LOCATION OP OPENS IN TOLL TELEPHONE CABLES 



47 



The chosen frequency of four cycles was used in this calculation. 

 These curves of phase angle and current magnitude are shown in 

 Figs. 14 and 15, and correspond to those shown in Figs. 11 and 12, 

 calculated by the other method. 



Since R increases with increase in length of line, the sensitivity 

 per ohm change in R will be better throughout the range of lengths if 

 the sensitivity for a given change in i? is a maximum when i? is a 

 maximum. Taking fifty miles as the average total length of line, and 



2r- 







10 20 



30 40 50 60 70 «0 

 Length of Line in Miles. 



Fig. 17 — Calculated sensitivity for lengths of non-loaded 19-gauge conductor 

 using the impedance bridge arrangement which gave the maximum sensitivity for 

 curve I in Fig. 16. Sensitivity for unbalance in the component: 



I — R with the phase of testing potential applied for balancing R. 

 II — r with the phase of testing potential applied for balancing r. 

 Ill — R with the phase of testing potential applied for balancing r. 

 IV- — r with the phase of testing potential applied for balancing R. 



assuming two bridge potentials ninety degrees apart, a set of sensi- 

 tivity curves was calculated for this length of line, the phase of the 

 field potential being varied on either side of the bridge testing poten- 

 tial. The lag of the field current from the field voltage calculated 

 from the field inductance and resistance was found to be about forty 

 degrees. The resulting sensitivity curves are shown in Fig. 16, and 

 these indicate a maximum sensitivity for R and r with the field poten- 

 tial in phase with the potential used to balance r. 



With the assumed conditions as determined by this calculation, 



