Application of a Method of Inspection Testing to Assurance Reliability

This paper describes the use of a sampling method of inspection testing for the purpose of controlling reliability in a system. The acceptable quality level (AQL) and mean failure free time can be estimated by the maximum likelihood method, assuming that errors are distributed by the Poisson Law. Hence, a choice of quality levels or reliability levels can be made. Single or multiple sampling plans may be used depending on the cost factors, the sample size, and the available information on reliability. The sample size, acceptance number, and cost due to Type I and Type II errors are each considered. One aim of inspection testing is to determine when preventable failures occur. An inspection lot in this case is a test run of a system for a given time. The system is accepted or rejected on the basis of the number of failures found in the sample tests. The object of the inspection system is (1) to accept the reliability of the system at least 100 (1-A) per cent of the time when the true life is more than T1 and (2) to accept the reliability of the system not more than a small proportion, B, of the time when the true mean life is less than T2, T2 ≪ T1.