PLC & Programming

Interlock

Definition

A condition that stops or prevents operation whenever it is present, including while equipment is already running.

Distinct from a permissive, which is only checked at the start request. Anything protecting people must be implemented in a hardwired safety circuit or a rated safety controller, not in standard PLC logic.

Interlocks and PermissivesA permissive lets you start. An interlock stops you. Confusing the two produces equipment that either will not run or will not protect itself.

Interlock

Definition

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