JP5170844B2 - Eddy current flaw detector and eddy current flaw detection method - Google Patents

Description

  The present invention relates to an eddy current flaw detector and an eddy current flaw detection method, and in particular, when a test object is flawed using an eddy current flaw probe, a distance (gap) between the coil of the eddy current flaw probe and the test object is detected, The present invention relates to an eddy current flaw detection apparatus and an eddy current flaw detection method for correcting the magnitude of a flaw signal detected according to the detected distance.

  When moving the eddy current flaw detection probe to inspect the inspection object, if the distance between the coil of the eddy current flaw detection probe and the inspection object fluctuates (so-called lift-off), the flaw signal also fluctuates and the flaw detection accuracy decreases. End up. However, since it is difficult to move the eddy current flaw detection probe while keeping the lift-off constant, a conventional eddy current is detected by a distance sensor or the like, and the magnitude of the scratch signal is corrected (adjusted) according to the detected lift-off. Current flaw detection devices have been proposed (see, for example, Patent Document 1 and Patent Document 2).

A conventional eddy current flaw detector (Patent Document 1) using an optical distance sensor for detecting lift-off will be described with reference to FIG.
FIG. 2A shows an eddy current flaw detection probe and a test object.
The coil 12 of the eddy current flaw detection probe is arranged so as to face the object to be inspected 11.
Distance sensors 131 to 133 are attached to the outer periphery of the coil 12 of the eddy current flaw detection probe. The distance sensors 131 to 133 detect the distance to the device under test 11, that is, lift-off, using light. The flaw detection apparatus using the eddy current flaw detection probe shown in FIG. 2A corrects the scratch signal using a signal corresponding to lift-off detected by the distance sensors 131 to 133.

FIG. 2B shows a specific configuration of the distance sensors 131 to 133 shown in FIG. Note that FIG. 2B shows only one distance sensor.
The distance sensor 13 includes a light source 141, a light receiver (photodiode) 142, a half mirror 143, and a lens 144. The light L1 emitted from the light source 141 is irradiated to the inspection object 11 via the half mirror 143 and the lens 144, and the light L2 reflected by the inspection object 11 is applied to the light receiving body 142 via the lens 144 and the half mirror 143. To reach. The correction unit 15 of the eddy current flaw detection apparatus detects (measures) lift-off using the received signal of the photoreceptor 142 and corrects the scratch signal using a signal corresponding to the detected lift-off.

  In order to detect lift-off, there is a technique in which an outer lift-off measurement coil of an optical distance sensor is used and a lift-off measurement coil is arranged on the outer periphery of an excitation coil of an eddy current flaw detection probe (Patent Document 2). The lift-off measuring device measures the lift-off using the detection signal of the lift-off measuring coil, and corrects the scratch signal by controlling the excitation current and the detection current of the eddy current flaw detection probe according to the lift-off.

JP 2006-138784 A Japanese Patent Laid-Open No. 2003-232776

Conventional eddy current flaw detectors must be provided with a distance sensor and lift-off measuring coil separate from the coil of the eddy current flaw probe, so that the eddy current flaw probe has a large size and a complicated structure. Since lift-off must be detected (measured) based on the detection signal of the lift-off measuring coil, a lift-off measuring / detecting means is required.
Further, since the conventional eddy current flaw detector has a distance sensor and a lift-off measurement coil attached to the outer periphery of the coil of the eddy current flaw probe, the position of the distance sensor and the lift-off measurement coil is the center of the coil of the eddy current flaw probe. The detection point of lift-off and the center point of flaw detection do not coincide with each other. Therefore, the conventional eddy current flaw detector has a lower lift-off correction accuracy.
An object of the present invention is to integrate a coil of an eddy current flaw detection probe and a lift-off detection means in view of the above-mentioned problems of a conventional eddy current flaw detection probe.

In order to achieve the object of the present invention, an eddy current flaw detection device according to claim 1 is a lift-off method using an excitation power source and an excitation coil for supplying a flaw detection excitation current and a lift-off detection current to the excitation coil of the eddy current flaw detection probe. An eddy current flaw detection device including a lift-off detection circuit for detecting a flaw and a flaw signal correction circuit for correcting a flaw signal by the lift-off detection circuit ,
A constant current drive circuit that drives the excitation coil at a constant current using the lift-off detection current is provided. The lift-off is detected as a drive voltage corresponding to lift-off from the constant-current drive circuit, and the lift- off detection circuit corresponds to the drive voltage. A correction voltage to be generated is generated .
The eddy current flaw detector according to claim 2 is the eddy current flaw detector according to claim 1, wherein the lift-off detection current is a flaw detection excitation current.
In the eddy current flaw detection method according to claim 3, a flaw detection excitation current and a lift-off detection current are supplied to the excitation coil of the eddy current flaw detection probe, and lift-off is detected by a lift-off detection circuit using the excitation coil. An eddy current flaw detection method for correcting
The lift-off, the detecting the exciting coil as a drive voltage corresponding to the lift-off from the constant current driving circuit for constant current driven by the lift off detection current, that you correct the flaw signal by the correction voltage corresponding to the drive voltage Features.

In the present invention, since the exciting coil also serves as a lift-off detection coil, there is no need to separately provide a lift-off detection sensor. Therefore, the eddy current flaw detection probe is small in size, simple in structure, and easy to assemble. In the present invention, since the excitation coil detects lift-off, the lift-off detection point and the flaw detection point always coincide. Therefore, the eddy current flaw detector according to the present invention can accurately correct the scratch signal based on the lift-off.
In the present invention, since the exciting coil is driven at a constant current, the lift-off can be taken out as a voltage, and the voltage is used for correcting the scratch signal, so that the scratch signal correcting means becomes simple.
In the present invention, since the flaw detection excitation power supply and the lift-off detection power supply are provided separately, it is not necessary to change the frequency of the lift-off detection current even if the frequency of the flaw detection excitation current is changed. Therefore, since it is not necessary to change the setting condition of the lift-off detection current every time flaw detection is performed, handling of the eddy current flaw detection apparatus is simplified, and flaw detection work is simplified.

  An eddy current flaw detector according to an embodiment of the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 21 denotes an excitation power source, and P denotes an eddy current flaw detection probe generally called a Θ probe, which includes an excitation coil EC and a detection coil DC. The excitation power supply 21 includes a flaw detection excitation power supply 211 and a lift-off detection power supply 212. Here, lift-off refers to the distance (gap) between the excitation coil EC of the eddy current flaw detection probe P and the inspection surface of an object to be inspected (not shown).
The excitation coil EC is supplied with a flaw detection excitation current having a predetermined frequency from the flaw detection excitation power supply 211 via the excitation amplifier 23. At the same time, a lift-off detection current having a predetermined frequency is supplied from the lift-off detection power supply 212 via the constant current drive circuit 221. Supplied. As the flaw detection excitation current and the lift-off detection current, for example, a frequency suitable for flaw detection and lift-off detection is selected from a plurality of frequencies obtained by dividing the common original oscillation frequency. For example, since the flaw detection excitation current has a frequency suitable for flaw detection depending on the material of the object to be inspected, a frequency suitable for flaw detection is selected every time flaw detection is taken into consideration. On the other hand, a lift-off detection current having the same frequency can be used even if the frequency of the flaw detection excitation current changes.

  When a flaw detection excitation current is supplied to the excitation coil EC, an eddy current is generated in the inspection object by the excitation coil EC. And when a to-be-inspected object has a crack, disorder arises in the eddy current, and a voltage induces in detection coil DC by the disorder of the eddy current. The induced voltage of the detection coil DC is applied to the synchronous detector 241 and detected by the synchronous detector 241 with a carrier wave having the same frequency as the flaw detection excitation current. The detection output of the synchronous detector 241 is supplied to the low pass filter 242. The low-pass filter 242 extracts a scratch signal from the detection output and supplies it to a scratch signal correction circuit (comprising an amplifier) 243. Here, the scratch signal is a signal generated due to a scratch on the object to be inspected.

  The constant current drive circuit 221 drives the exciting coil EC with a constant current by the lift-off detection current supplied from the lift-off detection power supply 212. When the exciting coil EC is driven at a constant current, the impedance of the exciting coil changes corresponding to the change in the distance between the exciting coil EC and the object to be inspected, that is, the change in lift-off, and the driving voltage changes. For example, when the lift-off is large, the impedance is increased and the drive voltage is increased. Conversely, when the lift-off is small, the impedance is decreased and the drive voltage is decreased. Therefore, when the lift-off changes, the lift-off detection circuit 222 can detect a drive voltage corresponding to the change. The lift-off correction circuit 223 generates a correction voltage corresponding to the drive voltage detected by the lift-off detection circuit 222 and supplies the correction voltage to the scratch signal correction circuit 243. The scratch signal correction circuit 243 adjusts the gain of the amplifier by the correction voltage of the lift-off detection circuit 222 to correct the magnitude of the scratch signal. That is, the scratch signal correction circuit 243 corrects or adjusts the size of the scratch signal in response to lift-off. Therefore, the output of the scratch signal correction circuit 243 provides a scratch signal FS that is not affected by lift-off.

  The correction voltage of the lift-off detection circuit 222 may be supplied to the excitation amplifier 23 to adjust the gain of the excitation amplifier 23. In that case, the excitation current is adjusted by the correction voltage of the lift-off detection circuit 222 and the magnitude of the scratch signal extracted by the low-pass filter 242 is corrected. Therefore, the excitation amplifier 23 is connected to the scratch signal correction circuit. It will also have a function. In that case, the scratch signal correction circuit 243 may not be provided.

In the eddy current flaw detector according to the present embodiment, the excitation coil EC is used for both detection of lift-off and flaw detection of the object to be inspected, so that it is not necessary to separately provide a lift-off detection sensor. Therefore, the eddy current flaw detection probe can be miniaturized, the structure becomes simple, and the assembly becomes easy. Further, since the excitation coil EC is used for both lift-off detection and flaw detection, the lift-off detection point and the flaw detection point always coincide. Therefore, the scratch signal is accurately corrected corresponding to the lift-off.
Since the eddy current flaw detector of this embodiment drives the exciting coil EC at a constant current by the lift-off detection current, the lift-off can be taken out as a voltage, and the gain of the scratch signal correction circuit can be adjusted using the voltage. Therefore, a means for correcting the scratch signal corresponding to the lift-off is simplified.
Further, since the eddy current flaw detection apparatus of this embodiment is provided with a lift-off detection power source and a flaw detection excitation power source separately, it is not necessary to change the frequency of the lift-off detection current even if the frequency of the flaw detection excitation current is changed. Therefore, it is not necessary to change the setting condition of the lift-off detection current every time flaw detection is performed, handling of the eddy current flaw detection apparatus is simplified, and flaw detection work is simplified.

In the above embodiment, the lift-off detection power source and the flaw detection excitation power source are provided separately. However, in the case of an eddy current flaw detection device that does not require changing the frequency of the flaw detection excitation power source, the flaw detection excitation current is used as the lift-off detection current. You can also In such a case, the flaw detection and the lift-off detection can be performed by the flaw detection excitation current by providing only the flaw detection excitation power source and driving the excitation coil at a constant current. In this case, since it is not necessary to provide a lift-off detection power source, the lift-off detection means is simplified.
In the above embodiment, the Θ probe has been described as an example. However, the present invention can be applied to any probe provided with an excitation coil without being limited to the Θ probe.

1 shows a configuration of an eddy current flaw detector according to an embodiment of the present invention. The structure of the conventional eddy current flaw detector is shown.

Explanation of symbols

21 Excitation power supply 211 Flaw detection excitation power supply 212 Lift-off detection power supply 221 Constant current drive circuit 222 Lift-off detection circuit 223 Lift-off correction circuit 23 Excitation amplifier 241 Synchronous detector 242 Low-pass filter 243 Scratch signal correction circuit EC Excitation coil DC detection coil

Claims (3)

Equipped with an excitation power source that supplies flaw detection excitation current and lift-off detection current to the excitation coil of the eddy current flaw detection probe, a lift-off detection circuit that detects lift-off using the excitation coil, and a scratch signal correction circuit that corrects scratch signals by the lift-off detection circuit Eddy current flaw detector ,
A constant current drive circuit that drives the excitation coil at a constant current using the lift-off detection current is provided. The lift-off is detected as a drive voltage corresponding to lift-off from the constant-current drive circuit, and the lift- off detection circuit corresponds to the drive voltage. An eddy current flaw detector characterized by generating a correction voltage .   2. The eddy current flaw detector according to claim 1, wherein the lift-off detection current is a flaw detection excitation current. An eddy current flaw detection method that supplies flaw detection excitation current and lift-off detection current to an excitation coil of an eddy current flaw detection probe, detects lift-off by a lift-off detection circuit using the excitation coil, and corrects a scratch signal by the lift-off ,
The lift-off, the detecting the exciting coil as a drive voltage corresponding to the lift-off from the constant current driving circuit for constant current driven by the lift off detection current, that you correct the flaw signal by the correction voltage corresponding to the drive voltage A characteristic eddy current flaw detection method.

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