RAM Commander may also calculate the PFH and PFD parameters as required by the IEC 61508 functional safety standard. You may get this calculation from the reports menu.

 

 

PFD (Probability of failure on demand) is calculated by the following formula:

where U is instantaneous unavailability at time t (Q(t) - see the Tree Unavailability calculation paragraph).

 

PFH (Probability of Failure per Hour) is calculated by the following formula:

where W(t) is frequency at time t (see the Frequency W(t) Calculation paragraph).