JP2001264360A - Dc current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a measurement error from occurring which is caused by a flux leakage. SOLUTION: Cores 11 and 12 of a detection core 1 divided into halves, and a magnetic sensor 15 inserted in between the cores 12 and detects a magnetic field applied to the detection core 1, are housed in a hollow/annular magnetic shield case 2. A feedback coil 16 is wound around outer perimeter of the magnetic shield case 2 corresponding to the outer perimeter of the arm of the core 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable measuring instrument for non-contact and high-precision measurement of DC current for maintenance of industrial equipment and power generation equipment, and for measuring current or current waveform flowing through a conductor. The present invention relates to a DC current detector used as a DC clamp meter for detecting and observing with high accuracy and simpler.

[0002]

2. Description of the Related Art As a conventional general DC clamp meter, a Hall element is frequently used, but it has a drawback that detection sensitivity is low, and a measurement range for a large current is narrow.
In addition, sufficient accuracy cannot be obtained due to poor temperature characteristics. For this reason, in the related art, the output of a magnetic sensor or a fluxgate type magnetic sensor constituted by a Hall element provided in the detection core is fed back to a feedback coil wound around the detection core, and the magnetic flux applied to the detection core becomes zero. A zero-magnetic-flux compensation type that performs direct current detection with such adjustment is widely known.

FIG. 9 is an explanatory view of a conventional DC clamp meter. In FIG.
Is a detection core that constitutes the detector main body, is configured to form a rectangular ring as a whole, and is laterally divided at a position closer to the upper end than the upper and lower intermediate portions to form a small downward U-shaped core member 32. Upward U-shaped core member 33
Consists of

[0004] The core member 33 has a feedback coil 35 wound around one of its arms, and is divided into left and right portions substantially at the center of a connecting portion connecting both arms, and this divided portion is formed of a Hall element. An output terminal of the magnetic sensor 36 is connected to one end of the feedback coil 35 via an amplifier 37 and the like, so that a feedback current i flows through the feedback coil 35. The other end of the feedback coil 35 is an output terminal.

In such a DC clamp meter, the measurement is performed in a state where the conductor to be detected 34 through which the current I flows passes through the space inside the detection core 31. Detected conductor 3
Assuming that the current flowing through 4 is I and the number of turns of the feedback coil 35 is N, the feedback current i is adjusted so that I−Ni = 0, and an output that exactly corresponds to the measured current I is obtained.

[0006]

However, in such a conventional DC clamp meter, the magnetic field formed by the conductor 34 to be detected and the magnetic field formed by the feedback coil 35 are applied to different locations on the detection core 31. As a result, a leakage magnetic flux is generated, and the cancellation between the measurement current and the feedback current becomes insufficient, which causes an error.

The present invention has been made in view of such circumstances, and has as its object to house a detection core and a magnetic sensor in a magnetic shield case, and to wind a feedback coil outside the magnetic shield case. As a result, the influence of the magnetic field of the feedback coil and its winding on the detection core, etc. can be ignored, improving the measurement accuracy, and the switching frequency of the magnetic sensor can be selected to the optimum operating frequency regardless of the measurement frequency range. A DC current detector is provided.

[0008]

According to a first aspect of the present invention, there is provided a direct current detector according to the present invention, wherein an annular detection core through which a conductor can penetrate, a feedback coil wound around the detection core, A magnetic sensor for detecting a magnetic field applied to the core, applying a magnetic field erasing current corresponding to the output of the magnetic sensor to the feedback coil so that the magnetic field applied to the detection core becomes zero, In the DC current detector configured to detect the current, the detection core and the magnetic sensor are housed in an annular magnetic shield case, and the feedback coil is wound around the outer periphery of the magnetic shield case. I do.

According to a second aspect of the present invention, in the direct current detector of the present invention, the magnetic sensor has a flux gate structure.

The DC current detector according to the present invention according to claim 3 is characterized in that the magnetic shield case is made of soft ferrite.

[0011]

First, the principle of the present invention will be described with reference to the principle explanatory diagram shown in FIG. FIG. 1 is a diagram illustrating the principle of a DC current detector according to the present invention. In FIG. 1, reference numeral 1 denotes a detection core, 2 denotes a magnetic shield case, and 3 denotes a conductor to be detected. The detection core 1 is formed in a rectangular ring shape, and is horizontally divided into two portions at positions closer to the upper end than the upper and lower substantially central portions, and the detection target 3 is formed.
The core portion 11 and the core portion 12 are relatively movable when penetrating through them, each having a large and small U-shape in a side view, and are combined in a rectangular ring shape at the time of measurement.

The core portion 12 is divided at a substantially central portion in the longitudinal direction, and a magnetic sensor 15 comprising a Hall element is provided here.
Is interposed. The detection core 1 and the magnetic sensor 15 are housed in a magnetic shield case 2 having a hollow rectangular annular shape (in FIG. 1, the core 11 and the core 12 of the detection core 1 are separated from each other, and 2 has been removed). The magnetic shield case is formed in an annular shape having a hollow rectangular shape, and is divided into large and small U-shaped portions at positions substantially corresponding to the division positions of the detection core 1. The core part 12 and the magnetic sensor 15 are housed in the case part 22 in a state where they are not in contact with each other. And the core part 12
Outer circumference of the magnetic shield case 2 corresponding to one arm of
Specifically, the feedback coil 16 is wound around the outer periphery of the case portion 22. The output terminal of the magnetic sensor 15 is led out through a hole formed in the wall of the magnetic shield case 2 and connected to one end of the feedback coil 16 via an amplifier 37 and the like. That is, the detection core 1 and the magnetic sensor 15 that constitute the detector main body are housed in the magnetic shield case 2, and only the feedback coil 16 is wound around the magnetic shield case 2.

In such a configuration, the magnetomotive force I-Ni
Since the magnetic force component generated locally other than the above is shielded by the magnetic shield case 2, the detection core 1 includes I-Ni
Is applied. Further, since the magnetic shield case 2 functions as a core material in a high frequency region in which the feedback coil 16 operates as a current transformer, the mutual inductance M ｛= ｛(L ₁ , L ₂ ), L
₁ : Inductance as viewed from the primary winding, L ₂ : Inductance as viewed from the secondary winding increases, which is effective in ensuring the accuracy of the current transformer ratio in the high frequency region.

The magnetic shield case 2 is made of permalloy (Ni-Fe alloy), silicon steel plate (Fe-Si
Alloy), soft ferrite and the like can be used. Permalloy or silicon steel sheet is desirable from the viewpoint of workability, etc.
Soft ferrite is particularly desirable because it has good frequency characteristics, is less expensive than permalloy, and does not require heat treatment such as magnetic annealing. High frequency range (200kHz
), Soft ferrite such as Mn-Zn ferrite is desirable.

When the magnetic sensor 15 has a flux gate structure, a magnetic flux generated in the detection core due to a current flowing through the detected conductor 3 essentially penetrating into the space inside the detection core is applied to the detection core. Since the magnetic switching is performed by applying a predetermined AC exciting current to the wound exciting coil, if the frequency of the current flowing through the detected conductor 3 is close to an integral multiple of the frequency of the AC exciting current, the two are mutually switched. It is likely to cause interference and malfunction.

However, in the configuration of the present invention, there is a magnetic shield case on the _j side of the magnetic sensor, and this shield case works as the core of the current transformer, so that the feedback coil 16 voluntarily has i = I / N. Electric current flows. Therefore, the secondary current flowing through the feedback coil cancels the magnetic field created by the primary current to be measured. As a result, the magnetic sensor having the flux gate structure is not affected by the AC magnetic field generated by the primary current.

Accordingly, since the AC magnetic field due to the primary current to be measured is not substantially applied to the core material in the magnetic shield case 2, no malfunction occurs, and a frequency characteristic exceeding the switching frequency of the magnetic sensor 15 is secured. it can.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings showing the configuration of an embodiment. In this embodiment, a fluxgate type magnetic sensor is used as a magnetic sensor which is a component of the detector main body.

A magnetic sensor having a fluxgate structure usually has an excitation coil and a detection coil wound around an annular detection core made of a soft magnetic material such as permalloy in a toroidal shape, and is disposed so as to penetrate into a space inside the detection core. The magnetic flux in the detection core due to the magnetic field generated by the DC current flowing through the detected conductor is magnetically switched by applying a predetermined AC exciting current to the exciting coil, and the detecting coil generates an electromotive force corresponding to a magnetic flux change accompanying the magnetic switching. Thus, the value of the current flowing through the conductor to be detected is measured. Such a configuration is already known and is frequently used in various fields, but is also effective as a magnetic sensor constituting the detector body of the present invention.

The present inventor has previously proposed a high-sensitivity fluxgate magnetic sensor in which the above basic configuration is further improved and a pair of annular detection cores are required as detection cores (Japanese Patent Application No. 10-338185). . In the following embodiments, a configuration using the above-described high-sensitivity fluxgate magnetic sensor will be described.

FIG. 2 is a perspective view showing the structure of the embodiment according to the present invention, FIG. 3 is a side sectional view taken along the line III-III of FIG. 2, and FIG. 4 shows a process of manufacturing the detector main body shown in FIG. FIG. In the figure, reference numeral 1 denotes a detection core. Detection core 1
Is a permalloy having a composition of 80% by weight of Ni, 5% by weight of Mo, and Fe, and is formed to a thickness of 0.5 mm.
Annealing treatment for improving magnetism is performed at 00 ° C. for about 3 hours. The detection core 1 is formed in a rectangular ring shape as shown in FIG. 4 and is horizontally divided into two portions at positions closer to the upper end than the upper and lower substantially central portions, and has two large and small U-shaped core portions 1.
Consists of 1 and 12. Lower U-shaped core 1
The connecting portion for connecting the arm portions 2 is formed by winding a magnet wire having a diameter of 0.18 mm for 100 turns around an outer periphery around which a polyimide tape 12a having a thickness of 20 μm is wound.
5a.

The shape of the detecting core 1 is not limited to a rectangular ring, but may be a ring or another ring shape. The dividing direction of the detecting core 1 is not limited to the case described above, but may be any direction. It may be divided into two, and the number of divisions may be divided into two or more.

A pair of such detection cores 1 is prepared, and FIG.
As shown in (b), the corresponding ends of the exciting coils 15a, 15a are connected to each other, and the current i can flow therethrough. Further, on the outer periphery of the connecting portion of these two detection cores 1, 1 as shown in FIG.
Around the outer circumference of a magnet wire with a diameter of 0.1 mm
The detection coil 15b is formed by winding 0 turns.

FIG. 5 shows a case where the detector body is a magnetic shield case 2.
FIG. 4 is an exploded perspective view showing a state in which the device is stored in the inside. The magnetic shield case 2 is made of a soft magnetic material such as Mn-Zn ferrite, and the magnetic shield case is formed as a hollow rectangular ring as a whole as shown in the figure. The upper part is horizontally divided into upper and lower parts 21 and 22 at positions higher than the upper part, and each part is further divided into body parts 21a and 22a and lid parts 21b and 22b each having a U-shaped cross section. The magnetic shield case 2 is divided into four parts before assembling. The magnetic shield case 2 is housed inside the detector body and assembled. Further, when the conductor 3 to be detected is passed through the through hole, a hollow rectangular shape is formed as shown in FIG. It becomes annular.

The shape of the magnetic shield case 2 is not limited to a hollow rectangular annular shape, but may be any shape that can accommodate the pair of detection cores 1 and 1 in a non-contact state.
The division position and the number of divisions may be determined as needed.

As shown in FIG. 3, the detection cores 1, 1 are made of a synthetic resin spacer 1 between the arms of the upper cores 11, 11, respectively.
7 and the arms of the lower core portions 12 and 12 are overlapped and overlapped on both outer sides thereof, and furthermore, the main body portion 21a of the upper portion 21 of the magnetic shield case 2 from both outer sides thereof.
The leaf springs 18a and 18b made of a non-magnetic material are fixed to each of the lid portions 21b so that the distance between the detection cores 1 is kept constant. Feedback coils 16, 16 are wound around the outer periphery of the assembled magnetic shield case 2, corresponding to the outer periphery of each arm of the lower core portions 12, 12 of the detection cores 1, 1. The feedback coil 16 is the lower core 1
Although the case where it is wound around two portions corresponding to the arms 2 and 12 is shown, only one of the portions may be wound.

After the conductor 3 to be detected is passed through the holes at the centers of the detection cores 1 and 1 and the magnetic shield case 2, the main body portions 21a and 22a and the lid portions 21b and 22b are bonded and fixed with an adhesive or the like. The DC current detector of the present invention is completed. As shown in FIG. 2, the excitation coil 15a is connected to the excitation output of the excitation / detection circuit, and a predetermined excitation current is applied. The detection coil 15b is connected to a detection input of the excitation / detection circuit. Further, the output of the excitation / detection circuit is connected to the feedback coil 16. Test results of a DC current detector using such a fluxgate type magnetic sensor will be described.

FIG. 7A is a graph showing the relationship between the measured current I (A) and the absolute value of the measurement error | Δi | (mA), and FIG. 7B shows the relationship when the scale is reduced. The result. The number of turns of the feedback coil 16 is 4000 turns. The solid line in the graph represents the result in the case of the embodiment of the present invention, and the broken line represents the result of the conventional product without using the magnetic shield case. From this result, it can be seen that the absolute value of the measurement error is much smaller in the embodiment of the present invention than in the conventional product.

FIG. 8A is a graph showing the temperature characteristic of the embodiment of the present invention, and the horizontal axis represents the measured temperature (° C.).
And the vertical axis shows the output current (mA). Temperature characteristics in a small current region where the measured current I is 1 A, 0.6 A, 0.2 A, etc., which is a problem in the Hall element, are flat,
It was confirmed that good temperature characteristics were exhibited. FIG.
(b) is a graph showing frequency characteristics when the measured current I = 2 A, in which the horizontal axis represents frequency f (kHz) and the vertical axis represents output fluctuation (dB). The solid line shows the result of the embodiment according to the present invention, and the broken line shows the result of the conventional product without using the magnetic shield case, and in the embodiment of the present invention, it is apparent from the comparison with the conventional product. Thus, it can be seen that the output fluctuation is substantially zero.

[0030]

According to the present invention, the accuracy of the measured current over a wide range is obtained, and the magnetic field generated by the secondary current flowing through the feedback coil and the magnetic field generated by the primary current flowing through the detected conductor are canceled. Unbalance can be neglected, the influence of the coil winding on the measurement accuracy is small, and stable measurement accuracy can be secured. In addition, measurement exceeding the switching frequency of the magnetic sensor becomes possible, and the optimum operating frequency (excitation frequency) can be selected as the switching frequency of the magnetic sensor regardless of the measurement frequency range.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a DC current detector according to the present invention.

FIG. 2 is a perspective view showing a configuration of an embodiment according to the present invention.

FIG. 3 is a side sectional view taken along line III-III in FIG. 2;

FIG. 4 is an explanatory diagram showing a process of producing the detector main body shown in FIG.

FIG. 5 is an exploded perspective view showing a state when the detector main body is housed in a magnetic shield case.

FIG. 6 is a perspective view showing a state where the detection core is housed in a magnetic shield case.

FIG. 7 is a graph showing test results of the DC current detector according to the present invention.

FIG. 8 is a graph showing test results of the DC current detector according to the present invention.

FIG. 9 is an explanatory view of a conventional DC clamp meter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detection core 2 Magnetic shield case 3 Conductor to be detected 11, 12 Core part 15 Magnetic sensor 16 Feedback coil

Claims (3)

[Claims] An annular detection core through which a conductor can pass; a feedback coil wound around the detection core;
A magnetic sensor for detecting a magnetic field applied to the detection core, applying a magnetic field erasing current corresponding to the output of the magnetic sensor to the feedback coil so that the magnetic field applied to the detection core becomes zero, In a direct current detector adapted to detect the current of the conductor, the detection core and the magnetic sensor are housed in an annular magnetic shield case, and the feedback coil is wound around the outer periphery of the magnetic shield case. Characterized DC current detector. 2. The direct current detector according to claim 1, wherein the magnetic sensor has a flux gate structure. 3. The direct current detector according to claim 1, wherein the magnetic shield case is made of soft ferrite.