Optimization of preventive maintenance interval

This paper combines the (normalized) cost and availability metrics into one new metric: availability/normalized cost. The new metric seems to provide more sensitivity for the optimization. The non-dimensional time interval that enables model unification also introduced. Repair cost to preventive maintenance cost ratio impact on system availability and normalized cost analyzed. The cost and availability models has been obtained by using Microsoft Excel and Visual Basic program to determine the value of the optimum non-dimensional preventive maintenance interval that maximizes the system availability or minimizes the system total cost or maximizes the system availability / system total cost ratio for 3-Out-of-4 repairable system under two preventive maintenance policy (simultaneous maintenance policy and staggered maintenance policy). We can conclude that policy of staggered maintenance can be recommended to replace the conventional simultaneous maintenance.