New models of safety-critical systems are built here. In these systems, when components fail, different defect states have different effects, hence need different ways to measure. In the models, there are two kinds of...New models of safety-critical systems are built here. In these systems, when components fail, different defect states have different effects, hence need different ways to measure. In the models, there are two kinds of failure modes of the components： one could be called failed-safe, and the other may be named failed- dangerous In practice, the so-called failed-dangerous components may lead a system to peril. However, failed-safe components will not. Reliability and safety issues are analyzed using Ion-Channel modeling theory to get count of repairs and time duration before the system becomes dangerous. In the closing section a numerical example is presented to illustrate the results obtained in the paper.展开更多
Quantitative safety assessment of safety systems plays an important role in decision making at all stages of system lifecycle, i.e., design, deployment and phase out. Most safety assessment methods consider only syste...Quantitative safety assessment of safety systems plays an important role in decision making at all stages of system lifecycle, i.e., design, deployment and phase out. Most safety assessment methods consider only system parameters, such as configuration, hazard rate, coverage, repair rate, etc. along with periodic proof-tests （or inspection）. Not considering demand rate will give a pessimistic safety estimate for an application with low demand rate such as nuclear power plants, chemical plants, etc. In this paper, a basic model of IEC 61508 is used. The basic model is extended to incorporate process demand and behavior of electronic- and/or computer-based system following diagnosis or proof-test. A new safety index, probability of failure on actual demand （PFAD） based on extended model and demand rate is proposed. Periodic proof-test makes the model semi-Markovian, so a piece-wise continuous time Markov chain （CTMC） based method is used to derive mean state probabilities of elementary or aggregated state. Method to determine probability of failure on demand （PFD） （IEC 61508） and PFAD based on these state probabilities are described. In example, safety indices of PFD and PFAD are compared.展开更多
基金Sponsored by 211 Project of Minzu University of China(021211030312)
文摘New models of safety-critical systems are built here. In these systems, when components fail, different defect states have different effects, hence need different ways to measure. In the models, there are two kinds of failure modes of the components： one could be called failed-safe, and the other may be named failed- dangerous In practice, the so-called failed-dangerous components may lead a system to peril. However, failed-safe components will not. Reliability and safety issues are analyzed using Ion-Channel modeling theory to get count of repairs and time duration before the system becomes dangerous. In the closing section a numerical example is presented to illustrate the results obtained in the paper.
文摘Quantitative safety assessment of safety systems plays an important role in decision making at all stages of system lifecycle, i.e., design, deployment and phase out. Most safety assessment methods consider only system parameters, such as configuration, hazard rate, coverage, repair rate, etc. along with periodic proof-tests （or inspection）. Not considering demand rate will give a pessimistic safety estimate for an application with low demand rate such as nuclear power plants, chemical plants, etc. In this paper, a basic model of IEC 61508 is used. The basic model is extended to incorporate process demand and behavior of electronic- and/or computer-based system following diagnosis or proof-test. A new safety index, probability of failure on actual demand （PFAD） based on extended model and demand rate is proposed. Periodic proof-test makes the model semi-Markovian, so a piece-wise continuous time Markov chain （CTMC） based method is used to derive mean state probabilities of elementary or aggregated state. Method to determine probability of failure on demand （PFD） （IEC 61508） and PFAD based on these state probabilities are described. In example, safety indices of PFD and PFAD are compared.
