A maintenance policy optimized with imperfect and/or partial monitoring

A system with two s-dependent units in parallel is considered. The on-line unit-level information indicating if both units are running or failed is imperfect and/or partial because of monitoring problems (possible non-detection of the failure time of each unit). A condition-based maintenance policy is optimized taking into account this information. The optimization scheme based on classical martingale results is valid when the observed failure rate of the system is monotone. Cases are identified when such a condition is verified (depending on the monitoring problems and the units failure rates). Numerical results show that the policy based on the on-line unit-level information performs better than a policy based only on the system-level information (considering no on-line unit-level information is available), even if the unit-level information is imperfect and/or partial. Numerical studies also allow identification of locally monotone cases for which the optimization scheme remains valid.