Regarding whether DCS can send signals to SIS
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I would like to ask the experts here: can DCS send dry contact DO signals to SIS? For example: a pneumatic on/off valve – water inlet valve controlled by DCS, and an emergency shut-off valve – feed valve controlled by SIS. Under normal conditions, the water inlet valve is closed while the feed valve is open. In the event of a hazard, the DCS must open the water inlet valve; simultaneously, the DCS sends a signal to the SIS, which then shuts down the feed valve via interlock. Is this feasible? What should be done if it’s not feasible?
It shouldn’t be possible; if it really involves safety concerns, then everything has to be included in the SIS
It’s possible in terms of operation, but it’s actually not allowed. The SIS system requires specialized instrumentation configuration. The SIS system is implemented to ensure system security. If two systems use the same instruments, it becomes dangerous when the DCS instruments fail and both the control valves and isolation valves stop working as well. So, you’re willing to install a cut-off valve, but not willing to add a gauge – it’s sacrificing something important for a trivial matter.
What you mentioned is doable in terms of operation, but the SIS logic is reversed.
The SIS system should not interfere with or replace the process control (DCS) system; it should always remain independent of the process control system.
This emergency shut-off valve should be controlled by the auxiliary control panel and on-site buttons, so as to be activated in emergency situations. There must be a safety reason for such a design. If a DCS signal can be used to trigger the operation of the SIS, then wouldn’t it be great if that operation could be carried out directly through the DCS? But the DCS security is no longer there, so it’s not possible.
SIS is a safety system that is strictly independent of DCS. The answer is no
Thank you all for your guidance; I have revised the plan again.