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BELL SYSTEM TECHNICAL JOURNAL 



Bridge Circuits 



The general principles of bridge shielding have been discussed by 

 Campbell ^ and the equal ratio-arm comparison bridge has been dis- 

 cussed in detail by Shackelton.'' The mechanical construction of the 

 bridge itself exclusive of standards is simplified by the fact that there 

 are comparatively few dials to be brought through the shielding. 



This bridge with the standards described above may be used for a 

 wide variety of measurements. A rather simple modification is the so- 



Fig. 7 — Shielded Resonance Bridge Network. 



called resonance bridge, in which the bridge unit is an equal ratio- 

 arm comparison type, and a resistance is balanced in one impedance 

 arm against a capacitance and an inductance connected in series in the 

 other impedance arm. The balance is usually efifected by adjusting 

 the resistance and capacitance. 



The shielded circuit of such a bridge is shown in Fig. 7. The 

 capacitance from C to D introduced by the shielding may be com- 

 pensated for in the usual way by the addition of an equal capacitance 

 across AD. In this circuit the coil is usually measured under the 



2 G. A. Campbell, "The Shielded Balance," Electrical World and Engineer, April 2, 

 1904, p. 647. 



»W. J. Shackelton, "A Shielded A-C. Inductance Bridge," A. I. E. E. Journal, 

 Feb., 1927. 



