JP2023014461A - Thinning distance detection system and method - Google Patents

Abstract

Kind Code: A1 A thickness reduction separation detecting means is provided which can determine the thickness reduction position and thickness reduction state even if the position of the thickness reduction portion is unknown, and which can be applied to aluminum. A thinning separation detection system includes a probe having an excitation coil and a detection coil, a pulse current generator, and a data analysis device. The excitation coil generates parallel magnetic flux in a single direction X parallel to the surface of the specimen, and the detection coil detects orthogonal magnetic flux perpendicular to the surface of the specimen. In step S1, a plurality of calibration curves ML showing the relationship between the second peak voltage difference ΔV2 and the detection distance L in a plurality of reference specimens having different thickness reduction amounts ΔT are created. In step S2, a second peak voltage difference ΔV2 is calculated at a plurality of probe positions XLi with respect to the actual specimen. In step S3, the thinning position and thinning state of the actual specimen are determined using the calibration curve ML from the probe relative distance ΔXL and the plurality of second peak voltage differences ΔV2. [Selection drawing] Fig. 4

Description

TECHNICAL FIELD The present invention relates to thinning distance detection means for detecting thinning of a member buried in the ground such as a lighting pole without excavating.

In recent years, deterioration of lighting poles is progressing. Visual inspection after excavation has traditionally been the mainstream for inspection of the buried part of the lighting pole, but it is costly and time-consuming.
Therefore, there has been proposed a means for detecting thinning of an embedded member without excavating it using a pulse current (for example, Patent Document 1).

In Patent Document 1, "Method for inspecting wall thinning of edge portion of partially buried structure", a measurement probe is set on the surface of a foundation portion such as the ground in a posture in which the central axis of the excitation coil is tilted, and the central axis directed to the edge. In this state, a pulse current is passed through the excitation coil to form an eddy current on the surface of the edge portion, and the intensity of the eddy current is detected over time to specify its duration. The state of thinning in the edge portion is determined by comparing the specified duration with reference data on the duration of the eddy current previously sampled at the same tilt angle for the healthy portion.

JP 2016-3995 A

In the method of Patent Document 1, when a direct-current pulse current flows through the excitation coil, eddy currents are generated on the surface of the object to be inspected due to changes in the magnetic flux formed thereby. permeate up to Moreover, attenuation of the eddy current accelerates when it reaches the back surface of the object to be inspected.
The center axis of the detection coil is coaxial with the center axis of the excitation coil, and the thinning state is determined by measuring the time from the formation of an eddy current by the detection coil to the start of acceleration of its attenuation. .

However, the method of Patent Document 1 has the following problems.
(1) It is necessary to position the central axis of the excitation coil toward the thinned portion of the object to be inspected.
Since the eddy current generated by the exciting coil permeates along the central axis of the exciting coil, it is impossible to determine the thinning state unless there is a thinned portion on the extension of the central axis.
Therefore, if the location of the thinned portion is unknown and, for example, the thinned portion is located outside the edge of the buried structure, it will be necessary to search for it using a large number of jigs.
(2) When the object to be inspected is a steel material, it is possible to detect large reduction in thickness due to corrosion, but it is difficult to apply the method to aluminum, which has a small reduction in thickness.

The present invention was created to solve the above problems. That is, an object of the present invention is to provide a thinning distance detection means that can determine the thinning position and thinning state even if the position of the thinning portion is unknown, and that can be applied to aluminum. That's what it is.

According to the present invention, a probe having an excitation coil for generating a unidirectional parallel magnetic flux parallel to the surface of the specimen and a detection coil for detecting a quadrature magnetic flux perpendicular to the surface;
a pulse current generator that applies a rectangular pulse current to the excitation coil;
a data analysis device for data analysis of the detected voltage generated in the detection coil,
After application of the pulse current, the detection voltages are, in order, the highest first peak voltage, the lowest first bottom voltage, the second highest peak voltage next to the first peak voltage, and the first bottom voltage. a constant convergence voltage intermediate the second peak voltage;
The data analysis device is
(A) A second peak voltage difference, which is the difference between the second peak voltage and the convergence voltage, and a detection distance, which is the distance from the probe to the thinning start point, in a plurality of reference specimens having different thinning amounts Store multiple calibration curves showing the relationship between
(B) Based on the plurality of second peak voltage differences at a plurality of probe positions with respect to the actual test body, using the calibration curve from the probe relative distance and the plurality of the second peak voltage differences, the actual test body thinning A metal loss separation detection system is provided for determining location and metal loss conditions.

Further, according to the present invention, using the thinning separation detection system described above,
(A) The second peak voltage difference, which is the difference between the second peak voltage and the convergence voltage, and the distance from the probe to the thinning start point in a plurality of reference specimens having different thinning amounts. a step of creating and storing a plurality of the calibration curves showing the relationship with the detection distance;
(B) detecting the detected voltage at a plurality of the probe positions with respect to the actual test object and calculating each of the second peak voltage differences;
(C) determining the thinning position and thinning state of the actual specimen using the calibration curve from the probe relative distance and the plurality of second peak voltage differences. be done.

The inventors of the present application applied a rectangular pulse current to generate parallel magnetic flux in a single direction parallel to the surface of the specimen, and by detecting orthogonal magnetic flux perpendicular to the surface, obtained the following new findings. .
(1) After application of the pulse current, the detected voltages are, in order, the highest first peak voltage, the lowest first bottom voltage, the second highest peak voltage next to the first peak voltage, and the first bottom voltage. and a constant convergence voltage intermediate the second peak voltage.
(2) In a plurality of specimens having different thickness reduction amounts, the relationship between the second peak voltage difference, which is the difference between the second peak voltage and the convergence voltage, and the detection distance, which is the distance from the probe to the thickness reduction start point, is , shows the correlation that can be represented by a single quadratic curve for different amounts of metal loss.
(3) The influence of the shape of the thinned portion of the specimen (eg, step, slope, through hole) is small.
(4) The magnitude of the change in volume of the thinned portion of the specimen affects the magnitude of the second peak voltage difference.

The present invention is based on the above-described novel findings.
According to the present invention, a plurality of calibration curves indicating the relationship between the second peak voltage difference and the detection distance are determined in advance and stored for a plurality of reference specimens having different thickness reduction amounts.
Next, detection voltages generated in the detection coil at a plurality of probe positions with respect to the actual test object are detected, and respective second peak voltage differences are calculated.

Since the probe relative distance corresponds to the difference in detection distance in each calibration curve, by selecting a calibration curve that has each second peak voltage difference and the difference in detection distance matches the probe relative distance, the actual It is possible to determine the thinning position and thinning state of the specimen.

1 is an explanatory diagram of a thinning separation detection system according to the present invention; FIG. It is explanatory drawing of the test method and test result using a thinning separation detection system. It is a figure which shows the relationship between a 2nd peak voltage difference and detection distance. 1 is an overall flow chart of a thickness reduction separation detection method according to the present invention; FIG. 4 is a diagram showing test results of Example 1. FIG. It is an enlarged view of FIG. 5(A). FIG. 4 is a schematic diagram showing a test state using a specimen with a slope. It is a schematic diagram which shows the test state using a cylindrical test body.

Preferred embodiments of the present invention will now be described with reference to the drawings. In addition, in each figure, the same code|symbol is attached|subjected to a common part, and the overlapping description is abbreviate|omitted.

FIG. 1 is an illustration of a thinning separation detection system 100 according to the present invention. In this figure, (A) is an overall block diagram, (B) is a side view of the probe 10, and (C) is a perspective view of the probe 10. As shown in FIG.

In FIG. 1A, a thinning separation detection system 100 includes a probe 10, a pulse current generator 20, and a data analysis device 30. FIG.

The probe 10 has an excitation coil 12 and a detection coil 14 . The exciting coil 12 is a coil that generates a uniform parallel magnetic flux in a single direction X (hereinafter referred to as “X direction”) parallel to the surface of the specimen 1 . Also, the detection coil 14 is a coil for detecting orthogonal magnetic flux perpendicular to the surface of the test object 1 .

The excitation coil 12 and the detection coil 14 are elongated detection coils so that the sum of the magnetic fluxes passing through the detection coil 14 approaches zero when there is no thinning.
1(B) and 1(C), the excitation coil 12 is a rectangular coil having a rectangular inner surface (hereinafter referred to as "first rectangular inner surface"). The short side of the first rectangular inner surface (hereinafter referred to as "first short side") is set to be greater than or equal to the plate thickness of the reference specimen 2 (described later), and the long side of the first rectangular inner surface (hereinafter referred to as "first long side") ) is set to be equal to or less than the width of the reference specimen 2 .
The specimen 1 and the reference specimen 2 have the same material and the same thickness.

In the examples described later, the test piece 1 and the reference test piece 2 are aluminum plates with a plate thickness of 6 mm and a width of 200 mm. The excitation coil 12 has a first short side of 40 mm, a first long side of 80 mm, and an axial length of 10 mm.

Further, when the probe 10 is used, the first long side of the excitation coil 12 is orthogonal to the X direction (single direction X) and positioned in the width direction Y (hereinafter referred to as "Y direction") of the specimen 1. One short side is positioned in a vertical direction Z (hereinafter referred to as "Z direction") perpendicular to the surface of the test piece 1 .

The detection coil 14 is a rectangular coil having a rectangular inner surface (hereinafter referred to as “second rectangular inner surface”) smaller than the first rectangular inner surface of the exciting coil 12 . The short side of the inner surface of the second rectangle (hereinafter referred to as “second short side”) is set to be equal to or less than the length of the exciting coil 12 in the axial direction, and the long side of the inner surface of the second rectangle (hereinafter referred to as “second long side”) It is set to be equal to or less than the first long side of the inner surface of one rectangle.

Further, when the probe 10 is used, the detection coil 14 is positioned between the excitation coil 12 and the specimen 1, the second short side is positioned in the X direction (single direction X), and the second long side is width It is located in the direction Y (Y direction).

In the example described later, the second short side of the detection coil 14 is 4 mm, the second long side is 40 mm, and the length in the axial direction is 3 mm. A gap in the vertical direction Z (Z direction) between the detection coil 14 and the excitation coil 12 is 6 mm.

In FIG. 1A, the pulse current generator 20 applies a rectangular pulse current to the exciting coil 12 .
In the embodiment described later, the pulse current generator 20 has a function generator 22 and a power amplifier 24. FIG. A function generator 22 generates a rectangular pulse current at a constant cycle. The power amplifier 24 amplifies the generated pulse current and sends it to the exciting coil 12 .
The frequency of the rectangular pulse current is preferably 5-20 Hz, more preferably 10 Hz.
In the embodiment, the current applied from the function generator 22 as a rectangular pulse (10 Hz, duty ratio 50%, Vp-p±0.8 V) was amplified 20 times by the power amplifier 24 and passed through the exciting coil 12 .

The data analysis device 30 data-analyzes the detected voltage generated in the detection coil 14 .
In the example described below, the data analysis device 30 has an oscilloscope 32 and a signal processor 34 . The oscilloscope 32 AD-converts the detected voltage for multiple cycles detected by the detection coil 14 . The signal processor 34 performs an averaging process (additional average 10 times, moving average 20 points) of the detected voltages for a plurality of cycles after AD conversion.

The data analysis device 30 also has a low-pass filter (not shown) that removes signals exceeding 200-300 Hz in an embodiment described later.
FFT was performed on the detection signals obtained in the verification test, and it was clarified that signals exceeding 200 to 300 Hz (preferably 250 Hz) are noise, and low frequencies below that are effective for remote thinning detection. made it Based on this result, the detection signal was evaluated using a signal passed through a 250 Hz low-pass filter.

Using the thinning distance detection system 100 described above, a test was conducted to detect the detection voltage V generated in the detection coil 14 in the specimen 1 having a thinning portion.
FIG. 2 is an explanatory diagram of a test method and test results using the thinning separation detection system 100. As shown in FIG. In this figure, (A) is a schematic diagram showing the test state, and (B) is a diagram showing changes in the obtained detection voltage V. As shown in FIG.

In FIG. 2(A), the specimen 1 is an aluminum plate, the plate thickness of the specimen 1 (hereinafter referred to as "healthy portion thickness T") is 6 mm, the plate thickness of the reduced portion (hereinafter referred to as "thickness t ) was 1 mm. Hereinafter, the difference between the thickness T of the healthy portion and the thickness t of the thinned portion is referred to as a thinned portion ΔT. In this example, the thickness reduction amount ΔT is 5 mm. Further, the X-direction distance from the thinning start point E to the thinning side end surface of the exciting coil 12 is hereinafter referred to as a detection distance L. As shown in FIG.
Further, the specimen 1 shown in FIG. 2(A) is hereinafter referred to as a "stepped specimen 1A".

From the preliminary test, it was clarified that if the edge of the specimen 1 is separated by 50 mm or more in the width direction Y and 100 mm or more in the length direction X, the influence of the edge is not affected. bottom.
All the specimens 1 and reference specimens 2 are aluminum plates with a plate thickness of 6 mm, a width of 200 mm, an overall length of 600 mm, and an overall length of the sound portion of 400 mm.

In FIG. 2(B), the horizontal axis represents the elapsed time from when the rectangular pulse current was turned off, and the vertical axis represents the detection voltage V generated in the detection coil 14 . In addition, the dashed line in the figure is for the case where the specimen 1 has no thinning portion, and the solid line is for the case where the thinning amount ΔT is 5 mm.
Note that the frequency of the rectangular pulse current is 10 Hz, and the current OFF duration is half (50 ms) of the period of 100 ms.

From this figure, it can be seen that the detected voltage V indicated by the solid line has the following features, unlike the detected voltage V indicated by the broken line.
(1) After application of the pulse current, it has a first peak voltage Vp1, a first bottom voltage Vb1, a second peak voltage Vp2, and a convergence voltage Ve in order.
(2) The first peak voltage Vp1 appears first after application of the pulse current and has the highest detected voltage V;
(3) The first bottom voltage Vb1 appears next to the first peak voltage Vp1 and has the lowest detection voltage V;
(4) The second peak voltage Vp2 appears next to the first bottom voltage Vb1 and has the next highest detection voltage V after the first peak voltage Vp1.
(5) The convergence voltage Ve has a substantially constant detected voltage intermediate the first bottom voltage Vb1 and the second peak voltage Vp2 after the second peak voltage Vp2.

The features (1) to (5) described above are obtained when the plate thickness (healthy portion thickness T) of the stepped specimen 1A is 6 mm and the thickness reduction amount ΔT is 2, 3, 4, and 5 mm in the examples described later. In addition, it was found that the reproducibility was high and the measurement error was small.

FIG. 3 is a diagram showing the relationship between the second peak voltage difference ΔV2 and the detection distance L. As shown in FIG. This figure shows the cases where the sound portion thickness T of the stepped specimen 1A is 6 mm, and the thickness reduction amount ΔT is 2, 3, 4, and 5 mm.
In this figure, the horizontal axis is the second peak voltage difference ΔV2 (that is, the difference between the second peak voltage Vp2 and the convergence voltage Ve), and the vertical axis is the detection distance L (that is, the thinning start point from the end face of the excitation coil 12 on the step side). X-direction distance to E).
From this figure, it can be seen that the second peak voltage difference ΔV2 and the detected distance L exhibit a high correlation that can be represented by a single quadratic curve for each different amount of thinning.

The data analysis device 30 in FIG. 1 is, for example, a computer (PC), and stores a plurality of calibration curves ML similar to those in FIG. 3 in a storage device.
A calibration curve ML shows the relationship between the second peak voltage difference ΔV2 and the detection distance L in a plurality of reference specimens 2 having different thickness reduction amounts ΔT.

In addition, based on the plurality of second peak voltage differences ΔV2 at the plurality of probe positions XLi with respect to the actual specimen 1 (“actual specimen”), the data analysis device 30 determines the probe relative distance ΔXL and the plurality of second peak voltage differences Using the calibration curve ML from ΔV2, the thinning position and thinning state of the actual specimen are determined.

The “plurality of probe positions” is the X-direction distance from the X-direction reference position X0 of the actual specimen to the end surface of the excitation coil 12 on the step side. The reference position X0 is preferably set in the vicinity of the ground surface, for example, when the actual specimen is a buried object such as underground.
Hereinafter, the probe position is assumed to be XLi. i is an integer (1, 2, 3, ...).
In this case, since the thinning position and thinning state of the actual specimen are unknown, the probe position XLi differs from the detection distance L in principle.

FIG. 4 is an overall flow chart of the thickness reduction separation detection method according to the present invention.
In this figure, the thickness reduction separation detection method has steps S1 to S3.

In step S1, a plurality of calibration curves ML showing the relationship between the second peak voltage difference ΔV2 and the detection distance L are created and stored for a plurality of reference specimens 2 having different thickness reduction amounts ΔT.

Step S1 has steps S11 to S13.
In step S11, a plurality of reference specimens 2 are prepared.
A plurality of (for example, four) reference specimens 2 are assumed to be, for example, the stepped specimen 1A shown in FIG. ), and the same amount of thickness reduction ΔT (for example, 2, 3, 4, 5 mm) are prepared.
In step S12, the detection voltage V is detected at a plurality of detection distances L using each reference specimen 2. FIG. A plurality of (for example, 4) detection distances L are, for example, 20, 30, 40, and 50 mm as in FIG. As a result, there are many (for example, 4×4=16) combinations of a plurality (for example, 4) of thinning amounts ΔT and a plurality (for example, 4) of detection distances L, which are similar to those in FIG. 2(B). can get.
In step S13, a plurality of calibration curves ML for each of a plurality of detection distances L are created and stored from changes in the detected voltage V thus obtained. A plurality of calibration curves ML are similar to those shown in FIG. 3, for example.

In step S2, the detection voltage V is detected at a plurality of probe positions XLi with respect to the actual test piece (actual test piece 1), and each second peak voltage difference ΔV2 is calculated.

Step S2 has steps S21 and S22.
In step S21, a plurality of probe positions XLi are set for the actual specimen (actual specimen 1). Two or more probe positions XLi are set at intervals in the X direction in the vicinity of the position where the thinning position is expected. This X-direction interval corresponds to the probe relative distance ΔXL.
In step S22, the detection voltage V is detected at the plurality of set probe positions XLi, and the respective second peak voltage differences ΔV2 are calculated.

In step S3, the thinning position and thinning state of the actual specimen are determined using the calibration curve ML from the probe relative distance ΔXL and the plurality of second peak voltage differences ΔV2.
When there are two probe positions XLi, the two second peak voltage differences ΔV2 calculated in step S2 can be regarded as two points located on one of the calibration curves ML (eg, FIG. 3).

For example, in FIG. 3, the intersections of parallel lines corresponding to two second peak voltage differences ΔV2 and a plurality of calibration curves ML are obtained, and the detection distance difference ΔL between two points on the same calibration curve ML is obtained. If the detected distance difference ΔL on any calibration curve matches or approximates the probe relative distance ΔXL, it can be determined that there is a thinning state corresponding to that calibration curve ML. Also, the thinning position of the actual specimen can be determined from the detection distance L of the two points on the calibration curve.

(Example 1)
(Thickness reduction detection test for stepped specimen 1A)
As the stepped test piece 1A shown in FIG. A specimen 1A with five steps having a thinned portion was prepared.
Further, the detection voltage V was measured for the test piece 1A with five steps, using the positions where the detection distance L described above was 20 mm, 30 mm, 40 mm, and 50 mm as measurement points.

5 is a diagram showing test results of Example 1. FIG. In this figure, (A) is an example in which the detection distance L is 20 mm, and (B) is an example in which it is 30 mm. Moreover, FIG. 6 is an enlarged view of FIG. 5(A).

5 and 6, the vertical axis indicates the detection voltage V of the detection coil 14, and the horizontal axis indicates time. Differences due to the presence or absence of thinning were mainly seen at three locations. When there was thinning, the first peak voltage Vp1 and the first bottom voltage Vb1 tended to decrease, and the second peak voltage Vp2 tended to increase. By using these indices, it can be said that a thickness reduction amount ΔT of 50% or more can be sufficiently detected even if the detection distance L is 50 mm.

Although the value of the second peak voltage Vp2 was small, a change with high reproducibility was obtained through a plurality of tests, and there was a tendency for measurement errors to be small.
At any thickness reduction amount ΔT, the second peak voltage difference ΔV2 decreased as the detection distance L increased. In addition, when compared at the same detection distance L, the second peak voltage difference ΔV2 showed a higher value as the thickness reduction amount ΔT increased.

From these results, as a result of comparing the second peak voltage difference ΔV2 (second peak voltage Vp2−convergence voltage Ve) with the convergence voltage Ve being the voltage at the time of convergence, a high correlation as shown in FIG. 3 described above was observed. was taken.

(Example 2)
(Thickness reduction detection test for specimen 1B with slope)
FIG. 7 is a schematic diagram showing a test state using the sloped specimen 1B.
As shown in this figure, a slope (inclined portion) was provided between the thinning start point E and the thinning portion as a specimen 1B with a slope, and the influence thereof was tested.
A test specimen 1A with a step having no slope was compared with the case where the thickness T of the healthy portion was 6 mm, the thickness t of the reduced portion was 3 mm, and the slope length Ls was 20 mm.
As a result of detecting the time change of the detection voltage V in the same manner as in FIGS. 5 and 6, it was found that even in the slope shape, a signal similar to that of the stepped specimen 1A was obtained, indicating that the shape of the thinned portion had little effect.

(Example 3)
(Thickness reduction detection test for specimen with through holes)
An elliptical through hole of 10 mm in the X direction and 50 mm in the Y direction was provided in the vicinity of the lower end of the slope of the thinned portion of the specimen 1B with the slope, and the same test as in Example 2 was performed.
As a result, the second peak voltage Vp2 showed a slightly higher value than the case without through holes.
Moreover, from the above results, it was considered that the degree of volume change of the thinned portion of the specimen 1 affected the magnitude of the second peak voltage difference ΔV2.

(Example 4)
(Thickness reduction detection test for cylindrical test piece 1C)
FIG. 8 is a schematic diagram showing a test state using the cylindrical test piece 1C.
A cylindrical test piece 1C having the same cross section as the stepped test piece 1A was prepared, and a test was conducted in the case where the surface of the test piece was curved.
In addition, in order to ensure the stability of the probe 10 on the curved surface, a jig 3 as shown in the figure was used to acquire data.

Although the amount of change at the time of thinning was smaller for the cylinder than for the flat plate, a change was observed in the second peak voltage Vp2 according to the thickness, similar to the test results for the flat plate. On the other hand, since the noise on the long-time side was large and the convergence voltage Ve was unstable, the second peak voltage difference ΔV2 at the detection distances of 40 mm and 50 mm for the cylinder showed values different from those for the flat plate.
It is considered that the second peak voltage difference ΔV2 at the cylinder detection distances of 40 mm and 50 mm was strongly affected by variations in the convergence voltage Ve because the second peak voltage Vp2 was small.

As described above, the inventor of the present application applies a rectangular pulse current to generate a parallel magnetic flux in a single direction parallel to the surface of the specimen 1, and detects an orthogonal magnetic flux perpendicular to the surface to obtain a new finding. got
The present invention is based on such new findings.

According to the present invention, a plurality of calibration curves ML indicating the relationship between the second peak voltage difference ΔV2 and the detection distance L are determined in advance and stored for a plurality of reference specimens 2 having different thickness reduction amounts ΔT.
Next, the detection voltage V generated in the detection coil 14 is detected at a plurality of probe positions XLi with respect to the actual test object, and each second peak voltage difference ΔV2 is calculated.

The probe relative distance ΔXL corresponds to the difference in the detection distances L in each calibration curve ML. Therefore, by selecting the calibration curve ML that has the respective second peak voltage differences ΔV2 and that the difference in the detection distance L matches the probe relative distance ΔXL, the thickness reduction position and thickness reduction state of the actual specimen are determined. be able to.

Moreover, as described above, with respect to the amount of thickness reduction ΔT of 50% or more, even when the specimen 1 was made of aluminum, a large difference was observed in the detection signal compared to the healthy portion even from a point 50 mm away.
Furthermore, by implementing the above-described thinning distance detection method on software, the thinning distance detection system 100 can improve the accuracy of determination of the thinning position and thinning state of the actual specimen.

It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

E: thinning starting point, L: detection distance, Ls: slope length, ΔL: detection distance difference,
ML calibration curve, T sound thickness, t thinning thickness, ΔT thinning amount,
V detection voltage, Vp1 first peak voltage, Vb1 first bottom voltage,
Vp2 second peak voltage, ΔV2 second peak voltage difference, Ve convergence voltage,
X unidirectional, X0 reference position, XLi probe position,
ΔXL probe relative distance, Y width direction, Z vertical direction, 1 specimen,
1A test body with step, 1B test body with slope, 1C circular tube test body,
2 reference specimen, 3 jig, 10 probe, 12 excitation coil,
14 detection coil, 20 pulse current generator,
22 function generator, 24 power amplifier,
30 data analysis device, 32 oscilloscope, 34 signal processor,
100 thinning separation detection system

Claims (6)

a probe having an excitation coil for generating a unidirectional parallel magnetic flux parallel to the surface of the specimen and a detection coil for detecting an orthogonal magnetic flux perpendicular to the surface;
a pulse current generator that applies a rectangular pulse current to the excitation coil;
a data analysis device for data analysis of the detected voltage generated in the detection coil,
After application of the pulse current, the detection voltages are, in order, the highest first peak voltage, the lowest first bottom voltage, the second highest peak voltage next to the first peak voltage, and the first bottom voltage. a constant convergence voltage intermediate the second peak voltage;
The data analysis device is
(A) A second peak voltage difference, which is the difference between the second peak voltage and the convergence voltage, and a detection distance, which is the distance from the probe to the thinning start point, in a plurality of reference specimens having different thinning amounts Store multiple calibration curves showing the relationship between
(B) Based on the plurality of second peak voltage differences at a plurality of probe positions with respect to the actual test body, using the calibration curve from the probe relative distance and the plurality of the second peak voltage differences, the actual test body thinning Thinning distance detection system to determine location and thinning condition. The excitation coil is a rectangular coil having a first rectangular inner surface,
A first short side of the first rectangular inner surface is set to be greater than or equal to the plate thickness of the reference specimen, and a first long side of the first rectangular inner surface is set to be equal to or less than the width of the reference specimen,
When using the probe, the first long side is perpendicular to the single direction and is positioned in the width direction of the specimen, and the first short side is positioned in the vertical direction perpendicular to the surface of the specimen. The thinning separation detection system according to claim 1, wherein: the detection coil is a rectangular coil having a second rectangular inner surface smaller than the first rectangular inner surface;
A second short side of the second rectangular inner surface is set to be equal to or less than the axial length of the excitation coil, and a second long side of the second rectangular inner surface is set to be equal to or less than the first long side of the first rectangular inner surface. cage,
When the probe is in use, the detection coil is positioned between the excitation coil and the specimen, the second short side is positioned in the single direction, and the second long side is positioned in the width direction. 3. The thinning separation detection system according to claim 2. The pulse current generator has a function generator that generates the rectangular pulse current at a constant cycle, and a power amplifier that amplifies the generated pulse current and feeds it to the excitation coil,
The data analysis device comprises an oscilloscope for AD-converting the detection voltage for multiple cycles detected by the detection coil, and a signal processor for averaging the detection voltage for multiple cycles after AD conversion. Item 2. A thinning separation detection system according to item 1. 5. The metal loss separation detection system of claim 4, wherein the data analyzer has a low pass filter that removes signals above 200-300 Hz. Using the thinning separation detection system according to claim 1,
(A) The second peak voltage difference, which is the difference between the second peak voltage and the convergence voltage, and the distance from the probe to the thinning start point in a plurality of reference specimens having different thinning amounts. a step of creating and storing a plurality of the calibration curves showing the relationship with the detection distance;
(B) detecting the detected voltage at a plurality of the probe positions with respect to the actual test object and calculating each of the second peak voltage differences;
(C) A thinning separation detection method comprising the step of determining the thinning position and thinning state of the actual specimen using the calibration curve from the probe relative distance and the plurality of second peak voltage differences.

Images