An electromagnetically coupled three-coil differential metal layer thickness measuring device and its manufacturing method

Abstract

This invention provides an electromagnetically coupled three-coil differential metal layer thickness measurement device and its manufacturing method. The device includes: a three-coil differential metal layer thickness sensor, a signal processor, and an AC signal generator. The sensor includes a filter capacitor, an excitation coil, and a detection coil. The filter capacitor is connected in parallel to the detection coil, and the excitation coil is tightly fitted below the detection coil. The detection coil includes two planar coils connected in series. The signal processor includes a lock-in amplifier and an operational amplifier. The lock-in amplifier has two signal channels for removing noise similar to the excitation signal from the picked-up signal. The operational amplifier amplifies the DC signal. The AC signal generator generates two identical AC signals; one signal is connected to the excitation coil, and the other signal, along with the detection coil, is connected to the lock-in amplifier. This invention has high sensitivity and detection speed, can evaluate various material properties, and is suitable for measuring the thickness of metallic materials.

Description

Technical Field

[0001] This invention relates to the fields of non-destructive thickness measurement and sensor technology, and more particularly to an electromagnetically coupled three-coil differential metal layer thickness measurement device and its manufacturing method. Background Technology

[0002] In the field of machinery manufacturing, the walls of various equipment and components gradually thin due to corrosion and friction during use. Regularly measuring the wall thickness of equipment is an effective means to monitor its status in real time, ensure its healthy operation, and reduce the risk of failure.

[0003] Eddy current testing offers advantages such as not damaging or altering the material surface, high sensitivity, fast detection speed, and the ability to assess various material properties, making it particularly suitable for measuring the thickness of metallic materials. In many industrial scenarios, thickness measurement inside metal machinery is mandatory, and regular thickness measurements help monitor the wear condition of equipment components. Furthermore, it plays a crucial role in ensuring the safe and efficient operation of equipment in production. In recent years, most metal layer thickness measurements have relied on the principle that metals of different thicknesses have different impedance values ​​at different frequencies, using frequency sweeping to differentiate metal thicknesses; however, the overall experiment is complex.

[0004] Current research on metal thickness measurement in lithium battery equalization technology faces the following issues:

[0005] While sweep frequency testing can ignore some lift-off effects, it is time-consuming. Measuring metal thickness using a single frequency can only measure one of the two metals: ferromagnetic or non-ferromagnetic. Furthermore, most of the analyzed features need to be extracted from the raw data. Algorithms that extract features from the raw data to distinguish metals of different thicknesses often require a large amount of data and complex post-processing. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an electromagnetically coupled three-coil differential metal layer thickness measurement device and its manufacturing method. This invention proposes an electromagnetically coupled three-coil differential metal layer thickness sensor capable of distinguishing between ferromagnetic and non-ferromagnetic metals such as iron, stainless steel, and aluminum under a single AC excitation frequency. Furthermore, it can extract one or more thickness-related features of different metals that are minimally affected by the lift-off distance from the raw data at different lift-off distances.

[0007] The technical means employed in this invention are as follows:

[0008] An electromagnetically coupled three-coil differential metal layer thickness measurement device includes: a three-coil differential metal layer thickness sensor, a signal processor, and an AC signal generator, wherein:

[0009] The three-coil differential metal layer thickness sensor includes a filter capacitor, an excitation coil, and a detection coil. The filter capacitor is connected in parallel to the detection coil, and the excitation coil is closely attached to the bottom of the detection coil. The detection coil includes two planar coils connected in series.

[0010] The signal processor includes a lock-in amplifier and an operational amplifier. The lock-in amplifier has two signal channels, and the two input signals have the same frequency and amplitude. It is used to remove noise similar to the excitation signal from the pickup signal and extract the response signal related to the excitation signal. The operational amplifier receives the DC signal output by the lock-in amplifier and is used to amplify the DC signal.

[0011] The AC signal generator is used to generate two AC signals with the same frequency, amplitude and phase. One AC signal is connected to the excitation coil, and the other AC signal is connected to the lock-in amplifier together with the detection coil. The lock-in amplifier compares, processes and amplifies the input signal, and then outputs a DC signal to the operational amplifier for secondary amplification.

[0012] Furthermore, the excitation coil is used to electromagnetically couple with the detection coil to acquire information from the three-coil differential metal layer thickness sensor and to transmit energy to the three-coil differential metal layer thickness sensor.

[0013] Furthermore, the two planar coils are connected in series and then in parallel with a filter capacitor to achieve the filtering and regulation functions in the circuit.

[0014] Furthermore, the excitation coil is made of enameled copper wire with a diameter of 70μm, and the coil has a single layer of 79 turns, an inner diameter of 1mm, and an outer diameter of 15mm.

[0015] Furthermore, both planar coils are made of enameled copper wire with a diameter of 70μm, and each coil has a single layer of 35 turns, an inner diameter of 1mm, and an outer diameter of 5mm.

[0016] Furthermore, both ends of the excitation coil and the detection coil are connected with leads, but there is no wire connection between the excitation coil and the detection coil. The leads are all located on one side of the three-coil differential metal layer thickness sensor.

[0017] Furthermore, the electromagnetically coupled three-coil differential metal layer thickness measurement device also includes a data acquisition card and a LabVIEW data acquisition unit. The data acquisition card is connected to an operational amplifier, and the LabVIEW data acquisition unit is connected to the data acquisition card. The data acquisition card is used to collect the signal after secondary amplification and input the collected signal to the LabVIEW data acquisition unit.

[0018] The present invention also provides a method for manufacturing the electromagnetically coupled three-coil differential metal layer thickness measuring device, comprising:

[0019] S1. Place the large-diameter coil in the lower layer as the excitation coil; place two small-diameter coils in the upper layer of the large-diameter coil as detection coils, and there is no wire connection between the excitation coil and the detection coil.

[0020] S2. Clean and inspect the excitation coil to ensure it meets the requirements. Select an acrylic plate of appropriate size to elevate the excitation coil, ensure it is tightly attached to the acrylic plate, and fix it in the center of the glass slide to achieve the best measurement results.

[0021] S3. Clean and inspect the detection coil to ensure that it meets the requirements. Fix the filter capacitor on the glass slide. Place the two detection coils horizontally opposite each other so that the detection coils are in close contact with the excitation coil. Connect one end of the two detection coils and connect the other end in parallel with the filter capacitor and weld them firmly.

[0022] S4. Use an AC signal generator to generate two AC signals with identical frequency, amplitude, and phase. One signal is input to the excitation coil, and the other signal is connected to the two signal channels of the lock-in amplifier along with the detection coil. The lock-in amplifier processes and amplifies these two signals, then outputs a stable DC signal to the operational amplifier, which is then amplified twice before being sent to the data acquisition card for data collection.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The present invention provides an electromagnetically coupled three-coil differential metal layer thickness measuring device, which can distinguish between ferromagnetic and non-ferromagnetic metals such as iron, stainless steel, and aluminum under a single AC excitation frequency.

[0025] 2. The present invention provides an electromagnetically coupled three-coil differential metal layer thickness measuring device, which can extract one or more thickness-related features of different metals with minimal impact from the lift-off distance using raw data at different lift-off distances.

[0026] 3. The electromagnetically coupled three-coil differential metal layer thickness measuring device provided by the present invention has high sensitivity and detection speed, can evaluate a variety of material properties, and is particularly suitable for measuring the thickness of metal materials.

[0027] 4. The electromagnetic coupling three-coil differential metal layer thickness measuring device provided by the present invention adopts a three-coil structure. The two pickup coils are wound in opposite ways, so that the signals generated by the coils cancel each other out. The initial value of the superimposed signal is 0, which increases its relative change value.

[0028] Based on the above reasons, this invention can be widely applied in fields such as sensors. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the electromagnetic coupling three-coil differential metal layer thickness measurement device of the present invention.

[0031] Figure 2 This is a schematic diagram of the electromagnetic coupling three-coil differential metal layer thickness measurement device of the present invention.

[0032] Figure 3 This is a structural diagram of the three-coil differential metal layer thickness sensor of the present invention.

[0033] Figure 4 This is a structural diagram of the signal processor of the present invention.

[0034] Figure 5 The amplitude diagram of the detection signal of different metal samples of the electromagnetically coupled three-coil differential metal layer thickness measuring device provided in the embodiment of the present invention.

[0035] Figure 6 The internal magnetic flux mode density of the coil in the electromagnetically coupled three-coil differential metal layer thickness measuring device provided in this embodiment of the invention.

[0036] Figure 7 This is a simulation diagram of the coil signals of the electromagnetically coupled three-coil differential metal layer thickness measuring device provided in an embodiment of the present invention.

[0037] Figure 8 This is a simplified schematic diagram of the electromagnetic coupling three-coil differential metal layer thickness measurement device detection system provided in an embodiment of the present invention.

[0038] Figure 9 The image shows the detection results of the electromagnetically coupled three-coil differential metal layer thickness measuring device provided in this embodiment of the invention at a 1mm lift-off distance for different stainless steel plate samples.

[0039] Figure 10 The image shows the detection results of the electromagnetically coupled three-coil differential metal layer thickness measuring device provided in this embodiment of the invention at different iron plate sample lift-off distances of 1 mm.

[0040] Figure 11The image shows the detection results of the electromagnetically coupled three-coil differential metal layer thickness measuring device provided in this embodiment of the invention at different aluminum plate sample lift-off distances of 1 mm.

[0041] In the figure: 1. Three-coil differential metal layer thickness sensor; 2. Signal processing circuit; 3. AC signal generator (RIGOL DG812 10MHZ dual channel); 4. Filter capacitor; 5. Excitation coil; 6. Detection coil; 7. Lock-in amplifier; 8. Operational amplifier; 9. Data acquisition card (DAQ) (NI USB_6211, National Instruments, USA); 10. LabVIEW data acquisition unit; 11. Test sample support platform; 12. Dual-axis linear synchronous belt sliding test bench. Detailed Implementation

[0042] 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.

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0045] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0046] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0047] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0048] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0049] like Figure 1As shown, the present invention provides an electromagnetically coupled three-coil differential metal layer thickness measurement device, comprising: a three-coil differential metal layer thickness sensor 1, a signal processor 2, and an AC signal generator 3, wherein:

[0050] The three-coil differential metal layer thickness sensor 1 includes a filter capacitor 4, an excitation coil 5, and a detection coil 6. The filter capacitor 4 is connected in parallel to the detection coil 6, and the excitation coil 5 is tightly fitted below the detection coil 6. The detection coil 6 includes two planar coils connected in series. Figure 2 , 3 As shown, the two planar coils are connected in series and then in parallel with the filter capacitor 4 to achieve specific filtering and adjustment functions in the circuit.

[0051] The signal processor 2 includes a lock-in amplifier 7 and an operational amplifier 8. The lock-in amplifier 7 has two signal channels, and the two input signals have the same frequency and amplitude. It is used to remove noise similar to the excitation signal from the picked-up signal and extract the response signal related to the excitation signal. The operational amplifier 8 receives the DC signal output by the lock-in amplifier 7 and uses it to amplify the DC signal to meet the input requirements of the subsequent data acquisition system, ensure signal strength and accuracy, and enable effective data acquisition and detailed signal analysis.

[0052] The AC signal generator 3 is used to generate two AC signals with the same frequency, amplitude, and phase, such as... Figure 4 As shown, one AC signal is connected to the excitation coil 5, and another AC signal is connected to the lock-in amplifier 7 together with the detection coil 6. The lock-in amplifier 7 compares, processes and amplifies the input signal, and then outputs a DC signal to the operational amplifier 8 for secondary amplification.

[0053] In a specific implementation, as a preferred embodiment of the present invention, the excitation coil 5 is used to electromagnetically couple with the detection coil 6 to obtain information from the three-coil differential metal layer thickness sensor 1 and to transmit energy to the three-coil differential metal layer thickness sensor 1.

[0054] In a specific implementation, as a preferred embodiment of the present invention, the excitation coil 5 is made of enameled copper wire with a diameter of 70μm, and the coil has a single layer of 79 turns, an inner diameter of 1mm, and an outer diameter of 15mm.

[0055] In a specific implementation, as a preferred embodiment of the present invention, both planar coils are wound with enameled copper wire with a diameter of 70μm. The coils are all single-layered with 35 turns, and the inner diameter is 1mm and the outer diameter is 5mm.

[0056] In a specific implementation, as a preferred embodiment of the present invention, both ends of the excitation coil 5 and the detection coil 6 are connected with leads, but there is no wire connection between the excitation coil 5 and the detection coil 6. The leads are all located on one side of the three-coil differential metal layer thickness sensor 1.

[0057] In a preferred embodiment of the present invention, the electromagnetically coupled three-coil differential metal layer thickness measurement device further includes a data acquisition card 9 and a LabVIEW data acquisition unit 10. The data acquisition card 9 is connected to the operational amplifier 8, and the LabVIEW data acquisition unit 10 is connected to the data acquisition card 9. The data acquisition card 9 is used to collect the signal after secondary amplification and input the collected signal to the LabVIEW data acquisition unit 10. In this embodiment, the LabVIEW data acquisition unit 10 is software for data acquisition and instrument control, capable of controlling the application of excitation to the coil and simultaneously acquiring its signal changes. The entire process from signal generation by the AC signal generator to the final signal being written from the data acquisition card 9 (DAQ) is connected via an RF radio frequency line, thus minimizing signal interference and eliminating the need for filtering.

[0058] The present invention also provides a method for manufacturing the electromagnetically coupled three-coil differential metal layer thickness measuring device, comprising:

[0059] S1. The large-diameter coil is placed on the lower layer as the excitation coil 5; two small-diameter coils are placed on the upper layer of the large-diameter coil as the detection coils 6, and there is no wire connection between the excitation coil 5 and the detection coils 6.

[0060] S2. Clean and inspect the excitation coil 5 to ensure that the excitation coil 5 meets the requirements. Select an acrylic plate of appropriate size to elevate the excitation coil 5, fit the excitation coil 5 tightly against the acrylic plate, and fix it at the center of the glass slide to achieve the best measurement effect.

[0061] S3. Clean and inspect the detection coil 6 to ensure that the detection coil 6 meets the requirements. Fix the filter capacitor 4 on the glass slide. Place the two detection coils 6 horizontally opposite each other so that the detection coil 6 is in close contact with the excitation coil 5. Connect one end of the two detection coils 6 and connect the other end in parallel with the filter capacitor 4 and weld them firmly.

[0062] S4. Two AC signals with identical frequency, amplitude, and phase are generated using AC signal generator 3. One signal is input to excitation coil 5, and the other signal and detection coil 6 are respectively connected to the two signal channels of lock-in amplifier 7. After processing and amplifying the two signals, lock-in amplifier 7 outputs a stable DC signal to operational amplifier 8, which is then amplified twice and sent to data acquisition card 9 for data collection.

[0063] Example 1

[0064] like Figure 5 The diagram shows the amplitude of detection signals for different metal samples obtained using the electromagnetically coupled three-coil differential metal layer thickness measuring device of this invention. When the sample first approaches the sensor, the iron sample and the aluminum sample are ferromagnetic and non-ferromagnetic materials, respectively, and therefore their induced voltages change in opposite directions. When the sample has completely passed the first pickup coil, the induced voltages of the aluminum and iron samples reach their peak and trough values, respectively. When the sensor is fully close to the sample, the influence of the secondary magnetic field disturbance on the aluminum sample gradually stabilizes, the magnetic flux density remains essentially unchanged, and the induced electromotive force returns to its level before approaching the sample. For the iron sample, due to the gradual increase in the reverse disturbance of the secondary magnetic field during the approach to the sensor, the coupling between the primary magnetic field enhancement and the secondary magnetic field disturbance still exists, the magnetic flux density change continues, and the induced electromotive force differs from that before approaching the sample. The stainless steel sample has a lower permeability than the iron sample, therefore its primary magnetic field enhancement is less than that of the iron sample, and its conductivity is less than that of the aluminum sample, therefore its secondary magnetic field disturbance intensity is less than that of the aluminum sample. When the stainless steel sample first approaches the sensor, the rate of primary magnetic field enhancement is greater than the rate of secondary magnetic field disturbance, and the induced voltage begins to change. When the sensor has completely passed the first pickup coil, the induced electromotive force (EMF) reaches its trough. When the sensor is fully close to the sample, the rate of disturbance in the secondary magnetic field is greater than the rate of enhancement of the primary magnetic field, and the induced EMF curve reaches its peak. Subsequently, the disturbance in the secondary magnetic field tends to stabilize, and the curve declines. Because the coupling between the enhancement of the primary magnetic field and the disturbance in the secondary magnetic field still exists, the magnetic flux density continues to change. At this time, the induced EMF of the detection coil is different from that before it approached the sample, but it is less than the change in the iron sample.

[0065] Example 2

[0066] like Figure 6 The figure shows the internal magnetic flux mode density of the coil in the electromagnetic coupling three-coil differential metal layer thickness measuring device of the present invention. The sensor parameters are as follows: the excitation coil is a single-layer planar coil with 79 turns, with an outer diameter of 15 mm and an inner diameter of 1 mm; the two planar coils in the detection coil are both single-layer planar coils with 35 turns, with an outer diameter of 5 mm and an inner diameter of 1 mm.

[0067] Example 3

[0068] like Figure 7 The diagram shown is a simulation of the coil signals in the electromagnetically coupled three-coil differential metal layer thickness measurement device of this invention. When using a single coil, the initial value of any of the planar coils in the detection coil is not zero, resulting in a small relative change in the signal. Therefore, we use a three-coil structure with the two pickup coils wound in opposite ways, causing the signals generated by the coils to cancel each other out, and the initial value of the superimposed signal is zero. Because the order of the signals is different, the time of change of the superimposed signal is different, which in turn causes the superimposed signal to change, increasing its relative change value.

[0069] Example 4

[0070] like Figure 8 The diagram shown is a schematic of the electromagnetic coupling three-coil differential metal layer thickness measurement device of the present invention. The present invention tested aluminum, iron and stainless steel materials of different thicknesses. In order to ensure the stability of the sample properties, the same metal samples of different thicknesses were processed from the same piece of metal. The sample types, thicknesses and numbers are shown in the table below.

[0071]

[0072] Example 5

[0073] like Figure 9 The image shows the detection results of the electromagnetically coupled three-coil differential metal layer thickness measuring device of the present invention at different stainless steel plate samples with a 1mm lift-off distance. The stainless steel plate samples numbered 1-5 were tested at a 50kHz excitation frequency and a 1mm lift-off distance, and the results are as follows. Figure 9 As shown, the sensor generates a peak and a trough when it passes the steel plate sample. As the sensor approaches the sample, the absolute value of the induced voltage changes from the base value to the trough gradually increases. It is also evident that the thicker the stainless steel plate sample, the smaller the absolute value of the resulting change amplitude. Furthermore, it can be observed that stainless steel plate samples of different thicknesses reach the peak at different times; the thinner the stainless steel plate sample, the earlier it reaches the peak. These two signal characteristics allow for the measurement and differentiation of the thickness of the stainless steel plate sample.

[0074] Example 6

[0075] like Figure 10 The image shows the detection results of the electromagnetically coupled three-coil differential metal layer thickness measuring device of the present invention at different 1mm lift-off distances for iron plate samples. For iron plate samples 6-9, detection was performed at a 50kHz excitation frequency and a 1mm lift-off distance. The induced voltage signal of the iron plate sample showed only one trough during the complete entry of the sensor into the sample area. As the sensor approached the sample, the absolute value of the induced voltage change from the base value to the trough gradually increased. The thicker the iron plate sample, the smaller the absolute value of the change amplitude. The thickness of the iron plate sample can be measured and distinguished by the magnitude of the induced voltage change amplitude.

[0076] Example 7

[0077] like Figure 11The image shows the detection results of the electromagnetically coupled three-coil differential metal layer thickness measuring device of the present invention at different aluminum plate samples with a 1mm lift-off distance. Aluminum plate samples No. 10-15 were tested at a 50kHz excitation frequency and a 1mm lift-off distance. The aluminum plate sample showed only one peak as the sensor fully entered the sample area. As the sensor approached the sample, the absolute value of the induced voltage gradually increased from the base value to the peak. The thicker the aluminum plate sample, the smaller the absolute value of the change amplitude. Simultaneously, as the sensor approached the aluminum plate sample and the induced voltage value began to change, the curvature of this part of the curve gradually decreased with the increase of the aluminum plate sample thickness. These two signal characteristics are used to measure and distinguish the thickness of the aluminum plate sample.

[0078] In summary, the electromagnetically coupled three-coil differential metal layer thickness measurement device provided by this invention features a unique double-vortex coil structure, enabling multi-feature differentiation of iron, aluminum, and stainless steel, along with their thicknesses, at the same frequency. It maintains excellent differentiation performance even at a maximum lift-off distance of 9mm. This invention can differentiate between ferromagnetic and non-ferromagnetic metals such as iron, stainless steel, and aluminum at a single AC excitation frequency. Furthermore, it can extract one or more thickness-related features of different metals with minimal impact from lift-off distance using raw data at different lift-off distances. The sensor structure of this invention is simple, with clear signal characteristics and high detection sensitivity, making it significant for the selection of thickness differentiation features and the application of metal thickness measurement technology.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electromagnetically coupled three-coil differential metal layer thickness measuring device, characterized in that, include: The system comprises a three-coil differential metal layer thickness sensor (1), a signal processor (2), and an AC signal generator (3), wherein: The three-coil differential metal layer thickness sensor (1) includes a filter capacitor (4), an excitation coil (5), and a detection coil (6). The filter capacitor (4) is connected in parallel to the detection coil (6), and the excitation coil (5) is closely attached to the bottom of the detection coil (6). The detection coil (6) includes two planar coils connected in series. The signal processor (2) includes a lock-in amplifier (7) and an operational amplifier (8). The lock-in amplifier (7) has two signal channels, and the two input signals have the same frequency and amplitude. It is used to remove noise similar to the excitation signal in the pickup signal and extract the response signal related to the excitation signal. The operational amplifier (8) receives the DC signal output by the lock-in amplifier (7) and is used to amplify the DC signal. The AC signal generator (3) is used to generate two AC signals with the same frequency, amplitude and phase. One AC signal is connected to the excitation coil (5), and the other AC signal is connected to the lock-in amplifier (7) together with the detection coil (6). The lock-in amplifier (7) compares, processes and amplifies the input signal, and then outputs a DC signal to the operational amplifier (8) for secondary amplification.

2. The electromagnetically coupled three-coil differential metal layer thickness measuring device according to claim 1, characterized in that, The excitation coil (5) is used to electromagnetically couple with the detection coil (6) to obtain information from the three-coil differential metal layer thickness sensor (1) and transmit energy to the three-coil differential metal layer thickness sensor (1).

3. The electromagnetically coupled three-coil differential metal layer thickness measuring device according to claim 1, characterized in that, The two planar coils are connected in series and then connected in parallel with the filter capacitor (4) to realize the filtering and regulation functions in the circuit.

4. The electromagnetically coupled three-coil differential metal layer thickness measuring device according to claim 1, characterized in that, The excitation coil (5) is made of enameled copper wire with a diameter of 70μm. The coil has a single layer of 79 turns, an inner diameter of 1mm, and an outer diameter of 15mm.

5. The electromagnetically coupled three-coil differential metal layer thickness measuring device according to claim 3, characterized in that, Both planar coils are made of enameled copper wire with a diameter of 70μm. The coils are single-layered with 35 turns, with an inner diameter of 1mm and an outer diameter of 5mm.

6. The electromagnetically coupled three-coil differential metal layer thickness measuring device according to claim 1, characterized in that, Both ends of the excitation coil (5) and the detection coil (6) are connected with leads, but there is no wire connection between the excitation coil (5) and the detection coil (6). The leads are all located on one side of the three-coil differential metal layer thickness sensor (1).

7. The electromagnetically coupled three-coil differential metal layer thickness measuring device according to claim 1, characterized in that, The electromagnetically coupled three-coil differential metal layer thickness measurement device also includes a data acquisition card (9) and a LabVIEW data acquisition unit (10). The data acquisition card (9) is connected to the operational amplifier (8), and the LabVIEW data acquisition unit (10) is connected to the data acquisition card (9). The data acquisition card (9) is used to collect the signal after secondary amplification and input the collected signal to the LabVIEW data acquisition unit (10).

8. A method for manufacturing a differential metal layer thickness measuring device based on any one of claims 1-7, characterized in that, include: S1. Place the large-diameter coil in the lower layer as the excitation coil (5); Two small-diameter coils are placed on top of the large-diameter coil as detection coils (6), and there is no wire connection between the excitation coil (5) and the detection coil (6); S2. Clean and inspect the excitation coil (5) to ensure that the excitation coil (5) meets the requirements. Select an acrylic plate of appropriate size to raise the excitation coil (5), fit the excitation coil (5) tightly with the acrylic plate, and fix it at the center of the glass slide to achieve the best measurement effect. S3. Clean and inspect the detection coil (6) to ensure that the detection coil (6) meets the requirements. Fix the filter capacitor (4) on the glass slide. Place the two detection coils (6) horizontally opposite each other so that the detection coil (6) and the excitation coil (5) are closely attached. Connect one end of the two detection coils (6) and the other end in parallel with the filter capacitor (4) and weld them firmly. S4. Use an AC signal generator (3) to generate two AC signals with the same frequency, amplitude and phase. One signal is input to the excitation coil (5), and the other signal and the detection coil (6) are respectively connected to the two signal channels of the lock-in amplifier (7). The lock-in amplifier (7) processes and amplifies the two signals and outputs a stable DC signal to the operational amplifier (8), which is then amplified twice and sent to the data acquisition card (9) for data collection.

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