1.1 l.(. I KU .11. ll:.\l.\.tM' I III IK .Iffl.ll.l I l(>.\.S ,»>.i 



AnothtT iist> whiih is iiKule of alternatinn rurri-iU capacity nuasiirr- 

 nK'iUs is in conneotitm with tlu' ojh-ii location test provided at toil 

 test boards. The essential features of tin- cirniit arrangement are 

 shown in Vi^. 1 1. 



The ordinary Murray eonneiiioii of tlie lest hoard i)riilv,'e is used, 

 the four arms of the liriil^e consisting; of one fixed l,0()()-ohm resistance 

 .1. a variable resistance R. a standard 1 ftf. condenser C and the open 



L"« i/^f Tmi 



DoS'Slance Laf^p 1 I Repeating CopI 



Kii;. 11 



condenser imder test C'x. Ordinary 20 cycle ringing current is used 

 as the measuring current and the galvanometer or voltmeter con- 

 nected through a reversing relay so that it will always read in one 

 direction. For the balanced condition of the bridge as indicated on 



the gaKanometer the relation ('v= . t" holds. Substituting the nu- 



merical values for A and C in the abo\ e formula Cx then equals y-r^- 



The above test (jrovides a means for determining the approximate 

 distributed capacity of a circuit up to the point where it is open. 

 With previous measurements on known lengths and similar types of 

 circuits available and assuming the distributed capacity propor- 

 tional to the length of circuit, this test provides a simple means for 

 determining the approximate distance out to the open. In practice 

 fairly gotxi results are obtained on loaded or non-loaded open wire 

 circuits up to 200 miles in length and on loaded or non-loaded cable 

 up to 40 miles in length. The degree of accuracy with which opens 

 can be located by this method depends, of course, on ha\ing good 

 unit capacity measurements for the different types of circuits in\ol\ed 

 in the testing work. 



(2) Capacity Unbalance Tests. If the electrostatic capacities between 

 wires and between wires and ground in telephone circuits are not 



