CyberCertPrepOT Security FundamentalsOT Fundamentals: Safety Systems & Physical SecurityMEDIUMFree question
A team considers stretching the proof test interval of a one out of one function from one year to two years. How does this change the average PFD?
- A.It leaves the average PFD unchanged
- B.It roughly doubles the average PFD
- C.It roughly halves the average PFD
- D.It squares the average PFD value
Why B is correct
For a simple single channel the PFDavg grows in proportion to the proof test interval, so doubling the interval roughly doubles the PFD. The function can drift out of its SIL band even though no hardware changed.
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