A dynamic compensation method for eddy current signals based on temperature adaptation

Abstract

The present invention provides a temperature-adaptive dynamic compensation method for eddy current signals, specifically comprising the following steps: obtaining a curve showing the conductivity and permeability of a test block as a function of temperature; scanning the surface of the test block using an eddy current sensor to determine the skin depth corresponding to the eddy current sensor at room temperature; using this skin depth as a constant skin depth, and based on the conductivity and permeability at the current temperature, calculating the optimal excitation frequency at the current temperature, and ensuring that the excitation coil of the eddy current sensor operates at the optimal excitation frequency; and dynamically adjusting the drive voltage applied to the excitation coil of the eddy current sensor using a PID control algorithm to compensate for the temperature-dependent impedance change of the excitation coil. The present invention provides a temperature-adaptive dynamic compensation method for eddy current signals, which achieves real-time dynamic compensation of eddy current signals in high-temperature environments by collaboratively adjusting the excitation frequency and drive voltage.

Description

Technical Field

[0001] The present invention relates to the technical field of eddy current displacement measurement, and in particular to a temperature-adaptive eddy current signal dynamic compensation method. Background Art

[0002] High-temperature alloy test blocks, commonly used in aerospace applications, are often used for high-temperature components such as aircraft engines, fuel chambers, and nozzles. These critical high-temperature components are crucial to the safe operation of the aircraft. However, in some cases, defect detection cannot be conducted until these high-temperature components have completely cooled down. Testing of these components at elevated temperatures is necessary. Traditional eddy current testing methods are easily affected by high temperatures, resulting in significantly reduced detection effectiveness or even missed detections.

[0003] Under high temperature conditions, the electrical conductivity and magnetic permeability of the test block material will change significantly, causing the eddy current detection signal to drift. Traditional eddy current detection compensation systems usually use a static compensation method, that is, calibration and compensation at a specific temperature, but this method is difficult to adapt to dynamic temperature fluctuations. Summary of the Invention

[0004] The purpose of the present invention is to improve and innovate the shortcomings and problems existing in the background technology and provide a temperature-adaptive eddy current signal dynamic compensation method.

[0005] A temperature-adaptive eddy current signal dynamic compensation method specifically comprises the following steps:

[0006] Obtain a curve showing how the conductivity and magnetic permeability of the test block change with temperature; scan the surface of the test block using an eddy current sensor to determine the skin depth corresponding to the eddy current sensor at room temperature; use this skin depth as a constant skin depth, and calculate the optimal excitation frequency at the current temperature based on the conductivity and magnetic permeability at the current temperature, and ensure that the excitation coil of the eddy current sensor operates at the optimal excitation frequency;

[0007] The PID control algorithm is used to dynamically adjust the driving voltage loaded on the excitation coil of the eddy current sensor to compensate for the change in the impedance of the excitation coil with temperature, ensuring that the magnetic field strength excited by the eddy current sensor remains stable at different temperatures.

[0008] A further solution is that, after ensuring that the magnetic field strength excited by the eddy current sensor remains stable at different temperatures, the method further includes:

[0009] Changing the ambient temperature of the test block under test, calibrating the defect voltage amplitude of the test block using an eddy current sensor, maintaining the relative position of the eddy current sensor and the test block under test unchanged during the calibration process, and generating a defect voltage amplitude gain mapping table at different temperatures, where the defect voltage amplitude is the voltage across the detection coil;

[0010] According to the defect voltage amplitude gain mapping table at different temperatures, the defect voltage amplitude adjusted by the programmable amplifier is calculated.

[0011] A further solution is that determining the skin depth corresponding to the eddy current sensor at room temperature; using the skin depth as a constant skin depth, and calculating the optimal excitation frequency at the current temperature based on the electrical conductivity and magnetic permeability at the current temperature specifically includes:

[0012] Set 25℃ as the initial room temperature, and find the conductivity and permeability at this temperature according to the curve of conductivity σ(T) and magnetic permeability u(T) changing with temperature, and use them as the initial conductivity σ0 and initial magnetic permeability u0, and calculate the initial skin depth with the detection excitation frequency ƒ0 at this temperature. 0:

[0013] ;

[0014] Get the initial skin depth 0, with the initial skin depth 0 as a constant skin depth, and according to the conductivity σ(T) and magnetic permeability u(T) at the current temperature, the optimal excitation frequency ƒ at the current temperature can be calculated:

[0015] .

[0016] A further solution is to use a PID control algorithm to dynamically adjust the driving voltage loaded on the excitation coil of the eddy current sensor to compensate for the change in the impedance of the excitation coil with temperature, thereby ensuring that the magnetic field strength excited by the eddy current sensor remains stable at different temperatures. Specifically, the method includes:

[0017] Obtain the relationship between impedance change and temperature;

[0018] Keep the driving voltage applied to the excitation coil of the eddy current sensor constant and obtain the current error after the impedance changes.

[0019] The PID control algorithm is used to dynamically adjust the driving voltage loaded on the excitation coil of the eddy current sensor according to the current error after the impedance changes to compensate for the impedance change with temperature;

[0020] Among them, the driving voltage loaded on the excitation coil of the eddy current sensor after the temperature changes is = + ;

[0021]

[0022] ;

[0023] I0=V0 / Z0;

[0024] ( );

[0025] in, is the proportionality coefficient, is the integration coefficient, is the differential coefficient, is the compensation voltage, V0 is the driving voltage at room temperature 25°C, Z0 is the excitation coil impedance at room temperature 25°C; ∆Z is the difference in excitation coil impedance at room temperature and high temperature, and ɑ is the impedance temperature variation coefficient; is the current error; I0 is the current of the excitation coil at room temperature of 25°C, T is the ambient temperature after the temperature change, Indicates normal ambient temperature.

[0026] A further solution is that the proportionality coefficient , integral coefficient and differential coefficients The acquisition process is as follows:

[0027] First, =0, =0, gradually increase Until the system oscillates with equal amplitude, the proportional coefficient recorded at this time is the critical gain The time difference between the two peaks of the waveform corresponding to the equal-amplitude oscillation is the oscillation period , and then calculate the integral coefficient according to the Ziegler-Nichols formula and differential coefficients .

[0028] A further solution is that the ambient temperature of the test block is changed, and the defect voltage amplitude of the test block is calibrated using an eddy current sensor. During the calibration process, the relative position of the eddy current sensor and the test block is kept unchanged. The defect voltage amplitude gain mapping table under different temperatures is generated specifically including:

[0029] Assume that the defect voltage amplitude magnification of the detection coil output is G, then the gain of the programmable gain amplifier PGA output at room temperature is G T0 for:

[0030]

[0031] Changing the ambient temperature of the test block to generate the defect voltage amplitude of the detection coil at different temperatures;

[0032] According to the defect voltage amplitude of the detection coil at different temperatures and the gain G output by the programmable gain amplifier at room temperature T0 , calculate the gain G of the programmable gain amplifier output at different temperatures T ;

[0033] The gain G of the programmable gain amplifier output at different temperatures T The calculation formula is as follows:

[0034] *V in0 = *V in ;

[0035] = *V in0 / V in ;

[0036] Where V in0 is the defect voltage amplitude output by the detection coil at room temperature, V in is the defect voltage amplitude output by the detection coil at different temperatures, is the gain of the programmable gain amplifier output at different temperatures.

[0037] A further solution is that the defect voltage amplitude after adjustment by the programmable amplifier The formula is as follows:

[0038] ;

[0039] Where, is the defect voltage amplitude output by the detection coil, is the defect voltage amplitude after adjustment by the programmable amplifier.

[0040] A further solution is that the use of the eddy current sensor to scan the surface of the test block to be inspected specifically includes: the axis of the eddy current sensor is scanned perpendicular to the surface of the test block to be inspected; during the scanning process, the distance between the eddy current sensor probe and the surface of the test block to be inspected remains unchanged, and the scanning is performed in a straight line with the position corresponding to the defect center as the center.

[0041] A further solution is that obtaining the curves of the conductivity and magnetic permeability of the test block under test as a function of temperature specifically includes:

[0042] Using JMatpro material simulation software, the content ratio of each element in the test block material is input into the software to obtain the curve of the conductivity and magnetic permeability of the test block as a function of temperature.

[0043] Compared with the existing technology, the present invention has the following advantages: It provides a temperature-adaptive dynamic compensation method for eddy current signals. This method achieves real-time dynamic compensation of eddy current signals in high-temperature environments through the coordinated adjustment of multiple parameters (excitation frequency, drive voltage, and signal gain). Specifically, the excitation frequency is dynamically adjusted based on real-time temperature changes to compensate for skin effect offsets caused by changes in conductivity. The drive voltage is regulated using a PID control algorithm to offset the increase in coil impedance caused by high temperatures. Simultaneously, the signal gain of the defect amplitude voltage output by the detection coil is adjusted in real time based on a defect voltage amplitude gain mapping table to ensure that the adjusted defect voltage amplitude remains stable at different temperatures. This method simplifies the circuit structure, avoids the complexity and noise issues associated with the stacking of multiple modules in traditional technologies, and significantly improves the system's reliability and detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0045] Figure 1 1 is a flow chart of a method for dynamic compensation of eddy current signals based on temperature adaptation provided by an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the structure of an eddy current sensor probe provided by an embodiment of the present invention for scanning defects;

[0047] Figure 3 Schematic diagram of curves showing defect voltage amplitudes at both ends of the detection coil at various temperatures obtained after excitation optimization and drive voltage compensation according to an embodiment of the present invention;

[0048] Figure 4 This is a schematic diagram of a curve obtained by amplifying the defect voltage amplitudes at both ends of the detection coil at various temperatures without any compensation provided by an embodiment of the present invention;

[0049] Figure 5 Schematic diagram of a curve showing the defect voltage amplitude at both ends of the detection coil at various temperatures obtained after excitation optimization, drive voltage, and gain compensation according to an embodiment of the present invention;

[0050] Figure 6 This is the circuit diagram of the eddy current sensor probe. DETAILED DESCRIPTION

[0051] In order to make the objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0053] See also Figure 1 The present invention provides a method for dynamic compensation of eddy current signals based on temperature adaptation, which specifically includes the following steps:

[0054] Step S1, obtaining a curve of the conductivity and magnetic permeability of the test block under test versus temperature; scanning the surface of the test block under test using an eddy current sensor to determine the skin depth corresponding to the eddy current sensor at room temperature; using the skin depth as a constant skin depth, and based on the conductivity and magnetic permeability at the current temperature, calculating the optimal excitation frequency at the current temperature, and making the excitation coil of the eddy current sensor operate at the optimal excitation frequency;

[0055] In this embodiment, when an eddy current sensor is used to scan the surface of the test block to be inspected, there is a defect on the test block to be inspected, and the axis of the eddy current sensor probe is scanned perpendicular to the surface of the test block to be inspected; during the scanning process, the distance between the eddy current sensor probe and the surface of the test block to be inspected remains unchanged, and the scanning is performed in a straight line with the position corresponding to the center of the defect as the center. At the same time, the temperature sensor is used to detect the real-time temperature of the environment in which the eddy current sensor is located.

[0056] like Figure 6 As shown, a high-frequency driving voltage is loaded on the excitation coil of the eddy current sensor. Under the excitation of the high-frequency driving voltage, the excitation coil of the eddy current sensor generates a high-frequency magnetic field around the excitation coil, and eddy currents are formed inside the test block under inspection near the excitation coil. Since the eddy current sensor probe is scanned in a straight line with the position corresponding to the defect center as the center, when the eddy current sensor probe moves to a position relative to the defect center, the alternating magnetic field generated by the eddy current of the test block under inspection will also change. The alternating magnetic field generated by the eddy current in the test block under inspection causes parameters such as the equivalent impedance in the detection coil to change, causing the detection coil to output different voltage signal defect amplitudes, thereby allowing the existence, position, approximate size and other information of the defect on the test block under inspection to be judged based on the voltage signal defect amplitude.

[0057] However, in high-temperature environments, the impedance of the excitation coil corresponding to the eddy-current sensor increases with rising temperature, weakening the intensity of the high-frequency magnetic field generated, which in turn causes the signal detected by the detection coil to attenuate. When the eddy-current sensor probe detects the same defect, the eddy-current signal generated will be inconsistent, even if the relative position of the eddy-current sensor probe and the defect remains the same. Furthermore, in high-temperature environments, the increased resistivity of the material corresponding to the excitation coil reduces the sensitivity and signal-to-noise ratio of the excitation coil. Therefore, it is necessary to address the problem of drift in the defect amplitude of the voltage signal output by the detection coil due to high temperature.

[0058] Specifically, you can first select an alloy test block of suitable material, use JMatpro material simulation software, input the proportion of each element in the test block material into the software, and then you can obtain the temperature change curve of the conductivity σ(T) and magnetic permeability u(T) of the test block and pre-store it in the database.

[0059] Set 25℃ as the initial room temperature, and find the conductivity and permeability at this temperature according to the curve of conductivity σ(T) and magnetic permeability u(T) changing with temperature, and use them as the initial conductivity σ0 and initial magnetic permeability u0, and calculate the initial skin depth with the detection excitation frequency ƒ0 at this temperature. 0:

[0060] ;

[0061] Get the initial skin depth 0, with the initial skin depth 0 as a constant skin depth, and according to the conductivity σ(T) and magnetic permeability u(T) at the current temperature, the optimal excitation frequency ƒ at the current temperature can be calculated:

[0062] ;

[0063] Finally, the output excitation frequency is dynamically adjusted through the DDS (direct digital synthesis) signal generator to ensure the skin depth 0 is kept constant to avoid distortion of the detection signal.

[0064] It should be noted that in this embodiment, maintaining a constant skin depth during eddy current testing means that the eddy currents can stably penetrate the material to a specific depth range. This ensures that the eddy currents interact with defects within this depth range in a relatively stable manner. The eddy current change signals received by the testing instrument due to the defects are consistent and reliable, enabling more accurate determination of information such as the presence, location, and approximate size of the defects.

[0065] Step S2: Using a PID control algorithm, dynamically adjust the driving voltage applied to the excitation coil of the eddy current sensor to compensate for the change in the impedance of the excitation coil with temperature, thereby ensuring that the magnetic field strength excited by the eddy current sensor remains stable at different temperatures;

[0066] Wherein, step S2 specifically includes the following steps:

[0067] Step S21, obtaining the relationship between impedance change and temperature;

[0068] Assuming the difference between the excitation coil impedance at room temperature (25°C) and the coil impedance at high temperature is ∆Z, and ɑ is the impedance temperature variation coefficient, the relationship between impedance change and temperature can be obtained:

[0069] ( );

[0070] Where T represents high temperature, Indicates normal temperature;

[0071] Step S22: maintaining the driving voltage applied to the excitation coil of the eddy current sensor unchanged, and obtaining the current error after the impedance changes;

[0072] Assuming the driving voltage at room temperature of 25℃ is V0 and the coil impedance is Z0, the room temperature current I0=V0 / Z0 can be obtained;

[0073] Keep the driving voltage V0 unchanged, then the high temperature current is Iz= ;

[0074] The current error is .

[0075] Step S23: Using a PID control algorithm, dynamically adjust the driving voltage applied to the excitation coil of the eddy current sensor according to the current error after the impedance changes, so as to compensate for the impedance change with temperature.

[0076] The control formula is as follows:

[0077] ;

[0078]

[0079] in is the proportional coefficient, which determines the response speed of the controller to the current error; is the integral coefficient, used to eliminate steady-state error; is the differential coefficient, which is used to predict future error changes and reduce the overshoot of the system. is the compensation voltage; the driving voltage loaded on the excitation coil of the eddy current sensor at high temperature is = + .

[0080] It should be noted that the proportionality coefficient , integral coefficient and differential coefficients The acquisition process is as follows:

[0081] First, turn off the effects of integration and differentiation, and let =0, =0, gradually increase Until the system oscillates with equal amplitude, the proportional coefficient recorded at this time is the critical gain The time difference between the two peaks of the waveform corresponding to the equal-amplitude oscillation is the oscillation period , and then calculate the integral coefficient according to the Ziegler-Nichols formula and differential coefficients :

[0082] In this embodiment, ; ; .

[0083] Step S3: Changing the ambient temperature of the same test block, calibrating the defect voltage amplitude of the test block using an eddy current sensor, maintaining the relative position of the eddy current sensor and the test block unchanged during the calibration process, and generating a defect voltage amplitude gain mapping table at different temperatures, where the defect voltage amplitude is the voltage across the detection coil;

[0084] It is understandable that after the above-mentioned frequency optimization and drive voltage compensation, the signal-to-noise ratio generated by the detection coil at high temperature is basically consistent with the signal-to-noise ratio at normal temperature, that is, the ratio between the defect voltage amplitude output by the detection coil when the eddy current sensor corresponds to the defect center and the defect voltage amplitude output by the detection coil when the eddy current sensor corresponds to the defect-free area is consistent at high temperature and normal temperature. However, when the relative position of the eddy current sensor and the test block under inspection remains unchanged, the defect voltage amplitude output by the detection coil is still inconsistent with the defect voltage amplitude at normal temperature; therefore, it is necessary to correct the voltage amplitude detected at the same defect location at different temperatures based on the voltage amplitude detected at the same defect location at normal temperature to avoid different voltage amplitudes when detecting the same defect location at different temperatures. The specific process is as follows:

[0085] Step S31: Assume that the defect voltage amplitude magnification of the detection coil output is G, then the gain of the programmable gain amplifier (PGA) output at room temperature is G T0 for:

[0086]

[0087] Step S32: changing the ambient temperature of the test block to generate defect voltage amplitudes of the detection coil at different temperatures;

[0088] Step S33: According to the defect voltage amplitude of the detection coil at different temperatures and the gain G output by the programmable gain amplifier (PGA) at room temperature, T0 , calculate the gain G of the programmable gain amplifier (PGA) output at different temperatures T ;

[0089] Specifically, since the defect voltage amplitude output by the detection coil at the same defect position at different temperatures after correction is consistent, the following formula is obtained:

[0090] *V in0 = *V in ;

[0091] = *V in0 / V in ;

[0092] Where V in0 is the defect voltage amplitude output by the detection coil at room temperature, V in is the defect voltage amplitude output by the detection coil at different temperatures, is the gain of the programmable gain amplifier (PGA) output at different temperatures.

[0093] It should be noted that by changing the ambient temperature of the test block under test, the defect voltage amplitude of the detection coil at different temperatures is generated. Since it is impossible to program any ambient temperature, it is impossible to obtain the defect voltage amplitude of the detection coil at any temperature. As shown in Table 1, in this embodiment, the gains of the programmable gain amplifier (PGA) output corresponding to ambient temperatures of 25°C, 70°C, 115°C, 160°C, and 205°C are obtained. In order to obtain the gains of the programmable gain amplifier (PGA) output at other ambient temperatures, the gains at other ambient temperatures can be obtained by interpolation using the data in Table 1.

[0094] Step S4: Calculate the defect voltage amplitude adjusted by the programmable amplifier according to the defect voltage amplitude gain mapping table at different temperatures;

[0095] Specifically, the defect voltage amplitude after adjustment by the programmable amplifier The formula is as follows:

[0096] ;

[0097] Where, is the defect voltage amplitude output by the detection coil, that is Figure 6 The voltage between nodes 2 and 4, is the output voltage signal adjusted by the programmable amplifier, that is, the defect voltage amplitude adjusted by the programmable amplifier.

[0098] In summary, the present invention provides a temperature-adaptive dynamic compensation method for eddy current signals, which achieves real-time dynamic compensation of eddy current signals in high-temperature environments through the coordinated adjustment of multiple parameters (excitation frequency, drive voltage, and signal gain). Specifically, the excitation frequency is dynamically adjusted according to real-time temperature changes to compensate for skin effect offsets caused by changes in conductivity; the drive voltage is adjusted using a PID control algorithm to offset the increase in coil impedance caused by high temperature; and the signal gain of the defect amplitude voltage output by the detection coil is adjusted in real time based on a defect voltage amplitude gain mapping table to ensure that the adjusted defect voltage amplitude remains stable at different temperatures. The method of the present invention simplifies the circuit structure, avoids the complexity and noise problems caused by the superposition of multiple modules in traditional technologies, and significantly improves the reliability and detection sensitivity of the system.

[0099] Solution testing:

[0100] Taking nickel-based alloy as the test piece, the initial temperature is set to 25°C and the maximum temperature is 205°C. The relationship between temperature, magnetic permeability and electrical conductivity can be obtained through JMatpro material simulation software, as shown in Table 1. The table shows that the electrical conductivity gradually decreases when the temperature is between 25°C and 205°C, while the relative magnetic permeability is 1 at the same temperature between 25°C and 205°C, which is basically unchanged. Therefore, the default magnetic permeability of nickel-based alloy is u=4π×10 -7 H / m (since the relative magnetic permeability of high-temperature nickel-based alloys relative to air (abbreviated as relative magnetic permeability) is 1, and the magnetic permeability of air is u=4π×10 -7 H / m, so the magnetic permeability of the alloy is u=4π×10 -7 H / m). At room temperature of 25℃, the frequency of the eddy current sensor probe detecting high temperature nickel-based alloy is ƒ0=500kHz, and the driving voltage is =6V, the output voltage gain of the detection coil is set to =20dB (since the voltage generated by the detection coil is generally very small, we usually give an initial gain to amplify the voltage). At this time, the conductivity of the high-temperature nickel-based alloy is σ0=2.70×10 6 S / m, magnetic permeability u=4π×10 -7 H / m, the initial skin depth can be obtained 0:

[0101] ;

[0102] Table 1 Mapping table of temperature, electrical conductivity and relative magnetic permeability of high-temperature nickel-based alloys

[0103]

[0104] If the temperature sensor measures the ambient temperature T = 160 ° C, the mapping table of nickel-based alloy temperature, conductivity and relative magnetic permeability shows that the conductivity σ (160 ° C) = 2.05 × 10 6 S / m, magnetic permeability u=4π×10 -7 H / m. Maintain skin depth =0.31mm remains unchanged, and the optimal frequency ƒ can be deduced by the skin depth formula:

[0105] ;

[0106] Finally, the DDS (direct digital synthesis) signal generator is used to dynamically adjust the output drive voltage excitation frequency ƒ to ensure the skin depth 0=0.31mm remains constant to avoid distortion of the detection signal.

[0107] At room temperature 25℃, coil impedance Z0=50Ω, driving voltage =6V, coil temperature coefficient ɑ=0.05Ω / ℃, according to the impedance change formula, the coil impedance at 160℃ is .

[0108] ;

[0109] ;

[0110] ;

[0111] To offset the change in coil impedance caused by high temperature, the PID controller dynamically adjusts the driving voltage applied to the excitation coil of the eddy current sensor to compensate for the change in the impedance of the excitation coil with temperature, ensuring that the magnetic field strength generated by the eddy current sensor remains stable at different temperatures.

[0112] Among them, the PID controller adjusts the driving voltage finally loaded on the excitation coil through the proportional term, the integral term and the differential term. for:

[0113] ;

[0114] Among them, the proportional coefficient , integral coefficient and differential coefficients The calculation process is as follows:

[0115] First, turn off the effects of integration and differentiation, and let =0, =0, gradually increase Until the system oscillates with equal amplitude, the proportional coefficient recorded at this time is the critical gain The time difference between the two peaks of the waveform corresponding to the equal-amplitude oscillation is the oscillation period , and then calculate the integral coefficient according to the Ziegler-Nichols formula and differential coefficients .

[0116] In this embodiment, the critical gain is determined =191.5, oscillation period =1.7s. The integral coefficient is calculated by the Ziegler-Nichols formula and differential coefficients :

[0117] ;

[0118] ;

[0119] ;

[0120] The compensation voltage ;

[0121] Finally, the driving voltage loaded on the excitation coil of the eddy current sensor at 160°C is obtained. = + 6.81V.

[0122] After frequency optimization and drive compensation, the signal-to-noise ratio generated by the detection coil at high temperature is basically consistent with the signal-to-noise ratio at room temperature. However, the defect voltage amplitude output by the detection coil is still inconsistent with the defect voltage amplitude at room temperature. Therefore, the present invention needs to correct the voltage amplitude of the same defect detected at different temperatures to avoid different voltage amplitudes when detecting the same defect at different temperatures. The specific process is as follows:

[0123] The eddy current sensor probe calibrates the gain of the programmable gain amplifier (PGA) output on the same defect of the same high-temperature nickel-based alloy test block, and generates a defect voltage amplitude gain mapping table at different temperatures, as shown in Table 2.

[0124] Table 2 Temperature amplitude gain mapping table

[0125]

[0126] From Table 2, we can see that at room temperature of 25℃, the gain is set to 20dB (amplification 100 times), and the defect voltage amplitude output by the detection coil is 3.2×10 -2 , the amplified defect voltage amplitude at room temperature (25°C) is:

[0127] ;

[0128] When the temperature is 160℃, we can see from the table that when the gain G T When the gain is adjusted from 20dB (100x amplification) to 20.7dB (117x amplification), the defect voltage amplitude (i.e. when the distance between the eddy current probe and the defect center is 0) can be amplified again to around 3.2V. The gain is adjusted in real time through the programmable gain amplifier (PGA):

[0129] ;

[0130] The signal amplitude is restored to around 3.2V, which improves the signal amplitude stability.

[0131] Finally, if Figure 5 As shown in the figure, the horizontal axis represents the distance between the detection coil and the defect center, and the vertical axis represents the defect voltage amplitude after gain compensation at each position; after adjusting the excitation frequency, driving voltage and gain compensation, the compensation signal at 160°C is consistent with the signal at room temperature 25°C. Figure 4 Figure 1 shows the defect voltage amplitude across the detection coil at various temperatures, obtained without any compensation and amplified by the same gain. At 160°C, the defect voltage amplitude when the eddy current sensor probe is 0°C from the defect center is only 1 / 5 of the voltage signal amplitude at a normal temperature of 25°C. After signal compensation, the defect voltage signal amplitude is essentially the same as at a normal temperature of 25°C, and the signal-to-noise ratio is also consistent with that at normal temperature.

[0132] Figure 2 This is a schematic diagram of the eddy current sensor probe scanning defects. The axis of the eddy current sensor probe is scanned perpendicular to the surface of the test block under inspection. During the scanning process, the distance between the eddy current sensor probe and the surface of the test block under inspection remains unchanged, and the scanning is performed in a straight line with the position corresponding to the center of the defect as the center.

[0133] Figure 3 The defect voltage amplitude at both ends of the detection coil at various temperatures is obtained after excitation optimization and driving voltage compensation. After the compensation in the first two steps, the defect voltage amplitude at various temperatures is already close to the defect voltage amplitude at room temperature.

[0134] Figure 4The corresponding curve diagram of the defect voltage amplitude at both ends of the detection coil at the temperature of 25℃~205℃ without any compensation is amplified with the same gain. Figure 5 Schematic diagram of the defect voltage amplitude curve across the detection coil at temperatures between 25°C and 205°C, obtained after excitation optimization, drive voltage, and gain compensation. The horizontal axis represents the distance between the eddy current probe and the defect center. The eddy current voltage signal amplitude at positions of -5mm to -2mm and 2mm to 5mm represent the defect-free position. Position 0 represents the maximum defect voltage signal amplitude. Comparing the voltage signal amplitude and signal-to-noise ratio before and after gain compensation shows that the temperature-adaptive compensation system stabilizes the compensated voltage signal amplitude to within 3% of the normal temperature voltage signal amplitude, while maintaining a virtually unchanged signal-to-noise ratio.

[0135] Figure 6 This is the circuit diagram of the eddy current sensor probe. The excitation coil is located between nodes 3 and 1, and the detection coil is located between nodes 4 and 2. Applying a drive voltage and excitation frequency to the excitation coil generates an alternating magnetic field from eddy currents in the conductor. The detection coil detects changes in the magnetic field generated by the eddy currents in the test piece and outputs a voltage indicating the defect amplitude.

[0136] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A temperature-adaptive eddy current signal dynamic compensation method, characterized in that: The specific steps include: Obtain a curve showing how the conductivity and magnetic permeability of the test block change with temperature; scan the surface of the test block using an eddy current sensor to determine the skin depth corresponding to the eddy current sensor at room temperature; use this skin depth as a constant skin depth, and calculate the optimal excitation frequency at the current temperature based on the conductivity and magnetic permeability at the current temperature, and ensure that the excitation coil of the eddy current sensor operates at the optimal excitation frequency; The PID control algorithm is used to dynamically adjust the driving voltage loaded on the excitation coil of the eddy current sensor to compensate for the change in the impedance of the excitation coil with temperature, ensuring that the magnetic field strength excited by the eddy current sensor remains stable at different temperatures. The method of ensuring that the magnetic field strength excited by the eddy current sensor at different temperatures remains stable also includes: Changing the ambient temperature of the test block under test, calibrating the defect voltage amplitude of the test block using an eddy current sensor, maintaining the relative position of the eddy current sensor and the test block under test unchanged during the calibration process, and generating a defect voltage amplitude gain mapping table at different temperatures, where the defect voltage amplitude is the voltage across the detection coil; According to the defect voltage amplitude gain mapping table at different temperatures, the defect voltage amplitude adjusted by the programmable amplifier is calculated; The PID control algorithm is used to dynamically adjust the driving voltage loaded on the excitation coil of the eddy current sensor to compensate for the change in the impedance of the excitation coil with temperature, ensuring that the magnetic field strength excited by the eddy current sensor remains stable at different temperatures. Specifically, the following steps are performed: Obtain the relationship between impedance change and temperature; Keep the driving voltage applied to the excitation coil of the eddy current sensor constant and obtain the current error after the impedance changes. The PID control algorithm is used to dynamically adjust the driving voltage loaded on the excitation coil of the eddy current sensor according to the current error after the impedance changes to compensate for the impedance change with temperature; Among them, the driving voltage loaded on the excitation coil of the eddy current sensor after the temperature changes is = + ; ； I0=V0 / Z0; ( )； in, is the proportionality coefficient, is the integration coefficient, is the differential coefficient, is the compensation voltage, V0 is the driving voltage at room temperature 25°C, Z0 is the excitation coil impedance at room temperature 25°C; ∆Z is the difference in excitation coil impedance at room temperature and high temperature, and ɑ is the impedance temperature variation coefficient; is the current error; I0 is the current of the excitation coil at room temperature of 25°C, T is the ambient temperature after the temperature change, Indicates normal ambient temperature.

2. The method for dynamic compensation of eddy current signals based on temperature adaptation according to claim 1, characterized in that: The step of determining the skin depth corresponding to the eddy current sensor at room temperature; using the skin depth as a constant skin depth and calculating the optimal excitation frequency at the current temperature based on the electrical conductivity and magnetic permeability at the current temperature specifically includes: Set 25℃ as the initial room temperature, and find the conductivity and permeability at this temperature according to the curve of conductivity σ(T) and magnetic permeability u(T) changing with temperature, and use them as the initial conductivity σ0 and initial magnetic permeability u0, and calculate the initial skin depth with the detection excitation frequency ƒ0 at this temperature. 0: ； Get the initial skin depth 0, with the initial skin depth 0 as a constant skin depth, and according to the conductivity σ(T) and magnetic permeability u(T) at the current temperature, the optimal excitation frequency ƒ at the current temperature can be calculated: 。 3. The method for dynamic compensation of eddy current signals based on temperature adaptation according to claim 1, characterized in that: The proportionality coefficient , integral coefficient and differential coefficients The acquisition process is as follows: First, =0, =0, gradually increase Until the system oscillates with equal amplitude, the proportional coefficient recorded at this time is the critical gain The time difference between the two peaks of the waveform corresponding to the equal-amplitude oscillation is the oscillation period , and then calculate the integral coefficient according to the Ziegler-Nichols formula and differential coefficients .

4. The method for dynamic compensation of eddy current signals based on temperature adaptation according to claim 1, characterized in that: The method of changing the ambient temperature of the test block to be tested, calibrating the defect voltage amplitude of the test block using an eddy current sensor, maintaining the relative position of the eddy current sensor and the test block to be tested unchanged during the calibration process, and generating a defect voltage amplitude gain mapping table under different temperatures specifically includes: Assume that the defect voltage amplitude magnification of the detection coil output is G, then the gain of the programmable gain amplifier PGA output at room temperature is G T0 for: Changing the ambient temperature of the test block to generate the defect voltage amplitude of the detection coil at different temperatures; According to the defect voltage amplitude of the detection coil at different temperatures and the gain G output by the programmable gain amplifier at room temperature T0 , calculate the gain G of the programmable gain amplifier output at different temperatures T ; The gain G of the programmable gain amplifier output at different temperatures T The calculation formula is as follows: *V in0 = *V in ; = *V in0 / V in ; Where V in0 is the defect voltage amplitude output by the detection coil at room temperature, V in is the defect voltage amplitude output by the detection coil at different temperatures, is the gain of the programmable gain amplifier output at different temperatures.

5. The method for dynamic compensation of eddy current signals based on temperature adaptation according to claim 1, characterized in that: The defect voltage amplitude after the programmable amplifier is adjusted The formula is as follows: ； Where, is the defect voltage amplitude output by the detection coil, is the defect voltage amplitude after adjustment by the programmable amplifier.

6. The method for dynamic compensation of eddy current signals based on temperature adaptation according to claim 1, characterized in that: The scanning of the surface of the test block by using the eddy current sensor specifically includes: The axis of the eddy current sensor is scanned perpendicular to the surface of the test block to be inspected; during the scanning process, the distance between the eddy current sensor probe and the surface of the test block to be inspected remains unchanged, and the scanning is performed in a straight line with the position corresponding to the defect center as the center.

7. The method for dynamic compensation of eddy current signals based on temperature adaptation according to claim 1, characterized in that: The step of obtaining the curves of the conductivity and magnetic permeability of the test block under test varying with temperature specifically includes: Using JMatpro material simulation software, the content ratio of each element in the test block material is input into the software to obtain the curve of the conductivity and magnetic permeability of the test block as a function of temperature.

Images