Single SIL3 output drives Well Tried Load

I have a single channel output design which uses SIL3 Qx8_PP to drive a Hydraulic Valve with no feedback.

If the Hydraulic valve is a well tried component with High MTTFd, is it possible for this to be a PLc circuit? Or is this specifically excluded by the manual?

In the SAFEX installation manual Section 13.3.4.2.1 Single-channel switching relay or semiconductor output without testing it states that only PLb is achievable.

In Table 90 there is mention of SIL2 outputs with Category B circuit. However, there is no mention of SIL3 Outputs with Category 1 circuits. Is this a deliberate exclusion or is this perhaps something that was not thought of?

https://www.boschrexroth.com/media/a3953377-1914-4249-94e7-a6dfa2df9292

Best reply by Dias

Hello Bruce,
attached please find a Sistema Performance-Level calculation, as I would do it for your application.In my opinion the examples, meant with good intentions, in the Safex-C manual are sometimes a bit misleading.

In my opinion it is completely fine to use the 2A output without testing and a well tried valve with the result of PL=c.

Hydr.zip

4.04KB

View original

1 reply