Diagnosis of Equipment Failures

This paper introduces several new concepts which are applicable to the problem of diagnosis of equipment failures. Following the definitions of an equipment, an element of the equipment, and the model of a test, a general diagram of a testing procedure is developed. The testing diagram is constructed in such a way that the various tests needed and the probability of failure of the elements are readily incorporated. While it is found that a completely general testing diagram becomes quite complicated even when the equipment under consideration is not intricate, a major simplification is obtained by introducing a simplified diagram with suitably restricted tests. This simplified testing diagram may be used repeatedly in order to find all the faulty elements of the equipment. With reference to the testing diagram, it is possible to compute the minimum average cost of diagnosing the equipment. This appears to be the most useful measure of the efficiency of a test procedure. The order of magnitude of this optimization problem is discussed and solutions for two special cases are obtained by analogy with an optimum coding problem.