MAGNETIC DKSIGX OF IIKLAY.S 



-11 



MAGNETOMOTIVE FORCE, CF 





 MAGNETOMOTIVE FORCE , ?7r= H £ 



Fig. 



Repeated magnetization of an electromagnet and its core. 



of a core or other part. It is eoiivenient to use it in this way for the 

 decreasing magnetization relation, as this is of interest only for a single 

 value of the gap reluctance, that for the operated position. 



The decreasing magnetization relations for an electromagnet and for 

 its core are shown in Figs. 7(a) and 7(b) respectivel}'. For decreasing 

 magnetization, a residual flux ^po remains when 3^ is reduced to zero, 

 determined by the same equilibrium conditions as apply to permanent 

 magnets. The curve for the magnet, Fig. 7(a), must pass through <po 

 and be asymptotic to the saturation flux <p" . 



This relation between ip and iT may be represented by an e(iuation of 

 the same form as equation (10), with B and B" replaced by ^p and ^p" , 

 with H and He replaced by '5 and $Pc , and the constant ^l" replaced hy 

 1 (R". losing the condition that q> = ^o for [F = to eliminalc ;Tr' , the 

 e( [nation may be written in the form 



<^o 



m'V 



<^0 



ipo 



(14) 



If the length /"and cross-section a of the core are known, together with 

 the magnetic constants of the core material and the rehictance iS\ of the 

 return jiath (external to the core), the constant term.s in (14) may be 

 evaluted. ^p" is equal to aB" , wliei-e />'" is the saluiation density of the 

 core material. .\s previously noted, the \ahies of B :,, in Table 1 may be 

 used as ellecti\-e values of B" . <po may l)e e^■alua(ed as the pei-manent 



