MAGNKTIC DESIGX OK IIKLAYS 



67 



Scnsilirih/ for Specific fronds 



'V\\v part of ir„,nK (IkiI cmii he rc^alizcd (l(>i)(Mi(is upon the shape of the 

 load cui'N'c. Il also dcpcMids upon the tfa\('l thi-()ii<>;h whicli llic load must 

 he moved. In principle, the lattei' may he adjusted to any desired \'alue 

 by the ehoiee of a lever arm determining the ratio of the travel at the 

 point of load actuation to the travel at the point where x has been 

 measurcnl in determining th(^ magnetic cireiiit constants, d'he use of a 

 le\'er arm liid<age, of course, changes the force recjuired, but^ the work V 

 and the shape of the load characteristic remain unchanged. 



In Fig. 26 is shown the pull curve relation of e(]uatioii (31), together 

 with two simple load curves: a constant load and one varying linearly 

 with travel. In the first case, let Fi be the constant load required, and 

 Xi the refjuired travel. The pull curve to operate this load must have 

 F = Fi at .r = Xi . Hence, from (31), Fi/Fo = 1/(1 + '/i)-. The work 

 I'r done against the load is Fi .ri , and the ratio of Vr to ]I\„ax is 

 therefore Fi Xi''(A6{oFq), or HiFi Fq . Hence the part of ]r,„:,x realized 

 against a constant load is given by: 



''' " (35) 



Tr„ 



(1 + u,Y 



The ratio I'cTFmax is shown plotted against Ui in Fig. 27. Its maxi- 

 nnnn \'alue is at Ui = 1, where the travel Xi = A(Ro . Maximum sensi- 



A(Rc 



Fig. 26 — Relations l)f>t\v('('n load and jiull curves. 



