202 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



with those for a gap of the same separation and projected area, but with 

 plane pole faces (a dome of infinite radius). 



Ampere Turn Sensitivity 



The effect of the relation between F and ^p on the release time cannot 

 be conveniently deduced from (6), which involves both the term in 2, 

 which varies with 9?, and the reluctance (Ry , which also enters the pull 

 relation. If the pull is expressed in terms of ;T, however, (9) shows that 

 the time varies inversely with 3^, and is .substantially independent of the 

 reluctance, provided z is in the usual range from 2 to 6. It follows that 

 maximum release time can be obtained for a given load if the \'alue of 5 



8 77"A 

 1.6 



0.8 

 0.6 



0.4 

 0.3 



0.2 



® 0.08 



a. 



0.06 



0.04 

 0.03 



0.02 



0.01 

 0.008 

 0.006 





Fig. 10 — Reluctance and pull relations of a domed pole face electromagnet. 



