RELIABILITY:CONCLUSIONS

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CONCLUSIONS

In recent decades, the delivery of systems that perform adequately for a specified period of time in a given environment has become an important goal for both industry and government. In the space program, higher system reliability means the difference between life and death. In general, the cost of maintaining and/or repairing electronic equipment during the first year of operation often exceeds the purchase cost, giving impetus to the study and development of reliability techniques.

This chapter has been concerned with determining system reliability (or bounds) from a knowledge of component reliability or characteristics of components, such as failure rate or mean time to failure. Even the desirable state of knowing these values may lead to cumbersome and sometimes crude results. However, it must be emphasized that these values, e.g., component reliability or mean time to failure, may not be known and are of- ten just the design engineers’ educated guesses. Furthermore, except in the case of the exponential distribution, knowledge of the mean time to failure leads to nothing but bounds. Also, it is evident that the reliability of components or systems depends heavily upon the failure rate, and the assumption of constant failure rate, which appears to be used frequently in practice, should not be made without careful analysis.

The contents of the chapter have not been concerned with the statistical aspects of reliability, i.e., estimating reliability from test data. This subject was omitted because the book’s emphasis is on probability models, but this is not a reflection on its importance. The statistical aspects of reliability may very well be the important problem. Statistical estimation of component reliability is well in hand, but estimation of system reliability from component data is virtually an unsolved problem.

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