JP2007263930A - Eddy current flaw detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an eddy current flaw detector, having satisfactory flaw detection performance and capable of fully discriminating the flaws from the noise. <P>SOLUTION: The eddy current tester includes a first flaw detection part 12, made of a plurality of coils 9a and 9d each of which generates eddy current in the same direction; a second flaw detection part 14 arranged adjacent to the first flaw detection part 12 and symmetric, with respect to a point and made of a plurality of coils 9b and 9c, which each generate an eddy current in the direction opposite to the coils 9a and 9d; and a signal processing part 7, with each receiving single absolute signals AS1, AS2, AS3, AS4 from the coils 9a, 9b, 9c, 9d and combining them. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an eddy current flaw detector.

In the eddy current flaw detector, a probe having a detection coil or the like is used. When detecting complex shapes to be inspected with this eddy current flaw detector, it is difficult to distinguish from defect signals due to variations in the distance (lift-off) between the probe and the inspection object, the inclination of the probe (coil), deformation of the inspection object, etc. A signal (noise) is generated.
In order to eliminate these noises, various methods are used. (For example, see Patent Document 1 and Patent Document 2)
These mostly incorporate coils as elements of the Wheatstone bridge so that the noises cancel each other.

JP 59-10846 A Japanese Patent No. 3343860

  However, none of the methods is capable of sufficiently detecting detection performance, detecting all types of defects, or distinguishing defects from noise.

  In view of the above problems, an object of the present invention is to provide an eddy current flaw detector that has good defect detection performance and can sufficiently distinguish between defects and noise.

In order to solve the above problems, the present invention employs the following means.
That is, the eddy current flaw detector according to the present invention is arranged in a substantially point-symmetric manner adjacent to the first flaw detection portion formed by a plurality of first coils that generate eddy currents in the same direction. A second flaw detection portion formed of a plurality of second coils that generate eddy currents in the opposite direction to the first coil, and a single absolute signal from each of the first coil and each second coil. And a signal processing unit for synthesizing them.

According to the present invention, the first flaw detection unit and the second flaw detection unit are excited and moved along the inspection target, and each of the plurality of first coils and the plurality of second coils constituting them, for example, of voltage or impedance An absolute signal indicating the change is transmitted to the signal processing unit. The signal processing unit synthesizes the received absolute signals to detect various defects.
At this time, the plurality of first coils forming the first flaw detection part generate eddy currents in the same direction, and the plurality of second coils forming the second flaw detection part generate eddy currents in the direction opposite to the first coil. Therefore, an eddy current directed in the opposite direction to the eddy current formed in the first flaw detection portion and the eddy current formed in the second flaw detection portion is formed.
Since the first flaw detection part and the second flaw detection part are arranged adjacent to each other and approximately point symmetrical, the eddy current of the first flaw detection part and the second flaw detection part are between the first flaw detection part and the second flaw detection part. The eddy current flows in the same direction, and in other areas, the flow is in the opposite direction.

For this reason, if the eddy current of the first flaw detection part and the eddy current of the second flaw detection part are combined, the effect of the eddy current is mutually canceled in other areas, while the first flaw detection part and the second flaw detection part Since eddy currents are concentrated in the same direction, the detection performance of minute defects can be improved.
Further, since the signal processing unit uses the absolute signals of the first coils and the second coils, it is possible to eliminate the necessity of exciting the first coils and the second coils all at once, and excite them in a time-sharing manner. be able to.
Thereby, for example, the exciting oscillator can be reduced in size.
The target center line connecting the intermediate points between the first flaw detection part and the second flaw detection part including the symmetrical center point is configured to be inclined with respect to the moving direction of the first flaw detection part and the second flaw detection part. It is suitable for performing good defect detection.
In addition, it is preferable that a plurality of first coils and a plurality of second coils are arranged along the target center line.

  In the eddy current flaw detector according to the present invention, the signal processing unit performs processing using time-series changes of the absolute signals.

Changes in the distance (lift-off) between the first flaw detection unit and the second flaw detection unit and the inspection target, the inclinations of the first flaw detection unit and the second flaw detection unit, and the inclination of the inspection target are applied to the first flaw detection unit and the second flaw detection unit. Since they occur simultaneously, the absolute signals of the first coils and the second coils fluctuate at substantially the same time.
On the other hand, for various defects, the time at which each first coil and each second coil pass through them is different, so the absolute signals of each first coil and each second coil have different times when viewed in time series. Fluctuates.
Therefore, when processing is performed using the time-series change of the absolute signal of each first coil and each second coil, the first flaw detection unit and the variation in the distance (lift-off) between the second flaw detection unit and the inspection object, the first flaw detection unit and Since the inclination of the second flaw detection part and the inclination of the inspection target can be distinguished from the defect, the signal discrimination can be improved.

  In the eddy current flaw detector according to the present invention, the signal processing unit performs processing using each of the absolute signals and a differential signal indicating a difference between them.

Since the absolute signal directly represents the distance fluctuation with the inspection object, the unevenness of the inspection object can be measured. Moreover, since the absolute value of the magnetic permeability and electric resistance of a test object can be measured, the amount of deposits such as magnetite can be measured, for example.
Furthermore, when a differential signal indicating the difference between the first coil and the second coil that form eddy currents in opposite directions is used, fluctuations are added, so that the measurement performance can be improved.

According to the present invention, since the eddy currents are concentrated in the same direction between the first flaw detection part and the second flaw detection part, it is possible to improve the detection performance of minute defects.
Further, since the signal processing unit uses the absolute signals of the first coils and the second coils, it is possible to eliminate the necessity of exciting the first coils and the second coils all at once, and excite them in a time-sharing manner. be able to.
Thereby, for example, the exciting oscillator can be reduced in size.

Hereinafter, an eddy current flaw detector 1 according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram showing a schematic configuration of an eddy current flaw detector 1.
The eddy current flaw detector 1 includes an oscillator 3, an inspection unit 5, and a signal processing unit 7.

The oscillator 3 supplies an alternating current to the inspection unit 5.
The inspection unit 5 includes four coils 9a, 9b, 9c, and 9d. The four coils 9a, 9b, 9c, 9d form substantially the same plane, and their centers are arranged at positions corresponding to the apexes of the substantially square.
Note that the four coils 9a, 9b, 9c, and 9d may be arranged so as to form a rhombus without forming a substantially square shape.
The four coils 9a, 9b, 9c, 9d are arranged clockwise in this order.

Since the coil 9a and the coil 9d are wound in the same phase, the eddy current 11a and the eddy current 11d generated by them are in the same direction, for example, counterclockwise.
As a result, a substantially oval eddy current 13 synthesized as shown in FIG. 2 is formed around the coil 9a and the coil 9d.
The coils 9a and 9d constitute the first coil of the present invention, and both constitute the first flaw detection portion 12.

Since the coil 9b and the coil 9c are in-phase and wound in the opposite phase to the coils 9a and 9d, the eddy current 11a and the eddy current 11d generated by them are in the same direction, for example, clockwise.
As a result, a substantially oval eddy current 15 synthesized as shown in FIG. 2 is formed around the coil 9b and the coil 9c.
The coils 9b and 9c each constitute a second coil of the present invention, and both constitute a second flaw detector 14.

The first flaw detection portion 12 formed by the coils 9a and 9d and the second flaw detection portion 14 formed by the coils 9b and 9c are arranged in a substantially point-symmetric relationship with respect to the center point C which is the center of the square. Yes. The first flaw detection unit 12 and the second flaw detection unit 14 have a mirror image relationship.
Since the eddy current 13 and the eddy current 15 are formed in opposite directions, their influences cancel each other on the outside and are strengthened on the inside. That is, since the eddy current 13 and the eddy current 15 are formed in the same direction at the intermediate position between the first flaw detection part 12 and the second flaw detection part 14 passing through the center point C, the concentrated eddy current 17 is formed by addition. Is done.

The signal processing unit 7 receives and processes signals from the coils 9a, 9b, 9c, 9d.
This signal is an absolute signal itself indicating, for example, impedance, voltage, etc. in each of the coils 9a, 9b, 9c, 9d.
The signal processing unit 7 receives the absolute signal AS1 of the coil 9a, the absolute signal AS2 of the coil 9b, the absolute signal AS3 of the coil 9c, and the absolute signal AS4 of the coil 9d and forms, for example, a differential signal of them. A process is performed such as forming a difference signal of the difference signal, checking a time-series change of each of these signals, and the like.

An operation of the eddy current flaw detector 1 according to the present embodiment configured as described above will be described.
The eddy current flaw detector 1 is positioned so that the coils 9a, 9b, 9c, 9d of the inspection unit 5 are at substantially equal intervals with respect to the inspection object 19.
At this time, the coil 9 a and the coil 9 c are positioned so as to be substantially aligned with the moving direction (Y direction) 21 of the eddy current flaw detector 1.
When an alternating current is simultaneously applied to the coils 9a, 9b, 9c, and 9d by the oscillator 3, the eddy current 17 that is formed is formed so as to have an inclination of approximately 45 ° with respect to the moving direction 21.

In this state, when the inspection unit 5 is moved along the movement direction 21, the eddy current 17 is formed to be inclined with respect to the movement direction 21, so that the Y direction along the movement direction 21 shown in FIG. The eddy current 17 intersects the defect KY or the X-direction defect KX substantially orthogonal to the moving direction 21 shown in FIG.
For this reason, the Y-direction defect KY or the X-direction defect KX can be detected.
Moreover, since the eddy current 17 is formed by concentrating the eddy currents of the coils 9a, 9b, 9c, and 9d, even a minute defect can be detected.
At this time, the signal processor 7 detects these defects by synthesizing the absolute signals AS1, AS2, AS3, and AS4 from the coils 9a, 9b, 9c, and 9d.

In the case of the oblique defect KK inclined with respect to the moving direction 21, there are situations in which the absolute signals AS1, AS2, AS3, AS4 of the coils 9a, 9b, 9c, 9d all fluctuate and are difficult to distinguish from lift-off.
In the case of the present embodiment, the absolute signals AS1, AS2, AS3, and AS4 are processed, so that these time series changes can be used for identification.
As for this identification, for example, an oblique defect KK inclined approximately 45 ° in the moving direction shown in FIG.

When the inspection unit 5 moves in the moving direction 21, first, the coil 9a and the coil 9b cross the oblique defect KK, and therefore the absolute signals AS1 and AS2 in which the coil 9a and the coil 9b fluctuate are sent to the signal processing unit 7.
Further, when the inspection unit 5 moves in the moving direction 21, the coils 9c and 9d cross the oblique defect KK, so that the absolute signals AS3 and AS4 in which the coils 9c and 9d fluctuate are sent to the signal processing unit 7.
Looking at the time series changes of these absolute signals AS1, AS2, AS3, AS4, the absolute signals AS3, AS4 change over time after the absolute signals AS1, AS2 change as shown in FIG. It becomes.

As described above, when the absolute signals AS1, AS2, AS3, and AS4 change in time series, it is determined that the oblique defect KK is present.
FIG. 6 shows the time series change of the absolute signals AS1, AS2, AS3, AS4 in the case of approximately 45 ° with respect to the moving direction 21, but when other angles are inclined, It is natural that the pattern changes in time series.
In any case, each absolute signal AS1, AS2, AS3, AS4 will fluctuate at different times.

On the other hand, in the case of lift-off, the distances between the coils 9a, 9b, 9c, 9d of the inspection unit 5 and the inspection object 19 fluctuate all at once, so that each absolute signal AS1, AS2, AS3, AS4 is shown in FIG. As shown in FIG. 7, it will fluctuate all at once.
At this time, the absolute signals AS1, AS2, AS3, AS4 increase when the coils 9a, 9b, 9c, 9d approach the inspection object 19, and the absolute signals AS1, AS2, AS3, AS4 decrease when they move away. The amount of lift-off can be calculated.

Next, the case where the inspection unit 5 is inclined and the defect will be described.
A case where the inspection unit 5 is inclined in a direction orthogonal to the A view, the B view, the C view, and the D view shown in FIG.
An inclination state in a direction orthogonal to the view A is shown by a two-dot chain line in FIG. Here, it inclines below centering on the right end of the coil 9b.
In this case, the coil 9d is closest to the inspection object 19, then the coil 9c and the coil 9a are close, and the coil 9b is the smallest amount of approach.
Therefore, the absolute signals AS1, AS2, AS3, and AS4 at this time fluctuate at the same time as shown in FIG.

An inclination state in a direction orthogonal to the view B is shown by a two-dot chain line in FIG. Here, the coil 9a and the coil 9b are inclined downward with the right ends thereof as the centers.
In this case, the coil 9c and the coil 9d are closest to the inspection object 19, and the approaching amount of the coil 9b and the coil 9a is small.
Accordingly, the absolute signals AS1, AS2, AS3, and AS4 at this time fluctuate at the same time as shown in FIG. 9B.

An inclination state in a direction orthogonal to the C view is shown by a two-dot chain line in FIG. Here, it inclines below centering on the right end of the coil 9a.
In this case, the coil 9c comes closest to the inspection object 19, then the coil 9b and the coil 9d approach, and the coil 9a has the smallest approach amount.
Therefore, the absolute signals AS1, AS2, AS3, and AS4 at this time fluctuate at the same time as shown in FIG. 9C.

An inclination state in a direction orthogonal to the D view is shown by a two-dot chain line in FIG. Here, the coil 9a and the coil 9d are inclined downward with the right ends as the centers.
In this case, the coil 9b and the coil 9c are closest to the inspection object 19, and the approaching amount of the coil 9a and the coil 9d is small.
Therefore, the absolute signals AS1, AS2, AS3, and AS4 at this time fluctuate at the same time as shown in FIG. 9 (d).

As described above, the four cases of the inclination of the inspection unit 5 have been representatively described. Similarly, the absolute signals AS1, AS2, AS3, and AS4 fluctuate at substantially the same time for other inclination patterns. .
The state of inclination, that is, the inclination direction and the inclination angle (inclination amount) can be determined by the amount of each absolute signal AS1, AS2, AS3, AS4.

On the other hand, detection of a Y-direction defect KY as shown in FIG. 3 will be described.
When the inspection unit 5 moves in the movement direction 21, the coil 9a first detects the Y-direction defect KY, and the absolute signal AS1 fluctuates.
Although the coil 9b and the coil 9d continue, since they do not engage with the Y-direction defect KY, the absolute signals AS2 and AS4 do not fluctuate.
Finally, the coil 9c detects the Y-direction defect KY, and the absolute signal AS3 fluctuates.
When these are processed in time series by the signal processing unit 7, the absolute signal AS1 and the absolute signal AS3 fluctuate at different times as shown in FIG.

The detection of the X-direction defect KX as shown in FIG. 4 will be described.
When the inspection unit 5 moves in the moving direction 21, the coil 9a first detects the X-direction defect KX, and the absolute signal AS1 fluctuates.
Next, the coil 9b and the coil 9d detect the X-direction defect KX, and the absolute signals AS2 and AS4 change at substantially the same time.
Finally, the coil 9c detects the X direction defect KX, and the absolute signal AS3 fluctuates.
When these are processed in time series by the signal processing unit 7, the absolute signals AS1, AS2, AS3, and AS4 fluctuate at different times as shown in FIG.

Thus, in the eddy current flaw detector 1 according to the present embodiment, the absolute signals AS1, AS2, AS3, AS4 of the coils 9a, 9b, 9c, 9d are each sent to the signal processing unit 7 and processed alone. The time series change of each absolute signal AS1, AS2, AS3, AS4 can be seen in the signal processing unit 7.
For this reason, it is possible to distinguish between a lift-off that varies at substantially the same time and a variation due to the inclination of the inspection unit 5 or the inspection object 19 and a variation due to a defect that varies at different times. That is, it is possible to greatly improve the distinguishability.

Since each absolute signal AS1, AS2, AS3, AS4 directly represents the distance variation between each coil 9a, 9b, 9c, 9d and the inspection object 19, the unevenness of the inspection object 19 can be measured.
Further, since each absolute signal AS1, AS2, AS3, AS4 can measure the magnetic permeability and electrical resistance, which are physical property values of the inspection object 19, as absolute values, the inspection object 19 whose physical property values are known, for example, The adhesion amount of magnetite can be measured.

Further, the signal processing unit 7 can generate a differential signal indicating the difference between the absolute signals AS1, AS2, AS3, and AS4.
For example, the differential signal DS1 indicating the difference between the absolute signal AS1 from the coil 9a of the first flaw detector 12 and the absolute signal AS3 from the coil 9c of the second flaw detector 14 is formed.
Since the coil 9a and the coil 9c are point-symmetric with respect to the center point C and form eddy currents in opposite directions, the differential signal DS1 indicating the difference between them is the absolute signal AS1, This is shown in a state in which the amount of AS3 variation is added.

Such a differential signal DS1 can improve the accuracy of measurement, for example, even if the absolute signals AS1 and AS3 have small fluctuations and are shown enlarged.
This is the same even when the differential signal DS2 indicating the difference between the absolute signal AS2 of the coil 9b and the absolute signal AS4 of the coil 9d is formed.
In addition, when the double differential signal HS1 (= DS1-DS2) indicating the difference between the differential signal DS1 and the differential signal DS2 is formed, the same information as that constituting the conventional Wheatstone bridge can be obtained. .

In the double differential signal HS1, for example, the differential values of the absolute signals AS1, AS2, AS3, and AS4 are shown. Therefore, the unevenness, magnetic permeability, electric resistance, and the like of the inspection object 19 that require absolute values are calculated. Cannot be used.
In addition, the size of lift-off, oblique defect KK, etc. cannot be detected.

Thus, in this embodiment, the absolute signals AS1, AS2, AS3, AS4 from the coils 9a, 9b, 9c, 9d are sent to the signal processing unit 7, and the signal processing unit 7 uses these absolute signals AS1, AS2 , AS3, AS4 are used to perform various processing, so that, for example, signals as shown in Table 1 can be obtained.
By using these signals in accordance with the purpose, various defects can be detected with high accuracy.

Since the amount of lift-off and tilt can be measured, the amplitude of the defect signal due to these fluctuations (that is, fluctuations in the absolute signals AS1, AS2, AS3, and AS4 due to the defects) can be corrected.
The absolute signals AS1, AS2, AS3, and AS4 are large when the coils 9a, 9b, 9c, and 9d are close to the inspection object 19, and are small when the coils 9a, 9b, 9c, and 9d are far away.
FIG. 12 shows the relationship between the defect depth and the amplitude when the lift-off amount is a parameter when the coils 9a, 9b, 9c, 9d are lifted off in the direction away from the inspection object 19.
When the lift-off is small, the distance away from the inspection object 19 of the coils 9a, 9b, 9c, 9d is small, and therefore the amplitude is larger than when the lift-off is large.

Also, as shown in FIG. 8B or FIG. 8C, the amount of defects when the angle of inclination (inclination) is used as a parameter when the other end is inclined so that the other end approaches the direction of the inspection object 19 as shown in FIG. The relationship between the defect depth and the amplitude is shown in FIG.
Since the coils 9a, 9b, 9c, and 9d are closer to the inspection object 19 as the inclination is larger, the amplitude is larger than that with a smaller inclination.

Since the signal processing unit 7 can calculate the lift-off amount and the tilt state as described above, the defect detection amplitude can be corrected with high accuracy.
Further, if the signal processing unit 7 holds a database of defect depth and amplitude using the lift-off amount and the tilt state as parameters as shown in FIGS. 14 and 15, the defect depth is estimated using the amplitude. Therefore, the measurement accuracy can be improved.

In the present embodiment, the coils 9a, 9b, 9c, and 9d are excited simultaneously. However, the present invention is not limited to this.
For example, as shown in FIG. 16, for example, a multiplexer 23 is interposed between the oscillator 3 and the coils 9a, 9b, 9c, 9d, so that the coils 9a, 9b, 9c, 9d can be connected from the oscillator 3 at high speed. You may make it excite by division | segmentation.
In this case, as shown in FIG. 17, for example, as shown in FIG. 17 (a) to FIG. 17 (d), the coil 9a, the coil 9b, the coil 9c, and the coil 9d are sequentially excited at high speed. To do.

In this way, the absolute signals AS1, AS2, AS3, AS4 from the coils 9a, 9b, 9c, 9d can be sent to the signal processing unit 7 and various processes similar to those described above can be performed to detect defects. .
Thus, when excitation is performed in a time division manner, the oscillator 3 can be reduced in size, and the eddy current flaw detector 1 can be reduced in size.

  Moreover, although the 1st flaw detection part 12 and the 2nd flaw detection part 14 are each formed with two coils, you may make it each form with three or more coils, without being limited to this.

1 is a block diagram showing an overall schematic configuration of an eddy current flaw detector according to an embodiment of the present invention. It is a top view which shows the whole schematic structure of the test | inspection part concerning one Embodiment of this invention. It is a top view which shows the state which the test | inspection part concerning one Embodiment of this invention has detected the Y direction defect. It is a top view which shows the state which the test | inspection part concerning one Embodiment of this invention has detected the X direction defect. It is a top view which shows the state which the test | inspection part concerning one Embodiment of this invention has detected the diagonal defect. It is a figure which shows the time-sequential change of an absolute signal when the test | inspection part concerning one Embodiment of this invention has detected the diagonal defect. It is a figure which shows the time-sequential change of an absolute signal when the test | inspection part concerning one Embodiment of this invention lifts off. The state which the test | inspection part concerning one Embodiment of this invention inclines is shown, (a) is the top view, (b) (c) is a side view. It is a figure which shows the time-sequential change of an absolute signal when the test | inspection part concerning one Embodiment of this invention inclines. It is a figure which shows the time-sequential change of an absolute signal when the test | inspection part concerning one Embodiment of this invention has detected the Y direction defect. It is a figure which shows the time-sequential change of an absolute signal when the test | inspection part concerning one Embodiment of this invention has detected the X direction defect. It is a figure which shows the relationship between the defect depth when a lift-off amount is used as a parameter, and the amplitude. It is a figure which shows the relationship between the defect depth at the time of using inclination as a parameter, and an amplitude. It is a figure which shows the relationship between the defect depth when a lift-off amount is used as a parameter, and the amplitude. It is a figure which shows the relationship between the defect depth at the time of using inclination as a parameter, and an amplitude. It is a block diagram which shows the whole schematic structure of another embodiment of the eddy current flaw detector concerning one Embodiment of this invention. It is a top view which shows the excitation state in the test | inspection part of the eddy current flaw detector shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Eddy current flaw detector 7 Signal processing part 9a Coil 9b Coil 9c Coil 9d Coil 12 First flaw detection part 14 Second flaw detection part C Center point AS1, AS2, AS3, AS4 Absolute signal DS1, DS2 Differential signal

Claims (3)

A first flaw detector formed by a plurality of first coils each generating eddy currents in the same direction;
A second flaw detection part formed by a plurality of second coils that are arranged substantially symmetrically next to the first flaw detection part and generate eddy currents in the opposite direction to the first coil, respectively.
A signal processing unit that receives the individual absolute signals from each of the first coils and the second coils, and synthesizes them;
An eddy current flaw detector comprising:   2. The eddy current flaw detector according to claim 1, wherein the signal processing unit performs processing using a time-series change of each of the absolute signals. 3. The eddy current flaw detector according to claim 2, wherein the signal processing unit performs processing using each of the absolute signals and a differential signal indicating a difference between the absolute signals.

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