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What Does Proven-In-Use Imply?

The functional safety standards, IEC 61508, IEC 61511, and ANSI/ISA 84.01 each specify the Safety Integrity Level performance parameter for Safety Instrumented Functions. For a Safety Instrumented Function to meet a specific Safety Integrity Level the sum of the average Probability of Failure on Demand (PFDavg) of all components, part of that Safety Instrumented Function, needs to fall in the PFDavg bandwidth related to that Safety Integrity Level.

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