THE L3 SYSTEM — QUALITY CONTROL IN MANUFACTURE 971 



1.3 SEQUENCE OF MANUFACTURING OPERATIONS 



The application of distribution requirements places added emphasis 

 on the proper sequence of the various operations required for the fabrica- 

 tion of the product. Normally, any assembly or finishing operation follow- 

 ing a process adjustment of a particular characteristic is designed to keep 

 that characteristic within maximum and minimum limits in the final 

 state. Such procedures often fail to satisfy the desired distribution and 

 it is necessary to rearrange the sequence of operations. Once the proper 

 sequence is established it must be rigidly maintained. 



1.4 TESTING 



As a result of refinements in design and in production methods em- 

 ployed for the critical components of the L3 amplifiers, the design en- 

 gineer has in many instances been able to specify limits closer than ever 

 before attained. The specification of such close limits may tax the pre- 

 cision of factory testing equipment and in many cases it has been neces- 

 sary to develop and construct new electrical and mechanical inspection 

 facilities. Measurement reproducibility as well as accuracy in terms of 

 absolute values is important since the measuring instrument ordinarily 

 indicates variations in repetitive readings, even though the product be- 

 ing measured remains constant. Once the characteristics of the measur- 

 ing instrument are determined and used as a basis for the specification 

 of limits, the measuring facility becomes an important part of the dis- 

 tribution control system and must be controlled the same as all other 

 elements of the system. This means careful watch over the maintenance 

 of factory inspection facilities so that these characteristics are controlled. 

 Obviously, an adjustment made on the measuring instrument in the 

 course of regular maintenance which introduces a significant bias or 

 shift, even though well within accuracy limits, may have to be taken 

 into consideration in the use of the instrument. One method of minimizing 

 this problem is to employ stable fixed standards whose characteristics 

 are numerically equal to or near the nominal value of the products being 

 tested. Such standards can be used for either calibrating the instrument 

 or as comparison standards in the actual measurement of the product. 

 These auxiliary standards must still be periodically checked and extreme 

 care taken to prevent any shift in their characteristics. 



2.0 Quality Control Methods 



2.1 conventional statistical quality control methods 



The concept of control as used here includes the use of data resulting 

 from measurements made on product produced under the same essential 



