AC voltage measurement circuit
View Patent ↗A voltage measurement circuit is operative to measure a high voltage AC signal and includes a capacitive divider circuit and a compensator circuit. The capacitive divider circuit includes first and second inputs, across which, in use, is received a high voltage AC signal and also includes second and third capacitors. First and second plates of each of the first, second and third capacitors are defined by conductive layers of a printed circuit board and the dielectric of each of the first, second and third capacitors being defined by a non-conducting part of the printed circuit board. A compensator circuit has a configurable transfer function and includes an input connected across the first and second plates of the third capacitor and an output. The compensator circuit is operative to change a voltage received at its input in accordance with the transfer function and to provide the changed voltage at its output.
1. A method for measuring a high voltage AC signal comprising:
applying a known voltage signal at an input of a capacitive divider circuit;
measuring a voltage at an output of the capacitive divider circuit;
determining a transfer function of a compensator circuit based upon relative, ideal impedances of capacitors of the capacitive divider circuit to alter the measured voltage such that it corresponds to a desired voltage;
configuring the compensator circuit with the determined transfer function; and
measuring a high voltage AC signal such that the compensator circuit is configured to change a voltage received at its input using the determined transfer function to provide a changed voltage at its output.
2. The method of claim 1 , further comprising determining the transfer function in dependence on solely one applied known voltage.
3. The method of claim 1 , further comprising determining the transfer function in dependence on two applied known voltages of different levels.
4. The method of claim 1 , further comprising determining the transfer function in dependence on more than two applied known voltages of different levels and respective corresponding measurements.
5. The method of claim 1 , further comprising operating the capacitive divider circuit as a DC isolator.
6. The method of claim 1 , further comprising storing at least one value for the transfer function in a storage device.
7. A voltage measurement circuit configured to measure a high voltage AC signal comprising:
a capacitive divider circuit including:
first and second inputs configured to receive a high voltage AC signal; and
first and second capacitors having first plates coupled to the first and second inputs, respectively; and
a third capacitor coupled across second plates of the first and second capacitors, each of the first, second and third capacitors formed in a printed circuit board; and
a compensator circuit having a configurable transfer function including:
an input electrically connected across the third capacitor; and
an output, the compensator circuit being configured to change a voltage received at its input in accordance with the configurable transfer function to provide the changed voltage at its output.
8. The voltage measurement circuit of claim 7 , wherein the capacitive divider circuit is configured to operate as a DC isolator.
9. The voltage measurement circuit of claim 8 , wherein the DC isolator further includes at least one of a parasitic impedance and an impedance provided by a discrete component.
10. The voltage measurement circuit of any claim 7 , wherein the voltage measurement circuit comprises a differential active circuit.
11. The voltage measurement circuit of claim 10 , wherein the differential active circuit includes at least one of a buffer and an amplifier.
12. The voltage measurement circuit of claim 7 , wherein the compensator circuit includes an analog to digital converter configured to convert a voltage measured across the third capacitor to a digital signal.
13. The voltage measurement circuit of claim 12 , wherein the compensator circuit includes digital processing circuitry configured to determine the transfer function in dependence on at least one applied known voltage and a corresponding voltage measured across the third capacitor.
14. The voltage measurement circuit of any claim 7 , wherein the compensator circuit includes at least one of a digital adder and a digital multiplier, with the digital adder being configured to receive a digital form of the measured voltage and to add an offset value to the digital measured voltage to thereby effect correction and the digital multiplier being configured to receive a digital form of the measured voltage and to multiply the digital measured voltage with a gain value to thereby effect correction.
15. The voltage measurement circuit of claim 7 , wherein a plate of at least one of the first, second and third capacitors is defined by a layer of metal in or on the printed circuit board.
16. The voltage measurement circuit of claim 15 , wherein first and second plates of a capacitor are formed on opposing upper and lower surfaces of the printed circuit board such that the non-conducting body of the printed circuit board constitutes the dielectric of the capacitor.
17. The voltage measurement circuit of claim 15 , wherein first and second plates of a capacitor are formed within the printed circuit board such that they are spaced apart from each other and with their footprints overlapping, whereby a non-conducting part of the printed circuit board between the first and second plates constitutes the dielectric of the capacitor.
18. The voltage measurement circuit of claim 7 , wherein the third capacitor includes at least in part a discrete capacitor.
19. The voltage measurement circuit of claim 7 , wherein the third capacitor is a parasitic capacitance.
20. The voltage measurement circuit of claim 7 , wherein the voltage measurement circuit further includes a rectification circuit is configured to rectify a high voltage AC signal before it reaches the capacitive divider.