Track circuits take many forms but their common purpose is to prove the absence of a train.
The simplest form of track circuit consists of a power source at one end of the track and a relay contact at the other end. The wheels of a train bridge the circuit between the rails and cause the relay to drop (de-enegergise).
More complex track circuits involve sending frequencies down a rail which can also detect roughly how far away the train is from the detection point.
Most track circuits can sometimes detect a broken rail, a useful safety feature that is lacking in axle counters . Other failures of the track circuit or wiring cause the track circuit to show “occupied”, a fail safe state. There are a very small number of track circuits that deliberately fail in the “clear” state. These are usually “train arrived” type of proving, where a false “train arrived” indication could cause problems. In SimSig, however, Track Circuits will always fail to the 'Occupied' state.
Last edited by GeoffM on 15/09/2016 at 03:00