Reliability Analysis of Multi-state System Based on Irrelevance Coverage Model

The irrelevance coverage model (ICM) is an extension of the imperfect fault coverage model (IFCM), which considers both uncovered failure and component irrelevance. In the ICM, an irrelevant component cannot occur an uncovered failure since it will be isolated (shutdown) from the system. In traditional ICM, the irrelevant component is triggered by a covered component failure. However, in the multi-state system (MSS), the degrade state of the operational components may also cause the other component to be irrelevant. To address this issue, the minimal irrelevance trigger (MIT) is redefined for the MSS by analyzing the relation between component states and system demand. Further, we extend the ICM to the MSS. We apply multi-state multi-valued decision diagram (MMDD) to calculate the reliability of the MSS in the ICM. The experimental result shows that not only the failure of component but also the deterioration of component may lead to component becoming irrelevant in the MSS.