JP2017053635A - Flaw detection probe and flaw detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect properly change of a magnetic field, even when having continuous fine ruggedness on a metal surface.SOLUTION: A flaw detection probe 12 includes a substrate 20, four magnetic sensors 24a, 24b, 24c, 24d for detecting a magnetic field in a surface direction on an arranged surface, and a signal output part 26 for outputting a signal based on a relative amount of each detection result by the four magnetic sensors. Two sets of each combination of two magnetic sensors aligned in the search direction determined beforehand on the substrate surface, are arranged oppositely in a search orthogonal direction orthogonal to the search direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a flaw detection probe and a flaw detection method used for searching for a flaw on a metal surface.

  In some cases, a flaw detector is used to nondestructively search flaws on metal surfaces (JIS Z2300: 2009). In the flaw detection apparatus, for example, an eddy current is generated on the metal surface while moving the flaw detection probe in the search direction, a magnetic field due to the eddy current is detected by a detection coil, and a flaw on the metal surface is specified based on the change in the magnetic field. .

  However, the flaw detection apparatus detects not only the case where a flaw exists on the metal surface, but also the change in the magnetic field when the distance between the flaw detection probe and the metal surface changes. Therefore, even if a change in the magnetic field is detected, it cannot be distinguished whether it is caused by a flaw on the metal surface or a change in the distance between the flaw detection probe and the metal surface (hereinafter simply referred to as “lift-off”).

  In view of this, a technique has been proposed in which four detection coils are provided in the flaw detection probe, and the detection coils arranged diagonally are connected in opposite phases to cancel the effect of lift-off (for example, Patent Document 1).

JP-A-10-197493

  As described above, the use of a flaw detection probe having four detection coils can detect a change in the magnetic field due to a flaw on the metal surface. However, in such a flaw detection probe, since four detection coils must be arranged side by side on a plane, the occupied area becomes large. Then, when fine irregularities continue on the metal surface, the distance between each of the four detection coils and the metal surface is different, and again, the flaw detection probe is affected by lift-off, and the change in the magnetic field cannot be detected properly. End up.

  In view of the above problems, an object of the present invention is to provide a flaw detection probe and a flaw detection method capable of appropriately detecting a change in a magnetic field even when fine irregularities are continuous on a metal surface.

  In order to solve the above-described problem, a flaw detection probe according to the present invention includes a substrate, four magnetic sensors for detecting a magnetic field in the surface direction of the arranged surface, and a signal based on a relative amount of detection results of each of the four magnetic sensors. A combination of two magnetic sensors arranged in a predetermined search direction on the surface of the substrate so as to be opposed to the search orthogonal direction orthogonal to the search direction. It is characterized by.

  An excitation coil may be further provided, and the center axis of the excitation coil may be orthogonal to the surface of the substrate.

  A plurality of exciting coils may be juxtaposed so that the directions of currents flowing between adjacent parts are equal, and the four magnetic sensors may be arranged so as to overlap different exciting coils in a combination unit of two magnetic sensors. .

  A plurality of flaw detection units each including four magnetic sensors may be provided, and the magnetic sensors of at least two flaw detection units among the plurality of flaw detection units may be arranged so as to overlap the excitation coil with respect to one excitation coil.

  The four magnetic sensors may be arranged such that their longitudinal directions are orthogonal to the search direction.

  Individual magnetic sensors in a combination of magnetic sensors may have different positions in the search direction from individual magnetic sensors in other opposing combinations.

  In order to solve the above-described problem, the flaw detection method of the present invention includes a substrate and four magnetic sensors for detecting a magnetic field in the surface direction of the arranged surface, and has a predetermined search direction on the surface of the substrate. A signal based on the relative amount of the detection results of each of the four magnetic sensors, in which two combinations of two magnetic sensors are moved in the search direction with two pairs of flaw detection probes arranged opposite to the search orthogonal direction orthogonal to the search direction. Is output.

  According to the present invention, even when fine irregularities are continuous on the metal surface, it is possible to appropriately detect a change in the magnetic field and thus to appropriately search for a flaw on the metal surface.

It is explanatory drawing which shows schematic structure of a flaw detection apparatus. It is a figure for demonstrating the function of a signal output part. It is explanatory drawing which showed the other example of the flaw detection probe. It is explanatory drawing which showed the other example of the flaw detection probe. It is explanatory drawing which showed the other detection aspect of the flaw detection probe.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

(Flaw detection apparatus 10)
FIG. 1 is an explanatory diagram showing a schematic configuration of the flaw detection apparatus 10. In FIG. 1, the electrical connection between the elements is omitted for convenience of explanation. The flaw detection apparatus 10 includes a flaw detection probe (probe) 12 for detecting a magnetic field and a nondestructive device 14 that identifies a flaw on a metal surface based on a signal output from the flaw detection probe 12. Test equipment. Here, the flaw detection probe 12 that is a feature of the present embodiment will be described in detail, and description of the receiver 14 will be omitted.

  The flaw detection probe 12 includes a substrate 20, an excitation coil 22, a magnetic sensor 24, and a signal output unit 26. The flaw detection probe 12 is connected to the flaw detection apparatus 10 indicated by a white arrow in FIG. A signal corresponding to a flaw on the metal surface is output while moving in a predetermined search direction. The movement of the flaw detection probe 12 may be automatically executed by an electric mechanism or may be manually performed.

  The substrate 20 is formed of, for example, deformable plate-shaped FPC (Flexible Printed Circuits), and a thin copper foil is pasted on the surface thereof for electrical wiring. The substrate 20 can be deformed, but the electrical characteristics of the wiring do not change depending on the deformation.

  As shown in FIG. 1, two exciting coils 22 (exciting coils 22a and 22b) are formed on the surface 20a of the substrate 20 in a spiral shape (ground shape), and each generates an magnetic flux by flowing an alternating current. To do. In the present embodiment, an eddy current is generated on the metal surface by causing a current to flow through the exciting coil 22 with the flaw detection probe 12 approaching the metal to be measured.

  Further, here, in order to prevent the generated magnetic flux from being canceled, the directions of the currents flowing in the portions adjacent to each other (indicated by a one-dot chain line in FIG. 1) in the exciting coils 22a and 22b are made equal. The coil winding direction is determined. For example, when the current flows in the direction indicated by the dashed arrow in the excitation coil 22a, the current flows in the direction indicated by the dashed arrow also in the excitation coil 22b.

  Here, the reason why the two exciting coils 22 are arranged side by side on the surface 20a of the substrate 20 is as follows. That is, in the case where the exciting coil 22 is formed in a spiral shape, in order to realize the number of turns of the coil that can generate a magnetic flux necessary for searching for a flaw on the metal surface, it is more preferable to divide the exciting coil 22 into two. This is because the occupied area can be reduced (about ½) compared to the case where the two are formed. Thus, the exciting coils 22a and 22b can perform sufficiently strong excitation with a small occupied area.

  The magnetic sensor 24 is composed of a columnar (bar-shaped, columnar, linear) magneto-impedance element such as an amorphous magnetic wire having a total length of 2.2 mm and a diameter of 30 μm, and the longitudinal direction is the upper side of the substrate 20. It is arranged along the surface 20a. And the magnetic sensor 24 detects the change (disturbance) of the magnetic field of the surface direction of the surface (upper surface 20a of the board | substrate 20) arrange | positioned based on the magnetic impedance effect from which an impedance changes with an external magnetic field. In this example, a magneto-impedance element is used as the magnetic sensor 24, but a plate-like magneto-resistive element (magneto resistive element) that detects a change in the surrounding magnetic field based on the magneto-resistance effect in which the resistance is changed by an external magnetic field. ) And the like. However, the shape of the magnetic sensor 24 is not limited to the columnar shape or the flat plate shape described above, and various shapes of the magnetic sensor 24 can be used.

  In the present embodiment, four magnetic sensors 24 are prepared (magnetic sensors 24a, 24b, 24c, 24d), and a search is performed on a surface (surface 20a on the upper side of the substrate 20) orthogonal to the central axis of the excitation coils 22a, 22b. The combination of the two magnetic sensors 24 arranged in the direction (the combination of the magnetic sensors 24a and 24b or the combination of the magnetic sensors 24c and 24d) is arranged on the central axis of the excitation coils 22a and 22b indicated by the hatched arrows. Two sets are arranged opposite to the search orthogonal direction orthogonal to the search direction on the orthogonal plane. One flaw detection unit 30 is configured by the four magnetic sensors 24a, 24b, 24c, and 24d.

  Here, as shown in the enlarged view of FIG. 1, the distance d1 (the distance between the magnetic sensors 24a and 24b or the distance between the magnetic sensors 24c and 24d) of the magnetic sensors 24 for each combination is approximately equal. In addition, the four magnetic sensors 24a, 24b are arranged so that the distance d2 (distance between the magnetic sensors 24a, 24c, distance between the magnetic sensors 24b, 24d) of the magnetic sensors 24 facing each other in the combination is approximately equal. , 24c, 24d are arranged. Such arrangement and posture will be described in detail later.

  Each of the four magnetic sensors 24a, 24b, 24c, and 24d has a fixed positional relationship with the exciting coil 22, and independently detects a magnetic field due to an eddy current generated on the metal surface.

  The signal output unit 26 includes a plurality of differential amplifiers, and outputs signals based on the relative amounts of detection results of the four magnetic sensors 24a, 24b, 24c, and 24d.

  FIG. 2 is a diagram for explaining the function of the signal output unit 26. Here, as shown in FIG. 2A, three differential amplifiers 26a, 26b, and 26c are prepared. The output terminal of the magnetic sensor 24a is connected to the positive input of the differential amplifier 26a, and the output terminal of the magnetic sensor 24b is connected to the negative input of the differential amplifier 26a. Therefore, the difference (A−B) between the magnetic sensor 24a and the magnetic sensor 24b is output from the differential amplifier 26a. The output terminal of the magnetic sensor 24c is connected to the positive input of the differential amplifier 26b, and the output terminal of the magnetic sensor 24d is connected to the negative input of the differential amplifier 26b. Therefore, the differential amplifier 26b outputs the difference between the magnetic sensor 24c and the magnetic sensor 24d (C−D). Here, A, B, C, and D are the outputs of the magnetic sensors 24a, 24b, 24c, and 24d, respectively.

  Further, the output terminal of the differential amplifier 26a is connected to the positive input of the differential amplifier 26c, and the output terminal of the differential amplifier 26b is connected to the negative input of the differential amplifier 26c. Therefore, from the differential amplifier 26c, a signal obtained by subtracting the difference between the magnetic sensor 24c and the magnetic sensor 24d from the difference between the differential amplifier 26a and the differential amplifier 26b, that is, the difference between the magnetic sensor 24a and the magnetic sensor 24b. (AB)-(CD) is output. Further, the connection mode of the signal output unit 26 is not limited to the above case, and it is sufficient if the result is (AB)-(CD). For example, the calculation result of B + C is subtracted from the calculation result of A + D. For example, various connection modes can be used instead.

  Here, the positional relationship between the four magnetic sensors 24a, 24b, 24c, and 24d is such that, as described above, two combinations of the two magnetic sensors 24 arranged in the search direction are opposed to each other in the search orthogonal direction. The distance d1 of the magnetic sensor 24 for each combination is approximately equal, and the distance d2 of the magnetic sensors 24 facing each other is approximately equal (see the enlarged view of FIG. 1). In particular, here, the individual magnetic sensors 24 in the combination are different from the individual magnetic sensors 24 in the opposite other combinations (the magnetic sensor 24c for the magnetic sensor 24a and the magnetic sensor 24d for the magnetic sensor 24b). A case where the positions are equal (distance in search direction = 0) will be described.

  If the four magnetic sensors 24a, 24b, 24c, and 24d have the above positional relationship, even if the distance between the flaw detection probe 12 and the metal surface 50 increases as shown in FIG. Since the magnetic sensors 24a, 24b, 24c, and 24d are equally affected, the output of the differential amplifier 26c is not affected. Specifically, even if the outputs A, B, C, and D of the magnetic sensors 24a, 24b, 24c, and 24d are equally changed by α, the output of the differential amplifier 26c (((A + α) − (B + α)) − ((C + α) − (D + α))) = (A−B) − (C−D), and it can be understood that there is no influence of lift-off.

  Further, as shown in FIG. 2C, even when the flaw detection probe 12 rotates about the search direction as an axis, the change in the distance does not affect the output of the differential amplifier 26c. Specifically, even if the outputs A and B of the magnetic sensors 24a and 24b change equally by α and the outputs C and D of the magnetic sensors 24c and 24d change equally by β, the output of the differential amplifier 26c. (((A + α) − (B + α)) − ((C + β) − (D + β))) = (A−B) − (C−D), and it can be understood that there is no influence of lift-off.

  Further, as shown in FIG. 2D, even if the flaw detection probe 12 rotates about the search orthogonal direction as an axis, the change in the distance does not affect the output of the differential amplifier 26c. Specifically, even if the outputs A and C of the magnetic sensors 24a and 24c change equally by α and the outputs B and D of the magnetic sensors 24b and 24d change equally by β, the output of the differential amplifier 26c. (((A + α) − (B + β)) − ((C + α) − (D + β))) = (A−B) − (C−D), and it can be understood that there is no influence of lift-off.

  Thus, by arranging the four magnetic sensors 24a, 24b, 24c, and 24d as described above and generating a signal based on the relative amount ((AB)-(CD)) of the output. (Standard comparison method) Even if the distance between each magnetic sensor 24a, 24b, 24c, 24d of the flaw detection probe 12 and the metal surface changes with the change of the attitude of the flaw detection probe 12, the influence of the lift-off can be suppressed. It becomes possible.

  Therefore, the signal output unit 26 can output a signal changed based on a flaw only when a flaw exists on the metal surface, regardless of the presence or absence of lift-off. For example, when a flaw exists in a position close to any of the magnetic sensors 24a, 24b, 24c, and 24d on the metal surface, a magnetic field change due to the flaw occurs only in the magnetic sensor 24 that is close to the flaw, and as a result, Only the signal of the magnetic sensor 24 at the corresponding position appears as a signal of the differential amplifier 26c.

  Further, the four magnetic sensors 24a, 24b, 24c, and 24d are arranged on the wiring of the exciting coil 22 as shown in FIG. In particular, in this embodiment, the four magnetic sensors 24a, 24b, 24c, and 24d are different excitation coils in units of combination of the two magnetic sensors 24 (a combination of the magnetic sensors 24a and 24b and a combination of the magnetic sensors 24c and 24d). They are arranged so as to overlap 22a and 22b (with the same position in the surface direction of the substrate 20). That is, the magnetic sensors 24a and 24b are disposed on the exciting coil 22a, and the magnetic sensors 24c and 24d are disposed on the exciting coil 22b.

  With this arrangement, the distance between the metal position where the large eddy current is generated and the magnetic sensor 24 can be minimized, so that the change in the magnetic field of the eddy current generated by the exciting coil 22 can be detected with high sensitivity. .

  Further, as shown in FIG. 1, the four magnetic sensors 24a, 24b, 24c, and 24d are arranged such that their longitudinal directions are orthogonal to the search direction. Thus, by arranging the four magnetic sensors 24a, 24b, 24c, and 24d in the same posture, the sensitivity of the four magnetic sensors 24a, 24b, 24c, and 24d with respect to the eddy current can be unified. In addition, by setting the longitudinal direction to be orthogonal to the search direction, as a result, the longitudinal direction of the magnetic sensor 24 can be in a positional relationship parallel to the metal surface, and the magnetic field of the eddy current generated by the exciting coil 22 can be increased. The change can be detected with high sensitivity.

  In this embodiment, since the flaw detection probe 12 is composed of a small magnetic sensor 24 such as an MI sensor, the distance between the magnetic sensors 24 can be shortened (for example, flaw detection in the enlarged view of FIG. 1). (Occupied area of unit 30 (magnetic detection region) = 1.6 mm × 1.2 mm). Therefore, even when fine irregularities continue on the metal surface, it is possible to appropriately search for defects on the metal surface without being affected by lift-off.

  Further, as shown in FIG. 1, the excitation coil 22 can be divided into two, and the four small magnetic sensors 24a, 24b, 24c, and 24d can all be arranged on the excitation coil 22 (substrate 20). The flaw detection probe 12 can be downsized (for example, 5.6 mm × 2.8 mm).

(Modification 1)
In the above-described embodiment, as the positional relationship of the four magnetic sensors 24a, 24b, 24c, and 24d, the individual magnetic sensors 24 in the combination are replaced with the individual magnetic sensors 24 in the other combinations that are opposite to each other. The case where the position in the search direction is made equal to the sensor 24c and the magnetic sensor 24d) with respect to the magnetic sensor 24b has been described. However, even if the positions of the search directions of the magnetic sensors 24 are different, the influence of lift-off can be avoided as in the case where the positions of the search directions are the same.

  FIG. 3 is an explanatory view showing another example of the flaw detection probe 12. Here, as shown in FIG. 3A, the individual magnetic sensors 24a and 24b in the combination of the magnetic sensors 24 are respectively positioned in the search direction with the individual magnetic sensors 24c and 24d in the other opposing combinations. Are different. Specifically, the magnetic sensor 24a is positioned forward in the search direction from the magnetic sensor 24c, and the magnetic sensor 24b is positioned forward in the search direction from the magnetic sensor 24d.

  Here, as shown in the enlarged view of FIG. 3A, the distance d1 (the distance between the magnetic sensors 24a and 24b, the distance between the magnetic sensors 24c and 24d) of the magnetic sensors 24 for each combination is approximately equal. Similarly, the distance d2 (distance between the magnetic sensors 24a and 24c, the distance between the magnetic sensors 24b and 24d) of the magnetic sensors 24 facing each other in the combination is approximately equal, and the distance d3 in the search direction is also equal. Four magnetic sensors 24a, 24b, 24c, and 24d are arranged so as to be equal.

  If the four magnetic sensors 24a, 24b, 24c, and 24d have the above positional relationship, even if the distance between the flaw detection probe 12 and the metal surface is increased as shown in FIG. Since the sensors 24a, 24b, 24c, and 24d are equally affected, the output of the differential amplifier 26c is not affected as in the case where the positions in the search direction of the opposing magnetic sensors 24 are the same among the combinations described above. Further, as shown in FIG. 3C, even if the flaw detection probe 12 is rotated with the search direction as an axis, the change in the distance does not affect the output of the differential amplifier 26c.

  In addition, as shown in FIG. 3D, when the flaw detection probe 12 rotates around the search orthogonal direction, the flaw detection probe is different because the positions of the magnetic sensors 24a and 24b and the magnetic sensors 24c and 24d differ in the search direction. The change in the distance between the surface 12 and the metal surface has an unequal effect on the magnetic sensors 24a, 24b, 24c, 24d. However, even in this case, the change in the distance does not affect the output of the differential amplifier 26c. Specifically, it is assumed that the output C of the magnetic sensor 24c changes to α + β with respect to the change α of the output A of the magnetic sensor 24a. In this case, the output D of the magnetic sensor 24d changes to γ + β with respect to the change γ of the output B of the magnetic sensor 24b. Here, the output of the differential amplifier 26c (((A + α) − (B + γ)) − ((C + α + β) − (D + γ + β))) = (A−B) − (C−D), which has no influence. Understandable.

  In addition, by shifting the magnetic sensor 24a and the magnetic sensor 24c or the magnetic sensor 24b and the magnetic sensor 24d in the search direction in this way, not only a flaw having a size corresponding to one magnetic sensor 24 but also two Even if it is a linear flaw extending over the magnetic sensor 24 and extending in the search orthogonal direction, the signals are not canceled out by the two magnetic sensors 24 juxtaposed in the search orthogonal direction, so that detection is performed appropriately. It becomes possible.

(Modification 2)
In the above-described embodiment, an example in which one set of flaw detection units 30 including four magnetic sensors 24a, 24b, 24c, and 24d is provided in one flaw detection probe 12 has been described. However, the present invention is not limited to this, and a single flaw detection probe 12 may be provided with a plurality of flaw detection units.

  FIG. 4 is an explanatory view showing another example of the flaw detection probe 12. Here, five excitation coils 22a, 22b, 22c, 22d, and 22e are juxtaposed on the substrate 20 in the search orthogonal direction so that the directions of the currents flowing through the adjacent portions are equal. Here, four flaw detection units 30a, 30b, 30c, and 30d are arranged so that one flaw detection unit 30 straddles two adjacent exciting coils 22.

  Therefore, among the five excitation coils 22, the excitation coil 22b located inside is arranged so as to overlap the two flaw detection units 30a and the flaw detection unit 30b, and the excitation coil 22c overlaps the two flaw detection units 30b and the flaw detection unit 30c. Thus, the exciting coil 22d is arranged so as to overlap the two flaw detection units 30c and the flaw detection unit 30d.

  With the configuration in which the single excitation coil 22 is arranged so as to overlap with the plurality of flaw detection units 30, it is possible to form many flaw detection units 30 on the flaw detection probe 12 while suppressing the occupied area of the excitation coil 22. .

  Further, the configuration in which a plurality of flaw detection units 30 are juxtaposed in the search orthogonal direction makes it possible to search for a flaw in the width direction (search orthogonal direction) of the flaw detection probe 12 at a time with respect to the metal surface. Furthermore, since each of the plurality of flaw detection units 30 independently searches for a flaw on the metal surface, one flaw can be detected simultaneously by the plurality of flaw detection units 30, and the detection results can be complemented to each other. .

  As described above, in the flaw detection apparatus 10 of the present embodiment, even when fine irregularities are continuous on the metal surface, a change in the magnetic field is appropriately detected, and accordingly, a flaw on the metal surface is appropriately searched. It becomes possible.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various modifications and variations can be made within the scope of the claims, and these are of course within the technical scope of the present invention. Is done.

  For example, in the above-described embodiment, an example in which an eddy current is generated on the metal surface by the excitation coil 22 and the change in the magnetic field is detected by the magnetic sensor 24 has been described. However, the present invention is not limited to this case, and can be applied to various applications in which the magnetic sensor 24 detects a change in the magnetic field.

  For example, as shown in FIG. 5, when two magnetic poles (S pole and N pole) are arranged on a ferromagnetic material while being separated from each other by a predetermined distance, a magnetic flux as indicated by an arrow is generated by the magnetic poles. Here, as shown in FIG. 5, when a flaw 62 is generated on the ferromagnetic material surface 60, the magnetic flux flows so as to avoid the space due to the flaw 62, and thus a leakage magnetic flux 64 is generated on the ferromagnetic material surface 60. Therefore, the magnetic sensor 24 can detect the magnetic field of the ferromagnetic material surface 60 and determine that there is a flaw at the location where the leakage magnetic flux 64 is generated. Thus, the flaw detection probe 12 having the magnetic sensor 24 can detect various changes in the magnetic field.

  In the above-described embodiment, the configuration in which the magnetic sensor 24 is disposed on the surface of the substrate 20 that does not face the metal (the upper surface 20a) has been described. However, the position of the magnetic sensor 24 is not limited to that position. Instead, it may be provided on the surface (lower surface) of the substrate 20 facing the metal.

  The present invention can be used for a flaw detection probe and a flaw detection method used for searching for a flaw on a metal surface.

12 Flaw Detection Probe 20 Substrate 22 Excitation Coil 24 Magnetic Sensor 26 Signal Output Unit 30 Flaw Detection Unit

Claims (7)

A substrate,
Four magnetic sensors for detecting the magnetic field in the surface direction of the arranged surface;
A signal output unit that outputs a signal based on a relative amount of detection results of each of the four magnetic sensors;
With
2. A flaw detection probe characterized in that two sets of two magnetic sensors arranged in a predetermined search direction are arranged on the surface of the substrate so as to face each other in a search orthogonal direction orthogonal to the search direction. An excitation coil,
The flaw detection probe according to claim 1, wherein a central axis of the excitation coil is orthogonal to a surface of the substrate. A plurality of the exciting coils are juxtaposed so that directions of currents flowing between adjacent parts are equal,
The flaw detection probe according to claim 2, wherein the four magnetic sensors are arranged so as to overlap different excitation coils in a combination unit of the two magnetic sensors. A plurality of flaw detection units comprising the four magnetic sensors are provided,
The flaw detection probe according to claim 3, wherein a magnetic sensor of at least two flaw detection units among the plurality of flaw detection units is arranged so as to overlap the excitation coil with respect to one excitation coil.   5. The flaw detection probe according to claim 1, wherein the four magnetic sensors are arranged so that their longitudinal directions are orthogonal to the search direction. 6.   6. The flaw detection according to claim 1, wherein the individual magnetic sensors in the combination of the magnetic sensors are different in position in the search direction from the individual magnetic sensors in the other opposing combinations. probe. A substrate and four magnetic sensors for detecting a magnetic field in the surface direction of the arranged surface, and a combination of two magnetic sensors arranged in a predetermined search direction on the surface of the substrate is arranged in the search direction. Two flaw detection probes arranged opposite to the orthogonal search orthogonal direction are moved in the search direction;
A flaw detection method comprising outputting a signal based on a relative amount of detection results of each of the four magnetic sensors.

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