1050 THE 



1.0 



0.9 



BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



O 0.6 



< 0.5 



2 4 6 8 10 12 14 16 18 20 



NUMBER OF CONTACT PAIRS 



(as used in early break-make TRANSFERS, or EQUIVALENT) 



Fig. 20 — Power used for AF and U relays with coils designed for least power. 



tively expensive because they contain as many turns of fine Avire as the 

 available space permits, and their use is economical only on relays which 

 are operated an appreciable portion of the time and where speed is 

 relatively unimportant. The reduced power required for the AF relay is 

 due principally to an improved magnetic structure, shorter travels for 

 similar contact combinations, and lower contact forces. 



Contact Performance 



The principal characteristics which must be considered in evaluating 

 contact performance include chatter, erosion or wear, susceptibility to 

 open contacts and locking, and changes in these characteristics with wear 

 of the relays. In general, all these features are improved on the AF relay 

 compared with the U type. 



Typical chatter on closure of make and break contacts on U and AF 

 relays built for moderate and fast operation is shown in Fig. 21. The 

 degree of improvement of the AF relay is striking. The reduction in 

 chatter has direct circuit advantages in reducing the possibility of false 



