SIS and DCS instrument classification issue
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Issues regarding the installation arrangement of SIS and DCS instruments: 1. Is it acceptable for SIS and DCS to share one pneumatic valve, with two solenoid valves used in series? (I recently heard that experts went to the factories in the area around our facility to conduct inspections, stating that this practice is not allowed and that two separate pneumatic valves must be installed.) 2. Regarding tank pressure: The SIS and DCS each use separate pressure transmitters, but they share the same pressure sensing point. Is this acceptable? Does the source point still need to be separated? 3. For the tank level gauge, since there are no additional mounting points on the tank, it is possible to use only one remote transmitted level gauge. A two-way safety barrier (one that meets the SIL rating) should be installed within the SIS cabinet, with one output connected to the DCS and the other to the SIS. Is this approach satisfactory?
To your first question, it definitely can’t be done that way; two separate valves are necessary. 2. The same source can be used. 3. It does not meet the requirements, but it can be explained – after all, the equipment determines what is impossible for us.
1. For pneumatic valves equipped with dual solenoids used in SIS and DCS systems, the safety instrument level must be taken into consideration. Those of Level I can be used together, but SIS control takes precedence over DCS control. Systems of Level II do not meet the requirements; safety standards dictate that the actuating elements should be separate. While dual solenoids do allow the control elements to be separated, the actuating elements themselves remain of the same type. 2. It is possible to use the same source for two separate transmitters, but the user must consider maintenance issues to prevent misoperation of the SIS due to maintenance work on DCS instruments. 3. As with the first question, consider the safety level; if it is level II, it does not meet the requirements, as the specifications dictate that the sensors should be separate.
If followed strictly according to the standards, nothing will work. Forget about creating a new device. For the renovation of old equipment, as long as you can convince the design institute to prepare the drawings for you, they will take responsibility for it. Because there is such a rule: if modifying the old device would cause greater harm, a compromise approach can be used.
GB/T50770 \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\"