PLC & Programming

Permissive

Definition

A condition that must be satisfied before equipment is allowed to start.

Checked at the start transition rather than continuously. A permissive that is also enforced while running is really an interlock, and it is worth deciding which you mean before writing the logic.

PermissivesThe conditions that must be true before a device may start: how permissives differ from interlocks and trips, the list a pump or feeder usually needs, coding them so the HMI can say why a start was refused, and the rules for time delays and bypasses.

Permissive

Definition

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