1030 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



5. The card is supported by the armature on one side and a restoring 

 spring on the other. The restoring spring supphes the force to hold the 

 armature against the backstop and to hold make contacts open when the 

 relay is unoperated, while the armature supplies the force to hold the 

 break contacts open when the relay is operated. However, since the 

 armature must also overcome the tension in the restoring spring, the 

 entire spring load must of course be overcome by the pull of the arma- 

 ture. 



6. The twin contacts are held in good registration with their asso- 

 ciated stationary contacts by means of molded guide slots in the station- 

 ary plastic member just behind the card. These guide slots are slightly 

 wider than the diameter of the twin wires so that these wires are free to 

 move in the direction of the armature movement, but are restrained 

 against lateral motion. 



7. The close proximity of the card to the contacts is important in 

 minimizing contact chatter and in substantiallv eliminating locked con- 

 tacts, i.e., contacts which fail to open because of interlocking of rough- 

 ened surfaces. The close spacing results in a rigid coupling between the 

 card and contacts, so that the static and dynamic forces associated with 

 the armature and card are available to break loose any incipient lock 

 which might develop. 



As the armature moves toward the core, the particular point in its 

 travel at which make contacts close and break contacts open depends 

 upon the dimensions of the card between the surface which bears against 

 the armature and the surfaces which engage the twin wires. By proper 

 selection of these dimensions, any contact can be controlled to operate 

 early or late in the travel as desired. By this means, several sequential 

 contact arrangements may be obtained. For example, if the break con- 

 tact in Fig. 4c is controlled by the card dimensions to open earlier in the 

 travel than its associated make contact closes, the resulting arrangement 

 is called an "early break-make" transfer. Similarly, an "early make- 

 break" transfer, often called a "continuity" may be obtained by selection 

 of card dimensions which will assure that the make contact closes before 

 the break contact opens. If both contacts operate simultaneously, the 

 result is a "non-seciuence" transfer. 



From the above it is evident that the card surfaces which engage the 

 twin wires must be in different positions for early contacts as compared 

 with late contacts. This is illustrated in Fig. 6 which shows an early 

 break-make, an early make-break and a non-sequence transfer side by 

 side. Of the contact pairs shown, only two operate early, and this is 

 accomplished by means of steps in the actuating surfaces of the card. 



