JPH0750074B2 - Eddy current flaw detector capable of thinning inspection - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for measuring the wall thickness of a pipe or the like based on an eddy current flaw detection method, and visualizes the shape of an object to be examined locally such as pitting corrosion. The thinning is also related to an eddy current flaw detector improved so that it can be displayed with high resolution.

[Prior art]

In the conventional eddy current flaw detection, changes in the electrical impedance of the eddy current probe were displayed on an oscilloscope, and changes in output due to the presence of defects etc. were visually observed. In this method, the impedance of the probe in the normal part of the subject is used as a reference, and the difference between the impedance of each part of the subject and the reference impedance is output as a vector amount. Impedance changes occur due to the presence of defects and changes in the subject's wall thickness, but the probe impedance is spatially gradual because of the amount of change corresponding to the integral of the change in the electrical characteristics of the subject in the magnetized region of the subject. Change to. Therefore, the presence of a defect or a change in the thickness of the object can be confirmed by the change in impedance, but it is not possible to know the minute spatial change of the change in the thickness of the defect or the object. No attempt has been made to visualize the shape of the specimen.

On the other hand, a vertical flaw detection method using ultrasonic waves is widely used as a method for visualizing the shape of a subject and measuring the wall thickness. In the vertical flaw detection method, ultrasonic waves are made incident from the surface of the subject and reflected waves from the inner surface of the subject are received. This is a method of multiplying the propagation time of the reflected wave by 1/2 of the speed of sound in the subject, and determining the subject's wall thickness.By using a focused ultrasonic beam that focuses in the vicinity of the inner surface of the subject, fine meat of each part of the subject can be obtained. You can grasp the thickness change. However, because the time width of the ultrasonic wave transmission pulse or the reflected wave pulse from the subject surface cannot be shortened,
It becomes impossible to measure the thickness of a subject with a thickness of 4 mm or less such that the reflected wave from the inner surface of the subject is received before these pulses are attenuated. The vertical flaw detection method using ultrasonic waves requires a cutlet plant (water, glycerin, etc.) for propagating the ultrasonic waves between the ultrasonic probe and the surface of the subject, and supplies, holds, and recovers them. It is necessary to equip the mechanism of. However, in a gas pipe or the like, the presence of a cutlet plant itself is often not allowed, and it cannot be applied to such a place.

As mentioned above, in the thickness reduction inspection, vertical flaw detection by ultrasonic waves is widely adopted, but it is difficult to apply to such thin materials, despite the fact that there are many inspection symmetries within a thickness of 4 mm,
Since the cutlet plant cannot be used for gas piping,
The scope of application is extremely limited.

In contrast, the eddy current flaw detection method does not require a cutlet plant,
It has a high detection sensitivity and is widely used as a method capable of easily detecting defects, but unlike the ultrasonic flaw detection method, its spatial resolution is remarkably low, and no attempt has been made to display an image of the shape of a subject by the signal.

Therefore, it has never been considered that the eddy current flaw detection method can be applied as an inspection method for thinning due to pitting corrosion of a subject.

[Problems to be solved by the invention]

In the above-mentioned conventional technology, it is not possible to apply to thinning inspection of thin materials, and since it is essential to use a cutlet plant, there is a problem that it is impossible to inspect in an environment where foreign substances such as gas pipes are prohibited. Atsuta

Therefore, the object of the present invention is to improve the eddy current flaw detection method unnecessary for the cutlet plant with respect to the above problems and expand the range of application, and to improve the low spatial resolution that is cited as a drawback of the eddy current flaw detection method. An object of the present invention is to provide an apparatus that enables thinning inspection by improving signal processing and imaging a subject shape with high resolution.

[Means for solving problems]

As a means to improve the low spatial resolution of the eddy current flaw detection method, focusing on the fact that the impedance change by this flaw detection method can be measured by a vector quantity, the spatial spectrum of this vector quantity and the spatial response of the measurement system are noted. By taking the spatial correlation of the relationship, the spatial resolution of the spatial spectrum is improved. Further, in imaging the shape of the subject by eddy current flaw detection for the first time, paying attention to the fact that the sum of squares of absolute values of the spatial spectrum with improved spatial resolution is proportional to the thickness of the subject, The sum of squares of absolute values is recorded in correspondence with the thickness of each part of the subject, and by displaying the subject shape as an image, the measurement of thinning due to eddy current flaw detection (for example, the presence of pitting corrosion) is achieved. It

As a specific configuration for applying the above-mentioned principle to a practical aspect to capture the cross-sectional shape of the subject as an image, the device of the present invention is
(A) means for scanning the eddy current probe along the surface of the subject, (b) a signal processing device for detecting the amount of change in the electrical impedance of the probe as a vector quantity at a constant distance interval of the above scanning, (c) Means for recording the change in the vector amount corresponding to the probe position for the scanning, and (d) Fourier transforming the change amount of the vector amount with respect to the scanning position of the probe to obtain a spatial frequency spectrum of the vector change amount. And (e) means for inverse Fourier transforming a spectrum obtained by dividing the above spatial frequency spectrum by a known spatial response frequency spectrum to calculate an actual spatial output spectrum, and (f) above A data processing device for outputting the sum of squares of the absolute values of the real space output spectrum, and (g) displaying the sum of squares as a figure in association with the scanning position. It is provided with a display means for.

[Action]

Prior to explaining the operation of the eddy current flaw detector of the present invention configured as described above, the principle of eddy current flaw detection will be outlined in advance. FIG. 2 shows an explanatory view schematically showing the principle.

In the figure, it is assumed that the probe output is observed while scanning the probe 1 along the surface of the subject 3 in the X-axis direction.
At this time, at the scanning position of the probe 1, the range of the shaded region 2 in the subject is a magnetized region, and the eddy current output due to the subject's electrical characteristics in this region is used as a reference. Probe 1 '
At the scanning position of 1, the subject electrical characteristics of the magnetized region 2'change due to the presence of the notch portion 4 as compared with the case of the scanning position of the probe 1, and accordingly, the probe output representing the impedance change at each scanning position is , The real part signal 5 and the imaginary part signal 6 are obtained. As you can see, the magnetized region
Probe output 5,6 because 2,2 'is spatially wide
Indicates a smooth change with respect to the scanning position X in the spatial integrated signal output. Therefore, even if the notch 4 is locally present, the signals 5 and 6 are spatially expanded, and the spatial resolution is considerably low corresponding to the expansion of the magnetized regions 2 and 2 '.

Now, the principle of how a spectrum having such a low spatial resolution can be made into a spectrum with improved resolution will be described.

A vector output signal composed of a real number part and an imaginary number part of the eddy current signal is O (x) as a function related to the scanning position X. On the other hand, the spatial resolution of the measurement system due to the spatial expansion of the magnetized region in the subject is expressed as a function of the scanning position X, R
It is represented by (x). If the ideal high spatial resolution is obtained, the true output signal of the eddy current is I
Let (x) be the respective functions O (x), R (x), I
The relationship of (x) is given by the following equation.

In the case of the relationship of the first expression, Fourier transform is performed on both sides as follows.

Where ω is the spatial frequency and j is Is an imaginary signal that represents

The integral in the second equation will be rewritten below.

That is, (ω), (ω), and (ω) are Fourier transform functions of the functions O (x), R (x), and I (x), respectively.

The second equation is rewritten using the third, fourth, and fifth equations as follows.

(Ω) = (ω) · (ω) (6) Therefore, if the function R (x) is known, that is, if (ω) is also known, the true output from the output signal O (x) is obtained by the following equation. The Fourier transform function (ω) of the signal I (x) is obtained.

(Ω) = (ω) / (ω) (7) In order to obtain the true output signal I (x), the following equation is used.

That is, the function I (x) can be obtained by inverse Fourier transforming the function obtained by dividing the function (ω) by (ω).

The content of the above processing procedure is shown in FIG. FIG. 2A shows a case in which the probe 3 scans the subject 3 having the notches 4 and 5 having different widths in the X direction. Output signal O at this time
The real part and the imaginary part of (x) become curves 11 and 12, respectively. This is Fourier transformed to obtain the function (ω).
On the other hand, as shown in (B) in the figure, the real part and the imaginary part of the output signal R (x) when the object 3 ′ having the notch 6 whose width is almost negligible are inspected by the probe 1 are represented by curves 13, And 14 This output R (x) corresponds to a function representing the spatial resolution of the measurement system. Fourier transform is performed on R (x) to obtain a function (ω).

Next, the function obtained by dividing (ω) by (ω) is inverse Fourier transformed to obtain I (x). As a result, the function I (x) is almost equal to the gap width of the notches 4 and 5 of the subject 3 shown in FIG. Spatial spectrum becomes 15,16 (Fig. (C))
reference). As described above, even with an output signal due to an eddy current having a low spatial resolution in the related art, if the response function R (x) of the measurement system that depends on the spatial expansion of the magnetized region is known, Fourier transform and its inverse transform are performed. An output spectrum with significantly improved spatial resolution is obtained by the structured data processing.

Next, a method for obtaining the thickness of the subject 3 from the obtained spectrum I (t) will be described.

An example of inspecting an object 3, 3 ′ having notches 4 and 5 having heights (depths) of d and d ′, respectively, is shown in FIG. 4 (A),
It shows in (B). The absolute value of the spatial spectrum I (t) obtained in each case is shown below.
V _mx , V ′ _mx . This ratio is the height (depth) of the notch d,
proportional to the square of d '. The reason is that the impedance detected by the probe 1 depends on the resistance to the eddy currents in the subject 3 or 3 ', but in the regions 7 and 7'indicated by the dotted lines in FIGS. The resistance to current depends on the electrical characteristics of the material, but eddy currents are blocked by the presence of the notches 3 and 3'excluding this region, and as a result, the probe output results in the notch height (depth). Squared (the strength of magnetization is
It is approximately proportional to (since it is inversely proportional to the square of the distance). Therefore, the height of the cutout is expressed by a mathematical expression as the spatial spectrum I (t).
The following is the correspondence with the absolute peak value of.

As described above, if the comparison with the peak value for the notch of the reference height (depth) from the obtained spatial spectrum I (t) is performed according to the ninth formula, the height of the unknown notch ( The depth can be obtained, and the height (depth) can be subtracted from the reference wall thickness to obtain the wall thickness at each position.

Based on the above-mentioned principle of wall thickness measurement by eddy current,
A specific example of the device of the present invention for measuring the wall thickness will be described below.

〔Example〕

FIG. 1 is a block diagram showing an overall configuration of an eddy current flaw detector according to an embodiment of the present invention, which is improved so that a thinning inspection can be performed.

The probe 1 is scanned by the scanning device 22. The trigger signal 53 is output from the scanning device 22 to the signal processing device 21 every time the vehicle travels a certain distance, and the scanning position signal 54 at that time is also output. In the signal processing device 21, the magnetizing current
The eddy current signal 52 detected by the probe 1 is input while being applied to 51. The amplitude change of the impedance due to the main signal 52 is extracted as the voltage signal of the amplitude of each of the real number part and the imaginary number part, and the value and the scanning position signal 54 are output to the data processing device 23 as the measurement data 55. The data processing device 23
Then, the input measurement data 55 is recorded as the output spectrum O (x) regarding the scanning position, the processing based on the equations from the second equation to the ninth equation is performed, and the position represented by the scanning position 54 and the position thereof are represented. Image data 56
Is output to the display device 24.

The display device 24 displays an image showing the thickness of the subject from the input image data 56.

The contents of each device will be described in detail below.

The internal configuration of the signal processing device 21 is shown in FIG. The frequency module 71 outputs a magnetizing current 51. The mixer module 72 electrically mixes the magnetizing current 51 and the eddy current signal 52 from the probe 1 to extract and output a voltage signal 61 in the real number domain and a voltage signal 62 in the imaginary number domain. The ADC 73 performs analog-digital conversion on the input voltage signals 61 and 62, and outputs them as real number data 63 and imaginary number data 64, respectively.

The latch memory 74c receives the scanning position 54 output from the scanning device 22, temporarily stores the value 54 at the time when the trigger signal 53 is input, and outputs the stored value. Similarly, the latch memory 74a,
74b temporarily stores the input values at the time of input of the trigger signal 53, that is, the real number data 63 and the imaginary number data 64, respectively, and outputs the stored values. These latch memories 74a, 74b, 74
Numerical data composed of the output value of c is output to the data processing device 23 as measurement data. On the other hand, the delay circuit 75 delays the trigger signal 53 by a time sufficient for all the latch memories 74a, 74b, 74c to temporarily store the data, and outputs it as the transmission signal 57 to the data processing device 23.

Next, the contents of the data processing device 23 will be described with reference to FIG.

First, in the real space output memory 75a and the imaginary space force memory 75b,
An address is designated by the scanning position signal 54, and real number data 63 and imaginary number data 64 are recorded for each input of the transmission signal 57. These recorded data consisting of real number and imaginary number are
This corresponds to O (x) in the third equation. When the recording is completed, the FFT module 76 performs the calculation of the third equation, and (ω)
Real number and imaginary number data of
a, stored in the imaginary frequency output memory 77b. Next, (ω) stored in the real and imaginary frequency response memories 78a, b
The vector division module 79 executes the operation of the seventh equation using (obtained by the fourth equation) and (ω) stored in the memories 77a and 77b, and the result (ω) is calculated as a real number. The true frequency memory 80a and the imaginary number are stored in the true frequency memory 80b. Next, using the values of the memories 80a and 80b, the inverse Fourier transform module 81 executes the operation of the equation (8), and the real and imaginary parts of the operation result I (x) are calculated as real and imaginary space true, respectively. It records in the value memories 82a and 82b.

In the calculation module 83, the contents of the memories 82a and 82b Ireal
The following calculation is performed using (x) and Iimag (x).

P (x) = C _x × X (11) where d _t is the thickness of the normal part of the subject and d _o is the response function R
The depth of the notch when measuring (x), I _o is the maximum absolute value of the output value I (x) at that time, and C _d and C _x are constants. The calculation results D (x) and P (x) in the tenth and eleventh equations are stored in the thickness memory 84 and the coordinate memory 85, respectively, and then the contents are output as image data 56 to the display device 24. The above is the operation content of the data processing device 22. Although the case where (ω) is already stored in the response memories 78a and 78b has been described here, (ω) is stored in the memories 78a and 78b from the outside.
It is also possible to input R (x) in the device 23 when R (x) is stored or input.
A configuration may be added in which a mechanism for converting (x) into (ω) by the FFT module 76 and storing it in the response memories 78a and 78b is added.

Next, the display device 24 will be described with reference to FIG. 7th
The figure shows a configuration in which the storage tube 87 is used as a display unit. Data D (x) 57 and data P that make up the image data 56
The digital value of (x) 58 is converted into an analog value by DACs 86a and 86b, and output as Z signal 65 and P signal 66, respectively. In the storage tube 87, Z on the P-axis position indicated by the value of the P signal 65
After displaying the axis origin, the Z-axis position indicated by the value of the Z signal 65 is displayed. By repeating this operation in sequence, the surface image 90 and the bottom image 91 are displayed on the screen. Here, when the Z-axis origin position is already known or can be already displayed, it is not necessary to repeatedly display the surface image 90 each time the image data 56 is input. When the complaint memory and CRT are used for the display unit, the input values D (x) 57, P (x) 58 are used as two-dimensional address information and a predetermined numerical value is stored in the frame memory address specified by this information. Let CRT the memorized place
The display device of the device of the present invention, even if it is displayed as an image in
Available as 24.

The above is the description of the operation of each device constituting the embodiment shown in FIG. 1, and the scanning is assumed to be one-dimensional scanning on the X-ray. However, the configuration is the same. However, in this case, the memory 75 shown in FIG.
a, 75b, 77a, 77b, 78a, 78b, 80a, 80b, 82a, 82b, 84a, 84b are all 2D memory, and FFT module 76 and inverse FFT module are 2D FFT and 2D inverse FFT functions, respectively. It becomes the structure which has. The two-dimensional FFT processing is shown by the following equation.

In addition, the processing of the two-dimensional inverse FFT is as shown by the following equation.

Further, in this case, the calculation contents of the calculation module 83 in FIG. 6 are as follows instead of the expressions 10 and 11.

_{P (x) = (C x} × x × cosθ-C y × y × sinθ) sin ...
(15) Here, C _y is a constant, and θ is an elevation angle and a turning angle, respectively, and video data for displaying the bottom view in a bird's-eye view is created in the bird's-eye view coordinate system (P, D) shown in FIG.

As described above, the thinning state of the subject can also be observed as a stereoscopic image by the bird's-eye view display in the X, Y two-dimensional scanning.

Next, there are cases where the surface of the subject has irregularities, and due to the irregularities, the distance between the probe and the surface of the subject fluctuates, so that an accurate wall thickness cannot be measured. In this case, how to correct the variation of the probe output due to the variation of the distance between the probe and the subject becomes a problem.

In this case, a correction probe is used. That is, if the high frequency probe 9 is used as shown in FIG. 9 (1), the magnetized region 2 is limited to the vicinity of the surface of the subject 3. Therefore, the output of the probe 9 changes depending on the change in the distance between the probe 9 and the surface of the subject 3. However, as shown in the figure, when the uneven portion on the surface of the subject is in a narrow portion, it is difficult to evaluate the surface unevenness with a single probe. Therefore, the probes 9 ′, 9 ″ having the same performance are arranged at equal distances Δx on both sides of the probe 9. The outputs of the probes 9, 9 ′, 9 ″ at this time are respectively O _s (x), O ′ _s. (X−Δx), O ″ _s (x + Δ
x), it is possible to judge the concave portion or the convex portion on the surface by using those outputs. That is, the evaluation value D
_{Get c} (x).

The phase of the vector D _c (x) is, for example, 0 to π / 2 radians, or The range can be determined as a concave portion, and the other range can be determined as a convex portion.

Further, the vector C _s (x) obtained by the calculation of the following equation becomes an output signal representing the distance between the probe and the surface in consideration of the partial surface unevenness.

C _s (x) = C _s (x) + (Δx) ² · D _c (x) / 2 (17) Implementation for accurately measuring the uneven condition of the subject 3 according to the above-mentioned principle. The tenth example is shown.

In the configuration of FIG. 10, compared to the configuration of FIG. 1, the probe 1 has three systems of probes 9, 9 ′, 9 ″, and accordingly, the signal processing device 21 in FIG. The signal processing device 25 is replaced by a channel signal processing device 25. The other devices have the same functions and configurations as those of the embodiment shown in Fig. 1. The concrete contents of the signal processing device 25 will be described with reference to Fig. 11. To do.

In the figure, a frequency module 71 'supplies a high-frequency magnetizing current 51 to the probes 9, 9', 9 ". The eddy current signal 52 from the probes 9, 9 ', 9" is sent from the probe 9 in the adder 100a. The difference between the signals from the probes 9 ′ and 9 ″ is calculated twice as the signal and output. This output is electrically mixed with the magnetizing current 51 by the mixer module 72b, and the vector shown in equation 16 is obtained. It becomes the signal D _c (x).

On the other hand, the signal from the probe 9 is independently mixed with the signal 51 by the mixer module 72a and the vector signal O
It is output as _s (x). The phase determiner 101 detects the position of the vector signal D _c (x) and outputs a signal 69 for distinguishing whether the surface is a concave portion or a convex portion depending on whether it is O to π / 2 or π / 3 radians or another angle. . Vector signal at adder 100b
O _s (x) and D _c (x) are input, and the vector signal O _s (x) shown in Expression 17 is output as the real number part signal 61 and the imaginary number part signal 62.

The ADC 73 converts the signals 61 and 62 into digital values and outputs the digital values to the digital input / output unit 26. The input / output unit 26 is the fifth
The configuration and function of the input / output unit 26 shown by the broken line in the figure are the same. In the embodiment of FIG. 10 using the signal processing device 25, the shape of the surface of the subject is displayed on the display device 24.

Next, FIG. 12 shows an embodiment for measuring the thickness of the subject while correcting the change in distance between the probe and the surface of the subject.

FIG. 12 shows the configuration of the signal processing device 28. The frequency module 71 and the mixer module 72 are the same as the modules in FIG. 5, and the input / output signal processing of the probe 1 for measuring the wall thickness is used to output the vector signal O (x) from the module 72.
To get On the other hand, the probes 9, 9 ', 9 "are the probes for correcting the surface unevenness, and the high frequency module 7
1 ', mixer module 72a is used. The adder 100c outputs the eddy current signals 51 ′ of the probes 9, 9 ′, 9 ″ to the O
_s (x), O _s (x−Δx), and O _s (x + Δx) are used to perform the arithmetic processing represented by the equations 16 and 17, and the addition result is electrically mixed by the mixer module 72a, Obtain the vector signal C _s (x). In the adder 100b, the vector constant α and the vector signal C are calculated from the vector signal O (x).
Vector signal O (x) -αC _{s from} which the product of _s (x) is subtracted
(X) is output, and the real and imaginary parts are output to ADC7
It is converted to a digital value at 3 and output to the digital input / output unit 26. This input / output unit 26 is a broken line portion in FIGS.
Identical to 26. In the configuration in which the device of FIG. 12 is replaced with the signal processing device 21 of FIG. 1 or the device 25 of FIG. 10, the display device 24 displays an accurate thickness distribution image on which the surface unevenness of the subject is corrected. To be done.

As another embodiment, the structure shown in FIG. 1 and the structure shown in FIG. 10 are used at the same time, and the thickness obtained by the apparatus shown in FIG.
It is also possible to use the addition result obtained by weighting the distance between the probe and the surface of the subject obtained by the device of FIG.

The configuration and operation of the embodiment of the present invention have been described above.

Examples of the device of the present invention will be described below.

Figure 13 shows a stainless steel plate with a wall thickness of 8 mm and a width of 3 mm and a height (depth).
The output voltage signal when using a subject with 6 mm and 4 mm notches is shown. On the other hand, the Fourier transform function (ω) of the response function R (t) in this device is divided into a real number part and an imaginary number part, and
Shown in Figure 14. An image of the object thickness distribution displayed by this device is shown in FIG. 15 in comparison with the output signal O (x). Although it is impossible to know the detailed wall thickness distribution from the mere output signal O (x), according to the present invention, as shown in FIG. The bottom image of
The thickness of the notch is 1.8 for true values of 2mm and 4mm, respectively.
It can be seen that the measurement results of mm and 4.1 mm are obtained, and the wall thickness can be measured even in a portion with a wall thickness of 4 mm or less.

〔The invention's effect〕

As is clear from the above-described embodiments, according to the present invention, the bottom surface of the subject can be visualized as an image close to a real shape by using the eddy current signal. Further, it is possible to measure the wall thickness with the spatial resolution significantly deteriorated due to the spatial expansion of the magnetized region. Therefore, it is possible to reliably visualize the portion where the wall thickness is locally reduced, for example, the state of wall thinning due to pitting corrosion. The wall thickness was 4m, which was difficult for the thinning inspection by ultrasonic method.
Since the thinning inspection within m can be done by the eddy current method, it can be applied to the test object such as gas pipe where the cutting plant is not allowed. Further, it becomes possible to perform an accurate thinning inspection in which the influence of surface irregularities is corrected.

[Brief description of drawings]

FIG. 1 is a block diagram showing the construction of one embodiment of the thickness reduction measuring apparatus according to the present invention. FIG. 2 is an explanatory diagram showing the principle of signal detection by the eddy current method. FIG. 3 is an explanatory diagram showing the principle of the spatial resolution improving method by Fourier transform and inverse transform. FIG. 4 is an explanatory view showing the development in which the eddy current output changes depending on the heights d and d'of the cut force notches 4 and 5. FIG. 5 is a signal processing device in the embodiment shown in FIG.
FIG. 23 is a detailed view showing the configuration of 21. FIG. 6 is an explanation showing the configuration of the data processing device 23 as well. FIG. 7 is a view showing the configuration of the display device 24 similarly. FIG. 8 is an explanatory view showing a bird's-eye direction for displaying a bird's-eye view of an image by two-dimensional scanning. FIG. 9 is an explanatory diagram showing that the magnetized region when a high-frequency magnetizing current is applied is limited to the vicinity of the surface of the subject. FIG. 10 is a block diagram showing an embodiment different from the above for measuring the unevenness of the surface of the subject. FIG. 11 is a detailed diagram showing the configuration of the signal processing device 25 in the device shown in FIG. FIG. 12 shows a structure of a signal processing device 28 for correcting the surface unevenness and performing an accurate thickness reduction inspection using the wall thickness measurement probe 1 and the surface unevenness correction probes 9, 9 ′, 9 ″. Fig. 13 is a block diagram showing an example, Fig. 13 is an explanatory diagram showing the shape of a subject and an output signal at that time in one example of measurement of thinning using the device of the present invention. Fig. 15 is a table showing a function obtained by Fourier-transforming the response function at the time of the experiment in Fig. 15. Fig. 15 is a device for producing a device according to the present invention from the detected output signal to visualize the thickness distribution of the object as a cross-sectional image. 2 is an explanatory view showing a comparison between the detection result and the actual shape in one example: 1 ... Probe, 21 ... Signal processing device, 22 ... Scanning device, 23 ... Data processing device, 24 ... Display Device, 25 ... Signal processing device, 26 ... Digital input section, 28 ... Signal processing device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Koike 1168 Moriyama-cho, Hitachi City, Ibaraki Prefecture Hiritsu Manufacturing Co., Ltd.Energy Research Institute (72) Inventor Kazunori Koga 1168 Moriyama-cho, Hitachi City, Ibaraki Hitachi Co., Ltd. Energy Research Institute (72) Inventor Toshiyuki Sawa 1168 Moriyama-cho, Hitachi City, Ibaraki Prefecture Hiritsu Seisakusho Energy Research Laboratory (56) Reference JP-A-60-135759 (JP, A) JP-A-60-146147 (JP , A)

Claims (2)

[Claims] 1. In an eddy current flaw detector, (a) a means for scanning an eddy current probe along the surface of a subject, and (b) a vector quantity indicating the amount of change in the electrical impedance of the probe at fixed intervals of the scanning. And (c) means for recording the change in the vector amount corresponding to the probe position for the scanning, and (d) the change amount in the vector amount for Fourier scanning with respect to the scanning position of the probe. Means for calculating the spatial frequency spectrum of the vector change amount, and (e) a spectrum obtained by dividing the above spatial frequency spectrum by a known spatial response frequency spectrum by inverse Fourier transform and outputting in real space Means for calculating a spectrum; (f) a data processing device for outputting the sum of squares of absolute values of the real space output spectrum;
(G) An eddy current flaw detector capable of thinning inspection, comprising display means for displaying the above sum of squares as a graphic corresponding to the scanning position. 2. The eddy current probe comprises (h) at least three auxiliary eddy current probes, and (i) a difference for calculating a secondary difference vector amount from the amount of change in electrical impedance of the auxiliary eddy current probe. The signal processing means and (j) sub-data processing means for outputting the sum of squares of the absolute values of the real-space difference spectra based on the second-order difference vector amount, and (k) the sub-data processing means. The means for displaying the image of the cross-sectional shape of the subject based on the sum of squares of absolute values of the real space difference spectrum calculated by the method according to claim 1, characterized in that Eddy current flaw detector capable of thinning inspection.