JP2017194420A - Voltage measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage measurement device capable of measuring voltage of a measuring object such as power line in a non-contact manner with high accuracy.SOLUTION: The voltage measurement device comprises: a detection unit 3 including transformers 313, 32 and switching elements 311, 312; a demodulation unit 4a; a voltage generation unit 4b changing and outputting a reference potential; and a data processing unit 4c determining the reference potential when the potential difference between a voltage to be measured and a reference potential becomes a predetermined value or less as the voltage to be measured. The detection unit 3 includes: a modulation circuit 31 modulating by the switching elements 311, 312 current flowing through coupling capacity of a power line 1 and a detection electrode 2 into a higher frequency; and the transformer 32 generating a detection signal from an output thereof. The data processing unit 4c changes the gain of a feedback loop gradually, and when a differential value of the amplitude of the detection signal at each gain before and after the change is within a predetermined range, sets either one of the gains to be the gain.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a voltage measurement device that measures a voltage applied to a measurement target such as a power line in a non-contact state with the measurement target.

2. Description of the Related Art Conventionally, a voltage measuring apparatus that measures a voltage applied to a power line in a non-contact manner using a coupling capacitance between the core of the power line and an electrode in a detection probe is known.
In this type of voltage measuring apparatus, the coupling capacitance changes due to the positional relationship of the detection probe with respect to the power line, the material of the insulation coating of the power line, the difference in dielectric constant depending on the surrounding environment such as temperature and humidity, and this becomes a measurement error. Therefore, there is a case where the voltage of the power line cannot be measured with high accuracy.
For this reason, the prior art described in patent documents 1-3 is known as a voltage measuring device which solves the above-mentioned problem.

The voltage measuring device described in Patent Documents 1 and 2 includes a detection electrode, a variable capacitance circuit including a capacitance changing function body such as a diode and a capacitor and a driving circuit thereof, a current detector, an amplifier circuit, a synchronous detection circuit, an integration circuit, A voltage generation circuit and the like are provided.
In these voltage measuring devices, the capacitance of the capacitance changing function body is changed, and the current flowing through the measurement target, for example, the coupling capacitance between the power line and the detection electrode, is changed according to the operating frequency of the capacitance changing function body. Has been. The current is converted into a voltage via a current detector, and a signal corresponding to the voltage of the power line is generated via a synchronous detection circuit, an amplifier circuit, an integration circuit, etc., and this signal is amplified by the voltage generation circuit. .

And, by connecting the detection electrode, capacitance change function body, current detector, and voltage generation circuit in series, the output of the voltage generation circuit is connected to the current detector side so that the current flowing through the current detector is reduced to zero. And the output voltage of the voltage generation circuit is controlled to be equal to the voltage of the power line.
According to this prior art, feedback control is performed so that the output voltage of the voltage generation circuit becomes equal to the voltage to be measured, so that it is possible to suppress the influence when the coupling capacitance between the measurement target and the detection electrode varies.

  Further, in Patent Document 3, the amplitude varies according to the potential difference between the voltage to be measured and the reference potential from a probe unit having the same detection electrode, capacitance changing function body, current detector and the like as in Patent Documents 1 and 2. While outputting a change detection signal, the gain of the feedback loop including the probe unit and the voltage generation circuit is increased by at least one step to calculate the difference value of the amplitude of the detection signal at each gain before and after the increase, and the difference value is predetermined. A voltage measuring device is disclosed in which a reference potential when converged within a range is an effective measurement value.

JP 2007-163415 A (paragraphs [0036] to [0054], FIG. 1, etc.) JP 2009-162608 A (paragraphs [0037] to [0051], FIG. 1, etc.) JP 2008-20270 A (paragraphs [0019] to [0054], FIG. 1, etc.)

In the voltage measuring devices according to Patent Documents 1 and 2, this voltage is matched with the voltage of the power line by controlling the output voltage of the voltage generation circuit fed back to the current detector side. However, since feedback control has a characteristic that a deviation based on proportional control occurs, the output voltage of the voltage generation circuit cannot be completely matched with the voltage of the power line.
In addition, the deviation varies depending on the gain of the feedback loop, and when the gain is large, the deviation is small, and when the gain is small, the deviation is large. The gain of the feedback loop is set so that the gain corresponds to.

However, in a voltage measuring device that measures the voltage of the power line in a non-contact manner, even when the detection electrode is securely fixed to the power line, the coupling capacity between the power line and the detection electrode changes due to changes in environmental conditions such as temperature and humidity. The sensitivity of the detection unit changes and the gain of the feedback loop changes to a value different from a preset value, and the gain cannot be confirmed.
It is also possible to set the gain of the feedback loop to a sufficiently large value in advance so that it can cope with environmental changes including the diameter of the power line to be measured. The noise resistance stability of the loop is impaired, and again the measurement accuracy cannot be ensured.

  On the other hand, according to the voltage measurement device according to Patent Document 3, the detection signal and the reference potential hardly change based on the difference value of the amplitude of the detection signal described above, and is extremely close to the lower limit value or the lower limit value. With the value of the feedback loop gain set to the value, the voltage to be measured can be measured with high accuracy and stability.

  However, in the voltage measuring devices according to Patent Documents 1 to 3, since the capacitance changing function body that changes the impedance in order to modulate the detection signal is connected in series between the detection electrode and the current detector, the capacitance change The drive signal (drive current) of the functional body may be detected as a noise component by the current detector, which may affect the measurement accuracy. As a countermeasure, in these voltage measuring devices, the capacitance changing function body is configured by a bridge made of a diode or the like so that the drive signal component is not detected by the current detector, but the equilibrium state of the bridge is strictly controlled. There is a risk that manufacturing or adjustment costs may increase.

  Therefore, a problem to be solved by the present invention is to provide a voltage measuring apparatus that can measure a voltage to be measured such as a power line with high accuracy at low cost.

In order to solve the above-described problem, the invention according to claim 1 is a voltage measuring device that measures a voltage to be measured applied to a measurement object via a detection electrode attached to the measurement object in a non-contact state. A detection unit that outputs a detection signal whose amplitude changes according to a potential difference between the voltage to be measured and a reference potential; a demodulation unit that extracts and outputs a frequency component of the voltage to be measured from the detection signal; and the detection A voltage generation unit that changes and outputs the reference potential so that the amplitude of the signal decreases, and a data processing unit that identifies the reference potential when the potential difference is equal to or less than a predetermined value as the measured voltage. Voltage measuring device,
The detector is
A modulation circuit that modulates the current flowing through the coupling capacitance between the measurement object and the detection electrode to a frequency higher than the frequency of the voltage to be measured by turning on / off a switching element; and the detection from the output of the modulation circuit A current detection circuit for generating a signal,
The data processing unit
The gain of the feedback loop including the detection unit, the demodulation unit, and the voltage generation unit is changed stepwise, and the difference value of either the amplitude of the detection signal or the reference potential at each gain before and after the change is within a predetermined range Any one of the gains is set as the gain of the feedback loop.

  According to a second aspect of the present invention, in the voltage measuring device according to the first aspect, the data processing unit sets the larger one of the gains as the gain of the feedback loop.

  The invention according to claim 3 is the voltage measuring apparatus according to claim 1 or 2, wherein the switching element and the current detection circuit are connected in series.

  The invention according to claim 4 is the voltage measuring apparatus according to claim 1 or 2, wherein the switching element and the current detection circuit are connected in parallel.

  According to a fifth aspect of the present invention, in the voltage measuring device according to any one of the first to fourth aspects, the current detection circuit includes a primary winding excited by a current flowing through the switching element, and the demodulator. And a secondary winding connected to the transformer.

  According to a sixth aspect of the present invention, in the voltage measuring device according to any one of the first to fifth aspects, the voltage generator boosts the signal voltage input from the demodulator to the primary winding, and boosts the voltage. A step-up transformer that outputs the subsequent voltage as the reference potential from the secondary winding is provided.

  The invention according to claim 7 is the voltage measuring device according to any one of claims 1 to 6, wherein a MOSFET is used as the switching element.

According to the present invention, since a measurement error due to a deviation that occurs during feedback control does not occur, a voltage to be measured such as a power line can be measured with high accuracy.
In addition, since the detection signal is modulated by turning on / off the switching element instead of the capacitance change function body configured by the bridge circuit, manufacturing or adjustment without requiring strict management of the bridge equilibrium state The above cost can be reduced.
Furthermore, the reference potential can be set over a wide range simply by changing the turns ratio of the step-up transformer in the voltage generation unit, and it is possible to accurately measure various voltages to be measured.

It is a lineblock diagram of the voltage measuring device concerning a 1st embodiment of the present invention. It is a specific block diagram of the modulation circuit in each embodiment of the present invention. Is a waveform diagram showing the voltage v ₁ and the reference potential V _r of the power line in the first embodiment of the present invention. It is a flowchart which shows the gain setting process which the data processing part of FIG. 1 performs. It is a block diagram of the detection part in 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of a voltage measuring apparatus according to a first embodiment of the present invention.
This voltage measuring device includes a detection electrode 2 and a measuring device main body 5 and measures an AC voltage v ₁ applied to a core wire 1 a of a power line 1 by a system power supply G in a non-contact manner. C ₀ indicates a coupling capacitance formed between the core wire 1 a and the detection electrode 2 when the detection electrode 2 is attached to the power line 1. Here, the detection electrode 2 is configured to be tightly wound around the outer peripheral surface of the power line 1.
Hereinafter, the voltage (measured voltage) v ₁ of the core wire 1 a is described as being synonymous with “voltage of the power line 1”.

The measurement apparatus main body 5 includes a detection unit 3 that functions as a sensor together with the detection electrode 2, and a measurement unit 4 that processes an output signal of the detection unit 3, and the detection unit 3 is a modulation circuit 31 connected to the detection electrode 2. And an insulating transformer 32 as a current detection circuit.
The modulation circuit 31 includes two switching elements 311 and 312 connected in series in opposite directions between the detection electrode 2 and the primary winding of the transformer 32, and a drive circuit that drives the switching elements 311 and 312. And a transformer 313.

FIG. 2 is a detailed circuit diagram of the modulation circuit 31. In the modulation circuit 31, n-type MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as the switching elements 311 and 312. Reference numeral 314 denotes a resistor connected in parallel to the secondary winding of the transformer 313.
n-type MOSFET, the driving signals S ₁ applied to the primary winding of the transformer 313 will be turned on when the "High" level, the input signal from the core 1a of the power line 1 is both positive and negative polarities of the signals, the two In the n-type MOSFET, the source terminals are connected to each other, and on the reverse biased MOSFET side, a current flows through a built-in body diode.

Returning to FIG. 1, the oscillation circuit 40 in the demodulation unit 4 a provided in the measurement unit 4 is connected to the primary side of the transformer 313. The oscillation circuit 40 outputs, for example, a rectangular-wave drive signal S ₁ having a frequency (several hundreds [kHz] to several [MHz]) sufficiently higher than the voltage v _{1 of a} commercial frequency (50 or 60 [Hz]), The switching elements 311 and 312 are turned on / off via the transformer 313.

For this reason, the current flowing through the switching elements 311 and 312 via the coupling capacitor C ₀ is modulated by the frequency of the drive signal S ₁ . Thus, in proportion to the magnitude of the current flowing through the switching element 311 and 312, and the detection signal S ₂ of the high frequency is transmitted to the measuring unit 4 via the transformer 32, in the measuring section 4, the voltage of the power line 1 v ₁ of the commercial frequency component is demodulated and amplified.
One end of the primary winding of the transformer 32 is connected to the switching element 312 and the other end of the primary winding is connected to the output side of the step-up transformer 45 in the voltage generator 4b described later.

  The measurement unit 4 includes a demodulation unit 4a, a voltage generation unit 4b, a data processing unit 4c, and a polarity determination circuit 47. The demodulation unit 4a includes a detection circuit 41, an amplification circuit 42, and a filter in addition to the oscillation circuit 40 described above. A circuit 43 is provided.

Detection circuit 41 at a timing transformer 32 in synchronization with the drive signal (detection signal) S ₁ from the oscillation circuit 40 is energized, and detects the detection signal S _2, for example, envelope outputted from the transformer 32. Analog signal S ₃ after detection is amplified by a preset appropriate amplification factor by the amplifier circuit 42, it is output as the detection signal S _4.

The filter circuit 43 passes only the commercial frequency component of the voltage v ₁ by filtering the frequency component of the detection signal S ₄ . Here, the detection unit 3 detects the voltage v ₁ by turning on / off the switching elements 311 and 312, and the phase of the detection signal S ₄ is advanced by 90 ° from the phase of the voltage v ₁ . For this reason, as a configuration of the filter circuit 43, for example, after passing through a secondary active low-pass (high frequency band removal) filter, passing through a primary high-pass (low frequency band removal) filter, the voltage v ₁ is obtained. It generates an analog signal S ₅ the combined phases.

The analog signal S ₅ is input to the voltage generator 4b, the polarity determination circuit 47 is also input to CPU48 in later data processing unit 4c.
The polarity determination circuit 47 receives the drive signal S ₁ and the analog signal S ₅ from the oscillation circuit 40, and detects the phase of the analog signal S ₅ with respect to the drive signal S ₁ to thereby detect the voltage v of the power line 1. ₁ and a polarity determination signal D ₁ indicating the polarity of a potential difference (v ₁ −V _r ) between a reference potential V _r described later and the polarity determination signal D ₁ are output to the voltage generation circuit 44 in the voltage generation unit 4 b. doing.
The voltage generation unit 4 b includes a voltage generation circuit 44, a step-up transformer 45, and a voltage dividing circuit 46. Voltage generation circuit 44 generates a reference signal _{S 6} based on the analog signal _{S 5} and the polarity determination signal _{D 1.}

The step-up transformer 45 is an insulating transformer, and there is a relationship of n ₂ > n ₁ between the number of turns n ₁ of the primary winding and the number of turns n ₂ of the secondary winding. Primary winding and secondary winding of the step-up transformer 45, one ends are commonly connected to the other end of the primary winding, the reference signal S ₆ is applied from the voltage generating circuit 44. Thus, the step-up transformer 45 boosts the reference signal S ₆ which is applied to the primary winding, the positive peak value (maximum voltage value) + V _a [V], the negative peak value (minimum voltage value) Is output from the other end of the secondary winding as a reference potential signal S ₇ (hereinafter also referred to as reference potential V _r ) as _a sine wave signal having an amplitude of 2V _a with −V _a [V]. This reference potential V _r is applied to the subsequent voltage dividing circuit 46 and the other end of the primary winding of the transformer 32 in the detection unit 3.
Voltage divider circuit 46 outputs a voltage signal S ₈ by a preset dividing ratio of the reference potential V _r by dividing.

The voltage signal S ₈ output an analog signal S ₅ output from the aforementioned filter circuit 43 from the voltage dividing circuit 46 are input to the data processing unit 4c, by the data processing unit 4c, the voltage of the power line 1 v ₁ process of measuring the and the gain setting process described below is executed.

The data processing unit 4c performs gain setting processing for setting the gain of the feedback loop of the voltage measuring device using, for example, the CPU 48 and the memory 49. Here, the feedback loop refers to a path constituted by the transformer 32, the detection circuit 41, the amplification circuit 42, the filter circuit 43, the voltage generation circuit 44, and the step-up transformer 45, and the CPU 48 has an appropriate current feedback loop gain. It is determined whether or not the value is correct. The memory 49 has a predetermined range (-V _dr or more and + V _dr or less) used in the gain setting process, and a plurality of amplification factors G _p1 , G _p2 , G _p3 ,... In the amplification circuit 42 of the demodulation unit 4a. ... ( _Gp1 < _Gp2 < _Gp3 <...) is stored in advance.

Hereinafter, the operation of the present embodiment will be described together with the operation of the data processing unit 4c.
First, when measuring the voltage v ₁ , the coupling electrode C ₀ is formed between the core wire 1 a and the detection electrode 2 by attaching the detection electrode 2 to the core wire 1 a of the power line 1 in a non-contact state.

When the detection electrode 2 is attached to the power line 1, the value of the coupling capacitance C ₀ is the area of the detection electrode 2 and the diameter of the power line 1 (strictly speaking, the diameter of the core wire 1 a of the power line 1 and the coating thickness of the power line 1). It depends on the dielectric constant of the coating. However, this capacitance value is constant when there is no change in the mounting condition due to environmental conditions such as temperature and humidity and the installation stress of the detection electrode 2.

In activated state of the measurement unit 4, the voltage generator 4b, starts generating the voltage generating circuit 44 of the reference signal S _6, detector reference potential V _r of the step-up transformer 45 is obtained by boosting the reference signal S ₆ 3 is applied to the primary winding of the transformer 32 in the circuit 3. Further, the voltage generating unit 4b, and the voltage signal _{S 8} to the voltage divider circuit 46 is obtained by dividing the reference voltage _{V r} min, and outputs the CPU48 of the data processing unit 4c.

On the other hand, in the demodulator 4 a, the oscillation circuit 40 generates the drive signal S ₁ and outputs it to the transformer 313, the detection circuit 41, and the polarity determination circuit 47 of the modulation circuit 31. Transformer 313 outputs an ON / OFF signal (pulse signal) from the secondary side on the basis of the drive signals S ₁ input to the primary side, thereby the switching elements 311, 312 on / off.

When the switching elements 311 and 312 are turned on, the primary winding of the transformer 32 is excited, and a detection signal S ₂ having a phase advanced by 90 ° with respect to the voltage v ₁ of the power line 1 is output from the secondary winding. Further, when the switching elements 311 and 312 are off, the primary winding of the transformer 32 is in a non-excited state, and as a result, the transformer 32 is reverse-excited and inverted by 90 ° phase with respect to the voltage v ₁ of the power line 1. signal _{S 2} is outputted.

At this time, a current having an amplitude corresponding to the potential difference (v ₁ −V _r ) between the voltage v ₁ of the power line ₁ and the reference potential V _r flows through the primary winding of the transformer 32. This current amplitude is increased when the potential difference _(v 1 -V _r) is large, the amplitude becomes small when the potential difference _(v 1 -V _r) is small.
Therefore, as shown in FIG. 3, when the measurement unit 4 starts measurement when the polarity of the voltage v ₁ of the power line 1 is positive (time t ₀ ), the reference potential V _r is 0 [V] at this time. Therefore, the potential difference (v ₁ −V _r ) becomes positive, and the amplitude of the current flowing through the primary winding of the transformer 32 changes according to the potential difference (v ₁ −V _r ) in the period of the drive signal S _1. It becomes an AC signal. Voltage induced in the secondary winding of the transformer 32 by the current is inputted to the detection circuit 41, amplifying circuit 42 an analog signal S ₃ that is envelope detection and outputs a detection signal S ₄ amplifies.

The detection signal S ₄ includes high-frequency noise that is generated when the switching elements 311 and 312 are turned on / off due to the influence of the leakage inductance of the transformer 32.
Therefore, as described above, if the filter circuit 43 is composed of a secondary active low-pass filter and a primary high-pass filter, high-frequency noise can be removed, and the entire filter circuit 43 passes only the commercial frequency band. By configuring the band pass filter to be performed, an analog signal (a signal having the same phase as the voltage v ₁ of the power line 1) S ₅ having a phase delayed by 90 ° from the detection signal S ₂ can be obtained. The analog signal _{S 5} is a signal whose amplitude changes in proportion to the potential difference _(v 1 -V _r).
Further, the polarity determination circuit 47, by detecting the phase of the analog signal _{S 5} to the drive signals _{S 1,} and generates a polarity determination signal _{D 1} indicative of the polarity of the potential difference _(v 1 -V _r), the voltage generating circuit 44 Output to.

When the polarity determination signal D ₁ indicates “positive”, the voltage generation circuit 44 outputs the reference signal S _{6 in} which the voltage is increased by an amount proportional to the amplitude of the analog signal S ₅ , and the polarity determination signal D ₁ is “ When “negative” is indicated, the reference signal S ₆ having a voltage decreased by an amount proportional to the amplitude of the analog signal S ₅ is output.

As described above, when the measurement unit 4 starts the measurement operation when the polarity of the voltage v ₁ of the power line 1 is positive, the reference signal S ₆ is initially 0 [V], and thus the potential difference (v ₁ −V _r ) is positive, and thus the polarity determination signal D ₁ is also positive. Therefore, the voltage generator circuit 44, and outputs the reference signal S ₆ with an increased voltage by an amount proportional to the amplitude of the analog signal S ₅ input. Step-up transformer 45 will continue to boost the reference signal S ₆ to produce a reference potential V _r, and applies the reference potential V _r to the other end of the primary winding of the transformer 32 (side opposite to the modulation circuit 31 side).
As a result, the potential difference (v ₁ −V _r ) gradually decreases in the feedback loop formed by the transformer 32, the detection circuit 41, the amplification circuit 42, the filter circuit 43, the voltage generation circuit 44, and the step-up transformer 45. Negative feedback control is performed.

As a result, the amplitude of the current flowing through the primary winding of the transformer 32 gradually decreases.
In general, in this type of voltage measurement device, the transient characteristics are set so that the convergence of the reference potential V _r to the voltage v ₁ is completed in a short time. Therefore, the reference potential _{V r,} as shown in FIG. 3, while overshooting the voltage _{v 1,} converges to the voltage _{v 1} at time _{t 1} has elapsed Δt from time _{t 0.} For this reason, the voltage v ₁ of the power line 1 can be obtained by measuring the reference potential V _r .

When the reference potential V _r exceeds the voltage v ₁ due to overshoot, the potential difference (v ₁ −V _r ) becomes a negative voltage, and the polarity determination signal D ₁ also exhibits a negative polarity. Therefore, the voltage generation circuit 44 outputs the reference signal S ₆ having reduced by the voltage value an amount proportional to the amplitude of the analog signal S ₅ input.
Thereafter, the measurement unit 4 continues the feedback operation to change the reference potential V _r so as to be within a certain deviation with respect to the voltage v ₁ of the power line 1 changing at the commercial frequency. As a result, the reference potential V _r becomes an AC signal having a commercial frequency that changes in synchronization with the voltage v ₁ .

On the other hand, the CPU48 of the data processing unit 4c, from time _{t 1} after the start of measurement (time _{t 0} in FIG. 3), performing the gain setting process shown in FIG.
In this gain setting process, the CPU 48 first detects the amplitude V _p1 of the analog signal S ₅ when the amplification factor of the amplifier circuit 42 is G _p0 as the first amplitude (step ST1), and stores the first amplitude in the memory. It memorize | stores in 49 1st amplitude memory area (step ST2).

Next, the CPU 48 increases the amplification factor of the amplifier circuit 42 by one step (step ST3). Specifically, reads the next larger gain _{G p1} of CPU48 is the amplification factor _{G p0} from the memory 49, the control signal _{D 2} corresponding to the amplification factor _{G p1} (e.g., a voltage level corresponding to the amplification factor _{G p1} A control signal D ₂ ) is generated and output to the amplifier circuit 42. Further, the CPU 48 detects the amplitude V _p2 of the analog signal S ₅ when the amplification factor of the amplifier circuit 42 is G _p1 as the second amplitude (step ST4), and uses the second amplitude V _p2 in the second memory 49. Store in the amplitude storage area (step ST5).
Thus, since the gain of the feedback loop of the voltage measuring device is also increased by sequentially increasing the amplification factor of the amplifier circuit 42 by the CPU 48, the potential difference (v ₁ −V _r ) after the amplification factor is increased is Smaller than before the increase.

Next, the CPU 48 reads the amplitudes V _p1 and V _p2 recorded in the first amplitude storage area and the second amplitude storage area, and calculates a difference value V _d (= V _p1 −V _p2 ) ( Step ST6). Then, the difference value _{V d,} the predetermined range _{(-V dr} or more, _{+ V dr} less. _{Here, V dr} is a positive value) is compared (step ST7).

Comparison of the result in step ST7, when the difference value _{V d} is outside the predetermined range (step ST7 NO), CPU 48 may first amplitude and the second amplitude _{V p2} stored in the second amplitude memory area of the memory 49 V _p1 is overwritten and stored in the first amplitude storage area (step ST8). If the difference value _Vd is within the predetermined range, the process is terminated (YES in step ST7).
Accordingly, the difference value V _d (= V _p1 −V _p2 ) calculated in step ST6 is always a difference value between amplitudes under two amplification factors that differ by one stage, and the CPU 48 determines the difference value in step ST7. until V _d is within a predetermined range, repeatedly executes the series of processes described above (ST1~ST8).
Above the description, compares the difference value V _d of the amplitude of the analog signal S ₅ with a predetermined range, the difference value of the reference potential V _r before and after the change of the amplification factor may be compared with a predetermined range.

As described above, the gain of the feedback loop of the voltage measuring device is gradually increased by increasing the amplification factor of the amplifier circuit 42 step by step, and the potential difference (v ₁ −V _r ) is gradually decreased. I will do it.
Note that, in step ST7, if the difference value V _d becomes within the predetermined range, the amplitude of the analog signal S ₅ in the current amplification factor, as compared to the amplitude of the analog signal S ₅ in the amplification factor of the first stage before The voltage measuring device measures the voltage v ₁ with a predetermined accuracy on the condition that it is only increased within the range of the difference value V _d . Therefore, since there is no need to increase the amplification factor of the amplifier circuit 42 any more, the CPU 48 ends the gain setting process (YES in step ST7).
Thus, according to this embodiment, as with Patent Document 3 described above, based on the difference value of the amplitude of the analog signal (detection signal) S _5, the detection signal and the reference potential hardly changes, and, With the feedback loop gain set to a lower limit value or a value very close to the lower limit value, the voltage v ₁ can be measured with high accuracy and stability.

Here, functions, operations, and the like of the voltage measuring device of the present invention are not limited to the above-described contents.
For example, in the embodiment previously described, each time the voltage measuring device starts the measurement operation, the amplifier circuit 42 immediately after the start of operation amplifies the detection signal S ₃ in the initial amplification factor G _p0, the control signal D ₂ from the CPU48 There when input is to change the amplification factor on the basis of the control signal D _2. However, at the start of the measurement operation, the CPU 48 sets the initial gain G _p0 of the amplifier circuit 42 to set the initial gain of the feedback loop, and the amplifier circuit 42 starts amplification of the detection signal S ₃ at the initial gain G _p0 . You may make it do.

As a result, the amplification factor (amplification factor when the difference value _Vd falls within the predetermined range) finally set in the amplification circuit 42 in the gain setting process already executed by the CPU 48 is initially amplified at the start of the next measurement operation. It can be set as a rate. Accordingly, and when measuring the voltage v ₁ of the power line 1 again, a plurality of voltages v ₁ of the power line 1 of the same type, it is possible to continuously measure in suitable measurement accuracy from the measurement beginning.

Specifically, any one of the amplification factors of the amplifier circuit 42 when the difference value V _d falls within a predetermined range (−V _dr or more and + V _dr or less) is determined when the CPU 48 starts the next measurement operation. The initial amplification factor can be set in the amplifier circuit 42. In this case, if the larger one of the two amplification factors when the difference value V _d falls within the predetermined range is set as the initial amplification factor, the gain of the feedback loop is set within a range in which the deterioration of the noise resistance characteristic can be avoided. The measurement accuracy can be further increased by increasing the measurement accuracy.

On the other hand, considering that the difference value V _d of the final amplification factor and its one step prior to amplification factor of the amplifier circuit 42 becomes within the predetermined range, even in the smaller amplification factor of the first stage before Measurement with sufficiently high accuracy and high reliability can be performed.
In particular, considering the noise resistance characteristics, it is desirable that the gain of the feedback loop be smaller as long as a predetermined accuracy can be ensured. Therefore, it is desirable that the CPU 48 sets the smaller amplification factor, that is, the amplification factor one step before the final amplification factor, as the initial amplification factor for the amplification circuit 42.

In this embodiment, the amplification factor to be set as the gain of the feedback loop is determined based on the difference value V _d , but the divided value (voltage signal S ₈ ) of the reference potential V _r by the voltage dividing circuit 46. The gain to be used as the gain of the feedback loop may be determined based on the difference value between the divided values before and after the gain corresponding to the gain of the feedback loop is increased by one step.
Furthermore, in this embodiment, the amplification factor of the amplifier circuit 42 is increased step by step, but conversely, it can be decreased step by step. In this case, the CPU 48 determines that the difference value V _d of each amplitude of the analog signal S ₅ at each amplification factor before and after the amplification factor of the amplification circuit 42 is decreased step by step within a predetermined range (−V _dr or more, V _dr or less) Select one of the amplification factors one stage before the outside. In this case, for the reason described above, it is desirable to select the larger amplification factor, that is, the amplification factor two stages before the final amplification factor.

According to this voltage measurement device, it is possible to reduce measurement errors caused by deviations caused by feedback control, and as a result, it is possible to measure the voltage v ₁ of the power line ₁ with high accuracy.
Further, the detection circuit 3 is configured by the modulation circuit 31 including the switching elements 311 and 312 and the transformer 32, and the bridge configuration capacitance changing function body is not used as in Patent Documents 1 to 3 described above, thereby providing a bridge. It is not necessary to manage the equilibrium state, and there is no fear that the manufacturing or adjustment costs will increase.

Further, since the obtained reference potential V _r by boosting the reference signal S ₆ the step-up transformer 45 which is generated by the voltage generating circuit 44, the output of only the reference potential V _r to change the turns ratio of the step-up transformer 45 The range can be changed. Therefore, it is possible to freely set the measurement range for various voltages to be measured, and as a result, it is possible to accurately measure a wide range of voltages.

Next, FIG. 5 is a configuration diagram of a detection unit in the second embodiment of the present invention.
In the detection unit 3A of the present embodiment, a series circuit of switching elements 311 and 312 is connected in parallel to a series circuit of a primary winding of a transformer 32 serving as a current detection circuit and a resistor 315. Other configurations are the same as those of the detection unit 3 in the first embodiment.
According to this embodiment, since the transformer 32 is energized when the switching element 311 and 312 is off, the detection signal by setting the detection timing based on a signal obtained by inverting the drive signals S ₁ In the detection circuit 41 detection of S ₂ is possible.

  The voltage measuring device of the present invention may be used alone, or a power measuring device can be configured by combining this voltage measuring device and a known current measuring device.

G: System power supply 1: Power line 1a: Core wire 2: Detection electrode 3, 3A: Detection unit 31: Modulation circuit 311, 312: Switching element 313: Transformer (drive circuit)
314, 315: resistor 32: transformer (current detection circuit)
4: Measurement unit 4a: Demodulation unit 4b: Voltage generation unit 4c: Data processing unit 40: Oscillation circuit 41: Detection circuit 42: Amplification circuit 43: Filter circuit 44: Voltage generation circuit 45: Step-up transformer 46: Voltage division circuit 47: Polarity determination circuit 48: CPU
49: Memory 5: Measuring device body

Claims (7)

A voltage measurement device that measures a voltage to be measured applied to a measurement object via a detection electrode that is attached to the measurement object in a non-contact state, and has an amplitude corresponding to a potential difference between the voltage to be measured and a reference potential A detection unit that outputs a detection signal that changes, a demodulation unit that extracts and outputs a frequency component of the voltage to be measured from the detection signal, and changes the reference potential so that the amplitude of the detection signal decreases. A voltage measuring device comprising: a voltage generating unit that outputs; and a data processing unit that identifies the reference potential as the voltage to be measured when the potential difference becomes a predetermined value or less,
The detector is
A modulation circuit that modulates the current flowing through the coupling capacitance between the measurement object and the detection electrode to a frequency higher than the frequency of the voltage to be measured by turning on / off a switching element; and the detection from the output of the modulation circuit A current detection circuit for generating a signal,
The data processing unit
The gain of the feedback loop including the detection unit, the demodulation unit, and the voltage generation unit is changed stepwise, and the difference value of either the amplitude of the detection signal or the reference potential at each gain before and after the change is within a predetermined range The voltage measuring device according to claim 1, wherein any one of the gains is set as a gain of the feedback loop. In the voltage measuring device according to claim 1,
The data processing unit
The voltage measuring device characterized in that the larger one of the gains is set as the gain of the feedback loop. In the voltage measuring device according to claim 1 or 2,
The voltage measuring device, wherein the switching element and the current detection circuit are connected in series. In the voltage measuring device according to claim 1 or 2,
A voltage measuring apparatus, wherein the switching element and the current detection circuit are connected in parallel. In the voltage measuring device according to any one of claims 1 to 4,
The voltage measuring device, wherein the current detection circuit is a transformer having a primary winding excited by a current flowing through the switching element and a secondary winding connected to the demodulator. In the voltage measuring device according to any one of claims 1 to 5,
The voltage generator includes a step-up transformer that boosts the signal voltage input to the primary winding from the demodulator and outputs the boosted voltage from the secondary winding as the reference potential. measuring device. In the voltage measuring device according to any one of claims 1 to 6,
A voltage measuring apparatus using a MOSFET as the switching element.

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