| Automatic Train Operation A computer-based system which controls train speed automatically in response to inputs from the signalling system - always under the protection of ATP |
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| Automatic Train Protection An automatic system which protects trains from collisions and excessive speed |
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SMC
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Systems Management Centre - Alcatel's Control Room front end. | |
| Channel Tunnel Rail Link The high-speed railway line beween London and the Channel Tunnel |
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| Docklands Light Railway An automatic light rail transit system in the East End of London, England - serving the busy Canary Wharf financial centre and linking London City Airport to London City (!) |
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| European Passenger Services The Operator of the international railway system which uses dedicated passenger Eurostar trains to operate between London, Paris and Brussels |
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| London Underground (Limited)
- also known as LUL The Operator of the London-based subway metro system |
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| Train à Grande Vitesse The high-speed train as found on main lines in France and Belgium |
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| Transmanche Link The Joint Venture company who constructed the Channel Tunnel |
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| Transmission Voie-Machine
430 The French (SNCF) transmission-based signalling system used on the Channel Tunnel and most TGV lines in mainland France. |
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| Vehicle On-Board Controller This is the trainborne "brains" behind the Alcatel SelTrac moving block signalling system. |
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| A special collection of rail components which contain moveable portions which allow a rail vehicle to move from one track to another. See also Switch Rail, Stock Rail, Clamplock, Points Machine | ||
| A machine which contains a motor to make the moveable portions of points slide across from one position to another. Point machines also often contain detection equipment and sometimes a facing point lock. | ||
| This is an arrangement which physically secures a set of points in one lie to guarantee that they cannot move during the passage of a rail vehicle across them. | ||
| Points have two possible positions, or lies - in most of the world these are known as "Normal" and "Reverse". Normal is traditionally the "straight ahead" lie, or, in the case of trap points, leading into the arrestor. In some parts of the world, points lies are named "left" and right". | ||
| A points operation, locking and detection system developed by British Rail in the 1980s. Clamplocks use (almost invariably) hydraulic actuators to drive the unlock>throw>lock cycle of the drive lock slide assembly. The name derives from the clamping manner in which locking is achieved by securing the closed switch rail to its stok rail. | ||
| The gap provided in rails where a the flange of a train wheel has to either cross through a rail at an angle (in the case of crossings) or very close to a switch rail (in the case of points). Strict minimum dimensions for flangeways exist and maintaining these for points is often challenging! | ||
| A crossing is an "X"-shaped rail assembly which connects two rails to each other at an angle, incorporating a flangeway, such that the wheel can cross in two possible movements. | ||
| A part of a set of points which slides on demand to force a train wheel to change from one rail to another. | ||
| A part of a set of points which the switch rail buts up against, but which is immoveable. | ||
| 1. An electrical cable providing
electrical continuity between metallic components, e.g. rails 2. A track circuit-related traction return component - see Impedance Bond and Resonating Bond |
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| The electrical connections between rails which affords a good connection for track circuiting and, where applicable, traction return current | ||
| A special bond, coloured red, which provides a critical traction return connection and must not be removed without special isolation arrangements. Often to be found near Substations. | ||
| A centre-tapped coil designed to permit a low resistance to DC traction return current but a high impedance to AC signalling signals. The high impedance is provided by the presence of an auxiliary winding which is connected into a tuned circuit. Impedance bonds are employed at the extremities of certain types of track circuit and are provided with traction return connections leading into the adjacent track circuit, normally to another impedance bond. See also Double Rail Track Circuit and Single Rail Track Circuit. | ||
| A coil, identical to an Impedance Bond, fitted at the centre (usually) which is employed to parallel traction return to an adjacent line. Also known as a "res-bond". | ||
| A special arrangement employed for Jointless Track Circuits which prevents a significant level of signalling current passing the zone, without employing IRJs. | ||
| See Tuned Zone. | ||
| Jointless Track Circuit - dispenses with the need for IRJs, saving costs and maintenance. Employs Tuned Zones to provide insulation from adjacent circuits. | ||
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Jointless
Track Circuit
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See JTC. | |
| A track circuit, normally found through Points and Crossings, which uses one rail for traction return (the "Common Rail") and the other for signalling current. The sigalling rail has IRJs, the common rail does not. | ||
| A track ciruit found on plain-line, which allows traction return to flow through each running rail equally. | ||
| A track circuit which employs dual tuned vibrating reeds at the Tx and Rx to guarantee passing only the correct frequency. | ||
| One example is the "VT1" dual vane relay circuit - using mains frequency as the signal source and assuring adjacent circuit integrity by shifting the signal phase by the use of variable capacitors. Normally used in DC traction areas. | ||
| Use DC voltage to energise simple relay circuits. Normally employed in AC traction areas. | ||
| The "TI" stands for "Traction Immune" - a modern replacement for old AC tracks. Often found with "S"-Type Impedance Bonds, they are distinguished by special tuning cards inside the bonds which require cutting links to configure them to a particuar frequency. | ||
| Uses a High Voltage Impulse stream to improve shunt characteristics - often used on industrial lines and sidings. | ||
| A Westinghouse Signals coded track circuit which employs a solid-state frequency generator and is capable of transmitting codes to trains. | ||
| An SNCF-type of jointless track circuit using tuned zones similar to British JTCs. Capable of transmitting many codes to trains. | ||
| The Ffestiniog Railway track - designed by Bob McGregor for use on Welsh heritage railway system. | ||
| The highest resistance connected across the running rails at a given point along the track circuit which will make the front contacts of the Track Relay just open. Tested using a decade resistance box. Important for safety - too low and trains may not be detected!!! | ||
| The lowest resistance connected across the running rails of a track circuit at a given locaion along its length at which the front contacts of the Track Relay close. Tested using a Decade Resistance Box. Needed for reliability - too high and the track circuit may not re-enerise after the passage of a train (particularly in the wet). See Ballast Resistance | ||
| The combined electrical resistance of the ballast, the sleepers (or slab), any points equipment present etc - which is presented to the track circuit apparatus. This changes wildly in the wet (reduces) - and track circuits threfore have to be designed to operate reliably when presented with a wide range of ballast resistances. See Pick-up Shunt. | ||
| Used in the Feed End, Relay End and also Resonating Bond equipment to adjust the resonance of the tuned circuit. Exposed live conductors - careful! | ||
| Two conductive materials which act as an electrical switch when moved in relation to each other. In signalling, often made of materials which cannot weld together under fault conditions. | ||
| A normally-open Contact. So named because, in old-fashioned glass-cased "fishtank" relays, these were physically at the front. | ||
| A normally-closed Contact. So named because, in old-fashioned glass-cased "fishtank" relays, these were physically at the back. | ||
| The end of the track circuit where the signalling current is injected into the track. See Tx. | ||
| The end of the track circuit where the presence of the signalling current is detected. See Rx. The train normally enters a track circuit via the relay end. | ||
| Transmitter - the equivalent of a Feed End in a modern type of Track Circuit. | ||
| Receiver - the equivalent of a Relay End in a modern type of Track Circuit. | ||
| A section of railway line which is logically (and sometimes electrically) insulated from its neighbours, in order to permit a signal to be sent along the rails and detected at the other end. Presence of this signal proves no train is in this section, as the metal wheels of a train would short this signal out. | ||
| A device which, normally galvanically, detects the presence of train axles and is able to determine their direction of movement and pass this infomation on to an evaluation device which keeps a record of how many axles are present on a given section of line. Used on some systems instead of Track Circuits for Deadlocking. | ||
| See Axle Counter. | ||
| Axle End Coupling (or Counter) - used to determine train axle rotation in trainborne applications. AECs tend to be digital in nature. Compare with Tachogenerator. | ||
| See Tachogenerator. | ||
| A small generator-type device used to determine train axle rotation. Although geared, not particularly accurate at low rotation speeds. Compare with AEC. | ||
| Automatic Train Control - comprising ATP, ATS and often ATO. | ||
| Automatic Train Supervision - normally the system in the Signalling Centre which provides scheduling, telemetric control of points and train despatch. | ||
| Diagnostic system used on SNCF to interrogate and monitor MCKT systems. | ||
| Module Commande Kontrole Telecommande - A remote telemetry system used on SNCF to allow remote route-setting etc. | ||
| Westinghouse's celebrated electronic signalling system. Provides ATP via coded track circuits in a very elegant manner. | ||
| Solid State Interlocking - developed by a tri-partite joint venture between GEC, Westinghouse and British Rail. Trackside functional modules designed especially to control signals and points and detect track circuits, connected to a multi-drop copper link leading to a triplicated, 2 out of 3 redundant electronic interlocking which was designed to be easy to interface with then common NX Panels. Modules include Signal Modules, Points Modules, Barrier Modules, Data Link Modules, Panel Processor Modules, Interlocking Processor Modules and Diagnostics Processor Modules. | ||
| A geographical type of relay interlocking made by Westinghouse, consisting of "sets", each of which is a complete "building block" made of relays and inter-connections, which fit in special racks and are inter-connected to form a complete interlocking. Greatly reduces inter-relay wiring as compared to a free-wired relay interlocking. | ||
| A signalling engineering company who are a world leader in the industry. Part of the original tri-partite group who developed SSI, and the manufacturers of such products as WestRACE, WestLOCK etc. Website. | ||
| A signalling engineering company pioneering moving-block automatic train control. Providing SELTRAC (manufactured by SEL of Germany) and their own SMC system as the front end. | ||
| A moving-block signalling system marketed by Alcatel Canada, employing off-the-shelf components from a German subsidiary called SEL (Standard Elektrik Lorenz), with their own SMC. | ||
| Pulse Width Modulation - a system for communicating analogue values at distance in many respects similar to FM, but where a square wave carrier is modulated by varying the pulse width to reflect the value. Note that 0% and 100% usually represent a fault condition, so are not used. Often used on trains to communication tractive effort demands as immunity to noise is normally adequate. | ||
| 1. The ability of the wheels
on a vehicle to provide movement when turned. 2. The supply of electricity which is converted by the vehicle's motors into movement. |
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| The traction supply to the trains, whether overhead or third rail, has to be provided with a return connection. Think of a simple battery - connecting a lamp to the "+" terminal has no effect until the return is provided by a connection to the "-" terminal. Exactly the same occurs with train traction supplies. In all except four-rail systems (e.g. LU), the traction return current passes through the running rails. As these are normally used for signalling purposes as well (see Track Circuits), there is significant potential (no pun intended) for interaction, and therefore signalling equipment has to be designed with immunity from traction return built-in. | ||
| Current flowing in a metallic item which is unintentional. A good example is traction return current flowing along a metal bridge deck instead of through the running rails - this can cause catastrophic damage and structural failure. | ||
| Equipment providing either traction or domestic current by stepping down from grid voltage. | ||
| Track Paralleling Hut - provides connection between adjacent lines for traction return purposes - incorporating imbalance monitoring equipment. | ||
| A cable provided to afford galvanic coupling between a trackside signalling system and a train. | ||
| A coil fitted to a train to connect with either an inductive loop or a signal induced in running rails. | ||
| See Antenna | ||
A mechanism to prevent controls being applied together which in conjunction would lead to an undesirable condition. Also used to mean a complete signalling interlocking installation, e.g. Relay Rom, etc |
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| An electro-mechanical device comprising a coil and contacts. Energisation of the coil causes the contacts to move, either close or open. | ||
| A relay used to indicate the absence of a train on a particular Track Circuit. Track Relays energise with the track clear, and drop when the track is occupied. | ||
| A form of relay designed to switch higher currents. | ||
| One half of a pair of conductive materials which act as a switch and are moved mechanically together or apart, often as part of a relay. | ||
| A device used by signalmen in signalboxes to operate points, signals, locks or releases. | ||
| A rotating form of contact, often attached to a lever. | ||
| A switch provided on a control panel - normally able to be both pushed and pulled. | ||
| Normally used to mean the train display panel provided to give signalmen indications of track circuit, signal and points status, and also control of points and signals. | ||
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Signal Box
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A building which houses signal levers or a panel, along with rudimentary accommodation for a signalman | |
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Backlock
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A lock which is employed to prevent a lever being replaced to normal when required to be prevented by control table needs. Often associated with approach locking or route locking. | |
| Any mechanical or electrical system which is able to permit or prevent operation of a control. | ||
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Locking
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This term is used in both adjectival and collective sense referring to the term "Lock". | |
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Interlock
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A system of locking which prevents two conflicting controls from being applied. One example would be circuitry preventing routes being set into one platform from opposite ends at the same time. | |
| A mechanism which restricts the speed of trains approaching a signal by maintaining it at Danger until the train has reached a particular point - normally determined by a track circuit being occupied for a given period of time. See also Approach Lighting | ||
| A system which prevents a route being cancelled in front of an approaching train if the driver can possibly have seen a non-Danger aspect. In some cases the system may permit aspect replacement. In all cases, the route is preserved until the train is proved stationary, usually by a particular track circuit (in isolation) being occupied for a given time. In the days of semaphore signalling, before modern vital timers, the signalman was obliged to turn a handle a number of times to close and then re-open a contact - and this took a significant time (known as "winding out"). | ||
| A system, employed on LUL, whereby a signal displays no aspect until the approaching train reaches a given point - normally determined by Delta or PD occupancy. May be thought of as a form of Approach Control | ||
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Aspect Replacement |
The setting of a more restrictive aspect on a signal - normally a Danger aspect. | |
| Locking which prevents the elements whch form a route from being used by other routes until the route is no longer set. | ||
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Track Locking
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Locking which holds route locking while the train is physically transitting the route. | |
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TORR
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Train Operated Route Release - refers to the releasing of locking of elements of a route sequentially which the train is transitting the route. For example, a set of ponts "early" in a route, once the train has passed over them and is past the fouling point, may be TORR released, alowing other routes to be set across them. | |
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Wind-out
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See Approach Locking | |
| A section of track, past the signal at the end of a given route, which forms part of the selection of the route. This prevents a route being set up to a signal with an obstruction immediately past the signal - because a train SPADing the signal would then collide with the obstruction. In brief, setting a route requires the overlap clear as well. | ||
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Swinging Overlap
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An overlap which contains a set of facing points, which, under certain conditions, may be swung from one lie to the other as the train approaches. | |
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Reduced Overlap
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An overlap which, under certain conditions, is shorter than normal. This is typically employed where a set of points in advance of the exit signal is required for a conflicting route - and selection of the route with the reduced overlap will apply approach control to enforce a slower-speed approach to this point. | |
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Detection
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A system of contacts which electrically proves the position of a mechanical item. Examples include points, level crossing barriers and even bridges. Note that the term is also used in connection with track circuits - they may be described as a form of "train detection". | |
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Control
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EKR
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Light Checking Relay - fitted within a signal head, this is a current relay whose coil is connected in series with the primary filament in a dual filament signal lamp. When the primary filament stops drawing current the EKR drops and the secondary filament is then switched into use. At the same time, another contact is made which sends an indication back to the controlling relay room that the secondary filament is in use. These indications are normally commoned, so determining remotely which has failed takes some skill and the co-operation of the signalman to clear different signals as required. | |
| A device used to indicate to drivers their authorisation for (or prohibition from) using a particular route. Signals come in a variety of types, including Semaphore, Shunt, Lunar, Banner and Colour Light | ||
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Aspect
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One of a number of possible displays exhibited by a signal. For instance, the red light part of a colour light signal is properly called the red aspect. | |
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Selection
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The items which are required in order to allow a function to be energised. Consists of a power source and contacts, as well as wiring. The contacts are often connected in complex configurations to enforce complicated conditions. | |
| A section of track between two signals. See also Route Locking. | ||
| Signal Passed At Danger. This is the industry name for a train passing a signal which is not showing a proceed aspect. | ||
| A special piece of track which allows road vehicles and rail vehicles to cross at the same level (as opposed to using a bridge), along with the (complex) signalling systems which normally accompany it to ensure segregation between each type of vehicle. | ||
| A signal aspect indicating the requirement for trains to stop at the signal. Also known as "On". See also Normal. | ||
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(1) A lie of points - in the case of trap points, leading a train into the arrestor. For other points, usually the most-used position (2) A signal lever position - with the lever at rest, not pulled out of the frame. For a signal lever this means the signal is "On", i.e. at Danger. For points, this means the points are Normal (see (1) immediately above). |
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(1) A lie of points - in the case of trap points, leading a train away from the arrestor and towads the main line. For other points, usually the least-used position - in the case of crossovers, the diverging lie. (2) A signal lever position - with the lever pulled out of the frame. For a signal lever this means the signal is "Off", i.e. at Proceed. For points, this means the points are Reverse (see (1) immediately above). |
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Proceed
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A green aspect - indicating that the route is clear and set up to the next signal (plus the Overlap). In three- (and more) aspect schemes, also indicates that the following route is also clear and set. | |
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Caution
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A signal aspect advising that the signal in advance is at danger. In a colour-light scheme, this is represented by displaying a yellow aspect. See Aspect Sequence. | |
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Aspect Sequence
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In a colour light signalling scheme, the signal in rear of an obstruction displays a red danger aspect. The signal before that will display a caution aspect (yellow), and the one before that will be at Proceed (green). In a four aspect system the third signal will display a double-yellow aspect, and a fourth signal will show Proceed. This is graphically explained here. |
Jonathan Groves MIET
MBCS MIEEE
Mobile: 07970 468354
Skype: 0208 123 1379 (C15JON)
Fax: 07970 682158