1989 – July – Moore – Communications for Signalling Systems

T. G. Moore, P. Eng.,M.I.R.S.E. Development Engineer, Signals Standards CityRail Engineering, State Rail Authority of NSW Ever since signalling safeworking advanced beyond the stage of a man with a red flag walking in front of the train, there has been a need to communicate information about the status of train movements to distant locations. Initially systems used the telegraph network which shared the communications network between signalling requirements and the need to communicate more general information. Subsequent systems such as block instruments and electric train staff used a dedicated circuit to meet their communication requirements. More complex systems involving relay interlockings used multiple dedicated electrical circuits to communicate the information status to relays at the distant location. These systems effectively absorbed a very wide band of the available circuits to transmit a small amount of information with a high level of security and integrity.