Determination of inspection intervals for a condition-based maintained system

A method for determining the optimum discrete time points of inspection monitoring for a deteriorating single-unit system under condition-based maintenance (GEM) is developed. The conditions of a system in a normal state, a symptom state or a failed state are considered. The transition between the states is described using a symptom-delay-time (SDT) model, The transition time from a normal state to a symptom state and from a symptom state to a failed state are derived from continuous deterioration processes. Failed-dangerous (FD) and failed-safe (FS) probabilities of imperfect inspection are taken into account. A minimization problem of the long-run average cost per unit time is formulated, an algorithm for obtaining the optimum solution is shown, and the nature and sensitivity of the proposed method are investigated.