LOCATION OF OPENS IN TOLL TELEPHONE CABLES 



53 



The galvanometer and the equipment required in the modified form 

 of the De Sauty bridge have been incorporated in a compact unit which 

 is shown in Fig. 23. This bridge, while being particularly adapted 

 to the 4-cycle impedance measurements required for open location 

 tests, is also applicable for direct-current bridge measurements. 

 Assembly details for the bridge arrangement are shown in Fig. 24. 



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Fig. 24 — Internal assembly of the impedance bridge. 



The alternating-current galvanometer is sufficiently sensitive to be 

 directly actuated by any significant unbalance of the impedance 

 bridge, so that it is unnecessary to use an amplifier, rectifier, or other 

 converting apparatus which may be difficult of adjustment or main- 

 tenance. 



A few additional features are outlined as some of the significant 

 results of this development of an improved open location method. 



It has been shown that the error, caused by the deviation from the 

 straight line relation between sending end admittance and physical 

 length of line, has been reduced to a value which may be neglected as 

 being less than the required accuracy of the open location method. 



As a result of an analysis of errors which are introduced by line 

 irregularities, methods were devised for applying corrections for all 

 such errors which are of a magnitude sufficient to interfere with the 

 desired accuracy. 



