1056 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



to 0.003 inch. Tlie improved stability is expected to permit final adjust- 

 ment and inspection of the relay at the time it is assembled without need 

 for readjustment after it is wired into equipment and installed into 

 service after shipment. 



Magnetic Interference 



In the past it has often been necessary to maintain large spacing be- 

 tween relays where critical values of current to operate or release the 

 relays must be maintained. In some cases special iron shields were used 

 for further magnetic isolation. Without these precautions, the leakage 

 flux from adjacent relays entered the magnetic circuit of the critical 

 relays and the operate or release currents varied according to whether 

 the adjacent relays were energized. 



]\Iagnetic interference between AF relays is substantially eliminated 

 as shown in Fig. 26. This is largely because of the low reluctance of the 

 magnetic circuit resulting from the one-piece core and the large pole 

 face areas between the core and armature. As shown in the figure, the 



I = INTERFERING RELAYS 

 C = CONTROL RELAY 



& 



& 



uj.^q: 20 





O^'O 





25 50 75 100 125 150 175 200 225 250 275 

 AMPERE TURNS TO JUST OPERATE CONTROL RELAY 



Fig. 26 — Typical magnetic interference between AF relays and between U 

 relays, with the rela.ys mounted in the pattern shown. 



