JPH052033A - Current sensor and setting method for range of detection current thereof - Google Patents

Abstract

PURPOSE:To improve a high-frequency response characteristic regarding a current sensor using a magnetoresistance element and a conductor through which a detection current flows and regarding a setting method of the range of the detection current thereof. CONSTITUTION:A current sensor is equipped with a conductor 1 which is made to generate a current magnetic field by making a detection current (i) flow therethrough, a magnetoresistance element 2 which is disposed corresponding to the conductor 1, supplied with an operating current and detects the current magnetic field, and a magnetic shield member 3 which shields the conductor 1 and the magnetoresistance element 2 from an external magnetic field. The magnetic shield member 3 is formed of an insulative soft ferrite material. For setting the range of the detection current, the shape of a section of a prescribed part of the conductor 1 facing the magneto-resistance element 2 is selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor and a method for setting a detection current range of the current sensor, and more particularly to a current sensor for improving high frequency response characteristics and a current for facilitating setting of the detection current range. The present invention relates to a method of setting a detection current range of a sensor.

As a current sensor, for the purpose of downsizing the sensor, improving the sensor sensitivity, and the like, a current sensor of the magnetoresistive effect type that employs a method of detecting a current magnetic field generated by a detection current through a magnetoresistive element. (Magnetic detection device) is proposed in Japanese Patent Laid-Open No. 1-299481.

[0003]

2. Description of the Related Art A conventional current sensor utilizing the magnetoresistive effect described in the above publication will be described with reference to FIG.
In the figure, 1 is a conductor, 2 is a magnetoresistive element, and 3 is a magnetic shielding container made of a permalloy plate. In this current sensor, a current magnetic field H is generated by a detection current i flowing into the conductor 1 from the outside, and the current magnetic field H is generated by a magnetoresistive element 2 which is separately supplied with a current for operation via a lead portion 6. The change in resistance is changed, and this change in resistance is detected through another detection unit. A magnetic shielding container 3 for magnetically shielding the current sensor from the external magnetic field Hex is arranged outside the current sensor so as to surround the entire current sensor.

[0004]

In the case of the current sensor described in the above publication, the magnetic shielding container 3 is made of a permalloy plate material. A magnetic shield made of a permalloy plate material is known as a very general and effective method for magnetic shield. However, this magnetic shield has a problem that an eddy current is generated inside the magnetic shield container due to the current magnetic field generated by the detected current. The magnetic field due to this eddy current acts to weaken the current magnetic field due to the detected current. Therefore, when the detected current has a steep waveform such as a pulse waveform, the output waveform of this current sensor is the pulse waveform of the detected current. Will not be faithfully reproduced, and it will not be possible to detect a pulse current with a high repetition frequency.

Further, the current sensor is required to be extremely small in size, and it is necessary to accommodate it in a small magnetic shield container, so that the structure such as the shape and size of the conductor and the magnetoresistive element is greatly restricted. For this reason, how to set the detection current range of the current sensor for detection currents with various current values, assuming that the structure is simplified, the manufacturing cost is reduced, and the structure is suitable for mass production. That is a problem. However, the above publication does not disclose this point.

In view of the above problems of the conventional current sensor, the first object of the present invention is to faithfully reproduce the detected current waveform in the output waveform of the sensor even for the detected current having a steep waveform such as a pulse waveform. It is to provide a current sensor with high accuracy even for a pulse current having a high repetition frequency.

Further, in view of the problems of the conventional current sensor, the second object of the present invention is to reduce the detection current range of the current sensor which can simplify the sensor shape, reduce the manufacturing cost, and enable mass production. It exists in providing the setting method.

[0008]

FIG. 1 is a conceptual diagram showing the basic configuration of the present invention. In the figure, 1 is a conductor, 2 is a magnetoresistive element, and 3 is a magnetic shield member. In the present invention, in order to achieve the first object, a conductor 1 that generates a current magnetic field via a detection current i, and a magnetoresistive element 2 that is supplied with an operating current and is arranged corresponding to the conductor 1. ,
In a current sensor including a magnetic shield member 3 for magnetically shielding the conductor 1 and the magnetoresistive element 2 from an external magnetic field, the magnetic shield member 3 is formed of an insulating soft ferrite material, and the second In order to achieve the above-mentioned object, a conductor 1 for generating a current magnetic field via a detection current i, a magnetoresistive element 2 which is supplied with an operating current and is arranged corresponding to the conductor 1, a conductor 1 and a magnetoresistive element Magnetic shield member 3 for magnetically shielding 2 from an external magnetic field
In the method for setting the detection current range of the current sensor, the cross section of the predetermined portion is further set by selecting the cross-sectional shape of the predetermined portion of the conductor 1 facing the magnetoresistive element 2. When the shape is selected, the width or thickness of the predetermined portion of the conductor 1 is changed.

[0009]

By forming the magnetic shield member from the insulating ferrite, it is possible to prevent the eddy current generated in the magnetic shield member due to the current magnetic field, so that there is no fear of weakening the current magnetic field. Since the frequency characteristic of permeability μ is uniform, the waveform of the detected current can be faithfully reproduced.

With the configuration in which the detection current range of the current sensor is set by selecting the cross-sectional shape of the predetermined portion of the conductor,
It is possible to supply a current sensor adaptable to a large number of detected current values without changing the shapes and dimensions of the magnetic resistance element and the magnetic shield member.

[0011]

The present invention will be further described with reference to the drawings. FIG. 2 is a perspective view showing a main part of the current sensor according to the embodiment of the present invention. In the figure, 1 is a conductor, 2 is a magnetoresistive element,
Reference numerals 3 respectively denote shield plates which form a magnetic shield member. In the current sensor of this embodiment, the magnetoresistive element 2 is supported on a support board 5 formed of a non-magnetic material, preferably a resin material, and the lead portion (not shown) of the magnetoresistive element 2 is illustrated in the support board 5. Seen above, it penetrates downward.

The conductor 1 has a wide width at the terminal portions 1A at both ends thereof, and a central portion (predetermined portion) 1 facing the magnetoresistive element 2 is formed.
It is formed to have a narrow width at B and is made of a strip-shaped copper plate as a whole, and is supported by an insulating material by a case (not shown) which also serves as an electrostatic shield.

Further, a conductor 1 in which a perpendicular line 2a passing through the center of the magnetoresistive element 2 intersects with the longitudinal centerline 1a of the conductor central portion 1B forms a predetermined portion facing the magnetoresistive element 2 at a central portion 1B. In, the size of the width a is selected as a predetermined value,
The magnetic shield plate 3 forming the magnetic shield member is inserted into and supported by the groove 51 of the support board 5 as shown by a part of the magnetic shield plate 3. In the case of the conductor 1 of this embodiment, the conductor thickness t
Is 3 mm, the total conductor length is about 30 mm, and the conductor width is about 15 mm in the 1A portion and about 5 mm as the value of a in the 1B portion.

FIGS. 3A and 3B are a side sectional view and a plan view showing the overall structure of the sensor of the embodiment shown in FIG. 2, respectively. As shown in the figure, the current sensor has a structure in which it is entirely covered with a case 4 that serves as an electrostatic shield, and a support board 5 is supported inside the case 4.

The magnetoresistive element 2 is housed in an insulating cover 8 and supported by the support board 5 via a lead portion 2A penetrating the support board 5, and the lead portion 2A and the external lead wire 6 are connected. It The large number of magnetic shield plates 3 are inserted into the premises of the support board 5 and are supported by the support board 5 as described above, and are removable for internal inspection or the like.

FIG. 4 shows the frequency characteristics of the general magnetic permeability μ of the insulating soft ferrite used as the magnetic shield in the current sensor of the present invention and the frequency characteristics of the magnetic permeability μ of permalloy, which is an ordinary magnetic shielding material. It is shown as a control.

As shown in the figure, each of the selected soft ferrite materials has a very flat frequency characteristic of magnetic permeability μ. Therefore, permalloy is used as a magnetic shield even when detecting an input current consisting of a pulse wave. Compared to the conventional current sensor used, the reproducibility of the input waveform in the output waveform is extremely good.

Returning to FIG. 3, the conductor 1 is supported on the upper part of the insulating base 7 via mounting bolts inserted into the mounting holes 9 and is arranged directly below the insulating cover 8 of the magnetoresistive element 2. Conductor 1
Are connected to the external leads 6 at the terminal portions 1A at both ends and supplied with the detection current i. The conductor 1 is a magnetoresistive element 2
The detected current range is set according to the size of the width a or the thickness t of the central portion 1B forming a predetermined portion facing with. Preferably, the thickness a is constant and the width a of the central portion 1B is
The selection of is adopted.

If the thickness t of the conductor 1 is made sufficiently smaller than the length of the central portion 1B, the electric current electric field generated in the magnetoresistive element 2 by the detected current i is H = (1 / 4π). (I / a). (. theta.1-.theta.2) (where .theta.1 and .theta.2 are the angles formed by the conductor surface and the line connecting the magnetic field measurement point and both sides of the conductor). By determining the relative position between the conductor 1 and the magnetoresistive element 2, θ1−θ2 becomes constant, and the magnitude of the magnetic field at the position of the magnetoresistive element 2 is selected by this formula by the width a of the central portion 1B of the conductor 1. It

The manner of selecting the conductor width is shown in the graph of FIG. In the figure, the horizontal axis represents the width of the central portion 1B of the conductor 1 forming a predetermined portion facing the magnetoresistive element 2, and the vertical axis represents the power loss (W) inside the conductor and the converted magnetic field generated by the passage of the detection current. (0e) is taken. In addition,
The values in the figure are values when the conductor thickness t is 3 mm.

Each of the curves (a) and (b) has a detected current of 2
The current loss and the generated magnetic field at 00A are represented by the curve (c),
(D) shows the current loss and the converted magnetic field when the detected current is 100 A, and the curves (e) and (f) show the current loss and the converted magnetic field when the detected current is 50 A, respectively. .

The arrow pointing downward at the current loss of 0.4 W means that the conductor width a is selected so that the power loss becomes 0.4 W or less for each detected current value. The upward arrow at the position of 150e of the magnetic field means that the conductor width is selected so that the magnetic field Hx of the detected current is 150e or more in consideration of the magnetic field detection sensitivity of the magnetoresistive element. .

For example, when the maximum value of the detected current is 100 A, from the position A of the curve (d) where the power loss is 0.4 W,
A conductor width of about 3 mm or more is obtained, and a conductor width of 12 mm or less is obtained from position B of the curve (c) on the generated magnetic field 150e. A conductor width within this range, for example, a conductor width of 7.5 mm is selected. .

In this way, the sensor is most suitable for detection currents of various magnitudes by simply selecting the conductor width a without changing the size, arrangement, shape, etc. of other members and elements. This is preferable because a wide magnetic field sensitivity range can be adapted.

Instead of selecting the width a of the predetermined portion of the conductor, the thickness t
It is also possible to set the detection current range by selecting, and it is also possible to set the detection current range by making the side surface of the conductor face the magnetoresistive element and selecting the width a of the conductor. It is included in the method for setting the detection current range of the current sensor. In the latter case, the formula of H = (1 / 4π) · (i / a) · log (r2 / r1) (r1 and r2 are the distances between the conductor side surfaces and the magnetoresistive element, respectively) is used with the thickness t being small. it can.

In the above-mentioned embodiment, the barber pole type magnetoresistive element is used as the magnetoresistive element. FIG. 6 is a schematic plan view showing the structure of the barber pole type magnetoresistive element 2 used in this embodiment.

In FIG. 6, each of the four magnetoresistive element portions 2-1 to 2-4 is connected as a Wheatstone bridge via the external terminals 21 to 24, and except for the conductor pattern forming direction. Have the same shape. The magnetoresistive element 2 of this type has a structure similar to that described in Japanese Patent Laid-Open No. 64-22076. In each of the magnetoresistive element portions 2-1 to 2-4, long linear portions 25 are connected in series in a zigzag shape.

FIG. 7 is a partially enlarged plan view of the magnetoresistive element portions 2-1 to 2-4 schematically showing the basic structure of the linear portion 25 of the barber pole type magnetoresistive element. ) Is two of the four magnetoresistive element parts 2-1 and 2
-3, the configuration of the linear portion 25 of FIG. 3 shows the configuration of the linear portion 25 of the other two magnetoresistive element portions 2-2 and 2-4. In the figure, 26 is a magnetic thin film made of, for example, permalloy (Ni-Fe), and 27 and 28 are conductor patterns made of, for example, gold (Au). The conductor patterns are electrode portions 27 at both ends and a strip-shaped conductor layer 28 at the center. It consists of and.

The magnetic thin film 26 is given a uniaxial magnetic anisotropy in the M direction in the figure and is initially magnetized, and the conductor patterns 27 and 28 are formed as thin layers on the magnetic film 26, and electrodes on both left and right ends are formed. It is formed in a barber pole-like pattern with a large number of strip-shaped conductor layers 28 which are inclined at 45 degrees with respect to the line connecting the portions 26 and arranged at predetermined intervals.

As shown in FIGS. 7A and 7B, the magnetoresistive element portions 2-1 and 2-3 and the magnetoresistive element portion 2-
2, 2-4 and the strip-shaped conductor layer 2 in directions different from each other by 90 degrees
8 are arranged, and the direction of any of the strip-shaped conductor layers is 45 degrees with the direction M of the initial magnetization and the direction of the current magnetic field H or 13
The direction is 5 degrees. According to this structure, the direction m of the current flowing through each magnetic thin film 26 is the illustrated direction, that is, the direction perpendicular to the major axis of the strip conductor layer 28.

FIG. 8 is an operation explanatory view showing a resistance change in each barber pole type magnetoresistive element portion. Curves (a) and (b) are shown in correspondence with (a) and (b) in the configuration explanatory view of the linear portion 25 of the magnetoresistive element shown in FIG. 7, respectively.

As shown in FIG. 8, as the current magnetic field H increases, the resistance values of the magnetoresistive element portions 2-1 and 2-3 having the linear portion 25 of FIG. The resistance values of the magnetoresistive element portions 2-2 and 2-4 having the 7 (b) linear portions 25 decrease.

Further, when the external magnetic field is reversed, the resistance change is reversed, which is different from the case where a normal magnetoresistive element causes the same resistance change in the positive and negative directions of the magnetic field. For this reason,
In the case of the current sensor of the embodiment configured as the Wheatstone bridge circuit, the polarity of the detected current can be determined.

The curves shown in FIGS. 9 (a) and 9 (b) represent the resistance changes when a bias magnetic field is applied to the magnetoresistive element by a permanent magnet in the direction opposite to the initial magnetization of the magnetic thin film 71 or in the forward direction, respectively. It is a characteristic view to show.

As shown in the figure, by selecting various directions and magnitudes of the bias magnetic field of the permanent magnet, it is possible to adapt to the magnitude of the control current of the specific circuit. Further, in the case of the forward bias shown in FIG. 9B, when the bias magnetic field is increased, the curve F sequentially shifts to the curve K, and there is an advantage that the relationship between the magnetic field and the resistance change becomes linear. In the case where the bias direction of the permanent magnet is set in the direction opposite to the direction of the initial magnetization as shown in (a) of the figure, the sensitivity of the magnetoresistive element decreases when the bias magnetic field is large, and the output characteristic is reversed when the bias magnetic field is larger.

FIG. 10 is a sectional view showing the general structure of a barber pole type magnetoresistive element. In the figure, an example in which a bias magnetic field of the permanent magnet 201 is applied in the same direction M ₀ as the initial magnetization direction M of the magnetic thin film of the magnetoresistive element 2 is shown.

In this magnetoresistive element 2, a Si substrate 202 is provided on a permanent magnet 201, and a SiO ₂ film 203, a permalloy magnetic thin film 204, is formed on the Si substrate 202.
The adhesion layer 205 and the conductor layer 206 are sequentially laminated and formed into a predetermined pattern, and the whole is covered with a protective layer 207 from above.

The magnetic thin film 204 is given uniaxial magnetic anisotropy in the M direction shown in the drawing, and is initially magnetized. As permanent magnets, ferrite magnets, Fe-Cr-Co magnets,
Alternatively, an alnico magnet or the like can be used.

FIG. 12 is a diagram for explaining an output waveform obtained through the current sensor of the above-mentioned embodiment and the amplifier attached to the current sensor. (A) shows a detected current (input current) waveform, and (b) shows The output waveforms of the current sensor of this embodiment are shown respectively.

As shown in the figure, the output waveform of the current sensor of this embodiment can reproduce the detected input current waveform quite faithfully, and the high frequency response characteristic (especially slew rate) is improved. There is.

For comparison with the output waveform of the above embodiment, the output waveform of a conventional current sensor of the type using a magnetic core and a coil is shown in FIG. Figure 5
Is a current sensor according to another embodiment of the present invention. The difference from the current sensor of the first embodiment shown in FIG. 2 is that the conductor 1 is exposed from the openings of the electrostatic shield case and the magnetic shield member and can be replaced from the lower side of the electrostatic case. .

In this way, there is an advantage that it is possible to deal with various detection current ranges by changing the cross-sectional shape of a predetermined portion of the conductor, for example, the conductor width in one current sensor. In this case, select the conductor width
If it is simply limited to the range of the central portion forming the predetermined portion, it is not necessary to change the shape of the conductor mounting portion, so that the compatibility of the conductors is ensured.

FIG. 13 is a perspective view showing an essential part of a current sensor according to another embodiment of the present invention, and FIG. 14 shows the relationship between the measured current, the generated magnetic field and the power loss of the current sensor using the conductor shown in FIG. FIG. 15 is a diagram (No. 1), and FIG. 15 is a diagram (No. 2) showing the relationship between the measured current, the generated magnetic field, and the power loss of the current sensor using the conductor shown in FIG.

In FIG. 13, 1 is a conductor, 2 is a magnetoresistive element, and the conductor 1 having a U-shape in plan view is a magnetoresistive element 2.
The central portion 1D facing each other is formed in a smaller cross section than the terminal portions 1C at both ends. The conductor 1 is arranged so that the center line 1a of the central portion (predetermined portion) 1D facing the magnetoresistive element 2 does not intersect the perpendicular 2a passing through the center of the magnetoresistive element 2, and the width of the central portion 1D is a, Assuming that the thickness is t, the cross-sectional shape of the central portion 1D with respect to the strength of the detected current changes the width a or the thickness t.

Therefore, for example, a detection current is 2 made of a copper plate.
When the conductor 1 of 00A has a U shape shown by a solid line in FIG. 13 and the thickness t is 6 mm and the width a is 4 mm, the detected current is 1
The conductor 1 of 00A is deleted as shown by a broken line in FIG. 13 to have a width a of 1.5 mm, and the detected current is 50 A, as shown by a chain double-dashed line in FIG. It will be 0.8 mm.

FIGS. 14A and 14B are for 50A, 100A and 200 formed by the method of changing the thickness of the central portion of the conductor shown in FIG.
The generated magnetic field (Oe) is actually measured for the A conductor 1 and the measured value is plotted. FIG. 15 shows a structure for 50A, 10 formed by the method of changing the width of the conductor central portion shown in FIG.
The generated magnetic field (Oe) was actually measured for the 0A and 200A conductors 1 and the measured values are plotted.

As is clear from FIGS. 14 and 15,
By changing the cross-sectional shape of the conductor center, 200A
From the conductor 1 for practical use to the conductor 1 for 50A and 100A,
Easily manufactured. However, when the U-shaped conductor 1 is used as a basic body, the change in the cross-sectional shape of the central portion of the conductor is advantageous when the thickness is changed rather than when the width is changed, because the generated magnetic field for a low current becomes larger.

[0048]

As described above, according to the present invention, since the magnetic shield member is formed of the insulating soft ferrite material, a current sensor having excellent high frequency response characteristics and capable of faithfully reproducing the detected current waveform is provided. Can be provided. Also, by setting the detection current range by selecting the conductor width, it is possible to handle various current values without the need to change the magnetic resistance element and the magnetic shielding member. Can be provided.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a current sensor of the present invention.

FIG. 2 is a perspective view of a main part of the current sensor according to the first embodiment.

3A and 3B are a cross-sectional view and a plan view of the current sensor according to the first embodiment.

FIG. 4 is an explanatory diagram of frequency characteristics of magnetic permeability μ of ferrite and permalloy.

FIG. 5 is a sectional view of a current sensor according to a second embodiment.

FIG. 6 is a schematic plan view of a barber pole type magnetoresistive element.

FIG. 7 is a structural explanatory view of a linear portion of a barber pole type magnetoresistive element.

FIG. 8 is an explanatory view of the action of a barber pole type magnetoresistive element.

FIG. 9 is an explanatory diagram of stabilization of a barber pole type magnetoresistive element by a bias magnetic field.

FIG. 10 is a structural cross-sectional view of a barber pole type magnetoresistive element.

FIG. 11 is a diagram showing the relationship between the conductor width of the current sensor and the power loss and generated magnetic field.

FIG. 12 is a waveform explanatory diagram of a current sensor.

FIG. 13 is a perspective view showing a main part of a current sensor according to another embodiment of the present invention.

14 is a diagram (part 1) showing the relationship between the measured current, the generated magnetic field, and the power loss of the current sensor using the conductor shown in FIG.

15 is a diagram (part 2) showing the relationship between the measured current, the generated magnetic field, and the power loss of the current sensor using the conductor shown in FIG.

FIG. 16 is a perspective view of a conventional current sensor using a magnetoresistive element.

[Explanation of symbols]

1 and 11 are conductors 1B and 1D are the central parts of the conductors (predetermined parts) 2 is a magnetoresistive element 3 is a magnetic shield member

Claims (8)

[Claims] 1. A conductor (1) for generating a current magnetic field by flowing a detection current (i), and a magnet arranged corresponding to the conductor (1) for receiving an operating current and detecting the current magnetic field. In a current sensor comprising a resistance element (2) and a magnetic shield member (3) for magnetically shielding the conductor (1) and the magnetoresistive element (2) from an external magnetic field, the magnetic shield member (3) is A current sensor characterized by being formed from an insulating soft ferrite material. 2. The conductor (1) according to claim 1, wherein a predetermined portion of the conductor (1) facing the magnetoresistive element (2) has a cross section smaller than that of another conductor portion. Current sensor. 3. The current sensor according to claim 2, wherein the conductor (1) has a center line in the lengthwise direction of the predetermined portion intersecting a perpendicular line passing through the center of the magnetoresistive element (2). . 4. The conductor (1) is characterized in that the center line in the lengthwise direction of the predetermined portion is displaced to one side from a perpendicular line passing through the center of the magnetoresistive element (2). The described current sensor. 5. The magnetic shield member (3) according to claim 1 or 2, wherein an opening larger than the shape of the conductor (1) is provided on the surface side where the conductor (1) is arranged. The described current sensor. 6. A conductor (1) for generating a current magnetic field via a detection current (i), and a magnetoresistor arranged corresponding to the conductor (1) and supplied with an operating current to detect the current magnetic field. A method for setting a detection current range of a current sensor, comprising: an element (2); and a magnetic shield member (3) that magnetically shields the conductor (1) and the magnetoresistive element (2) from an external magnetic field. A method of setting a detection current range of a current sensor, characterized in that the range of the detection current (i) is set by selecting a cross-sectional shape of a predetermined portion facing the magnetoresistive element (2). 7. The method for setting a detection current range of a current sensor according to claim 6, wherein the selection of the cross-sectional shape of the predetermined portion of the conductor (1) is a change of the width dimension of the predetermined portion. 8. The method for setting the detected current range of a current sensor according to claim 6, wherein the selection of the cross-sectional shape of the predetermined portion of the conductor (1) is a change in the thickness dimension of the predetermined portion. .