E.STIMATTOX AXD COXTUOL OF ()T'i:i! ATI', TlMl'; OF KKLA^S 



13 



tho equivalent values of the closed gap reluctance, Ihe leaka«i;e icluclance, 

 and the pole face area respectively. Procedures for esliniating these 

 (juaiitities from the magnet's dimensions and material constants are 

 described in the article cited above,' while methods for their experi- 

 mental evaluation are described in another article in this issue." WIumi 

 equation (4) applies, the pull F is given hy • 



{(^h^f 



St A (Rz, + (Ro + 



F = 



Tn normal operation, the flux level lies in ihe region of linear magnetiza- 

 tion, and eciuations (4) and (5) apply through the greater i)art of the 

 period of flux de\'elopment determining the operate time. Tn what fol- 



Fig. 1 — Equivalent magnetic circuit of an electromagnet. 



lows, some simplification of notation is obtained by writing Xq for A(Ro 

 and Cl for ((Ro + (^l)/S{o , so that these equations become: 



{C\ - l){xo + x) 



(R = (Rr 



ClXo -{- X 



F = 



ClXq -\- X / 8irA 



(4A) 



(5A) 



Thus the dynamic relations are given by (2) and (3), in which (R and 

 F are given by (4) and (5) respectively. The magnetic circuit constants 

 can be evaluated by the methods cited above, and the other constant 

 terms are known or given quantities, with the exception of the eddy 

 current conductance Ge ■ Evaluation of this term requires determination 

 of the conditions under which such a constant term can adequately 

 represent the effects of eddy currents. 



EDDY CURRENT CONDUCTANCE 



Fig. 2 shows a simple electromagnet with a cylindrical core of length ( 

 and diameter D. If (R is the reluctance, the magnetomotive force {Fc of 



