COMPUTERS CAN NOW PERFORM VITAL FUNCTIONS SAFELY
O B Linde · Railway gazette international · 1979
Early attempts to apply data processors to tasks previously reserved for vital relays concentrated on redundancy and voting systems as protection against hardware failure. When logic performed by fail-safe relays, with predictable failure modes, is replaced by computers with unpredictable failure modes, several factors must be considered. Not enough attention was devoted to software with the computers and no complex program can be considered foolproof even after a lengthy period in service. L. M. Ericsson utilizes parallel running of non-identical programs with multi-stage comparison to guard against failures. This technique has been applied to large interlockings and to on-train signaling and speed-control systems. Ahead is the possibility that the functions of logic and output checking may be carried out within a single microprocessor, using fault-tolerant programming.