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BELL SYSTEM TECHNICAL JOURNAL 



methods of taking care of this admittance may be used. It may be 

 concentrated in the arm consisting of a capacitance and considered 

 part of it, or an admittance across one impedance arm may be com- 

 pensated for by a resistance across the other impedance arm. Both 

 methods have been used in the construction of these bridges. A more 

 detailed discussion of the shielding involved in this type of bridge is 

 contained in a previous paper by the present author.^ 



Fig. 9 — Shielded Comparison Type Bridge, Top Panel Removed. 



Details of Construction 



We have discussed so far the admittance introduced by the shielding 

 without going into details as to the form which this admittance takes 

 although it has been broadly assumed that it is principally due to 

 capacitance. Since it generally forms an integral part of the measuring 

 circuit, it is obvious that as much consideration should be given to it 

 as to the rest of the circuit. While the admittance is due essentially 

 to capacitance, the necessary supports introduce a certain amount of 

 conductance which causes some difficulty in obtaining compensation. 



For instance, in the typical equal ratio-arm bridge circuit where the 

 admittance across one arm requires compensation in the other arm, 

 it is a simple matter to use an adjustable condenser for the com- 

 pensation of capacitance. However, if the conductance is left un- 



® J. G. Ferguson, "Measurement of Inductance by the Shielded Owen Bridge," 

 Bell System Technical Journal, July, 1927, pp. 375-386. 



