A condition-based inspection-maintenance policy for critical systems with an unreliable monitor system

In real-world industrial systems, many critical systems that achieve the main function are typically continuously monitored by a monitor system to ensure their reliability. Both the critical system and the monitor system degrade gradually. Research on the maintenance design of a critical system with an unreliable monitor system is limited. Hence, this paper proposes a condition-based inspection-maintenance policy for this kind of system. When the monitor system functions well, the performance of the critical system is obtained by the monitor system, while the status of the monitor system is detected by periodic inspections. When the monitor system fails, the performance of the critical system and the monitor system are detected by examinations when a warning is given or at each periodic inspection time. The corresponding maintenance actions are performed when their performance exceeds the predefined thresholds. The semi-regenerative process is used to calculate the long-run expected cost of a two-component critical system with a monitor system. The simulation method is introduced for a multi-component critical system with a monitor system. Finally, the proposed policy is applied to the battery pack system with a battery management system in EVs to illustrate the feasibility and efficiency of the proposed policy.