What's the difference between PFD and PFH?
I use Markov model to calculate PFD. How to calculate PFH using Markov model?
Hi Dai Fei,
Please refer to IEC 61508 for the details regarding PFD and PFH. As far as I understood, PFH is rate or frequency, but PFD is function of time. The relation can be simplified as:
PFD = PFH(detectable failure in time interval T) * T/2 + PFH(undetectable failures) * t
I think, from Markov Model viewpoint, PFH equal to sum of the element of transition-matrix P in
PFH is the average of the matrix P over a period time. After you sum or integrate the matrix P, you need to divide the sum by the time Tm to get the PFH.
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