Non-contact high-voltage electrometer architecture with low-voltage feedback
First Claim
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1. A voltmeter for measuring an unknown voltage Vs on a target surface without contacting the target surface, the voltmeter comprising:
- a voltage measuring circuit having a detector plate forming a capacitance Cm with the target surface; and
a movable shutter for selectively exposing the detector plate to the target surface, wherein the voltage measuring circuit (1) measures, in a first sampling stage, a charge Vs*B, where B is proportional to Cm;
(2) measures, in a second sampling stage, a charge Vp*B, where Vp is a known voltage introduced by the voltage measuring circuit;
(3) determines the value B based on the known voltage Vp; and
(4) determines the value Vs based on the determined value B, and wherein the shutter is placed in a closed position substantially blocking the detector plate from the target surface for resetting the voltage measuring circuit prior to measuring the charge Vs*B and the shutter is moved into an opened position exposing the detector plate to the target surface for measuring the charges Vs*B and Vp*B.
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Abstract
A voltmeter measures an unknown voltage on a target surface using multiple sampling stages or a parallel reference capacitor. A movable shutter may alternately be closed during resetting of a voltage measuring circuit and opened so as to expose a detector plate to the target surface during two sampling stages. Alternatively, the shutter may be used to modulate exposure of a detector plate to the target surface.
47 Citations
19 Claims
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1. A voltmeter for measuring an unknown voltage Vs on a target surface without contacting the target surface, the voltmeter comprising:
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a voltage measuring circuit having a detector plate forming a capacitance Cm with the target surface; and a movable shutter for selectively exposing the detector plate to the target surface, wherein the voltage measuring circuit (1) measures, in a first sampling stage, a charge Vs*B, where B is proportional to Cm;
(2) measures, in a second sampling stage, a charge Vp*B, where Vp is a known voltage introduced by the voltage measuring circuit;
(3) determines the value B based on the known voltage Vp; and
(4) determines the value Vs based on the determined value B, and wherein the shutter is placed in a closed position substantially blocking the detector plate from the target surface for resetting the voltage measuring circuit prior to measuring the charge Vs*B and the shutter is moved into an opened position exposing the detector plate to the target surface for measuring the charges Vs*B and Vp*B. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for measuring an unknown voltage Vs on a target surface, the method comprising:
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resetting a voltage measuring circuit with a shutter in a closed position so as to substantially block a detector plate of the voltage measuring circuit from exposure to the target surface; a moving the shutter into an opened position so as to expose the detector plate with a capacitance of Cm to the target surface; measuring a charge Vs*B using the detector plate, where B is proportional to Cm; measuring a charge Vp*B with the shutter still in the opened position, where Vp is a known voltage; determining the value of B based on the known voltage Vp; and determining the value of Vs based on the determined value B. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A voltmeter for measuring an unknown voltage Vs on a target surface without contacting the target surface, the voltmeter comprising:
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a voltage measuring circuit having a first detector plate forming a capacitance Cm with the target surface and a second detector plate forming a capacitance N*Cm with the target surface, where N is a known constant representing that the second detector plate is N times the size of the first detector plate; and a movable shutter for modulating exposure of the first detector plate to the target surface, wherein the voltage measuring circuit comprises; a nominal modulation capacitance circuit for measuring a first charge proportional to Vs*dCm/dt using the first detector plate; a parallel capacitance circuit for measuring a second charge proportional to N*Cm*dVp/dt using the second detector plate, where Vp is a known voltage modulated in phase and frequency with the modulated exposure of the first detector plate; a comparison circuit for comparing the first and second charges; and a controller for adjusting the magnitude of Vp based on the comparison circuit until the first and second charges are equal and determining Vs based on the voltage Vp. - View Dependent Claims (18, 19)
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Specification