SIL4 Timer relay

Timer for delaying the attraction of an N.S1 signaling relay

Timers are used to delay the attraction of a “N.S1” type signaling relay. They are usually used with track circuits to suppress possible nuisance caused by point-and-track kills.

Placed as an interface between an N.S1 relay and its command, the relay can only activate following a continuous command of a selected minimum duration. Any disappearance of the command, however short, resets its time delay and drops the relay if the latter is active.

This block has a SIL4 security level. In the absence of a command, a fault cannot cause the output relay to activate. Likewise, faults cannot shorten the selected time delay.