Plant Hazard Analysis and Safety Instrumentation Systems

5.0. Safety Instrumented System Logic Solver

It is a well-known fact that in order to achieve plant safety, it is necessary that in SIS loop all the three basic components, viz. sensor, logic solver, and final element must be reliable. Although from the reports it has been found that 8–10% of failures are due to logic solver, yet proper care is taken to see that logic solver is all the time available. Even though failure rate of logic solver is lower, yet it is important because in SIS loop logic solver actually takes the corrective actions. In order to achieve the combination of safety and fault tolerance, a reliable SIS is required, which can bring the plant to a safe state when necessary. Until recently, the thought of a safety system brings ...