RESISTANCE MEASURING APPARATUS

• US 20090322358A1
• Filed: 06/17/2009
• Published: 12/31/2009
• Est. Priority Date: 06/30/2008
• Status: Active Grant

• Current Assignee: Hioki Denki Kabushiki Kaisha (Hioki E.E. Corporation)
• Original Assignee: Hioki Denki Kabushiki Kaisha (Hioki E.E. Corporation)
• Inventors: Imaizumi, Satoshi
• Granted Patent: US 8,914,249 B2
• Time in Patent Office: Days
• US Class Current: 324/713
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• CPC Class Codes: G01R 27/20 Measuring earth resistance; Measuring contact resistance, e.g. of earth connections, e.g. plates

Abstract

A resistance measuring apparatus includes: a voltage injector that injects an AC signal into a circuit by applying an AC voltage to an injection coil; a current measuring unit that measures an AC current produced in the circuit by the injection coil using a detection coil; a processing unit that calculates the circuit resistance from the AC signal voltage and the measured AC current; and a reference signal generator that outputs a binary reference signal that has a same period as the AC voltage and is synchronized to the clock. The voltage injector generates a stepped wave whose amplitude changes in synchronization with a clock, applies a signal based thereon as the AC voltage. The current measuring unit converts the current in the detection coil to a voltage signal, carries out synchronous detection using the reference signal, and measures the AC current based on the synchronous detection result.

Claims

1. A resistance measuring apparatus comprising:

a voltage injecting unit that injects a testing AC signal into a measured circuit by applying an AC voltage to an injection coil;

a current measuring unit that detects and measures an AC current, which is flowing in the measured circuit due to injection of the testing AC signal, using a detection coil; and

a processing unit that calculates a resistance value of the measured circuit based on a voltage value of the injected testing AC signal and a measured value of the AC current,

wherein the voltage injecting unit generates a stepped wave whose amplitude changes in synchronization with a reference clock and applies a signal based on the stepped wave as the AC voltage,

the resistance measuring apparatus further includes a reference signal generating unit that synchronizes a binary signal with a same period as the AC voltage to the reference clock and outputs the binary signal as a reference signal, and

the current measuring unit converts a current flowing in the detection coil due to the injection of the testing AC signal to a voltage signal, carries out synchronous detection on the voltage signal using the reference signal, and measures a current value of the AC current based on a signal obtained by the synchronous detection.

2. The resistance measuring apparatus according to claim 1,

wherein the voltage injecting unit carries out a filtering process on the stepped wave and applies a signal generated by subjecting the stepped wave to the filtering process to the injection coil as the AC voltage.

3. The resistance measuring apparatus according to claim 1,

wherein the reference signal generating unit includes a flip-flop that synchronizes the binary signal to the reference clock and outputs the synchronized binary signal as the reference signal.

4. The resistance measuring apparatus according to claim 1,

wherein the reference signal generating unit includes a comparator that generates the binary signal based on the AC voltage.

5. The resistance measuring apparatus according to claim 4,

wherein the comparator is constructed of a comparator that exhibits hysteresis.

6. The resistance measuring apparatus according to claim 1,

wherein the voltage injecting unit includes a class D amplifier that amplifies the signal based on the stepped wave to generate the AC voltage.

7. The resistance measuring apparatus according to claim 1,

wherein the voltage injecting unit includes:

a counter that changes a count value in synchronization with the reference clock between a start value and an end value that are set in advance; and

a D/A conversion circuit that generates the stepped wave based on the count value.

8. The resistance measuring apparatus according to claim 7,

wherein the D/A conversion circuit is constructed of a resistance ladder circuit.

9. A resistance measuring apparatus comprising:

a voltage injecting unit that injects a testing AC signal into a measured circuit by applying an AC voltage to an injection coil;

a current measuring unit that detects and measures an AC current, which is flowing in the measured circuit due to injection of the testing AC signal, using a detection coil;

a processing unit that calculates a resistance value of the measured circuit based on a voltage value of the injected testing AC signal and a measured value of the AC current; and

a single clamp-type housing that houses the injection coil and the detection coil,

wherein the voltage injecting unit applies a signal that is synchronized to a reference signal as the AC voltage, and

the current measuring unit converts a current flowing in the detection coil due to the injection of the testing AC signal to a voltage signal, carries out synchronous detection on the voltage signal using the reference signal, and measures a current value of the AC current based on a signal obtained by the synchronous detection.

10. The resistance measuring apparatus according to claim 9,

wherein the voltage injecting unit includes a class D amplifier that amplifies the signal that is synchronized to the reference signal to generate the AC voltage.

11. The resistance measuring apparatus according to claim 9,

wherein the injection coil and the detection coil are enclosed in the housing so as to be stacked in a thickness direction thereof.

12. The resistance measuring apparatus according to claim 9,

wherein the injection coil and the detection coil are formed with respectively different diameters, one coil out of the injection coil and the detection coil with a smaller diameter is positioned inside another coil out of the injection coil and the detection coil, and the injection coil and the detection coil are enclosed inside the housing so as to be disposed on a same plane.

13. A resistance measuring apparatus comprising:

a voltage injecting unit that injects a testing AC signal into a measured circuit by applying an AC voltage to an injection coil;

a current measuring unit that detects and measures an AC current, which is flowing in the measured circuit due to injection of the testing AC signal, using a detection coil; and

a processing unit that calculates a resistance value of the measured circuit based on a voltage value of the injected testing AC signal and a measured value of the AC current,

wherein the voltage injecting unit intermittently applies the AC voltage,

the resistance measuring apparatus further comprises a reference signal generating unit that generates a binary signal in synchronization with the applied AC voltage and outputs the binary signal as a reference signal, and

the current measuring unit includes;

a current-to-voltage converting circuit that converts a current flowing in the detection coil due to the injection of the testing AC signal to a voltage signal;

a synchronous detection circuit that carries out synchronous detection on the voltage signal using the reference signal;

a DC removal circuit that integrates a detection output signal outputted from the synchronous detection circuit, removes a DC component, and outputs an AC component; and

an AC amplifier circuit that amplifies the AC component, wherein the current measuring unit measures the current value of the AC current.

14. The resistance measuring apparatus according to claim 13,

wherein the reference signal generating unit includes a comparator that generates the binary signal based on the applied AC voltage.

15. A resistance measuring apparatus comprising:

a voltage injecting unit that injects a testing AC signal into a measured circuit;

a current measuring unit that detects and measures an AC current, which is flowing in the measured circuit due to injection of the testing AC signal, using a detection coil; and

a processing unit that calculates a resistance value of the measured circuit based on the injected testing AC signal and the measured AC current,

wherein the voltage injecting unit generates the testing AC signal in synchronization with a reference signal,

the current measuring unit includes;

a first amplifier unit that includes at least a first operational amplifier with an inverted input terminal connected to one end of the detection coil and a non-inverted input terminal into which a reference voltage is inputted, converts a current flowing in the detection coil to a first voltage signal, and outputs the first voltage signal;

a second amplifier unit that includes at least a second operational amplifier with an inverted input terminal connected to another end of the detection coil and a non-inverted input terminal into which the reference voltage is inputted, converts a current flowing in the detection coil to a second voltage signal with opposite phase to the first voltage signal, and outputs the second voltage signal;

a first extraction unit that carries out synchronous detection on the first voltage signal and the second voltage signal in synchronization with the reference signal to extract a positive polarity signal composed of only positive side parts of waveforms of the first voltage signal and the second voltage signal;

a second extraction unit that carries out synchronous detection on the first voltage signal and the second voltage signal in synchronization with the reference signal to extract a negative polarity signal composed of only negative side parts of waveforms of the first voltage signal and the second voltage signal; and

a third amplifier unit that outputs a difference signal on a difference between the positive polarity signal and the negative polarity signal, and

the processing unit calculates a current value based on a voltage value of the testing AC signal and the difference signal and calculates a resistance value of the measured circuit based on the voltage value and the current value.

17. The resistance measuring apparatus according to claim 15, further comprising:

a first capacitance element that is disposed so as to come after the first operational amplifier and removes a DC component included in the first voltage signal; and

a second capacitance element that is disposed so as to come after the second operational amplifier and removes a DC component included in the second voltage signal.

19. The resistance measuring apparatus according to claim 17, further comprising:

a first filter unit that removes a harmonic component of the testing AC signal included in the first voltage signal; and

a second filter unit that removes a harmonic component of the testing AC signal included in the second voltage signal.

16. A resistance measuring apparatus comprising:

a voltage injecting unit that injects a testing AC signal into a measured circuit;

a current measuring unit that detects and measures an AC current, which is flowing in the measured circuit due to injection of the testing AC signal, using a detection coil; and

a processing unit that calculates a resistance value of the measured circuit based on the injected testing AC signal and the measured AC current,

wherein the voltage injecting unit generates the testing AC signal in synchronization with a reference signal,

the current measuring unit includes;

a first amplifier unit that includes at least a first operational amplifier with an inverted input terminal connected to one end of the detection coil and a non-inverted input terminal into which a reference voltage is inputted, converts a current flowing in the detection coil to a first voltage signal, and outputs the first voltage signal;

a second amplifier unit that includes at least a second operational amplifier with an inverted input terminal connected to another end of the detection coil and a non-inverted input terminal into which the reference voltage is inputted, converts a current flowing in the detection coil to a second voltage signal with opposite phase to the first voltage signal, and outputs the second voltage signal;

a third amplifier unit that outputs a difference signal on a difference between the first voltage signal and the second voltage signal; and

an extraction unit that carries out synchronous detection on the difference signal in synchronization with the reference signal to extract a single-polarity signal composed of one of a positive-side part and a negative-side part of a waveform of the difference signal, and

the processing unit calculates a current value based on a voltage value of the testing AC signal and the single-polarity signal and calculates a resistance value of the measured circuit based on the voltage value and the current value.

18. The resistance measuring apparatus according to claim 16, further comprising:

a first capacitance element that is disposed so as to come after the first operational amplifier and removes a DC component included in the first voltage signal; and

a second capacitance element that is disposed so as to come after the second operational amplifier and removes a DC component included in the second voltage signal.

20. The resistance measuring apparatus according to claim 18, further comprising:

a first filter unit that removes a harmonic component of the testing AC signal included in the first voltage signal; and

a second filter unit that removes a harmonic component of the testing AC signal included in the second voltage signal.

21. A resistance measuring apparatus comprising:

a voltage injecting unit that injects a testing AC signal into a measured circuit;

a current detecting unit that detects an AC current, which is flowing in the measured circuit due to injection of the testing AC signal, using a detection coil;

a storage unit that stores an offset current value for a current value of an AC current flowing in the detection coil; and

a processing unit that carries out a resistance calculating process that subtracts the offset current value from the current value of the AC current flowing in the detection coil to calculate a current value flowing in the detection coil and calculates a resistance value of the measured circuit based on the current value and a voltage value of the testing AC signal that is injected,

wherein the processing unit is operable when the resistance value calculated in the resistance calculating process is in an offset updating possible state that is one state out of a state where the resistance value is equal to or greater than a resistance threshold set in advance and a state where the resistance value is negative, to carry out an offset updating process that stores the current value of the AC current flowing in the detection coil in the storage unit as a new offset current value.

23. The resistance measuring apparatus according to claim 21,

wherein the processing unit is operable when the offset updating possible state continues for a predetermined time or longer, to carry out the offset updating process.

25. The resistance measuring apparatus according to claim 21,

further comprising an operation unit that generates an updating signal in accordance with an operation content and outputs the updating signal to the processing unit,

wherein the processing unit is operable only when the updating signal has been inputted and the offset updating possible state is present, to carry out the offset updating process.

27. The resistance measuring apparatus according to claim 21,

wherein the voltage injecting unit generates the testing AC signal in synchronization with a reference signal,

the current detecting unit includes:

a first amplifier unit that includes at least a first operational amplifier with an inverted input terminal connected to one end of the detection coil and a non-inverted input terminal into which a reference voltage is inputted, converts a current flowing in the detection coil to a first voltage signal, and outputs the first voltage signal;

a second amplifier unit that includes at least a second operational amplifier with an inverted input terminal connected to another end of the detection coil and a non-inverted input terminal into which the reference voltage is inputted, converts a current flowing in the detection coil to a second voltage signal with opposite phase to the first voltage signal, and outputs the second voltage signal;

a first extraction unit that carries out synchronous detection on the first voltage signal and the second voltage signal in synchronization with the reference signal to extract a positive polarity signal composed of only positive side parts of waveforms of the first voltage signal and the second voltage signal;

a second extraction unit that carries out synchronous detection on the first voltage signal and the second voltage signal in synchronization with the reference signal to extract a negative polarity signal composed of only negative side parts of waveforms of the first voltage signal and the second voltage signal; and

a differential amplifier unit that outputs a difference signal on a difference between the positive polarity signal and the negative polarity signal, and

the current detecting unit detects the AC current flowing in the measured circuit based on the difference signal.

29. The resistance measuring apparatus according to claim 21,

wherein the voltage injecting unit generates the testing AC signal in synchronization with a reference signal,

the current detecting unit includes:

a first amplifier unit that includes at least a first operational amplifier with an inverted input terminal connected to one end of the detection coil and a non-inverted input terminal into which a reference voltage is inputted, converts a current flowing in the detection coil to a first voltage signal, and outputs the first voltage signal;

a second amplifier unit that includes at least a second operational amplifier with an inverted input terminal connected to another end of the detection coil and a non-inverted input terminal into which the reference voltage is inputted, converts a current flowing in the detection coil to a second voltage signal with opposite phase to the first voltage signal, and outputs the second voltage signal;

a third amplifier unit that outputs a difference signal on a difference between the first voltage signal and the second voltage signal; and

an extraction unit that carries out synchronous detection on the difference signal in synchronization with the reference signal to extract a single-polarity signal composed of one of the positive-side part and the negative-side part of a waveform of the difference signal, and

the current detecting unit detects the AC current flowing in the measured circuit based on the single polarity signal.

22. A resistance measuring apparatus comprising:

a voltage injecting unit that injects a testing AC signal into a measured circuit;

a current detecting unit that detects an AC current, which is flowing in the measured circuit due to injection of the testing AC signal, using a detection coil;

a storage unit that stores an offset current value for a current value of an AC current flowing in the detection coil; and

a processing unit that carries out a resistance calculating process that subtracts the offset current value from the current value of the AC current flowing in the detection coil to calculate a current value flowing in the detection coil and calculates a resistance value of the measured circuit based on the current value and a voltage value of the testing AC signal that is injected,

wherein the processing unit is operable when the calculated current value is in an offset updating possible state where the current value is equal to or less than a current threshold set in advance, to carry out an offset updating process that stores the current value of the AC current flowing in the detection coil in the storage unit as a new offset current value.

24. The resistance measuring apparatus according to claim 22,

wherein the processing unit is operable when the offset updating possible state continues for a predetermined time or longer, to carry out the offset updating process.

26. The resistance measuring apparatus according to claim 22,

further comprising an operation unit that generates an updating signal in accordance with an operation content and outputs the updating signal to the processing unit,

wherein the processing unit is operable only when the updating signal has been inputted and the offset updating possible state is present, to carry out the offset updating process.

28. The resistance measuring apparatus according to claim 22,

wherein the voltage injecting unit generates the testing AC signal in synchronization with a reference signal,

the current detecting unit includes:

a first amplifier unit that includes at least a first operational amplifier with an inverted input terminal connected to one end of the detection coil and a non-inverted input terminal into which a reference voltage is inputted, converts a current flowing in the detection coil to a first voltage signal, and outputs the first voltage signal;

a second amplifier unit that includes at least a second operational amplifier with an inverted input terminal connected to another end of the detection coil and a non-inverted input terminal into which the reference voltage is inputted, converts a current flowing in the detection coil to a second voltage signal with opposite phase to the first voltage signal, and outputs the second voltage signal;

a first extraction unit that carries out synchronous detection on the first voltage signal and the second voltage signal in synchronization with the reference signal to extract a positive polarity signal composed of only positive side parts of waveforms of the first voltage signal and the second voltage signal;

a second extraction unit that carries out synchronous detection on the first voltage signal and the second voltage signal in synchronization with the reference signal to extract a negative polarity signal composed of only negative side parts of waveforms of the first voltage signal and the second voltage signal; and

a differential amplifier unit that outputs a difference signal on a difference between the positive polarity signal and the negative polarity signal, and

the current detecting unit detects the AC current flowing in the measured circuit based on the difference signal.

30. The resistance measuring apparatus according to claim 22,

wherein the voltage injecting unit generates the testing AC signal in synchronization with a reference signal,

the current detecting unit includes:

a first amplifier unit that includes at least a first operational amplifier with an inverted input terminal connected to one end of the detection coil and a non-inverted input terminal into which a reference voltage is inputted, converts a current flowing in the detection coil to a first voltage signal, and outputs the first voltage signal;

a second amplifier unit that includes at least a second operational amplifier with an inverted input terminal connected to another end of the detection coil and a non-inverted input terminal into which the reference voltage is inputted, converts a current flowing in the detection coil to a second voltage signal with opposite phase to the first voltage signal, and outputs the second voltage signal;

a third amplifier unit that outputs a difference signal on a difference between the first voltage signal and the second voltage signal; and

an extraction unit that carries out synchronous detection on the difference signal in synchronization with the reference signal to extract a single-polarity signal composed of one of the positive-side part and the negative-side part of a waveform of the difference signal, and

the current detecting unit detects the AC current flowing in the measured circuit based on the single polarity signal.