APPARATUS FOR SIGNALLING SYSTEM

22,492 APPARATUS FOR SIGNALLING SYSTEM Apparatus for a signalling system. The apparatus includes a plurality of remote control units each of which is arranged to store self-check timing data therein. This data has a value representing a predetermined period of time the expiration of which corresponds to a predetermined time of day differing from the times of day associated with at least some of the other remote control units. At or following this particular time of day, a self-check operation is initiated for communicating a self-check message, including identification number data identifying the remote control unit, to a centralized communications center. A computer at the communications center receives and processes self-check messages produced by the remote control units and operates in response to each message from a remote control unit to note the identification number data therein and, using this data, to derive self-check timing data for use by the remote control unit in the next self-check operation. The self-check timing data has a value representing a period of time the expiration of which corresponds to the same time of day at or following which the last self-check operation was initiated by the remote control unit. The new self-check timing data is communicated back to the remote control unit for use thereby in initiating the next self-check operation.