DESIGN FACTORS INFLUENCING KKI.l A HILITV OF KKLAVS 



V)',).3 



Iho displacement and hence the friction is hirse, aside from the fact 

 that it is iiKhcati\'e of a I'apid rate of weai', the i-ehiy would he unstable. 



While the wear of the i-elay parts can he niiuiinized hy j^ood (l('sii;ii, 

 it cainiot he eliminated entirely, especially foi- i-elays re(|uii'ed to operate 

 a \ery hir^e number of times during their life. Foi' telephone i-elays the 

 design obj(>cti\'e is for a 40-year life. 'Die effects of weai- on peitoiinaiice 

 to a great (^xtent can ofttimes be counteracted by ingenious design. 

 Fig. 10 is an illusti'ation of such a case.'' Thv diagram on the left shows 

 a moving system of a relay in which the contact springs ai-e stud ac- 

 tuated. The moving spi-ings are tensioned toward the ai'mature and exert 

 a force tending to open the contacts. When the armature operates, the 

 stud presses the moving springs into engagement with the stationary 

 springs. There is no contact force when engagement is first made and 

 further flexing of the spring is necessary to build up the contact force 

 to the desired \'alue when the armature reaches its fully operated posi- 

 tion. As the contacts and studs Avear, it is apparent that the contact 

 force and conseciuently the load on the armature decreases rapidly. The 

 stud wear becomes cumulative in its effect on tlie outside pair of springs 

 as more springs are added to the pile-up. 



The diagram to the right shows a moving system of a relay using 

 what is called "lift-off" card actuation. The moving springs are ten- 



. STUD ACTUATION 



CARD LIFT-OFF ACTUATION 



I 



UNOPERATED 



STUD RING 

 STAKED HERE 



tk: 



H 



=^ 



OPERATED 



r 



5 



B 



Fig. 10 — Two moving sj^steins of relays in relation to i\w. effeets of wear on 

 their performance. 



