1114 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



TWIN-WIRE 



ARMATURE 

 BACK-STOP 



WINDING 

 TERMINALS 



MOUNTING 

 BRACKET 



ARMATURE 

 HEEL- STOP 



HEEL 

 PLATE 



Fig. 2 — Top view of rela}' showing location of parts. 



plate, as sho\\ai in Fig. 2. The wire spring assemblies form two rows, 

 each containing 15 make contacts. Each contact pair consists of moving 

 twin contacts on separate twin wires, associated with a single stationary- 

 contact. The stationarj' springs are supported close to the contacts bj^ 

 arms extending from the bracket. A detailed view of all parts and sub- 

 assemblies for a 30-make contact relay is shown in Fig. 3. Moving con- 

 tacts are pretensioned by relatively large pre-deflections as shown in 

 Fig. 4. The method used in flat spring multicontact relays to obtain 

 contact force is illustrated for comparison. It is apparent that contact 

 force obtained by the "buckle" method depends on operating stud 

 length and therefore is subject to change due to wear. The new preten- 

 sioned wire springs are supported and actuated by a single molded 

 phenolic card by the "card release" method as illustrated in Fig. 5. 

 In the unoperated position, the card is held against the core by a re- 

 storing spring, which also supplies the force to open all contacts. In 

 the operated position, the armature supplies the force to move the card, 

 releasing the twin wires and closing all contacts. This method of actua- 

 tion has some important advantages: 



1. Contact force is essentially independent of gauging and wear. 



2. The effects of wear at points in the relay which affect gauging are 

 compensating to some degree, and therefore tend to minimize changes 

 in gauging. 



3. Dimensional variations controlling contact separation and armature 

 travel are reduced, making possible shorter annature travel, faster 



