418 



ELECTRICAL MEASUREMENTS 



balance obtained by adjusting L'. The arrangement is then 

 a simple impedance bridge, and at balance 



Z M Z if Zi M _ Zix ~h Z M 



Zx Z P Z N Z N + Zip 



The opposed secondaries of the mutual inductances are next 

 introduced into the detector circuit by throwing the switches to 

 position 2 and a balance obtained by adjusting ra P . 



FIG. 243. Connections for Campbell method of comparing mutual 



in'ductances. 



At balance the two secondary e.m.fs. must be equal, or 



- J 



m P 



/7 I /7 J /7 



Ax T ^M ^tf 



I J. ^ "f" ^^ _ Z M 



= Z N + Z P ~ Z N 



Z P 



RM 



and 



m x = 



R 



(51) 



Measurement of Mutual Inductance in Terms of Capacity. 

 The connections for the Carey Foster method of comparing a 

 mutual inductance with a capacity, as modified by Heydweiller, 26 

 are shown in Fig. 244. C is a condenser; r, Ri and # 2 are 

 non-inductive resistances. r% is the resistance and L 2 the self- 

 inductance of the secondary of the mutual inductance. 

 The impedances are 



Z =R l 



Z 2 = (R* + r 2 ) 



