SAMPLING PROCEDURES AND TABLES FOR LIFE AND RELIABILITY TESTING BASED ON THE WEIBULL DISTRIBUTION (RELIABLE LIFE CRITERION)

Abstract : The report outlines an acceptance-sampling procedure and presents tables of related sampling-inspection plans for the evaluation of lot quality in terms of reliable life which is the life beyond which some specified proportion of the items will survive. Tables of plans are supplied for three reliability indices, .50, .90, and .99. The Weibull distribution, including the exponential and the Rayleigh distributions as special cases, is assumed as a statistical model for item lifelength. The evaluation of sample items is by attributes with lifetesting being truncated at the end of a specified period of time. Tables of conversion factors are also provided from which other sampling-inspection plans of desired form can be designed and for use in evaluating the operating characteristics of other specified sampling-inspection plans in terms of item reliable life. A supplementary procedure and associated tables of factors are also included for use in determining the minimum lifetesting time required for sample items to provide assurance at a confidence level of .95 that the items in the lot or population meet the reliable life specified. Factors are provided for this alternative procedure for a representative range of sample sizes and acceptance numbers. Another table of factors are provided for lot evaluation under this procedure in terms of mean item life.