A device used to count axles in to and out of a Track Section . An axle counter head is bolted to a rail. Within the head are two sensors which detect an axle rolling over the top of it. The combination of the two sensors allow it to determine the direction of travel. Each head forms both the counter into a track section and the counter out of another track section. If the number of axles entering the section differs from the number of axles leaving the section then it will be shown as occupied. If the numbers are equal then it will be unoccupied. Thus, the end result (occupied or clear) is similar to track circuits .
Axle counters can become easily disturbed by engineering/maintenance vehicles and operations. In modern facilities there are means provided to allow the signaller to reset the axle counter to a clear state. Doing so requires a sequence of operations which involve talking the driver of a train past a red signal in order to "sweep" the section to ensure it is clear of obstruction. This can even be achieved from an adjacent line in certain circumstances. Older installations required co-operative reset procedures by a technician and the signaller simultaneously; others still only required a technician to reset the counter.
See also Axle counter (Wikipedia) for more detail and illustrations.
Last edited by GeoffM on 15/09/2016 at 03:00