iec 61508 PFD/PFH?
iec 61508 PFD/PFH?
(OP)
Hello!
I have so called "continuous process". I'm trying to calculate failure probability of safety function. Process safety function demand is estimated 0.3/year. Does the term system equivalent down time"TGE" in PFD calculation means that for example if i have measurement combination 2oo3 and it is down so my whole process is down. So is it wrong to use PFD calculation and i have to use PFH calculation despite safety function demand says use PFD calculation? I have to think whole process not only demand of safety function, correct?
-jussu
I have so called "continuous process". I'm trying to calculate failure probability of safety function. Process safety function demand is estimated 0.3/year. Does the term system equivalent down time"TGE" in PFD calculation means that for example if i have measurement combination 2oo3 and it is down so my whole process is down. So is it wrong to use PFD calculation and i have to use PFH calculation despite safety function demand says use PFD calculation? I have to think whole process not only demand of safety function, correct?
-jussu





RE: iec 61508 PFD/PFH?
With a 0.3/year demand rate you are covered for >0.6/year prooftest for "low demand". The limiting factor is probably the final element prooftesting.