OT - SIL Verification

I am working on the design for a Compact GuardLogix system. All of the inputs are simple pushbuttons that will activate a simple safety sequence. This is a SIL 1 system.

Does anyone have an example for SIL verification calculation? More specifically, I need assistance in coming up with a failure probability (PFD) for the pushbuttons. The IEC standards basically admit that a lot of field devices don't publish these numbers.

You can download something like Pilz PAScal or Sistema and import the manufactorers library and it will give you all the info you need.

We use PAScal and you can build your safety functions using the manufacturers libraries and it will produce a PDF for you for your technical file in about 10 minutes.

Sistema is free, but has a learning curve. PAScal you have to pay for, but from memory you can use it unlicensed on a job to job basis. You then just download the sistema library for any manufacturer.

I know that Pilz have a software application Pascal for calculating SIL and PL levels.

The producer of push buttons that are used in a safety related circuit would need to provided the numbers you need. Buttons or switches for which these numbers are not available should not be used in a safety circuit.

Toine said:

The producer of push buttons that are used in a safety related circuit would need to provided the numbers you need. Buttons or switches for which these numbers are not available should not be used in a safety circuit.

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You can still use them in the circuit, the machinery safety standards give guidelines as to what numbers to assume if they are not published. I guess they are working off a "worst case" scenario, so without the numbers, the results you get might be significantly lower than the reality might suggest.

I haven't used Pascal, though I've seen it used, and I believe that it takes those "worst case" assumptions into consideration when working it out.

E-Stop buttons should be in the program with numbers, but things like reset buttons and such aren't safety devices and I don't believe they effect the SIL rating.

As the gentleman says above, Reset PBs aren't part of the safety function and can be ignored. It is even possible to have a reset PB on the screen on the PLC

Thank you for the help so far. I have been using SISTEMA. Rockwell provides a SISTEMA library which contains information for many of their products. But one thing I haven't been able to find is the useful/expected lifetime of components. I can't even find it for the Compact GuardLogix hardware.

Also, I see a lot of reference to proof test intervals, but am not sure how to calculate those either.

Are those values obtainable in SISTEMA or pascal?