58 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



reference to the two structures shown schematically in Fig. 22, where 

 Fig. 22(a) represents the familiar "end-on" armature type of construc- 

 tion, and Fig. 22(b) represents the "flat type" relay of Bell System use. 

 The dashed lines indicate the path along which the length of the parts is 

 measured, while the lined areas are those of the main, heel, and side 

 gaps. 



The core reluctance, (Re , is determined from eciuation (17), taking the 

 length as between the points 1 and 2 in both figures. The permeability 

 is taken at the nominal maximum value throughout all iron parts. 



The closed gap reluctance, (R02 , is the sum of the following: 



A. The iron reluctance, determined from equation (17) taking the 

 lengths of the several parts as measured around the path 2-3-4-5-6-1. 

 In each term the cross-sectional area a is that of the part through which 

 the flux passes. In Fig. 22(b) of course, the two side sections are added 

 to give the total section. 



B. The contact gap reluctances computed as x/ai and x/a2 , taking 

 X as for an air gap of 0.005 cm. The reluctance of the joint at 1 in Fig. 

 22(a) is computed in the same way, and included in the sum. 



C. The "stop pin" air gap reluctance, computed as x/Ai , where A2 is 

 the effective pole face area as determined below, and x is the separation 

 at the measuring point for the stop pin opening. 



(a) END-ON ARMATURE TYPE (b) FLAT TYPE 



Fig. 22 — Magnetic circuit components of tj'pical relay structures. 



