nr.slux cii.iK.icrr.h-isrns or rii.r.CTKo.\f.iG.\T.rs 21,1 



various designs it is founii that tlic most eftuieiU core (lesion is ob- 

 tained by choosing a core flux licnsity at the maximum pcrniealjihty 

 of the core iron. If this reasoning is applied to a 5,000 gram relay 

 a saving of approximately five per cent core energy' results over 

 working at a high density but the core section is increased in the 



Fig. 5 — Curves of Core Section and Pole Face Flux Density vs. Pull 



ratio of six to one. Obviously the small improvement in efficiency 

 results in an unreasonable increase in size and consequently first cost 

 and is seldom if ever warranted by the requirements. Applying 

 the same reasoning, however, to a five gram relay we obtain a reduc- 

 tion in core energy- of approximately 20 per cent and although the core 

 section has greatly increased this increase has practically no influence 

 on the size or first cost of the magnet. Of course, a further con- 

 sideration is mechanical strength as where light loads arc encountered 

 the core section, needed magnetically, may be entirely too small to 



