Design of a Small-Sized Interlocking System with High Availability

An Interlocking System consists of an interlocking logical unit and power controlling unit. After this logical unit calculates the relationship among the train position, the rail shifting position and the signal, it decides the aspect of signal. Power controlling unit supplies electrical power to the switch motor and the bulb of signal according to the decision of the logical unit. This paper proposes a small-sized interlocking system which uses triplex redundant off-the-shelf controller with fail-safe checker as a interlocking logical unit. 2-outof-3 voter circuit ensure the safety of parallel output from the interlocking logical unit. This circuit satisfy the condition of “Totally Self-Checking” (by D. A. Anderson) and also the condition of “High Availability”. In other words, any kind of a single fault never leads hazardous state and this circuit has ability of safety after single fault occurring.