702 ELECTRICAL MEASUREMENTS 



The testing transformer is operated with one terminal 

 grounded. The other terminal, of the condenser type, fur- 

 nishes the capacity necessary for the operation of the arrange- 

 ment. Variations of the frequency from the normal value are 

 indicated and measured by the frequency meter at the top of 

 the panel. 



Referring to the diagram, Fig. 441, it will be seen that the full 

 potential difference which is applied to the specimen is also 

 impressed between the outer conducting layer of the condenser 

 terminal C, i.e., its outside flange, and the conductor H. For 



Fi*ed Ketiitonce 



FIG. 442. Section of Simplex Peak-voltmeter. 



the first half wave the charging current flowing to the condenser 

 C passes through Vi, and for the second half wave through 

 V*. The unidirectional current through V\ is measured by the 

 pivoted moving coil galvanometer, M, which is arranged for 

 switchboard use. 



Theoretically, the electrical valves may introduce a small 

 error, for if the voltage wave is greatly distorted the current 

 flowing to the condenser may have negative values during a half- 

 cycle. In order that the net value of the current flowing through 

 the condenser may be measured, these negative values should be 

 included in the current which flows through the galvanometer. 



Another method of measuring peak voltages is by the use of 

 an instrument based on the oscillograph principle, such as the 

 Simplex Vibrating Voltmeter, a section of which is shown in Fig. 



