Reset sequence follower

Automatic circuit recloser. A self-controlled device for automatically interrupting and reclosing an alternating-current circuit, with a predetermined sequence of opening and reclosing followed by resetting, hold closed, or lockout. 

Race elimination. Race conditions can exist in the circuit because there was no accounting for the period of time for which a signal stays at a particular logic level between events. Three types of race conditions are possible not enough time to synchronize an event before another on the same wire cancels it out a set or reset AND condition that may never be true because one of the input events is followed too closely by another on the same wire and a set or reset condition that is true at other times during the sequence of events and will cause an unwanted setting or resetting to occur. 

During start up of a process unit operation there may be indicators to show that the SIS cannot permit start up until certain conditions have been met or reset. As these clear down the next step in the start up can be followed. These indicators are sometimes known as permissives and are used as milestones in a start up sequence. 

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