METAL DETECTOR
A Project Report
Submitted by:Rahul Rajendra Akale
In partial fulfillment for the award of B.Sc In physics 2012-13
C.H.M.E SOCIETY’S BHONSALA MILITARY COLLEGE RAMBHOOMI NASHIK-422005
University of pune Pune-411007
Examination seat no: ___________
University of Pune
“Bonafide Certificate””
Certificate that this project report “Metal Detector” is the Bonafide work of Rahul Rajendra Akale of T.Y.B.sc (physics) during the academic year 2012-13, who carried out the project work under my supervision.
Signature
Internal Examiner
Signature
External Examiner
Acknowledgement I wish to thank the principle Dr.S.H.Kochargaonkar of my college for permitting me to use all the facilities available in the institution for my project work. I would like to thank the head of physics department Dr.Mrs.Aruna.D.Joshi, the teaching staff of my college for their support in completing the work successfully. I am grateful to my guide Mr.Pradeep.J.Ikankar for his encouragement, guidance and supervision of my project work. I was fortunate project work form Bhonsala Military College, Nashik. I express my thankfulness to them. My classmate have been great help to me during the project work. My ideas were shaped and refined progressively through my discussion with them all. Professor like Mr.Sunil.K.Bhavsar, who was not directly but indirectly involved in my preparatory practical work. I heartily appreciate their contribution and thank them too.
Date:-
Signature Rahul Akale T.Y.B.Sc. Year 2012-13
INDEX
SR NO:
CONTENTS:
1
ABSTRACT
2
CONCEPT
3
INTRODUCTION
4
COMPONENTS LIST
5
RESISTORS
6
CAPACITORS
7
VARIABLE RESISTORS
8
COIL
9
CIRCUIT DIAGRAM
10
WORKING
11
APPLICATIONS
12
CONCLUSION
13
BIBLIOGRAPHY
1-Abstract Metal detectors are fascination machines. Many of the people who use them are just as enthusiastic about extolling the virtues of their favorite metal detector as they are about setting off in search of buried treasure. This is the primary means by which we determine how well we are doing our jobs, and what sort of things we need to do better. Sometimes though, communication is difficult. The most commonly used metal detection technology is very low frequency (VLF), also known as induction balance. In this type of metal detector, there are two rings: an outer coil called the transmitter coil and an inner coil called the receiver coil. The transmitter coil has an electric current running through it, which creates an electromagnetic field. This magnetic pulse interacts with any conductive object it passes over, causing that object to create a weaker magnetic field of its own; it is this magnetic pulse from the object that the receiver coil senses. The receiver coil is shielded from the transmitter coil's magnetic field, but can pick up magnetic pulses sent by other objects. The receiver coil amplifies these frequencies and sends them to the control box for analysis.
2- Concept Metal detectors work by transmitting an electromagnetic field from the search coil into the ground. Any metal objects (targets) within the electromagnetic field will become energized and retransmit an electromagnetic field of their own. The detector’s search coil receives the retransmitted field and alerts the user by producing a target response. Special metal detectors are capable of discriminating between different target types and can be set to ignore unwanted targets. Battery: The battery provides power to the detector. Control Box: The control box contains the detector’s electronics. This is where the transmit signal is generated and the receive signal is processed and converted into a target response. Search Coil: The detector’s search coil transmits the electromagnetic field into the ground and receives the return electromagnetic field from a target. Transmit Electromagnetic Field: The transmit electromagnetic field energises targets to enable them to be detected. Target: A target is any metal object that can be detected by a metal detector. In this example, the detected target is treasure, which is a good (accepted) target. Unwanted Target: Unwanted targets are generally ferrous (attracted to a magnet), such as nails, but can also be non-ferrous, such as bottle tops. If the metal detector is set to reject unwanted targets then a target response will not be produced for those targets. Receive Electromagnetic Field: The receive electromagnetic field is generated from energised targets and is received by the search coil. Target Response: When a good (accepted) target is detected the metal detector will produce an audible response, such as a beep or change in tone. Many Minelab detectors also provide a visual display of target information.
3- Introduction A metal detector is a device which responds to metal that may not be readily apparent. The simplest form of a metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field. If a piece of electrically conductive metal is close to the coil, eddy currents will be induced in the metal, and this produces a magnetic field of its own. If another coil is used to measure the magnetic field (acting as a magnetometer), the change in the magnetic field due to the metallic object can be detected. The first industrial metal detectors were developed in the 1960s and were used extensively for mining and other industrial applications. Uses include de-mining (the detection of land mines), the detection of weapons such as knives and guns (specially in airport security),geophysical prospecting, archaeology and treasure hunting. Metal detectors are also used to detect foreign bodies in food, and in the construction industry to detect steel reinforcing bars in concrete and pipes and wires buried in walls and floors. The fact is that all of these scenarios are valid. Metal-detector technology is a huge part of our lives, with a range of uses that spans from leisure to work to safety. The metal detectors in airports, office buildings, schools, government agencies and prisons help ensure that no one is bringing a weapon onto the premises. Consumer-oriented metal detectors provide millions of people around the world with an opportunity to discover hidden treasures (along with lots of junk).
4- COMPONENTS LIST 1
Components name
Specification
No of units
Resistors
56kΩ
2
3.3kΩ
1
22kΩ
1
2.7kΩ
1
2.2kΩ
1
680E
2
15kΩ
1
2
Variable resistor
5K3386Trim
1
3
Capacitors
1PF
2
1KPF
1
220PF
1
270PF
1
12KPF/100V
1
100/25V
1
4
Transistors
BC 547 PH
4
5
Diode
IN 4148
4
6
LED
5MM Red Led
1
7
Coil
Metal Detector
8
Buzzer
VK 27 CT (S)
1
9
Power supply
9V Snapper
1
10
PCB
VK 557 PCB
1
Coil
1
5- RESISTORS A resistor is a component of an circuit that resists the flow of electrical current. It has two terminals across which electricity must pass, and it is designed to drop the voltage of the current as it flows from one terminal to the other. Resistors are primarily used to create and maintain maintain known safe currents within electrical components The amount of resistance offered by a resistor is determined by its physical construction. A carbon composition resistor has resistive carbon packed into a ceramic cylinder, while a carbon film resistor consists of a similar ceramic tube, but has conductive carbon film wrapped around the outside. Metal film or metal oxide resistors are made much the same way, but with metal instead of carbon. A wire wound resistor,, made with metal wire wrapped around clay, y, plastic, or fiberglass tubing, offers resistance at higher power levels. Those used for applications that must withstand high temperatures are typically made of materials such as cermets, a ceramic-metal metal composite, or tantalum,, a rare metal, so that they can endure the heat. The unit for measuring resistance is the OHM.. (The Greek letter Ω - called Omega). Higher resistance values are represented by "k" (kilo-ohms) ohms) and M (Meg ohms).
Fig: Resistor symbols
6- CAPACITORS A capacitor is a passive electronic component that stores energy in the form of an electrostatic field. In its simplest form, a capacitor consists of two conducting plates separated by an insulating material called the dielectric.. The capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the separation between the plates. Capacitance also depends on the dielectric constant of the substance separating the plates. Electrolytic capacitors are ‘polarized’ which means they have a positive and negative lead and must be positioned in a circuit the right way round They also have a much higher capacitance than non-electrolytic non capacitors. Non-electrolytic electrolytic capacitors usually have a lower capacitance. They are not polarized and can be placed anyway round in a circuit. circuit They are normally used to smooth a current in a circuit.
Fig: Capacitor symbol
7- VARIABLE RESISTORS Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermets (ceramic and metal mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available. Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a potentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require further adjustment. Variable resistors are often called potentiometers in books and catalogues. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm
SYMBOL:
8- COIL An electromagnetic coil (or simply a "coil") is formed when a conductor (usually an insulated solid copper wire) is wound around a core or form to create an inductor or electromagnet. When electricity is passed through a coil, it generates heat. One loop of wire is usually referred to as a turn, and a coil consists of one or more turns. For use in an electronic circuit, electrical connection terminals called taps are often connected to a coil. Coils are often coated with varnish or wrapped with insulating tape to provide additional insulation and secure them in place. A completed coil assembly with taps is often called a winding. A transformer is an electromagnetic device that has a primary winding and a secondary winding that transfers energy from one electrical circuit to another by inductive coupling without moving parts. The term tickler coil usually refers to a feedback coil, which is often the third coil placed in relation to a primary coil and secondary coil. A coil tap is a wiring feature found on some electrical transformers, inductors and coil pickups, all of which are sets of wire coils. The coil tap(s) are points in a wire coil where a conductive patch has been exposed (usually on a loop of wire that extends out of the main coil body). As self induction is larger for larger coil diameter the current in a thick wire tries to flow on the inside. The ideal use of copper is achieved by foils. Sometimes this means that a spiral is a better alternative. Multilayer coils have the problem of interlayer capacitance, so when multiple layers are needed the shape needs to be radically changed to a short coil with many layers so that the voltage between consecutive layers is smaller.
9- CIRCUIT DIAGRAM
10- WORKING Metal detectors work on the principle of transmitting a magnetic field and analyzing a return signal from the target and environment. The transmitted magnetic field varies in time, usually at rates of fairly high-pitched audio signals. The magnetic transmitter is in the form of a transmit coil with a varying electric current fl owing through it produced by transmit electronics. The receiver is in the form of a receive coil connected to receive and signal processing electronics. The transmit coil and receive coil are sometimes the same coil.
The coils are within a coil housing which is usually simply called “the coil,” and all the electronics are within the electronics housing attached to the coil via an electric cable and commonly called the “control box”. This changing transmitted magnetic field causes electric currents to flow in metal targets.
These electric currents are called eddy currents, which in turn generate a weak magnetic field, but their generated magnetic field is different from the transmitted magnetic field in shape and strength. It is the altered shape of this regenerated magnetic field that metal detectors use to detect metal targets. (The different “shape” may be in the form of a time delay.)The regenerated magnetic field from the eddy currents causes an alternating voltage signal at the receive coil. This is amplified by the electronics because relatively deeply buried targets produce signals in the receive coil which can be millions of times weaker than the signal in the transmit coil, and thus need to be amplified to a reasonable level for the electronics to be able to process. In summary: 1. Transmit signal from the electronics causes transmit electrical current in transmit coil.
2. Electrical current in the transmit coil causes a transmitted magnetic field. 3. Transmitted magnetic field causes electrical currents to flow in metal targets (called eddy currents.) 4. Eddy currents generate a magnetic field. This field is altered compared to the transmitted field. 5. Receive coil detects the magnetic field generated by eddy currents as a very small voltage. 6. Signal from receive coil is amplified by receive electronics, then processed to extract signal from the target, rather than signals from other environment magnetic sources such as earth’s magnetic field. As with most introductions, the above brief description is oversimplified. The signal induced in the receive coil, by the magnetic field of the eddy current, can be thought of as made up of two simultaneous components, not just an altered component: • One component is the same shape as the transmit signal. This is called the reactive signal (“X”). Because it is the same shape as the transmit field, the signal, by definition, responds immediately to whatever the transmit signal is doing. • When this X component is subtracted from the eddy current induced signal in the receive coil, the shape of the remaining Signal depends only upon the history of the transmitted field, and not the instantaneous value. This signal is called the resistive or loss component (“R”).Both the target X and R signals vary depending on the distance of the target from the coil; the further away, the weaker the transmitted magnetic field at the object, and the weaker the received signal from the eddy currents; thus the weaker the receive coil R and X signals which, as stated, may be very weak for deep targets.
• The received signal is usually processed by the electronics to produce at least 2 signals: the strength of one signal is proportional to the R signal strength or magnitude, but is no longer an alternating signal. Similarly, the other signal is also not an alternating signal, but rather a signal simply related to X signal strength or magnitude only. Unfortunately, both the terms “X signal” and “R signal” may refer to both these two different meanings: the one meaning referring to the alternating receive signal at the transmit frequency, and the other meaning to the strength of the received signals or magnitude (how big they are). So the term “X signal” may refer to the alternating X signal waveform at the transmit frequency, or just the X signal strength or magnitude, which of course changes as the coil is moved about over different areas of ground. The same applies to the R signal. •This dual meaning of the same term is common in electronics. For example, when referring to a received mediumwave signal, it is not always clear if an engineer is referring to the signal at the medium-wave frequency, or its varying magnitude; namely, the information transmitted regardless of the transmit frequency. In metal detectors, the terms “X” and “R” signal, usually refer to their magnitudes, not the alternating signals. These X and R signals (magnitudes) are further processed to give an output signal which may be reported to an operator in a number of different ways, the two most common being: 1. A ground balanced audio signal, whose loudness is usually proportional to the received signal strength from the eddy currents in metal targets.
2. A discriminated signal which only makes an audio “beep” when a target with selected properties is detected. These properties may be varied by a metal detector operator varying the controls of the metal detector. Most discriminating metal detectors also have a visual display which indicates properties of a detected metal target.
11- Applications 1. Archaeology Many historic artifacts from post Paleolithic age are metallic. These valuable items which generally include pots, vessels, weapons like spears, swords, tools like hammers, chisels etc can be easily detected with metal detectors of appropriate calibration. Their excavation and preservation is greatly facilitated due to metal detectors.
2. Hobbies Coin shooting is looking for coins after an event involving many people, like a baseball game, or simply looking for any old coins. Serious coin shooters will spend hours, days and months doing historical research to locate long lost sites that have the potential to give up historical and collectible coins. Prospecting is looking for valuable metals like gold and silver in their natural forms, such as nuggets or flakes. Metal detecting is very similar to coin shooting except that the metal detectorist is after any type of historical artifact. Metal detectorists may be dedicated to preserving historical artifacts, and often have considerable expertise. Coins, bullets, buttons, axe heads, and buckles are just a few of the items that are commonly found by relic hunters; in general the potential is far greater in Europe and Asia than many other parts of the world.
Beach combing is hunting for lost coins or jewelry on a beach. Beach hunting can be as simple or as complicated as one wishes to make it. Many dedicated beach hunters also familiarize themselves with tide movements and beach erosion. There are two main techniques for beach hunting. The first one is called "gridding", which is when you search in a pattern. For example, you start from the beach line, and work your way down to the shoreline, move to the side a little, and repeat the process. The next technique is called "Random searching". Random searching is when you walk around the beach in no particular pattern.
3. Security screening In common with the developments in other uses of metal detectors both alternating current and pulse systems are used, and the design of the coils and the electronics has moved forward to improve the discrimination of these systems. In 1995 systems such as the Metor 200 appeared with the ability to indicate the approximate height of the metal object above the ground, enabling security personnel to more rapidly locate the source of the signal. Smaller hand held metal detectors are also used to locate a metal object on a person more precisely.
4. Industrial metal detectors Industrial metal detectors are used in the pharmaceutical, food, beverage, textile, garment, plastics, chemicals, lumber, and packaging industries. Contamination of food by metal shards from broken processing machinery during the manufacturing process is
a major safety issue in the food industry. Metal detectors for this purpose are widely used and integrated into the production line. Current practice at garment or apparel industry plants is to apply metal detecting after the garments are completely sewn and before garments are packed to check whether there is any metal Contamination (needle, broken needle, etc.) in the garments. This needs to be done for safety reasons.
12- Conclusion After designing, simulating, assembling, soldering and testing the circuit, we came to the conclusion that our circuit of the metal detector is working satisfactorily and has negligible amount of unexpected functioning.
13- BIBILOGRAPHY www.google.com www.kellycodetectors.com/functioning.html www.howdoesstuffwork.co.uk www.wikipedia.org http://electronics.howstuffworks.com/gadgets/othergadgets/metal-detector.htm http://www.minelab.com/consumer/knowledge-base/how-dometal-detectors-work.html www.geotech1.com/pages/metdet/projects/rakes/rakes2_150.pdf http://www.electronic-circuitsdiagrams.com/sensorsimages/sensorsckt4.shtml www.555-timer-circuits.com/metal-detector.html
