JP2019078714A - Fluxgate sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluxgate sensor in which a signal to be amplified is less likely to disappear due to the influence of noise. A fluxgate sensor characterized by having a noise suppression filter for suppressing noise inside. [Selection diagram] FIG. 13

Description

  The present invention relates to a flux gate sensor.

  Conventionally, a flux gate sensor is utilized for a magnetic detection device etc. (for example, patent document 1).

JP, 2013-253920, A

  When detecting a small magnetism using a flux gate sensor, it is conceivable to increase the amplification factor of the loop filter of the flux gate sensor having a feedback loop. However, in this configuration, when the range of the input voltage that can be amplified is substantially narrowed and relatively large noise is superimposed on the signal, the output is saturated beyond this range of the input voltage, and the signal component disappears. I will.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a flux gate sensor in which a signal to be amplified is unlikely to disappear due to the influence of noise.

In order to solve the above-mentioned subject, the flux gate sensor of the present invention,
In a flux gate sensor having a feedback loop that cancels the external magnetic field by the current correlated to the output signal,
A noise suppression filter for suppressing noise is provided in the feedback loop.

  According to this flux gate sensor, it is possible to prevent signal loss (clipping) due to saturation in the feedback loop, and it is possible to take a wide dynamic range while maintaining the resolution of the measurement band.

In the flux gate sensor described above,
The noise suppression filter is
The noise of 50 Hz or 60 Hz may be suppressed.

  According to this flux gate sensor, since it is possible to remove large noise generated by the 50/60 Hz AC power line, it is possible to effectively suppress the occurrence of clipping.

In the flux gate sensor described above,
The noise suppression filter is
It may include any of a notch filter, a band elimination filter, and a high pass filter.

  According to this flux gate sensor, various filters can be used.

In the flux gate sensor described above,
The noise suppression filter is
It may be configured by a digital filter.

  According to this flux gate sensor, the S / N ratio can be increased.

  According to the present invention, it is possible to provide a flux gate sensor in which the signal to be amplified is less likely to disappear due to the influence of noise.

It is a perspective view showing a foreign matter detection device of this embodiment. FIG. 2 is a view showing a cross section in the radial direction of the opening portion of the foreign object detection device 1; FIG. 2 is a projection view showing the positional relationship inside the foreign object detection device 1 along the vertical direction. It is a schematic diagram which shows the change of the magnetic field in, when circular magnetic shield S1 is used. It is a figure showing cylindrical magnetic shield 10A. It is a schematic diagram which shows the direction in which the magnetic force line which goes to an opening bends. It is a figure which shows the modification of the cross-sectional shape of a magnetic shield. It is a figure which shows the modification of a carrying-in entrance and an exit. It is a figure which shows the modification of a magnetic shield. It is a figure which shows the modification of the magnetic shield which combined the several shield part. It is a figure showing the modification which made the number of shield layers near the opening of a magnetic shield increase locally. It is sectional drawing which shows the modification which increased the number of shield layers near the opening of a magnetic shield locally. FIG. 2 is a block diagram showing a configuration of a flux gate sensor 2 that can be adopted in the magnetic sensor unit 16; It is a figure which shows an example of the signal in a feedback loop. FIG. 6 is a block diagram showing the configuration of a determiner that can be installed on the output side of the magnetic sensor unit 16; It is a figure which shows an example of reference | standard data. It is a figure which shows an example of the result of frequency analysis. It is a figure showing an example of distance with a table.

[Technical background of foreign object detection device]
First, the background of the foreign matter detection device of the present embodiment will be described.

  With the widespread use of electric vehicles and smartphones in recent years, various batteries have been developed, and one of such batteries is one using a sheet-like material formed of aluminum, copper, a synthetic resin or the like. If metal foreign matter is mixed in the process of manufacturing these sheet-like materials, this causes a problem such as heat generation and ignition of the battery. As in these examples, it may be desirable to detect metallic foreign matter mixed in a sheet-like material. The foreign matter detection device described below is for solving such a problem, and detects foreign matter using magnetism.

[Configuration of foreign object detection device]
Hereinafter, an embodiment of a foreign matter detection device will be described using the drawings. FIG. 1 is a perspective view showing the foreign matter detection device of the present embodiment.

  The foreign object detection device 1 of the present embodiment detects the magnetism generated from the metal foreign object mixed in the sheet-like work W, and is provided in the magnetic shield 10 and the inner space partitioned by the magnetic shield 10. It has a magnetic sensor. In FIG. 1, the transport direction of the workpiece W is indicated by an arrow from the lower left to the upper right, and the workpiece W transported along this transport direction, the shield circumferential surface portion 11, the shield right end portion 12, and the shield left end portion A cylindrical magnetic shield 10 of 13 is shown. In addition, it is shown that the work W is transported from the loading port 14 to the inside of the magnetic shield 10. The shield circumferential surface portion 11 is formed with two openings, a carry-in port 14 and a carry-out port 15 which are transport ports of the work W. The loading port 14 and the unloading port 15 are elongated openings adapted to the width and thickness of the work W. The work W is of nonmagnetic material (for example, polyethylene, non-woven fabric) which does not have magnetic property. The magnetism of the workpiece W detected by the foreign matter detection device 1 is due to the process of magnetizing the metal foreign matter. In this embodiment, it is assumed that magnetic flux lines are applied in the direction perpendicular to the surface of the workpiece W before being transported to the inside of the magnetic shield 10 by this processing.

  In the foreign matter detection device 1 according to the present embodiment, the direction passing from the loading port 14 to the unloading port 15 is referred to as the front-rear direction. A direction perpendicular to the longitudinal direction and parallel to the longitudinal direction of the inlet 14 and the outlet 15 is referred to as a lateral direction, and a direction orthogonal to both the longitudinal direction and the lateral direction is referred to as a vertical direction. The axial direction of the magnetic shield 10 in FIG. 1 is parallel to the left and right direction. Moreover, the conveyance direction of the workpiece | work W and the front-back direction are the same direction.

  FIG. 2 is a diagram showing a cross section in the radial direction of the opening of the foreign object detection device 1. FIG. 3 is a projection view showing the positional relationship inside the foreign object detection device 1 along the vertical direction. As shown in FIG. 2, the shield circumferential surface portion 11 is configured by a total of three layers of shields, a first layer 111, a second layer 112, and a third layer 113, in order from the outside. Each layer is fixed via a nonmagnetic member (for example, polyacetal resin) without contacting each other. Note that a conductive material may be used for the buffer member to remove electrical noise generated in the magnetic shield 10. In the following description, in the region where the loading opening 14 is formed, these layers are referred to as the first layer loading opening 141, the second layer loading opening 142, and the third layer loading opening 143 sequentially from the outside. Moreover, in the area | region in which the outlet 15 was formed, these layers are called the 1st layer outlet 151, the 2nd layer outlet 152, and the 3rd layer outlet 153 sequentially from the outer side.

  Further, FIG. 2 shows that a magnetic sensor unit 16 is provided inside the magnetic shield 10. The magnetic sensor unit 16 includes a total of five magnetic sensors: a first sensor 161, a second sensor 162, a third sensor 163, a fourth sensor 164, and a fifth sensor 165. It is shown in FIG. 3 that these magnetic sensors are aligned in the left-right direction in accordance with the width of the work W. In the present embodiment, a flux gate sensor is used for these magnetic sensors, but the present invention is not limited to this. The detection directions of the magnetism of these magnetic sensors are all perpendicular to the surface of the work W.

[Functional Outline of Foreign Object Detection Device 1]
The foreign object detection device 1 described in the present embodiment targets the workpiece W after the process (for example, passing a strong magnetic field) that magnetizes the metal foreign object that may be mixed inside is targeted, and there is a metal foreign object. It detects the magnetism that arises from there. If the metal foreign matter is not mixed in the work W, the magnetism is not detected from the work W, but if the metal foreign matter is mixed in the work W, the magnetism remains in the portion where the metal foreign matter is mixed. For example, when magnetism is detected by the first sensor 161 of the magnetic sensor unit 16, metal foreign matter is mixed in at the right end in the transport direction of the workpiece W. As described above, based on the detection result of the magnetism of the workpiece W conveyed to the foreign matter detection device 1, it is possible to identify the location where the metal foreign matter is mixed. As shown in FIG. 3, in the present embodiment, the first sensor 161 to the fifth sensor 165 are alternately arranged in the front-rear direction. For example, when arranged in a straight line with respect to the width (in the left and right direction), the number that can be arranged depending on the size of the magnetic sensor is limited. More magnetic sensors can be arranged to improve detection accuracy. In addition, not only the arrangement of FIG. 3 but, for example, each of the first sensor 161 to the fifth sensor 165 is shifted in the left-right direction and the front-rear direction, and other sensors are not arranged in the left-right direction and the front-rear direction It may be arranged diagonally.

  In the detection of the metal foreign substance described above, the detection accuracy is lowered because the magnetic sensor unit 16 is influenced by a magnetic field (for example, geomagnetism) caused by other than the metal foreign substance. For this reason, in the foreign matter detection device 1 of the present embodiment, a so-called passive magnetic shield 10 using permalloy having a high magnetic permeability (which easily passes magnetism) is employed. The magnetic flux is easily absorbed in the material of the magnetic shield 10, and the external magnetic field can be prevented from affecting the magnetic sensor unit 16. The magnetic shielding material used for the magnetic shield 10 is not limited to permalloy, and may be, for example, a cobalt amorphous alloy.

[About the shape of the magnetic shield 10]
As an example of a conventional magnetic shield, Patent Document 1 describes a rectangular magnetic shield formed by a flat surface. In this magnetic shield, the internal magnetic field can be weaker than the external magnetic field by detouring so that the magnetic field lines do not enter the internal space. However, with respect to the plane constituting such a magnetic shield, there is a problem that magnetic force lines colliding in the perpendicular direction easily penetrate the internal space through the magnetic shield.

  FIG. 4 is a schematic view showing the change of the magnetic field when the circular magnetic shield S1 is used. In FIG. 4, lines of magnetic force going from the left to the right indicate magnetic fields going from the N pole side to the S pole side. In FIG. 4, although the magnetic field lines (middle magnetic field lines) vertically collided with the magnetic shield S1 penetrate into the inner space, the other magnetic field lines pass through the material of the magnetic shield S1 (bypassing the inner space) It is shown. When the magnetic shield is configured as a curved surface in this manner, the range in which the magnetic force lines vertically collide can be reduced, and the shielding effect can be enhanced.

  The magnetic shield 10 in the foreign object detection device 1 of the present embodiment is cylindrical in shape, and as shown in FIG. 2, the shape of the plane orthogonal to the left-right direction is circular like the magnetic shield S1 in FIG. . That is, in the magnetic shield 10, curved surfaces are provided in any of the front-rear direction and the vertical direction in FIG.

  In the foreign matter detection device 1 of the present embodiment, in order to convey the workpiece W to be inspected, it is necessary to provide openings such as the loading port 14 and the unloading port 15. However, when such an opening is provided, the magnetism is likely to penetrate from there, and the problem of the shielding effect of the magnetism from the direction in which the opening is provided is reduced. In this embodiment, in order to enhance the shielding effect to the magnetism from the direction in which the opening is provided, a configuration in which the opening is formed on the curved surface is adopted. In this embodiment, as shown in FIG. 1, a cylindrical magnetic shield is horizontally disposed. However, for example, a vertically arranged magnetic shield 10A as shown in FIG. 5 is employed. You may In the magnetic shield 10 </ b> A, an opening for transporting the work W is formed along the circumferential direction of the magnetic shield 10.

  Here, magnetic lines of force toward the opening will be described with reference to FIG. FIG. 6 is a schematic view showing a direction in which magnetic lines of force toward the opening bend. First, as shown in FIG. 6A, among the magnetic lines of force toward the opening (longitudinal direction in FIG. 1), the magnetic lines near the long side are drawn to the magnetic shield 10 and bent in the vertical direction of FIG. On the other hand, as shown in FIG. 6 (B), among the magnetic lines of force toward the opening (longitudinal direction in FIG. 1), the magnetic lines near the short side are drawn to the magnetic shield 10 and bent in the lateral direction of FIG.

  In the present embodiment, the openings (the loading port 14 and the unloading port 15) for transporting the workpiece W are formed along the axial direction of the magnetic shield 10, and the traveling direction of the magnetic lines of force shown in FIG. The circumferential direction of the magnetic shield 10 is obtained. In this case, as in the case where the magnetic lines of force collide with the curved surface (see FIG. 4), the magnetic lines of force traveling in this direction will pass through the material of the magnetic shield 10 (bypassing the inner space). On the other hand, the traveling direction of the magnetic lines of force shown in FIG. 6B is the axial direction of the magnetic shield 10. In this case, as in the case where the lines of magnetic force collide with the plane, the lines of magnetic force traveling in this direction may pass through the magnetic shield 10 and enter the internal space.

  On the other hand, in the magnetic shield 10A of FIG. 5, an opening for transporting the work W is formed along the circumferential direction of the magnetic shield 10A, and the traveling direction of magnetic lines of force shown in FIG. It becomes an axial direction. In this case, as in the case where the lines of magnetic force collide with the plane, the lines of magnetic force traveling in this direction may pass through the magnetic shield 10A and enter the internal space. On the other hand, the traveling direction of the magnetic force lines shown in FIG. 6B is the circumferential direction of the magnetic shield 10A. In this case, as in the case where the magnetic lines of force collide with the curved surface (see FIG. 4), the magnetic lines of force traveling in this direction will pass through the material of the magnetic shield 10A (bypassing the inner space).

  From the above, when the elongated openings (the inlet 14 and the outlet 15) for transporting the workpiece W are provided, the magnetic shield 10 of FIG. 1 is more in comparison with the magnetic shield 10A of FIG. The magnetic lines of force can be shielded (or diverted). Therefore, as in the present embodiment, it is preferable that the elongated openings (the inlet 14 and the outlet 15) for transporting the work W be formed along the axial direction of the magnetic shield 10.

  As described above, in the magnetic shield 10 of the present embodiment, a cylindrical one having a curved surface in which an opening is formed is employed. Here, the size of the magnetic shield 10 in the radial direction is constant, but the diameter does not have to be constant in providing the curved surface as described above, and for example, the diameter approaches the middle of the axial direction May be thick.

  Further, although the magnetic shield 10 of the present embodiment has a circular cross-sectional shape in the radial direction, the present invention is not limited to this shape when providing the curved surface in which the opening is formed in the axial direction. For example, as in the magnetic shield S2 shown in FIG. 7A, when a magnetic shield having an elliptical cross section (or a combination of parabola) is used, the magnetic shield S1 shown in FIG. The shielding effect against magnetism can be enhanced. However, in this case, the shielding effect against the magnetism in the vertical direction of the drawing is smaller than that of the magnetic shield S1 shown in FIG. As described above, as the magnetic shield has a shape along the direction of the magnetic lines of force to be shielded, the magnetic lines of force can be passed through the material, so when shielding the magnetism from a specific direction as shown in FIG. By adopting a cross-sectional shape, the shielding effect can be enhanced. Further, as shown in FIG. 7 (B), as in the magnetic shield S3 in the shape of a racetrack whose cross section includes a straight line, the entire surface does not necessarily have to be a curved surface. However, when this magnetic shield S3 is employed, the shielding effect on the magnetism in the vertical direction of the figure is reduced compared to the magnetic shield S1 shown in FIG. Furthermore, the structure which combined the curved surface as shown to FIG. 7C may be sufficient, and a cross section as shown to FIG. 7D may be a thing of a semicircle. That is, as long as it is a hollow columnar magnetic shield having a curved surface in which the opening is formed, it is not limited to the cylindrical shape.

  As described above, in the case of a hollow columnar magnetic shield having a curved surface in which an opening is formed in the circumferential surface, the magnetic shielding effect on the side on which the opening is provided can be enhanced. Further, when the entire peripheral surface is formed as a curved surface as in the magnetic shield 10 of the present embodiment, for example, a curved surface is provided in the direction of detection of magnetism by the magnetic sensor (vertical direction in FIG. 1). In some cases, the impact can be reduced.

  Further, as in the present embodiment, when the magnetic shield 10 is formed by a curved surface, the magnetic shield 10 can be made more difficult to bend than when it is formed by a flat surface. If the magnetic shield 10 passing through magnetism is bent, it will be as if a magnetic field were generated, and the detection accuracy of the magnetic sensor unit 16 will be reduced, but in the present embodiment such problems can be made less likely to occur. . Furthermore, by using a curved surface, a larger space can be secured with less shielding material, and cost and weight can be reduced.

  Further, in the present embodiment, the work W is configured to go straight between the loading port 14 and the unloading port 15, but as shown in FIG. 8A, the direction of the work W is halfway along using the roller R or the like. The magnetic sensor unit 16 may be arranged at a position away from the loading port 14 or the unloading port 15 by changing it. Further, as shown in FIG. 8 (B), one opening may be shared as an inlet and an outlet.

  Moreover, in this embodiment, although the structure which makes the shield right end part 12 and the shield left end part 13 which were provided in the edge part of the magnetic shield 10 a plane is used, it is good also as a structure using a curved surface. In this case, the effect of shielding the magnetism from the end side can be enhanced. FIG. 9A shows a magnetic shield 10B employing a hemispherical shield right end 12B and a shield left end 13B as an example of this.

  Further, instead of the cylindrical shape as in the present embodiment, the entire shape of the magnetic shield may be spherical as in a magnetic shield 10C shown in FIG. 9 (B). In addition, with spherical shape here, a cross section may not be a circular thing but an elliptical thing.

  Further, for example, as in a magnetic shield 10D shown in FIG. 10A, a configuration in which a plurality of shield parts are combined may be adopted. FIG. 10A shows a magnetic shield 10D in which the first shield portion 10DA and the second shield portion 10DB are combined. Each of the first shield portion 10DA and the second shield portion 10DB is in the form of a hollow column as shown in FIG. 10B, and has a curved surface having an elongated opening in the axial direction on the circumferential surface And their axes are arranged to coincide with each other. Further, the first shield portion 10DA and the second shield portion 10DB are different in radial size from the adjacent shield portions, and as a result, as shown in FIG. A hollow columnar magnetic shield 10D can be configured as a whole in a state where a part of the surface is overlapped. At this time, as shown in FIG. 10A, by connecting the openings formed in each of the shield portions in the axial direction, the openings for transporting the work W can be formed in the axial direction. Although the example which combined two shield parts was explained in Drawing 10 (A), it may be three or more and it is not limited to two.

  In the case of combining the shield portions of a multilayer structure as in the magnetic shield 10 shown in FIG. 1, the radial sizes of the layers may be made different so that the layers of the adjacent shield portions do not collide with each other. For example, when each of the first shield portion 10DA and the second shield portion 10DB shown in FIG. 10A has a two-layer structure, the first shield portion 10DA of the first shield portion 10DA, the first shield portion 10DA, The second layer, the first layer of the second shield 10DB, and the second layer of the second shield 10DB may be overlapped in this order, or the first layer of the first shield 10DA, the second The first layer of the shield portion 10DB, the second layer of the first shield portion 10DA, and the second layer of the second shield portion 10DB may be overlapped in this order.

  In the magnetic shield combining the plurality of shield portions described above, the relative positional relationship between the shield portions in the axial direction may be changed. When this configuration is adopted, the length of the opening can be appropriately adjusted in accordance with the width of the work W by changing the relative positional relationship between the shield portions. FIG. 10C shows that the opening for transporting the workpiece W is smaller than that in FIG. 10A by bringing the shield portion closer than in FIG. When the shields are cylindrical as shown in FIG. 10A, one of the shields is rotated about the axis with respect to the other shields in a state where the peripheral surfaces of the shields are overlapped. You may be able to In this case, since the circumferential position of the opening formed in the shield part is shifted, the circumferential size of the opening as the entire magnetic shield can be reduced (the width can be narrowed).

  In addition, you may employ | adopt not only the structure of FIG.10 (C) but the other structure which can adjust the length of opening. For example, in order to narrow the opening of the foreign object detection device 1, a lid member may be provided using the same material as the magnetic shield 10 and closing at least one end side of the opening. By using this lid member, the magnetic shielding effect can be enhanced when the width of the work W is smaller than the opening.

[About the multilayer structure of the magnetic shield 10]
The magnetic shield 10 according to the present embodiment employs a shield circumferential surface portion 11 in three layers. The shield circumferential surface portion 11 may be a single layer, but by multilayering as in the present embodiment, the effect of shielding the magnetism can be enhanced. In addition, in order to suppress generation | occurrence | production of the noise by the vibration of the magnetic shield 10, you may be filled with the material which has the effect which prevents vibration, such as a urethane foam and sorboscein, between these layers.

  Further, in the vicinity of the opening of the magnetic shield 10 of the present embodiment, a diagram made of the same material as those layers between the first layer 111 and the second layer 112 or between the second layer 112 and the third layer 113 A shield member 17 as shown in 11 (A) may be provided so as not to be in contact with the respective layers. In this case, the number of shield layers in the vicinity of the opening of the magnetic shield 10E is set as shown in the cross-sectional views of FIG. 11B and FIG. The structure is increased locally, and the magnetic shielding effect can be enhanced. The thickness of this shield member may be the same as the thickness of each layer of the magnetic shield, or may be different.

[About the flux gate sensor]
Hereinafter, an example of a flux gate sensor employable as the magnetic sensor unit 16 will be described using the drawings.

  FIG. 13 is a block diagram showing the configuration of the flux gate sensor 2 that can be employed in the magnetic sensor unit 16 of the present embodiment.

  In the flux gate sensor 2, the frequency 2 f signal from the oscillator 201 is divided by a frequency divider 202 into one half to become a frequency f signal. This signal passes through an amplifier 203 for amplifying the current, a capacitor 204 for removing a direct current component, and a resistor 205, and an excitation coil 207 wound around a racetrack shaped core 206 using a high permeability material such as permalloy. , 208, an excitation current of frequency f is supplied. Here, the excitation current is not particularly limited, such as a rectangular wave, a sine wave, or a triangular wave, but is assumed to be large enough to saturate the magnetic flux in the core 206. That is, the above-mentioned exciting current repeats the change of the saturated and non-saturated state of the magnetic flux in the core 206. The exciting coils 207 and 208 are wound by the same number of turns in opposite directions to each of the parallel portions of the core. In addition, a detection coil 209 is wound around the outer circumference of the portion where the exciting coils 207 and 208 are wound.

  In the detection coil 209, when there is no influence of the external magnetic field, the magnetic fluxes generated in the excitation coils 207 and 208 cancel each other, and no induced current is generated in the detection coil 209. On the other hand, when the external magnetic field (the direction of the arrow in the figure) is present, a frequency component (frequency 2f) twice the frequency of the excitation current is output according to the strength. Therefore, the strength of the external magnetic field can be measured based on the component of frequency 2 f among the signals output from the detection coil 209.

  In the flux gate sensor 2, a signal from the detection coil 209 (hereinafter referred to as a detection signal) is input to the multiplier 212 through a capacitor 210 for removing a direct current component and an amplifier 211 for amplifying current. In the multiplier 212, the detection signal is multiplied with the signal of frequency 2 f from the oscillator 201. As a result, a DC component proportional to the magnitude of the frequency 2f component is obtained. In addition to this component, components of even multiples of the frequency f can be obtained, but passing these components through the low pass filter 213 is removed. Then, through the noise removal filter 214 and the loop filter 215, an output according to the strength of the external magnetic field is obtained. The output of the loop filter 215 is input to the voltage-current converter 216 (for example, a resistor), and the feedback current Ifb output from the voltage-current converter 216 is supplied to the detection coil 209. A circuit in which a current resulting from the output of the detection coil 209 is fed back to the detection coil 209 is referred to as a feedback loop.

[About feedback loop]
In the above feedback loop, the input voltage (hereinafter, Ve) to the loop filter 215 is influenced by the magnetic flux from the external magnetic field and the magnetic flux from the feedback current Ifb, and is minimized if these fluxes are canceled in the core 206. The magnitude of the feedback current Ifb is determined by the output voltage (hereinafter, Vc) from the loop filter 215. The loop filter 215 outputs a voltage proportional to the strength of the external magnetic field, but this output can also be used as a voltage for canceling the magnetic flux due to the external magnetic field, for example, an integrator and amplifier (PI control Can be composed of

  Here, a case where an integrator is used as the loop filter 215 will be described as an example. When the magnetic flux due to the external magnetic field is not canceled by the magnetic flux due to the feedback current Ifb (when the voltage Ve is not minimum), the feedback current Ifb increases according to the magnitude of the voltage Ve. When the feedback current Ifb increases, the magnetic flux due to the external magnetic field of the core 206 is gradually offset by the magnetic flux of the detection coil 209 generated accordingly, and the voltage Ve is decreased. When the magnetic flux due to the external magnetic field is canceled by this operation, the voltage Ve is minimized and the value of the feedback current Ifb is maintained. With this configuration, the feedback current Ifb becomes a current having a magnitude that causes the core 206 to generate a magnetic flux that cancels the external magnetic field, and the loop filter 215 outputs a value reflecting the magnitude of the external magnetic field.

[About the noise removal filter in the feedback loop]
In the foreign matter detection device 1 of the present embodiment, a so-called passive magnetic shield 10 is employed. Other types of magnetic shields include those using the Meissner effect due to superconductivity and those using an active magnetic shield that cancels the magnetic field, but because the apparatus becomes large and the cost increases, It may not be easy to install. In the foreign matter detection device 1 of the present embodiment, such a problem is small and versatility is high, but the magnetism can not be shielded sufficiently as compared with other magnetic shields as described above, and noise may sometimes be affected.

  Here, the problem in the case where the detection signal on which such noise is superimposed is input to the loop filter 215 will be described. For example, in the foreign matter detection device 1 according to the present embodiment, in order to detect a smaller metal foreign matter mixed in the work W, it may be required to detect minute magnetism. It is conceivable to increase the amplification factor. However, even if the amplification factor of the loop filter 215 is set large, it can not be amplified beyond the output range, and the output is saturated if the input voltage is too large. That is, when the amplification factor of the loop filter 215 is increased, the range of the input voltage that can be amplified is substantially narrowed.

  For example, in order to detect a signal as shown in FIG. 14A, it is assumed that the amplification factor in the loop filter 215 is set so that the signal in the range of ± Va falls within the output range ± Vb of the loop filter 215. As a result, the range of input voltage that can be amplified is substantially ± Va.

  FIG. 14B shows an example of noise having a portion exceeding the range of ± Va which is the range of the input voltage. Further, FIG. 14 (C) shows a waveform in which the noise shown in FIG. 14 (B) is superimposed on the signal shown in FIG. 14 (A), but in this waveform, ± Va in FIG. It has been shown that the pulses that were within the range extend outside the range of ± Va. In the loop filter 215, the amplification factor corresponding to the input voltage up to the range of ± Va is set. Therefore, when the signal shown in FIG. 14C is input, the upper limit and the upper limit as shown in FIG. The output may be saturated and the pulse may disappear in the part beyond the lower limit (± Vb). In this case, the detection signal shown in FIG. 14A can not be obtained even if the noise removal filter is subsequently passed.

  As described above, depending on the amplification factor of the loop filter 215, a phenomenon in which part of the signal does not appear may occur (hereinafter, clipping). For this reason, in the flux gate sensor 2 shown in FIG. 13, a noise removal filter for attenuating noise components is provided at a stage before the loop filter 215. In FIG. 14E, the waveform is within the range of ± Vb by applying a noise removal filter to the signal shown in FIG. 14C to attenuate the noise component and then amplifying it with the loop filter 215. It is shown. By adopting this configuration, unnecessary and large signals can be attenuated before being input to the loop filter 215, and as shown in FIG. 14E, the signals can be contained within the available range so that clipping is less likely to occur. . Thereby, the dynamic range can be made wide while maintaining the resolution of the measurement band.

  The flux gate sensor provided with the noise removal filter in the feedback loop described above is not limited to the case of using the foreign matter detection device as in the present embodiment, and an external magnetic field based on the output from the detection coil. Any flux gate sensor that generates a feedback current that cancels out can be employed. Further, the method of the flux gate sensor is not limited to the balanced flux gate sensor as shown in FIG. 13 but can be applied to the orthogonal flux gate sensor.

  Also, the noise targeted by the above noise removal filter is not particularly limited, but for example, it is intended to target large noise such as noise due to a 50 Hz or 60 Hz magnetic field generated by an AC power line. Is preferred. In addition, the configuration of the noise removal filter is not particularly limited, and a filter such as a notch filter, a band elimination filter, a high pass filter, or a combination thereof can be employed. The noise removal filter is not limited to an analog filter, and may be a digital filter.

[About the judgment unit]
When determining the presence or absence of a metal foreign object based on the output from the magnetic sensor unit 16, there is a method of determining whether or not the threshold value is exceeded. In this method, noise exceeding the threshold may be mixed depending on the place where the inspection is performed, and detection accuracy such as occurrence of false detection may be lowered.

  There is also a method of determining the average of the outputs of the plurality of magnetic sensors (the first sensor 161 to the fifth sensor 165), and determining whether the difference between the average and the output of each magnetic sensor exceeds a threshold. When this method is adopted, it is possible to eliminate noise with a small source with a small distance by difference. However, even with noise from the same source, the influence on each magnetic sensor may differ depending on the shape of the magnetic shield, the position of the magnetic sensor, etc., and the above method may not be able to exclude the influence of the noise. .

  Therefore, in order to eliminate the influence of such noise and perform more accurate detection, the output of the magnetic sensor in the absence of the workpiece W is used as a reference, and in the actual inspection, based on the difference with this reference It is preferable to adopt a configuration for determining whether or not foreign matter is mixed. Hereinafter, a determiner which is an example of such a configuration will be described with reference to FIG.

  Based on the output signal from the magnetic sensor unit 16 (one of the first sensor 161 to the fifth sensor 165), the determiner 3 shown in FIG. 15 determines whether metal foreign matter is mixed or not, and the result Outputs a determination signal based on In this determination unit 3, two operation modes are provided: a reference generation mode for generating reference data to be a determination reference, and a determination mode for determining whether metal foreign matter is mixed using the reference data. It is done. These operation modes are switched based on a signal (mode signal) from mode switching means (not shown) such as an input device operable by the user. Although this determination unit 3 is configured to output the mode signal based on the input from the user, the mode signal is output based on the input from the sensor that determines whether the work W is being transported. As in the configuration described above, the mode signal may be switched automatically without any operation. For example, when a magnetizing device for magnetizing the work W is separately provided, the mode signal may be switched in conjunction with the operating state of the magnetizing device.

  The determination unit 3 includes an AD conversion unit 301, a sampling unit 302, an FFT unit 303, a feature extraction unit 304, a reference generation unit 305, a distance calculation unit 306, and a determination unit 307.

  The signal from the magnetic sensor unit 16 input to the determination unit 3 is converted into a digital signal by the AD conversion unit 301 and then sampled by the sampling unit 302 at a predetermined cycle. The discrete Fourier transform is performed on the sampled data by the FFT unit 303, and the result of the frequency analysis is output to the feature extraction unit 304. Although Fourier transform is used in this example, wavelet transform may be performed, for example, as long as frequency analysis is performed. Also, the window function is not particularly limited, and various known window functions can be used.

  The feature extraction unit 304 selects, from the frequency analysis result by the FFT unit 303, a component having a power spectrum equal to or greater than a predetermined threshold. This data is sent to both the reference generation unit 305 and the distance calculation unit 306.

  While receiving the mode signal indicating the reference generation mode, the reference generation unit 305 generates or updates reference data using the data from the feature extraction unit 304. The details of the reference data will be described later with reference to FIG. Further, while receiving the mode signal indicating the determination mode, generation of reference data and the like are not performed, and the latest reference data is sent to the distance calculation unit 306.

  While receiving the mode signal indicating the determination mode, the distance calculation unit 306 calculates the distance between the reference data generated by the reference generation unit 305 and the data from the feature extraction unit 304.

  In the determination unit 307, when the distance calculated by the distance calculation unit 306 is equal to or greater than a predetermined threshold (or when it exceeds the threshold), a predetermined signal is output. Note that the present invention is not limited to this configuration, and different signals may be output when the distance calculated by the distance calculation unit 306 is equal to or greater than a predetermined threshold (or when it exceeds the threshold). . In any case, any signal may be output based on whether the distance calculated by the distance calculation unit 306 is equal to or greater than a predetermined threshold (or whether the threshold is exceeded). In this configuration, two types of information (for example, detection of metallic foreign matter and non-detection of metallic foreign matter) can be made distinguishable by providing one threshold that is a condition of signal output. A plurality of such threshold values may be provided to output a plurality of types of determination signals corresponding to more information.

[Operation example of reference generation mode]
Hereinafter, an example of the operation in the reference generation mode will be described. In the reference generation mode, reference data is generated or updated (reference generation unit 305).

  In the foreign matter detection device 1, when there is no influence of external magnetism and the work W is not transported, the output of the magnetic sensor unit 16 is 0 if there is no magnetic noise, but various magnetic noises actually exist. Therefore, the output from the magnetic sensor unit 16 in this case is due to the magnetic noise. Here, by generating reference data in which the feature of the magnetic noise is reflected, it is possible to detect a metal foreign object by comparison with the reference data. In the following, the case of generating reference data reflecting the characteristics of magnetic noise will be described.

  The reference data is a characteristic power spectrum stored for spectrum numbers, and the initial value is zero. Here, it is assumed that the result of the frequency analysis shown in FIG. 16 (A) is obtained. The result of the frequency analysis shown in FIG. 16A is for the output from the magnetic sensor unit 16 in the state where the work W is not conveyed. From the result of this frequency analysis, a threshold of 0 dB is selected, and frequency components (spectrum Nos. 132 and 278) of the power spectrum exceeding this threshold are selected. Then, among the reference data, the power spectrum of the reference data corresponding to these components is updated to the value of the power spectrum of the selected component. This updated reference data is shown in FIG. 16 (B). This reference data reflects two large frequency components that are characteristic of magnetic noise. Note that this threshold is an example and can be set as appropriate. Alternatively, a predetermined number of components may be selected in order of the power spectrum size without using a threshold, and the method of feature extraction is not particularly limited.

  During the reference generation mode, the result of the frequency analysis is sequentially generated based on the signal from the magnetic sensor unit 16, and the reference data is sequentially updated using this result. Specifically, the value of the power spectrum exceeding the threshold is selected, and the power spectrum of the portion corresponding to the selected frequency component in the reference data is updated to the value of the selected power spectrum. The power spectrum of the reference data corresponding to the component below the threshold is updated to zero.

  In the case of the above configuration, when sudden magnetic noise occurs, reference data reflecting this may be created, and the determination accuracy of the metal foreign object may decrease. Therefore, for example, reference data may be created using the average value of the power spectrum in multiple frequency analysis results instead of one time, or data of frequency components exceeding the threshold may be prepared multiple times, and these average values may be used. Reference data may be created. Alternatively, the reference data may be updated by weighting each of the immediately preceding reference data and the frequency component exceeding the newly selected threshold value. With regard to this weight, by increasing the ratio of the new extracted component to the immediately preceding reference data, the degree to which the above change is reflected increases in proportion to this. These configurations can be appropriately set according to the state of the magnetic noise.

  In addition, it is also possible to use the result of frequency analysis as reference data as it is, without performing feature extraction by selection of a power spectrum like the above-mentioned example.

[Operation example of judgment mode]
Hereinafter, an example of the operation in the determination mode will be described. In the determination mode, after calculating the distance indicating the degree of difference of the reference data with respect to the result of frequency analysis obtained from the output from the magnetic sensor unit 16 (distance calculation unit 306), the determination signal is output based on this distance Then (determination unit 307).

  For example, it is assumed that the result of the frequency analysis shown in FIG. 17A is obtained for the output from the magnetic sensor unit 16 in the state where the work W is being transported. In the determination mode, from the result of the frequency analysis, 0 dB is used as a threshold, and frequency components (spectrum No. 44, 132, 205, 278, 405) of the power spectrum exceeding this threshold are selected. This selected frequency component is shown in FIG. 17 (B).

  Next, the distance to the reference data is calculated with the selected frequency component as the determination target. Here, as shown in FIG. 18, the absolute value of the difference between the reference data whose power spectrum is not 0 (No. 132, 278) and the determination target (No. 44, 132, 205, 278, 405) Is calculated and the sum is taken as the distance. When there is no component in the determination target corresponding to one whose power spectrum is not 0 among the reference data, calculation is performed assuming that the power spectrum of the frequency component in the determination target is 0. As a result, in the example of FIG. 18, it is shown that 38.8 is derived as the value of the distance. Although the distance is calculated by selecting frequency components exceeding the threshold value in this example, the distance may be calculated using the result of frequency analysis as it is without selecting a specific component. Although the distance obtained by the above-described distance calculation is the Manhattan distance, the distance here is not particularly limited, and may be Euclidean distance or the like.

  Once the distance is calculated, a predetermined signal is output if this value is greater than or equal to the threshold. For example, as a result of trial calculation of the distance using the above-mentioned reference data in advance, it becomes clear that it becomes about 20 or more if the metal foreign substance is included, and this value is set as the threshold value. In this case, the distance 38.8 is equal to or greater than the threshold 20, and a predetermined signal is output. The foreign matter detection device 1 can be notified that there is a possibility that metal foreign matter is mixed in by receiving an output of this signal to indicate that the foreign matter is detected.

[About the effect and modification of the judgment unit]
According to the determiner 3 described above, background noise can be reduced from a signal at the time of an actual inspection, so that the S / N ratio can be improved and detection accuracy can be improved. Also, learning of background noise (generation of reference data) makes the difference between the background noise and the detection signal clearer, and the threshold can be easily determined.

  In addition, although the foreign material detection apparatus 1 of this embodiment is for detecting the metal foreign material of the sheet-like workpiece | work W, said determination device 3 detects the metal foreign material of the workpiece | work conveyed by a conveyor, for example. It can also be adopted as a foreign matter detection device. For example, in order to switch the mode signal in conjunction with the operation state of the magnetizing device of the work conveyed by the conveyor, when the required time from the magnetizing device to the magnetic sensor is n seconds, The reference generation mode may be switched to the determination mode at a timing n seconds (or around n seconds) after the work passes the magnetizing device. Note that this configuration can be said to switch between the reference generation mode and the determination mode based on the position of the work. In this configuration, the reference generation mode and the determination mode can be switched as needed, and reference data can be effectively generated to improve detection accuracy.

  Moreover, although the above-mentioned determination device 3 demonstrated the structure using the reference data which reflected the feature of the magnetic noise, the feature of the state in which the metal foreign material was mixed is reflected by using the work in the state in which the metal foreign material was mixed. The reference data may be generated and used to calculate the distance. In this configuration, as the distance decreases, the possibility that metal foreign matter is mixed increases. Therefore, a signal is output when the threshold is not exceeded, and an output indicating that the foreign matter is detected is performed in response to this signal. The foreign substance detection device may be configured as follows.

  Further, for example, a first reference generation mode and a second reference generation mode are prepared so that a plurality of reference data can be used, and in each of these modes, the first reference data is generated as the second reference data. You may In this configuration, it is possible to prepare, for example, first reference data reflecting the characteristics of magnetic noise in the absence of a work and second reference data reflecting the characteristics of the state in which metal foreign matter is mixed. In this case, if the above distance calculation is performed on each reference data and a signal is output according to the magnitude of the distance, it is determined which state is closer by the output of the signal. Can. In this case, the threshold value as in the case of one reference data becomes unnecessary.

  In addition, when the determination unit 307 outputs a signal, it is preferable to separately store the reference data used for calculating the distance and the result of the frequency analysis before and after the output of the signal. In this configuration, it is possible to determine a more appropriate threshold value, a method of feature selection, a method of distance calculation, and the like based on the stored information, and it is possible to improve detection accuracy.

[Others]
Although the above-described foreign matter detection device 1 is directed to a sheet-like work W, for example, the above-described configurations can also be adopted when targeting a plate-like work transported by a conveyor.

  Hereinafter, the configuration of the invention described in the present specification will be shown. In addition, the structure of said embodiment corresponding to the structure of the following invention is described in parentheses.

In the above description,
A magnetic sensor (for example, the first sensor 161 to the fifth sensor 165) for detecting the magnetism of a sheet-like or plate-like workpiece (for example, the workpiece W);
A magnetic shield (eg, magnetic shield 10) covering the magnetic sensor;
The magnetic shield is
A hollow column (see FIG. 1 and FIG. 2) having a curved surface (for example, the shield circumferential surface portion 11) on the circumferential surface,
The foreign substance detection device is characterized in that a transfer port (e.g., the loading port 14 and the output port 15) which is an elongated opening for transporting the work is formed on the curved surface.

  According to the foreign matter detection device, the detection accuracy of the metal foreign matter can be hardly reduced.

In the foreign matter detection device described above,
The magnetic shield is
The foreign substance detection device is characterized in that the transport port is formed on the curved surface along an axial direction (see FIG. 1).

  According to the foreign matter detection device, the detection accuracy of the metal foreign matter can be further reduced.

In the foreign matter detection device described above,
The magnetic shield is
A plurality of shield sections which are hollow columns and have curved surfaces in which elongated openings are formed along the axial direction on the circumferential surface, and the respective axes coincide (for example, the first shield section 10DA and With a second shield 10DB),
The plurality of shield parts are
The size in the radial direction is different from that of the other adjacent shield part (in FIG. 10, the size in the radial direction of the first shield part 10DA and the second shield part 10DB is different),
At least a portion of each circumferential surface overlaps at least a portion of the circumferential surface of the other adjacent shield portion, and the opening formed in each is axially connected to the opening formed in the other adjacent shield portion Can form the transfer port (see FIG. 10A),
Furthermore, the plurality of shield parts are
The foreign substance detection device is characterized in that the positional relationship in the axial direction can be changed with respect to other shield parts (see FIG. 10C).

  According to the foreign matter detection device, the size of the transfer port can be changed in accordance with the width of the work.

In the foreign matter detection device described above,
The foreign substance detection device is characterized in that the shape at the end of the magnetic shield is a curved surface curved outward (for example, the shield right end 12B and the shield left end 13B in FIG. 9A). .

  According to this foreign matter detection device, it is possible to suppress the entry of magnetism from the shield end.

Also,
A magnetic sensor (for example, the first sensor 161 to the fifth sensor 165) for detecting the magnetism of a sheet-like or plate-like workpiece (for example, the workpiece W);
A magnetic shield (for example, a magnetic shield 10C of FIG. 9B) covering the magnetic sensor;
The magnetic shield is
Hollow and spherical,
The foreign substance detection device is characterized in that a transfer port which is an elongated opening for transferring the work is formed (see a modification of FIG. 9B).

  According to the foreign matter detection device, the detection accuracy of the metal foreign matter can be hardly reduced.

In the foreign matter detection device described above,
A foreign material detection device comprising the same material as the magnetic shield and having a lid member for closing an end of the portion where the transfer port is formed (see [about the shape of the magnetic shield 10]); Is described.

  According to the foreign matter detection device, the size of the transfer port can be changed in accordance with the width of the work.

In the foreign matter detection device described above,
The magnetic shield is
It has a plurality of shield layers (for example, the first layer 111, the second layer 112, and the third layer 113),
Each of the plurality of shield layers is
A foreign matter detection device is described, which is characterized in that it is not in contact with each other.

  According to the foreign matter detection device, the shielding effect of magnetism by the magnetic shield can be enhanced.

In the foreign matter detection device described above,
The magnetic shield is
A foreign matter detection device characterized in that a shield member (for example, a shield member 17) not in contact with the shield layer is provided between the plurality of shield layers in a portion where the transfer port is formed; Have been described.

  According to the foreign matter detection device, the shielding effect of magnetism by the magnetic shield can be enhanced.

In the foreign matter detection device described above,
The magnetic shield is
A foreign substance detection device is described, which is characterized in that an anti-vibration material is filled between adjacent shield layers (refer to [Multilayer structure of the magnetic shield 10]).

  According to this foreign matter detection device, it is possible to prevent the generation of noise due to the vibration of the magnetic shield.

Also, in the above explanation,
In a flux gate sensor (for example, flux gate sensor 2 in FIG. 13) having a feedback loop that cancels an external magnetic field by a current correlated with an output signal,
A fluxgate sensor characterized in that a noise suppression filter (for example, the noise removal filter 214 in FIG. 13) for suppressing noise is provided in the feedback loop.

  According to this flux gate sensor, clipping can be prevented from occurring in the feedback loop, and a wide dynamic range can be taken while maintaining the resolution of the measurement band.

In addition, the flux gate sensor described above,
The noise suppression filter is
A fluxgate sensor is described which is characterized in that it suppresses noise of 50 Hz or 60 Hz (see [about noise removal filter in feedback loop]).

  According to this flux gate sensor, since it is possible to remove large noise generated by the 50/60 Hz AC power line, it is possible to effectively suppress the occurrence of clipping.

In addition, the flux gate sensor described above,
The noise suppression filter is
A fluxgate sensor is described which is characterized in that it includes any of a notch filter, a band elimination filter, and a high pass filter (see [about noise removal filter in feedback loop]).

  According to this flux gate sensor, various filters can be used.

In addition, the flux gate sensor described above,
The noise suppression filter is
A fluxgate sensor is described, characterized in that it is composed of a digital filter (see [About noise removal filter in feedback loop]).

  According to this flux gate sensor, the S / N ratio can be increased.

Also, in the above explanation,
In a foreign matter detection device (for example, the foreign matter detection device 1) having a magnetic sensor (for example, the first sensor 161 to the fifth sensor 165) for detecting the magnetism of the work (for example, the work W)
Frequency analysis means (for example, FFT unit 303 in FIG. 15) that analyzes the frequency of the signal from the magnetic sensor;
Mode switching means (for example, an input device etc. which can be operated by the user) for switching between the reference generation mode and the determination mode;
A data generation unit (for example, a reference generation unit 305 in FIG. 15) that generates or updates reference data indicating the feature of the signal using the result of frequency analysis by the frequency analysis unit when the reference generation mode is set. )When,
Distance calculation means (for example, distance calculation unit 306 in FIG. 15) for calculating distance using the result of frequency analysis by the frequency analysis means and the reference data when the determination mode is set;
And an output unit (e.g., the determination unit 307 in FIG. 15) configured to output a predetermined signal based on whether the distance exceeds a predetermined threshold value. There is.

  According to the foreign matter detection device, the detection accuracy of the metal foreign matter can be enhanced.

In the foreign matter detection device described above,
The mode switching means is
The foreign substance detection device is characterized in that the reference generation mode and the determination mode are switched based on the position of the work (refer to [effects of determination unit and modified example]).

  According to the foreign matter detection device, it is possible to switch between the reference generation mode and the determination mode as needed, and it is possible to effectively generate reference data and to improve detection accuracy.

In the foreign matter detection device described above,
Storage means for storing information;
The storage means is
It stores the reference data used when outputting the predetermined signal, the signal from the magnetic sensor before and after the output, or the result of the frequency analysis by the frequency analysis unit before and after the output ([Determination Device, and the above-mentioned foreign matter detection device is described.

  According to the foreign matter detection device, it is possible to determine a more appropriate threshold value, a method of feature selection, a method of distance calculation, and the like based on the stored information, and it is possible to improve detection accuracy.

Also,
In a foreign matter detection device having a magnetic sensor for detecting the magnetism of a work,
Frequency analysis means for frequency analyzing a signal from the magnetic sensor;
Mode switching means for switching and setting the first reference generation mode, the second reference generation mode, and the determination mode;
First data generation means for generating or updating first reference data indicating characteristics of the signal using the result of frequency analysis by the frequency analysis means when the first reference generation mode is set; ,
And second data generation means for generating or updating second reference data indicating characteristics of the signal using the result of the frequency analysis by the frequency analysis means when the second reference generation mode is set. ,
When the determination mode is set, the first distance is calculated using the result of the frequency analysis by the frequency analysis means and the first reference data, and the result of the frequency analysis by the frequency analysis means Distance calculation means for calculating a second distance using the second reference data;
A foreign matter detection device characterized by comprising: an output means for outputting a predetermined signal when the first distance is larger than the second distance; ) Is described.

  According to this foreign matter detection device, it can be determined whether or not any reference data is close, and a threshold as in the case of one reference data becomes unnecessary.

In the foreign matter detection device described above,
Storage means for storing information;
The storage means is
The first reference data used in the output of the predetermined signal, the second reference data used in the output, and the signal from the magnetic sensor before and after the output or before and after the output A foreign substance detection device is described, which stores the result of the frequency analysis by the frequency analysis means in the above (refer to [the effect of the determination unit and the modified example]).

  According to this foreign matter detection device, it is possible to determine a more appropriate method of feature selection and distance calculation based on the stored information, and it is possible to improve detection accuracy.

DESCRIPTION OF SYMBOLS 1 Foreign object detection apparatus 10 Magnetic shield 11 Shield peripheral surface part 12 Shield right end part 13 Shield left end part 14 Inlet 15 Out port 16 Magnetic sensor part 17 Shield member 2 Flux gate sensor 214 Noise removal filter 3 Judgment unit 303 FFT unit 305 Reference generation part 306 Distance calculation unit 307 Determination unit

Claims (4)

In a flux gate sensor having a feedback loop that cancels the external magnetic field by the current correlated to the output signal,
A fluxgate sensor comprising a noise suppression filter for suppressing noise in the feedback loop. A flux gate sensor according to claim 1, wherein
The noise suppression filter is
A flux gate sensor characterized by suppressing 50 Hz or 60 Hz noise. A flux gate sensor according to claim 1 or 2, wherein
The noise suppression filter is
A flux gate sensor characterized by including any of a notch filter, a band elimination filter, and a high pass filter. The flux gate sensor according to any one of claims 1 to 3, wherein
The noise suppression filter is
A flux gate sensor characterized by comprising a digital filter.

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