DYNAMIC MEASUREMENTS ON ELECTROMAGNETIC DEVICES 1437 



five switched wires are necessary. The change from flux rise to flux de- 

 cay by another switch as sho^vn in Fig. 10, converts the contact switch- 

 ing to provide the proper instrument closing time, with the time dials 

 now reading time from the beginning of the open of the A circuit. 



Coincidence Circuits. Each coincidence circuit consists of triodes, one 

 for each marked wire. The circuit for the B cycle is shown in Fig. 15. Each 

 selector switch wire connects to a grid, but all the cathodes of a set of 

 coincidence tubes use a common cathode resistor. Except for the instant 

 chosen, at least one coincidence tube has a high potential on its grid and 

 the plate current through that tube holds the cathode resistor at a high 

 potential. Only at the chosen time are all plates of the counter tubes con- 

 ducting and therefore at a low potential. This abruptly drops the cathode 

 potential of the coincidence circuit for one cycle of the oscillator, recur- 

 ring every 1000 cycles. 500 cycles after each start pulse a similar stop 



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B 



COUNTER 



