Method for the evaluation of the number of defective products in a sample based on a single measurement result

We describe the methods of statistical quality control of finished products (methods of statistical quality control by an alternative criterion). The analyzed methods make it possible to reduce the time of control of a batch of products. We note that a sample or a batch should be fully controlled. However, in the case of application of a single inspection tool, the inspection time of a sample is not smaller than the sum of inspection times of all products in the sample. The aim of the present work is to develop a method aimed at the evaluation of the number of defective products of a certain class in a sample by using a single inspection tool based on the use of specimens. This method enables us to minimize the sample inspection time. The specimens are connected in parallel to the controlled products and then connected to form a series circuit. All products in the sample are controlled together with the specimens, the total value of the controlled parameter is determined for the circuit, and the number of defective products in the sample is computed by the formula proposed by the author. The efficiency of the proposed method is confirmed by an example of monitoring of electromagnetic relays. The sample inspection time, in this case, reduces down to the inspection time of a single product. We recommend to use the method for the inspection of samples and batches of products in which defects are regarded either as unilateral deviation of the controlled parameter or as its location in one of the two possible states. As products of this kind, we can mention, e.g., contact-type electromagnetic relays.