Flammable toxic gas signal connected to PLC
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Can combustible and toxic gas signals be connected directly to the PLC? Does the PLC have dedicated cards for receiving signals from combustible and toxic gases?
The project I just worked on contained toxic substances that ended up in the PLC; otherwise, there would be no other control system available.
Is it necessary to install a separate AI card on the PLC specifically for receiving toxic gas alarm signals?
Gas alarm signals usually go into a separate alarm system, using independent audible and visual alarms. If the conditions are not met, at least it should be connected to a separate terminal block and a separate AI card for the PLC.
This practice already violates existing regulations.
Firstly, are the combustible and toxic signals you mentioned purely indicative alarm signals? In that case, it should be placed in an independent system and cannot share it with the process control system. If participating in fire safety interlock protection, the SIL level needs to be considered. Analyze each specific problem individually. The first one is common
Please refer to clause 5.3.2 of standard GB50493-2009； Standard SY6503-2016, Clause 6.3.2.
I studied 5.3.2 of GB50493. Forgive me, I only remembered the fourth one.
It is not possible to connect it to a PLC; an independent gas detection and alarm controller must be used. The current standards refer to GB50493-2009, but these standards may be updated this year or next. It is best to design in accordance with the new draft version, otherwise further modifications may be required after the system is built.
Forget those replies above – you think they’re all some fancy petrochemical projects; if things were done according to your design concepts, those companies would go bankrupt in just a few days. That is, large design companies can at most offer standalone components.
The inspection and audit personnel have now clearly stipulated that a separate GDS system must be established for flammable and toxic gases; if such a system is not available, it is temporarily acceptable to integrate it with the SIS system. However, it is not allowed to connect flammable and toxic gases to DCS or PLCs used in production, and corrective action will be required. Differences may exist depending on the region