Non-contact voltage measurement device
In a non-contact voltage measurement device that can precisely measure an alternating-current voltage with a simple structure, a first capacitor and second capacitor, having mutually correlated capacitances, are respectively formed between a first electrode and a conductor and between a second electrode and the conductor. An alternating-current signal is given between the first electrode and a first reference potential. When a switch is off, a first charge detecting signal matching charges accumulated in the second capacitor by the alternating-current signal is created with the second electrode kept at the first reference potential. When the switch is on, a second charge detecting signal matching charges accumulated in the second capacitor by the alternating-current voltage is created with the second electrode kept at a second reference potential. A measurement of the alternating-current voltage is calculated in a calculating unit, according to the first charge detecting signal and second charge detecting signal.
1. A non-contact voltage measurement device that measures an alternating voltage applied to a conductor, without electrical direct contact with the conductor, the device comprising:
a first electrode that forms a first capacitor with the conductor, the first capacitor having a first capacitance;
a second electrode that forms a second capacitor with the conductor, the second capacitor having a second capacitance correlating with the first capacitance;
a signal source that provides an alternating-current signal between the first electrode and a first potential;
a charge detecting unit that maintains the second electrode at a certain potential with respect to a reference potential, thereby generating a charge detecting signal corresponding to a charge accumulated in the second capacitor;
a switch provided between the first potential and a second potential, the reference potential being set at the first potential when the switch is turned off, and being set at the second potential when the switch is turned on to measure the alternating voltage; and
a calculating unit that calculates a value of the alternating voltage based on a first charge detecting signal obtained when the switch is turned off and a second charge detecting signal obtained when the switch is turned on.
2. The non-contact voltage measurement device according to claim 1 , wherein the signal source generates the alternating-current signal having a frequency higher than a frequency of the alternating voltage.
3. The non-contact voltage measurement device according to claim 1 , wherein:
the conductor has a conductor flat surface facing the first electrode and the second electrode; and
the first electrode has a first flat surface parallel to and facing the conductor flat surface, and the second electrode has a second flat surface parallel to and facing the conductor flat surface, the first and second flat surfaces being equally distant from the conductor flat surface.
4. The non-contact voltage measurement device according to claim 3 , wherein the first and second flat surfaces have a same shape and a same area such that the first capacitor and the second capacitor have a same capacitance.
5. The non-contact voltage measurement device according to claim 3 , wherein the first electrode and the second electrode are arranged adjacent to each other.
6. The non-contact voltage measurement device according to claim 1 , further comprising a guard ring that encloses at least one of the first electrode and the second electrode.
7. A non-contact voltage measurement device that measures an alternating voltage applied to a conductor, without electrical direct contact with the conductor, the device comprising:
a first electrode that forms a first capacitor with the conductor, the first capacitor having a first capacitance;
a second electrode that forms a second capacitor with the conductor, the second capacitor having a second capacitance correlating with the first capacitance;
a third electrode that forms a third capacitor with the conductor, the third capacitor having a third capacitance correlating with the first capacitance;
a signal source that provides an alternating-current signal between the first electrode and a first reference potential;
a first charge detecting unit that maintains the second electrode at a certain potential with respect to the first reference potential, thereby generating a first charge detecting signal corresponding to a charge accumulated in the second capacitor;
a second charge detecting unit that maintains the third electrode at a certain potential with respect to a second reference potential for measuring the alternating voltage, thereby generating a second charge detecting signal corresponding to a charge accumulated in the third capacitor; and
a calculating unit that calculates a value measurement of the alternating voltage based on the first charge detecting signal and the second charge detecting signal.
8. The non-contact voltage measurement device according to claim 7 , wherein the signal source generates the alternating-current signal having a frequency higher than a frequency of the alternating voltage.
9. The non-contact voltage measurement device according to claim 7 , wherein:
the conductor has a conductor flat surface facing the first electrode, the second electrode, and the third electrode; and
the first electrode has a first flat surface parallel to and facing the conductor flat surface, the second electrode has a second flat surface parallel to and facing the conductor flat surface, and the third electrode has a third flat surface parallel to and facing the conductor flat surface, the first, second, and third flat surfaces being equally distant from the conductor flat surface.
10. The non-contact voltage measurement device according to claim 9 wherein the first, second, and third flat surfaces have a same shape and a same area such that the first capacitor, the second capacitor, and the third capacitor have a same capacitance.
11. The non-contact voltage measurement device according to claim 9 , wherein the first electrode and the second electrode are arranged adjacent to each other.
12. The non-contact voltage measurement device according to claim 7 , further comprising at least one of:
a first guard ring that encloses at least one of the first electrode and the second electrode; and
a second guard ring that encloses the third electrode.
13. A non-contact voltage measurement device that measures an alternating voltage applied to a conductor, without electrical direct contact with the conductor, the device comprising:
a plurality of electrodes that form respective capacitors with the conductor, the plurality of capacitors having mutually correlated capacitances;
a signal source that provides an alternating-current signal between a first reference potential and a first electrode among the plurality of electrodes;
a detecting unit that generates a first charge detecting signal corresponding to a charge accumulated in the capacitor formed by a second electrode among the plurality of electrodes by applying the alternating-current signal while maintaining the second electrode at a certain potential with respect to the first reference potential, and also generates a second charge detecting signal corresponding to a charge accumulated in the capacitor formed by a third electrode among the plurality of electrodes by applying the alternating-current voltage while maintaining the third electrode at a certain potential with respect to a second reference potential for measuring the alternating voltage; and
a calculating unit that calculates a value of the alternating voltage based on the first charge detecting signal and the second charge detecting signal.
14. The non-contact voltage measurement device according to claim 1 , further comprising a second switch that selectively connects the first electrode to the signal source and to the second reference potential.