Eddy current fault detector

Abstract

Provided is an eddy-current flaw detection device that removes a noise signal resulting from the vibration of the eddy-current flaw detection device or the eccentricity or vibration of an object under inspection. The eddy-current flaw detection device comprises a pair of detection coils 10a, 10b that are disposed so as to be on the same axis as and removed from an object 3 under inspection and a bridge circuit having two circuit branches configured from the detection coils such that the magnetic fields generated by the detection coils 10a, 10b have reverse phases. A pair of excitation coils 11a, 11b are disposed on the same axis as the pair of detection coils 10a, 10b so as to sandwich the detection coils 10a, 10b. The distance D between each detection coil and the excitation coil adjacent thereto is set such that vibration noise signals produced by the excitation coils and detected by the detection coils positioned next to the excitation coils have reverse phases from vibration noise signals produced by the detection coils and detected by the detection coils.

Description

Eddy current flaw detection equipment

[0001] The present invention relates to an eddy current flaw detector, and more particularly to an eddy current flaw detector that includes a coil that generates an eddy current in a surface layer of an object to be inspected and a signal processing unit that processes a signal resulting from an impedance change of the coil, and that inspects the object for defects and the like based on the signal.

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

[0003] Patent No. 2882856

[0004] In the eddy current flaw detector described in Patent Document 1, if there are no flaws or foreign objects inside the conductor, the induced currents flowing through the resonant coils are canceled out and no change occurs. In contrast, in the above-mentioned device, if there are flaws or foreign objects inside the conductor, a bias occurs in the magnetic fields generated by each detection coil, resulting in a difference in the induced current values ​​generated by each resonant coil. This difference in current flows, causing the resonant coils to resonate. This allows the above-mentioned device to improve the S / N ratio.

[0005] However, in the above-mentioned Patent Document 1, when a noise signal is generated due to vibration of the eddy current flaw detector or eccentricity or vibration of the object to be inspected, the noise signal causes a decrease in the S / N ratio.

[0006] Furthermore, in the above-mentioned Patent Document 1, an amplifier circuit for amplifying the output of each resonance coil is required, which makes the device complicated.

[0007] An object of the present invention is to provide an eddy current flaw detector that can eliminate noise signals due to vibration of the inspection device and eccentricity or vibration of the object to be inspected without complicating the device.

[0008] The present invention is an eddy current flaw detection device comprising a pair of detection coils arranged coaxially and spaced apart from each other without contacting the object to be inspected, and a bridge circuit in which each detection coil forms two sides of a bridge so that the magnetic fields generated by these detection coils are in opposite phase, wherein a pair of excitation coils are arranged coaxially with each detection coil so as to sandwich the pair of detection coils, and the distance between a detection coil and the excitation coil arranged adjacent to it is set to a distance at which the phase of a noise signal due to eccentricity or vibration excited by the excitation coil and detected by the adjacent detection coil changes, and the noise signal due to eccentricity or vibration excited by the detection coil and detected by the detection coil.

[0009] Furthermore, in the present invention, it is preferable that the distance between the detection coil and the excitation coil arranged adjacent to it is set to a distance such that a noise signal due to eccentricity or vibration excited by the excitation coil and detected by the adjacent detection coil is in opposite phase to a noise signal due to eccentricity or vibration excited by the detection coil and detected by the detection coil.

[0010] Furthermore, the present invention is preferably configured such that AC power is supplied to the excitation coil, and the phase of the AC power supplied to the excitation coil is converted so that a noise signal due to eccentricity or vibration that is excited by the excitation coil and detected by the detection coil located adjacent to the excitation coil and a noise signal due to eccentricity or vibration that is supplied to the detection coil and excited by the detection coil and detected by the detection coil are in opposite phases.

[0011] The present invention can also be configured to include an oscillator, a power amplifier that amplifies AC output from the oscillator, an excitation phase converter that converts the phase of the AC output from the oscillator, and an excitation power amplifier that amplifies the AC output from the excitation phase converter, and to provide AC power from the power amplifier to the detection coil and AC power from the excitation power amplifier to the excitation coil.

[0012] Furthermore, the object to be inspected is a round bar material, and the detection coil and the excitation coil are through coils, and the distance between the detection coil and the excitation coil placed next to it can be set based on the difference between the outer diameter of the round bar material and the inner diameter of the detection coil and the excitation coil.

[0013] The present invention can also be configured to include a probe arranged in close proximity to the object under test, the probe being formed in a cylindrical or semi-cylindrical shape and having the detection coil and excitation coil provided inside.

[0014] According to the present invention, it is possible to provide an eddy current flaw detector that can eliminate noise signals caused by vibration of the inspection device and eccentricity or vibration of the object to be inspected, thereby improving the S / N ratio.

[0015] FIG. 1 is a schematic diagram of an eddy current flaw detector and an object under test according to the present invention. FIG. 2A is a schematic circuit diagram showing the configuration of the detection coil portion of an eddy current flaw detector according to the present invention. FIG. 2B is a schematic circuit diagram showing the configuration of the excitation coil portion of an eddy current flaw detector according to the present invention. FIG. 3 is a block diagram showing an eddy current flaw detector according to a first embodiment of the present invention. FIG. 4 is a schematic diagram for explaining a specific example in which the removal of noise signals due to vibration of an eddy current flaw detector according to the present invention and eccentricity or vibration of an object under test was confirmed. FIG. 5 is a measurement diagram showing the results of measuring the change in impedance of the detection coil when the distance between the detection coil and the excitation coil placed adjacent to it is changed and the detection coil and the excitation coil are excited independently. FIG. 6 is an explanatory diagram showing the composite signal of the detection coil when the distance between the detection coil and the excitation coil placed adjacent to it is changed and the detection coil and the excitation coil are excited independently. FIG. 7 is an explanatory diagram showing the relationship between distance and phase when the distance between the detection coil and the excitation coil placed adjacent to it is changed. FIG. 8 is a block diagram showing an eddy current flaw detector according to a second embodiment of the present invention.

[0016] Next, an eddy current flaw detector according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. Note that the eddy current flaw detector according to the present invention is not limited to the following embodiment, and can be appropriately modified and implemented within the scope of the present invention.

[0017] As shown in Fig. 1, a device under test 3 of the present invention is a conductor such as a pipe or a round bar. A probe 10 is disposed in close proximity to the device under test 3. The probe 10 is formed in a cylindrical or semi-cylindrical shape, and is provided therein with a pair of detection coils 10a, 10b and a pair of excitation coils 11a, 11b sandwiching the detection coils 10a, 10b. In this embodiment, the probe 10 is formed in a cylindrical shape. The pair of detection coils 10a, 10b and the pair of excitation coils 11a, 11b provided therein are configured as feedthrough coils.

[0018] The detection coils 10a, 10b and the excitation coils 11a, 11b are arranged coaxially and spaced apart from each other and in a non-contact manner relative to the object under test 3. The probe 10 and the object under test 3 move relative to each other. That is, with the eddy current flaw detection device, there are two cases: one in which the probe 10 moves relative to the object under test 3 to inspect the object under test 3, and one in which the object under test 3 moves relative to the fixed probe 10. With the eddy current flaw detection device of this embodiment, the probe 10 moves in the direction of the arrow in the figure relative to the object under test 3 to inspect the condition of the surface, etc. of the object under test 3.

[0019] In this embodiment, the object to be inspected 3 is a metal round bar.

[0020] In this embodiment, the detection coils 10a, 10b are spaced apart from the adjacent excitation coils 11a, 11b by a distance D. As shown in Fig. 1, the excitation coil 11a and the detection coil 10a are spaced apart by a distance D, and the excitation coil 11b and the detection coil 10b are spaced apart by a distance D. This distance D will be described later.

[0021] Next, the circuit configuration of this embodiment will be outlined with reference to Figures 2A and 2B. Figure 2A is a schematic circuit diagram showing the configuration of the detection coil portion of the eddy current flaw detector according to the present invention, and Figure 2B is a schematic circuit diagram showing the configuration of the excitation coil portion of the eddy current flaw detector according to the present invention.

[0022] As shown in FIG. 2A, the bridge circuit 24 is composed of detection coils 10a and 10b and resistors 12a and 12b. The detection coils 10a and 10b are connected as two arms of the bridge circuit 24, and the resistors 12a and 12b are connected as the other two arms of the bridge circuit 24.

[0023] An AC output from an AC power supply 30 (in FIG. 3, oscillator 21 and power amplifier 22) is applied to detection coils 10a and 10b via bridge circuit 24, exciting the object under test 3 and generating eddy currents. The detection coils 10a and 10b detect impedance changes accompanying changes in magnetic flux generated by the eddy currents using a detection unit 31 (in FIG. 3, phase detector 27, etc.).

[0024] The detection coils 10 a and 10 b are differentially connected so that the magnetic fields they generate are in opposite phases. In this embodiment, the detection coils 10 a and 10 b excite the object under test 3 and detect changes in impedance that accompany changes in magnetic flux generated by eddy currents.

[0025] As shown in Fig. 2B, AC output from AC power supply 30 (oscillator 21 and excitation power amplifier 23 in Fig. 3) is supplied to excitation coils 11a and 11b, exciting them. The excitation from excitation coils 11a and 11b excites device under test 3, generating eddy currents. Excitation coil 11a is wound so that the magnetic field it generates is in phase with detection coil 10a. Excitation coil 11b is wound so that the magnetic field it generates is in phase with detection coil 10b.

[0026] The detection coil 10a also detects a change in impedance that accompanies a change in magnetic flux generated by an eddy current from the object under test 3 due to the excitation coil 11a.

[0027] The detection coil 10b also detects a change in impedance that accompanies a change in magnetic flux generated by an eddy current from the object under test 3 due to the excitation coil 11b.

[0028] In this way, the detection coil 10a detects a change in the composite impedance based on the excitation of its own coil 10a and the excitation of the excitation coil 11a. The detection coil 10b detects a change in the composite impedance based on the excitation of its own coil 10b and the excitation of the excitation coil 11b. If there is no abnormality in the device under test 3, the output signal of this bridge circuit 24 is set to zero balance.

[0029] The output between terminals A and B in FIG. 2A is output from the detection unit 31, and the device under test 3 can be inspected based on this output signal.

[0030] Next, the eddy current flaw detector according to the first embodiment of the present invention will be further described with reference to the block diagram of FIG.

[0031] As shown in FIG. 3, the eddy current flaw detector 100 includes an oscillator 21 , a power amplifier 22 , an exciting power amplifier 23 , a bridge circuit 24 , a detection phase converter 26 , an amplifier 25 , and a phase detector 27 .

[0032] As shown in FIG. 2A, the bridge circuit 24 is composed of the detection coils 10a and 10b of the probe 10 and resistors 12a and 12b.

[0033] The AC output from the oscillator 21 is amplified by a power amplifier 22 and is applied to the detection coils 10a and 10b via a bridge circuit 24. The AC output from the oscillator 21 is also amplified by an excitation power amplifier 23 and is applied to the excitation coils 11a and 11b.

[0034] The object under test 3 is excited by AC outputs applied to the detection coil 10a, excitation coil 11a, detection coil 10b, and excitation coil 11b, respectively. Then, the detection coils 10a and 10b detect a change in impedance accompanying a change in magnetic flux generated by eddy currents.

[0035] The unbalanced output between the detection coils 10a and 10b output from the bridge circuit 24 is amplified by an amplifier 25 and sent to a phase detector 27. The AC output from the oscillator 21 is given to a detection phase converter 26. The output of this detection phase converter 26 is given to the phase detector 27.

[0036] 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 phase shift of 90 degrees from the excitation signal, and supplies the converted signal to the phase detector 27 .

[0037] The unbalanced output amplified by the amplifier 25 and the output of the detection phase converter 26 are given to a phase detector 27, and the outputs of the detection coils 10a and 10b are detected together with the output of the detection phase converter 26.

[0038] The phase detector 27 synchronously detects the unbalanced output using a signal that is in phase with the excitation signal to output an X-axis eddy current signal, and also synchronously detects the unbalanced output using a signal that is 90 degrees out of phase with the excitation signal to output a Y-axis eddy current signal. The detected X-axis and Y-axis eddy current signals are then input into a signal processing device 28 via a filter (not shown) and an A / D converter (not shown), and the measurement results and the like are displayed on an output unit 29 such as a display. The signal processing device 28 may be, for example, a personal computer (PC) connected to the eddy current flaw detector 100.

[0039] In this embodiment, damage to the object under test 3 is detected based on the output values ​​from the detection coils 10a and 10b.

[0040] In the above-mentioned eddy current flaw detection device 100, when vibration of the probe 10 or the object under test 3 or eccentricity between the probe 10 and the object under test 3 occurs, the distance between the detection coils 10a, 10b and the object under test 3, and the distance between the excitation coils 11a, 11b and the object under test 3 change, respectively, and noise signals are generated.

[0041] When the probe 10 moves, the movement of the probe 10 generates vibrations in the probe 10, which changes the distances between the detection coils 10a and 10b and the device under test 3 and the distances between the excitation coils 11a and 11b and the device under test 3, respectively, generating noise signals. When the device under test 3 moves, the movement of the device under test 3 generates vibrations in the device under test 3, which changes the distances between the detection coils 10a and 10b and the device under test 3 and the distances between the excitation coils 11a and 11b and the device under test 3, respectively, generating noise signals. Furthermore, even when the probe 10 or the device under test 3 does not vibrate, if there is eccentricity between the detection coils 10a and 10b and the device under test 3 or between the excitation coils 11a and 11b and the device under test 3, the distances between the detection coils 10a and 10b and the device under test 3 and the distances between the excitation coils 11a and 11b and the device under test 3, respectively, generating noise signals.

[0042] For this reason, in this specification, noise signals due to eccentricity or vibration refer to noise signals generated by changes in the relative distance between the detection coils 10a, 10b and the object under test 3 due to vibration of the coil or object under test or eccentricity of the coil or object under test.

[0043] The inventors have carefully 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, and have found that there exists 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 due to eccentricity or vibration excited by the detection coil and detected by the detection coil.

[0044] Furthermore, the inventors have thoroughly investigated the distance between the surface of the object under test 3 and the detection coils 10a, 10b, and have found that there are optimal values ​​for the distance between the surface of the object under test 3 and the detection coils 10a, 10b, and for the distance D between the detection coil and the excitation coil disposed adjacent to it.

[0045] The inventors have confirmed that, for example, when the object under test 2 is a metal round bar and the detection coils 10a, 10b and excitation coils 11a, 11b are through coils, there is an optimum value for the distance D between the detection coil and the excitation coil arranged adjacent to it, depending on the difference between the outer diameter of the round bar and the inner diameter of the coils. A specific example of this confirmation will be described later.

[0046] In the first embodiment of the present invention, a distance D between an excitation coil and an adjacent detection coil is determined at which noise signals due to eccentricity or vibration are in opposite phase. Each coil is arranged on the probe 10 so that the distance D between the excitation coil 11a and the detection coil 10a and the distance D between the excitation coil 11b and the detection coil 10b are the same. This makes it possible to eliminate noise due to eccentricity or vibration even when vibration occurs in the probe 10 of the eddy current flaw detector 100 or the object under test 3 is eccentric.

[0047] By optimally setting the distance D between the excitation coil and the detection coil, the vibration noise signal excited by the excitation coil and detected by the adjacent detection coil will be in opposite phase to the vibration noise signal excited by the detection coil and detected by the detection coil, i.e., the phase will be shifted by 180 degrees. As a result, the composite signal of the excitation coil and detection coil generated by noise due to eccentricity or vibration can be attenuated.

[0048] It was also confirmed that the eddy current signal generated by the detection coil and the adjacent excitation coil does not change due to scratches or other imperfections in the test object 3. As a result, noise caused by eccentricity or vibration can be eliminated, improving the S / N ratio.

[0049] Next, a specific example of the present invention will be described with reference to Figures 4 to 7. In this example, a round bar material was made eccentric, and the change in impedance was detected by a detection coil, and it was confirmed that noise signals due to vibration or eccentricity of the test object could be eliminated.

[0050] FIG. 4 is a schematic diagram for explaining a specific example in which the removal of noise due to vibration of the eddy current flaw detector according to the present invention and eccentricity or vibration of the test object has been confirmed.

[0051] The probe 10 of the specific example shown in Figure 4 has detection coils 10a, 10b and a pair of excitation coils 11a, 11b sandwiching the detection coils 10a, 10b. The detection coils 10a, 10b and the excitation coils 11a, 11b have the same inner diameter. An object under test 3 made of a metal round bar is inserted into these coils 10a, 10b, 11a, 11b. The difference between the inner diameter of these coils 10a, 10b, 11a, 11b and the outer diameter of the object under test 3 is 4 mm.

[0052] 4, the object under test 3 was tilted and moved in the direction indicated by the arrow in the figure, with the center (c) of the radial and longitudinal direction between the detection coils 10a and 10b as the center, and was stopped at a position where the movement distance d of the end of the object under test 3 was 2 mm.

[0053] The detection coils 10a, 10b and the excitation coils 11a, 11b were supplied with AC power having an excitation frequency of 16 kHz and a magnetomotive force of 133 × 10 mA. The change in impedance was detected by the detection coils 10a, 10b. The AC power to the detection coils 10a, 10b and the excitation coils 11a, 11b was controlled so that only the detection coils 10a, 10b were supplied with power, and so that only the excitation coils 11a, 11b were supplied with power.

[0054] In this specific example, the excitation coil 11a is represented as coil C1, the detection coil 10a as coil C2, the detection coil 10b as coil C3, and the excitation coil 11b as coil C4.

[0055] Using the specific example of probe 10 shown in FIG. 4, the supply of AC power to the coil was varied to detect changes in impedance.

[0056] First, AC power was applied to only coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b) to excite them, and changes in impedance were detected from coil C2 (detection coil 10a) and coil C3 (detection coil 10b). The detection results are represented as C1 and C4, and are shown in Table 1 and Figure 5.

[0057] The probe 10 used for the confirmation had the distance D between the excitation coil and the detection coil changed to 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm.

[0058]

[0059] Similarly, AC power was supplied only to coil C2 (detection coil 10a) and coil C3 (detection coil 10b) to excite them, and changes in impedance were detected from coil C2 (detection coil 10a) and coil C3 (detection coil 10b). The detection results are represented as C2 and C3, and are shown in Table 2 and FIG. 5.

[0060]

[0061] In Tables 1, 2, and Figure 5, the impedance change of the detection coil is multiplied by the exciting AC frequency and signals with a phase difference of 0 and 90 degrees, and the phase difference voltage and voltage amplitude are calculated to be on a two-dimensional plane. In Figure 5, the X-axis is the in-phase component (IN-PHASE) and the Y-axis is the quadrature component (QUADRATURE).

[0062] 5, circles represent the results of C1 and C4, and squares represent the results of C2 and C3. The symbols attached to the circles correspond to the distance D between the excitation coil and the detection coil.

[0063] 5, when only coil C2 (detection coil 10a) and coil C3 (detection coil 10b) are excited, the value remains constant even when the test object 3 is moved. In other words, the value remains constant even when the test object 3 is eccentric or vibrates.

[0064] 5, when only coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b) are excited, the detected value differs when the distance D between the excitation coil and the detection coil differs. In other words, when the object under test 3 is eccentric or vibrates, the voltage amplitude and phase differ.

[0065] It can be seen from FIG. 5 that the detection result of excitation of only coil C2 (detection coil 10a) and coil C3 (detection coil 10b) is different in phase from the detection result of excitation of only coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b).

[0066] Next, the results of calculating the composite signal of the detection values ​​obtained by exciting coil C2 (detection coil 10a) and coil C3 (detection coil 10b) and the detection values ​​obtained by exciting coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b) are shown in Table 3 and Fig. 6. Table 3 and Fig. 6 are calculated in the same way as Table 1, Table 2 and Fig. 5 above.

[0067]

[0068] From Table 3 and Fig. 6, it can be seen that when the detection value obtained by exciting coil C2 (detection coil 10a) and coil C3 (detection coil 10b) is combined 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 noise due to eccentricity or vibration can be reduced. In Fig. 6, the triangle marks represent the combined signal, and the symbol attached to the triangle marks corresponds to the distance D between the excitation coil and the detection coil.

[0069] 6, because the phases of the detection signals are different, noise due to eccentricity or vibration is canceled out, thereby reducing noise. It can be seen that there exists a distance D between the excitation coil and the detection coil at which the eccentricity noise or vibration noise signal excited by coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b) and detected by the detection coils 10a and 10b is in opposite phase to the eccentricity noise or vibration noise signal excited by coil C2 (detection coil 10a) and coil C3 (detection coil 10b) and detected by the detection coils 10a and 10b.

[0070] Next, to confirm the distance D between the excitation coil and the detection coil at which the two detection signals are in opposite phase, the phases of the two detection signals were calculated and the results are shown in Table 4 and Figure 7. In Figure 7, C2 and C3 are phase values ​​of the detection values ​​when coil C2 (detection coil 10a) and coil C3 (detection coil 10b) are excited, and C1 and C4 are phase values ​​of the detection values ​​when coil C1 (excitation coil 11a) and coil C4 (excitation coil 11b) are excited. Also in Figure 7, circles represent the results for C1 and C4, and squares represent the results for C2 and C3.

[0071]

[0072] From Table 4 and Figure 7, it can be seen that 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 approximately 180 degrees. Therefore, there is a distance where the distance D between the excitation coil and the detection coil is approximately 6 mm, at which the phases are opposite. By setting the distance D between the excitation coil and the detection coil to this distance at which the phases are opposite, it is possible to cancel out noise due to eccentricity or vibration and eliminate the noise. It was also confirmed that the eddy current signal due to scratches, etc. on the test object 3 does not change.

[0073] As a result, it was confirmed that according to the present invention, by setting the distance D between the excitation coil and the detection coil to a distance that results in opposite phases, noise due to eccentricity or vibration can be eliminated and the S / N ratio can be improved.

[0074] Furthermore, when the distance D between the excitation coil and the detection coil is between 4 mm and 10 mm, the phases of the two signals differ. That is, the detection signal from the detection coils 10a and 10b obtained by applying AC power to the excitation coils 11a and 11b and the detection signal from the detection coils 10a and 10b obtained by applying AC power to the detection coils 10a and 10b are different in phase from each other. Furthermore, combining the two detection signals can reduce noise caused by eccentricity or vibration. Even if the two detection signals are not in opposite phase, noise caused by eccentricity or vibration is reduced, improving the S / N ratio. To reliably eliminate noise caused by eccentricity or vibration, it is preferable to set the distance D between the excitation coil and the detection coil so that the two detection signals are in opposite phase. However, noise caused by eccentricity or vibration can be reduced by simply changing 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 required S / N ratio.

[0075] In the specific example described above, the difference between the inner diameter of the coil and the outer diameter of the object under test 3 inserted into the coil was 4 mm. The difference between the outer diameter of the object under test and the inner diameter of the coil is not limited to this and can be various sizes, and it has been confirmed that there is a distance D between the excitation coil and the detection coil at which the two detection signals are in opposite phase. In other words, there is an optimal value for the distance D between the excitation coil and the detection coil depending on the distance between the surface of the object under test and the coil.

[0076] In the first embodiment described above, in order to reliably eliminate noise due to eccentricity or vibration, the distance D between the excitation coil and the detection coil is set so that the two detection signals are in opposite phase.

[0077] In the second embodiment shown in Fig. 8, the distance D between the excitation coil and the detection coil is set to a predetermined value, and if the difference between the inner diameters of the coils 10a, 10b, 11a, and 11b and the outer diameter of the device under test 3 prevents the two detection signals from being in opposite phase, the phase of the signal supplied to the excitation coil is converted and adjusted so that the two signals are in opposite phase. For this reason, in the second embodiment shown in Fig. 8, the AC output from the oscillator 21 is supplied to an excitation phase converter 40. Note that the second embodiment shown in Fig. 8 is the same as the first embodiment except for the provision of the excitation phase converter 40, and therefore the same parts are designated by the same reference numerals and their description will be omitted.

[0078] 8, the AC output from the oscillator 21 is supplied to an excitation phase converter 40. This excitation phase converter 40 converts the phase of the AC power for excitation supplied to the excitation coils 10c and 10d. This phase converter 40 converts the phase of the AC power supplied to the excitation coils 11a and 11b so that the phases of the two detection signals are opposite to each other.

[0079] The AC power phase-converted by the excitation phase converter 40 is applied to the excitation power amplifier 23, where it is amplified and applied to the excitation coils 11a and 11b.

[0080] As a result, the excitation coils 11a and 11b are excited by being supplied with AC power that has been phase-converted by the excitation phase converter 40, and the phase signals of the detection signals from the detection coils 10a and 10b and the detection signals from the detection coils 10a and 10b that have been excited by being supplied with AC power are opposite in phase, thereby improving the S / N ratio.

[0081] In the above-described embodiment, the case where a through coil is used has been described, but the present invention can be applied not only to through coils but also to internal coils and top coils, and similar effects can be obtained.

[0082] 3: Inspected object 10: Probe 10a: Detection coil 10b: Detection coil 11a: Excitation coil 11b: Excitation coil 20: Eddy current flaw detector 21: Oscillator 22: Power amplifier 23: Excitation power amplifier 24: Bridge circuit 25: Amplifier 26: Detection phase converter 27: Phase detector 28: Signal processing device 29: Output section 30: AC power supply 40: Excitation phase converter D: Distance

Claims

DEPCT661. Eddy current fault detection device comprising: a pair of contactless and coaxially spaced detection coils relative to the sample; and a bridge circuit on both sides of which detection coils are constructed so that the magnetic fields generated by the detection coils are in opposite phase, where a pair of excitation coils are coaxially spaced relative to the detection coils in such a manner that they are clamped between them, and the distance between the detection coils and the adjacent excitation coils is defined as the distance at which the phase difference between the eccentric or vibration noise generated in the excitation coil and detected by its adjacent detection coil and the eccentric or vibration noise generated in the detection coil and detected by its adjacent detection coil changes.2.Eddy current fault detection device according to claim 1, where the distance between the detecting coil and the excitation coil, which are arranged adjacent to each other, is defined such that the noise caused by eccentricity or vibration, which is triggered in the excitation coil and detected by its adjacent detecting coil, and the noise caused by eccentricity or vibration, which is triggered in the detecting coil and detected by its adjacent detecting coil, are in opposite phase.

3. Eddy current fault detection device according to claim 1, where the phase of the alternating current supplied to the excitation coil is transformed such that the noise caused by eccentricity or vibration, which is triggered in the excitation coil by the alternating current supply and detected by its adjacent detecting coil, and the noise caused by eccentricity or vibration, which is triggered in the detecting coil by the alternating current supply and detected by its adjacent detecting coil, are in opposite phase. 4.Eddy current fault detection device according to claim 3, which consists of: an oscillator; a power amplifier to amplify the AC output from the oscillator; a phase converter for the excitation which transforms the phase of the AC output from the oscillator; and a power amplifier for the excitation which amplifies the AC output from the phase converter for the excitation, where the power amplifier supplies AC power to the detection coil and the power amplifier for the excitation supplies AC power to the excitation coil.

5. Eddy current fault detection device according to claims 1 through 4, where the sample is a cylindrical rod, the detection coil and the excitation coil are surrounding coils, and the distance between the detection coil and the excitation coil, which are arranged adjacent to each other in that section, is determined by the difference between the outer diameter of the cylindrical rod and the inner diameter of the detection coil and the excitation coil. 6.Eddy current fault detection device under claim 5, which consists of a detector positioned close to the sample, where the detector is molded into a cylinder or hemispheric shape and contains the detection coil and excitation coil.