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BELL SYSTEM TECIISICAL JOURNAL 



the magnetizing ampere turns were reduced by the high resistance of 

 the loop. Ad\'antage was taken of silicon steel, a new material at 

 that time, which had a higher permeability than Norway iron and 

 less pronounced residual magnetic effects, after saturation. In 

 addition, it had greater tensile strength and, since the new t\pe 

 relay core was rectangular in shape and therefore had the stiffness 

 of a beam, it was possible to make a core of silicon steel of such small 

 cross section that the flux density was much higher with a small 



Fig. 12 — -"B" type relay 



magnetizing force than it would be with a Nor\vay iron core of the 

 minimum cross section necessary for structural strength. A super- 

 visory relay was, therefore, produced which was similar in con- 

 struction to the line and cutoff relays and occupied the same mounl- 

 ing space. It was necessary to develop a dust protecting cover for 

 this new relay which was also cross-talk-proof, in order to prevent 

 the reproduction of conversation by mutual induction between 

 adjacent relays. The design of this relay was such that spring ten- 

 sions and contact adjustments were controlled by screws mounled 

 in a brass plate at the front of the relay. The increased sensiti\it\' 

 of this relay over that of the round core type permitted the limits 

 for substation loop resistance to be increased from 7')() to 1,000 ohms, 

 and the combined resistance of the windings to be reduced from 12 

 to '.1.1 ohms, which decreased the transmission loss in the relay about 

 'M) pi-r ciMii. In addilinn, this new relay was sujierior ii Hasliiui; 

 ability and al>;i releasc-d on a higher number of ampere turn>. Tlu' 



