Proof testing is a requirement of safety instrumented systems to ensure that everything is working and performing as expected.
Testing must include the verification of the entire system, logic solver, sensors, and final elements.
The interval is the period of time that the testing occurs. The testing frequency varies for each SIS and is dependent on the technology, system architecture, and target SIL level.
The proof-test interval is an important component of the probability of failure on demand calculation for the system.