JP2002107386A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce measurement errors depending on the position of an MI element placed. SOLUTION: In this invention, a notch is provided in the center part of a primary conductor 1 and a secondary conductor 1' and the primary conductor 1, and the secondary conductor 1' are integrated into one. A small window 2 is provided as an opening, and a magnetic sensor, consisting of a pair of thin film MI elements 3 and 3' with different detection sensitivity directions, is placed in the small window 2. Even if a large current flows in the conductor, consisting of the primary conductor 1 and the secondary conductor 1', the inside of the small window 2 is in a small magnetic field region, and the detection sensitivity of the thin film MI elements 3 and 3' remains optimum. Furthermore, by arranging the one magnetic sensor 3 and the other magnetic sensor 3' canceling disturbance noise and thermal drift, so as to have detection sensitivity in different directions, a current output 6 can be attained by taking the difference between the output values of simple detection circuits 4 and 4'.

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. 7, 71 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 circuit breaker, and 72 is a small window notched and opened at the center of the primary conductor 71 so as to bisect the current path along the longitudinal direction. , 73 are flux gate elements arranged in alignment with the central part in the small window 72,
Alternatively, the magnetic sensor 74 of the MI element is a current detection circuit connected to the magnetic sensor 73.

In the figure, the width of the primary conductor 71 is A, the thickness is B, the width of the small window is C, and the length is D, along the longitudinal direction of the primary conductor 71 (the direction in which the current I flows). The center line is represented by O.

For example, the width A of the primary conductor 71 is 20 mm, the thickness B is 3 mm, the width C of the small window 72 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. 1 shows a magnetic field intensity distribution of one half of the one side.

As is apparent from the magnetic field strength distribution diagram shown in FIG. 8, the magnetic field strength is zero at the center point in the small window 2 along the center line O, and its peripheral area 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 73 of the flux gate element or the MI element in the small window in a position aligned with the minute magnetic field region, the primary conductor 7
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 72 is opened at the center of the primary conductor 71 to form a small magnetic field region inside the small window 72, and the flux is adjusted by adjusting the position to the central portion in the small window. By installing a magnetic sensor having a high detection accuracy for a minute magnetic field such as the gate element or the MI element 73, the current flowing through the primary conductor 71 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 in a small window opened in the primary conductor 71, the magnetic sensor is arranged around the primary conductor 71 like a normal 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, the present applicant has integrated the primary conductor and the secondary conductor, provided a cutout in the center of the primary conductor and the secondary conductor, provided a small window for branching the current path as an opening, and performed detection. By providing a magnetic sensor using a pair of MI elements in which the sensitivity direction is reversed, using the same conductive material for the primary conductor and the secondary conductor, and taking the sensor value of the magnetic sensor using the MI element, Magnetic field detection eliminates the need for sensor placement accuracy, cancels disturbance noise and signals, and cancels thermal drift. It is intended to provide a sensor.

The present invention is a current sensor which incorporates a magnetic sensor using two MI elements having different detection sensitivity directions in the small window, and can also be constituted by an MI element having a symmetric MI characteristic. Incorporating an asymmetric MI element prevents the configuration from becoming complicated and can be expected to reduce costs. Further, by using the same conductive material for the primary conductor and the secondary conductor, the current branched to the current path becomes (1/2) I
This is a current sensor that does not require the accuracy of the sensor installation position and can detect a current by obtaining a difference between sensor values in an output with a simple detection circuit.

Although any type of MI element can surely perform high-precision magnetic detection, variations in the MI characteristics of the MI element and peaks in the rate of change in impedance are not more than ± several [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 primary conductor and the secondary conductor are integrated, and a cutout is made at the center of the primary conductor and the secondary conductor, and a small window for branching the current path is provided as an opening. By providing the small magnetic field region, the external magnetic field H _B [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. The current can be detected in the circuit.

Further, by using the same conductive material for the primary conductor and the secondary conductor, the current is halved.

[0026]

According to a first aspect of 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, wherein the primary conductor and the secondary conductor are integrated. And a notch in the center of the primary and secondary conductors, providing a small window for branching the current path as an opening, providing the primary and secondary conductors with the same conductive material,
A current sensor characterized by providing a magnetic sensor using a pair of MI elements whose detection sensitivity directions are opposite to each other and detecting a magnetic field by taking a difference between sensor values of the magnetic sensor using the MI element. According to a second aspect of the present invention, there is provided a current sensor according to the first aspect, further comprising a magnetic sensor using two MI elements having different detection sensitivity directions reversed in the small window. is there.

According to a third aspect, 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 sensor has an asymmetric MI characteristic. The current sensor according to claim 1 or 2, wherein:

[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.

FIG. 1 (top view), FIG. 2
(Cross-sectional view) will be described. 1, 1 'is a rectangular conductor in which a primary conductor 1 and a secondary conductor 1' as a main circuit conductor in which a magnetic sensor comprising a magnetic impedance element whose magnetic field detection sensitivity is reversed are integrated, and 2 is a primary conductor. 1,
A cutout is made at the center of the secondary conductor 1 'so as to branch off the current path along the longitudinal direction, and a small window provided integrally with the primary and secondary conductors. A current detection circuit connected to a magnetic sensor composed of the thin-film MI elements 3 and 3 'so that the magnetic sensor composed of the impedance elements 3 and 3' (thin-film MI element) has a detection magnetic field sensitivity in the opposite direction. It is.

The primary conductor 1 and the secondary conductor 1 'are shown in FIG.
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. The magnetic field strength

When the primary conductor 1 and the secondary conductor 1 'are made of the same conductive material, the magnetic field intensity is symmetric with respect to the center line O in the width direction of the conductor, and the respective resistance values are the same. Therefore, the current flowing in the conductive material of the primary conductor 1 and the secondary conductor 1 'is branched into two. The magnetic field intensity is symmetric in the width direction of the conductor with respect to the center line O, and coincides with the zero magnetic field region G.

At this time, the thin-film MI elements 3 and 3 ′ having different detection magnetic field directions symmetrically with respect to the center line O are provided inside the small window 2.

The magnetic fields H and H 'sensed by the thin film MI elements 3 and 3' are given by H = (I / 2πr) H '= (I / 2πr') where r and r 'are the radii of the lines of magnetic force. The magnetic fields H [Oe] and H '[Oe] that appear are formed. The magnetic field has a small magnetic field gradient suitable for the thin-film MI element, and the thin-film MI elements 3 and 3 'are provided therein to detect the magnetic field in the small magnetic field. As a result, a small magnetic field gradient is generated in the small magnetic field, and the two thin-film MI elements 3, 3 'output simple sensor values with high accuracy by the simple current detection circuits 4, 4', respectively, and take the difference therebetween. Thus, the current output 6 can be detected without being affected by a disturbance magnetic field or thermal drift. At that time, the conventional position accuracy is not required. In addition, since the primary conductor 1 and the secondary conductor 1 'are each provided with a notch at the center thereof, it is easy to process, and the connector may be used when integrated, and the same conductive material may be used. It is also possible to weld them.

Next, a second embodiment of the present invention will be described with reference to FIG. 3 (top view) and FIG. 4 (side view). The reference numerals and explanations are the same as in the first embodiment, and will not be repeated. Also, here, the other elements are the same except for the arrangement of the elements. One element is arranged in the zero magnetic field region G. Even with such a structure, since a small magnetic field gradient is present in a small magnetic field, the current detection 6 can be obtained by taking the difference between the respective detection outputs in the detection circuits 4 and 4 '.

Next, a third embodiment of the present invention will be described with reference to FIG. 5 (top view) and FIG. 6 (side view). The reference numerals and explanations are omitted because they are the same as those of the third embodiment. Also, here, the other elements are the same except for the arrangement of the elements. One element is placed in a small magnetic field region, and a small magnetic field gradient is formed near the other element. Even in such a structure, since a small magnetic field gradient exists in a small magnetic field, each of the detection circuits 4, 4 '
Thus, current detection can be obtained by taking the difference between the respective detection outputs.

The thin-film MI element requires a bias magnetic field ΔH _ex [Oe] because the impedance change rate—the external magnetic field H _ex is almost symmetric with respect to the external magnetic field. The bias magnetic field is applied to make the characteristics asymmetric.

MI element elements 3, 3 'arranged so that bias magnetic fields _{Hb in} directions opposite to each other are applied to the magnetic field generated in the small window by the above-described detected current.
The voltages V ₁ , V ′ ₂ are read out, and the currents I ₁ , I ′ ₂ are obtained, and the difference between them is taken. Can be obtained.

As described above, the magnetic sensor using the pair of MI elements 3 and 3 'is built in the small window 2 so as to have detection sensitivity in different directions, respectively, and the one magnetic sensor and the other magnetic sensor are used. By taking the difference between them, disturbance noise in the sensor detection sensitivity direction can be canceled, and compactness can be realized. In addition, the current flowing through the conductor is provided with a small magnetic field gradient in the small magnetic field region, and the sensor value can be accurately detected by the simple detection circuits 4 and 4 'regardless of the sensor installation accuracy, and the difference between the sensor values can be used as the current detection 6. . In addition, since the magnetic sensor having an ultra-small external dimension is disposed so as to be built in the small window 2 opened in the primary conductor 1, it is most suitable for a current sensor in which a high current flows even in a vehicle or the like. Further, since the current sensor uses an MI element capable of removing disturbance noise and thermal drift and capable of detecting a stable magnetic field, there is no need to secure a special space.

Further, since the notch is formed in the center of the primary conductor 1 and the secondary conductor 1 'in advance, there is an advantage that the conductor can be easily processed, and the connector can be easily integrated or welded.

F whose MI characteristic is 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.

A soft magnetic thin film having an asymmetric MI characteristic is used.
Of the cross type thin film MI elements 13 and 13 '
Although the structure is not shown, the bias magnetic field is
ΔH _ex[Oe] does not need to be applied, and
By incorporating it in the small window 2 so that the detection sensitivity is reversed,
By taking the difference between the outputs of the detection circuits 4 and 4 ', the output 6 can be obtained.
Of course, it is included in the present application.

[0042]

As described above, according to the present invention, a notch is formed at the center of the primary conductor and the secondary conductor, and a small window is opened at the center of the primary conductor and the secondary conductor. And a magnetic sensor comprising a pair of MI elements whose detection sensitivity directions are opposite to each other is provided in the small window, and a current can be detected by a simple detection circuit by taking a difference between sensor value outputs, and a primary conductor and a secondary conductor are provided. Have the same resistance value, the current path can be branched into half. Further, the current sensor is characterized by removing disturbance noise and thermal drift and performing stable magnetic field detection. Further, a similar effect can be achieved without applying a bias magnetic field. Further, compactness 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 according to a first embodiment of the present invention.

FIG. 2 shows a first embodiment according to the present invention.
It is A sectional drawing.

FIG. 3 is a top view showing a current sensor provided with an MI element as a magnetic sensor according to a second embodiment of the present invention.

FIG. 4 shows a second embodiment according to the present invention.
It is B sectional drawing.

FIG. 5 is a top view showing a current sensor in which an MI element is provided as a magnetic sensor according to a third embodiment of the present invention.

FIG. 6 shows a third embodiment according to the present invention.
It is C sectional drawing.

FIG. 7 is a perspective view of an automatic breaker using these magnetic sensors on which a conventional MI element is installed.

FIG. 8 shows a conventional magnetic field strength distribution diagram.

[Brief description of reference numerals]

 1, primary conductor 1 'secondary conductor 2, small window 3, 3' thin film MI element 4, 4 'detection circuit 5, magnetic field line 6, ..Current output 13, 13 ': cross-type thin-film MI element O: central line G: zero magnetic field region

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 Stanley F term (reference) in Electric Co., Ltd. 2G017 AA01 AB07 AD51 2G025 AA05 AA08 AB01 5E081 AA18 CC12 GG05

Claims (4)

[Claims] 1. 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, wherein the primary conductor and the secondary conductor are integrated and the primary and secondary conductors are integrated. A notch is provided at the center, the primary conductor and the secondary conductor are formed of the same conductive material, and a small window for branching the current path is provided as an opening.
A current sensor comprising a magnetic sensor using an I element, and detecting a magnetic field by taking a difference between sensor values of the magnetic sensor using the MI element. 2. The current sensor according to claim 1, further comprising a magnetic sensor using two MI elements having different detection sensitivity directions reversed 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 the MI element has an asymmetric MI characteristic.