MAGNKTK' DKSUiX (»F HHLAYS 



Fig. 4 — C.vclic magnetization relations. 



and can be considered to approach zero as B approaches the saturation 

 density B" . 



In the design and operation of ordinary electromagnets, the aspects 

 of the y. — B relation of practical importance are (1) the order of magni- 

 tude of M through the central portion of the curve, which determines the 

 approximate magnitude of the (minor) contribution of the iron path to 

 the total reluctance, and (2) the value of B at which ^ becomes relati\-ely 

 small (less, for example, than 1000). At or near this value of B, the mag- 

 netic path reluctance increases rapidly for small increments in J5, limit- 

 ing the field strength and pull attainable. In the core, this limiting value 

 of B, together with the cross section a, limits the flux (p{ = aB) which 

 the core can supply; conversely, this value of B establishes the core cross- 

 section a required to attain a desired value of (p. The exact value of B 

 which is effectively limiting varies with the design conditions, but is 

 approximately measured by th(^ (l(Misity H m at which /i ecjuals 1000. 



Demagnetization Relations 



For decreasing magnetization, as in relay release, the pertin(Mit B — If 

 relation is the return portion of the major hysteresis loop, the loop start- 

 ing from a point on the normal curv(^ near saturation, such as the loop 

 2-3-4 of Fig. 4. Nearly the same looj) is obtained for any location of the 

 point 2 well beyond the knee of the curve. The distinguishing feature of 

 this relation is the existence of the remanence Br at the point 3, where 



