ELECTRICAL MEASUREMENT 



85 



range being a change in input and output transformers, as it is not 

 found practicable to design these transformers to give efficient opera- 

 tion over such a wide frequency range. 



Fig. 10 — Capacitance and conductance bridge with cover removed, showing method 

 of assembly and shielding 



A comparison of this bridge with the impedance bridge already 

 mentioned shows it to be essentially the same circuit, the capacitance 

 bridge having conductance shunts not included in the impedance 

 bridge which allow a conductance balance to be made more readily. 

 It is obvious that any two impedances can be compared on this 

 bridge. Inductances may be measured by parallel resonance by simply 

 placing them in the AD arm in parallel with the standard condenser 

 and effecting a balance with it. This method is used to some extent 

 for the measurement of large inductances. 



Capacitance Unbalance. In order to keep cross-talk low in long 

 cable circuits, it is necessary to have a high degree of capacitance 

 balance between the various conductors in the cable, more particu- 

 larly between the four conductors of a phantom group. The un- 

 balances of interest are the phantom to each side circuit and the 

 side-to-side unbalances. These may be measured on a capacitance 

 bridge by measuring all of the direct capacitances ^ associated with 

 the group and computing the unbalances required. A special circuit, 

 however, is generally used which measures directly the particular un- 



