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BELL SYSTEM TECHNICAL JOURNAL 



advantage that it involves the frequency, but it has the compensating 

 advantage that the method, being essentially a direct measurement of 

 the resistance of the resonant circuit, is very accurate for the measure- 

 ment of effective resistance. 



The condenser may equally well be shunted across the unknown, 

 in which case the bridge circuit is called a parallel resonance bridge. 

 However, if the ratio of reactance to resistance of the unknown is 

 not high, the expression for the series inductance in this case is not as 

 simple as that for series resonance, and is not independent of the 

 value of the effective resistance, that is the two adjustments are not 

 independent. 



Fig. 4 shows the forms taken by the CD arm for resonance measure- 

 ments. Fig. 4a is the series resonant circuit using an adjustable 

 capacitance standard. Fig. Ab is the parallel circuit using an adjustable 

 capacitance standard. 



CO- 



■^ 





(a) 



Rx 



c o- 



^w^ 



Cs 



A^A^ 



-OD 



(b) 



Fig. 4— (a) The CD arm of the bridge as used for series resonance measurements, {b) 

 The CD arm of the bridge as used for parallel resonance measurements. 



