MEASUREMENT OF POTENTIAL DIFFERENCE 259 



The voltage is applied at / and I'] between ab and be are two 

 condensers which can be short-circuited at will, thus altering 

 the range of the instrument. They are placed within the highly 

 insulated condenser terminal, T, and are brought into action by 

 means of a silk cord. The fixed attracting elements are at 

 B and B'. The movable element consists of two hollow metal 

 cylinders M and M r which are united by a suitable web. This 

 system hangs freely from a single pivot resting in a jewel. The 

 usual controlling spring and zero adjustment are provided. 



There is no electrical connection to the movable element; 

 on the application of the voltage, charges are induced on it. 



Diagrammatic Arrangcmcut 



of Uigb-Tension 

 Electrostatic Voltmeter 



CALIBRATION CURVES OF 

 120-000 VOLT WESTINC.HOUSE ELECTROSTATIC 



VOLTMETER 

 (a ) 80 'KUorolt Setting. Condenser 'a 'Uhort 



Circuited 

 ( 6) 40 KUoTolt Betting, Condensere'a'Vnd"6 



bbort Circuited 



With Neither Condenser Short Circuited, the 

 M.-t.-r Rcadi Directlj in Kllorolts on Lower 



40 



*! 



30. 

 'a 



Kg 



S 



19 Kil 



20 30 40 50 60 70 80 



Divisioirs on Upper Qnilorm Seals 



90 100 



FIG. 145. Westinghouse high-range electrostatic voltmeter. 



As the curved plates B and B' and the movable parts are not 

 concentric, the latter will move so as to increase the electro- 

 static capacity of the arrangement; that is, in the direction of 

 the arrow. The plates B and B' are so bent that the scale is 

 approximately uniform over a considerable portion of its length. 

 All the working parts are immersed in oil, and as the movable 

 element is hollow, the weight is practically removed from the 

 jewel and pivot. 



These voltmeters are made for potentials as high as 200,000 

 volts. Instruments having a range of 25,000 volts, both con- 

 densers being short-circuited, will read up to 100,000 volts with 

 both condensers in service. 



