Non-contact DC voltage measurement device with oscillating sensor
Systems and methods for measuring direct current (DC) voltage of an insulated conductor (e.g., insulated wire) are provided, without requiring a galvanic connection between the conductor and a test electrode or probe. A non-contact DC voltage measurement device may include a conductive sensor that is mechanically oscillated. The insulated conductor under test serves as a first conductive element or electrode of a coupling capacitor, and the vibrating conductive sensor serves as a second conductive element or electrode of the coupling capacitor. The oscillation of the conductive sensor provides the coupling capacitor with a time-varying capacitance value. The measurement device detects current flowing through the coupling capacitor, and determines the DC voltage in the insulated conductor using the detected current and the time-varying capacitance. The determined DC voltage may be output to a display or transmitted to an external system via a wired or wireless connection.
1. A device to measure direct current (DC) voltage in an insulated conductor, the device comprising:
a housing;
a conductive sensor physically coupled to the housing, the conductive sensor selectively positionable proximate the insulated conductor without galvanically contacting the insulated conductor, wherein the conductive sensor capacitively couples with the insulated conductor;
a conductive internal ground guard which at least partially surrounds the conductive sensor and is galvanically isolated from the conductive sensor, the internal ground guard sized and dimensioned to shield the conductive sensor from stray currents;
a conductive reference shield which surrounds at least a portion of the housing and is galvanically insulated from the internal ground guard, the conductive reference shield sized and dimensioned to reduce currents between the internal ground guard and an external ground;
a mechanical oscillator operatively coupled to the conductive sensor, in operation, the mechanical oscillator causes the conductive sensor to mechanically oscillate according to a mechanical oscillation amplitude and a mechanical oscillation frequency such that a distance between the conductive sensor and the insulated conductor varies periodically according to the mechanical oscillation amplitude and the mechanical oscillation frequency;
a common mode reference voltage source which, in operation, generates an alternating current (AC) reference voltage having a reference frequency, the common mode reference voltage source electrically coupled between the internal ground guard and the conductive reference shield;
a sensor signal measurement subsystem electrically coupled to the conductive sensor, wherein the sensor signal measurement subsystem, in operation, generates a sensor current signal indicative of current conducted through the conductive sensor; and
control circuitry communicatively coupled to the sensor signal measurement subsystem, wherein, in operation, the control circuitry:
receives the sensor current signal from the sensor signal measurement subsystem; and
determines the DC voltage in the insulated conductor based at least in part on the received sensor current signal.
2. The device of claim 1 , wherein the control circuitry determines the DC voltage in the insulated conductor based at least in part on the received sensor current signal, the mechanical oscillation frequency, the AC reference voltage, and the reference frequency.
3. The device of claim 1 , wherein the mechanical oscillator comprises a piezoelectric effect mechanical oscillator.
4. The device of claim 1 , wherein the mechanical oscillator comprises a microelectromechanical (MEMS) mechanical oscillator.
5. The device of claim 1 , wherein the control circuitry, in operation:
converts the received sensor current signal to a digital signal; and
processes the digital signal to obtain a frequency domain representation of the sensor current signal.
6. The device of claim 5 , wherein the control circuitry implements a fast Fourier transform (FFT) to obtain the frequency domain representation of the sensor current signal.
7. The device of claim 6 , wherein the common mode reference voltage source generates the AC reference voltage in phase with a window of the FFT implemented by the control circuitry.
8. The device of claim 1 , wherein the control circuitry comprises at least one electronic filter which filters the received sensor current signal.
9. The device of claim 1 , wherein the control circuitry processes the sensor current signal to determine an insulated conductor current component and a reference current component, the insulated conductor current component indicative of the current conducted through the conductive sensor due to the voltage in the insulated conductor, and the reference current component indicative of the current conducted through the conductive sensor due to the voltage of the common mode reference voltage source.
10. The device of claim 9 , wherein the control circuitry determines the frequency of the determined insulated conductor current component of the sensor current signal.
11. The device of claim 1 , wherein, in operation, the sensor signal measurement subsystem receives an input current from the conductive sensor, and the sensor current signal comprises a voltage signal indicative of the input current received from the conductive sensor.
12. The device of claim 1 , wherein the sensor signal measurement subsystem comprises an operational amplifier, which operates as a current-to-voltage converter.
13. A method of operating a device to measure direct current (DC) voltage in an insulated conductor, the device comprising a housing, a conductive sensor physically coupled to the housing which is selectively positionable proximate an insulated conductor without galvanically contacting the conductor, a conductive internal ground guard which at least partially surrounds the conductive sensor and is galvanically isolated from the conductive sensor, wherein the internal ground guard is sized and dimensioned to shield the conductive sensor from stray currents, a conductive reference shield which surrounds at least a portion of the housing and is galvanically insulated from the internal ground guard, wherein the conductive reference shield is sized and dimensioned to reduce currents between the internal ground guard and an external ground, the method comprising:
mechanically oscillating the conductive sensor according to a mechanical oscillation amplitude and a mechanical oscillation frequency such that a distance between the conductive sensor and the insulated conductor varies periodically according to the mechanical oscillation amplitude and the mechanical oscillation frequency;
causing a common mode reference voltage source to generate an alternating current (AC) reference voltage having a reference frequency, the common mode reference voltage source electrically coupled between the internal ground guard and the conductive reference shield;
generating, by a sensor signal measurement subsystem, a sensor current signal indicative of current conducted through the conductive sensor;
receiving, by control circuitry, the sensor current signal from the sensor signal measurement subsystem; and
determining, by the control circuitry, the DC voltage in the insulated conductor based at least in part on the received sensor current signal.
14. The method of claim 13 , wherein generating the sensor current signal comprises:
receiving an input current from the conductive sensor; and
generating a voltage signal indicative of the input current received from the conductive sensor.
15. The method of claim 13 , wherein the sensor current signal is generated utilizing an operational amplifier operating as a current-to-voltage converter.
16. The method of claim 13 , wherein mechanically oscillating the conductive sensor comprises mechanically oscillating the conductive sensor using a piezoelectric effect mechanical oscillator.
17. The method of claim 13 , wherein mechanically oscillating the conductive sensor comprises mechanically oscillating the conductive sensor using a microelectromechanical (MEMS) mechanical oscillator.
18. The method of claim 13 , wherein determining the DC voltage in the insulated conductor comprises:
converting, by at least one processor, the received sensor current signal to a digital signal; and
processing, by at least one processor, the digital signal to obtain a frequency domain representation of the sensor current signal.
19. The method of claim 18 , wherein processing the digital signal comprises implementing a fast Fourier transform (FFT) to obtain the frequency domain representation of the sensor current signal.
20. The method of claim 13 , wherein determining the DC voltage in the insulated conductor comprises electronically filtering the received sensor current signal.
21. A device to measure direct current (DC) voltage in an insulated conductor, the device comprising:
a conductive sensor selectively positionable proximate the insulated conductor without galvanically contacting the insulated conductor, wherein the conductive sensor capacitively couples with the insulated conductor;
a mechanical oscillator operatively coupled to the conductive sensor, in operation, the mechanical oscillator causes the conductive sensor to mechanically oscillate to vary the capacitance between the conductive sensor and the insulated conductor with respect to time;
a conductive internal ground guard which at least partially surrounds the conductive sensor and is galvanically isolated from the conductive sensor;
a conductive reference shield which surrounds at least a portion of the housing and is galvanically insulated from the internal ground guard;
a common mode reference voltage source which, in operation, generates an alternating current (AC) reference voltage having a reference frequency, the common mode reference voltage source electrically coupled between the internal ground guard and the conductive reference shield;
a sensor signal measurement subsystem electrically coupled to the conductive sensor, wherein the sensor signal measurement subsystem, in operation, generates a sensor current signal indicative of current conducted through the conductive sensor; and
control circuitry communicatively coupled to the sensor signal measurement subsystem, wherein, in operation, the control circuitry:
receives the sensor current signal from the sensor signal measurement subsystem; and
determines the DC voltage in the insulated conductor based at least in part on the received sensor current signal.
22. The device of claim 21 , wherein, in operation, the control circuitry determines the DC voltage in the insulated conductor based on the received sensor current signal and based on the variation of the capacitance between the conductive sensor and the insulated conductor with respect to time.
23. The device of claim 21 , wherein the mechanical oscillator comprises at least one of a piezoelectric effect mechanical oscillator or a microelectromechanical (MEMS) mechanical oscillator.