Must the instruments and control equipment in the SIS system be SIL-certified?
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I have a rather naive question: do the instruments and control devices in the SIS system necessarily need to be SIL-certified? I have been working on the renovation of a SIS system recently, and after consulting with several well-known manufacturers, I found that the price of instruments and control devices with SIL certification is twice or even several times higher than that of those without such certification. If all instruments and equipment were to be of the SIL-certified type, the cost would be unaffordable. So there is the previous question
On-site instruments do not necessarily need to be certified, but the manufacturer must provide parameters such as dangerous failure undetected, so that it is possible to calculate the PFD.
In my opinion, it’s not about obtaining a SIL certification; rather, it’s necessary to evaluate the SIL level of the SIFs within the SIS, to determine whether they meet the requirements based on the characteristics of the process. Any deficiencies need to be addressed. Our instrumentation and control equipment currently has TUV certification.
The regulations require something that is practically impossible to achieve; the cost is too high, and it does not reflect reality.
It’s not necessary; as long as you have the relevant parameters, calculate the PFD for those without SIL certification, convert it to a SIL rating, and then check whether the SIL rating of the entire circuit meets the requirements
Not all instruments need to have an SIL safety integrity level certification. The SIS SIL3 certification level should be a comprehensive certification.
A straightforward question, but indeed difficult to answer. It’s not about whether it is necessarily needed, but rather how theory matches practice. To give the simplest example, if there is only one loop, one sensing element, one logic server, and one final element, and all of them achieve SIL3, then, without considering redundancy, this small system essentially reaches SIL2 to SIL3 (the reason it’s not certain is due to other assumptions and parameters as well). So, for you, requiring these instruments to have SIL certification is the simplest way to ensure that this small system meets SIL3 certification, as it means you have to do fewer things ； Of course, you can also request that these instruments not come with SIL certification, and instead provide only the parameters needed to calculate the PFD, so that you can carry out the calculations yourself. Even if we ignore the issue of integrity, to assess the safety integrity of a system, it is necessary to take into account the failure rate of each component (SE/LS/FE). Do you think you’re capable of handling this calculation and assessment process? Don’t you find it cumbersome? Then, if some odd manufacturer claims to be able to provide something but fails to do so later on, or if the data they give you is inconsistent over time or changes, that’s when your troubles start~~~ What if the manufacturer provides directly the SIL certification issued by an international authoritative certification body, which already includes all the necessary parameters? Wouldn’t it make the evaluation process and results of the safety instrument system more manageable and reliable? We’re all workers; there’s no need to complicate things too much ； Perhaps this is also the advantage of standardization, and one of the reasons why authoritative certification bodies remain successful over time.
Authentication is not necessary; in IEC61508, empirical evidence can be used – that is, you can prove that the requirements for a certain SIL level are met based on your own experience of use and the data provided by the manufacturer. Authentication is actually just a gimmick. There are also few certified ones in the domestic market.