17.1 Reliability and Availability A chemical reactor is protected against runaway by injection of an inhibitor, which is triggered by a temperature switch high (TISH). Since the value of the batch is...

17.1 Reliability and Availability

A chemical reactor is protected against runaway by injection of an inhibitor, which is triggered by a temperature switch high (TISH). Since the value of the batch is high, it is important to avoid false alarms (active failures), which lead to unwanted inhibitor injection and to the loss of a batch. On the other hand, process safety is important too, thus passive failures (failure on demand) must be avoided. Consequently, for the temperature sensor, a voting system with an architecture two out of

three (2oo3) was chosen.

Question

1.Explain qualitatively why a voting system of type 2oo3 represents a good compromise between availability and reliability for triggering the inhibitor injection.