Railway signalling

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About Railway Signalling Railway Signalling Signalling is one of the most important parts of the many components which make up a railway system. Train movement safety depends on it and the control and efficient management of trains depends on them. Over the years many signalling and train control systems have been evolved. The journey started with very simple systems such as simple coloured flags and semaphore arms to that today a highly technical and complex electrical and electronic systems. Here is an attempt to explain, in simple terms, how railway signalling really works.

Fig-1 Semaphore Signals that stoop (lower quadrant)

Fig-2 Semaphore Signals that raise (upper quadrant) Nowadays IR has converted what are known as Color Light Signals (CLS) with Multiple aspects where the color of Light indicates meaning to Drivers ( Now called Loco Pilots)

Why Signalling is required? In road transportation the direction and speed of a vehicle are controlled by the driver and the different vehicles share the same way at the same time in both the directions. However in Rail transport the the driver controls only the start / stop and speed of the train and the direction is controlled by the track components themselves. There is no steering wheel. One more factor to be considered is that the trains are very large vehicles and hence need large distances to increase and decrease speed i.e to start and stop also. Hence they need to be separated by considerable distances while traveling behind one another. Thus the signaling has the following basic functions :-

1. Arranging safe reception and dispatch of trains onto required lines at stations. 2.

Ensuring that trains are not received on occupied lines

3. Ensuring that two trains donot enter the same part of the track between two stations (Also called block signaling) 4. Optimizing the utilization of track and other assettes by allowing the dealing of maximum no of trains at highest speeds permitted by track and train vehicles safely. 5. Achieve all the above in a manner called " Fail Safe" which makes signalling a unique field of Engineering as every component and particularly the combination shall not fail to an unsafe end result at any cost. To achieve the above functions the follwing devices are used : 1. Track circuits : are simple electric gadgets that are filtted to tracks and detect the presence of trains over that portion of the track. They prevent allowing of signals on the same portion by fixing the signals at Danger (RED) position till such time the trains leaves that portion. Thus this gadget allows dealing of trains without colloisions.

Fig 3b - The Track Circuit - Without Train (Signal can turn Green)

Fig 3b - The Track Circuit - Occupied by train (Signal goes to Red) The diagram above shows how the track circuit is applied to a section or block of track. A low voltage from a battery is applied to one of the running rails in the block and returned via the other. A relay at the entrance to the section detects the voltage and energises to connect a separate supply to the green lamp of the signal. The signal turns and remains RED.

The track circuit requires that the two rails are insulated from each other electrically and therefore can work only when we have either wooden or concrete sleepers. The same purpose of detecting train presence is achieved by another new electronic gadget called “axle counter” which works by counting the axles entering and the axles leaving the given section of track.

Fig 4 - The Functioning of Axle Counters

Other Components : ○

Point machines ( to change points; read below about points)

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Relay or Electronic Interlocking for correlating all field gears before clearing signals)

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Panels with yard diagram for taking orders from Station master

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Block Instruments for ensuring that two trains donot enter the space between two stations in an unsafe manner.

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Lifting barriers to ensure road vehicles are not allowed during train movements

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Signals of different types to inform driver to move or stop

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Dataloggers to monitor correct sequences and pre warning or analyzing unsafe outcomes

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Automatic Signalling which works without humanintervention in busy sections esp in suburban transport

○ Advanced Train wraning and train protection systems ○

Powersupply systems to support reliable and safe working of Signalling

Signalling at Stations :We are aware that though there are only one or two lines between stations (called block section); at stations there are many lines onto which the trains are allowed to be received and dispatched. We have also learned that a train driver cannot steer his train in the required direction. Thus railway is called guided transportation. The track itself modifies its components dynamically to lead the train to required line (platform). An important part of the track that achieves routing of trains is a point. Point also called Turnout

Fig 5 : A point is capable of changing the route of a train , a train by itself cannot do so Points are switched ie changed from one position to another to change the couse of train. Of course all required points are to be switched to the required positions to lead to a given line before lighting up the signal and shall remain so untill complete arrival of train. The railway signalling does the change over of points, their locking and holding of the route without any unsafe discretion of the station master. All such points and connected line at a station is known as a yard. A typical simplified signalling diagram is indicated below:

Fig 6 : Yard Signalling sketch of a small station on Double Line (Double Line Means seperate tracks between stations for UP and DOWN direction trains). Welcome to IRSSE Website....... Web Publisher R.V.B. Babu, IRSSE

Sign In or Register Links and Other Interests FAILSAFE ENGINEERING INTRODUCTION : Fail-safe or fail-secure describes a device or feature which, in the event of failure, responds in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel. Fail-safe components of a system are distinguished from fail-secure components in that, in the former, component failure allows but does not cause or invite a certain improper system behavior, whereas in the latter, component failure does not allow a certain improper system behavior, although some proper behaviors are impeded. For example, . a pass word improperly fed may prevent access (by OS) which is a failure for the genuine owner/user but will not allow undue access without thorough verification of authenticity. ........ for detailed explnantion visit the related page on this site.

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FAIL SAFE ENGINEERING INTRODUCTION : Fail-safe or fail-secure describes a device or feature which, in the event of failure, responds in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel. Fail-safe components of a system are distinguished from fail-secure components in that, in the former, component failure allows but does not cause or invite a certain improper system behavior, whereas in the latter, component failure does not allow a certain improper system behavior, although some proper behaviors are impeded. For example, . a pass word improperly fed may prevent access (by OS) which is a failure but ensures safety for the genuine owner/user but will not allow you to reset it without thorough verification of authenticity. Multiple trails with wrong pass word lead to access lock up which is failsafe outcome since it protects the data or other assettes of customer. Also a power controlled access control door is so designed that if power fails , the door will allow egress(exit) but not ingress.(entry). This failsafe concept. All Railway Signalling installations are required to meet this meticulously. That means when any failure in any component takes place, the signal shall be fixed at RED bringing train to a stop but shall NEVER allow the signal to go to YELLOW or GREEN under such condition. Electronics in Failsafe Design : Electronic devices are not inherently failsafe and tend to behave erratically. Designers are using the power of microprocessors for control of railroad, aircraft, and space vehicles to minimize the dangers of complex transportation systems. A mean time between unsafe failures (MTBUF) for transportation is one billion hours, or once in 23 years for 500 units in continuous operation.

Good safety architecture includes redundancy in various forms, such as additional equipment. Redundancy is achieved by duplicating components, or by use of diverse components or use of redundant software. It is critical that the first failure of a controller be detected, so that human monitors can take action before a fault-induced catastrophe occurs. A microprocessor's highly reliable circuits can continuously confirm the operating status of components, and automatic monitors can interrupt the system when an error occurs. The first microprocessor interlockings for railroads have entered service in the US, Canada and Europe and in India (In india they were first introduced since 1993). Use of microprocessors for aircraft safety is also described. .

Welcome to IRSSE Website....... Web Publisher R.V.B. Babu, IRSSE



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Indian Railway Service of Signal Engineers

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is IRSSE ?

Secunderabad, India

IRSSE stands for Indian Railway Service of Signal Engineers , an Organized Gazetted Government service of the Government of India. The incumbents are selected by the Union Public Services Commission, the apex gazetted recruitment body of the Goverment of India. The examination consists of CESE ; all india written test followed by interview for selected candidates. Based on the marks obtained, a choice can be made to join this service. It has been common in the past 20-25 years for toppers from EEE/ECE streams of CESE to join this service. This site is created by one of the mebers of this service with a view to creating public awareness about this important service responsible for safe and speedy train travel and creating user friendly Passenger information systems and public interfaces.

Brief Role Signal Engineers in Railway take care of Train safety in Operations, Capacity enhancement, Corporateand Operational Telecom and IT services, creation of Electronic interfaces for Passenger information dispersal and creation of advanced Signal and Telecom (and IT) assettes as per Operational Requirements.

Signals are Sentinels of safety

This Day in His

The First Defen

In 1419, a mob of C hall of Prague and k council by throwing known as "defenest inequality between nobility, the First D prolonged Hussite W afterward and conti Second Defenestrat

UNDER CONSTRUCTION Under Construction... may take about a month. Site building started on 26-07-2009 Welcome to IRSSE Website....... Web Publisher R.V.B. Babu, IRSSE

Sign In or Register Links and Other Interests FAILSAFE ENGINEERING INTRODUCTION : Fail-safe or fail-secure describes a device or feature which, in the event of failure, responds in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel. Fail-safe components of a system are distinguished from fail-secure components in that, in the former, component failure allows but does not cause or invite a certain improper system behavior, whereas in the latter, component failure does not allow a certain improper system behavior, although some proper behaviors are impeded. For example, . a pass word improperly fed may prevent access (by OS) which is a failure for

the genuine owner/user but will not allow undue access without thorough verification of authenticity. ........ for detailed explnantion visit the related page on this site.




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Role and Function

Functional Role : The service abbreviated as IRSSE has the job of Managing the vast Signalling and Telecommunication (S&T) infrastructure of the Indian Railways. This basically is technomanagerial in nature. The Signalling is a function essential for Safe Train operations and Maximizing the utilization of fixed and moving assets (Train rakes, locos, Track, Over Head Power Eqpt etc). Telecom on the other hand caters for Both Safety related , Operational and Administrative

communication needs of the Huge IR network. The Copper Cable, Optical Fibre Telecom and Microwave Links span several Lakh km. General Management: Like all other IR Engineering (IRSE, IRSEE, IRSME) and Civil service Cadres (like IRTS, IRPS and IRAS) , the IRSSE has the responsibility of contributing to the General management of railways. In IR, the general management posts are GM (general manager), DRM (Divisional Railway Manager), SDGM (Senior Deputy General Manager and CVO and the posts of Chief Safety Officers(CSO) and SrDSO.

Organization The Engineers recruited for IRSSE are normally part of Signal & Telecom (S&T) Department of Indian Railways (IR). APEX LEVEL :The S&T Organization is headed at apex level (ie Railway Board) by ML (Member-eLectrical)who heads Electrical and S&T branches. He is assisted by two Addl Secy rank (equivalent to GM) officers v.i.z Additional Member (Signal) and AM(tele). ZONES :The Indian Railways has 16 Zonal Railways with an average Track length of about 4000 km and average staff strength of about 80,000 headed by GMs. The Zonal Organizational structure of Signal Engineers is headed by CSTE (Chief S&T Engr) who is assisted by CSE (Chief Signal Engr), CCE (Chief Telecom Enr), CSTE (Planning), CSTE(Projects) and CSTE(Construction) and DyCSTEs, SSTEs etc. DIVISIONS : Each Zone is divided into 4-7 Divisions each with an average track length of about 1000 km and staff strength of about 15000 headed overall by DRM (Divisional Railway Manager). The Division is the basic operational Unit and a Profit Centre.

At this Level the Signal Engineers are Headed by SrDSTE (Senior Divisional S&T Engineer) who is in turn assisted by DSTEs and ADSTEs. An IRSSE officer starts his career as an ADSTE who is the Team leader of about 100-200 staff. Welcome to IRSSE Website....... Web Publisher R.V.B. Babu, IRSSE




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Railway Signaling [ 1. Introduction ] [ 2. Track Circuit ] [ 3. Relays ] [ 4. Signals ] [ 5. Moter Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System ]

Career Photo Album Railway Sri Lanka

Hello Railway Enthusiast, Welcome to my site of Railway Signaling. During one of my undergrad training, I was attached to the Signal and Telecommunication Department of the Sri Lanka Railways. It was amazing to learn how a set of simple engineering techniques put together form the bottom line safety gear of the railways. Believe me; no Differential Equations or Discrete Cosine Transforms! Just relays, sensors, power supplies and of course signal heads. Yes, it is a centaury old system, but, still serves its purpose. Following are the elements of signaling as used in Sri Lanka Railways. 1. Introduction

You can visit the Model Rail 2. Track Circuit Club of Sri Lanka web 3. Relays site here. 3.1 Types of Relays 4. Signals 4.1 Automatic Signals 4.2 Controlled Signals 4.3 Call-on Signal 4.4 Typical Signal Layout 5. Moter Points 6. Gate barriers 7. Automatic Blocking System 7.1 Route Establishment 7.2 Train on Line 7.3 Release of Route

[ 1. Introduction ] [ 2. Track Circuit ] [ 3. Relays ] [ 4. Signals ] [ 5. Moter Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System ] © R. Jayanthan Last updated on 01 January, 2002


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1. Introduction [ Up ] Career Photo Album Railway Sri Lanka

The heart of the signaling system is the interlocking plant. This can be claimed as the decision making part of the system. The signal outputs are based on the track occupancy, motor point status, output of the remote end signal and the input from traffic controller.

This plant ensures that before a signal goes in to 'clear' (green) state, it is absolutely safe for a train to enter into the track segment. The traffic

controllers commands are not executed if it is not safe to do so. The interlocking plant is built out of electromechanical relays. We will discuss the type of relays under the respective section. Now we will move on to the first element: Track Circuit; which is used to sense the presence of a train on a track segment..

[ Up ] [ 1. Introduction ] [ 2. Track Circuit ] [ 3. Relays ] [ 4. Signals ] [ 5. Moter Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System ] © R. Jayanthan Last updated on 01 January, 2002


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2. Track Circuit [ Up ]

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Track circuit is one of the primary input for a signal interlocking plant. Opps ! hold on. What is an 'interlocking plant'? It is the control logic behind the signaling system. The signal cannot be 'green' while there is another train on track segment ahead. The system should able to detect the condition of the track segment: occupied or not. The tracks are segmented into 'blocks'. Each block is track circuited separately. The figure below illustrates a track circuit.

The track circuit consists of a power supply on one end and a directional (polarized) relay on the other end. The power supply has a 6V battery kept charged by a 6V/6A rectifier. In case of power failure the battery will supply power to the circuit. The track relay (TR), which has a resistance of 30 ohm and a pickup voltage of 1.4 volt, is normally held in picked-up state the circuit being completed via the rails. When a train enters the segment the axels of the train short circuit the supply to the relay and the relay drops. The contacts of the track relays appear in most of the safety circuits of the interlocking plant. The interlocking logic is arranged such that only one train can be permitted to enter a section. If you carefully observe, the track circuit is fail safe; if the circuit fails it will indicate occupancy. The variable resister is introduced into the circuit such that it can be tuned to make the system works under all weather conditions. The rails are insulated to separate the adjacent track circuits. The polarity of the adjacent track circuit is always reversed, so that the power supply of one circuit cannot operate the relay of the other circuit should the insulate between the circuits breakdown. Within one track circuit the rails are electrically connected by two wires (for safety). The minimum length of track circuit is depends on the degree of control necessary and the maximum length is limited by the weather conditions. On the Northern line from Loco Junction (Maradana) to Veyangoda, the

segments have a maximum length of 2000 feet. On the Southern line from Loco Junction to Wadduwa, due to the saline atmosphere along the cost line, the track circuits are limited to 1500 feet max. Now that we have looked upon the track relay we will get into discuss the types of Relays used in the railway signaling.



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3. Relays [ Up ] [ 3.1 Types of Relays ]

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Relays are electro-mechanical devices used for switching. Relays are used to make the signaling logic circuits in the interlocking plants. They consists of one or two magnetic coils (electro magnets) and a set of contacts.

Railway Sri Lanka

Magnetic System The magnetic system of the relay illustrated below (JRK 10 type) consists of a cylindrical iron core with coil (pale blue near the bottom), two pole pieces and an armature. Larger relays (JRK 11) have two iron cores united at the rear with a yoke and the front end being provided with pole pieces. The armature extends across both pole pieces. Iron core, pole pieces and armature are made out of iron with excellent magnetic properties. The armatures are so balanced that the vibration on the unit will not affect the relay operation. [Move the mouse over the relay to activate it!]

Contacts The relay contacts can be classified into four types. A relay unit will contain a combination of these types . Front contact - NO

Back contact - NC Front/ Back contact Make before break contact

The contact springs are made out of nickel and the contacts tips are silver. The front contacts are of twin contacts and the back contacts are single contact type. The rear end of the contact springs are fixed between two blocks of transfer molded carbonate plastic reinforced with glass fibre. The stationary contact springs are supported at their free ends by a strip with notches, which limits the spring movement. The lower end of this strip is attached to the magnet support. The movable contact springs are guided by an actuating strip which at the lower end attached by bearings to the armature and at the upper end to the upper most movable contact spring. The front edge of the actuating strip provided with slots, which lock the spring and guide the movement of the contacts.

The rear end of every contact spring has eight forked terminals. This provides a very dependable connections to the plug board terminals, when the relays are plugged in.

[ Up ] [ 3.1 Types of Relays ] [ 1. Introduction ] [ 2. Track Circuit ] [ 3. Relays ] [ 4. Signals ] [ 5. Moter Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System ] © R. Jayanthan Last updated on 01 January, 2002 Free site is hosted by

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3.1 Types of Relays [ Up ]

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Relays can be categorized according to the magnetic system and operation.

Neutral Relays Railway Sri Lanka

This is the most elementary type of relay. The neutral relays have a magnetic coil, which operates the relay at a specified current, regardless of the polarity of the voltage applied. Biased Relays

Biased relays have a permanent magnet above the armature. The relay operates if the current through the coil winding establishes a magnetomotive force that opposes the flux by the permanent magnet. If the fluxes are in the same direction, the relay will not operate, even for a greater current through the coil. Polarized Relays

Like the biased relays, the polarized relays operate only when the current through the coil in one direction. But there the principle is different. The relay coil has a diode connected in series with it. This blocks the current in the reverse direction. The major difference between biased relays and polarized relays is that the former allows the current to pass through in the reverse direction, but does the not operate the relay and the later blocks the current in reverse direction. You can imagine how critical these properties when relays are connected in series to form logic circuits. Magnetic Stick Relays or Permopolarized Relays

These relays have a magnetic circuit with high remanence. Two coils, one to operate (pick up) and one to release (drop) are present. The relay is activated by a current in the operate coil. On the interruption of the current the armature remains in picked up position by the residual magnetism. The relay is released by a current through the release coil. Slow Release Relays

These relays have a capacitor connected in parallel to their coil. When the operating current is interrupted the release of relay is delayed by the stored charge in the capacitor. The relay releases as the capacitor discharges through the coil. Relays for AC

These are neutral relays and picked up for a.c. current through their coil. These are very fast in action and used on power circuits of the point motors, where high current flows through the contacts. A normal relay would be slow and make sparks which in turn may weld the contacts together. All relays have two operating values (voltages), one pick-up and the other other drop away. The pick-up value is higher than the drop away value.

[ Up ] © R. Jayanthan Last updated on 01 January, 2002


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4. Signals [ Up ] [ 4.1 Automatic Signals ] [ 4.2 Controlled Signals ] [ 4.3 Call-on Signal ] [ 4.4 Typ ical Signal Layout ] Career Photo Album Railway Sri Lanka

Signal posts carries signal light units consisting one or more aspects. This is the final stage of communication that gives the driver necessary orders and warnings about the track segments ahead. The signal aspects are powered individually by 110 V a .c. and each aspect has its own step down transformer. In the secondary circuit a relay is connected in series with the lamp to get the indication back to the interlocking plant. The figure below illustrates the circuit of a signal aspect.

Signal can be classified according to their mode of operation as follows: Automatic Blocking Signal Automat ic Automatic Approach Signal Signals High Controlled Signal Controll ed Dwarf Controlled Signal

[ Up ] [ 4.1 Automatic Signals ] [ 4.2 Controlled Signals ] [ 4.3 Call-on Signal ] [ 4.4 Typical Signal Layout ] [ 1. Introduction ] [ 2. Track Circuit ] [ 3. Relays ] [ 4. Signals ] [ 5. Moter Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System ] © R. Jayanthan Last updated on 01 January, 2002


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4.1 Automatic Signals [ Up ]

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Railway Sri Lanka

Automatic Signals can be identified by the circular number plate bearing the distinctive number of that signal post and the gray color mast. They may contain one, two or three aspects of one or more units. Only one aspect can be lit in a unit at a given time. The automatic signals are approach lit; i.e. light up only when a train approaches. This arrangement is used to conserve power. The automatic signals operates according to the track conditions ahead and are not controlled by the controller.

4.1.1 Automatic Block Signal Automatic block signaling is used to control trains between two stations. A detailed discussion about automatic block signals can be found here. These signals have one unit of three aspects and have the following meanings: RED

Dange train on immediate block r;

AMBE Cautio train on the block after the next, prepare to R n; stop at the next signal GREE Proce line clear for the next two or more blocks N ed:

4.1.2 Automatic Approach Signal These signals are placed immediately before the controlled signals. These signals have one unit with three aspects on the main post and another unit with two aspects on a support bracket below the main unit. These signals indicate that a controlled signal is being reached and show the route that will be taken at a controlled speed. These are also called distance signals or outer home signals. The aspects of the signals are as follows. RED

Dan train on the section ahead

ger; AMBER over AM Caut controlled signal ahead is BER ion; Danger AMBER over GR Proc going on the loop line EEN eed; GREEN over AM Proc going on the main line BER eed;

The upper unit (three aspects) refers to the main line and the lower unit refers to the loop line.

[ Up ] [ 4.1 Automatic Signals ] [ 4.2 Controlled Signals ] [ 4.3 Call-on Signal ] [ 4.4 Typical Signal Layout ] © R. Jayanthan Last updated on 01 January, 2002


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4.2 Controlled Signals [ Up ]

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The controlled signals normally show 'danger' aspect (RED) and are controlled by the train controllers. They have a square number plate and their mast and base are painted with red and white stripes.

Railway Sri Lanka

4.2.1 High Controlled Signal The high controlled signals control and guide the trains into the yard. These signals will normally have two units of three aspects in line. The upper unit corresponds to the main line and the lower unit corresponds to the immediate loop line. Some high controlled signals will also have, below the second unit, a third unit of one aspect (AMBER). These are found at the points where there are more than one turn out. The second unit have a speed restriction of 48 km/h and the third unit has 16 km/h. The meanings of the aspects are given below. RED

Danger ; Stop

AMBER over RED

Going on main line; starter not given

RED over AMBER

Going on loop line; starter not given

GREEN over RED

Going on main line; starter given

RED over GREEN

Going on loop line; starter given

In three unit signals RED over RED over Caution; more than one AMBER turn out

4.2.2 Dwarf Controlled Signal Dwarf controlled signals may have one unit of two or three aspects. They are used as exit (starter) signals, where there is a general speed restriction.



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4.3 Call-on Signal [ Up ] Career Photo Album Railway Sri Lanka

To enter locomotive in the yard while shunting, the high controlled signals cannot be given because of the presence of the coaches on the same line (platform). In this situation a call-on signal is used. The call-on signal, which is mounted above the base of the high controlled signal, has three lamps and two aspects as illustrated below.



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4.4 Typical Signal Layout [ Up ] Career Photo Album

The simple station layout below depicts the positions of the respective signals in a typical yard.

Railway Sri Lanka

The first signal a train will see when arriving from left is the one before last ABS signal. It will inform the track condition ahead. It may show 'caution' if a train is awaiting to enter or just entering the station yard. The second will the last ABS which is also the outer home signal. It will hint about the platform the train will be stopping or passing through (if it is an express train). The third will be the inner home (high controlled) signal. This will allow the train to enter the

station yard or pass through the station if it is an non-stopping station for that particular train. If the train stops at the station, when ready the starter (dwarf controlled) signal is given to proceed.



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5. Moter Points [ Up ] Career Photo Album Railway Sri Lanka

Point is a place where the track branches off. The points can be either manually switched (lever frame) or motor driven. Most of the points in the color light area are motor points and can be controlled by the Maradana control office.

The point motor is powered by 110V d.c. supplied by the nearby relay house. When an order is given to switch the point, power is given to the motor in the respective direction. The motion is used to either push or pull the drive rod. Point machine has contacts for detection of the switching. These contacts are operated by the long and short detection rods. When the point is set properly an indication is obtained by the relay house through these contacts. The allowable gap between the stock rail and the switch blade is 3mm. When a foreign material such as a stone prevents the point from setting properly, the indication contacts stay neutral and no indication is sent. The clutch mechanism in the point machine will start slipping in order to protect the machine from mechanical damages. The safety relay attached to the motor circuit will cut off power in 15 seconds. When no indication is obtained at the control office, the controller will inform the Signal and Telecommunication Inspector (STI) in charge of the respective yard. On receipt of the information, STI will go to the motor point in question and remove the obstacle. The point machine has a facility to operate it by manual cranking. Once the point is cranked, the operation is finished and the indication will received by the control office. Some points in the color light area are of lever frame type. They are not frequently switched during routine operations. These type of points are

protected by a device called "magnetic lock", which has to be released by the controller at the central office to enable station master to switch the point. After the operation is completed station master will switch the point back to its normal position and it is locked by the controller. This ensures that all the points are under the controller at the central office.



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6. Gate barriers [ Up ] Career Photo Album Railway Sri Lanka

Gate barrier protects the level crossing. In the color light area gate barriers are automatically operated when a train approaches it from either direction. The gate machine has 110V d.c. motor to operate the gate. It also consists of contacts to get indication of the status of the gate. The figure below illustrates a gate barrier system.

The gate barrier has two signals on the track on either side of the road. The signal at the distance is called an early warning. It has two aspects of amber and green. The five lamps are arranged in a manner to represent letter "W" for Warning. The amber aspect means the gate is not protected. This signal is located at a distance to allow the driver of the train to apply brakes and stop the train if necessary. The green aspect means the gate is protected and the train can pass the gate at its normal speed. The signal near the gate has a similar arrangement; red on top unit and green on lower unit. If the gate is protected the green aspect will be lit and if not the red. The gate barrier system also has flashing two unit warning signals on either side of the track for the road traffic. A warning bell is also fixed on the mast. It rings before and while the gate is closing. The circuits are wired in such a manner a failure on the gate motor circuit will result in the continuous ringing of the bell. In such an occasion the gate-man will inform this to the nearest station master using the gate telephone and he in turn will inform the STI.



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7. Automatic Blocking System [ Up ] [ 7.1 Route Establishment ] [ 7.2 Train on Line ] [ 7.3 Release of Route ] Career Photo Album Railway Sri Lanka

Automatic block signaling (ABS) safeguards the train operations between stations and an effective means of increasing the line capacity. In the color light area, where the trains are worked on the ABS, each running rail is divided into a series of blocks sections (track between the stations) and station sections (track between entry and exit signal). Each section is track circuited separately. Entry into each block section is governed by the automatic block signals at the entry point of the section. (Signals 1, 2 and 3 in the coming pages). The train leaving station block A and entering station block B will be controlled by the controlled signals at respective stations. The color light area has dual tracks and under normal operation the up trains will be using up line and the down trains will be using the down line. [ Continue... ]

[ Up ] [ 7.1 Route Establishment ] [ 7.2 Train on Line ] [ 7.3 Release of Route ] [ 1. Introduction ] [ 2. Track Circuit ] [ 3. Relays ] [ 4. Signals ] [ 5. Moter Points ] [ 6. Gate barriers ] [ 7. Automatic Blocking System ] © R. Jayanthan Last updated on 01 January, 2002


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7.1 Route Establishment [ Up ]

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Railway Sri Lanka

Operation In the figure below consider the line between station A and Station B, which is divided in to 4 blocks. The signals at A and B are home signals (controlled signals) and the signals 1, 2 and 3 are automatic blocking signals. In the reverse direction the entire track segment is treated as one block. Establishment of route

In the idle condition controlled signals show 'danger' and the ABS signals are extinguished.

When a train is to be dispatched from station A to station B, a "black" current is sent from station A to station B.

If the line is free, i.e. all track relays are picked up, the "black" current arrives at station B and blocks there the dispatch of a train from station B to station A. Station B acknowledges by sending a "yellow" current. The first block post (signal 3) signal lights up and show 'caution'. This block post send the current on, but now as "green" current.

The "green" current passes to the remaining block posts and their signal switch on to 'proceed'. When the current reaches station A, the home signal (starter) shows 'proceed'. There after the black current is cut off. The direction of movement is now locked.

[ Continued... ]

[ Up ] [ 7.1 Route Establishment ] [ 7.2 Train on Line ] [ 7.3 Release of Route ] © R. Jayanthan Last updated on 01 January, 2002


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7.2 Train on Line [ Up ] Career Photo Album

As soon as the train passes the controlled signal at station A, the signal switches to 'danger'. Note that the "green" current is short circuited by the train axle and does not reach signal A.

Railway Sri Lanka

Sooner or later the the controlled (home) signal at station B will be set to 'proceed' by the controller. As a result signal 3 switches to 'proceed' as well. When the train leaves the first block, the the signal 1 switches to 'danger' since the "green" current is now cut off by the train. This signal post sends a "yellow" current backward. Since the signal A is a controlled signal it ignores the "yellow" current and remains 'danger'.

As the train enters block 3, the "yellow" current set the signal 1 to 'caution'. "Green" current is sent to the previous signal. Now a new train can be dispatched on the line from A to B and ABS ensures at least on block space between the two trains.

The train proceeds and the "green" current switches the signal 1 to 'proceed'.

Now you can deduce the aspect meanings of the ABS signal. Red Stop! Train on next block Amber Train on block after next; proceed with caution Green Normal speed; next two blocks are unoccupied

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7.3 Release of Route

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When the train has passed the home signal at station B and the signal is turned 'danger' and the release of the route is automatically started. The release current ("black") is sent from station B to station A.

Railway Sri Lanka

When the release current reaches station A, it checks that the exit signal does not show 'proceed', i.e station A is not intending to dispatch another train toward station B. If it does show 'proceed', release of route will not take place. If signal A shows 'danger', a black current is sent back to station B.

Route is released when the current reaches station B. The signal aspect currents ("yellow" and "green") are cut off and the block signal are extinguished. The "black" current from A is also cut off and the system returns to idle condition.

Design All the information is transmitted on a two wire under ground cable. The aspect currents "yellow" and "green" are d.c. with opposite polarity and the locking and releasing current, "black", is a.c. The wires are connected with filters in block posts. This enables simultaneous transmission of d.c. and a.c. on the same wire pair. The locking relays in the block posts are of magnetic stick type and once picked up by the locking current, they remain picked up until the release current is applied. If a ABS post is locked and it receives no

aspect current it shows 'danger' and sends a "yellow" current to the post at the back. If it receives "yellow" or "green" aspect current it will show 'caution' or 'proceed' aspect and send a "green" current to the post at the back. When the releasing take place all aspects are extinguished. The controlled signal do not respond to aspect current but take it into consideration when a order to is given. It turns 'danger' as soon as the train passes it.

The spacing of block signals varies from 4000 to 8000 feet according to the curvatures on the running rail and the visibility. On double line area only one block is provided between station in the reverse direction.


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Railway Signalling using Wireless Sensor Networks Railway Signalling is safety critical domain, where still traditional technology is in use. There are many reasons for using traditional technology; one of the main reasons being the proven Safety performance of the older systems (Relay Based). As the rail traffic is increasing and with higher speed of trains there is an acute need for modernization of Railway Signalling Technology. Even with the advent of Microprocessor based technology, the problems have not been solved. The current railway signalling technology involves huge amount of physical wiring used to receive inputs and drive outputs to the field functions, which is very difficult to maintain and up-gradation of this infrastructure is every signal engineer’s nightmare. This paper proposes the use of Wireless sensor networks in Railway Signalling

domain which combines the Ground base signalling and the On–Board Signalling using customized routing algorithm, which is suitable for high Speed Railway Traffic which reduces the physical wiring to the bare minimum by applying distributed architecture to the field functions which are connected by Wireless Network. The most important part of the railways is to carry out operations like safe movement of trains, this is achieved by Signalling. The Railway signalling is governed by a concept called Interlocking. Many interlocking system still in use follow either relay based technology or the Microprocessor based technology called Electronic Interlocking System (EIS). Relay based systems are very huge in size and have cumbersome wiring to perform operations. The advent of Electronic Interlocking systems reduced the relays and wiring to some extent, but still uses traditional copper cabling to be connected to the field functions such as signals, Track Detection equipment, points (Switches). In modern signalling systems, the signal and switch status needs to be sent to the On-Board Computers in the locomotives, this involves traditional radios connected to the wayside field functions that communicate this information to the OBC. This involves laying out track loops or balises that send this information to the OBC, these loops are venerable to climatic conditions such as ballast resistance, water flooding during rains, etc. Due to the failsafe nature of these systems the cabling has to be redundant, this results in large maze of complex wiring that is very difficult to maintain and upgrade. There is need to upgrade the existing Railway Signalling Infrastructure and addition of new technologies like failsafe wireless communications which shall combine both the ground based signalling (Interlocking Systems) and the Locomotives (On Board Computers of the train) which directly leads to simple distributed architecture which are highly maintainable and easy to upgrade in future.

Sandeep Patalay http://verificationandvalidation.blogspot.com/

Tags: Railway Signalling, Signal Designer, Signal Engineer, Signalling, Wireless Sensor Network

This entry was posted on Saturday, July 10th, 2010 at 7:36 pm and is filed under Signalling. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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Home | About | Interactive Forum | Useful Links | News | Downloads | Rail Courses | Contact « Supply Chain Management Indian Train Accidents-Reasons and Solutions »

Railway Signalling using Wireless Sensor Networks

Railway Signalling is safety critical domain, where still traditional technology is in use. There are many reasons for using traditional technology; one of the main reasons being the proven Safety performance of the older systems (Relay Based). As the rail traffic is increasing and with higher speed of trains there is an acute need for modernization of Railway Signalling Technology. Even with the advent of Microprocessor based technology, the problems have not been solved. The current railway signalling technology involves huge amount of physical wiring used to receive inputs and drive outputs to the field functions, which is very difficult to maintain and upgradation of this infrastructure is every signal engineer’s nightmare. This paper proposes the use of Wireless sensor networks in Railway Signalling domain which combines the Ground base signalling and the On–Board Signalling using customized routing algorithm, which is suitable for high Speed Railway Traffic which reduces the physical wiring to the bare minimum by applying distributed architecture to the field functions which are connected by Wireless Network. The most important part of the railways is to carry out operations like safe movement of trains, this is achieved by Signalling. The Railway signalling is governed by a concept called Interlocking. Many interlocking system still in use follow either relay based technology or the Microprocessor based technology called Electronic Interlocking System (EIS). Relay based systems are very huge in size and have cumbersome wiring to perform operations. The advent of Electronic Interlocking systems reduced the relays and wiring to some extent, but still uses traditional copper cabling to be connected to the field functions such as signals, Track Detection equipment, points (Switches). In modern signalling systems, the signal and switch status needs to be sent to the On-Board Computers in the locomotives, this involves traditional radios connected to the wayside field functions that communicate this information to the OBC. This involves laying out track loops or balises that send this information to the OBC, these loops are venerable to climatic conditions such as ballast resistance, water flooding during rains, etc. Due to the failsafe nature of these systems the cabling has to be redundant, this results in large maze of complex wiring that is very difficult to maintain and upgrade. There is need to upgrade the existing Railway Signalling Infrastructure and addition of new technologies like failsafe wireless communications which shall combine both the ground based signalling (Interlocking Systems) and the Locomotives (On Board Computers of the train) which directly leads to simple distributed architecture which are highly maintainable and easy to upgrade in future.

Sandeep Patalay

http://verificationandvalidation.blogspot.com/

Tags: Railway Signalling, Signal Designer, Signal Engineer,Signalling, Wireless Sensor Network

This entry was posted on Saturday, July 10th, 2010 at 7:36 pm and is filed underSignalling. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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A Snapshot of Railway Signalling Monday, January 25th, 2010

Complex Railway Signalling Simplified In Railway Signalling the term ‘interlocking’ is very important. Interlocking means operation or status of one signalling apparatus is decided by another or depends on the status of other. A railway signalling is a highly safety critical system,which are fail safe(even if any thing fails ,fails in safe condition).

In order to achieve a safe operation (to give a green signal),the signalling system assure that the track ahead of the signal to the next is free.

In other words signals may not be operated to permit conflicting train movement to take place at the same time. The interlocking ensure the switches(the electric or pneumatic equipment lead the train to different track) and other appliances in the route must be set in position before a signal allow the train to enter in to that route(between two signals).

When a route is set ,the train is given a the signal(yellow for example ,the first proceed aspect or green) to proceed with the movement and the interlocking ensures all the switches and other movable appliances(say trainstop for an example,a simple electro mechanical or pneumatic device mounted just outside the track which make the train to apply break automatic , if the driver overshoot a red signal) in the route are locked in position ,until either the train complete the journey of the route set or the proceed signal is withdrawn and sufficient time has passed to ensure that a train approaching that signal replaced or withdrawn(green to red by an operator or a system) has had an opportunity to stop before over shooting that signal.

Mechanical Interlocking The above mentioned operations can be achieved either mechanical(outdated),electrically(with the help of relays) or electronically(with the help of computer ,named as solid state interlocking). In olden days signals are controlled by manually operated levers ,which operates signals,swtiches ,derailer (forcefully derail the train before a standstil the train

enter in to another

track in

operation).Reliability ,time delay in operation ,inefficiency,wear and tear t more mecanical devices were some of the drawbacks. Electrical Interlocking It was later replaced by better relay interlocking,which was achieved by electrical highly reliable relays ,make and break depends on the status of other relays/appartus. In a complex interlocking 20’s of relays will be operating to ensure a single route is free before the signal goes ‘clear’. There may be 100’s of relays operating for a complex yard or station for a secure operational requirement. Based on the route request from an operator (entry exit) or OCS or GUI or ATS ,the relays will start checking

the

availablility

of

that

route,based

on

the

status

of

the

track,other

signals,points(switches)etc and make the route “locked’ for a safe operation by ensuring all the elements are “Set”,”locked’ and “detected” in desired condition. One of the disadvantages of this system is large requirement of signalling hut(Where signalling control appartus housed) to mount 100’s of relays for a single area. Electronic/Solid State Interlocking

This is the most modern interlocking ,(before anything could replace!!!)started installing in late 80’s,are generally soild state(Appartus made out of solid materials!!!) where wired network of relays are replaced by software logic running on a special hardware(a microcontroller assembly). Modification of the network with a solid state interlocking is easy compared to relay interlocking as the software logic modification is easy compared to the hard wired elements. SSI(Solid State Interlocking) is used as a product name as well,which is the first generation electronic interlocking,jointly developed by British rail,GEC(Alstom) and Westinghouse. Second

generation

SSI

is

known

as

CBI(Computer

Based

Interlocking),where

SmartLock(Alstom,France),Microlok(Ansaldo,Italy/USA),Westlock(Westinghouse,UK) are some of the product examples.

Each system uses its own style of programming ,and has merits and demerits. Generally,a PBI(Processor Based Interlocking) or a CBI consists of a CPU card(where the system software process according to the application logic), a power supply card, Input/Output Cards(I/O cards) a device driving card to mention a few.. There are flash memories,EEPROM(Electrically Erasable Program Read Only Memory) where an experienced application logic person write the logic(replacing the hard relay functions with software)and load into the flash memory.(Burn an EPROM or load through a serial port)

The I/O cards are responsible for Input and Outputs.Input card read the status of the the field equipments(Switch position,Track Occupancy,Trainstop Position,Route Request and Cancel,Point Call etc). Where as Output cards drives the output to set the route in desired condition,after the application logic is processor based on the input status. The system is programmed in such a way that,it takes the most solid input before changing the status to ensure a fail safe operation. (For example a track is showing ,occupied and free alternatively ,known as bobbing,the system will consider that track as occupied until the Input card read a stable un occupied status) There are serial communication ports available in the PBI for communicating with other systems,to make hot stand by arrangement,and with adjacent interlocking. Serial communication ports are 485,232/432 Depends on the application ,modem are used to communicate with a long distance train control system or other PBI.

For the sake of explanation,I can generalize the discussion and stick to Microlok ,one of the cheap and popular systems. Here the application logic is written in terms of Boolean equation.

The Boolean operators (AND,OR ,NOT are most commonly used,where as other operators like XOR are also available) Microlok syntax for AND is ‘ * ‘ ,for OR ‘+‘ , and NOT is ‘~‘ For explanation I can show a simple logic here, ASSIGN

~A42VSNR * ~42VSNJR * I2_42MA_HR * ~ACE19.6U_VSNR * ~CE19.6U_VSNJR *

CE19.6U_VCSR

TO 42MA_HR;

Here ,to drive the software relay for controlling the yellow aspect of 42 signal A route various status of other relay has been proved… Some of the logic can be very complex…Another example below

ASSIGN

(37M_RUR + 37S_RUR + 39MA_RUR + 39SA_RUR) * ((40ATP1 + 302NLR) * 37ATP1 *

I1_37BTP * I1_CE20.1ATP * I1_CE20.3ATP * I1_CE20.5ATP * I1_CE20.5BTP * I1_CE20.7ATP * I1_CE21.1ATP * I1_CE21.3ATP * I1_CE21.5ATP * I1_CE21.5BTP * I1_CE22.1ATP * I1_CE22.1BTP * I1_CE22.9ATP * I1_CE22.9BTP * I1_201ATP * I1_203ATP * I1_205ATP * I1_207ATP * (I1_207BTP + I1_303RLR) * (I1_216ATP + I1_303NLR) * I1_218M_NLR * I1_218M_USR * I1_218S_NLR * I1_218S_USR * I1_216MB_NLR * I1_216MB_USR * I1_216SB_NLR * I1_216SB_USR + I3_MP_EG_DL_DDSR

+

MP_EG_DL_SEC_JR)

TO

37_39A_YR,O3_37_39A_YR;

Depend on the interlocking there could be around 5000 Assign statements….for each interlocking data….

This is an example taken from a data detailing just two assign statements,apart from this we need to assign ports for communication,re direct logic,log bits define all the Boolean bits ,baud rate and many other things..

Processor based system explained above is the brain of the system…which operates on the status of the external situation ,commands from the operator or an automated system..

Technology is moving forward…Introduction of Automatic Train Operation(ATO),Automatic Train Protection(ATP),and Automatic Tran Supervision (ATS) make the system work with out human interface.

As per the train schedule loaded on to the ATS system ,a train located miles away in a yard come to the platform on right time,open the door and set to go when you are in.

Where as a train protection system ,calculate a speed profile based on the train ahead and ahead signal status to apply service break or maintain speed depend on other trains!!!

There are systems On borad can be be set to run manual or auto mode .GPS based signalling is the latest trend.Thanks to ERTMS (European Rail Transport Management System) which could allow inter operable between railways and system across the boundary,run train on more than 450KM/HR…

Now its time to literally flying train ,flying in a vacuum tunnel floating on English Channel with two times speed of an aeroplane…Yes our new generation can get ready to fly on a train !!! One can realise the complexity of system running a train over 450KmPH Deepu Dharmarajan Signal Design Engineer/Consultant. Tags: Computer Based Interlocking, ERTMS, History of Railway Signalling, Railway Signalling, Route Relay Interlocking, SSI, Train Control Systems Posted in Signalling | 3 Comments »

Analysis of Failures of Solid State Interlocking Systems Sunday, January 3rd, 2010

1. Lack of domain Knowledge in Signalling and Traditional Route Relay interlocking Systems, This creates a technological gap between the software programmers and the Domain consultants. This leads to Errors in software, which might lead to unsafe failures of the system 2.Increasing the complexity of the System by Employing distributed architecture, which is difficult to validate and verify and difficult to maintain, thus leading to very high time repair 3. Extending the working scope of the Interlocking systems for monitoring and other non-Interlocking functions, which leads to degraded performance of the system 4. Employing Non-Formal Interlocking principles instead of traditional RRI Principles leads to software complexity. For Ex: The Geographical method needs every system that is installed for new Yard needs validation, which is not practicable. 5. Since the software and hardware is so complex, complete test of the system is not possible and most of the faults are revealed at the field Installation stage or during normal working of the system in field. The software is to be changed for every yard , the software structure should be in a generic form, but we seldom see a generic form and this the stage errors creep in. 6. The lack of standardization in the railway working principles and the core Interlocking principles,

the software developers are forced to do changes in the software for every yard in Different railway zones, this is the time that errors in the software creep in. 7. Because of the above said reasons the Interlocking systems have failed to create the necessary confidence in the railway operators. Because of this reason the Solid state Interlocking systems have become unpopular. If we examine broadly the reasons for failure and lack of reliability and maintainability that are forced by the designers are as follows: 1. Lack of standardization of interlocking principles, every railway zone has its own set of rules and principles which are conflicting with other railways, this makes the life of the developers difficult because they have change their systems settings and software accordingly. 2. There is no standard book or reference available describing the core interlocking principles, since these rules are only known by the people working in this domain. 3. Increase in the complexity of the software leads to difficulty in testing, since most of the Interlocking systems are sequential machines they are error prone are very difficult to test. Sandeep Patalay

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Railway signaling Railway signaling is a safety system used on railways to prevent trains from colliding. Trains are uniquely susceptible to collision because, running on fixed rails, they are not capable of avoiding a collision by steering away, as can a road vehicle; furthermore, trains cannot decelerate rapidly, and are frequently operating at speeds where by the time the driver/engineer can see an obstacle, the train cannot stop in time to avoid colliding with it. Most forms of train control involve messages being passed from those in charge of the rail network or portions of it to the train crew; these are known as 'signals' and from this the topic of train control is known as 'signaling'.

Table of contents 1 Timetable Operation 2 Timetable and Train Order 3 Signals 4 Blocks 5 History of block signaling 6 Modern railway signaling 7 Notes on U.S. Signalling 8 Notes on UK signal colour order 9 See Also 10 External Links

Timetable Operation The simplest form of operation, in terms of equipment at least, is operation according to a timetable. Everything is laid down in advance and every train crew knows the timetable. Trains can only operate in pre-arranged time periods, during which they have 'possession' of the track and no other train can operate. When trains are operating in opposing directions on a single-line railroad, meets are scheduled, where each train must wait for the other at a point they can pass. Neither is permitted to move until the other has arrived. The timetable system has several disadvantages. The first is that there is no positive confirmation that the track ahead is clear; only that it should be clear. This system does not allow for breakdowns and other such problems. The timetable is set up in such a way that there should be sufficient time between trains for the crew of a broken-down or delayed train to walk back up the line far enough to set up warning flags, flares and the explosive devices known as detonators or torpedoes (UK and US practice, respectively) which alert a train crew to a blocked track ahead. The second problem is the timetable system's inflexibility; trains cannot be added or delayed; trains cannot be rescheduled. The third is a corollary of the second; the timetable system is inefficient. To give a little flexibility, the timetable must give trains a broad swath of time to allow for some delay. Thus, the line is possessed by the train for much longer than is really necessary. Nonetheless, this system permits operation on a vast scale, with no requirements for any kind of communication that travels faster than a train. Timetable operation was the normal mode of operation on American railroads in the early days.

Timetable and Train Order

With the advent of the telegraph, a more sophisticated system became possible. The telegraph allows the dissemination of alterations to the timetable, known as train orders. These override the timetable, allowing the cancellation, rescheduling and addition of trains, and most anything else. Sufficient time must be given, however, so that all train crews can receive the changed orders. Train crews generally receive the orders at the next station at which they stop; or sometimes orders are handed up to a locomotive 'on the run' via a long staff. Timetable and train order operation was commonly used on American railroads until the 1960s, including some quite large operations such as the Wabash Railroad and the Nickel Plate Road. Timetable and train order was not used widely outside North America.

Signals Timetable and train order operation still has some significant flaws, such as an overreliance on the ability of the crew of a stranded train to let other trains know of the problem, and a general intolerance for human error. When everything goes perfectly it works well, but mistakes are easy and deadly. Timetable and train order is only suitable for railway lines which carry relatively little traffic, and is unworkable on busy rail lines because it requires great seperation between trains. Where this is the case, physical signals need to be used (either mechanical semaphore signals, or - more commonly in the modern era - electric light signals) to show the train crew whether the line ahead is occupied and to ensure that sufficient space is kept between trains to allow them to stop.

Blocks If two trains cannot be running on the same section of track at the same time, then they cannot collide. This notion forms the basis of most signalling systems. The rail network is divided into sections, known as blocks. Two trains are not allowed to be in the same block at the same time. A train cannot enter a block until it is permitted, generally by a signal that the block ahead is empty. On high-speed railways (where trains travel at speeds faster than 200 km/h (125 mph) the trains travel too fast for the driver to see conventional lineside signals, so a system of in-cab signals transmitted byradio are used.

History of block signaling In the very early days of railways, on double-tracked railway lines, where trains traveled in one direction on the same stretch of track, a means was needed to space out the trains to ensure that they did not collide. In the very early days of railways, men were employed to stand next to the line at certain intervals with a stop watch, these men used hand signals to signal to train drivers that a proceeding train had passed more or less than a certain number of minutes ago, this was called "time interval working". If a train had passed the man only a short while ago, the following

train was expected to slow down or stop to allow sufficient space to develop between the trains, to prevent a collision. This system was however flawed as the watch-man had no way of knowing whether the proceeding train had cleared the tracks ahead. And so if the proceeding train broke down or stopped for some reason, the following train would have no way of knowing, and collide with it rear-on. Accidents of this type were common in the early days of railways. However with the invention of the electrical telegraph, it became possible for the ahead station or signal box to send a message (usually a bell ring) back to confirm that a train had passed and that the line ahead was clear, this was called the "block system". mechanical semaphore signals replace hand signals in the early 1840s. And when the all clear signal was received, a signalman in a signal box would pull a lever which would move the signal into the all clear position. This required that signal boxes were spaced at regular intervals along the line.

Modern railway signaling On most modern railways, detection of the train's position on the line, and signal changing are done automatically. and colour light signals have largely replaced mechanical ones. The light signals mean: • green: proceed at full speed. • yellow: proceed slowly. • red: Stop. Railway signalling differs from the traffic lights used on roads, in that trains cannot stop quickly (for instance a train travelling at 160 km/h (100 mph) would need several kilometres to stop). Therefore on a railway, trains need to be given advanced warning of a red stop signal so that they can slow down to a speed where they can stop quickly (a yellow signal). Put another way, yellow signals (generally) do not indicate an impending change to a red signal at the same location. Rather, a yellow signal gives a train advance warning that the following signal will be red. To achieve this the railway is divided into 'blocks', blocks consist of the strech of track between two signals. Trains are automatically detected when they enter a block, this is done by what is known as a "track circuit". The track at either end of the block is electrically insulated, and within the block a small electrical current passes through the track, when a train passes a signal and

enters a block, the metal wheels and axle of the train short-circuits the current, this short-circuiting, triggers a switch. When the switch is triggered, the signal which the train has just passed, automatically turns from green to red, and the signal behind that one automatically turns yellow, the signal behind that one will turn green. If any train is following behind, the yellow signal will warn it to slow down in order to stop at the next signal, if however the train in front has passed into the next block, the following train will come across another yellow signal. If the train in front is travelling faster than the following train and clears two blocks, the following train will come across a green signal. In the UK a variation of this is used whereby each set of signal lights has four lights in order from top down: amber, green, amber, red. The red, and green signals are used as described, as is the lower amber light. The upper amber light is used to provide a 'double amber' signal which serves as a warning that the next block is on amber, thus providing a warning of a red signal a further block in advance. Double signalling is sometimes used; this is the method used in some areas of New South Wales, Australia. It derives from semaphore signalling. Two sets of lights are displayed, one atop each other, and the topmost light represents the condition of the lights at the current signal, and the lower is the condition at the next signal. Some lights have a small lamp at the bottom; this is an indication to continue at low speed. The double signals indicate: • green over green: continue • green over red: caution, next signal at stop • green over yellow: caution, next signal at green over red • red over red: stop ○ red over red with small lamp lit: low speed, 25 km/h. The track circuit is also used by signalmen to detect exactly where a train is on a line, in a signal box, a map of the strech of track the signal box is controlling is usually put up on the wall, when a train enters a particular block, a light representing that block on the map will light up to show a trains location. Track circuits are also used to trigger automatic barriers on level crossings. (Grade crossings in U.S. usage)

Notes on U.S. Signalling U.S. railways used far greater variety of signalling systems than other countries. There have never been national standards for signal appearance and operation. Each of the

hundreds of rail lines developed its own signalling techniques. Further, there is a good deal of bidirectional track in the U.S., and also a fair amount of "dark track" with no signalling equipment installed.

Notes on UK signal colour order The green below and red above colour order of British railway signals (as opposed to the red above and green below of traffic lights on roads) derives from the gaslit colour lenses of the old semaphore signals. The design of semaphore signal ultimately settled on by most of the british railway network had a raised arm for 'go' and a lowered arm for 'stop', thus ensuring as a safety precaution that if the arm failed gravity would set it to stop. Since the lights for night use were at the post end of the semaphore arm this meant that in order for the correct colour to show it was necessary to place red at the bottom and green at top. The requirement of road signals that a stop light should be visible over a queue of traffic and as far back as possible (thus demanding an order with red above)doesn't really apply to railways with a block signalling system as no there should be no traffic queuing within a block, there being only one train in a block at the time. Also red need not be at the top for maximum visisbility over distance as the driver of a train will already be expecting a red signal, having just passed an amber one, which level of davance warning is altogether missing with road signals.

See Also • Railway signal

External Links http://www.lundsten.dk/us_signaling/index.html

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resentation Transcript ENSURING SAFETY FOR INDIAN RAILWAYS THROUGH GPS : ENSURING SAFETY FOR INDIAN RAILWAYS THROUGH GPS Presented by J.HINA AAFREEN

TABLE OF CONTENTS : TABLE OF CONTENTS INTRODUCTION STATISTICS ON RAIL ACCIDENTS WHAT IS GPS? APPLICATION OF GPS WHY GPS HERE? COMPONENTS AND FUNCTIONS PRINCIPLE OF WORKING ONBOARD UNIT DESIGN IMPLEMENTATION NEEDS CONCLUSION

INTRODUCTION : INTRODUCTION Indian railways is the biggest railway network in the world On the other hand it has faced large number of accidents due to negligence,techinical fault etc…. Even though we have got

many techniques of preventing these accidents NO METHOD CAN BE MORE EFFECTIVE AS THAT OF GPS

WHAT IS GPS : WHAT IS GPS GPS – Global Positioning System A network radionavigation system formed from a constellation of minimum of the 24 satellites rotating in 6 orbitals and their ground stations

APPLICATION OF GPS : APPLICATION OF GPS Mapping and GIS Data Capture Navigation Vehicle Tracking Mining & Construction

WHY GPS HERE ? : WHY GPS HERE ? To avoid rail accidents It is highly efficient The system is highly reliable and informations are highly secured systems promise radical improvements to many systems that impact all people main function of GPS is to get the interconnectivity of the various points in the track

PRINCIPLE OF WORKING : PRINCIPLE OF WORKING Whenever a train will move over the track there will be vibrations that will be created on the track. These vibrations that are produced on the track are dependent on the speed of the train, load or the weight of the train A software traces these vibrations using microphones and convert these vibrations in such a form that they can be compared with the already existing data of the database If there will be any problem on the track, bridge etc. such as the removal of the fish plates the vibrations produced from the train will change (they will either get damped or will get excited which is a noticeable change from the ideal case)

PRINCIPLE OF WORKING : PRINCIPLE OF WORKING If the obtained data and the stored data are the same then normal signal is send to the receivers from the satellite If the vibrations from the track are more or less then emergency signal is send to the receivers

COMPONENTS & FUNCTIONS : COMPONENTS & FUNCTIONS Microphone sensors Needs critical selection as huge amount of the vibrations or the noises are created that are not possible to get recognized from a large distances Traces the vibrations and sends to DBMS Proposed sensor-CARBON SENSORS used in telephone Fiber optic wires Transmits the traced vibration data to DBMS quickly

COMPONENTS & FUNCTIONS : COMPONENTS & FUNCTIONS Software and DBMS programs that can perform some tasks that are assigned to them DBMS is the Data Base Management System which can store a huge amount of the data in them S/W converts vibrations from sensors into some graphical forms and transfers to DBMS which contains preloaded data that are analysed in normal conditions

ONBOARD UNIT DESIGN : ONBOARD UNIT DESIGN continuously measure different parameters, tag the data with time and position information, reports irregular conditions consists of communication satellite antennae, satellite positioning antennae , the on-board receiver system and communication interface devices, etc

IMPLEMENTATION NEEDS : IMPLEMENTATION NEEDS Need of the towers for the transfer of the data to the various destinations A high tech visual display system to show the actual position of the trains along with other details like visual and audio warning systems Receivers and the transmitters tuned to proper frequencies and in accordance to the network The train driver’s cabin must be such that the driver will come to know about the track,weather, bridges and constructional status in advance Good communication system. This can be achieved by the use of the GPS ITSELF

OPERATING FREQUENCY : OPERATING FREQUENCY Uplink frequency-5.925 to 6.425 GHz Downlink frequency-3.700 to 4.200 GHz may change as per the advancements that are made and the system requirements

TRAIN COLLISION : TRAIN COLLISION

REMEDY THROUGH GPS : REMEDY THROUGH GPS Consider two trains of same or different weights,speeds approaching towards each other in the same track with GPS n/w installed in it The microphone sensors traces the vibrations 35km prior to its arrival As two trains are approaching in the same track the vibrations gets excited This produces emergency signal with alarm and this is transmitted to the control rooms and to loco

EXPECTED BENEFITS : EXPECTED BENEFITS Railway Safety Automation in the Work Reduction in the Stress Levels because of the good equipments and machinery Time Delays: As every time the position of the train will be known thus there will not be any time delays Train Traffic Control: due to continuous monitoring of the trains there will be a good train traffic control

HOW GPS OVERCOMES : HOW GPS OVERCOMES The implementation time is large and the cost is high to some non technocrats A survey says that the total loss for our government rates to few hundred crores So just by investing a small sum of this loss,the accidents and losses can be overcome once for all

CONCLUSION : CONCLUSION The benefits and advantages of the proposed method outnumber the problems and disadvantages. By considering this method for the most important transport system in India the most valuable ‘human life’ and the national property can be protected Thus the integration of GPS, sensors along with software systems can be effectively used to provide safety as well as huge income to the Indian Railway

REFERENCE : REFERENCE www.trimble.com www.discoveryindia.com www.irsuggestions.com www.howstuffworks.com

Slide 21: THANK YOU

Slide 22: QUERIES

Railway signalling

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