OPTIMAL REPLACEMENT POLICIES FOR SYSTEMS WITH MULTIPLE STANDBY COMPONENTS

We consider two new preventive replacement policies for a multiple-com ponent cold-standby system. The failure rate of the component in opera tion is constant. The system is inspected at random points over time t o determine whether it is to be replaced. The replacement decision is based on the number of failed components at the time of inspection. Th ere are two replacement options if the complete system fails during op eration: i) replace the system if an inspection reveals that it has fa iled (system failure is not self-announcing), and ii) replace the syst em the instant it fails (system failure is self-announcing). There is a threshold value on the number of failed components (at the time of i nspection) which minimizes the mean total cost. We develop a simple ef ficient procedure to find the optimal threshold value, We compare the cost of operating a system that is inspected at random points in time, with the cost of operating a system that is monitored continuously th rough an attached monitoring device, and discuss cost tradeoffs.