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Proof Test and PFD
avg
•
In the context of IEC 61508 / 61511; the object of proof testing is to reveal
dangerous undetected failures, e.g. excluding failures detected by automatic
diagnostic mechanisms.
•
Dangerous undetected failures are failures that will result in the loss of the
safety function, not necessarily deviation from equipment specification.
•
Typically the dangerous undetected failures along with the proof test
frequencies are the main driver behind the achieved PFD
avg
of a Safety
Function.
•
Therefore the estimate PFD
avg
of a Safety Function will be greatly affected by
implementing a different proof test frequency.