -7.155 -6.991 -6.821
-7.447 -7.296 -7.139 -6.975 -6.804
-7.432 -7.281 -7.123 -6.958 -6.787
-7.417 -7.265 -7.107 -6.941 -6.769
-7.403 -7.250 -7.090 -6.924 -6.752
-7.388 -7.234 -7.074 -6.907 -6.734
-7.373 -7.219 -7.058 -6.890 -6.716
-240 -230 -220 -210 -200
-6.716 -6.536 -6.351 -6.159 -5.962
-6.699 -6.518 -6.332 -6.140 -5.942
-6.681 -6.500 -6.313 -6.120 -5.922
-6.663 -6.481 -6.294 -6.101 -5.902
-6.645 -6.463 -6.275 -6.081 -5.882
-6.627 -6.444 -6.256 -6.061 -5.862
-6.609 -6.426 -6.236 -6.042 -5.842
-6.591 -6.407 -6.217 -6.022 -5.821
-6.573 -6.388 -6.198 -6.002 -5.801
-6.555 -6.370 -6.179 -5.982 -5.781
-190 -180 -170 -160 -150
-5.760 -5.553 -5.341 -5.125 -4.903
-5.740 -5.532 -5.320 -5.103 -4.881
-5.719 -5.511 -5.298 -5.081 -4.859
-5.699 -5.490 -5.277 -5.059 -4.836
-5.678 -5.469 -5.255 -5.037 -4.814
-5.657 -5.448 -5.233 -5.015 -4.791
-5.637 -5.426 -5.212 -4.992 -4.769
-5.616 -5.405 -5.190 -4.970 -4.746
-5.595 -5.384 -5.168 -4.948 -4.724
-140 -130 -120 -110 -100
-4.678 -4.449 -4.215 -3.978 -3.737
-4.655 -4.425 -4.192 -3.954 -3.713
-4.633 -4.402 -4.168 -3.930 -3.688
-4.610 -4.379 -4.144 -3.906 -3.664
-4.587 -4.356 -4.121 -3.882 -3.640
-4.564 -4.332 -4.097 -3.858 -3.615
-4.541 -4.309 -4.073 -3.834 -3.591
-4.518 -4.286 -4.050 -3.810 -3.566
-90 -80 -70 -60 - 50
-3.493 -3.245 -2.994 -2.740 -2.483
-3.468 -3.220 -2.969 -2.714 -2.457
-3.443 -3.195 -2.943 -2.689 -2.431
-3.419 -3.170 -2.918 -2.663 -2.405
-3.394 -3.145 -2.893 -2.638 -2.379
-3.369 -3.120 -2.867 -2.612 -2.353
-3.344 -3.095 -2.842 -2.586 -2.327
-40 -30 -20 -10 0
-2.223 -1.961 -1.695 -1.428 -1.158
-2.197 -1.934 -1.669 -1.401 -1.131
-2.171 -1.908 -1.642 -1.374 -1.104
-2.145 -1.881 -1.615 -1.347 -1.076
-2.118 -1.855 -1.589 -1.320 -1.049
-2.092 -1.828 -1.562 -1.293 -1.022
-2.066 -1.802 -1.535 -1.266 -0.995
0 10 20 30 40
-0.886 -0.611 -0.334 -0.056 0.225
50 60 70 80 90
0.507 0.791 1.076 1.364 1.652
0.535 0.819 1.105 1.392 1.681
0.563 0.848 1.134 1.421 1.710
0.592 0.876 1.162 1.450 1.739
0.620 0.905 1.191 1.479 1.768
0.649 0.933 1.220 1.508 1.797
0.677 0.962 1.249 1.537 1.826
0.705 0.991 1.277 1.566 1.855
0.734 1.019 1.306 1.594 1.884
0.762 1.048 1.335 1.623 1.913
100 110 120 130 140
1.942 2.234 2.527 2.821 3.116
1.972 2.263 2.556 2.850 3.145
2.001 2.292 2.585 2.880 3.175
2.030 2.322 2.615 2.909 3.204
2.059 2.351 2.644 2.938 3.234
2.088 2.380 2.673 2.968 3.264
2.117 2.409 2.703 2.997 3.293
2.146 2.439 2.732 3.027 3.323
2.175 2.468 2.762 3.057 3.353
150 160 170 180 190
3.412 3.709 4.007 4.306 4.606
3.442 3.739 4.037 4.336 4.636
3.471 3.769 4.067 4.366 4.666
3.501 3.798 4.097 4.396 4.696
3.531 3.828 4.127 4.426 4.726
3.560 3.858 4.157 4.456 4.757
3.590 3.888 4.187 4.486 4.787
3.620 3.918 4.217 4.516 4.817
200 210 220 230 240
4.907 5.209 5.511 5.814 6.117
4.937 5.239 5.541 5.844 6.147
4.967 5.269 5.571 5.874 6.178
4.997 5.299 5.602 5.905 6.208
5.028 5.329 5.632 5.935 6.239
5.058 5.360 5.662 5.965 6.269
5.088 5.390 5.692 5.996 6.299
250 260 270 280 290
6.421 6.726 7.031 7.336 7.642
6.452 6.756 7.061 7.367 7.673
6.482 6.787 7.092 7.398 7.704
6.512 6.817 7.122 7.428 7.734
6.543 6.848 7.153 7.459 7.765
6.573 6.878 7.184 7.489 7.795
°F
0
6
7
8
10
°F
8.133 8.439 8.747 9.054 9.362
8.163 8.470 8.777 9.085 9.392
8.194 8.501 8.808 9.115 9.423
8.225 8.532 8.839 9.146 9.454
8.255 8.562 8.869 9.177 9.485
300 310 320 330 340
-290 -280 -270 -260 -250
350 9.485 9.515 9.546 9.577 9.608 9.639 9.669 9.700 9.731 360 9.793 9.823 9.854 9.885 9.916 9.947 9.977 10.008 10.039 370 10.101 10.131 10.162 10.193 10.224 10.255 10.285 10.316 10.347 380 10.409 10.440 10.470 10.501 10.532 10.563 10.594 10.625 10.655 390 10.717 10.748 10.779 10.810 10.840 10.871 10.902 10.933 10.964
9.762 10.070 10.378 10.686 10.995
9.793 10.101 10.409 10.717 11.025
350 360 370 380 390
-6.536 -6.351 -6.159 -5.962 -5.760
-240 -230 -220 -210 -200
400 410 420 430 440
11.025 11.334 11.642 11.951 12.260
11.056 11.365 11.673 11.982 12.290
11.087 11.396 11.704 12.013 12.321
11.118 11.426 11.735 12.044 12.352
11.149 11.457 11.766 12.074 12.383
11.180 11.488 11.797 12.105 12.414
11.211 11.519 11.828 12.136 12.445
11.241 11.550 11.858 12.167 12.476
11.272 11.581 11.889 12.198 12.506
11.303 11.612 11.920 12.229 12.537
11.334 11.642 11.951 12.260 12.568
400 410 420 430 440
-5.574 -5.363 -5.146 -4.926 -4.701
-5.553 -5.341 -5.125 -4.903 -4.678
-190 -180 -170 -160 -150
450 460 470 480 490
12.568 12.877 13.185 13.494 13.802
12.599 12.907 13.216 13.524 13.833
12.630 12.938 13.247 13.555 13.864
12.661 12.969 13.278 13.586 13.894
12.691 13.000 13.308 13.617 13.925
12.722 13.031 13.339 13.648 13.956
12.753 13.062 13.370 13.679 13.987
12.784 13.093 13.401 13.709 14.018
12.815 13.123 13.432 13.740 14.049
12.846 13.154 13.463 13.771 14.079
12.877 13.185 13.494 13.802 14.110
450 460 470 480 490
-4.495 -4.262 -4.026 -3.786 -3.542
-4.472 -4.239 -4.002 -3.761 -3.517
-4.449 -4.215 -3.978 -3.737 -3.493
-140 -130 -120 -110 -100
500 510 520 530 540
14.110 14.418 14.727 15.035 15.343
14.141 14.449 14.757 15.065 15.373
14.172 14.480 14.788 15.096 15.404
14.203 14.511 14.819 15.127 15.435
14.233 14.542 14.850 15.158 15.466
14.264 14.573 14.881 15.189 15.496
14.295 14.603 14.911 15.219 15.527
14.326 14.634 14.942 15.250 15.558
14.357 14.665 14.973 15.281 15.589
14.388 14.696 15.004 15.312 15.620
14.418 14.727 15.035 15.343 15.650
500 510 520 530 540
-3.320 -3.070 -2.817 -2.560 -2.301
-3.295 -3.044 -2.791 -2.535 -2.275
-3.270 -3.019 -2.766 -2.509 -2.249
-3.245 -2.994 -2.740 -2.483 -2.223
-90 -80 -70 -60 -50
550 560 570 580 590
15.650 15.958 16.266 16.573 16.881
15.681 15.989 16.296 16.604 16.911
15.712 16.020 16.327 16.635 16.942
15.743 16.050 16.358 16.665 16.973
15.773 16.081 16.389 16.696 17.003
15.804 16.112 16.419 16.727 17.034
15.835 16.143 16.450 16.758 17.065
15.866 16.173 16.481 16.788 17.096
15.897 16.204 16.512 16.819 17.126
15.927 16.235 16.542 16.850 17.157
15.958 16.266 16.573 16.881 17.188
550 560 570 580 590
-2.040 -1.775 -1.508 -1.239 -0.967
-2.013 -1.749 -1.482 -1.212 -0.940
-1.987 -1.722 -1.455 -1.185 -0.913
-1.961 -1.695 -1.428 -1.158 -0.886
-40 -30 -20 -10 0
600 610 620 630 640
17.188 17.495 17.802 18.109 18.416
17.219 17.526 17.833 18.140 18.446
17.249 17.556 17.863 18.170 18.477
17.280 17.587 17.894 18.201 18.508
17.311 17.618 17.925 18.232 18.538
17.341 17.649 17.955 18.262 18.569
17.372 17.679 17.986 18.293 18.600
17.403 17.710 18.017 18.324 18.630
17.434 17.741 18.048 18.354 18.661
17.464 17.771 18.078 18.385 18.692
17.495 17.802 18.109 18.416 18.722
600 610 620 630 640
-0.858 -0.831 -0.803 -0.776 -0.749 -0.721 -0.694 -0.666 -0.639 -0.611 -0.583 -0.556 -0.528 -0.501 -0.473 -0.445 -0.418 -0.390 -0.362 -0.334 -0.307 -0.279 -0.251 -0.223 -0.195 -0.168 -0.140 -0.112 -0.084 -0.056 -0.028 0.000 0.028 0.056 0.084 0.112 0.140 0.168 0.196 0.225 0.253 0.281 0.309 0.337 0.365 0.394 0.422 0.450 0.478 0.507
0 10 20 30 40
650 660 670 680 690
18.722 19.029 19.336 19.642 19.949
18.753 19.060 19.366 19.673 19.979
18.784 19.090 19.397 19.704 20.010
18.814 19.121 19.428 19.734 20.041
18.845 19.152 19.458 19.765 20.071
18.876 19.182 19.489 19.795 20.102
18.906 19.213 19.520 19.826 20.132
18.937 19.244 19.550 19.857 20.163
18.968 19.274 19.581 19.887 20.194
18.998 19.305 19.612 19.918 20.224
19.029 19.336 19.642 19.949 20.255
650 660 670 680 690
0.791 1.076 1.364 1.652 1.942
50 60 70 80 90
700 710 720 730 740
20.255 20.561 20.868 21.174 21.480
20.286 20.592 20.898 21.205 21.511
20.316 20.623 20.929 21.235 21.542
20.347 20.653 20.960 21.266 21.572
20.378 20.684 20.990 21.297 21.603
20.408 20.715 21.021 21.327 21.634
20.439 20.745 21.052 21.358 21.664
20.469 20.776 21.082 21.389 21.695
20.500 20.806 21.113 21.419 21.726
20.531 20.837 21.143 21.450 21.756
20.561 20.868 21.174 21.480 21.787
700 710 720 730 740
2.205 2.497 2.791 3.086 3.382
2.234 2.527 2.821 3.116 3.412
100 110 120 130 140
750 760 770 780 790
21.787 22.093 22.400 22.706 23.013
21.817 22.124 22.430 22.737 23.044
21.848 22.154 22.461 22.768 23.074
21.879 22.185 22.492 22.798 23.105
21.909 22.216 22.522 22.829 23.136
21.940 22.246 22.553 22.860 23.166
21.971 22.277 22.584 22.890 23.197
22.001 22.308 22.614 22.921 23.228
22.032 22.338 22.645 22.952 23.258
22.063 22.369 22.676 22.982 23.289
22.093 22.400 22.706 23.013 23.320
750 760 770 780 790
3.650 3.948 4.246 4.546 4.847
3.679 3.977 4.276 4.576 4.877
3.709 4.007 4.306 4.606 4.907
150 160 170 180 190
800 810 820 830 840
23.320 23.627 23.934 24.241 24.549
23.350 23.657 23.964 24.272 24.579
23.381 23.688 23.995 24.303 24.610
23.412 23.719 24.026 24.333 24.641
23.442 23.749 24.057 24.364 24.672
23.473 23.780 24.087 24.395 24.702
23.504 23.811 24.118 24.426 24.733
23.535 23.842 24.149 24.456 24.764
23.565 23.872 24.180 24.487 24.795
23.596 23.903 24.210 24.518 24.826
23.627 23.934 24.241 24.549 24.856
800 810 820 830 840
5.118 5.420 5.723 6.026 6.330
5.148 5.450 5.753 6.056 6.360
5.178 5.480 5.783 6.087 6.391
5.209 5.511 5.814 6.117 6.421
200 210 220 230 240
850 860 870 880 890
24.856 25.164 25.473 25.781 26.090
24.887 25.195 25.504 25.812 26.121
24.918 25.226 25.534 25.843 26.152
24.949 25.257 25.565 25.874 26.183
24.979 25.288 25.596 25.905 26.214
25.010 25.318 25.627 25.936 26.245
25.041 25.349 25.658 25.967 26.276
25.072 25.380 25.689 25.998 26.307
25.103 25.411 25.720 26.028 26.338
25.134 25.442 25.750 26.059 26.369
25.164 25.473 25.781 26.090 26.400
850 860 870 880 890
6.604 6.909 7.214 7.520 7.826
6.634 6.939 7.245 7.550 7.857
6.665 6.970 7.275 7.581 7.887
6.695 7.000 7.306 7.612 7.918
6.726 7.031 7.336 7.642 7.949
250 260 270 280 290
900 910 920 930 940
26.400 26.710 27.020 27.330 27.642
26.431 26.741 27.051 27.362 27.673
26.462 26.772 27.082 27.393 27.704
26.493 26.803 27.113 27.424 27.735
26.524 26.834 27.144 27.455 27.766
26.555 26.865 27.175 27.486 27.797
26.586 26.896 27.206 27.517 27.829
26.617 26.927 27.237 27.548 27.860
26.648 26.958 27.268 27.579 27.891
26.679 26.989 27.299 27.610 27.922
26.710 27.020 27.330 27.642 27.953
900 910 920 930 940
6
7
8
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
°F
1
2
3
4
5
9
Z-216
1 7.979 8.286 8.593 8.900 9.208
2 8.010 8.317 8.624 8.931 9.238
3 8.041 8.347 8.654 8.962 9.269
4 8.071 8.378 8.685 8.992 9.300
5
J
8.102 8.409 8.716 9.023 9.331
9
Z
+ –
Revised Thermocouple Reference Tables
J
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
Iron vs. Copper-Nickel + – Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 1382°F 0 to 750°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Reducing, Vacuum, Inert; Limited Use in Oxidizing at High Temperatures; Not Recommended for Low Temperatures TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
950 960 970 980 990
27.953 28.266 28.579 28.892 29.206
27.985 28.297 28.610 28.923 29.238
28.016 28.328 28.641 28.955 29.269
28.047 28.359 28.672 28.986 29.301
28.078 28.391 28.704 29.018 29.332
28.109 28.422 28.735 29.049 29.363
28.141 28.453 28.767 29.080 29.395
28.172 28.485 28.798 29.112 29.426
28.203 28.516 28.829 29.143 29.458
28.234 28.547 28.861 29.175 29.489
28.266 28.579 28.892 29.206 29.521
950 960 970 980 990
1600 1610 1620 1630 1640
50.060 50.411 50.762 51.112 51.460
50.095 50.446 50.797 51.147 51.495
50.130 50.481 50.832 51.181 51.530
50.165 50.517 50.867 51.216 51.565
50.200 50.552 50.902 51.251 51.599
50.235 50.587 50.937 51.286 51.634
50.271 50.622 50.972 51.321 51.669
50.306 50.657 51.007 51.356 51.704
50.341 50.692 51.042 51.391 51.738
50.376 50.727 51.077 51.425 51.773
50.411 50.762 51.112 51.460 51.808
1600 1610 1620 1630 1640
1000 1010 1020 1030 1040
29.521 29.836 30.153 30.470 30.788
29.552 29.868 30.184 30.502 30.819
29.584 29.900 30.216 30.533 30.851
29.616 29.931 30.248 30.565 30.883
29.647 29.963 30.279 30.597 30.915
29.679 29.995 30.311 30.629 30.947
29.710 30.026 30.343 30.660 30.979
29.742 30.058 30.375 30.692 31.011
29.773 30.089 30.406 30.724 31.043
29.805 30.121 30.438 30.756 31.074
29.836 30.153 30.470 30.788 31.106
1000 1010 1020 1030 1040
1650 1660 1670 1680 1690
51.808 52.154 52.500 52.844 53.188
51.843 52.189 52.534 52.879 53.222
51.877 52.224 52.569 52.913 53.256
51.912 52.258 52.603 52.947 53.290
51.947 52.293 52.638 52.982 53.325
51.981 52.327 52.672 53.016 53.359
52.016 52.362 52.707 53.050 53.393
52.051 52.396 52.741 53.085 53.427
52.085 52.431 52.776 53.119 53.462
52.120 52.465 52.810 53.153 53.496
52.154 52.500 52.844 53.188 53.530
1650 1660 1670 1680 1690
1050 1060 1070 1080 1090
31.106 31.426 31.746 32.068 32.390
31.138 31.458 31.778 32.100 32.422
31.170 31.490 31.811 32.132 32.455
31.202 31.522 31.843 32.164 32.487
31.234 31.554 31.875 32.196 32.519
31.266 31.586 31.907 32.229 32.551
31.298 31.618 31.939 32.261 32.584
31.330 31.650 31.971 32.293 32.616
31.362 31.682 32.003 32.325 32.648
31.394 31.714 32.035 32.358 32.681
31.426 31.746 32.068 32.390 32.713
1050 1060 1070 1080 1090
1700 1710 1720 1730 1740
53.530 53.871 54.211 54.550 54.888
53.564 53.905 54.245 54.584 54.922
53.598 53.939 54.279 54.618 54.956
53.632 53.973 54.313 54.652 54.990
53.667 54.007 54.347 54.686 55.023
53.701 54.041 54.381 54.719 55.057
53.735 54.075 54.415 54.753 55.091
53.769 54.109 54.449 54.787 55.124
53.803 54.143 54.483 54.821 55.158
53.837 54.177 54.516 54.855 55.192
53.871 54.211 54.550 54.888 55.225
1700 1710 1720 1730 1740
1100 1110 1120 1130 1140
32.713 33.037 33.363 33.689 34.016
32.746 33.070 33.395 33.722 34.049
32.778 33.102 33.428 33.754 34.082
32.810 33.135 33.460 33.787 34.115
32.843 33.167 33.493 33.820 34.148
32.875 33.200 33.526 33.853 34.180
32.908 33.232 33.558 33.885 34.213
32.940 33.265 33.591 33.918 34.246
32.973 33.298 33.624 33.951 34.279
33.005 33.330 33.656 33.984 34.312
33.037 33.363 33.689 34.016 34.345
1100 1110 1120 1130 1140
1750 1760 1770 1780 1790
55.225 55.561 55.896 56.230 56.564
55.259 55.595 55.930 56.264 56.597
55.293 55.628 55.963 56.297 56.630
55.326 55.662 55.997 56.330 56.663
55.360 55.695 56.030 56.364 56.697
55.393 55.729 56.063 56.397 56.730
55.427 55.762 56.097 56.430 56.763
55.461 55.796 56.130 56.464 56.796
55.494 55.829 56.164 56.497 56.829
55.528 55.863 56.197 56.530 56.863
55.561 55.896 56.230 56.564 56.896
1750 1760 1770 1780 1790
1150 1160 1170 1180 1190
34.345 34.674 35.005 35.337 35.670
34.378 34.707 35.038 35.370 35.703
34.411 34.740 35.071 35.403 35.736
34.444 34.773 35.104 35.437 35.770
34.476 34.806 35.138 35.470 35.803
34.509 34.840 35.171 35.503 35.837
34.542 34.873 35.204 35.536 35.870
34.575 34.906 35.237 35.570 35.903
34.608 34.939 35.270 35.603 35.937
34.641 34.972 35.304 35.636 35.970
34.674 35.005 35.337 35.670 36.004
1150 1160 1170 1180 1190
1800 1810 1820 1830 1840
56.896 57.227 57.558 57.888 58.217
56.929 57.260 57.591 57.920 58.249
56.962 57.293 57.624 57.953 58.282
56.995 57.326 57.657 57.986 58.315
57.028 57.360 57.690 58.019 58.348
57.062 57.393 57.723 58.052 58.381
57.095 57.426 57.756 58.085 58.414
57.128 57.459 57.789 58.118 58.446
57.161 57.492 57.822 58.151 58.479
57.194 57.525 57.855 58.184 58.512
57.227 57.558 57.888 58.217 58.545
1800 1810 1820 1830 1840
1200 1210 1220 1230 1240
36.004 36.339 36.675 37.013 37.352
36.037 36.373 36.709 37.047 37.386
36.071 36.406 36.743 37.081 37.420
36.104 36.440 36.777 37.114 37.454
36.138 36.473 36.810 37.148 37.488
36.171 36.507 36.844 37.182 37.522
36.205 36.541 36.878 37.216 37.556
36.238 36.574 36.912 37.250 37.590
36.272 36.608 36.945 37.284 37.624
36.305 36.642 36.979 37.318 37.658
36.339 36.675 37.013 37.352 37.692
1200 1210 1220 1230 1240
1850 1860 1870 1880 1890
58.545 58.872 59.199 59.526 59.851
58.578 58.905 59.232 59.558 59.884
58.610 58.938 59.265 59.591 59.916
58.643 58.971 59.297 59.623 59.949
58.676 59.003 59.330 59.656 59.982
58.709 59.036 59.363 59.689 60.014
58.741 59.069 59.395 59.721 60.047
58.774 59.101 59.428 59.754 60.079
58.807 59.134 59.460 59.786 60.112
58.840 59.167 59.493 59.819 60.144
58.872 59.199 59.526 59.851 60.177
1850 1860 1870 1880 1890
1250 1260 1270 1280 1290
37.692 38.033 38.375 38.718 39.063
37.726 38.067 38.409 38.753 39.097
37.760 38.101 38.444 38.787 39.132
37.794 38.135 38.478 38.822 39.166
37.828 38.169 38.512 38.856 39.201
37.862 38.204 38.546 38.890 39.235
37.896 38.238 38.581 38.925 39.270
37.930 38.272 38.615 38.959 39.305
37.964 38.306 38.650 38.994 39.339
37.999 38.341 38.684 39.028 39.374
38.033 38.375 38.718 39.063 39.408
1250 1260 1270 1280 1290
1900 1910 1920 1930 1940
60.177 60.501 60.826 61.149 61.473
60.209 60.534 60.858 61.182 61.505
60.242 60.566 60.890 61.214 61.537
60.274 60.599 60.923 61.246 61.570
60.307 60.631 60.955 61.279 61.602
60.339 60.663 60.987 61.311 61.634
60.371 60.696 61.020 61.343 61.667
60.404 60.728 61.052 61.376 61.699
60.436 60.761 61.085 61.408 61.731
60.469 60.793 61.117 61.440 61.763
60.501 60.826 61.149 61.473 61.796
1900 1910 1920 1930 1940
1300 1310 1320 1330 1340
39.408 39.755 40.103 40.452 40.801
39.443 39.790 40.138 40.487 40.836
39.478 39.825 40.173 40.522 40.872
39.512 39.859 40.207 40.556 40.907
39.547 39.894 40.242 40.591 40.942
39.582 39.929 40.277 40.626 40.977
39.616 39.964 40.312 40.661 41.012
39.651 39.998 40.347 40.696 41.047
39.686 40.033 40.382 40.731 41.082
39.720 40.068 40.417 40.766 41.117
39.755 40.103 40.452 40.801 41.152
1300 1310 1320 1330 1340
1950 1960 1970 1980 1990
61.796 62.118 62.441 62.763 63.085
61.828 62.151 62.473 62.795 63.117
61.860 62.183 62.505 62.827 63.149
61.893 62.215 62.537 62.860 63.181
61.925 62.247 62.570 62.892 63.214
61.957 62.280 62.602 62.924 63.246
61.989 62.312 62.634 62.956 63.278
62.022 62.344 62.666 62.988 63.310
62.054 62.376 62.699 63.020 63.342
62.086 62.409 62.731 63.053 63.374
62.118 62.441 62.763 63.085 63.406
1950 1960 1970 1980 1990
1350 1360 1370 1380 1390
41.152 41.504 41.856 42.210 42.564
41.187 41.539 41.892 42.245 42.599
41.222 41.574 41.927 42.281 42.635
41.258 41.610 41.962 42.316 42.670
41.293 41.645 41.998 42.351 42.706
41.328 41.680 42.033 42.387 42.741
41.363 41.715 42.068 42.422 42.777
41.398 41.751 42.104 42.458 42.812
41.433 41.786 42.139 42.493 42.848
41.469 41.821 42.174 42.528 42.883
41.504 41.856 42.210 42.564 42.919
1350 1360 1370 1380 1390
2000 2010 2020 2030 2040
63.406 63.728 64.049 64.370 64.691
63.439 63.760 64.081 64.402 64.723
63.471 63.792 64.113 64.435 64.756
63.503 63.824 64.146 64.467 64.788
63.535 63.856 64.178 64.499 64.820
63.567 63.889 64.210 64.531 64.852
63.599 63.921 64.242 64.563 64.884
63.632 63.953 64.274 64.595 64.916
63.664 63.985 64.306 64.627 64.948
63.696 64.017 64.338 64.659 64.980
63.728 64.049 64.370 64.691 65.012
2000 2010 2020 2030 2040
1400 1410 1420 1430 1440
42.919 43.274 43.631 43.988 44.346
42.954 43.310 43.667 44.024 44.382
42.990 43.346 43.702 44.060 44.418
43.025 43.381 43.738 44.096 44.454
43.061 43.417 43.774 44.131 44.490
43.096 43.452 43.809 44.167 44.525
43.132 43.488 43.845 44.203 44.561
43.167 43.524 43.881 44.239 44.597
43.203 43.559 43.917 44.275 44.633
43.239 43.595 43.953 44.310 44.669
43.274 43.631 43.988 44.346 44.705
1400 1410 1420 1430 1440
2050 2060 2070 2080 2090
65.012 65.333 65.654 65.974 66.295
65.044 65.365 65.686 66.006 66.327
65.076 65.397 65.718 66.038 66.359
65.109 65.429 65.750 66.070 66.391
65.141 65.461 65.782 66.102 66.423
65.173 65.493 65.814 66.134 66.455
65.205 65.525 65.846 66.166 66.487
65.237 65.557 65.878 66.199 66.519
65.269 65.590 65.910 66.231 66.551
65.301 65.622 65.942 66.263 66.583
65.333 65.654 65.974 66.295 66.615
2050 2060 2070 2080 2090
1450 1460 1470 1480 1490
44.705 45.064 45.423 45.782 46.141
44.741 45.099 45.458 45.818 46.177
44.777 45.135 45.494 45.853 46.212
44.812 45.171 45.530 45.889 46.248
44.848 45.207 45.566 45.925 46.284
44.884 45.243 45.602 45.961 46.320
44.920 45.279 45.638 45.997 46.356
44.956 45.315 45.674 46.033 46.392
44.992 45.351 45.710 46.069 46.428
45.028 45.387 45.746 46.105 46.464
45.064 45.423 45.782 46.141 46.500
1450 1460 1470 1480 1490
2100 2110 2120 2130 2140
66.615 66.935 67.255 67.575 67.895
66.647 66.967 67.287 67.607 67.927
66.679 66.999 67.319 67.639 67.959
66.711 67.031 67.351 67.671 67.991
66.743 67.063 67.383 67.703 68.023
66.775 67.095 67.415 67.735 68.055
66.807 67.127 67.447 67.767 68.087
66.839 67.159 67.479 67.799 68.119
66.871 67.191 67.511 67.831 68.150
66.903 67.223 67.543 67.863 68.182
66.935 67.255 67.575 67.895 68.214
2100 2110 2120 2130 2140
1500 1510 1520 1530 1540
46.500 46.858 47.216 47.574 47.931
46.535 46.894 47.252 47.610 47.967
46.571 46.930 47.288 47.646 48.003
46.607 46.966 47.324 47.681 48.038
46.643 47.001 47.359 47.717 48.074
46.679 47.037 47.395 47.753 48.110
46.715 47.073 47.431 47.788 48.145
46.751 47.109 47.467 47.824 48.181
46.786 47.145 47.503 47.860 48.217
46.822 47.181 47.538 47.896 48.252
46.858 47.216 47.574 47.931 48.288
1500 1510 1520 1530 1540
2150 2160 2170 2180 2190
68.214 68.534 68.853 69.171 69.490
68.246 68.566 68.884 69.203 69.521
68.278 68.597 68.916 69.235 69.553
68.310 68.629 68.948 69.267
68.342 68.661 68.980 69.299
68.374 68.693 69.012 69.330
68.406 68.725 69.044 69.362
68.438 68.757 69.076 69.394
68.470 68.789 69.108 69.426
68.502 68.821 69.139 69.458
68.534 68.853 69.171 69.490
2150 2160 2170 2180 2190
1550 1560 1570 1580 1590
48.288 48.644 48.999 49.353 49.707
48.324 48.679 49.034 49.389 49.742
48.359 48.715 49.070 49.424 49.778
48.395 48.750 49.105 49.460 49.813
48.430 48.786 49.141 49.495 49.848
48.466 48.822 49.176 49.530 49.883
48.502 48.857 49.212 49.566 49.919
48.537 48.893 49.247 49.601 49.954
48.573 48.928 49.283 49.636 49.989
48.608 48.964 49.318 49.672 50.024
48.644 48.999 49.353 49.707 50.060
1550 1560 1570 1580 1590
°F
0
1
2
3
4
5
6
7
8
9
10
°F
0
1
2
3
4
5
6
7
8
9
10
°F
Z-217
°F
°F
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 2282°F – 200 to 1250°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Clean Oxidizing and Inert; Limited Use in Vacuum or Reducing; Wide Temperature Range; Most Popular Calibration TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
+ –
Thermocouple Grade
Nickel-Chromium vs. Nickel-Aluminum
Revised Thermocouple Reference Tables
K
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °F
-10
-9
-8
-7
-6
-5
-450
-4
-3
-2
-1
0
°F
°F
0
6
7
8
10
°F
-6.458 -6.457 -6.457 -6.456 -6.456 -450
100 110 120 130 140
1.521 1.749 1.977 2.207 2.436
1.543 1.771 2.000 2.230 2.459
1
1.566 1.794 2.023 2.253 2.483
2
1.589 1.817 2.046 2.276 2.506
3
1.612 1.840 2.069 2.298 2.529
4
1.635 1.863 2.092 2.321 2.552
5
1.657 1.886 2.115 2.344 2.575
1.680 1.909 2.138 2.367 2.598
1.703 1.931 2.161 2.390 2.621
1.726 1.954 2.184 2.413 2.644
9
1.749 1.977 2.207 2.436 2.667
100 110 120 130 140
-440 -430 -420 -410 -400
-6.456 -6.446 -6.431 -6.409 -6.380
-6.455 -6.445 -6.429 -6.406 -6.377
-6.454 -6.444 -6.427 -6.404 -6.373
-6.454 -6.443 -6.425 -6.401 -6.370
-6.453 -6.441 -6.423 -6.398 -6.366
-6.452 -6.440 -6.421 -6.395 -6.363
-6.451 -6.438 -6.419 -6.392 -6.359
-6.450 -6.436 -6.416 -6.389 -6.355
-6.449 -6.435 -6.414 -6.386 -6.352
-6.448 -6.433 -6.411 -6.383 -6.348
-6.446 -6.431 -6.409 -6.380 -6.344
-440 -430 -420 -410 -400
150 160 170 180 190
2.667 2.897 3.128 3.359 3.590
2.690 2.920 3.151 3.382 3.613
2.713 2.944 3.174 3.405 3.636
2.736 2.967 3.197 3.428 3.659
2.759 2.990 3.220 3.451 3.682
2.782 3.013 3.244 3.474 3.705
2.805 3.036 3.267 3.497 3.728
2.828 3.059 3.290 3.520 3.751
2.851 3.082 3.313 3.544 3.774
2.874 3.105 3.336 3.567 3.797
2.897 3.128 3.359 3.590 3.820
150 160 170 180 190
-390 -380 -370 -360 -350
-6.344 -6.301 -6.251 -6.195 -6.133
-6.340 -6.296 -6.246 -6.189 -6.126
-6.336 -6.292 -6.241 -6.183 -6.119
-6.332 -6.287 -6.235 -6.177 -6.113
-6.328 -6.282 -6.230 -6.171 -6.106
-6.323 -6.277 -6.224 -6.165 -6.099
-6.319 -6.272 -6.218 -6.158 -6.092
-6.315 -6.267 -6.213 -6.152 -6.085
-6.310 -6.262 -6.207 -6.146 -6.078
-6.306 -6.257 -6.201 -6.139 -6.071
-6.301 -6.251 -6.195 -6.133 -6.064
-390 -380 -370 -360 -350
200 210 220 230 240
3.820 4.050 4.280 4.509 4.738
3.843 4.073 4.303 4.532 4.760
3.866 4.096 4.326 4.555 4.783
3.889 4.119 4.349 4.578 4.806
3.912 4.142 4.372 4.601 4.829
3.935 4.165 4.395 4.623 4.852
3.958 4.188 4.417 4.646 4.874
3.981 4.211 4.440 4.669 4.897
4.004 4.234 4.463 4.692 4.920
4.027 4.257 4.486 4.715 4.943
4.050 4.280 4.509 4.738 4.965
200 210 220 230 240
-340 -330 -320 -310 -300
-6.064 -5.989 -5.908 -5.822 -5.730
-6.057 -5.981 -5.900 -5.813 -5.720
-6.049 -5.973 -5.891 -5.804 -5.711
-6.042 -5.965 -5.883 -5.795 -5.701
-6.035 -5.957 -5.874 -5.786 -5.691
-6.027 -5.949 -5.866 -5.776 -5.682
-6.020 -5.941 -5.857 -5.767 -5.672
-6.012 -5.933 -5.848 -5.758 -5.662
-6.004 -5.925 -5.840 -5.749 -5.652
-5.997 -5.917 -5.831 -5.739 -5.642
-5.989 -5.908 -5.822 -5.730 -5.632
-340 -330 -320 -310 -300
250 260 270 280 290
4.965 5.192 5.419 5.644 5.869
4.988 5.215 5.441 5.667 5.892
5.011 5.238 5.464 5.690 5.914
5.034 5.260 5.487 5.712 5.937
5.056 5.283 5.509 5.735 5.959
5.079 5.306 5.532 5.757 5.982
5.102 5.328 5.554 5.779 6.004
5.124 5.351 5.577 5.802 6.026
5.147 5.374 5.599 5.824 6.049
5.170 5.396 5.622 5.847 6.071
5.192 5.419 5.644 5.869 6.094
250 260 270 280 290
-290 -280 -270 -260 -250
-5.632 -5.529 -5.421 -5.308 -5.190
-5.622 -5.519 -5.410 -5.296 -5.178
-5.612 -5.508 -5.399 -5.285 -5.166
-5.602 -5.497 -5.388 -5.273 -5.153
-5.592 -5.487 -5.377 -5.261 -5.141
-5.581 -5.476 -5.365 -5.250 -5.129
-5.571 -5.465 -5.354 -5.238 -5.117
-5.561 -5.454 -5.343 -5.226 -5.104
-5.550 -5.443 -5.331 -5.214 -5.092
-5.540 -5.432 -5.320 -5.202 -5.079
-5.529 -5.421 -5.308 -5.190 -5.067
-290 -280 -270 -260 -250
300 310 320 330 340
6.094 6.317 6.540 6.763 6.985
6.116 6.339 6.562 6.785 7.007
6.138 6.362 6.585 6.807 7.029
6.161 6.384 6.607 6.829 7.052
6.183 6.406 6.629 6.852 7.074
6.205 6.429 6.652 6.874 7.096
6.228 6.451 6.674 6.896 7.118
6.250 6.473 6.696 6.918 7.140
6.272 6.496 6.718 6.941 7.163
6.295 6.518 6.741 6.963 7.185
6.317 6.540 6.763 6.985 7.207
300 310 320 330 340
-240 -230 -220 -210 -200
-5.067 -4.939 -4.806 -4.669 -4.527
-5.054 -4.926 -4.793 -4.655 -4.513
-5.042 -4.913 -4.779 -4.641 -4.498
-5.029 -4.900 -4.766 -4.627 -4.484
-5.016 -4.886 -4.752 -4.613 -4.469
-5.003 -4.873 -4.738 -4.599 -4.455
-4.991 -4.860 -4.724 -4.584 -4.440
-4.978 -4.847 -4.711 -4.570 -4.425
-4.965 -4.833 -4.697 -4.556 -4.411
-4.952 -4.820 -4.683 -4.542 -4.396
-4.939 -4.806 -4.669 -4.527 -4.381
-240 -230 -220 -210 -200
350 360 370 380 390
7.207 7.429 7.650 7.872 8.094
7.229 7.451 7.673 7.894 8.116
7.251 7.473 7.695 7.917 8.138
7.273 7.495 7.717 7.939 8.161
7.296 7.517 7.739 7.961 8.183
7.318 7.540 7.761 7.983 8.205
7.340 7.562 7.783 8.005 8.227
7.362 7.584 7.806 8.027 8.250
7.384 7.606 7.828 8.050 8.272
7.407 7.628 7.850 8.072 8.294
7.429 7.650 7.872 8.094 8.316
350 360 370 380 390
-190 -180 -170 -160 -150
-4.381 -4.231 -4.076 -3.917 -3.754
-4.366 -4.215 -4.060 -3.901 -3.738
-4.351 -4.200 -4.044 -3.885 -3.721
-4.336 -4.185 -4.029 -3.869 -3.705
-4.321 -4.169 -4.013 -3.852 -3.688
-4.306 -4.154 -3.997 -3.836 -3.671
-4.291 -4.138 -3.981 -3.820 -3.655
-4.276 -4.123 -3.965 -3.803 -3.638
-4.261 -4.107 -3.949 -3.787 -3.621
-4.246 -4.091 -3.933 -3.771 -3.604
-4.231 -4.076 -3.917 -3.754 -3.587
-190 -180 -170 -160 -150
400 410 420 430 440
8.316 8.539 8.761 8.985 9.208
8.338 8.561 8.784 9.007 9.231
8.361 8.583 8.806 9.029 9.253
8.383 8.605 8.828 9.052 9.275
8.405 8.628 8.851 9.074 9.298
8.427 8.650 8.873 9.096 9.320
8.450 8.672 8.895 9.119 9.343
8.472 8.694 8.918 9.141 9.365
8.494 8.717 8.940 9.163 9.388
8.516 8.739 8.962 9.186 9.410
8.539 8.761 8.985 9.208 9.432
400 410 420 430 440
-140 -130 -120 -110 -100
-3.587 -3.417 -3.243 -3.065 -2.884
-3.571 -3.400 -3.225 -3.047 -2.865
-3.554 -3.382 -3.207 -3.029 -2.847
-3.537 -3.365 -3.190 -3.011 -2.829
-3.520 -3.348 -3.172 -2.993 -2.810
-3.503 -3.330 -3.154 -2.975 -2.792
-3.486 -3.313 -3.136 -2.957 -2.773
-3.468 -3.295 -3.119 -2.938 -2.755
-3.451 -3.278 -3.101 -2.920 -2.736
-3.434 -3.260 -3.083 -2.902 -2.718
-3.417 -3.243 -3.065 -2.884 -2.699
-140 -130 -120 -110 -100
450 9.432 9.455 9.477 9.500 9.522 9.545 9.567 9.590 9.612 9.635 9.657 460 9.657 9.680 9.702 9.725 9.747 9.770 9.792 9.815 9.837 9.860 9.882 470 9.882 9.905 9.927 9.950 9.973 9.995 10.018 10.040 10.063 10.086 10.108 480 10.108 10.131 10.153 10.176 10.199 10.221 10.244 10.267 10.289 10.312 10.334 490 10.334 10.357 10.380 10.402 10.425 10.448 10.471 10.493 10.516 10.539 10.561
450 460 470 480 490
-90 -80 -70 -60 -50
-2.699 -2.511 -2.320 -2.126 -1.929
-2.680 -2.492 -2.301 -2.106 -1.909
-2.662 -2.473 -2.282 -2.087 -1.889
-2.643 -2.454 -2.262 -2.067 -1.869
-2.624 -2.435 -2.243 -2.048 -1.850
-2.605 -2.416 -2.223 -2.028 -1.830
-2.587 -2.397 -2.204 -2.008 -1.810
-2.568 -2.378 -2.185 -1.988 -1.790
-2.549 -2.359 -2.165 -1.969 -1.770
-2.530 -2.339 -2.146 -1.949 -1.749
-2.511 -2.320 -2.126 -1.929 -1.729
-90 -80 -70 -60 -50
500 510 520 530 540
10.561 10.789 11.017 11.245 11.474
10.584 10.811 11.039 11.268 11.497
10.607 10.834 11.062 11.291 11.519
10.629 10.857 11.085 11.313 11.542
10.652 10.880 11.108 11.336 11.565
10.675 10.903 11.131 11.359 11.588
10.698 10.925 11.154 11.382 11.611
10.720 10.948 11.176 11.405 11.634
10.743 10.971 11.199 11.428 11.657
10.766 10.994 11.222 11.451 11.680
10.789 11.017 11.245 11.474 11.703
500 510 520 530 540
-40 -30 -20 -10 0
-1.729 -1.527 -1.322 -1.114 -0.905
-1.709 -1.507 -1.301 -1.094 -0.883
-1.689 -1.486 -1.281 -1.073 -0.862
-1.669 -1.466 -1.260 -1.052 -0.841
-1.649 -1.445 -1.239 -1.031 -0.820
-1.628 -1.425 -1.218 -1.010 -0.799
-1.608 -1.404 -1.198 -0.989 -0.778
-1.588 -1.384 -1.177 -0.968 -0.756
-1.568 -1.363 -1.156 -0.947 -0.735
-1.547 -1.343 -1.135 -0.926 -0.714
-1.527 -1.322 -1.114 -0.905 -0.692
-40 -30 -20 -10 0
550 560 570 580 590
11.703 11.933 12.163 12.393 12.624
11.726 11.956 12.186 12.416 12.647
11.749 11.978 12.209 12.439 12.670
11.772 12.001 12.232 12.462 12.693
11.795 12.024 12.255 12.485 12.716
11.818 12.047 12.278 12.508 12.739
11.841 12.070 12.301 12.531 12.762
11.864 12.093 12.324 12.554 12.785
11.887 12.116 12.347 12.577 12.808
11.910 12.140 12.370 12.600 12.831
11.933 12.163 12.393 12.624 12.855
550 560 570 580 590
0 10 20 30 40
-0.692 -0.478 -0.262 -0.044 0.176
-0.671 -0.650 -0.628 -0.607 -0.586 -0.564 -0.543 -0.521 -0.500 -0.478 -0.457 -0.435 -0.413 -0.392 -0.370 -0.349 -0.327 -0.305 -0.284 -0.262 -0.240 -0.218 -0.197 -0.175 -0.153 -0.131 -0.109 -0.088 -0.066 -0.044 -0.022 0.000 0.022 0.044 0.066 0.088 0.110 0.132 0.154 0.176 0.198 0.220 0.242 0.264 0.286 0.308 0.330 0.353 0.375 0.397
0 10 20 30 40
600 610 620 630 640
12.855 13.086 13.318 13.549 13.782
12.878 13.109 13.341 13.573 13.805
12.901 13.132 13.364 13.596 13.828
12.924 13.155 13.387 13.619 13.851
12.947 13.179 13.410 13.642 13.874
12.970 13.202 13.433 13.665 13.898
12.993 13.225 13.457 13.689 13.921
13.016 13.248 13.480 13.712 13.944
13.040 13.271 13.503 13.735 13.967
13.063 13.294 13.526 13.758 13.991
13.086 13.318 13.549 13.782 14.014
600 610 620 630 640
50 60 70 80 90
0.397 0.619 0.843 1.068 1.294
0.619 0.843 1.068 1.294 1.521
50 60 70 80 90
650 660 670 680 690
14.014 14.247 14.479 14.713 14.946
14.037 14.270 14.503 14.736 14.969
14.060 14.293 14.526 14.759 14.993
14.084 14.316 14.549 14.783 15.016
14.107 14.340 14.573 14.806 15.039
14.130 14.363 14.596 14.829 15.063
14.154 14.386 14.619 14.853 15.086
14.177 14.410 14.643 14.876 15.109
14.200 14.433 14.666 14.899 15.133
14.223 14.456 14.689 14.923 15.156
14.247 14.479 14.713 14.946 15.179
650 660 670 680 690
°F
0
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
°F
0.419 0.642 0.865 1.090 1.316
1
0.441 0.664 0.888 1.113 1.339
2
0.463 0.686 0.910 1.136 1.362
3
0.486 0.709 0.933 1.158 1.384
4
0.508 0.731 0.955 1.181 1.407
5
0.530 0.753 0.978 1.203 1.430
0.552 0.776 1.000 1.226 1.453
0.575 0.798 1.023 1.249 1.475
6
7
8
0.597 0.821 1.045 1.271 1.498
9
Z-218
Z
+ –
Revised Thermocouple Reference Tables
K
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
Nickel-Chromium vs. Nickel-Aluminum
+ –
Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 2282°F – 200 to 1250°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Clean Oxidizing and Inert; Limited Use in Vacuum or Reducing; Wide Temperature Range; Most Popular Calibration TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
700 710 720 730 740
15.179 15.413 15.647 15.881 16.116
15.203 15.437 15.671 15.905 16.139
15.226 15.460 15.694 15.928 16.163
15.250 15.483 15.717 15.952 16.186
15.273 15.507 15.741 15.975 16.209
15.296 15.530 15.764 15.998 16.233
15.320 15.554 15.788 16.022 16.256
15.343 15.577 15.811 16.045 16.280
15.366 15.600 15.834 16.069 16.303
15.390 15.624 15.858 16.092 16.327
15.413 15.647 15.881 16.116 16.350
700 710 720 730 740
1300 1310 1320 1330 1340
29.315 29.548 29.780 30.012 30.243
29.338 29.571 29.803 30.035 30.267
29.362 29.594 29.826 30.058 30.290
29.385 29.617 29.849 30.081 30.313
29.408 29.640 29.873 30.104 30.336
29.431 29.664 29.896 30.128 30.359
29.455 29.687 29.919 30.151 30.382
29.478 29.710 29.942 30.174 30.405
29.501 29.733 29.965 30.197 30.429
29.524 29.757 29.989 30.220 30.452
29.548 29.780 30.012 30.243 30.475
1300 1310 1320 1330 1340
750 760 770 780 790
16.350 16.585 16.820 17.055 17.290
16.374 16.608 16.843 17.078 17.314
16.397 16.632 16.867 17.102 17.337
16.421 16.655 16.890 17.125 17.361
16.444 16.679 16.914 17.149 17.384
16.468 16.702 16.937 17.173 17.408
16.491 16.726 16.961 17.196 17.431
16.514 16.749 16.984 17.220 17.455
16.538 16.773 17.008 17.243 17.478
16.561 16.796 17.031 17.267 17.502
16.585 16.820 17.055 17.290 17.526
750 760 770 780 790
1350 1360 1370 1380 1390
30.475 30.706 30.937 31.167 31.398
30.498 30.729 30.960 31.190 31.421
30.521 30.752 30.983 31.213 31.444
30.544 30.775 31.006 31.236 31.467
30.567 30.798 31.029 31.260 31.490
30.590 30.821 31.052 31.283 31.513
30.613 30.844 31.075 31.306 31.536
30.637 30.868 31.098 31.329 31.559
30.660 30.891 31.121 31.352 31.582
30.683 30.914 31.144 31.375 31.605
30.706 30.937 31.167 31.398 31.628
1350 1360 1370 1380 1390
800 810 820 830 840
17.526 17.761 17.997 18.233 18.469
17.549 17.785 18.020 18.256 18.492
17.573 17.808 18.044 18.280 18.516
17.596 17.832 18.068 18.303 18.539
17.620 17.855 18.091 18.327 18.563
17.643 17.879 18.115 18.351 18.587
17.667 17.902 18.138 18.374 18.610
17.690 17.926 18.162 18.398 18.634
17.714 17.950 18.185 18.421 18.657
17.738 17.973 18.209 18.445 18.681
17.761 17.997 18.233 18.469 18.705
800 810 820 830 840
1400 1410 1420 1430 1440
31.628 31.857 32.087 32.316 32.545
31.651 31.880 32.110 32.339 32.568
31.674 31.903 32.133 32.362 32.591
31.697 31.926 32.156 32.385 32.614
31.720 31.949 32.179 32.408 32.636
31.743 31.972 32.202 32.431 32.659
31.766 31.995 32.224 32.453 32.682
31.789 32.018 32.247 32.476 32.705
31.812 32.041 32.270 32.499 32.728
31.834 32.064 32.293 32.522 32.751
31.857 32.087 32.316 32.545 32.774
1400 1410 1420 1430 1440
850 860 870 880 890
18.705 18.941 19.177 19.414 19.650
18.728 18.965 19.201 19.437 19.674
18.752 18.988 19.224 19.461 19.697
18.776 19.012 19.248 19.485 19.721
18.799 19.035 19.272 19.508 19.745
18.823 19.059 19.295 19.532 19.768
18.846 19.083 19.319 19.556 19.792
18.870 19.106 19.343 19.579 19.816
18.894 19.130 19.366 19.603 19.839
18.917 19.154 19.390 19.626 19.863
18.941 19.177 19.414 19.650 19.887
850 860 870 880 890
1450 1460 1470 1480 1490
32.774 33.002 33.230 33.458 33.685
32.796 33.025 33.253 33.480 33.708
32.819 33.047 33.275 33.503 33.730
32.842 33.070 33.298 33.526 33.753
32.865 33.093 33.321 33.548 33.776
32.888 33.116 33.344 33.571 33.798
32.911 33.139 33.366 33.594 33.821
32.933 33.161 33.389 33.617 33.844
32.956 33.184 33.412 33.639 33.867
32.979 33.207 33.435 33.662 33.889
33.002 33.230 33.458 33.685 33.912
1450 1460 1470 1480 1490
900 910 920 930 940
19.887 20.123 20.360 20.597 20.834
19.910 20.147 20.384 20.621 20.857
19.934 20.171 20.407 20.644 20.881
19.958 20.194 20.431 20.668 20.905
19.981 20.218 20.455 20.692 20.929
20.005 20.242 20.479 20.715 20.952
20.029 20.265 20.502 20.739 20.976
20.052 20.289 20.526 20.763 21.000
20.076 20.313 20.550 20.786 21.023
20.100 20.336 20.573 20.810 21.047
20.123 20.360 20.597 20.834 21.071
900 910 920 930 940
1500 1510 1520 1530 1540
33.912 34.139 34.365 34.591 34.817
33.935 34.161 34.388 34.614 34.840
33.957 34.184 34.410 34.637 34.862
33.980 34.207 34.433 34.659 34.885
34.003 34.229 34.456 34.682 34.908
34.025 34.252 34.478 34.704 34.930
34.048 34.275 34.501 34.727 34.953
34.071 34.297 34.524 34.750 34.975
34.093 34.320 34.546 34.772 34.998
34.116 34.343 34.569 34.795 35.020
34.139 34.365 34.591 34.817 35.043
1500 1510 1520 1530 1540
950 960 970 980 990
21.071 21.308 21.544 21.781 22.018
21.094 21.331 21.568 21.805 22.042
21.118 21.355 21.592 21.829 22.066
21.142 21.379 21.616 21.852 22.089
21.165 21.402 21.639 21.876 22.113
21.189 21.426 21.663 21.900 22.137
21.213 21.450 21.687 21.924 22.160
21.236 21.473 21.710 21.947 22.184
21.260 21.497 21.734 21.971 22.208
21.284 21.521 21.758 21.995 22.232
21.308 21.544 21.781 22.018 22.255
950 960 970 980 990
1550 1560 1570 1580 1590
35.043 35.268 35.493 35.718 35.942
35.065 35.291 35.516 35.740 35.964
35.088 35.313 35.538 35.763 35.987
35.110 35.336 35.560 35.785 36.009
35.133 35.358 35.583 35.807 36.032
35.156 35.381 35.605 35.830 36.054
35.178 35.403 35.628 35.852 36.076
35.201 35.426 35.650 35.875 36.099
35.223 35.448 35.673 35.897 36.121
35.246 35.471 35.695 35.920 36.144
35.268 35.493 35.718 35.942 36.166
1550 1560 1570 1580 1590
1000 1010 1020 1030 1040
22.255 22.492 22.729 22.966 23.203
22.279 22.516 22.753 22.990 23.226
22.303 22.540 22.776 23.013 23.250
22.326 22.563 22.800 23.037 23.274
22.350 22.587 22.824 23.061 23.297
22.374 22.611 22.847 23.084 23.321
22.397 22.634 22.871 23.108 23.345
22.421 22.658 22.895 23.132 23.368
22.445 22.682 22.919 23.155 23.392
22.468 22.705 22.942 23.179 23.416
22.492 22.729 22.966 23.203 23.439
1000 1010 1020 1030 1040
1600 1610 1620 1630 1640
36.166 36.390 36.613 36.836 37.059
36.188 36.412 36.635 36.859 37.081
36.211 36.434 36.658 36.881 37.104
36.233 36.457 36.680 36.903 37.126
36.256 36.479 36.702 36.925 37.148
36.278 36.501 36.725 36.948 37.170
36.300 36.524 36.747 36.970 37.193
36.323 36.546 36.769 36.992 37.215
36.345 36.568 36.792 37.014 37.237
36.367 36.591 36.814 37.037 37.259
36.390 36.613 36.836 37.059 37.281
1600 1610 1620 1630 1640
1050 1060 1070 1080 1090
23.439 23.676 23.913 24.149 24.386
23.463 23.700 23.936 24.173 24.409
23.487 23.723 23.960 24.197 24.433
23.510 23.747 23.984 24.220 24.457
23.534 23.771 24.007 24.244 24.480
23.558 23.794 24.031 24.267 24.504
23.581 23.818 24.055 24.291 24.527
23.605 23.842 24.078 24.315 24.551
23.629 23.865 24.102 24.338 24.575
23.652 23.889 24.126 24.362 24.598
23.676 23.913 24.149 24.386 24.622
1050 1060 1070 1080 1090
1650 1660 1670 1680 1690
37.281 37.504 37.725 37.947 38.168
37.304 37.526 37.748 37.969 38.190
37.326 37.548 37.770 37.991 38.212
37.348 37.570 37.792 38.013 38.235
37.370 37.592 37.814 38.036 38.257
37.393 37.615 37.836 38.058 38.279
37.415 37.637 37.858 38.080 38.301
37.437 37.659 37.881 38.102 38.323
37.459 37.681 37.903 38.124 38.345
37.481 37.703 37.925 38.146 38.367
37.504 37.725 37.947 38.168 38.389
1650 1660 1670 1680 1690
1100 1110 1120 1130 1140
24.622 24.858 25.094 25.330 25.566
24.646 24.882 25.118 25.354 25.590
24.669 24.905 25.142 25.377 25.613
24.693 24.929 25.165 25.401 25.637
24.717 24.953 25.189 25.425 25.660
24.740 24.976 25.212 25.448 25.684
24.764 25.000 25.236 25.472 25.708
24.787 25.024 25.260 25.495 25.731
24.811 25.047 25.283 25.519 25.755
24.835 25.071 25.307 25.543 25.778
24.858 25.094 25.330 25.566 25.802
1100 1110 1120 1130 1140
1700 1710 1720 1730 1740
38.389 38.610 38.830 39.050 39.270
38.411 38.632 38.852 39.072 39.292
38.433 38.654 38.874 39.094 39.314
38.455 38.676 38.896 39.116 39.335
38.477 38.698 38.918 39.138 39.357
38.499 38.720 38.940 39.160 39.379
38.522 38.742 38.962 39.182 39.401
38.544 38.764 38.984 39.204 39.423
38.566 38.786 39.006 39.226 39.445
38.588 38.808 39.028 39.248 39.467
38.610 38.830 39.050 39.270 39.489
1700 1710 1720 1730 1740
1150 1160 1170 1180 1190
25.802 26.037 26.273 26.508 26.743
25.825 26.061 26.296 26.532 26.767
25.849 26.084 26.320 26.555 26.790
25.873 26.108 26.343 26.579 26.814
25.896 26.132 26.367 26.602 26.837
25.920 26.155 26.390 26.626 26.861
25.943 26.179 26.414 26.649 26.884
25.967 26.202 26.437 26.673 26.907
25.990 26.226 26.461 26.696 26.931
26.014 26.249 26.484 26.720 26.954
26.037 26.273 26.508 26.743 26.978
1150 1160 1170 1180 1190
1750 1760 1770 1780 1790
39.489 39.708 39.927 40.145 40.363
39.511 39.730 39.949 40.167 40.385
39.533 39.752 39.970 40.189 40.407
39.555 39.774 39.992 40.211 40.429
39.577 39.796 40.014 40.232 40.450
39.599 39.817 40.036 40.254 40.472
39.620 39.839 40.058 40.276 40.494
39.642 39.861 40.080 40.298 40.516
39.664 39.883 40.101 40.320 40.537
39.686 39.905 40.123 40.341 40.559
39.708 39.927 40.145 40.363 40.581
1750 1760 1770 1780 1790
1200 1210 1220 1230 1240
26.978 27.213 27.447 27.681 27.915
27.001 27.236 27.471 27.705 27.939
27.025 27.259 27.494 27.728 27.962
27.048 27.283 27.517 27.752 27.986
27.072 27.306 27.541 27.775 28.009
27.095 27.330 27.564 27.798 28.032
27.119 27.353 27.588 27.822 28.056
27.142 27.377 27.611 27.845 28.079
27.166 27.400 27.635 27.869 28.103
27.189 27.424 27.658 27.892 28.126
27.213 27.447 27.681 27.915 28.149
1200 1210 1220 1230 1240
1800 1810 1820 1830 1840
40.581 40.798 41.015 41.232 41.449
40.603 40.820 41.037 41.254 41.470
40.624 40.842 41.059 41.276 41.492
40.646 40.864 41.081 41.297 41.514
40.668 40.885 41.102 41.319 41.535
40.690 40.907 41.124 41.341 41.557
40.711 40.929 41.146 41.362 41.578
40.733 40.950 41.167 41.384 41.600
40.755 40.972 41.189 41.405 41.622
40.777 40.994 41.211 41.427 41.643
40.798 41.015 41.232 41.449 41.665
1800 1810 1820 1830 1840
1250 1260 1270 1280 1290
28.149 28.383 28.616 28.849 29.082
28.173 28.406 28.640 28.873 29.106
28.196 28.430 28.663 28.896 29.129
28.219 28.453 28.686 28.919 29.152
28.243 28.476 28.710 28.943 29.176
28.266 28.500 28.733 28.966 29.199
28.289 28.523 28.756 28.989 29.222
28.313 28.546 28.780 29.013 29.245
28.336 28.570 28.803 29.036 29.269
28.360 28.593 28.826 29.059 29.292
28.383 28.616 28.849 29.082 29.315
1250 1260 1270 1280 1290
1850 1860 1870 1880 1890
41.665 41.881 42.096 42.311 42.526
41.686 41.902 42.118 42.333 42.548
41.708 41.924 42.139 42.354 42.569
41.730 41.945 42.161 42.376 42.591
41.751 41.967 42.182 42.397 42.612
41.773 41.988 42.204 42.419 42.633
41.794 42.010 42.225 42.440 42.655
41.816 42.032 42.247 42.462 42.676
41.838 42.053 42.268 42.483 42.698
41.859 42.075 42.290 42.505 42.719
41.881 42.096 42.311 42.526 42.741
1850 1860 1870 1880 1890
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
Z-219
°F
°F
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 2282°F – 200 to 1250°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Clean Oxidizing and Inert; Limited Use in Vacuum or Reducing; Wide Temperature Range; Most Popular Calibration TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
+ –
Thermocouple Grade
Nickel-Chromium vs. Nickel-Aluminum
Revised Thermocouple Reference Tables
K
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
1900 1910 1920 1930 1940
42.741 42.955 43.169 43.382 43.595
42.762 42.976 43.190 43.403 43.616
42.783 42.998 43.211 43.425 43.638
42.805 43.019 43.233 43.446 43.659
42.826 43.040 43.254 43.467 43.680
42.848 43.062 43.275 43.489 43.701
42.869 43.083 43.297 43.510 43.723
42.891 43.104 43.318 43.531 43.744
42.912 43.126 43.339 43.552 43.765
42.933 43.147 43.361 43.574 43.787
42.955 43.169 43.382 43.595 43.808
1900 1910 1920 1930 1940
2250 2260 2270 2280 2290
50.006 50.206 50.405 50.604 50.802
50.026 50.226 50.425 50.624 50.822
50.046 50.246 50.445 50.644 50.842
50.066 50.266 50.465 50.664 50.862
50.086 50.286 50.485 50.684 50.882
50.106 50.306 50.505 50.703 50.901
50.126 50.326 50.525 50.723 50.921
50.146 50.346 50.545 50.743 50.941
50.166 50.366 50.564 50.763 50.961
50.186 50.385 50.584 50.783 50.981
50.206 50.405 50.604 50.802 51.000
2250 2260 2270 2280 2290
1950 1960 1970 1980 1990
43.808 44.020 44.232 44.444 44.655
43.829 44.041 44.253 44.465 44.676
43.850 44.063 44.275 44.486 44.697
43.872 44.084 44.296 44.507 44.719
43.893 44.105 44.317 44.528 44.740
43.914 44.126 44.338 44.550 44.761
43.935 44.147 44.359 44.571 44.782
43.957 44.169 44.380 44.592 44.803
43.978 44.190 44.402 44.613 44.824
43.999 44.211 44.423 44.634 44.845
44.020 44.232 44.444 44.655 44.866
1950 1960 1970 1980 1990
2300 2310 2320 2330 2340
51.000 51.198 51.395 51.591 51.787
51.020 51.217 51.414 51.611 51.806
51.040 51.237 51.434 51.630 51.826
51.060 51.257 51.453 51.650 51.845
51.079 51.276 51.473 51.669 51.865
51.099 51.296 51.493 51.689 51.885
51.119 51.316 51.512 51.708 51.904
51.139 51.336 51.532 51.728 51.924
51.158 51.355 51.552 51.748 51.943
51.178 51.375 51.571 51.767 51.963
51.198 51.395 51.591 51.787 51.982
2300 2310 2320 2330 2340
2000 2010 2020 2030 2040
44.866 45.077 45.287 45.497 45.706
44.887 45.098 45.308 45.518 45.727
44.908 45.119 45.329 45.539 45.748
44.929 45.140 45.350 45.560 45.769
44.950 45.161 45.371 45.580 45.790
44.971 45.182 45.392 45.601 45.811
44.992 45.203 45.413 45.622 45.832
45.014 45.224 45.434 45.643 45.852
45.035 45.245 45.455 45.664 45.873
45.056 45.266 45.476 45.685 45.894
45.077 45.287 45.497 45.706 45.915
2000 2010 2020 2030 2040
2350 51.982 2360 52.177 2370 52.371 2380 52.565 239052.759
52.002 52.197 52.391 52.585 52.778
52.021 52.216 52.410 52.604 52.797
52.041 52.235 52.430 52.623 52.817
52.060 52.255 52.449 52.643 52.836
52.080 52.274 52.468 52.662 52.855
52.099 52.294 52.488 52.681 52.875
52.119 52.313 52.507 52.701 52.894
52.138 52.333 52.527 52.720 52.913
52.158 52.352 52.546 52.739 52.932
52.177 52.371 52.565 52.759 52.952
2350 2360 2370 2380 2390
2050 2060 2070 2080 2090
45.915 46.124 46.332 46.540 46.747
45.936 46.145 46.353 46.560 46.768
45.957 46.165 46.373 46.581 46.789
45.978 46.186 46.394 46.602 46.809
45.999 46.207 46.415 46.623 46.830
46.019 46.228 46.436 46.643 46.851
46.040 46.249 46.457 46.664 46.871
46.061 46.269 46.477 46.685 46.892
46.082 46.290 46.498 46.706 46.913
46.103 46.311 46.519 46.726 46.933
46.124 46.332 46.540 46.747 46.954
2050 2060 2070 2080 2090
2400 2410 2420 2430 2440
52.952 53.144 53.336 53.528 53.719
52.971 53.163 53.355 53.547 53.738
52.990 53.183 53.375 53.566 53.757
53.010 53.202 53.394 53.585 53.776
53.029 53.221 53.413 53.604 53.795
53.048 53.240 53.432 53.623 53.814
53.067 53.260 53.451 53.643 53.833
53.087 53.279 53.470 53.662 53.852
53.106 53.298 53.490 53.681 53.871
53.125 53.317 53.509 53.700 53.890
53.144 53.336 53.528 53.719 53.910
2400 2410 2420 2430 2440
2100 2110 2120 2130 2140
46.954 47.161 47.367 47.573 47.778
46.975 47.181 47.387 47.593 47.798
46.995 47.202 47.408 47.614 47.819
47.016 47.223 47.429 47.634 47.839
47.037 47.243 47.449 47.655 47.860
47.057 47.264 47.470 47.675 47.880
47.078 47.284 47.490 47.696 47.901
47.099 47.305 47.511 47.716 47.921
47.119 47.326 47.531 47.737 47.942
47.140 47.346 47.552 47.757 47.962
47.161 47.367 47.573 47.778 47.983
2100 2110 2120 2130 2140
2450 2460 2470 2480 2490
53.910 54.100 54.289 54.479 54.668
53.929 54.119 54.308 54.498 54.687
53.948 54.138 54.327 54.517 54.705
53.967 54.157 54.346 54.536 54.724
53.986 54.176 54.365 54.554 54.743
54.005 54.195 54.384 54.573 54.762
54.024 54.214 54.403 54.592 54.781
54.043 54.233 54.422 54.611 54.800
54.062 54.252 54.441 54.630 54.819
54.081 54.271 54.460 54.649 54.837
54.100 54.289 54.479 54.668 54.856
2450 2460 2470 2480 2490
2150 2160 2170 2180 2190
47.983 48.187 48.391 48.595 48.798
48.003 48.208 48.411 48.615 48.818
48.024 48.228 48.432 48.635 48.838
48.044 48.248 48.452 48.656 48.859
48.065 48.269 48.473 48.676 48.879
48.085 48.289 48.493 48.696 48.899
48.105 48.310 48.513 48.717 48.919
48.126 48.330 48.534 48.737 48.940
48.146 48.350 48.554 48.757 48.960
48.167 48.371 48.574 48.777 48.980
48.187 48.391 48.595 48.798 49.000
2150 2160 2170 2180 2190
2500 54.856 54.875 54.894
2200 2210 2220 2230 2240
49.000 49.202 49.404 49.605 49.806
49.021 49.223 49.424 49.625 49.826
49.041 49.243 49.444 49.645 49.846
49.061 49.263 49.465 49.666 49.866
49.081 49.283 49.485 49.686 49.886
49.101 49.303 49.505 49.706 49.906
49.122 49.323 49.525 49.726 49.926
49.142 49.344 49.545 49.746 49.946
49.162 49.364 49.565 49.766 49.966
49.182 49.384 49.585 49.786 49.986
49.202 49.404 49.605 49.806 50.006
2200 2210 2220 2230 2240
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
Z-220
0
1
2
°F
2500
3
4
5
6
7
8
9
10
°F
Z
+ –
Revised Thermocouple Reference Tables
E
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°F
-10
-9
-8
-7
-6
-5
-450
-4
Thermocouple Grade
Nickel-Chromium vs. Copper-Nickel + – Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 1652°F – 200 to 900°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 1.7°C or 0.5% Above 0°C 1.7°C or 1.0°C Below 0°C Special: 1.0°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Limited Use in Vacuum or Reducing; Highest EMF Change per Degree TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts -3
-2
-1
0
°F
°F
0
6
7
8
10
°F
-9.835 -9.834 -9.833 -9.832 -9.830 -450
100 110 120 130 140
2.281 2.628 2.977 3.330 3.685
2.316 2.663 3.012 3.365 3.720
1
2.351 2.698 3.048 3.400 3.756
2
2.385 2.733 3.083 3.436 3.792
3
2.420 2.767 3.118 3.471 3.827
4
2.454 2.802 3.153 3.507 3.863
5
2.489 2.837 3.188 3.542 3.899
2.524 2.872 3.224 3.578 3.935
2.558 2.907 3.259 3.613 3.970
2.593 2.942 3.294 3.649 4.006
9
2.628 2.977 3.330 3.685 4.042
100 110 120 130 140
-440 -430 -420 -410 -400
-9.830 -9.809 -9.775 -9.729 -9.672
-9.829 -9.806 -9.771 -9.724 -9.666
-9.827 -9.803 -9.766 -9.718 -9.659
-9.825 -9.800 -9.762 -9.713 -9.653
-9.823 -9.797 -9.758 -9.707 -9.646
-9.821 -9.793 -9.753 -9.702 -9.639
-9.819 -9.790 -9.749 -9.696 -9.632
-9.817 -9.786 -9.744 -9.690 -9.625
-9.814 -9.782 -9.739 -9.684 -9.618
-9.812 -9.779 -9.734 -9.678 -9.611
-9.809 -9.775 -9.729 -9.672 -9.604
-440 -430 -420 -410 -400
150 160 170 180 190
4.042 4.403 4.766 5.131 5.500
4.078 4.439 4.802 5.168 5.537
4.114 4.475 4.839 5.205 5.574
4.150 4.511 4.875 5.242 5.611
4.186 4.547 4.912 5.278 5.648
4.222 4.584 4.948 5.315 5.685
4.258 4.620 4.985 5.352 5.722
4.294 4.656 5.021 5.389 5.759
4.330 4.693 5.058 5.426 5.796
4.366 4.729 5.095 5.463 5.833
4.403 4.766 5.131 5.500 5.871
150 160 170 180 190
-390 -380 -370 -360 -350
-9.604 -9.525 -9.436 -9.338 -9.229
-9.597 -9.517 -9.427 -9.327 -9.218
-9.589 -9.508 -9.417 -9.317 -9.207
-9.581 -9.500 -9.408 -9.306 -9.195
-9.574 -9.491 -9.398 -9.295 -9.184
-9.566 -9.482 -9.388 -9.285 -9.172
-9.558 -9.473 -9.378 -9.274 -9.160
-9.550 -9.464 -9.368 -9.263 -9.148
-9.542 -9.455 -9.358 -9.252 -9.136
-9.534 -9.446 -9.348 -9.241 -9.124
-9.525 -9.436 -9.338 -9.229 -9.112
-390 -380 -370 -360 -350
200 210 220 230 240
5.871 6.244 6.620 6.998 7.379
5.908 6.281 6.658 7.036 7.417
5.945 6.319 6.695 7.074 7.455
5.982 6.356 6.733 7.112 7.493
6.020 6.394 6.771 7.150 7.532
6.057 6.432 6.809 7.188 7.570
6.094 6.469 6.847 7.226 7.608
6.132 6.507 6.884 7.264 7.647
6.169 6.544 6.922 7.302 7.685
6.207 6.582 6.960 7.341 7.723
6.244 6.620 6.998 7.379 7.762
200 210 220 230 240
-340 -330 -320 -310 -300
-9.112 -8.986 -8.852 -8.710 -8.561
-9.100 -8.973 -8.839 -8.696 -8.546
-9.088 -8.960 -8.825 -8.681 -8.530
-9.075 -8.947 -8.811 -8.666 -8.515
-9.063 -8.934 -8.797 -8.652 -8.499
-9.050 -8.920 -8.782 -8.637 -8.483
-9.038 -8.907 -8.768 -8.622 -8.468
-9.025 -8.893 -8.754 -8.607 -8.452
-9.012 -8.880 -8.739 -8.591 -8.436
-8.999 -8.866 -8.725 -8.576 -8.420
-8.986 -8.852 -8.710 -8.561 -8.404
-340 -330 -320 -310 -300
250 260 270 280 290
7.762 8.147 8.535 8.924 9.316
7.800 8.186 8.573 8.963 9.355
7.839 8.224 8.612 9.002 9.395
7.877 8.263 8.651 9.041 9.434
7.916 8.302 8.690 9.081 9.473
7.954 8.340 8.729 9.120 9.513
7.993 8.379 8.768 9.159 9.552
8.031 8.418 8.807 9.198 9.591
8.070 8.457 8.846 9.237 9.631
8.108 8.496 8.885 9.277 9.670
8.147 8.535 8.924 9.316 9.710
250 260 270 280 290
-290 -280 -270 -260 -250
-8.404 -8.240 -8.069 -7.891 -7.707
-8.388 -8.223 -8.052 -7.873 -7.688
-8.372 -8.206 -8.034 -7.855 -7.670
-8.356 -8.189 -8.017 -7.837 -7.651
-8.339 -8.173 -7.999 -7.819 -7.632
-8.323 -8.155 -7.981 -7.800 -7.613
-8.307 -8.138 -7.963 -7.782 -7.593
-8.290 -8.121 -7.945 -7.763 -7.574
-8.273 -8.104 -7.928 -7.745 -7.555
-8.257 -8.087 -7.910 -7.726 -7.536
-8.240 -8.069 -7.891 -7.707 -7.516
-290 -280 -270 -260 -250
300 310 320 330 340
9.710 10.106 10.503 10.903 11.305
9.749 10.145 10.543 10.943 11.345
9.789 10.185 10.583 10.983 11.385
9.828 10.225 10.623 11.024 11.426
9.868 10.265 10.663 11.064 11.466
9.907 10.304 10.703 11.104 11.506
9.947 10.344 10.743 11.144 11.547
9.987 10.384 10.783 11.184 11.587
10.026 10.424 10.823 11.224 11.627
10.066 10.464 10.863 11.265 11.668
10.106 10.503 10.903 11.305 11.708
300 310 320 330 340
-240 -230 -220 -210 -200
-7.516 -7.319 -7.116 -6.907 -6.692
-7.497 -7.299 -7.096 -6.886 -6.671
-7.478 -7.279 -7.075 -6.865 -6.649
-7.458 -7.259 -7.054 -6.843 -6.627
-7.438 -7.239 -7.033 -6.822 -6.605
-7.419 -7.219 -7.013 -6.801 -6.583
-7.399 -7.198 -6.992 -6.779 -6.561
-7.379 -7.178 -6.971 -6.757 -6.539
-7.359 -7.157 -6.950 -6.736 -6.516
-7.339 -7.137 -6.928 -6.714 -6.494
-7.319 -7.116 -6.907 -6.692 -6.472
-240 -230 -220 -210 -200
350 360 370 380 390
11.708 12.113 12.520 12.929 13.339
11.749 12.154 12.561 12.970 13.380
11.789 12.195 12.602 13.011 13.421
11.830 12.235 12.643 13.052 13.462
11.870 12.276 12.684 13.093 13.504
11.911 12.317 12.724 13.134 13.545
11.951 12.357 12.765 13.175 13.586
11.992 12.398 12.806 13.216 13.627
12.032 12.439 12.847 13.257 13.668
12.073 12.480 12.888 13.298 13.710
12.113 12.520 12.929 13.339 13.751
350 360 370 380 390
-190 -180 -170 -160 -150
-6.472 -6.246 -6.014 -5.777 -5.535
-6.449 -6.223 -5.991 -5.753 -5.510
-6.427 -6.200 -5.967 -5.729 -5.486
-6.405 -6.177 -5.943 -5.705 -5.461
-6.382 -6.154 -5.920 -5.681 -5.436
-6.359 -6.130 -5.896 -5.656 -5.412
-6.337 -6.107 -5.872 -5.632 -5.387
-6.314 -6.084 -5.849 -5.608 -5.362
-6.291 -6.061 -5.825 -5.584 -5.337
-6.269 -6.037 -5.801 -5.559 -5.312
-6.246 -6.014 -5.777 -5.535 -5.287
-190 -180 -170 -160 -150
400 410 420 430 440
13.751 14.164 14.579 14.995 15.413
13.792 14.205 14.620 15.037 15.454
13.833 14.247 14.662 15.078 15.496
13.875 14.288 14.704 15.120 15.538
13.916 14.330 14.745 15.162 15.580
13.957 14.371 14.787 15.204 15.622
13.999 14.413 14.828 15.245 15.664
14.040 14.454 14.870 15.287 15.706
14.081 14.496 14.912 15.329 15.748
14.123 14.537 14.953 15.371 15.790
14.164 14.579 14.995 15.413 15.831
400 410 420 430 440
-140 -130 -120 -110 -100
-5.287 -5.035 -4.777 -4.515 -4.248
-5.262 -5.009 -4.751 -4.489 -4.221
-5.237 -4.984 -4.725 -4.462 -4.194
-5.212 -4.958 -4.699 -4.436 -4.167
-5.187 -4.932 -4.673 -4.409 -4.140
-5.162 -4.907 -4.647 -4.382 -4.113
-5.136 -4.881 -4.621 -4.355 -4.086
-5.111 -4.855 -4.594 -4.329 -4.058
-5.086 -4.829 -4.568 -4.302 -4.031
-5.060 -4.803 -4.542 -4.275 -4.004
-5.035 -4.777 -4.515 -4.248 -3.976
-140 -130 -120 -110 -100
450 460 470 480 490
15.831 16.252 16.673 17.096 17.520
15.873 16.294 16.715 17.138 17.562
15.915 16.336 16.758 17.181 17.605
15.957 16.378 16.800 17.223 17.647
15.999 16.420 16.842 17.265 17.690
16.041 16.462 16.884 17.308 17.732
16.083 16.504 16.927 17.350 17.775
16.125 16.547 16.969 17.392 17.817
16.168 16.589 17.011 17.435 17.860
16.210 16.631 17.054 17.477 17.902
16.252 16.673 17.096 17.520 17.945
450 460 470 480 490
-90 -80 -70 -60 -50
-3.976 -3.700 -3.420 -3.135 -2.846
-3.949 -3.672 -3.391 -3.106 -2.816
-3.922 -3.645 -3.363 -3.077 -2.787
-3.894 -3.617 -3.335 -3.048 -2.758
-3.867 -3.589 -3.306 -3.020 -2.729
-3.839 -3.561 -3.278 -2.991 -2.699
-3.811 -3.532 -3.249 -2.962 -2.670
-3.784 -3.504 -3.221 -2.933 -2.641
-3.756 -3.476 -3.192 -2.904 -2.611
-3.728 -3.448 -3.163 -2.875 -2.582
-3.700 -3.420 -3.135 -2.846 -2.552
-90 -80 -70 -60 -50
500 510 520 530 540
17.945 18.371 18.798 19.227 19.656
17.987 18.414 18.841 19.269 19.699
18.030 18.456 18.884 19.312 19.742
18.073 18.499 18.927 19.355 19.785
18.115 18.542 18.969 19.398 19.828
18.158 18.585 19.012 19.441 19.871
18.200 18.627 19.055 19.484 19.914
18.243 18.670 19.098 19.527 19.957
18.286 18.713 19.141 19.570 20.000
18.328 18.756 19.184 19.613 20.043
18.371 18.798 19.227 19.656 20.086
500 510 520 530 540
-40 -30 -20 -10 0
-2.552 -2.255 -1.953 -1.648 -1.339
-2.523 -2.225 -1.923 -1.617 -1.308
-2.493 -2.195 -1.893 -1.587 -1.277
-2.463 -2.165 -1.862 -1.556 -1.245
-2.434 -2.135 -1.832 -1.525 -1.214
-2.404 -2.105 -1.801 -1.494 -1.183
-2.374 -2.074 -1.771 -1.463 -1.152
-2.344 -2.044 -1.740 -1.432 -1.120
-2.315 -2.014 -1.709 -1.401 -1.089
-2.285 -1.984 -1.679 -1.370 -1.057
-2.255 -1.953 -1.648 -1.339 -1.026
-40 -30 -20 -10 0
550 560 570 580 590
20.086 20.517 20.950 21.383 21.817
20.129 20.561 20.993 21.426 21.860
20.172 20.604 21.036 21.470 21.904
20.216 20.647 21.080 21.513 21.947
20.259 20.690 21.123 21.556 21.991
20.302 20.733 21.166 21.600 22.034
20.345 20.777 21.209 21.643 22.078
20.388 20.820 21.253 21.686 22.121
20.431 20.863 21.296 21.730 22.165
20.474 20.906 21.339 21.773 22.208
20.517 20.950 21.383 21.817 22.252
550 560 570 580 590
0 10 20 30 40
-1.026 -0.709 -0.389 -0.065 0.262
-0.994 -0.963 -0.931 -0.900 -0.868 -0.836 -0.805 -0.773 -0.741 -0.709 -0.677 -0.645 -0.614 -0.582 -0.550 -0.517 -0.485 -0.453 -0.421 -0.389 -0.357 -0.324 -0.292 -0.260 -0.227 -0.195 -0.163 -0.130 -0.098 -0.065 -0.033 0.000 0.033 0.065 0.098 0.131 0.163 0.196 0.229 0.262 0.294 0.327 0.360 0.393 0.426 0.459 0.492 0.525 0.558 0.591
0 10 20 30 40
600 610 620 630 640
22.252 22.687 23.124 23.561 23.999
22.295 22.731 23.167 23.604 24.042
22.339 22.774 23.211 23.648 24.086
22.382 22.818 23.255 23.692 24.130
22.426 22.862 23.298 23.736 24.174
22.469 22.905 23.342 23.780 24.218
22.513 22.949 23.386 23.823 24.262
22.556 22.993 23.429 23.867 24.305
22.600 23.036 23.473 23.911 24.349
22.644 23.080 23.517 23.955 24.393
22.687 23.124 23.561 23.999 24.437
600 610 620 630 640
50 60 70 80 90
0.591 0.924 1.259 1.597 1.938
0.924 1.259 1.597 1.938 2.281
50 60 70 80 90
650 660 670 680 690
24.437 24.876 25.316 25.757 26.198
24.481 24.920 25.360 25.801 26.242
24.525 24.964 25.404 25.845 26.286
24.569 25.008 25.448 25.889 26.331
24.613 25.052 25.493 25.933 26.375
24.657 25.096 25.537 25.977 26.419
24.701 25.140 25.581 26.022 26.463
24.745 25.184 25.625 26.066 26.507
24.789 25.228 25.669 26.110 26.552
24.832 25.272 25.713 26.154 26.596
24.876 25.316 25.757 26.198 26.640
650 660 670 680 690
°F
0
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
°F
0.624 0.957 1.292 1.631 1.972
1
0.657 0.990 1.326 1.665 2.006
2
0.691 1.024 1.360 1.699 2.041
3
0.724 1.057 1.394 1.733 2.075
4
0.757 1.091 1.427 1.767 2.109
5
0.790 1.124 1.461 1.801 2.144
0.824 1.158 1.495 1.835 2.178
0.857 1.192 1.529 1.869 2.212
6
7
8
0.890 1.225 1.563 1.904 2.247
9
Z-221
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 1652°F – 200 to 900°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 1.7°C or 0.5% Above 0°C 1.7°C or 1.0°C Below 0°C Special: 1.0°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Limited Use in Vacuum or Reducing; Highest EMF Change per Degree TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
+ –
Thermocouple Grade
Nickel-Chromium vs. Copper-Nickel
Revised Thermocouple Reference Tables
E
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
700 710 720 730 740
26.640 27.082 27.525 27.969 28.413
26.684 27.127 27.570 28.013 28.457
26.728 27.171 27.614 28.057 28.501
26.773 27.215 27.658 28.102 28.546
26.817 27.259 27.703 28.146 28.590
26.861 27.304 27.747 28.191 28.635
26.905 27.348 27.791 28.235 28.679
26.950 27.392 27.836 28.279 28.724
26.994 27.437 27.880 28.324 28.768
27.038 27.481 27.924 28.368 28.813
27.082 27.525 27.969 28.413 28.857
700 710 720 730 740
1300 1310 1320 1330 1340
53.466 53.908 54.350 54.791 55.232
53.510 53.952 54.394 54.835 55.276
53.555 53.997 54.438 54.879 55.320
53.599 54.041 54.482 54.924 55.364
53.643 54.085 54.527 54.968 55.408
53.687 54.129 54.571 55.012 55.453
53.732 54.173 54.615 55.056 55.497
53.776 54.218 54.659 55.100 55.541
53.820 54.262 54.703 55.144 55.585
53.864 54.306 54.747 55.188 55.629
53.908 54.350 54.791 55.232 55.673
1300 1310 1320 1330 1340
750 760 770 780 790
28.857 29.302 29.747 30.193 30.639
28.901 29.346 29.792 30.238 30.684
28.946 29.391 29.836 30.282 30.728
28.990 29.435 29.881 30.327 30.773
29.035 29.480 29.925 30.371 30.818
29.079 29.525 29.970 30.416 30.862
29.124 29.569 30.015 30.461 30.907
29.168 29.614 30.059 30.505 30.952
29.213 29.658 30.104 30.550 30.996
29.257 29.703 30.148 30.595 31.041
29.302 29.747 30.193 30.639 31.086
750 760 770 780 790
1350 1360 1370 1380 1390
55.673 56.113 56.553 56.992 57.431
55.717 56.157 56.597 57.036 57.475
55.761 56.201 56.641 57.080 57.519
55.805 56.245 56.685 57.124 57.563
55.849 56.289 56.729 57.168 57.607
55.893 56.333 56.773 57.212 57.651
55.937 56.377 56.816 57.256 57.695
55.981 56.421 56.860 57.300 57.738
56.025 56.465 56.904 57.344 57.782
56.069 56.509 56.948 57.387 57.826
56.113 56.553 56.992 57.431 57.870
1350 1360 1370 1380 1390
800 810 820 830 840
31.086 31.533 31.980 32.427 32.875
31.130 31.577 32.025 32.472 32.920
31.175 31.622 32.069 32.517 32.965
31.220 31.667 32.114 32.562 33.010
31.264 31.711 32.159 32.606 33.054
31.309 31.756 32.204 32.651 33.099
31.354 31.801 32.248 32.696 33.144
31.398 31.846 32.293 32.741 33.189
31.443 31.890 32.338 32.786 33.234
31.488 31.935 32.383 32.830 33.278
31.533 31.980 32.427 32.875 33.323
800 810 820 830 840
1400 1410 1420 1430 1440
57.870 58.308 58.746 59.184 59.621
57.914 58.352 58.790 59.228 59.665
57.958 58.396 58.834 59.271 59.708
58.002 58.440 58.878 59.315 59.752
58.045 58.484 58.921 59.359 59.796
58.089 58.527 58.965 59.402 59.839
58.133 58.571 59.009 59.446 59.883
58.177 58.615 59.053 59.490 59.927
58.221 58.659 59.096 59.534 59.970
58.265 58.702 59.140 59.577 60.014
58.308 58.746 59.184 59.621 60.058
1400 1410 1420 1430 1440
850 860 870 880 890
33.323 33.772 34.220 34.669 35.118
33.368 33.816 34.265 34.714 35.163
33.413 33.861 34.310 34.759 35.208
33.458 33.906 34.355 34.804 35.253
33.503 33.951 34.400 34.849 35.298
33.547 33.996 34.445 34.893 35.343
33.592 34.041 34.489 34.938 35.387
33.637 34.086 34.534 34.983 35.432
33.682 34.130 34.579 35.028 35.477
33.727 34.175 34.624 35.073 35.522
33.772 34.220 34.669 35.118 35.567
850 860 870 880 890
1450 1460 1470 1480 1490
60.058 60.494 60.930 61.366 61.801
60.101 60.538 60.974 61.409 61.845
60.145 60.581 61.017 61.453 61.888
60.189 60.625 61.061 61.496 61.932
60.232 60.669 61.105 61.540 61.975
60.276 60.712 61.148 61.583 62.018
60.320 60.756 61.192 61.627 62.062
60.363 60.799 61.235 61.671 62.105
60.407 60.843 61.279 61.714 62.149
60.451 60.887 61.322 61.758 62.192
60.494 60.930 61.366 61.801 62.236
1450 1460 1470 1480 1490
900 910 920 930 940
35.567 36.016 36.466 36.915 37.365
35.612 36.061 36.511 36.960 37.410
35.657 36.106 36.556 37.005 37.455
35.702 36.151 36.601 37.050 37.500
35.747 36.196 36.646 37.095 37.545
35.792 36.241 36.691 37.140 37.590
35.837 36.286 36.736 37.185 37.635
35.882 36.331 36.781 37.230 37.680
35.927 36.376 36.826 37.275 37.725
35.972 36.421 36.870 37.320 37.770
36.016 36.466 36.915 37.365 37.815
900 910 920 930 940
1500 1510 1520 1530 1540
62.236 62.670 63.104 63.538 63.971
62.279 62.714 63.148 63.581 64.014
62.323 62.757 63.191 63.624 64.057
62.366 62.800 63.234 63.668 64.101
62.410 62.844 63.278 63.711 64.144
62.453 62.887 63.321 63.754 64.187
62.496 62.931 63.364 63.798 64.230
62.540 62.974 63.408 63.841 64.274
62.583 63.017 63.451 63.884 64.317
62.627 63.061 63.494 63.927 64.360
62.670 63.104 63.538 63.971 64.403
1500 1510 1520 1530 1540
950 960 970 980 990
37.815 38.265 38.714 39.164 39.614
37.860 38.309 38.759 39.209 39.659
37.905 38.354 38.804 39.254 39.704
37.950 38.399 38.849 39.299 39.749
37.995 38.444 38.894 39.344 39.794
38.040 38.489 38.939 39.389 39.839
38.085 38.534 38.984 39.434 39.884
38.130 38.579 39.029 39.479 39.929
38.175 38.624 39.074 39.524 39.974
38.220 38.669 39.119 39.569 40.019
38.265 38.714 39.164 39.614 40.064
950 960 970 980 990
1550 1560 1570 1580 1590
64.403 64.835 65.267 65.698 66.129
64.447 64.879 65.310 65.741 66.172
64.490 64.922 65.353 65.784 66.215
64.533 64.965 65.396 65.827 66.258
64.576 65.008 65.440 65.871 66.301
64.619 65.051 65.483 65.914 66.344
64.663 65.094 65.526 65.957 66.387
64.706 65.138 65.569 66.000 66.430
64.749 65.181 65.612 66.043 66.473
64.792 65.224 65.655 66.086 66.516
64.835 65.267 65.698 66.129 66.559
1550 1560 1570 1580 1590
1000 1010 1020 1030 1040
40.064 40.513 40.963 41.412 41.862
40.109 40.558 41.008 41.457 41.907
40.154 40.603 41.053 41.502 41.952
40.199 40.648 41.098 41.547 41.997
40.243 40.693 41.143 41.592 42.042
40.288 40.738 41.188 41.637 42.087
40.333 40.783 41.233 41.682 42.132
40.378 40.828 41.278 41.727 42.176
40.423 40.873 41.323 41.772 42.221
40.468 40.918 41.368 41.817 42.266
40.513 40.963 41.412 41.862 42.311
1000 1010 1020 1030 1040
1600 1610 1620 1630 1640
66.559 66.989 67.418 67.846 68.274
66.602 67.031 67.460 67.889 68.317
66.645 67.074 67.503 67.932 68.359
66.688 67.117 67.546 67.974 68.402
66.731 67.160 67.589 68.017 68.445
66.774 67.203 67.632 68.060 68.488
66.817 67.246 67.675 68.103 68.530
66.860 67.289 67.718 68.146 68.573
66.903 67.332 67.760 68.188 68.616
66.946 67.375 67.803 68.231 68.659
66.989 67.418 67.846 68.274 68.701
1600 1610 1620 1630 1640
1050 1060 1070 1080 1090
42.311 42.760 43.209 43.658 44.107
42.356 42.805 43.254 43.703 44.152
42.401 42.850 43.299 43.748 44.197
42.446 42.895 43.344 43.793 44.242
42.491 42.940 43.389 43.838 44.286
42.536 42.985 43.434 43.883 44.331
42.581 43.030 43.479 43.928 44.376
42.626 43.075 43.524 43.972 44.421
42.671 43.120 43.569 44.017 44.466
42.715 43.165 43.613 44.062 44.511
42.760 43.209 43.658 44.107 44.555
1050 1060 1070 1080 1090
1650 1660 1670 1680 1690
68.701 69.128 69.554 69.979 70.404
68.744 69.171 69.597 70.022 70.447
68.787 69.213 69.639 70.064 70.489
68.829 69.256 69.682 70.107 70.531
68.872 69.298 69.724 70.149 70.574
68.915 69.341 69.767 70.192 70.616
68.957 69.384 69.809 70.234 70.659
69.000 69.426 69.852 70.277 70.701
69.043 69.469 69.894 70.319 70.744
69.085 69.511 69.937 70.362 70.786
69.128 69.554 69.979 70.404 70.828
1650 1660 1670 1680 1690
1100 1110 1120 1130 1140
44.555 45.004 45.452 45.900 46.347
44.600 45.049 45.497 45.944 46.392
44.645 45.093 45.541 45.989 46.437
44.690 45.138 45.586 46.034 46.481
44.735 45.183 45.631 46.079 46.526
44.780 45.228 45.676 46.123 46.571
44.824 45.273 45.720 46.168 46.616
44.869 45.317 45.765 46.213 46.660
44.914 45.362 45.810 46.258 46.705
44.959 45.407 45.855 46.302 46.750
45.004 45.452 45.900 46.347 46.794
1100 1110 1120 1130 1140
1700 1710 1720 1730 1740
70.828 71.252 71.675 72.097 72.518
70.871 71.294 71.717 72.139 72.561
70.913 71.336 71.759 72.181 72.603
70.955 71.379 71.801 72.223 72.645
70.998 71.421 71.844 72.266 72.687
71.040 71.463 71.886 72.308 72.729
71.082 71.506 71.928 72.350 72.771
71.125 71.548 71.970 72.392 72.813
71.167 71.590 72.012 72.434 72.855
71.209 71.632 72.055 72.476 72.897
71.252 71.675 72.097 72.518 72.939
1700 1710 1720 1730 1740
1150 1160 1170 1180 1190
46.794 47.241 47.688 48.135 48.581
46.839 47.286 47.733 48.179 48.625
46.884 47.331 47.777 48.224 48.670
46.929 47.375 47.822 48.268 48.715
46.973 47.420 47.867 48.313 48.759
47.018 47.465 47.911 48.358 48.804
47.063 47.509 47.956 48.402 48.848
47.107 47.554 48.001 48.447 48.893
47.152 47.599 48.045 48.492 48.937
47.197 47.643 48.090 48.536 48.982
47.241 47.688 48.135 48.581 49.027
1150 1160 1170 1180 1190
1750 1760 1770 1780 1790
72.939 73.360 73.780 74.199 74.618
72.981 73.402 73.821 74.241 74.659
73.023 73.444 73.863 74.283 74.701
73.066 73.486 73.905 74.324 74.743
73.108 73.528 73.947 74.366 74.785
73.150 73.570 73.989 74.408 74.827
73.192 73.612 74.031 74.450 74.869
73.234 73.654 74.073 74.492 74.910
73.276 73.696 74.115 74.534 74.952
73.318 73.738 74.157 74.576 74.994
73.360 73.780 74.199 74.618 75.036
1750 1760 1770 1780 1790
1200 1210 1220 1230 1240
49.027 49.472 49.917 50.362 50.807
49.071 49.517 49.962 50.407 50.851
49.116 49.561 50.006 50.451 50.895
49.160 49.606 50.051 50.495 50.940
49.205 49.650 50.095 50.540 50.984
49.249 49.695 50.140 50.584 51.029
49.294 49.739 50.184 50.629 51.073
49.338 49.784 50.229 50.673 51.118
49.383 49.828 50.273 50.718 51.162
49.428 49.873 50.318 50.762 51.206
49.472 49.917 50.362 50.807 51.251
1200 1210 1220 1230 1240
1800 1810 1820 1830
75.036 75.454 75.872 76.289
75.078 75.496 75.913 76.331
75.120 75.161 75.203 75.245 75.287 75.329 75.370 75.412 75.454 1800 75.538 75.579 75.621 75.663 75.705 75.746 75.788 75.830 75.872 1810 75.955 75.997 76.039 76.081 76.122 76.164 76.206 76.248 76.289 1820 76.373 1830
1250 1260 1270 1280 1290
51.251 51.695 52.138 52.581 53.024
51.295 51.739 52.182 52.625 53.068
51.340 51.783 52.227 52.670 53.112
51.384 51.828 52.271 52.714 53.157
51.428 51.872 52.315 52.758 53.201
51.473 51.916 52.360 52.803 53.245
51.517 51.961 52.404 52.847 53.289
51.561 52.005 52.448 52.891 53.334
51.606 52.049 52.493 52.935 53.378
51.650 52.094 52.537 52.980 53.422
51.695 52.138 52.581 53.024 53.466
1250 1260 1270 1280 1290
°F
0
1
2
3
4
5
6
7
8
9
10
°F
0
1
°F
Z-222
2
3
4
5
6
7
8
9
10
°F
°F
Z
+ –
Revised Thermocouple Reference Tables
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°F
-10
-9
-8
T -7
-6
-5
-4
Thermocouple Grade
Copper vs. Copper-Nickel + – Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 328 to 662°F – 200 to 350°C Extension Grade – 76 to 212°F – 60 to 100°C LIMITS OF ERROR (whichever is greater) Standard: 1.0°C or 0.75% Above 0°C 1.0°C or 1.5% Below 0°C Special: 0.5°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Mild Oxidizing, Reducing Vacuum or Insert; Good Where Moisture Is Present; Low Temperature and Cryogenic Applications TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
-3
-2
-1
0
°F
°F
0
6
7
8
10
°F
2.712 2.958 3.207 3.459 3.712
2.737 2.983 3.232 3.484 3.738
1
2.761 3.008 3.257 3.509 3.763
2
2.786 3.033 3.282 3.534 3.789
3
2.810 3.058 3.307 3.560 3.814
4
2.835 3.082 3.333 3.585 3.840
5
2.860 3.107 3.358 3.610 3.866
2.884 3.132 3.383 3.636 3.891
2.909 3.157 3.408 3.661 3.917
2.934 3.182 3.433 3.687 3.943
9
2.958 3.207 3.459 3.712 3.968
150 160 170 180 190
-6.258 -6.257 -6.256 -6.255 -6.254 -450
150 160 170 180 190
-440 -430 -420 -410 -400
-6.254 -6.240 -6.217 -6.187 -6.150
-6.253 -6.238 -6.215 -6.184 -6.146
-6.252 -6.236 -6.212 -6.180 -6.141
-6.251 -6.234 -6.209 -6.177 -6.137
-6.250 -6.232 -6.206 -6.173 -6.133
-6.248 -6.230 -6.203 -6.170 -6.128
-6.247 -6.227 -6.200 -6.166 -6.124
-6.245 -6.225 -6.197 -6.162 -6.119
-6.243 -6.222 -6.194 -6.158 -6.115
-6.242 -6.220 -6.191 -6.154 -6.110
-6.240 -6.217 -6.187 -6.150 -6.105
-440 -430 -420 -410 -400
200 210 220 230 240
3.968 4.227 4.487 4.750 5.015
3.994 4.253 4.513 4.776 5.042
4.020 4.279 4.540 4.803 5.068
4.046 4.305 4.566 4.829 5.095
4.071 4.331 4.592 4.856 5.122
4.097 4.357 4.618 4.882 5.148
4.123 4.383 4.645 4.909 5.175
4.149 4.409 4.671 4.935 5.202
4.175 4.435 4.697 4.962 5.228
4.201 4.461 4.724 4.988 5.255
4.227 4.487 4.750 5.015 5.282
200 210 220 230 240
-390 -380 -370 -360 -350
-6.105 -6.053 -5.994 -5.930 -5.860
-6.100 -6.047 -5.988 -5.923 -5.853
-6.095 -6.042 -5.982 -5.916 -5.845
-6.090 -6.036 -5.976 -5.909 -5.838
-6.085 -6.030 -5.969 -5.902 -5.830
-6.080 -6.025 -5.963 -5.896 -5.823
-6.075 -6.019 -5.956 -5.888 -5.815
-6.069 -6.013 -5.950 -5.881 -5.808
-6.064 -6.007 -5.943 -5.874 -5.800
-6.059 -6.001 -5.937 -5.867 -5.792
-6.053 -5.994 -5.930 -5.860 -5.785
-390 -380 -370 -360 -350
250 260 270 280 290
5.282 5.551 5.823 6.096 6.371
5.309 5.578 5.850 6.123 6.399
5.336 5.605 5.877 6.151 6.426
5.363 5.632 5.904 6.178 6.454
5.389 5.660 5.932 6.206 6.482
5.416 5.687 5.959 6.233 6.510
5.443 5.714 5.986 6.261 6.537
5.470 5.741 6.014 6.288 6.565
5.497 5.768 6.041 6.316 6.593
5.524 5.795 6.068 6.343 6.621
5.551 5.823 6.096 6.371 6.648
250 260 270 280 290
-340 -330 -320 -310 -300
-5.785 -5.705 -5.620 -5.532 -5.439
-5.777 -5.697 -5.612 -5.523 -5.429
-5.769 -5.688 -5.603 -5.513 -5.420
-5.761 -5.680 -5.594 -5.504 -5.410
-5.753 -5.672 -5.585 -5.495 -5.400
-5.745 -5.663 -5.577 -5.486 -5.391
-5.737 -5.655 -5.568 -5.476 -5.381
-5.729 -5.646 -5.559 -5.467 -5.371
-5.721 -5.638 -5.550 -5.458 -5.361
-5.713 -5.629 -5.541 -5.448 -5.351
-5.705 -5.620 -5.532 -5.439 -5.341
-340 -330 -320 -310 -300
300 310 320 330 340
6.648 6.928 7.209 7.492 7.777
6.676 6.956 7.237 7.520 7.805
6.704 6.984 7.265 7.549 7.834
6.732 7.012 7.294 7.577 7.863
6.760 7.040 7.322 7.606 7.891
6.788 7.068 7.350 7.634 7.920
6.816 7.096 7.378 7.663 7.949
6.844 7.124 7.407 7.691 7.977
6.872 7.152 7.435 7.720 8.006
6.900 7.181 7.463 7.748 8.035
6.928 7.209 7.492 7.777 8.064
300 310 320 330 340
-290 -280 -270 -260 -250
-5.341 -5.240 -5.135 -5.025 -4.912
-5.332 -5.230 -5.124 -5.014 -4.900
-5.322 -5.219 -5.113 -5.003 -4.889
-5.312 -5.209 -5.102 -4.992 -4.877
-5.301 -5.198 -5.091 -4.980 -4.865
-5.291 -5.188 -5.081 -4.969 -4.854
-5.281 -5.177 -5.070 -4.958 -4.842
-5.271 -5.167 -5.059 -4.946 -4.830
-5.261 -5.156 -5.048 -4.935 -4.818
-5.250 -5.145 -5.036 -4.923 -4.806
-5.240 -5.135 -5.025 -4.912 -4.794
-290 -280 -270 -260 -250
350 360 370 380 390
8.064 8.352 8.643 8.935 9.229
8.092 8.381 8.672 8.964 9.259
8.121 8.410 8.701 8.994 9.288
8.150 8.439 8.730 9.023 9.318
8.179 8.468 8.759 9.052 9.347
8.208 8.497 8.789 9.082 9.377
8.237 8.526 8.818 9.111 9.406
8.266 8.555 8.847 9.141 9.436
8.294 8.585 8.876 9.170 9.466
8.323 8.614 8.906 9.200 9.495
8.352 8.643 8.935 9.229 9.525
350 360 370 380 390
-240 -230 -220 -210 -200
-4.794 -4.673 -4.548 -4.419 -4.286
-4.783 -4.661 -4.535 -4.406 -4.273
-4.771 -4.648 -4.523 -4.393 -4.259
-4.759 -4.636 -4.510 -4.380 -4.246
-4.746 -4.624 -4.497 -4.366 -4.232
-4.734 -4.611 -4.484 -4.353 -4.218
-4.722 -4.599 -4.471 -4.340 -4.205
-4.710 -4.586 -4.458 -4.326 -4.191
-4.698 -4.573 -4.445 -4.313 -4.177
-4.685 -4.561 -4.432 -4.300 -4.163
-4.673 -4.548 -4.419 -4.286 -4.149
-240 -230 -220 -210 -200
400 9.525 9.555 9.584 9.614 9.644 9.673 410 9.822 9.852 9.882 9.912 9.942 9.972 420 10.122 10.152 10.182 10.212 10.242 10.272 430 10.423 10.453 10.483 10.513 10.543 10.574 440 10.725 10.755 10.786 10.816 10.847 10.877
9.703 10.002 10.302 10.604 10.907
9.733 10.032 10.332 10.634 10.938
9.763 10.062 10.362 10.664 10.968
9.793 10.092 10.392 10.695 10.999
9.822 10.122 10.423 10.725 11.029
400 410 420 430 440
-190 -180 -170 -160 -150
-4.149 -4.009 -3.865 -3.717 -3.565
-4.136 -3.995 -3.850 -3.702 -3.550
-4.122 -3.980 -3.836 -3.687 -3.535
-4.108 -3.966 -3.821 -3.672 -3.519
-4.094 -3.952 -3.806 -3.657 -3.504
-4.080 -3.937 -3.791 -3.642 -3.488
-4.066 -3.923 -3.777 -3.626 -3.473
-4.052 -3.908 -3.762 -3.611 -3.457
-4.037 -3.894 -3.747 -3.596 -3.441
-4.023 -3.879 -3.732 -3.581 -3.426
-4.009 -3.865 -3.717 -3.565 -3.410
-190 -180 -170 -160 -150
450 460 470 480 490
11.029 11.335 11.643 11.951 12.262
11.060 11.366 11.673 11.982 12.293
11.090 11.396 11.704 12.013 12.324
11.121 11.427 11.735 12.044 12.355
11.151 11.458 11.766 12.075 12.386
11.182 11.489 11.797 12.106 12.418
11.213 11.519 11.828 12.138 12.449
11.243 11.550 11.859 12.169 12.480
11.274 11.581 11.890 12.200 12.511
11.304 11.612 11.920 12.231 12.543
11.335 11.643 11.951 12.262 12.574
450 460 470 480 490
-140 -130 -120 -110 -100
-3.410 -3.251 -3.089 -2.923 -2.754
-3.394 -3.235 -3.072 -2.906 -2.737
-3.379 -3.219 -3.056 -2.889 -2.719
-3.363 -3.203 -3.040 -2.873 -2.702
-3.347 -3.187 -3.023 -2.856 -2.685
-3.331 -3.171 -3.006 -2.839 -2.668
-3.315 -3.154 -2.990 -2.822 -2.651
-3.299 -3.138 -2.973 -2.805 -2.633
-3.283 -3.122 -2.956 -2.788 -2.616
-3.267 -3.105 -2.940 -2.771 -2.598
-3.251 -3.089 -2.923 -2.754 -2.581
-140 -130 -120 -110 -100
500 510 520 530 540
12.574 12.887 13.202 13.518 13.836
12.605 12.919 13.234 13.550 13.868
12.636 12.950 13.265 13.582 13.900
12.668 12.982 13.297 13.614 13.932
12.699 13.013 13.328 13.645 13.964
12.730 13.045 13.360 13.677 13.995
12.762 13.076 13.392 13.709 14.027
12.793 13.108 13.423 13.741 14.059
12.824 13.139 13.455 13.772 14.091
12.856 13.171 13.487 13.804 14.123
12.887 13.202 13.518 13.836 14.155
500 510 520 530 540
-90 -80 -70 -60 -50
-2.581 -2.405 -2.225 -2.043 -1.857
-2.564 -2.387 -2.207 -2.024 -1.838
-2.546 -2.369 -2.189 -2.006 -1.819
-2.529 -2.351 -2.171 -1.987 -1.800
-2.511 -2.334 -2.153 -1.969 -1.781
-2.493 -2.316 -2.134 -1.950 -1.762
-2.476 -2.298 -2.116 -1.931 -1.743
-2.458 -2.280 -2.098 -1.913 -1.724
-2.440 -2.262 -2.079 -1.894 -1.705
-2.423 -2.244 -2.061 -1.875 -1.686
-2.405 -2.225 -2.043 -1.857 -1.667
-90 -80 -70 -60 -50
550 560 570 580 590
14.155 14.476 14.797 15.121 15.445
14.187 14.508 14.830 15.153 15.477
14.219 14.540 14.862 15.185 15.510
14.251 14.572 14.894 15.218 15.543
14.283 14.604 14.926 15.250 15.575
14.315 14.636 14.959 15.283 15.608
14.347 14.669 14.991 15.315 15.640
14.379 14.701 15.023 15.347 15.673
14.411 14.733 15.056 15.380 15.705
14.444 14.765 15.088 15.412 15.738
14.476 14.797 15.121 15.445 15.771
550 560 570 580 590
-40 -30 -20 -10 0
-1.667 -1.475 -1.279 -1.081 -0.879
-1.648 -1.456 -1.260 -1.061 -0.859
-1.629 -1.436 -1.240 -1.041 -0.839
-1.610 -1.417 -1.220 -1.021 -0.818
-1.591 -1.397 -1.200 -1.001 -0.798
-1.572 -1.378 -1.181 -0.980 -0.777
-1.552 -1.358 -1.161 -0.960 -0.757
-1.533 -1.338 -1.141 -0.940 -0.736
-1.514 -1.319 -1.121 -0.920 -0.716
-1.494 -1.299 -1.101 -0.900 -0.695
-1.475 -1.279 -1.081 -0.879 -0.675
-40 -30 -20 -10 0
600 610 620 630 640
15.771 16.098 16.426 16.756 17.086
15.803 16.130 16.459 16.789 17.120
15.836 16.163 16.492 16.822 17.153
15.869 16.196 16.525 16.855 17.186
15.901 16.229 16.558 16.888 17.219
15.934 16.262 16.591 16.921 17.252
15.967 16.295 16.624 16.954 17.286
15.999 16.327 16.657 16.987 17.319
16.032 16.360 16.690 17.020 17.352
16.065 16.393 16.723 17.053 17.385
16.098 16.426 16.756 17.086 17.418
600 610 620 630 640
0 10 20 30 40
-0.675 -0.467 -0.256 -0.043 0.173
-0.654 -0.633 -0.613 -0.592 -0.571 -0.550 -0.530 -0.509 -0.488 -0.467 -0.446 -0.425 -0.404 -0.383 -0.362 -0.341 -0.320 -0.299 -0.278 -0.256 -0.235 -0.214 -0.193 -0.171 -0.150 -0.129 -0.107 -0.086 -0.064 -0.043 -0.022 0.000 0.022 0.043 0.065 0.086 0.108 0.130 0.151 0.173 0.195 0.216 0.238 0.260 0.282 0.303 0.325 0.347 0.369 0.391
0 10 20 30 40
650 660 670 680 690
17.418 17.752 18.086 18.422 18.759
17.452 17.785 18.120 18.456 18.793
17.485 17.819 18.153 18.490 18.827
17.518 17.852 18.187 18.523 18.861
17.552 17.886 18.221 18.557 18.894
17.585 17.919 18.254 18.591 18.928
17.618 17.952 18.288 18.624 18.962
17.652 17.986 18.321 18.658 18.996
17.685 18.019 18.355 18.692 19.030
17.718 18.053 18.389 18.725 19.064
17.752 18.086 18.422 18.759 19.097
650 660 670 680 690
50 60 70 80 90
0.391 0.611 0.834 1.060 1.288
0.413 0.634 0.857 1.083 1.311
0.435 0.656 0.879 1.105 1.334
0.457 0.678 0.902 1.128 1.357
0.479 0.700 0.924 1.151 1.380
0.501 0.723 0.947 1.174 1.403
0.523 0.745 0.969 1.196 1.426
0.545 0.767 0.992 1.219 1.449
0.567 0.790 1.015 1.242 1.472
0.589 0.812 1.037 1.265 1.496
0.611 0.834 1.060 1.288 1.519
50 60 70 80 90
700 710 720 730 740
19.097 19.437 19.777 20.118 20.460
19.131 19.471 19.811 20.152 20.495
19.165 19.505 19.845 20.187 20.529
19.199 19.539 19.879 20.221 20.563
19.233 19.573 19.913 20.255 20.597
19.267 19.607 19.947 20.289 20.632
19.301 19.641 19.982 20.323 20.666
19.335 19.675 20.016 20.358 20.700
19.369 19.709 20.050 20.392 20.735
19.403 19.743 20.084 20.426 20.769
19.437 19.777 20.118 20.460 20.803
700 710 720 730 740
100 110 120 130 140
1.519 1.752 1.988 2.227 2.468
1.542 1.776 2.012 2.251 2.492
1.565 1.799 2.036 2.275 2.517
1.588 1.823 2.060 2.299 2.541
1.612 1.846 2.083 2.323 2.565
1.635 1.870 2.107 2.347 2.590
1.658 1.893 2.131 2.371 2.614
1.682 1.917 2.155 2.395 2.639
1.705 1.941 2.179 2.420 2.663
1.729 1.964 2.203 2.444 2.687
1.752 1.988 2.227 2.468 2.712
100 110 120 130 140
°F
0
6
7
8
10
°F
-450
1
2
3
4
5
9
750 20.803 20.838 20.872
°F
Z-223
0
1
2
750
3
4
5
6
7
8
9
10
°F
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °F FREFERENCE JUNCTION AT 32°F Extension Grade
Thermocouple Grade
NONE ESTABLISHED
Platinum-10% Rhodium vs. Platinum
Revised Thermocouple Reference Tables
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts °F
-10
-9
-50
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
S
°F
°F
0
6
7
8
10
°F
-0.236 -0.233 -0.231 -0.229 -0.227 -0.224 -0.222 -0.220 -0.218
-50
400 410 420 430 440
1.478 1.526 1.573 1.621 1.669
1.483 1.531 1.578 1.626 1.674
1.488 1.535 1.583 1.631 1.679
1.493 1.540 1.588 1.636 1.684
1.497 1.545 1.592 1.640 1.689
1.502 1.550 1.597 1.645 1.693
1.507 1.554 1.602 1.650 1.698
1.512 1.559 1.607 1.655 1.703
1.516 1.564 1.612 1.660 1.708
1.521 1.569 1.616 1.664 1.713
9
1.526 1.573 1.621 1.669 1.718
400 410 420 430 440
-0.213 -0.190 -0.165 -0.140 -0.114
-40 -30 -20 -10 0
-0.218 -0.194 -0.170 -0.145 -0.119
-0.215 -0.192 -0.168 -0.142 -0.116
-0.194 -0.170 -0.145 -0.119 -0.092
-40 -30 -20 -10 0
450 460 470 480 490
1.718 1.766 1.815 1.864 1.913
1.722 1.771 1.820 1.869 1.918
1.727 1.776 1.825 1.874 1.923
1.732 1.781 1.829 1.878 1.928
1.737 1.786 1.834 1.883 1.933
1.742 1.790 1.839 1.888 1.938
1.747 1.795 1.844 1.893 1.942
1.752 1.800 1.849 1.898 1.947
1.756 1.805 1.854 1.903 1.952
1.761 1.810 1.859 1.908 1.957
1.766 1.815 1.864 1.913 1.962
450 460 470 480 490
0 10 20 30 40
-0.092 -0.064 -0.035 -0.006 0.024
-0.089 -0.086 -0.084 -0.081 -0.078 -0.075 -0.073 -0.070 -0.067 -0.064 -0.061 -0.058 -0.056 -0.053 -0.050 -0.047 -0.044 -0.041 -0.038 -0.035 -0.033 -0.030 -0.027 -0.024 -0.021 -0.018 -0.015 -0.012 -0.009 -0.006 -0.003 0.000 0.003 0.006 0.009 0.012 0.015 0.018 0.021 0.024 0.027 0.030 0.033 0.037 0.040 0.043 0.046 0.049 0.052 0.055
0 10 20 30 40
500 510 520 530 540
1.962 2.012 2.062 2.111 2.162
1.967 2.017 2.067 2.116 2.167
1.972 2.022 2.072 2.121 2.172
1.977 2.027 2.076 2.126 2.177
1.982 2.032 2.081 2.131 2.182
1.987 2.037 2.086 2.136 2.187
1.992 2.042 2.091 2.141 2.192
1.997 2.047 2.096 2.147 2.197
2.002 2.052 2.101 2.152 2.202
2.007 2.057 2.106 2.157 2.207
2.012 2.062 2.111 2.162 2.212
500 510 520 530 540
50 60 70 80 90
0.055 0.087 0.119 0.153 0.186
0.058 0.090 0.123 0.156 0.190
0.062 0.093 0.126 0.159 0.193
0.065 0.097 0.129 0.163 0.197
0.068 0.100 0.133 0.166 0.200
0.071 0.103 0.136 0.169 0.204
0.074 0.106 0.139 0.173 0.207
0.077 0.110 0.143 0.176 0.210
0.081 0.113 0.146 0.180 0.214
0.084 0.116 0.149 0.183 0.217
0.087 0.119 0.153 0.186 0.221
50 60 70 80 90
550 560 570 580 590
2.212 2.262 2.313 2.364 2.415
2.217 2.267 2.318 2.369 2.420
2.222 2.272 2.323 2.374 2.425
2.227 2.277 2.328 2.379 2.430
2.232 2.283 2.333 2.384 2.435
2.237 2.288 2.338 2.389 2.440
2.242 2.293 2.343 2.394 2.445
2.247 2.298 2.348 2.399 2.450
2.252 2.303 2.354 2.404 2.455
2.257 2.308 2.359 2.410 2.461
2.262 2.313 2.364 2.415 2.466
550 560 570 580 590
100 110 120 130 140
0.221 0.256 0.292 0.328 0.365
0.224 0.260 0.295 0.332 0.369
0.228 0.263 0.299 0.335 0.372
0.231 0.267 0.303 0.339 0.376
0.235 0.270 0.306 0.343 0.380
0.238 0.274 0.310 0.346 0.384
0.242 0.277 0.313 0.350 0.387
0.245 0.281 0.317 0.354 0.391
0.249 0.285 0.321 0.357 0.395
0.252 0.288 0.324 0.361 0.399
0.256 0.292 0.328 0.365 0.402
100 110 120 130 140
600 610 620 630 640
2.466 2.517 2.568 2.620 2.672
2.471 2.522 2.574 2.625 2.677
2.476 2.527 2.579 2.630 2.682
2.481 2.532 2.584 2.635 2.687
2.486 2.537 2.589 2.641 2.692
2.491 2.543 2.594 2.646 2.697
2.496 2.548 2.599 2.651 2.703
2.502 2.553 2.604 2.656 2.708
2.507 2.558 2.610 2.661 2.713
2.512 2.563 2.615 2.666 2.718
2.517 2.568 2.620 2.672 2.723
600 610 620 630 640
150 160 170 180 190
0.402 0.440 0.479 0.518 0.557
0.406 0.444 0.483 0.522 0.561
0.410 0.448 0.487 0.526 0.565
0.414 0.452 0.490 0.530 0.569
0.417 0.456 0.494 0.534 0.573
0.421 0.459 0.498 0.538 0.577
0.425 0.463 0.502 0.541 0.581
0.429 0.467 0.506 0.545 0.585
0.433 0.471 0.510 0.549 0.589
0.436 0.475 0.514 0.553 0.593
0.440 0.479 0.518 0.557 0.597
150 160 170 180 190
650 660 670 680 690
2.723 2.775 2.827 2.880 2.932
2.729 2.781 2.833 2.885 2.937
2.734 2.786 2.838 2.890 2.943
2.739 2.791 2.843 2.895 2.948
2.744 2.796 2.848 2.901 2.953
2.749 2.801 2.854 2.906 2.958
2.755 2.807 2.859 2.911 2.964
2.760 2.812 2.864 2.916 2.969
2.765 2.817 2.869 2.922 2.974
2.770 2.822 2.874 2.927 2.979
2.775 2.827 2.880 2.932 2.985
650 660 670 680 690
200 210 220 230 240
0.597 0.638 0.679 0.720 0.762
0.601 0.642 0.683 0.724 0.766
0.605 0.646 0.687 0.728 0.770
0.609 0.650 0.691 0.732 0.774
0.613 0.654 0.695 0.737 0.779
0.617 0.658 0.699 0.741 0.783
0.622 0.662 0.703 0.745 0.787
0.626 0.666 0.708 0.749 0.791
0.630 0.670 0.712 0.753 0.795
0.634 0.675 0.716 0.758 0.800
0.638 0.679 0.720 0.762 0.804
200 210 220 230 240
700 710 720 730 740
2.985 3.037 3.090 3.143 3.196
2.990 3.042 3.095 3.148 3.201
2.995 3.048 3.100 3.153 3.206
3.000 3.053 3.106 3.159 3.212
3.006 3.058 3.111 3.164 3.217
3.011 3.063 3.116 3.169 3.222
3.016 3.069 3.122 3.174 3.227
3.021 3.074 3.127 3.180 3.233
3.027 3.079 3.132 3.185 3.238
3.032 3.085 3.137 3.190 3.243
3.037 3.090 3.143 3.196 3.249
700 710 720 730 740
250 260 270 280 290
0.804 0.847 0.889 0.933 0.977
0.808 0.851 0.894 0.937 0.981
0.812 0.855 0.898 0.942 0.985
0.817 0.859 0.902 0.946 0.990
0.821 0.864 0.907 0.950 0.994
0.825 0.868 0.911 0.955 0.998
0.829 0.872 0.915 0.959 1.003
0.834 0.877 0.920 0.963 1.007
0.838 0.881 0.924 0.968 1.012
0.842 0.885 0.928 0.972 1.016
0.847 0.889 0.933 0.977 1.021
250 260 270 280 290
750 760 770 780 790
3.249 3.302 3.355 3.409 3.462
3.254 3.307 3.361 3.414 3.468
3.259 3.313 3.366 3.419 3.473
3.265 3.318 3.371 3.425 3.478
3.270 3.323 3.377 3.430 3.484
3.275 3.329 3.382 3.435 3.489
3.281 3.334 3.387 3.441 3.494
3.286 3.339 3.393 3.446 3.500
3.291 3.345 3.398 3.451 3.505
3.297 3.350 3.403 3.457 3.510
3.302 3.355 3.409 3.462 3.516
750 760 770 780 790
300 310 320 330 340
1.021 1.065 1.110 1.155 1.200
1.025 1.069 1.114 1.159 1.205
1.029 1.074 1.119 1.164 1.209
1.034 1.078 1.123 1.168 1.214
1.038 1.083 1.128 1.173 1.218
1.043 1.087 1.132 1.177 1.223
1.047 1.092 1.137 1.182 1.227
1.052 1.096 1.141 1.186 1.232
1.056 1.101 1.146 1.191 1.237
1.061 1.105 1.150 1.196 1.241
1.065 1.110 1.155 1.200 1.246
300 310 320 330 340
800 810 820 830 840
3.516 3.570 3.623 3.677 3.731
3.521 3.575 3.629 3.683 3.737
3.527 3.580 3.634 3.688 3.742
3.532 3.586 3.640 3.694 3.748
3.537 3.591 3.645 3.699 3.753
3.543 3.596 3.650 3.704 3.758
3.548 3.602 3.656 3.710 3.764
3.553 3.607 3.661 3.715 3.769
3.559 3.613 3.667 3.721 3.775
3.564 3.618 3.672 3.726 3.780
3.570 3.623 3.677 3.731 3.786
800 810 820 830 840
350 360 370 380 390
1.246 1.292 1.338 1.385 1.431
1.250 1.296 1.343 1.389 1.436
1.255 1.301 1.347 1.394 1.441
1.260 1.306 1.352 1.399 1.445
1.264 1.310 1.357 1.403 1.450
1.269 1.315 1.361 1.408 1.455
1.273 1.319 1.366 1.413 1.460
1.278 1.324 1.371 1.417 1.464
1.283 1.329 1.375 1.422 1.469
1.287 1.333 1.380 1.427 1.474
1.292 1.338 1.385 1.431 1.478
350 360 370 380 390
850 860 870 880 890
3.786 3.840 3.894 3.949 4.003
3.791 3.845 3.900 3.954 4.009
3.796 3.851 3.905 3.959 4.014
3.802 3.856 3.910 3.965 4.020
3.807 3.862 3.916 3.970 4.025
3.813 3.867 3.921 3.976 4.030
3.818 3.872 3.927 3.981 4.036
3.823 3.878 3.932 3.987 4.041
3.829 3.883 3.938 3.992 4.047
3.834 3.889 3.943 3.998 4.052
3.840 3.894 3.949 4.003 4.058
850 860 870 880 890
°F
0
6
7
8
10
°F
°F
0
6
7
8
10
°F
1
2
-0.211 -0.187 -0.163 -0.137 -0.111
3
-0.208 -0.185 -0.160 -0.135 -0.108
4
-0.206 -0.182 -0.158 -0.132 -0.106
5
-0.204 -0.180 -0.155 -0.129 -0.103
-0.201 -0.178 -0.153 -0.127 -0.100
-0.199 -0.175 -0.150 -0.124 -0.097
-0.197 -0.173 -0.148 -0.122 -0.095
9
Z-224
1
2
3
4
5
9
Z
+ –
Revised Thermocouple Reference Tables
S
NONE ESTABLISHED
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°F
-10
-9
900 910 920 930 940
4.058 4.113 4.167 4.222 4.277
4.063 4.118 4.173 4.228 4.283
4.069 4.123 4.178 4.233 4.288
4.074 4.129 4.184 4.239 4.294
4.080 4.134 4.189 4.244 4.299
950 960 970 980 990
4.332 4.388 4.443 4.498 4.554
4.338 4.393 4.449 4.504 4.559
4.343 4.399 4.454 4.510 4.565
4.349 4.404 4.460 4.515 4.571
1000 1010 1020 1030 1040
4.610 4.665 4.721 4.777 4.833
4.615 4.671 4.727 4.782 4.838
4.621 4.676 4.732 4.788 4.844
1050 1060 1070 1080 1090
4.889 4.945 5.001 5.058 5.114
4.895 4.951 5.007 5.063 5.120
1100 1110 1120 1130 1140
5.171 5.227 5.284 5.341 5.398
1150 1160 1170 1180 1190
Thermoelectric Voltage in Millivolts 0
°F
°F
0
6
7
8
4.085 4.140 4.195 4.250 4.305
4.091 4.145 4.200 4.255 4.310
4.096 4.151 4.206 4.261 4.316
4.102 4.156 4.211 4.266 4.321
4.107 4.162 4.217 4.272 4.327
4.113 4.167 4.222 4.277 4.332
900 910 920 930 940
1400 1410 1420 1430 1440
6.913 6.973 7.032 7.092 7.152
6.919 6.979 7.038 7.098 7.158
6.925 6.985 7.044 7.104 7.164
6.931 6.991 7.050 7.110 7.170
6.937 6.997 7.056 7.116 7.176
6.943 7.003 7.062 7.122 7.182
6.949 7.008 7.068 7.128 7.188
6.955 7.014 7.074 7.134 7.194
6.961 7.020 7.080 7.140 7.200
6.967 7.026 7.086 7.146 7.206
6.973 7.032 7.092 7.152 7.212
1400 1410 1420 1430 1440
4.355 4.410 4.465 4.521 4.576
4.360 4.415 4.471 4.526 4.582
4.366 4.421 4.476 4.532 4.587
4.371 4.426 4.482 4.537 4.593
4.377 4.432 4.487 4.543 4.598
4.382 4.437 4.493 4.548 4.604
4.388 4.443 4.498 4.554 4.610
950 960 970 980 990
1450 1460 1470 1480 1490
7.212 7.273 7.333 7.393 7.454
7.218 7.279 7.339 7.399 7.460
7.224 7.285 7.345 7.405 7.466
7.230 7.291 7.351 7.411 7.472
7.236 7.297 7.357 7.418 7.478
7.242 7.303 7.363 7.424 7.484
7.249 7.309 7.369 7.430 7.490
7.255 7.315 7.375 7.436 7.496
7.261 7.321 7.381 7.442 7.502
7.267 7.327 7.387 7.448 7.508
7.273 7.333 7.393 7.454 7.514
1450 1460 1470 1480 1490
4.626 4.682 4.738 4.794 4.850
4.632 4.688 4.743 4.799 4.855
4.637 4.693 4.749 4.805 4.861
4.643 4.699 4.755 4.810 4.866
4.648 4.704 4.760 4.816 4.872
4.654 4.710 4.766 4.822 4.878
4.660 4.715 4.771 4.827 4.883
4.665 4.721 4.777 4.833 4.889
1000 1010 1020 1030 1040
1500 1510 1520 1530 1540
7.514 7.575 7.636 7.697 7.758
7.521 7.581 7.642 7.703 7.764
7.527 7.587 7.648 7.709 7.770
7.533 7.593 7.654 7.715 7.776
7.539 7.600 7.660 7.721 7.783
7.545 7.606 7.667 7.728 7.789
7.551 7.612 7.673 7.734 7.795
7.557 7.618 7.679 7.740 7.801
7.563 7.624 7.685 7.746 7.807
7.569 7.630 7.691 7.752 7.813
7.575 7.636 7.697 7.758 7.819
1500 1510 1520 1530 1540
4.900 4.956 5.013 5.069 5.125
4.906 4.962 5.018 5.075 5.131
4.911 4.968 5.024 5.080 5.137
4.917 4.973 5.030 5.086 5.142
4.923 4.979 5.035 5.092 5.148
4.928 4.984 5.041 5.097 5.154
4.934 4.990 5.046 5.103 5.159
4.939 4.996 5.052 5.109 5.165
4.945 5.001 5.058 5.114 5.171
1050 1060 1070 1080 1090
1550 1560 1570 1580 1590
7.819 7.881 7.942 8.003 8.065
7.825 7.887 7.948 8.010 8.071
7.832 7.893 7.954 8.016 8.077
7.838 7.899 7.960 8.022 8.083
7.844 7.905 7.966 8.028 8.090
7.850 7.911 7.973 8.034 8.096
7.856 7.917 7.979 8.040 8.102
7.862 7.923 7.985 8.047 8.108
7.868 7.930 7.991 8.053 8.114
7.874 7.936 7.997 8.059 8.121
7.881 7.942 8.003 8.065 8.127
1550 1560 1570 1580 1590
5.176 5.233 5.290 5.347 5.404
5.182 5.239 5.295 5.352 5.409
5.188 5.244 5.301 5.358 5.415
5.193 5.250 5.307 5.364 5.421
5.199 5.256 5.312 5.369 5.426
5.205 5.261 5.318 5.375 5.432
5.210 5.267 5.324 5.381 5.438
5.216 5.273 5.330 5.386 5.443
5.222 5.278 5.335 5.392 5.449
5.227 5.284 5.341 5.398 5.455
1100 1110 1120 1130 1140
1600 1610 1620 1630 1640
8.127 8.189 8.250 8.312 8.375
8.133 8.195 8.257 8.319 8.381
8.139 8.201 8.263 8.325 8.387
8.145 8.207 8.269 8.331 8.393
8.151 8.213 8.275 8.337 8.399
8.158 8.219 8.281 8.343 8.406
8.164 8.226 8.288 8.350 8.412
8.170 8.232 8.294 8.356 8.418
8.176 8.238 8.300 8.362 8.424
8.182 8.244 8.306 8.368 8.431
8.189 8.250 8.312 8.375 8.437
1600 1610 1620 1630 1640
5.455 5.512 5.569 5.627 5.684
5.461 5.518 5.575 5.632 5.690
5.466 5.523 5.581 5.638 5.695
5.472 5.529 5.586 5.644 5.701
5.478 5.535 5.592 5.649 5.707
5.483 5.541 5.598 5.655 5.713
5.489 5.546 5.604 5.661 5.718
5.495 5.552 5.609 5.667 5.724
5.501 5.558 5.615 5.672 5.730
5.506 5.563 5.621 5.678 5.736
5.512 5.569 5.627 5.684 5.741
1150 1160 1170 1180 1190
1650 1660 1670 1680 1690
8.437 8.499 8.562 8.624 8.687
8.443 8.505 8.568 8.630 8.693
8.449 8.512 8.574 8.637 8.699
8.455 8.518 8.580 8.643 8.706
8.462 8.524 8.587 8.649 8.712
8.468 8.530 8.593 8.655 8.718
8.474 8.537 8.599 8.662 8.724
8.480 8.543 8.605 8.668 8.731
8.487 8.549 8.612 8.674 8.737
8.493 8.555 8.618 8.680 8.743
8.499 8.562 8.624 8.687 8.749
1650 1660 1670 1680 1690
1200 1210 1220 1230 1240
5.741 5.799 5.857 5.915 5.972
5.747 5.805 5.863 5.920 5.978
5.753 5.811 5.868 5.926 5.984
5.759 5.816 5.874 5.932 5.990
5.764 5.822 5.880 5.938 5.996
5.770 5.828 5.886 5.944 6.001
5.776 5.834 5.891 5.949 6.007
5.782 5.839 5.897 5.955 6.013
5.788 5.845 5.903 5.961 6.019
5.793 5.851 5.909 5.967 6.025
5.799 5.857 5.915 5.972 6.030
1200 1210 1220 1230 1240
1700 1710 1720 1730 1740
8.749 8.812 8.875 8.938 9.001
8.756 8.819 8.882 8.945 9.008
8.762 8.825 8.888 8.951 9.014
8.768 8.831 8.894 8.957 9.020
8.775 8.837 8.900 8.964 9.027
8.781 8.844 8.907 8.970 9.033
8.787 8.850 8.913 8.976 9.039
8.793 8.856 8.919 8.983 9.046
8.800 8.863 8.926 8.989 9.052
8.806 8.869 8.932 8.995 9.058
8.812 8.875 8.938 9.001 9.065
1700 1710 1720 1730 1740
1250 1260 1270 1280 1290
6.030 6.089 6.147 6.205 6.264
6.036 6.094 6.153 6.211 6.269
6.042 6.100 6.158 6.217 6.275
6.048 6.106 6.164 6.223 6.281
6.054 6.112 6.170 6.228 6.287
6.060 6.118 6.176 6.234 6.293
6.065 6.124 6.182 6.240 6.299
6.071 6.129 6.188 6.246 6.305
6.077 6.135 6.193 6.252 6.310
6.083 6.141 6.199 6.258 6.316
6.089 6.147 6.205 6.264 6.322
1250 1260 1270 1280 1290
1750 1760 1770 1780 1790
9.065 9.128 9.192 9.255 9.319
9.071 9.134 9.198 9.261 9.325
9.077 9.141 9.204 9.268 9.331
9.084 9.147 9.211 9.274 9.338
9.090 9.153 9.217 9.281 9.344
9.096 9.160 9.223 9.287 9.351
9.103 9.166 9.230 9.293 9.357
9.109 9.172 9.236 9.300 9.363
9.115 9.179 9.242 9.306 9.370
9.122 9.185 9.249 9.312 9.376
9.128 9.192 9.255 9.319 9.382
1750 1760 1770 1780 1790
1300 1310 1320 1330 1340
6.322 6.381 6.439 6.498 6.557
6.328 6.387 6.445 6.504 6.563
6.334 6.392 6.451 6.510 6.569
6.340 6.398 6.457 6.516 6.575
6.346 6.404 6.463 6.522 6.581
6.351 6.410 6.469 6.528 6.587
6.357 6.416 6.475 6.534 6.593
6.363 6.422 6.481 6.539 6.598
6.369 6.428 6.486 6.545 6.604
6.375 6.434 6.492 6.551 6.610
6.381 6.439 6.498 6.557 6.616
1300 1310 1320 1330 1340
1800 1810 1820 1830 1840
9.382 9.446 9.510 9.574 9.638
9.389 9.453 9.517 9.581 9.645
9.395 9.459 9.523 9.587 9.651
9.402 9.465 9.529 9.594 9.658
9.408 9.472 9.536 9.600 9.664
9.414 9.478 9.542 9.606 9.671
9.421 9.485 9.549 9.613 9.677
9.427 9.491 9.555 9.619 9.683
9.434 9.497 9.561 9.626 9.690
9.440 9.504 9.568 9.632 9.696
9.446 9.510 9.574 9.638 9.703
1800 1810 1820 1830 1840
1350 1360 1370 1380 1390
6.616 6.675 6.735 6.794 6.853
6.622 6.681 6.741 6.800 6.859
6.628 6.687 6.746 6.806 6.865
6.634 6.693 6.752 6.812 6.871
6.640 6.699 6.758 6.818 6.877
6.646 6.705 6.764 6.824 6.883
6.652 6.711 6.770 6.830 6.889
6.658 6.717 6.776 6.836 6.895
6.664 6.723 6.782 6.842 6.901
6.669 6.729 6.788 6.847 6.907
6.675 6.735 6.794 6.853 6.913
1350 1360 1370 1380 1390
1850 1860 1870 1880 1890
9.703 9.767 9.831 9.896 9.961
9.709 9.773 9.838 9.902 9.967
9.716 9.780 9.844 9.909 9.973
9.722 9.786 9.851 9.915 9.980
9.728 9.793 9.857 9.922 9.986
9.735 9.799 9.864 9.928 9.993
9.741 9.748 9.754 9.761 9.767 9.806 9.812 9.819 9.825 9.831 9.870 9.877 9.883 9.889 9.896 9.935 9.941 9.948 9.954 9.961 9.999 10.006 10.012 10.019 10.025
1850 1860 1870 1880 1890
°F
0
6
7
8
°F
°F
0
4
-5
Extension Grade
-2
3
-6
+ –
-3
2
-7
Platinum-10% Rhodium vs. Platinum
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °F FREFERENCE JUNCTION AT 32°F
-4
1
-8
Thermocouple Grade
5
-1
9
10
Z-225
1
1
2
2
3
3
4
4
5
5
6
7
8
9
9
10
10
°F
°F
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °F FREFERENCE JUNCTION AT 32°F Extension Grade
Thermocouple Grade
NONE ESTABLISHED
Platinum-10% Rhodium vs. Platinum
Revised Thermocouple Reference Tables
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts
S
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
1900 1910 1920 1930 1940
10.025 10.090 10.155 10.220 10.285
10.032 10.097 10.162 10.227 10.292
10.038 10.103 10.168 10.233 10.298
10.045 10.110 10.175 10.240 10.305
10.051 10.116 10.181 10.246 10.311
10.058 10.123 10.188 10.253 10.318
10.064 10.129 10.194 10.259 10.324
10.071 10.136 10.201 10.266 10.331
10.077 10.142 10.207 10.272 10.337
10.084 10.149 10.214 10.279 10.344
10.090 10.155 10.220 10.285 10.350
1900 1910 1920 1930 1940
2400 2410 2420 2430 2440
13.348 13.415 13.483 13.550 13.617
13.354 13.422 13.489 13.557 13.624
13.361 13.429 13.496 13.563 13.631
13.368 13.435 13.503 13.570 13.638
13.375 13.442 13.510 13.577 13.644
13.381 13.449 13.516 13.584 13.651
13.388 13.456 13.523 13.590 13.658
13.395 13.462 13.530 13.597 13.665
13.402 13.469 13.537 13.604 13.671
13.408 13.476 13.543 13.611 13.678
13.415 13.483 13.550 13.617 13.685
2400 2410 2420 2430 2440
1950 1960 1970 1980 1990
10.350 10.416 10.481 10.547 10.612
10.357 10.422 10.488 10.553 10.619
10.363 10.429 10.494 10.560 10.625
10.370 10.435 10.501 10.566 10.632
10.376 10.442 10.507 10.573 10.638
10.383 10.448 10.514 10.579 10.645
10.390 10.455 10.520 10.586 10.651
10.396 10.461 10.527 10.592 10.658
10.403 10.468 10.533 10.599 10.665
10.409 10.475 10.540 10.606 10.671
10.416 10.481 10.547 10.612 10.678
1950 1960 1970 1980 1990
2450 2460 2470 2480 2490
13.685 13.752 13.820 13.887 13.955
13.692 13.759 13.826 13.894 13.961
13.698 13.766 13.833 13.901 13.968
13.705 13.773 13.840 13.907 13.975
13.712 13.779 13.847 13.914 13.982
13.719 13.786 13.853 13.921 13.988
13.725 13.793 13.860 13.928 13.995
13.732 13.800 13.867 13.934 14.002
13.739 13.806 13.874 13.941 14.009
13.746 13.813 13.880 13.948 14.015
13.752 13.820 13.887 13.955 14.022
2450 2460 2470 2480 2490
2000 2010 2020 2030 2040
10.678 10.743 10.809 10.875 10.941
10.684 10.750 10.816 10.882 10.948
10.691 10.757 10.822 10.888 10.954
10.697 10.763 10.829 10.895 10.961
10.704 10.770 10.836 10.901 10.967
10.711 10.776 10.842 10.908 10.974
10.717 10.783 10.849 10.915 10.981
10.724 10.789 10.855 10.921 10.987
10.730 10.796 10.862 10.928 10.994
10.737 10.803 10.868 10.934 11.000
10.743 10.809 10.875 10.941 11.007
2000 2010 2020 2030 2040
2500 2510 2520 2530 2540
14.022 14.089 14.157 14.224 14.292
14.029 14.096 14.164 14.231 14.298
14.036 14.103 14.170 14.238 14.305
14.042 14.110 14.177 14.245 14.312
14.049 14.116 14.184 14.251 14.319
14.056 14.123 14.191 14.258 14.325
14.063 14.130 14.197 14.265 14.332
14.069 14.137 14.204 14.272 14.339
14.076 14.143 14.211 14.278 14.346
14.083 14.150 14.218 14.285 14.352
14.089 14.157 14.224 14.292 14.359
2500 2510 2520 2530 2540
2050 2060 2070 2080 2090
11.007 11.073 11.139 11.205 11.272
11.014 11.080 11.146 11.212 11.278
11.020 11.086 11.152 11.219 11.285
11.027 11.093 11.159 11.225 11.291
11.033 11.099 11.166 11.232 11.298
11.040 11.106 11.172 11.238 11.305
11.047 11.113 11.179 11.245 11.311
11.053 11.119 11.185 11.252 11.318
11.060 11.126 11.192 11.258 11.325
11.066 11.132 11.199 11.265 11.331
11.073 11.139 11.205 11.272 11.338
2050 2060 2070 2080 2090
2550 2560 2570 2580 2590
14.359 14.426 14.494 14.561 14.629
14.366 14.433 14.501 14.568 14.635
14.373 14.440 14.507 14.575 14.642
14.379 14.447 14.514 14.581 14.649
14.386 14.453 14.521 14.588 14.655
14.393 14.460 14.528 14.595 14.662
14.400 14.467 14.534 14.602 14.669
14.406 14.474 14.541 14.608 14.676
14.413 14.480 14.548 14.615 14.682
14.420 14.487 14.554 14.622 14.689
14.426 14.494 14.561 14.629 14.696
2550 2560 2570 2580 2590
2100 2110 2120 2130 2140
11.338 11.404 11.471 11.537 11.604
11.345 11.411 11.477 11.544 11.610
11.351 11.418 11.484 11.550 11.617
11.358 11.424 11.491 11.557 11.624
11.364 11.431 11.497 11.564 11.630
11.371 11.437 11.504 11.570 11.637
11.378 11.444 11.511 11.577 11.644
11.384 11.451 11.517 11.584 11.650
11.391 11.457 11.524 11.590 11.657
11.398 11.464 11.531 11.597 11.664
11.404 11.471 11.537 11.604 11.670
2100 2110 2120 2130 2140
2600 2610 2620 2630 2640
14.696 14.763 14.830 14.898 14.965
14.703 14.770 14.837 14.904 14.972
14.709 14.777 14.844 14.911 14.978
14.716 14.783 14.851 14.918 14.985
14.723 14.790 14.857 14.925 14.992
14.729 14.797 14.864 14.931 14.998
14.736 14.803 14.871 14.938 15.005
14.743 14.810 14.877 14.945 15.012
14.750 14.817 14.884 14.951 15.019
14.756 14.824 14.891 14.958 15.025
14.763 14.830 14.898 14.965 15.032
2600 2610 2620 2630 2640
2150 2160 2170 2180 2190
11.670 11.737 11.804 11.870 11.937
11.677 11.744 11.810 11.877 11.944
11.684 11.750 11.817 11.884 11.951
11.690 11.757 11.824 11.890 11.957
11.697 11.764 11.830 11.897 11.964
11.704 11.770 11.837 11.904 11.971
11.710 11.777 11.844 11.910 11.977
11.717 11.784 11.850 11.917 11.984
11.724 11.790 11.857 11.924 11.991
11.730 11.797 11.864 11.931 11.997
11.737 11.804 11.870 11.937 12.004
2150 2160 2170 2180 2190
2650 2660 2670 2680 2690
15.032 15.099 15.166 15.233 15.300
15.039 15.106 15.173 15.240 15.307
15.045 15.113 15.180 15.247 15.314
15.052 15.119 15.186 15.254 15.321
15.059 15.126 15.193 15.260 15.327
15.066 15.133 15.200 15.267 15.334
15.072 15.139 15.207 15.274 15.341
15.079 15.146 15.213 15.280 15.347
15.086 15.153 15.220 15.287 15.354
15.092 15.160 15.227 15.294 15.361
15.099 15.166 15.233 15.300 15.367
2650 2660 2670 2680 2690
2200 2210 2220 2230 2240
12.004 12.071 12.138 12.205 12.272
12.011 12.078 12.145 12.211 12.278
12.017 12.084 12.151 12.218 12.285
12.024 12.091 12.158 12.225 12.292
12.031 12.098 12.165 12.232 12.299
12.037 12.104 12.171 12.238 12.305
12.044 12.111 12.178 12.245 12.312
12.051 12.118 12.185 12.252 12.319
12.058 12.124 12.191 12.258 12.325
12.064 12.131 12.198 12.265 12.332
12.071 12.138 12.205 12.272 12.339
2200 2210 2220 2230 2240
2700 2710 2720 2730 2740
15.367 15.434 15.501 15.568 15.635
15.374 15.441 15.508 15.575 15.642
15.381 15.448 15.515 15.582 15.649
15.388 15.455 15.521 15.588 15.655
15.394 15.461 15.528 15.595 15.662
15.401 15.468 15.535 15.602 15.669
15.408 15.475 15.542 15.608 15.675
15.414 15.481 15.548 15.615 15.682
15.421 15.488 15.555 15.622 15.689
15.428 15.495 15.562 15.628 15.695
15.434 15.501 15.568 15.635 15.702
2700 2710 2720 2730 2740
2250 2260 2270 2280 2290
12.339 12.406 12.473 12.540 12.607
12.346 12.413 12.480 12.547 12.614
12.352 12.419 12.486 12.554 12.621
12.359 12.426 12.493 12.560 12.627
12.366 12.433 12.500 12.567 12.634
12.372 12.439 12.507 12.574 12.641
12.379 12.446 12.513 12.580 12.648
12.386 12.453 12.520 12.587 12.654
12.392 12.460 12.527 12.594 12.661
12.399 12.466 12.533 12.601 12.668
12.406 12.473 12.540 12.607 12.675
2250 2260 2270 2280 2290
2750 2760 2770 2780 2790
15.702 15.769 15.835 15.902 15.969
15.709 15.775 15.842 15.909 15.975
15.715 15.782 15.849 15.915 15.982
15.722 15.789 15.855 15.922 15.989
15.729 15.795 15.862 15.929 15.995
15.735 15.802 15.869 15.935 16.002
15.742 15.809 15.875 15.942 16.009
15.749 15.815 15.882 15.949 16.015
15.755 15.822 15.889 15.955 16.022
15.762 15.829 15.895 15.962 16.029
15.769 15.835 15.902 15.969 16.035
2750 2760 2770 2780 2790
2300 2310 2320 2330 2340
12.675 12.742 12.809 12.876 12.944
12.681 12.748 12.816 12.883 12.950
12.688 12.755 12.822 12.890 12.957
12.695 12.762 12.829 12.896 12.964
12.701 12.769 12.836 12.903 12.971
12.708 12.775 12.843 12.910 12.977
12.715 12.782 12.849 12.917 12.984
12.722 12.789 12.856 12.923 12.991
12.728 12.796 12.863 12.930 12.997
12.735 12.802 12.870 12.937 13.004
12.742 12.809 12.876 12.944 13.011
2300 2310 2320 2330 2340
2800 2810 2820 2830 2840
16.035 16.102 16.168 16.235 16.301
16.042 16.108 16.175 16.241 16.308
16.049 16.115 16.182 16.248 16.314
16.055 16.122 16.188 16.255 16.321
16.062 16.128 16.195 16.261 16.328
16.069 16.135 16.202 16.268 16.334
16.075 16.142 16.208 16.275 16.341
16.082 16.148 16.215 16.281 16.347
16.089 16.155 16.221 16.288 16.354
16.095 16.162 16.228 16.294 16.361
16.102 16.168 16.235 16.301 16.367
2800 2810 2820 2830 2840
2350 2360 2370 2380 2390
13.011 13.078 13.146 13.213 13.280
13.018 13.085 13.152 13.220 13.287
13.024 13.092 13.159 13.226 13.294
13.031 13.098 13.166 13.233 13.301
13.038 13.105 13.173 13.240 13.307
13.045 13.112 13.179 13.247 13.314
13.051 13.119 13.186 13.253 13.321
13.058 13.125 13.193 13.260 13.328
13.065 13.132 13.199 13.267 13.334
13.072 13.139 13.206 13.274 13.341
13.078 13.146 13.213 13.280 13.348
2350 2360 2370 2380 2390
2850 2860 2870 2880 2890
16.367 16.434 16.500 16.566 16.632
16.374 16.440 16.506 16.572 16.638
16.381 16.447 16.513 16.579 16.645
16.387 16.453 16.520 16.586 16.652
16.394 16.460 16.526 16.592 16.658
16.400 16.467 16.533 16.599 16.665
16.407 16.473 16.539 16.605 16.671
16.414 16.480 16.546 16.612 16.678
16.420 16.486 16.553 16.619 16.685
16.427 16.493 16.559 16.625 16.691
16.434 16.500 16.566 16.632 16.698
2850 2860 2870 2880 2890
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
Z-226
°F
°F
Z
+ –
Revised Thermocouple Reference Tables
S
NONE ESTABLISHED
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
Platinum-10% Rhodium vs. Platinum
+ –
Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °F FREFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
2900 2910 2920 2930 2940
16.698 16.764 16.829 16.895 16.961
16.704 16.770 16.836 16.902 16.967
16.711 16.777 16.843 16.908 16.974
16.718 16.783 16.849 16.915 16.981
16.724 16.790 16.856 16.922 16.987
16.731 16.797 16.862 16.928 16.994
16.737 16.803 16.869 16.935 17.000
16.744 16.810 16.876 16.941 17.007
16.751 16.816 16.882 16.948 17.013
16.757 16.823 16.889 16.954 17.020
16.764 16.829 16.895 16.961 17.026
2900 2910 2920 2930 2940
3100 3110 3120 3130 3140
17.998 18.061 18.124 18.187 18.248
18.004 18.068 18.130 18.193 18.255
18.011 18.074 18.137 18.199 18.261
18.017 18.080 18.143 18.205 18.267
18.023 18.086 18.149 18.211 18.273
18.030 18.093 18.155 18.218 18.279
18.036 18.099 18.162 18.224 18.285
18.042 18.105 18.168 18.230 18.292
18.049 18.112 18.174 18.236 18.298
18.055 18.118 18.180 18.242 18.304
18.061 18.124 18.187 18.248 18.310
3100 3110 3120 3130 3140
2950 2960 2970 2980 2990
17.026 17.092 17.157 17.223 17.288
17.033 17.099 17.164 17.229 17.295
17.040 17.105 17.171 17.236 17.301
17.046 17.112 17.177 17.242 17.308
17.053 17.118 17.184 17.249 17.314
17.059 17.125 17.190 17.255 17.321
17.066 17.131 17.197 17.262 17.327
17.072 17.138 17.203 17.268 17.334
17.079 17.144 17.210 17.275 17.340
17.085 17.151 17.216 17.282 17.347
17.092 17.157 17.223 17.288 17.353
2950 2960 2970 2980 2990
3150 3160 3170 3180 3190
18.310 18.371 18.431 18.491 18.551
18.316 18.377 18.437 18.497 18.557
18.322 18.383 18.443 18.503 18.562
18.328 18.389 18.449 18.509 18.568
18.334 18.395 18.455 18.515 18.574
18.341 18.401 18.461 18.521 18.580
18.347 18.407 18.467 18.527 18.586
18.353 18.413 18.473 18.533 18.592
18.359 18.419 18.479 18.539 18.598
18.365 18.425 18.485 18.545 18.603
18.371 18.431 18.491 18.551 18.609
3150 3160 3170 3180 3190
3000 3010 3020 3030 3040
17.353 17.418 17.483 17.548 17.613
17.360 17.425 17.490 17.555 17.620
17.366 17.431 17.496 17.561 17.626
17.373 17.438 17.503 17.568 17.633
17.379 17.444 17.509 17.574 17.639
17.386 17.451 17.516 17.581 17.645
17.392 17.457 17.522 17.587 17.652
17.399 17.464 17.529 17.594 17.658
17.405 17.470 17.535 17.600 17.665
17.412 17.477 17.542 17.607 17.671
17.418 17.483 17.548 17.613 17.678
3000 3010 3020 3030 3040
3200 18.609 18.615 18.621 18.627 18.633 18.638 18.644 18.650 18.656 18.661 18.667 3200 3210 18.667 18.673 18.679 18.684 18.690 3210
3050 3060 3070 3080 3090
17.678 17.742 17.807 17.871 17.935
17.684 17.749 17.813 17.877 17.941
17.691 17.755 17.819 17.884 17.947
17.697 17.762 17.826 17.890 17.954
17.704 17.768 17.832 17.896 17.960
17.710 17.775 17.839 17.903 17.966
17.717 17.781 17.845 17.909 17.973
17.723 17.787 17.852 17.915 17.979
17.729 17.794 17.858 17.922 17.985
17.736 17.800 17.864 17.928 17.992
17.742 17.807 17.871 17.935 17.998
3050 3060 3070 3080 3090
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
Z-227
0
1
2
3
4
5
6
7
8
9
10
°F
°F
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F Extension Grade
Thermocouple Grade NONE ESTABLISHED
Platinum-13% Rhodium vs. Platinum
Revised Thermocouple Reference Tables
R
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts °F
-10
-9
-50
-8
-7
-6
-5
-4
-3
-2
-1
0
°F
°F
0
6
7
8
10
°F
-0.226 -0.224 -0.222 -0.220 -0.218 -0.216 -0.214 -0.212 -0.210
-50
400 410 420 430 440
1.508 1.558 1.607 1.658 1.708
1.513 1.563 1.612 1.663 1.713
1
1.518 1.568 1.617 1.668 1.718
2
1.523 1.572 1.622 1.673 1.723
3
1.528 1.577 1.627 1.678 1.728
4
1.533 1.582 1.632 1.683 1.733
5
1.538 1.587 1.638 1.688 1.739
1.543 1.592 1.643 1.693 1.744
1.548 1.597 1.648 1.698 1.749
1.553 1.602 1.653 1.703 1.754
9
1.558 1.607 1.658 1.708 1.759
400 410 420 430 440
-0.205 -0.183 -0.160 -0.136 -0.110
-40 -30 -20 -10 0
-0.210 -0.188 -0.165 -0.141 -0.116
-0.208 -0.185 -0.162 -0.138 -0.113
-0.188 -0.165 -0.141 -0.116 -0.090
-40 -30 -20 -10 0
450 460 470 480 490
1.759 1.810 1.861 1.913 1.965
1.764 1.815 1.867 1.918 1.970
1.769 1.820 1.872 1.923 1.975
1.774 1.825 1.877 1.929 1.981
1.779 1.831 1.882 1.934 1.986
1.784 1.836 1.887 1.939 1.991
1.790 1.841 1.892 1.944 1.996
1.795 1.846 1.898 1.949 2.002
1.800 1.851 1.903 1.955 2.007
1.805 1.856 1.908 1.960 2.012
1.810 1.861 1.913 1.965 2.017
450 460 470 480 490
0 10 20 30 40
-0.090 -0.063 -0.035 -0.006 0.024
-0.087 -0.084 -0.082 -0.079 -0.076 -0.073 -0.071 -0.068 -0.065 -0.063 -0.060 -0.057 -0.054 -0.051 -0.049 -0.046 -0.043 -0.040 -0.037 -0.035 -0.032 -0.029 -0.026 -0.023 -0.020 -0.017 -0.015 -0.012 -0.009 -0.006 -0.003 0.000 0.003 0.006 0.009 0.012 0.015 0.018 0.021 0.024 0.027 0.030 0.033 0.036 0.039 0.042 0.045 0.048 0.051 0.054
0 10 20 30 40
500 510 520 530 540
2.017 2.070 2.122 2.175 2.229
2.022 2.075 2.128 2.181 2.234
2.028 2.080 2.133 2.186 2.239
2.033 2.085 2.138 2.191 2.245
2.038 2.091 2.144 2.197 2.250
2.043 2.096 2.149 2.202 2.255
2.049 2.101 2.154 2.207 2.261
2.054 2.107 2.159 2.213 2.266
2.059 2.112 2.165 2.218 2.271
2.064 2.117 2.170 2.223 2.277
2.070 2.122 2.175 2.229 2.282
500 510 520 530 540
50 60 70 80 90
0.054 0.086 0.118 0.151 0.184
0.057 0.089 0.121 0.154 0.188
0.060 0.092 0.124 0.157 0.191
0.064 0.095 0.127 0.161 0.194
0.067 0.098 0.131 0.164 0.198
0.070 0.102 0.134 0.167 0.201
0.073 0.105 0.137 0.171 0.205
0.076 0.108 0.141 0.174 0.208
0.079 0.111 0.144 0.177 0.212
0.082 0.114 0.147 0.181 0.215
0.086 0.118 0.151 0.184 0.218
50 60 70 80 90
550 560 570 580 590
2.282 2.336 2.390 2.444 2.498
2.287 2.341 2.395 2.449 2.504
2.293 2.347 2.401 2.455 2.509
2.298 2.352 2.406 2.460 2.515
2.304 2.357 2.411 2.466 2.520
2.309 2.363 2.417 2.471 2.526
2.314 2.368 2.422 2.477 2.531
2.320 2.374 2.428 2.482 2.537
2.325 2.379 2.433 2.487 2.542
2.330 2.384 2.438 2.493 2.547
2.336 2.390 2.444 2.498 2.553
550 560 570 580 590
100 110 120 130 140
0.218 0.254 0.289 0.326 0.363
0.222 0.257 0.293 0.329 0.366
0.225 0.261 0.296 0.333 0.370
0.229 0.264 0.300 0.337 0.374
0.232 0.268 0.304 0.340 0.378
0.236 0.271 0.307 0.344 0.382
0.239 0.275 0.311 0.348 0.385
0.243 0.278 0.315 0.352 0.389
0.246 0.282 0.318 0.355 0.393
0.250 0.286 0.322 0.359 0.397
0.254 0.289 0.326 0.363 0.400
100 110 120 130 140
600 610 620 630 640
2.553 2.608 2.663 2.718 2.773
2.558 2.613 2.668 2.724 2.779
2.564 2.619 2.674 2.729 2.785
2.569 2.624 2.679 2.735 2.790
2.575 2.630 2.685 2.740 2.796
2.580 2.635 2.690 2.746 2.801
2.586 2.641 2.696 2.751 2.807
2.591 2.646 2.701 2.757 2.812
2.597 2.652 2.707 2.762 2.818
2.602 2.657 2.713 2.768 2.824
2.608 2.663 2.718 2.773 2.829
600 610 620 630 640
150 160 170 180 190
0.400 0.439 0.478 0.517 0.557
0.404 0.443 0.482 0.521 0.561
0.408 0.447 0.486 0.525 0.565
0.412 0.450 0.489 0.529 0.569
0.416 0.454 0.493 0.533 0.573
0.420 0.458 0.497 0.537 0.578
0.423 0.462 0.501 0.541 0.582
0.427 0.466 0.505 0.545 0.586
0.431 0.470 0.509 0.549 0.590
0.435 0.474 0.513 0.553 0.594
0.439 0.478 0.517 0.557 0.598
150 160 170 180 190
650 660 670 680 690
2.829 2.885 2.941 2.997 3.054
2.835 2.891 2.947 3.003 3.059
2.840 2.896 2.952 3.009 3.065
2.846 2.902 2.958 3.014 3.071
2.851 2.907 2.964 3.020 3.076
2.857 2.913 2.969 3.026 3.082
2.863 2.919 2.975 3.031 3.088
2.868 2.924 2.980 3.037 3.093
2.874 2.930 2.986 3.042 3.099
2.879 2.935 2.992 3.048 3.105
2.885 2.941 2.997 3.054 3.110
650 660 670 680 690
200 210 220 230 240
0.598 0.639 0.681 0.723 0.766
0.602 0.643 0.685 0.727 0.770
0.606 0.647 0.689 0.732 0.774
0.610 0.652 0.693 0.736 0.779
0.614 0.656 0.698 0.740 0.783
0.618 0.660 0.702 0.744 0.787
0.623 0.664 0.706 0.749 0.792
0.627 0.668 0.710 0.753 0.796
0.631 0.672 0.715 0.757 0.800
0.635 0.677 0.719 0.761 0.805
0.639 0.681 0.723 0.766 0.809
200 210 220 230 240
700 710 720 730 740
3.110 3.167 3.224 3.281 3.339
3.116 3.173 3.230 3.287 3.344
3.122 3.179 3.236 3.293 3.350
3.127 3.184 3.241 3.298 3.356
3.133 3.190 3.247 3.304 3.362
3.139 3.196 3.253 3.310 3.367
3.144 3.201 3.258 3.316 3.373
3.150 3.207 3.264 3.321 3.379
3.156 3.213 3.270 3.327 3.385
3.161 3.218 3.276 3.333 3.390
3.167 3.224 3.281 3.339 3.396
700 710 720 730 740
250 260 270 280 290
0.809 0.853 0.897 0.941 0.986
0.813 0.857 0.901 0.946 0.991
0.818 0.861 0.906 0.950 0.995
0.822 0.866 0.910 0.955 1.000
0.826 0.870 0.915 0.959 1.005
0.831 0.875 0.919 0.964 1.009
0.835 0.879 0.923 0.968 1.014
0.839 0.883 0.928 0.973 1.018
0.844 0.888 0.932 0.977 1.023
0.848 0.892 0.937 0.982 1.027
0.853 0.897 0.941 0.986 1.032
250 260 270 280 290
750 760 770 780 790
3.396 3.454 3.512 3.570 3.628
3.402 3.460 3.517 3.576 3.634
3.408 3.465 3.523 3.581 3.640
3.413 3.471 3.529 3.587 3.645
3.419 3.477 3.535 3.593 3.651
3.425 3.483 3.541 3.599 3.657
3.431 3.489 3.546 3.605 3.663
3.437 3.494 3.552 3.610 3.669
3.442 3.500 3.558 3.616 3.675
3.448 3.506 3.564 3.622 3.680
3.454 3.512 3.570 3.628 3.686
750 760 770 780 790
300 310 320 330 340
1.032 1.078 1.124 1.171 1.218
1.036 1.082 1.129 1.175 1.223
1.041 1.087 1.133 1.180 1.227
1.046 1.092 1.138 1.185 1.232
1.050 1.096 1.143 1.190 1.237
1.055 1.101 1.147 1.194 1.242
1.059 1.105 1.152 1.199 1.246
1.064 1.110 1.157 1.204 1.251
1.069 1.115 1.161 1.208 1.256
1.073 1.119 1.166 1.213 1.261
1.078 1.124 1.171 1.218 1.265
300 310 320 330 340
800 810 820 830 840
3.686 3.745 3.803 3.862 3.921
3.692 3.751 3.809 3.868 3.927
3.698 3.757 3.815 3.874 3.933
3.704 3.762 3.821 3.880 3.939
3.710 3.768 3.827 3.886 3.945
3.716 3.774 3.833 3.892 3.951
3.721 3.780 3.839 3.898 3.957
3.727 3.786 3.845 3.904 3.963
3.733 3.792 3.851 3.909 3.969
3.739 3.798 3.856 3.915 3.975
3.745 3.803 3.862 3.921 3.980
800 810 820 830 840
350 360 370 380 390
1.265 1.313 1.361 1.410 1.459
1.270 1.318 1.366 1.415 1.464
1.275 1.323 1.371 1.420 1.469
1.280 1.328 1.376 1.425 1.473
1.284 1.332 1.381 1.429 1.478
1.289 1.337 1.386 1.434 1.483
1.294 1.342 1.390 1.439 1.488
1.299 1.347 1.395 1.444 1.493
1.304 1.352 1.400 1.449 1.498
1.308 1.356 1.405 1.454 1.503
1.313 1.361 1.410 1.459 1.508
350 360 370 380 390
850 860 870 880 890
3.980 4.040 4.099 4.159 4.219
3.986 4.046 4.105 4.165 4.225
3.992 4.052 4.111 4.171 4.231
3.998 4.058 4.117 4.177 4.237
4.004 4.064 4.123 4.183 4.243
4.010 4.069 4.129 4.189 4.249
4.016 4.075 4.135 4.195 4.255
4.022 4.081 4.141 4.201 4.261
4.028 4.087 4.147 4.207 4.267
4.034 4.093 4.153 4.213 4.273
4.040 4.099 4.159 4.219 4.279
850 860 870 880 890
°F
0
6
7
8
10
°F
°F
0
6
7
8
10
°F
1
2
-0.203 -0.181 -0.158 -0.133 -0.108
3
-0.201 -0.179 -0.155 -0.131 -0.105
4
-0.199 -0.176 -0.153 -0.128 -0.103
5
-0.197 -0.174 -0.150 -0.126 -0.100
-0.194 -0.172 -0.148 -0.123 -0.097
-0.192 -0.169 -0.145 -0.121 -0.095
-0.190 -0.167 -0.143 -0.118 -0.092
9
Z-228
1
2
3
4
5
9
Z
+ –
Revised Thermocouple Reference Tables
R
NONE ESTABLISHED
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°F
0
1
900 910 920 930 940
4.279 4.339 4.399 4.459 4.520
4.285 4.345 4.405 4.465 4.526
4.291 4.351 4.411 4.471 4.532
4.297 4.357 4.417 4.477 4.538
4.303 4.363 4.423 4.483 4.544
950 960 970 980 990
4.580 4.641 4.702 4.763 4.824
4.586 4.647 4.708 4.769 4.831
4.593 4.653 4.714 4.775 4.837
4.599 4.659 4.720 4.782 4.843
1000 1010 1020 1030 1040
4.886 4.947 5.009 5.071 5.133
4.892 4.954 5.015 5.077 5.139
4.898 4.960 5.021 5.083 5.145
1050 1060 1070 1080 1090
5.195 5.257 5.320 5.382 5.445
5.201 5.264 5.326 5.389 5.451
1100 1110 1120 1130 1140
5.508 5.571 5.634 5.697 5.761
1150 1160 1170 1180 1190
Thermoelectric Voltage in Millivolts 10
°F
°F
0
6
7
8
4.309 4.369 4.429 4.489 4.550
4.315 4.375 4.435 4.495 4.556
4.321 4.381 4.441 4.502 4.562
4.327 4.387 4.447 4.508 4.568
4.333 4.393 4.453 4.514 4.574
4.339 4.399 4.459 4.520 4.580
900 910 920 930 940
1400 1410 1420 1430 1440
7.461 7.529 7.596 7.664 7.732
7.468 7.535 7.603 7.671 7.739
7.475 7.542 7.610 7.677 7.745
7.481 7.549 7.616 7.684 7.752
7.488 7.556 7.623 7.691 7.759
7.495 7.562 7.630 7.698 7.766
7.502 7.569 7.637 7.705 7.772
7.508 7.576 7.644 7.711 7.779
7.515 7.583 7.650 7.718 7.786
7.522 7.589 7.657 7.725 7.793
7.529 7.596 7.664 7.732 7.800
1400 1410 1420 1430 1440
4.605 4.666 4.727 4.788 4.849
4.611 4.672 4.733 4.794 4.855
4.617 4.678 4.739 4.800 4.861
4.623 4.684 4.745 4.806 4.867
4.629 4.690 4.751 4.812 4.874
4.635 4.696 4.757 4.818 4.880
4.641 4.702 4.763 4.824 4.886
950 960 970 980 990
1450 1460 1470 1480 1490
7.800 7.868 7.936 8.005 8.073
7.807 7.875 7.943 8.011 8.080
7.813 7.882 7.950 8.018 8.087
7.820 7.888 7.957 8.025 8.094
7.827 7.895 7.964 8.032 8.101
7.834 7.902 7.970 8.039 8.108
7.841 7.909 7.977 8.046 8.114
7.847 7.916 7.984 8.053 8.121
7.854 7.922 7.991 8.059 8.128
7.861 7.929 7.998 8.066 8.135
7.868 7.936 8.005 8.073 8.142
1450 1460 1470 1480 1490
4.904 4.966 5.028 5.090 5.152
4.910 4.972 5.034 5.096 5.158
4.917 4.978 5.040 5.102 5.164
4.923 4.984 5.046 5.108 5.170
4.929 4.991 5.052 5.114 5.176
4.935 4.997 5.059 5.121 5.183
4.941 5.003 5.065 5.127 5.189
4.947 5.009 5.071 5.133 5.195
1000 1010 1020 1030 1040
1500 1510 1520 1530 1540
8.142 8.211 8.280 8.349 8.418
8.149 8.218 8.287 8.356 8.425
8.156 8.225 8.294 8.363 8.432
8.163 8.232 8.301 8.370 8.439
8.169 8.238 8.308 8.377 8.446
8.176 8.245 8.314 8.384 8.453
8.183 8.252 8.321 8.391 8.460
8.190 8.259 8.328 8.398 8.467
8.197 8.266 8.335 8.405 8.474
8.204 8.273 8.342 8.411 8.481
8.211 8.280 8.349 8.418 8.488
1500 1510 1520 1530 1540
5.207 5.270 5.332 5.395 5.458
5.214 5.276 5.338 5.401 5.464
5.220 5.282 5.345 5.407 5.470
5.226 5.289 5.351 5.414 5.476
5.232 5.295 5.357 5.420 5.483
5.239 5.301 5.364 5.426 5.489
5.245 5.307 5.370 5.432 5.495
5.251 5.313 5.376 5.439 5.502
5.257 5.320 5.382 5.445 5.508
1050 1060 1070 1080 1090
1550 1560 1570 1580 1590
8.488 8.557 8.627 8.697 8.767
8.495 8.564 8.634 8.704 8.774
8.502 8.571 8.641 8.711 8.781
8.509 8.578 8.648 8.718 8.788
8.516 8.585 8.655 8.725 8.795
8.523 8.592 8.662 8.732 8.802
8.530 8.599 8.669 8.739 8.809
8.537 8.606 8.676 8.746 8.816
8.544 8.613 8.683 8.753 8.823
8.551 8.620 8.690 8.760 8.830
8.557 8.627 8.697 8.767 8.837
1550 1560 1570 1580 1590
5.514 5.577 5.640 5.704 5.767
5.520 5.583 5.647 5.710 5.773
5.527 5.590 5.653 5.716 5.780
5.533 5.596 5.659 5.723 5.786
5.539 5.602 5.666 5.729 5.792
5.546 5.609 5.672 5.735 5.799
5.552 5.615 5.678 5.742 5.805
5.558 5.621 5.685 5.748 5.812
5.565 5.628 5.691 5.754 5.818
5.571 5.634 5.697 5.761 5.824
1100 1110 1120 1130 1140
1600 1610 1620 1630 1640
8.837 8.908 8.978 9.049 9.120
8.844 8.915 8.985 9.056 9.127
8.852 8.922 8.992 9.063 9.134
8.859 8.929 8.999 9.070 9.141
8.866 8.936 9.007 9.077 9.148
8.873 8.943 9.014 9.084 9.155
8.880 8.950 9.021 9.091 9.162
8.887 8.957 9.028 9.098 9.169
8.894 8.964 9.035 9.106 9.176
8.901 8.971 9.042 9.113 9.184
8.908 8.978 9.049 9.120 9.191
1600 1610 1620 1630 1640
5.824 5.888 5.952 6.016 6.080
5.831 5.894 5.958 6.022 6.086
5.837 5.901 5.965 6.029 6.093
5.843 5.907 5.971 6.035 6.099
5.850 5.913 5.977 6.041 6.106
5.856 5.920 5.984 6.048 6.112
5.862 5.926 5.990 6.054 6.119
5.869 5.933 5.997 6.061 6.125
5.875 5.939 6.003 6.067 6.131
5.882 5.945 6.009 6.074 6.138
5.888 5.952 6.016 6.080 6.144
1150 1160 1170 1180 1190
1650 1660 1670 1680 1690
9.191 9.262 9.333 9.404 9.476
9.198 9.269 9.340 9.411 9.483
9.205 9.276 9.347 9.419 9.490
9.212 9.283 9.354 9.426 9.497
9.219 9.290 9.361 9.433 9.504
9.226 9.297 9.369 9.440 9.512
9.233 9.304 9.376 9.447 9.519
9.240 9.312 9.383 9.454 9.526
9.248 9.319 9.390 9.461 9.533
9.255 9.326 9.397 9.469 9.540
9.262 9.333 9.404 9.476 9.547
1650 1660 1670 1680 1690
1200 1210 1220 1230 1240
6.144 6.209 6.273 6.338 6.403
6.151 6.215 6.280 6.345 6.409
6.157 6.222 6.286 6.351 6.416
6.164 6.228 6.293 6.358 6.422
6.170 6.235 6.299 6.364 6.429
6.176 6.241 6.306 6.370 6.435
6.183 6.247 6.312 6.377 6.442
6.189 6.254 6.319 6.383 6.448
6.196 6.260 6.325 6.390 6.455
6.202 6.267 6.332 6.396 6.461
6.209 6.273 6.338 6.403 6.468
1200 1210 1220 1230 1240
1700 1710 1720 1730 1740
9.547 9.619 9.691 9.763 9.835
9.555 9.626 9.698 9.770 9.843
9.562 9.634 9.706 9.778 9.850
9.569 9.641 9.713 9.785 9.857
9.576 9.648 9.720 9.792 9.864
9.583 9.655 9.727 9.799 9.872
9.590 9.662 9.734 9.806 9.879
9.598 9.670 9.742 9.814 9.886
9.605 9.677 9.749 9.821 9.893
9.612 9.684 9.756 9.828 9.900
9.619 9.691 9.763 9.835 9.908
1700 1710 1720 1730 1740
1250 1260 1270 1280 1290
6.468 6.533 6.598 6.664 6.730
6.474 6.540 6.605 6.671 6.736
6.481 6.546 6.612 6.677 6.743
6.488 6.553 6.618 6.684 6.749
6.494 6.559 6.625 6.690 6.756
6.501 6.566 6.631 6.697 6.762
6.507 6.572 6.638 6.703 6.769
6.514 6.579 6.644 6.710 6.776
6.520 6.585 6.651 6.716 6.782
6.527 6.592 6.657 6.723 6.789
6.533 6.598 6.664 6.730 6.795
1250 1260 1270 1280 1290
1750 9.908 9.915 9.922 1760 9.980 9.987 9.995 1770 10.053 10.060 10.067 1780 10.126 10.133 10.140 1790 10.198 10.206 10.213
9.929 10.002 10.075 10.147 10.220
9.937 10.009 10.082 10.155 10.228
9.944 10.016 10.089 10.162 10.235
9.951 10.024 10.096 10.169 10.242
9.958 10.031 10.104 10.177 10.250
9.966 10.038 10.111 10.184 10.257
9.973 10.046 10.118 10.191 10.264
9.980 10.053 10.126 10.198 10.271
1750 1760 1770 1780 1790
1300 1310 1320 1330 1340
6.795 6.861 6.927 6.994 7.060
6.802 6.868 6.934 7.000 7.067
6.809 6.874 6.941 7.007 7.073
6.815 6.881 6.947 7.013 7.080
6.822 6.888 6.954 7.020 7.086
6.828 6.894 6.960 7.027 7.093
6.835 6.901 6.967 7.033 7.100
6.841 6.907 6.974 7.040 7.106
6.848 6.914 6.980 7.047 7.113
6.855 6.921 6.987 7.053 7.120
6.861 6.927 6.994 7.060 7.126
1300 1310 1320 1330 1340
1800 1810 1820 1830 1840
10.271 10.345 10.418 10.491 10.565
10.279 10.352 10.425 10.499 10.572
10.286 10.359 10.433 10.506 10.580
10.293 10.367 10.440 10.513 10.587
10.301 10.374 10.447 10.521 10.594
10.308 10.381 10.455 10.528 10.602
10.315 10.389 10.462 10.535 10.609
10.323 10.396 10.469 10.543 10.616
10.330 10.403 10.477 10.550 10.624
10.337 10.411 10.484 10.557 10.631
10.345 10.418 10.491 10.565 10.638
1800 1810 1820 1830 1840
1350 1360 1370 1380 1390
7.126 7.193 7.260 7.327 7.394
7.133 7.200 7.267 7.334 7.401
7.140 7.206 7.273 7.340 7.407
7.146 7.213 7.280 7.347 7.414
7.153 7.220 7.287 7.354 7.421
7.160 7.226 7.293 7.360 7.428
7.166 7.233 7.300 7.367 7.434
7.173 7.240 7.307 7.374 7.441
7.180 7.247 7.313 7.381 7.448
7.186 7.253 7.320 7.387 7.454
7.193 7.260 7.327 7.394 7.461
1350 1360 1370 1380 1390
1850 1860 1870 1880 1890
10.638 10.712 10.786 10.860 10.934
10.646 10.720 10.794 10.868 10.942
10.653 10.727 10.801 10.875 10.949
10.661 10.734 10.808 10.883 10.957
10.668 10.742 10.816 10.890 10.964
10.675 10.749 10.823 10.897 10.972
10.683 10.757 10.831 10.905 10.979
10.690 10.764 10.838 10.912 10.986
10.698 10.771 10.845 10.920 10.994
10.705 10.779 10.853 10.927 11.001
10.712 10.786 10.860 10.934 11.009
1850 1860 1870 1880 1890
°F
0
6
7
8
°F
°F
0
1
2
3
4
5
6
7
8
9
10
4
5
Extension Grade
8
3
4
+ –
7
2
3
Platinum-13% Rhodium vs. Platinum
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
6
1
2
Thermocouple Grade
5
9
9
10
Z-229
1
2
3
4
5
9
10
°F
°F
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F Extension Grade
Thermocouple Grade NONE ESTABLISHED
Platinum-13% Rhodium vs. Platinum
Revised Thermocouple Reference Tables
R
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts °F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
1900 1910 1920 1930 1940
11.009 11.083 11.158 11.233 11.307
11.016 11.091 11.165 11.240 11.315
11.024 11.098 11.173 11.247 11.322
11.031 11.106 11.180 11.255 11.330
11.039 11.113 11.188 11.262 11.337
11.046 11.121 11.195 11.270 11.345
11.053 11.128 11.203 11.277 11.352
11.061 11.135 11.210 11.285 11.360
11.068 11.143 11.218 11.292 11.367
11.076 11.150 11.225 11.300 11.375
11.083 11.158 11.233 11.307 11.382
1900 1910 1920 1930 1940
2400 2410 2420 2430 2440
14.848 14.926 15.005 15.083 15.161
14.856 14.934 15.012 15.091 15.169
14.864 14.942 15.020 15.099 15.177
14.871 14.950 15.028 15.106 15.185
14.879 14.958 15.036 15.114 15.193
14.887 14.965 15.044 15.122 15.200
14.895 14.973 15.052 15.130 15.208
14.903 14.981 15.059 15.138 15.216
14.911 14.989 15.067 15.146 15.224
14.918 14.997 15.075 15.153 15.232
14.926 15.005 15.083 15.161 15.240
2400 2410 2420 2430 2440
1950 1960 1970 1980 1990
11.382 11.457 11.533 11.608 11.683
11.390 11.465 11.540 11.615 11.691
11.397 11.472 11.548 11.623 11.698
11.405 11.480 11.555 11.631 11.706
11.412 11.487 11.563 11.638 11.714
11.420 11.495 11.570 11.646 11.721
11.427 11.502 11.578 11.653 11.729
11.435 11.510 11.585 11.661 11.736
11.442 11.518 11.593 11.668 11.744
11.450 11.525 11.600 11.676 11.751
11.457 11.533 11.608 11.683 11.759
1950 1960 1970 1980 1990
2450 2460 2470 2480 2490
15.240 15.318 15.397 15.475 15.553
15.248 15.326 15.404 15.483 15.561
15.255 15.334 15.412 15.491 15.569
15.263 15.342 15.420 15.499 15.577
15.271 15.349 15.428 15.506 15.585
15.279 15.357 15.436 15.514 15.593
15.287 15.365 15.444 15.522 15.601
15.295 15.373 15.451 15.530 15.608
15.302 15.381 15.459 15.538 15.616
15.310 15.389 15.467 15.546 15.624
15.318 15.397 15.475 15.553 15.632
2450 2460 2470 2480 2490
2000 2010 2020 2030 2040
11.759 11.834 11.910 11.986 12.062
11.766 11.842 11.918 11.994 12.070
11.774 11.850 11.925 12.001 12.077
11.782 11.857 11.933 12.009 12.085
11.789 11.865 11.941 12.016 12.092
11.797 11.872 11.948 12.024 12.100
11.804 11.880 11.956 12.032 12.108
11.812 11.888 11.963 12.039 12.115
11.819 11.895 11.971 12.047 12.123
11.827 11.903 11.979 12.054 12.131
11.834 11.910 11.986 12.062 12.138
2000 2010 2020 2030 2040
2500 2510 2520 2530 2540
15.632 15.710 15.789 15.867 15.946
15.640 15.718 15.797 15.875 15.954
15.648 15.726 15.805 15.883 15.962
15.655 15.734 15.812 15.891 15.969
15.663 15.742 15.820 15.899 15.977
15.671 15.750 15.828 15.907 15.985
15.679 15.758 15.836 15.915 15.993
15.687 15.765 15.844 15.922 16.001
15.695 15.773 15.852 15.930 16.009
15.703 15.781 15.860 15.938 16.017
15.710 15.789 15.867 15.946 16.024
2500 2510 2520 2530 2540
2050 2060 2070 2080 2090
12.138 12.214 12.291 12.367 12.443
12.146 12.222 12.298 12.375 12.451
12.153 12.230 12.306 12.382 12.459
12.161 12.237 12.313 12.390 12.466
12.169 12.245 12.321 12.397 12.474
12.176 12.252 12.329 12.405 12.482
12.184 12.260 12.336 12.413 12.489
12.191 12.268 12.344 12.420 12.497
12.199 12.275 12.352 12.428 12.505
12.207 12.283 12.359 12.436 12.512
12.214 12.291 12.367 12.443 12.520
2050 2060 2070 2080 2090
2550 2560 2570 2580 2590
16.024 16.103 16.181 16.260 16.338
16.032 16.111 16.189 16.268 16.346
16.040 16.119 16.197 16.276 16.354
16.048 16.126 16.205 16.283 16.362
16.056 16.134 16.213 16.291 16.370
16.064 16.142 16.221 16.299 16.378
16.071 16.150 16.228 16.307 16.385
16.079 16.158 16.236 16.315 16.393
16.087 16.166 16.244 16.323 16.401
16.095 16.174 16.252 16.330 16.409
16.103 16.181 16.260 16.338 16.417
2550 2560 2570 2580 2590
2100 2110 2120 2130 2140
12.520 12.597 12.673 12.750 12.827
12.528 12.604 12.681 12.758 12.835
12.535 12.612 12.689 12.765 12.842
12.543 12.620 12.696 12.773 12.850
12.551 12.627 12.704 12.781 12.858
12.558 12.635 12.712 12.788 12.865
12.566 12.643 12.719 12.796 12.873
12.574 12.650 12.727 12.804 12.881
12.581 12.658 12.735 12.812 12.889
12.589 12.666 12.742 12.819 12.896
12.597 12.673 12.750 12.827 12.904
2100 2110 2120 2130 2140
2600 2610 2620 2630 2640
16.417 16.495 16.574 16.652 16.731
16.425 16.503 16.582 16.660 16.738
16.432 16.511 16.589 16.668 16.746
16.440 16.519 16.597 16.676 16.754
16.448 16.527 16.605 16.683 16.762
16.456 16.534 16.613 16.691 16.770
16.464 16.542 16.621 16.699 16.778
16.472 16.550 16.629 16.707 16.785
16.480 16.558 16.636 16.715 16.793
16.487 16.566 16.644 16.723 16.801
16.495 16.574 16.652 16.731 16.809
2600 2610 2620 2630 2640
2150 2160 2170 2180 2190
12.904 12.981 13.058 13.135 13.213
12.912 12.989 13.066 13.143 13.220
12.919 12.996 13.073 13.151 13.228
12.927 13.004 13.081 13.158 13.236
12.935 13.012 13.089 13.166 13.243
12.942 13.019 13.097 13.174 13.251
12.950 13.027 13.104 13.182 13.259
12.958 13.035 13.112 13.189 13.267
12.966 13.043 13.120 13.197 13.274
12.973 13.050 13.128 13.205 13.282
12.981 13.058 13.135 13.213 13.290
2150 2160 2170 2180 2190
2650 2660 2670 2680 2690
16.809 16.887 16.966 17.044 17.122
16.817 16.895 16.973 17.052 17.130
16.825 16.903 16.981 17.060 17.138
16.832 16.911 16.989 17.067 17.146
16.840 16.919 16.997 17.075 17.154
16.848 16.926 17.005 17.083 17.161
16.856 16.934 17.013 17.091 17.169
16.864 16.942 17.020 17.099 17.177
16.872 16.950 17.028 17.107 17.185
16.879 16.958 17.036 17.114 17.193
16.887 16.966 17.044 17.122 17.200
2650 2660 2670 2680 2690
2200 2210 2220 2230 2240
13.290 13.367 13.445 13.522 13.600
13.298 13.375 13.452 13.530 13.608
13.305 13.383 13.460 13.538 13.615
13.313 13.390 13.468 13.545 13.623
13.321 13.398 13.476 13.553 13.631
13.329 13.406 13.483 13.561 13.639
13.336 13.414 13.491 13.569 13.646
13.344 13.421 13.499 13.577 13.654
13.352 13.429 13.507 13.584 13.662
13.359 13.437 13.514 13.592 13.670
13.367 13.445 13.522 13.600 13.677
2200 2210 2220 2230 2240
2700 2710 2720 2730 2740
17.200 17.279 17.357 17.435 17.513
17.208 17.286 17.365 17.443 17.521
17.216 17.294 17.373 17.451 17.529
17.224 17.302 17.380 17.458 17.537
17.232 17.310 17.388 17.466 17.544
17.240 17.318 17.396 17.474 17.552
17.247 17.326 17.404 17.482 17.560
17.255 17.333 17.412 17.490 17.568
17.263 17.341 17.419 17.498 17.576
17.271 17.349 17.427 17.505 17.583
17.279 17.357 17.435 17.513 17.591
2700 2710 2720 2730 2740
2250 2260 2270 2280 2290
13.677 13.755 13.833 13.911 13.989
13.685 13.763 13.841 13.919 13.996
13.693 13.771 13.848 13.926 14.004
13.701 13.778 13.856 13.934 14.012
13.709 13.786 13.864 13.942 14.020
13.716 13.794 13.872 13.950 14.028
13.724 13.802 13.880 13.957 14.035
13.732 13.810 13.887 13.965 14.043
13.740 13.817 13.895 13.973 14.051
13.747 13.825 13.903 13.981 14.059
13.755 13.833 13.911 13.989 14.066
2250 2260 2270 2280 2290
2750 2760 2770 2780 2790
17.591 17.669 17.747 17.825 17.903
17.599 17.677 17.755 17.833 17.911
17.607 17.685 17.763 17.841 17.919
17.615 17.693 17.771 17.849 17.926
17.622 17.700 17.778 17.856 17.934
17.630 17.708 17.786 17.864 17.942
17.638 17.716 17.794 17.872 17.950
17.646 17.724 17.802 17.880 17.958
17.654 17.732 17.810 17.888 17.965
17.661 17.739 17.817 17.895 17.973
17.669 17.747 17.825 17.903 17.981
2750 2760 2770 2780 2790
2300 2310 2320 2330 2340
14.066 14.144 14.222 14.300 14.379
14.074 14.152 14.230 14.308 14.386
14.082 14.160 14.238 14.316 14.394
14.090 14.168 14.246 14.324 14.402
14.098 14.176 14.254 14.332 14.410
14.105 14.183 14.261 14.340 14.418
14.113 14.191 14.269 14.347 14.425
14.121 14.199 14.277 14.355 14.433
14.129 14.207 14.285 14.363 14.441
14.137 14.215 14.293 14.371 14.449
14.144 14.222 14.300 14.379 14.457
2300 2310 2320 2330 2340
2800 2810 2820 2830 2840
17.981 18.059 18.137 18.214 18.292
17.989 18.067 18.144 18.222 18.300
17.997 18.074 18.152 18.230 18.307
18.004 18.082 18.160 18.238 18.315
18.012 18.090 18.168 18.245 18.323
18.020 18.098 18.175 18.253 18.331
18.028 18.105 18.183 18.261 18.338
18.035 18.113 18.191 18.269 18.346
18.043 18.121 18.199 18.276 18.354
18.051 18.129 18.206 18.284 18.362
18.059 18.137 18.214 18.292 18.369
2800 2810 2820 2830 2840
2350 2360 2370 2380 2390
14.457 14.535 14.613 14.691 14.770
14.465 14.543 14.621 14.699 14.777
14.472 14.551 14.629 14.707 14.785
14.480 14.558 14.637 14.715 14.793
14.488 14.566 14.644 14.723 14.801
14.496 14.574 14.652 14.730 14.809
14.504 14.582 14.660 14.738 14.817
14.511 14.590 14.668 14.746 14.824
14.519 14.597 14.676 14.754 14.832
14.527 14.605 14.683 14.762 14.840
14.535 14.613 14.691 14.770 14.848
2350 2360 2370 2380 2390
2850 2860 2870 2880 2890
18.369 18.447 18.524 18.602 18.679
18.377 18.455 18.532 18.610 18.687
18.385 18.462 18.540 18.617 18.695
18.393 18.470 18.548 18.625 18.702
18.400 18.478 18.555 18.633 18.710
18.408 18.486 18.563 18.640 18.718
18.416 18.493 18.571 18.648 18.725
18.424 18.501 18.579 18.656 18.733
18.431 18.509 18.586 18.664 18.741
18.439 18.517 18.594 18.671 18.749
18.447 18.524 18.602 18.679 18.756
2850 2860 2870 2880 2890
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
Z-230
°F
°F
Z
+ –
Revised Thermocouple Reference Tables
R
NONE ESTABLISHED
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
Platinum-13% Rhodium vs. Platinum + – Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 2642°F 0 to 1450°C Extension Grade 32 to 300°F 0 to 150°C LIMITS OF ERROR (whichever is greater) Standard: 1.5°C or 0.25% Special: 0.6°C or 0.1% COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
2900 2910 2920 2930 2940
18.756 18.834 18.911 18.988 19.065
18.764 18.841 18.918 18.995 19.072
18.772 18.849 18.926 19.003 19.080
18.779 18.857 18.934 19.011 19.088
18.787 18.864 18.941 19.018 19.095
18.795 18.872 18.949 19.026 19.103
18.803 18.880 18.957 19.034 19.111
18.810 18.887 18.965 19.042 19.118
18.818 18.895 18.972 19.049 19.126
18.826 18.903 18.980 19.057 19.134
18.834 18.911 18.988 19.065 19.141
2900 2910 2920 2930 2940
3100 3110 3120 3130 3140
20.281 20.356 20.430 20.503 20.576
20.289 20.363 20.437 20.510 20.583
20.296 20.371 20.444 20.518 20.591
20.304 20.378 20.452 20.525 20.598
20.311 20.385 20.459 20.532 20.605
20.319 20.393 20.466 20.540 20.612
20.326 20.400 20.474 20.547 20.620
20.333 20.407 20.481 20.554 20.627
20.341 20.415 20.488 20.562 20.634
20.348 20.422 20.496 20.569 20.641
20.356 20.430 20.503 20.576 20.649
3100 3110 3120 3130 3140
2950 2960 2970 2980 2990
19.141 19.218 19.295 19.372 19.448
19.149 19.226 19.303 19.379 19.456
19.157 19.234 19.310 19.387 19.463
19.165 19.241 19.318 19.395 19.471
19.172 19.249 19.326 19.402 19.479
19.180 19.257 19.333 19.410 19.486
19.188 19.264 19.341 19.418 19.494
19.195 19.272 19.349 19.425 19.502
19.203 19.280 19.356 19.433 19.509
19.211 19.287 19.364 19.440 19.517
19.218 19.295 19.372 19.448 19.525
2950 2960 2970 2980 2990
3150 3160 3170 3180 3190
20.649 20.721 20.792 20.863 20.933
20.656 20.728 20.799 20.870 20.940
20.663 20.735 20.806 20.877 20.947
20.670 20.742 20.813 20.884 20.954
20.678 20.749 20.821 20.891 20.961
20.685 20.756 20.828 20.898 20.968
20.692 20.764 20.835 20.905 20.975
20.699 20.771 20.842 20.912 20.982
20.706 20.778 20.849 20.919 20.989
20.714 20.785 20.856 20.926 20.996
20.721 20.792 20.863 20.933 21.003
3150 3160 3170 3180 3190
3000 3010 3020 3030 3040
19.525 19.601 19.677 19.753 19.829
19.532 19.609 19.685 19.761 19.837
19.540 19.616 19.692 19.769 19.845
19.547 19.624 19.700 19.776 19.852
19.555 19.631 19.708 19.784 19.860
19.563 19.639 19.715 19.791 19.867
19.570 19.647 19.723 19.799 19.875
19.578 19.654 19.730 19.807 19.882
19.586 19.662 19.738 19.814 19.890
19.593 19.670 19.746 19.822 19.898
19.601 19.677 19.753 19.829 19.905
3000 3010 3020 3030 3040
3200 21.003 21.010 21.016 21.023 21.030 21.037 21.044 21.051 21.058 21.065 21.071 3200 3210 21.071 21.078 21.085 21.092 21.099 3210
3050 3060 3070 3080 3090
19.905 19.981 20.056 20.132 20.207
19.913 19.989 20.064 20.139 20.214
19.920 19.996 20.072 20.147 20.222
19.928 20.004 20.079 20.154 20.229
19.936 20.011 20.087 20.162 20.237
19.943 20.019 20.094 20.169 20.244
19.951 20.026 20.102 20.177 20.252
19.958 20.034 20.109 20.184 20.259
19.966 20.041 20.117 20.192 20.266
19.973 20.049 20.124 20.199 20.274
19.981 20.056 20.132 20.207 20.281
3050 3060 3070 3080 3090
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
Z-231
0
1
2
3
4
5
6
7
8
9
10
°F
°F
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 3092°F 0 to 1700°C Extension Grade 32 to 212°F 0 to 100°C LIMITS OF ERROR (whichever is greater) Standard: 0.5°C over 800°C Special: NOT ESTABLISHED COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature; Common Use in Glass Industry TEMPERATURE IN DEGREES °F Extension REFERENCE JUNCTION AT 32°F Grade
Thermocouple Grade
NONE ESTABLISHED
Platinum-30% Rhodium vs. Platinum-6% Rhodium
Revised Thermocouple Reference Tables
B
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts °F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
6
7
8
10
°F
0.479 0.497 0.516 0.534 0.553
0.481 0.499 0.517 0.536 0.555
0.483 0.501 0.519 0.538 0.557
0.485 0.503 0.521 0.540 0.559
0.486 0.505 0.523 0.542 0.561
0.488 0.506 0.525 0.544 0.563
0.490 0.508 0.527 0.546 0.565
0.492 0.510 0.529 0.547 0.567
0.494 0.512 0.530 0.549 0.569
0.495 0.514 0.532 0.551 0.570
0.497 0.516 0.534 0.553 0.572
600 610 620 630 640
30 40
0.000 0.000 0.000 0.000 -0.001 -0.001 -0.001 -0.001 -0.001 -0.001 -0.001 -0.001 -0.001 -0.001 -0.001 -0.002 -0.002 -0.002 -0.002 -0.002
30 40
600 610 620 630 640
50 60 70 80 90
-0.002 -0.002 -0.003 -0.002 -0.002
100 110 120 130 140
1
2
3
4
5
9
-0.002 -0.003 -0.003 -0.002 -0.002
-0.002 -0.003 -0.003 -0.002 -0.002
-0.002 -0.003 -0.003 -0.002 -0.001
-0.002 -0.003 -0.003 -0.002 -0.001
-0.002 -0.003 -0.002 -0.002 -0.001
-0.002 -0.003 -0.002 -0.002 -0.001
-0.002 -0.003 -0.002 -0.002 -0.001
-0.002 -0.003 -0.002 -0.002 -0.001
50 60 70 80 90
650 660 670 680 690
0.572 0.592 0.612 0.632 0.653
0.574 0.594 0.614 0.634 0.655
0.576 0.596 0.616 0.636 0.657
0.578 0.598 0.618 0.638 0.659
0.580 0.600 0.620 0.640 0.661
0.582 0.602 0.622 0.642 0.663
0.584 0.604 0.624 0.644 0.665
0.586 0.606 0.626 0.646 0.667
0.588 0.608 0.628 0.648 0.669
0.590 0.610 0.630 0.650 0.671
0.592 0.612 0.632 0.653 0.673
650 660 670 680 690
-0.001 -0.001 -0.001 -0.001 0.000 0.000 0.001 0.001 0.002 0.002 0.002 0.002 0.004 0.004 0.004 0.005 0.006 0.006 0.007 0.007
0.000 0.001 0.003 0.005 0.007
0.000 0.001 0.003 0.005 0.007
0.000 0.001 0.003 0.005 0.008
0.000 0.001 0.003 0.005 0.008
0.000 0.002 0.003 0.006 0.008
0.000 0.002 0.004 0.006 0.009
0.000 0.002 0.004 0.006 0.009
100 110 120 130 140
700 710 720 730 740
0.673 0.694 0.716 0.738 0.760
0.675 0.697 0.718 0.740 0.762
0.678 0.699 0.720 0.742 0.764
0.680 0.701 0.722 0.744 0.766
0.682 0.703 0.725 0.746 0.769
0.684 0.705 0.727 0.749 0.771
0.686 0.707 0.729 0.751 0.773
0.688 0.709 0.731 0.753 0.775
0.690 0.712 0.733 0.755 0.778
0.692 0.714 0.735 0.757 0.780
0.694 0.716 0.738 0.760 0.782
700 710 720 730 740
-0.002 -0.002 -0.003 -0.002 -0.002
-0.002 -0.002 -0.003 -0.002 -0.002
150 160 170 180 190
0.009 0.012 0.015 0.019 0.023
0.009 0.012 0.016 0.019 0.023
0.009 0.013 0.016 0.020 0.024
0.010 0.013 0.016 0.020 0.024
0.010 0.013 0.017 0.021 0.025
0.010 0.014 0.017 0.021 0.025
0.011 0.014 0.017 0.021 0.026
0.011 0.014 0.018 0.022 0.026
0.011 0.015 0.018 0.022 0.027
0.012 0.015 0.019 0.023 0.027
0.012 0.015 0.019 0.023 0.027
150 160 170 180 190
750 760 770 780 790
0.782 0.805 0.828 0.851 0.875
0.784 0.807 0.830 0.853 0.877
0.787 0.809 0.832 0.856 0.879
0.789 0.812 0.835 0.858 0.882
0.791 0.814 0.837 0.860 0.884
0.793 0.816 0.839 0.863 0.886
0.796 0.818 0.842 0.865 0.889
0.798 0.821 0.844 0.867 0.891
0.800 0.823 0.846 0.870 0.894
0.802 0.825 0.849 0.872 0.896
0.805 0.828 0.851 0.875 0.898
750 760 770 780 790
200 210 220 230 240
0.027 0.032 0.037 0.043 0.049
0.028 0.033 0.038 0.043 0.049
0.028 0.033 0.038 0.044 0.050
0.029 0.034 0.039 0.044 0.050
0.029 0.034 0.039 0.045 0.051
0.030 0.035 0.040 0.046 0.052
0.030 0.035 0.041 0.046 0.052
0.031 0.036 0.041 0.047 0.053
0.031 0.036 0.042 0.047 0.053
0.032 0.037 0.042 0.048 0.054
0.032 0.037 0.043 0.049 0.055
200 210 220 230 240
800 810 820 830 840
0.898 0.923 0.947 0.972 0.997
0.901 0.925 0.950 0.974 1.000
0.903 0.927 0.952 0.977 1.002
0.906 0.930 0.955 0.979 1.005
0.908 0.932 0.957 0.982 1.007
0.910 0.935 0.959 0.984 1.010
0.913 0.937 0.962 0.987 1.012
0.915 0.940 0.964 0.989 1.015
0.918 0.942 0.967 0.992 1.017
0.920 0.945 0.969 0.994 1.020
0.923 0.947 0.972 0.997 1.022
800 810 820 830 840
250 260 270 280 290
0.055 0.061 0.068 0.075 0.083
0.055 0.062 0.069 0.076 0.083
0.056 0.062 0.069 0.077 0.084
0.057 0.063 0.070 0.077 0.085
0.057 0.064 0.071 0.078 0.086
0.058 0.065 0.072 0.079 0.086
0.059 0.065 0.072 0.080 0.087
0.059 0.066 0.073 0.080 0.088
0.060 0.067 0.074 0.081 0.089
0.060 0.067 0.074 0.082 0.090
0.061 0.068 0.075 0.083 0.090
250 260 270 280 290
850 860 870 880 890
1.022 1.048 1.074 1.100 1.127
1.025 1.051 1.077 1.103 1.130
1.027 1.053 1.079 1.106 1.132
1.030 1.056 1.082 1.108 1.135
1.033 1.058 1.085 1.111 1.138
1.035 1.061 1.087 1.114 1.140
1.038 1.064 1.090 1.116 1.143
1.040 1.066 1.092 1.119 1.146
1.043 1.069 1.095 1.122 1.148
1.045 1.071 1.098 1.124 1.151
1.048 1.074 1.100 1.127 1.154
850 860 870 880 890
300 310 320 330 340
0.090 0.099 0.107 0.116 0.125
0.091 0.099 0.108 0.117 0.126
0.092 0.100 0.109 0.118 0.127
0.093 0.101 0.110 0.119 0.128
0.094 0.102 0.111 0.120 0.129
0.094 0.103 0.112 0.121 0.130
0.095 0.104 0.112 0.121 0.131
0.096 0.105 0.113 0.122 0.132
0.097 0.105 0.114 0.123 0.133
0.098 0.106 0.115 0.124 0.134
0.099 0.107 0.116 0.125 0.135
300 310 320 330 340
900 910 920 930 940
1.154 1.181 1.208 1.236 1.264
1.157 1.184 1.211 1.239 1.267
1.159 1.186 1.214 1.242 1.270
1.162 1.189 1.217 1.245 1.273
1.165 1.192 1.220 1.247 1.276
1.167 1.195 1.222 1.250 1.278
1.170 1.197 1.225 1.253 1.281
1.173 1.200 1.228 1.256 1.284
1.176 1.203 1.231 1.259 1.287
1.178 1.206 1.233 1.262 1.290
1.181 1.208 1.236 1.264 1.293
900 910 920 930 940
350 360 370 380 390
0.135 0.145 0.155 0.165 0.176
0.136 0.146 0.156 0.166 0.177
0.137 0.147 0.157 0.167 0.178
0.138 0.148 0.158 0.168 0.179
0.139 0.149 0.159 0.170 0.180
0.140 0.150 0.160 0.171 0.182
0.141 0.151 0.161 0.172 0.183
0.142 0.152 0.162 0.173 0.184
0.143 0.153 0.163 0.174 0.185
0.144 0.154 0.164 0.175 0.186
0.145 0.155 0.165 0.176 0.187
350 360 370 380 390
950 960 970 980 990
1.293 1.321 1.350 1.379 1.409
1.296 1.324 1.353 1.382 1.412
1.298 1.327 1.356 1.385 1.415
1.301 1.330 1.359 1.388 1.418
1.304 1.333 1.362 1.391 1.421
1.307 1.336 1.365 1.394 1.424
1.310 1.339 1.368 1.397 1.427
1.313 1.342 1.371 1.400 1.430
1.316 1.344 1.374 1.403 1.433
1.318 1.347 1.377 1.406 1.436
1.321 1.350 1.379 1.409 1.439
950 960 970 980 990
400 410 420 430 440
0.187 0.199 0.211 0.223 0.235
0.188 0.200 0.212 0.224 0.236
0.190 0.201 0.213 0.225 0.238
0.191 0.202 0.214 0.226 0.239
0.192 0.203 0.215 0.228 0.240
0.193 0.205 0.217 0.229 0.242
0.194 0.206 0.218 0.230 0.243
0.195 0.207 0.219 0.231 0.244
0.196 0.208 0.220 0.233 0.245
0.198 0.209 0.222 0.234 0.247
0.199 0.211 0.223 0.235 0.248
400 410 420 430 440
1000 1010 1020 1030 1040
1.439 1.469 1.499 1.530 1.561
1.442 1.472 1.502 1.533 1.564
1.445 1.475 1.505 1.536 1.567
1.448 1.478 1.508 1.539 1.570
1.451 1.481 1.511 1.542 1.573
1.454 1.484 1.515 1.545 1.576
1.457 1.487 1.518 1.548 1.580
1.460 1.490 1.521 1.552 1.583
1.463 1.493 1.524 1.555 1.586
1.466 1.496 1.527 1.558 1.589
1.469 1.499 1.530 1.561 1.592
1000 1010 1020 1030 1040
450 460 470 480 490
0.248 0.261 0.275 0.288 0.303
0.249 0.263 0.276 0.290 0.304
0.251 0.264 0.277 0.291 0.305
0.252 0.265 0.279 0.293 0.307
0.253 0.267 0.280 0.294 0.308
0.255 0.268 0.282 0.296 0.310
0.256 0.269 0.283 0.297 0.311
0.257 0.271 0.284 0.298 0.313
0.259 0.272 0.286 0.300 0.314
0.260 0.273 0.287 0.301 0.316
0.261 0.275 0.288 0.303 0.317
450 460 470 480 490
1050 1060 1070 1080 1090
1.592 1.624 1.655 1.687 1.720
1.595 1.627 1.659 1.691 1.723
1.598 1.630 1.662 1.694 1.726
1.601 1.633 1.665 1.697 1.729
1.605 1.636 1.668 1.700 1.733
1.608 1.639 1.671 1.704 1.736
1.611 1.643 1.675 1.707 1.739
1.614 1.646 1.678 1.710 1.743
1.617 1.649 1.681 1.713 1.746
1.620 1.652 1.684 1.716 1.749
1.624 1.655 1.687 1.720 1.752
1050 1060 1070 1080 1090
500 510 520 530 540
0.317 0.332 0.347 0.362 0.378
0.319 0.333 0.348 0.364 0.380
0.320 0.335 0.350 0.365 0.381
0.321 0.336 0.352 0.367 0.383
0.323 0.338 0.353 0.369 0.384
0.324 0.339 0.355 0.370 0.386
0.326 0.341 0.356 0.372 0.388
0.327 0.342 0.358 0.373 0.389
0.329 0.344 0.359 0.375 0.391
0.330 0.345 0.361 0.377 0.393
0.332 0.347 0.362 0.378 0.394
500 510 520 530 540
1100 1110 1120 1130 1140
1.752 1.785 1.818 1.852 1.886
1.756 1.789 1.822 1.855 1.889
1.759 1.792 1.825 1.859 1.892
1.762 1.795 1.828 1.862 1.896
1.765 1.798 1.832 1.865 1.899
1.769 1.802 1.835 1.869 1.903
1.772 1.805 1.838 1.872 1.906
1.775 1.808 1.842 1.875 1.909
1.779 1.812 1.845 1.879 1.913
1.782 1.815 1.849 1.882 1.916
1.785 1.818 1.852 1.886 1.920
1100 1110 1120 1130 1140
550 560 570 580 590
0.394 0.411 0.427 0.444 0.462
0.396 0.412 0.429 0.446 0.463
0.397 0.414 0.431 0.448 0.465
0.399 0.416 0.432 0.449 0.467
0.401 0.417 0.434 0.451 0.469
0.402 0.419 0.436 0.453 0.470
0.404 0.421 0.437 0.455 0.472
0.406 0.422 0.439 0.456 0.474
0.407 0.424 0.441 0.458 0.476
0.409 0.426 0.443 0.460 0.478
0.411 0.427 0.444 0.462 0.479
550 560 570 580 590
1150 1160 1170 1180 1190
1.920 1.954 1.988 2.023 2.058
1.923 1.957 1.992 2.027 2.062
1.926 1.961 1.995 2.030 2.065
1.930 1.964 1.999 2.034 2.069
1.933 1.968 2.002 2.037 2.072
1.937 1.971 2.006 2.041 2.076
1.940 1.975 2.009 2.044 2.079
1.944 1.978 2.013 2.048 2.083
1.947 1.981 2.016 2.051 2.086
1.950 1.985 2.020 2.055 2.090
1.954 1.988 2.023 2.058 2.094
1150 1160 1170 1180 1190
°F
0
6
7
8
10
°F
°F
0
6
7
8
1
2
3
4
5
9
Z-232
1
2
3
4
5
9
10
°F
Z
+ –
Revised Thermocouple Reference Tables
B
NONE ESTABLISHED
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°F
0
1
1200 1210 1220 1230 1240
2.094 2.129 2.165 2.201 2.237
2.097 2.133 2.169 2.205 2.241
2.101 2.136 2.172 2.208 2.245
2.104 2.140 2.176 2.212 2.248
2.108 2.143 2.179 2.216 2.252
1250 1260 1270 1280 1290
2.274 2.311 2.348 2.385 2.423
2.278 2.315 2.352 2.389 2.427
2.281 2.318 2.355 2.393 2.431
2.285 2.322 2.359 2.397 2.434
1300 1310 1320 1330 1340
2.461 2.499 2.538 2.576 2.615
2.465 2.503 2.541 2.580 2.619
2.469 2.507 2.545 2.584 2.623
1350 1360 1370 1380 1390
2.654 2.694 2.734 2.774 2.814
2.658 2.698 2.738 2.778 2.818
1400 1410 1420 1430 1440
2.854 2.895 2.936 2.978 3.019
1450 1460 1470 1480 1490
Thermoelectric Voltage in Millivolts °F
°F
0
6
7
8
2.111 2.147 2.183 2.219 2.256
2.115 2.151 2.187 2.223 2.259
2.118 2.154 2.190 2.226 2.263
2.122 2.158 2.194 2.230 2.267
2.126 2.161 2.197 2.234 2.270
2.129 2.165 2.201 2.237 2.274
1200 1210 1220 1230 1240
1800 1810 1820 1830 1840
4.673 4.723 4.774 4.824 4.875
4.678 4.728 4.779 4.829 4.880
4.683 4.733 4.784 4.834 4.885
4.688 4.738 4.789 4.839 4.890
4.693 4.743 4.794 4.844 4.895
4.698 4.748 4.799 4.850 4.900
4.703 4.754 4.804 4.855 4.905
4.708 4.759 4.809 4.860 4.911
4.713 4.764 4.814 4.865 4.916
4.718 4.769 4.819 4.870 4.921
4.723 4.774 4.824 4.875 4.926
1800 1810 1820 1830 1840
2.289 2.326 2.363 2.400 2.438
2.292 2.329 2.367 2.404 2.442
2.296 2.333 2.370 2.408 2.446
2.300 2.337 2.374 2.412 2.450
2.303 2.341 2.378 2.416 2.453
2.307 2.344 2.382 2.419 2.457
2.311 2.348 2.385 2.423 2.461
1250 1260 1270 1280 1290
1850 1860 1870 1880 1890
4.926 4.977 5.028 5.080 5.132
4.931 4.982 5.034 5.085 5.137
4.936 4.987 5.039 5.090 5.142
4.941 4.992 5.044 5.096 5.147
4.946 4.998 5.049 5.101 5.153
4.951 5.003 5.054 5.106 5.158
4.957 5.008 5.059 5.111 5.163
4.962 5.013 5.065 5.116 5.168
4.967 5.018 5.070 5.121 5.173
4.972 5.023 5.075 5.127 5.179
4.977 5.028 5.080 5.132 5.184
1850 1860 1870 1880 1890
2.472 2.511 2.549 2.588 2.627
2.476 2.515 2.553 2.592 2.631
2.480 2.518 2.557 2.596 2.635
2.484 2.522 2.561 2.600 2.639
2.488 2.526 2.565 2.604 2.643
2.492 2.530 2.569 2.607 2.647
2.495 2.534 2.572 2.611 2.651
2.499 2.538 2.576 2.615 2.654
1300 1310 1320 1330 1340
1900 1910 1920 1930 1940
5.184 5.236 5.288 5.341 5.394
5.189 5.241 5.294 5.346 5.399
5.194 5.246 5.299 5.351 5.404
5.199 5.252 5.304 5.357 5.410
5.205 5.257 5.309 5.362 5.415
5.210 5.262 5.315 5.367 5.420
5.215 5.267 5.320 5.373 5.425
5.220 5.273 5.325 5.378 5.431
5.225 5.278 5.330 5.383 5.436
5.231 5.283 5.336 5.388 5.441
5.236 5.288 5.341 5.394 5.447
1900 1910 1920 1930 1940
2.662 2.702 2.742 2.782 2.822
2.666 2.706 2.746 2.786 2.826
2.670 2.710 2.750 2.790 2.830
2.674 2.714 2.754 2.794 2.834
2.678 2.718 2.758 2.798 2.838
2.682 2.722 2.762 2.802 2.842
2.686 2.726 2.766 2.806 2.846
2.690 2.730 2.770 2.810 2.850
2.694 2.734 2.774 2.814 2.854
1350 1360 1370 1380 1390
1950 1960 1970 1980 1990
5.447 5.500 5.553 5.607 5.661
5.452 5.505 5.559 5.612 5.666
5.457 5.511 5.564 5.618 5.671
5.463 5.516 5.569 5.623 5.677
5.468 5.521 5.575 5.628 5.682
5.473 5.527 5.580 5.634 5.688
5.479 5.532 5.585 5.639 5.693
5.484 5.537 5.591 5.644 5.698
5.489 5.543 5.596 5.650 5.704
5.495 5.548 5.601 5.655 5.709
5.500 5.553 5.607 5.661 5.715
1950 1960 1970 1980 1990
2.859 2.899 2.940 2.982 3.023
2.863 2.903 2.944 2.986 3.027
2.867 2.908 2.949 2.990 3.032
2.871 2.912 2.953 2.994 3.036
2.875 2.916 2.957 2.998 3.040
2.879 2.920 2.961 3.002 3.044
2.883 2.924 2.965 3.007 3.048
2.887 2.928 2.969 3.011 3.052
2.891 2.932 2.973 3.015 3.057
2.895 2.936 2.978 3.019 3.061
1400 1410 1420 1430 1440
2000 2010 2020 2030 2040
5.715 5.769 5.823 5.878 5.932
5.720 5.774 5.828 5.883 5.938
5.725 5.780 5.834 5.888 5.943
5.731 5.785 5.839 5.894 5.949
5.736 5.790 5.845 5.899 5.954
5.742 5.796 5.850 5.905 5.960
5.747 5.801 5.856 5.910 5.965
5.752 5.807 5.861 5.916 5.971
5.758 5.812 5.867 5.921 5.976
5.763 5.818 5.872 5.927 5.982
5.769 5.823 5.878 5.932 5.987
2000 2010 2020 2030 2040
3.061 3.103 3.145 3.188 3.230
3.065 3.107 3.149 3.192 3.235
3.069 3.111 3.154 3.196 3.239
3.073 3.116 3.158 3.200 3.243
3.078 3.120 3.162 3.205 3.248
3.082 3.124 3.166 3.209 3.252
3.086 3.128 3.171 3.213 3.256
3.090 3.132 3.175 3.218 3.261
3.094 3.137 3.179 3.222 3.265
3.099 3.141 3.183 3.226 3.269
3.103 3.145 3.188 3.230 3.273
1450 1460 1470 1480 1490
2050 2060 2070 2080 2090
5.987 6.042 6.098 6.153 6.209
5.993 6.048 6.103 6.159 6.214
5.998 6.053 6.109 6.164 6.220
6.004 6.059 6.114 6.170 6.225
6.009 6.064 6.120 6.175 6.231
6.015 6.070 6.125 6.181 6.237
6.020 6.075 6.131 6.186 6.242
6.026 6.081 6.136 6.192 6.248
6.031 6.086 6.142 6.197 6.253
6.037 6.092 6.147 6.203 6.259
6.042 6.098 6.153 6.209 6.264
2050 2060 2070 2080 2090
1500 1510 1520 1530 1540
3.273 3.317 3.360 3.404 3.448
3.278 3.321 3.365 3.408 3.452
3.282 3.325 3.369 3.413 3.457
3.286 3.330 3.373 3.417 3.461
3.291 3.334 3.378 3.422 3.466
3.295 3.338 3.382 3.426 3.470
3.299 3.343 3.386 3.430 3.474
3.304 3.347 3.391 3.435 3.479
3.308 3.352 3.395 3.439 3.483
3.312 3.356 3.400 3.444 3.488
3.317 3.360 3.404 3.448 3.492
1500 1510 1520 1530 1540
2100 2110 2120 2130 2140
6.264 6.320 6.377 6.433 6.490
6.270 6.326 6.382 6.439 6.495
6.276 6.332 6.388 6.444 6.501
6.281 6.337 6.394 6.450 6.507
6.287 6.343 6.399 6.456 6.512
6.292 6.349 6.405 6.461 6.518
6.298 6.354 6.410 6.467 6.524
6.304 6.360 6.416 6.473 6.529
6.309 6.365 6.422 6.478 6.535
6.315 6.371 6.427 6.484 6.541
6.320 6.377 6.433 6.490 6.546
2100 2110 2120 2130 2140
1550 1560 1570 1580 1590
3.492 3.537 3.581 3.626 3.672
3.497 3.541 3.586 3.631 3.676
3.501 3.546 3.590 3.635 3.681
3.506 3.550 3.595 3.640 3.685
3.510 3.555 3.599 3.644 3.690
3.514 3.559 3.604 3.649 3.694
3.519 3.563 3.608 3.653 3.699
3.523 3.568 3.613 3.658 3.703
3.528 3.572 3.617 3.662 3.708
3.532 3.577 3.622 3.667 3.712
3.537 3.581 3.626 3.672 3.717
1550 1560 1570 1580 1590
2150 2160 2170 2180 2190
6.546 6.603 6.660 6.718 6.775
6.552 6.609 6.666 6.723 6.781
6.558 6.615 6.672 6.729 6.786
6.563 6.620 6.677 6.735 6.792
6.569 6.626 6.683 6.740 6.798
6.575 6.632 6.689 6.746 6.804
6.580 6.637 6.695 6.752 6.809
6.586 6.643 6.700 6.758 6.815
6.592 6.649 6.706 6.763 6.821
6.597 6.655 6.712 6.769 6.827
6.603 6.660 6.718 6.775 6.833
2150 2160 2170 2180 2190
1600 1610 1620 1630 1640
3.717 3.763 3.809 3.855 3.901
3.722 3.767 3.813 3.859 3.906
3.726 3.772 3.818 3.864 3.910
3.731 3.776 3.822 3.869 3.915
3.735 3.781 3.827 3.873 3.920
3.740 3.786 3.832 3.878 3.924
3.744 3.790 3.836 3.882 3.929
3.749 3.795 3.841 3.887 3.934
3.753 3.799 3.845 3.892 3.938
3.758 3.804 3.850 3.896 3.943
3.763 3.809 3.855 3.901 3.948
1600 1610 1620 1630 1640
2200 2210 2220 2230 2240
6.833 6.890 6.948 7.006 7.065
6.838 6.896 6.954 7.012 7.070
6.844 6.902 6.960 7.018 7.076
6.850 6.908 6.966 7.024 7.082
6.856 6.913 6.971 7.030 7.088
6.861 6.919 6.977 7.035 7.094
6.867 6.925 6.983 7.041 7.100
6.873 6.931 6.989 7.047 7.105
6.879 6.937 6.995 7.053 7.111
6.884 6.942 7.000 7.059 7.117
6.890 6.948 7.006 7.065 7.123
2200 2210 2220 2230 2240
1650 1660 1670 1680 1690
3.948 3.994 4.041 4.089 4.136
3.952 3.999 4.046 4.093 4.141
3.957 4.004 4.051 4.098 4.146
3.962 4.009 4.056 4.103 4.151
3.966 4.013 4.060 4.108 4.155
3.971 4.018 4.065 4.112 4.160
3.976 4.023 4.070 4.117 4.165
3.980 4.027 4.075 4.122 4.170
3.985 4.032 4.079 4.127 4.174
3.990 4.037 4.084 4.131 4.179
3.994 4.041 4.089 4.136 4.184
1650 1660 1670 1680 1690
2250 2260 2270 2280 2290
7.123 7.182 7.240 7.299 7.358
7.129 7.187 7.246 7.305 7.364
7.135 7.193 7.252 7.311 7.370
7.141 7.199 7.258 7.317 7.376
7.146 7.205 7.264 7.323 7.382
7.152 7.211 7.270 7.329 7.388
7.158 7.217 7.276 7.335 7.394
7.164 7.223 7.281 7.340 7.400
7.170 7.229 7.287 7.346 7.406
7.176 7.234 7.293 7.352 7.412
7.182 7.240 7.299 7.358 7.417
2250 2260 2270 2280 2290
1700 1710 1720 1730 1740
4.184 4.232 4.280 4.328 4.377
4.189 4.237 4.285 4.333 4.382
4.194 4.242 4.290 4.338 4.387
4.198 4.246 4.295 4.343 4.392
4.203 4.251 4.299 4.348 4.397
4.208 4.256 4.304 4.353 4.401
4.213 4.261 4.309 4.358 4.406
4.217 4.266 4.314 4.362 4.411
4.222 4.270 4.319 4.367 4.416
4.227 4.275 4.324 4.372 4.421
4.232 4.280 4.328 4.377 4.426
1700 1710 1720 1730 1740
2300 2310 2320 2330 2340
7.417 7.477 7.536 7.596 7.656
7.423 7.483 7.542 7.602 7.662
7.429 7.489 7.548 7.608 7.668
7.435 7.495 7.554 7.614 7.674
7.441 7.501 7.560 7.620 7.680
7.447 7.507 7.566 7.626 7.686
7.453 7.512 7.572 7.632 7.692
7.459 7.518 7.578 7.638 7.698
7.465 7.524 7.584 7.644 7.704
7.471 7.530 7.590 7.650 7.710
7.477 7.536 7.596 7.656 7.716
2300 2310 2320 2330 2340
1750 1760 1770 1780 1790
4.426 4.475 4.524 4.574 4.623
4.431 4.480 4.529 4.579 4.628
4.436 4.485 4.534 4.584 4.633
4.441 4.490 4.539 4.589 4.638
4.445 4.495 4.544 4.593 4.643
4.450 4.500 4.549 4.598 4.648
4.455 4.504 4.554 4.603 4.653
4.460 4.509 4.559 4.608 4.658
4.465 4.514 4.564 4.613 4.663
4.470 4.519 4.569 4.618 4.668
4.475 4.524 4.574 4.623 4.673
1750 1760 1770 1780 1790
2350 2360 2370 2380 2390
7.716 7.776 7.836 7.897 7.957
7.722 7.782 7.842 7.903 7.963
7.728 7.788 7.848 7.909 7.969
7.734 7.794 7.854 7.915 7.975
7.740 7.800 7.860 7.921 7.981
7.746 7.806 7.866 7.927 7.987
7.752 7.812 7.872 7.933 7.994
7.758 7.818 7.878 7.939 8.000
7.764 7.824 7.884 7.945 8.006
7.770 7.830 7.891 7.951 8.012
7.776 7.836 7.897 7.957 8.018
2350 2360 2370 2380 2390
°F
0
6
7
8
°F
°F
0
6
7
8
4
5
Extension Grade
8
3
4
+ –
7
2
3
Platinum-30% Rhodium vs. Platinum-6% Rhodium
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 3092°F 0 to 1700°C Extension Grade 32 to 212°F 0 to 100°C LIMITS OF ERROR (whichever is greater) Standard: 0.5°C over 800°C Special: NOT ESTABLISHED COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature; Common Use in Glass Industry TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
6
1
2
Thermocouple Grade
5
9
9
10
10
Z-233
1
1
2
2
3
3
4
4
5
5
9
9
10
10
°F
°F
+ –
MAXIMUM TEMPERATURE RANGE Thermocouple Grade 32 to 3092°F 0 to 1700°C Extension Grade 32 to 212°F 0 to 100°C LIMITS OF ERROR (whichever is greater) Standard: 0.5°C over 800°C Special: NOT ESTABLISHED COMMENTS, BARE WIRE ENVIRONMENT: Oxidizing or Inert; Do Not Insert in Metal Tubes; Beware of Contamination; High Temperature; Common Use in Glass Industry TEMPERATURE IN DEGREES °F Extension REFERENCE JUNCTION AT 32°F Grade
Thermocouple Grade
NONE ESTABLISHED
Platinum-30% Rhodium vs. Platinum-6% Rhodium
Revised Thermocouple Reference Tables
B
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Thermoelectric Voltage in Millivolts °F
0
1
2
3
4
2400 2410 2420 2430 2440
8.018 8.079 8.140 8.201 8.262
8.024 8.085 8.146 8.207 8.268
8.030 8.091 8.152 8.213 8.274
8.036 8.097 8.158 8.219 8.280
8.042 8.103 8.164 8.225 8.286
2450 2460 2470 2480 2490
8.323 8.385 8.446 8.508 8.570
8.329 8.391 8.453 8.514 8.576
8.336 8.397 8.459 8.521 8.582
8.342 8.403 8.465 8.527 8.589
2500 2510 2520 2530 2540
8.632 8.694 8.756 8.819 8.881
8.638 8.700 8.763 8.825 8.887
8.644 8.707 8.769 8.831 8.894
2550 2560 2570 2580 2590
8.944 9.006 9.069 9.132 9.195
8.950 9.013 9.075 9.138 9.201
2600 2610 2620 2630 2640
9.258 9.321 9.385 9.448 9.511
2650 2660 2670 2680 2690
9.575 9.639 9.702 9.766 9.830
5
6
7
8
8.048 8.109 8.170 8.231 8.293
8.054 8.115 8.176 8.237 8.299
8.060 8.121 8.182 8.244 8.305
8.066 8.127 8.188 8.250 8.311
8.073 8.134 8.195 8.256 8.317
9
8.079 8.140 8.201 8.262 8.323
10
2400 2410 2420 2430 2440
°F
8.348 8.409 8.471 8.533 8.595
8.354 8.416 8.477 8.539 8.601
8.360 8.422 8.483 8.545 8.607
8.366 8.428 8.490 8.551 8.613
8.372 8.434 8.496 8.558 8.620
8.379 8.440 8.502 8.564 8.626
8.385 8.446 8.508 8.570 8.632
2450 2460 2470 2480 2490
8.651 8.713 8.775 8.837 8.900
8.657 8.719 8.781 8.844 8.906
8.663 8.725 8.787 8.850 8.912
8.669 8.731 8.794 8.856 8.919
8.675 8.738 8.800 8.862 8.925
8.682 8.744 8.806 8.869 8.931
8.688 8.750 8.812 8.875 8.937
8.694 8.756 8.819 8.881 8.944
2500 2510 2520 2530 2540
8.956 9.019 9.082 9.145 9.208
8.962 9.025 9.088 9.151 9.214
8.969 9.031 9.094 9.157 9.220
8.975 9.038 9.101 9.164 9.227
8.981 9.044 9.107 9.170 9.233
8.988 9.050 9.113 9.176 9.239
8.994 9.057 9.119 9.182 9.245
9.000 9.063 9.126 9.189 9.252
9.006 9.069 9.132 9.195 9.258
2550 2560 2570 2580 2590
9.264 9.328 9.391 9.454 9.518
9.271 9.334 9.397 9.461 9.524
9.277 9.340 9.404 9.467 9.530
9.283 9.347 9.410 9.473 9.537
9.290 9.353 9.416 9.480 9.543
9.296 9.359 9.423 9.486 9.550
9.302 9.366 9.429 9.492 9.556
9.309 9.372 9.435 9.499 9.562
9.315 9.378 9.442 9.505 9.569
9.321 9.385 9.448 9.511 9.575
2600 2610 2620 2630 2640
9.581 9.645 9.709 9.772 9.836
9.588 9.651 9.715 9.779 9.843
9.594 9.658 9.721 9.785 9.849
9.600 9.664 9.728 9.792 9.856
9.607 9.670 9.734 9.798 9.862
9.613 9.677 9.741 9.804 9.868
9.619 9.683 9.747 9.811 9.875
9.626 9.690 9.753 9.817 9.881
9.632 9.696 9.760 9.824 9.888
9.639 9.702 9.766 9.830 9.894
2650 2660 2670 2680 2690
2700 9.894 9.900 9.907 9.913 9.920 9.926 9.932 9.939 9.945 2710 9.958 9.964 9.971 9.977 9.984 9.990 9.996 10.003 10.009 2720 10.022 10.028 10.035 10.041 10.048 10.054 10.061 10.067 10.073 2730 10.086 10.093 10.099 10.105 10.112 10.118 10.125 10.131 10.138 2740 10.150 10.157 10.163 10.170 10.176 10.183 10.189 10.195 10.202
9.952 10.016 10.080 10.144 10.208
9.958 10.022 10.086 10.150 10.215
2700 2710 2720 2730 2740
2750 2760 2770 2780 2790
10.215 10.279 10.344 10.408 10.473
10.221 10.286 10.350 10.414 10.479
10.228 10.292 10.356 10.421 10.485
10.234 10.298 10.363 10.427 10.492
10.240 10.305 10.369 10.434 10.498
10.247 10.311 10.376 10.440 10.505
10.253 10.318 10.382 10.447 10.511
10.260 10.324 10.389 10.453 10.518
10.266 10.331 10.395 10.460 10.524
10.273 10.337 10.402 10.466 10.531
10.279 10.344 10.408 10.473 10.537
2750 2760 2770 2780 2790
2800 2810 2820 2830 2840
10.537 10.602 10.666 10.731 10.796
10.544 10.608 10.673 10.738 10.802
10.550 10.615 10.679 10.744 10.809
10.556 10.621 10.686 10.751 10.815
10.563 10.628 10.692 10.757 10.822
10.569 10.634 10.699 10.763 10.828
10.576 10.641 10.705 10.770 10.835
10.582 10.647 10.712 10.776 10.841
10.589 10.653 10.718 10.783 10.848
10.595 10.660 10.725 10.789 10.854
10.602 10.666 10.731 10.796 10.861
2800 2810 2820 2830 2840
2850 2860 2870 2880 2890
10.861 10.925 10.990 11.055 11.120
10.867 10.932 10.997 11.062 11.127
10.874 10.938 11.003 11.068 11.133
10.880 10.945 11.010 11.075 11.140
10.887 10.951 11.016 11.081 11.146
10.893 10.958 11.023 11.088 11.153
10.900 10.964 11.029 11.094 11.159
10.906 10.971 11.036 11.101 11.166
10.913 10.977 11.042 11.107 11.172
10.919 10.984 11.049 11.114 11.179
10.925 10.990 11.055 11.120 11.185
2850 2860 2870 2880 2890
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
2900 2910 2920 2930 2940
11.185 11.250 11.315 11.380 11.445
11.192 11.257 11.321 11.386 11.451
11.198 11.263 11.328 11.393 11.458
11.205 11.270 11.334 11.399 11.464
11.211 11.276 11.341 11.406 11.471
11.218 11.282 11.347 11.412 11.477
11.224 11.289 11.354 11.419 11.484
11.231 11.295 11.360 11.425 11.490
11.237 11.302 11.367 11.432 11.497
11.244 11.308 11.373 11.438 11.503
11.250 11.315 11.380 11.445 11.510
2900 2910 2920 2930 2940
2950 2960 2970 2980 2990
11.510 11.575 11.640 11.705 11.770
11.516 11.582 11.647 11.712 11.777
11.523 11.588 11.653 11.718 11.783
11.529 11.595 11.660 11.725 11.790
11.536 11.601 11.666 11.731 11.796
11.542 11.608 11.673 11.738 11.803
11.549 11.614 11.679 11.744 11.809
11.555 11.621 11.686 11.751 11.816
11.562 11.627 11.692 11.757 11.822
11.568 11.634 11.699 11.764 11.829
11.575 11.640 11.705 11.770 11.835
2950 2960 2970 2980 2990
3000 3010 3020 3030 3040
11.835 11.900 11.965 12.030 12.095
11.842 11.907 11.972 12.037 12.102
11.848 11.913 11.978 12.043 12.108
11.855 11.920 11.985 12.050 12.115
11.861 11.926 11.991 12.056 12.121
11.868 11.933 11.998 12.063 12.128
11.874 11.939 12.004 12.069 12.134
11.881 11.946 12.011 12.076 12.141
11.887 11.952 12.017 12.082 12.147
11.894 11.959 12.024 12.089 12.154
11.900 11.965 12.030 12.095 12.160
3000 3010 3020 3030 3040
3050 3060 3070 3080 3090
12.160 12.225 12.290 12.355 12.420
12.166 12.231 12.296 12.361 12.426
12.173 12.238 12.303 12.368 12.433
12.179 12.244 12.309 12.374 12.439
12.186 12.251 12.316 12.381 12.446
12.192 12.257 12.322 12.387 12.452
12.199 12.264 12.329 12.394 12.458
12.205 12.270 12.335 12.400 12.465
12.212 12.277 12.342 12.407 12.471
12.218 12.283 12.348 12.413 12.478
12.225 12.290 12.355 12.420 12.484
3050 3060 3070 3080 3090
3100 3110 3120 3130 3140
12.484 12.549 12.614 12.679 12.743
12.491 12.556 12.620 12.685 12.750
12.497 12.562 12.627 12.692 12.756
12.504 12.569 12.633 12.698 12.763
12.510 12.575 12.640 12.704 12.769
12.517 12.582 12.646 12.711 12.776
12.523 12.588 12.653 12.717 12.782
12.530 12.595 12.659 12.724 12.789
12.536 12.601 12.666 12.730 12.795
12.543 12.607 12.672 12.737 12.801
12.549 12.614 12.679 12.743 12.808
3100 3110 3120 3130 3140
3150 3160 3170 3180 3190
12.808 12.872 12.937 13.001 13.066
12.814 12.879 12.943 13.008 13.072
12.821 12.885 12.950 13.014 13.079
12.827 12.892 12.956 13.021 13.085
12.834 12.898 12.963 13.027 13.092
12.840 12.905 12.969 13.034 13.098
12.847 12.911 12.976 13.040 13.104
12.853 12.918 12.982 13.047 13.111
12.860 12.924 12.989 13.053 13.117
12.866 12.931 12.995 13.059 13.124
12.872 12.937 13.001 13.066 13.130
3150 3160 3170 3180 3190
3200 3210 3220 3230 3240
13.130 13.194 13.259 13.323 13.387
13.137 13.201 13.265 13.329 13.393
13.143 13.207 13.271 13.336 13.400
13.149 13.214 13.278 13.342 13.406
13.156 13.220 13.284 13.348 13.412
13.162 13.227 13.291 13.355 13.419
13.169 13.233 13.297 13.361 13.425
13.175 13.239 13.304 13.368 13.432
13.182 13.246 13.310 13.374 13.438
13.188 13.252 13.316 13.380 13.444
13.194 13.259 13.323 13.387 13.451
3200 3210 3220 3230 3240
3250 3260 3270 3280 3290
13.451 13.515 13.579 13.642 13.706
13.457 13.521 13.585 13.649 13.712
13.464 13.527 13.591 13.655 13.719
13.470 13.534 13.598 13.661 13.725
13.476 13.540 13.604 13.668 13.731
13.483 13.547 13.610 13.674 13.738
13.489 13.553 13.617 13.680 13.744
13.496 13.559 13.623 13.687 13.750
13.502 13.566 13.630 13.693 13.757
13.508 13.572 13.636 13.700 13.763
13.515 13.579 13.642 13.706 13.769
3250 3260 3270 3280 3290
3300 13.769 13.776 13.782 13.789 13.795 13.801 13.808 13.814 13.820
°F
Z-234
0
1
2
3
4
5
6
7
8
°F
3300
9
10
°F
Z
+ –
Revised Thermocouple Reference Tables
Nickel-14.2% Chromium-1.4% Silicon vs. Nickel-4.4% Silicon0.1% Magnesium +
N
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
°F
-10
-9
-8
-7
-6
-5
-450
-4
Thermocouple Grade
– Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 450 to 2372°F – 270 to 1300°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Alternative to Type K; More Stable at High Temperatures TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
-3
-2
-1
0
°F
°F
0
6
7
8
10
°F
-4.345 -4.345 -4.345 -4.344 -4.344 -450
100 110 120 130 140
1.004 1.156 1.309 1.463 1.619
1.019 1.171 1.324 1.479 1.635
1
1.034 1.186 1.340 1.494 1.650
2
1.049 1.202 1.355 1.510 1.666
3
1.065 1.217 1.371 1.525 1.682
4
1.080 1.232 1.386 1.541 1.697
5
1.095 1.248 1.402 1.557 1.713
1.110 1.263 1.417 1.572 1.729
1.125 1.278 1.432 1.588 1.744
1.141 1.294 1.448 1.603 1.760
9
1.156 1.309 1.463 1.619 1.776
100 110 120 130 140
-440 -430 -420 -410 -400
-4.344 -4.339 -4.330 -4.316 -4.299
-4.344 -4.338 -4.329 -4.315 -4.297
-4.343 -4.337 -4.327 -4.313 -4.295
-4.343 -4.337 -4.326 -4.312 -4.293
-4.342 -4.336 -4.325 -4.310 -4.291
-4.342 -4.335 -4.324 -4.308 -4.288
-4.341 -4.334 -4.322 -4.306 -4.286
-4.341 -4.333 -4.321 -4.305 -4.284
-4.340 -4.332 -4.319 -4.303 -4.282
-4.340 -4.331 -4.318 -4.301 -4.279
-4.339 -4.330 -4.316 -4.299 -4.277
-440 -430 -420 -410 -400
150 160 170 180 190
1.776 1.934 2.093 2.253 2.415
1.791 1.950 2.109 2.269 2.431
1.807 1.965 2.125 2.285 2.447
1.823 1.981 2.141 2.301 2.463
1.839 1.997 2.157 2.318 2.480
1.855 2.013 2.173 2.334 2.496
1.870 2.029 2.189 2.350 2.512
1.886 2.045 2.205 2.366 2.528
1.902 2.061 2.221 2.382 2.545
1.918 2.077 2.237 2.398 2.561
1.934 2.093 2.253 2.415 2.577
150 160 170 180 190
-390 -380 -370 -360 -350
-4.277 -4.251 -4.220 -4.185 -4.145
-4.275 -4.248 -4.217 -4.181 -4.141
-4.272 -4.245 -4.213 -4.177 -4.137
-4.270 -4.242 -4.210 -4.174 -4.133
-4.267 -4.239 -4.206 -4.170 -4.128
-4.264 -4.236 -4.203 -4.166 -4.124
-4.262 -4.233 -4.199 -4.162 -4.120
-4.259 -4.230 -4.196 -4.158 -4.115
-4.256 -4.226 -4.192 -4.154 -4.111
-4.254 -4.223 -4.189 -4.150 -4.106
-4.251 -4.220 -4.185 -4.145 -4.102
-390 -380 -370 -360 -350
200 210 220 230 240
2.577 2.741 2.906 3.072 3.240
2.594 2.758 2.923 3.089 3.257
2.610 2.774 2.939 3.106 3.273
2.626 2.791 2.956 3.123 3.290
2.643 2.807 2.973 3.139 3.307
2.659 2.824 2.989 3.156 3.324
2.676 2.840 3.006 3.173 3.341
2.692 2.857 3.022 3.189 3.358
2.708 2.873 3.039 3.206 3.374
2.725 2.890 3.056 3.223 3.391
2.741 2.906 3.072 3.240 3.408
200 210 220 230 240
-340 -330 -320 -310 -300
-4.102 -4.054 -4.001 -3.945 -3.884
-4.097 -4.049 -3.996 -3.939 -3.878
-4.092 -4.043 -3.990 -3.933 -3.872
-4.088 -4.038 -3.985 -3.927 -3.866
-4.083 -4.033 -3.979 -3.921 -3.859
-4.078 -4.028 -3.974 -3.915 -3.853
-4.073 -4.023 -3.968 -3.909 -3.846
-4.068 -4.017 -3.962 -3.903 -3.840
-4.064 -4.012 -3.957 -3.897 -3.833
-4.059 -4.007 -3.951 -3.891 -3.827
-4.054 -4.001 -3.945 -3.884 -3.820
-340 -330 -320 -310 -300
250 260 270 280 290
3.408 3.578 3.748 3.920 4.093
3.425 3.595 3.766 3.937 4.110
3.442 3.612 3.783 3.955 4.128
3.459 3.629 3.800 3.972 4.145
3.476 3.646 3.817 3.989 4.162
3.493 3.663 3.834 4.007 4.180
3.510 3.680 3.851 4.024 4.197
3.527 3.697 3.869 4.041 4.215
3.544 3.714 3.886 4.058 4.232
3.561 3.731 3.903 4.076 4.250
3.578 3.748 3.920 4.093 4.267
250 260 270 280 290
-290 -280 -270 -260 -250
-3.820 -3.752 -3.679 -3.604 -3.524
-3.813 -3.745 -3.672 -3.596 -3.516
-3.807 -3.738 -3.665 -3.588 -3.508
-3.800 -3.730 -3.657 -3.580 -3.499
-3.793 -3.723 -3.650 -3.572 -3.491
-3.786 -3.716 -3.642 -3.564 -3.483
-3.779 -3.709 -3.634 -3.556 -3.474
-3.773 -3.702 -3.627 -3.548 -3.466
-3.766 -3.694 -3.619 -3.540 -3.458
-3.759 -3.687 -3.611 -3.532 -3.449
-3.752 -3.679 -3.604 -3.524 -3.441
-290 -280 -270 -260 -250
300 310 320 330 340
4.267 4.442 4.618 4.795 4.973
4.284 4.459 4.635 4.813 4.991
4.302 4.477 4.653 4.830 5.008
4.319 4.495 4.671 4.848 5.026
4.337 4.512 4.688 4.866 5.044
4.354 4.530 4.706 4.884 5.062
4.372 4.547 4.724 4.901 5.080
4.389 4.565 4.742 4.919 5.098
4.407 4.583 4.759 4.937 5.116
4.424 4.600 4.777 4.955 5.134
4.442 4.618 4.795 4.973 5.152
300 310 320 330 340
-240 -230 -220 -210 -200
-3.441 -3.354 -3.264 -3.171 -3.074
-3.432 -3.345 -3.255 -3.161 -3.064
-3.424 -3.336 -3.246 -3.151 -3.054
-3.415 -3.327 -3.236 -3.142 -3.044
-3.407 -3.318 -3.227 -3.132 -3.034
-3.398 -3.309 -3.218 -3.123 -3.024
-3.389 -3.300 -3.208 -3.113 -3.014
-3.380 -3.291 -3.199 -3.103 -3.004
-3.372 -3.282 -3.189 -3.093 -2.994
-3.363 -3.273 -3.180 -3.084 -2.984
-3.354 -3.264 -3.171 -3.074 -2.974
-240 -230 -220 -210 -200
350 360 370 380 390
5.152 5.332 5.512 5.694 5.877
5.170 5.350 5.531 5.712 5.895
5.188 5.368 5.549 5.731 5.913
5.206 5.386 5.567 5.749 5.932
5.224 5.404 5.585 5.767 5.950
5.241 5.422 5.603 5.785 5.968
5.259 5.440 5.621 5.804 5.987
5.277 5.458 5.639 5.822 6.005
5.295 5.476 5.658 5.840 6.024
5.314 5.494 5.676 5.858 6.042
5.332 5.512 5.694 5.877 6.060
350 360 370 380 390
-190 -180 -170 -160 -150
-2.974 -2.871 -2.765 -2.656 -2.544
-2.964 -2.860 -2.754 -2.645 -2.533
-2.954 -2.850 -2.743 -2.634 -2.522
-2.943 -2.839 -2.733 -2.623 -2.510
-2.933 -2.829 -2.722 -2.612 -2.499
-2.923 -2.818 -2.711 -2.601 -2.488
-2.912 -2.808 -2.700 -2.589 -2.476
-2.902 -2.797 -2.689 -2.578 -2.465
-2.892 -2.786 -2.678 -2.567 -2.453
-2.881 -2.776 -2.667 -2.556 -2.442
-2.871 -2.765 -2.656 -2.544 -2.430
-190 -180 -170 -160 -150
400 410 420 430 440
6.060 6.245 6.430 6.616 6.803
6.079 6.263 6.449 6.635 6.822
6.097 6.282 6.467 6.653 6.841
6.116 6.300 6.486 6.672 6.859
6.134 6.319 6.504 6.691 6.878
6.152 6.337 6.523 6.710 6.897
6.171 6.356 6.542 6.728 6.916
6.189 6.374 6.560 6.747 6.934
6.208 6.393 6.579 6.766 6.953
6.226 6.411 6.597 6.784 6.972
6.245 6.430 6.616 6.803 6.991
400 410 420 430 440
-140 -130 -120 -110 -100
-2.430 -2.313 -2.193 -2.072 -1.947
-2.418 -2.301 -2.181 -2.059 -1.935
-2.407 -2.289 -2.169 -2.047 -1.922
-2.395 -2.277 -2.157 -2.035 -1.910
-2.384 -2.265 -2.145 -2.022 -1.897
-2.372 -2.254 -2.133 -2.010 -1.884
-2.360 -2.242 -2.121 -1.997 -1.872
-2.348 -2.230 -2.108 -1.985 -1.859
-2.337 -2.218 -2.096 -1.972 -1.846
-2.325 -2.206 -2.084 -1.960 -1.834
-2.313 -2.193 -2.072 -1.947 -1.821
-140 -130 -120 -110 -100
450 460 470 480 490
6.991 7.179 7.369 7.559 7.750
7.010 7.198 7.388 7.578 7.769
7.029 7.217 7.407 7.597 7.788
7.047 7.236 7.426 7.616 7.807
7.066 7.255 7.445 7.635 7.826
7.085 7.274 7.464 7.654 7.845
7.104 7.293 7.483 7.673 7.865
7.123 7.312 7.502 7.692 7.884
7.142 7.331 7.521 7.711 7.903
7.161 7.350 7.540 7.731 7.922
7.179 7.369 7.559 7.750 7.941
450 460 470 480 490
-90 -80 -70 -60 -50
-1.821 -1.692 -1.562 -1.430 -1.296
-1.808 -1.679 -1.549 -1.416 -1.282
-1.795 -1.666 -1.536 -1.403 -1.269
-1.783 -1.653 -1.522 -1.390 -1.255
-1.770 -1.640 -1.509 -1.376 -1.242
-1.757 -1.627 -1.496 -1.363 -1.228
-1.744 -1.614 -1.483 -1.349 -1.214
-1.731 -1.601 -1.470 -1.336 -1.201
-1.718 -1.588 -1.456 -1.323 -1.187
-1.705 -1.575 -1.443 -1.309 -1.174
-1.692 -1.562 -1.430 -1.296 -1.160
-90 -80 -70 -60 -50
500 510 520 530 540
7.941 8.134 8.327 8.520 8.715
7.960 8.153 8.346 8.540 8.734
7.980 8.172 8.365 8.559 8.754
7.999 8.191 8.385 8.579 8.773
8.018 8.211 8.404 8.598 8.793
8.037 8.230 8.423 8.617 8.812
8.057 8.249 8.443 8.637 8.832
8.076 8.269 8.462 8.656 8.851
8.095 8.288 8.482 8.676 8.871
8.114 8.307 8.501 8.695 8.890
8.134 8.327 8.520 8.715 8.910
500 510 520 530 540
-40 -30 -20 -10 0
-1.160 -1.023 -0.884 -0.744 -0.603
-1.146 -1.009 -0.870 -0.730 -0.589
-1.133 -0.995 -0.856 -0.716 -0.575
-1.119 -0.981 -0.842 -0.702 -0.561
-1.105 -0.967 -0.828 -0.688 -0.546
-1.092 -0.954 -0.814 -0.674 -0.532
-1.078 -0.940 -0.800 -0.660 -0.518
-1.064 -0.926 -0.786 -0.646 -0.504
-1.050 -0.912 -0.772 -0.632 -0.490
-1.037 -0.898 -0.758 -0.617 -0.475
-1.023 -0.884 -0.744 -0.603 -0.461
-40 -30 -20 -10 0
550 560 570 580 590
8.910 9.105 9.302 9.499 9.696
8.929 9.125 9.321 9.519 9.716
8.949 9.145 9.341 9.538 9.736
8.968 9.164 9.361 9.558 9.756
8.988 9.184 9.381 9.578 9.776
9.008 9.204 9.400 9.598 9.795
9.027 9.223 9.420 9.617 9.815
9.047 9.243 9.440 9.637 9.835
9.066 9.262 9.459 9.657 9.855
9.086 9.282 9.479 9.677 9.875
9.105 9.302 9.499 9.696 9.895
550 560 570 580 590
0 10 20 30 40
-0.461 -0.318 -0.174 -0.029 0.116
-0.447 -0.433 -0.418 -0.404 -0.390 -0.375 -0.361 -0.347 -0.332 -0.318 -0.304 -0.289 -0.275 -0.260 -0.246 -0.232 -0.217 -0.203 -0.188 -0.174 -0.159 -0.145 -0.131 -0.116 -0.102 -0.087 -0.073 -0.058 -0.044 -0.029 -0.015 0.000 0.014 0.029 0.043 0.058 0.072 0.087 0.101 0.116 0.130 0.145 0.159 0.174 0.188 0.203 0.217 0.232 0.246 0.261
0 10 20 30 40
600 610 620 630 640
9.895 10.093 10.293 10.493 10.693
9.914 10.113 10.313 10.513 10.713
9.934 10.133 10.333 10.533 10.733
9.954 10.153 10.353 10.553 10.753
9.974 10.173 10.373 10.573 10.774
9.994 10.193 10.393 10.593 10.794
10.014 10.213 10.413 10.613 10.814
10.034 10.233 10.433 10.633 10.834
10.054 10.253 10.453 10.653 10.854
10.073 10.273 10.473 10.673 10.874
10.093 10.293 10.493 10.693 10.894
600 610 620 630 640
50 60 70 80 90
0.261 0.407 0.555 0.703 0.853
0.407 0.555 0.703 0.853 1.004
50 60 70 80 90
650 660 670 680 690
10.894 11.096 11.298 11.501 11.704
10.914 11.116 11.318 11.521 11.724
10.934 11.136 11.338 11.541 11.744
10.955 11.156 11.359 11.561 11.765
10.975 11.177 11.379 11.582 11.785
10.995 11.197 11.399 11.602 11.805
11.015 11.217 11.419 11.622 11.826
11.035 11.237 11.440 11.643 11.846
11.055 11.257 11.460 11.663 11.867
11.076 11.278 11.480 11.683 11.887
11.096 11.298 11.501 11.704 11.907
650 660 670 680 690
°F
0
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
°F
0.275 0.422 0.570 0.718 0.868
1
0.290 0.437 0.584 0.733 0.883
2
0.305 0.451 0.599 0.748 0.898
3
0.319 0.466 0.614 0.763 0.913
4
0.334 0.481 0.629 0.778 0.928
5
0.349 0.496 0.644 0.793 0.943
0.363 0.510 0.659 0.808 0.958
0.378 0.525 0.674 0.823 0.974
6
7
8
0.393 0.540 0.688 0.838 0.989
9
Z-235
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 450 to 2372°F – 270 to 1300°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Alternative to Type K; More Stable at High Temperatures TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
+ –
Thermocouple Grade
Revised Thermocouple Reference Tables
Nickel-14.2% Chromium-1.4% Silicon vs. Nickel-4.4% Silicon0.1% Magnesium +
N
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
– Extension Grade
Thermoelectric Voltage in Millivolts °F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
700 710 720 730 740
11.907 12.111 12.316 12.521 12.726
11.928 12.132 12.336 12.542 12.747
11.948 12.152 12.357 12.562 12.768
11.968 12.173 12.377 12.583 12.788
11.989 12.193 12.398 12.603 12.809
12.009 12.214 12.418 12.624 12.829
12.030 12.234 12.439 12.644 12.850
12.050 12.255 12.459 12.665 12.871
12.071 12.275 12.480 12.685 12.891
12.091 12.295 12.500 12.706 12.912
12.111 12.316 12.521 12.726 12.932
700 710 720 730 740
1300 1310 1320 1330 1340
24.701 24.919 25.137 25.356 25.574
24.723 24.941 25.159 25.377 25.596
24.745 24.963 25.181 25.399 25.618
24.767 24.985 25.203 25.421 25.639
24.788 25.007 25.225 25.443 25.661
24.810 25.028 25.247 25.465 25.683
24.832 25.050 25.268 25.487 25.705
24.854 25.072 25.290 25.508 25.727
24.876 25.094 25.312 25.530 25.748
24.897 25.116 25.334 25.552 25.770
24.919 25.137 25.356 25.574 25.792
1300 1310 1320 1330 1340
750 760 770 780 790
12.932 13.139 13.346 13.553 13.760
12.953 13.159 13.366 13.574 13.781
12.974 13.180 13.387 13.594 13.802
12.994 13.201 13.408 13.615 13.823
13.015 13.221 13.428 13.636 13.844
13.036 13.242 13.449 13.657 13.864
13.056 13.263 13.470 13.677 13.885
13.077 13.284 13.491 13.698 13.906
13.098 13.304 13.511 13.719 13.927
13.118 13.325 13.532 13.740 13.948
13.139 13.346 13.553 13.760 13.969
750 760 770 780 790
1350 1360 1370 1380 1390
25.792 26.010 26.229 26.447 26.665
25.814 26.032 26.250 26.469 26.687
25.836 26.054 26.272 26.491 26.709
25.858 26.076 26.294 26.512 26.731
25.879 26.098 26.316 26.534 26.752
25.901 26.119 26.338 26.556 26.774
25.923 26.141 26.360 26.578 26.796
25.945 26.163 26.381 26.600 26.818
25.967 26.185 26.403 26.622 26.840
25.989 26.207 26.425 26.643 26.862
26.010 26.229 26.447 26.665 26.883
1350 1360 1370 1380 1390
800 810 820 830 840
13.969 14.177 14.386 14.595 14.804
13.989 14.198 14.407 14.616 14.825
14.010 14.219 14.428 14.637 14.846
14.031 14.240 14.448 14.658 14.867
14.052 14.260 14.469 14.679 14.888
14.073 14.281 14.490 14.700 14.909
14.094 14.302 14.511 14.721 14.930
14.114 14.323 14.532 14.742 14.951
14.135 14.344 14.553 14.763 14.972
14.156 14.365 14.574 14.784 14.993
14.177 14.386 14.595 14.804 15.014
800 810 820 830 840
1400 1410 1420 1430 1440
26.883 27.102 27.320 27.538 27.756
26.905 27.124 27.342 27.560 27.778
26.927 27.145 27.364 27.582 27.800
26.949 27.167 27.385 27.604 27.822
26.971 27.189 27.407 27.625 27.844
26.993 27.211 27.429 27.647 27.866
27.014 27.233 27.451 27.669 27.887
27.036 27.254 27.473 27.691 27.909
27.058 27.276 27.495 27.713 27.931
27.080 27.298 27.516 27.735 27.953
27.102 27.320 27.538 27.756 27.975
1400 1410 1420 1430 1440
850 860 870 880 890
15.014 15.225 15.435 15.646 15.857
15.035 15.246 15.456 15.667 15.878
15.056 15.267 15.477 15.688 15.900
15.077 15.288 15.498 15.709 15.921
15.098 15.309 15.520 15.731 15.942
15.119 15.330 15.541 15.752 15.963
15.140 15.351 15.562 15.773 15.984
15.162 15.372 15.583 15.794 16.005
15.183 15.393 15.604 15.815 16.027
15.204 15.414 15.625 15.836 16.048
15.225 15.435 15.646 15.857 16.069
850 860 870 880 890
1450 1460 1470 1480 1490
27.975 28.193 28.411 28.629 28.847
27.996 28.215 28.433 28.651 28.869
28.018 28.236 28.455 28.673 28.891
28.040 28.258 28.476 28.694 28.912
28.062 28.280 28.498 28.716 28.934
28.084 28.302 28.520 28.738 28.956
28.105 28.324 28.542 28.760 28.978
28.127 28.345 28.564 28.782 29.000
28.149 28.367 28.585 28.803 29.021
28.171 28.389 28.607 28.825 29.043
28.193 28.411 28.629 28.847 29.065
1450 1460 1470 1480 1490
900 910 920 930 940
16.069 16.281 16.493 16.705 16.918
16.090 16.302 16.514 16.727 16.939
16.111 16.323 16.535 16.748 16.961
16.132 16.344 16.557 16.769 16.982
16.154 16.366 16.578 16.790 17.003
16.175 16.387 16.599 16.812 17.025
16.196 16.408 16.620 16.833 17.046
16.217 16.429 16.642 16.854 17.067
16.238 16.450 16.663 16.875 17.088
16.260 16.472 16.684 16.897 17.110
16.281 16.493 16.705 16.918 17.131
900 910 920 930 940
1500 1510 1520 1530 1540
29.085 29.283 29.501 29.719 29.937
29.087 29.305 29.523 29.741 29.958
29.109 29.327 29.545 29.762 29.980
29.130 29.348 29.566 29.784 30.002
29.152 29.370 29.588 29.806 30.024
29.174 29.392 29.610 29.828 30.046
29.196 29.414 29.632 29.850 30.067
29.218 29.436 29.653 29.871 30.089
29.239 29.457 29.675 29.893 30.111
29.261 29.479 29.697 29.915 30.133
29.283 29.501 29.719 29.937 30.154
1500 1510 I520 I530 IS40
950 960 970 980 990
17.131 17.344 17.558 17.772 17.986
17.152 17.366 17.579 17.793 18.007
17.174 17.387 17.601 17.814 18.028
17.195 17.408 17.622 17.836 18.050
17.216 17.430 17.643 17.857 18.071
17.238 17.451 17.665 17.879 18.093
17.259 17.472 17.686 17.900 18.114
17.280 17.494 17.707 17.921 18.136
17.302 17.515 17.729 17.943 18.157
17.323 17.536 17.750 17.964 18.178
17.344 17.558 17.772 17.986 18.200
950 960 970 980 990
1550 1560 1570 1580 1590
30.154 30.372 30.590 30.807 31.025
30.176 30.304 30.611 30.829 31.047
30.198 30.416 30.633 30.851 31.068
30.220 30.437 30.655 30.873 31.090
30.242 30.459 30.677 30.894 31.112
30.263 30.481 30.699 30.916 31.133
30.285 30.503 30.720 30.938 31.155
30.307 30.524 30.742 30.960 31.177
30.329 30.546 30.764 30.981 31.199
30.350 30.568 30.786 31.003 31.220
30.372 30.590 30.807 31.025 31.242
1550 1560 1570 1580 1590
1000 1010 1020 1030 1040
18.200 18.414 18.629 18.844 19.059
18.221 18.436 18.650 18.865 19.081
18.243 18.457 18.672 18.887 19.102
18.264 18.479 18.693 18.908 19.124
18.286 18.500 18.715 18.930 19.145
18.307 18.522 18.736 18.951 19.167
18.328 18.543 18.758 18.973 19.188
18.350 18.565 18.779 18.994 19.210
18.371 18.586 18.801 19.016 19.231
18.393 18.608 18.822 19.037 19.253
18.414 18.629 18.844 19.059 19.274
1000 1010 1020 1030 1040
1600 1610 1620 1630 1640
31.242 31.450 31.677 31.894 32.111
31.264 31.481 31.698 31.916 32.133
31.286 31.503 31.720 31.937 32.154
31.307 31.525 31.742 31.959 32.176
31.329 31.546 31.764 31.981 32.198
31.351 31.568 31.785 32.002 32.219
31.373 31.590 31.807 32.024 32.241
31.394 31.612 31.829 32.046 32.263
31.416 31.633 31.850 32.068 32.284
31.438 31.655 31.872 32.089 32.306
31.459 31.677 31.894 32.111 32.328
1600 1610 1620 1630 1640
1050 1060 1070 1080 1090
19.274 19.490 19.705 19.921 20.137
19.296 19.511 19.727 19.943 20.159
19.317 19.533 19.749 19.964 20.181
19.339 19.554 19.770 19.986 20.202
19.360 19.576 19.792 20.008 20.224
19.382 19.598 19.813 20.029 20.245
19.404 19.619 19.835 20.051 20.267
19.425 19.641 19.857 20.072 20.289
19.447 19.662 19.878 20.094 20.310
19.468 19.684 19.900 20.116 20.332
19.490 19.705 19.921 20.137 20.353
1060 1060 1070 1060 1090
1650 1660 1670 1680 1690
32.328 32.545 32.716 32.978 33.195
32.350 32.566 32.783 32.000 33.216
32.371 32.588 32.805 32.021 33.238
32.393 32.610 32.826 32.043 33.260
32.415 32.631 32.848 33.065 33.281
32.436 32.653 32.870 35.086 33.303
32.458 32.675 32.891 33.108 33.325
32.480 32.696 32.913 33.130 33.346
32.501 32.718 32.935 33.151 33.368
32.523 32.740 32.956 33.173 33.389
32.545 32.761 32.978 33.195 33.411
1650 1660 1670 1680 1690
1100 1110 1120 1130 1140
20.353 20.570 20.786 21.003 21.220
20.375 20.591 20.808 21.025 21.241
20.397 20.613 20.830 21.046 21.263
20.418 20.635 20.851 21.068 21.285
20.440 20.656 20.873 21.090 21.306
20.462 20.678 20.895 21.111 21.328
20.483 20.700 20.916 21.133 21.350
20.505 20.721 20.938 21.155 21.371
20.527 20.743 20.960 21.176 21.393
20.548 20.765 20.981 21.198 21.415
20.570 20.786 21.003 21.220 21.437
1100 1110 1120 1130 1140
1700 1710 1720 1730 1740
33.411 33.627 33.844 34.060 34.276
33.433 33.649 33.865 34.081 34.297
33.454 33.671 33.887 34.103 34.319
33.476 33.692 33.908 34.124 34.340
33.498 33.714 33.930 34.146 34.362
33.519 33.736 33.952 34.168 34.384
33.541 33.757 33.973 34.189 34.405
33.563 33.779 33.995 34.211 34.427
33.584 33.800 34.016 34.232 34.448
33.606 33.822 34.038 34.254 34.470
33.627 33.844 34.060 34.276 34.491
1700 1710 1720 1730 1740
1150 1160 1170 1180 1190
21.437 21.654 21.871 22.088 22.305
21.458 21.675 21.892 22.110 22.327
21.480 21.697 21.914 22.131 22.349
21.502 21.719 21.936 22.153 22.370
21.523 21.740 21.958 22.175 22.392
21.545 21.762 21.979 22.197 22.414
21.567 21.784 22.001 22.218 22.436
21.588 21.806 22.023 22.240 22.457
21.610 21.827 22.044 22.262 22.479
21.632 21.849 22.066 22.284 22.501
21.654 21.871 22.088 22.305 22.523
1150 1160 1170 1180 1190
1750 1760 1770 1790 1790
34.491 34.707 34.923 35.138 35.353
34.513 34.729 34.944 35.160 35.375
34.535 34.750 34.966 35.181 35.396
34.556 34.772 34.987 35.203 35.418
34.578 34.793 35.009 35.224 35.439
34.599 34.815 35.030 35.246 35.461
34.621 34.836 35.052 35.267 35.482
34.642 34.858 35.073 35.289 35.504
34.664 34.879 35.095 35.310 35.525
34.686 34.901 35.116 35.332 35.547
34.707 34.923 35.138 35.353 35.568
1750 1760 1770 1780 1790
1200 1210 1220 1230 1240
22.523 22.740 22.958 23.176 23.393
22.544 22.762 22.980 23.197 23.415
22.566 22.784 23.001 23.219 23.437
22.588 22.805 23.023 23.241 23.459
22.610 22.827 23.045 23.263 23.480
22.631 22.849 23.067 23.284 23.502
22.653 22.871 23.088 23.306 23.524
22.675 22.893 23.110 23.328 23.546
22.697 22.914 23.132 23.350 23.568
22.718 22.936 23.154 23.372 23.589
22.740 22.958 23.178 23.393 23.611
1200 1210 1220 1230 1240
1800 1810 1820 1830 1840
35.568 35.783 35.998 35.213 36.427
35.590 35.805 35.019 35.234 36.449
35.611 35.826 36.041 36.256 36.470
35.633 35.848 36.062 36.277 36.491
35.654 35.869 36.084 36.298 36.513
35.676 35.891 36.105 36.320 36.534
35.697 35.912 36.127 36.341 36.556
35.719 35.934 36.148 36.363 36.577
35.740 35.955 36.170 36.384 36.599
35.762 35.977 36.191 36.406 36.620
35.783 35.998 36.213 36.427 36.641
1800 1810 1820 1830 1840
1250 1260 1270 1280 1290
23.611 23.829 24.047 24.265 24.483
23.633 23.851 24.069 24.287 24.505
23.655 23.873 24.091 24.309 24.527
23.676 23.894 24.112 24.330 24.548
23.698 23.916 24.134 24.352 24.570
23.720 23.938 24.156 24.374 24.592
23.742 23.960 24.178 24.396 24.614
23.764 23.982 24.200 24.418 24.636
23.785 24.003 24.221 24.439 24.658
23.807 24.025 24.243 24.461 24.679
23.829 24.047 24.265 24.483 24.701
1250 1260 1270 1280 1290
1850 1860 1870 1880 18901
36.841 36.855 37.069 37.283 37.497
36.663 36.877 37.091 37.305 37.518
36.684 36.898 37.112 37.326 37.539
36.706 36.920 37.134 37.347 37.561
36.727 36.941 37.155 37.369 37.582
36.748 36.962 37.176 37.390 37.603
36.770 36.984 37.198 37.411 37.625
36.791 37.005 37.219 37.433 37.646
38.813 37.027 37.240 37.454 37.667
36.834 37.048 37.262 37.475 37.689
36.855 37.069 37.283 37.497 37.710
1850 1860 1870 1880 1890
°F
0
1
2
3
4
5
6
7
8
9
10
°F
0
1
2
3
4
5
6
7
8
9
10
°F
Z-236
°F
°F
Z
+ –
Revised Thermocouple Reference Tables
Nickel-14.2% Chromium-1.4% Silicon vs. Nickel-4.4% Silicon0.1% Magnesium +
N
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
– Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade – 450 to 2372°F – 270 to 1300°C Extension Grade 32 to 392°F 0 to 200°C LIMITS OF ERROR (whichever is greater) Standard: 2.2°C or 0.75% Above 0°C 2.2°C or 2.0% Below 0°C Special: 1.1°C or 0.4% COMMENTS, BARE WIRE ENVIRONMENT: Alternative to Type K; More Stable at High Temperatures TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
1900 1910 1920 1930 1940
37.710 37.923 38.136 38.349 38.562
37.731 37.945 38.158 38.370 38.583
37.753 37.966 38.179 38.392 38.604
37.774 37.987 38.200 38.413 38.626
37.795 38.009 38.222 38.434 38.647
37.817 38.030 38.243 38.456 38.668
37.838 38.051 38.264 38.477 38.689
37.859 38.073 38.285 38.498 38.711
37.881 38.094 38.307 38.519 38.732
37.902 38.115 38.328 38.541 38.753
37.923 38.136 38.349 38.562 38.774
1900 1910 1920 1930 1940
2150 2160 2170 2180 2190
42.976 43.184 43.391 43.598 43.805
42.997 43.205 43.412 43.619 43.826
43.018 43.225 43.433 43.640 43.846
43.039 43.246 43.453 43.660 43.867
43.059 43.267 43.474 43.681 43.888
43.080 43.288 43.495 43.702 43.908
43.101 43.308 43.515 43.722 43.929
43.122 43.329 43.536 43.743 43.950
43.142 43.350 43.557 43.764 43.970
43.163 43.370 43.578 43.784 43.991
43.184 43.391 43.598 43.805 43.012
2150 2160 2170 2180 2190
1950 1960 1970 1980 1990
38.774 38.986 39.198 39.410 39.622
38.795 39.008 39.220 39.431 39.643
38.817 38.029 39.241 39.453 39.664
38.838 39.050 39.262 39.474 39.685
38.859 39.071 39.283 39.495 39.706
38.880 39.093 39.304 39.516 39.728
38.902 39.114 39.326 39.537 39.749
38.923 39.135 39.347 39.558 39.770
38.944 39.156 39.368 39.580 39.791
38.965 39.177 39.389 39.601 39.812
38.986 39.198 39.410 39.622 39.833
1950 1960 1970 1980 1990
2200 2210 2220 2230 2240
44.012 44.218 44.424 44.629 44.835
44.032 44.238 44.444 44.650 44.855
44.053 44.259 44.465 44.671 44.876
44.073 44.280 44.485 44.691 44.896
44.094 44.300 44.506 44.712 44.917
44.115 44.321 44.527 44.732 44.937
44.135 44.341 44.547 44.753 44.958
44.156 44.362 44.568 44.773 44.978
44.177 44.383 44.588 44.794 44.999
44.197 44.403 44.609 44.814 45.019
44.218 44.424 44.629 44.835 45.040
2200 2210 2220 2230 2240
2000 2010 2020 2030 2040
39.833 40.044 40.255 40.466 40.677
39.854 40.066 40.276 40.487 40.698
39.875 40.087 40.297 40.508 40.719
39.897 40.108 40.319 40.529 40.740
39.918 40.129 40.340 40.550 40.761
39.939 40.150 40.361 40.571 40.782
39.960 40.171 40.382 40.592 40.803
39.981 40.192 40.403 40.613 40.824
40.002 40.213 40.424 40.634 40.845
40.023 40.234 40.445 40.655 40.866
40.044 40.255 40.466 40.677 40.887
2000 2010 2020 2030 2040
2250 2260 2270 2280 2290
45.040 45.245 45.449 45.653 45.857
45.060 45.265 45.469 45.674 45.877
45.081 45.286 45.490 45.694 45.898
45.101 45.306 45.510 45.714 45.918
45.122 45.326 45.531 45.735 45.938
45.142 45.347 45.551 45.755 45.959
45.163 45.367 45.572 45.775 45.979
45.183 45.388 45.592 45.796 45.999
45.204 45.408 45.612 45.816 46.020
45.224 45.429 45.633 45.837 46.040
45.245 45.449 45.653 45.857 46.060
2250 2260 2270 2280 2290
2050 2060 2070 2080 2090
40.887 41.097 41.307 41.516 41.725
40.908 41.118 41.328 41.537 41.746
40.929 41.139 41.349 41.558 41.767
40.95O 41.160 41.370 41.579 41.788
40.971 41.181 41.390 41.600 41.809
40.992 41.202 41.411 41.621 41.830
41.013 41.223 41.432 41.642 41.851
41.034 41.244 41.453 41.663 41.872
41.055 41.265 41.474 41.684 41.893
41.076 41.286 41.495 41.705 41.914
41.097 41.307 41.516 41.725 41.935
2050 2060 2070 2080 2090
2300 2310 2320 2330 2340
46.060 46.263 46.466 46.668 48.870
46.081 46.284 46.486 46.688 46.890
46.101 46.304 46.506 46.709 46.910
46.121 46.324 46.527 46.729 48.931
46.142 46.344 46.547 46.749 46.951
46.162 46.365 46.567 46.769 46.971
46.182 46.385 48.587 48.789 48.991
46.202 46.405 46.608 46.810 47.011
46.223 46.425 46.628 48.830 47-031
46.243 46.446 46.648 46.850 47.051
46.263 46.466 46.668 46.870 47.071
2300 2310 2320 2330 2340
2100 2110 2120 2130 2140
41.935 42.143 42.352 42.560 42.768
41.955 42.164 42.373 42.581 42.789
41.976 42.185 42.394 42.602 42.810
41.997 42.206 42.415 42.623 42.831
42.018 42.227 42.435 42.644 42.852
42.039 42.248 42.456 42.664 42.872
42.060 42.269 42.477 42.685 42.893
42.081 42.289 42.498 42.706 42.914
42.102 42.310 42.519 42.727 42.935
42.123 42.331 42.540 42.748 42.956
42.143 42.352 42.560 42.768 42.976
2100 2110 2120 2130 2140
2350 47.071 47.092 47.112 47.132 47.152 47.172 47.192 47.212 47.232 47.252 47.272 2350 2360 47.272 47.292 47.312 47.333 47.353 47.373 47.393 47.413 47.433 47.453 47.473 2360 2370 47.473 47.493 47.513 2370
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
Z-237
0
1
2
3
4
5
6
7
8
9
10
°F
°F
MAXIMUM TEMPERATURE RANGE Thermocouple Grade -32 to 4208°F -0 to 2320°C Extension Grade 32 to 1600°F 0 to 870°C LIMITS OF ERROR (whichever is greater) Standard: 4.5°C to 425°C 1.0% to 2320°C Special: Not Established COMMENTS, BARE WIRE ENVIRONMENT: Vacuum, Inert; Hydrogen; Beware of Embrittlement; Not Practical Below 750°F; Not for Oxidizing Atmosphere TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
+ –
Thermocouple Grade
NONE ESTABLISHED
Tungsten5% Rhenium vs. Tungsten26% Rhenium
Revised Thermocouple Reference Tables
C
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °C
0
1
6
7
8
0 10 20 30 40
0.000 0.135 0.272 0.412 0.554
0.013 0.148 0.286 0.426 0.568
0.026 0.162 0.300 0.440 0.583
0.040 0.176 0.314 0.454 0.597
0.053 0.189 0.328 0.469 0.612
10
°C
°C
0
0.067 0.203 0.342 0.483 0.626
0.080 0.217 0.356 0.497 0.640
0.094 0.231 0.370 0.511 0.655
0.107 0.244 0.384 0.525 0.669
0.121 0.258 0.398 0.540 0.684
0.135 0.272 0.412 0.554 0.698
0 10 20 0 40
500 510 520 530 540
8.655 8.849 9.044 9.239 9.434
50 60 70 80 90
0.698 0.845 0.993 1.144 1.296
0.713 0.860 1.008 1.159 1.312
0.727 0.874 1.023 1.174 1.327
0.742 0.889 1.038 1.189 1.342
0.757 0.904 1.053 1.205 1.358
0.771 0.919 1.068 1.220 1.373
0.786 0.934 1.083 1.235 1.389
0.801 0.948 1.098 1.250 1.404
0.815 0.963 1.114 1.266 1.420
0.830 0.978 1.129 1.281 1.435
0.845 0.993 1.144 1.296 1.451
50 60 70 80 90
100 110 120 130 140
1.451 1.607 1.765 1.925 2.087
1.466 1.623 1.781 1.941 2.103
1.482 1.639 1.797 1.957 2.119
1.497 1.654 1.813 1.973 2.135
1.513 1.670 1.829 1.989 2.152
1.529 1.686 1.845 2.006 2.168
1.544 1.702 1.861 2.022 2.184
1.560 1.718 1.877 2.038 2.201
1.576 1.733 1.893 2.054 2.217
1.591 1.749 1.909 2.070 2.233
1.607 1.765 1.925 2.087 2.250
150 160 170 180 190
2.250 2.415 2.581 2.749 2.918
2.266 2.431 2.598 2.766 2.935
2.283 2.448 2.614 2.783 2.952
2.299 2.464 2.631 2.800 2.969
2.316 2.481 2.648 2.816 2.986
2.332 2.498 2.665 2.833 3.003
2.349 2.514 2.682 2.850 3.020
2.365 2.531 2.698 2.867 3.038
2.382 2.548 2.715 2.884 3.055
2.398 2.564 2.732 2.901 3.072
200 210 220 230 240
3.089 3.261 3.434 3.609 3.785
3.106 3.278 3.452 3.627 3.803
3.123 3.296 3.469 3.644 3.820
3.140 3.313 3.487 3.662 3.838
3.158 3.330 3.504 3.679 3.856
3.175 3.348 3.522 3.697 3.873
3.192 3.365 3.539 3.714 3.891
3.209 3.382 3.557 3.732 3.909
3.227 3.400 3.574 3.750 3.927
250 260 270 280 290
3.962 4.140 4.319 4.500 4.681
3.980 4.158 4.337 4.518 4.699
3.998 4.176 4.355 4.536 4.717
4.015 4.194 4.373 4.554 4.736
4.033 4.212 4.391 4.572 4.754
4.051 4.230 4.410 4.590 4.772
4.069 4.248 4.428 4.608 4.790
4.087 4.266 4.446 4.627 4.809
300 310 320 330 340
4.863 5.047 5.231 5.416 5.601
4.882 5.065 5.249 5.434 5.620
4.900 5.083 5.268 5.453 5.639
4.918 5.102 5.286 5.471 5.657
4.937 5.120 5.305 5.490 5.676
4.955 5.139 5.323 5.508 5.695
4.973 5.157 5.342 5.527 5.713
350 360 370 380 390
5.788 5.975 6.163 6.352 6.541
5.807 5.994 6.182 6.371 6.560
5.825 6.013 6.201 6.390 6.579
5.844 6.032 6.220 6.409 6.598
5.863 6.050 6.239 6.427 6.617
5.882 6.069 6.257 6.446 6:636
400 410 420 430 440
6.731 6.921 7.112 7.304 7.496
6.750 6.940 7.131 7.323 7.515
6. 69 6.959 7.151 7.342 7.534
6.788 6.979 7.170 7.361 7.553
6.807 6.998 7.189 7.380 7.572
450 460 470 480 490
7.688 7.881 8.074 8.267 8.461
7.707 7.900 8.093 8.287 8.480
7.726 7.919 8.112 8.306 8.500
7.746 7.939 8.132 8.325 8.519
7.765 7.958 8.151 8.345 8.539
°C
0
1
2
2
3
3
4
4
5
6
7
8
10
°C
8.772 8.966 9.161 9.356 9.551
8.791 8.986 9.180 9.375 9.570
8.810 9.005 9.200 9.395 9.590
8.830 9.024 9.219 9.414 9.609
8.849 9.044 9.239 9.434 9.629
500 510 520 530 540
550 9.629 9.648 9.668 9.687 9.707 9.726 9.746 9.765 9.785 560 9.824 9.843 9.863 9.883 9.902 9.922 9.941 9.961 9.980 570 10.019 10.039 10.058 10.078 10.097 10.117 10.137 10.156 10.176 580 10.215 10.234 10.254 10.273 10.293 10.312 10.332 10.352 10.371 590 10.410 10.430 10.449 10.469 10.488 10.508 10.528 10.547 10.567
9.804 10.000 10.195 10.391 10.586
9.824 10.019 10.215 10.410 10.606
550 560 570 580 590
100 110 120 130 140
600 610 620 630 640
10.606 10.801 10.997 11.192 11.388
10-625 10.821 11.016 11.212 11.407
10.645 10.840 11.036 11.231 11.427
10.664 10.860 11.055 11.251 11.446
10.684 10.879 11.075 11.270 11.466
10.703 10.899 11.095 11.290 11.485
10.723 10.919 11.114 11.310 11.505
10.743 10.938 11.134 11.329 11.525
10.762 10.958 11.153 11.349 11.544
10.782 10.977 11.173 11.368 11.564
10.801 10.997 11.192 11.388 11.583
600 610 620 630 640
2.415 2.581 2.749 2.918 3.089
150 160 170 180 190
650 660 670 680 690
11.583 11.778 11.974 12.169 12.364
11.603 11.798 11.993 12.188 12.383
11.622 11.817 12.013 12.208 12.403
11.642 11.837 12.032 12.227 12.422
11.661 11.857 12.052 12.247 12.442
11.681 11.876 12.071 12.266 12.461
11.700 11.896 12.091 12.286 12.481
11.720 11.915 12.110 12.305 12.500
11.739 11.935 12.130 12.325 12-519
11.759 11.954 12.149 12.344 12.539
11.778 11.974 12.169 12.364 12.558
650 660 670 680 690
3.244 3.417 3.592 3.767 3.944
3.26 3.434 3.609 3.785 3.962
200 210 220 230 240
700 710 720 730 740
12.558 12.753 12.947 13.142 13.336
12.578 12.772 12.967 13.161 13.355
12.597 12.792 12.986 13.180 13.374
12.617 12.811 13.006 13.200 13.394
12.636 12.831 13.025 13.219 13.413
12.656 12.850 13.045 13.239 13.432
12.675 12.870 13.064 13.258 13.452
12.695 12.889 13.083 13.277 13.471
12.714 12.909 13.103 13.297 13.491
12.734 12.928 13.122 13.316 13.510
12.753 12.947 13.142 13.336 13.529
700 710 720 730 740
4.104 4.284 4.464 4.645 4.827
4.122 4.301 4.482 4.663 4.845
4.140 4.319 4.500 4.681 4.863
250 260 270 280 290
750 760 770 780 790
13.529 13.723 13.916 14.109 14.302
13.549 13.742 13.935 14.128 14.321
13.568 13.761 13.955 14.147 14.340
13.587 13.781 13.974 14.167 14.359
13.607 13.800 13.993 14.186 14.378
13.626 13.819 14.012 14.205 14.398
13.645 13.839 14.032 14.224 14.417
13.665 13.858 14.051 14.244 14.436
13.684 13.877 14 .070 14.263 14.455
13.703 13.897 14.090 14.282 14.475
13.723 13.916 14.109 14.302 14.494
750 760 770 780 790
4.992 5.175 5.360 5.546 5.732
5.010 5.194 5.379 5.564 5.751
5.028 5.212 5.397 5.583 5.769
5.047 5.231 5.416 5.601 5.788
300 310 320 330 340
800 810 820 830 840
14.494 14.686 14.877 15.069 15.260
14.513 14.705 14.897 15.088 15.279
14.532 14.724 14.916 15.107 15.298
14-551 14.743 14.935 15.126 15.317
14.571 14.762 14.954 15.145 15.336
14.590 14.782 14.973 15.164 15.355
14.609 14.801 14.992 15.183 15.374
14.628 14.820 15.011 15.202 15.393
14.647 14.839 15.030 15.221 15.412
14.667 14.858 15.050 15.241 15.431
14.686 14.877 15.069 15.260 15.450
800 810 820 830 840
5.900 6.088 6.276 6.465 6.655
5.919 6.107 6.295 6.484 6.674
5.938 6.126 6.314 6.503 6.693
5.956 6.144 6.333 6.522 6.712
5.975 6.163 6.352 6.541 6.731
350 360 370 380 390
850 860 870 880 890
15.450 15.640 15.830 16.020 16.208
15.469 15.659 15.849 16.038 16.227
15.488 15.678 15.868 16.057 16.246
15.507 15.697 15.887 16.076 16.265
15.526 15.716 15.906 16.095 16.284
15.545 15.735 15.925 16.114 16.303
15.564 15.754 15.944 16.133 16.322
15.583 15.773 15.963 16.152 16.340
15.602 15.792 15.982 16.171 16.359
15.621 15.811 16.001 19.190 16.378
15.640 15.830 16.020 16.208 16.397
850 860 870 880 890
6.826 7.017 7.208 7.400 7.592
6.845 7.036 7.227 7.419 7.611
6.864 7.055 7.246 7.438 7.630
6.883 7.074 7.265 7.457 7.649
6.902 7.093 7.285 7.476 7.669
6.921 7.112 7.304 7.496 7.688
400 410 420 430 440
900 910 920 930 940
16.397 16.585 16.773 16.960 17.147
16.416 16.604 16.791 16.979 17.165
16.435 16.623 16.810 16.997 17.184
16.453 16.641 16.829 17.016 17.203
16.472 16.660 16.848 17.035 17.221
16.491 16.679 16.866 17.053 17.240
16.510 16.698 16.885 17.072 17.258
16.529 16.716 16.904 17.091 17.277
16.547 16.735 16.923 17.109 17.296
16.566 16.754 16.941 17.128 17.314
16.585 16.773 16.960 17.147 17.333
900 910 920 930 940
7.784 7.977 8.170 8.364 8.558
7.804 7.996 8.190 8.383 8.577
7.823 8.016 8.209 8.403 8.597
7.842 8.035 8.229 8.422 8.616
7.861 8.054 8.248 8.422 8.636
7.881 8.074 8.267 8.461 8.655
450 460 470 480 490
950 960 970 980 990
17.333 17.519 17.704 17.889 18.073
17.352 17.537 17.723 17.907 18.092
17.370 17.556 17.741 17.926 18.110
17.389 17.574 17.760 17.944 18.128
17.407 17.593 17.778 17.963 18.147
17.426 17.611 17.796 17.981 18.165
17.444 17.630 17.815 17.999 18.184
17.463 17.648 17.833 18.018 18.202
17.482 17.667 17.852 18.036 18.220
17.500 17.686 17.870 18.055 18.239
17.519 17.704 17.889 18.073 18.257
950 960 970 980 990
6
7
8
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
°C
5
9
9
Z-238
1 8.674 8.869 9.063 9.258 9.453
2 8.694 8.888 9.083 9.278 9.473
3 8.713 8.908 9.102 9.297 9.492
4 8.733 8.927 9.122 9.317 9.512
5 8.752 8.947 9.141 9.336 9.531
9
Z
+ –
Revised Thermocouple Reference Tables
NONE ESTABLISHED
Tungsten5% Rhenium vs. Tungsten26% Rhenium
C
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
+ –
Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade -32 to 4208°F -0 to 2320°C Extension Grade 32 to 1600°F 0 to 870°C LIMITS OF ERROR (whichever is greater) Standard: 4.5°C to 425°C 1.0% to 2320°C Special: Not Established COMMENTS, BARE WIRE ENVIRONMENT: Vacuum, Inert; Hydrogen; Beware of Embrittlement; Not Practical Below 750°F; Not for Oxidizing Atmosphere TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
Thermoelectric Voltage in Millivolts
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
1000 1010 1020 1030 1040
18.257 18.440 18.623 18.805 18.987
18.275 18.459 18.641 18.824 19.005
18.294 18.477 18.660 18.842 19.023
18.312 18.495 18.678 18.860 19.041
18.330 18.513 18.696 18.878 19.060
18.349 18.532 18.714 18.896 19.078
18.367 18.550 18.732 18.914 19.096
18.385 18.568 18.751 18.933 19.114
18.404 18.587 18.769 18.951 19.132
18.422 18.605 18.787 18.969 19.150
18.440 18.623 18.805 18.987 19.168
1000 1010 1020 1030 1040
1500 1510 1520 1530 1540
26.722 26.876 27.030 27.183 27.335
26.738 26.892 27.045 27.198 27.350
26.753 26.907 27.060 27.213 27.365
26.768 26.922 27.076 27.228 27.380
26.784 26.938 27.091 27.244 27.396
26.799 26.953 27.106 27.259 27.411
26.815 26.968 27.121 27.274 27.426
26.830 26.984 27.137 27.289 27.441
26.845 26.999 27.152 27.304 27.456
26.861 27.014 27.167 27.320 27.471
26.876 27.030 27.183 27.335 27.486
1500 1510 1520 1530 1540
1050 1060 1070 1080 1090
19.168 19.349 19.529 19.709 19.888
19.186 19.367 19.547 19.727 19.905
19.204 19.385 19.565 19.744 19.923
19.223 19.403 19.583 19.762 19.941
19.241 19.421 19.601 19.780 19.959
19.259 19.439 19.619 19.798 19.977
19.277 19.457 19.637 19.816 19.995
19.295 19.475 19.655 19.834 20.013
19.313 19.493 19.673 19.852 20.030
19.331 19.511 19.691 19.870 20.048
19.349 19.529 19.709 19.888 20.066
1050 1060 1070 1080 1090
1550 1560 1570 1580 1590
27.486 27.637 27.788 27.938 28.087
27.502 27.653 27.803 27.953 28.102
27.517 27.668 27.818 27.968 28.117
27.532 27.683 27.833 27.983 28.132
27.547 27.698 27.848 27.997 28.146
27.562 27.713 27.863 28.012 28.161
27.577 27.728 27.878 28.027 28.176
27.592 27.743 27.893 28.042 28.191
27.607 27.758 27.908 28.057 28.206
27.622 27.773 27.923 28.072 28.221
27.637 27.788 27.938 28.087 28.236
1550 1560 1570 1580 1590
1100 1110 1120 1130 1140
20.066 20.244 20.421 20.598 20.774
20.084 20.262 20.439 20.616 20.792
20.102 20.279 20.457 20.633 20.809
20.120 20.297 20.474 20.651 20.827
20.137 20.315 20.492 20.669 20.845
20.155 20.333 20.510 20.686 20.862
20.173 20.350 20.527 20.704 20.880
20.191 20.368 20.545 20.721 20.897
20.208 20.386 20.563 20.739 20.915
20.226 20.404 20.580 20.757 20.932
20.066 20.421 20.598 20.774 20.950
1100 1110 1120 1130 1140
1600 1610 1620 1630 1640
28.236 28.531 28.531 28.678 28.824
28.250 28.398 28.546 28.692 28.838
28.265 28.413 28.560 28.707 28.853
28.280 28.428 28.575 28.722 28.868
28.295 28.443 28.590 28.736 28.882
28.310 28.457 28.604 28.751 28.897
28.324 28.472 28.619 28.765 28.911
28.339 28.487 28.634 28.780 28.926
28.354 28.502 28.648 28.795 28.940
28.369 28.516 28.663 28.809 28.955
28.531 28.531 28.678 28.824 28.969
1600 1610 1620 1630 1640
1150 1160 1170 1180 1190
20.950 21.125 21.299 21.473 21.647
20.967 21.142 21.317 21.491 21.664
20.985 21.160 21.334 21.508 21.681
21.002 21.177 21.352 21.525 21.698
21.020 21.195 21.369 21.543 21.716
21.037 21.212 21.386 21.560 21.733
21.055 21.230 21.404 21.577 21.750
21.072 21.247 21.421 21.595 21.768
21.090 21.265 21.439 21.612 21.785
21.107 21.282 21.456 21.629 21.802
21.125 21.299 21.473 21.647 21.819
1150 1160 1170 1180 1190
1650 1660 1670 1680 1690
28.969 29.114 29.259 29.402 29.546
28.984 29.129 29.273 29.417 29.560
28.998 29.143 29.287 29.431 29.574
29.013 29.158 29.302 29.445 29.588
29.027 29.172 29.316 29.460 29.603
29.042 29.187 29.331 29.474 29.617
29.056 29.201 29.345 29.488 29.631
29.071 29.215 29.359 29.503 29.645
29.085 29.230 29.374 29.517 29.660
29.100 29.244 29.388 29.531 29.674
29.114 29.259 29.402 29.546 29.688
1650 1660 1670 1680 1690
1200 1210 1220 1230 1240
21.819 21.991 22.163 22.334 22.504
21.837 22.009 22.180 22.35 22.521
21.854 22.026 22.197 22.368 22.538
21.871 22.043 22.214 22.385 22.555
21.888 22.060 22.231 22.402 22.572
21.905 22.077 22.249 22.419 22.589
21.923 22.094 22.266 22.436 22.606
21.940 22.112 22.283 22.453 22.623
21.957 22.129 22.300 22.470 22.640
21.974 22.146 22.317 22.487 22.657
21.991 22.163 22.334 22.504 22.674
1200 1210 1220 1230 1240
1700 1710 1720 1730 1740
29.688 29.830 29.971 30.112 30.252
29.702 29.844 29.985 30.126 30.266
29.716 29.858 29.999 30.140 30.280
29.731 29.872 30.013 30.154 30.294
29.745 29.886 30.027 30.168 30.308
29.759 29.901 30.041 30.182 30.321
29.773 29.915 30.056 30.196 30.335
29.787 29.929 30.070 30.210 30.349
29.802 29.943 30.084 30.224 30.363
29.816 29.957 30.098 30.238 30.377
29.830 29.971 30.112 30.252 30.391
1700 1710 1720 1730 1740
1250 1260 1270 1280 1290
22.674 22.843 23.012 23.180 23.347
22.691 22.860 23.029 23.196 23.364
22.708 22.877 23.045 23.213 23.380
22.725 22.894 23.062 23.230 23.397
22.742 22.911 23.079 23.247 23.414
22.759 22.928 23.096 23.263 23.431
22.776 22.944 23.113 23.280 23.447
22.792 22.961 23.129 23.297 23.464
22.809 22.978 23.146 23.314 23.481
22.826 22.995 23.163 23.330 23.497
22.843 23.012 23.180 23.347 23.514
1250 1260 1270 1280 1290
1750 1760 1770 1780 1790
30.391 30.530 30.668 30.805 30.942
30.405 30.544 30.682 30.819 30.956
30.419 30.557 30.695 30.833 30.969
30.433 30.571 30.709 30.846 30.983
30.447 30.585 30.723 30.860 30.997
30.460 30.599 30.737 30.874 31.010
30.474 30.613 30.750 30.887 31.024
30.488 30.627 30.764 30.901 31.038
30.502 20.640 30.778 30.915 31.051
30.516 30.654 30.792 20.928 31.065
30.530 30.668 30.805 30.942 31.078
1750 1760 1770 1780 1790
1300 1310 1320 1330 1340
23.514 23.680 23.846 24.010 24.175
23.530 23.697 23.862 24.027 24.191
23.547 23.713 23.879 24.043 24.208
23.564 23.730 23.895 24.060 24.224
23.580 23.746 23.912 24.076 24.240
23.597 23.763 23.928 24.093 24.257
23.614 23.779 23.945 24.109 24.273
23.630 23.796 23.961 24.126 24.290
23.647 23.812 23.978 24.142 24.306
23.663 23.829 23.994 24.158 24.322
23.680 23.846 24.010 24.175 24.339
1300 1310 1320 1330 1340
1800 1810 1820 1830 1840
31.078 31.214 31.349 31.483 31.617
31.092 31.227 31.362 31.496 31.630
31.105 31.241 31.376 31.510 31.643
31.119 31.254 31.389 31.523 31.656
31.133 31.268 31.403 31.536 31.670
31.146 31.281 31.416 31.550 31.683
31.160 31.295 31.429 31.563 31.696
31.173 31.308 31.443 31.577 31.710
31.187 31.322 31.456 31.590 31.723
31.200 31.335 31.470 31.603 31.736
31.214 31.349 31.483 31.617 31.749
1800 1810 1820 1830 1840
1350 1360 1370 1380 1390
24.339 24.502 24.664 24.826 24.988
24.355 24.518 24.680 24.842 25.004
24.371 24.534 24.697 24.859 25.020
24.388 24.551 24.713 24.875 25.036
24.404 24.567 24.729 24.891 25.052
24.420 24.583 24.745 24.907 25.068
24.437 24.599 24.762 24.923 25.084
24.453 24.616 24.778 24.939 25.100
24.46 24.632 24.794 24.955 25.116
24.485 24.648 24.810 24.971 24.132
24.502 24.664 24.826 24.988 25.148
1350 1360 1370 1380 1390
1850 1860 1870 1880 1890
31.749 31.882 32.013 32.144 32.274
31.763 31.895 32.026 32.157 32.287
31.776 31.908 32.040 32.170 32.300
31.789 31.921 32.053 31.183 31.313
31.802 31.934 32.066 32.196 32.326
31.816 31.948 32.079 32.209 32.339
31.829 31.961 32.092 32.222 32.352
31.842 31.974 32.105 32.235 32.365
31.855 31.987 32.118 32.248 32.378
31.869 32.000 32.131 32.261 32.391
31.882 32.013 32.144 32.274 32.404
1850 1860 1870 1880 1890
1400 1410 1420 1430 1440
25.148 25.308 25.468 25.627 25.785
25.164 25.324 25.484 25.643 25.801
25.180 25.340 25.500 25.658 25.817
25.196 25.356 25.516 25.674 25.832
25.212 25.372 25.532 25.690 25.848
25.228 25.388 25.547 25.706 25.864
25.244 25.404 25.563 25.722 25.880
25.260 25.420 25.579 25.738 25.896
25.276 25.436 25.595 25.753 25.911
25.292 25.452 25.611 25.769 25.927
25.308 25.468 25.627 25.785 25.943
1400 1410 1420 1430 1440
1900 1910 1920 1930 1940
32.404 32.533 32.661 32.788 32.915
32.417 32.546 32.674 32.801 32.928
32.430 32.558 32.686 32.814 32.940
32.443 32.571 32.699 32.826 32.953
32.456 32.584 32.712 32.839 32.966
32.468 32.597 32.725 32.852 32.978
32.481 32.610 32.737 32.864 32.991
32.494 32.623 32.750 32.877 33.003
32.507 32.635 32.763 32.890 33.016
32.520 32.648 32.776 32.902 33.028
32.533 32.661 32.788 32.915 33.041
1900 1910 1920 1930 1940
1450 1460 1470 1480 1490
25.943 26.100 26.256 26.412 26.568
25.959 26.116 26.272 26.428 26.583
25.974 26.131 26.288 26.443 26.599
25.990 26.147 26.303 26.459 26.614
26.006 26.163 26.319 26.474 26.629
26.021 26.178 26.334 26.490 26.645
26.037 26.194 26.350 26.505 26.660
26.053 26.209 26.366 26.521 26.676
26.069 26.225 26.381 26.537 26.691
26.084 26.241 26.397 26.552 26.707
26.100 26.256 26.412 26.568 26.722
1450 1460 1470 1480 1490
1950 1960 1970 1980 1990
33.041 33.166 33.291 33.415 33.538
33.054 33.179 33.303 33.427 33.550
33.066 33.191 33.316 33.439 33.562
33.079 33.204 33.328 33.452 33.575
33.091 33.216 33.341 33.464 33.587
33.104 33.229 33.353 33.476 33.599
33.116 33.241 33.365 33.489 33.611
33.129 33.254 33.378 33.501 33.623
33.141 33.266 33.390 33.513 33.636
33.154 33.278 33.402 33.525 33.648
33.166 33.291 33.415 33.538 33.660
1950 1960 1970 1980 1990
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
Z-239
°C
°C
MAXIMUM TEMPERATURE RANGE Thermocouple Grade -32 to 4208°F -0 to 2320°C Extension Grade 32 to 1600°F 0 to 870°C LIMITS OF ERROR (whichever is greater) Standard: 4.5°C to 425°C 1.0% to 2320°C Special: Not Established COMMENTS, BARE WIRE ENVIRONMENT: Vacuum, Inert; Hydrogen; Beware of Embrittlement; Not Practical Below 750°F; Not for Oxidizing Atmosphere TEMPERATURE IN DEGREES °C REFERENCE JUNCTION AT 0°C
+ –
Thermocouple Grade
NONE ESTABLISHED
Tungsten5% Rhenium vs. Tungsten26% Rhenium
Revised Thermocouple Reference Tables
C
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
0
1
2
3
4
5
6
7
8
9
10
2000 2010 2020 2030 2040
33.660 33.782 33.902 34.022 34.142
33.672 33.794 33.914 34.034 34.153
33.684 33.806 33.926 34.046 34.165
33.697 33.818 33.938 34.058 34.177
33.709 33.830 33.950 34.070 34.189
33.721 33.842 33.962 34.082 34.201
33.733 33.854 33.974 34.094 34.213
33.745 33.866 33.986 34.106 34.225
33.757 33.878 33.998 34.118 34.236
33.769 33.890 34.010 34.130 34.248
33.782 33.902 34.022 34.142 34.260
2000 2010 2020 2030 2040
2200 2210 2220 2230 2240
35.932 36.036 36.138 36.240 36.341
35.942 36.046 36.149 36.250 36.351
35.953 36-056 36.159 36.260 36.361
35.963 36.067 36.169 36.271 36.371
35.973 36.077 36.179 36.281 36.381
35.984 36.087 36.189 36.291 36.391
35.994 36.097 36.200 36.301 36.401
36.004 36.108 36.210 36.311 36.411
36.015 36.118 36.220 36.321 36.421
36.025 36.128 36.230 36.331 36.431
36.036 36.138 36.240 36.341 36.441
2200 2210 2220 2230 2240
2050 2060 2070 2080 2090
34.260 34.378 34.494 34.610 34.725
34.272 34.389 34.506 34.622 34.737
34.284 34.401 34.518 34.633 34.748
34.295 34.413 34.529 34.645 34.760
34.307 34.424 34.541 34.656 34.771
34.319 34.436 34.552 34.668 34.782
34.331 34.448 34.564 34.679 34.794
34.342 34.459 34.576 34.691 34.805
34.354 34.471 34.587 34.702 34.817
34.366 34.483 34.599 34.714 34.828
34.378 34.494 34.610 34.725 34.839
2050 2060 2070 2080 2090
2250 2260 2270 2280 2290
36.441 36.539 36.637 36.733 36.828
36.451 36.549 36.646 36.743 36.838
36.460 36.559 36.656 36.752 36.847
36.470 36.569 36.666 36.762 36.857
36.480 36.578 36.675 36.771 36.866
36.490 36.588 36.685 36.781 36.875
36-500 36.598 36.695 36.790 36.885
36.510 36.608 36.704 36.800 36.894
36.520 36.617 36.714 36.809 36.903
36.529 36.627 36.723 36.819 36.913
36.539 36.637 36.733 36.828 36.922
2250 2260 2270 2280 2290
2100 2110 2120 2130 2140
34.839 34.953 35.065 35.177 35.288
34.851 34.964 35.077 35.188 35.299
34.862 34.975 35.088 35.199 35.310
34.874 34.987 35.099 35.210 35.321
34.885 34.998 35.110 35.221 35.332
34.896 35.009 35.121 35.232 35.343
34.908 35.020 35.132 35.243 35.353
34.919 35.032 34.144 35.254 35.364
34.930 35.043 35.155 35.265 35.375
34.942 35.054 35.166 35.277 35.386
34.953 35.065 35.177 35.288 35.397
2100 2110 2120 2130 2140
2300 36.922 36.932 36.941 36.950 36.959 36.969 36.978 36.987 36.997 37.006 37.015 2300 2310 37.015 37.024 37.033 37.043 37.052 37.061 37.070 37.079 37.088 37.097 37.107 2310
2150 2160 2170 2180 2190
35.397 35.506 35.614 35.721 35.827
35.408 35.517 35.625 35.731 35.837
35.419 35.528 35.635 35.742 35.848
35.430 35.539 35.646 35.753 35.858
35.441 35.549 35.657 35.763 35.869
35.452 35.560 35.668 35.774 35.879
35.463 35.571 35.678 35.784 35.890
35.474 35.582 35.689 35.795 35.900
35.484 35.592 35.700 35.806 35.911
35.495 35.603 35.710 35.816 35.921
35.506 35.614 35.721 35.827 35.932
2150 2160 2170 2180 2190
°C
0
1
2
3
4
5
6
7
8
9
10
°C
°C
Z-240
0
1
2
3
4
5
6
7
8
9
10
°C
°C
Z
+ –
Revised Thermocouple Reference Tables
Tungsten5% Rhenium vs. Tungsten26% Rhenium
C
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
1
2
3
4
5
6
MAXIMUM TEMPERATURE RANGE Thermocouple Grade -32 to 4208°F -0 to 2320°C Extension Grade 32 to 1600°F 0 to 870°C LIMITS OF ERROR (whichever is greater) Standard: 4.5°C to 425°C 1.0% to 2320°C Special: Not Established COMMENTS, BARE WIRE ENVIRONMENT: Vacuum, Inert; Hydrogen; Beware of Embrittlement; Not Practical Below 750°F; Not for Oxidizing Atmosphere TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
0
0 10 20 30 40
-0.234 -0.162 -0.089 -0.015 0.059
7
8
9
50 60 70 80 90
0.135 0.211 0.288 0.365 0.443
0.142 0.218 0.295 0.373 0.451
0.150 0.226 0.303 0.381 0.459
0.157 0.234 0.311 0.389 0.467
0.165 0.241 0.319 0.396 0.475
0.173 0.249 0.326 0.404 0.483
0.180 0.257 0.334 0.412 0.491
0.188 0.264 0.342 0.420 0.499
0.196 0.272 0.350 0.428 0.506
0.203 0.280 0.357 0.436 0.514
100 110 120 130 140
0.522 0.602 0.682 0.763 0.845
0.530 0.610 0.690 0.771 0.853
0.538 0.618 0.698 0.779 0.861
0.546 0.626 0.706 0.788 0.869
0.554 0.634 0.714 0.796 0.878
0.562 0.642 0.723 0.804 0.886
0.570 0.650 0.731 0.812 0.894
0.578 0.658 0.739 0.820 0.902
0.586 0.666 0.747 0.828 0.911
150 160 170 180 190
0.927 1.010 1.093 1.178 1.262
0.935 1.018 1.102 1.186 1.271
0.944 1.027 1.110 1.194 1.279
0.952 1.035 1.119 1.203 1.288
0.960 1.043 1.127 1.211 1.296
0.968 1.052 1.135 1.220 1.305
0.977 1.060 1.144 1.228 1.313
0.985 1.068 1.152 1.237 1.322
200 210 220 230 240
1.348 1.434 1.520 1.607 1.695
1.356 1.442 1.529 1.616 1.703
1.365 1.451 1.537 1.625 1.712
1.373 1.459 1.546 1.633 1.721
1.382 1.468 1.555 1.642 1.730
1.390 1.477 1.563 1.651 1.739
1.399 1.485 1.572 1.660 1.748
250 260 270 280 290
1.783 1.872 1.961 2.051 2.141
1.792 1.880 1.970 2.060 2.150
1.801 1.889 1.979 2.069 2.159
1.809 1.898 1.988 2.078 2.168
1.818 1.907 1.997 2.087 2.177
1.827 1.916 2.006 2.096 2.186
300 310 320 330 340
2.232 2.323 2.415 2.507 2.600
2.241 2.332 2.424 2.516 2.609
2.250 2.341 2.433 2.525 2.618
2.259 2.350 2.442 2.535 2.628
2.268 2.360 2.451 2.544 2.637
350 360 370 380 390
2.693 2.786 2.880 2.975 3.070
2.702 2.796 2.890 2.984 3.079
2.711 2.805 2.899 2.994 3.089
2.721 2.815 2.909 3.003 3.098
400 410 420 430 440
3.165 3.261 3.357 3.454 3.551
3.175 3.271 3.367 3.463 3.560
3.184 3.280 3.376 3.473 3.570
450 460 470 480 490
3.648 3.746 3.844 3.942 4.041
3.658 3.756 3.854 3.952 4.051
3.668 3.765 3.864 3.962 4.061
°F
0
10
°F
°F
0
6
7
8
10
°F
0 10 20 30 40
500 510 520 530 540
4.140 4.240 4.339 4.440 4.540
4.150 4.250 4.349 4.450 4.550
4.160 4.260 4.359 4.460 4.560
4.170 4.270 4.369 4.470 4.570
4.180 4.280 4.379 4.480 4.580
4.190 4.290 4.389 4.490 4.590
4.200 4.299 4.399 4.500 4.600
4.210 4.309 4.410 4.510 4.610
4.220 4.319 4.420 4.520 4.621
4.230 4.329 4.430 4.530 4.631
4.240 4.339 4.440 4.540 4.641
500 510 520 530 540
0.211 0.288 0.365 0.443 0.522
50 60 70 80 90
550 560 570 580 590
4.641 4.742 4.843 4.945 5.047
4.651 4.752 4.853 4.955 5.057
4.661 4.762 4.863 4.965 5.067
4.671 4.772 4.874 4.975 5.077
4.681 4.782 4.884 4.985 5.087
4.691 4.792 4.894 4.996 5.098
4.701 4.803 4.904 5.006 5.108
4.711 4.813 4.914 5.016 5.118
4.722 4.823 4.924 5.026 5.128
4.732 4.833 4.935 5.036 5.139
4.742 4.843 4.945 5.047 5.149
550 560 570 580 590
0.594 0.674 0.755 0.837 0.919
0.522 0.682 0.763 0.845 0.927
100 10 120 130 140
600 610 620 630 640
5.149 5.251 5.354 5.457 5.560
5.159 5.261 5.364 5.467 5.570
5.169 5.272 5.375 5.478 5.581
5.180 5.282 5.385 5.488 5.591
5.190 5.292 5.395 5.498 5.601
5.200 5.303 5.405 5.508 5.612
5.210 5.313 5.416 5.519 5.622
5.220 5.323 5.426 5.529 5.632
5.231 5.333 5.436 5.539 5.643
5.241 5.344 5.447 5.550 5.653
5.251 5.354 5.457 5.560 5.664
600 610 620 630 640
0.993 1.077 1.161 1.245 1.330
1.002 1.085 1.169 1.254 1.339
1.010 1.093 1.178 1.262 1.348
150 160 170 180 190
650 660 670 680 690
5.664 5.767 5.871 5.975 6.080
5.674 5.778 5.882 5.986 6.090
5.684 5.788 5.892 5.996 6.100
5.695 5.798 5.902 6.007 6.111
5.705 5.809 5.913 6.017 6.121
5.715 5.819 5.923 6.027 6.132
5.726 5.830 5.934 6.038 6.142
5.736 5.840 5.944 6.048 6.153
5.746 5.850 5.954 6.059 6.163
5.757 5.861 5.965 6.069 6.174
5.767 5.871 5.975 6.080 6.184
650 660 670 680 690
1.408 1.494 1.581 1.668 1.756
1.416 1.503 1.590 1.677 1.765
1.425 1.511 1.598 1.686 1.774
1.434 1.520 1.607 1.695 1.783
200 210 220 230 240
700 710 720 730 740
6.184 6.289 6.394 6.499 6.604
6.195 6.299 6.404 6.509 6.615
6.205 6.310 6.415 6.520 6.625
6.216 6.320 6.425 6.531 6.636
6.226 6.331 6.436 6.541 6.646
6.236 6.341 6.446 6.552 6.657
6.247 6.352 6.457 6.562 6.668
6.257 6.362 6.467 6.573 6.678
6.268 6.373 6.478 6.583 6.689
6.278 6.383 6.488 6.594 6.699
6.289 6.394 6.499 6.604 6.710
700 710 720 730 740
1.836 1.925 2.015 2.105 2.195
1.845 1.934 2.024 2.114 2.204
1.854 1.943 2.033 2.123 2.213
1.863 1.952 2.042 2.132 2.223
1.872 1.961 2.051 2.141 2.232
250 260 270 280 290
750 760 770 780 790
6.710 6.815 6.921 7.027 7.134
6.720 6.826 6.932 7.038 7.144
6.731 6.837 6.943 7.049 7.155
6.741 6.847 6.953 7.059 7.165
6.752 6.858 6.964 7.070 7.176
6.763 6.868 6.974 7.080 7.187
6.773 6.879 6.985 7.091 7.197
6.784 6.890 6.996 7.102 7.208
6.794 6.900 7.006 7.112 7.219
6.805 6.911 7.017 7.123 7.229
6.815 6.921 7.027 7.134 7.240
750 760 770 780 790
2.277 2.369 2.461 2.553 2.646
2.286 2.378 2.470 2.562 2.655
2.295 2.387 2.479 2.572 2.665
2.305 2.396 2.488 2.581 2.674
2.314 2.405 2.498 2.590 2.683
2.323 2.415 2.507 2.600 2.693
300 310 320 330 340
800 810 820 830 840
7.240 7.346 7.453 7.560 7.667
7.250 7.357 7.464 7.570 7.677
7.261 7.368 7.474 7.581 7.688
7.272 7.378 7.485 7.592 7.699
7.282 7.389 7.496 7.602 7.709
7.293 7.400 7.506 7.613 7.720
7.304 7.410 7.517 7.624 7.731
7.314 7.421 7.528 7.634 7.741
7.325 7.432 7.538 7.645 7.752
7.336 7.442 7.549 7.656 7.763
7.346 7.453 7.560 7.667 7.774
800 810 820 830 840
2.730 2.824 2.918 3.013 3.108
2.740 2.833 2.928 3.022 3.118
2.749 2.843 2.937 3.032 3.127
2.758 2.852 2.947 3.041 3.137
2.768 2.862 2.956 3.051 3.146
2.777 2.871 2.965 3.060 3.156
2.786 2.880 2.975 3.070 3.165
350 360 370 380 390
850 860 870 880 890
7.774 7.881 7.988 8.095 8.203
7.784 7.891 7.999 8.106 8.213
7.795 7.902 8.009 8.117 8.224
7.806 7.913 8.020 8.127 8.235
7.816 7.924 8.031 8.138 8.246
7.827 7.934 8.042 8.149 8.256
7.838 7.945 8.052 8.160 8.267
7.849 7.956 8.063 8.170 8.278
7.859 7.966 8.074 8.181 8.289
7.870 7.977 8.085 8.192 8.300
7.881 7.988 8.095 8.203 8.310
850 860 870 880 890
3.194 3.290 3.386 3.483 3.580
3.204 3.299 3.396 3.492 3.590
3.213 3.309 3.405 3.502 3.599
3.223 3.319 3.415 3.512 3.609
3.232 3.328 3.425 3.522 3.619
3.242 3.338 3.434 3.531 3.629
3.251 3.348 3.444 3.541 3.638
3.261 3.357 3.454 3.551 3.648
400 410 420 430 440
900 910 920 930 940
8.310 8.418 8.526 8.633 8.741
8.321 8.429 8.536 8.644 8.752
8.332 8.439 8.547 8.655 8.763
8.343 8.450 8.558 8.666 8.774
8.353 8.461 8.569 8.677 8.785
8.364 8.472 8.580 8.687 8.795
8.375 8.483 8.590 8.698 8.806
8.386 8.493 8.601 8.709 8.817
8.396 8.504 8.612 8.720 8.828
8.407 8.515 8.623 8.731 8.839
8.418 8.526 8.633 8.741 8.849
900 910 920 930 940
3.677 3.775 3.873 3.972 4.071
3.687 3.785 3.883 3.982 4.081
3.697 3.795 3.893 3.992 4.091
3.707 3.805 3.903 4.002 4.101
3.716 3.814 3.913 4.011 4.110
3.726 3.824 3.923 4.021 4.120
3.736 3.834 3.932 4.031 4.130
3.746 3.844 3.942 4.041 4.140
450 460 470 480 490
950 960 970 980 990
8.849 8.957 9.066 9.174 9.282
8.860 8.968 9.076 9.185 9.293
8.871 8.979 9.087 9.195 9.304
8.882 8.990 9.098 9.206 9.314
8.893 9.001 9.109 9.217 9.325
8.903 9.011 9.120 9.228 9.336
8.914 9.022 9.130 9.239 9.347
8.925 9.033 9.141 9.250 9.358
8.936 9.044 9.152 9.260 9.369
8.947 9.055 9.163 9.271 9.379
8.957 9.066 9.174 9.282 9.390
950 960 970 980 990
6
7
8
10
°F
°F
0
6
7
8
10
°F
-0.227 -0.220 -0.213 -0.206 -0.198 -0.191 -0.184 -0.177 -0.169 -0.162 -0.155 -0.148 -0.140 -0.133 -0.126 -0.118 -0.111 -0.104 -0.096 -0.089 -0.082 -0.074 -0.067 -0.060 -0.052 -0.045 -0.037 -0.030 -0.023 -0.015 -0.008 0.000 0.007 0.014 0.022 0.029 0.037 0.044 0.052 0.059 0.067 0.074 0.082 0.089 0.097 0.104 0.112 0.120 0.127 0.135
2
+ –
Extension Grade
°F
1
Thermocouple Grade
3
4
5
9
Z-241
1
1
2
2
3
3
4
4
5
5
9
9
MAXIMUM TEMPERATURE RANGE Thermocouple Grade -32 to 4208°F -0 to 2320°C Extension Grade 32 to 1600°F 0 to 870°C LIMITS OF ERROR (whichever is greater) Standard: 4.5°C to 425°C 1.0% to 2320°C Special: Not Established COMMENTS, BARE WIRE ENVIRONMENT: Vacuum, Inert; Hydrogen; Beware of Embrittlement; Not Practical Below 750°F; Not for Oxidizing Atmosphere TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
+ –
Thermocouple Grade
NONE ESTABLISHED
Tungsten5% Rhenium vs. Tungsten26% Rhenium
Revised Thermocouple Reference Tables
C
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °F
0
1
2
3
4
1000 1010 1020 1030 1040
9.390 9.499 9.607 9.715 9.824
9.401 9.509 9.618 9.726 9.835
9.412 9.520 9.629 9.737 9.846
9.423 9.531 9.640 9.748 9.857
9.434 9.542 9.650 9.759 9.867
1050 1060 1070 1080 1090
9.932 10.041 10.150 10.258 10.367
9.943 10.052 10.160 10.269 10.378
9.954 10.063 10.171 10.280 10.388
9.965 10.074 10.182 10.291 10.399
1100 1110 1120 1130 1140
10.475 10.584 10.693 10.801 10.910
10.486 10.595 10.703 10.812 10.921
10.497 10.606 10.714 10.823 10.932
1150 1160 1170 1180 1190
11.019 11.127 11.236 11.344 11.453
11.029 11.138 11.247 11.355 11.464
1200 1210 1220 1230 1240
11.561 11.670 11.778 11.887 11.995
1250 1260 1270 1280 1290
5
6
7
8
°F
°F
0
1
2
3
4
5
6
7
8
9
10
9.444 9.553 9.661 9.770 9.878
9.455 9.564 9.672 9.781 9.889
9.466 9.575 9.683 9.791 9.900
9.477 9.585 9.694 9.802 9.911
9.488 9.596 9.705 9.813 9.922
9
9.499 9.607 9.715 9.824 9.932
10
1000 1010 1020 1030 1040
1500 1510 1520 1530 1540
14.792 14.899 15.005 15.111 15.217
14.803 14.909 15.016 15.122 15.228
14.814 14.920 15.026 15.132 15.238
14.824 14.931 15.037 15.143 15.249
14.835 14.941 15.047 15.154 15.260
14.846 14.952 15.058 15.164 15.270
14.856 14.962 15.069 15.175 15.281
14.867 14.973 15.079 15.185 15.291
14.877 14.984 15.090 15.196 15.302
14.888 14.994 15.101 15.207 15.313
14.899 15.005 15.111 15.217 15.323
1500 1510 1520 1530 1540
9.976 10.084 10.193 10.302 10.410
9.987 10.095 10.204 10.312 10.421
9.998 10.106 10.215 10.323 10.432
10.008 10.117 10.226 10.334 10.443
10.019 10.128 10.236 10.345 10.454
10.030 10.139 10.247 10.356 10.464
9.932 10.150 10.258 10.367 10.475
1050 1060 1070 1080 1090
1550 1560 1570 1580 1590
15.323 15.429 15.535 15.640 15.746
15.334 15.440 15.545 15.651 15.756
15.344 15.450 15.556 15.661 15.767
15.355 15.461 15.566 15.672 15.777
15.366 15.471 15.577 15.683 15.788
15.376 15.482 15.588 15.693 15.799
15.387 15.492 15.598 15.704 15.809
15.397 15.503 15.609 15.714 15.820
15.408 15.514 15.619 15.725 15.830
15.418 15.524 15.630 15.735 15.841
15.429 15.535 15.640 15.746 15.851
1550 1560 1570 1580 1590
10.508 10.617 10.725 10.834 10.942
10.519 10.627 10.736 10.845 10.953
10.530 10.638 10.747 10.856 10.964
10.541 10.649 10.758 10.866 10.975
10.551 10.660 10.769 10.877 10.986
10.562 10.671 10.780 10.888 10.997
10.573 10.682 10.790 10.899 11.008
10.584 10.693 10.801 10.910 11.019
1100 1110 1120 1130 1140
1600 1610 1620 1630 1640
15.851 15.956 16.062 16.167 16.271
15.862 15.967 16.072 16.177 16.282
15.872 15.977 16.083 16.187 16.292
15.883 15.988 16.093 16.198 16.303
15.893 15.998 16.104 16.208 16.313
15.904 16.009 16.114 16.219 16.324
15.914 16.020 16.125 16.229 16.334
15.925 16.030 16.135 16.240 16.345
15.935 16.041 16.146 16.250 16.355
15.946 16.051 16.156 16.261 16.366
15.956 16.062 16.167 16.271 16.376
1600 1610 1620 1630 1640
11.040 11.149 11.257 11.366 11.475
11.051 11.160 11.268 11.377 11.485
11.062 11.171 11.279 11.388 11.496
11.073 11.181 11.290 11.399 11.507
11.084 11.192 11.301 11.409 11.518
11.095 11.203 11.312 11.420 11.529
11.105 11.214 11.323 11.431 11.540
11.116 11.225 11.333 11.442 11.551
11.127 11.236 11.344 11.453 11.561
1150 1160 1170 1180 1190
1650 1660 1670 1680 1690
16.376 16.481 16.585 16.689 16.794
16.387 16.491 16.596 16.700 16.804
16.397 16.502 16.606 16.710 16.814
16.407 16.512 16.616 16.721 16.825
16.418 16.522 16.627 16.731 16.835
16.428 16.533 16.637 16.741 16.846
16.439 16.543 16.648 16.752 16.856
16.449 16.554 16.658 16.762 16.866
16.460 16.564 16.669 16.773 16.877
16.470 16.575 16.679 16.783 16.887
16.481 16.585 16.689 16.794 16.898
1650 1660 1670 1680 1690
11.572 11.681 11.789 11.898 12.006
11.583 11.692 11.800 11.909 12.017
11.594 11.702 11.811 11.919 12.028
11.605 11.713 11.822 11.930 12.039
11.616 11.724 11.833 11.941 12.050
11.627 11.735 11.844 11.952 12.060
11.637 11.746 11.854 11.963 12.071
11.648 11.757 11.865 11.974 12.082
11.659 11.768 11.876 11.984 12.093
11.670 11.778 11.887 11.995 12.104
1200 1210 1220 1230 1240
1700 1710 1720 1730 1740
16.898 17.001 17.105 17.209 17.312
16.908 17.012 17.116 17.219 17.323
16.918 17.022 17.126 17.230 17.333
16.929 17.033 17.136 17.240 17.343
16.939 17.043 17.147 17.250 17.35
16.950 17.053 17.157 17.261 17.364
16.960 17.064 17.167 17.271 17.374
16.970 17.074 17.178 17.281 17.385
16.981 17.084 17.188 17.292 17.395
16.991 17.095 17.198 17.302 17.405
17.001 17.105 17.209 17.312 17.416
1700 1710 1720 1730 1740
12.104 12.212 12.320 12.429 12.537
12.115 12.223 12.331 12.439 12.548
12.125 12.234 12.342 12.450 12.558
12.136 12.245 12.353 12.461 12.569
12.147 12.255 12.364 12.472 12.580
12.158 12.266 12.374 12.483 12.591
12.169 12.277 12.385 12.494 12.602
12.180 12.288 12.396 12.504 12.612
12.190 12.299 12.407 12.515 12.623
12.201 12.310 12.418 12.526 12.634
12.212 12.320 12.429 12.537 12.645
1250 1260 1270 1280 1290
1750 1760 1770 1780 1790
17.416 17.519 17.622 17.725 17.827
17.426 17.529 17.632 17.735 17.838
17.436 17.539 17.642 17.745 17.848
17.447 17.550 17.653 17.755 17.858
17.457 17.560 17.663 17.766 17.868
17.467 17.570 17.673 17.776 17.879
17.477 17.581 17.683 17.786 17.889
17.488 17.591 17.694 17.796 17.899
17.498 17.601 17.704 17.807 17.909
17.508 17.611 17.714 17.817 17.920
17.519 17.622 17.725 17.827 17.930
1750 1760 1770 1780 1790
1300 1310 1320 1330 1340
12.645 12.753 12.861 12.969 13.077
12.656 12.764 12.872 12.980 13.088
12.667 12.775 12.883 12.991 13.098
12.677 12.785 12.893 13.001 13.109
12.688 12.796 12.904 13.012 13.120
12.699 12.807 12.915 13.023 13.131
12.710 12.818 12.926 13.034 13.142
12.721 12.829 12.937 13.045 13.152
12.731 12.839 12.947 13.055 13.163
12.742 12.850 12.958 13.066 13.174
12.753 12.861 12.969 13.077 13.185
1300 1310 1320 1330 1340
1800 1810 1820 1830 1840
17.930 18.032 18.134 18.237 18.339
17.940 18.042 18.145 18.247 18.349
17.950 18.053 18.155 18.257 18.359
17.961 18.063 18.165 18.267 18.369
17.971 18.073 18.175 18.277 18.379
17.981 18.083 18.186 18.288 18.389
17.991 18.094 18.196 18.298 18.400
18.002 18.104 18.206 18.308 18.410
18.012 18.114 18.216 18.318 18.420
18.022 18.124 18.226 18.328 18.430
18.032 18.134 18.237 18.339 18.440
1800 1810 1820 1830 1840
1350 1360 1370 1380 1390
13.185 13.292 13.400 13.508 13.615
13.196 13.303 13.411 13.519 13.626
13.206 13.314 13.422 13.529 13.637
13.217 13.325 13.432 13.540 13.648
13.228 13.336 13.443 13.551 13.658
13.239 13.346 13.454 13.562 13.669
13.249 13.357 13.465 13.572 13.680
13.260 13.368 13.476 13.583 13.691
13.271 13.379 13.486 13.594 13.701
13.282 13.389 13.497 13.605 13.712
13.292 13.400 13.508 13.615 13.723
1350 1360 1370 1380 1390
1850 1860 1870 1880 1890
18.440 18.542 18.643 18.745 18.846
18.450 18.552 18.653 18.755 18.856
18.461 18.562 18.664 18.765 18.866
18.471 18.572 18.674 18.775 18.876
18.481 18.582 18.684 18.785 18.886
18.491 18.593 18.694 18.795 18.896
18.501 18.603 18.704 18.805 18.906
18.511 18.613 18.714 18.815 18.916
18.522 18.623 18.724 18.826 18.927
18.532 18.633 18.735 18.836 18.937
18.542 18.643 18.745 18.846 18.947
1850 1860 1870 1880 1890
1400 1410 1420 1430 1440
13.723 13.830 13.937 14.045 14.152
13.734 13.841 13.948 14.055 14.162
13.744 13.852 13.959 14.066 14.173
13.755 13.862 13.970 14.077 14.184
13.766 13.873 13.980 14.087 14.195
13.776 13.884 13.991 14.098 14.205
13.787 13.895 14.002 14.109 14.216
13.798 13.905 14.012 14.120 14.227
13.809 13.916 14.023 14.130 14.237
13.819 13.927 14.034 14.141 14.248
13.830 13.937 14.045 14.152 14.259
1400 1410 1420 1430 1440
1900 1910 1920 1930 1940
18.947 19.048 19.148 19.249 19.349
18.957 19.058 19.158 19.259 19.359
18.967 19.068 19.168 19.269 19.369
18.977 19.078 19.178 19.279 19.379
18.987 19.088 19.188 19.289 19.389
18.997 19.098 19.198 19.299 19.399
19.007 19.108 19.208 19.309 19.409
19.017 19.118 19.218 19.319 19.419
19.027 19.128 19.229 19.329 19.429
19.037 19.138 19.239 19.339 19.439
19.048 19.148 19.249 19.349 19.449
1990 1910 1920 1930 1940
1450 1460 1470 1480 1490
14.259 14.366 14.472 14.579 14.686
14.269 14.376 14.483 14.590 14.696
14.280 14.387 14.494 14.601 14.707
14.291 14.398 14.504 14.611 14.718
14.302 14.408 14.515 14.622 14.728
14.312 14.419 14.526 14.632 14.739
14.323 14.430 14.536 14.643 14.750
14.334 14.440 14.547 14.654 14.760
14.344 14.451 14.558 14.664 14.771
14.355 14.462 14.569 14.675 14.782
14.366 14.472 14.579 14.686 14.792
1450 1460 1470 1480 1490
1950 1960 1970 1980 1990
19.449 19.549 19.649 19.748 19.848
19.459 19.559 19.659 19.758 19.858
19.469 19.569 19.669 19.768 19.868
19.479 19.579 19.679 19.778 19.878
19.489 19.589 19.689 19.788 19.888
19.499 19.599 19.699 19.798 19.898
19.509 19.609 19.709 19.808 19.907
19.519 19.619 19.719 19.818 19.917
19.529 19.629 19.729 19.828 19.927
19.539 19.639 19.738 19.838 19.937
19.549 19.649 19.748 19.848 19.947
1950 1960 1970 1980 1990
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
Z-242
°F
°F
Z
+ –
Revised Thermocouple Reference Tables
NONE ESTABLISHED
Tungsten5% Rhenium vs. Tungsten26% Rhenium
C
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
+ –
Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade -32 to 4208°F -0 to 2320°C Extension Grade 32 to 1600°F 0 to 870°C LIMITS OF ERROR (whichever is greater) Standard: 4.5°C to 425°C 1.0% to 2320°C Special: Not Established COMMENTS, BARE WIRE ENVIRONMENT: Vacuum, Inert; Hydrogen; Beware of Embrittlement; Not Practical Below 750°F; Not for Oxidizing Atmosphere TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
2000 2010 2020 2030 2040
19.947 20.046 20.145 20.244 20.343
19.957 20.056 20.155 20.254 20.352
19.967 20.066 20.165 20.264 20.362
19.977 20.076 20.175 20.274 20.372
19.987 20.086 20.185 20.283 20.382
19.997 20.096 20.195 20.293 20.392
20.007 20.106 20.204 20.303 20.402
20.017 20.116 20.214 20.313 20.411
20.026 20.125 20.224 20.323 20.421
20.036 20.135 20.234 20.333 20.431
20.046 20.145 20.244 20.343 20.441
2000 2010 2020 2030 2040
2500 2510 2520 2530 2540
24.682 24.772 24.862 24.952 25.041
24.691 24.781 24.871 24.961 25.050
24.700 24.790 24.880 24.970 25.059
24.709 24.799 24.889 24.979 25.068
24.718 24.808 24.898 24.988 25.077
24.727 24.817 24.907 24.996 25.086
24.736 24.826 24.916 25.005 25.095
24.745 24.835 24.925 25.014 25.104
24.754 24.844 24.934 25.023 25.113
24.763 24.853 24.943 25.032 25.122
24.772 24.862 24.952 25.041 25.130
2500 2510 2520 2530 2540
2050 2060 2070 2080 2090
20.441 20.539 20.637 20.735 20.833
20.451 20.549 20.647 20.745 20.843
20.461 20.559 20.657 20.755 20.852
20.470 20.569 20.667 20.765 20.862
20.480 20.578 20.676 20.774 20.872
20.490 20.588 20.686 20.784 20.882
20.500 20.598 20.696 20.794 20.891
20.510 20.608 20.706 20.804 20.901
20.520 20.618 20.716 20.813 20.911
20.529 20.627 20.725 20.823 20.921
20.539 20.637 20.735 20.833 20.930
2050 2060 2070 2080 2090
2550 2560 2570 2580 2590
25.130 25.219 25.308 25.397 25.486
25.139 25.228 25.317 25.406 25.494
25.148 25.237 25.326 25.415 25.503
25.157 25.246 25.335 25.424 25.512
25.166 25.255 25.344 25.432 25.521
25.175 25.264 25.353 25.441 25.530
25.184 25.273 25.362 25.450 25.539
25.193 25.282 25.370 25.459 25.547
25.202 25.291 25.379 25.468 25.556
25.211 25.299 25.388 25.477 25.565
25.219 25.308 25.397 25.486 25.574
2550 2560 2570 2580 2590
2100 2110 2120 2130 2140
20.930 21.028 21.125 21.222 21.319
20.940 21.037 21.135 21.232 21.328
20.950 21.047 21.144 21.241 21.338
20.960 21.057 21.154 21.251 21.348
20.969 21.067 21.164 21.261 21.357
20.979 21.076 21.173 21.270 21.367
20.989 21.086 21.183 21.280 21.377
20.999 21.096 21.193 21.290 21.386
21.008 21.106 21.203 21.299 21.396
21.018 21.115 21.212 21.309 21.406
21.028 21.125 21.222 21.319 21.415
2100 2110 2120 2130 2140
2600 2610 2620 2630 2640
25.574 25.662 25.750 25.838 25.925
25.583 25.671 25.759 25.846 25.934
25.592 25.680 25.76 25.855 25.943
25.600 25.688 25.776 25.864 25.952
25.609 25.697 25.785 25.873 25.960
25.618 25.706 25.794 25.882 25.969
25.627 25.715 25.803 25.890 25.978
25.636 25.724 25.811 25.899 25.986
25.644 25.732 25.820 25.908 25.995
25.653 25.741 25.829 25.917 26.004
25.662 25.750 25.838 25.925 26.013
2600 2610 2620 2630 2640
2150 2160 2170 2180 2190
21.415 21.512 21.608 21.704 21.800
21.425 21.521 21.618 21.714 21.810
21.435 21.531 21.627 21.723 21.819
21.444 21.541 21.637 21.733 21.829
21.454 21.550 21.647 21.743 21.838
21.464 21.560 21.656 21.752 21.848
21.473 21.570 21.666 21.762 21.858
21.483 21.579 21.675 21.771 21.867
21.493 21.589 21.685 21.781 21.877
21.502 21.599 21.695 21.791 21.886
21.512 21.608 21.704 21.800 21.896
2150 2160 2170 2180 2190
2650 2660 2670 2680 2690
26.013 26.100 26.187 26.274 26.360
26.021 26.109 26.196 26.282 26.369
26.030 26.117 26.204 26.291 26.378
26.039 26.126 26.213 26.300 26.386
26.048 26.135 26.222 26.308 26.395
26.056 26.143 26.230 26.317 26.404
26.065 26.152 26.239 26.326 26.412
26.074 26.161 26.248 26.334 26.421
26.082 26.170 26.256 26.343 26.430
26.091 26.178 26.265 26.352 26.438
26.100 26.187 26.274 26.360 26.447
2650 2660 2670 2680 2690
2200 2210 2220 2230 2240
21.896 21.991 22.087 22.182 22.277
21.905 22.001 22.096 22.192 22.286
21.915 22.011 22.106 22.201 22.296
21.925 22.020 22.115 22.211 22.305
21.934 22.030 22.125 22.220 22.315
21.944 22.039 22.134 22.230 22.324
21.953 22.049 22.144 22.239 22.334
21.963 22.058 22.153 22.249 22.343
21.972 22.068 22.163 22.258 22.353
21.982 22.077 22.172 22.268 22.362
21.991 22.087 22.182 22.277 22.372
2200 2210 2220 2230 2240
2700 2710 2720 2730 2740
26.447 26.533 26.619 26.705 26.791
26.455 26.542 26.628 26.714 26.799
26.464 26.550 26.636 26.722 26.808
26.473 26.559 26.645 26.731 26.816
26.481 26.568 26.654 26.739 26.825
26.490 26.576 26.662 26.748 26.834
26.499 26.585 26.671 26.756 26.842
26.507 26.593 26.679 26.765 26.851
26.516 26.602 26.688 26.774 26.859
26.524 26.611 26.696 26.782 26.868
26.533 26.619 26.705 26.791 26.876
2700 2710 2720 2730 2740
2250 2260 2270 2280 2290
22.372 22.466 22.561 22.655 22.749
22.381 22.476 22.570 22.665 22.759
22.391 22.485 22.580 22.674 22.768
22.400 22.495 22.589 22.683 22.777
22.410 22.504 22.599 22.693 22.787
22.419 22.514 22.608 22.702 22.796
22.429 22.523 22.618 22.712 22.806
22.438 22.533 22.627 22.721 22.815
22.448 22.542 22.636 22.730 22.824
22.457 22.551 22.646 22.740 22.834
22.466 22.561 22.655 22.749 22.843
2250 2260 2270 2280 2290
2750 2760 2770 2780 2790
26.876 26.962 27.047 27.132 27.216
26.885 26.970 27.055 27.140 27.225
26.893 26.979 27.064 27.149 27.233
26.902 26.987 27.072 27.157 27.242
26.910 26.996 27.081 27.166 27.250
26.919 27.004 27.089 27.174 27.259
26.927 27.013 27.098 27.183 27.267
26.936 27.021 27.106 27.191 27.276
26.945 27.030 27.115 27.200 27.284
26.953 27.038 27.123 27.208 27.293
26.962 27.047 27.132 27.216 27.301
2750 2760 2770 2780 2790
2300 2310 2320 2330 2340
22.843 22.937 23.030 23.124 23.217
22.853 22.946 23.040 23.133 23.226
22.862 22.956 23.049 23.142 23.236
22.871 22.965 23.058 23.152 23.245
22.881 22.974 23.068 23.161 23.254
22.890 22.984 23.077 23.170 23.263
22.899 22.993 23.086 23.180 23.273
22.909 23.002 23.096 23.189 23.282
22.918 23.012 23.105 23.198 23.291
22.928 23.021 23.114 23.208 23.301
22.937 23.030 23.124 23.217 23.310
2300 2310 2320 2330 2340
2800 2810 2820 2830 2840
27.301 27.385 27.470 27.554 27.637
27.309 27.394 27.478 27.562 27.646
27.318 27.402 27.486 27.570 27.654
27.326 27.411 27.495 27.579 27.663
27.335 27.419 27.503 27.587 27-671
27.343 27.428 27.512 27.596 27.679
27.352 27.436 27.520 27.604 27.688
27.360 27.444 27.528 27.612 27.696
27.369 27.453 27.537 27.621 27.704
27.377 27.461 27.545 27.629 27.713
27.385 27.470 27.554 27.637 27.721
2800 2810 2820 2830 2840
2350 2360 2370 2380 2390
23.310 23.403 23.495 23.588 23.680
23.319 23.412 23.505 23.597 23.689
23.328 23.421 23.514 23.606 23.698
23.338 23.431 23.523 23.615 23.708
23.347 23.440 23.532 23.625 23.717
23.356 23.449 23.542 23.634 23.726
23.366 23.458 23.551 23.643 23.735
23.375 23.468 23.560 23.652 23.744
23.384 23.477 23.569 23.662 23.754
23.393 23.486 23.579 23.671 23.763
23.403 23.495 23.588 23.680 23.772
2350 2360 2370 2380 2390
2850 2860 2870 2880 2890
27.721 27.805 27.888 27.971 28.054
27.729 27.813 27.896 27.979 28.062
27.738 27.821 27.904 27.988 28.070
27.746 27.830 27.913 27.996 28.079
27.755 27.838 27.921 28.004 28.087
27.763 27.846 27.929 28.012 28.095
27.771 27.855 27.938 28.021 28.103
27.780 27.863 27.946 28.029 28.112
27.788 27.871 27.954 28.037 28.120
27.796 27.880 27.963 28.046 28.128
27.805 27.888 27.971 28.054 28.137
2850 2860 2870 2880 2890
2400 2410 2420 2430 2440
23.772 23.864 23.956 24.047 24.138
23.781 23.873 23.965 24.056 24.147
23.790 23.882 23.974 24.065 24.157
23.800 23.891 23.983 24.074 24.166
23.809 23.901 23.992 24.084 24.175
23.818 23.910 24.001 24.093 24.184
23.827 23.919 24.010 24.102 24.193
23.836 23.928 24.020 24.111 24.202
23.846 23.937 24.029 24.120 24.211
23.855 23.946 24.038 24.129 24.220
23.864 23.956 24.047 24.138 24.229
2400 2410 2420 2430 2440
2900 2910 2920 2930 2940
28.137 28.219 28.301 28.384 28.466
28.145 28.227 28.310 28.392 28.474
28.153 28.236 28.318 28.400 28.482
28.161 28.244 28.326 28.408 28.490
28.170 28.252 28.334 28.416 28.498
28.178 28.260 28.342 28.425 28.506
28.186 28.268 28.351 28.433 28.515
28.194 28.277 28.359 28.441 28.523
28.203 28.285 28.367 28.449 28.531
28.211 28.293 28.375 28.457 28.539
28.219 28.301 28.384 28.466 28.547
2900 2910 2920 2930 2940
2450 2460 2470 2480 2490
24.229 24.320 24.411 24.502 24.592
24.239 24.330 24.420 24.511 24.601
24.248 24.339 24.429 24.520 24.610
24.257 24.348 24.438 24.529 24.619
24.266 24.357 24.447 24.538 24.628
24.275 24.366 24.456 24.547 24.637
24.284 24.375 24.466 24.556 24.646
24.293 24.384 24.475 24.565 24.655
24.302 24.393 24.484 24.574 24.664
24.311 24.402 24.493 24.583 24.673
24.320 24.411 24.502 24.592 24.682
2450 2460 2470 2480 2490
2950 2960 2970 2980 2990
28.547 28.629 28.710 28.791 28.872
28.555 28.637 28.718 28.800 28.881
28.564 28.645 28.727 28.808 28.889
28.572 28.653 28.725 28.816 28.897
28.580 28.661 28.743 28.824 28.905
28.588 28.670 28.751 28.832 28.913
28.596 28.678 28.759 28.840 28.921
28.604 28.686 28.767 28.848 28.929
28.613 28.694 28.775 28.856 28.937
28.621 28.702 28.783 28.864 28.945
28.629 28.710 28.791 28.872 28.953
2950 2960 2970 2980 2990
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
Z-243
°F
°F
MAXIMUM TEMPERATURE RANGE Thermocouple Grade -32 to 4208°F -0 to 2320°C Extension Grade 32 to 1600°F 0 to 870°C LIMITS OF ERROR (whichever is greater) Standard: 4.5°C to 425°C 1.0% to 2320°C Special: Not Established COMMENTS, BARE WIRE ENVIRONMENT: Vacuum, Inert; Hydrogen; Beware of Embrittlement; Not Practical Below 750°F; Not for Oxidizing Atmosphere TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
+ –
Thermocouple Grade
NONE ESTABLISHED
Tungsten5% Rhenium vs. Tungsten26% Rhenium
Revised Thermocouple Reference Tables
C
TYPE
Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
+ –
Extension Grade
Thermoelectric Voltage in Millivolts °F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
3000 3010 3020 3030 3040
28.953 29.034 29.114 29.195 29.275
28.961 29.042 29.122 29.203 29.283
28.969 29-050 29.130 29.211 29.291
28.978 29.058 29.138 29.219 29.299
28.986 29.066 29.147 29.227 29.307
28.994 29.074 29.155 29.235 29.315
29.002 29.082 29.163 29.243 29.323
29.010 29.090 29.171 29.251 29.331
29.018 29.098 29.179 29.259 29.339
29.026 29.106 29.187 29.267 29.347
29.034 29.114 29.195 29.275 29.355
3000 3010 3020 3030 3040
3500 3510 3520 3530 3540
32.746 32.817 32.887 32.957 33.027
32.753 32.824 32.894 32.964 33.034
32.760 32.831 32.901 32.971 33.041
32.767 32.838 32.908 32.978 33.048
32.774 32.845 32.915 32.985 33.055
32.781 32.852 32.922 32.992 33.062
32.788 32.859 32.929 32.999 33.069
32.795 32.866 32.936 33.006 33.076
32.802 32.873 32.943 33.013 33-083
32.809 32.880 32.950 33.020 33.090
32.817 32.887 32.957 33.027 33.097
3500 3510 3520 3530 3540
3050 3060 3070 3080 3090
29.355 29.434 29.514 29.593 29.672
29.363 29.442 29.522 29.601 29.680
29.371 29.450 29.530 29.609 29.688
29.379 29.458 29.538 29.617 29.696
29.386 29.466 29.546 29.625 29.704
29.394 29.474 29.553 29.633 29.712
29.402 29.482 29.561 29.641 29.720
29.410 29.490 29.569 29.648 29.727
29.418 29.498 29.577 29.656 29.735
29.426 29.506 29.585 29.664 29.743
29.434 29.514 29.593 29.672 29.751
3050 3060 3070 3080 3090
3550 3560 3570 3580 3590
33.097 33.166 33.236 33.305 33.374
33.104 33.173 33.243 33.312 33.380
33.111 33.180 33.249 33.318 33.387
33.118 33.187 33.256 33.325 33.394
33.125 33.194 33.263 33.332 33.401
33.132 33.201 33.270 33.339 33.408
33.139 33.208 33.277 33.346 33.415
33.146 33.215 33.284 33.353 33.422
33.152 33.222 33.291 33.360 33.428
33.159 33.229 33.298 33.367 33.435
33.166 33.236 33.305 33.374 33.442
3550 3560 3570 3580 3590
3100 3110 3120 3130 3140
29.751 29.830 29.908 29.987 30.065
29.759 29.838 29.916 29.995 30.073
29.767 29.846 29.924 30.002 30.081
29.775 29.853 29.932 30.010 30.088
29.783 29.861 29.940 30.018 30.096
29.791 29.869 29.948 30.026 30.104
29.798 29.877 29.955 30.034 30.112
29.806 29.885 29.963 30.041 30.119
29.814 29.893 29.971 30.049 30.127
29.822 29.901 29.979 30.057 30.135
29.830 29.908 29.987 30.065 30.143
3100 3110 3120 3130 3140
3600 3610 3620 3630 3640
33.442 33.510 33.579 33.647 33.714
33.449 33.517 33.585 33.653 33.721
33.456 33.524 33.592 33.660 33.728
33.463 33.531 33.599 33.667 33.734
33.469 33.538 33.606 33.674 33.741
33.476 33.545 33.613 33.680 33.748
33.483 33.551 33.619 33.687 33.755
33.490 33.558 33.626 33.694 33.761
33.497 33.565 33.633 33.701 33.768
33.504 33.572 33.640 33.707 33.775
33.510 33.579 33.647 33.714 33.782
3600 3610 3620 3630 3640
3150 3160 3170 3180 3190
30.143 30.221 30.298 30.376 30.453
30.151 30.228 30.306 30.383 30.460
30.158 30.236 30.314 30.391 30.468
30.166 30.244 30.321 30.399 30.476
30.174 30.252 30.329 30.406 30.484
30.182 30.259 30.337 30.414 30.491
30.190 30.267 30.345 30.422 30.499
30.197 30.275 30.352 30.430 30.507
30.205 30.283 30.360 30.437 30.514
30.213 30.290 30.368 30.445 40.522
30.221 30.298 30.376 30.453 30.530
3150 3160 3170 3180 3190
3650 3660 3670 3680 3690
33.782 33.849 33.916 33.982 34.049
33.788 33.856 33.922 33.989 34.056
33.795 33.862 33.929 33.996 34.062
33.802 33.869 33.936 34.002 34-069
33.809 33.876 33.942 34.009 34.075
33.815 33.882 33.949 34.016 34.082
33.822 33:889 33.956 34.022 34.089
33.829 33.896 33.962 34.029 34.095
33.835 33.902 33.969 34.036 34.102
33.842 33.909 33.976 34.042 34.109
33.849 33.916 33.982 34.049 34.115
3650 3660 3670 3680 3690
3200 3210 3220 3230 3240
30.530 30.607 30.683 30.760 30.836
30.537 30.614 30.691 30.767 30.843
30.545 30.622 30.698 30.775 30.851
30.553 30.630 30.706 30.782 30.859
30.561 30.637 30.714 30.790 30.866
30.568 30.645 30.721 30.798 30.874
30.576 30.653 30.729 30.805 30.881
30.584 30.660 30.737 30.813 30.889
30.591 30.668 30.744 30.821 30.897
30.599 30.676 30.752 30.828 30.904
30.607 30.683 30.760 30.836 30.912
3200 3210 3220 3230 3240
3700 3710 3720 3730 3740
34.115 34.181 34.247 34.312 34.378
34.122 34.188 34.253 34.319 34.384
34.128 34.194 34.260 34.325 34.391
34.135 34.201 34.267 34.332 34.397
34.142 34.207 34.273 34.338 34.404
34.148 34.214 34.280 34.345 34.410
34.155 34.221 34.286 34.351 34.417
34.161 34.227 34.293 34.358 34.423
34.168 34.234 34.299 34.365 34.430
34.175 34.240 34.306 34.371 34.436
34.181 34.247 34.312 34.378 34.442
3700 3710 3720 3730 3740
3250 3260 3270 3280 3290
30.912 30.988 31.063 31.139 31.214
30.919 30.995 31.071 31.146 31.221
30.927 31.003 31.078 31.154 31.229
30.935 31.010 31.086 31.161 31.236
30.942 31.018 31.093 31.169 31.244
30.950 31.025 31.101 31.176 31.251
30.957 31.033 31.109 31.184 31.259
30.965 31.041 31.116 31.191 31.266
30.972 31.048 31.124 31.199 31.274
30.980 31.056 31.131 31.206 31.281
30.988 31.063 31.139 31.214 31.289
3250 3260 3270 3280 3290
3750 3760 3770 3780 3790
34.442 34.507 34.572 34.636 34.700
34.449 34.514 34.578 34.642 34.706
34.455 34-520 34.585 34.649 34.713
34.462 34.527 34.591 34.655 34.719
34.468 34.533 34.597 34.661 34.725
34.475 34.539 34.604 34.668 34.732
34.481 34.546 34.610 34.674 34.738
34.488 34.552 34.617 34.681 34.744
34.494 34.559 34.623 34.687 34.751
34.501 34.565 34.629 34.693 34.757
34.507 34.572 34.636 34.700 34.763
3750 3760 3770 3780 3790
3300 3310 3320 3330 3340
31.289 31.364 31.438 31.513 31.587
31.296 31.371 31.446 31.520 31.594
31.304 31.379 31.453 31.528 31.602
31.311 31.386 31.461 31.535 31.609
31.319 31.394 31.468 31.542 31.617
31.326 31.401 31.476 31.550 31.624
31.334 31.408 31.483 31.557 31.631
31.341 31.416 31.490 31.565 31.639
31.349 31.423 31.498 31.572 31.646
31.356 31.431 31.505 31.580 31.654
31.364 31.438 31.513 31.587 31.661
3300 3310 3320 3330 3340
3800 3810 3820 3830 3840
34.763 34.827 34.890 34.953 35.015
34.770 34.833 34.896 34.959 35.022
34.776 34.839 34.903 34.965 35.028
34.782 34.846 34.909 34.972 35.034
34.789 34.852 34.915 34.978 35.040
34.795 34.858 34.921 34.984 35.047
34.802 34.865 34.928 34.990 35.053
34.808 34.871 34.934 34.997 35.059
34.814 34.877 34.940 35.003 35.065
34.821 34.884 34.947 35.009 35.072
34.827 34.890 34.953 35.015 35.078
3800 3810 3820 3830 3840
3350 3360 3370 3380 3390
31.661 31.735 31.808 31.882 31.955
31.668 31.742 31.816 31.889 31.962
31.676 31.749 31.823 31.896 31.969
31.683 31.757 31.830 31.904 31.977
31.690 31.764 31.838 31.911 31.984
31.698 31.772 31.845 31.918 31.991
31.705 31.779 31.852 31.926 31.999
31.713 31.786 31.860 31.933 32.006
31.720 31.794 31.867 31.940 32.013
31.727 31.801 31.874 31.948 32.021
31.735 31.808 31.882 31.955 32.028
3350 3360 3370 3380 3390
3850 3860 3870 3880 3890
35.078 35.140 35.202 35.263 35.324
35.084 35.146 35.208 35.269 35.330
35.090 35.152 35.214 35.275 35.336
35.096 35.158 35.220 35.281 35.343
35.103 35.165 35.226 35.288 35.349
35.109 35.171 35.132 35.294 35.355
35.115 35.177 35.238 35.300 35.361
35.121 35.183 35.245 35.306 35.367
35.127 35.189 35.251 35.312 35.373
35.134 35.195 35.257 35.318 35.379
35.140 35.202 35.263 35.324 35.385
3850 3860 3870 3880 3890
3400 3410 3420 3430 3440
32.028 32.101 32.173 32.246 32.318
32.035 32.108 32.180 32.253 32.325
32.042 32.115 32.188 32.260 32.332
32.050 32.122 32.195 32.267 32.339
32.057 32.130 32.202 32.274 32.346
32.064 32.137 32.209 32.282 32.354
32.072 32.144 32.217 32.289 32.361
32.079 32.151 32.224 32.296 32.368
32.086 32.159 32.231 32.303 32.375
32.093 32.166 32.238 32.310 32.382
32.101 32.173 32.246 32.318 32.390
3400 3410 3420 3430 3440
3900 3910 3920 3930 3940
35.385 35.446 35.506 35.566 35.626
35.391 35.452 35.512 35.572 35.632
35.397 35.458 35.518 35.578 35.638
35.403 35.464 35.524 35.584 35.644
35.409 35.470 35.530 35.590 35.650
35.415 35.476 35.536 35.596 35.656
35.422 35.482 35.542 35.602 35.662
35.428 35.488 35.548 35.608 35.668
35.434 35.494 35.554 35.614 35.673
35.440 35.500 35.560 35.620 35.679
35.446 35.506 35.566 35.626 35.685
3900 3910 3920 3930 3940
3450 3460 3470 3480 3490
32.390 32.461 32.533 32.604 32.675
32.397 32.468 32.540 32.611 32.682
32.404 32.476 32.547 32.618 32.689
32.411 32.483 32.554 32.625 32.696
32.418 32.490 32.561 32.632 32.703
32.425 32.497 32.568 32.640 32.711
32.433 32.504 32.576 32.647 32.718
32.440 32.511 32.583 32.654 32.725
32.447 32.518 32.590 32.661 31.732
32.454 32.526 32.597 32.668 32.739
32.461 32.533 32.604 32.675 32.746
3450 3460 3470 3480 3490
3950 3960 3970 3980 3990
35.685 35.744 35.803 35.862 35.920
35.691 35.750 35.809 35.868 35.926
35.697 35.756 35.815 35.873 35.932
35.703 35.762 35.821 35.879 35.937
35.709 35.768 35.827 35.885 35.943
35.715 35.774 35.833 35.891 35.949
35.721 35.780 35.838 35.897 35.955
35.727 35.786 35.844 35.903 35.961
35.733 35.792 35.850 35.908 35.966
35.739 35.797 35.856 35.914 35.972
35.744 35.803 35.862 35.920 35.978
3950 3960 3970 3980 3990
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
Z-244
°F
°F
Z
+ –
Revised Thermocouple Reference Tables
NONE ESTABLISHED
Tungsten5% Rhenium vs. Tungsten26% Rhenium
C
TYPE Reference Tables N.I.S.T. Monograph 175 Revised to ITS-90
Thermocouple Grade
+ –
Extension Grade
MAXIMUM TEMPERATURE RANGE Thermocouple Grade -32 to 4208°F -0 to 2320°C Extension Grade 32 to 1600°F 0 to 870°C LIMITS OF ERROR (whichever is greater) Standard: 4.5°C to 425°C 1.0% to 2320°C Special: Not Established COMMENTS, BARE WIRE ENVIRONMENT: Vacuum, Inert; Hydrogen; Beware of Embrittlement; Not Practical Below 750°F; Not for Oxidizing Atmosphere TEMPERATURE IN DEGREES °F REFERENCE JUNCTION AT 32°F
Thermoelectric Voltage in Millivolts
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
4000 4010 4020 4030 4040
35.978 36.036 36.093 36.150 36.206
35.984 36.041 36.099 36.155 36.212
35.989 36.047 36.104 36.161 36.218
35.995 36:053 36.110 36.167 36.223
36.001 36.058 36.116 36.172 36.229
36.007 36.064 36.121 36.178 36.235
36.013 36.070 36-127 36.184 36.240
36.018 36.076 36.133 36.189 36.246
36.024 36.081 36.138 36.195 36.251
36.030 36.087 36.144 36.201 36.257
36.036 36.093 36.150 36.206 36.263
4000 4010 4020 4030 4040
4100 4110 4120 4130 4140
36.539 36.594 36.647 36.701 36.754
36.545 36.599 36.653 36.706 36.760
36.550 36.604 36.658 36.712 36.765
36.556 36.610 36.664 36.717 36.770
36-561 36.615 36.669 36.722 36.775
36.566 36.621 36.674 36.728 36.781
36.572 36.626 36.680 36.733 36.786
36.577 36.631 36.685 36.738 36.791
36.583 36.637 36.690 36.744 36.797
36.588 36.642 36.696 36.749 36.802
36.594 36.647 36.701 36.754 36.807
4100 4110 4120 4130 4140
4050 4060 4070 4080 4090
36.263 36.319 36.374 36.430 36.485
36.268 36.324 36.380 36.435 36.490
36.274 36.330 36.385 36.441 36.496
36.280 36.335 36.391 36.446 36.501
36.285 36.341 36.397 36.452 36.507
36.291 36.347 36.402 36.457 36.512
36.296 36.352 36.408 36.463 36.517
36.302 36.358 36.413 36.468 36:523
36.308 36.363 36.419 36.474 36.528
36.313 36.369 36.424 36.479 36.534
36.319 36.374 36.430 36.485 36.539
4050 4060 4070 4080 4090
4150 4160 4170 4180 4190
36.807 36.860 36.912 36.964 37.015
36.812 36.865 36.917 36.969 37.020
36.818 36.870 36.922 36.974 37.025
36.823 36.875 36.927 36.979 37.030
36.828 36.881 36.933 36.984 37.035
36.833 36.886 36.938 36.989 37.041
36.839 36.891 36.943 36.994 37.046
36.844 36.896 36.948 37.000 37.051
36.849 36.901 36.953 37.005 37.056
36.854 36.907 36.958 37.010 37.061
36.860 36.912 36.964 37.015 37.066
4150 4160 4170 4180 4190
°F
0
1
2
3
4
5
6
7
8
9
10
°F
°F
0
1
2
3
4
5
6
7
8
9
10
Z-245
°F
°F
Tungsten vs. Tungsten-26% Rhenium - Type G* Temperature in Degrees F DEGREES F 0° 0° -.016 100° 0.079 200° 0.299 300° 0.634 400° 1.075 500° 1.613 600° 2.238 700° 2.943 800° 3.720 900° 4.562 1000° 5.461 1100° 6.412 1200° 7.407 1300° 8.441 1400° 9.509 1500° 10.606 1600° 11.725 1700° 12.864 1800° 14.018 1900° 15.182 2000° 16.353 2100° 17.527 Adopted March 4, 1974
20° -.007 0.113 0.357 0.714 1.175 1.731 2.373 3.093 3.884 4.737 5.647 6.607 7.611 8.652 9.726 10.828 11.952 13.094 14.250 15.415 16.587 17.762
Reference Junction at 32°F 40° 0.006 0.153 0.420 0.799 1.279 1.853 2.511 3.246 4.049 4.915 5.836 6.805 7.816 8.865 9.945 11.051 12.179 13.324 14.482 15.649 16.822 17.997
60° 0.026 0.197 0.487 0.887 1.387 1.978 2.652 3.401 4.218 5.095 6.026 7.004 8.023 9.078 10.164 11.275 12.407 13.555 14.715 15.884 17.057 18.232
80° 0.050 0.246 0.559 0.979 1.498 2.106 2.796 3.559 4.389 5.277 6.218 7.205 8.232 9.293 10.384 11.500 12.635 13.786 14.948 16.118 17.292 18.467
DEGREES F 2200° 2300° 2400° 2500° 2600° 2700° 2800° 2900° 3000° 3100° 3200° 3300° 3400° 3500° 3600° 3700° 3800° 3900° 4000° 4100° 4200°
0° 18.701 19.873 21.038 22.195 23.341 24.474 25.591 26.690 27.769 28.827 29.862 30.871 31.854 32.809 33.733 34.626 35.486 36.312 37.101 37.853 38.564
20° 18.936 20.106 21.270 22.425 23.569 24.699 25.812 26.907 27.983 29.036 30.066 31.070 32.047 32.996 33.914 34.801 35.654 36.473 37.254 37.998
40° 19.170 20.340 21.502 22.655 23.796 24.923 26.033 27.124 28.195 29.244 30.269 31.268 32.240 33.182 34.094 34.974 35.821 36.632 37.406 38.142
60° 19.405 20.573 21.734 22.884 24.023 25.146 26.253 27.340 28.407 29.451 30.471 31.464 32.430 33.367 34.273 35.146 35.986 36.790 37.557 38.285
80° 19.639 20.806 21.965 23.113 24.249 25.369 26.472 27.555 28.618 29.657 30.672 31.660 32.620 33.551 34.450 35.317 36.150 36.946 37.705 38.425
Tungsten-5% Rhenium vs. Tungsten-26% Rhenium - Type C* Temperature in Degrees F DEGREES F 0° 0° -.234 100° 0.522 200° 1.348 300° 2.232 400° 3.165 500° 4.140 600° 5.149 700° 6.184 800° 7.240 900° 8.310 1000° 9.390 1100° 10.475 1200° 11.561 1300° 12.645 1400° 13.723 1500° 14.792 1600° 15.851 1700° 16.898 1800° 17.930 1900° 18.947 2000° 19.947 2100° 20.930 Adopted March 4, 1974
20° -.089 0.682 1.520 2.415 3.357 4.339 5.354 6.394 7.453 8.526 9.607 10.693 11.778 12.861 13.937 15.005 16.062 17.105 18.134 19.148 20.145 21.125
Reference Junction at 32°F 40° 0.059 0.845 1.695 2.600 3.551 4.540 5.560 6.604 7.667 8.741 9.824 10.910 11.995 13.077 14.152 15.217 16.271 17.312 18.339 19.349 20.343 21.319
60° 0.211 1.010 1.872 2.786 3.746 4.742 5.767 6.815 7.881 8.957 10.041 11.127 12.212 13.292 14.366 15.429 16.481 17.519 18.542 19.549 20.539 21.512
80° 0.365 1.178 2.051 2.975 3.942 4.945 5.975 7.027 8.095 9.174 10.258 11.344 12.429 13.508 14.579 15.640 16.689 17.725 18.745 19.748 20.735 21.704
DEGREES F 2200° 2300° 2400° 2500° 2600° 2700° 2800° 2900° 3000° 3100° 3200° 3300° 3400° 3500° 3600° 3700° 3800° 3900° 4000° 4100° 4200°
0° 21.896 22.843 23.772 24.682 25.574 26.447 27.301 28.137 28.953 29.751 30.530 31.289 32.028 32.746 33.442 34.115 34.763 35.385 35.978 36.539 37.066
20° 22.087 23.030 23.956 24.862 25.750 26.619 27.470 28.301 29.114 29.908 30.683 31.438 32.173 32.887 33.579 34.247 34.890 35.506 36.093 36.647
40° 22.277 23.217 24.138 25.041 25.925 26.791 27.637 28.466 29.275 30.065 30.836 31.587 32.318 33.027 33.714 34.378 35.015 35.626 36.206 36.754
60° 22.466 23.403 24.320 25.219 26.100 26.962 27.805 28.629 29.434 30.221 30.988 31.735 32.461 33.166 33.849 34.507 35.140 35.744 36.319 36.860
80° 22.655 23.588 24.502 25.397 26.274 27.132 27.971 28.791 29.593 30.376 31.139 31.882 32.604 33.305 33.982 34.636 35.263 35.862 36.430 36.964
Tungsten-3% Rhenium vs. Tungsten-25% Rhenium - Type D* Temperature in Degrees F DEGREES F 0° 20° 0° -.163 -.063 100° 0.390 0.515 200° 1.058 1.204 300° 1.824 1.988 400° 2.673 2.851 500° 3.590 3.781 600° 4.564 4.765 700° 5.584 5.793 800° 6.640 6.855 900° 7.725 7.945 1000° 8.830 9.053 1100° 9.951 10.176 1200° 11.080 11.307 1300° 12.215 12.443 1400° 13.352 13.579 1500° 14.489 14.717 1600° 15.624 15.850 1700° 16.752 16.976 1800° 17.870 18.093 1900° 18.979 19.199 2000° 20.075 20.293 2100° 21.158 21.373 Adopted March 4, 1974 Hoskins Manufacturing Company
Reference Junction at 32°F 40° 0.043 0.644 1.354 2.154 3.032 3.973 4.967 6.003 7.071 8.165 9.277 10.402 11.534 12.670 13.807 14.944 16.076 17.200 18.315 19.419 20.510 21.588
60° 0.154 0.778 1.507 2.324 3.216 4.168 5.171 6.214 7.288 8.386 9.501 10.628 11.761 12.897 14.034 15.171 16.302 17.424 18.537 19.638 20.726 21.802
80° 0.269 0.916 1.664 2.497 3.402 4.365 5.377 6.427 7.506 8.608 9.726 10.854 11.988 13.125 14.262 15.398 16.527 17.647 18.758 19.857 20.943 22.015
DEGREES F 2200° 2300° 2400° 2500° 2600° 2700° 2800° 2900° 3000° 3100° 3200° 3300° 3400° 3500° 3600° 3700° 3800° 3900° 4000° 4100° 4200°
0° 22.228 23.283 24.323 25.348 26.358 27.352 28.329 29.290 30.233 31.158 32.063 32.948 33.809 34.646 35.455 36.233 36.976 37.681 38.341 38.951 39.506
20° 22.440 23.492 24.529 25.551 26.558 27.548 28.523 29.480 30.419 31.340 32.242 33.122 33.979 34.810 35.613 36.384 37.120 37.816 38.467 39.067
40° 22.651 23.701 24.735 25.754 26.757 27.745 28.715 29.669 30.605 31.522 32.420 33.295 34.147 34.973 35.770 36.535 37.263 37.950 38.591 39.180
60° 22.863 23.909 24.940 25.956 26.956 27.940 28.908 29.858 30.790 31.703 32.596 33.467 34.314 35.135 35.926 36.683 37.404 38.082 38.714 39.291
80° 23.073 24.116 25.145 26.157 27.154 28.135 29.099 30.046 30.974 31.884 32.772 33.639 34.481 35.295 36.080 36.831 37.543 38.213 38.834 39.400
*Not an ANSI designation
Z-246
Z
CHROMEGA® VS. GOLD-0.07 ATOMIC PERCENT IRON THERMOCOUPLE Table of Temperature vs. Thermoelectric Voltage Temperature (KELVIN)
E, µV
Temperature (KELVIN)
E, µV
Temperature (KELVIN)
E, µV
Temperature (KELVIN)
E, µV
545.40 561.86 578.31 594.76 611.22
70 71 72 73 74
1136.21 1153.80 1171.44 1189.12 1206.84
105 106 107 108 109
1776.71 1795.73 1814.78 1833.86 1852.99
3 4
28.02 39.94
35 36 37 38 39
5 6 7 8 9
52.84 66.58 81.01 96.02 111.51
40 41 42 43 44
627.68 644.16 660.65 677.16 693.69
75 76 77 78 79
1224.60 1242.40 1260.25 1278.14 1296.08
110 111 112 113 114
1872.14 1891.34 1910.57 1929.83 1949.13
10 11 12 13 14
127.39 143.58 160.02 176.65 193.42
45 46 47 48 49
710.24 726.82 743.43 760.07 776.74
80 81 82 83 84
1314.05 1332.07 1350.13 1368.23 1386.37
115 116 117 118 119
1968.46 1987.82 2007.22 2026.65 2046.11
15 16 17 18 19
210.29 227.23 244.21 261.21 278.20
50 51 52 53 54
793.45 810.20 826.98 843.80 860.66
85 86 87 88 89
1404.56 1422.79 1441.05 1459.36 1477.71
120 121 122 123 124
2065.61 2085.14 2104.70 2124.29 2143.91
20 21 22 23 24
295.18 312.14 329.06 345.94 362.77
55 56 57 58 59
877.56 894.50 911.49 928.51 945.58
90 91 92 93 94
1496.10 1514.53 1533.00 1551.52 1570.07
125 126 127 128 129
2163.56 2183.24 2202.96 2222.70 2242.47
25 26 27 28 29
379.56 396.31 413.01 429.67 446.29
60 61 62 63 64
962.70 979.85 997.05 1014.29 1013.58
95 96 97 98 99
1588.66 1607.29 1625.96 1644.67 1663.42
130 131 132 133 134
2262.27 2282.10 2301.96 2321.85 2341.76
30 31 32 33 34
462.87 479.43 495.95 512.45 528.93
65 66 67 68 69
1048.91 1066.28 1083.70 1101.16 1118.66
100 101 102 103 104
1682.21 1701.03 1719.90 1738.80 1757.74
135 136 137 138 139
2361.70 2381.68 2401.67 2421.70 2441.75
Z-247
Z Temperature (KELVIN)
E, µV
Temperature (KELVIN)
E, µV
Temperature (KELVIN)
E, µV
Temperature (KELVIN)
E, µV
140 141 142 143 144
2461.83 2481.94 2502.07 2522.23 2542.42
175 176 177 178 179
3180.19 3201.12 3222.07 3243.04 3264.03
210 211 212 213 214
3923.82 3945.38 3966.95 3988.54 4010.15
245 246 247 248 249
4686.39 4708.38 4730.37 4752.38 4774.39
145 146 147 148 149
2562.63 2582.87 2603.13 2623.42 2643.73
180 181 182 183 184
3285.03 3306.06 3327.11 3348.18 3369.27
215 216 217 218 219
4031.77 4053.40 4075.06 4096.72 4118.40
250 251 252 253 254
4796.41 4818.45 4840.49 4862.54 4884.60
150 151 152 153 154
2664.07 2684.44 2704.82 2725.24 2745.67
185 186 187 188 189
3390.37 3411.50 3432.64 3453.80 3474.98
220 221 222 223 224
4140.09 4161.80 4183.52 4205.26 4227.01
255 256 257 258 259
4906.68 4928.76 4950.85 4972.96 4995.07
155 156 157 158 159
2766.14 2786.62 2807.13 2827.67 2848.22
190 191 192 193 194
3496.18 3517.40 3538.63 3559.88 3581.15
225 226 227 228 229
4248.77 4270.55 4292.33 4314.13 4335.95
260 261 262 263 264
5017.20 5039.34 5061.49 5083.65 5105.83
160 161 162 163 164
2868.80 2889.41 2910.03 2930.68 2951.35
195 196 197 198 199
3602.44 3623.75 3645.07 3666.41 3687.77
230 231 232 233 234
4357.77 4379.61 4401.45 4423.31 4445.18
265 266 267 268 269
5128.01 5150.21 5172.42 5194.64 5216.87
165 166 167 168 169
2972.05 2992.77 3013.50 3034.27 3055.05
200 201 202 203 204
3709.14 3730.54 3751.95 3773.37 3794.82
235 236 237 238 239
4467.06 4488.95 4510.85 4532.76 4554.68
270 271 272 273 274
5239.11 5261.36 5283.62 5305.88 5328.16
170 171 172 173 174
3075.85 3096.68 3117.52 3138.39 3159.28
205 206 207 208 209
3816.28 3837.75 3859.25 3880.76 3902.28
240 241 242 243 244
4576.61 4598.55 4620.49 4642.45 4664.42
275 276 277 278 279
5350.44 5372.73 5395.02 5417.31 5439.61
Z-248
Space for Transmitters in Probe Assembly Heads HEAD
TRANSMITTER SPACE
PROBES
Model Number
Diameter, mm (in)
Height, mm (in)
Typical
NB1
47.6 (1 7⁄8)
19.0 (3⁄4)
NB1-ICSS-14G-12 PR-12-2-100-1/8-6-E
NB2
31.7 (1 1⁄4)
19.0 (3⁄4)
NB2-ICSS-14G-24 PR-14-2-100-1/8-6-E
NB3
57.1 (2 1⁄4)
25.4 (1)
NB1-ICSS-14G-12 PR-18-2-100-1/8-6-E
NB4
22.2 (7⁄8)
9.5 (3⁄8)
NB4-ICSS-14G-12 PR-19-2-100-1/8-6-E
NEPA, NEPB
69.8 (2 3⁄4)
38.1 (1 1⁄2)
NEPB-ICSS-14G-12 NEPB-2-100-1/8-6-E
NBS
50.8 (2)
31.7 (1 1⁄4)
NBS-ICSS-14G-12 NBS-2-100-1/8-6-E
NSA, NSB, NSC
50.8 (2)
31.7 (1 1⁄4)
NSB-ICSS-14G-12 NSB-2-100-1/8-6-E
NBB
47.6 (1 7⁄8)
19.0 (3⁄4)
NBB-ICSS-14G-12 NBB-2-100-1/8-6-E
NBN
50.8 (2)
19.0 (3⁄4)
NBN-ICSS-14G-12 NBN-2-100-1/8-6-E
NBG
44.4 (1 3⁄4)
19.0 (3⁄4)
NBG-ICSS-14G-12 NBG-2-100-1/8-6-E
NXT
47.6 (1 7⁄8)
50.8 (2)
NXT-ICSS-14G-12 NXT-2-100-1/8-6-E
HEP-TX
76.2 (3)
50.8 (2)
HEP-TX-100-J1 HEP-TX-110-PT1
HEP-TX70
76.2 (3)
50.8 (2)
HEP-TX71-J-50-350C HEP-TX75-50-350C
Z-249
Platinum Resistance Temperature Detectors Detector Interchangeability Tolerance Chart Tolerance 0.9
2.25
Z OHMS
deg C
0.8
2.0
0.7
1.75
Basic Detector Resistance at 0°C Is 100 ohms
CLASS B DIN 43760-1980 BS 1904 0.6
1.5
0.5
1.25
JIS C1604-1981 0.5
JIS C1604-1981 0.2
-200
-100
0.4
1.0
0.3
0.75
0.2
0.5
0.1
0.25
0 TEMPERATURE °C
CLASS A DIN 43760-1980 BS 1904
JIS C1604-1981 0.15
100
200
Z-250
300
400
500
RTD Tables According to DIN EN 60751 for Class B and Class A
Resistance vs Temperature Tables According to DIN EN 60751 for Class B and Class A ∝ = .00385 per ITS-90 t ≥ 0°C : R(t) = R0 · (1 + A · t + B · t 2) with A = 3,9083 · 10-3 °C-1 B = -5,775 · 10-7 °C-2 R0 = 100Ω
t < 0°C : R(t) = R0 · [1 + A · t + B · t 2 + C ·(t - 100°C) · t 3) with A = 3,9083 · 10-3 °C-1 B = -5,775 · 10-7 °C-2 C = -4,183 · 10-13 °C R0 = 100Ω Class B: dt = ±(0.3 + 0.005 · lt l)°C Class A dt = ±(0.15 + 0.002 · lt l)°C
Z-251
RTD Temperature vs. Resistance Table For European Curve, Alpha = .00385, ITS-90 °C
Ohms
-200 199 198 197 196 195 194 193 192 191 190 189 188 187 186 185 184 183 182 181 180 179 178 177 176 175 174 173 172 171 170 169 168 167 166 165 164 163 162 161 160 159 158 157 156 155 154 153 152 151 150 149 148 147 146 145 144 143 142 141
18.52 18.96 19.39 19.82 20.25 20.68 21.11 21.54 21.97 22.40 22.83 23.26 23.69 24.12 24.55 24.97 25.39 25.82 26.25 26.67 27.10 27.52 27.95 28.37 28.80 29.22 29.65 30.07 30.49 30.92 31.34 31.76 32.18 32.61 33.03 33.45 33.86 34.28 34.70 35.12 35.54 35.96 36.38 36.80 37.22 37.63 38.05 38.47 38.89 39.31 39.72 40.14 40.56 40.97 41.39 41.80 42.22 42.64 43.05 43.46
1° Celsius Increments
Diff.
°C
Ohms
Diff.
°C
Ohms
Diff.
°C
Ohms
Diff.
°C
Ohms
Diff.
°C
Ohms
Diff.
0.44 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.42 0.42 0.43 0.43 0.42 0.43 0.42 0.43 0.42 0.43 0.42 0.43 0.42 0.42 0.43 0.42 0.42 0.42 0.43 0.42 0.42 0.41 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.41 0.42 0.42 0.42 0.42 0.41 0.42 0.42 0.41 0.42 0.41 0.42 0.42 0.41 0.41
-140 139 138 137 136 135 134 133 132 131 130 129 128 127 126 125 124 123 122 121 120 119 118 117 116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81
43.88 44.29 44.71 45.12 45.53 45.95 46.35 46.76 47.18 47.59 48.00 48.41 48.82 49.23 49.64 50.06 50.47 50.88 51.29 51.70 52.11 52.52 52.92 53.33 53.74 54.15 54.56 54.97 55.38 55.78 56.19 56.60 57.00 57.41 57.82 58.22 58.63 59.04 59.44 59.85 60.26 60.67 61.07 61.48 61.87 62.29 62.69 63.10 63.50 63.91 64.30 64.70 65.11 65.51 65.91 66.31 66.72 67.12 67.52 67.92
0.42 0.41 0.42 0.41 0.41 0.42 0.40 0.41 0.42 0.41 0.41 0.41 0.41 0.41 0.41 0.42 0.41 0.41 0.41 0.41 0.41 0.41 0.40 0.41 0.41 0.41 0.41 0.41 0.41 0.40 0.41 0.41 0.40 0.41 0.41 0.40 0.41 0.41 0.40 0.41 0.41 0.41 0.40 0.41 0.41 0.42 0.40 0.41 0.40 0.41 0.39 0.40 0.41 0.40 0.40 0.40 0.41 0.40 0.40 0.40
-80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21
68.33 68.73 69.13 69.53 69.93 70.33 70.73 71.13 71.53 71.93 72.33 72.73 73.13 73.53 73.93 74.33 74.73 75.13 75.53 75.93 76.33 76.73 77.13 77.52 77.92 78.32 78.72 79.11 79.51 79.91 80.31 80.70 81.10 81.50 81.89 82.29 82.69 83.08 83.48 83.88 84.27 84.67 85.06 85.46 85.85 86.25 86.64 87.04 87.43 87.83 88.22 88.62 89.01 89.40 89.80 90.19 90.59 90.98 91.37 91.77
0.41 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.39 0.40 0.40 0.40 0.39 0.40 0.40 0.40 0.39 0.40 0.40 0.39 0.40 0.40 0.39 0.40 0.40 0.39 0.40 0.39 0.40 0.39 0.40 0.39 0.40 0.39 0.40 0.39 0.40 0.39 0.39 0.40 0.39 0.40 0.39 0.39 0.40
-20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
92.16 92.55 92.95 93.34 93.73 94.12 94.52 94.91 95.30 95.69 96.09 96.48 96.87 97.26 97.65 98.04 98.44 98.83 99.22 99.61
0.39 0.39 0.40 0.39 0.39 0.39 0.40 0.39 0.39 0.39 0.40 0.39 0.39 0.39 0.39 0.39 0.40 0.39 0.39 0.39
±0 +1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
100.00 100.39 100.78 101.17 101.56 101.95 102.34 102.73 103.12 103.51 103.90 104.29 104.68 105.07 105.46 105.85 106.24 106.63 107.02 107.40 107.79 108.18 108.57 108.96 109.35 109.73 110.12 110.51 110.90 111.28 111.67 112.06 112.45 112.83 113.22 113.61 113.99 114.38 114.77 115.15 115.54 115.93 116.31 116.70 117.08 117.47 117.85 118.24 118.62 119.01 119.40 119.78 120.16 120.55 120.93 121.32 121.70 122.09 122.47 122.86
0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.38 0.39 0.39 0.39 0.39 0.39 0.38 0.39 0.39 0.39 0.38 0.39 0.39 0.39 0.38 0.39 0.39 0.38 0.39 0.39 0.38 0.39 0.39 0.38 0.39 0.38 0.39 0.38 0.39 0.38 0.39 0.39 0.38 0.38 0.39 0.38 0.39 0.38 0.39 0.38 0.39
+60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119
123.24 123.62 124.01 124.39 124.77 125.17 125.55 125.93 126.32 126.70 127.08 127.46 127.85 128.23 128.61 128.99 129.38 129.76 130.14 130.52 130.90 131.28 131.67 132.05 132.43 132.81 133.19 133.57 133.95 134.33 134.71 135.09 135.47 135.85 136.23 136.61 136.99 137.37 137.75 138.13 138.51 138.89 139.27 139.65 140.03 140.39 140.77 141.15 141.53 141.91 142.29 142.66 143.04 143.42 143.80 144.18 144.56 144.94 145.32 145.69
0.38 0.38 0.39 0.38 0.38 0.40 0.38 0.38 0.39 0.38 0.38 0.38 0.39 0.38 0.38 0.38 0.39 0.38 0.38 0.38 0.38 0.38 0.39 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.36 0.38 0.38 0.38 0.38 0.38 0.37 0.38 0.38 0.38 0.38 0.38 0.38 0.38 0.37
Note: At 100°C, resistance is 138.50 ohms.
(DIN 43 760)
Z-252
Z
RTD Temperature vs. Resistance Table For European Curve, Alpha = .00385, ITS-90 °C
Ohms
Diff.
+120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179
146.07 146.45 146.82 147.20 147.58 147.95 148.33 148.71 149.08 149.46 149.83 150.21 150.58 150.96 151.34 151.71 152.09 152.46 152.84 153.21 153.58 153.95 154.32 154.71 155.08 155.46 155.83 156.21 156.58 156.96 157.33 157.71 158.08 158.45 158.83 159.20 159.56 159.94 160.31 160.68 161.05 161.43 161.80 162.17 162.54 162.91 163.28 163.66 164.03 164.40 164.77 165.14 165.51 165.88 166.25 166.62 167.00 167.37 167.74 168.11
0.38 +180 0.38 181 0.37 182 0.38 183 0.38 184 0.37 185 0.38 186 0.38 187 0.37 188 0.38 189 0.37 190 0.38 191 0.37 192 0.38 193 0.38 194 0.37 195 0.38 196 0.37 197 0.38 198 0.37 199 0.37 200 0.37 201 0.37 202 0.39 203 0.37 204 0.38 205 0.37 206 0.38 207 0.37 208 0.38 209 0.37 210 0.38 211 0.37 212 0.37 213 0.38 214 0.37 215 0.36 216 0.38 217 0.37 218 0.37 219 0.37 220 0.38 221 0.37 222 0.37 223 0.37 224 0.37 225 0.37 226 0.38 227 0.37 228 0.37 229 0.37 230 0.37 231 0.37 232 0.37 233 0.37 234 0.37 235 0.38 236 0.37 237 0.37 238 0.37 239
°C
1° Celsius Increments
Ohms
Diff.
°C
Ohms
Diff.
°C
Ohms
Diff.
168.48 168.85 169.22 169.59 169.96 170.33 170.69 171.06 171.43 171.80 172.17 172.54 172.91 173.27 173.64 174.01 174.39 174.75 175.12 175.49 175.86 176.23 176.59 176.96 177.33 177.70 178.06 178.43 178.80 179.16 179.53 179.90 180.26 180.63 180.99 181.36 181.73 182.09 182.46 182.82 183.19 183.55 183.92 184.28 184.65 185.01 185.38 185.74 186.11 186.47 186.84 187.20 187.56 187.93 188.29 188.65 189.02 189.38 189.74 190.11
0.37 0.37 0.37 0.37 0.37 0.37 0.36 0.37 0.37 0.37 0.37 0.37 0.37 0.36 0.37 0.37 0.38 0.36 0.37 0.37 0.37 0.37 0.36 0.37 0.37 0.37 0.36 0.37 0.37 0.36 0.37 0.37 0.36 0.37 0.36 0.37 0.37 0.36 0.37 0.36 0.37 0.36 0.37 0.36 0.37 0.36 0.37 0.36 0.37 0.36 0.37 0.36 0.36 0.37 0.36 0.36 0.37 0.36 0.36 0.37
+240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299
190.47 190.83 191.20 191.56 191.92 192.28 192.66 193.02 193.38 193.74 194.10 194.47 194.83 195.19 195.55 195.90 196.26 196.62 196.98 197.35 197.71 198.07 198.43 198.79 199.15 199.51 199.87 200.23 200.59 200.95 201.31 201.67 202.03 202.38 202.74 203.10 203.46 203.82 204.18 204.54 204.90 205.25 205.61 205.97 206.33 206.70 207.05 207.41 207.77 208.13 208.48 208.84 209.20 209.55 209.91 210.27 210.62 210.98 211.34 211.69
0.36 0.36 0.37 0.36 0.36 0.36 0.38 0.36 0.36 0.36 0.36 0.37 0.36 0.36 0.36 0.35 0.36 0.36 0.36 0.37 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.35 0.36 0.36 0.36 0.36 0.36 0.36 0.36 0.35 0.36 0.36 0.36 0.37 0.35 0.36 0.36 0.36 0.35 0.36 0.36 0.35 0.36 0.36 0.35 0.36 0.36 0.35
+300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359
212.05 212.40 212.76 213.12 213.47 213.83 214.19 214.55 214.90 215.26 215.61 215.97 216.32 216.68 217.03 217.39 217.73 218.08 218.44 218.79 219.15 219.50 219.85 220.21 220.56 220.91 221.27 221.62 221.97 222.32 222.68 223.03 223.38 223.73 224.09 224.45 224.80 225.15 225.50 225.85 226.21 226.56 226.91 227.26 227.61 227.96 228.31 228.66 229.01 229.36 229.72 230.07 230.42 230.77 231.12 231.47 231.81 232.16 232.51 232.86
0.36 +360 0.35 361 0.36 362 0.36 363 0.35 364 0.36 365 0.36 366 0.36 367 0.35 368 0.36 369 0.35 370 0.36 371 0.35 372 0.36 373 0.35 374 0.36 375 0.34 376 0.35 377 0.36 378 0.35 379 0.36 380 0.35 381 0.35 382 0.36 383 0.35 384 0.35 385 0.36 386 0.35 387 0.35 388 0.35 389 0.36 390 0.35 391 0.35 392 0.35 393 0.36 394 0.36 395 0.35 396 0.35 397 0.35 398 0.35 399 0.36 400 0.35 401 0.35 402 0.35 403 0.35 404 0.35 405 0.35 406 0.35 407 0.35 408 0.35 409 0.34 410 0.35 411 0.35 412 0.35 413 0.35 414 0.35 415 0.36 416 0.35 417 0.35 418 0.35 419
Note: At 100°C, resistance is 138.50 ohms.
°C
Ohms
Diff.
233.21 233.56 233.91 234.26 234.60 234.95 235.30 235.65 236.00 236.35 236.70 237.05 237.40 237.75 238.09 238.44 238.79 239.14 239.48 239.83 240.18 240.52 240.87 241.22 241.56 241.91 242.25 242.60 242.95 243.29 243.64 243.98 244.33 244.67 245.02 245.36 245.71 246.05 246.40 246.74 247.09 247.43 247.78 248.12 248.46 248.81 249.15 249.50 249.84 250.18 250.53 250.89 251.21 251.55 251.90 252.24 252.59 252.94 253.28 253.62
0.35 +420 0.35 421 0.35 422 0.35 423 0.36 424 0.35 425 0.35 426 0.35 427 0.35 428 0.35 429 0.35 430 0.35 431 0.35 432 0.35 433 0.34 434 0.35 435 0.35 436 0.35 437 0.34 438 0.35 439 0.35 440 0.34 441 0.35 442 0.35 443 0.34 444 0.35 445 0.34 446 0.35 447 0.35 448 0.34 449 0.35 450 0.34 451 0.35 452 0.34 453 0.35 454 0.34 455 0.35 456 0.34 457 0.35 458 0.34 459 0.35 460 0.34 461 0.35 462 0.34 463 0.34 464 0.35 465 0.34 466 0.35 467 0.34 468 0.34 469 0.35 470 0.34 471 0.34 472 0.34 473 0.35 474 0.34 475 0.35 476 0.35 477 0.34 478 0.34 479
°C
Ohms
Diff.
253.96 254.30 254.65 254.99 255.33 255.67 256.01 256.35 256.70 257.04 257.38 257.72 258.06 258.40 258.74 259.08 259.42 259.76 260.10 260.44 260.78 261.12 261.46 261.80 262.14 262.48 262.83 263.17 263.50 263.84 264.18 264.52 264.86 265.20 265.54 265.87 266.21 266.55 266.89 267.22 267.56 267.90 268.24 268.57 268.91 269.25 269.58 269.92 270.26 270.59 270.93 271.27 271.60 271.94 272.27 272.61 272.95 273.28 273.62 273.95
0.34 0.34 0.35 0.34 0.34 0.34 0.34 0.34 0.35 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.34 0.35 0.34 0.33 0.34 0.34 0.34 0.34 0.34 0.34 0.33 0.34 0.34 0.34 0.33 0.34 0.34 0.34 0.33 0.34 0.34 0.33 0.34 0.34 0.33 0.34 0.34 0.33 0.34 0.33 0.34 0.34 0.33 0.34 0.33
(DIN 43 760)
Z-253
RTD Temperature vs. Resistance Table For European Curve, Alpha = .00385, ITS-90 °C
Ohms
Diff.
+480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541
274.29 274.62 274.96 275.29 275.63 275.96 276.31 276.64 276.97 277.31 277.64 277.98 278.31 278.64 278.98 279.31 279.64 279.98 280.31 280.64 280.98 281.31 281.64 281.97 282.31 282.64 282.97 283.30 283.63 283.97 284.30 284.63 284.96 285.29 285.62 285.95 286.30 286.63 286.96 287.29 287.62 287.95 288.28 288.61 288.94 289.27 289.60 289.93 290.26 290.59 290.92 291.25 291.58 291.90 292.23 292.56 292.90 293.23 293.56 293.89 294.21 294.54
0.34 +542 0.33 543 0.34 544 0.33 545 0.34 546 0.33 547 0.34 548 0.33 549 0.33 550 0.34 551 0.33 552 0.34 553 0.33 554 0.33 555 0.34 556 0.33 557 0.33 558 0.34 559 0.33 560 0.33 561 0.34 562 0.33 563 0.33 564 0.33 565 0.34 566 0.33 567 0.33 568 0.33 569 0.33 570 0.34 571 0.33 572 0.33 573 0.33 574 0.33 575 0.33 576 0.33 577 0.35 578 0.33 579 0.33 580 0.33 581 0.33 582 0.33 583 0.33 584 0.33 585 0.33 586 0.33 587 0.33 588 0.33 589 0.33 590 0.33 591 0.33 592 0.33 593 0.33 594 0.32 595 0.33 596 0.33 597 0.34 598 0.33 599 0.33 600 0.33 601 0.32 602 0.33 603
°C
1° Celsius Increments
Ohms
Diff.
°C
Ohms
Diff.
°C
Ohms
Diff.
294.87 295.20 295.53 295.85 296.18 296.51 296.84 297.16 297.49 297.82 298.14 298.47 298.80 299.12 299.45 299.78 300.10 300.43 300.75 301.08 301.41 301.73 302.06 302.38 302.71 303.03 303.36 303.68 304.01 304.33 304.66 304.98 305.30 305.63 305.95 306.28 306.60 306.92 307.25 307.57 307.89 308.22 308.54 308.86 309.19 309.51 309.83 310.15 310.48 310.80 311.12 311.45 311.78 312.10 312.43 312.75 313.07 313.39 313.71 314.04 314.36 314.68
0.33 0.33 0.33 0.32 0.33 0.33 0.33 0.32 0.33 0.33 0.32 0.33 0.33 0.32 0.33 0.33 0.32 0.33 0.32 0.33 0.33 0.32 0.33 0.32 0.33 0.32 0.33 0.32 0.33 0.32 0.33 0.32 0.32 0.33 0.32 0.33 0.32 0.32 0.33 0.32 0.32 0.33 0.32 0.32 0.33 0.32 0.32 0.32 0.33 0.32 0.32 0.33 0.33 0.32 0.33 0.32 0.32 0.32 0.32 0.33 0.32 0.32
+604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665
315.00 315.32 315.64 315.96 316.28 316.60 316.92 317.24 317.56 317.88 318.20 318.52 318.85 319.17 319.49 319.81 320.12 320.44 320.76 321.08 321.40 321.72 322.03 322.34 322.66 322.98 323.30 323.61 323.93 324.25 324.57 324.88 325.21 325.53 325.85 326.16 326.48 326.79 327.11 327.43 327.74 328.06 328.38 328.69 329.01 329.32 329.64 329.95 330.27 330.58 330.90 331.21 331.53 331.84 332.16 332.47 332.79 333.10 333.41 333.73 334.04 334.36
0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.33 0.32 0.32 0.32 0.31 0.32 0.32 0.32 0.32 0.32 0.31 0.31 0.32 0.32 0.32 0.31 0.32 0.32 0.32 0.31 0.33 0.32 0.32 0.31 0.32 0.31 0.32 0.32 0.31 0.32 0.32 0.31 0.32 0.31 0.32 0.31 0.32 0.31 0.32 0.31 0.32 0.31 0.32 0.31 0.32 0.31 0.31 0.32 0.31 0.32
+666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727
334.68 334.99 335.31 335.62 335.93 336.25 336.56 336.87 337.18 337.50 337.81 338.12 338.43 338.75 339.06 339.37 339.68 339.99 340.30 340.62 340.94 341.25 341.55 341.87 342.18 342.49 342.80 343.11 343.42 343.73 344.04 344.35 344.66 344.97 345.28 345.59 345.90 346.21 346.52 346.83 346.15 347.46 347.76 348.07 348.38 348.69 349.00 349.31 349.61 349.92 350.23 350.54 350.85 351.15 351.46 351.77 352.07 352.38 352.69 352.99 353.30 353.61
0.32 +728 0.31 729 0.32 730 0.31 731 0.31 732 0.32 733 0.31 734 0.31 735 0.31 736 0.32 737 0.31 738 0.31 739 0.31 740 0.32 741 0.31 742 0.31 743 0.31 744 0.31 745 0.31 746 0.32 747 0.32 748 0.31 749 0.30 750 0.32 751 0.31 752 0.31 753 0.31 754 0.31 755 0.31 756 0.31 757 0.31 758 0.31 759 0.31 760 0.31 761 0.31 762 0.31 763 0.31 764 0.31 765 0.31 766 0.31 767 0.32 768 0.31 769 0.30 770 0.31 771 0.31 772 0.31 773 0.31 774 0.31 775 0.30 776 0.31 777 0.31 778 0.31 779 0.31 780 0.30 781 0.31 782 0.31 783 0.30 784 0.31 785 0.31 786 0.30 787 0.31 788 0.31 789
Note: At 100°C, resistance is 138.50 ohms.
Z-254
°C
Ohms
Diff.
353.91 354.22 354.53 354.83 355.14 355.44 355.75 356.06 356.37 356.68 356.98 357.29 357.59 357.90 358.20 358.51 358.81 359.12 359.42 359.72 360.03 360.33 360.64 360.94 361.24 361.55 361.85 362.15 362.46 362.76 363.06 363.36 363.67 363.97 364.27 364.57 364.88 365.18 365.49 365.79 366.09 366.40 366.70 367.00 367.30 367.60 367.90 368.20 368.50 368.81 369.11 369.41 369.71 370.01 370.31 370.61 370.91 371.21 371.52 371.82 372.12 372.41
0.30 +790 0.31 791 0.31 792 0.30 793 0.31 794 0.30 795 0.31 796 0.31 797 0.31 798 0.31 799 0.30 800 0.31 801 0.30 802 0.31 803 0.30 804 0.31 805 0.30 806 0.31 807 0.30 808 0.30 809 0.31 810 0.30 811 0.31 812 0.30 813 0.30 814 0.31 815 0.30 816 0.30 817 0.31 818 0.30 819 0.30 820 0.30 821 0.31 822 0.30 823 0.30 824 0.30 825 0.31 826 0.30 827 0.31 828 0.30 829 0.30 830 0.31 831 0.30 832 0.30 833 0.30 834 0.30 835 0.30 836 0.30 837 0.30 838 0.31 839 0.30 840 0.30 841 0.30 842 0.30 843 0.30 844 0.30 845 0.30 846 0.30 847 0.31 848 0.30 849 0.30 850 0.29
°C
Ohms
Diff.
372.71 373.01 373.31 373.61 373.91 374.21 374.51 374.80 374.10 375.40 375.70 376.00 376.29 376.59 376.89 377.19 377.49 377.79 378.09 378.39 378.68 378.98 379.28 379.57 379.87 380.17 380.46 380.76 381.05 381.35 381.65 381.94 382.24 382.53 382.83 383.12 383.42 383.71 384.01 384.30 384.60 384.89 385.18 385.48 385.77 386.07 386.37 386.66 386.96 387.25 387.55 387.84 388.13 388.42 388.72 389.01 389.31 389.61 389.90 390.19 390.48
0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.29 0.30 0.30 0.30 0.30 0.29 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.29 0.30 0.30 0.29 0.30 0.30 0.29 0.30 0.29 0.30 0.30 0.29 0.30 0.29 0.30 0.29 0.30 0.29 0.30 0.29 0.30 0.29 0.29 0.30 0.29 0.30 0.30 0.29 0.30 0.29 0.30 0.29 0.29 0.29 0.30 0.29 0.30 0.30 0.29 0.29 0.29
(DIN 43 760)
Z
RTD Temperature vs. Resistance Table For American Curve, Alpha = .00392
1° Celsius Increments
°C
Ohms
°C
Ohms
°C
Ohms
°C
Ohms
°C
Ohms
°C
Ohms
°C
Ohms
°C
Ohms
°C
Ohms
-100 -99 -98 -97 -96 -95 -94 -93 -92 -91 -90 -89 -88 -87 -86 -85 -84 -83 -82 -81 -80 -79 -78 -77 -76 -75 -74 -73 -72 -71 -70 -69 -68 -67 -66 -65 -64 -63 -62 -61 -60 -59 -58 -57 -56 -55 -54 -53 -52 -51 -50 -49 -48 -47 -46 -45 -44 -43 -42 -41 -40 -39
59.57 59.98 60.39 60.80 61.21 61.63 62.04 62.45 62.86 63.27 63.68 64.09 64.50 64.91 65.32 65.73 66.14 66.55 66.96 67.36 67.77 68.18 68.59 69.00 69.41 69.81 70.22 70.63 71.04 71.44 71.85 72.26 72.66 73.07 73.48 73.88 74.29 74.70 75.10 75.51 75.91 76.32 76.72 77.13 77.53 77.94 78.34 78.75 79.15 79.56 79.96 80.36 80.77 81.17 81.58 81.98 82.38 82.79 83.19 83.59 83.99 84.40
-38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
84.80 85.20 85.60 86.01 86.41 86.81 87.21 87.61 88.01 88.42 88.82 89.22 89.62 90.02 90.42 90.82 91.22 91.62 92.02 92.42 92.82 93.22 93.62 94.02 94.42 94.82 95.22 95.62 96.02 96.42 96.81 97.21 97.61 98.01 98.41 98.81 99.20 99.60 100.00 100.40 100.80 101.19 101.59 101.99 102.38 102.78 103.18 103.57 103.97 104.37 104.76 105.16 105.56 105.95 106.35 106.74 107.14 107.53 107.93 108.32 108.72 109.11
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85
109.51 109.90 110.30 110.69 111.09 111.48 111.88 112.27 112.66 113.06 113.45 113.84 114.24 114.63 115.02 115.42 115.81 116.20 116.59 116.99 117.38 117.77 118.16 118.56 118.95 119.34 119.73 120.12 120.51 120.91 121.30 121.69 122.08 122.47 122.86 123.25 123.64 124.03 124.42 124.81 125.20 125.59 125.98 126.37 126.76 127.15 127.54 127.93 128.32 128.71 129.09 129.48 129.87 130.26 130.65 131.04 131.42 131.81 132.20 132.59 132.98 133.36
86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147
133.75 134.14 134.52 134.91 135.30 135.68 136.07 136.46 136.84 137.23 137.62 138.00 138.39 138.77 139.16 139.55 139.93 140.32 140.70 141.09 141.47 141.86 142.24 142.63 143.01 143.39 143.78 144.16 144.55 144.93 145.31 145.70 146.08 146.47 146.85 147.23 147.61 148.00 148.38 148.76 149.15 149.53 149.91 150.29 150.67 151.06 151.44 151.82 152.20 152.58 152.96 153.35 153.73 154.11 154.49 154.87 155.25 155.63 156.01 156.39 156.77 157.15
148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209
157.53 157.91 158.29 158.67 159.05 159.43 159.81 160.19 160.57 160.95 161.33 161.70 162.08 162.46 162.84 163.22 163.60 163.97 164.35 164.73 165.11 165.48 165.86 166.24 166.62 166.99 167.37 167.75 168.12 168.50 168.88 169.25 169.63 170.00 170.38 170.76 171.13 171.51 171.88 172.26 172.63 173.01 173.38 173.76 174.13 174.51 174.88 175.26 175.63 176.01 176.38 176.75 177.13 177.50 177.88 178.25 178.62 179.00 179.37 179.74 180.12 180.49
210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271
180.86 181.23 181.61 181.98 182.35 182.72 183.09 183.47 183.84 184.21 184.58 184.95 185.32 185.70 186.07 186.44 186.81 187.18 187.55 187.92 188.29 188.66 189.03 189.40 189.77 190.14 190.51 190.88 191.25 191.62 191.99 192.36 192.73 193.09 193.46 193.83 194.20 194.57 194.94 195.31 195.67 196.04 196.41 196.78 197.14 197.51 197.88 198.25 198.61 198.98 199.35 199.71 200.08 200.45 200.81 201.18 201.55 201.91 202.28 202.64 203.01 203.38
272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333
203.74 204.11 204.47 204.84 205.20 205.57 205.93 206.30 206.66 207.02 207.39 207.75 208.12 208.48 208.85 209.21 209.57 209.94 210.30 210.66 211.03 211.39 211.75 212.11 212.48 212.84 213.20 213.56 213.93 214.29 214.65 215.01 215.37 215.74 216.10 216.46 216.82 217.18 217.54 217.90 218.26 218.63 218.99 219.35 219.71 220.07 220.43 220.79 221.15 221.51 221.87 222.23 222.59 222.94 223.30 223.66 224.02 224.38 224.74 225.10 225.46 225.81
334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395
226.17 226.53 226.89 227.25 227.61 227.96 228.32 228.68 229.04 229.39 229.75 230.11 230.46 230.82 231.18 231.53 231.89 232.25 232.60 232.96 233.31 233.67 234.03 234.38 234.74 235.09 235.45 235.80 236.16 236.51 236.87 237.22 237.58 237.93 238.28 238.64 238.99 239.35 239.70 240.05 240.41 240.76 241.11 241.47 241.82 242.17 242.53 242.88 243.23 243.58 243.94 244.29 244.64 244.99 245.35 245.70 246.05 246.40 246.75 247.10 247.46 247.81
396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457
248.16 248.51 248.86 249.21 249.56 249.91 250.26 250.61 250.96 251.31 251.66 252.01 252.36 252.71 253.06 253.41 253.76 254.11 254.46 254.80 255.15 255.50 255.85 256.20 256.55 256.89 257.24 257.59 257.94 258.29 258.63 258.98 259.33 259.67 260.02 260.37 260.72 261.06 261.41 261.75 262.10 262.45 262.79 263.14 263.49 263.83 264.18 264.52 264.87 265.21 265.56 265.90 266.25 266.59 266.94 267.28 267.63 267.97 268.31 268.66 269.00 269.35
Z-255
Thermistor Resistance vs. Temperature Part NO. Ω @25°C BODY END TEMP. °C
44004 44033 2252 BLACK ORANGE YELLOW ORANGE
- 80 79 78 77 76 75 74 73 72 71
1660K 1518K 1390K 1273K 1167K 1071K 982.8K 902.7K 829.7K 763.1K
-70 69 68 67 66 65 64 63 62 61
702.3K 646.7K 595.9K 549.4K 506.9K 467.9K 432.2K 399.5K 369.4K 341.8K
-60 59 58 57 56 55 54 53 52 51
44005 44030 3000 BLACK ORANGE
44007 44034 5000 BLACK ORANGE
44006 44031 10,000 BLACK ORANGE
44008 44032 30,000 BLACK ORANGE
GREEN VIOLET BLACK YELLOW RESISTANCE Ω
BLUE BROWN
GRAY RED
2211K 2022K 1851K 1696K 1555K 1426K 1309K 1202K 1105K 1016K
PART NO. Ω @25°C BODY END TEMP. °C
44004 44033 2252 BLACK ORANGE
44005 44030 3000 BLACK ORANGE
YELLOW ORANGE
GREEN BLACK
44007 44034 5000 BLACK ORANGE
44006 44031 10,000 BLACK ORANGE
VIOLET BLUE YELLOW BROWN RESISTANCE Ω
44008 44032 30,000 BLACK ORANGE GRAY RED
3685K 3371K 3086K 2827K 2592K 2378K 2182K 2005K 1843K 1695K
3558K 3296K 3055K 2833K 2629K 2440K 2266K 2106K 1957K 1821K
-20 19 18 17 16 15 14 13 12 11
21.87K 20.64K 19.48K 18.40K 17.39K 16.43K 15.54K 14.70K 13.91K 13.16K
29.13K 27.49K 25.95K 24.51K 23.16K 21.89K 20.70K 19.58K 18.52K 17.53K
48.56K 45.83K 43.27K 40.86K 38.61K 36.49K 34.50K 32.63K 30.88K 29.23K
78.91K 74.91K 71.13K 67.57K 64.20K 61.02K 58.01K 55.17K 52.48K 49.94K
271.2K 256.5K 242.8K 229.8K 217.6K 206.2K 195.4K 185.2K 175.6K 166.6K
935.4K 861.4K 793.7K 731.8K 675.2K 623.3K 575.7K 532.1K 492.1K 455.3K
1560K 1436K 1323K 1220K 1126K 1039K 959.9K 887.2K 820.5K 759.2K
1694K 1577K 1469K 1369K 1276K 1190K 1111K 1037K 968.4K 904.9K
-10 9 8 7 6 5 4 3 2 -1
12.46K 11.81K 11.19K 10.60K 10.05K 9534 9046 8586 8151 7741
16.60K 15.72K 14.90K 14.12K 13.39K 12.70K 12.05K 11.44K 10.86K 10.31K
27.67K 26.21K 24.83K 23.54K 22.32K 21.17K 20.08K 19.06K 18.10K 17.19K
47.54K 45.27K 43.11K 41.07K 39.14K 37.31K 35.57K 33.93K 32.37K 30.89K
158.0K 150.0K 142.4K 135.2K 128.5K 122.1K 116.0K 110.3K 104.9K 99.80K
316.5K 293.2K 271.7K 252.0K 233.8K 217.1K 201.7K 187.4K 174.3K 162.2K
421.5K 390.5K 361.9K 335.7K 311.5K 289.2K 268.6K 249.7K 232.2K 216.0K
702.9K 651.1K 603.5K 559.7K 519.4K 482.2K 447.9K 416.3K 387.1K 360.2K
845.9K 791.1K 740.2K 692.8K 648.8K 607.8K 569.6K 534.1K 501.0K 470.1K
0 +1 2 3 4 5 6 7 8 9
7355 6989 6644 6319 6011 5719 5444 5183 4937 4703
9796 9310 8851 8417 8006 7618 7252 6905 6576 6265
16.33K 15.52K 14.75K 14.03K 13.34K 12.70K 12.09K 11.51K 10.96K 10.44K
29.49K 28.15K 26.89K 25.69K 24.55K 23.46K 22.43K 21.45K 20.52K 19.63K
94.98K 90.41K 86.09K 81.99K 78.11K 74.44K 70.96K 67.66K 64.53K 61.56K
-50 49 48 47 46 45 44 43 42 41
151.0K 140.6K 131.0K 122.1K 113.9K 106.3K 99.26K 92.72K 86.65K 81.02K
201.1K 187.3K 174.5K 162.7K 151.7K 141.6K 132.2K 123.5K 115.4K 107.9K
335.3K 312.3K 291.0K 271.3K 253.0K 236.2K 220.5K 205.9K 192.5K 180.0K
441.3K 414.5K 389.4K 366.0K 344.1K 323.7K 304.6K 286.7K 270.0K 254.4K
+10 11 12 13 14 15 16 17 18 19
4482 4273 4074 3886 3708 3539 3378 3226 3081 2944
5971 5692 5427 5177 4939 4714 4500 4297 4105 3922
9951 9486 9046 8628 8232 7857 7500 7162 6841 6536
18.79K 17.98K 17.22K 16.49K 15.79K 15.13K 14.50K 13.90K 13.33K 12.79K
58.75K 56.07K 53.54K 51.13K 48.84K 46.67K 44.60K 42.64K 40.77K 38.99K
-40 39 38 37 36 35 34 33 32 31
75.79K 70.93K 66.41K 62.21K 58.30K 54.66K 51.27K 48.11K 45.17K 42.42K
101.0K 94.48K 88.46K 82.87K 77.66K 72.81K 68.30K 64.09K 60.17K 56.51K
168.3K 157.5K 147.5K 138.2K 129.5K 121.4K 113.9K 106.9K 100.3K 94.22K
239.8K 226.0K 213.2K 201.1K 189.8K 179.2K 169.3K 160.0K 151.2K 143.0K
884.6K 830.9K 780.8K 733.9K 690.2K 649.3K 611.0K 575.2K 541.7K 510.4K
+ 20 21 22 23 24 25 26 27 28 29
2814 2690 2572 2460 2354 2252 2156 2064 1977 1894
3748 3583 3426 3277 3135 3000 2872 2750 2633 2523
6247 5972 5710 5462 5225 5000 4787 4583 4389 4204
12.26K 11.77K 11.29K 10.84K 10.41K 10.00K 9605 9227 8867 8523
37.30K 35.70K 34.17K 32.71K 31.32K 30.00K 28.74K 27.54K 26.40K 25.31K
-30 29 28 27 26 25 24 23 22 21
39.86K 37.47K 35.24K 33.15K 31.20K 29.38K 27.67K 26.07K 24.58K 23.18K
53.10K 49.91K 46.94K 44.16K 41.56K 39.13K 36.86K 34.73K 32.74K 30.87K
88.53K 83.22K 78.26K 73.62K 69.29K 65.24K 61.45K 57.90K 54.58K 51.47K
135.2K 127.9K 121.1K 114.6K 108.6K 102.9K 97.49K 92.43K 87.66K 83.16K
481.0K 453.5K 427.7K 403.5K 380.9K 359.6K 339.6K 320.9K 303.3K 286.7K
+ 30 31 32 33 34 35 36 37 38 + 39
1815 1739 1667 1599 1533 1471 1412 1355 1301 1249
2417 2317 2221 2130 2042 1959 1880 1805 1733 1664
4029 3861 3702 3549 3404 3266 3134 3008 2888 2773
8194 7880 7579 7291 7016 6752 6500 6258 6026 5805
24.27K 23.28K 22.33K 21.43K 20.57K 19.74K 18.96K 18.21K 17.49K 16.80K
Note: Data in black refer to thermistors with ±0.2°C interchangeability. Data in brown refer to thermistors with ±0.1°C interchangeability. Temperature/resistance figures are the same for both types. Note: Only thermistors with ±0.2°C interchangeability are available encased in Teflon as standard parts. For Part No. of Teflon encased thermistors add 100 to part No. of ±0-2°C interchangeable thermistor. Example: 44005 is a standard thermistor. 44105 is a Teflon encased thermistor with the same resistance values.
Z-256
Z
Thermistor Resistance vs. Temperature Part NO.
44004 44033
44005 44030
44007 44034
44006 44031
44008 44032
PART NO.
44004 44033
44005 44030
44007 44034
44006 44031
44008 44032
Ω @25°C
2252
3000
5000
10,000
30,000
Ω @25°C
2252
3000
5000
10,000
30,000
BODY
BLACK ORANGE
BLACK ORANGE
BLACK ORANGE
BLACK ORANGE
BLACK ORANGE
BODY
BLACK ORANGE
BLACK ORANGE
BLACK ORANGE
BLACK ORANGE
BLACK ORANGE
END
YELLOW ORANGE
GREEN BLACK
VIOLET YELLOW
BLUE BROWN
GRAY RED
END
YELLOW ORANGE
GREEN BLACK
VIOLET YELLOW
BLUE BROWN
GRAY RED
RESISTANCE Ω
TEMP. °C +40 41 42 43 44 45 46 47 48 49
1200 1152 1107 1064 1023 983.8 946.2 910.2 875.8 842.8
+50 51 52 53 54 55 56 57 58 59
RESISTANCE Ω
TEMP. °C
1598 1535 1475 1418 1363 1310 1260 1212 1167 1123
2663 2559 2459 2363 2272 2184 2101 2021 1944 1871
5592 5389 5193 5006 4827 4655 4489 4331 4179 4033
16.15K 15.52K 14.92K 14.35K 13.80K 13.28K 12.77K 12.29K 11.83K 11.39K
+100 101 102 103 104 105 106 107 108 109
152.8 148.4 144.2 140.1 136.1 132.3 128.6 125.0 121.6 118.2
203.8 197.9 192.2 186.8 181.5 176.4 171.4 166.7 162.0 157.6
339.6 329.8 320.4 311.3 302.5 294.0 285.7 277.8 270.1 262.6
816.8 794.6 773.1 752.3 732.1 712.6 693.6 675.3 657.5 640.3
2069 2009 1950 1894 1840 1788 1737 1688 1640 1594
811.3 781.1 752.2 724.5 697.9 672.5 648.1 624.8 602.4 580.9
1081 1040 1002 965.0 929.6 895.8 863.3 832.2 802.3 773.7
1801 1734 1670 1608 1549 1493 1439 1387 1337 1290
3893 3758 3629 3504 3385 3270 3160 3054 2952 2854
10.97K 10.57K 10.18K 9807 9450 9109 8781 8467 8166 7876
+110 111 112 113 114 115 116 117 118 119
115.0 111.8 108.8 105.8 103.0 100.2 97.6 95.0 92.5 90.0
153.2 149.0 145.0 141.1 137.2 133.6 130.0 126.5 123.2 119.9
255.4 248.4 241.6 235.1 228.7 222.6 216.7 210.9 205.3 199.9
623.5 607.3 591.6 576.4 561.6 547.3 533.4 519.9 506.8 494.1
1550 1507 1465 1425 1386 1348 1311 1276 1241 1208
+60 61 62 63 64 65 66 67 68 69
560.3 540.5 521.5 503.3 485.8 469.0 452.9 437.4 422.5 408.2
746.3 719.9 694.7 670.4 647.1 624.7 603.3 582.6 562.9 543.7
1244 1200 1158 1117 1079 1041 1006 971.1 938.0 906.3
2760 2669 2582 2497 2417 2339 2264 2191 2122 2055
7599 7332 7076 6830 6594 6367 6149 5940 5738 5545
+120 121 122 123 124 125 126 127 128 129
87.7 85.4 83.2 71.1 79.0 77.0 75.0 73.1 71.3 69.5
116.8 113.8 110.8 107.9 105.2 102.5 99.9 97.3 94.9 92.5
194.7 189.6 184.7 179.9 175.3 170.8 166.4 162.2 158.1 154.1
481.8 469.8 458.2 446.9 435.9 425.3 414.9 404.9 395.1 385.6
1176 1145 1114 1085 1057 1029 1002 976.3 951.1 926.7
+70 71 72 73 74 75 76 77 78 79
394.5 381.2 368.5 356.2 344.5 333.1 322.3 311.8 301.7 292.0
525.4 507.8 490.9 474.7 459.0 444.0 429.5 415.6 402.2 389.3
875.7 846.4 818.3 791.2 765.1 740.0 715.9 692.7 670.3 648.8
1990 1928 1868 1810 1754 1700 1648 1598 1549 1503
5359 5180 5007 4842 4682 4529 4381 4239 4102 3970
+130 131 132 133 134 135 136 137 138 139
67.8 66.1 64.4 62.9 61.3 59.8 58.4 57.0 55.6 54.3
90.2 87.9 85.7 83.6 81.6 79.6 77.6 75.8 73.9 72.2
150.3 146.5 142.9 139.4 136.0 132.6 129.4 126.3 123.2 120.3
376.4 367.4 358.7 350.3 342.0 334.0 326.3 318.7 311.3 304.2
903.0 880.0 857.7 836.1 815.0 794.6 774.8 755.6 736.9 718.8
+80 81 82 83 84 85 86 87 88 89
282.7 273.7 265.0 256.7 248.6 240.9 233.4 226.2 219.3 212.6
376.9 364.9 353.4 342.2 331.5 321.2 311.3 301.7 292.4 283.5
628.1 608.2 588.9 570.4 552.6 535.4 518.8 502.8 487.4 472.6
1458 1414 1372 1332 1293 1255 1218 1183 1149 1116
3843 3720 3602 3489 3379 3273 3172 3073 2979 2887
+140 141 142 143 144 145 146 147 148 149
53.0 51.7 50.5 49.3 48.2 47.0 45.9 44.9 43.8 42.8
70.4 68.8 67.1 65.5 64.0 62.5 61.1 59.6 58.3 56.9
117.4 114.6 111.9 109.2 106.7 104.2 101.8 99.40 97.10 94.87
297.2 290.4 283.8 277.4 271.2 265.1 259.2 253.4 247.8 242.3
701.2 684.1 667.5 651.3 635.6 620.3 605.5 591.1 577.1 563.5
+90 91 92 93 94 95 96 97 98 99
206.1 199.9 193.9 188.1 182.5 177.1 171.9 166.9 162.0 157.3
274.9 266.6 258.6 250.9 243.4 236.2 229.3 222.6 216.1 209.8
458.2 444.4 431.0 418.2 405.7 393.7 382.1 370.9 360.1 349.7
1084 1053 1023 994.2 966.3 939.3 913.2 887.9 863.4 839.7
2799 2714 2632 2552 2476 2402 2331 2262 2195 2131
+150
41.9
55.6
92.70
237.0
550.2
Note: Data in black refer to thermistors with ±0.2°C interchangeability. Data in blue refer to thermistors with 0.1°C interchangeability. Temperature/resistance figures are the same for both types. Note: Only thermistors with ±0.2°C interchangeability are available encased in Teflon as standard parts. For Part No. of Teflon encased thermistors add 100 to part No. of ±0.2°C interchangeable thermistors. Example: 44005 is a standard thermistor. 44105 is a Teflon encased thermistor with the same resistance values.
Z-257
Resistance vs Temperature for Series “700” Linear Thermistors T1 RESISTANCE VERSUS TEMPERATURE -30 to +100°C TEMP°C RES
These tables give the resistance values for T1 and T2 as defined on Page F-10 for the 44018 Linear Response Thermistor which is used in the Series 700 Linear Thermistor Probes. Resistance in ohms. Temperature in °C.
TEMP°C RES
TEMP°C RES
TEMP°C RES
TEMP°C RES
-30 29 28 27 26 25 24 23 22 21
106.2K 99.82K 93.88K 88.32K 83.12K 78.26K 73.72K 69.46K 65.48K 61.74K
0 +1 2 3 4 5 6 7 8 9
19.59K 18.62K 17.70K 16.83K 16.01K 15.24K 14.50K 13.81K 13.15K 12.53K
+30 31 32 33 34 35 36 37 38 39
4834 4634 4442 4260 4084 3918 3760 3610 3466 3328
+60 61 62 63 64 65 66 67 68 69
1493 1440 1389 1341 1294 1249 1207 1165 1126 1087
+90 91 92 93 94 95 96 97 98 99
549.8 533.2 517.2 501.8 486.8 472.4 458.6 445.2 432.2 419.6
-20 19 18 17 16 15 14 13 12 11
58.26K 54.98K 51.90K 49.02K 46.32K 43.78K 41.40K 39.16K 37.04K 35.06K
+10 11 12 13 14 15 16 17 18 19
11.94K 11.38K 10.85K 10.35K 9878 9428 9000 8594 8210 7844
+40 41 42 43 44 45 46 47 48 49
3196 3070 2950 2836 2726 2620 2520 2424 2334 2246
+70 71 72 73 74 75 76 77 78 79
1051 1016 981.8 949.4 918.0 888.0 859.0 831.2 804.4 773.6
+100
407.6
-10 9 8 7 6 5 4 3 2 -1
33.20K 31.49K 29.80K 28.24K 26.78K 25.40K 24.10K 22.88K 21.72K 20.62K
+20 21 22 23 24 25 26 27 28 29
7496 7166 6852 6554 6270 6000 5744 5500 5266 5046
+50 51 52 53 54 55 56 57 58 59
2162 2080 2004 1930 1859 1792 1727 1664 1605 1547
+80 81 82 83 84 85 86 87 88 89
753.8 729.8 706.8 684.4 663.0 642.4 622.6 603.4 584.8 567.0
T2 RESISTANCE VERSUS TEMPERATURE -30 to +100°C TEMP°C RES
TEMP°C RES
TEMP°C RES
TEMP°C RES
TEMP°C RES
-30 29 28 27 26 25 24 23 22 21
481.0K 453.5K 427.7K 403.5K 380.9K 359.6K 339.6K 320.9K 303.3K 286.7K
0 +1 2 3 4 5 6 7 8 9
94.98K 90.41 K 86.09K 81.99K 78.11 K 74.44K 70.96K 67.66K 64.53K 61.56K
+30 31 32 33 34 35 36 37 38 39
24.27K 23.28K 22.33K 21.43K 20.57K 19.74K 18.96K 18.21K 17.49K 16.80K
+60 61 62 63 64 65 66 67 68 69
7599 7332 7076 6830 6594 6367 6149 5940 5738 5545
+90 91 92 93 94 95 96 97 98 99
2799 2714 2632 2552 2476 2402 2331 2262 2195 2131
-20 19 18 17 16 15 14 13 12 11
271.2K 256.5K 242.8K 229.8K 217.6K 206.2K 195.4K 185.2K 175.6K 166.6K
+10 11 12 13 14 15 16 17 18 19
58.75K 56.07K 53.54K 51.13K 48.84K 46.67K 44.60K 42.64K 40.77K 38.99K
+40 41 42 43 44 45 46 47 48 49
16.15K 15.52K 14.92K 14.35K 13.80K 13.28K 12.77K 12.29K 11.83K 11.39K
+70 71 72 73 74 75 76 77 78 79
5359 5180 5007 4842 4682 4529 4381 4239 4102 3970
+100
2069
-10 9 8 7 6 5 4 3 2 -1
158.0K 150.0K 142.4K 135.2K 128.5K 122.1 K 116.0K 110.3K 104.9K 99.80K
+20 21 22 23 24 25 26 27 28 29
37.30K 35.70K 34.17K 32.71K 31.32K 30.00K 28.74K 27.54K 26.40K 25.31 K
+50 51 52 53 54 55 56 57 58 59
10.97K 10.57K 10.18K 9807 9450 9109 8781 8467 8166 7876
+80 81 80 83 84 85 86 87 88 89
3843 3720 3602 3489 3379 3273 3172 3073 2979 2887
Z-258
Z
Temperature Conversion Chart °C = 5⁄9 (°F - 32) Kelvin = °C + 273.15
°F = 9⁄5°C + 32 Rankine = °F + 459.67
TABLE EXAMPLE: To Convert 1000°C to °F, look up 1000 and read left To Convert 1000°F to °C, look up 1000 and read right
to °F
From
to °C
to °F
From
to °C
to °F
From
to °C
to °F
From
to °C
to °F
From
-
-458 -456 -454 -452 -450
-272.22 -271.11 -270.00 -268.89 -267.78
-
-308 -306 -304 -302 -300
-188.89 -187.78 -186.67 -185.56 -184.44
-252.4 -248.2 -245.2 -241.6 -238.0
-158 -156 -154 -152 -150
-105.56 -104.44 -103.33 -102.22 -101.11
+17.6 +21.2 +24.8 +28.4 +32.0
-8 -6 -4 -2 0
-22.22 -21.11 -20.00 -18.89 -17.78
287.6 291.2 294.8 298.4 302.0
142 144 146 140 150
61.11 62.22 63.33 64.44 65.56
-
-448 -446 -444 -442 -440
-266.67 -265.56 -264.44 -263.33 -262.22
-
-298 -296 -294 -292 -290
-183.33 -182.22 -181.11 -180.00 -178.89
-234.4 -230.2 -227.2 -223.6 -220.0
-148 -146 -144 -142 -140
-100.00 -98.89 -97.78 -96.67 -95.56
+35.6 +39.2 +42.8 +46.4 +50.0
2 4 6 8 10
-16.67 -15.56 -14.44 -13.33 -12.22
305.6 309.2 312.8 316.4 320.0
152 154 156 158 160
66.67 67.78 68.89 70.00 71.11
-
-438 -436 -434 -432 -430
-261.11 -260.00 -258.89 -257.78 -256.67
-
-288 -286 -284 -282 -280
-177.78 -176.67 -175.56 -174.44 -173.33
-216.4 -212.8 -209.2 -205.6 -202.0
-138 -136 -134 -132 -130
-94.44 -93.33 -92.22 -91.11 -90.00
+53.6 +57.2 +60.8 +64.4 +68.0
12 14 16 18 20
-11.11 -10.00 -8.89 -7.78 -6.67
323.6 327.2 330.8 334.4 338.0
162 164 166 168 170
72.22 73.33 74.44 75.56 76.67
-
-428 -426 -424 -422 -420
-255.56 -264.44 -253.33 -252.22 -251.11
-457.6 -454.0
-278 -276 -274 -272 -270
-172.22 -171.11 -170.00 -168.89 -167.78
-198.4 -194.2 -191.2 -187.6 -184.0
-128 -126 -124 -122 -120
-88.89 -87.78 -86.67 -85.56 -84.44
+71.6 +75.2 +78.8 +82.4 +86.0
22 24 26 28 30
-5.56 -4.44 -3.33 -2.22 -1.11
341.6 345.2 348.8 352.4 356.0
172 174 176 178 180
77.78 78.89 80.00 81.11 82.22
-
-418 -416 -414 -412 -410
-250.00 -248.89 -247.78 -246.67 -245.56
-450.4 -446.8 -443.2 -439.6 -436.0
-268 -266 -264 -262 -260
-166.67 -165.56 -164.44 -163.33 -162.22
-180.4 -176.8 -173.2 -169.6 -166.0
-118 -116 -114 -112 -110
-83.33 -82.22 -81.11 -80.00 -78.89
+89.6 +93.2 +96.8 +100.4 +104.0
32 34 36 38 40
0.00 1.11 2.22 3.33 4.44
359.6 363.2 366.8 370.4 374.0
182 184 186 188 190
83.33 84.44 85.56 86.67 87.78
-
-408 -406 -404 -402 -400
-244.44 -243.33 -242.22 -241.11 -240.00
-432.4 -428.8 -425.2 -421.6 -418.0
-258 -256 -254 -252 -250
-161.11 -160.00 -158.89 -157.78 -156.67
-162.4 -158.8 -155.2 -151.6 -148.0
-108 -106 -104 -102 -100
-77.78 -76.67 -75.56 -74.44 -73.33
107.6 111.2 114.2 118.4 122.0
42 44 46 48 50
5.56 6.67 7.78 8.89 10.00
377.6 381.2 384.8 388.4 392.0
192 194 196 198 200
88.89 90.00 91.11 92.22 93.33
-
-398 -396 -394 -392 -390
-238.89 -237.78 -236.67 -235.56 -234.44
-414.4 -410.8 -407.2 -403.6 -400.0
-248 -246 -244 -242 -240
-155.56 -154.44 -153.33 -152.22 -151.11
-144.4 -140.8 -137.2 -133.6 -130.0
-98 -96 -94 -92 -90
-72.22 -71.11 -70.00 -68.89 -67.78
125.6 129.2 132.8 136.4 140.0
52 54 56 58 60
11.11 12.22 13.33 14.44 15.56
395.6 399.2 402.8 406.4 410.0
202 204 206 208 210
94.44 95.56 96.67 97.78 98.89
-
-388 -386 -384 -382 -380
-233.33 -232.22 -231.11 -230.00 -228.89
-396.4 -392.8 -389.2 -385.6 -382.0
-238 -236 -234 -232 -230
-150.00 -148.89 -147.78 -146.67 -145.56
-126.4 -122.2 -119.2 -115.6 -112.0
-88 -86 -84 -82 -80
-66.67 -65.56 -64.44 -63.33 -62.22
143.6 147.2 150.8 154.4 158.0
62 64 66 68 70
16.67 17.78 18.89 20.00 21.11
413.6 417.2 420.8 424.4 428.0
212 214 216 218 220
100.00 101.11 102.22 103.33 104.44
-
-378 -376 -374 -372 -370
-227.78 -226.67 -225.56 -224.44 -223.33
-378.4 -374.8 -371.2 -367.6 -364.0
-228 -226 -224 -222 -220
-144.44 -143.33 -142.22 -141.11 -140.00
-108.4 -104.8 -101.2 -97.6 -94.0
-78 -76 -74 -72 -70
-61.11 -60.00 -58.89 -57.78 -56.67
161.6 165.2 168.8 172.4 176.0
72 74 76 78 80
22.22 23.33 24.44 25.56 26.67
431.6 435.2 438.8 442.4 446.0
222 224 226 228 230
105.56 106.67 107.78 108.89 110.00
-
-368 -366 -364 -362 -360
-222.22 -221.11 -220.00 -218.89 -217.78
-360.4 -356.8 -353.2 -349.6 -346.0
-218 -216 -214 -212 -210
-138.89 -137.78 -136.67 -135.56 -134.44
-90.4 -86.8 -83.2 -79.6 -76.0
-68 -66 -64 -62 -60
-55.56 -54.44 -53.33 -52.22 -51.11
179.6 183.2 186.8 190.4 194.0
82 84 86 88 90
27.78 28.89 30.00 31.11 32.22
449.6 453.2 456.8 460.4 464.0
232 234 236 238 240
111.11 112.22 113.33 114.44 115.56
-
-358 -356 -354 -352 -350
-216.67 -215.56 -214.44 -213.33 -212.22
-342.4 -338.8 -335.2 -331.6 -328.0
-208 -206 -204 -202 -200
-133.33 -132.22 -131.11 -130.00 -128.89
-72.4 -68.8 -65.2 -61.6 -58.0
-58 -56 -54 -52 -50
-50.00 -48.89 -47.78 -46.67 -45.56
197.6 201.2 204.8 208.4 212.0
92 94 96 98 100
33.33 34.44 35.56 36.67 37.78
467.6 471.2 474.8 478.4 482.0
242 244 246 248 250
116.67 117.78 118.89 120.00 121.11
-
-348 -346 -344 -342 -340
-211.11 -210.00 -208.89 -207.78 -206.67
-324.4 -320.8 -317.2 -313.6 -310.0
-198 -196 -194 -192 -190
-127.78 -126.67 -125.56 -124.44 -123.33
-54.4 -50.8 -47.2 -43.6 -40.0
-48 -46 -44 -42 -40
-44.44 -43.33 -42.22 -41.11 -40.00
215.6 219.2 222.8 226.4 230.0
102 104 106 108 110
38.89 40.00 41.11 42.22 43.33
485.6 489.2 492.8 496.4 500.0
252 254 256 258 260
122.22 123.33 124.44 125.56 126.67
-
-338 -336 -334 -332 -330
-205.56 -204.44 -203.33 -202.22 -201.11
-306.4 -302.8 -299.2 -295.6 -292.0
-188 -186 -184 -182 -180
-122.22 -121.11 -120.00 -118.89 -117.78
-36.4 -32.8 -29.2 -25.6 -22.0
-38 -36 -34 -32 -30
-38.89 -37.78 -36.67 -35.56 -34.44
233.6 237.2 240.2 244.4 248.0
112 114 116 118 120
44.44 45.56 46.67 47.78 48.89
503.6 507.2 510.8 514.4 518.0
262 264 266 268 270
127.78 128.89 130.00 131.11 132.22
-
-328 -326 -324 -322 -320
-200.00 -198.89 -197.78 -196.67 -195.56
-288.4 -284.8 -281.2 -277.6 -274.0
-178 -176 -174 -172 -170
-116.67 -115.56 -114.44 -113.33 -112.22
-18.4 -14.8 -11.2 -7.6 -4.0
-28 -26 -24 -22 -20
-33.33 -32.22 -31.11 -30.00 -28.89
251.6 255.2 258.8 262.4 266.0
122 124 126 128 130
50.00 51.11 52.22 53.33 54.44
521.6 525.2 528.8 532.4 536.0
272 274 276 278 280
133.33 134.44 135.56 136.67 137.78
-
-318 -316 -314 -312 -310
-194.44 -193.33 -192.22 -191.11 190.00 1
-270.4 -266.8 -263.2 -259.6 -256.0
-168 -166 -164 -162 -160
-111.11 -110.00 -108.89 -107.78 106.67
-0.4 +3.2 +6.8 +10.4 +14.0
-18 -16 -14 -12 -10
-27.78 -26.67 -25.56 -24.44 - 23.33
269.6 273.2 276.8 280.4 284.0
132 134 136 138 140
55.56 56.67 57.78 58.89 60.00
539.6 543.2 546.8 550.4 594.0
282 284 286 288 290
138.89 140.00 141.11 142.22 143.33
Z-259
to °C
to °F
From
to °C
to °F
From
to °C
to °F
From
to °C
to °F
From
to °C
to °F
From
to °C
557.6 561.2 564.8 568.4 572.0
292 294 296 298 300
144.44 145.56 146.67 147.78 148.89
870.8 874.4 878.0 881.6 885.2
466 468 470 472 474
241.11 242.22 243.33 244.44 245.56
1832.0 1850.0 1868.0 1886.0 1904.0
1000 1010 1020 1030 1040
537.78 543.33 548.89 554.44 560.00
3398.0 3416.0 3434.0 3452.0 3470.0
1870 1880 1890 1900 1910
1021.1 1026.7 1032.2 1037.8 1043.3
4964.0 4982.0 5000.0 5018.0 5036.0
2740 2750 2760 2770 2780
1504.4 1510.0 1515.6 1521.1 1526.7
575.6 579.2 582.8 586.4 590.0
302 304 306 308 310
150.00 151.11 152.22 153.33 154.44
888.8 892.4 896.0 899.6 903.2
476 478 480 482 484
246.67 247.78 248.89 250.00 251.11
1922.0 1940.0 1958.0 1976.0 1994.0
1050 1060 1070 1080 1090
565.56 571.11 576.67 582.22 587.78
3488.0 3506.0 3524.0 3542.0 3560.0
1920 1930 1940 1950 1960
1048.9 1054.4 1060.0 1065.6 1071.1
5054.0 5072.0 5090.0 5108.0 5126.0
2790 2800 2810 2820 2830
1532.2 1537.8 1543.3 1548.9 1554.4
593.6 597.2 600.8 604.4 608.0
312 314 316 318 320
155.56 156.67 157.78 158.89 160.00
906.8 910.4 914.0 917.6 921.2
486 488 490 492 494
252.22 253.33 254.44 255.56 256.67
2012.0 2030.0 2048.0 2066.0 2084.0
1100 1110 1120 1130 1140
593.33 598.89 604.44 610.00 615.56
3578.0 3596.0 3614.0 3632.0 3650.0
1970 1980 1990 2000 2010
1076.7 1082.2 1087.8 1093.3 1098.9
5144.0 5162.0 5180.0 5198.0 5216.0
2840 2850 2860 2870 2880
1560.0 1565.6 1571.1 1576.7 1582.2
611.6 615.2 618.8 622.4 626.0
322 324 326 328 330
161.11 162.22 163.33 164.44 165.56
924.8 928.4 932.0 935.6 939.2
496 498 500 502 504
257.78 258.89 260.00 261.11 262.22
2102.0 2120.0 2138.0 2156.0 2174.0
1150 1160 1170 1180 1190
621.11 626.67 632.22 637.78 643.33
3668.0 3686.0 3704.0 3722.0 3740.0
2020 2030 2040 2050 2060
1104.4 1110.0 1156.6 1121.1 1126.7
5234.0 5252.0 5270.0 5288.0 5306.0
2890 2900 2910 2920 2930
1597.8 1593.3 1598.9 1604.4 1610.0
629.6 633.2 636.8 640.4 644.0
332 334 336 338 340
166.67 167.78 168.89 170.00 171.11
942.8 946.4 950.0 953.6 957.2
506 508 510 512 514
263.33 264.44 265.56 266.67 267.78
2192.0 2210.0 2228.0 2246.0 2264.0
1200 1210 1220 1230 1240
648.89 654.44 660.00 665.56 671.11
3758.0 3776.0 3794.0 3812.0 3830.0
2070 2080 2090 2100 2110
1132.2 1137.8 1143.3 1148.9 1154.4
5324.0 5342.0 5360.0 5378.0 5396.0
2940 2950 2960 2970 2980
1615.6 1621.1 1626.7 1632.2 1637.2
647.6 651.2 654.8 658.4 662.0
342 344 346 348 350
172.22 173.33 174.44 175.56 176.67
960.8 964.4 968.0 971.6 975.2
516 518 520 522 524
268.89 270.00 271.11 272.22 273.33
2282.0 2300.0 2318.0 2336.0 2354.0
1250 1260 1270 1280 1290
676.67 682.22 687.78 693.33 698.89
3848.0 3866.0 3884.0 3902.0 3920.0
2120 2130 2140 2150 2160
1160.0 1165.6 1171.1 1176.7 1182.2
5414.0 5432.0 5450.0 5468.0 5486.0
2990 3000 3010 3020 3030
1643.3 1648.9 1654.4 1660.0 1665.6
665.6 669.2 672.8 676.4 680.0
352 354 356 358 380
177.78 178.89 180.00 181.11 182.22
978.8 982.4 986.0 989.6 993.2
526 528 530 532 534
274.44 276.56 276.67 277.78 278.89
2372.0 2390.0 2408.0 2426.0 2444.0
1300 1310 1320 1330 1340
704.44 710.00 715.56 721.11 726.67
3938.0 3956.0 3974.0 3992.0 4010.0
2170 2180 2190 2200 2210
1187.8 1193.3 1198.9 1204.4 1210.0
5504.0 5522.0 5540.0 5588.0 5576.0
3040 3050 3060 3070 3080
1671.1 1676.7 1682.2 1687.8 1693.3
683.6 687.2 690.8 694.4 698.0
362 364 366 368 370
183.33 184.44 186.56 186.67 187.78
996.8 1000.4 1004.0 1007.6 1011.2
536 538 540 542 544
280.00 281.11 282.22 283.33 284.44
2462.0 2480.0 2498.0 2516.0 2534.0
1350 1360 1370 1380 1390
732.22 737.78 743.33 748.89 754.44
4028.0 4046.0 4064.0 4082.0 4100.0
2220 2230 2240 2250 2260
1215.6 1221.1 1226.7 1232.2 1237.8
5594.0 5612.0 5702.0 5792.0 5882.0
3090 3100 3150 3200 3250
1698.9 1704.4 1732.2 1760.0 1787.8
701.6 705.2 708.8 712.4 716.0
372 374 376 378 380
188.89 190.00 191.11 192.22 193.33
1014.8 1018.4 1022.0 1040.0 1058.0
546 548 550 560 570
285.56 286.67 287.78 293.33 298.89
2552.0 2570.0 2588.0 2606.0 2624.0
1400 1410 1420 1430 1440
760.00 765.56 771.11 776.67 782.22
4118.0 4136.0 4154.0 4172.0 4190.0
2270 2280 2290 2300 2310
1243.3 1248.9 1254.4 1260.0 1265.6
5972.0 6062.0 6152.0 6242.0 6332.0
3300 3350 3400 3450 3500
1815.6 1843.3 1871.1 1898.9 1926.7
719.6 723.2 726.8 730.4 734.0
382 384 386 388 390
194.44 195.56 196.67 197.78 198.89
1076.0 1094.0 1112.0 1130.0 1148.0
580 590 600 610 620
304.44 310.00 315.56 321.11 326.67
2642.0 2660.0 2678.0 2696.0 2714.0
1450 1460 1470 1480 1490
787.78 793.33 798.89 804.44 810.00
4208.0 4226.0 4244.0 4262.0 4280.0
2320 2330 2340 2350 2360
1271.1 1276.7 1282.2 1287.8 1293.3
6422.0 6512.0 6602.0 6692.0 6782.0
3550 3600 3650 3700 3750
1954.4 1982.2 2010.0 2037.8 2065.6
737.6 741.2 744.8 748.4 752.0
392 394 396 398 400
200.00 201.11 202.22 203.33 204.44
1166.0 1184.0 1202.0 1220.0 1238.0
630 640 650 660 670
332.22 337.78 343.33 348.89 354.44
2732.0 2750.0 2768.0 2786.0 2804.0
1500 1510 1520 1530 1540
815.56 821.11 826.67 832.22 837.78
4298.0 4316.0 4334.0 4352.0 4370.0
2370 2380 2390 2400 2410
1298.9 1304.4 1310.0 1315.6 1321.1
6972.0 6962.0 7052.0 7142.0 7232.0
3800 3850 3900 3950 4000
2093.3 2121.1 2148.9 2176.7 2204.4
755.6 759.2 762.8 766.4 770.0
402 404 406 408 410
205.66 206.67 207.78 208.89 210.00
1256.0 1274.0 1292.0 1310.0 1328.0
680 690 700 710 720
360.00 365.56 371.11 376.67 382.22
2822.0 2840.0 2858.0 2876.0 2894.0
1550 1560 1570 1580 1590
843.33 848.89 854.44 860.00 865.56
4388.0 4406.0 4424.0 4442.0 4460.0
2420 2430 2440 2450 2460
1326.7 1332.2 1337.8 1343.3 1348.9
7322.0 7412.0 7502.0 7592.0 7682.0
4050 4100 4150 4200 4250
2232.2 2260.0 2287.8 2315.6 2343.3
773.6 777.2 780.8 784.4 788.0
412 414 416 418 420
211.11 212.22 213.33 214.44 215.56
1346.0 1364.0 1382.0 1400.0 1418.0
730 740 750 760 770
387.78 393.33 398.89 404.44 410.00
2912.0 2930.0 2948.0 2966.0 2984.0
1600 1610 1620 1630 1640
871.11 876.67 882.22 887.78 893.33
4478.0 4496.0 4514.0 4532.0 4550.0
2470 2480 2490 2500 2510
1354.4 1360.0 1365.6 1371.1 1376.7
7772.0 7862.0 7952.0 8042.0 8132.0
4300 4350 4400 4450 4450
2371.1 2398.9 2426.7 2454.4 2482.2
791.6 795.2 798.8 802.4 806.0
422 424 426 428 430
216.67 217.78 218.89 220.00 221.11
1436.0 1454.0 1472.0 1490.0 1508.0
780 790 800 810 820
415.56 421.11 426.67 432.22 437.78
3002.0 3020.0 3038.0 3056.0 3074.0
1650 1660 1670 1680 1690
898.89 904.44 910.00 915.56 921.11
4568.0 4586.0 4604.0 4622.0 4640.0
2520 2530 2540 2550 2560
1382.2 1387.2 1393.3 1398.9 1404.4
8222.0 8312.0 8402.0 8492.0 8582.0
4550 4600 4650 4700 4750
2510.0 2537.8 2565.6 2593.3 2621.1
809.6 813.2 816.8 820.4 824.0
432 434 436 438 440
222.22 223.33 224.44 225.56 226.67
1526.0 1544.0 1562.0 1580.0 1598.0
830 840 850 860 870
443.33 448.89 454.44 460.00 465.56
3092.0 3110.0 3128.0 3146.0 3164.0
1700 1710 1720 1730 1740
926.67 932.22 937.78 943.33 948.89
4658.0 4676.0 4694.0 4712.0 4730.0
2570 2680 2590 2600 2610
1410.0 1415.6 1421.1 1426.7 1432.2
8672.0 8762.0 8852.0 8942.0 9032.0
4800 4850 4900 4950 5000
2648.9 2676.7 2704.4 2732.2 2760.0
827.6 831.2 834.8 838.4 842.0
442 444 446 448 450
227.78 228.89 230.00 231.11 232.22
1616.0 1634.0 1652.0 1670.0 1688.0
880 890 900 910 920
471.11 476.67 482.22 487.78 493.33
3182.0 3200.0 3218.0 3236.0 3254.0
1750 1760 1770 1780 1790
954.44 960.00 965.56 971.11 976.67
4748.0 4766.0 4784.0 4802.0 4820.0
2620 2630 2640 2650 2660
1437.8 1443.3 1448.9 1454.4 1460.0
9122.0 9212.0 9302.0 9392.0 9482.0
5050 5100 5150 5200 5250
2787.8 2815.6 2843.3 2871.1 2898.9
845.6 849.2 852.2 856.4 860.0
452 454 456 458 460
233.33 234.44 235.56 236.67 237.78
1706.0 1724.0 1742.0 1760.0 1778.0
930 940 950 960 970
498.89 504.44 510.00 515.66 521.11
3272.0 3290.0 3308.0 3326.0 3344.0
1800 1810 1820 1830 1840
982.22 997.78 993.33 998.89 1004.40
4838.0 4856.0 4974.0 4892.0 4910.0
2670 2680 2690 2700 2710
1465.6 1471.1 1467.7 1482.2 1487.8
9572.0 9662.0 9752.0 9842.0 9932.0
5300 5350 5400 5450 5500
2926.7 2954.4 2982.2 3010.0 3037.8
863.6 867.2
462 464
238.89 240.00
1796.0 1814.0
980 990
526.67 532.22
3362.0 3380.0
1850 1860
1010.0 1015.6
4928.0 4946.0
2720 2730
1493.3 1498.9
10,002.0 10,112.0
5550 5600
3065.6 3093.3
Z-260
Z
TECHNICAL DATA SECTION Reference Section TERMINOLOGY ACF = A/D = ATM = BTU = cc/min =
Actual Cubic Feet Analog to Digital Atmospheres British Thermal Units Cubic Centimeters per Minute CFH = Standard Cubic Feet per Hour (SCFH) Specific Heat CP = C.S. = Carbon Steel D= Diameter Dia. = Diameter Diam. = Diameter D/A = Digital to Analog EMI = Electromagnetic Interference EPR = Ethylene Propylene Rubber FDA = Food and Drug Administration FNPT = Female National Pipe Thread FPM = Feet Per Minute FPS = Feet Per Second F.S. = Full Scale FT = Feet gals = Gallons gpm = Gallons Per Minute gph = Gallons Per Hour HF = Latent Heat of Fusion H/L = High-Low HV = Latent Heat of Vaporization I.D. = Inside Diameter I/0 = Input/Output k= Thermal Conductivity Ibs = Pounds 2 Ibs/in = Pounds Per Square Inch lpm = Liters Per Minute L/min = Liters Per Minute mL/min = Milliliters Per Minute MNPT = Male National Pipe Thread ms = Milliseconds m/s = Meters Per Second MSEC = Milliseconds NiCad = Nickel Cadmium NO/NC = Normally Open/ Normally Closed NPT = National Pipe Thread O.D. = Outside Diameter P-P = Peak to Peak PSIA = Pounds Per Square Inch Absolute PSID = Pounds Per Square Inch Differential PSIG = Pounds Per Square Inch Gage PVC = Polyvinyl Chloride PVDF = Polyvinylidene Fluoride (Kynaol) RF = Raised Face RFI = Radio Frequency Interference RMS = Root Mean Square SCCM = Standard Cubic Centimeters per Minute SCHED. NO. = Schedule Number SCFH = Standard Cubic Feet per Hour SCFM = Standard Cubic Feet per Minute SLM = Standard Liters per Minute SLPM = Standard Liters per Minute sq.ft. = Square Feet SSU = Saybolt Seconds Universal ∆T = Temperature Rise TTL = Transistor-Transistor Logic W= Watts W-hr = Watt-Hours W/in2 2 Watt Density WT= Weight of Material
Conversion Factors TO OBTAIN Atmospheres BTU BTU Centimeters Cm of Hg @ 0 deg C Cm of Hg @ 0 deg C Cm of Hg @ 0 deg C Cm of Hg @ 0 deg C Cm/(sec)(sec) Centipoises Centistokes Cu cm Cu cm Cu cm Cu cm Cu cm Cu cm/sec Cu ft Cu ft Cu ft Cu ft/min Cu ft/min Cu ft/sec Cu ft/sec Cu in. Cu in. Cu in. Cu meters Cu meters Cu meters/hr Cu meters/kg Cu meters/min Cu meters/sec Feet Ft/min Ft/sec Ft/(sec)(sec) Ft/(sec)(sec) Gal (Imperial, liq.) Gal (USA, liq.) Gal (USA, liq.) Gal (USA, liq.) Gal (USA, liq.) Gal (USA, liq.) Gal (USA, liq.) Gal (USA, liq.)/min Gal (USA, liq.)/min Gal (USA, liq.)/sec Grams
Z-261
MULTIPLY In HG@32ºF Watt-hours KWh Inches Atmospheres Grams/sq. cm Lb/sq in. Lb/sq ft Gravity Centistokes Centipoises Cu ft Cu in. Gal (USA, liq.) Liters Quarts (USA, liq.) Cu ft/min Cu meters Gal (USA, liq.) Liters Cu meters/sec Gal (USA, liq.)/sec Gal (USA, liq.)/min Liters/min Cu centimeters Gal (USA, liq.) Liters Gal (USA, liq.) Liters Gal/min Cu ft/lb Cu ft/min Gal/min Meters Cm/sec Meters/sec Gravity (sea level) Meters/(sec)(sec) Gal (USA, liq.) Barrels (Petroleum, USA) Cu ft Cu meters Cu yards Gal (Imperial, liq.) Liters Cu ft/sec Cu meters/hr Liters/min Pounds (avoir.)
BY 0.033421 3.412 3412 2.540 76.0 0.07356 5.1715 0.035913 980.665 Density 1/density 28,317 16-387 3785.43 1000.03 946.358 472.0 35.314 0.13368 0.03532 2118.9 8.0192 0.0022280 0.0005886 0.061023 231.0 61.03 0.0037854 0.001000028 0.22712 0.062428 0.02832 0.000063088 3.281 1.9685 3.2808 32.174 3.2808 0.83268 42 7.4805 264.173 202.2 1.2010 0.2642 448.83 4.4029 0.0044028 453.5924
Conversion Factors TO OBTAIN Grams/(cm)(sec) Grams/cu cm Grams/cu cm Grams/cu cm Inches Inches of Hg @ 32˚ F Inches of Hg @ 32˚ F Inches of Hg @ 32˚ F Inches/deg F Kg Kg-cal/sq meter Kg/cu meter Kg/(hr)(meter) Kg/liter Kg/meter Kg/sq cm Kg/sq meter KWh KWh Liters Liters Liters Liters Liters Liters/kg Liters/min Liters/min Liters/sec Liters/sec Meters Meters/sec Mete rs/sec)(sec) Ounces Pounds (avoir.) Pounds/cu ft Pounds/cu ft Pounds/cu in. Pounds/(hr)(ft) Pounds/inch Pounds/(sec)(ft) Pounds/gal. (USA, liq.) Pounds/gal. (USA, liq.) Pounds/gal. (USA, liq.) Sq centimeters Sq centimeters Sq ft Sq in. Sq meters W-hr W-hr
MULTIPLY Centipoises Lb/cu ft Lb/cu in. Lb/gal Centimeters Atmospheres Lb/sq in. In. of H2O @ 4°C Cm/deg C Pounds (avoir.) BTU/sq ft Lb/cu ft Centipoises Lb/gal (USA, liq.) Lb/ft Lb/sq in. Lb/sq ft BTU watt-hours Cu ft Cu in. Cu meters Gal (Imperial, liq.) Gal (USA, liq.) Cu ft/lb Cu ft/sec Gal (USA, liq.)/min Cu ft/min Gal/min Feet Ft/sec Ft/(sec)(sec) Grams Kg Grams/cu cm Pounds/gal Grams/cu cm Centipoises Grams/cm Centipoises Kg/liter Pounds/cu ft Pounds/cu in. Sq ft Sq in. Sq meters Sq centimeters Sq ft BTU KWh
BY 0.01 0.016018 27.680 0.119826 0.3937 29.921 2.0360 0.07355 0.21872 0.45359 2.712 16.018 3.60 0.11983 1.488 0.0703 4.8824 .0002930 .001 28.316 0.01639 999.973 4.546 3.785306 62.42621 1698.963 3.785 0.47193 0.063088 0.3048 0.3048 0.3048 0.035274 2.2046 62.428 7.48 0.036127 2.42 0.0056 0.000672 8.3452 0.1337 231 929.0 6.4516 10.764 0.155 0.0929 .2390 1000
METRIC PREFIXES MEGA = KILO = HECTO = DECA= DECI= CENTI = MILLI= MICRO =
1,000,000 1,000 100 10 .1 .01 .001 .000,001
Z
TEMPERATURE CONVERSION FORMULAS: ˚F = (9/5 ˚C) + 32 ˚C = (˚F - 32) x 5/9
National Pipe Taper Thread Dimensions NPT SIZE THREADS PER INCH 1 ⁄16 27 1 ⁄8 27 1 ⁄4 18 3 ⁄8 18 1 ⁄2 14 3 ⁄4 14 1 111⁄2 11⁄4 111⁄2
DIM “A” (IN) .312 .405 .540 .675 .840 1.050 1.315 1.660
DIM “B” (IN) .261 .264 .402 .408 .534 .546 .683 .707
1°47' A
B EFECTIVE THREAD
®
Z-262
OHM’S LAW VARIATIONS OF OHM’S LAW
S TT
VOLTS
AM P
ES ER
WA
E E W I2R R R E EI W I W/R WR E R E I W W E2 W T S I IR I2 OH 2
110 115 120 208 220 230 240 277 380 415 440 460 480 550
Rated Voltage 110 115
100% 109% 119%
91% 100% 109%
OHMS =
VOLTS AMPERES
OHMS =
VOLTS2 WATTS
OHMS =
WATTS2 AMPERES2
AMPERES
4.2 8.4 12.5 16.7 20.9 25 31.3 41.7 50 62.5 83.4 105 125 209 313 417
2.3 4.6 6.9 9.1 11.4 13.7 17.1 22.8 27.3 34.1 45.5 56.9 68.2 114 171 228
2.1 4.2 6.3 8.4 10.5 12.5 15.7 20.9 25 31.2 41.7 52.1 62.5 105 157 209
2.8 5.6 8.4 11.2 13.9 16.7 20.9 27.8 33.4 41.7 55.6 69.5 83.4 139 209 278
2.5 4.9 7.3 9.7 12.1 14.5 18.1 24.1 29 36.2 48.2 60.3 72.3 121 181 241
1.4 2.7 4 5.3 6.6 7.9 9.9 13.2 15.8 19.7 26.3 32.9 39.4 65.7 98.6 132
1.3 2.5 3.7 4.9 6.1 7.3 9.1 12.1 14.5 18.1 24.1 30.1 36.2 60.3 90.4 121
Percent of rated wattage for various applied voltages Applied Voltage
WATTS AMPERES
OHMS
M
L 4.8 9.7 14.5 19.3 24.1 28.9 36.1 48.1 57.7 72.2 96.2 121 145 241 361 481
VOLTS =
S
VO 8.4 16.7 25 33.4 41.7 50 62.5 83.4 100 125 167 209 250 417 625 834
ßßß WATTS œ ß ß ß ßxßOHMS
VOLTS = AMPERES x OHMS
Table 11 Currents for resistance heating loads Single phase Three phase balanced load kW 120V 208V 240V 440V 480V 208V 240V 440V 480V 1 2 3 4 5 6 7.5 10 12 15 20 25 30 50 75 100
VOLTS =
120
208
220
230
240
84% 92% 100% 300%
28% 31% 33% 100% 112% 122% 133%
25% 27% 30% 89% 100% 109% 119%
23% 25% 27% 82% 91% 100% 109%
21% 23% 25% 75% 84% 92% 100% 133%
Z-263
AMPERES =
VOLTS OHMS
AMPERES =
WATTS VOLTS
AMPERES =
WATTS OHMS
WATTS WATTS =
VOLTS2 OHMS
WATTS = AMPERES2 x OHMS WATTS = VOLTS x AMPERES
Currents for resistance heating loads Heating elements are frequently used at voltages other than those shown in our catalog. The percentages shown below are used to determine the resulting wattage. Should you wish to use a heater on a voltage not shown above, you may calculate the resultant wattage with this formula: 2 Actual Wattage = Rated Wattage x Applied Voltage Rated Voltage2
277
380
415
440
460
480
550
16% 17% 19% 56% 63% 69% 75% 100% 188%
8.4% 9.0% 10% 30% 34% 37% 40% 53% 100% 119%
7% 7.6% 8.4% 25% 28% 31% 33% 45% 84% 100% 112% 123%
6.2% 6.7% 7.4% 22% 25% 27% 30% 40% 74% 89% 100% 109% 119% 156%
5.7% 6.2% 6.8% 20% 23% 25% 27% 36% 68% 81% 91% 100% 109% 143%
5.2% 5.7% 6.3% 19% 21% 23% 25% 33% 63% 75% 84% 92% 100% 131%
4% 4.3% 4.8% 14% 16% 17% 19% 25% 47% 57% 64% 70% 76% 100%
Electrical Units
Quantity Current Quantity Electromotive force Resistance Resistivity Conductance Conductivity Capacitance Permittivity Relative permittivity Self-inductance Mutual inductance Energy Active power Reactive power Apparent power Power factor Reactance, inductive Reactance, capacitive Impedance Conductance Susceptance Admittance Frequency Period Time constant Angular velocity
Symbol I, i Q, q E, e R, r r G, g g C e er L M J kwh W jQ VA pf XL XC Z G B Y f T T ω
Equation I=E/R; I = E/Z; I = Q/t Q = it; Q = CE E = IR; E = W/Q R=E/I; R = rl /A r = RA / I G =g A / l G = A/rl g = 1/r; g = I/ RA C = Q/E
er = e/eo L = - N(df/dt) M = K(L1L2) 1/2 J = eit kwh = kw/3600; 3.6 MJ W = J/t; W = EI cos U Q = El sin U VA = El pf = W/VA; pf = W/(W + jQ) XL = 2pfL XC = 1/(2pfC) Z = E/I Z = R + j(XL - XC) G = R/Z2 B = X/Z2 Y =I/E; Y = G + jB f = 1/T T = 1/f L/R; RC ω = 2πf
SI unit SI unit symbol Ampere A Coulomb C Volt V Ohm Ω Ohm-metre Ω•m Siemens S Siemens/meter S/m Farad F Farads/meter F/m Numerical Henry H Henry H Joule J Kilowatthour kWh Watt W Var var Volt-ampere VA Ohm Ohm Ohm Siemens Siemens Siemens Hertz Second Second Radians/second
Ω Ω Ω S S S Hz s s rad/s
Ratio of Magnitude of CGS unit SI to cgs unit Abampere 10-1 Abcoulomb 10-1 Abvolt 108 Abohm 109 Abohm-cm 1011 Abmho 10-9 Abmho/cm 10-11 Abfarad* 10-9 Stat farad*/cm 8.85 X 10-12 Numerical I Abhenry 109 Abhenry 109 Erg 107 36 X 1012 Abwatt 107 Abvar 107
Abohm Abohm Abohm Abmho Abmho Abmho Cps Hz Second Second Radians/second
1 109 109 109 10-9 10-9 10-9 1 1 1 1
*1 Abfarad (EMU Units) = 9 X 10-20 stat farads (ESU units).
Reproduced with Permission from McGraw-Hill, Marks’ Standard Handbook for Mechanical Engineers, 8th ed. Authors: Baumeister, et al. Copyright 1987
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