Definition:
A Proof Test is a planned, periodic test carried out to detect dangerous undetected failures in a Safety Instrumented Function (SIF) or its components that are not detected during normal operation. Proof testing is critical to maintaining the designed Safety Integrity Level (SIL) of a system over time.
Proof tests can vary depending on the component and the approach by the facility.
Key Points:
- Must be thorough enough to detect failures not caught by automatic diagnostics.
- Proof Test Interval (TI) directly impacts the Probability of Failure on Demand (PFDavg).
- Proof Test Coverage (Cpt) measures how effective a proof test is at detecting hidden dangerous failures.
- Proof testing requirements should be clearly defined in the Safety Requirements Specification (SRS).
Example:
A shutdown valve is stroked and functionally tested every 12 months to verify it closes properly in response to a trip signal, thereby fulfilling its proof test requirement.
See also: Proof Test Interval (TI), Proof Test Coverage (Cpt)
Cited Source:
- IEC 61511-1:2016, Clauses 11.9 and 16.2.