. Electrical instruments and telephones of the Signal corps . eneral application and canbe made in situations where the Murray test can not. The connec-tions for this tast are shown in figure 19G. The various parts of thecircuit are given the same letter designations as for the Murray testof figures 194 and 195. 278 ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. AVith the circuit of figure IDG adjust the variable resistance arm Rof the AMieatstone bridge until the galvanometer is not deflected,record the values of ,1, 5, and R. Now disconnect the ground frombattery and connect as shown by dot
. Electrical instruments and telephones of the Signal corps . eneral application and canbe made in situations where the Murray test can not. The connec-tions for this tast are shown in figure 19G. The various parts of thecircuit are given the same letter designations as for the Murray testof figures 194 and 195. 278 ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. AVith the circuit of figure IDG adjust the variable resistance arm Rof the AMieatstone bridge until the galvanometer is not deflected,record the values of ,1, 5, and R. Now disconnect the ground frombattery and connect as shown by dotted line and measure the com-bined resistance of the leads C C and the two conductors a h inseries; call this value r. Combining the results of the two measure-ments taken above, the resistance of the conductor from the point oftest to the fault is— Br-AR A + B C. Check the measurements and calculations obtained by the aboveprocess by reversing tho connections of the bridge to the conductorsat either end of the leads and obtain a second set of readings. If the. Fig. 196. new values of bridge readings be designated as .1, B\ and /?, theneAv value of the resistance to the fault is— ^^A{r±BJ_^,A + B If ( equal the total resistance of the bad wire the distance to the fault is -^-^r where /. is the total length of the wire. The check measurements should always be made when using either the Varleyor the Murray loop test, as the time and labor required are incon-siderable and the certainty of location is uuich increased. For crossed wires the method of figure 197a should be used. Thecircuit, it will be noted, is the same as on figure 19(j. except that onewire of the crossed pair is used to replace the earth connection. ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. 279 LOCATION OF FAULTS IN TELEGRAPH LINES. In order to secure the best possible result iu the working of telegraph lineswe nuist keep down the resistance of the conductor in the circuit and increasethe resistance of the in
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