I did my homework, purchased certified devices, and specified physical redundancy. I expected an uneventful SIL Verification but the assessor is telling me that I have functions failing Architectural Constraints in the sensor and final element groups. How can that be?
Low demand mode Safety Instrumented Function (SIF) design is verified against three criteria:
- Probability of Failure on Demand
- Architectural Constraints
- Systematic Capability
Probability of Failure on Demand (PFDavg) is a statistical evaluation based on random failure data representing the likelihood that a SIF will fail to perform properly when there is a process demand. Systematic Capability is an evaluation of the potential that SIF will fail…