MAGNKTIC DKSIGX OF RELAYS 01 



l\v coinparison, those two expressions are identical for all \alues of x, 

 pro\"itlecl the t'oUowing coiulitioiis are satisfied: 



(ftt = (Re + (Rl2, 

 A(rI = A2(Rl2, 



.4((Ro + tRj = Ao((Ro2 + (R/.2). 



I'pon collect ing terms, the relations between design and e([uivalent 

 circuits are given by: 



(Rl = (Re + (R/.2, 



A = A2/p\ (25) 



(Ro = p"(Ro2 + p(Rc, 



where : 



P = 1 + (Rc/(Rl2. 



Thus the magnetization relations in the low density region can l)e 

 represented by the reluctance given by (24), corresponding to the simple 

 parallel circuit of Fig. 23, provided the constants are evaluated from 

 those of the design circuit by means of eciuations (25). The evaluation 

 of the pull and of the field energy in the low density region can therefoi'e 

 be conducted in terms of the simpler relations applying to the equivalent 

 circuit. 



As these simpler relations suffice to define the performance, they may 

 be readily evaluated experimentally, using the procedures described in 

 a companion article. While these equivalent constants provide a simple 

 and convenient means for the description and analysis of performance, 

 they are related to the dimensions of the structure only through the 

 conditions of equivalence given by equations (25). 



Special Magnetic Circuits 



The reluctance of most ordinary electromagnets can be expressed in 

 terms of the series parallel magnetic circuit of Fig. 21, as in the two cases 

 of Fig. 22 discussed above. Differences in configuration may affect the 

 detailed procedure for estimating the constants, but the same circuit 

 schematic applies. There are, however, other magnetic structures re- 

 quiring different magnetic circuits for their representation. For purposes 

 of illustration, a summary discussion of three such cases is given here. 



For armature saturation, or cases where the flux density in the armature 

 exceeds that of the core, as in some high speed relays, the magnetic cir- 



