The L3 Coaxial System: Application of Quality Control Requirements in the Manufacture of Components

The application of quality control procedures, in addition to conventional maximum and minimum limits, is an important factor in the manufacture of components for the L3 carrier repeaters. In this application, control chart techniques are used for providing assurance that the average of each characteristic subject to control is held close to a desired value and that, collectively, individual units have a desired distribution about this average value. The three-cell method is frequently used under certain conditions encountered in the manufacture of these components when sampling procedures cannot be applied. This method consists of measuring each unit of product, classifying conforming units into one of three cells and the selection of groups of five units each to provide the desired distribution. Case histories of a number of factory applications of these methods are presented. 1.0 1.1 INTRODUCTION GENERAL Statistical quality control methods are well known and useful industrial tools for economically controlling quality during manufacture. These methods have as one of their goals the shipment of product meeting the end requirements for a particular quality characteristic. The application of such methods also makes possible the delivery of a product whose quality is statistically uniform as, for example, having a distribution whose average is maintained consistently close to the design center. Bell Telephone Laboratories engineers have made use of these principles in the development of the new L3 long distance carrier system which will employ hundreds of repeaters in tandem.