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Information Technology Journal
Year: 2013  |  Volume: 12  |  Issue: 20  |  Page No.: 5477 - 5481

Calculation of the Probability of Failure on Demand of Redundant Systems Using Markov Model

Yanli Zhang, Jun Dai and Dasheng Zhu    

Abstract: It is necessary to calculate the "Probability of Failure on Demand" (PFD) and "Probability of Failure of Safety" (PFS) for the assessment of the "Safety Integrity Level" (SIL) of a Safety Instrumented System (SIS) in the international standard IEC 61508 (2000). To fulfill the high safety and availability requirements redundant channels are often used which are normally homogeneous. Whereas, in order to minimize the potential Common Cause Failures (CCF) for very high safety requirements (e.g. SIL4) it may be advisable to build up a heterogeneous system with different hardware/software platforms. For such type of heterogeneous systems the calculation of the PFD is a challenge because the failure rates of the particular channels are different in general and no formulas are included in the standard. Within the scope of this work, the physical block diagram and the voting diagram for 2oo3 redundant system are introduced, then based on them, the Markov-model method is used to simulate these redundant systems, including both the homogeneous and the heterogeneous systems.

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