PFD and PFH

Fei Dai

Prodigy 70 points

What's the difference between PFD and PFH?

I use Markov model to calculate PFD. How to calculate PFH using Markov model?

Thanks

over 14 years ago

0 QJ Wang over 14 years ago

TI__Guru**** 196776 points

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

Regards,

0 Fei Dai over 14 years ago in reply to QJ Wang

Prodigy 70 points

I think, from Markov Model viewpoint, PFH equal to sum of the element of transition-matrix P in dangerous state. Right?

0 QJ Wang over 13 years ago in reply to Fei Dai

TI__Guru**** 196776 points

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.

Regards,

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PFD and PFH