A model to determine the optimal critical level and the monitoring intervals in condition-based maintenance

In condition-based maintenance, a common practice is to record a condition reading at a regular interval, and once the reading is higher than a pre-set critical level, the item monitored is declared faulty and repair or replacement may be initiated. However, surprisingly both in practice and theory, little attention has been paid to whether or not the critical level and the monitoring interval are set in a cost effective way. This paper reports on the development of a model that can be used to determine the optimal critical level and interval in condition-based maintenance in terms of a criterion of interest. The model is established on the basis of the random coefficient growth model where the coefficients of the regression growth model are assumed to follow known distribution functions. A simple example is given in the paper to illustrate the modelling ideas.