INDUCTANCE AND CAPACITY 



399 



Inductance Measurements. In the comparison of an induct- 

 ance with a variable standard inductance the connections shown 

 in Fig. 233 may be used. 



The ratio arms R M and R N are non-inductive resistances. 

 The variable standard of self-inductance is at P (see page 386). 

 L x is the unknown inductance and R is an adjustable non- 

 inductive resistance which, if necessary, may be placed in series 

 with the unknown inductance by changing the lead from c to 

 e. A and D are sources of alternating and direct current, 

 respectively; T and G are the corresponding detectors (compare 

 Fig. 226). 



FIG. 233. Diagram of impedance bridge for comparing inductances. 

 The impedances of the bridge arms are 



Z M = RM 

 Z N = R N 



Z P = R P 

 Z x = Rx 



Substituting these values in the general equation (26) and 

 separating the quadrature components, the two conditions which 

 must be fulfilled in order that the bridge may be balanced 

 follow : 



From the horizontal component, 



From the vertical component, 



RM 

 ~R~N 



(30) 



(31) 



