JP2020094914A - Flux gate type magnetic sensor - Google Patents

Abstract

To provide a self-excited flux gate type magnetic sensor capable of not only detecting disconnection of detection coils, but also continuing magnetism detection operation.SOLUTION: A flux gate type magnetic sensor 1 includes: a magnetic sensor element 10 for detecting a magnetic field; a self-oscillation circuit 20 connected to the magnetic sensor element 10; a frequency detection circuit 30 for detecting an oscillatory frequency of the self-oscillation circuit 20; and an abnormality detection circuit 40 for detecting that the oscillatory frequency is lower than a predetermined threshold. The magnetic sensor element 10 includes a plurality of detection coils 12A, 12B connected in parallel.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fluxgate type magnetic sensor, and more particularly to a structure of a magnetic sensor element and a method for detecting an abnormality thereof.

2. Description of the Related Art As a magnetic sensor used for a current sensor or an electronic compass, a fluxgate type magnetic sensor configured by winding a coiled wire around a magnetic core is known.

In the conventional fluxgate type magnetic sensor, when the coil-shaped wiring is broken, the output is immediately lost without going through the output deterioration process, and thus failure prediction is difficult. In order to solve such a problem, for example, Patent Document 1 describes a fluxgate magnetic sensor capable of detecting the disconnection of the exciting coils by monitoring the resistance of the exciting coils connected in parallel.

JP, 2016-194453, A

However, the conventional fluxgate type magnetic sensor described in Patent Document 1 can detect the disconnection of the exciting coil, but cannot detect the disconnection of the detecting coil, and thus can be applied to the self-excited type. Can not. Further, depending on the application of the fluxgate magnetic sensor, it is required that the magnetic detection operation can be continued without being completely stopped due to a failure, and improvement in reliability of the fluxgate magnetic sensor is required.

Therefore, it is an object of the present invention to provide a self-excited fluxgate type magnetic sensor that can detect a disconnection of a detection coil and can continue a magnetic detection operation.

In order to solve the above problems, a fluxgate type magnetic sensor according to the present invention detects a magnetic sensor element for detecting a magnetic field, a self-excited oscillation circuit connected to the magnetic sensor element, and an oscillation frequency of the self-excited oscillation circuit. And a malfunction detecting circuit for detecting that the oscillation frequency is below a predetermined threshold, and the magnetic sensor element includes a plurality of detecting coils connected in parallel.

According to the present invention, disconnection of the detection coil can be detected even if it is a self-excited type. In addition, the detection coil can be divided into a redundant configuration, and even if one of the detection coils is disconnected, the remaining detection coils can be used to continue the magnetic detection operation, avoiding a complete stop of the magnetic detection operation. Therefore, the reliability of the fluxgate magnetic sensor can be improved.

In the present invention, the self-excited oscillation circuit performs a self-excited oscillation operation using a first threshold voltage during normal operation when the abnormality detection circuit does not output the alarm signal, and the abnormality detection circuit causes the alarm signal to be generated. It is preferable to perform the self-excited oscillation operation using a second threshold voltage different from the first threshold voltage in the abnormal state in which is output. By changing the threshold voltage used for switching the polarity in the self-excited oscillation circuit according to the presence/absence of abnormality detection, the detection sensitivity of the magnetic field at the time of abnormality can be adjusted, and the reliability of the output of the fluxgate magnetic sensor can be adjusted. Can be increased.

The magnetic coupling constants of the plurality of detection coils are preferably +0.8 or less. When the magnetic coupling coefficient is +0.8 or less, it is possible to detect a change in magnetic field even when the magnetic sensor element is composed of a parallel circuit of a plurality of detection coils.

It is preferable that the magnetic sensor element has three or more detection coils, and the detection coils are arranged so that mutual inductance is the same. In this case, the plurality of detection coils may be arranged at equal intervals on the circumference, and the coil axes of the plurality of detection coils may be arranged on the same plane. Alternatively, the plurality of detection coils may be arranged such that their coil axes are parallel to each other. With this configuration, the magnetic sensor element can be configured by using three or more detection coils, and the redundancy of the detection coils that configure the magnetic sensor element can be further enhanced.

As described above, according to the present invention, it is possible to provide a self-excited fluxgate magnetic sensor capable of not only detecting the disconnection of the detection coil but also continuing the magnetic detection operation.

FIG. 1 is a block diagram schematically showing the configuration of a fluxgate magnetic sensor according to the first embodiment of the present invention. FIG. 2 is a waveform diagram showing the oscillation voltage of the self-excited oscillation circuit and the current (shunt voltage) flowing through the magnetic sensor element. FIG. 3 is a diagram for explaining a change in the inductance of the magnetic sensor element before and after disconnection, where (a) shows before disconnection (when normal) and (b) shows after disconnection. FIG. 4 is a graph showing the response characteristics of the shunt voltage of the magnetic sensor element before and after disconnection. FIG. 5 is a diagram for explaining a case where the polarity switching reference voltage of the self-excited oscillation circuit is changed after disconnection. FIG. 6 is a schematic plan view showing a first modification of the magnetic sensor element 10. FIG. 7 is a schematic perspective view showing a second modification of the magnetic sensor element 10.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram schematically showing the configuration of a fluxgate magnetic sensor according to the first embodiment of the present invention.

As shown in FIG. 1, the fluxgate magnetic sensor 1 includes a magnetic sensor element 10 for detecting a magnetic field, a self-excited oscillation circuit 20 connected to the magnetic sensor element 10, and an oscillation frequency of the self-excited oscillation circuit 20. A frequency detection circuit 30 for detecting and an abnormality detection circuit 40 for detecting that the oscillation frequency detected by the frequency detection circuit 30 is below a predetermined threshold value are provided.

The magnetic sensor element 10 is configured by using a plurality of detection coils composed of coil-shaped wiring wound around a magnetic core. In particular, the magnetic sensor element 10 according to the present embodiment has magnetic cores 11A and 11B, respectively. It is composed of a parallel circuit of two wound detection coils 12A and 12B. Although the two detection coils 12A and 12B are connected in parallel outside the self-excited oscillation circuit 20, they may be connected in parallel inside the self-excited oscillation circuit 20. The inductances L of the detection coils 12A and 12B are the same.

FIG. 2 is a waveform diagram showing the oscillation voltage of the self-excited oscillation circuit 20 and the current (shunt voltage) flowing through the magnetic sensor element 10.

The self-excited oscillation circuit 20 alternately outputs a positive side constant voltage and a negative side constant voltage. As shown in FIG. 2, the current flowing through the magnetic sensor element 10 to which the constant voltage on the positive side is applied gradually increases, and the voltage measured through the shunt resistor (shunt voltage) also increases proportionally. The self-excited oscillation circuit 20 switches the polarity of the constant voltage when the shunt voltage reaches a predetermined threshold voltage (+V _TH1 or −V _TH1 ). By repeating such a polarity switching operation, the self-excited oscillation circuit 20 outputs an oscillation voltage.

The frequency detection circuit 30 detects the oscillation frequency of the self-excited oscillation circuit 20. For example, in the case of being affected by the external magnetic field, either one of the positive side and the negative side constant voltage application time becomes long and the other becomes short. For example, in FIG. 2, the negative constant voltage application time T2 is longer than the positive constant voltage application time T1. This time difference is proportional to the magnitude of the external magnetic field. The frequency detection circuit 30 can calculate the magnitude of the external magnetic field from the difference between the application time of the positive side constant voltage and the application time of the negative side constant voltage, that is, the magnitude of the distortion of the oscillation frequency.

The abnormality detection circuit 40 monitors a large change in the oscillation frequency of the self-excited oscillation circuit 20 detected by the frequency detection circuit 30, and when the oscillation frequency falls below a predetermined threshold, the magnetic sensor element 10 is checked for abnormality such as disconnection. It is judged that it has occurred and an alarm signal is output.

FIG. 3 is a diagram for explaining a change in the inductance of the magnetic sensor element 10 before and after the wire breakage, where (a) shows before the wire breaks (when normal) and (b) shows after the wire breakage.

As shown in FIGS. 3A and 3B, the magnetic sensor element 10 is a parallel circuit of the first detection coil 12A and the second detection coil 12B, and the first and second detection coils 12A and 12B. Are arranged so that the direction of the magnetic field generated when a current is passed through the first detection coil 12A is the same as the direction of the magnetic field generated when a current is passed through the second detection coil 12B. Therefore, the mutual inductance M between the first and second detection coils 12A and 12B becomes negative.

The self-inductance of the first and second detection coils 12A and 12B is L, the mutual inductance is M, and the magnetic coupling coefficient is k (where −1≦k≦1). As shown in FIG. 3A, the combined inductance L _{before in a} normal state in which the two detection coils 12A and 12B form a parallel circuit is as follows.

L _before =(L+M)/2=(1+k)L/2

On the other hand, the combined inductance L _after when one of the two detection coils 12A and 12B is broken is as follows.

L _after =L (>L _before )

That is, the inductance L _after of the magnetic sensor element 10 _after disconnection is larger than the inductance L _{before before} disconnection.

When the inductance of the magnetic sensor element 10 changes as described above due to the disconnection, the oscillation frequency of the self-excited oscillation circuit 20 connected to the magnetic sensor element 10 also changes. As shown in FIG. 4, the response characteristics of the shunt voltage in the normal state (before the disconnection) are relatively steep, but the change in the shunt voltage after the disconnection is affected by the increase of the inductance of the magnetic sensor element 10 and compared. Becomes gentle. Therefore, the time t2 until the shunt voltage of the magnetic sensor element 10 reaches the polarity switching reference voltage V _TH1 (first threshold voltage) becomes longer than the time t1 before the disconnection. That is, after the wire breakage, the inductance of the magnetic sensor element 10 increases, the polarity switching period (pulse width of the oscillation voltage) becomes wider, and the polarity switching frequency (oscillation frequency) becomes smaller.

For example, when the magnetic coupling coefficient k=−0.5, the inductance _before disconnection L _before =0.25 L, the inductance _after disconnection L _after =L, and the inductance _after disconnection L _after is the inductance _before disconnection L _before It is about 4 times. Therefore, the oscillation frequency f _{after after} disconnection is approximately 1/4 of the oscillation frequency f _{before before} disconnection (f _after ≈f _before /4).

In this way, the abnormality detection circuit 40 can detect the disconnection of the detection coil forming the magnetic sensor element 10 from the change in the oscillation frequency. Further, even if the inductance of the magnetic sensor element 10 changes, its output does not become zero, so that the magnetic detection operation can be continued.

The magnetic coupling constant between the first and second detection coils 12A and 12B is preferably +0.8 or less. When the magnetic coupling coefficient is close to 1, it becomes difficult to distinguish the difference between the change in the oscillation frequency due to the external magnetic field and the change in the oscillation frequency due to the disconnection. However, if the magnetic coupling coefficient is 0.8 or less, it is possible to detect the change in the oscillation frequency due to the disconnection by using the magnetic sensor element configured by the parallel circuit of the plurality of detection coils.

The alarm signal output by the abnormality detection circuit 40 is preferably fed back to the self-excited oscillation circuit 20. As shown in FIG. 5, after the disconnection, the time until the shunt voltage reaches the polarity switching reference voltage (first threshold voltage) V _TH1 (about half of the oscillation cycle) becomes long, and the oscillation frequency becomes small. When the magnitude of the external magnetic field is obtained in such a state, the measurement error of the magnitude of the magnetic field may increase. Therefore, when the disconnection is detected by the abnormality detection circuit 40, the polarity switching reference voltage is switched from V _TH1 (first threshold voltage) to V _TH2 (second threshold voltage) as shown in FIG. The self-excited oscillation circuit 20 performs the self-excited oscillation operation using the first threshold voltage V _TH1 when normal, but performs the self-excited oscillation operation using the second threshold voltage V _TH2 when abnormal. By doing so, the oscillation frequency before and after the disconnection can be made substantially constant, and the measurement error of the external magnetic field can be reduced. When the abnormality detection circuit 40 detects disconnection, the amplification factor of the amplifier included in the self-excited oscillation circuit 20 or the frequency detection circuit 30 may be changed in addition to changing the threshold voltage to control the output characteristic. Feedback can be provided to various circuit elements.

As described above, the flux gate type magnetic sensor 1 according to the present embodiment is divided into two pairs in which the detection coil and the magnetic core are electrically parallel to each other. Since the disconnection is detected, the disconnection of the detection coil can be detected even by the self-excited type. Further, the detection coil can be divided into two pairs to have a redundant configuration, and even if one of the detection coils is disconnected, the magnetic detection operation can be continued using the remaining detection coils. Therefore, it is possible to avoid a complete stop of the magnetic detection operation, and it is possible to improve the reliability of the fluxgate magnetic sensor.

FIG. 6 is a schematic plan view showing a first modification of the magnetic sensor element 10.

As shown in FIG. 6, the magnetic sensor element 10 is characterized in that it is configured by using four detection coils 12A, 12B, 12C and 12D. The first to fourth detection coils 12A, 12B, 12C, and 12D are coil-shaped wirings wound around the first to fourth magnetic cores 11A, 11B, 11C, and 11D, respectively. The coil axes of the detection coils 12A and 12C are parallel to the X-axis direction, and the coil axes of the second and fourth detection coils 12B and 12D are parallel to the Y-axis direction. The four detection coils 12A, 12B, 12C, 12D have the same inductance, and form a parallel circuit of the four detection coils.

In the present embodiment, the four detection coils 12A, 12B, 12C, 12D are arranged on the same plane so as to have a rotationally symmetric positional relationship. That is, the four detection coils are arranged at equal intervals on the circumference. The coil axes of the four detection coils 12A, 12B, 12C, and 12D are all parallel to the XY plane, and are arranged rotationally symmetrical when viewed from the Z-axis direction orthogonal to the XY plane. When the first to fourth detection coils 12A to 12D are arranged in this way, the mutual inductances of the respective detection coils are the same, so that it is possible to maintain the balance of the magnetic field detection sensitivities of the respective detection coils. Further, since the four detection coils are used, the redundancy of the detection coils forming the magnetic sensor element 10 can be further enhanced.

FIG. 7 is a schematic perspective view showing a second modification of the magnetic sensor element 10.

As shown in FIG. 7, the magnetic sensor element 10 is characterized in that the four detection coils 12A, 12B, 12C, and 12D are arranged such that their coil axes are parallel to each other. The point is that they are arranged so as to have a symmetrical positional relationship when viewed from the extending X-axis direction. That is, the coil axes of the four detection coils 12A, 12B, 12C, and 12D are all parallel to the X axis, and are arranged at equal intervals on the circumference when viewed from the X axis direction. Even with such a configuration, since the mutual inductances of the first to fourth detection coils 12A to 12D are the same, it is possible to maintain the balance of the magnetic field detection sensitivities of the respective detection coils. Further, since the four detection coils are used, the redundancy of the detection coils forming the magnetic sensor element 10 can be further enhanced.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. It goes without saying that it is included in the range.

For example, in the above embodiment, the magnetic sensor element 10 is configured by using two or four detection coils, but the number of detection coils is not particularly limited, and may be three or five or more. It may be.

1 Fluxgate type magnetic sensor 10 Magnetic sensor element 11A, 11B, 11C, 11D Magnetic core 12A, 12B, 12C, 12D Detection coil 20 Self-excited oscillation circuit 30 Frequency detection circuit 40 Abnormality detection circuit f _after Oscillation frequency f _before disconnection Oscillation frequency before disconnection k Magnetic coupling coefficient L Inductance of detection coil L _after Composite inductance _after disconnection L _before Composite inductance _before disconnection M Mutual inductance T1 Positive side constant voltage application time T2 Negative side constant voltage application time V _TH1 polarity switching reference voltage (first threshold voltage)
V _TH2 polarity switching reference voltage (second threshold voltage)

Claims (6)

A magnetic sensor element for detecting a magnetic field,
A self-excited oscillation circuit connected to the magnetic sensor element,
A frequency detection circuit for detecting the oscillation frequency of the self-excited oscillation circuit,
An abnormality detection circuit for detecting that the oscillation frequency is below a predetermined threshold,
The flux sensor type magnetic sensor, wherein the magnetic sensor element includes a plurality of detection coils connected in parallel. The self-oscillation circuit,
In the normal time when the abnormality detection circuit does not output the alarm signal, the self-excited oscillation operation is performed using the first threshold voltage,
The flux gate type magnetic sensor according to claim 1, wherein a self-excited oscillation operation is performed using a second threshold voltage different from the first threshold voltage when the abnormality detection circuit is outputting the alarm signal in an abnormality. .. The fluxgate magnetic sensor according to claim 1, wherein the magnetic coupling constants of the plurality of detection coils are +0.8 or less. The flux gate type magnetic according to any one of claims 1 to 3, wherein the magnetic sensor element has three or more detection coils, and the detection coils are arranged so as to have the same mutual inductance. Sensor. The plurality of detection coils are arranged at equal intervals on the circumference,
The fluxgate type magnetic sensor according to claim 4, wherein the coil axes of the plurality of detection coils are arranged on the same plane. The flux gate type magnetic sensor according to claim 4, wherein the plurality of detection coils are arranged such that their coil axes are parallel to each other.

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