SLOW RELEASE RELAY DESIGN 205 



and hence an optimum value of A, corresponding to llic nuixinnun 

 sliown by each curve in Fig. 11. 



AG Relay Pull 



3 



The AG relay is a slow release relay \\\t\\ a domed pole face, to which 

 the relations given above apply apiiroximatoly. M. A. Logan and (). C. 

 "Worley developed a more exact expression for the pull in this case, in 

 which an increment to the pull is given by the secondary pole faces on 

 the side legs of the armature, which mate with the side legs of the E 

 .shaped core member. A further increment to the pull is given by the 

 area at the main gap which lies outside the dome proper. Their analysis 

 may be summarized in the notation used here by writing: 



(Ri - (Rz = (R. + ^^"^'^ 



(Rg + (Ri 



where Ri is the iron reluctance, (R^ is the side gap reluctance, and the 

 main gap reluctance is that of the domed gap (Rg in parallel with that of 



the remaining area, (Ep . Substituting /?/ — fR/ for cRr; in (10), there is 

 ol)tained the following expression for the pull: 



^ ^ 2Tr{NI + {NDcY /(Ms ( (Ro \' (^(Rp 



(Rf \ dx \(Ro + (Rp/ dx 



, , (Rp \ d(S{G 



(Ro + ^p) dx 



(18) 



An expression for diSia/dx is given in Fig. 9, while dOis/dx and d()]r/dx 

 are given by 1/As and l/^4p , where As and Ap are the effecti^'e pole 

 face areas for these two gaps. For the dimensions applying to the AG 

 relay, these additional terms introduce minor but significant corrections 

 to the values of F computed from (17). 



Engineering Pull Data 



In determining the requirements for slow release relays, the estima- 

 tion of the range of variation in pull is a major problem. A procedure for 

 such estimation developed by M. A. Logan makes effective use of the 

 relation between F and (NI + (NI)c) in (Ifi). This relation gives a 

 linear plot of slope two when F is plotted against (AU -f (NI)c) on 

 logarithmic paper. A basic plot of this nature may be experimentally 

 determined for a model having nominal values of coercive force He , to 

 Avhich (.V/)c is proportional, and of finish thickness and side gap scpara- 



