JP2003121517A - Magnetic detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of accuracy and enable high accuracy measurement by preventing the mix of an error component, based on hysteresis of a magnetic impedance element. SOLUTION: The magnetic detector comprises a magnetic sensor 1, wound with a detection coil 12 on the circumference of the magnetic impedance element 11 formed with an amorphous wire of which impedance varies corresponding to the magnitude of an external magnetic field; a detection circuit 40 detecting the impedance of the magnetic impedance element 11, to which a pulse current is applied, varied by an external magnetic field as a voltage signal, based on the induced voltage of the detection coil 12; and a hysteresis compensation circuit 7 enables detection of the impedance signal in the other of the characteristics of the magnetic impedance signal, by applying a hysteresis compensation pulse to the magnetic impedance element 11 in advance of the detection of the impedance signal, when the pulse current is not applied to the magnetic impedance element 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-impedance element whose impedance changes according to the magnitude of an external magnetic field, and a current is applied to the magneto-impedance element to change the impedance of the magneto-impedance element around the magneto-impedance element. The present invention relates to a magnetic detection device that detects a voltage signal based on an induced voltage of a coil means wound around a coil.

[0002]

2. Description of the Related Art A conventional magnetic detector (Japanese Patent Laid-Open No. 6-1769).
30, JP-A-2000-180521), since the impedance of the magneto-impedance element changes with high sensitivity in response to an external magnetic field, this impedance change is detected by a signal conversion circuit. Since it has a characteristic, an error occurs in the measured value due to the history of the magneto-impedance element being exposed to the external magnetic field regardless of whether it is measured or not.

Therefore, a conventional magnetic sensor (Japanese Patent Laid-Open No. 2000-
180521) eliminates the error of the measurement value due to the hysteresis characteristic of the magneto-impedance element,
In a magnetic sensor in which a negative feedback coil NC and a bias coil BC are wound around a magnetic core using a magneto-impedance element M made of a thin film as shown in 0, an oscillating circuit O for applying a high frequency current to both ends of the magnetic core. A buffer circuit B interposed between the magnetic core and the impedance to adjust impedance mismatch, and a magnetic change amount of the external magnetic field from a change amount of a high frequency current which changes according to an external magnetic field applied to the magnetic impedance element. The detection circuit R for detection and the hysteresis cancellation circuit H for eliminating the hysteresis of the magnetic impedance element were provided.

Further, in the above-mentioned conventional magnetic sensor, when a large negative external magnetic field is applied, as a countermeasure against the detection voltage being largely changed due to the influence of the hysteresis of the magneto-impedance element, a pulse having a constant width and a constant width is used. And a transistor was applied to the bias coil of the magneto-impedance element.

Further, in the above conventional magnetic sensor,
As described in the above publication, it is considered that the output becomes unstable by applying the hysteresis pulse, but by setting the pulse width and the pulse amplitude to the frequency characteristics of the operational amplifier or more, the circuit including the operational amplifier becomes a low-pass filter. It worked and was immune to the effects of hysteresis pulses.

[0006]

In the above-mentioned conventional magnetic sensor, the drawing of FIG. 19 described in the above publication shows that when a magnetic field is applied to the reset point by a hysteresis pulse, the amplitude of the high frequency becomes almost maximum at that time. It represents.

When analyzed in time series with reference to FIG. 11, the amplitude of the high frequency voltage across the magneto-impedance element during the period of 400 ns in which the hysteresis pulse shown in (f) of FIG. 11 rises is shown in FIG. (C)
It is almost the maximum value as shown in.

As a result, the drawing shown in FIG.
Since the detecting unit in 5 converts the amplitude of the high frequency into the direct current, the direct current signal corresponding to the measured magnetic field corresponds to the amplitude of the high frequency having the maximum value in the period of 400 ns as shown in FIG. 11 (d). The pulsed voltage will be superimposed.

Since the AMP section has the function of the low-pass filter as described above, the output signal does not have such a pulse-like waveform but corresponds to the increase in high frequency as shown in FIG. 11 (e). The averaged DC voltage is superimposed on the measurement signal as the original signal component as an error component (noise). Therefore, the above-mentioned conventional magnetic sensor has a problem that the accuracy is deteriorated due to the mixing of the error as described above, and the measurement cannot be performed with high accuracy.

Therefore, in order to solve the problem in the above-described conventional device that applies a hysteresis pulse during the detection of the impedance signal, the present inventor changes the timing of the detection of the impedance signal and the application of the hysteresis pulse to change the impedance. Attention was paid to the point of the present invention in which a hysteresis pulse is applied to the coil means or the magneto-impedance element at a timing that does not give an error to the measurement signal.

Based on the above-mentioned points of interest, the present inventor applies the current to the magneto-impedance element whose impedance changes according to the magnitude of the external magnetic field, and changes the impedance of the magneto-impedance element changed by the external magnetic field to the magnetic impedance. In a magnetic detection device for detecting a voltage signal based on an induced voltage of a coil means wound around an element, a hysteresis compensation pulse is applied to the coil means or the magneto-impedance element prior to the detection of the impedance signal. The result of further research and development focusing on the technical idea of the present invention that enables detection of the impedance signal in one of the hysteresis characteristics of the magneto-impedance element and compensates for the hysteresis of the magneto-impedance element , The magnetic impedance By preventing contamination of the error amount based on the hysteresis of the dance elements, to prevent the deterioration of accuracy, we have reached the present invention to achieve the object of enabling highly accurate measurement.

[0012]

In the magnetic detector of the present invention (the first invention according to claim 1), coil means is wound around a magneto-impedance element whose impedance changes according to the magnitude of an external magnetic field. A rotating magnetic sensor, a detection circuit that detects the impedance of the magneto-impedance element changed by an external magnetic field when a current is applied to the magneto-impedance element as a voltage signal based on the induced voltage of the coil means, and the detection of the impedance signal Prior to the above, a hysteresis compensation circuit that applies a hysteresis compensation pulse to the coil means or the magnetic impedance element to enable detection of the impedance signal in one of the hysteresis characteristics of the magnetic impedance element. is there.

In the magnetic detection device of the present invention (the second invention according to claim 2), in the first invention, the hysteresis compensation circuit is wound around the magneto-impedance element composed of an amorphous wire. The hysteresis coil is applied to the detection coil as the coil means when the current is not applied to the magneto-impedance element, and the sample hold circuit as the detection circuit allows the hysteresis coil to have one of the characteristics in one of the hysteresis characteristics. The impedance signal is detected by sampling and holding it as a voltage signal based on the induced voltage of the detection coil in synchronization with the current application timing.

In the magnetic detector of the present invention (the third invention according to claim 3), in the first invention, the hysteresis compensating circuit is wound around the magneto-impedance element constituted by an amorphous wire. A hysteresis compensation pulse is applied to the negative feedback coil as the coil means on the basis of a negative feedback current in synchronization with power-on, and a sample hold circuit as the detection circuit causes the hysteresis characteristic in one of the characteristics. The impedance signal is detected by sampling and holding it as a voltage signal based on the induced voltage of the detection coil as the coil means in synchronization with the current application timing of the magneto-impedance element.

[0015]

According to the magnetic detector of the first aspect of the present invention having the above-described structure, the magneto-impedance element whose impedance is changed according to the magnitude of the external magnetic field is applied with a current and is changed by the external magnetic field. The impedance of is detected by the detection circuit as a voltage signal based on the induced voltage of the coil means wound around the magneto-impedance element,
Prior to the detection of the impedance signal, a hysteresis compensation pulse is applied to the coil means or the magnetic impedance element to enable detection of the impedance signal in one of the hysteresis characteristics of the magnetic impedance element. By preventing the mixing of the error component based on the hysteresis of the magneto-impedance element, by compensating for the hysteresis of the magneto-impedance element, it is possible to prevent deterioration of accuracy and enable highly accurate measurement. .

In the magnetic detection device of the second invention having the above structure, in the first invention, the hysteresis compensating circuit serves as the coil means wound around the magneto-impedance element composed of an amorphous wire. A hysteresis compensation pulse is applied to the detection coil when a current is not applied to the magneto-impedance element, and a sample hold circuit as the detection circuit causes the impedance signal in one of the hysteresis characteristics to Since it is detected by sampling and holding it as a voltage signal based on the induced voltage of the detection coil in synchronization with the application timing, it enables highly sensitive magnetic measurement by the amorphous wire, and it can also detect the magnetic field measured by the conventional device. Corresponding DC signal Thereby preventing the direct current component of the hysteresis canceling pulse averaged is superimposed, an effect of enabling highly accurate measurement.

In the magnetic detector of the third invention having the above-mentioned structure, in the first invention, the hysteresis compensating circuit serves as the coil means wound around the magnetic impedance element composed of an amorphous wire. A hysteresis compensation pulse is applied to the negative feedback coil based on the negative feedback current in synchronization with power-on, and the impedance signal in one of the hysteresis characteristics is changed by the sample hold circuit as the detection circuit. Since it is detected by sampling and holding as a voltage signal based on the induced voltage of the detection coil as the coil means in synchronization with the application timing of the current of the impedance element, it enables highly sensitive magnetic measurement by the amorphous wire, Negative feedback voltage in the feedback coil Is applied to keep the magneto-impedance element at a zero magnetic field, and a DC component obtained by averaging the hysteresis cancel pulse is prevented from being superimposed on a DC signal corresponding to the measured magnetic field as in the conventional device, and the accuracy is high. It has the effect of enabling measurement.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention will be described below.
This will be described with reference to the drawings.

(First Embodiment) As shown in FIG. 1, the magnetic detection device of the first embodiment includes a magneto-impedance element 11 composed of an amorphous wire whose impedance changes in accordance with the magnitude of an external magnetic field. A pulse current is applied to the magnetic sensor 1 around which a detection coil 12 as a coil means is wound, and the impedance of the magnetic impedance element 11 changed by an external magnetic field is applied to the detection coil 12.
Detection circuit 4 for detecting as a voltage signal based on the induced voltage of
0, prior to the detection of the impedance signal, a hysteresis compensation pulse is applied when a pulse current is not applied to the magneto-impedance element 11, and the impedance signal of one of the hysteresis characteristics of the magneto-impedance element is applied. And a hysteresis compensation circuit 7 that enables detection.

In the electronic circuit of the first embodiment, the pulse power supply 3 for applying a pulse current to the magneto-impedance element 11 and the initialization excitation circuit 7 serving as the hysteresis compensation circuit are provided with the excitation timing and period of the above-mentioned circuit. A timer circuit 5 for giving a signal is provided.

The magnetic impedance element (MI element) 1
1 is a magnetic substance having conductivity, and usually has a diameter of 20 to 30.
An amorphous wire (wire) having a length of μm and a few mm, a thin film structure, or the like is adopted. In the first embodiment, the amorphous wire is adopted as an example. As described above, the MI element changes its impedance in response to an external magnetic field. The MI element generally has a high magnetic impedance effect for high frequencies of several tens of MHz or more. In the first embodiment, a C-MOS logic element is used to perform pulse driving with a pulse width of 15 ns, thereby approximately driving at a high frequency. The operation will be described below with reference to the time chart shown in FIG.

The pulse power supply 3 includes a multivibrator 31.
As the original oscillator, it outputs two pulses P1 and P2 that repeat at the oscillation frequency. In the first embodiment, the oscillation frequency of the multivibrator 31 is set to 1 MHz as an example.

The first pulse P1 waveform-shapes the rectangular wave of the multivibrator by the differentiator 33 and the inverter 34 and outputs a pulse having a pulse width of 15 ns as shown in FIG. The second pulse P2 is a pulse having a pulse width of 15 ns shown in FIG. 2B by the post-differentiation circuit 35 and the inverter 36 that pass the output of the multivibrator through the delay circuit 32.
Output P2.

The delay circuit 32 obtains a delay time of 4 ns by connecting two C-MOS inverters in series. Therefore, from the viewpoint of pulse P2, P1 leads by 4ns. Since the pulse P2 is connected to the MI element, when a pulse as shown in FIG. 2B is generated, a current corresponding to the impedance determined by the external magnetic field (ambient magnetic field) flows through the MI element.

The detection coil 12 induces a voltage corresponding to the impedance of the MI element by electromagnetically coupling with the MI element as shown in FIG. This detection coil 12
The waveform of (d) of (1) is a damped oscillation, which is determined by the inductance of the detection coil, stray capacitance and loss. Here, in the waveform of FIG. 2C, the impedance of the MI element, that is, the most suitable voltage corresponding to the external magnetic field is the p point, that is, the maximum value.

Therefore, the analog switch S1 of the sample and hold circuit 4 as the detection circuit 40 which is closed before the pulse P2 is applied to the MI element is set at the maximum time of the induced voltage of the detection coil 12, that is, the time of the point p. It is opened based on the pulse P1. As a result, the measurement signal corresponding to the impedance of the MI element, that is, the magnitude of the external magnetic field is stored in the capacitor C.

This measurement signal is amplified to a predetermined voltage by the amplifier 6 and output together with (d) of FIG. 2 held in the sample hold circuit 4 until the next pulse P2 is applied. The pulse P1 precedes P2 by 4 ns because the actual opening / closing operation of the switch S1 ((f) in FIG. 2) is
Because it is delayed by 4 ns from the drive pulse P1 in (e) of FIG.
By storing the voltage at the maximum point p of the waveform of the detection coil 12 in the capacitor C, the sample hold circuit 4 can sufficiently follow the voltage of the detection coil 12 and hold the maximum value with high accuracy.

However, the MI element as the magneto-impedance element 11 has a slight hysteresis phenomenon, and the output signal of the circuit of FIG. 1 has a large change in the external magnetic field from negative to positive as shown in FIG. 4 (arrow A). At that time and when changing from positive to negative (arrow B), a hysteresis loop appears and the sensitivity to the magnetic field is almost constant, but a zero point shift (offset) appears. That is, even if the same magnetic field is measured, the indicated value may differ depending on what magnetic field the MI element or the magnetic measuring device including the MI element has been exposed to in the past. For example, in Fig. 5 showing the experimental results, the output voltage is a, b for the external magnetic field of H1.
Takes two different values of the point.

The initialization excitation circuit 7 is composed of a switch S3 and a resistor R7 for current adjustment. The excitation switch S3 is a timer circuit 5
The MI element is initialized and excited by applying a current from the direct current power source of the electronic circuit to the detection coil 12 at a predetermined time and for a predetermined period by the pulse signal P3.

The relationship between each output of the pulse power supply 3 and the output P3 of the timer circuit 5 is shown in FIG. The output of pulse power supply 3 is P1
Precedes P2 by a number (ns). Both the pulse widths of P1 and P2 are, for example, about 15 ns, and the pulse repetition period is, for example, about 1 μs. Therefore, the initialization excitation of the MI element can be performed at almost any timing in the period of 1 μs, but in the first embodiment, the timer circuit 5 is connected to the delay circuit 32 to obtain a signal that serves as a trigger. Therefore, the timer 5 is set to operate approximately at the center of the repetition of the pulses P1 and P2, that is, about 0.5 μs before the rise of the pulses P1 and P2. Also timer 5
The pulse width of is determined by the magnetic characteristics of the MI element 11 and the transient characteristics of the wound detection coil 12, but here an example of 100 ns is shown.

Since P1 and P2 and the pulse P3 of the timer 5 are in a synchronous relationship, the MI element is always initialized after the MI element is initialized at the timing of the pulse of the timer 5, so that stable and highly accurate measurement can be performed. You can enable it.

That is, in FIG. 3, when the pulse P3 of the timer 5 for performing the initialization excitation rises positively as shown in FIG. 3A, the switch S3 of the initialization excitation circuit 7 is closed.
As a result, the initialization excitation circuit 7 connected to the power supply Vdd
A current for initialization excitation flows into the detection coil 12 through the resistor R7 of FIG. 3 as shown in FIG. This current has a first-order lag because the rise of the current is determined mainly by the time constant of the coil inductance and resistance R7. This final value causes an offset in the curves of the forward path (lower characteristic line) LC and the return path (upper characteristic line) UC.
In order to use the lower characteristic line LC for measurement as an example of the hysteresis loop shown in FIG. 5, a negative magnetic field Ha larger than that in the hysteresis loop is applied to the MI element as initialization excitation. When the pulse P3 ends, if the ambient magnetic field is zero, the lower characteristic line LC of the hysteresis loop in FIG.
The upper Q point becomes the operating point and the initialization of the MI element is completed.

Therefore, since the initialization is carried out at a time of 0.5 μs immediately before the measurement of the magnetic field with the P1 and P2 pulses having a period of 1 μs, it is possible to perform a highly accurate measurement without the influence of hysteresis.

In the first embodiment, FIG. 6 shows an experimental example for confirming that the influence of hysteresis has disappeared. The horizontal axis of FIG. 6 is the positive and negative magnetic fields applied from the outside for the test, and the vertical axis is the measurement signal, but it can be seen that no hysteresis loop is seen and the offset error disappears.

In the above conventional magnetic sensor, MI
It is necessary to constantly supply direct current to the bias coil to maximize the sensitivity of the device, which is disadvantageous because the battery is quickly consumed.
This bias coil is used for excitation for hysteresis cancellation, a dedicated circuit for excitation is provided, and the magnetic field is detected from the voltage drop across the MI element as the thin film core. It does not have a coil.

In the first embodiment, since the amorphous wire as the MI element has a high sensitivity, it is possible to detect a weak magnetic field, and since the sensitivity is uniform, the bias coil is unnecessary, and an extra direct current is unnecessary. Since there is no need to pass a current, and one terminal of the detection coil can be connected to an arbitrary voltage, there are few parts for single power supply operation, which simplifies the design, and an excitation current for hysteresis compensation is passed for initialization. Therefore, there is an advantage that a bias coil or a dedicated exciting coil is unnecessary.

Further, in the conventional magnetic sensor, the detection circuit is a rectification circuit using a diode, and a direct current is supplied to compensate the voltage attenuation. However, the optimum value of the DC current of the diode changes with the temperature change, and the non-linearity is not compensated, and the conversion accuracy into the DC signal is poor.

In the first embodiment, since the detection circuit is composed of the sample and hold circuit by the analog switch, there is no non-linear characteristic, so that the conversion accuracy to the DC signal is good regardless of the magnitude of the signal. In addition, there is an advantage that extra DC current is not passed and circuit parts therefor are unnecessary, and the accuracy with respect to temperature change is good.

Further, since the conventional magnetic sensor applies a hysteresis cancel pulse at a constant repetition during measurement in which a high-frequency current is continuously applied, noise as a direct current component is superimposed on the measurement signal as described above. Remain.

In the first embodiment, since the hysteresis compensation pulse is applied when the detection current is not applied to the detection coil 12, the hysteresis compensation pulse is not superimposed as noise on the measurement signal. Have.

In the conventional magnetic sensor, the high-frequency oscillation circuit is composed of a C-MOS IC, an oscillator, and a sine wave oscillator composed of a low-pass filter. In the first embodiment, however, a C-MOS logic IC is used. Since the pulse oscillator is configured only by itself, it has an advantage that the stability of voltage and frequency is good with few inexpensive parts.

Further, in the conventional magnetic sensor, M
Since the I element is driven by the buffer circuit, a circuit for compensating the temperature characteristic of the transistor is required, the number of parts is increased, and the circuit configuration is complicated. On the other hand, in the first embodiment, the logic IC is used. Since it is directly driven only by itself, it has advantages that a buffer circuit is not required, voltage stability is high, it is not affected by temperature changes, the number of parts is small, and the circuit configuration is simple.

(Second Embodiment) In the magnetic detector of the second embodiment, as shown in FIG. 7, a hysteresis compensation circuit 7 is wound around the magneto-impedance element 11 composed of an amorphous wire. In addition, a hysteresis compensating pulse is applied to the negative feedback coil 13 serving as the coil means based on the negative feedback current in synchronization with power-on, and a sample hold circuit serving as the detection circuit 40.
By 44, sample and hold the impedance signal in one of the hysteresis characteristics as a voltage signal based on the induced voltage of the detection coil 12 as the coil means in synchronization with the current application timing of the magneto-impedance element 11. The difference between the first embodiment and the first embodiment will be described below. The difference will be mainly described below, and the same portions will be denoted by the same reference numerals and description thereof will be omitted.

The magnetic detector of the second embodiment is configured to realize a measuring device with higher accuracy than the magnetic detector of the first embodiment described above. A signal obtained by converting the impedance change of the MI element as the magneto-impedance element 11 into a voltage is negatively fed back to the negative feedback coil 13, which is a second coil wound around the MI element, so that the magnetic field inside the MI element is reduced. The magnetic field is canceled and the magnetic field inside the MI element is always kept at zero regardless of the magnitude of the external magnetic field. Further, the feedback current for keeping the internal magnetic field of the MI element at zero corresponds to the magnitude of the external magnetic field accurately, so that the feedback current can be converted into a voltage and used as a measurement signal of the magnetic field. Keeping the MI element at zero magnetic field means MI
Since the element is always operated at one point, the problem of non-linearity of the MI element is eliminated, so very high linearity can be expected.

In the circuit shown in FIG. 7, the voltage induced in the detection coil 12 is stored in the sample hold circuit 44. The two resistors of the sample hold circuit 44 generate a first reference potential for operating the electronic circuit with a unipolar power source. The amplifier circuit 66 is composed of a circuit including four operational amplifiers OP1 to OP4,
OP1 to OP3 form an instrumentation amplifier circuit. The function of the instrumentation amplifier is to ensure that the electronic circuit operates on a single pole power supply.
2 is to generate the reference potential and to amplify and output the signal of the sample and hold 44 at a high magnification based on the reference potential.

OP4 is a third reference potential generator whose potential for passing the amplified output of OP2 through the negative feedback coil 3 is Vdd / 2. The measurement signal can be taken out as a voltage from the output terminal c point of OP2, which is the source of the negative current feedback.

However, when the second magnetic detection device is exposed to a large external magnetic field while being transported or left unattended during a rest period during which measurement is not performed, that is, when the power is not turned on, the hysteresis effect of the MI element is generated. Occurs and the operating point after the power is turned on, that is, the zero point, is not always the same as that when the measurement was previously performed, and an offset error occurs. Therefore, in the second embodiment
The importance of the initialization excitation circuit of the MI element will be explained.

In the second embodiment, the functions of the timer circuit 5 and the initialization excitation circuit 7 in the first embodiment are realized by utilizing a part of the negative feedback circuit composed of the timing capacitor D and OP2 and OP4. is doing.

Next, the structure and operation of the timer circuit and the initialization excitation circuit will be described. The circuit of OP4 is the third reference potential generator as described above, but this reference potential is set to Vdd / 2 by the two resistors R15 and R16 connected to the positive input terminal of OP4. The timing capacitor D consists of the positive electrode of the power supply and the two resistors R15 and R
A desired first-order lag time constant can be set by appropriately selecting the value of the capacitor D which is inserted between the 16 connection points.

In FIG. 8, as shown in (A), the power switch
Consider immediately after the SB is launched. As shown in (B), the positive input terminal a of OP4 instantly rises to the positive power supply voltage Vdd by the timing capacitor D, and then the resistors R15, R1.
It decays toward Vdd / 2 with a time constant of 6 and capacitor D. At this time, at the output terminal b of OP4, the output voltage is saturated and keeps a constant value for a predetermined period as shown in (C) of FIG.
Eventually, it shifts to Vdd / 2 as the input voltage decays. The circuit composed of the timing capacitor D and the resistors R15, R16 and OP4 realizes the function of the timer 5.

On the other hand, the output terminal C point of OP2 is settled to Vdd / 2 instantly when the power switch is turned on as shown in (D) because the circuit before the input terminal has no delay element. As a result, immediately after the power is turned on, a current flows through the negative feedback coil 3 from the point b to the point c through the negative feedback coil 3 and the resistors R5 and R6 as shown in FIG. 8 (E). As a result, the negative initialization excitation Ha of FIG. 4 can be applied to the MI element, and the operating point can be shifted to the Q point on the lower characteristic line LC. On this characteristic line LC, the magnetic field is measured by P1 and P2 shown in (F) and (G) of FIG.

In the second embodiment, since the MI element is always kept at zero magnetic field by the negative feedback, that is, the operating point does not move, the influence of hysteresis does not appear. Therefore, it is not necessary to perform initialization excitation during measurement, and highly accurate magnetic field measurement can be performed with the minimum number of parts, and other effects similar to those of the first embodiment are achieved.

An experiment was conducted to confirm the effect of the second embodiment. The indicated values of the signals immediately after the power was turned on 50 times under the same conditions were summarized by frequency with and without the initialization excitation circuit. The result of Figure 9
Shown in (a) and (b). From this, when using initialization excitation
In the case of (b), the result that the width of the variation of the indicated value, that is, the offset, is reduced to 1/6 of that in the case where it is not used is obtained. As is apparent from the above, the second embodiment is
It realizes highly accurate magnetic measurement.

In the second embodiment, since the negative feedback coil also serves as the coil for initialization excitation, the amplifier circuit (OP2, OP4) for negative feedback provides the current capacity required for initialization excitation. In order to sufficiently satisfy the requirements, there is an advantage that the number of components can be reduced and the circuit configuration can be simplified by using the same function.

The above-described embodiments are merely examples for explanation, and the present invention is not limited to them. Those skilled in the art will recognize from the claims, the detailed description of the invention and the description of the drawings. Modifications and additions can be made without departing from the technical idea of the present invention.

In the above embodiment, the application of the current to the magnetic sensor has been described as an example in which the current is directly applied to the magneto-impedance element.
The present invention is not limited to these, and a technical method adopting an embodiment in which a current is applied to a coil means wound around the magneto-impedance element to indirectly realize the operation of the magneto-impedance element. There is room.

[Brief description of drawings]

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

FIG. 2 is a time chart diagram showing waveforms in the pulse power supply, the magnetic impedance element, and the detection coil of the first embodiment.

FIG. 3 is a time chart diagram showing a relationship between an applied pulse and an initialization pulse of the magneto-impedance element in the first embodiment.

FIG. 4 is a diagram for explaining a characteristic line used when measuring a hysteresis loop of the magneto-impedance element according to the first embodiment.

FIG. 5 is a diagram showing a hysteresis loop obtained by an experiment before performing hysteresis compensation of the magneto-impedance element in the first embodiment.

FIG. 6 is a diagram showing a hysteresis loop obtained by an experiment when the magneto-impedance element according to the first embodiment is subjected to hysteresis compensation.

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

FIG. 8 is a time chart diagram showing the waveform of each point on the circuit in the magnetic detection apparatus of the second embodiment.

FIG. 9 is a diagram showing an experimental result of variation in an indicated value with and without initialization excitation immediately after power-on in the magnetic detection apparatus of the second embodiment.

FIG. 10 is a block circuit diagram showing a conventional magnetic sensor.

FIG. 11 is a time chart showing waveforms of various parts on a circuit in a conventional magnetic sensor.

[Explanation of symbols]

1 Magnetic sensor 11 Magnetic impedance element 12 detection coil 40 detection circuit 7 Hysteresis compensation circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshinobu Honzo             1 Wanowari, Arao-cho, Tokai-shi, Aichi             Chi Micro Intelligent Co., Ltd.             Within (72) Inventor Hitoshi Aoyama             1 Wanowari, Arao-cho, Tokai-shi, Aichi             Chi Micro Intelligent Co., Ltd.             Within (72) Inventor Masaki Mori             1 Wanowari, Arao-cho, Tokai-shi, Aichi             Chi Micro Intelligent Co., Ltd.             Within (72) Inventor Eiji Kako             1 Wanowari, Arao-cho, Tokai-shi, Aichi             Chi Micro Intelligent Co., Ltd.             Within F term (reference) 2G017 AA01 AB07 AD51 BA05

Claims (3)

[Claims] 1. A magnetic sensor in which coil means is wound around a magneto-impedance element whose impedance changes according to the magnitude of an external magnetic field, and a magnetic sensor in which a current is applied to the magneto-impedance element and which is changed by the external magnetic field. A detection circuit that detects the impedance of the impedance element as a voltage signal based on the induced voltage of the coil means, and a hysteresis compensation pulse is applied to the coil means or the magneto-impedance element prior to the detection of the impedance signal, and the magnetic A hysteresis detecting circuit that enables detection of the impedance signal in one of the hysteresis characteristics of the impedance element. 2. The electric current is applied to the magneto-impedance element according to claim 1, wherein the hysteresis compensation circuit is wound around the magneto-impedance element formed of an amorphous wire, and the detection coil serving as the coil means applies the electric current to the magneto-impedance element. While applying a pulse for hysteresis compensation when not being performed, by the sample hold circuit as the detection circuit,
The magnetic detection device, wherein the impedance signal in one of the hysteresis characteristics is detected by sampling and holding the impedance signal as a voltage signal based on an induced voltage of the detection coil in synchronization with a current application timing. 3. The negative feedback coil as defined in claim 1, wherein the hysteresis compensation circuit is provided in a negative feedback coil as the coil means wound around the magneto-impedance element formed of an amorphous wire, in synchronization with power-on. While applying a pulse for hysteresis compensation based on the feedback current, by the sample hold circuit as the detection circuit,
The impedance signal in one of the hysteresis characteristics is detected by sampling and holding it as a voltage signal based on the induced voltage of the detection coil as the coil means in synchronization with the current application timing of the magneto-impedance element. Characteristic magnetic detection device.