1034 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



CORE 



*^ 



ARMATURE 



Fig. 8 — Magnetic structure of the AF relay. 



The core is a simple one-piece E-shape section of sufficient thickness of 

 1 per cent sihcon u-on to produce the magnetic flux needed to meet the 

 force and speed requirements and to provide the main member to which 

 all other parts are assembled. The silicon iron has appreciably higher 

 electrical resistance than ordinary magnetic iron and this, together with 

 the rectangular cross-sections of the legs, reduces eddy currents as needed 

 for high speed operation and release. The one-piece construction avoids 

 welded or butt joints common to many magnets. These joints are re- 

 sponsible for added reluctance and hence decrease the magnet sensitivity 

 and require added electrical power to operate a given load. The relatively 

 wide spacing of the legs increases leakage reluctance and, in turn, in- 

 creases the useful magnetic flux. 



After a cellulose acetate filled coiF has been assembled to the middle 

 leg of the core, a core plate, shown in Fig. 9, is forced over the ends of 

 the E-shaped core to hold the three legs in good alignment for proper 

 mating with the armature. The core plate also provides the backstop 

 for the armature and serves as a means of gang adjustment of the con- 

 tacts covered more completely under the Relay Adjustment section of 

 this paper. 



The armature is spring supported in a very definite manner to produce 



^ C. Schneider, "Cellulose Acetate Filled Coils", Bell Lab. Record, Nov., 1951, 

 p. 514. 



