MAGNETIC DESIGN OF llELAYS 73 



by xiICl , and Fo by F" . Iiito<>;ration thorcforo gives an expression for 

 the work W similar to eciiiation (33), with Ui replaced by Ui/Cl and 

 ir,„.,x , or AiRoFo , replaced ])y ITsat. , or Cz,A(RoFo'- There is thus ob- 

 tained : 



W = -^^^ TF3at. (43) 



As (43) is of the same form as (33), with u replaced by Ui/Cl , the 

 relations between the load and pull curves are the same in the two cases. 

 Thus the ratios Vc/Wa^t. and FL/TFsat. may be obtained from (35) 

 and (37), or from Fig. 27, by using Ui/Cl to replace ii. Maximum output 

 is thus obtained when Ui/Cl = 1, and the gap reluctance Xi/A at the 

 point of closest approach equals Cl . Thus the optimum leverage for 

 maximum output differs from that for maximum sensitivity by the 

 factor Cl . 



9 DISCUSSION 



A applications 



The applications of the magnetization relations considered in this 

 article are confined to the static characteristics: the sensitivity and work 

 capacitj' attainable when no specific timing requirements are imposed. 

 As the same relations control both the electrical and mechanical response 

 of an electromagnet under dynamic as well as under static conditions, 

 the material outlined here has further applications in other aspects of 

 magnet performance, as illustrated in the companion articles appearing 

 in this issue of the Journal. ' 



The sensitivity and work capacity discussed above relate essentially 

 to the operate characteristics. The other static characteristics of relay 

 performance are those for release, and for marginal performance. The 

 release characteristics are primarily dependent upon the operated load 

 in relation to the pull at the closed gap. The rising pull characteristic as 

 the gap is closed tends to give an operated pull well in excess of the 

 operated load, giving a release ampere turn value small compared with 

 the operate value. The coercive force tends to further decrease the re- 

 lease value, and imposes the need for stop pins to assure release. A high 

 ratio of release to operate can be attained by providing a rising load 

 characteristic to match the pull, by using high stop pins (thus increasing 

 (Ro), 01- by using a core or armature section that saturates in the latter 

 part of the tra\'el. A detailed discussion of the provisions for mai'ginal 

 operation is outside the scope of the present article, but ob\'iously in- 



