Functional Safety 2016

SRS for an inhibit SIF

• Use terminology “inhibit” not permissive. It causes great confusion to refer to a

permissive. The SIF is an inhibit function!

• Consider sensor failure state – typically failed sensor = inhibit.

• Consider software latch of the inhibit signal. Don’t want transmitter latching in

the “no inhibit” state. (PSHH can be the safe state)

• SIL3 requires HFT of 1. This means two final elements!