184 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



parts, each of which exactly represents, as individual relays, the two 

 series relays. This is done by first assigning the total of the winding 

 resistances for equal A'' IR values. The two equivalent relays then form a 

 voltage divider, independent of frequency. The RC network next is 

 drawn as two series RC networks as shown in Fig. 19. The procedure 

 now is to determine the component RC values to have the identical 

 voltage divider effect as the relays. Then the two equal voltage points 

 can be connected as shown by the dotted line and no circulating current 

 will flow. The resultant is a three node circuit and each branch can be 

 considered independently, using the method of the preceding section. 



There are four unknowns and hence four equations are needed. They 

 are 



Rvl + ^22 = R, 



C1C2 



N,' Ni 



Rn R 



22 



(39) 



Ci + C2 



, = C, Ni'Ci = #2 C2 



The solutions for the four unknowns are shown on Fig. 19. 



For experimental measurements, each is transformed again by means 

 of Fig. 5. Note that the time constants all are equal, as they must be, 

 because the same current flows through all elements. However, the initial 

 ampere turns A^7 are different by virtue of Nit^N^ . Thus only one circuit 

 like Fig. 5 need be set up. Measurements then are made with two dif- 

 ferent voltages to provide the two different ampere turns and the two 

 release times. By choosing the subscript 1 network to represent the 

 actual circuit, then no subscript confusion results in arriving at the 

 simulating circuit of Fig. 5. 



Release Time jor Similar Parallel Relays and an RC Shunt 



Similar parallel relays are split as shown in Fig. 20. Two equal parallel 

 RC networks are first drawn. One is then assigned to each, and then the 

 pairs are divided. The release times are each equal to that of one of the 

 separated circuits. 



Summary 



The release time of fast electromagnets is influenced much more than 

 the operate time by the fit of the magnetic parts. For release, the small 

 non-magnetic stop disc introduces a relatively small stabilizing air gap 

 compared to the open gap of the operate case. Secondly, the release 

 always starts after an applied magnetomotive force which differs as 



