NEW GENERAL PURPOSE RELAY 1047 



towuid the core, and the inagiK'tic pull acting on the armature for \-arious 

 numbers of ampere turns in the winding. These pull and load curves are 

 also measured at the card. 



Examination of the load curxes shows several features of the I'elay. 

 'i'he armature hack tension, or force, holding the armature against the 

 backstop is al)out Go grams in this case. As the ai'mature moves toward 

 the core, the spring load increases along the upper of the two nearly- 

 jiarallel load curx'cs until it reaches a final value of about 440 grams in 

 the operated position. As the armature is allowed to return to its original 

 position, a second cur\-e, just below the original curve, is obtained. The 

 area between these two cur\es is a measure of the energy loss due to 

 mechanical hysteresis, or friction, in the relay. As can be seen from the 

 curves, the friction in the new relay is very low and is a small fi'action 

 of the spring load at all \alues of armature travel. 



The shape of the load curves is characteristic of AF relays with inter- 

 mediate travel (0.044 inch). The load increases rapidly in two regions, 

 corresponding to the intervals in which the early and late contacts 

 operate. The rapid increases are caused by the armature and card picking 

 up the additional load of the twdn wire springs. Each of the 48 twin 

 wires is picked up almost abruptly at various points and the summation 

 of these additions to the load gives the irregular appearance shown. 



The pull curves of Fig. 17 are for essentially static conditions since 

 the armature was restrained to move slowly through its travel while the 

 curves were automatically recorded. These curves are of interest because 

 they show the ampere turns necessary to assure operation of the relay 

 and also values which will assure the armature will not leave the back- 

 stop. For example, the "critical load point," or point on the load curve 

 which requires the greatest number of ampere turns, is seen to occur at 

 0.025-inch travel and 250 grams, Avhich under static conditions would 

 require at least 160 ampere turns in the winding to assure complete 

 operation. On the other hand, as little as 94 ampere turns could cause the 

 armature to leave the backstop and might cause operation of one or two 

 contacts. Hence, a lower value must be maintained to assure that the 

 armature will remain at rest against the backstop. This information is 

 important for relays having non-operate requirements. Similar informa- 

 tion may be obtained for limiting ampere turn values which will assure 

 that the armature will remain in the operated position (hold require- 

 ments) and, again, w'hich will assure complete release to the backstop 

 position (release requirements). 



