100 THE BELL SYSTEM TECHXICAL JOURNAL, JANUARY 1954 



0.02 



0.01 



0.02 0.04 0.06 0.08 0.10 0.12 0.14 



TRAVEL, X, IN CENTIMETERS 



Fig. 12 — Evaluation of magnetic circuit constants from pull data. 



Evaluation of Equivalent Magnetic Circuit Constants 



The low density pull is given approximately by equation (13), to 

 which the dashed F' lines of Fig. 11 conform. These lines coincide with 

 the actual pull curves at the points of tengency, which must correspond 

 to the minimum reluctance values. Taking F as F', (13) may be written 

 in the form: 



Values of NI/F' have been determined for the dashed lines of Fig. lb 

 and are plotted against x in Fig. 12 — the plot marked JF/(47r\/F')- In 

 agreement with (18) these points determine a straight line. The slope 

 and intercept have been used to determine the values of (Ro and .4 listed 

 under 'Tull Results" in Table II. 



As the reluctance (Re in the circuit of Fig. 5 is identical in form with 

 the reluctance (R of Fig. 4, the pull for Fig. 5 is given by an expression 

 similar to (13), with ff, (Ro , and A replaced by ^e , (R02 , and Ao , respec- 

 tively. As the two circuits arc ec^uivalent at the points of minimimi re- 

 luctance and the corresponding points of tangency for the pull curves, 

 the pull at these points is the same for the two cases. Thus if the ratio 

 of ^E to ^ is determined at the points of tangency, a plot of CF£-/(47r\/F') 

 against x should conform to: 



^t^VF' 



= (R02 



/ 



2 "^ V'27rA2 



(19) 



