What is proof testing and why is it important for SIS?

Proof testing is periodic testing of SIS components to verify they will function on demand and to detect dangerous undetected failures. Since SIS components may sit idle for long periods, failures can accumulate undetected (dangerous undetected failures reduce PFDavg). Proof tests exercise the complete safety function from sensor through logic solver to final element. Test intervals are determined by SIL calculations - shorter intervals required for higher SIL or lower-quality components. Proof test procedures must achieve high diagnostic coverage and be documented for regulatory compliance.