JP7627031B2 - Eddy current testing equipment - Google Patents

Description

The present invention relates to an eddy current inspection device. More specifically, the present invention relates to a mutual induction type eddy current inspection device that includes an excitation coil that generates an excitation magnetic field to generate eddy currents in the surface layer of an object to be inspected, a pair of differentially connected detection coils, and a signal processing unit that processes signals resulting from impedance changes in the detection coils, and inspects defects, etc. in the object to be inspected based on the signals.

Eddy current flaw detectors are used as a surface inspection technique to detect the presence or absence of defects such as scratches by inducing eddy currents on the surface of the object being inspected and detecting the changes in the reactive magnetic field created by these eddy currents. There are two types of eddy current flaw detectors: a self-comparison type, in which the excitation coil and detection coil are configured as a single coil, and a mutual induction type, in which each is configured as a separate coil. It is desirable to improve the signal-to-noise ratio of these eddy current flaw detectors.

For example, Patent Document 1 discloses an eddy current flaw detector in which a pair of detection coils are arranged coaxially and out of contact with a conductor to be inspected, a pair of resonant coils are arranged coaxially with 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.

In the eddy current flaw detector described in the above-mentioned Patent Document 1, if there is no flaw or foreign object inside the conductor, the induced current flowing through the resonant coil is canceled out and there is no change. In contrast, in the above-mentioned device, if there is a flaw or foreign object inside the conductor, a bias occurs in the magnetic field generated by each detection coil, resulting in a difference in the induced current value generated by each resonant coil, and this difference in current flows, causing the resonant coil to resonate. As a result, the above-mentioned device can improve the S/N ratio.

Patent No. 2882856

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 test object, the S/N ratio decreases due to the noise signal.

In addition, in the above-mentioned Patent Document 1, an amplifier circuit is required for each resonant coil to amplify the output, which makes the device complicated.

The objective of the present invention is 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 being inspected without complicating the device.

The present invention is an eddy current flaw detection device comprising a pair of detection coils arranged coaxially and spaced apart from the object to be inspected, and a bridge circuit in which the two sides of a bridge are formed by the detection coils so that the magnetic fields generated by these detection coils are in opposite phase. The device comprises a first excitation coil that generates an excitation magnetic field to generate eddy currents in the surface layer of the object to be inspected, and a second excitation coil that generates an excitation magnetic field to generate eddy currents in the surface layer of the object to be inspected, and is composed of a pair of coil parts arranged coaxially with the detection coils so as to sandwich the pair of detection coils, and the distance between the detection coil and the coil part of the second 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 second excitation coil and detected by the adjacent detection coil changes from that of a noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil.

By configuring the present invention as described above, it is possible to change the phase of a noise signal resulting from the vibration of the inspection device and the eccentricity or vibration of the object under test obtained from the excitation magnetic field by the first excitation coil, and a noise signal resulting from the vibration of the inspection device and the eccentricity or vibration of the object under test obtained from the excitation magnetic field by the second excitation coil. As a result, the noise signals are superimposed on each other, making it possible to reduce the noise signals and improving the S/N ratio.

In addition, the present invention can be configured such that the first excitation coil is composed of a pair of coil sections arranged coaxially with the pair of detection coils so as to sandwich the pair of detection coils, and the coil sections of the first excitation coil are arranged between the detection coil and each coil section of the second excitation coil.

The present invention can also be configured so that the first excitation coil is arranged concentrically with the detection coil and on the outer periphery of the detection coil.

In addition, in the present invention, it is preferable to set the distance between the detection coil and the second excitation coil arranged adjacent to it so that the noise signal due to eccentricity or vibration excited by the second excitation coil and detected by the detection coil arranged adjacent to it is in opposite phase to the noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil.

By configuring the present invention as described above, the noise signal due to the vibration of the inspection device and the eccentricity or vibration of the object under test obtained from the excitation magnetic field by the first excitation coil and the noise signal due to the vibration of the inspection device and the eccentricity or vibration of the object under test obtained from the excitation magnetic field by the second excitation coil are in opposite phase. As a result, the noise signals are superimposed on each other, making it possible to cancel out the noise signals and improving the S/N ratio.

The present invention is also preferably configured to convert the phase of the AC power to be provided to the second excitation coil so that the noise signal due to eccentricity or vibration excited by the second excitation coil and detected by the detection coil located adjacent to the second excitation coil is in opposite phase to the noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil by the first excitation coil.

As described above, the present invention is configured to convert the phase of the AC power provided to the second excitation coil and provide it to the second excitation coil, so that the noise signal resulting from the excitation magnetic field of the first excitation coil and the vibration of the inspection device and the eccentricity or vibration of the object under test are in opposite phase to the noise signal resulting from the excitation magnetic field of the second excitation coil and the vibration of the inspection device and the eccentricity or vibration of the object under test. As a result, the noise signals are superimposed on each other, making it possible to cancel each other out and improving the S/N ratio.

The present invention also includes an oscillator, a first power amplifier that amplifies an AC output from the oscillator, a second excitation phase converter that converts the phase of the AC output from the oscillator, and a second power amplifier that amplifies the AC output from the second excitation phase converter, and can be configured so that AC power is supplied from the first power amplifier to the first excitation coil, and AC power is supplied from the second power amplifier to the second excitation coil.

In addition, the object to be inspected is a metallic round bar material or a metallic round pipe material, the detection coil, the first excitation coil, and the second excitation coil are through coils, and the distance between the detection coil and the second excitation coil is set based on the difference between the outer diameter of the metallic round bar material or the metallic round pipe material and the inner diameter of the detection coil and the second excitation coil.

The present invention also provides an eddy current inspection probe in which the object to be inspected is a metallic round pipe material or a metallic round bar material, and the eddy current inspection probe is arranged in close proximity to the object to be inspected and has the detection coil, the first excitation coil, and the second excitation coil, and the eddy current inspection probe can be configured to be cylindrical or semi-cylindrical.

In addition, the present invention can be configured so that the object to be inspected is a metal square pipe material or a metal square bar material, and is equipped with an eddy current inspection probe arranged in close proximity to the object to be inspected and having the detection coil, the first excitation coil and the second excitation coil, and the eddy current inspection probe is formed in a rectangular pipe shape formed to surround the object to be inspected, or in the shape of a rectangular plate arranged at a distance from the surface of the object to be inspected.

The present invention provides an eddy current flaw detector that can eliminate noise signals caused by vibration of the inspection device and eccentricity or vibration of the object being inspected, improving the S/N ratio.

FIG. 1 is a schematic diagram of an eddy current flaw detector and an object to be inspected according to a first embodiment of the present invention. FIG. 2 is a schematic circuit diagram showing the configuration of an eddy current flaw detector according to the first embodiment of the present invention. FIG. 3 is a block diagram showing an eddy current flaw detector according to the first embodiment of the present invention. FIG. 4 is a schematic diagram for explaining the removal of noise signals due to vibration of the eddy current flaw detector according to the present invention and eccentricity or vibration of the test object. FIG. 5 is a schematic diagram of an eddy current flaw detector and an object to be inspected according to a second embodiment of the present invention. FIG. 6 is a schematic circuit diagram showing the configuration of an eddy current flaw detector according to the second embodiment of the present invention. FIG. 7 is a block diagram showing an eddy current flaw detector according to a second embodiment of the present invention. FIG. 8 is a block diagram showing an eddy current flaw detector according to a third embodiment of the present invention.

Next, an eddy current flaw detector according to an embodiment of the present invention will be specifically described with reference to the attached drawings. Note that the eddy current flaw detector according to the present invention is not limited to the embodiment shown below, and can be modified as appropriate without departing from the gist of the invention.

As shown in FIG. 1, the object to be inspected 3 of the present invention is a conductor, such as a round metal pipe or a round metal bar. An eddy current inspection probe 1 is placed close to the object to be inspected 3, and a flaw inspection is performed by detecting changes in eddy currents generated in the object to be inspected 3. The eddy current inspection probe 1 detects flaws and thinning of the object to be inspected 3 by eddy current inspection. In the following, flaws, thinning, etc. are collectively referred to as defects.

The eddy current inspection probe 1 used in the eddy current inspection device according to the first embodiment of the present invention is formed in a cylindrical or semi-cylindrical shape and includes a pair of detection coils 10a, 10b, a first excitation coil 11 that generates an excitation magnetic field to generate eddy currents in the surface layer of the object to be inspected 3, and a second excitation coil 12. The second excitation coil 12 is composed of a pair of coil parts 12a, 12b that are arranged coaxially with the detection coils 10a, 10b so as to sandwich the pair of detection coils 10a, 10b. The eddy current inspection probe 1 according to the first embodiment of the present invention is a probe used in a mutual induction type eddy current inspection device. The first excitation coil 11 is used as a mutual induction excitation coil. The second excitation coil 12 is used as a noise cancellation excitation coil.

In this first embodiment, the pair of detection coils 10a, 10b, the first excitation coil 11, and the second excitation coil 12 are composed of through coils.

The first excitation coil 11 is composed of a pair of coil sections 11a, 11b arranged coaxially to sandwich a pair of detection coils 10a, 10b. The coil section 11a of the first excitation coil 11 is arranged between the detection coil 10a and the coil section 12a of the second excitation coil 12, and the coil section 11b of the first excitation coil 11 is arranged between the detection coil 10b and the coil section 12b of the second excitation coil 12.

By applying an alternating current to the pair of coil parts 11a, 11b constituting the first excitation coil 11 and generating an excitation magnetic field, eddy currents are generated in the surface layer part of the inspection object 3. By applying an alternating current to the pair of coil parts 12a, 12b constituting the second excitation coil 12 and generating an excitation magnetic field, eddy currents are generated in the surface layer part of the inspection object 3.

The pair of detection coils 10a, 10b are differentially connected. The pair of differentially connected detection coils 10a, 10b are connected to a bridge circuit. The pair of detection coils 10a, 10b detect changes in eddy currents generated in the inspected object 3. When the voltages generated in the pair of detection coils 10a, 10b differ, a signal indicating that a defect has been detected is output from the bridge circuit.

The detection coils 10a, 10b, the pair of coil sections 11a, 11b constituting the first excitation coil 11, and the pair of coil sections 12a, 12b constituting the second excitation coil 12 are arranged coaxially spaced apart and out of contact with the object to be inspected 3. The eddy current inspection probe 1 and the object to be inspected 3 move relative to each other. That is, in the eddy current inspection device 100, the eddy current inspection probe 1 moves relative to the object to be inspected 3 in one case and the object to be inspected 3 moves relative to the fixed eddy current inspection probe 1 in another case. In the eddy current inspection device 100 of this embodiment, the eddy current inspection probe 1 moves relative to the object to be inspected 3 in the direction of the arrow in the figure, inspects the condition of the surface of the object to be inspected 3, and detects the presence or absence of defects.

In this embodiment, the test object 3 is a metal round pipe material or a metal round bar material.

In this embodiment, the detection coils 10a, 10b are spaced apart by a distance D from the coil portions 12a, 12b of the second excitation coil 12 that are disposed adjacent to them. As shown in FIG. 1, the coil portion 12a of the second excitation coil 12 and the detection coil 10a are spaced apart by a distance D, and the coil portion 12b of the second excitation coil 12 and the detection coil 10b are spaced apart by a distance D. This distance D will be described later.

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

As shown in FIG. 2, the bridge circuit 24 is composed of detection coils 10a and 10b and resistors 13a and 13b. The detection coils 10a and 10b are connected as two sides of the bridge circuit 24, and the resistors 13a and 13b are connected as the other two sides of the bridge circuit 24.

A first excitation coil 11 consisting of a pair of coil sections 11a, 11b is provided so as to sandwich the detection coils 10a, 10b. This embodiment is a mutual induction type eddy current flaw detector that excites the first excitation coil 11 and detects with the detection coils 10a, 10b.

A mutual induction type eddy current flaw detector can increase the excitation voltage generated by the excitation coil. In other words, in a self-induction type, the size of the coil is restricted due to its relationship with the bridge circuit. In contrast, in a mutual induction type, there is no such restriction, so there is freedom in the size of the coil and it is easy to increase the excitation voltage. By increasing the excitation voltage, the detection signal can be increased. For example, when the clearance between the detection coil and the object being inspected is large, i.e., when the charging rate is low, the detection signal can be increased by increasing the excitation voltage, thereby improving detection accuracy.

The AC output from the AC power supply 30 (in FIG. 3, the oscillator 21 and the first power amplifier 22) is applied to the coil portions 11a and 11b of the first excitation coil 11, which excites the coil portions 11a and 11b. The excitation from the coil portions 11a and 11b excites the surface portion of the test object 3, which generates eddy currents. The detection coils 10a and 10b detect the impedance change caused by the change in magnetic flux generated by the eddy currents using the detection portion 31 (in FIG. 3, the phase detector 27, etc.).

The detection coils 10a and 10b are differentially connected so that the magnetic fields they generate are in opposite phase to each other. In this embodiment, the first excitation coil 11 excites the test object 3, and the detection coils 10a and 10b detect the change in impedance that accompanies the change in magnetic flux generated by eddy currents.

As shown in FIG. 2, a second excitation coil 12 consisting of a pair of coil portions 12a, 12b is provided to sandwich the detection coils 10a, 10b. AC output from an AC power source 30 (oscillator 21 and second power amplifier 23 in FIG. 3) is provided to the coil portions 12a, 12b that constitute the second excitation coil 12, exciting the coil portions 12a, 12b. The excitation from the coil portions 12a, 12b excites the surface layer of the test object 3, generating eddy currents. This second excitation coil 12 is used as a noise cancellation excitation coil.

The coil portion 12a is wound so that the magnetic field it generates is in phase with the coil portion 11a of the first excitation coil 11. The coil portion 12b is wound so that the magnetic field it generates is in phase with the coil portion 11b of the first excitation coil 11.

The detection coil 10a also detects changes in impedance that accompany changes in magnetic flux generated by eddy currents from the test object 3 through the coil section 12a.

The detection coil 10b also detects changes in impedance that accompany changes in magnetic flux generated by eddy currents from the test object 3 through the coil section 12b.

In this way, the detection coil 10a detects a change in the synthetic impedance based on the excitation of the coil portion 11a of the first excitation coil 11 and the excitation of the coil portion 12a of the second excitation coil 12. The detection coil 10b detects a change in the synthetic impedance based on the excitation of the coil portion 11b of the first excitation coil 11 and the excitation of the coil portion 12b of the second excitation coil 12. And, if there is no abnormality in the test subject 3, the output signal of this bridge circuit 24 is set to be zero-balanced.

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

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 in FIG. 3.

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

As shown in Figure 2, the bridge circuit 24 is composed of detection coils 10a and 10b and resistors 13a and 13b of the eddy current flaw detection probe 1.

The AC output from the oscillator 21 is amplified by the first power amplifier 22 and is provided to the coil section (mutual induction excitation coil section) 11a, 11b of the first excitation coil 11. The AC output from the oscillator 21 is amplified by the second power amplifier 23 and is provided to the coil section (noise cancellation coil section) 12a, 12b of the second excitation coil 12.

The object 3 is excited by AC output applied to the coil portion 11a of the first excitation coil 11, the coil portion 12a of the second excitation coil 12, the coil portion 11b of the first excitation coil 11, and the coil portion 12b of the second excitation coil 12. Then, the detection coils 10a and 10b detect the impedance change associated with the change in the magnetic flux generated by the eddy current.

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

The detection phase converter 26 converts the signal from the oscillator 21 into a signal with the same phase as the excitation signal and a signal with a phase shift of 90 degrees relative to the excitation signal, and provides the signal to the phase detector 27.

The unbalanced output amplified by the amplifier 25 and the output of the detection phase converter 26 are provided to the 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.

The phase detector 27 synchronously detects the unbalanced output using a signal of the same phase as 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 is, for example, a personal computer (PC) connected to the eddy current flaw detector 100.

In this embodiment, damage to the subject 3 is detected based on the output values from the detection coils 10a and 10b.

In the above-mentioned eddy current flaw detection device 100, when vibration of the eddy current flaw detection probe 1 or the object to be inspected 3 or eccentricity between the eddy current flaw detection probe 1 and the object to be inspected 3 occurs, the distance between the detection coils 10a, 10b and the object to be inspected 3, and the distance between the first excitation coil 11 (coil portions 11a, 11b) and the second excitation coil 12 (coil portions 12a, 12b) and the object to be inspected 3 change, respectively, and noise signals are generated.

When the eddy current inspection probe 1 moves, the movement of the eddy current inspection probe 1 generates vibrations in the eddy current inspection probe 1, which changes the distance between the detection coils 10a, 10b and the object 3 and the distance between the first excitation coil 11 (coil parts 11a, 11b) and the second excitation coil 12 (coil parts 12a, 12b) and the object 3, respectively, generating noise signals. Also, when the object 3 moves, the movement of the object 3 generates vibrations in the object 3, which changes the distance between the detection coils 10a, 10b and the object 3 and the distance between the first excitation coil 11 (coil parts 11a, 11b) and the second excitation coil 12 (coil parts 12a, 12b) and the object 3, respectively, generating noise signals. Furthermore, even if the eddy current flaw detection probe 1 or the object under test 3 does not vibrate, if there is eccentricity between the detection coils 10a, 10b and the object under test 3, or between the first excitation coil 11 (coil portions 11a, 11b) and the second excitation coil 12 (coil portions 12a, 12b) and the object under test 3, the distance between the detection coils 10a, 10b and the object under test 3 and the distance between the first excitation coil 11 (coil portions 11a, 11b) and the second excitation coil 12 (coil portions 12a, 12b) and the object under test 3 will change, generating a noise signal.

For this reason, in this specification, a noise signal due to eccentricity or vibration means a noise signal that is generated due to a change in the relative distance between the detection coils 10a, 10b and the object under test 3 caused by vibration of the coil or object under test or eccentricity of the coil or object under test.

Here, the inventors have thoroughly studied the relationship between the distance D between the detection coil 10a and the coil portion 12a of the second excitation coil 12 and the distance D between the detection coil 10b and the coil portion 12b of the second excitation coil 12 and the noise signal. As a result, it was found that there exists a distance D at which the phase of the vibration noise signal excited by the second excitation coil 12 and detected by the adjacent detection coil is opposite to that of the noise signal due to eccentricity or vibration excited by the first excitation coil 11 and detected by the detection coil.

The inventors have confirmed that, for example, when the subject 3 is a metal round bar material, and the detection coils 10a, 10b, the first excitation coil 11, and the second excitation coil 12 are through coils, there is an optimal 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 material and the inner diameter of the coils.

The first embodiment of the present invention determines the distance D between the second excitation coil and the adjacent detection coil at which the noise signals due to eccentricity or vibration are in opposite phase. The detection coils 10a, 10b, the first excitation coil 11, and the second excitation coil 12 are arranged in the eddy current flaw detection probe 1 so that the distance D between the coil portion 12a of the second excitation coil 12 and the detection coil 10a is equal to the distance D between the coil portion 12b of the second excitation coil 12 and the detection coil 10b is equal to the distance D. This makes it possible to eliminate noise due to eccentricity or vibration even when vibration of the eddy current flaw detection probe 1 of the eddy current flaw detection device 100 or eccentricity of the test object 3 occurs.

By optimally setting the distance D between the second excitation coil and the detection coil, the vibration noise signal excited by the second excitation coil and detected by the adjacent detection coil will be in opposite phase to the vibration noise signal excited by the first excitation 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.

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

Next, a specific example of the present invention will be described with reference to Figure 4. In this specific example, the round bar material is made eccentric, and the impedance change is detected by the detection coil, and it has been confirmed that noise signals caused by vibration or eccentricity of the test object can be eliminated.

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

The specific example of the eddy current flaw detection probe 1 shown in FIG. 4 has a pair of coil sections 11a, 11b constituting a first excitation coil 11, sandwiching the detection coils 10a, 10b. A pair of coil sections 12a, 12b constituting a second excitation coil 12 is provided to sandwich the pair of coil sections 11a, 11b.

The inner diameters of the detection coils 10a and 10b, the coil portions 11a and 11b of the first excitation coil 11, and the coil portions 12a and 12b of the second excitation coil 12 are the same. The test object 3, which is made of a metal round bar, is inserted into these coils.

As shown in FIG. 4, the test object 3 was tilted in the direction of the arrow in the figure by a movement distance d of the end, centered on the radial and longitudinal center (c) between the detection coils 10a and 10b.

AC power is applied to the coil sections 11a and 11b of the first excitation coil 11 and the coil sections 12a and 12b of the second excitation coil 12. The change in impedance is detected by the detection coils 10a and 10b. The AC power to the coil sections 11a and 11b of the first excitation coil 11 and the coil sections 12a and 12b of the second excitation coil 12 is controlled so that only the first excitation coil 11 is applied, or only the second excitation coil 12 is applied.

The inventors have confirmed that the detection result of excitation of only the first excitation coil 11 and the detection result of excitation of only the second excitation coil 12 are in different phases.

Next, since the phases of the detection signals calculated from the composite signal of the detection values obtained by exciting the first excitation coil 11 and the second excitation coil 12 are different, it can be seen that noise due to eccentricity or vibration is offset and the noise can be reduced.

The second excitation coil and the detection coil are considered to have a distance D at which the phases of the two detection signals are almost opposite, that is, the phases of the two are approximately 180 degrees. 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 caused by eccentricity or vibration and eliminate the noise.

In this way, according to the present invention, by setting the distance D between the excitation coil and the detection coil to a distance that results in an opposite phase, noise due to eccentricity or vibration can be eliminated, and the S/N ratio can be improved.

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

Next, a second embodiment of the present invention will be described with reference to Figs. 5 to 7. Fig. 5 is a schematic diagram of an eddy current flaw detector and an object to be inspected according to the second embodiment of the present invention, Fig. 6 is a schematic circuit diagram showing the configuration of an eddy current flaw detector according to the second embodiment of the present invention, and Fig. 7 is a block diagram showing an eddy current flaw detector according to the second embodiment of the present invention. Note that the second embodiment is the same as the first embodiment except for the configuration of the second excitation coil, so the same parts are given the same reference numerals and their description will be omitted.

The eddy current inspection probe 1 used in the eddy current inspection device according to the second embodiment of the present invention is formed in a cylindrical or semi-cylindrical shape and includes a pair of detection coils 10a, 10b, a first excitation coil 110 that generates an excitation magnetic field to generate an eddy current in the surface layer of the inspected object 3, and a second excitation coil 12. The second excitation coil 12 is composed of a pair of coil parts 12a, 12b that are arranged coaxially with the detection coils 10a, 10b so as to sandwich the pair of detection coils 10a, 10b. The eddy current inspection probe 1 according to the second embodiment of the present invention is a probe used in a mutual induction type eddy current inspection device. The first excitation coil 110 is used as a mutual induction excitation coil. The second excitation coil 12 is used as a noise cancellation excitation coil.

The first excitation coil 11 in the first embodiment is composed of a pair of coil sections 11a, 11b arranged coaxially to sandwich the pair of detection coils 10a, 10b, whereas the first excitation coil 110 in the second embodiment is arranged concentrically with the detection coils 10a, 10b. In this way, by arranging the first excitation coil 110 concentrically with the detection coils 10a, 10b, the length of the eddy current flaw detection probe 1 can be made shorter than that of the probe in the first embodiment.

Figure 6 is a schematic circuit diagram showing the configuration of the detection coil portion of the eddy current flaw detector according to the present invention. As shown in Figure 6, the bridge circuit 24 is composed of detection coils 10a and 10b and resistors 13a and 13b, with the detection coils 10a and 10b being connected as two sides of the bridge circuit 24, and the resistors 13a and 13b being connected as the other two sides of the bridge circuit 24.

A first excitation coil 110 is provided to cover the detection coils 10a and 10b. A second excitation coil 12 consisting of a pair of coil portions 12a and 12b is provided to sandwich the detection coils 10a and 10b. This embodiment is a mutual induction type eddy current flaw detector that excites with the first excitation coil 11 and detects with the detection coils 10a and 10b. Other than the configuration of the first excitation coil 110, the configuration is the same as that of the first embodiment.

Next, the eddy current flaw detector according to the second embodiment of the present invention will be further described with reference to the block diagram in FIG. 7.

As shown in FIG. 7, the eddy current flaw detector 100 includes an oscillator 21, a first power amplifier 22, a second power amplifier 23, a bridge circuit 24, a detection phase converter 26, an amplifier 25, and a phase detector 27.

As shown in Figure 6, the bridge circuit 24 is composed of detection coils 10a and 10b and resistors 13a and 13b of the eddy current flaw detection probe 1.

The AC output from the oscillator 21 is amplified by the first power amplifier 22 and provided to the first excitation coil 110. The AC output from the oscillator 21 is also amplified by the second power amplifier 23 and provided to the coil sections (noise cancellation coil sections) 12a and 12b of the second excitation coil 12.

The object 3 is excited by AC output applied to the first excitation coil 110 and the coil portion 12a and coil portion 12b of the second excitation coil 12, respectively. Then, the detection coils 10a and 10b detect the impedance change associated with the change in magnetic flux generated by the eddy current.

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

The detection phase converter 26 converts the signal from the oscillator 21 into a signal with the same phase as the excitation signal and a signal with a phase shift of 90 degrees relative to the excitation signal, and provides the signal to the phase detector 27.

The unbalanced output amplified by the amplifier 25 and the output of the detection phase converter 26 are provided to the 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.

In this embodiment, damage to the subject 3 is detected based on the output values from the detection coils 10a and 10b.

Next, an eddy current flaw detector according to a third embodiment of the present invention will be described with reference to the block diagram of FIG.
In the third embodiment shown in Fig. 8, the distance D between the second excitation coil and the detection coil is set to a predetermined value, and if the detection signals are not in opposite phase, the phase of the signal given to the second excitation coil is converted and adjusted so that the signals are in opposite phase. Therefore, in the third embodiment shown in Fig. 8, the AC output from the oscillator 21 is given to a second excitation phase converter 40. Note that the third embodiment shown in Fig. 8 is the same as the first embodiment except for the provision of the second excitation phase converter 40, and therefore the same parts are given the same reference numerals and description thereof will be omitted.

As shown in FIG. 8, the AC output from the oscillator 21 is provided to the second excitation phase converter 40. This second excitation phase converter 40 converts the phase of the excitation AC power provided to the coil portions 12a and 12b of the second excitation coil 12. This second excitation phase converter 40 converts the phase of the AC power provided to the coil portions 12a and 12b of the second excitation coil 12 so that the phases of both detection signals are in opposite phases.

The AC power phase-converted by the second excitation phase converter 40 is provided to the second power amplifier 23, amplified by the second power amplifier 23, and provided to the coil portions 12a and 12b of the second excitation coil 12.

As a result, the coil sections 12a and 12b constituting the second excitation coil 12 are excited by being supplied with AC power that has been phase-converted by the second excitation phase converter 40, and the detection signals from the detection coils 10a and 10b and the coil sections 11a and 11b of the first excitation coil 11 are excited by being supplied with AC power, so that the phase signals of the detection signals from the detection coils 10a and 10b are in opposite phase, thereby improving the S/N ratio.

In the above embodiment, a case where a through coil is used is described, but the present invention can be applied not only to through coils, but also to internally inserted coils and top-mounted coils, and the same effects can be obtained.

In the above-described embodiment, the case where the object to be inspected is a metallic round pipe material or a metallic round bar material has been described, but the object to be inspected is not limited to a metallic round pipe material or a metallic round bar material, and can also be a metallic square pipe material or a metallic square column material. In this case, the eddy current inspection probe may be formed in a rectangular pipe shape formed to surround the object to be inspected, or in a rectangular plate shape arranged at a distance from the surface of the object to be inspected.

1: Eddy current flaw detection probe 3: Test object 10a: Detection coil 10b: Detection coil 11: First excitation coil 12: Second excitation coil 21: Oscillator 22: First power amplifier 23: Second 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 31: Detection section 40: Second excitation phase converter 100: Eddy current flaw detection device

Claims (9)

An eddy current flaw detector comprising a pair of detection coils arranged coaxially and spaced apart from each other in a non-contact manner with respect to an object to be inspected, and a bridge circuit in which two sides of a bridge are formed by the detection coils so that magnetic fields generated by the detection coils are in opposite phases,
a first excitation coil that generates an excitation magnetic field to generate an eddy current in a surface layer portion of the object to be inspected;
a second excitation coil configured with a pair of coil sections arranged coaxially with the pair of detection coils so as to sandwich the pair of detection coils, the second excitation coil generating an excitation magnetic field to generate an eddy current in a surface layer portion of the object to be inspected;
An eddy current flaw detection device, wherein the distance between the detection coil and the coil portion of the second excitation coil arranged adjacent to it is set to a distance at which a phase change occurs between a noise signal due to eccentricity or vibration excited by the second excitation coil and detected by the adjacent detection coil, and a noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil. The eddy current flaw detector according to claim 1,
An eddy current flaw detection device, wherein the first excitation coil is composed of a pair of coil sections arranged coaxially with each of the pair of detection coils so as to sandwich the pair of detection coils, and the coil sections of the first excitation coil are arranged between the detection coil and each coil section of the second excitation coil. The eddy current flaw detector according to claim 1,
An eddy current flaw detection device, wherein the first excitation coil is arranged concentrically with the detection coil and on the outer circumferential side of the detection coil. The eddy current flaw detector according to any one of claims 1 to 3,
An eddy current flaw detection device, wherein the distance between the detection coil and the second excitation coil arranged adjacent to it is set to a distance such that a noise signal due to eccentricity or vibration excited by the second excitation coil and detected by the detection coil arranged adjacent to it has an opposite phase to a noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil. The eddy current flaw detector according to any one of claims 1 to 4,
an eddy current flaw detection device which converts the phase of the AC power to be provided to the second excitation coil so that a noise signal due to eccentricity or vibration that is excited by the second excitation coil and detected by the detection coil located adjacent to the second excitation coil and a noise signal due to eccentricity or vibration that is excited by the first excitation coil and detected by the detection coil by providing AC power to the first excitation coil are in opposite phase to each other. The eddy current flaw detector according to any one of claims 1 to 5,
a first power amplifier that amplifies an AC output from the oscillator; a second excitation phase converter that converts a phase of the AC output from the oscillator; and a second power amplifier that amplifies the AC output from the second excitation phase converter,
an eddy current flaw detector that applies AC power from the first power amplifier to the first excitation coil, and applies AC power from the second power amplifier to the second excitation coil. The eddy current flaw detector according to any one of claims 1 to 6,
the test object is a metal round bar material or a metal round pipe material, the detection coil, the first excitation coil, and the second excitation coil are through coils, and a distance between the detection coil and the second excitation coil is set based on a difference between an outer diameter of the metal round bar material or the metal round pipe material and an inner diameter of the detection coil and the second excitation coil;
Eddy current testing equipment. The eddy current flaw detector according to any one of claims 1 to 6,
the test object is a metal round pipe material or a metal round bar material,
an eddy current flaw detection probe disposed adjacent to the object to be inspected and having the detection coil, the first excitation coil, and the second excitation coil;
The eddy current testing apparatus, wherein the eddy current testing probe is formed in a cylindrical or semi-cylindrical shape. The eddy current flaw detector according to any one of claims 1 to 6,
The test piece is a metal square pipe material or a metal square bar material,
an eddy current flaw detection probe disposed adjacent to the object to be inspected and having the detection coil, the first excitation coil, and the second excitation coil;
An eddy current flaw detection device, wherein the eddy current flaw detection probe is formed in a rectangular pipe shape formed to surround the object to be inspected or in a rectangular plate shape arranged at a distance from the surface of the object to be inspected.

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