JP2006208146A - Magnetic field detecting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To favorably eliminate an influence of an external induction noise to allow measurement and drive, even in making measurement, connecting a measuring instrument to an output end via a long cable, in a differential amplification type magnetic field detecting circuit using two magnetic impedance effect elements. <P>SOLUTION: This magnetic field detecting circuit is provided with a negative feedback circuit 5 for negative-feeding back an output from a differential amplification circuit 4 to the first magnetic impedance effect element 1a and the second magnetic impedance effect element 1b, via the first negative feedback magnetic field coil 5a and the second negative feedback magnetic field coil 5b. An off-set means 40 is provided in the differential amplification circuit 4 to make an output voltage from the differential amplification circuit 4 when both terminal input voltages v<SB>1</SB>, v<SB>2</SB>satisfy v<SB>1</SB>=v<SB>2</SB>brought into a prescribed voltage V<SB>0</SB>, and a bias voltage impression circuit 50 is provided in the negative feedback circuit 5 to negate the voltage V<SB>0</SB>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic field detection circuit using a magnetic impedance effect element.

As an amorphous alloy wire, an amorphous alloy wire having zero magnetostriction or negative magnetostriction has been developed, which has an outer shell portion in which magnetic domains whose spontaneous magnetization directions are opposite to each other in the circumferential direction of the wire are separated by a domain wall. Yes.
The inductance voltage component in the output voltage between both ends of the wire generated when a high frequency current is applied to the zero magnetostrictive or negative magnetostrictive amorphous magnetic wire is easily increased in the circumferential direction by the circumferential magnetic flux generated in the cross section of the wire. It occurs due to the magnetized outer shell being magnetized in the circumferential direction. Accordingly, the circumferential magnetic permeability μθ depends on the circumferential magnetization of the outer shell.
Therefore, when an external magnetic field is applied to the energized amorphous wire, the magnetic flux acting on the outer shell portion having the easily magnetizable property in the circumferential direction is obtained by synthesizing the circumferential magnetic flux and the external magnetic flux by the energization. Is deviated from the circumferential direction and magnetization in the circumferential direction is less likely to occur, the circumferential permeability μθ is changed, and the inductance voltage is changed.
Thus, this fluctuation phenomenon is called a magnetic inductance effect, and an amorphous wire or the like that exhibits this effect is called a magnetic inductance effect element.

Further, when the frequency of the energization current is in the order of MHz, a high-frequency skin effect appears greatly, and the skin depth δ = (2ρ / wμθ) ^1/2 (μθ is the circumferential permeability, as described above, and ρ is (The electrical resistivity, w indicates the angular frequency, respectively) varies with μθ, and this μθ varies with the external magnetic field as described above, so that the resistance voltage component in the output voltage across the wire also varies with the external magnetic field. Become.
Thus, this fluctuation phenomenon is called a magnetoimpedance effect, and an amorphous wire or the like that exhibits this effect is called a magnetoimpedance effect element.

  Therefore, an external magnetic field detection method using the magneto-impedance effect element (see, for example, Patent Document 1) and an external magnetic field detection method using the magnetic inductance effect (see, for example, Patent Document 2) have been proposed.

  In the above, the positive and negative of the external magnetic field causes the circumferential shift φ of the magnetic field to be positive or negative, but the reduction factor cos (± φ) of the circumferential magnetic field does not change, so the degree of decrease in μθ is positive or negative in the direction of the external magnetic field. Does not change. Accordingly, the external magnetic field-output characteristics are almost symmetrical with respect to the y axis when the magnetic field is on the x axis and the output is on the y axis. It is also known to be non-linear.

As shown in FIG. 4A, the magnetic field detection circuit using this magneto-impedance effect element basically includes (1) a high-frequency power source 2 ′ for applying a high-frequency excitation current to the magneto-impedance effect element 1 ′, 2) a magneto-impedance effect element 1 ′, (3) a detection circuit 3 ′ that demodulates a modulated wave obtained by modulating the high-frequency excitation current (carrier wave) with an external magnetic field applied to the magneto-impedance effect element, and (4) a demodulated wave. It comprises an amplifier 4 'for amplifying, and (5) a detected magnetic field display unit 7'.
In FIG. 4B, (a) shows a detected magnetic field _Hex applied to the magnetic impedance effect element, (B) shows a high-frequency excitation current wave (carrier wave) Ic passed through the magnetic impedance effect element, and (C) shows. A modulated wave as an output of the magnetic impedance effect element, (D) shows an envelope waveform of the modulated wave, and (E) shows a demodulated wave. 4F shows the output V of the amplifier, and the peak value thereof is adjusted so that + Vcc to 0 and −Vcc to 0 are stored with respect to the power supply voltages + Vcc and −Vcc of the amplifier.

The relationship between the amplitude Hex of the magnetic field to be detected and the amplitude of the output V can be expressed as shown in FIG.
Therefore, in the circuit of FIG. 4A, it is known to linearize the characteristics as shown in FIG. 5B by applying negative feedback with a negative feedback coil 50 ′. In FIG. 5B, Δw is a range in which the gain A without negative feedback is very large and the gain is determined only by the feedback rate β.
Furthermore, in the circuit shown in FIG. 4A, it is also known to apply a bias magnetic field with a bias coil as indicated by 6 'to obtain a linear characteristic capable of discriminating polarity as shown in FIG. That is, the characteristic of (b) in FIG. 5 is moved in the direction of the arrow by the bias magnetic field as shown in (c) of FIG. 5, and the maximum range −Hmax to + Hmax of the detected magnetic field is within the range of the oblique line region Δw ′. It is also well known that the linear characteristic passes through the origin by zero point adjustment as shown in FIG.

As is well known, when a current is passed through a conductor, a magnetic field is generated, and when there is a defect such as a flaw, the magnetic field changes within a certain interval b between the defective portions as shown in FIG.
Therefore, when the magnetic field detection elements are arranged at a predetermined interval and the magnetic field sensor that outputs the difference between the outputs of the two magnetic field detection elements is moved along the conductor, the output is 0 except for the defective part. The flaw information output is detected.
In this case, since the magnetic field sensor is movable and the output measuring instrument is normally fixed, the measuring instrument is connected to the output end of the magnetic field sensor via a long cable.
Conventionally, two magnetic impedance effect elements are used, the output of each magnetic impedance effect element is detected and differentially amplified by a differential amplifier, and + Vcc (+2 V), −Vcc (−2 V) are applied to the differential amplifier. It is known to use a dual power supply type (Patent Document 3).

JP 7-181239 A JP-A-6-283344 JP 2000-193729 A

In this case, [the the detected magnetic field applied to the magnetic chair are impedance effect element and _{H ex1, H ex2, K} given by _(H ex1 _{-H ex2)]} output of the differential amplifier, level output voltage of the differential amplifier Since H is 0, _adjustment is made so that it is within the range of + Vcc to 0 for H _ex1 > H _{ex2 and −Vcc} to 0 for H _ex1 <H _ex2 .

  When connecting a measuring instrument to the output terminal of this differential amplifier via a long cable as described above, invasion of external induction noise is inevitable, and if there is other electrical equipment at the measurement site, the noise is large, This noise may reduce the measurement accuracy.

  The object of the present invention is to detect the influence of externally induced noise even in a differential amplification type magnetic field detection circuit using two magneto-impedance effect elements, even if a measuring instrument is connected to the output end via a long cable. It is an object of the present invention to provide a magnetic field detection circuit capable of measuring and driving with a good elimination.

The magnetic field detection circuit according to claim 1 includes a first magneto-impedance effect element, a second magneto-impedance effect element, a first bias magnetic field coil for applying a bias magnetic field to the first magnetic impedance effect element, and a second magnetic impedance. A second bias magnetic field coil for applying a bias magnetic field to the effect element, an excitation current source for supplying an excitation current to each magnetic impedance effect element, and each magnetic impedance effect by a detected magnetic field applied to each magnetic impedance effect element A first detection circuit and a second detection circuit for detecting the output of each magnetic impedance effect element having a waveform in which the excitation current of the element is modulated, and a differential amplification circuit for differentially amplifying the outputs v ₁ and v ₂ of each detection circuit And the output of the differential amplifier circuit to the first magnetic feedback effect element and the second magnetic impedance effect element. And via a second negative feedback magnetic field coil and a negative feedback circuit for negatively fed back, attached offset means for the output voltage of the differential amplifier circuit for v 1 ₌ v ₂ with the predetermined voltage V ₀ to the differential amplifier and, wherein the annexed bias voltage applying circuit for canceling the voltage V ₀ to the negative feedback circuit.

  A magnetic field detection circuit according to a second aspect is the magnetic field detection circuit according to the first aspect, wherein a detected magnetic field measuring instrument is connected to an output end of the differential amplifier circuit via a cable.

  A magnetic field detection circuit according to a third aspect is the magnetic field detection circuit according to the first or second aspect, wherein the first magnetic impedance effect element and the second magnetic impedance effect element are shifted by a predetermined distance, and both magnetic impedance effect elements are It is characterized in that the axial center directions are aligned.

  A magnetic field detection circuit according to a fourth aspect is the magnetic field detection circuit according to the first or second aspect, wherein the first magnetic impedance effect element and the second magnetic impedance effect element are arranged in parallel at a predetermined interval. And

  The magnetic field detection circuit according to claim 5 is the magnetic field detection circuit according to any one of claims 1 to 4, wherein each magnetic impedance effect element is attached to one side of each substrate piece, and the magnetic impedance effect element is provided on the other side of each substrate piece. And an iron core that forms a magnetic circuit is attached, and a coil for bias magnetic field and a coil for negative feedback magnetic field for each magnetic impedance effect element are wound around each iron core.

(1) The output voltage of the differential amplifier circuit when V ₁ = v ₂ is sufficiently high V ₀ relative to the inputs v ₁ and v ₂ to the differential amplifier circuit, and a measuring instrument is connected to the differential amplifier end Even if external inductive noise enters from the long cable to be connected, the differential amplifier circuit output is cut and measured according to the offset by the voltage V ₀ , thereby eliminating noise below the cut value and improving the S The detected magnetic field can be measured with the / N ratio.
(2) Applying a negative voltage to the negative feedback circuit for negatively feeding back the output of the differential amplifier circuit to the first magnetic impedance effect element and the second magnetic impedance effect element, and applying negative feedback in a state in which the V ₀ is canceled. Therefore, it is possible to prevent a current from flowing in the negative feedback circuit due to the output voltage V ₀ of the differential amplifier circuit when v ₁ = v ₂ , and it is possible to eliminate waste of the power source for maintaining the voltage V ₀ .

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1-1 shows an embodiment of a magnetic field detection circuit according to the present invention.
In FIG. 1-1, 1a and 1b are the 1st magnetic impedance effect element and the 2nd magnetic impedance effect element which were arrange | positioned at predetermined intervals, and the direction of spontaneous magnetization is mutually opposite with respect to the wire circumferential direction. An amorphous alloy ribbon or an amorphous alloy sputtered film is used in addition to a zero magnetostrictive or negative magnetostrictive amorphous alloy wire having an outer shell having a structure in which magnetic domains in directions are alternately separated by domain walls. As these magneto-impedance effect elements, transition metals and non-metal alloys having a non-metal composition of 10 to 30 atomic%, especially transition metals and non-metal alloys account for 10 to 30 atomic%. The transition metal is Fe and Co and the nonmetal is B and Si, or the transition metal is Fe and the nonmetal is B and Si. For example, the composition Co _70.5 B ₁₅ can be used. Si ₁₀ Fe _{4.5 having} a length of 2000 μm to 6000 μm and an outer diameter of 30 μm to 50 μmφ can be used.
Reference numeral 2 denotes a power source for applying a high-frequency excitation current to the first magnetic impedance effect element 1a and the second magnetic impedance effect element 1b, and an equal excitation current is applied to these magnetic impedance effect elements 1a and 1b by the power source 2. It is assembled into a bridge circuit so that it can flow. Reference numerals 3a and 3b denote detection circuits connected to the output terminals of the magnetic impedance effect elements 1a and 1b, respectively, and an RC smoothing circuit 32 is connected to the output side of the diode 31 as shown in FIG. What connected the capacitor | condenser 33 can be used.

1-1, if the excitation current flowing through each magnetic impedance effect element 1a, 1b is Ic and the detected magnetic field applied to each magnetic impedance effect element is _Hex , the output of the magnetic impedance effect element is as shown in FIG. -2 (c), the excitation current Ic of (b) of FIG. 4-2 becomes a modulated wave modulated by the detected magnetic field _Hex shown in (a) of FIG. The output of the impedance effect element is demodulated by the detection circuit to obtain a detected magnetic field signal indicated by (e) in FIG.

In FIG. 1-1, 4 is an operational differential amplifier circuit, and the demodulated detected magnetic field signal is input to both input terminals of the differential amplifier circuit. A detected magnetic field signal based on the detected magnetic field H _ex1 applied to the first magnetic impedance effect element 1a is represented by v ₁ , and a detected magnetic field signal based on the detected magnetic field H _ex2 applied to the second magnetic impedance effect element 1b is represented by v ₁ . v ₂ to. Reference numeral 40 denotes offset means for setting the output voltage of the differential amplifier circuit 4 when v ₁ = v ₂ to a predetermined voltage V _0, and kVcc (k ≦ 1) is applied to the voltage reference terminal using the power supply voltage Vcc. It can be set as the structure which applies this voltage.
When the differential amplifier circuit 4 is a dual power supply type using a + Vcc power supply and a -Vcc power supply, V ₀ is V ₀ = kVcc, and when the differential amplifier circuit 4 is a single power supply type using only a + Vcc power supply, V0 = (0.5 + k) Vcc.

5 is a negative feedback circuit for negatively feeding back the output of the differential amplifier circuit 4 each magnetic chairs are impedance effect element 1a, to 1b, has been inserted a bias voltage application circuit 50 for canceling the voltage V _0. The bias voltage applying circuit 50 can use a voltage follower that inputs a divided voltage k′Vcc of + Vcc to a non-inverting input terminal, and is set to k ′ = k or k ′ = (0.5 + k). The Accordingly, when the inputs v1 and v2 to both input terminals of the differential amplifier circuit 4 are equal, it is possible to prevent a direct current from flowing unnecessarily to the negative feedback circuit, and it is possible to prevent waste of + Vcc in the offset means.

Reference numerals 5a and 5b denote a first bias magnetic field coil and a second bias magnetic field coil for applying a bias magnetic field to each of the magnetic impedance effect elements 1a and 1b. As shown in FIG. Hex can be detected by detecting the polarity.
Reference numeral 7 denotes a measuring instrument connected to the output end of the differential amplifier circuit 4 via a long flexible cable 8.

The magnetic field detection circuit according to the present invention is mounted on a substrate as a mobile sensor, and can be used by connecting a fixed measuring instrument to the output end of the differential amplifier circuit via a long cable.
When the mobile sensor is moved along a path along which the magnetic field changes as shown in FIG. 6, the magnetic field Hex1 and the second magnetic field acting on the first magnetic impedance effect element when passing through the magnetic field changing portion. A difference is generated in the magnetic field Hex2 acting on the impedance effect element, and the output V of the differential amplifier circuit is a value obtained by offsetting ± K | Hex1−Hex2 | by the voltage V ₀ , that is, ± K | H _ex1. -H _ex2 | + is given by _{V 0.}
That is, when H _ex1 > H _ex2 , it is given by K (H _ex1 −H _ex2 ) + V ₀ , and when H _ex2 > H _ex1 , it is given by −K (H _ex2 −H _ex1 ) + V ₀ .
And Thus, even if the outer guide noise entering the long cable _8, to set the _{V 0} and K such that _{-K (H ex2 -H ex1) +} V 0 = E a sufficiently large value in a positive, If the output of the differential amplifier circuit 4 is measured by cutting the voltage E or less with the measuring instrument 7, noise having a peak value below the voltage E can be cut, and the detection accuracy can be increased accordingly.

  The external magnetic field noise acting on the magnetic field sensor including the magnetic impedance effect elements 1a and 1b is input to the differential amplifier circuit with the same value and the same phase, and the internal noise generated in the detection circuits 3a and 3b is also differential. Since the same value and the same phase are input to the amplifier circuit 4, the influence of these noises can be eliminated.

  The magnetic field change shown in FIG. 6 is accompanied by disturbance of the magnetic field generated by the current, and causes a change in the magnetic field component perpendicular to the current direction and a change in the magnetic field component in the current direction. On the other hand, the magnetosensitive direction of the magnetic impedance effect element is the axial direction. Accordingly, as shown in FIG. 2A, the first magneto-impedance effect element 1a and the second magneto-impedance effect element 1b are shifted by a predetermined distance, and the axial direction of both the magnetic impedance effect elements 1a and 1b Can be arranged to match. Further, as shown in FIG. 2B, the first magneto-impedance effect element 1a and the second magneto-impedance effect element 1b can be arranged in parallel at a predetermined interval.

The magnetic field detection circuit according to the present invention is not limited to the above embodiment.
Instead of the peak hold circuit in the detection circuit, an RC low-pass filter may be used. The temperature characteristics can be changed by using a capacitor of these peak hold circuit or RC low-pass filter as a temperature compensation capacitor.

For the magneto-impedance effect element, zero magnetostrictive or negative magnetostrictive amorphous wire, amorphous ribbon, amorphous sputtered film or the like can be used. The frequency of the high frequency excitation current is in the order of MHz.
Even in the case of a carrier wave having a frequency lower than this, the carrier wave can be amplitude-modulated by an external magnetic field due to the above-described magnetic inductance effect, and the present invention can also be implemented using a magnetic inductance effect element.

As the high-frequency carrier wave, a normal high-frequency wave such as a continuous sine wave, a pulse wave, or a triangular wave can be used. For example, a normal oscillation circuit such as a Hartley oscillation circuit, a Colpitts oscillation circuit, a collector-tuned oscillation circuit, or a base-tuned oscillation circuit can be used. In addition, a triangular wave generator that integrates a square wave output of a crystal oscillator through an integration circuit through a DC component cut capacitor and amplifies the triangular wave of the integrated output by an amplifier circuit, and a triangular wave generator that uses a CMOS-IC as an oscillation unit are used. be able to.
It is also possible to use a sine wave, a pulse wave, or a triangular burst wave to reduce power consumption.

  In the above embodiment, the excitation current is a carrier wave, the carrier wave is amplitude-modulated by a detected magnetic field, and the modulated wave is demodulated by a detection circuit to extract a detected magnetic field signal. An appropriate detection circuit can be used as long as the detected magnetic field signal amount corresponding to the detected magnetic field can be extracted from the magnetic field detection signal based on the detected magnetic field.

The negative feedback magnetic field coil 5a (5b) and the bias magnetic field coil 6a (6b) can be wound around the magneto-impedance effect element 1a (1b).
Further, as shown in FIG. 3, a negative feedback magnetic field coil and a bias magnetic field coil can be wound around an iron core constituting a magneto-impedance effect element and a loop magnetic circuit.
3A is a side view showing an example of a magnetic impedance effect unit with an iron core, FIG. 3B is a bottom view, and FIG. 3C is a cross-sectional view of FIG. FIG.
In FIG. 3, reference numeral 100 denotes a substrate piece, and for example, a ceramic plate can be used. Reference numeral 101 denotes an electrode provided on one side of the substrate piece, and includes a magneto-impedance effect element connecting projection 102. This electrode can be provided by printing and baking a conductive paste, for example, a silver paste. 1x is a magneto-impedance effect element connected between the protrusions 102 and 102 of the electrodes 101 and 101 by soldering or welding. As described above, an amorphous wire, amorphous ribbon, sputtered film, or the like having zero or negative magnetostriction can be used. 103 is a C-type iron core, 5x is a negative feedback coil wound around the C-type iron core, and 6x is a bias magnetic field coil, and the magneto-impedance effect element 1x and the C-type iron core 103 constitute a loop magnetic circuit. Thus, both ends of the C-shaped iron core 103 are fixed to the other surface of the substrate piece 100 with an adhesive or the like. The iron core material may be a magnetic material having a small residual magnetic flux density. Examples thereof include permalloy, ferrite, iron, amorphous magnetic alloy, magnetic powder mixed plastic, and the like.

It is drawing which shows one Example of the magnetic field detection circuit based on this invention. It is drawing which shows an example of the detection circuit in the circuit of FIGS. 1-2. It is drawing which shows the example of different arrangement | positioning of the magneto-impedance effect element in the magnetic field detection circuit which concerns on this invention. It is drawing which shows an example of the magneto-impedance effect element unit used in the magnetic field detection circuit which concerns on this invention. It is drawing which shows the conventional magnetic field detection circuit. It is drawing which shows the waveform in the circuit of FIGS. It is drawing which shows the output characteristic of a magneto-impedance effect element. It is drawing which shows the distribution state of a to-be-detected magnetic field.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a 1st magneto-impedance effect element 1b 2nd magneto-impedance effect element 2 Excitation current source 3a 1st detection circuit 3b 2nd detection circuit 4 Differential amplification circuit 40 Predetermined voltage offset means 5 Negative feedback circuit 5a 1st negative feedback magnetic field coil 5b Second negative feedback magnetic field coil 50 Bias voltage application circuit 6a First bias magnetic field coil 6b Second bias magnetic field coil 7 Measuring instrument 8 Cable

Claims (5)

A first magnetic impedance effect element, a second magnetic impedance effect element, a first bias magnetic field coil that applies a bias magnetic field to the first magnetic impedance effect element, and a second magnetic field that applies a bias magnetic field to the second magnetic impedance effect element A coil with a bias magnetic field, an excitation current source that supplies an excitation current to each magnetic impedance effect element, and a waveform in which the excitation current of each magnetic impedance effect element is modulated by a detected magnetic field applied to each magnetic impedance effect element. A first detection circuit and a second detection circuit for detecting each magnetic impedance effect element output, a differential amplification circuit for differentially amplifying the outputs v ₁ and v ₂ of each detection circuit, and an output of the differential amplification circuit for the first The first negative feedback magnetic field coil and the second negative magnetic feedback field coil are provided on the first magnetic impedance effect element and the second magnetic impedance effect element. And a negative feedback circuit for negatively fed back to, v 1 ₌ v offset means to the predetermined voltage V ₀ the output voltage of the differential amplifier circuit for ₂ annexed to the differential amplifier circuit, the voltage V to the negative feedback circuit A magnetic field detection circuit comprising a bias voltage application circuit for canceling _zero . The magnetic field detection circuit according to claim 1, wherein a detected magnetic field measuring instrument is connected to an output end of the differential amplifier circuit via a cable. 3. The first magneto-impedance effect element and the second magneto-impedance effect element are arranged so as to be shifted from each other by a predetermined distance, and the axial directions of the two magnetic impedance effect elements are aligned with each other. Magnetic field detection circuit. 3. The magnetic field detection circuit according to claim 1, wherein the first magneto-impedance effect element and the second magneto-impedance effect element are arranged in parallel at a predetermined interval. Each magnetic impedance effect element is attached to one surface of each substrate piece, and an iron core that forms a magnetic circuit with the magnetic impedance effect element is attached to the other surface of each substrate piece, and each magnetic impedance element is attached to each iron core. 5. A magnetic field detection circuit according to claim 1, wherein a bias magnetic field coil and a negative feedback magnetic field coil are wound around the effect element.

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