Must programming within the SIS system use inverse logic?
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I have a question: must programming within the SIS system use inverse logic?
It’s not mandatory; for safety in case of power loss, it’s better to use inverse logic……
No, just the DI point is sufficient
This is likely related to the design; being counter-intuitive has its advantages – it gets triggered in the event of a power loss, whether it’s due to a faulty sensor or a broken connection
Perhaps it wasn’t explained clearly enough; let me restate it: The DI and DO points are definitely triggered at bit 0, while bit 1 is in normal operation； Can we use a 1-bit flip-flop for the logic related to input and output, with 0 representing the normal state? Are there specific regulations that outline this?
It’s probably related to the habits of the design institute*. But being illogical actually fits with SIS’s safety characteristics
I’ve found the relevant standard: HG/T20511-2014 Guidelines for the Design of Signal Alarm and Safety Interlock Systems. Note 4.3.1 explains it very clearly.