High voltage measuring apparatus

Claim 1

High voltage measuring apparatus comprising: a high voltage series circuit adapted to be connected across the output of an unknown high voltage D.C. source, said circuit including first and second elements connected in series, said first and second elements being a resistor and a variable capacitor, respectively; an excitation source of an A.C. signal; means connected from said excitation source to increase and to decrease the capacitance of said variable capacitor periodically as a function of said A.C. signal; utilization means connected from the junction of said resistor and said variable capacitor, said utilization means including a D.C. blocking capacitor connected from said junction, a synchronous detector, intermediate means connected from the output electrode of said D.C. blocking capacitor to impress an A.C. voltage on said synchronous detector directly proportional to that appearing on the output electrode of said D.C. blocking capacitor, said synchronous detector also being connected from the output of said excitation source to produce a D.C. output voltage directly proportional to the peak amplitude of said A.C. voltage, said utilization means including a voltmeter connected from the output of said synchronous detector; said intermediate means including a differential amplifier, the output electrode of said D.C. blocking capacitor being connected to the noninverting input of said amplifier, the output of said amplifier being connected to the input of said synchronous detector, a first auxiliary resistor connected from the output of said amplifier to the inverting input thereof, and a second auxiliary resistor connected from a first point of reference potential to said inverting input.