Redundant-system demonstrated-reliability approximation using piece-part failure rates

A method of obtaining the reliability of a redundant system when only the part force-of-mortality estimates (hazard rates) for electronic parts are available is presented. Part failures are reported without specifying whether the parts are configured in series or in parallel. The sum of all the part failure rates in the system, recorded from the turn-on date of the system up to the present time of monitoring, and the sum of the failure rates of all the parts in the system recorded up to a certain previous time after the system turn-on date are calculated. The system reliability for a certain critical mission time, with or without redundancy, is calculated at that previous time. The method is useful in field-equipment reliability monitoring because exact computation is impossible without knowing whether the failed parts are configured in series or in parallel. Generally, Monte Carlo simulation should be used only to verify the results calculated through an analytic method, if such a method is available and is neither time consuming nor cost prohibitive. A dimensionless reliability parameter is introduced.<
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