1024 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



Fig. 1 — AF type relay, with contact cover detached. 



of resistance values and to operate contacts which vary from one pair 

 to as many as fourteen or more. The basic relay design must also be 

 capable of pro\dding such features as fast operation and release, slow 

 release, high sensiti^dty, heavy duty and marginal operation. These 

 functions are performed satisfactorily in present crossbar switching sys- 

 tems by U, UA, UB and Y type relays.^- ^- '^- ^ However, ■\^^th an objective 

 of a fort3^-year life for new s^^^tching sj'stems and a trend toward unat- 

 tended operation of switching offices, it is important to attain the best 

 in the performance and reliability of relays. 



The general purpose relay must be designed to produce the best eco- 

 nomic balance, when used in telephone switching S3'stems, so that the 

 annual charges are minimized. The major ingredients of these annual 

 charges are manufacturing expense, operating electrical power, speed of 

 operation and release, space recjuired and maintenance costs which in- 

 clude reUability and life. 



2. REQUIREMENTS AND OBJECTIVES 



The requirements for a new general purpose relaj^ were initialh' 

 broadly stated to be performance and maintenance at least equal to the 



2 H. N. Wagar, "The U-Tvpe Relay", Bell Lab. Record, May, 1938, p. 300. 



3 H. M. Knapp, "The UB Relay", Bell Lab. Record, Oct., 1949, p. 355. 



^ F. A. Zupa, "The Y-Type Relay", Bell Lab. Record, May, 1938, p. 310. 

 *W. C. Slauson, "Improved U, UA and Y Tj^pe Relays", Bell Lab. Record, 

 Oct., 1951, p. 466. 



