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.
This paper describes the transmission system for transmitting control data to shift the position of the vibration sensor attached to the arm of the robot in one direction and for transmittion vibration data obrained from the vibration sensor in the other direction. Data was transmitted using a pair of optical couplers thorugh a plastic optical fiber. Vibration of the device under test, which was two-dimensionally read from the vibration sensor in the range of 10 Hz to 1kHz, was satisfactorily transmitted while control data to specify the measuring position on the device under test was transmitted. The experiment was successful.