JP2002286821A - Magnetic field detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensitive magnetic field detection apparatus for detecting timing when an external magnetic field exceeds a specific level. SOLUTION: A pulse current is supplied to a magneto-sensing element 10 for indicating magnetic impedance effect where impedance that is a constituent in the direction of a detection axis changes for excitation in an orbital direction. The induced voltage of a detection coil 20 that is wound in an orbital direction of the magneto-sensing element 10 is detected by an electronic switch 401 that is turned on in synchronization with a pulse current, and a detection means 40 for retaining a voltage corresponding to the peak. The output of the detection means 40 is compared with a specific level by a comparator 501.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly sensitive magnetic field detecting device. The present invention particularly relates to an apparatus capable of detecting a timing at which a magnetic field exceeds a predetermined level. As a specific application example, the present invention can be applied to a rotation sensor of an automobile ABS or a magnetic scale. INDUSTRIAL APPLICATION This invention can be used for the detection apparatus which can detect the presence of a minute magnetic field, and can detect the reversal of the direction of a minute magnetic field with high precision.

[0002]

2. Description of the Related Art Conventionally, Hall elements, MR elements, magnetic pickups and the like have been known as sensors for detecting a magnetic field. However, since the detection sensitivity of these sensors is low, the detectable magnetic field is only about 1.6 × 10 4 A / m. When a high-frequency current of 200 KHz or more is applied to an amorphous wire having a diameter of about 50 μm as a small element for detecting the magnitude of a direct-current or low-frequency magnetic field with high sensitivity, an amorphous wire having a diameter of about 50 μm is subjected to an external magnetic field component parallel to the wire. A phenomenon in which the impedance changes greatly was discovered. Then, a detection element that detects the magnitude of the external magnetic field itself using this principle has been proposed (Japanese Patent Laid-Open No. 7-181239).
issue).

Further, two different external magnetic fields are applied to the same terminal voltage within a range of 0 to 400 A / m of the external magnetic field due to a change in the terminal voltage due to a change in impedance. This is because the magnetic field around 0 to 400 A / m cannot be uniquely determined from the voltage between terminals.
An azimuth sensor in which a DC bias magnetic field is applied to offset the zero point has been proposed (JP-A-7-248365).
issue).

[0004]

As described above, a high-sensitivity magnetic field detection sensor called a so-called magneto-impedance element has been proposed. Further, a magnetic field detection apparatus using this magneto-impedance element which can be applied to various uses. Development is required. Therefore, the present invention provides a characteristic in which a circumferential magnetization vector of a wire showing a change characteristic of a magnetic impedance (hereinafter, referred to as a “magnetic impedance characteristic”) corresponding to the magnitude of an external magnetic field changes with the magnitude of the external magnetic field. It is an object of the present invention to provide a new magnetic field detection device for detecting a magnetic field exceeding a predetermined level in a binary manner.
Another object is to realize a high-sensitivity magnetic field detection device capable of detecting a magnetic field change of a magnet linear scale, a magnet rotor, or the like, and detecting a displacement incrementally. Another object is to appropriately set the magnitude of the bias magnetic field so that an appropriate detection magnetic field range can be obtained. Another object is to realize a highly sensitive magnetic field detection device having excellent temperature characteristics.
Another object is to provide a simple structure, a low detection threshold,
The object is to realize a highly sensitive magnetic field detection device. Another object of the present invention is to perform detection with low power consumption. These objects are objects individually achieved by each of the inventions disclosed in the present application, and it is not to be understood that the present invention achieves all of these objects.

[0005]

According to the first aspect of the present invention, there is provided a magneto-sensitive element exhibiting a magneto-impedance effect in which the impedance changes with an external magnetic field which is a component in a detection axis direction, and the magneto-sensitive element. A detection coil for detecting a component inclined in the axial direction with an external magnetic field in the axial direction, and a oscillating means for supplying a pulse current or an AC current to the magneto-sensitive element, A detecting means for detecting a voltage induced in the detecting coil, and a comparing means for comparing an output signal of the detecting means with a predetermined level and outputting a comparison result as a binary signal.

The present magnetic field detecting device is a device for detecting whether an external magnetic field in a detection axis direction is larger or smaller than a predetermined level. The magneto-sensitive element is, for example, a linear element, and when the external magnetic field in the axial direction is zero, the change in magnetic flux generated by passing a pulse current or an alternating current is only in the circumferential direction, and The magnetic flux linked to the detection coil wound in the circumferential direction of the magnetic element is zero, and no voltage is induced in the detection coil. Next, when an external magnetic field is applied, the magnetization vector of the linear magneto-sensitive element is inclined in the axial direction, and the magnetization vector is rotated in the circumferential direction by the circumferential magnetic field generated by the pulse current or the alternating current. Since the axial component of the change in magnetic flux links with the detection coil, a voltage is induced in the detection coil.
By detecting the magnitude of the induced voltage, the magnetic field in the axial direction can be measured. The present invention is based on such a principle.

A voltage corresponding to the axial component of the magnetization vector of the magneto-sensitive element is detected by the detecting means, and the voltage is detected by the comparing means.
The output signal of the detection means is compared with a predetermined level, and the comparison result is output from the comparison means. The oscillating means for supplying a pulse current or an alternating current to the magneto-sensitive element may be a constant current source, a constant voltage source, or not.

The magnetic sensing element desirably has magnetic anisotropy that is easily magnetized in the circumferential direction. As a result, the change in the magnetic impedance due to the external magnetic field is large, and the detection sensitivity can be improved. One such material is an amorphous magnetic material. Desirably, a linear magnetic body is good. As described above, the present invention can detect a magnetic field with high sensitivity, detect a magnetic field change of a magnet linear scale, a magnet rotor, or the like with high sensitivity, and output a magnetic field change with a pulse. It can be used.

Since the pulse current contains a high-frequency component, it is a concept included in a kind of high-frequency current. or,
The pulse current or the high-frequency current may be, for example, a signal applied for only one cycle or a periodic signal applied repeatedly.

According to a second aspect of the present invention, in addition to the first aspect, a bias means for applying an arbitrary magnetic field to the magneto-sensitive element is provided. Other configurations are the same as those of the first aspect. According to the present invention, it is possible to detect whether the external magnetic field is larger or smaller than the bias magnetic field applied to the magneto-sensitive element. Therefore, the bias magnetic field can be set in relation to the measurement environment and the magnitude of the magnetic field to be detected. For example, if a bias magnetic field larger than the noise magnetic field is applied, a binary signal can be output with respect to an external magnetic field whose change is larger than the bias magnetic field, and the noise resistance is improved. The direction of the bias magnetic field to be applied may be any direction, and is determined according to the noise magnetic field.

A third aspect of the present invention is characterized in that the magneto-sensitive element is made of an amorphous magnetic material. With this configuration, it is possible to increase the magnetic anisotropy such that the magnetic permeability in the circumferential direction is larger than the magnetic permeability in the axial direction.

According to a fourth aspect of the present invention, the magneto-sensitive element is a wire made of an amorphous magnetic material. With this configuration, it is possible to increase the magnetic anisotropy such that the magnetic permeability in the circumferential direction is larger than the magnetic permeability in the axial direction.

According to a fifth aspect of the present invention, the detection means has an electronic switch for passing only a first pulse appearing in the detection coil in synchronization with the pulse current, and holds a signal corresponding to a peak value thereof. Characterized by having a circuit that performs With this configuration, the high-frequency noise component is removed, so that a magnetic field change that changes at a frequency lower than the frequency of the pulse current or the alternating current applied to the magneto-sensitive element can be detected with high accuracy.

The invention according to claim 6 is characterized in that the bias means is an electromagnet for passing a direct current through the coil or a permanent magnet. By using an electromagnet as the bias means, the magnitude of the bias magnetic field can be easily changed. When a permanent magnet is used, power saving can be achieved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Note that the present invention is not limited to the embodiments described below. First Embodiment A specific configuration of a magnetic field detection device is as shown in FIG. It comprises a magnetic sensing element 10, a detection coil 20, an oscillating means 30, a detecting means 40 and a comparing means 50. Magnetic sensing element 10
Is made of, for example, a linear zero magnetostrictive amorphous magnetic material. In particular, an amorphous wire linearly extending in the detection axis direction is used. Amorphous magnetic materials include, for example,
Magnetic materials such as CoSiB-based, FeCoSiB-based, and FeSiB-based alloys can be used. The specific dimensions are 2 mm in length and 30 μm in diameter. The detection coil 20 is wound around the amorphous wire of the magneto-sensitive element 10 in the circumferential direction. The number of turns is, for example, 40 times.

The oscillating means 30 includes a C-MOS inverter Q
A rectangular wave is oscillated by an oscillator composed of 1 and Q2, a resistor R1 and a capacitor C1. This square wave is differentiated by a differentiating circuit composed of a capacitor C2 and a resistor R2, and a C-MOS
The voltage is applied to the magneto-sensitive element 10 via the inverter Q5. A pulse current is supplied to the magneto-sensitive element 10 by such a circuit. The pulse current has a rise time of about 5n, for example.
s. Further, the rectangular wave is differentiated by a differentiating circuit including another capacitor C3 and a resistor R3, and is applied to a control signal terminal of a subsequent electronic switch 401 via a C-MOS inverter Q6.

One end of the detection coil 20 wound around the magnetic sensing element 10 is connected to the electronic switch 4 in the detection means 40.
01 is connected to the input terminal. Electronic switch 401
More specifically, as an example, an analog switch including a transistor can be used. Next, the signal that has passed through the electronic switch 401 is input to the capacitor C4 and the comparison means 50 in the next stage. This electronic switch 401
Will charge the capacitor C4 while the electronic switch 401 is on, and hold the charged signal while the electronic switch 401 is off.

The detection coil 20 has an inductance, but also has a stray capacitance, and also has an inductance, a stray capacitance, and an input capacitance of the electronic switch 401 in other lines. Therefore, the voltage between the terminals of the detection coil 20 includes not only a single pulse in response to the pulse current but also a subsequent vibration waveform. Therefore, in order to extract only the components that respond to the pulse current,
An electronic switch 401 is provided. In order to achieve phase synchronization between the timing of the peak of the voltage between the terminals of the detection coil 20 and the timing when the electronic switch 401 is completely turned on, a pulse supplied to the magneto-sensitive element 10 in response to the control signal of the switch 401 The current is C-MOS inverter Q
3, Q4 delays about 10 ns. In short, a control signal may be applied to the electronic switch 401 so as to be turned on only in a period in which only a signal component proportional to an external magnetic field is passed in response to a pulse current.

The output signal of the detecting means 40 is input to the comparing means 50. The signal terminal of the detection means 40 is connected to the inverting input terminal of the comparator 501,
Are applied as a predetermined level to a non-inverting input terminal of the second circuit. Then, the output signal of the comparator 501 constituting the comparing means 50 is output as a binary signal. This output signal is a signal in which the magnitude of the magnetic field to be detected is determined in a binary manner.

With the above configuration, the signal output from the detection means 40 has a characteristic as shown in FIG. 2 with respect to an external magnetic field applied in the axial direction of the magneto-sensitive element 10. When the external magnetic field is increased from zero to about +200 A / m, the output voltage increases almost in proportion to the external magnetic field, and decreases when the external magnetic field further increases, and the output voltage Eo when the external magnetic field is zero.
Asymptotically. In addition, the external magnetic field is reversed from zero to -200.
When the output voltage is increased to A / m, the output voltage decreases, and when the external magnetic field is higher than that, the output voltage increases so as to approach the voltage Eo when the external magnetic field is zero. This value is compared with a predetermined level by the comparator 501. Thus, it is detected whether the magnetic field to be detected is larger than a predetermined level. For example, if the predetermined level to be compared is set to the output voltage Eo of the detection means when the external magnetic field is zero, the direction of the magnetic field can be stably output as a binary signal over a wide range of the external magnetic field.

FIG. 3 shows the result of an experiment to confirm the temperature dependency of the output signal of the detection means 40 with respect to the external magnetic field.
Shown in In a region where the output is substantially proportional to an external magnetic field, the output is stable against a change in temperature. Therefore, in the magnetic field detection device having this configuration, a binary signal having excellent temperature characteristics can be obtained.

Second Embodiment Next, a description will be given of a magnetic field detecting apparatus provided with bias means for applying an arbitrary magnetic field to a magneto-sensitive element. FIG. 4 shows an embodiment of the magnetic field detecting device in which a thin film magnet is disposed as the bias means 60 near the magneto-sensitive element 10. In FIG. 4, the configuration other than the bias unit 60 is the same as that of the above-described embodiment. FIG. 5 shows a thin film magnet in the axial direction of the magneto-sensitive element 10 at −40.
9 is an experimental example showing an output voltage of the detection unit 40 with respect to an external magnetic field when a bias magnetic field of 0 A / m is applied.
If the directions of the north pole and south pole of the thin film magnet are reversed, then +400
A / m bias magnetic field will be applied. If the predetermined level to be compared by the comparator 501 is the same Eo as the predetermined level described in the above embodiment, -400A
It detects whether the external magnetic field is greater than / m and outputs a binary signal.

In this embodiment, the absolute value of the noise magnetic field is 40
When it is smaller than 0 A / m, a binary signal can be output with respect to an external magnetic field (magnetic field to be measured) having an absolute value of 400 A / m or more, and the noise resistance is higher than that of the above-described first embodiment. improves. When a permanent magnet is used as in the present embodiment, no current is required for generating a bias magnetic field, so that power saving can be achieved.

FIG. 6 shows another embodiment in which a bias magnetic field is applied to the magneto-sensitive element 10. The configuration other than the configuration of the bias unit 60 is the same as that of the above-described embodiment. Bias means 60
Is composed of a coil wound in the circumferential direction of the magneto-sensitive element 10 and a resistor connected to one end of the coil. The bias magnetic field is generated by passing a current through the coil via a resistor. This bias magnetic field can be varied by adjusting the magnitude of the current flowing through the coil that generates the bias magnetic field. More specifically, it can be easily achieved by adjusting the value of the resistor.

Third Embodiment Next, a detecting apparatus which uses a pair of a magneto-sensitive element, a detecting coil and a detecting means to remove in-phase noise and the like to improve the detecting accuracy is shown in FIGS. 7 and 8. It will be described based on the following. As shown in FIG. 7, a pair of magneto-sensitive elements 10 and 10 '
, A pulse current is supplied from one end of each. Detection coils 20 and 20 'are wound around the pair of magneto-sensitive elements 10 and 10' in the circumferential direction, respectively. FIG. 8 shows an apparatus for detecting the reversal timing of the magnetic poles of the magnetic scale. The pair of magneto-sensitive elements and the detection coil are provided near the magnet of the magnetic scale at a phase interval of 180 degrees as the magnetic field phase.

In FIG. 7, signals from the detection coils 20 and 20 'provided at a phase interval of 180 degrees in the magnetic field phase are input to detection means 40 and 40', respectively. Therefore, the output signals of the detection means 40 and 40 'change as shown in FIGS. 8 (b) and 8 (c). That is, the phases are different by 180 degrees. These detection means 4
The output signals of 0 and 40 'are input to a differential amplifier 70,
The output changes as shown in FIG. And
The output signal of the differential amplifier 70 is compared with a voltage of a predetermined level by a comparator 501 constituting the comparing means 50, thereby outputting a binary signal as shown in FIG.

In the case of the present embodiment, a pair of the magneto-sensitive element and the detection coil is used, and the magnetic field to be measured is installed at a position where the phase of the magnetic field to be measured is different by 180 degrees. I'm asking. Therefore, a double signal change can be obtained with respect to the change of the magnetic field to be measured in the external magnetic field, and the noise magnetic field which is uniformly applied to the pair of magneto-sensitive elements and the detection coil can be obtained. Therefore, the output of the differential amplifier becomes zero. Therefore, in this embodiment, a common-mode noise can be removed, and a magnetic field detection device with improved detection accuracy can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a magnetic field detection device according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of a detection unit output voltage versus an external magnetic field according to the embodiment;

FIG. 3 is a characteristic diagram showing a change in an output voltage of a detection unit versus an external magnetic field according to a temperature according to the first embodiment;

FIG. 4 is a circuit diagram of a magnetic field detection device according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram of a detection unit output voltage versus an external magnetic field according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram of a magnetic field detection device showing another example of the second embodiment of the present invention.

FIG. 7 is a circuit diagram of a magnetic field detection device according to a third embodiment of the present invention.

FIG. 8 is a timing chart showing operation characteristics of the embodiment.

[Explanation of symbols]

 10, 10 '... magnetic sensing element 20, 20' ... detection coil 30 ... oscillation means 40, 40 '... detection means 401, 401' ... electronic switch 50 ... comparison means 501 ... comparator 60 ... permanent magnet 70 ... differential amplifier

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazumasa Sumi, 1 Wanowari, Arao-cho, Tokai-shi, Aichi Prefecture Inside Aichi Steel Co., Ltd. Term (reference) 2F077 JJ06 JJ15 PP05 TT58 2G017 AA01 AB05 AB07 AC09 AD51 BA05

Claims (6)

[Claims] 1. A magneto-sensitive element which is excited in a circumferential direction by a pulse current or a high-frequency current, has both ends connected to electrodes, and has an impedance which changes in accordance with an external magnetic field; A detecting coil; an oscillating unit that supplies the pulse current or the alternating current to the magneto-sensitive element; a detecting unit that detects an induced voltage of the coil that changes according to an external magnetic field; and a predetermined output signal of the detecting unit. A comparison means for comparing the level with the level and outputting a comparison result as a binary signal. 2. A magneto-sensitive element which is excited in a circumferential direction by a pulse current or a high-frequency current, has both ends connected to electrodes, and has an impedance which changes according to an external magnetic field, and is wound in a circumferential direction of the magneto-sensitive element. A detection coil, a bias unit for applying a bias magnetic field to the magneto-sensitive element, an oscillating unit for supplying the pulse current or the alternating current to the magneto-sensitive element, and an induced voltage of the coil that changes according to an external magnetic field. A magnetic field detection apparatus comprising: a detection unit for detecting; and a comparison unit for comparing an output signal of the detection unit with a predetermined level and outputting a comparison result as a binary signal. 3. The magnetic field detecting device according to claim 1, wherein the magneto-sensitive element is made of an amorphous magnetic material. 4. The magnetic field detecting device according to claim 1, wherein the magneto-sensitive element is a wire made of an amorphous magnetic material. 5. The detection means has an electronic switch for passing only a first pulse appearing in the detection coil in synchronization with the pulse current, and has a circuit for holding a signal corresponding to a peak value thereof. The magnetic field detection device according to claim 1 or 2, wherein: 6. The magnetic field detecting device according to claim 2, wherein the biasing means is an electromagnet that supplies a direct current to the coil or a permanent magnet.