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BELL SYSTEM TECHNICAL JOURNAL 



3. The direct capacitance balance of arms BC and CD. 



4. The direct conductance balance of arms BC and CD. 



5. The series inductance balance of the interior wiring to the im- 

 pedance terminals of arms BC and CD. 



As was explained in the foregoing two switches are provided for 

 independently reversing the ratio arms {AB and AD) and also the 

 outside connected impedances. These, therefore, afford a very con- 

 venient means of checking the above balances of the bridge network. 

 By a suitable choice of the test condition under which the reversals 

 are made, a fairly good approximation of the effect of the separate 

 items can be made. The following series of tests indicate how this 

 was done on one of these bridges. 



The junction point C was first grounded. Then, with a telephone 

 receiver as the detector and with a test current having a frequency 

 of 1600 cycles, the setting of the condenser Ch was varied until a 

 balance was obtained. The arms Zs and Zx were both open-circuited 

 in this test; hence the capacitances shunting these arms alone deter- 

 mined the balance point. This balance was very sharp indicating that 

 the shunting conductances were either very small or else accidentally 

 well balanced. Leaving the condenser set at its balance point, there 

 was then connected into one of the impedance arms a toroidal self 

 inductance standard having a nominal inductance of 0.200 henry and 

 an effective resistance of about 50 ohms. In the other arm there was 

 connected a similar standard of the same nominal but of slightly 

 lower actual value in series with a small adjustable inductance and 

 adjustable resistance, each of sufficient range to effect a balance of 

 the corresponding constants. The extension inductance was gradu- 

 ated in steps of one microhenry and the resistance in steps of 0.001 

 ohm. Balances for the four combination settings of the reversing 

 switches, 5r and ^z, were then made, only the extension elements 

 being varied in getting these balances. Readings as given in Table 

 IV were obtained. 



TABLE IV 



