80 THE BELL SYSTEM TECHNICAL JOURXAL, JANUARY 1954 



relations. The consequent dependence of the pull and timing characteris- 

 tics upon the magnetization relations makes the measurement and analy- 

 sis of the latter fundamental to the understanding of performance and 

 its relation to design. 



Procedures are described in this article for the evaluation from meas- 

 ured magnetization relations of a few parameters which suffice for the 

 determination of the pull and of the field energy under given conditions. 

 These parameters, the magnetic circuit constants, characterize the elec- 

 tromagnet to which they apply. They are used as measures of per- 

 formance in comparing different structures, or in studying the effect of 

 dimensional or material variations in a particular design. 



In addition to their significance as parameters summarizing measured 

 magnetization relations, the magnetic circuit constants may be inter- 

 preted as the observed values of quantities postulated m the magnetic 

 circuit approximation to static field theory. This approximation is dis- 

 cussed in a companion article, which describes methods of estimating 

 the values of the magnetic circuit constants from the configuration, 

 dimensions, and materials constant of the electromagnet. Comparison of 

 observed and estimated values of these constants has served as a guide 

 in developing these methods of estimation. A complete design method- 

 ology is provided by the ability to both estimate and measure the mag- 

 netic circuit constants characterizing the performance of electromagnets. 



In the experimental evaluation of the magnetic circuit constants de- 

 scribed in this article, the basic method is that employing measured 

 magnetization relations. Because of the dependency of the pull upon the 

 magnetization relations, pull measurements may also be used, subject to 

 certain limitations, for the evaluation of the magnetic circuit constants. 

 The article includes description of procedures for doing this. 



The notation used in this article conforms to the list that is given 

 on page 257. 



2 MAGNETIZATION RELATIONS 



The magnetization relations of an electromagnet give the average 

 flux ip linked per turn of the winding as a function of the two determining 

 variables: applied ampere turns AT/ and armature position x. The rela- 

 tions are usually shown, as in Fig. 1, as a family of curves giving <p 

 versus ^l for various values of x. Armature motion is usually rotary, 

 and the choice of the location at which x is measured is a matter of con- 

 venience. The curves of Fig. 1 apply to the electromagnet shown in Fig. 

 2, the AJ (heavy duty) type of wire spring relay described in an article 



