Does the SIS system count IO points for redundancy?
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As the title suggests, when counting the IO points in a SIS system, is it necessary to have 1:1 redundancy for all types of points—AI/AO/DI/DO—and is this done to ensure that all cards are configured with redundancy? The SIL ratings are SIL1 and SIL2; this should have nothing to do with the actual SIL level, right? Is there any relevant standard that serves as a basis for this?
In accordance with GBT 50770-2013 Code for Design of Safety Instrumented Systems in Petrochemical Industries, 5.0.14 states that redundant technology shall be employed for components such as the central processing unit, input/output units, communication units, and power supply units of logic controllers. As I understand it, if you are to follow this standard, then it should be redundant
SIL2 level, redundancy is required
This situation is relatively rare; once the SIL rating is clear, it’s sufficient to consult the relevant design institute. SIS generally requires triple or dual redundancy for the CPU; moreover, there is no need to use a SIS system for SIL1 levels, as DCS systems can meet the requirements of SIL1 on their own
Generally, redundancy is used to improve safety and reliability. If it can be ensured that the SFF of the I/O cards is large enough, that’s also fine