LOCATION OP OPENS IN TOLL TELEPHONE CABLES 



43 



respect to the bridge potential, Fig. 12 the magnitude of «3, and Fig. 

 13 the relative sensitivities obtained with different frequencies and 

 different lengths of line. These sensitivities are proportional to iz 

 (Fig. 12) and to the cosine of the angle between i-^ and the field current 



^ 3.2 



10 



% 3.0 



1 2.8 



CO 



2 2.4 

 •^ 2.2 

 I 2.0 



I '■« 



S '•& 



J 1.4 



TO 

 -g 1.2 



1.0 



.8 



.b 



.4 



.2 



.0 



10 20 30 40 50 60 70 



Length of Line in Miles 



Fig. 12 — Magnitude of the unbalance current for measurements, on the impedance 

 of non-loaded 19-gauge cable, at frequencies of four, eight, and twenty cycles. 



of the alternating-current galvanometer. In the calculation of the 

 curves of Fig. 13 the field current of the galvanometer was assumed to 

 be in phase with the bridge potential for the case of an unbalance in r, 

 and leading the bridge potential by ninety degrees for the case of an 

 unbalance in Xn. 



Referring to Fig. 11, it is seen that for short lengths of line the un- 

 balance current caused by unbalancing r is almost in phase with the 

 voltage, while the unbalance current due to unbalancing Xb leads the 

 voltage by approximately ninety degrees. As the length of line 

 increases, the phase angles tend to lag from these positions, due to 



