Forum Topic

Montag, 19. Mai 2008 10:53:10

PFS（probability of failing safely）is one of the most important parameters of the SIS(safety instrumented system), which is related with economy of factory. It does not matter if safe failures are detected or not .both will cause a shutdown. Then it will waste the money. So I think it is very important, But I don’t find the formula of PFS in the IEC61508. I just find the formula in the Control Systems Safety Evalution and Reability. Besides this ,where can I find PFS formula in other way, then I can compare those.

Samstag, 07. Juni 2008 13:49:35

There are books available that list PFS formulas. But you should not use these standard formulas. You should learn to make your own reliabilities models with markov, fta, or other modeling tools.

Montag, 14. Juli 2008 09:54:46

I just have a question. When we calculate the level of SIS, we use the concept of PFDavg which means the average of PFD happens during the whole process, so, but I can’t find the concept of PFSavg that use in SIS. Does it exist?

Mittwoch, 16. Juli 2008 18:41:42

61508 and 61511 do not talk about this. They do no care about spurious trips.

ISA S84 and its technical reports do talk about PFS.

But just because it is not in a standard it does not mean it is not important.

Donnerstag, 17. Juli 2008 05:03:35

First of all,thank you for help me .I find that there is a new concept (STL) in your web, which will be

more convenient to calculate the PFS. Can you mail me more

information about STL. Thank you very much!my e-

mail:2002043127@163.com

Samstag, 18. Oktober 2008 04:29:51

nice to meet you ! now I want to do sil research, can you send me the pdf about Control Systems Safety Evalution and Reability if you have? thank you very much ! my e_mail is zgdstormflash@gmail.com