292 



ELECTRICAL MEASUREMENTS 



the potentiometer is attached to the outside circuits; a change- 

 over switch, for quickly substituting alternating for direct cur- 

 rent; and the phase shifter; this last device is best operated from a 

 single-phase circuit by means of a phase-splitting condenser and 

 resistance. This arrangement is best because any single-phase 

 supply, of good wave form, can be used and all doubt as to the 

 exact quadrature of the two phases eliminated. 



The phases can be adjusted to within 0.l, the procedure being 

 as follows: Join the 100-volt supply to the two terminals marked 

 Phase 1 on the phase-shifting transformer. The condenser and 



ctu A D ii fc VoS. [Bat. [Rotor Galv.Vib.Galv. 



FIG. 167. Diagram for Drysdale-Tinsley alternating- and direct-current 



potentiometer. 



resistance, in series with the terminals marked Phase 2, are also 

 connected across the 100-volt supply. The secondary is then 

 turned by the tangent screw until the pointer marked AXIS, is 

 at on the dial. By means of the rheostat of the potenti- 

 ometer, the current is adjusted until the dynamometer reads 

 exactly 50. Then the tangent screw is turned until the AXIS 

 pointer is at 45 leading. If the dynamometer reads higher or 

 lower than 50 the capacity is altered until the reading is correct. 

 The AXIS pointer is then turned to 90 and the resistance altered 



