Axle counter1 Axle counter An axle counter is a device on a railway that detects the passing of a train in lieu of the more common track circuit. A counting head (or 'detection point') is installed at each end of the section, and as each axle passes the head at the start of the section, a counter increments. A detection point comprises two independent sensors, therefore the device can detect the direction of a train by the order in which the sensors are passed. As the train passes a similar counting head at the end of the section, the counter decrements. If the net count is evaluated as zero, the section is presumed to be clear for a second train. An axle counter detection point in the UK This is carried out by safety critical computers called 'evaluators' which are centrally located, with the detection points located at the required sites in the field. The detection points are either connected to the evaluator via dedicated copper cable or via a telecommunications transmission system. This allows the detection points to be located significant distances from the evaluator. This is useful when using centralised interlocking equipment but less so when signalling equipment is distributed at the lineside in equipment cabinets. History Axle counters were first introduced in the 1960s in Germany. [1] Advantages Unlike track circuits, axle counters do not require insulated rail joints to be installed. This avoids breaking the continuity of long welded rails for insulated joints to be inserted. Axle counters are particularly useful on electrified railways as they eliminate traction bonding and impedance bonds. Axle counters require no bonding and less cabling in comparison to track circuits, and are therefore generally less expensive to install and maintain. Axle counters do not suffer problems with railhead contamination, e.g. due to rust or compacted leaf residue, that can affect the correct operation of track circuits. Axle counters are used in places such as wet tunnels (such as the Severn Tunnel), where ordinary track circuits are unreliable. Axle counters are also useful on steel structures (such as the Forth Bridge), which prevent the normal operation of track circuits. Axle counters are also useful on long sections where several intermediate track circuits may be saved. A Frauscher axle counter sensor, for example, can be 8,500m from the evaluation unit, while the latest ALTPRO axle counter sensor model ZK24 can even go up to 49 km from the unit. If the counter unit fails or becomes disconnected. and one each for counting in each direction. . In Auckland. Turnouts Where there are turnouts. spur or loop tracks the use of counters is more costly to implement to detect trains appearing and disappearing from a track segment. New Zealand. Track circuits also allow for the use of clips that instantly shunt the circuit and mark the track as occupied. kinds of broken rails.Axle counter 2 Cables The axle counter cable of 8. though only to a limited extent in AC traction areas and not in the common rail in DC traction areas. this is known as 'wheel rock'. axle counters will be used on the main lines. but any headshunts connected to sidings will use ordinary track circuits. an axle counter unit needs to be provided for each leg of that turnout. which can also be used for CBI cables. Disadvantages Axle counters may 'forget' how many axles are in a section for various reasons such as a power failure. This can prove problematic at stations or other areas where cars are shunted. A manual override is therefore necessary to reset the system. This manual override introduces the human element which may be unreliable.000m would typically be buried in a plastic conduit. This results in the section of line being monitored showing occupied in the event of persisting technical fault or loss of telegrams. joined and divided. a train will pass undetected into a block that would otherwise be regarded as unoccupied. Ordinary track circuits have a blind spot of about a metre in length from the wiring connections to the insulated joint. This. The section then requires a reset command and further interaction to restore to service. These can be used by crews or maintenance personnel to quickly report an unsafe condition or mark a section of track out of service. where main lines have hand operated switches to siding. Siding and shunting movements Axles counters have problems maintaining correct counts when train wheels stop directly on the counter mechanism.000m or 49. Broken rails The track circuit provides additional functionality of detecting many. was not proven during the subsequent inquiry. An accident occurred in the Severn Tunnel and is thought to be due to improper restoration of an axle counter. Axle counters offer no such facility. Fail safety Axle counters only provide intermittent positive indication of a rail vehicle as it passes a fixed location. Modern axle counter equipment transmits data from the trackside apparatus to the indoor equipment via telegrams. The cables have four cores: two for power (pos and neg). across an ISDN line. Also. however. however not all. Track circuits provide continuous real time detection over a track segment and any loss of power or disconnected wire results in a safe signal indication to the train. This can happen only on one side of a track block.Croatia [14] Scribd [15] [16] . Makes • • • • • • • • • • • • • Argenia Railway Technologies Inc. • Co-operative reset requires both the technician and signaller to co-operate to reset and then restore the section into service. [9] CEL [10] [11] Duvine [12] Zvonimir Viduka .Croatia [13] ALTPRO . This logically proves the section free of obstruction and therefore allows the section to change its output to 'clear'. [2] Celindia [3] Frauscher [4] . It is problematic for a long track section due to the long time required for the train to pass at a slow speed. This type of reset is now only used on schemes which fringe on an existing scheme which utilizes this type of reset arrangement. because of magnetic field curvature. • Un-conditional reset (no aspect restriction) has the section reset irrespective of the last count action. [8] GGTronics. sometimes with varying amounts of automation or human input.Axle counter 3 Electromagnetic brakes Magnetic brakes are used on high speed trains (maximum speed greater than 160 km/h). They can sometimes be mistakenly detected by axle counters as another axle. These are physically large pieces of metal mounted on the bogie of the vehicle. This at least shows that any trains in the section at time of reset were moving out. or other issues. The protecting signals are cleared immediately after a reset. The modern AzLM variant of axle counter is 'eddy current' brake proof and the magnetic effect of the braking system described above is overcome. defects of track geometry. only a few centimetres above the track. The signal protecting the reset section is held at danger by signalling logic outside of the axle counter evaluator to enforce a low speed 'sweep' of the section prior to restoration to service. this type of reset is used under 'EPR' 'Engineer's Possession Reminder' and a series of procedures are carried out to ensure the section of line is clear of vehicles and tools before the reset is performed. leading the signalling system into confusion and also requiring reset of the detection memory. In the UK. therefore count information remains stable even when a vehicle fitted with magnetic brakes is braking whilst traversing the rail contacts of a detection point. • Conditional reset (with aspect restriction) has the section reset only if the last count was in the outward direction. by holding its output as 'occupied' until the train is successfully detected as passing through the section. Most countries use a variation of the above four methods.ACS2000 Siemens [5] Thales Group [6] GE Transportation [7] Stesalit Ltd. Reset and restoration There are four methods of securing the reset and restoration of axle counters into service: • Preparatory reset uses the internal logic of the axle counter system to enforce that a train must proceed through a reset section at slow speed. doc [14] http:/ / www. html [8] http:/ / www. britishinventionshow. electropedia. duvine. altpro. com [5] http:/ / aunz.com. au/ docs/ eng/ type-approvals/ signal/ 08-08-10-009.artc. htm [13] http:/ / www. html [9] http:/ / www. com/ index. com. celindia. in/ Electronic_sys1. (http://extranet. com/ doc/ 38872545/ Axle-Counter) External links • Electropedia (http://www. argeniarailwaytech. htm [3] http:/ / www. scribd. co. com/ Mobility/ RI/ Pages/ TS_SignallingSystemsProductsandSystems. com/ Portfolio/ Security/ D3S_axle_counter/ ?pid=1568 [7] http:/ / www. com/ show/ 2003_exhibitors.Axle counter 4 References [1] http:/ / extranet. thalesgroup. in/ UniversalAxle. co. uk/ rail. asp?ID=10 [10] http:/ / www. asp [11] http:/ / www. com/ Products. frauscher.nsf/display?openform&ievref=821-03-41) • ARTC level crossing example . asp [4] http:/ / www. com/ eng [15] Scribd (http:/ / www. siemens. stesalit-inc.au/docs/eng/signal/procedures/design/ESI-03-02. ggtronics. com/ embeddedsoft. co.org/iev/iev.electropedia. nsf/ display?openform& ievref=821-03-41 [12] http:/ / www. scribd. org/ iev/ iev. aspx [6] http:/ / www. celindia. pdf) . pdf [2] http:/ / www. com/ rail/ rail-products/ signaling-a-communication/ crossing-control/ axle-counter-sca. com/ doc/ 5989881/ Axle-Counter) [16] Scribd (http:/ / www. getransportation. artc. 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