Frequently Asked Question

We recently updated our SERH database and noticed that we have an option to add Rosemount 1199 remote seals into our calculations. They are a SIL 2/3 rated device but drop my PFDavg number by 30 points. I cannot get my numbers anywhere near a SIL-2 calc w
Last Updated a year ago

The PFDavg calculation takes many parameters into consideration. Obviously adding components to a SIF will increase its probability of failure (assuming these are all in series/no redundancy), however this is necessary to accurately calculate the performance of your SIF. A product that is certified compliant with SIL x does not necessarily meet a SIL x giving the rest of the components in the SIF including how diagnosed failures are dealt with. Typically we see the final elements being dominant. Without having more details on your specific SIF, do you have the PLC detection behavior set for the sensors, i.e. did you specify that the PLC will detect any out of range signal?

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