The L3 Coaxial System 



Application of Quality Control Requirements in the 

 Manufacture of Components 



By R. F. GARRETT, T. L. TUFFNELL and R. A. WADDELL 



(Manuscript received April 27, 1953) 



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 charac- 

 teristic 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 Introduction 



1.1 GENERAL 



Statistical quality control methods are well kno\vn and useful indus- 

 trial tools for economically controlling quality during manufacture. 

 These methods have as one of their goals the shipment of product meet- 

 ing 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 dis- 

 tribution 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. 



An important factor in the application of statistical quality control 

 methods is the specification of distribution requirements in addition to 



