466 



BELL SYSTEM TECHNICAL JOURNAL 



MILLIAMMETER 



Fig. 35 — -Visual bridge balance indicator circuit. 



input to the indicator is amplified and the rectified output is indicated 

 by the reading of a D.C. milHammeter. When the bridge is balanced 

 there is no input to the indicator so that the milliammeter pointer 



Cb+^bm 



GROUND l||| 1 1 ( B 



cb 



PHANTOM TO WHITE SIDE UNBALANCE: 

 AGROUND 2 [C| + C2-(C3+C4)+2-(Cw-Cwm)j 



PHANTOM TO BLACK SIDE UNBALANCE^ 

 2[C| + C4-(C2 + C3J + ^(Cb-Cbm)] 



BM) i| |||i GROUND 



Cbm 



•CwM 

 ^^ GROUND 



Fig. 36 — Phantoni-to-side capacitance unbalances. 



