Communication signal
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Based on past design experience, communication signals should not be used only for alarm and display purposes; they cannot be utilized for control and interlocking functions. But no relevant regulatory provisions can be found; I seek advice from experts – which standard contains relevant descriptions.
As I recall, some guidelines state that it is not allowed or not recommended to use communication signals in chaining
It cannot participate in interlocking regardless of whether there are regulations or not. The communication is unstable and prone to interference; if involved in interlocking systems, be prepared for a lot of hassle, as it will be difficult to identify the source of the faults.
Communication signals can only be used for alarm and display purposes; they cannot be used for control or interlocking. What communication signal? Is the Internet considered a communication signal these days, and is it stable?
For instruments, signals transmitted over network cables are considered communication signals, as opposed to those transmitted via direct wiring.
No standards are needed; the delay of communication signals is generally at least 3 seconds or more. How can such a delay be used for control sequences? This single fact is sufficient. The 3-second device might have exploded already
One can refer to GB/T50770 \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\" and HG/T 20511-2014 \"Code for Design of Signal Alarm and Interlock Systems\", which specify the requirements regarding the use of communication signals in interlock systems. Communication signals cannot be used in interlocking.
Both of these specifications do mention something related to chains, but they don’t state that communication prevents participation in or control over chains
The issue lies with Siemens’ safety modules; the SIS interlock signals are all transmitted via communication, using DP PN and other protocols. As long as there is authentication for such communication, I think it should be fine.
Clause 6.1.5 of GB/T50770: Measurement instruments shall not use fieldbuses or other communication methods as input signals for safety instrumented systems.
Are all bus-type instruments that transmit signals via communication unable to participate in interlocking? ? I don’t know what you mean. Maybe what you mean are the security level requirements? ? ?