JP2020038113A - Current measuring device and current measuring method - Google Patents

Abstract

To provide a non-clamp shaped current measuring device capable of measuring a current of an electric wire to be measured without clamping to the electric wire to be measured.SOLUTION: A current measuring device comprises a proximity sensor 11 which acquires information on a distance to a conductor of an electric wire to be measured and a magnetic sensor 12 which acquires information on a magnetic field generated with a current flowing through the electric wire to be measured, and a measuring device body 20 comprises a CPU 26 as computing means which computes a value of the current flowing through the electric wire to be measured from the information on the magnetic field that the magnetic sensor 12 acquires and the information on the distance to the conductor of the electric wire to be measured that the proximity sensor 11 acquires.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a current measuring device and a current measuring method.

2. Description of the Related Art A clamp meter is used to measure the current of an electric wire to be measured in a live state.
In this clamp meter, a clamp sensor, which is a current sensor, is attached to an electric wire to be measured, and the current of the electric wire to be measured is measured. Some clamp sensors include a magnetic core that forms a closed magnetic path arranged in a ring around the electric wire to be measured, and a magnetic sensor including a Hall element and a detection coil that detect the magnetism of the magnetic core. There is also a cable type flexible current sensor.

  In any case, in order to measure the current of the wire under test in the live state, there must be a space around the wire under test to mount the clamp sensor around the wire under test, such as a wall. In places where the electric wire to be measured is attached so that it cannot be removed, measurement using the clamp sensor cannot be performed.

  In order to solve such a problem, there is a proposal of a current measuring device that measures the current of the electric wire to be measured without approaching the electric wire to be measured and clamping the sensor.

The first proposal is a measuring device provided with a terminal capable of contacting a coating of a wire to be measured, the terminal having a magnetic sensor for detecting a magnetic field generated by a current flowing through the wire to be measured, and a magnetic field detected by the magnetic sensor. And, provided an operating unit that can input or select the standard information of the measurement target wire, based on the information of the thickness of the coating of the measurement target wire and the thickness of the conductor determined by the standard of the measurement target wire, the distance to the conductor and And the magnetic field detected by the magnetic sensor to calculate the current of the electric wire to be measured.
Another proposal is a current measuring device described in Patent Literature 1, in which a magnetic detection coil having the same shape is parallel to the electric wire to be measured, and the relative distance to the electric wire to be measured is shifted by a predetermined dimension. A magnetic sensor is provided to calculate the distance to the conductor of the measurement target wire from the difference between the magnetic fields detected by the two magnetic detection coils, and to calculate the current flowing through the measurement target wire from the obtained distance and the detected magnetic field. is there.

JP-A-7-159449

In the first current measuring device described above, it is necessary to input standard information of an electric wire to be measured or to select standard information. When the standard of the electric wire to be measured is not known, the distance to the conductor of the electric wire to be measured is not determined, so that the measurement value cannot be calculated. Further, the operator must input or select the standard information of the electric wire to be measured every time the measurement is performed, so that the operation may be complicated.
Further, in the current measuring device described in Patent Literature 1, it is necessary to provide two magnetic detection coils for detecting a magnetic field at a distance where a significant difference occurs in a magnetic field that can be detected with respect to a measurement target.
This indicates that the sensor portion provided with the two magnetic detection coils requires a considerable distance from the electric wire to be measured, and thus the size of the sensor becomes large. There is a problem that does not fit.

  The present invention proposes a current measuring device and a current measuring method which can measure a current without clamping a sensor to an electric wire to be measured, and which is small, does not require a complicated measuring operation, and can perform an accurate measurement. The purpose is to:

  A first aspect of the present invention is a current measuring device, a proximity sensor that obtains information on the distance to a conductor of a measurement target wire, and a magnetic sensor that obtains information on a magnetic field generated by a current flowing through the measurement target wire. And calculating means for calculating a value of a current flowing through the wire to be measured from information on the magnetic field obtained by the magnetic sensor and information on a distance to the conductor of the wire to be measured obtained by the proximity sensor. And

  The proximity sensor is an eddy current sensor, and the planar shape of the coil of the eddy current sensor is a shape in which the longitudinal direction of the coil extends in the extension direction of the electric wire to be measured, and a plurality of coils are stacked. Preferably, it is configured.

  Another aspect of the present invention is a current measuring method, in which a magnetic sensor acquires information of a magnetic field generated by a current flowing through a measurement target wire, and an eddy current sensor acquires information of a distance to a conductor of the measurement target wire. The calculating means calculates the value of the current flowing through the electric wire to be measured from the acquired information on the magnetic field and the information on the distance of the electric wire to be measured to the conductor.

  The proximity sensor can more accurately determine the distance to the conductor of the electric wire to be measured, so that accurate current measurement can be performed. In addition, since the sensor unit is provided with the magnetic sensor and the proximity sensor, a portable and portable device can be provided.

It is a figure showing the composition of the current measuring device of a first embodiment of the present invention. It is a schematic diagram explaining the measurement principle of the present invention. It is a figure explaining that an eddy current sensor consists of laminated coils. FIG. 4 is a diagram illustrating a configuration in which an eddy current sensor and a Hall element sensor of a current sensor are mounted.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a current measuring device according to a first embodiment of the present invention. An eddy current sensor 11 detects a distance of a wire to be measured to a conductor 2, and detects the detected distance and a magnetic field. A configuration is shown in which a current flowing through the conductor 2 of the electric wire to be measured is detected from a magnetic field detected by the Hall element sensor 12 as a sensor.

The current measuring device according to the present embodiment includes a sensor unit 10 and a measuring device main body 20.
The sensor unit 10 includes an eddy current sensor 11 that is a proximity sensor that detects a distance of the electric wire to be measured to the conductor 2 and a Hall element sensor 12 that is a magnetic sensor that detects a magnetic field generated by a current flowing through the conductor 2 of the electric conductor to be measured. And The measuring device main body 20 includes an analog / digital converter 23 to which a signal from the eddy current sensor 11 is input, an analog / digital converter 24 to which a signal from the Hall element sensor 12 is input, and the analog / digital converters 23 and 24. (Central Processing Unit) 26 as a calculation means to which the digital signal is input, a memory 27 for storing programs or data, calculation results and the like, and connected to the CPU 26 via an interface (I / O) 28. An operation unit 31, a communication unit 32, and a display unit 33 are provided.

The operation of the current measuring device shown in FIG. 1 will be described.
The signal output from the eddy current sensor 11 is converted into a digital signal by the analog / digital converter 23 and input to the CPU 26. Further, a signal output from the Hall element sensor 12 is converted into a digital signal by an analog / digital converter 24 and input to the CPU 26. The CPU 26 calculates the distance between the eddy current sensor and the conductor 2 of the electric wire to be measured based on the signal from the eddy current sensor 11 based on the program stored in the memory 27, and measures the distance and the measurement from the Hall element sensor 12. Based on information on the magnetic field generated by the current flowing through the conductor 2 of the target electric wire, the value of the current flowing through the conductor 2 of the target electric wire is calculated and output and displayed on the display unit 33.

The principle of current detection according to the present invention will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating the principle of current detection according to the present invention.
The eddy current sensor 11 and the Hall element sensor 12 are provided on a substrate 13 of the current sensor 10. The eddy current sensor 11 and the Hall element sensor 12 are provided on the substrate 13 in the axial direction of the conductor 2 of the electric wire to be measured. It is provided in close proximity.

  Here, an alternating current I flows through the conductor 2 of the electric wire to be measured. Due to the current I, a circumferential induction magnetic field is generated around the axis of the conductor 2. This induction magnetic field is a magnetic field clockwise with respect to the direction of the current flowing through the conductor 2. This induction magnetic field can be detected by the Hall element sensor 12 having a magnetic flux sensing surface orthogonal to the magnetic flux.

On the other hand, when a high-frequency constant current of several MHz is applied to the detection coil, the eddy current sensor 11 changes the impedance of the detection coil due to the eddy current generated on the surface of the opposing conductor 2. This is a proximity sensor that detects a distance.
As shown in FIG. 2, the magnetic field generated by the eddy current sensor 11 is formed in a cross-sectional direction orthogonal to the axis of the conductor 2, and the direction is also orthogonal to the induced magnetic field generated by the current flowing through the conductor 2. I do. Since the frequency of the magnetic field generated by the eddy current sensor 11 is higher than several kHz, the frequency of the induced magnetic field generated by the current flowing through the conductor 2 detected by the Hall element sensor 12, that is, the commercial frequency of 50 Hz or 60 Hz The detection band is different from the frequency.
Therefore, the magnetic field generated by the current in the conductor 2 and the magnetic field of the eddy current sensor 11 do not affect each other, and have different frequencies. Therefore, it is possible to separate the detection signal through a filter. Thus, information on the distance to the conductor 2 is obtained from the signal of the eddy current sensor 11, and information on the induced magnetic field of the current flowing through the conductor 2 is obtained from the signal of the Hall element sensor 12.

  The principle that the current of the conductor 2 is obtained based on the induction magnetic field detected by the Hall element sensor 12 and the distance to the conductor detected by the eddy current sensor will be described.

真空中の透磁率μ_０は、μ_０＝４π×１０^−７であるから、導体２を流れる電流値Ｉは、

により、渦電流センサ１１から得られた距離Ｙ（Ｙ＝ｒ）と、ホール素子センサ１２とから得られた磁界の強さ（Ｘ）から、導体２の電流値を求めることができる。 The current I flowing through the conductor 2 is expressed by the following equation (1) according to Ampere's law.
I = 2πrH (1)
Where H is the strength of the magnetic field (magnetic field around the conductor)
r is the distance between the measurement point of H and the conductor. H is expressed by the following formula using the definitions of magnetic flux density and magnetic permeability.
H = B / μ ₀ (2)
Here, the magnetic permeability μ ₀ is the magnetic permeability in the air. The magnetic permeability of the air is different from the magnetic permeability of the vacuum, but may be treated as the same. the μ ₀ is used.
B is the magnetic flux density detected by the Hall element sensor, which is considered to be equal to the intensity X of the magnetic field (around the conductor) measured by the magnetic sensor. If the distance r from the conductor is Y, ,

Since the magnetic permeability μ _{0 in} vacuum is μ ₀ = 4π × 10 ⁻⁷ , the current value I flowing through the conductor 2 is

Accordingly, the current value of the conductor 2 can be obtained from the distance Y (Y = r) obtained from the eddy current sensor 11 and the magnetic field strength (X) obtained from the Hall element sensor 12.

Although the above calculation is a method of theoretically obtaining a current value, the following correction may be performed to reduce variations due to characteristics such as insulation coating of the electric wire, thickness of the electric wire, and location.
A plurality of types of wires having different insulation coating thicknesses are prepared, and the distance detected by the proximity sensor 11 is corrected. Then, a known current is caused to flow through this electric wire, and a correction formula that makes the current equal to the actually flowing current is created and stored in the memory 27. Each time the measurement is performed, the displayed current value is corrected using the correction formula stored in the memory 27.

Next, the configuration of the eddy current sensor 11 will be described with reference to FIG.
The eddy current sensor 11 detects that the inductance of the detection coil of the sensor changes due to the eddy current generated in the conductor 2, and the magnetic field generated by the detection coil of the eddy current sensor 11 leaks out of the conductor 2. Therefore, it is necessary to take measures to prevent the sensitivity from decreasing.
In the present embodiment, the shape of the detection coil of the eddy current sensor 11 is such that a 10-turn conductor is formed on the substrate, the longitudinal direction is the axial direction of the conductor 2, and the short direction is the width direction of the conductor 2. This detection coil was formed into a rectangular shape and laminated in ten layers. The respective layers were connected to each other by through holes. The length and width of this detection coil was 6 × 3 mm.
Since the leakage of the magnetic field is small in the width direction of the conductor 2 of the electric wire to be measured and the magnetic coupling is long in the axial direction of the conductor 2, the sensitivity as the eddy current sensor 11 can be improved.

FIG. 4 is a schematic diagram for explaining a structure for mounting the eddy current sensor 11 and the Hall element sensor 12 further.
The eddy current sensor 11 has detection coils stacked in multiple layers, and the magnetic flux sensing direction of the detection coils is orthogonal to the axial direction of the conductor 2 of the electric wire to be measured. The stacked body of the stacked detection coils is attached to the substrate 13 of the sensor unit 10. On the other hand, the magnetic flux sensing direction of the Hall element sensor is parallel to the axial direction of the conductor 2 and orthogonal to the magnetic flux sensing direction of the detection coil, so that the magnetic flux sensitivity sensing direction of the Hall element sensor is orthogonal to the substrate 13. A substrate on which the Hall element sensor 12 is mounted is provided in a direction perpendicular to the substrate 13 so that the Hall element sensor 12 is mounted thereon.

  Although the shape of the detection coil of the eddy current sensor is a rectangle of 6 × 3 mm as described above, the shape may be an ellipse or a rhombus whose shape is flat in the axial direction of the conductor 2. Although the number of layers is set to 10, the number of layers can be selected as needed.

(Other embodiments)
The sensitivity of the eddy current sensor 11 depends on the strength of the magnetic coupling between the detection coil and the conductor 2 of the electric wire to be measured. The highest sensitivity is obtained when the detection coil is parallel to the conductor, that is, when the magnetic field generated by the detection coil is perpendicular to the conductor. On the other hand, when the detection coil is inclined with respect to the conductor, the magnetic coupling is weakened, and the sensitivity is reduced.
For this reason, by providing a plurality of eddy current sensors 11, even if the conductor is inclined with respect to the conductor 2 of the electric wire to be measured, the uncertainty due to the inclination can be compensated.

The contact surface of the current sensor 10 with the electric wire to be measured may be formed so that the eddy current sensor 11 and the electric wire to be measured can be in contact with each other without tilting. The surface to be contacted with the electric wire to be measured may have a shape having grooves in the axial direction.
In the above-described embodiment, an example has been described in which a Hall element sensor is used as the magnetic sensor, but a magnetic sensor using an inductance may be used.

2 Conductor 10 Sensor Unit 11 Eddy Current Sensor 12 Hall Element Sensor 13 Substrate 20 Measuring Device Main Body 23, 24 Analog / Digital Converter 26 CPU
27 Memory 28 Interface (I / O)
31 operation unit 32 communication unit 33 display unit (LCD)
34 Sound output unit

Claims (3)

A proximity sensor that acquires information on the distance of the electric wire to be measured to the conductor,
A magnetic sensor that acquires information on a magnetic field generated by a current flowing through the electric wire to be measured,
It is provided with arithmetic means for calculating a current value flowing through the electric wire to be measured from information on the magnetic field acquired by the magnetic sensor and information on the distance to the conductor of the electric wire to be measured acquired by the proximity sensor. Characteristic current measuring device. The current measuring device according to claim 1,
The proximity sensor is an eddy current sensor,
A current measuring device, wherein a planar shape of a coil of the eddy current sensor is a shape in which a longitudinal direction of the coil extends in a direction in which the electric wire to be measured extends, and a plurality of coils are stacked. . The magnetic sensor acquires information on the magnetic field generated by the current flowing through the electric wire to be measured,
Eddy current sensor acquires information on the distance to the conductor of the electric wire to be measured,
A current measuring method, wherein a calculating means calculates a value of a current flowing through the electric wire to be measured from information of the acquired magnetic field and information of a distance of the electric wire to be measured to a conductor.

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