A metal plate thickness measurement method and system based on electromagnetic eddy current

Abstract

The application discloses a metal plate thickness measurement method and system based on electromagnetic eddy current, and the method comprises the following steps: building an eddy current detection system, adopting a coaxial excitation-receiving eddy current sensor, obtaining mutual inductance signal changes caused by the metal plate through the eddy current sensor in a sweep frequency measurement mode; calculating a characteristic frequency point at which the real part and the imaginary part of the mutual inductance signal are equal, and the characteristic point is recorded as a cross frequency; adjusting n times of lift-off distances respectively, and calculating the cross frequency at which the real part and the imaginary part of the mutual inductance signal are equal again; performing logarithmic processing on the n cross frequency points, and adopting linear fitting to obtain the relationship between the cross frequency logarithm and the lift-off distance; through a large number of calculations, it is found that the slope of the fitting straight line is irrelevant to the conductivity, so that additional calibration of the electromagnetic characteristics of the plate is not needed, the slope of the fitting straight line is only determined by the thickness of the plate, and effective measurement of the thickness of the plate can be realized.

Description

Technical Field

[0001] This invention relates to the field of non-contact measurement technology of metal material dimensions using magnetic eddy currents, and in particular to a method and system for measuring the thickness of metal plates based on electromagnetic eddy currents. Background Technology

[0002] Sheet metal is commonly used in the manufacture of support towers for power transmission lines, such as steel and aluminum alloys. These materials require good mechanical strength and corrosion resistance. Furthermore, power fittings are metal components used in power systems to support, fix, connect, and protect conductors and equipment, such as suspension clamps, tension clamps, and connecting fittings. These fittings are typically made of high-strength aluminum alloys to ensure their reliability and durability under electrical loads. Because sheet metal is more prone to deformation or failure under abnormal loads during service, thinning of metal components that need to withstand complex loads such as bending moments and shear forces further reduces their stability. The thickness of sheet metal directly affects the load-bearing capacity and durability of the structure; accurate thickness measurement ensures structural safety. Eddy current testing is a non-destructive testing method that utilizes the principle of electromagnetic induction. It assesses certain properties or thickness information of conductive materials and workpieces by detecting changes in induced eddy currents within the tested object, and is of great significance for monitoring the quality of metal products. This invention discloses a method for measuring the thickness of metal sheets based on electromagnetic eddy currents. It employs a coaxial excitation-receiving eddy current sensor. The sensor obtains the changes in mutual inductance signals caused by the metal sheet at different lift-off distances using a frequency sweep measurement mode. The crossover frequency, where the real and imaginary parts of the mutual inductance signal are equal, is then calculated. A linear fitting method is used to obtain the relationship between the logarithm of the crossover frequency and the lift-off distance. The slope of the fitted line is independent of conductivity and is determined solely by the sheet thickness, enabling effective measurement of sheet thickness. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] Therefore, this invention proposes a method for measuring the thickness of metal sheets based on electromagnetic eddy currents. By utilizing measurement results at different lift-off distances, the influence of the electromagnetic properties of metal on the thickness is eliminated, theoretically improving the accuracy of metal sheet thickness measurement.

[0005] Another objective of this invention is to provide a metal sheet thickness measurement system based on electromagnetic eddy currents.

[0006] To achieve the above objectives, this invention proposes a method for thickness measurement and imaging of metal plates based on electromagnetic eddy currents, comprising:

[0007] An eddy current detection system was built, and a coaxial cylindrical eddy current sensor with one excitation and one reception was designed.

[0008] An analytical theoretical model of eddy currents was established based on the sensor structure, and eddy current detection was performed on the metal sheet.

[0009] The mutual inductance sweep frequency signal of the plate coil is acquired based on the adjusted coil lift-off distance, and the frequency points where the real and imaginary parts of the mutual inductance sweep frequency signal are equal are extracted and recorded as the crossover frequency.

[0010] When the required number of coil lift-off distance adjustments is reached, different crossover frequencies are obtained at different lift-off distances;

[0011] The fitting slope is obtained by using a linear fit to the relationship between the logarithm of different cross frequencies and the lift-off distance;

[0012] The plate thickness measurement results are obtained based on the relationship between the fitting slope and the plate thickness.

[0013] The metal sheet thickness measurement method based on electromagnetic eddy currents in this invention may also have the following additional technical features:

[0014] In one embodiment of the present invention, an analytical theoretical model of eddy currents is established based on the structure of the sensor, including:

[0015]

[0016] In the formula

[0017]

[0018]

[0019]

[0020]

[0021] Where σ is the conductivity, d is the thickness of the metal plate, K is the sensor coefficient, and φ(α) is related to the electromagnetic properties and thickness of the metal component, determining the phase of the eddy current response signal.

[0022] In one embodiment of the present invention, the fitting slope is determined by the thickness of the plate:

[0023] log(ω n+1 )=k1l n+1 +b1 (6)

[0024] Where k1 is the fitting slope, l n+1 For different lift-off distances.

[0025] In one embodiment of the present invention, linear fitting is used to characterize the relationship between the thickness of the plate and the fitting slope k1:

[0026] k1=k2d+b2(7).

[0027] In one embodiment of the present invention, when the coil probe is located above the j-th metal plate to be tested, the cross frequency of the mutual inductance signal under different lift-off distances is extracted. Equation (6) is used to describe the relationship between the lift-off distance, the cross frequency, and the logarithm. The slope k is then... j Substituting into equation (7), we obtain the thickness of the j-th metal plate to be measured:

[0028]

[0029] To achieve the above objectives, another aspect of the present invention proposes a metal sheet thickness measurement system based on electromagnetic eddy currents, comprising:

[0030] The sensor design module is used to build an eddy current detection system and design a coaxial excitation-receiver cylindrical eddy current sensor.

[0031] The eddy current detection module is used to establish an analytical theoretical model of eddy currents based on the structure of the sensor and to perform eddy current detection on metal sheets.

[0032] The frequency point extraction module is used to acquire the mutual inductance sweep frequency signal of the plate coil based on the adjusted coil lift-off distance, and extract the frequency points where the real part and imaginary part of the mutual inductance sweep frequency signal are equal and record them as cross frequencies.

[0033] The different cross frequency calculation module is used to obtain different cross frequencies at different lift-off distances when it is determined that the required number of coil lift-off distance adjustments has been reached.

[0034] The fitting slope calculation module is used to obtain the fitting slope by utilizing the relationship between the logarithm of different cross frequencies and the lift-off distance of the linear fitting.

[0035] The plate thickness measurement module is used to obtain the plate thickness measurement result based on the relationship between the fitted slope and the plate thickness.

[0036] The method and system for measuring the thickness of metal plates based on electromagnetic eddy currents in this invention have been found through extensive calculations to be independent of the slope of the fitted straight line and the conductivity. Therefore, there is no need for additional calibration of the electromagnetic properties of the plate. The slope of the fitted straight line is determined only by the thickness of the plate, which can achieve effective measurement of the plate thickness.

[0037] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0039] Figure 1 This is a flowchart of a metal sheet thickness measurement method based on electromagnetic eddy currents according to an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the swept-frequency eddy current response signal according to an embodiment of the present invention;

[0041] Figure 3 This is a graph showing the relationship between the logarithm of the cross frequency of the eddy current response signal and the lift-off distance for samples with different conductivity levels according to an embodiment of the present invention.

[0042] Figure 4 This is a graph showing the relationship between the slope of the fitted straight line and the thickness of the metal sheet according to an embodiment of the present invention;

[0043] Figure 5 This is a structural diagram of a metal sheet thickness measurement system based on electromagnetic eddy currents according to an embodiment of the present invention. Detailed Implementation

[0044] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0045] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0046] The following description, with reference to the accompanying drawings, describes a method and system for measuring the thickness of metal sheets based on electromagnetic eddy currents according to embodiments of the present invention.

[0047] Figure 1 This is a flowchart of a metal sheet thickness measurement method based on electromagnetic eddy currents according to an embodiment of the present invention, as shown below. Figure 1 As shown, the method includes:

[0048] S1. Build an eddy current detection system and design a coaxial excitation-receiver cylindrical eddy current sensor.

[0049] In this embodiment of the invention, an eddy current detection system is constructed, and a coaxial cylindrical eddy current sensor with one excitation and one reception is designed and placed on top of a metal plate.

[0050] Specifically, the coaxial excitation and receiving cylindrical eddy current sensor has an inner diameter of 0.5 mm and an outer diameter of 2 mm, with a spacing of 1 mm between the two coils and 100 turns in each coil.

[0051] S2. Based on the structure of the sensor, an analytical theoretical model of eddy current is established, and eddy current detection is performed on the metal sheet.

[0052] In this embodiment of the invention, an eddy current analytical theoretical model is established, and eddy current detection is performed on the metal plate. The obtained mutual inductance sweep frequency signal M(ω) of the plate coil is stored in the computer. The computer extracts the frequency point where the real part and the imaginary part of the coil sweep frequency signal are equal, and this frequency point is recorded as the crossover frequency.

[0053] Specifically, the electromagnetic parameters of the sample are set in the analytical theoretical model, and the analytical theoretical model is established, including the conductivity σ and the thickness d of the metal plate. The analytical model is as follows:

[0054]

[0055] In the formula

[0056]

[0057]

[0058]

[0059] In the formula, K is the coefficient of the sensor, which determines the amplitude of the signal. φ(α) is related to the electromagnetic properties and thickness of the metal component, and determines the phase of the eddy current response signal.

[0060] S3. Based on the adjusted coil lift-off distance, acquire the mutual inductance sweep frequency signal of the plate coil, and extract the frequency points where the real and imaginary parts of the mutual inductance sweep frequency signal are equal as the cross frequency.

[0061] In this embodiment of the invention, the height of the sensor is adjusted to change the lift-off distance of the coil. At the new lift-off distance, the acquired mutual inductance sweep frequency signal M(ω) of the plate coil is stored in the computer, and the computer still determines the crossover frequency where the real and imaginary parts of the coil sweep frequency signal are equal.

[0062] Specifically, the mutual inductance sweep signal M(ω) of the sheet metal coil is obtained by sweeping eddy current calculation using an analytical model, with the excitation frequency ranging from 10 Hz to 1 MHz. The real part of the mutual inductance change mainly characterizes the reflected magnetic field energy, while the imaginary part characterizes the heat loss of the eddy current. When the real and imaginary parts are equal, the emitted magnetic field energy is equal to the heat loss energy. This characteristic point is closely related to the thickness of the metal. The crossover frequency point where the real and imaginary parts of the coil sweep signal are equal is extracted, such as... Figure 2 As shown.

[0063] S4, when it is determined that the required number of coil lift-off distance adjustments has been reached, different cross frequencies are obtained under different lift-off distances.

[0064] Specifically, step S3 is repeated until the required maximum liftoff distance is reached, thus obtaining the crossover frequency ω at different liftoff distances. n+1 .

[0065] S5, the fitting slope is obtained by using the relationship between the logarithm of different cross frequencies and the lift-off distance in linear fitting.

[0066] For different cross frequencies ω n+1 Logarithmic processing was performed, and linear fitting was used to obtain the logarithm of the cross frequency and the lift-off distance l. n+1 The slope k1 of the fitted line is independent of the conductivity σ and is determined solely by the thickness d of the plate.

[0067] log(ω n+1 )=k1l n+1 +b1(6)

[0068] Specifically, the crossover frequency ω at different lift-off distances n+1 Logarithmic processing was performed, and linear fitting was used to obtain the logarithm of the cross frequency and the lift-off distance l. n+1 The relationship is as follows. The slope k1 of the fitted line is independent of the conductivity σ. Further steps include:

[0069] Using an analytical theoretical model, l was calculated at different lift-off distances. n+1 Cross frequency ω n+1 The lift-off distance ranges from 1mm to 3mm, with a crossover frequency ω. n+1 Logarithmic processing is performed, and a linear fitting function is used to characterize the logarithm of the cross frequency and the lift-off distance l. n+1 Relationship;

[0070] The electrical conductivity σ of the metal sheet was changed to 18 MS / m, 38 MS / m, and 58 MS / m, respectively, and l was calculated at different lift-off distances based on the analytical theoretical model. n+1 Cross frequency ω n+1 Then, regarding the cross frequency ω n+1 Perform logarithmic processing to calculate the logarithm of the cross frequency and the lift-off distance l. n+1 The slope of the linear fitting function was found to remain unchanged with variations in conductivity σ. Figure 3 As shown;

[0071] The thickness 'd' of the metal sheet is varied, ranging from 1 mm to 5 mm in 1 mm increments. Then, the lift-off distance 'l' is calculated using an analytical theoretical model at different lift-off distances. n+1 Cross frequency ω n+1 For cross frequency ω n+1 Perform logarithmic processing to calculate the logarithm of the cross frequency and the lift-off distance l.n+1 The slope of the linear fitting function was calculated, and it was found that the fitting slope changes with the thickness d.

[0072] S6. The plate thickness measurement result is obtained based on the relationship between the fitting slope and the plate thickness.

[0073] Specifically, the slope k1 of the fitted line corresponding to different thicknesses of the sheet is measured. Linear fitting is still used to characterize the relationship between thickness d and the slope k1, as follows: Figure 4 As shown;

[0074] k1=k2d+b2 (7)

[0075] Furthermore, in one embodiment of the present invention, the slope k1 of the fitted line corresponding to different thicknesses of the sheet metal is measured, and linear fitting is used to characterize the relationship between thickness d and the slope k1. The key feature is that the fitted slope k1 for different thicknesses is calculated, and it monotonically decreases with increasing thickness; therefore, the sheet metal thickness information can be uniquely determined through the fitted slope k1. A linear fitting function is used to describe the relationship between thickness d and the slope k1, and the correlation coefficient of the fitting can reach 0.999.

[0076] When the coil probe is positioned above the j-th metal plate to be tested, the crossover frequency of the mutual inductance signal at different lift-off distances is extracted. The linear equation log(ω) is then used. n+1 )=k j l n+1 +b j Describe the relationship between lift-off distance, crossover frequency, and logarithm. Indicate the relationship between slope k. j Substituting into formula (8), the thickness of the j-th metal plate to be measured can be obtained:

[0077]

[0078] According to the electromagnetic eddy current-based metal sheet thickness measurement method of this invention, extensive calculations have revealed that the slope of the fitted straight line is independent of conductivity. Therefore, no additional calibration of the sheet's electromagnetic properties is required; the slope of the fitted straight line is determined solely by the sheet's thickness, enabling effective sheet thickness measurement. Furthermore, by utilizing measurement results at different lift-off distances, the influence of metal electromagnetic properties on thickness is eliminated, theoretically improving the accuracy of metal sheet thickness measurement.

[0079] To achieve the above embodiments, such as Figure 5 As shown, this embodiment also provides a metal sheet thickness measurement system 10 based on electromagnetic eddy currents, including:

[0080] Sensor design module 100 is used to build an eddy current detection system and design a coaxial excitation-receiver cylindrical eddy current sensor.

[0081] Eddy current detection module 200 is used to establish an analytical theoretical model of eddy current based on the structure of the sensor and to perform eddy current detection on metal sheets;

[0082] The frequency point extraction module 300 is used to acquire the mutual inductance sweep frequency signal of the plate coil based on the adjusted coil lift-off distance, and extract the frequency points where the real part and imaginary part of the mutual inductance sweep frequency signal are equal and record them as cross frequencies.

[0083] The different cross frequency calculation module 400 is used to obtain different cross frequencies at different lift-off distances when it is determined that the required number of coil lift-off distance adjustments has been reached.

[0084] The fitting slope calculation module 500 is used to obtain the fitting slope by utilizing the relationship between the logarithm of different cross frequencies and the lift-off distance of linear fitting.

[0085] The plate thickness measurement module 600 is used to obtain the plate thickness measurement result based on the relationship between the fitted slope and the plate thickness.

[0086] Furthermore, an analytical theoretical model of eddy currents is established based on the sensor's structure, including:

[0087]

[0088] In the formula

[0089]

[0090] Where σ is the conductivity, d is the thickness of the metal plate, K is the sensor coefficient, and φ(α) is related to the electromagnetic properties and thickness of the metal component, determining the phase of the eddy current response signal.

[0091] Furthermore, the slope of the fit is determined by the thickness of the plate:

[0092] log(ω n+1 )=k1l n+1 +b1 (6)

[0093] Where k1 is the fitting slope, l n+1 For different lift-off distances.

[0094] Furthermore, linear fitting is used to characterize the relationship between the thickness of the plate and the fitting slope k1:

[0095] k1=k2d+b2 (7).

[0096] Furthermore, when the coil probe is located above the j-th metal plate to be tested, the cross frequency of the mutual inductance signal under different lift-off distances is extracted. Equation (6) is used to describe the relationship between the lift-off distance, the cross frequency, and the logarithm. The slope k is then... j Substituting into equation (7), we obtain the thickness of the j-th metal plate to be measured:

[0097]

[0098] According to an embodiment of the present invention, the metal sheet thickness measurement system based on electromagnetic eddy currents, through extensive calculations, has found that the slope of the fitted straight line is independent of the conductivity. Therefore, no additional calibration of the electromagnetic properties of the sheet is required; the slope of the fitted straight line is determined solely by the sheet thickness, enabling effective sheet thickness measurement. Furthermore, by utilizing measurement results at different lift-off distances, the influence of the metal's electromagnetic properties on thickness is eliminated, theoretically improving the accuracy of metal sheet thickness measurement.

[0099] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0100] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A method for measuring the thickness of metal plates based on electromagnetic eddy currents, characterized in that, include: An eddy current detection system was built, and a coaxial cylindrical eddy current sensor with one excitation and one reception was designed. An analytical theoretical model of eddy currents was established based on the sensor structure, and eddy current detection was performed on the metal sheet. The mutual inductance sweep frequency signal of the plate coil is acquired based on the adjusted coil lift-off distance, and the frequency points where the real and imaginary parts of the mutual inductance sweep frequency signal are equal are extracted and recorded as the crossover frequency. When the required number of coil lift-off distance adjustments is reached, different crossover frequencies are obtained at different lift-off distances; The fitting slope is obtained by using a linear fit to the relationship between the logarithm of different cross frequencies and the lift-off distance; The plate thickness measurement results are obtained based on the relationship between the fitting slope and the plate thickness.

2. The method according to claim 1, characterized in that, An analytical theoretical model of eddy currents is established based on the sensor structure, including: In the formula Where σ is the conductivity, d is the thickness of the metal plate, K is the sensor coefficient, and φ(α) is related to the electromagnetic properties and thickness of the metal component, determining the phase of the eddy current response signal.

3. The method according to claim 1, characterized in that, The fitting slope is determined by the thickness of the plate: log(ω n+1 )=k1l n+1 +b1(6) Where k1 is the fitting slope, l n+1 For different lift-off distances.

4. The method according to claim 1, characterized in that, The relationship between the thickness of the plate and the fitting slope k1 is characterized by linear fitting: k1=k2d+b2(7).

5. The method according to claim 1, characterized in that, When the coil probe is located above the j-th metal plate to be tested, the cross frequency of the mutual inductance signal under different lift-off distances is extracted. Equation (6) is used to describe the relationship between the lift-off distance, the cross frequency, and the logarithm. The slope k is then... j Substituting into equation (7), we obtain the thickness of the j-th metal plate to be measured:

6. A metal sheet thickness measurement system based on electromagnetic eddy currents, characterized in that, include: The sensor design module is used to build an eddy current detection system and design a coaxial excitation-receiver cylindrical eddy current sensor. The eddy current detection module is used to establish an analytical theoretical model of eddy currents based on the structure of the sensor and to perform eddy current detection on metal sheets. The frequency point extraction module is used to acquire the mutual inductance sweep frequency signal of the plate coil based on the adjusted coil lift-off distance, and extract the frequency points where the real part and imaginary part of the mutual inductance sweep frequency signal are equal and record them as cross frequencies. The different cross frequency calculation module is used to obtain different cross frequencies at different lift-off distances when it is determined that the required number of coil lift-off distance adjustments has been reached. The fitting slope calculation module is used to obtain the fitting slope by utilizing the relationship between the logarithm of different cross frequencies and the lift-off distance of the linear fitting. The plate thickness measurement module is used to obtain the plate thickness measurement result based on the relationship between the fitted slope and the plate thickness.

7. The system according to claim 6, characterized in that, An analytical theoretical model of eddy currents is established based on the sensor structure, including: In the formula Where σ is the conductivity, d is the thickness of the metal plate, K is the sensor coefficient, and φ(α) is related to the electromagnetic properties and thickness of the metal component, determining the phase of the eddy current response signal.

8. The system according to claim 6, characterized in that, The fitting slope is determined by the thickness of the plate: log(ω n+1 )=k1l n+1 +b1(6) Where k1 is the fitting slope, l n+1 For different lift-off distances.

9. The system according to claim 6, characterized in that, The relationship between the thickness of the plate and the fitting slope k1 is characterized by linear fitting: k1=k2d+b2(7).

10. The system according to claim 6, characterized in that, When the coil probe is located above the j-th metal plate to be tested, the cross frequency of the mutual inductance signal under different lift-off distances is extracted. Equation (6) is used to describe the relationship between the lift-off distance, the cross frequency, and the logarithm. The slope k is then... j Substituting into equation (7), we obtain the thickness of the j-th metal plate to be measured:

Images