Abstract
The bigger and more complex a system becomes, the more difficult to identify its true condition:whether it is in good state or bad state. Conditioning monitoring maintenance which utilizes a monitor to get information on the true state plays a role in such an occasion. But, a monitor has two kinds of faults;"no alarm(fail to operate)"when the system is in a bad state, and"raising alarm(fail to idle)"when in a good state. This article deals with a monitoring system which consists of multiple monitors with variable thresholds for raising alarm. A sufficient condition is shown under which the optimal maintenance policy is given by k-out-of-n monitoring systems in the terms of expected risk in the case where n equals 3 and 4. Also, the optimal thresholds of multiple monitors are given by an equal value for every monitor.
