A voltmeter for the measurement and comparison of peak and r.m.s. values of recurrent voltage waves

The construction is described of a voltmeter circuit suitable for the measurement of d.c. 50-c/s peak, and 50-c/s r.m.s. voltages. This circuit has a range of 200¿1000 volts, and can be used with a reistance potential divider for measurements up to 120 kV. It consists essentially of an electrostatic instrument in combination with a diode rectifier and a reservoir capacitor. With the present apparatus the accuracy of measurement is estimated to be within ± 2% for d.c. voltages and ± 3% for 50-c/s voltages. Peak factors should be measurable to ± 1%, and ripple voltages on d.c. supplies to within 10% of the ripple, i.e. to 1% of the full voltage for 10% ripple.