JPH08152464A - Flux-gate magnetic sensor - Google Patents

Abstract

PURPOSE: To obtain a flux-gate magnetic sensor by which both the direction and the magnitude of a magnetic field can be measured without installing a phase detection circuit by impressing a bias magnetic field to a sensor body and moving the range of a magnetic field as an object to be measured to a linear region from a nonlinear region. CONSTITUTION: An exciting circuit 38 supplies an AC exciting signal (at a frequency (f)) having an amplitude, at which a core 30 is saturated, to a coil 32 for excitation. A BPF 40 takes out secondary harmonics 2f from a coil 34 for detection. A detection circuit 42 detects the secondary harmonics 2f from the BPF 40. A bias magnetic field HB is applied in advance to a sensor body 36 from a bias-magnetic-field generation source 44, and a magnetic field H as an object to be measured is measured in such a way that the sum H+HB of the bias magnetic field HB and the magnetic field H is shifted to a linear region from a nonlinear region. Generally, the range of the magnetic field H as the object to be measured is known in advance. As a result, when the bias magnetic field HB is selected so as to match the range, the magnitude and the direction of the magnetic field can be found without detecting a plane. As a result, a phase detection circuit is not required, and an apparatus can be simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluxgate type magnetic sensor. More specifically, by providing a bias magnetic field generating source near the sensor body, the direction and magnitude of the magnetic field can be detected without phase detection. The present invention relates to a fluxgate type magnetic sensor capable of measuring both of the above. Since this type of magnetic sensor has high sensitivity and sharp directivity, it is useful for detecting geomagnetism, for example.

[0002]

2. Description of the Related Art A fluxgate type magnetic sensor is a magnetic sensor utilizing the magnetic non-linearity of a high permeability magnetic material (for example, nickel-iron alloy), and is highly sensitive, easy to handle, and has a sharp directivity. It is used to measure the direction component of magnetic force. The principle of this fluxgate type magnetic sensor is to use a sensor body in which an exciting coil and a detecting coil are wound around a core made of a high magnetic permeability material, and an AC excitation signal of an amplitude that causes the core to saturate is applied to the exciting coil. This excites the core and obtains the external magnetic field from the output voltage of the detection coil.

FIG. 8 shows a general configuration example of a conventional flux gate type magnetic sensor. The exciting coil 11 of the sensor body 10 is supplied with an AC exciting signal (frequency f) having an amplitude that saturates the core 13 from the exciting circuit 12, and the detecting coil 1
4 output signal to even harmonics (usually 2nd harmonic 2
f) is taken out by the bandpass filter 15. Then, the phase detection circuit 17 detects the phase difference between the reference signal 2f obtained by multiplying the excitation signal by the frequency multiplication circuit 16 and the second harmonic 2f, and the detection is performed by the detection circuit 18 to detect the external magnetic field. Find the orientation and size. The phase detection circuit 17
It can be omitted when only the magnitude of the magnetic field needs to be measured, but it is necessary when the direction of the magnetic field must be determined. This is because when the even harmonics are detected, a symmetrical output voltage is obtained with respect to the positive and negative magnetic fields.

The measuring principle is as follows. As shown in FIG. 9, it is assumed that a sinusoidally changing current is applied to an exciting coil of a core (magnetization curve is indicated by reference symbol a) made of a highly permeable material that is easily saturated. If the external DC magnetic field to be measured is not applied, the output waveform will also be a symmetric waveform due to the symmetry of the magnetization curve, so the even harmonic components are not included (shown by the solid line). However, when an external DC magnetic field ΔH is applied, it becomes asymmetric as shown by the broken line, and even harmonic components appear. When this even harmonic component (usually the second harmonic component) is detected, the magnitude of the output voltage is almost proportional to the magnitude of the DC magnetic field.

[0005]

In the conventional fluxgate type magnetic sensor shown in FIG. 8, in many cases, the phase detection circuit part is the most complicated, the number of required parts is large, and adjustment is required even after assembly. Becomes Therefore, this phase detection circuit portion requires considerable cost and labor in constructing the magnetic sensor.

An object of the present invention is to provide a fluxgate type magnetic sensor which can measure both the direction and the magnitude of a magnetic field without a phase detection circuit.

[0007]

A fluxgate magnetic sensor according to the present invention is a sensor body in which an exciting coil and a detecting coil are wound around a core made of a high-permeability magnetic material, and the exciting coil has a core. An excitation circuit that supplies an alternating-current excitation signal with an amplitude that saturates, a bandpass filter that extracts a specific even-order harmonic from the detection coil, and a diode that is inserted in series with the output signal of the bandpass filter in parallel And a bias magnetic field generation source that is located near the sensor body and applies a bias magnetic field to the sensor body to move the magnetic field range to be measured from a non-linear region to a linear region. are doing. A feature of the present invention is that a frequency multiplication circuit for an excitation signal and a complicated phase detection circuit, which are conventionally required, are not required, and a bias magnetic field generation source is additionally provided instead.

The bias magnetic field generating source used in the present invention may be a permanent magnet or a bias coil through which a constant current flows. Usually, these are arranged so that the magnetic field is oriented in the axial direction of the detection coil, and they are incorporated in a housing to be integrated as a sensor unit. In the case of the bias coil, it is preferable to wind the detection coil concentrically with the detection coil and connect a constant current source for supplying a constant bias magnetic field current thereto.

[0009]

In general, when even-order harmonics are detected by a detection circuit using a diode, a symmetrical output voltage is obtained with respect to the positive and negative magnetic fields. Further, the output voltage is linear with respect to the magnetic field in the range where the absolute value of the magnetic field is large, but the output voltage is non-linear with respect to the magnetic field due to the nonlinearity of the diode in the range where the absolute value of the magnetic field is small. Therefore, the direction of the magnetic field cannot be determined as it is, and the magnitude of the magnetic field cannot be easily obtained from the output voltage in the nonlinear region.

Therefore, in the present invention, a constant DC bias magnetic field is applied to the sensor body from the bias magnetic field generation source.
As a result, the external magnetic field applied to the sensor body is a magnetic field to be measured with a bias magnetic field superimposed thereon. By properly selecting the magnitude of the bias magnetic field, the measurement range including the non-linear region can be moved to the linear region. Then, the magnitude of the external magnetic field can be easily obtained from the output voltage, and by subtracting a known bias magnetic field from the external magnetic field, the direction and magnitude of the magnetic field to be measured can be easily obtained.

[0011]

1 is a block diagram showing an embodiment of a fluxgate type magnetic sensor according to the present invention. This magnetic sensor includes a sensor body 36 in which an exciting coil 32 and a detecting coil 34 are wound around a core 30 made of a high-permeability magnetic material (for example, nickel-iron alloy), and the exciting coil 32 has a core 30. Excitation circuit 38 for supplying an AC excitation signal (frequency f) having an amplitude that saturates, and the detection coil 34.
Bandpass filter 4 for extracting the second harmonic 2f from the
0 and a detection circuit 42 for detecting a second harmonic by combining a diode D inserted in series with the output signal from the bandpass filter 40 and a capacitor C arranged in parallel, and the vicinity of the sensor body 36. And a bias magnetic field generation source 44 which is located at the position where the bias magnetic field is applied to the sensor main body 36 to move the magnetic field range to be measured from the non-linear region to the linear region.

According to the present invention, the detection characteristic of the diode is
Paying attention to the fact that it is linear in the range where the absolute value of the magnetic field is large, the bias magnetic field H _B is applied to the sensor body 36 in advance, and the sum H + H _B with the magnetic field H to be measured is linear. The measurement is made so that it comes to the area. Since the range of the magnetic field H to be measured is generally known in advance, the magnitude and direction of the magnetic field can be obtained without detecting the phase by selecting the bias magnetic field H _B accordingly.

This measuring principle will be described in more detail with reference to FIG. The curve shown in FIG. 2 shows the detection characteristic of the diode. The range of the magnetic field to be measured is -H ₁ ≤
Let H ≦ H ₂ . H _B −H ₁ > H ₀ , that is, H _B > H ₁ +
A bias magnetic field H _B that gives H ₀ is selected and applied to the sensor body 36 in advance. The bias magnetic field H _B may be generated by any method such as passing a constant current through a permanent magnet or a coil, but it needs to be stable. By doing this, the range of the magnetic field to be originally measured is −H ₁ ≦ H ≦ H
₂ , the magnetic field H _i applied to the sensor body 36 (H _i =
H + H _B ) is H _B −H ₁ ≦ H _i ≦ H _B + H ₂ , whereas the output voltage after detection is V ₁ ≦ V ≦
Linearity can be maintained in the range of V ₂ . Therefore, the output voltage V of the linear portion and the magnetic field H _i applied to the sensor body are
Can be expressed as V = aH _i + b. Here, a and b are constants that can be obtained in advance by calibration. Therefore, the magnetic field H _i applied to the sensor body can be obtained as H _i = (V−b) / a. On the other hand, since H _i = H + H _B and H _B is known, the magnetic field H can be obtained from the following equation. H = (V−b) / a−H _B ... The direction of the magnetic field can also be known from the sign of the magnetic field H obtained from the above equation.

An example of the sensor body and the bias magnetic field generation source is shown in FIG. The sensor main body 50 is made of a magnetic material having high magnetic permeability (specifically, nickel-iron alloy, for example) and is parallel to each other.
The cores 52a and 52b of the book are made into one set, and the exciting coils 54a and 54b are respectively wound and connected so that the directions of the exciting magnetic fields are opposite to each other, and the detecting coil 5 is provided outside them.
6 is provided. By doing so, the even harmonics of the output on the detection side can be added, and the odd harmonics can be subtracted to zero, so that the even S / N becomes very good. A cylindrical permanent magnet 58 is used as a bias magnetic field generation source, and the permanent magnet 58 is arranged in the housing 59 at a distance L from the sensor main body 50 so that the magnetic field is oriented in the axial direction of the detection coil 56 to form a sensor unit. . In this case, the strength of the bias magnetic field is adjusted by freely adjusting the distance L between the sensor body 50 and the permanent magnet 58 in the housing 59.

FIG. 4 is obtained by using the flux gate type magnetic sensor as described above when the bias magnetic field H _B is applied (shown by a solid line) and when the bias magnetic field H _B is not applied and measured as it is (shown by a broken line). It is a comparison of output voltages after detection. The external magnetic field was changed by putting a magnetic sensor in the solenoid coil and changing the current passed through the solenoid coil, and various values were measured. FIG.
As can be seen from the above, the magnetic field in the solenoid coil including the direction could be obtained by the output voltage after detection.

FIG. 5 shows an example in which geomagnetism is detected using the above fluxgate type magnetic sensor. When the magnetic sensor is rotated in the horizontal plane, the output voltage after detection changes sinusoidally, which is maximum in magnetic north and minimum in the opposite south direction. The solid line drawn horizontally in the approximate center of the figure corresponds to the bias magnetic field, and indicates that the direction of the magnetic field is positive when the output voltage is higher than this and negative when the output voltage is low.

As can be seen from these examples, by applying an appropriate bias magnetic field, it is possible to obtain the magnitude and direction of the magnetic field just by using a simple detection circuit, as in the case of using a circuit considering the phase. You can

FIG. 6 shows an example in which a three-axis sensor is constructed. When configuring such a multi-axis sensor, it is possible to use only one permanent magnet. The distance L from the origin to the end surface of the permanent magnet 58 and the angles θ and φ of the axes of the permanent magnet 58 are adjusted. The X-axis, Y-axis, and Z-axis sensor main bodies 50 have the same configuration as that shown in FIG. 3 here, so description thereof will be omitted.

In FIG. 3 or 6, instead of the permanent magnet, a bias coil may be arranged at that position. In that case, a constant current source for supplying a constant bias magnetic field current is connected to the bias coil. The constant current source is
It is possible to apply a desired bias magnetic field by making the current value freely adjustable to a desired value and applying a constant current.

FIG. 7 shows an example in which a bias coil is wound around the sensor body. A is the case of a parallel core similar to that shown in FIG. A bias coil 60 is concentrically wound around the detection coil 56 to form a sensor unit. A constant current source 61 is connected to the bias coil 60. In B, the ring core is used, and the exciting coil 64 is wound around the ring core 62, and the detecting coil 66 is arranged outside thereof. Then, a bias coil 70 is concentrically wound around the detection coil 66. A constant current source 71 is also connected to the bias coil 70. In any case,
Such a coil arrangement is preferable because the sensor unit can be downsized. The strength of the bias magnetic field is adjusted by the number of turns and the current value. The bias magnetic field is proportional to the product of the number of turns and the current value.

The structure of the sensor body on which the present invention is based may be of various types conventionally used. For example, the form of the core includes a single core, a parallel core, a ring core, a wire core, a tube core, a helical core, and the like, in which the exciting magnetic field by the exciting coil is parallel to the external magnetic field, orthogonal, and mixed There are types. The present invention is applicable to all these types.
In the method of passing a constant current through the bias coil, it is easy to change the bias value by changing the value of the energizing current depending on the purpose, and the sensitivity can be checked by passing alternating currents.

[0022]

As described above, according to the present invention, since the phase detecting circuit which is conventionally required for measuring both the direction and the magnitude of the magnetic field is not required, the apparatus is simplified and the adjustment after the assembly is performed. Is also easy and extremely easy to handle.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a fluxgate type magnetic sensor according to the present invention.

FIG. 2 is an explanatory diagram of the measurement principle.

FIG. 3 is an explanatory diagram showing an example of a positional relationship between a sensor body and a permanent magnet.

FIG. 4 is an explanatory diagram showing an example of magnetic field measurement in a solenoid coil.

FIG. 5 is an explanatory diagram showing an example of geomagnetic measurement.

FIG. 6 is an explanatory diagram showing an example of a positional relationship between a triaxial sensor body and a permanent magnet.

FIG. 7 is an explanatory diagram showing an example of a positional relationship between a sensor body and a bias coil.

FIG. 8 is a configuration diagram showing an example of a conventional flux gate type magnetic sensor.

FIG. 9 is an explanatory diagram of the measurement principle.

[Explanation of symbols]

 30 core 32 excitation coil 34 detection coil 36 sensor body 38 excitation circuit 40 bandpass filter 42 detection circuit 44 bias magnetic field generation source

Claims (3)

[Claims] 1. A sensor body in which an exciting coil and a detecting coil are wound around a core made of a high-permeability magnetic material, and an exciting circuit for supplying the exciting coil with an AC exciting signal having an amplitude with which the core is saturated. A bandpass filter for extracting a specific even harmonic from the detection coil, a detection circuit in which a diode inserted in series with the output signal of the bandpass filter and a capacitor arranged in parallel are combined, and the sensor A flux gate type magnetic sensor, comprising: a bias magnetic field generation source that is located near the main body and applies a bias magnetic field to the sensor main body to move the magnetic field range to be measured from a non-linear region to a linear region. 2. The bias magnetic field generation source is a permanent magnet,
The sensor body and the permanent magnet are integrated in a housing so that the magnetic field is oriented in the axial direction of the detection coil.
The magnetic sensor described. 3. The bias magnetic field generation source comprises a bias coil and a constant current source for supplying a constant current thereto, and the bias coil is wound around the outer circumference of the detection coil and concentrically with the detection coil. The magnetic sensor according to claim 1.