154 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



Maximum Time Given 



For a specified maximum time, the above process is repeated for 

 several assumed circuit powers until the specified time is bracketed. 

 Then by interpolation of the optimum times indicated, the minimum 

 power, maximum resistance and optimimi turns are determined. As an 

 example, Fig. 4 can be used to demonstrate the method. Assume that the 

 three curves were computed for different circuit powers, rather than for 

 different contact spring loads. A line is drawn through the minima. The 

 intersection of this line with the required operate time determines the 

 number of turns. For instance, if 30 millisec were required, the turns 

 would be 12,500. The circuit power at this same intersection can be 

 interpolated for, using the known circuit powers associated with the 

 three curves. 



It is not economical to have a different winding for each spring com- 

 bination. For this reason, a winding is designed for the maximum spring 

 load and then used for smaller loads. The operate time will always be 

 less with the smaller loads. 



Measurements of Time Curves 



Before considering mass controlled operation, the simulation of 

 windings will be discussed. In the above description for establishing the q 

 curves, it was pointed out that by adjusting an external series resistor 

 and the battery voltage to maintain constant final current, the coil 

 constant N'/R was altered without changing q. This can be further 

 extended to permit simulation of any winding for test purposes providing 

 only that the experimental coil fills the winding volume as much or more 

 than the coil to be simulated. For this purpose, a special test winding 



CIRCUIT TO BE SIMULATED 



4 E, 



N,,R, 



SIMULATING CIRCUIT 



-y(^v-i 



C2,Q2 



^3 = lt^' 



R. =I^Vr, 



Fig. 5 — Simulation of winding circuit for timing tests. 



^^-) 



R„= 1^1 R, 



^^ = 1-n:-)^' 



