Relay Measuring Equipment 



By II. N. WAGAR 



(M;iiiuscTii)t received Seiitembor 25, 1953) 



The wide variety of technical problems encountered in telephone relay 

 design calls for quantitative measurements of many kinds, involving static 

 performance and dynamic performance. The present article describes some 

 of the more important rneasuring tools for this purpose, as used in Bell 

 Telephone Laboratories. Instrumentation for evaluation of force, flux, dis- 

 placement, time, or their combination, is described. 



IXTRODUCTION 



Msitors to the switching development areas in the Bell Telephone 

 Laboratories are often surprised at the extensive amount of measuring 

 equipment used to study so simple a device as the telephone relay. This 

 is because, though the relay itself may be simple, the problems requiring 

 study are extremely complex. Because relays are used in such large quan- 

 tities, their characteristics affect the economy of the telephone switching 

 system. Not only is their manufacturing cost important; their quality 

 also affects the central office cost. For example, an efficient design lowers 

 the central office power plant cost, and faster-acting relays enable fewer 

 common control units to handle more traffic, which further reduces the 

 cost. These and related objectives pose many complex technical prob- 

 lems invohnng mechanics, magnetics, kinetics, heating, and the like. 



The scope of relay analysis may be judged from the other articles in 

 this issue. In every case there is need for measurement. Sometimes this 

 (luantitative work is needed to confirm an analytical relation, sometimes 

 to learn more concerning the basic phenomena, and often to characterize 

 the performance of a test model. This article will describe some of the 

 most-used measuring tools for the study of relays. 



Several kinds of measurements are required. In the first place, there 

 are force measurements. Each relay must press the desired number of 

 contacts together with a suitable force. To do this, a magnet must be 

 pi-()vided which can move the springs, through whatever distance is re- 

 (juired. Thus, measurement is needed of force-displacement characteris- 



