JP7170323B2 - Nondestructive inspection measurement system and nondestructive inspection measurement method - Google Patents

Description

The present invention relates to a nondestructive inspection measurement system and a nondestructive inspection measurement method.

As shown in Patent Documents 1 to 6, in an eddy current flaw detection device using electromagnetic induction, a sine wave generator, a drive circuit that drives an excitation coil, a sensor consisting of an excitation coil and a detection coil, and an amplifier that amplifies the output of the detection coil A device composed of an analysis circuit including a circuit and a synchronous detection circuit has been proposed and used.

Measurement of the dimensions of a member provided inside a subject is widely performed using the above-described apparatus.
For example, Patent Literature 7 discloses a calibrating device for a nondestructive inspection measurement system as follows. A calibration device for a nondestructive inspection measurement system applies a sinusoidal signal or a composite signal composed of a plurality of sinusoidal waves having different frequencies to an excitation coil, a detection coil, and to the excitation coil to excite the tube body, and detects and a computer that detects changes in the voltage output from the coil. The calibrator calibrates the detection results in the computer by incorporating the amplitude and phase difference of the voltage changes output from the sensing coil at calibration points of known thickness on the tube body as variables into the simultaneous equations. This calibration device performs calibration by setting a plurality of different calibration conditions at each calibration point, and incorporating the amplitude and phase difference of the voltage change output from the detection coil under each calibration condition into simultaneous equations.

Table 8 shows the experimental results of the prior art, for example, shown in the above-mentioned Patent Document 7. The subject in this experiment has an outer can and an inner can. Both the outer can and the inner can are formed in a kiln shape, the inner can is provided inside the outer can, and the inner can is invisible from the outside. In this experiment, the thickness of the inner can is measured.

ここで、係数ａ、ｂ、定数項ｃは、較正として、内缶の厚さｔ２が既知の３点（ｔ２１、ｔ２２、ｔ２３）において、実際に内缶の厚さｔ２を測定し、その各々における、振幅比ｘ、位相差ｙ、内缶の厚さｔ２の測定値の組み合わせ（ｘ１、ｙ１、ｔ２１）、（ｘ２、ｙ２、ｔ２２）、（ｘ３、ｙ３、ｔ２３）を上式に入力した、次の数式７として示される連立方程式を解くことにより、決定することができる。

表８において、「振幅比３３Ｈｚ」、「位相差３３Ｈｚ（ｒａｄ）」、「ｔ２較正値（ｍｍ）」の欄の第１行、第２行、及び第３行の各々は、上記の（ｘ１、ｙ１、ｔ２１）、（ｘ２、ｙ２、ｔ２２）、（ｘ３、ｙ３、ｔ２３）のそれぞれの組み合わせの実際の数値を記載したもので、上記の連立方程式を表形式で表したものである。
この連立方程式を解いて求めた係数ａ、ｂ、定数項ｃの値は、表８中のａ、ｂ、ｃと示されたそれぞれの欄に記載されている。 An estimation formula for estimating the thickness t2 of the inner can, where x is the amplitude ratio and y is the phase difference, can be formulated as the following formula 6 using the coefficients a and b and the constant term c.

Here, the coefficients a, b, and the constant term c are obtained by actually measuring the thickness t2 of the inner can at three points (t21, t22, t23) where the thickness t2 of the inner can is known, as a calibration, and , the combination of the measured values of the amplitude ratio x, the phase difference y, and the inner can thickness t2 (x1, y1, t21), (x2, y2, t22), (x3, y3, t23) was input into the above equation , can be determined by solving the system of equations shown as Equation 7 below.

In Table 8, each of the 1st, 2nd, and 3rd rows in the columns of "amplitude ratio 33 Hz", "phase difference 33 Hz (rad)", and "t2 calibration value (mm)" is the above (x1 , y1, t21), (x2, y2, t22), and (x3, y3, t23), and represents the above simultaneous equations in tabular form.
The values of the coefficients a, b and constant term c obtained by solving the simultaneous equations are listed in the columns labeled a, b and c in Table 8, respectively.

More specifically, in this experiment, the ternary simultaneous equations shown as Equation 8 are used to calibrate the estimated thickness values. That is, under the condition that the ambient temperature is 10.4° C., the gap between the inner can and the outer can is 80 mm and the thickness t2 of the inner can is 35 mm and 25 mm. The amplitude ratio and the phase difference are calculated for each of the cases where the length t2 is 35 mm, and the results of these calculations are substituted into Equation 7 to obtain the following Equation 8.

In Equation 8 above, coefficients a, b, and a constant term c are used, and in each result, a value obtained by multiplying the amplitude ratio by the coefficient a, a value obtained by multiplying the phase difference by the coefficient b, and a constant term c , and the equation is formulated so that this matches the known thickness t2.
By solving these three equations as simultaneous equations, the values of the unknowns a, b, and c, as shown in Table 8, are determined. Using the values of these coefficients a, b and constant term c, and letting x be the amplitude ratio and y be the phase difference, the following estimation formula for estimating the thickness t2 of the inner can is formulated.

FIG. 23 is an example of estimating and measuring the thickness t2 of the inner can based on the above estimation formula, and is a graph showing the measurement results when the ambient temperature is 10.4°C. FIG. 24 is a graph obtained by adding the measurement results when the ambient temperature is 11.4° C. to FIG. 23 with a dashed line.

Japanese Patent No. 3753499 Japanese Patent No. 3266128 JP 2010-48552 A Japanese Patent No. 3896489 JP 2010-54352 A Japanese Patent No. 4756409 Japanese Patent Application Publication No. 2018-59804

FIG. 23 shows an accurate value when the thickness t2 of the inner can is 35 mm, but the value becomes inaccurate when the value of the interval Gap changes. Also, as shown in FIG. 24, when the ambient temperature rises to 11.4° C., the values are even more inaccurate.

As described above, the conventional apparatus is required to reduce the influence of the measurement conditions when measuring the dimensions of the subject body provided inside the subject.
The measurement conditions include, for example, the distance, spacing, and temperature of the body of the subject from the outer surface of the subject or members forming the outer surface. That is, as shown in FIGS. 23 and 24, the precision of the measurement results may be reduced due to changes in the interval Gap and temperature.
In particular, there are many situations in which the distance cannot be grasped when measuring the dimensions of the body of the subject. As such a case, for example, when the subject includes a tubular subject body and an envelope provided outside the subject body to cover the outside of the subject body, the influence of the envelope A situation is assumed in which the thickness of the body of the subject is measured except for . Alternatively, in the case where the subject is a double can body composed of an outer can and an inner can, as described in the above experiment, the distance between the outer can and the inner can cannot be observed from the outside. , a situation in which the thickness of the inner can, which is the subject body, is to be accurately measured. Furthermore, when the test object is reinforced concrete, the distance between the concrete surface and the reinforcing bar, that is, the amount of "covering" in the industry term, is unknown. A situation to measure is assumed.
In this way, even if the measurement conditions, particularly the distance and spacing of the subject body from the outer surface of the subject or the members constituting the outer surface of the subject cannot be grasped, the dimensions of the subject body can be accurately grasped. is desired.

The problem to be solved by the present invention is to provide a non-destructive inspection measurement system and a non-destructive inspection measurement method that can reduce the influence of measurement conditions and measure the dimensions of a subject body provided in the subject with high accuracy. It is to be.

In order to solve the above problems, the present invention employs the following means. That is, the present invention includes an excitation coil that excites a subject body provided in a subject, and an output voltage corresponding to a magnetic field change generated in the subject body when the subject body is excited by the excitation coil. A sine wave signal or a composite signal composed of a plurality of sine waves having different frequencies is applied to the detection coil and the excitation coil for exciting the subject body, and the voltage output from the detection coil is detected. and a measuring device for measuring dimensions of the subject body, wherein the measuring device measures a plurality of portions of the subject body having known and different dimensions. For each dimension, under each of a plurality of different measurement conditions, the voltage output from the detection coil is measured, the amplitude ratio and phase difference between this and the reference voltage are calculated, and the amplitude ratio and the phase difference are divided by 2. A slope-at-calibration calculator that obtains a straight line connecting at least two points corresponding to the measurement results on the amplitude ratio-phase difference plane and calculates the slope of the straight line; Constructing a system of equations from the relationship between a dimension and the gradient-based value calculated for that dimension, and based on the solution, estimating the dimension when measuring the dimension, the gradient-based a calibration unit that establishes an estimation formula with the values obtained as variables as variables; and a measurement unit that estimates and measures the dimensions of the portion of the subject body to be measured based on the estimation formula. To provide a non-destructive inspection measurement system.
According to the configuration as described above, before measuring the dimensions of the portion to be measured of the subject body, for each of the plurality of portions having known and different dimensions, under each of the plurality of different measurement conditions, Measure the voltage output from the detection coil, calculate the amplitude ratio and phase difference between this and the reference voltage, and obtain at least two measurement results on the amplitude ratio-phase difference plane with the amplitude ratio and phase difference as two axes. A straight line connecting the points corresponding to is obtained, and the gradient of the straight line is calculated. If the dimensions are the same and the measurement conditions are changed, the amplitude ratio and the phase difference are roughly proportional. The slope is a value that suppresses the influence of the measurement conditions.
When estimating and measuring the dimensions of the part of the body of the subject to be measured, solve simultaneous equations constructed from the relationship between the dimensions and the values based on the gradients calculated for the dimensions. Then, an estimation formula is formulated, and the dimensions are obtained based on this formula.
Therefore, it is possible to reduce the influence of the measurement conditions and measure the dimensions of the subject body provided in the subject with high accuracy.

In one aspect of the invention, the calibrator comprises, for each of a plurality of said dimensions, a multi-dimensional linear Formulating equations and solving them as the simultaneous equations to calculate coefficients representing the relationship between the dimensions and the slope-based values, and applying the coefficients with the slope-based values as the variables. By doing so, the estimation formula is established.
According to the configuration as described above, it is possible to appropriately implement the nondestructive inspection measurement system as described above.

In another aspect of the present invention, the measuring unit measures the voltage output from the detection coil as a voltage at the time of measurement for the portion to be measured of the subject body, and compares this voltage with the reference voltage. Calculate the measured amplitude ratio and the measured phase difference, which are the amplitude ratio and phase difference, and calculate the measured gradient, which is the gradient on the corresponding amplitude ratio-phase difference plane, and the measured gradient is substituted for the variables in the estimation formula to calculate and measure the dimensions.
According to the configuration as described above, it is possible to appropriately implement the nondestructive inspection measurement system as described above.

In another aspect of the present invention, the slope-at-calibration calculation unit further calculates intersections between the straight lines obtained for each of the plurality of dimensions, and the measurement unit calculates on the amplitude ratio-phase difference plane The slope of a straight line connecting the measurement point corresponding to the amplitude ratio and the phase difference at the measurement and the intersection point is calculated as the slope at the measurement.
According to the configuration as described above, it is possible to appropriately implement the nondestructive inspection measurement system as described above.

In another aspect of the present invention, the measurement condition includes the distance from the outer surface of the subject or a member forming the outer surface to the subject body.
According to the configuration as described above, the influence of the distance from the outer surface of the subject or the member constituting the outer surface to the subject body is reduced, and the subject body provided in the subject with high accuracy. dimensions can be measured.

In another aspect of the present invention, the slope-at-calibration calculator applies a frequency to the excitation coil that is different from the frequency of the sine wave signal or the composite signal applied to the excitation coil when calculating the gradient. Then, by measuring the voltage output from the detection coil and calculating the different frequency amplitude ratio, which is the amplitude ratio between this and the reference voltage, or the different frequency phase difference, which is the phase difference with the reference voltage, The calibrating unit, for each of the plurality of dimensions and temperatures, the relationship between the dimension, the gradient-based value calculated for the dimension, and the different frequency amplitude ratio or the different frequency phase difference Then, based on the solution, the estimation formula is formulated.
According to the configuration described above, when calculating the gradient in the calibration gradient calculator, a frequency different from the frequency of the signal applied to the excitation coil is applied to the excitation coil, and the voltage output from the detection coil is measured. A different-frequency amplitude ratio, which is the amplitude ratio between this and the reference voltage, or a different-frequency phase difference, which is the phase difference with the reference voltage, is calculated and reflected in the simultaneous equations. Since different frequencies are affected by eddy currents differently in their amplitude or phase difference, the effect of temperature can be properly accounted for by constructing and solving simultaneous equations that reflect the amplitude ratio or phase difference of different frequencies. You can formulate an estimation formula that takes into account.
Therefore, it is possible to reduce the influence of temperature and measure the dimensions of the body of the subject provided in the subject with high accuracy.

In another aspect of the invention, the subject body is a plate, the dimension is the thickness of the plate, the slope-based value is the slope, and in the system of equations: Said dimension and said slope are in a proportional relationship.
According to the configuration as described above, when the subject body is a flat plate or a kiln-shaped plate, the thickness thereof can be measured with high accuracy.

In another aspect of the present invention, the subject body is a rod with a circular cross section, and the dimension is the square of the difference between the diameter of a circle of a reference size and the diameter of the cross section of the rod. Yes, and in the simultaneous equations, the dimension and the value based on the gradient are in a proportional relationship.
If the object body is a bar with a circular cross-section, when the lines of magnetic force generated by the exciting coil enter the bar, the direction of the magnetic field generated by the penetrating magnetic flux is opposite to the direction of the magnetic field formed. Since the eddy currents flow, the lines of magnetic force are canceled by the eddy currents and do not enter the inside of the rod, but flow near the surface of the rod and escape to the opposite side of the entry point. For this reason, in the case of a rod with a circular cross section, the slope, that is, the slope when the proportional relationship between the amplitude ratio and the phase difference is expressed as a straight line, is not the diameter of the rod, but a circle of some standard size. When defined, the relationship is proportional to the square of the difference between the diameter of this circle and the cross-sectional diameter of the rod to be measured.
Therefore, according to the configuration as described above, when the object body is a rod with a circular cross section, the diameter can be measured with high accuracy.

In another aspect of the present invention, the subject body is a rod with a square cross section, and the dimension is the length of the diagonal of the square of the reference size and the length of the diagonal of the cross section of the rod. It is the square of the difference, and in the system of equations, the dimension and the gradient-based value are proportional.
If the subject body is a bar with a square cross section, the magnetic field lines generated by the exciting coils should be arranged to form a magnetic field opposite to the direction of the magnetic field formed by the penetrating magnetic flux when entering the bar. Since the eddy currents flow, the lines of magnetic force are canceled by the eddy currents and do not enter the inside of the rod, but flow near the surface of the rod and escape to the opposite side of the entry point. For this reason, in the case of a bar with a square cross section, the slope, that is, the slope when the proportional relationship between the amplitude ratio and the phase difference is expressed as a straight line, is obtained by defining a square of some standard size as this square. The relationship is proportional to the square of the difference between the length of the diagonal line and the length of the diagonal line of the cross section of the rod to be measured.
Therefore, according to the configuration as described above, when the object body is a rod with a square cross section, the thickness can be measured with high accuracy.

In another aspect of the present invention, for a plurality of portions of the body of the subject having known and different dimensions, the length of the rod and the length of the rod calculated by the gradient calculation unit during calibration are calculated for each of the plurality of dimensions. A straight line connecting points corresponding to at least two measurement results on a length-gradient plane having the gradient as two axes is obtained, and a secondary gradient, which is the gradient of the straight line, is obtained as a value based on the gradient. A second-order gradient calculation unit during calibration is provided for calculating, and the calibration unit constructs simultaneous equations from the relationship between the dimension and the second-order gradient calculated for each of the plurality of dimensions. , the above estimation formula is formulated based on the solution.
When the subject body is a rod and the length of the rod is short, the dimension is the length-gradient with the length and the gradient of the rod as two axes, rather than the gradient calculated as described above. The relationship is proportional to the quadratic gradient, which is the gradient of the straight line connecting the points on the plane, corresponding to the correspondence between at least two lengths and gradients.
According to the configuration as described above, the simultaneous equations are constructed from the relationship between each dimension and the secondary gradient calculated for each dimension. A quadratic gradient relationship is reflected.
Therefore, when the object body is a rod and the length of the rod is short, the influence of the measurement conditions is reduced, and the dimensions of the object body provided inside the object can be measured with high accuracy. be.

Further, the present invention includes an excitation coil that excites a subject body provided in a subject, and outputting a voltage corresponding to a magnetic field change generated in the subject body when the subject body is excited by the excitation coil. A sine wave signal or a composite signal composed of a plurality of sine waves having different frequencies is applied to the detection coil and the excitation coil for exciting the subject body, and the voltage output from the detection coil is detected. and a non-destructive inspection measuring method for measuring the dimensions of the subject body, wherein a plurality of different measurement conditions are applied to a plurality of portions of the subject body having known and different dimensions for each of the plurality of dimensions In each of, measure the voltage output from the detection coil, calculate the amplitude ratio and phase difference between this and the reference voltage, and measure the amplitude ratio and the phase difference on the two axes of the amplitude ratio-phase difference plane determining a straight line connecting points corresponding to at least two measurements at , calculating the slope of the straight line, and for each of a plurality of said dimensions, based on said dimension and said slope calculated for said dimension A simultaneous equation is constructed from the relationship with the value obtained, and based on the solution, an estimation formula for estimating the dimension at the time of measurement of the dimension is formulated with the value based on the gradient as a variable, and the estimation Provided is a non-destructive testing and measuring method for estimating and measuring the dimensions of the portion to be measured of the subject body based on the formula.
According to the configuration as described above, before measuring the dimensions of the portion to be measured of the subject body, for each of the plurality of portions having known and different dimensions, under each of the plurality of different measurement conditions, Measure the voltage output from the detection coil, calculate the amplitude ratio and phase difference between this and the reference voltage, and obtain at least two measurement results on the amplitude ratio-phase difference plane with the amplitude ratio and phase difference as two axes. A straight line connecting the points corresponding to is obtained, and the gradient of the straight line is calculated. If the dimensions are the same and the measurement conditions are changed, the amplitude ratio and the phase difference are roughly proportional. The slope has a value in which the influence of measurement conditions is suppressed.
When estimating and measuring the dimensions of the part of the body of the subject to be measured, solve simultaneous equations constructed from the relationship between the dimensions and the values based on the gradients calculated for the dimensions. Then, an estimation formula is formulated, and the dimensions are obtained based on this formula.
Therefore, it is possible to reduce the influence of the measurement conditions and measure the dimensions of the subject body provided in the subject with high accuracy.

According to the present invention, it is possible to provide a nondestructive inspection measurement system and a nondestructive inspection measurement method that can reduce the influence of measurement conditions and measure the dimensions of a subject body provided in the subject with high accuracy. .

It is a figure which shows the structure of the nondestructive test measurement system in embodiment of this invention. It is a schematic plan view of a sensor of the non-destructive inspection measurement system in the above embodiment. 10 is a graph showing the relationship between the amplitude ratio and the phase difference when the frequency is 33 Hz and the temperature is 10.4° C. in an example using the nondestructive inspection measurement system of the above embodiment. 10 is a graph showing the relationship between the amplitude ratio and the phase difference when the frequency is 33 Hz and the temperatures are 10.4° C. and 11.4° C. in an example using the nondestructive inspection measurement system of the above embodiment. 10 is a graph showing the relationship between the amplitude ratio and the phase difference when the frequency is 39 Hz and the temperatures are 10.4° C. and 11.4° C. in an example using the nondestructive inspection measurement system of the above embodiment. 10 is a graph showing the relationship between the amplitude ratio and the phase difference when the frequency is 57 Hz and the temperatures are 10.4° C. and 11.4° C. in an example using the non-destructive inspection measurement system of the above embodiment. 10 is a graph showing the relationship between the amplitude ratio and the phase difference when the frequency is 69 Hz and the temperatures are 10.4° C. and 11.4° C. in an example using the nondestructive inspection measurement system of the above embodiment. 10 is a graph showing the relationship between the amplitude ratio and the phase difference when the frequency is 87 Hz and the temperatures are 10.4° C. and 11.4° C. in an example using the nondestructive inspection measurement system of the above embodiment. It is a graph which shows the measurement result in the Example using the nondestructive test measurement system in the said embodiment. It is a flow chart of the nondestructive inspection measurement method using the nondestructive inspection measurement system in the above-mentioned embodiment. It is a figure which shows the structure of the nondestructive test measurement system in the 1st modification of the said embodiment. It is a graph which shows the measurement result in the Example using the nondestructive test measurement system in the 1st modification of the said embodiment. It is a figure which shows the structure of the nondestructive test measurement system in the 2nd modification of the said embodiment. It is a schematic plan view of the sensor of the non-destructive inspection measurement system in the second modification of the above embodiment. It is a graph which shows the relationship of an amplitude ratio and a phase difference in the Example using the nondestructive test measurement system in the 2nd modification of the said embodiment. FIG. 16 is a partially enlarged view of FIG. 15; It is explanatory drawing of the effect|action of the nondestructive test measurement system in the 2nd modification of the said embodiment. 10 is a graph showing measurement results when the distance between the outer surface of the subject and the body of the subject is 36.5 mm in an example using the non-destructive inspection measurement system in the second modified example of the above embodiment. 10 is a graph showing measurement results when the distance between the outer surface of the subject and the body of the subject is 56.5 mm in an example using the non-destructive inspection measurement system in the second modified example of the above embodiment. It is a figure which shows the structure of the nondestructive test measurement system in the 3rd modification of the said embodiment. FIG. 11 is a graph showing the relationship between the length of the subject body and the gradient in an example using the non-destructive inspection measurement system in the third modified example of the embodiment; FIG. It is a graph which shows the measurement result in the Example using the nondestructive test measurement system in the 3rd modification of the said embodiment. FIG. 10 is a graph showing the results when the frequency is 33 Hz and the temperature is 10.4° C. in the example using the conventional technology; FIG. FIG. 10 is a graph showing the results when the frequency is 33 Hz and the temperatures are 10.4° C. and 11.4° C. in an example using the conventional technology;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The non-destructive inspection measurement system according to the present embodiment includes an excitation coil that excites the subject body provided in the subject, and a voltage corresponding to the magnetic field change generated in the subject body when the subject body is excited by the excitation coil. A sine wave signal or a composite signal consisting of multiple sine waves with different frequencies is applied to the detection coil that outputs the , and the excitation coil that excites the body of the subject, and the voltage output from the detection coil is detected. and a measuring device for measuring dimensions of a subject body, wherein the measuring device measures a plurality of different measurement conditions for each of the plurality of dimensions for a plurality of portions of the subject body having known and different dimensions. In each of, measure the voltage output from the detection coil, calculate the amplitude ratio and phase difference between this and the reference voltage, and measure the amplitude ratio and phase difference on two axes, at least on the amplitude ratio-phase difference plane A straight line connecting the points corresponding to the two measurement results is obtained, and the slope of the straight line is calculated. A calibration unit that constructs simultaneous equations based on the relationship between the values and a measurement unit that estimates and measures the dimensions of a portion of the body of the subject to be measured based on the formula.

FIG. 1 is a diagram showing the configuration of a nondestructive inspection measurement system according to an embodiment of the present invention. FIG. 2 is a schematic plan view of the sensor of the nondestructive inspection measurement system in this embodiment.
The non-destructive inspection measurement system 10 in this embodiment measures the dimensions of the subject body 202 provided inside the subject 2 .
The subject body 202 is a plate in this embodiment. The subject 2 to be inspected, particularly in this embodiment, has an outer can 201 with a thickness t1 and an inner can (subject body) 202 with a thickness t2 separated by a gap Gap, and has a two-layer structure. there is Both the outer can 201 and the inner can 202 are formed in a kiln shape, the inner can 202 is provided inside the outer can 201, and the inner can 202 cannot be visually recognized from the outside. In this embodiment, the nondestructive inspection measurement system 10 measures the thickness (dimension) t2 of the inner can 202 .
The subject 2 may be any conductive metal such as stainless steel or general steel, and may be flat or curved.
Note that FIG. 1 shows only a part of the cross-sectional structure of the subject 2 .

The nondestructive inspection measurement system includes a sensor 1 and a measurement device 3.
The sensor 1 comprises a detector 12 and six exciters 11 .
The detector 12 is provided near the center of the housing 1a forming the sensor 1 when the sensor 1 is viewed from above. The detector 12 has a detection coil 121 . The detection coil 121 is an air core coil in this embodiment. The sensitivity of the detection coil 121 increases when a magnetic core such as ferrite is used. , the air-core coil provides better characteristics.
When the detector 12 is provided with the lower surface 1b of the housing 1a of the sensor 1 along the outer surface 201a of the outer can 201, the central axis C12 of the detection coil 121 is normal to the outer surface 201a of the subject 2. is provided in the sensor 1 so as to correspond to .

The exciter 11 is provided so as to surround the detector 12 when the sensor 1 is viewed from above as shown in FIG. The exciter 11 includes an excitation core 111 , a feedback coil 112 and an excitation coil 113 .
Exciting core 111 is made of a magnetic material such as a laminated silicon steel plate. The exciting core 111 has a shape of a bar-shaped member bent at two points, and the bent portions serve as boundaries to form a first core portion 111a, a second core portion 111b, and a third core portion 111c. formed. The first core portion 111a and the third core portion 111c are formed so as to be bent in the same direction with respect to the second core portion 111b located in the middle. The excitation core 111 is arranged such that the second core portion 111b is substantially parallel to the bottom surface 1b of the housing 1a, and the tips of the first core portion 111a and the third core portion 111c approach toward the bottom surface 1b of the housing 1a. It is positioned within the housing 1a so as to do so. The first core portion 111a is provided so as to be positioned closer to the detector 12 than the third core portion 111c. In this manner, a total of six exciters 11 are arranged radially around the detector 12 so that magnetic fluxes are concentrated directly below the detector 12 .

A feedback coil 112 is wound around the first core portion 111 a of the exciter 11 .
Each of the excitation coils 113 includes a first excitation coil 113a, a second excitation coil 113b, and a third excitation coil 113c.
The first excitation coil 113 a is wound around the feedback coil 112 . Due to the configuration of the first core portion 111a as already described, the central axis C13 of the first exciting coil 113a is provided so as to intersect the central axis C12 of the detection coil 121 on the subject 2 side.
The first excitation coils 113a, the second excitation coils 113b, and the third excitation coils 113c of all the exciters 11 are all wound in the same direction and connected in series with each other. Although each excitation coil 113 has been described as including three excitation coils 113a, 113b, and 113c, these may be formed as one body.
Also, the feedback coils 112 of all the exciters 11 are connected in series with each other. Feedback coil 112 and excitation coil 113 are not connected.
In this way, the excitation coils 113 and the feedback coils 112 of the six exciters 11 are all additively connected in series in the same direction in terms of magnetic flux, and balanced input and output are balanced to improve noise immunity. It is configured.

In such a sensor 1 , when the exciting coil 113 is excited, the exciting coil 113 excites the exciting core 111 , thereby generating magnetic flux in the exciting core 111 . A feedback coil 112 captures the magnetic flux generated within this exciting core 111 . The resulting output captured by feedback coil 112 is used as a reference voltage.
In addition, the excitation coil 113 similarly excites the inner can 202 of the subject 2 , thereby generating a magnetic flux within the inner can 202 . A detection coil 121 captures the magnetic flux generated within this inner can 202 . The resulting output voltage captured by the sensing coil 121 is compared to a reference voltage and used to measure the thickness t2 of the inner can 202 . The detection coil 121 may be wound in a simple manner and grounded at the center point, but since the amount of magnetic flux captured varies depending on the winding radius, even if the center of the number of turns is grounded, the output will not be completely balanced. Therefore, in the present embodiment, bifilar winding is used to achieve a perfectly balanced output, thereby improving noise resistance.

Thus, the excitation coil 113 excites the subject body 202 provided inside the subject 2 . Further, the detection coil 121 outputs a voltage corresponding to a magnetic field change generated in the subject body 202 when the subject body 202 is excited by the excitation coil 113 .

The measuring device 3 includes a digital/analog converter (DAC) 301 , an analog/digital converter (ADC) 302 , a power amplifier 303 , a multiplexer 304 , a computer 305 and a display/data acquisition section 306 .
The computer 305 digitally generates a composite of single-frequency or multi-frequency sinusoidal signals. DAC 301 converts the signal generated and digitally synthesized by computer 305 into an analog signal. The power amplifier 303 amplifies the analog signal from the DAC 301 and supplies it to the first exciting coil 113 a , the second exciting coil 113 b and the third exciting coil 113 c of the sensor 1 . This analog signal excites the excitation coil 113 with an alternating voltage. When the exciting coil 113 is excited, a magnetic field change occurs in the outer can 201 and the inner can 202 which are the subject. The overall magnetic field around the detection coil 121 changes due to the eddy current that flows according to the change in the magnetic field of the outer can 201 and the inner can 202, and the detection coil 121 outputs a voltage change including the change due to the eddy current. Although it is extremely difficult to distinguish and detect only magnetic field changes due to eddy currents, the detection coil 121 detects magnetic field changes including magnetic field changes due to eddy currents.

As already explained, the feedback coil 112 captures the magnetic flux generated in the exciting core 111 when the first exciting coil 113a is excited. A signal from the feedback coil 112 is transmitted to the ADC 302 via the multiplexer 304, converted into a digital signal by the ADC 302, and feedback-processed by the computer 305 so as to keep the excitation magnetic flux constant.

The voltage generated in the detection coil 121 and the voltage output from the feedback coil 112 are input to the multiplexer 304 . ADC 302 converts the output of multiplexer 304 into a digital signal and outputs it to computer 305 . Computer 305 performs measurement and analysis processing based on the output from ADC 302 .
The computer 305 compares the voltage output from the detection coil 121 and the reference voltage, that is, the voltage output from the feedback coil 112, and calculates their amplitude ratio and phase difference. More specifically, the computer 305 calculates the amplitude ratio by using the amplitude value of the output of the feedback coil 112 as the denominator and the amplitude value of the output of the detection coil 121 as the numerator. As a result, the influence of voltage fluctuations and the like in the measurement system is suppressed. Similarly, computer 305 calculates the difference between the output phase of feedback coil 112 and the output phase of detection coil 121 as the phase difference.
A display/data acquisition unit 306 displays and acquires data of the results of measurement and analysis processing in the computer 305 .

When measuring the dimensions or thickness of the subject body, that is, the inner can 202 using such a non-destructive inspection measurement system 10, while moving the sensor 1 along the outer surface 201a of the subject 2, The computer 305 generates a sine wave signal or a composite signal composed of a plurality of sine waves having different frequencies at a plurality of portions of the inner can 202 where the thickness t2 is known to excite the exciting coil 113 . The computer 305 calculates the amplitude ratio and phase difference of the voltage change output from the detection coil 121 according to the excitation of the excitation coil 113 .
The amplitude ratio and phase difference between the voltage output from the detection coil 121 and the feedback coil 112 in the portion where the thickness t2 is known are calculated based on the thickness t2 of the inner can 202 estimated from this amplitude ratio and phase difference. The purpose is to calibrate the estimation result by checking the actual thickness of the measured part. Calibration will be explained in detail later.
Here, when performing measurement by varying the frequency of the sine wave signal, the plurality of sine wave signals are digitally generated by the computer 305, the synthesized digital signal is converted to an analog signal by the DAC 301, Exciting coil 113 is excited via power amplifier 303 . The output of the detection coil 121 is substantially sampled by a multiplexer 304, held, converted into a digital signal by an ADC 302, processed by a computer 305 by fast Fourier transform (FFT), and output as amplitude and phase difference for each frequency. The output of feedback coil 112 is similarly converted into a digital signal via multiplexer 304 and ADC 302, fast Fourier transformed by computer 305, and output as amplitude and phase difference for each frequency. Ultimately, the amplitude is output as an amplitude ratio for each frequency, with the amplitude corresponding to the output of the feedback coil 112 as the denominator and the amplitude corresponding to the output of the detection coil 121 as the numerator. Similarly, for the phase difference, the phase difference corresponding to the output of the detection coil 121 is calculated based on the phase difference corresponding to the feedback coil 112, and is output as the phase difference for each frequency. In the fast Fourier transform (FFT) of general signals, it is necessary to insert a window function filter such as a Hamming window in order to prevent the occurrence of discontinuous portions after sampling. When a plurality of sinusoidal signals are digitally generated by the computer 305, they are not continuous waves, but a preamble that rises exponentially from zero and a post that falls exponentially to zero. Since it is possible to omit the insertion of a window function by using a burst signal provided with a postamble, it is omitted.
In this way, by using the fast Fourier transform (FFT), it is possible to simultaneously detect the amplitude ratio and phase difference of each sine wave of each frequency, resulting in high measurement efficiency.

In general, the waveform of a sine wave signal can be uniquely specified if the three constants of frequency, amplitude and phase are determined. Therefore, the computer 305 uses fast Fourier transform (FFT) as a waveform analysis processing method to calculate the amplitude and phase.
A voltage value is usually taken as the amplitude, but the value itself of the output of the detection coil 121 often fluctuates due to fluctuation factors such as temperature and voltage fluctuation. Therefore, in order to suppress fluctuations in the measurement system, as already explained, by generalizing the amplitude ratio to the output voltage of the detection coil 121 with the amplitude of the output voltage of the feedback coil 112 as the denominator, Highly accurate data acquisition is possible.
As the phase, the phase difference between the input phase to the feedback coil 112 and the output of the detection coil 121 is expressed in radians.

Here, in the computer 305, the frequency sequence of each frequency of the sine wave signal to be generated is treated as a prime number sequence with a base of 3 in order to prevent the so-called aliasing phenomenon in which the respective harmonics fall into each other's frequency domain. , in this embodiment, for example, 33, 39, 57, 69 and 87 Hz. The reason for avoiding frequencies near 50 and 60 Hz is to prevent the influence of power supply noise. In addition, in this embodiment, 8192 points of data are acquired as fast Fourier transform (FFT), so sampling is performed at a sampling frequency of 3 (Hz)×8192=24,576 (Hz).

Next, calibration in this embodiment will be described.
Before using the nondestructive inspection measurement system 10 to actually measure the thickness t2 of the inner can 202, the nondestructive inspection measurement system 10 needs to be calibrated. Calibration is performed by varying the thickness t2 of the inner can 202 of the subject 2 and the gap between the outer can 201 and the inner can 202, measuring the output voltage of the detection coil 121, and detecting the thickness t2 and the gap Gap. This is done by examining the relationship with the output voltage of the coil 121 . Therefore, ideally, if the subject 2 has a plurality of portions with known and different thicknesses t2 and gaps, calibration can be performed by checking the output voltage of the detection coil 121 at these portions. However, if there is no portion in the subject 2 that satisfies such conditions, a simulated body that can change the thickness t2 and the gap Gap is created and used for calibration.
In this embodiment, the position of the subject body, that is, the inner can 202, in the subject 2 is determined from the inner can 201, which is a member forming the outer surface 201a of the subject 2, as described above. 202, but it is needless to say that the distance from the outer surface 201a of the subject 2, that is, the sum of the thickness t1 of the outer can 201 and the gap Gap may be used.

In order to calibrate the non-destructive inspection measurement system 10 and estimate and measure the thickness t2 of the inner can 202 using this calibration result, the computer 305 includes a gradient calculation section 310 during calibration, a calibration section 311, and a measurement section. 312.

Calibration slope calculator 310 performs measurement using sensor 1 at a specific frequency, with known first thickness t21 of inner can 202, and at known first gap Gap1 between outer can 201 and inner can 202. The amplitude ratio and phase difference are calculated by and plotted on an amplitude ratio-phase difference plane with the amplitude ratio as the horizontal axis and the phase difference as the vertical axis. In addition, the calibration gradient calculator 310 changed the gap Gap between the outer can 201 and the inner can 202 to a second gap Gap2 different from the first gap Gap1, and the sensor 1 was used under the same conditions. Amplitude ratio and phase difference are calculated from the measurements and plotted on the amplitude ratio-phase difference plane. Calibration slope calculator 310 calculates a first straight line connecting these two points plotted on the amplitude ratio-phase difference plane.
The calibrated slope calculator 310 also calculates, by measurement using the sensor 1, at a known second thickness t22 different from the first thickness t21 and at a third gap Gap3 between the outer can 201 and the inner can 202: Amplitude ratio and phase difference are calculated and plotted on the amplitude ratio-phase difference plane. In addition, the calibration gradient calculator 310 changed the gap Gap between the outer can 201 and the inner can 202 to a fourth gap Gap4 different from the third gap Gap3, and the sensor 1 was used under the same conditions. Amplitude ratio and phase difference are calculated from the measurements and plotted on the amplitude ratio-phase difference plane. Calibration slope calculator 310 calculates a second straight line connecting these two points plotted on the amplitude ratio-phase difference plane.
In the above description, the first gap Gap1 and the third gap Gap3, and the second gap Gap2 and the fourth gap Gap4 may be the same or different.

Next, calibration gradient calculator 310 obtains an intersection point P0 on an extension line of the first straight line and the second straight line.
Further, calibration gradient calculator 310 calculates the gradient of the first straight line and the gradient of the second straight line on the amplitude ratio-phase difference plane.

In this way, the calibration-time gradient calculator 310 sets a plurality of different measurement conditions Gap1, Gap2, and measurement conditions Gap1, Gap2, and measurement Under each of the conditions Gap3 and Gap4, the voltage output from the detection coil 121 is measured, the amplitude ratio and phase difference between this and the reference voltage are calculated, and the amplitude ratio and phase difference are used as two axes. A straight line connecting the points corresponding to the at least two measurements on the plane is obtained, and the gradient of the straight line is calculated.
In addition, the calibration gradient calculator 310 calculates the intersection P0 between the straight lines obtained for each of the plurality of thicknesses t21 and t22.
In addition, the measurement conditions include the distance from the outer surface 201a of the subject 2 or from the member 201 forming the outer surface 201a to the subject body 202 . In this embodiment, this distance is the gap Gap between the outer can 201 and the inner can 202 .

As will be described later in detail using embodiments such as FIG. 3, there is a proportional relationship between the thickness t2 of the inner can 202 and the gradient calculated for the straight line corresponding to the thickness t2. To establish. That is, the thickness t2 of the inner can 202 can be expressed by, for example, a linear expression of t2=ax+b, where x is the gradient, a is a coefficient applied to the gradient, and b is a constant.
As already explained, the calibration gradient calculator 310 calculates gradient values corresponding to a plurality of thicknesses t21 and t22 of the inner can 202 . Therefore, the calibration unit 311 substitutes the thicknesses t21 and t22 of the inner can 202 and the values of the gradients corresponding to these into the above linear equations, respectively, to obtain a two-dimensional simultaneous equation with variables a and b as To construct. The calibration unit 311 solves this to derive the values of a and b. By substituting these derived values of a and b into the above linear expression, the calibration unit 311 uses the gradient as a variable, and when this is input, the thickness t2 of the inner can 202 can be calculated. formulate.

In this way, the calibration unit 311 calculates the thicknesses t21 and t22 (dimensions) and the gradients calculated for the thicknesses t21 and t22 (the gradient A simultaneous equation is constructed from the relationship with the base value), and based on the solution, an estimation formula is formulated with the gradient as a variable to estimate the thickness t2 when the thickness t2 is measured.
More specifically, the calibration unit 311 calculates, for each of a plurality of thicknesses t21 and t22 of the inner can 202, a multi-dimensional is formulated, and these are solved as simultaneous equations to calculate the coefficient representing the relationship between the thickness t2 and the gradient, and the coefficient is applied with the gradient as a variable to formulate an estimation formula.
In this simultaneous equation, the thickness and the gradient are in a proportional relationship.

When actually estimating and measuring the thickness t2 of the inner can 202, the measurement unit 312 operates the sensor 1 at an arbitrary portion of the subject 2 to be measured where the thickness t2 is unknown. The output voltage from the coil 121 is measured as the voltage during measurement, and the amplitude ratio and phase difference during measurement, which are the amplitude ratio and phase difference between the voltage during measurement and the reference voltage, are calculated. The measurement unit 312 plots the measured amplitude ratio and the measured phase difference as measurement points on the amplitude ratio-phase difference plane, and plots this measurement point and the intersection point P0 on the extension line of the first straight line and the second straight line. Calculate the measured slope, which is the slope of the measured line connecting . The measurement unit 312 calculates and measures the thickness t<b>2 of the inner can 202 at the measured portion on the subject 2 by substituting the gradient at the time of measurement into the estimation formula formulated by the calibration unit 311 .
In this case, if the gap Gap between the outer can 201 and the inner can 202 can be changed at the measured portion of the subject 2, then the gradient on the amplitude ratio-phase difference plane may be obtained and substituted into the estimation formula. .

In this manner, the measurement unit 312 estimates and measures the thickness t2 of the portion of the inner can 202 to be measured based on the estimation formula.
More specifically, the measurement unit 312 measures the voltage output from the detection coil 121 as the measurement voltage for the portion of the inner can 202 to be measured. Calculate a certain measured amplitude ratio and measured phase difference, calculate the measured gradient that is the gradient on the amplitude ratio-phase difference plane corresponding to these, and substitute the measured gradient for the variables of the estimation formula Calculate and measure thickness.
Here, the measurement unit 312 calculates the gradient of a straight line connecting the measurement point corresponding to the amplitude ratio and phase difference at measurement on the amplitude ratio-phase difference plane and the intersection point P0 as the gradient at measurement.

Next, more detailed behaviors of the gradient calculation unit 310 during calibration, the calibration unit 311, and the measurement unit 312 as described above will be described together with an embodiment of the nondestructive inspection measurement system 10. FIG.

[Example 1]
The detector 12 uses the detection coil 121 shown in FIG. It has a strong structure. The bifilar winding is used because, in the case of multi-layer winding, there is a difference in the diameter between the start and the end of winding, which causes a difference in magnetic flux to be captured. This is because a simple winding method using a single wire does not produce a balanced output even if the center of the number of turns is grounded. By connecting the windings in additive series and grounding the middle point of the windings, it is possible to obtain a perfectly balanced output, thereby enhancing the noise resistance performance.
The excitation core 111 of the exciter 11 is constructed by laminating 100 oriented silicon steel sheets with a thickness of 100 μm and a width of 10 mm, and a PEW wire with a diameter of 0.30 mmφ wound 130 times as a feedback coil 112 thereon. is doing. On the excitation core 111 and the feedback coil 112, as the excitation coil 113, a PEW wire with a diameter of 1 mmΦ is wound a total of 200 times.
The overall dimensions of the sensor 1 are 160 mm in width, 440 mm in length, and 130 mm in height, and the sensor 1 is large-sized as a sensor.
As the outer can 201 and the inner can 202 constituting the test object 2, flat plates of stainless steel SUS304 having a width and a length of 800 mm were used. The thickness t1 of the outer can 201 was fixed at 30 mm. The inner can 202 is configured to be replaceable with a flat plate having a thickness t2 of any one of 25, 28, 30, 32 and 35 mm. The gap Gap between the outer can 201 and the inner can 202 was configured to be variable to any one of 70, 80, and 90 mm.

The computer 305 of the measuring device 3 was configured to generate a digital signal obtained by synthesizing sine waves of five frequencies of 33, 39, 57, 69 and 87 Hz. This signal is converted to an analog signal via DAC 301 and output to sensor 1 via power amplifier 303 for use in driving exciter 11 .
The power amplifier 303 has an output voltage of 4 V and an output current of about 0.35 A, which drives the six exciting coils 113 connected in series.
A Fast Fourier Transform (FFT) is performed in the measuring device 3 . In the fast Fourier transform, it is necessary to sample 2 n pieces of data. , 87 Hz to acquire the amplitude ratio and phase difference independently at each of the five frequencies. The output of the feedback coil 112 is used as a reference for amplitude and phase, and the amplitude is obtained as a ratio thereof, that is, an amplitude ratio, and the phase is obtained as a difference therefrom, that is, a phase difference. Hereinafter, in the data of the first embodiment, the amplitude ratio is expressed as A33Hz (A: Amplitude, 33Hz, an anonymous number because of the ratio) and the phase difference as P33Hz (P: Phase, 33Hz, unit: radian).
Both the DAC 301 and ADC 302 of this embodiment employ a 16-bit system and both have sufficient precision and accuracy.

FIG. 3 shows an example of the measurement results, where the temperature is 10.4° C., the frequency is 33 Hz, the thickness t1 of the outer can 201 is fixed at 30 mm, and the thickness t2 of the inner can 202 is set at 25, 28, 30, 32, 35 mm, the output voltage of the detection coil 121 is measured for each gap of 70, 80, 90 mm in each of these, and the amplitude ratio and phase difference between this output voltage and the reference voltage by the feedback coil 112 are calculated, It is plotted on an amplitude ratio-phase difference plane in which the horizontal axis is the amplitude ratio and the vertical axis is the phase difference. Here, the measurement results for the same thickness t2 of the inner can 202 are located on the same straight line when connecting the points with different gaps Gap, as indicated by the dashed-dotted line in FIG. That is, for each different thickness t2, a correspondingly different straight line is generated. These straight lines intersect at the intersection point P01.
FIG. 4 shows the graph for the temperature of 10.4° C. shown in FIG. These results are superimposed and indicated by a dashed line. It can be seen that even if the conditions of the straight line and broken line in FIG. 4 differ, that is, the temperature differs by only 1° C., the calculated amplitude ratio and phase difference fluctuate, resulting in a change in the measurement result of the thickness t2. However, the change is translational. This indicates that the temperature coefficient of the volume resistivity of stainless steel SUS304 is as large as 1.1×10̂-3 and is affected by it. 5, 6, 7 and 8 show the measurement results when the frequency is changed from FIG. 4 to 39, 57, 69 and 87 Hz. As the frequency increases, the extension direction of the straight lines centering on the intersection point between the straight lines rotates clockwise.
As is clear from FIG. 3, the measured values at the points where the thickness t2 of the inner can 202 is the same and the interval Gap is different are arranged on a straight line on the amplitude ratio-phase difference plane. intersect at one intersection. The behaviors of the calibration gradient calculator 310, the calibrator 311, and the measurement unit 312 in this embodiment are based on these experimental facts.

Considering that the gap Gap between the outer can 201 and the inner can 202 is unknown or cannot be changed depending on the subject 2, a simulated body with a variable gap Gap is created and used to measure the measurement device 3. Description will be made assuming that the calibration is performed and the actual subject 2 is measured.
For example, with respect to the simulated object, the temperature is fixed at 10.4° C., the frequency is fixed at 33 Hz, and the thickness t1 of the outer can 201 is fixed at 30 mm, as shown in FIG. , and the spacing Gap to 70 mm. Calibration gradient calculator 310 measures the output voltage of detection coil 121 in this state, calculates the amplitude ratio and the phase difference, and plots the result as point PA1 on the amplitude ratio-phase difference plane. Furthermore, the interval Gap of the simulated body is changed to 90 mm, and the calibration gradient calculation unit 310 measures the output voltage of the detection coil 121 in this state to calculate the amplitude ratio and the phase difference, and the result is the amplitude ratio - position Plot as point PA2 on the phase difference plane. Calibration gradient calculator 310 obtains first straight line LA1 connecting these two points PA1 and PA2, and calculates the gradient of first straight line LA1.
Next, the simulated body is set to a state in which only the thickness t2 of the inner can 202 is changed to 35 mm from the measurement conditions corresponding to the measurement result shown as point PA1 as described above. Calibration gradient calculator 310 measures the output voltage of detection coil 121 in this state, calculates the amplitude ratio and the phase difference, and plots the result as point PA3 on the amplitude ratio-phase difference plane. Furthermore, the interval Gap of the simulated body is changed to 90 mm, and the calibration gradient calculation unit 310 measures the output voltage of the detection coil 121 in this state to calculate the amplitude ratio and the phase difference, and the result is the amplitude ratio - position Plot as point PA4 on the phase difference plane. Calibration gradient calculator 310 obtains a second straight line LA2 connecting these two points PA3 and PA4, and calculates the gradient of second straight line LA2.
Table 1 shows the above results. In Table 1, as a result corresponding to each of the first and second straight lines LA1 and LA2, the amplitude ratio of each of the points PA5 and PA6 corresponding to the case where the gap Gap on these straight lines LA1 and LA2 is 80 mm − Coordinate values on the phase difference plane, calculated gradients, etc. are described.

The calibration gradient calculator 310 calculates the coordinates of the intersection point P01 of the two straight lines LA1 and LA2 obtained for each of a plurality of thicknesses t2 of the inner can 202, that is, when t2 is 25 mm and 35 mm. to calculate

本式、及び以下の説明に使用する各式において、「＊」は、乗算を意味するものとして使用する。
表１において、「勾配」、「ｔ２機械的寸法」の欄の第１行と第２行の各々は、上記の（ｘ１、ｔ２１）、（ｘ２、ｔ２２）のそれぞれの組み合わせの実際の数値を記載したもので、上記の連立方程式を表形式で表したものである。
較正部３１１は、上記数式１を解いて、係数ａと定数ｂの値を導出する。求められた係数ａと定数ｂの値は、表１中のａ、ｂと示されたそれぞれの欄に記載されている。連立方程式の解法としては、逆行列式法、クラメール法等既知の方法を使用すれば良く、本実施形態においては、コンピュータ上の計算において、桁落ちの心配が少ないとされるクラメール法を用いている。後述の各変形例において、連立方程式は、上記の表１と同様の表形式で表示する。
較正部３１１は、この解、すなわち内缶２０２の厚さｔ２と勾配との関係を表す係数を基に、勾配を変数として係数を適用することにより、厚さｔ２の測定時に厚さｔ２を推定する推定式を立式する。より詳細には、導出した係数ａ、定数ｂの値を上記の一次式に代入することで、勾配を変数として、次のような推定式を立式する。

Next, the calibration unit 311 constructs simultaneous equations from the relationship between the thickness t2 and the gradient calculated for the thickness t2 for each of the plurality of thicknesses t2 of the inner can 202 .
Assuming that the gradient is x, a is a coefficient applied to the gradient, and b is a constant, the thickness t2 can be expressed by, for example, a linear expression of t2=ax+b.
Here, the coefficient a and the constant b are obtained by actually measuring the thickness t2 of the inner can at two points (t21, t22) where the thickness t2 of the inner can is known, as a calibration, and obtaining the slope x and By inputting the combination of measured values (x1, t21) and (x2, t22) of the thickness t2 of the inner can into the above equation, the simultaneous equations shown as the following Equation 1 can be constructed and solved. can.

In this equation and each equation used in the following description, "*" is used to mean multiplication.
In Table 1, each of the 1st and 2nd rows in the columns of "gradient" and "t2 mechanical dimension" indicates actual numerical values for the above combinations of (x1, t21) and (x2, t22). It is a tabular representation of the above system of equations.
The calibrator 311 solves Equation 1 above to derive the values of the coefficient a and the constant b. The obtained values of the coefficient a and the constant b are listed in the columns labeled a and b in Table 1, respectively. As a method for solving the simultaneous equations, known methods such as the inverse matrix method and the Cramer method may be used. I am using In each modified example described later, simultaneous equations are displayed in a tabular format similar to Table 1 above.
Based on this solution, that is, the coefficient representing the relationship between the thickness t2 of the inner can 202 and the slope, the calibration unit 311 applies a coefficient using the slope as a variable to estimate the thickness t2 when measuring the thickness t2. Formulate an estimation formula. More specifically, by substituting the values of the derived coefficient a and constant b into the above linear expression, the following estimation formula is formulated with the gradient as a variable.

When actually estimating and measuring the thickness t2 of the inner can 202, the measurement unit 312 operates the sensor 1 at an arbitrary portion of the subject 2 to be measured where the thickness t2 is unknown. The output voltage from the coil 121 is measured as the voltage during measurement, and the amplitude ratio and phase difference during measurement, which are the amplitude ratio and phase difference between the voltage during measurement and the reference voltage, are calculated.
The measurement unit 312 plots the measurement points corresponding to the measured amplitude ratio and the measured phase difference on the amplitude ratio-phase difference plane, and obtains the gradient of the straight line connecting this measurement point and the intersection point P01. The measurement unit 312 calculates the value of t2 at the measurement point by substituting this gradient into the above estimation formula.

FIG. 9 shows the measurement results. In FIG. 9, the solid line indicates the case when the temperature is 10.4°C, and the dashed line indicates the case when the temperature is 11.4°C. When the temperature is 10.4° C., the three lines corresponding to the gap gaps of 70, 80, and 90 mm are almost overlapped, indicating that the gap gap is compensated. The 25, 30, and 35 mm flat plates used as the specimen bodies have the same thickness as the standard products as they came out of the blast furnace, but the 28 mm and 32 mm flat plates were cut from 30 mm and 35 mm flat plates, respectively. It is presumed that the electromagnetic induction physical properties changed due to processing. However, it is clear that the variation in the spacing Gap is compensated for as it has changed.
In this embodiment, the object body 202 has been described as a flat plate, but the effect of the present invention is the same even if the object body 202 has a curved surface.

Next, a nondestructive inspection and measurement method using the nondestructive inspection and measurement system 10 will be described with reference to FIGS. 1 to 9 and 10. FIG. FIG. 10 is a flow chart of the non-destructive inspection measurement method.
This non-destructive inspection and measurement method includes an excitation coil that excites the subject body provided in the subject, and outputs a voltage that corresponds to the magnetic field change that occurs in the subject body when the subject body is excited by the excitation coil. A sine wave signal or a composite signal composed of a plurality of sine waves having mutually different frequencies is applied to the detection coil and an excitation coil for exciting the body of the subject, and the voltage output from the detection coil is detected. A non-destructive inspection measurement method for measuring the dimensions of a body, wherein for a plurality of portions of a body of a subject having known and different dimensions, output from a detection coil under each of a plurality of different measurement conditions for each of the plurality of dimensions Measure the applied voltage and calculate the amplitude ratio and phase difference between this and the reference voltage, and take the amplitude ratio and phase difference as two axes, the points corresponding to at least two measurement results on the amplitude ratio-phase difference plane Obtaining a straight line connecting between, calculating the gradient of the straight line, constructing simultaneous equations from the relationship between the dimension and the value based on the gradient calculated for the dimension for each dimension, Based on the solution, an estimation formula is formulated with the values based on the gradient as variables to estimate the dimensions when measuring the dimensions. Estimate and measure.

Calibration slope calculator 310 performs measurement using sensor 1 at a specific frequency, with known first thickness t21 of inner can 202, and at known first gap Gap1 between outer can 201 and inner can 202. The amplitude ratio and phase difference are calculated by and plotted on an amplitude ratio-phase difference plane with the amplitude ratio as the horizontal axis and the phase difference as the vertical axis. In addition, the calibration gradient calculator 310 changed the gap Gap between the outer can 201 and the inner can 202 to a second gap Gap2 different from the first gap Gap1, and the sensor 1 was used under the same conditions. Amplitude ratio and phase difference are calculated from the measurements and plotted on the amplitude ratio-phase difference plane. Calibration slope calculator 310 calculates a first straight line connecting these two points plotted on the amplitude ratio-phase difference plane.
The calibrated slope calculator 310 also calculates, by measurement using the sensor 1, at a known second thickness t22 different from the first thickness t21 and at a third gap Gap3 between the outer can 201 and the inner can 202: Amplitude ratio and phase difference are calculated and plotted on the amplitude ratio-phase difference plane. In addition, the calibration gradient calculator 310 changed the gap Gap between the outer can 201 and the inner can 202 to a fourth gap Gap4 different from the third gap Gap3, and the sensor 1 was used under the same conditions. Amplitude ratio and phase difference are calculated from the measurements and plotted on the amplitude ratio-phase difference plane. Calibration slope calculator 310 calculates a second straight line connecting these two points plotted on the amplitude ratio-phase difference plane.
Calibration gradient calculator 310 calculates the gradient of the first straight line and the gradient of the second straight line on the amplitude ratio-phase difference plane (step S1).

Calibration gradient calculator 310 obtains an intersection point P0 on the extension line of the first straight line and the second straight line (step S3).

The calibrator 311 constructs a binary simultaneous equation based on the thicknesses t21 and t22 of the inner can 202 and the gradient values corresponding to these (step S5).
The calibration unit 311 solves this and formulates an estimation formula (step S7).

When actually estimating and measuring the thickness t2 of the inner can 202, the measurement unit 312 operates the sensor 1 at an arbitrary portion of the subject 2 to be measured where the thickness t2 is unknown. The output voltage from the coil 121 is measured as the voltage during measurement, and the amplitude ratio and phase difference during measurement, which are the amplitude ratio and phase difference between the voltage during measurement and the reference voltage, are calculated. The measurement unit 312 plots the measured amplitude ratio and the measured phase difference as measurement points on the amplitude ratio-phase difference plane, and plots this measurement point and the intersection point P0 on the extension line of the first straight line and the second straight line. is calculated, which is the slope of the measurement straight line connecting (step S9).
The measuring unit 312 calculates and measures the thickness t2 of the inner can 202 at the measured portion on the subject 2 by substituting the gradient at the time of measurement into the estimation formula formulated by the calibrating unit 311 (step S11 ).

Next, effects of the nondestructive inspection measurement system 10 and the nondestructive inspection measurement method described above will be described.

The nondestructive inspection measurement system 10 of this embodiment includes an exciting coil 113 that excites a subject body 202 provided in the subject 2 , and an excitation coil 113 that excites the subject body 202 . A sine wave signal or a composite signal composed of a plurality of sine waves having mutually different frequencies is applied to the detection coil 121 that outputs a voltage corresponding to the generated magnetic field change and to the excitation coil 113 for exciting the subject body 202, a measuring device 3 that detects the voltage output from the detection coil 121 and measures the dimension t2 of the subject body 202, wherein the measuring device 3 measures the dimension of the subject body 202 For a plurality of portions where t2 is known and different, the voltage output from the detection coil 121 is measured under each of a plurality of different measurement conditions for each of a plurality of dimensions t2, and the amplitude ratio and phase difference between this and the reference voltage are determined. , find a straight line connecting at least two points corresponding to the measurement results on the amplitude ratio-phase difference plane with the amplitude ratio and the phase difference as two axes, and calculate the slope of the straight line Gradient calculation during calibration From the relationship between the dimension t2 and the gradient-based value calculated for the dimension t2 for each dimension t2, a system of equations is constructed, and based on the solution, the dimension t2 A calibration unit 311 that formulates an estimation formula with a value based on the gradient as a variable for estimating the dimension t2 when measuring and a measurement unit 312 that estimates and measures.
In addition, the non-destructive inspection and measurement method of this embodiment includes the excitation coil 113 that excites the subject body 202 provided in the subject 2, and the excitation coil 113 that excites the subject body 202. A sine wave signal or a composite signal composed of a plurality of sine waves with mutually different frequencies is applied to the detection coil 121 that outputs a voltage corresponding to the magnetic field change occurring in the body 202 and to the excitation coil 113 to excite the subject body 202. , a non-destructive inspection measuring method for detecting the voltage output from the detection coil 121 and measuring the dimension t2 of the subject body 202, wherein for a plurality of portions with known and different dimensions t2 of the subject body 202, For each of a plurality of dimensions t2, under each of a plurality of different measurement conditions, the voltage output from the detection coil 121 is measured, and the amplitude ratio and phase difference between this and the reference voltage are calculated. Obtain a straight line connecting points corresponding to at least two measurement results on the amplitude ratio-phase difference plane, calculate the gradient of the straight line, and calculate the dimension t2 and the dimension for each of a plurality of dimensions t2 Construct a system of equations from the relationship with the slope-based values calculated for t2, and use the slope-based values as variables to estimate the dimension t2 when the dimension t2 is measured. Then, based on the estimation formula, the dimension t2 of the portion of the subject body 202 to be measured is estimated and measured.
According to the configuration described above, before measuring the dimension t2 of the portion to be measured of the subject body 202, a plurality of different measurement conditions are applied to a plurality of portions having known and different dimensions t2 for each dimension t2. , the voltage output from the detection coil 121 is measured, and the amplitude ratio and phase difference between this and the reference voltage are calculated. A straight line connecting points corresponding to at least two measurements is obtained, and the slope of the straight line is calculated. If the measurement conditions are changed while the dimension t2 is the same, the amplitude ratio and the phase difference are approximately proportional. The slope in the case is a value in which the influence of the measurement conditions is suppressed.
When estimating and measuring the dimension t2 of the portion to be measured of the subject body 202, the relationship between the dimension t2 and the value based on the gradient calculated for the dimension t2 is used. By solving the simultaneous equations, an estimation formula is formulated, and the dimension t2 is obtained based on this formula.
Therefore, it is possible to reduce the influence of measurement conditions and measure the dimension t2 of the subject body 202 provided in the subject 2 with high accuracy.

In addition, the calibration unit 311 formulates a multidimensional linear equation representing the relationship between the dimension t2 and the value based on the gradient calculated for the dimension t2, for each of the multiple dimensions t2, By solving these equations as simultaneous equations, a coefficient representing the relationship between the dimension t2 and the value based on the slope is calculated, and an estimation formula is formulated by applying the coefficient with the value based on the slope as a variable.
In addition, the measurement unit 312 measures the voltage output from the detection coil 121 as the voltage at the time of measurement for the portion to be measured of the subject body 202, and measures the amplitude ratio and phase difference between this and the reference voltage. Calculate the amplitude ratio and the phase difference at the time of measurement, calculate the gradient at the time of measurement, which is the gradient on the amplitude ratio-phase difference plane corresponding to these, and use the value based on the gradient at the time of measurement as a variable in the estimation formula Substitute to calculate and measure the dimension t2.
In addition, the calibration gradient calculation unit 310 further calculates the intersection points between the straight lines obtained for each of the plurality of dimensions t2, and the measurement unit 312 calculates the amplitude ratio-measurement amplitude ratio on the phase difference plane and the measurement time The slope of a straight line connecting the measurement point corresponding to the phase difference and the intersection is calculated as the slope during measurement.
According to the configuration as described above, the nondestructive inspection measurement system 10 as described above can be appropriately realized.

Further, the measurement conditions include the distance from the outer surface 201a of the subject 2 or the member 201 forming the outer surface 201a to the subject body 202 .
According to the above configuration, the influence of the distance Gap from the outer surface 201a of the subject 2 or the member 201 constituting the outer surface 201a to the subject body 202 is reduced, and the inside of the subject 2 can be measured with high accuracy. It is possible to measure the dimension t2 of the subject body 202 provided in the .

The subject body 202 is a plate, the dimension t2 is the thickness t2 of the plate, and the value based on the gradient is the gradient. In the simultaneous equations, the dimension t2 and the gradient are in a proportional relationship. .
According to the configuration as described above, the thickness t2 can be measured with high accuracy when the subject body 202 is a flat plate or a kiln-shaped plate.

[First modification of the embodiment]
Next, with reference to FIG. 11, a first modified example of the nondestructive inspection measurement system 10 and the nondestructive inspection measurement method shown as the above embodiment will be described. FIG. 11 is a diagram showing the configuration of a nondestructive inspection measurement system 40 in the first modified example. The nondestructive inspection measurement system 40 in the first modified example differs from the nondestructive inspection measurement system 10 in the above embodiment in that the computer 405 of the measurement device 403 compensates for fluctuations in the measurement result due to the ambient temperature of the object 2. points are different.

The object 2 to be subjected to electromagnetic induction is generally a metal, and the eddy current is affected by the electrical resistance of that metal. On the other hand, the temperature coefficient of electrical resistance of metals is very large. For example, the temperature coefficient of electrical resistance of stainless steel SUS304 is 1.1×10^-3. Therefore, since the measured value is strongly affected by temperature, the measurement accuracy can be improved by considering the temperature. However, since the subject body 202 is provided inside the subject 2, the temperature cannot be directly detected.
In this modification, focusing on the fact that in general metals, the amplitude of high frequencies is often strongly affected by eddy currents, the amplitude ratio of high frequencies is incorporated into calibration as an index of temperature, and calibration and measurement are performed. Temperature compensation is performed by
Conceptually, in addition to the configuration of the above embodiment, a frequency different from the frequency used in the gradient calculation unit 310 during calibration in the above embodiment, which is higher in this modification, is used to measure at different temperatures. Then, the slope and the amplitude ratio or phase difference on the amplitude ratio-phase difference plane due to the variation of the interval Gap are introduced into simultaneous equations for calibration and temperature compensation.

More specifically, the calibrated gradient calculator 410 in this modified example performs the following processing. Here, in the above embodiment, each measurement is performed under the same temperature conditions and by applying the same frequency to the detection coil 121, as shown in Table 1, for example. Let this temperature and frequency be the first temperature and the first frequency.
Calibration gradient calculator 410 first performs measurements corresponding to Table 1 above, as in the above embodiment. That is, the slope-at-calibration calculator 410 calculates a known At each of a plurality of different intervals Gap, the voltage output from the detection coil 121 is measured, the amplitude ratio and phase difference between this and the reference voltage are calculated, and the amplitude ratio and the phase difference are used as two axes. Obtaining first and second straight lines connecting points corresponding to at least two measurement results on the phase difference plane, and calculating the gradients of the first and second straight lines as the two first temperature gradients .
Next, calibration gradient calculator 410 applies a signal of a first frequency to sensing coil 121 under a second temperature different from the first temperature to obtain at least one type of thickness t2. , at each of a plurality of known and different intervals Gap, the voltage output from the detection coil 121 is measured and the amplitude ratio and phase difference between this and the reference voltage are calculated, and at least 2 on the amplitude ratio-phase difference plane. A straight line connecting the points corresponding to the two measurement results is obtained, and the gradient of the straight line is calculated as the second temperature gradient.
Further, the calibrated slope calculator 410 detects a signal at a second frequency different from the first frequency, which is higher in this modification, under each of the first temperature and the second temperature. , the voltage output from the detection coil 121 is measured, and the different-frequency amplitude ratio, which is the amplitude ratio between this and the reference voltage, is calculated.
The calibration unit 411 constructs simultaneous equations from the relationship between the thickness t2, the first temperature gradient, the second temperature gradient, and the different frequency amplitude ratio for each of a plurality of thicknesses t2 and temperatures, and based on the solution Formulate an estimation formula for
The measurement unit 412 estimates and measures the thickness t2 of the portion of the inner can 202 to be measured based on the estimation formula.

Hereinafter, more detailed behaviors of the gradient calculation unit 410 during calibration, the calibration unit 411, and the measurement unit 412 as described above will be described together with an embodiment of the nondestructive inspection measurement system 40. FIG.

[Example 2]
As shown in FIG. 9 shown in the above embodiment, when the temperature is 11.4° C., different values are shown than when the temperature is 10.4° C., and the changes are parallel. mobile. Therefore, some temperature compensation needs to be done to reflect this translation. As temperature compensation, there is a method in which a temperature detection element such as a thermocouple is provided and the measurement is performed based on the measurement result. In many cases, it is generally difficult. Therefore, it is desirable to compensate based on the data acquired by the sensor 1, if possible. Therefore, we focused on the data in the high frequency region.
As shown in FIG. 8, when the frequency is 87 Hz, the phase does not change much with temperature, but the amplitude ratio changes greatly. This is because the higher the frequency, the larger the eddy current, and the eddy current is affected by the electrical resistance of the object under test, which is greatly affected by temperature changes in the electrical resistance. Therefore, the measurement result when the frequency is 87 Hz is incorporated into the simultaneous equations as a kind of thermometer.

Specifically, the slope-at-calibration calculator 410 first sets the temperature to a first temperature, such as 10.4° C., and sets the frequency to a first frequency, such as 33 Hz. is changed, the measurement shown in Table 1 in the above embodiment is performed, and the slope corresponding to each of the plurality of straight lines LA1 and LA2 described in the slope column of Table 1 is used as the first temperature time slope calculate.

Next, calibration slope calculator 410 changes the temperature to the second temperature of 11.4° C. and performs measurement without changing the frequency from the first frequency. Here, the thickness t1 of the outer can 201 was fixed at 30 mm, the thickness t2 of the inner can 202 was fixed at 35 mm, and the gap Gap was changed to 70, 80 and 90 mm. This yields the measurement results shown as points PB1, PB2, PB3 in FIG. Among them, for example, a third straight line LB3 connecting points PB1 and PB3 is determined, and the gradient of the third straight line LB3 is calculated as the second temperature gradient.
Table 2 shows the above results. In Table 2, as a result corresponding to each of the first and second straight lines LA1 and LA2 in the above embodiment and the third straight line LB3 in this modified example, the distances on these straight lines LA1, LA2, and LB3 The coordinate values on the amplitude ratio-phase difference plane, the calculated gradients, etc. of each of the points PA5, PA6, and PB2 corresponding to the case where the gap is 80 mm are described.

Further, the gradient calculation unit 410 during calibration fixes the thickness t2 of the inner can 202 to 35 mm under the measurement conditions of each of the points PA5, PA6, and PB2 as shown as "A87Hz_35_80" in Table 2, and the interval Gap is 80 mm, measurement is performed when the frequency is changed to the second frequency of 87 Hz, which is higher than the first frequency of 33 Hz, and the different frequency amplitude ratio, which is the amplitude ratio in each case, is calculated. The measurement result under this measurement condition corresponds to the case where the frequency is 87 Hz in FIG. 8 shown in the above embodiment. At points PA5 and PA6, the only difference in the measurement conditions is the thickness t2 of the inner can 202. In the measurement using the second frequency, the thickness t2 was fixed at 35 mm. These correspond to the same point PB4, and as a result the same values are stored in Table 2. Point PB2 corresponds to point PB5 in FIG.

Next, the calibrating unit 411 determines the relationship between the thickness t2, the gradient calculated for the thickness t2, and the different-frequency amplitude ratio for each of the plurality of thicknesses t2 and temperatures of the inner can 202, Build a system of equations.
If the gradient is x, the different frequency amplitude ratio is y, a is a coefficient applied to the gradient, b is a coefficient applied to the different frequency amplitude ratio, and c is a constant, the thickness t2 is, for example, t2 = ax + by + c. be able to. For this equation, the calibration unit 411 constructs and solves a ternary simultaneous equation for the coefficients a, b, and constant c by substituting each value in Table 2 in the same manner as in the above-described embodiment. Derive the values listed in the respective columns denoted as a, b, c in 2.
Based on this solution, that is, the coefficient representing the relationship between the thickness t2 of the inner can 202, the slope, and the different frequency amplitude ratio, the calibration unit 411 applies the coefficient with the slope and the different frequency amplitude ratio as variables, An estimation formula for estimating the thickness t2 when measuring the thickness t2 is formulated. More specifically, by substituting the values of the derived coefficients a, b, and constant c into the above linear expression, the following estimation formula is formulated with the gradient and the different-frequency amplitude ratio as variables.

When actually estimating and measuring the thickness t2 of the inner can 202, the measurement unit 412 operates the sensor 1 at an arbitrary portion to be measured on the subject 2 and measures the output voltage from the detection coil 121. The measured voltage is measured, and the measured amplitude ratio and the measured phase difference, which are the amplitude ratio and phase difference between the measured voltage and the reference voltage, are calculated.
The measuring unit 412 plots the points corresponding to the measured amplitude ratio and the measured phase difference on the amplitude ratio-phase difference plane corresponding to the temperature at the time of measurement, and obtains the gradient of the straight line connecting this point and the intersection point. . The measurement unit 412 also acquires the value of the different-frequency amplitude ratio corresponding to the temperature at the time of measurement from a table or the like stored in the computer 405 . The measurement unit 412 calculates the t2 value at the measurement point by substituting this gradient and the different-frequency amplitude ratio into the above estimation formula.

FIG. 12 shows the measurement results. When the temperature is 11.4° C. and the gap Gap is 90 mm, there is a slight error in the measurement of the thickness t2 of the inner can 202, but sufficiently accurate results are derived under other conditions.
Table 3 tabulates the results of calculating the measured values using the derived coefficients and constants a, b, and c. Table 4 shows two straight lines connecting two points and a set of simultaneous equations for obtaining the intersection point P01 (x0, y0) of the two straight lines. there is It is configured so that the values of x0 and y0 are automatically calculated by inputting the measured values into this macro.

It goes without saying that the first modified example has the same effect as the already described embodiment.
In particular, in the present modified example, calibration gradient calculator 410 applies a frequency higher than the frequency of the sine wave signal or composite signal applied to excitation coil 113 when calculating the gradient to excitation coil 113, and from detection coil 121, The output voltage is measured, and the different frequency amplitude ratio, which is the amplitude ratio between this and the reference voltage, is calculated. Simultaneous equations are constructed from the relationship between the value based on the gradient calculated for and the different frequency amplitude ratio, and an estimation equation is formulated based on the solution.
According to the configuration as described above, a higher frequency than the signal applied to the excitation coil 113 is applied to the excitation coil 113 when calculating the gradient in the calibration gradient calculator 410, and the detection coil 121 outputs the A different frequency amplitude ratio, which is an amplitude ratio between the measured voltage and the reference voltage, is calculated and reflected in the simultaneous equations. High-frequency amplitudes are strongly affected by eddy currents, so by constructing and solving simultaneous equations that reflect the high-frequency amplitude ratio, it is possible to formulate an estimation formula that appropriately considers the effects of temperature.
Therefore, it is possible to reduce the influence of temperature and measure the dimensions of the subject body 202 provided in the subject 2 with high accuracy.

[Second Modification of Embodiment]
Next, a second modification of the nondestructive inspection measurement system 10 and the nondestructive inspection measurement method shown as the above embodiment will be described with reference to FIGS. 13 and 14. FIG. FIG. 13 is a diagram showing the configuration of a nondestructive inspection measurement system 50 in the second modified example. FIG. 14 is a schematic plan view of the sensor 1C of the nondestructive inspection measurement system 50 according to the second modified example. The nondestructive inspection measurement system 50 according to the second modified example differs from the nondestructive inspection measurement system 10 according to the above-described embodiment in the object to be inspected.
The diameter of a rod-shaped object, particularly a round rod-shaped object body 202C embedded in the object 2C is affected by the distance between the sensor 1C and the object body 2C, that is, lift-off (abbreviated as LO). There is a great demand for accurate measurement without fail. An example of this is the desire to accurately measure the diameter of rebar in reinforced concrete regardless of how deep it is embedded in the concrete, ie, the amount of "cover" in the industry term.
In this modified example, such a request is met, and the subject main body 202C is a rod with a circular cross section. The subject 2C to be inspected is, particularly in this modified example, a pillar or beam made of, for example, reinforced concrete. In the subject 2C, a reinforcing bar 202C is embedded in the concrete 201C at a position spaced LO from the outer surface 201a. In FIG. 13, the reinforcing bar 202C extends in a direction perpendicular to the plane of the paper. In addition, the reference of LO is measured below as the center of the circular cross section. The diameter D of the reinforcing bar 202C is the diameter of this cross section.

The configuration of the sensor 1C differs from that of the above embodiment only in that it comprises four exciters 11 as shown in FIG. Therefore, detailed description of the sensor 1C is omitted.

In this modified example, since the body of the subject is different from that of the above embodiment as described above, the calibration gradient calculation unit 510, the calibration unit 511, and the measurement unit 512 provided in the measuring device 503, particularly the computer 505, Behavior is different from the above embodiment.
In this modification, the nondestructive inspection measurement system 50 finally measures the diameter D of the reinforcing bar 202C. When measuring the diameter of the reinforcing bar 202C, the measuring device 503 measures the square of the difference between the diameter of a circle of a predetermined reference size stored in the computer 505 and the diameter of the reinforcing bar 202C as a dimension. calculate. Based on this dimension value, the computer 505 calculates the diameter D of the rebar 202C.
Conceptually, in this modification, the amplitude ratio and phase difference of reinforcing bars 202C with different thicknesses are measured by changing the distance between the sensor 1C and the reinforcing bars 202C, and measured on the amplitude ratio-phase difference plane. Calibration and measurement are performed assuming that the slope of the straight line connecting the points is proportional to the square of the thickness difference.

Hereinafter, more detailed behaviors of the gradient calculation unit 510 during calibration, the calibration unit 511, and the measurement unit 512 as described above will be described together with an embodiment of the nondestructive inspection measurement system 50. FIG.

[Example 3]
The sensor 1C was formed to have a housing with a width of 120 mm, a length of 440 mm, and a height of 130 mm.
Reinforcing bars used in general reinforced concrete are deformed reinforcing bars such as D9 and D13, which have knot-shaped unevenness on the surface to improve adhesion to concrete, and are not suitable for precise comparative measurement. Therefore, in this example, round steel reinforcing bars for reinforced concrete were used. However, since there are individual differences in electromagnetic induction physical properties such as electrical resistance and relative permeability, even among round steel reinforcing bars of the same standard, preliminary measurements were carried out and standard ones were selected. In addition, standard products were used for reinforcing bars with diameters of 9 mmΦ and 13 mmΦ, but there is no standard product for 11 mmΦ, so from the same individual long reinforcing bars with a diameter of 13 mmΦ, 13 mmΦ, 48.3 cm and lathe cutting 11mmΦ and 48.3cm were created in order to eliminate individual differences.

FIG. 15 shows an example of the measurement results, in which three types of reinforcing bars 202C with the same length L of 48.3 cm and diameters D of 9, 11, and 13 mm are attached to two types of LOs of 36.5 mm and 56.5 mm. The output voltage of the detection coil 121 was measured at a frequency of 6 Hz for a total of 6 different cases, and the results of calculating the amplitude ratio and the phase difference were plotted on the amplitude ratio-phase difference plane.
The reason for setting the frequency to a low frequency of 6 Hz is that steel has magnetism, and if there is magnetism, a large eddy current is generated when the frequency increases, and the resulting demagnetizing field causes the magnetic lines of force to penetrate into the subject. This is because it becomes difficult to

When the diameter D is 9 mmΦ, 11 mmΦ, and 13 mmΦ, the straight lines connecting the points where LO is 36.5 mm and 56.5 mm are straight lines LC1, LC2, and LC3, respectively. Focusing on the gradients of each of these straight lines LC1, LC2, and LC3, the reinforcing bar 202C with a diameter D of 11 mmΦ has a diameter value of 11 mmΦ, which is the middle value between 9 mmΦ and 13 mmΦ. , and shows a tendency close to the gradient when the diameter D is 13 mmΦ.
FIG. 16 is an enlarged view of the lower right portion of FIG. In the above embodiment, for example, as shown using FIG. 3, each straight line intersects at one intersection point. do not do. The intersection of the extrapolation lines of the straight lines LC2 and LC3 is on the extrapolation line of the straight line LC3. It is estimated that it will move towards From these experimental facts, when the subject body 202C is a bar with a circular cross section, the change in the diameter D is not only the change in the LO direction from the subject body 202C to the outer surface 201a of the subject 2C. , LO direction and the direction of extension of the subject body 202C, which is orthogonal to the direction of elongation of the subject body 202C, also affects the gradient. In other words, it was found that the slope varies in proportion to the square of the difference in diameters, rather than the squared difference in diameters, ie, the difference in cross-sectional area, which is usually easily considered.
This is considered to be based on the following events. That is, when the subject body 202C is excited by the excitation coil 113, an eddy current is generated. As shown in FIG. 17, the demagnetizing field 202b produced by this eddy current makes it difficult for the magnetic flux to enter the body 202C under test. Therefore, the magnetic flux 202c bypasses and passes through the surface layer of the subject body 202C. Therefore, the entire cross-sectional area of the cross section of the reinforcing bar 202C, that is, the square of the diameter is not related, but the difference in the surface layer, that is, the difference in the surface layer = (difference in thickness of the surface layer x difference in length of the surface layer). is also related to the difference in diameter, and it can be interpreted that the square of the difference in diameter is related to the experimental fact.

In this modified example, the definition of dimensions is different from that of the above-described embodiment, but the substantial processing contents of the slope-at-calibration calculation unit 510, the calibration unit 511, and the measurement unit 512 are the same as those of the above-described embodiment.
Here, the predetermined reference diameter D is assumed to be 13 mmΦ. Also, the difference between the diameter D of the reinforcing bar 202C to be measured and the reference diameter is represented by δD. For example, when the diameter D of the reinforcing bar 202C to be measured is 13 mmΦ, δD=0, and when the diameter D is 9 mmΦ, δD=4. Also, the square of δD is expressed as (δD)̂2 in terms of fonts.
The calibration slope calculator 510 calculates slopes for each of the straight lines LC3 and LC1 as described above, for example. The diameter D of each of the points PC2 and PC1 corresponding to the case where the LO on the straight lines LC3 and LC1 is 36.5 mm, the amplitude ratio, the phase difference, the slope calculated by the slope calculation unit 510 at calibration, and the reference The square of the difference from the diameter (δD)^2 is shown in Table 5 below. The fact that the square of the difference from the reference diameter (δD)̂2 is a negative number indicates that the diameter of the reinforcing bar 202C is smaller than the reference diameter.

The calibration unit 511 constructs simultaneous equations based on Table 5 above.
Assuming that the gradient is x, a is a coefficient applied to the gradient, and b is a constant, the square of the difference between the diameter of the reinforcing bar 202C and the reference diameter (δD)̂2 is, for example, a linear expression of (δD)̂2=ax+b can be expressed as For this equation, the calibration unit 511 constructs and solves a binary simultaneous equation for the coefficient a and the constant b by substituting each value in Table 5 in the same manner as in the above embodiment, thereby obtaining The values described in the respective columns indicated as a and b are derived.
Based on this solution, that is, the coefficient representing the relationship between the square of the difference between the diameter of the reinforcing bar 202C and the reference diameter (δD)̂2 and the slope, the calibration unit 511 applies a coefficient using the slope as a variable. , an estimation formula for estimating the square of the difference between the diameter of the reinforcing bar 202C and the reference diameter (δD)̂2 at the time of measurement. More specifically, by substituting the values of the derived coefficient a and constant b into the above linear expression, the following estimation formula is formulated with the gradient as a variable.

When actually estimating and measuring the diameter D of the reinforcing bar 202C, the measurement unit 512 operates the sensor 1C at an arbitrary portion to be measured on the object 2C to measure the output voltage from the detection coil 121. The measured voltage is measured as a voltage, and the measured amplitude ratio and the measured phase difference, which are the amplitude ratio and phase difference between the measured voltage and the reference voltage, are calculated.
The measurement unit 512 plots the points corresponding to the measured amplitude ratio and the measured phase difference on the amplitude ratio-phase difference plane, and obtains the gradient of the straight line connecting this point and the intersection point. The measurement unit 512 calculates the square of the difference (δD)̂2 between the diameter of the reinforcing bar 202C and the reference diameter at the measurement point by substituting this gradient into the above estimation formula. Based on the value of the square of the difference between the diameter of the reinforcing bar 202C and the reference diameter (δD)^2, the measurement unit 512 calculates the square root of this value and adds or subtracts it from the reference diameter value. Calculate the diameter D by

18 and 19 show the measurement results. In this case, as shown in FIG. 13, the sensor 1C scans and measures in the horizontal direction of the paper surface, and in FIGS. there is FIG. 18 shows a case where LO is 36.5 mm, and (δD)^2 is measured to be approximately −4 for a reinforcing bar with a diameter D of 11 mmΦ. Therefore, δD is -2, the diameter D is 13-2=11 (mm), and the diameter D of the reinforcing bar 202C of 11 mmΦ is accurately measured. FIG. 19 shows the case where LO is 56.5 mm. Even if the LO changes, the diameter D is accurately measured for the case of the rebar 202C with 11 mmΦ.

It goes without saying that the second modified example has the same effect as the already described embodiment.
In particular, in this modified example, the subject main body 202C is a rod with a circular cross section, and the dimension is the square of the difference between the diameter of the circle having the reference size and the diameter of the cross section of the rod. In the equation, the values based on dimension and slope are proportional.
If the object body 202C is a bar with a circular cross section, when the magnetic lines of force generated by the excitation coil 113 enter the bar, they form a magnetic field opposite to the direction of the magnetic field formed by the entering magnetic flux. Since the eddy current flows like this, the lines of magnetic force are canceled by the eddy current and do not enter the inside of the rod, but flow near the surface of the rod and escape to the opposite side of the intrusion point. For this reason, in the case of a rod with a circular cross section, the slope, that is, the slope when the proportional relationship between the amplitude ratio and the phase difference is expressed as a straight line, is not the diameter of the rod, but a circle of some standard size. When defined, the relationship is proportional to the square of the difference between the diameter of this circle and the cross-sectional diameter of the rod to be measured.
Therefore, according to the configuration as described above, when the subject body 202C is a rod with a circular cross section, the diameter can be measured with high accuracy.

[Third modification of the embodiment]
Next, with reference to FIG. 20, a third modification of the nondestructive inspection measurement system 10 and the nondestructive inspection measurement method shown as the above embodiment will be described. This modification is a further modification of the second modification. FIG. 20 is a diagram showing the configuration of a nondestructive inspection measurement system 60 in the third modified example. The nondestructive inspection measurement system 60 in the third modification is different from the nondestructive inspection measurement system 50 in the second modification in that the length of the subject body 202C and the length calculated in the second modification described in Table 5 are The difference is that the quadratic gradient is calculated based on the obtained gradient, and the simultaneous equations and the estimated equation are formulated based on this.
When actually measuring the diameter of the rod-shaped subject body 202C as shown in the second modified example, the length of the subject body 202C affects the measurement accuracy. More specifically, if the subject body 202C has a length greater than or equal to a certain length, the effect in the length direction will be saturated and constant, but if the length is shortened, the effect will appear. In the nondestructive inspection measurement system 60 of this modified example, the influence of this length is reduced.

FIG. 21 is a graph showing the relationship between the slope calculated for each of the straight lines LC1, LC2, and LC3 and the length of the reinforcing bar 202C in the second modified example. In FIGS. 15 and 16, the length of the reinforcing bar 202C is 48.3 cm, so the straight line LC1 in FIGS. 15 and 16 corresponds to the point PD1, the straight line LC2 to the point PD2, and the straight line LC3 to the point PD3, respectively. do. Straight lines LD1, LD2, and LD3 indicate changes in gradient when the length of the reinforcing bars 202C with diameters D of 9 mmΦ, 11 mmΦ, and 13 mmΦ is changed, respectively.
When the length of the reinforcing bar 202C is 70 cm or more, the gradient is saturated and becomes almost constant. concentrates on one point P0.
The horizontal axis coordinate L of P0 is about -9.2. Since the horizontal axis is the length of the reinforcing bar 202C, it cannot be a negative value. It is estimated to be near 0. Therefore, based on the gradient value calculated by the calibration gradient calculator 510, the gradient of the gradient with respect to the length L, that is, δ gradient/δL, is quadratically calculated on the length-gradient plane shown in FIG. Calculate as gradient (value based on gradient).
The computer 605 of the measuring device 603 in this modified example includes a secondary gradient calculation section 613 during calibration, and the secondary gradient calculation section 613 during calibration calculates the secondary gradient as described above. Based on this, the calibration unit 611 in this modified example constructs simultaneous equations.
Table 6 is obtained by adding second-order gradients to the straight lines LC3 and LC1 of the third modified example to Table 5.

The calibration unit 611 constructs simultaneous equations based on Table 6 above.
Assuming that the secondary gradient is x, a is a coefficient applied to the secondary gradient, and b is a constant, the square of the difference between the diameter of the reinforcing bar 202C and the reference diameter (δD)̂2 is, for example, (δD)̂2= It can be represented by a linear expression of ax+b. For this equation, the calibration unit 611 constructs and solves a binary simultaneous equation for the coefficient a and the constant b by substituting each value in Table 6 in the same manner as in the above embodiment, thereby obtaining The values described in the respective columns indicated as a and b are derived.
Based on this solution, that is, the coefficient representing the relationship between the square of the difference between the diameter of the reinforcing bar 202C and the reference diameter (δD)^2 and the secondary gradient, the coefficient is calculated using the secondary gradient as a variable. By applying an estimation formula to estimate the square of the difference between the diameter of the rebar 202C and the reference diameter (δD)̂2 when measured. More specifically, by substituting the values of the derived coefficient a and constant b into the above linear expression, the following estimation expression is formulated with the secondary gradient as a variable.

When actually estimating and measuring the diameter D of the reinforcing bar 202C, the measurement unit 612 operates the sensor 1C at an arbitrary portion to be measured on the object 2C to measure the output voltage from the detection coil 121. The measured voltage is measured as a voltage, and the measured amplitude ratio and the measured phase difference, which are the amplitude ratio and phase difference between the measured voltage and the reference voltage, are calculated.
The measurement unit 612 plots the points corresponding to the measured amplitude ratio and the measured phase difference on the amplitude ratio-phase difference plane, obtains the gradient of the straight line connecting this point and the intersection, and further calculates 2 Calculate the next gradient. The measurement unit 612 calculates the square of the difference (δD)̂2 between the diameter of the reinforcing bar 202C and the reference diameter at the measurement point by substituting this secondary gradient into the above estimation formula. Based on the value of the square of the difference between the diameter of the reinforcing bar 202C and the reference diameter (δD)^2, the measurement unit 612 calculates the square root of this value and adds or subtracts it from the reference diameter value. Calculate the diameter D by

Table 7 is a table showing the results in more detail, and FIG. 22 is a graph thereof.
As shown in Table 7, FIG. 22, even if LO changes from 36.5 mm to 56.5 mm and the length of the reinforcing bar 202C changes from 48.3 cm to 83 cm, it is not affected by them, The diameter of the 11 mmΦ rebar 202C was measured to be exactly 10.91 mm.

It goes without saying that the third modification has the same effect as the embodiment already described.
In particular, in this modification, for a plurality of portions of the subject body 202C with known and different dimensions, the length of the rod and the gradient calculated by the calibration-time gradient calculator 510 are used as two axes for each of the plurality of dimensions. A straight line connecting points corresponding to at least two measurement results on the length-slope plane is obtained, and the secondary slope, which is the slope of the straight line, is calculated as a value based on the slope. Equipped with a calculation unit 613, the calibration unit 611 constructs simultaneous equations from the relationship between each dimension and the quadratic gradient calculated for each dimension, and based on the solution, an estimation formula formulate.
When the subject body 202C is a rod and the length of the rod is short, the length of the rod and the gradient are taken as two axes rather than the gradient calculated as in the second modified example. The relationship is proportional to the quadratic slope, which is the slope of the straight line connecting the points corresponding to the measurement results, corresponding to at least two length-slope correspondences on the length-slope plane.
According to the configuration as described above, the simultaneous equations are constructed from the relationship between each dimension and the secondary gradient calculated for each dimension. A quadratic gradient relationship is reflected.
Therefore, when the subject body 202C is a rod and the length of the rod is short, the influence of the measurement conditions is reduced, and the dimensions of the subject body 202C provided in the subject 2C can be determined with high accuracy. It is measurable.

It should be noted that the nondestructive inspection measurement system and nondestructive inspection measurement method of the present invention are not limited to the above-described embodiments and modifications described with reference to the drawings, and various other variations can be made within the technical scope thereof. Modifications are possible.

For example, in the above-described second and third modifications, the cross section of the body of the subject is circular, but it may be of another shape, such as a square. That is, the subject body may be a bar with a square cross section.
In this case, if the dimension to be measured is the square of the difference between the length of the diagonal of the square of the standard size and the length of the diagonal of the cross section of the rod, By setting "the diameter" to "the length of the diagonal line", it is possible to construct a non-destructive inspection measurement system corresponding to this case.

Further, in the first modified example, the calibration gradient calculator 410 applies to the excitation coil a frequency higher than the frequency of the sine wave signal or the synthesized signal applied to the excitation coil 113 when calculating the gradient, and detects The voltage output from the coil 121 is measured and the different frequency amplitude ratio, which is the amplitude ratio between this and the reference voltage, is calculated. Simultaneous equations were constructed from the relationship between the value based on the gradient calculated for t2 and the different frequency amplitude ratio, and an estimation equation was formulated based on the solution. This is because in general metals, when the frequency is high, the amplitude ratio is larger than the phase difference due to temperature fluctuation.
However, for example, when the body of the subject is made of an alloy with high electrical resistance, or when the thickness of the body of the subject is thin, when the frequency is low, the fluctuation due to temperature is greater than the amplitude ratio. Sometimes the difference is even greater. Therefore, a phase difference may be used as an index of temperature.
That is, the gradient-at-calibration calculator applies to the excitation coil a frequency different from, more specifically, a frequency lower than the frequency of the sine wave signal or synthesized signal applied to the excitation coil when calculating the gradient, and detects Measure the voltage output from the coil and calculate the different frequency phase difference, which is the phase difference between this and the reference voltage, Simultaneous equations may be constructed from the relationship between the values based on the gradients calculated in , and the different frequency phase differences, and the estimated equation may be formulated based on the solution.
According to the configuration described above, a frequency different from, more specifically, a frequency lower than the frequency of the signal applied to the excitation coil when calculating the gradient in the calibration gradient calculation unit is applied to the excitation coil, The voltage output from the detection coil is measured, and the different frequency phase difference, which is the phase difference between this and the reference voltage, is calculated and reflected in the simultaneous equations. If the frequency is different, the phase difference is affected differently by the eddy current. Therefore, by constructing and solving simultaneous equations that reflect the phase difference of different frequencies, an estimation formula that appropriately considers the effect of temperature can be obtained. can be established.
Therefore, it is possible to reduce the influence of the temperature and measure the dimensions of the subject body provided in the subject with high accuracy.

In addition to this, it is possible to select the configurations mentioned in the above-described embodiment and each modified example, or to change them to other configurations as appropriate, without departing from the gist of the present invention.

10, 40, 50, 60 non-destructive inspection measurement system 1, 1C sensor 112 feedback coil 113 excitation coil 121 detection coil 3, 403, 503, 603 measuring device 305, 405, 505, 605 computer 310, 410, 510 gradient during calibration Calculation units 311, 411, 511, 611 Calibration units 312, 412, 512, 612 Measurement unit 613 Calibration second-order gradient calculation units 2, 2C Subject 201 Outer can 201C Concrete 201a Outer surface 202 Inner can (subject body)
202C reinforcing bar (subject body)
Gap The distance from the subject to the body of the subject

Claims (11)

an excitation coil that excites a subject body provided in the subject; a detection coil that outputs a voltage corresponding to a change in the magnetic field generated in the subject body when the subject body is excited by the excitation coil; A sinusoidal signal or a composite signal composed of a plurality of sinusoidal waves having mutually different frequencies is applied to the excitation coil to excite the subject body, and a voltage output from the detection coil is detected to detect the subject body. A non-destructive inspection measurement system comprising a measuring device that measures the dimensions of
The measuring device is
For a plurality of portions of the subject body having known and different dimensions, the voltage output from the detection coil is measured under each of a plurality of different measurement conditions for each of the plurality of dimensions, and the measured voltage is used as a reference voltage. Calculate the amplitude ratio and phase difference of, obtain a straight line connecting points corresponding to at least two measurement results on the amplitude ratio-phase difference plane with the amplitude ratio and the phase difference as two axes, and a calibrated slope calculator for calculating the slope;
For each of a plurality of said dimensions, construct a system of equations from the relationship between that dimension and the slope-based value calculated for that dimension, and based on the solution, the dimension at the time of measurement of said dimension a calibration unit that formulates an estimation formula with variables based on the gradient, which estimates
a measurement unit for estimating and measuring the dimension of the portion of the subject body to be measured based on the estimation formula;
A non-destructive inspection measurement system. The calibrator formulates, for each of a plurality of the dimensions, a multidimensional linear equation representing the relationship between the dimension and the slope-based value calculated for the dimension, calculating coefficients representing the relationship between the dimensions and the gradient-based values by solving the simultaneous equations, and formulating the estimation equations by applying the coefficients with the gradient-based values as the variables; The non-destructive inspection measurement system according to claim 1, wherein: The measurement unit measures the voltage output from the detection coil as a voltage at the time of measurement for the portion to be measured of the subject body, and measures the amplitude ratio and phase difference between this voltage and the reference voltage. Calculate the amplitude ratio and the phase difference at the time of measurement, calculate the gradient at the time of measurement that is the gradient on the amplitude ratio-phase difference plane corresponding to these, and calculate the value based on the gradient at the time of measurement in the estimation formula 3. The non-destructive inspection and measurement system according to claim 1, wherein said dimension is calculated and measured by substituting for said variable of . The slope-at-calibration calculation unit further calculates intersections between the straight lines obtained for each of the plurality of dimensions,
The measuring unit calculates the gradient of a straight line connecting the measurement point corresponding to the measured amplitude ratio and the measured phase difference on the amplitude ratio-phase difference plane and the intersection point as the measured gradient. The non-destructive inspection measurement system according to claim 3. 5. The non-destructive inspection measurement system according to any one of claims 1 to 4, wherein the measurement conditions include a distance from the outer surface of the subject or a member constituting the outer surface to the subject body. The gradient-at-calibration calculator applies to the excitation coil a frequency different from the frequency of the sine wave signal or the synthesized signal applied to the excitation coil when calculating the gradient, and outputs from the detection coil Measure the voltage and calculate the different frequency amplitude ratio, which is the amplitude ratio between this and the reference voltage, or the different frequency phase difference, which is the phase difference with the reference voltage,
The calibrating unit, for each of the plurality of dimensions and temperatures, the relationship between the dimension, the gradient-based value calculated for the dimension, and the different frequency amplitude ratio or the different frequency phase difference 6. The non-destructive inspection measurement system according to any one of claims 1 to 5, wherein the simultaneous equations are constructed from and the estimated equations are formulated based on the solutions. the subject body is a plate, the dimension is the thickness of the plate,
the slope-based value is the slope;
7. The nondestructive inspection measurement system according to any one of claims 1 to 6, wherein in said simultaneous equations, said dimension and said gradient are in a proportional relationship. The subject body is a rod with a circular cross section,
The dimension is the square of the difference between the diameter of a circle of a standard size and the diameter of the cross section of the rod,
7. The nondestructive inspection measurement system according to any one of claims 1 to 6, wherein in the simultaneous equations, the dimension and the gradient-based value are in a proportional relationship. The subject body is a rod with a square cross section,
The dimension is the square of the difference between the length of the diagonal of a square with a standard size and the length of the diagonal of the cross section of the rod,
7. The non-destructive inspection measurement system according to any one of claims 1 to 6, wherein in said simultaneous equations, said dimension and said gradient-based value are in a proportional relationship. For a plurality of portions of the body of the subject having known and different dimensions, the length of the rod and the length of the gradient calculated by the gradient calculation unit during calibration as two axes for each of the plurality of dimensions - A second-order gradient calculator during calibration that obtains a straight line connecting points corresponding to at least two measurement results on a gradient plane and calculates a second-order gradient that is the gradient of the straight line as a value based on the gradient with
The calibration unit constructs simultaneous equations from the relationship between the dimensions and the secondary gradients calculated for the dimensions for each of the plurality of dimensions, and formulates the estimation formula based on the solutions. The nondestructive inspection measurement system according to claim 8 or 9, wherein an excitation coil that excites a subject body provided in the subject; a detection coil that outputs a voltage corresponding to a change in the magnetic field generated in the subject body when the subject body is excited by the excitation coil; A sinusoidal signal or a composite signal composed of a plurality of sinusoidal waves having mutually different frequencies is applied to the excitation coil to excite the subject body, and a voltage output from the detection coil is detected to detect the subject body. A non-destructive inspection measuring method for measuring the dimensions of
For a plurality of portions of the subject body having known and different dimensions, the voltage output from the detection coil is measured under each of a plurality of different measurement conditions for each of the plurality of dimensions, and the measured voltage is used as a reference voltage. Calculate the amplitude ratio and phase difference of, obtain a straight line connecting points corresponding to at least two measurement results on the amplitude ratio-phase difference plane with the amplitude ratio and the phase difference as two axes, and compute the gradient,
For each of a plurality of said dimensions, construct a system of equations from the relationship between that dimension and the slope-based value calculated for that dimension, and based on the solution, the dimension at the time of measurement of said dimension formulating an estimation formula with variables based on the gradient,
A non-destructive inspection and measurement method for estimating and measuring the dimensions of the portion to be measured of the subject body based on the estimation formula.

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