JPS6114569A - Detector for eddy current flaw detection - Google Patents

Abstract

PURPOSE:To improve the operation efficiency without increasing the number of signal processing circuits by connecting plural detection coils arranged around a material to be inspected and constituting a group of detection coils, and providing an optional number of coil groups in the axial direction of the material to be inspected. CONSTITUTION:Couples of detection coils 11 and 12, 13 and 14, 15 and 16, and 17 and 18 coupled differentially are arranged around the material 1 to be inspected at equal intervals and connected properly to form a detection coil group 10, and detection coil groups 20, 30, and 40 are formed of coils 21-28, 31-38 and 41- 48 similarly. The coil groups 10-40 are arranged in the axial direction of the material 1 to be inspected, which is supplied with an alternating magnetic field from exciting coils 51-54 provided relatively to the respective detection coils. Consequently, variation in the level of a detection signal with the length of a defect is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an eddy current flaw detection detector used in an eddy current flaw detection device that performs flaw detection while rotating a material to be inspected and a detection coil relative to each other.

(B) Prior Art In order to detect minute defects with high sensitivity, it is necessary to reduce the diameter of the detection coil in accordance with the length of the defect. As the diameter of the detection coil becomes smaller, the flaw detection range by the same scanning becomes narrower, and the efficiency of flaw detection decreases. In order to improve work efficiency, flaw detection may be performed by disposing a plurality of detection coils in the axial direction of the material to be inspected. In this case, if a signal processing circuit is provided for each detection coil, the number of signal processing circuits increases, resulting in an expensive device and problems of poor operability and maintainability. Therefore, as shown in Figure 3, the number of signal processing circuits is reduced by connecting a plurality of detection coils arranged in the axial direction of the material to be inspected and connecting these to the negative signal processing circuit. Measures have been proposed and implemented.

In FIG. 3 f8+, 1 is a material to be inspected, and 2a to 2d are differentially coupled detection coils, which are arranged along the axial direction of the material to be inspected 1. The detection coils 28 to 2d constitute a detection coil group 2 connected in series. The plurality of detection coil groups 2 to 5 are arranged at equal intervals around the inspected material 1, as shown in FIG.

A signal processing circuit 6 is provided for each detection coil group.

However, the conventional eddy current flaw detector shown in FIG. 3 has the following drawbacks.

For example, suppose that the material to be inspected 1 has a relatively short defect 7 and a relatively long defect 8. At this time, the signals taken out from this detection coil group are as shown in FIG. 3(C). In other words, even if defect 7 and defect 8 have the same depth, defect 7
Defect 8 gives an impedance change to only one detection coil 2d, whereas defect 8 causes an impedance change to only occur in one detection coil 2d.
gives an impedance change to. Therefore, the magnitude of the detection signal S2 based on the defect 8 is larger than the detection signal S1 based on the defect 7 even if the defects have the same depth. Considering that defective defects are determined based on the depth of the defect rather than the length of the defect, it is inconvenient that the magnitude of the detection signal depends on the length of the defect as described above. . Therefore, conventional eddy current flaw detection detectors are
The disadvantage is that the detection results are unreliable. In addition, in conventional eddy current detectors, the so-called lift-off effect appears in the same way in each detection coil, so the noise generated in each detection coil is added together and output, resulting in a signal-to-noise ratio (S/
This has the disadvantage that the N ratio) decreases.

(c) Purpose The present invention provides an eddy current flaw detection detector that can improve the efficiency of flaw detection without significantly increasing the number of signal processing circuits and can perform highly reliable flaw detection. It is intended to.

Another object of the present invention is to provide an eddy current flaw detection detector that can improve the S/N ratio.

(d) Configuration The eddy current flaw detection detector according to the present invention is an eddy current flaw detection detector used in an eddy current flaw detection device that performs flaw detection while relatively rotating a material to be inspected and a detection coil, and A feature is that an arbitrary number of detection coil groups formed by connecting a plurality of detection coils arranged around the material are provided along the axial direction of the material to be inspected.

(E) Embodiment FIG. 1 is an explanatory diagram schematically showing the structure of an embodiment of an eddy current flaw detection detector according to the present invention. In the same figure (a), a pair of differentially coupled detection coils 11 and 12, detection coils 13 and 14, detection coils 15 and 16, and detection coils 17 and 18 are close to the surface of the inspected material 1, They are arranged at equal intervals around it. Each detection coil 11 to 18 is
They are connected as appropriate to form a negative detection coil group 10. Similarly, the detection coils 21 to 28 form a detection coil group 20, the detection coils 31 to 38 form a detection coil group 30, and the detection coils 41 to 48 form a detection coil group 40, respectively. These detection coil groups 10 to 40 are arranged along the axial direction of the inspected material 1 as schematically shown in FIG. This is an excitation coil that applies an alternating magnetic field to the inspected material 1. However,
This excitation coil is not required if the detection coil also serves as an excitation coil.

FIG. 2 is an explanatory diagram showing the connection relationship of each detection coil, taking the detection coil group 10 as an example. At the terminal of each detection coil, ◯ indicates the start of coil winding, and ◯ indicates the end of coil winding. Figure (a) shows the coil group of detection coils 11, 13, 15, and 17 connected in series, and the detection coil 1.
2.14.16.18 coil groups are differentially coupled. In addition, in the same figure (bl is a pair of detection coils 11, 12.13, 14.15, 16.17 and 18 that are differentially coupled and connected in series. In any case, the same difference There is no difference in that a dynamic output can be obtained.Therefore, the detection signal of each detection coil group is given to the signal processing circuit 6 provided corresponding to each detection coil group.

Next, the operation of the eddy current flaw detection detector configured as described above will be explained.

For example, when a long defect 8 as shown in FIG. It never happens. Therefore, the detection signal when short defect 7 is detected and the detection signal when long defect 8 is detected have approximately the same magnitude. However, if defects appear on the surface of the inspected material at the same intervals as the detection coils of the detection coil group are arranged (90' intervals in the example of Fig. 1),
As a result of adding the signals of each detection coil, the detection signal of the detection coil group becomes larger. However, in this form,
Since defects rarely appear, they rarely pose a problem in actual use.

Furthermore, since the detection coils constituting each detection coil group are arranged around the material to be inspected 1, the gap between the detection coils 11, 12 and the material to be inspected 1 may be increased due to vibration of the material to be inspected 1, for example. When it becomes larger, the detection coil 15.1 opposite to this
6 and the material to be inspected 1 becomes smaller. Therefore, the effect of lift-off occurring in each of the detection coils does not appear much in the detection signal of the detection coil group, which is extracted as the sum of the signals of each detection coil.

In the above embodiment, four pairs of detection coils in a differential relationship were provided on the surface of the material to be inspected 1.

However, the present invention is not limited to this, and the number of detection coils to be provided may be appropriately determined in relation to the efficiency of flaw detection work.

Moreover, in the above-mentioned Example, the number of detection coil groups provided along the axial direction of the inspected material 1 was explained as four sets. However, the number of detection coil groups is determined as appropriate in relation to work efficiency, the number of signal processing circuits, and the like.

(F) Effect The eddy current flaw detection detector according to the present invention forms a detection coil group by connecting a plurality of detection coils arranged around the material to be inspected, so the defect length of the material to be inspected is The magnitude of the detection signal does not change depending on the magnitude of the detection signal. Therefore, according to the present invention, the reliability of flaw detection can be improved.

Further, according to the present invention, it is only necessary to provide a negative signal processing circuit for a detection coil group formed of a plurality of detection coils, so that when a signal processing circuit is provided for each detection coil, In comparison, the number of signal processing circuits can be reduced.

Further, by appropriately setting the number of detection coils constituting the detection coil group and the number of detection coil groups, the efficiency of flaw detection work can be improved.

Furthermore, according to the present invention, it is possible to reduce the influence of the lift-off effect that occurs in each detection coil, so the S/
The N ratio can be improved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing the configuration of an embodiment of the eddy current flaw detection detector according to the present invention, FIG. 2 is an explanatory diagram showing the connection relationship of detection coils constituting a detection coil group, and FIG. FIG. 2 is an explanatory diagram schematically showing the configuration of a conventional eddy current flaw detection detector. 1... Material to be inspected, 11-18.21-28.31-3
8.41-48...detection coil, 10.20.30.
40...Detection coil group. Patent applicant Shimadzu Corporation Representative Patent attorney Takaharu Ohnishi Figure 1 (a) (b) n

Claims (1)

[Claims] (1) In an eddy current flaw detection detector used in an eddy current flaw detection device that performs flaw detection while rotating the inspected material and the detection coil relative to each other, multiple detection coils arranged around the inspected material are connected. 1. A detector for eddy current flaw detection, characterized in that an arbitrary number of detection coil groups are provided along the axial direction of a material to be inspected.