What components are included in a safety instrumented system?
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This post was last edited by Huagong Jianghu on 2020-3-6 at 12:42. I am majoring in process engineering. My knowledge of instruments is only superficial. I’ve been learning *SIS recently. It is known that a safety instrumented system generally includes a sensor subsystem, a logic controller subsystem, and an actuator subsystem. It’s not very clear what specific components are included in each of the three systems when further broken down. The sensors should be arranged in the following order: field measurement elements, transmitters, and safety barriers. The logic controllers should be arranged in the following order: input cards, DI cards (are these two cards the same thing?) ）、CPU, DO card, output card (are the two the same thing? ), the actuators include: relays, safety barriers, and control valves. Is this understanding correct? I would appreciate some guidance from experts in instrumentation: what exactly is included in each step? What are the basic functions? Which ones are one-to-one?
I have a question: when performing SIL calculations, where is the boundary between sensors, controllers, and actuators?
I have a question: When performing SIL calculations, where are the boundaries between the three sections? Thank you
SIL calculation is carried out on a circuit basis.
Yes, that’s right. When calculating an SIF loop, it is necessary to calculate the PFDavg for the sensor, controller, and actuator separately and then add them together. I noticed that the examples in the literature are quite brief. During calculation, some methods add up the failure rates of the sensing elements, transmitters, and safety barriers to obtain the overall failure rate of the sensor, thereby calculating its PFD; controllers only have their CPU’s failure rate taken into account, while actuators may include solenoid valves or not. Where exactly is the boundary between the three parts?