The Operation Modes of E/E/PE System and Their Influence on Determining and Verifying the Safety Integrity Level

摘要

The standard PN-EN 61508 introduces some probabilistic criteria for the E/E/PE systems that can operate in different modes of operation, which are related to the safety integrity level (SIL). For the control and protection systems, operating in a low demand mode, the criterion is the average probability of dangerous failure on demand PFDavg. In case of systems working in a continuous mode of operation or high demand, the criterion is probability of dangerous failure per hour PFH. In practice, the E/E/PE systems implement many safety-related functions (SRFs), which have different requirements for high and low demands. Thus, there is the problem with choosing proper probabilistic criterion for determining required SIL for a safety-related function to be implemented by these systems as well as in the process of quantitative verification of SIL for considered architectures.