Abstract: A track circuit receiver is driven by the signal across an impedance bond and operates a relay to disconnect the signal so causing the relay to cycle. In series with the receiver input is a signal from the center tap of the impedance bond, which is normally at earth potential and does not affect the relay cycling. In the event of a rail break a significant output is obtained from the center tap, which either cancels or replaces the original receiver input signal but on a permanent basis uncontrolled by the relay. The relay therefore ceases to cycle in either event and thus provides a break indication.

Abstract: A data communication apparatus adapted for use as a train describer system has a multiplicity of modules serially connected in a closed loop, each such module being arranged to transmit data to, and receive data from the two adjacent modules in the loop, a plurality of the modules located at spaced positions around the loop also being "interconnection" modules adapted to transmit data directly to and receive data directly from the adjacent interconnecting module or modules of the plurality.