Are there any specified standards regarding the number of voting options for chemical process interlock sensors, such as three-out-of-two or two-out-of-two?
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Are there any specified standards regarding the number of voting options for chemical process interlock sensors, such as three-out-of-two or two-out-of-two? We only do individual pickups here; we want to have standards that are more convincing.
In the case of a DCS system, the importance of the process is the key factor to consider. If the consequences of a shutdown due to faults in the channels or instruments are severe, such as significant financial losses, a 3-out-of-2 configuration can be used, as the additional cost of instruments is relatively lower compared to the cost of a shutdown. While a 2-out-of-2 configuration improves reliability, it reduces safety; therefore, a good strategy is needed to prevent failures in operation
Hardware Margin.png If it meets the requirements in the SIS reference image