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Thursday 11 August 2005

Diagnostic tests vs proof tests: The IEC 61508 Way

Periodic proof testing is a common practice in industry to verify whether safety equipment can perform its intended function. It is used by end-users in the process, oil&gas and chemical industries to detect hidden failures and improve the reliability of their safety systems. What is not correct though it to use the proof test as a diagnostic test and take credit for it when calculating the safe failure fraction. This is a common misconception in industry.

TUV Rheinland, together with Risknowlogy, has written a paper to explain the differences and the effects diagnostics and proof tests have on the performance of safety instrumented systems. The paper demonstrates the difference between diagnostic tests and proof tests and what effect they have on the PFD of the safety function. A special performance indicator is used to express this influence and show the effect.

Download your copy of the paper