DCS and SIS share one isolation valve; how is it usually wired?
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As the title suggests, without considering whether it is compliant or not, how is it achieved that SIS and DCS both interlock with the same isolation valve? Are two solenoid valves connected in series to the isolation valve, one connected to the DCS and the other to the SIS? What about the feedback signal, one or two?
Feedback is sent to the SIS, and communication takes place between the SIS and the DCS.
It’s not allowed to connect them in this way; the sis units must be separate. You can only add another valve
Both DCS and SIS use normally closed contacts; the two outputs are connected in parallel and sent to the field solenoid valves. Valve position feedback can be achieved using two intermediate relays to feed the signals into the DCS and SIS systems respectively.
Parallel output is not possible; priority must be given to the SIS. If the SIS interlocks, the valve cannot be actuated； SIS is not interlocked; it is controlled by DCS
SIS priority? What kind of prioritization method? Do you understand? Which one acts first depends on the set values; generally, the SIS serves as the final level of protection. By \"priority,\" do you mean that the SIS acts first? You tell me about it
If SIL1 is used as the cut-off valve for high liquid level at the tank inlet, and when SIS and DCS are used together with DCS taking control, it is not necessary to deactivate the SIS interlocks. In this case, the solenoid valves of the SIS interlocks remain energized, keeping the air path of the control valves open without affecting DCS control； And when the SIS interlock activates, the solenoid valve is powered off, cutting off the air supply to the control valve; at this point, the DCS cannot control the valve ； However, since DCS and SIS are shared, a new LOPA assessment must be conducted; following this reassessment, there may be changes in the SIL level requirements. It should be noted that the shared equipment components between SIS and DCS have an impact on the requirements for PFD (PFH), HFT, and SC of the SIF. Common use is only permissible under the prerequisites that the requirements for shared equipment components are met, the average probability of hazardous failures is low enough, the relevant SIFs have been verified to meet the requirements of their safety integrity levels, all requirements of the safety lifecycle are satisfied, the impacts of DCS operation and maintenance on the SIS are fully considered, and relevant inspection and maintenance procedures are developed in accordance with functional safety standards.
The feedback signal goes into the SIS via the solenoid valve, and then this feedback signal is transmitted to the DCS. The solenoid valve is controlled through hardwired signals from the DCS
With the DCS switch and the SIS RS flip-flop, the DCS can operate normally only when there is no interlock trigger
It can be connected in the format shown in the diagram, with the DCS and SIS systems controlling separate solenoid valves, and the feedback signals going to the DCS system