Eddy current flaw detection device

Abstract

The present invention provides an eddy current flaw detection device for eliminating noise signals caused by vibration of the eddy current flaw detection device, eccentricity or vibration of a detected object. The eddy current flaw detection device comprises: a pair of detection coils (10a, 10b) coaxially and separately arranged with the detected object (3); and a bridge circuit using each detection coil to form two sides of a bridge so that the magnetic fields generated by these detection coils (10a, 10b) have opposite phases, a pair of excitation coils (11a, 11b) are coaxially arranged with each detection coil (10a, 10b) in a manner of sandwiching the pair of detection coils (10a, 10b), and the distance (D) between the detection coil and the excitation coil arranged next to it is set to a distance at which the phase between the vibration noise signal excited by the excitation coil and detected by the detection coil located next to it becomes opposite to the phase between the vibration noise signal excited by the detection coil and detected by the detection coil.

Description

Technical Field

[0001] The present invention relates to an eddy current flaw detection device. In more detail, the eddy current flaw detection device of the present invention comprises a coil for generating eddy currents on the surface of a detected object and a signal processing unit for processing a signal caused by an impedance change of the coil, and inspecting defects of the detected object based on the signal. Background Art

[0002] For example, Patent Document 1 discloses an eddy current flaw detection device, in which a pair of detection coils are arranged non-contactingly and coaxially with a conductor serving as a detected object, a pair of resonant coils are arranged coaxially with each detection coil, and a capacitor circuit is provided in the resonant coil, so that the magnetic fields generated between the pair of detection coils are in phase with each other.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 2882856 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] In the eddy current flaw detection device described in the above-mentioned patent document 1, when there are no flaws or foreign matter inside the conductor, the induced currents flowing through the resonant coils cancel each other out and therefore do not change. In contrast, in the above-mentioned device, when there are flaws or foreign matter inside the conductor, the magnetic field generated by each detection coil will be biased, so the induced current values ​​generated by each resonant coil will be different, and when the different currents flow through, the resonant coil will resonate. As a result, the above-mentioned device can improve the signal-to-noise ratio (S / N ratio).

[0008] However, in the above-mentioned Patent Document 1, there is a problem that when a noise signal is generated by vibration of the eddy current flaw detection device or eccentricity or vibration of the object to be detected, the noise signal causes a decrease in the S / N ratio.

[0009] Furthermore, in Patent Document 1, each of the resonance coils also requires an amplifier circuit to amplify the output, so there is also a problem that the device is complicated.

[0010] The technical problem of the present invention is to provide an eddy current flaw detection device which can eliminate noise signals caused by vibration of the inspection device, eccentricity or vibration of the object to be inspected, without complicating the device.

[0011] Technical solutions adopted to solve technical problems

[0012] The present invention provides an eddy current flaw detection device, comprising: a pair of detection coils that are non-contacting and coaxially separated from the object to be detected; and a bridge circuit in which the detection coils form two sides of a bridge in order to make the magnetic field generated by the detection coils have opposite phases, a pair of excitation coils are coaxially arranged with the detection coils in the middle, and the distance between the detection coil and the excitation coil arranged next to it is set to: the distance of the phase change between the noise signal caused by eccentricity or vibration excited by the excitation coil and detected by the detection coil located next to it and the noise signal caused by eccentricity or vibration excited by the detection coil and detected by the detection coil.

[0013] In addition, the present invention preferably sets the distance between the detection coil and the excitation coil arranged next to it to be a distance at which the phases of the noise signal caused by eccentricity or vibration excited by the excitation coil and detected by the detection coil located next to it and the noise signal caused by eccentricity or vibration excited by the detection coil and detected by the detection coil become opposite.

[0014] In addition, the present invention is preferably configured to change the phase of the alternating current supplied to the excitation coil so that the phase of the noise signal caused by eccentricity or vibration detected by the detection coil located adjacent to the excitation coil caused by the alternating current supplied to the excitation coil becomes opposite to the phase of the noise signal caused by eccentricity or vibration detected by the detection coil caused by the alternating current supplied to the detection coil caused by the excitation coil.

[0015] In addition, the present invention may include: an oscillator; a power amplifier for amplifying the AC output from the oscillator; an excitation phase converter for converting the phase of the AC output from the oscillator; and an excitation power amplifier for amplifying the AC output from the excitation phase converter, the power amplifier providing AC power to the detection coil, and the excitation power amplifier providing AC power to the excitation coil.

[0016] In addition, the detected object is a round rod, the detection coil and the excitation coil are through coils, and the distance between the detection coil and the excitation coil arranged next to it is set based on the difference between the outer diameter of the round rod and the inner diameters of the detection coil and the excitation coil.

[0017] Furthermore, the present invention may include a probe arranged close to the detected object, wherein the probe is formed in a cylindrical or semi-cylindrical shape and has the detection coil and the excitation coil disposed therein.

[0018] Effects of the Invention

[0019] According to the present invention, it is possible to provide an eddy current flaw detection device that can eliminate noise signals caused by vibration of an inspection device and eccentricity or vibration of a test object and improve the S / N ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the eddy current flaw detection device and the object to be detected according to the present invention.

[0021] Figure 2A This is a schematic circuit diagram showing the structure of a detection coil portion of an eddy current flaw detection device according to the present invention.

[0022] Figure 2B This is a schematic circuit diagram showing the structure of an exciting coil portion of an eddy current flaw detection device according to the present invention.

[0023] Figure 3 This is a block diagram showing an eddy current flaw detection device according to the first embodiment of the present invention.

[0024] Figure 4 It is a schematic diagram for explaining a specific example of confirming the elimination of noise signals caused by the vibration of the eddy current flaw detection device of the present invention and the eccentricity or vibration of the object to be detected.

[0025] Figure 5 This is a measurement diagram showing the results of measuring the impedance change of the detection coil when the distance between the detection coil and the exciting coil arranged next to it is changed and the excitation of the detection coil and the excitation of the exciting coil are independent of each other.

[0026] Figure 6 This is an explanatory diagram showing a composite signal of the detection coil when the distance between the excitation of the detection coil and the excitation coil arranged next to it is changed and the excitation of the detection coil and the excitation of the excitation coil are independent of each other.

[0027] Figure 7 1 is an explanatory diagram showing the relationship between the distance and the phase when the distance between the detection coil and the exciting coil arranged next to the detection coil is changed.

[0028] Figure 8 This is a block diagram showing an eddy current flaw detection device according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0029] Next, the eddy current flaw detection device according to the embodiment of the present invention will be described in detail based on the drawings. The eddy current flaw detection device according to the present invention is not limited to the following embodiment, and can be appropriately modified within the scope of the gist.

[0030] like Figure 1As shown, the object to be detected 3 of the present invention is, for example, a conductor such as a pipe or a round rod. The probe 10 is arranged close to the object to be detected 3. The probe 10 is formed into a cylindrical or semi-cylindrical shape, and a pair of excitation coils 11a and 11b are provided inside the probe 10 in a manner that sandwiches a pair of detection coils 10a and 10b. In the present embodiment, the probe 10 is formed into a cylindrical shape. The pair of detection coils 10a and 10b and the pair of excitation coils 11a and 11b provided inside are composed of through coils.

[0031] The detection coils 10a, 10b and the exciting coils 11a, 11b are arranged in a non-contact and coaxially separated manner with the object to be detected 3. The probe 10 and the object to be detected 3 move relative to each other. That is, in some eddy current flaw detection devices, the probe 10 moves relative to the object to be detected 3 to inspect the object to be detected 3, while in some eddy current flaw detection devices, the object to be detected 3 moves relative to the fixed probe 10. In the eddy current flaw detection device of this embodiment, the probe 10 moves relative to the object to be detected 3 in the direction of the arrow in the figure to inspect the state of the surface of the object to be detected 3, etc.

[0032] In this embodiment, the object to be detected 3 is a round metal bar.

[0033] In this embodiment, the detection coils 10a and 10b are arranged with a distance D between them and the excitation coils 11a and 11b respectively arranged next to them. Figure 1 As shown in FIG. 1 , the exciting coil 11 a and the detecting coil 10 a and the exciting coil 11 b and the detecting coil 10 b are arranged at a distance D from each other. The distance D will be described later.

[0034] Next, refer to Figure 2A and 2B An outline of the circuit configuration of this embodiment will be described. Figure 2A is a schematic circuit diagram showing the structure of the detection coil portion of the eddy current flaw detection device involved in the present invention, Figure 2B This is a schematic circuit diagram showing the structure of an exciting coil portion of an eddy current flaw detection device according to the present invention.

[0035] like Figure 2A As shown, the bridge circuit 24 includes detection coils 10a, 10b and resistors 12a, 12b. The detection coils 10a, 10b are connected as two sides of the bridge circuit 24, and the resistors 12a, 12b are connected as the other two sides of the bridge circuit 24.

[0036] The AC power supply 30 ( Figure 3 The AC output of the oscillator 21 and the power amplifier 22 is supplied to the detection coils 10a and 10b via the bridge circuit 24, and the detected body 3 is excited to generate eddy current. The detection coils 10a and 10b are connected to the detection unit 31 (in Figure 3The phase detector 27 (in the figure) detects the impedance change caused by the change of the magnetic flux generated by the eddy current.

[0037] The detection coils 10a and 10b are differentially connected so that the generated magnetic fields are in opposite phases. In this embodiment, the detection coils 10a and 10b excite the object 3 and detect impedance changes caused by changes in magnetic flux generated by eddy current.

[0038] like Figure 2B As shown, the AC power source 30 (at Figure 3 The AC output of the oscillator 21 and the excitation power amplifier 23 is provided to the excitation coils 11a and 11b to excite the excitation coils 11a and 11b. The detection object 3 is excited by the excitation of the excitation coils 11a and 11b, and eddy current is generated. The excitation coil 11a is wound in such a way that the magnetic field generated is in phase with the detection coil 10a. The excitation coil 11b is wound in such a way that the magnetic field generated is in phase with the detection coil 10b.

[0039] The detection coil 10 a also detects impedance changes associated with changes in magnetic flux generated by the eddy current from the detection object 3 generated by the exciting coil 11 a .

[0040] The detection coil 10 b also detects impedance changes associated with changes in magnetic flux generated by the eddy current from the detection object 3 generated by the exciting coil 11 b.

[0041] Thus, the detection coil 10a detects the change in the synthetic impedance based on the excitation of the self coil 10a and the excitation of the excitation coil 11a. In addition, the detection coil 10b detects the change in the synthetic impedance based on the excitation of the self coil 10b and the excitation of the excitation coil 11b. And, when there is no abnormality in the detected body 3, the output signal of the bridge circuit 24 is set to zero balance.

[0042] Figure 2A The output between the terminals A and B is output by the detection section 31, and the inspection of the object 3 can be performed based on the output signal.

[0043] Next, refer to Figure 3 The block diagram further illustrates the eddy current flaw detection device involved in the first embodiment of the present invention.

[0044] like Figure 3 As shown, the eddy current flaw detection device 100 includes an oscillator 21 , a power amplifier 22 , an excitation power amplifier 23 , a bridge circuit 24 , a detection phase converter 26 , an amplifier 25 , and a phase detector 27 .

[0045] The bridge circuit 24 is as follows Figure 2AAs shown, the probe 10 is composed of detection coils 10a, 10b and resistors 12a, 12b.

[0046] The AC output from the oscillator 21 is amplified by the power amplifier 22 and supplied to the detection coils 10a and 10b via the bridge circuit 24. Furthermore, the AC output from the oscillator 21 is amplified by the excitation power amplifier 23 and supplied to the excitation coils 11a and 11b.

[0047] The AC outputs supplied to the detection coil 10a, the exciting coil 11a, the detection coil 10b, and the exciting coil 11b excite the detection object 3. Then, the detection coils 10a and 10b detect impedance changes caused by changes in magnetic flux generated by eddy currents.

[0048] The unbalanced output between the detection coils 10a and 10b output from the bridge circuit 24 is amplified by the amplifier 25 and transmitted to the phase detector 27. The AC output from the oscillator 21 is supplied to the detection phase converter 26. The output of the detection phase converter 26 is supplied to the phase detector 27.

[0049] The detection phase converter 26 converts the signal from the oscillator 21 into a signal having the same phase as the excitation signal and a signal having a 90-degree phase shift relative to the excitation signal, and supplies the signal to the phase detector 27 .

[0050] The unbalanced output amplified by the amplifier 25 and the output of the detection phase converter 26 are supplied to the phase detector 27, and the outputs of the detection coils 10a and 10b are added to the output of the detection phase converter 26 to be detected.

[0051] The phase detector 27 performs synchronous detection on the unbalanced output by a signal having the same phase as the excitation signal and outputs an X-axis eddy current signal, and performs synchronous detection on the unbalanced output by a signal having a 90-degree phase shift relative to the excitation signal and outputs a Y-axis eddy current signal. Then, the detected X-axis and Y-axis eddy current signals are input to the signal processing device 28 via a filter (not shown) or an A / D converter (not shown), and the measurement results are displayed on an output unit 29 such as a display. The signal processing device 28 includes, for example, a personal computer (PC) connected to the eddy current flaw detection device 100.

[0052] In the present embodiment, damage or the like of the object 3 is detected based on the output values ​​from the detection coils 10 a and 10 b .

[0053] However, in the above-mentioned eddy current flaw detection device 100, when the probe 10 or the object 3 to be detected vibrates or eccentricity occurs between the probe 10 and the object 3 to be detected, the distance between the detection coils 10a, 10b and the object 3 to be detected, and the distance between the excitation coils 11a, 11b and the object 3 to be detected will change respectively, thereby generating noise signals.

[0054] When the probe 10 moves, the probe 10 vibrates due to the movement of the probe 10, and the distances between the detection coils 10a, 10b and the detected object 3 and the distances between the excitation coils 11a, 11b and the detected object 3 change, respectively, thereby generating noise signals. In addition, when the detected object 3 moves, the detected object 3 vibrates due to the movement of the detected object 3, and the distances between the detection coils 10a, 10b and the detected object 3 and the distances between the excitation coils 11a, 11b and the detected object 3 change, respectively, thereby generating noise signals. Furthermore, even when the probe 10 or the detected object 3 does not vibrate, when there is eccentricity between the detection coils 10a, 10b and the detected object 3 or between the excitation coils 11a, 11b and the detected object 3, the distances between the detection coils 10a, 10b and the detected object 3 and the distances between the excitation coils 11a, 11b and the detected object 3 change, respectively, thereby generating noise signals.

[0055] It can be seen from this that in this specification, the noise signal caused by eccentricity or vibration refers to the noise signal generated by the change in the relative distance between the detection coils 10a, 10b and the detected object 3 caused by the vibration of the coil or the detected object or the eccentricity of the coil or the detected object.

[0056] Here, the inventors have studied the relationship between the distance D between the detection coil 10a and the excitation coil 11a and the distance D between the detection coil 10b and the excitation coil 11b and the noise signal. As a result, it is known that there is a distance D at which the vibration noise signal excited by the excitation coil and detected by the adjacent detection coil is in opposite phase to the noise signal generated by eccentricity or vibration excited by the detection coil and detected by the detection coil.

[0057] The inventors have conducted in-depth research on the interval between the surface of the detected object 3 and the detection coils 10a, 10b. As a result, it has been found that there are optimal values ​​for the interval between the surface of the detected object 3 and the detection coils 10a, 10b and the distance D between the detection coils and the exciting coils arranged next to them.

[0058] The inventors have confirmed that, for example, when the detected object 2 is a metal round bar, and the detection coils 10a, 10b and the excitation coils 11a, 11b are through coils, the distance D between the detection coil and the excitation coil located next to it has an optimal value according to the difference between the outer diameter of the round bar and the inner diameter of the coil. A specific example of the confirmation will be described later.

[0059] The first embodiment of the present invention obtains a distance D at which noise signals caused by eccentricity or vibration between the excitation coil and the adjacent detection coil have opposite phases. Each coil is arranged on the probe 10 so that the distance D is between the excitation coil 11a and the detection coil 10a and the distance D is between the excitation coil 11b and the detection coil 10b. Thus, even when the probe 10 of the eddy current flaw detection device 100 vibrates or the object 3 is eccentric, the noise caused by eccentricity or vibration can be eliminated.

[0060] By setting the distance D between the excitation coil and the detection coil to be optimal, the phase of the vibration noise signal excited by the excitation coil and detected by the adjacent detection coil and the vibration noise signal excited by the detection coil and detected by the detection side coil become opposite phases, that is, the phase is shifted by 180 degrees. As a result, the combined signal of the excitation coil and the detection coil generated by the noise caused by eccentricity or vibration can be attenuated.

[0061] Furthermore, it was confirmed that the eddy current caused by the detection coil and the adjacent exciting coil does not change the signal of the eddy current caused by the flaws of the object 3. As a result, noise caused by eccentricity or vibration can be eliminated and the S / N ratio can be improved.

[0062] Next, refer to Figures 4 to 7 In this specific example, a round bar was eccentrically disposed, and impedance changes were detected by a detection coil, thereby confirming that noise signals caused by vibration or eccentricity of the object to be detected could be eliminated.

[0063] Figure 4 This is a schematic diagram for explaining a specific example in which it is confirmed that a noise signal caused by vibration of the eddy current flaw detection device according to the present invention, eccentricity or vibration of the object to be detected is eliminated.

[0064] Figure 4The probe 10 of the specific example shown is provided with detection coils 10a, 10b and a pair of excitation coils 11a, 11b sandwiching the detection coils 10a, 10b. The inner diameters of the detection coils 10a, 10b and the excitation coils 11a, 11b are the same. The object to be detected 3 made of a metal round bar is inserted into these coils 10a, 10b, 11a, 11b. The difference between the inner diameters of these coils 10a, 10b, 11a, 11b and the outer diameter of the object to be detected 3 is 4 mm.

[0065] like Figure 4 As shown, the object 3 is tilted and moved in the direction of the arrow in the figure, with the center (c) between the detection coils 10a and 10b in the radial and longitudinal directions as the center. Then, the object 3 stops at a position where the moving distance d of the end portion is 2 mm.

[0066] An alternating current with an excitation frequency of 16 kHz and a magnetomotive force of 133×10 mA is supplied to the detection coils 10a, 10b and the excitation coils 11a, 11b. The change in impedance is detected by the detection coils 10a, 10b. The alternating current supplied to the detection coils 10a, 10b and the excitation coils 11a, 11b is controlled so that the alternating current supplied to the detection coils 10a, 10b and the excitation coils 11a, 11b is supplied only to the detection coils 10a, 10b, and only to the excitation coils 11a, 11b.

[0067] In this specific example, the exciting coil 11 a is represented as the coil C1 , the detecting coil 10 a is represented as the coil C2 , the detecting coil 10 b is represented as the coil C3 , and the exciting coil 11 b is represented as the coil C4 .

[0068] use Figure 4 The probe 10 of the illustrated specific example detects impedance changes by changing the alternating current supplied to the coil.

[0069] First, AC power is supplied to only coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b) for excitation, and impedance changes are detected from coil C2 (detection coil 10a) and coil C3 (detection coil 10b). The detection results are represented by C1 and C4, and the results are shown in Tables 1 and Figure 5 shown.

[0070] The probe 10 used for confirmation was such that the distance D between the exciting coil and the detecting coil was changed to 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm.

[0071] [Table 1]

[0072]

[0073] Similarly, only the coils C2 (detection coil 10a) and C3 (detection coil 10b) are excited by AC power, and the impedance change is detected from the coils C2 (detection coil 10a) and C3 (detection coil 10b). The detection results are represented by C2 and C3, and the results are shown in Tables 2 and Figure 5 shown.

[0074] [Table 2]

[0075]

[0076] In Table 1, Table 2 and Figure 5 In , the signal with a phase difference of 0 and 90 degrees with the AC frequency of the excitation is multiplied by the impedance change of the detection coil, and the phase difference voltage and voltage amplitude are calculated to express it on a two-dimensional plane. Figure 5 In the figure, the X-axis is the in-phase component (IN-PHASE) and the Y-axis is the quadrature component (QUADRATURE).

[0077] exist Figure 5 In FIG. 1 , the 0 mark indicates the results of C1 and C4, and the □ mark indicates the results of C2 and C3. The symbol marked with 0 corresponds to the distance D between the excitation coil and the detection coil.

[0078] From Table 2 and Figure 5 It can be seen that when only coil C2 (detection coil 10a) and coil C3 (detection coil 10b) are excited, the value taken is fixed even if the object 3 is moved. In other words, the value taken is fixed even if the object 3 is eccentric or vibrates.

[0079] In addition, according to Table 1 and Figure 5 When only coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b) are excited, if the distance D between the excitation coil and the detection coil is different, the detection value is also different. That is, when the detected body 3 is eccentric or vibrates, the voltage amplitude and phase are different.

[0080] from Figure 5 It can be seen that the detection result when only the coil C2 (detection coil 10a) and the coil C3 (detection coil 10b) are excited is different in phase from the detection result when only the coil C1 (excitation coil 11a) and the coil C4 (excitation coil 11b) are excited.

[0081] Next, Table 3 and Figure 6 The calculation results of the synthetic signal of the detection value obtained by exciting the coil C2 (detection coil 10a) and the coil C3 (detection coil 10b) and the detection value obtained by exciting the coil C1 (excitation coil 11a) and the coil C4 (excitation coil 11b) are shown. Figure 6 In accordance with the above Table 1, Table 2 and Figure 5Calculate in the same way.

[0082] [Table 3]

[0083]

[0084] From Table 3 and Figure 6 It can be seen that if the detection value obtained by exciting coil C2 (detection coil 10a) and coil C3 (detection coil 10b) is synthesized with the detection value obtained by exciting coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b), the signal approaches the zero point position, and the noise caused by eccentricity or vibration is reduced. Figure 6 In FIG. 1 , the mark △ represents the synthetic signal, and the symbol marked with △ corresponds to the distance D between the excitation coil and the detection coil.

[0085] like Figure 6 As shown, since the phases of each detection signal are different, the noise caused by eccentricity or vibration cancels out, thereby reducing the noise. It can be seen that there is a distance D between the excitation coil and the detection coil, and at this distance D, the eccentricity noise or vibration noise signal detected by the detection coils 10a and 10b when the coil C1 (excitation coil 11a) and the coil C4 (excitation coil 11b) are excited and the phases of the eccentricity noise or vibration noise signal detected by the detection coils 10a and 10b are opposite to the phases of the eccentricity noise or vibration noise signal detected by the detection coils 10a and 10b when the coil C2 (detection coil 10a) and the coil C3 (detection coil 10b) are excited.

[0086] Next, in order to confirm the distance D between the excitation coil and the detection coil where the two detection signals are in opposite phases, the calculation results of the phases of the two detection signals are shown in Tables 4 and Figure 7 In Figure 7 In , C2 and C3 are phase values ​​of the detection values ​​obtained by exciting coil C2 (detection coil 10a) and coil C3 (detection coil 10b), and C1 and C4 are phase values ​​of the detection values ​​obtained by exciting coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b). Figure 7 In the table, the ○ mark indicates the results of C1 and C4, and the □ mark indicates the results of C2 and C3.

[0087] [Table 4]

[0088]

[0089] According to Table 4 and Figure 7, when the distance D between the excitation coil and the detection coil is 6 mm, the phases of the two detection signals are almost opposite, that is, the phases of the two are almost 180 degrees. Therefore, the distance D between the excitation coil and the detection coil has a distance at which the phases become opposite near 6 mm. Setting the distance D between the excitation coil and the detection coil to the distance at which the phases become opposite can offset the noise caused by eccentricity or vibration, thereby eliminating the noise. In addition, it was confirmed that the signal of the eddy current caused by the scratches of the detected object 3 did not change.

[0090] As a result, according to the present invention, it was confirmed that by setting the distance D between the exciting coil and the detecting coil to a distance at which the exciting coil and the detecting coil are in opposite phases, it is possible to eliminate noise caused by eccentricity or vibration and improve the S / N ratio.

[0091] In addition, when the distance D between the excitation coil and the detection coil is within the range of 4 mm to 10 mm, the phases of the two signals are different. That is, the detection signals from the detection coils 10a and 10b obtained by providing alternating current to the excitation coils 11a and 11b for excitation and the detection signals from the detection coils 10a and 10b obtained by providing alternating current to the detection coils 10a and 10b for excitation are different in phase. Then, when the two detection signals are synthesized, the noise caused by eccentricity or vibration can be reduced. Even if the two detection signals are not in opposite phases, the noise caused by eccentricity or vibration can be reduced, thereby improving the S / N ratio. In order to reliably eliminate the noise caused by eccentricity or vibration, it is preferred to set the distance D between the excitation coil and the detection coil so that the two detection signals become opposite phases. However, in order to reduce the noise caused by eccentricity or vibration, it is sufficient to change the phases of the two detection signals. Therefore, the distance D between the excitation coil and the detection coil can be set according to the requirements for the S / N ratio.

[0092] In the above specific example, the difference between the inner diameter of the coil and the outer diameter of the object 3 to be detected inserted into the coil is 4 mm. The difference between the outer diameter of the object to be detected and the inner diameter of the coil is not limited to this, and it is confirmed that there is a distance D between the excitation coil and the detection coil that makes the two detection signals have opposite phases under various sizes. That is, the distance D between the excitation coil and the detection coil has an optimal value depending on the distance between the surface of the object to be detected and the coil.

[0093] In the first embodiment described above, in order to reliably eliminate noise caused by eccentricity or vibration, the distance D between the exciting coil and the detecting coil is set so that the two detection signals become opposite in phase.

[0094] Figure 8In the second embodiment shown, the distance D between the excitation coil and the detection coil is set to a predetermined value. Due to the difference between the inner diameter of the coils 10a, 10b, 11a, 11b and the outer diameter of the detected body 3, when the two detection signals do not become opposite in phase, the phase of the signal supplied to the excitation coil is changed and adjusted so that the phases of the two signals are opposite. Figure 8 In the second embodiment shown, the AC output from the oscillator 21 is supplied to the excitation phase converter 40. Figure 8 The second embodiment shown is the same as the first embodiment except that an excitation phase converter 40 is provided, and therefore the same parts are denoted by the same reference numerals and their description is omitted.

[0095] like Figure 8 As shown, the AC output from the oscillator 21 is supplied to the excitation phase converter 40. The excitation phase converter 40 converts the phase of the excitation AC supplied to the excitation coils 10c and 10d. The phase converter 40 converts the phase of the AC supplied to the excitation coils 11a and 11b so that the phases of the two detection signals become opposite phases.

[0096] The AC power whose phase is converted by the excitation phase converter 40 is supplied to the excitation power amplifier 23, amplified by the excitation power amplifier 23, and supplied to the excitation coils 11a and 11b.

[0097] As a result, the detection signal from the detection coil 10a, 10b obtained by exciting the excitation coil 11a, 11b with the alternating current after phase conversion by the excitation phase converter 40 and the phase signal of the detection signal from the detection coil 10a, 10b obtained by exciting the detection coil 10a, 10b with the alternating current are in opposite phases, thereby improving the S / N ratio.

[0098] Although the case of using the through coil has been described in the above embodiment, the present invention is applicable not only to the through coil but also to an interpolated coil and an upper coil, and the same effect can be obtained.

[0099] Description of symbols

[0100] 3: Detected object

[0101] 10: Probe

[0102] 10a: Detection coil

[0103] 10b: Detection coil

[0104] 11a: Excitation coil

[0105] 11b: Excitation coil

[0106] 20: Eddy current flaw detection device

[0107] 21: Oscillator

[0108] 22: Power Amplifier

[0109] 23: Power amplifier for excitation

[0110] 24: Bridge circuit

[0111] 25: Amplifier

[0112] 26: Phase converter for detection

[0113] 27: Phase detector

[0114] 28: Signal processing device

[0115] 29: Output

[0116] 30: AC power supply

[0117] 40: Phase converter for excitation

[0118] D: Distance.

Claims

1. An eddy current flaw detection device, comprising: A pair of detection coils having the same inner diameter and arranged coaxially and non-contactingly with the detected object and separated from each other; And a bridge circuit in which the detection coils form both sides of the bridge in order to make the magnetic fields generated by the detection coils have opposite phases, characterized in that: A pair of exciting coils are arranged coaxially with the detection coils so as to sandwich the pair of detection coils, and the pair of exciting coils and the pair of detection coils have the same inner diameter. The distance between the detection coil and the excitation coil arranged next to it is set so that the phase between the noise signal caused by eccentricity or vibration detected by the detection coil located next to it when excited by the excitation coil and the noise signal caused by eccentricity or vibration detected by the detection coil when excited by the detection coil changes, thereby reducing the distance of the noise caused by eccentricity or vibration when the two noise signals are synthesized.

2. The eddy current flaw detection device according to claim 1, characterized in that: The distance between the detection coil and the excitation coil arranged next to it is set to a distance at which the phases of the noise signal generated by eccentricity or vibration detected by the detection coil located next to it when excited by the excitation coil are opposite to the phases of the noise signal generated by eccentricity or vibration detected by the detection coil when excited by the detection coil.

3. The eddy current flaw detection device according to claim 1, characterized in that: The phase of the alternating current supplied to the excitation coil is changed so that a noise signal generated by eccentricity or vibration, which is excited by the excitation coil when the alternating current is supplied to the excitation coil and detected by the detection coil located nearby, and a noise signal generated by eccentricity or vibration, which is excited by the detection coil when the alternating current is supplied to the detection coil and detected by the detection coil, become opposite in phase.

4. The eddy current flaw detection device according to claim 3, characterized in that: include: an oscillator; a power amplifier for amplifying an AC output from the oscillator; an excitation phase converter for converting the phase of the AC output from the oscillator; and an excitation power amplifier for amplifying the AC output from the excitation phase converter, The detection coil is supplied with alternating current from the power amplifier, and the exciting coil is supplied with alternating current from the excitation power amplifier.

5. The eddy current flaw detection device according to any one of claims 1 to 4, characterized in that: The detected object is a round bar, the detection coil and the excitation coil are through coils, and the distance between the detection coil and the excitation coil arranged next to it is set based on the difference between the outer diameter of the round bar and the inner diameters of the detection coil and the excitation coil.

6. The eddy current flaw detection device according to claim 5, characterized in that: comprising a probe arranged close to the object to be detected, The probe is formed in a cylindrical or semi-cylindrical shape, and the detection coil and the excitation coil are arranged inside.

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