ANALYSIS OF TULL AND MACXK'nzA'riOX MKASrUKMKNTS 



83 



It follows tVoin tlK\s(> considerations of onorgy balance Ihal IIh* mag- 

 net i/at ion relations determine the relations anions; the electrical inj^iut 

 to the coil, the stored energy, and the mechanical onlput attainable. 

 Hence, any generally appli('al)le and simple expression for the mag- 

 netization relations, even if purely empirical, would i)r()vidc a con- 

 \(Miient means for evaluating and describing the performance charac- 

 teristies. 



The expressions given below for the magnetization relations are not 

 purely empirical, but are those obtained as approximate solutions to the 

 magnetic field ec^uations by the magnetic circuit method. When experi- 

 mentally e\aluated, however, their utility in tlefining the characteristics 

 of the electromagnet to which they apply is independent of this interpre- 

 tation, and depends only on their conformity to the observed magnetiza- 

 1 ion relations. 



It is convenient to formulate the expressions for the magnetization 

 cur\-es in terms of the reluctance (R, the ratio 3^/v?, where JF is the mag- 

 netomoti\e force -ixNI. The observations of Fig. 1 are plotted in Fig. 3 

 in the form of curves giving (R vs. NI for various values of x. A constant 

 \'alue of tp is represented in such a plot by a straight line through the 

 origin. The radial lines used as supplementary co-ordinates are spaced 

 to gi\'e a convenient scale for (p. 



The reluctance curves of Fig. 3 are similar in character to those apply- 

 ing to most ordinary electromagnets. Each curve has a relatively flat 

 characteristic in the vicinity of a minimum located on a common flux 



FLUX, yp, IN MAXWELLS 

 3000 4000 5000 



12 16 20 24 



ABAMPERE TURNS , NI 



Fig. 3 — Reluct, ■incc curves. 



