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为了能够定量评估安全系统的可靠性,并考虑影响安全性、可用性的诸多因素,提出用Markov模型定量计算安全系统可靠性指标的方法。通过状态转移矩阵预先迭代相乘来降低计算量,并给出了使计算量最小的最佳迭代次数。计算结果表明:要求时失效概率随迭代次数增大而增大,且在最佳迭代次数误差仅为1%,说明该方法是保守又安全的,有良好的计算精度。功能测试周期增大1倍后,安全完整性下降了一个水平,故应选择正确的功能测试周期以保证达到目标安全完整性水平。
In order to quantitatively evaluate the reliability of the safety system and consider the factors that affect the safety and availability, a method of quantitatively calculating the reliability index of the safety system by using the Markov model is proposed. The state transition matrix is pre-iteratively multiplied to reduce the amount of computation, and the optimal number of iterations is given to minimize the amount of computation. The results show that the probability of failure increases with the number of iterations, and the error of the best iteration number is only 1%. It shows that the method is conservative and safe with good calculation accuracy. When the functional test cycle is doubled, the safety integrity is reduced by one level. Therefore, the correct functional test cycle should be selected to ensure that the target safety integrity level is achieved.