JP2002107384A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor using MI elements, capable of canceling disturbance noise in sensor detection sensitivity directions and making its size compact. SOLUTION: A magnetic sensor can accurately detect a very small magnetic field with an MI element 3 or 13 from very small magnetic field gradient in a small magnetic field region, by providing notches to a primary conductor 1 and a secondary conductor 1' with different resistance values, providing a small window in the middle of combined conductor, and utilizing generation of small magnetic field region in the small window 2, so as to contain the MI element 3 on a central line O in the small window 2 and the central line O and a magnetic field region G do not coincide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor using a magneto-impedance element (hereinafter referred to as an MI element). The present invention relates to a current sensor using an MI element that can obtain a detection magnetic field over the same.

[0002]

2. Description of the Related Art In a conventional auto breaker, current detection is performed by employing a normal current transformer in which a current carrying conductor of a main circuit is a primary conductor and a secondary coil is wound around an iron core. The market requirements for these circuit breakers, earth leakage circuit breakers, and other auto breakers require smaller and more compact products, and in line with this demand, improve the miniaturization of various components and improve the arrangement of components. As a result, the external dimensions have been reduced, but this has limitations.

[0003] On the other hand, various magnetic sensors have been developed.
There is also known a magnetic sensor type current transformer which measures a current flowing through a primary conductor in the form of a magnetic field intensity proportional to the current.

Moreover, these magnetic sensors are so small that they cannot be compared with ordinary current transformers. If this magnetic sensor type current transformer is replaced with an ordinary current transformer,
It is greatly expected to promote the miniaturization and compactness of the auto breaker described above.

[0005] However, auto breakers such as wiring breakers and earth leakage breakers are categorized in a wide range from a minimum of 5 A to a maximum of 6000 A depending on the frame. It is possible to adjust. On the other hand, the Hall element and the magnetoresistive element described above have an inherent problem in that the resolution is reduced under a minute magnetic field due to the influence of an unbalanced voltage and the like. It is difficult to measure current accurately.

On the other hand, a flux gate element or an MI element is known as a magnetic sensor capable of detecting a minute magnetic field with high accuracy. In particular, the operation range of the flux gate element and the MI element is a very small magnetic field of 10 gauss or less at most, and it is difficult to apply the flux gate element and the MI element to an auto breaker having a large rated current. Therefore, a means is used to provide a current sensor applied to a magnetic sensor that can measure the current flowing through the primary conductor with high accuracy over a wide range by using a magnetic sensor such as a flux gate element or MI element that exhibits high accuracy in detecting a minute magnetic field. Have been.

[0007] These means are achieved by opening a small window that bisects the current path at the center of the primary conductor, and arranging a magnetic sensor of a flux gate element or MI element at the center of the small window. . It is preferable to use a rectangular conductor as the primary conductor. As is well known, when a current flows through a conductor, a magnetic field is generated around the conductor,
The direction and strength of the magnetic field are determined by Biot-Savart's law. When the same current is applied to two conductors arranged in parallel in the same direction, the magnetic field intensity becomes zero at the center between the conductors, and the magnetic field intensity increases as the conductor approaches the conductor on both sides.

Therefore, if a rectangular conductor is adopted as a primary conductor through which a current flows, and a small window is opened so as to cut off a central portion of the conductor and divide the current path into two, conductor portions on both sides of the small window are sandwiched. Are in the same state as the two parallel conductors described above, and the magnetic field strength in the space of the small window is zero at the center, and the magnetic field strength increases as going to both side directions. Then, a minute magnetic field region is formed.

Therefore, if a flux gate element or an MI element is installed in such a manner as to be positioned in the small magnetic field region formed in the central portion of the small window, the current flowing through the primary conductor by these magnetic sensors can be changed from small current to large current. It can be detected accurately over a wide range up to the current.

In addition, if the small window corresponds to the external dimensions of the magnetic sensor, the elements of the magnetic sensor can be accommodated in the small window, so that no extra space is required for installing the magnetic sensor.

These embodiments will be described with reference to the drawings. In FIG. 3, 31 is a circuit breaker for wiring,
A primary conductor (rectangular conductor) as a main circuit conductor incorporated in an auto breaker such as an earth leakage breaker, and 32 is a small window notched and opened at the center of the primary conductor 31 so as to bisect the current path along the longitudinal direction. , 33 are flux gate elements arranged in alignment with the central part in the small window 32,
Alternatively, the magnetic sensor 34 of the MI element is a current detection circuit connected to the magnetic sensor 33.

In the figure, the width of the primary conductor 31 is A, the thickness is B, the width of the small window is C, and the length is D, and the primary conductor 31 extends in the longitudinal direction (current I direction). The center line is represented by O.

For example, the width A of the primary conductor 31 is 20 mm, the thickness B is 3 mm, the width C of the small window 32 is 5 mm, the length D is 10 mm, and the small window 72 when a current of 100 A flows through the primary conductor. When the magnetic field strength inside of is calculated by calculation, the magnetic field strength distribution is as shown in FIG. The magnetic field intensity distribution is symmetrical in the width direction of the conductor with respect to the center line O,
FIG. 5 shows the magnetic field intensity distribution of one half of the magnetic field.

As is apparent from the magnetic field strength distribution diagram shown in FIG. 5, the magnetic field strength is zero at the center point in the small window 2 along the center line O, and its peripheral region has a width of about 1 mm in the width direction. , There exists a minute magnetic field region (represented by an oblique broken line) with a magnetic field intensity of 5 Gauss or less.

Therefore, by positioning the magnetic sensor 33 of the flux gate element or the MI element in the small window in a position aligned with the small magnetic field region, the primary conductor 3
The current flowing through the first circuit, that is, the load current flowing through the main circuit of the auto breaker can be accurately detected over a wide range from small current to large current.

With such a configuration, a small window 32 is opened at the center of the primary conductor 31 to form a minute magnetic field region inside the small window 32, and the flux is aligned with the center of the small window. By installing a magnetic sensor such as the gate element or the MI element 33 that has high detection accuracy for a minute magnetic field, the current flowing through the primary conductor 31 can be accurately detected over a wide range.

Moreover, since the magnetic sensor having an ultra-small external dimension can be arranged so as to fit within a small window opened in the primary conductor 31, the magnetic sensor is arranged around the primary conductor 31 like an ordinary current transformer. There is no need to secure a special space for installing a current breaker. Therefore, by adopting the current transformer in an auto breaker such as a circuit breaker for wiring or an earth leakage breaker, the size and size of the auto breaker product can be reduced. Can be achieved.

As described above, in the conventional technology, in a current transformer applied to a magnetic sensor for measuring a current flowing through a primary conductor in the form of a magnetic field intensity proportional to the current, a central portion of the primary conductor portion as a rectangular conductor is used. A small window that bisects the current path, a small magnetic field is formed at the center of the small window, and a magnetic sensor is arranged in this small magnetic field region to measure the current flowing through the primary conductor.

[0019]

A small window is opened at the center of the primary conductor and a magnetic sensor is installed. When the MI element is placed at the center, the magnetic field at the center is zero. Due to the positional accuracy of the magnetic field, the measurement of the magnetic field varies in the positive and negative directions, the measurement error increases, and the sensor installation position requires considerably high accuracy.

Also, a small window is opened at the center of the primary conductor,
Since one magnetic sensor is installed, it is not possible to distinguish between disturbance noise and a signal and to cancel thermal drift, resulting in poor measurement reliability.

Therefore, in the current sensor for measuring the current flowing through the primary conductor and the secondary conductor in the form of a magnetic field intensity proportional to the current, the present applicant has cut out a notch at the center of the primary conductor and the secondary conductor. Then, by integrating the primary conductor and the secondary conductor, a small window that branches the current path is opened, and a magnetic sensor using a pair of MI elements whose detection sensitivity directions are reversed in the small window is provided. By taking the difference between the sensor values of the magnetic sensors using the MI element, by detecting the magnetic field, it is possible to cancel the disturbance noise in the sensor detection sensitivity direction and use a MI element that can be made compact. Current sensor.

Although any type of MI element can certainly perform high-precision magnetic detection, the variation in MI characteristics of the MI element and the peak of the rate of change of impedance are ±± O [O
e], which is made asymmetric by shifting by applying a bias magnetic field or the like. One of the peaks of the asymmetric characteristic is also + number [Oe], and in detail, is near +3 [Oe]. The area is as narrow as ± 3 [Oe] and the conventional MI
In the element detection circuit, linearity could be obtained only in the range of ± 3 [Oe]. ± 4 [Oe],
In a region where the output is saturated as ± 5 [Oe], detection is impossible.

In the present invention, the external magnetic field HB [Oe] generated in the small window can be reduced even if the current flowing through the primary conductor and the secondary conductor is a large current. Current detection is now possible.

Further, by using the same conductive material for the primary conductor and the secondary conductor, the current is halved. Also,
When the primary conductor and the secondary conductor are made of different conductive materials, the resistance values of the conductive materials are different, so that the current ratio can be branched depending on the resistance values.

[0025]

According to the present invention, there is provided a current sensor for measuring a current flowing through a primary conductor and a secondary conductor in the form of a magnetic field intensity proportional to the current. By opening a small window that branches the current path by integrating the primary conductor and the secondary conductor,
A magnetic sensor using an MI element is provided in the small window.
2. A current sensor for detecting a magnetic field by a magnetic sensor using an element. 2. The current sensor according to claim 1, wherein a small magnetic field gradient is generated in the small window, and an MI element is formed in the small window. It is a current sensor characterized by being incorporated.

According to a third aspect of the present invention, in the current sensor according to the first or second aspect, the MI element has a symmetric MI characteristic. In a fourth aspect, the MI element has an asymmetric MI characteristic. The current sensor according to claim 1 or 2, wherein:

According to a fifth aspect of the present invention, in the current sensor according to the first aspect, the primary conductor and the secondary conductor are made of different conductive materials. The current sensor according to claim 1, wherein a conductive material is used.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. Here, a thin-film magnetic impedance element (hereinafter, a thin-film MI element) formed of a magnetic thin film will be described, but the same applies to a wire-type magnetic impedance element. In FIG. 1, reference numerals 1 and 1 ′ denote rectangular conductors obtained by integrating a primary conductor and a secondary conductor as main circuit conductors in which a magnetic sensor including a magnetic impedance element whose magnetic field detection sensitivity is reversed is integrated. Conductor 1, secondary conductor 1 '
A notch is provided at the center of the current path so as to branch off along the longitudinal direction of the element, and a small window provided integrally with the primary conductor and the secondary conductor is provided with a magnetic impedance element (thin-film MI element).
Incorporates the thin-film MI elements 3 in the small windows 2 such that the detection magnetic field sensitivity of the magneto-impedance elements 3 (thin-film MI elements) is in the opposite direction. Reference numeral 4 denotes a current detection circuit connected to a magnetic sensor including the thin-film MI element 3.

In the drawing, the primary conductor 1 and the secondary conductor 1 'are shown.
The center line along the longitudinal direction (the direction in which the current I flows) is denoted by O. FIG. 2 is a sectional view taken along the line AA of FIG. 5 is the line of magnetic force. In the small window 2, the magnetic field strength is a minute magnetic field region, and the magnetic field lines 5
Are also indicated by dotted lines.

When the primary conductor 1 and the secondary conductor 1 'are made of the same conductive material, the magnetic field strength is symmetric with respect to the center line O in the width direction of the conductor, but made of different conductive materials. In this case, the respective resistance values are different, and the current flowing through the conductor is higher in the lower resistance, so that the current density is higher, and the magnetic field strength is symmetrical in the width direction of the conductor with respect to the center line O. However, the magnetic field strength of a conductor with a high current density and a low resistance value becomes stronger, and the magnetic field strength of a conductor with a low current density and a high resistance value is weaker, and the zero magnetic field region G is closer to the conductor side with a higher resistance value. appear.

Therefore, the center line O does not coincide with the zero magnetic field region G in the minute magnetic field. Therefore, along the center line O, the thin film M
One I element 3 can be arranged. At that time, there is no need for a position system as in the past. In a small magnetic field,
A small magnetic field gradient is generated and a simple current detection circuit 4 can output a simple sensor value with high accuracy even with a single thin film MI element.

The magnetic field H sensed by each thin-film MI element 3
Forms a magnetic field H [Oe] represented by H = (I / 2πr) where r is the radius of the line of magnetic force. This magnetic field becomes a small magnetic field region suitable for the thin film MI element, and a small magnetic field gradient is obtained, and the minute magnetic field is detected by providing the thin film MI element 3 therein.

Therefore, since the detection circuit 4 can be formed in the thin-film MI element 3 by a small magnetic field gradient in a small magnetic field, the small magnetic field is detected by the thin-film MI element 3 and the current is detected by the magnetic sensor. it can.

The thin-film MI element 3 requires a bias magnetic field ΔHex [Oe] because the rate of change in impedance—external magnetic field Hex is almost symmetrical with the external magnetic field being positive or negative. The bias magnetic field is applied to make the characteristics asymmetric.

The voltage voltage V1 across the MI element element 3 arranged so that the bias magnetic field ΔHb is applied is read in the minute magnetic field region in the minute magnetic field generated in the small window by the detection current described above. , I1, the output of the small magnetic field region can be obtained using the detection circuit 4 having a simple structure.

In the thin film MI element 3, since the above-mentioned MI characteristics are previously symmetric, the bias magnetic field ΔH
By applying b [Oe], the MI characteristic is shifted to be asymmetric. This is not necessary in the cross-type thin-film MI element 13 because the MI characteristic is asymmetric. In the thin-film MI element 3 as well, a cross-type thin-film MI element 13 using an easy axis of magnetization of a laminated soft magnetic thin film using an amorphous thin film is not particularly shown, but aluminum wire bonding is performed at both ends.
An electrode made of Au wire or the like or a lead wire is directly connected to the lead wire, and a high-frequency current is applied to both ends.

Therefore, conventionally, detection was possible only in a narrow magnetic field range of ± several [Oe]. However, the primary conductor 1 and the secondary current 1 ′ are notched to form a small window at the center of the integrated conductor. 2, the magnetic field generated in the small window 2 becomes a small magnetic field region even when a large current flows, and the zero magnetic field region (center line O) inside the small window 2 does not coincide with the small magnetic field region. By obtaining the magnetic field gradient and incorporating the MI element in each of the zero magnetic field regions, any circuit can obtain the sensor value of the detection output to obtain the current output 6 and obtain the output voltage VOUT [V]-
It has become possible to obtain the relationship of the detected current value [A].

Although not particularly shown, when the primary conductor 1 and the secondary conductor 1 'are integrated with the same conductive material, the center line O and the zero magnetic field region G naturally coincide with each other. At that time, the MI element 3 is built in on the center line O, and the MI element 3 is shifted from the center line O by utilizing the minute magnetic field gradient in the minute magnetic field region, thereby detecting a highly accurate minute magnetic field. Output as a sensor value, a current output can be obtained with a simple current detection circuit 6, and it is not necessary to increase the accuracy of the MI element installation position.

F, whose MI characteristics are symmetric like the thin-film MI element
The MI element of the magnetic wire using the eCoSiB magnetic wire is not particularly shown, but it goes without saying that it is included in the present application.

The structure of a cross-type thin film MI element 13 which is a stacked type using a soft magnetic thin film having an asymmetric MI characteristic has the following structure.
Although not particularly shown, the bias magnetic field ΔHex
There is no need to apply [Oe], and a cutout is formed in the primary conductor 1 and the secondary conductor 1 ′ having different resistance values to form a small window 2, and a cross-type thin film MI element is provided in the small window 2. 1
The present application naturally includes that the sensor value of the output of the detection circuit 4 is obtained as the current output 6 by incorporating the sensor circuit 3.

As described above, a small window is provided by notching and integrating the primary conductor and the secondary conductor having different resistance values, and the small window is small even if it is the center of the integrated conductor. A small magnetic field region is generated in the window, and a magnetic sensor 3 using the MI element is built in the small window 2 so that the center line O does not match the zero magnetic field region G, and a small magnetic field gradient is generated in the small magnetic field region. Since one MI element 3 or 13 is built in the small window 2 on the center line O, it is not necessary to increase the accuracy of the arrangement position. And the sensor value is output as a current output 6 by the current detection circuit.

Further, the current flowing through the conductor can be detected over a wide range with high accuracy. In addition, since the magnetic sensor having an ultra-small outer dimension is disposed so as to be built in the small window 2 of the integrated conductor, it is most suitable for a current sensor such as a vehicle for which a high current flows. In addition, since the current sensor uses one MI element 3 or 13, it can be made compact and does not require a special space.

The F characteristic in which the MI characteristics are symmetric as in the case of the thin film MI element
The MI element of the magnetic wire using the eCoSiB magnetic wire is not particularly shown, but it goes without saying that it is included in the present application.

The structure of a cross-type thin film MI element 13 using a soft magnetic thin film having an asymmetric MI characteristic has the following structure.
Although not particularly shown, the bias magnetic field ΔHex
There is no need to apply [Oe], and by incorporating it in the small window 2, the output of the current detection circuit 4 is used as a sensor value and the current output 6
Is naturally included in the present application.

[0045]

As described above, according to the present invention, a small window is provided by forming a notch in the primary conductor and the secondary conductor to integrate the primary conductor and the secondary conductor, and a minute magnetic field region is generated in the small window. By using the magnetic field gradient, the magnetic field strength generated by the current flowing in the primary and secondary conductors with different resistance values and the primary and secondary conductors with the same resistance value allows the MI element to detect a small magnetic field with a simple detection circuit. This is a current sensor that outputs a sensor value and can detect current with a simple current detection circuit.It can easily and stably detect a magnetic field without having to adjust the position accuracy in a small window to high accuracy as before. It is a current sensor that can be used. In addition, a similar effect can be achieved without applying a bias magnetic field, and further, a compact sensor can be achieved, and a current sensor that can cope with a large current without requiring an extra space for a vehicle can be achieved.

[Brief description of the drawings]

FIG. 1 is a top view showing a current sensor provided with an MI element as a magnetic sensor in an embodiment according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG. 1 according to the present invention.

FIG. 3 is a diagram showing a conventional current sensor in which a small window is opened using a primary conductor.

FIG. 4 is a diagram showing a magnetic field of a conventional primary conductor.

[Explanation of symbols]

 1, primary conductor 1 ', secondary conductor 2, small window 3, thin-film MI element 4, current detection circuit 5, current detection output 13, ..Cross-section thin-film MI element O: Center line G: Zero magnetic field region line

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Ueno 2-9-13 Nakameguro, Meguro-ku, Tokyo Inside Stanley Electric Co., Ltd. (72) Inventor Takuya Kazama 2-9-13 Nakameguro, Meguro-ku, Tokyo No. Stanley Electric Co., Ltd. F-term (reference) 2G017 AA01 AB07 AD51 2G025 AA05 AB01

Claims (6)

[Claims] In a current sensor for measuring a current flowing through a primary conductor and a secondary conductor in the form of a magnetic field intensity proportional to the current, a notch is formed in a center portion of the primary conductor and the secondary conductor.
By integrating the primary conductor and the secondary conductor, a small window that branches the current path is opened, and a magnetic sensor using an MI element is provided in the small window, and a magnetic sensor using the MI element is used. A current sensor for detecting a magnetic field. 2. The current sensor according to claim 1, wherein a small magnetic field gradient is generated in the small window, and the MI element is built in the small window. 3. The current sensor according to claim 1, wherein the MI element has a symmetric MI characteristic. 4. The current sensor according to claim 1, wherein said MI characteristic is asymmetric. 5. The current sensor according to claim 1, wherein the primary conductor and the secondary conductor are made of different conductive materials. 6. The current sensor according to claim 1, wherein the primary conductor and the secondary conductor are made of the same conductive material.