992 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



annealed, the corresponding changes caused by aging will be about a 

 15 per cent decrease in maximum permeability and 15 to 20 per cent 

 increase in coercive force. 



The improvement in aging effect on relay performance obtained by 

 the hj^drogen treatment is illustrated in Fig. 7.' This was obtained on a 

 design of relay having a closely coupled magnetic circuit for use in time 

 delay circuits. The ordinates show the change in residual grams; hours 

 of aging are plotted as abscissae. Residual grams represent the force with 

 which the armature is held attracted to the core by the residual flux 

 remaining in the magnetic circuit after the electrical circuit through its 

 winding is opened. This force is a measure of the coercive force of the 

 magnetic material. As was noted, the effect of aging is to increase the 

 coercive force and hence the residual grams. For this relay, a change in 

 residual grams will cause a change in the delay time of the relay under 

 a given adjustment and is therefore important. 



How hydrogen annealing improves the pull characteristics of a relay 

 is shown in Fig. 8. This was taken on a relay designed for sensitive and 

 marginal circuit applications. The curves show the grams pull, plotted 

 as ordinates, produced on the relay armature at a given air gap by various 

 values of ampere turns on the relay plotted as abscissae. The abilit}^ 

 of the hydrogen treated relay to operate given loads on considerably 

 smaller currents is obvious. This improvement is due to the higher 

 permeabilities obtained by the hydrogen anneal. 



There are other magnetic materials available for use in relays and in 

 which the aging effect is practically non-existent or is considerably 

 smaller than that just described. Several kinds of nickel-iron alloys 

 known as permalloy are widely used in the telephone sj^stem where their 



W 120 



2 



O 100 



< 



O 80 



< 

 I 

 O 20 



100 200 300 400 500 600 700 800 900 1000 

 HOURS AGING 



Fig. 7 — Improvement in aging effect by hydrogen anneal. 



