Array eddy current detection method and system based on differential motion and amplitude decoupling

Abstract

The invention discloses an array eddy current detection method and system based on differential and amplitude decoupling, and the method comprises the steps: employing a differential array eddy current probe to collect a defect signal, enabling an excitation coil to be connected with a B end of an AD698, and enabling a receiving coil to be connected with an A end of the AD698; and an amplitude decoupling and phase compensation mechanism is introduced to improve the signal stability and the anti-interference capability in the detection process. The system realizes excitation signal output, received signal synchronous demodulation and amplitude extraction through an AD698 chip, the output form is the ratio of a received signal to an excitation signal, and the response capability to a weak defect signal is enhanced. And in combination with a multi-channel control strategy, automatic scanning and stable switching of a plurality of detection areas can be realized. In the data processing stage, time domain features such as peak values, peak-to-peak values and signal width are extracted, a quantitative evaluation model of the angle, depth and length of the crack is constructed based on the change rule of the time domain features, and reliable technical support is provided for crack detection and life prediction of the metal part with the complex structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic nondestructive testing, and in particular to an array eddy current testing method and system based on differential and amplitude decoupling. BACKGROUND

[0002] Carbon steel and its alloys are widely used in key structural components in petrochemical, energy, transportation and other industries, such as pressure vessels, steam pipes and rails, due to their good mechanical and economic properties. These components are often subjected to high temperature, high pressure, high stress and corrosive environment during service, which can easily produce stress corrosion cracks (SCC). Due to the strong concealment, fast initiation and great harm of such cracks, sensitive and reliable nondestructive testing and monitoring means are urgently needed for state identification and evaluation.

[0003] Eddy current testing (ECT) is based on electromagnetic induction principle, has the advantages of non-contact, high response speed, and is suitable for conductive materials, and has been widely used in the detection of surface and near-surface defects of metals. However, the traditional ECT system usually adopts a single-channel structure, which cannot meet the detection requirements of multi-position synchronous detection and wide coverage, and seriously restricts its engineering promotion. In order to solve the above problems, array eddy current testing technology has become an important development direction. The so-called array eddy current testing technology is to design and package multiple eddy current testing coils according to the geometry of the detected workpiece, and then process the detection signals through fast electronic control to realize fast and effective detection of the surface and near-surface of the part. Its detection coverage area is several times that of a single channel, which can significantly improve the detection efficiency and spatial resolution. However, the current array eddy current system is designed separately for the excitation module and the data processing module, which leads to large system volume, poor portability, weak adaptability to complex working conditions and other problems.

[0004] The present application is based on the principle of differential signal processing, and designs an array eddy current testing system around the AD698 chip, combining amplitude decoupling and phase compensation mechanism, which effectively reduces the system volume and improves the anti-interference ability and sensitivity of the system. Combined with the AD698 chip and its peripheral circuit, synchronous output of excitation signal, synchronous demodulation of differential signal and accurate extraction of amplitude signal can be realized, so as to reduce the volume of the instrument and realize the miniaturization design of the array eddy current testing system.

[0005] Therefore, it is of important technical significance and application value to develop an array eddy current testing system based on differential signal processing and amplitude decoupling, which has high sensitivity and high stability detection capability, and can improve the detection accuracy of stress corrosion cracks and the generalizability of engineering application. SUMMARY

[0006] 1. The technical problem to be solved:

[0007] In order to solve the above technical problems, the application provides an array eddy current detection method and system based on differential and amplitude decoupling, which integrates a high-precision signal conditioning module and its peripheral circuit to construct a high-sensitivity and high-integration signal acquisition and processing platform, realizes accurate acquisition and analysis of multi-channel eddy current signals, and meets the efficient detection requirements of complex workpieces.

[0008] 2. Technical solution:

[0009] An array eddy current detection method based on differential and amplitude decoupling is applied to nondestructive detection of cracks by using a differential array eddy current probe. The method is characterized in that: an AD698 chip is used to realize multi-channel control of the differential array eddy current probe; the excitation signal of the excitation coil of the differential array eddy current probe is connected to the B terminal of the primary end of the AD698 chip, and the signal of one channel of the receiving signals of the multiple channels of the receiving coil is transmitted to the A terminal of the secondary end based on a preset sequence; the AD698 chip outputs the ratio change of the secondary end receiving signal and the primary end excitation signal, and uses the ratio change of different channels as the basis for whether the corresponding workpiece position has damage.

[0010] Further, the multi-channel control of the differential array eddy current probe by using the AD698 chip is specifically realized by using an AD698-based signal conditioning module; the AD698-based signal conditioning module includes an AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, a preamplifier and a filter circuit; the phase lag / lead network performs phase compensation on the secondary end receiving signal of the AD698 chip, so that the phase of the secondary end receiving signal is aligned with that of the primary end excitation signal; the compensated signal enters the amplitude decoupling and demodulation circuit, and outputs an amplitude signal that can reflect defect information; before the receiving signal enters the AD698 chip, the signal is amplified and the noise is suppressed by sequentially passing through the preamplifier and the filter circuit, thereby improving the signal-to-noise ratio and amplitude stability of the receiving signal; wherein the preamplifier is a low-noise high-precision operational amplifier, and the filter circuit is an RC passive filter network.

[0011] Further, the excitation coil and the detection coil are connected to the AD698 chip through respective analog switch chips; the switch channels of the analog switch chips are controlled by a microcontroller to realize synchronous switching of multi-channel excitation and reception.

[0012] Further, the amplitude signal outputted by the AD698-based signal conditioning module, which can reflect the defect information, is adjusted in excitation frequency and demodulation bandwidth by external capacitors; wherein the first capacitor connected to the 6th and 7th pins of the AD698 chip is used to set the excitation frequency, and the second capacitor connected to the 8th and 9th pins, the third capacitor connected to the 16th and 17th pins, and the fourth capacitor connected to the 18th and 19th pins are used to adjust the demodulation bandwidth, so that the outputted excitation signal can adapt to the spectral characteristics of different defect response signals.

[0013] Further, the method comprises the following steps:

[0014] Step 1: build a multi-channel eddy current detection platform; the multi-channel eddy current detection platform comprises a differential array eddy current probe, an AD698-based signal conditioning module, an analog switch chip, a microcontroller, a data acquisition module, and an upper computer processing system; the AD698-based signal conditioning module comprises an AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, a preamplification and filtering circuit;

[0015] Step 2: arrange the excitation coil and the receiving coil of the differential array eddy current probe at a plurality of detection regions on the surface of the workpiece to be measured according to specific working conditions, control the analog switch chip by the microcontroller to realize channel switching of the excitation and receiving coils, and sequentially connect the collected multi-channel receiving signals to the AD698 chip for signal conditioning;

[0016] Step 3: pre-process the voltage signal received by the receiving coil; after the signal of the receiving coil is amplified by a low-noise high-precision operational amplifier, high-frequency interference and power supply noise are suppressed by an RC passive filter network, and then the phase of the detection signal is adjusted by a phase compensation circuit to align with the phase of the excitation signal, and then the signal is synchronously demodulated by the amplitude decoupling and demodulation circuit of the AD698-based signal conditioning module and an amplitude signal is outputted, data acquisition is completed by an analog-to-digital converter, and time domain characteristics including peak value, peak-to-peak value, and signal width are extracted;

[0017] Step 4: input the extracted time domain characteristics into a preset defect recognition and prediction model in the upper computer processing system, analyze and predict the angle, length, and depth parameters of the defect according to the crack response change rule;

[0018] Step 5: realize visual output of the detection results in the upper computer interface for online state evaluation and engineering decision support.

[0019] The array eddy current detection system based on differential and amplitude decoupling comprises a differential array eddy current probe, an AD698-based signal conditioning module, an analog switch chip, a microcontroller, a data acquisition module, and an upper computer processing system;

[0020] The excitation coil and the receiving coil of the differential array eddy current probe are arranged on the surface of the measured object, and the received signals collected by the excitation coil and the receiving coil are transmitted to the signal conditioning module based on AD698 through an analog switch chip; the analog switch chip is controlled by a microcontroller to realize synchronous switching of the excitation coil and the receiving coil;

[0021] The signal conditioning module based on AD698 includes an AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, and a preamplification and filtering circuit; after the multi-channel received signals pass through the preamplification and filtering circuit, they enter the AD698 chip, and the phase lag / lead network adjusts the phase of the received signals to make it strictly aligned with the phase of the excitation signal; the amplitude decoupling and demodulation circuit synchronously demodulates the received signals input into the AD698 chip and outputs amplitude signals;

[0022] The data acquisition module converts the amplitude signals output by the signal conditioning module based on AD698 into digital output;

[0023] The host computer processing system extracts the time domain features of the peak value, peak-to-peak value and signal width for crack identification, and predefines a defect identification and prediction model, inputs the extracted time domain features into the defect identification and prediction model, analyzes and predicts the angle, length and depth parameters of the defect, and displays it in a visual manner.

[0024] 3. Beneficial effects:

[0025] (1) The method provides an array eddy current detection method based on differential and amplitude decoupling, adopts a differential array eddy current probe structure, and constructs a signal conditioning module with an AD698 chip as the core. The AD698 chip integrates a constant current excitation source, synchronous demodulation and low pass filtering functions, and is suitable for amplitude extraction and defect response analysis of eddy current signals. The differential array eddy current probe includes multiple excitation coils and multiple pairs of differential receiving coils. In this method, the excitation coil is connected to the B terminal of the AD698 chip to provide a stable reference signal, and the receiving coil is connected to the A terminal in a differential manner to collect the defect response signal. The AD698 chip realizes synchronous demodulation by calculating the ratio of the received signal to the excitation signal (A / B), and outputs the amplitude change characteristics related to the defect. The differential structure effectively suppresses common mode noise and enhances the response capability to local changes of cracks.

[0026] (2) The method provides an array eddy current detection method based on differential and amplitude decoupling, which realizes independent extraction of the amplitude of the excitation signal and the response signal through the AD698 chip, effectively eliminates the interference of phase disturbance on amplitude measurement. At the same time, the method configures a phase compensation module, adjusts the defect response signal through a phase lag or lead network, makes it strictly aligned with the phase of the excitation reference signal, eliminates the influence of phase difference on amplitude measurement, and thus significantly improves the detection sensitivity and the accuracy of amplitude measurement.

[0027] (3) The method provides an array eddy current detection method based on differential and amplitude decoupling, wherein the output of the receiving coil is first subjected to preamplification by a low-noise high-precision operational amplifier and is connected to an RC passive filter network to suppress high-frequency interference and power supply noise before being connected to the AD698, so that the signal-to-noise ratio and signal stability are significantly improved.

[0028] (4) The method provides an array eddy current detection method based on differential and amplitude decoupling, wherein, to realize the multi-channel detection function, an analog switch chip is used, the channel switching of the analog switch chip is controlled by a microcontroller, and dynamic connection between multiple probe channels and the AD698 chip is realized. The on-off of the excitation coil and the receiving coil is controlled synchronously by the analog switch chip, so that the integrity and synchronism of the signal path during the switching process are ensured.

[0029] (5) The method provides an array eddy current detection method based on differential and amplitude decoupling, wherein the amplitude output signal of the AD698 is collected by a high-precision multi-channel analog-to-digital converter. The analog-to-digital converter supports multi-channel synchronous sampling and high-speed parallel output, ensures the time sequence consistency of the multi-point detection data, and provides accurate basic data for subsequent signal processing and analysis.

[0030] In summary, the method has the multi-channel detection capability, realizes the sub-regional, rapid and high-precision crack detection of complex structural parts, overcomes the problem of large overall volume of the traditional eddy current instrument, and is suitable for on-site industrial online monitoring and real-time diagnosis. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The equivalent circuit diagram of the LVDT sensor (a) and the eddy current sensor (b) in the principle description of the application;

[0032] Figure 2 The phase lag / lead network circuit diagram in the application;

[0033] Figure 3 The overall circuit block diagram of the multi-channel eddy current detection system based on differential and amplitude decoupling;

[0034] Figure 4 The typical peripheral circuit connection schematic diagram of the AD698 chip in the application;

[0035] Figure 5 The relationship between the excitation voltage and the resistor R1 in the application;

[0036] Figure 6 The comparison diagram of the consistency of detection signals between different channels;

[0037] Figure 7 The detection result diagram corresponding to different crack lengths;

[0038] Figure 8 are detection result graphs corresponding to different crack angles;

[0039] Figure 9 are detection result graphs corresponding to different crack depths;

[0040] Figure 10 is a detection result graph of a cluster crack defect. DETAILED DESCRIPTION

[0041] The application will be described in detail below with reference to the accompanying drawings.

[0042] An array eddy current detection method based on differential and amplitude decoupling is applied to nondestructive detection of cracks by using a differential array eddy current probe; characterized in that: an AD698 chip is used to realize multi-channel control of the differential array eddy current probe; an excitation signal of an excitation coil of the differential array eddy current probe is connected to the B end of the primary end of the AD698 chip, and a signal of one channel of a plurality of channels of a receiving signal of a receiving coil is transmitted to the A end of the secondary end based on a preset sequence; the AD698 chip outputs a ratio change of the secondary end receiving signal and the primary end excitation signal, and uses the ratio change of different channels as a basis for whether the workpiece position corresponding to the channel has damage.

[0043] Further, the multi-channel control of the differential array eddy current probe by using the AD698 chip is specifically realized by using an AD698-based signal conditioning module; the AD698-based signal conditioning module includes an AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, a preamplifier and a filter circuit; the phase lag / lead network performs phase compensation on the secondary end receiving signal of the AD698 chip, so that the phase of the secondary end receiving signal is aligned with the phase of the primary end excitation signal; the compensated signal enters the amplitude decoupling and demodulation circuit, and outputs an amplitude signal capable of reflecting defect information; before the receiving signal enters the AD698 chip, the receiving signal sequentially passes through the preamplifier and the filter circuit to realize amplification of the signal and suppression of noise, thereby improving the signal-to-noise ratio and amplitude stability of the receiving signal; wherein the preamplifier is a low-noise high-precision operational amplifier, and the filter circuit is an RC passive filter network.

[0044] Further, the excitation coil and the detection coil are connected to the AD698 chip through respective analog switch chips; the switch channels of the analog switch chips are controlled by a microcontroller to realize synchronous switching of multi-channel excitation and reception.

[0045] Further, the amplitude signal outputted by the AD698-based signal conditioning module, which can reflect the defect information, is adjusted in excitation frequency and demodulation bandwidth by external capacitors; wherein the first capacitor connected to the 6th and 7th pins of the AD698 chip is used to set the excitation frequency, and the second capacitor connected to the 8th and 9th pins, the third capacitor connected to the 16th and 17th pins, and the fourth capacitor connected to the 18th and 19th pins are used to adjust the demodulation bandwidth, so that the outputted excitation signal can adapt to the spectral characteristics of different defect response signals.

[0046] Further, the method comprises the following steps:

[0047] Step 1: build a multi-channel eddy current detection platform; the multi-channel eddy current detection platform comprises a differential array eddy current probe, an AD698-based signal conditioning module, an analog switch chip, a microcontroller, a data acquisition module, and an upper computer processing system; the AD698-based signal conditioning module comprises an AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, a preamplification and filtering circuit;

[0048] Step 2: arrange the excitation coil and the receiving coil of the differential array eddy current probe at a plurality of detection regions on the surface of the workpiece to be measured according to specific working conditions, control the analog switch chip by the microcontroller to realize channel switching of the excitation and receiving coils, and sequentially connect the collected multi-channel receiving signals to the AD698 chip for signal conditioning;

[0049] Step 3: pre-process the voltage signal received by the receiving coil; after the signal of the receiving coil is amplified by a low-noise high-precision operational amplifier, high-frequency interference and power supply noise are suppressed by an RC passive filter network, and then the phase of the detection signal is adjusted by a phase compensation circuit to align with the phase of the excitation signal, and then the signal is synchronously demodulated by the amplitude decoupling and demodulation circuit of the AD698-based signal conditioning module and an amplitude signal is outputted, data acquisition is completed by an analog-to-digital converter, and time domain characteristics including peak value, peak-to-peak value, and signal width are extracted;

[0050] Step 4: input the extracted time domain characteristics into a preset defect recognition and prediction model in the upper computer processing system, analyze and predict the angle, length, and depth parameters of the defect according to the crack response change rule;

[0051] Step 5: realize visual output of the detection results in the upper computer interface for online state evaluation and engineering decision support.

[0052] The array eddy current detection system based on differential and amplitude decoupling comprises a differential array eddy current probe, an AD698-based signal conditioning module, an analog switch chip, a microcontroller, a data acquisition module, and an upper computer processing system;

[0053] The excitation coil and the receiving coil of the differential array eddy current probe are arranged on the surface of the measured object, and the received signals collected by the excitation coil and the receiving coil are transmitted to the signal conditioning module based on AD698 through an analog switch chip; the analog switch chip is controlled by a microcontroller to realize synchronous switching of the excitation coil and the receiving coil;

[0054] The signal conditioning module based on AD698 includes an AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, a preamplification and filtering circuit; after the multi-channel received signals pass through the preamplification and filtering circuit, they enter the AD698 chip, and the phase lag / lead network adjusts the phase of the received signals to make it strictly aligned with the phase of the excitation signal; the amplitude decoupling and demodulation circuit synchronously demodulates the received signals input into the AD698 chip and outputs amplitude signals;

[0055] The data acquisition module converts the amplitude signals output by the signal conditioning module based on AD698 into digital output;

[0056] The host computer processing system extracts the time domain features of the peak value, peak-to-peak value and signal width for crack identification, and pre-sets a defect identification and prediction model, inputs the extracted time domain features into the defect identification and prediction model, analyzes and predicts the angle, length and depth parameters of the defect, and displays it in a visual manner.

[0057] Principle and verification description:

[0058] As shown in Figure 1 (a), the AD698 chip used in this method is essentially a signal conditioning of LVDT (Linear Variable Differential Transformer) sensor. LVDT is usually composed of one excitation coil (primary) and two reverse series detection coils (secondary), and the position change of the central magnetic core will cause the change of magnetic coupling. AD698 can detect the change of magnetic flux between A end (detection coil) and B end (excitation coil), thereby realizing high-precision measurement of the displacement of the magnetic core.

[0059] As shown in Figure 1 (b), the differential magnetic coupling principle of LVDT is applied to the differential array eddy current probe in eddy current detection; specifically, the excitation coil is connected to the B end of AD698, and the receiving coil is connected to the A end in a differential manner. When there is a defect on the surface of the conductive workpiece, the electromagnetic field generated by the excitation coil will be disturbed, causing the change of the magnetic flux coupling between the excitation coil and the receiving coil, and finally outputting the electric signal responding to the defect characteristics by the AD698 chip.

[0060] The two inputs of AD698 receive the signals of the primary coil and the secondary coil of the probe, and the A / B ratio is calculated by the duty cycle divider and a square wave signal is output. When A / B = 1, the duty cycle is 100%. The square wave signal is converted into a direct current voltage by a reference current source and an external resistance, and an amplitude signal proportional to A / B is output. The output relationship can be expressed as:

[0061] V OUT = I ref × A / B × R2 (1)

[0062] In the above formula, V OUT represents the output direct current voltage; I ref represents the reference current; R2 is the external resistance;

[0063] In the amplitude measurement process, there is a phase coupling between the excitation signal and the defect response signal (i.e. the received signal). The response signal amplitude not only contains amplitude information, but also is disturbed by phase changes. In order to eliminate the phase disturbance, the phase compensation technology is introduced in the signal conditioning module in the method. The system simultaneously collects the excitation reference signal and the defect response signal, and accurately adjusts the response signal through the phase lag / lead network, so that it is strictly aligned with the reference signal, and the influence of the phase difference on the amplitude measurement is eliminated. Figure 2 The phase lag / lead network circuit diagram in the application, the compensated signal enters the amplitude decoupling and demodulation circuit, ensures that the output amplitude only reflects the defect information, and significantly improves the independence, stability and accuracy of the measurement.

[0064] Figure 3 It is a circuit block diagram of a multi-channel eddy current detection system based on differential and amplitude decoupling. The system is composed of multiple parallel channels, and each channel is equipped with an independent eddy current sensor, an AD698 signal conditioning module and its peripheral circuit. As shown in the figure, the overall system includes an excitation and receiving module, a differential synchronous demodulation module, a preamplification and filtering circuit, and a backend control and signal acquisition processing module, realizes multi-channel synchronous acquisition and demodulation, supports high-resolution nondestructive detection of complex structures. The positive and negative terminals of the excitation coil and the receiving coil of each channel are connected to the corresponding pins of AD698 through analog switches, and the synchronous switching of multi-channel excitation and reception is controlled by a microcontroller, ensuring that the signal path is complete and free of interference, realizing multi-probe time-sharing multiplexing, and improving the expansibility and detection efficiency of the system.

[0065] Figure 4 It is a typical peripheral circuit structure of AD698. The chip integrates a sine wave excitation source and a demodulation circuit, which can output stable excitation signals and synchronously demodulate the differential signals at the receiving end. The key peripheral circuits include frequency setting capacitor C1 (adjusting excitation frequency), bandwidth setting capacitors C2, C3 and C4 (setting the response bandwidth of the measurement system), and the calculation formula is as follows:

[0066] C1 = 35 μF gHz / f 激励 (2)

[0067] C2 = C3 = C4 = 10 -4 μFgHz / f 带宽 (3)

[0068] In the above formula, μF is microfarad; Hz is hertz; f 激励 The excitation frequency, f, is the frequency of the excitation signal. 带宽 Indicates bandwidth frequency.

[0069] by Figure 1 To illustrate the excitation signal and received signal of the AD698 chip in this application, such as... Figure 1 As shown in (a), when the primary induction coil L P After being excited by an externally applied voltage U, the two secondary induction coils L S1 and L S2 An induced voltage will be generated in the middle. When the entire equivalent circuit is considered to be in an ideal state, and at the same time, the manufacturing differences between the two secondary coils are not considered, when the iron core C is in the middle of the two secondary coils (L S1 and L S2 When L is at the center position (completely symmetrical), S1 The mutual inductance coefficients M1 and L S2 The mutual inductance coefficients M2 are equal. The equivalent circuit symbols and their meanings are shown in the table below.

[0070] Table 1 Circuit parameter symbols and their explanations

[0071]

[0072]

[0073] Current I S It is also formed at the instant the secondary current coil is connected to the load, when I S The mutual inductance M1 and M2 between the primary coil and the two secondary coils acts as a reaction force on the primary coil L. P At this time, mutual inductance M3 will appear between the two secondary coils. According to Kirchhoff's laws:

[0074]

[0075] Similarly, we can conclude that:

[0076] jwI P (M2-M1)+I S [R S1 +R S2 +R L +jw(L S1 +LS2 M3) = 0 (5)

[0077] From equations 4, 5 we have:

[0078]

[0079] Where:

[0080]

[0081] The final output voltage is:

[0082] U OUT = I S R L (8)

[0083] Let the displacement of the core C be S, when the core is at the center position, M1 = M2 = M, then let

[0084]

[0085] We can get:

[0086] M1 - M2 = 2kS (10)

[0087] Then,

[0088]

[0089] The mutual inductance M3 of the secondary coil L S1 and the secondary coil L S2 is considered as a constant, let:

[0090] L = L2 + L3 - 2M3 (12)

[0091] Then the final output voltage can be represented as:

[0092]

[0093] Assuming the ratio of the output voltage U OUT to the core displacement S is the sensitivity S n , then:

[0094]

[0095] Substituting equation (13) into equation (11) we get:

[0096]

[0097] According to the above formula, the S nThe amplitude of the excitation voltage applied to the primary coil of the AD698 chip is proportional to the sensitivity. In order to adjust the amplitude of the excitation signal, a resistor R1 is introduced into the circuit. The selection of R1 can be set according to the relationship between the effective value of the excitation voltage and the resistance value in the middle of the curve. It should be noted that the maximum excitation output voltage of the AD698 chip does not exceed 24V, and the value of R1 should be reasonably selected within this range to avoid overvoltage. Figure 5

[0098] Before the received signal enters the AD698 chip A, it is first amplified by a high-performance operational amplifier with low noise preamplification, effectively improving the signal amplitude and signal-to-noise ratio. Subsequently, through the RC passive filtering module, high-frequency interference and power supply noise are suppressed, and signal stability and purity are improved. After amplification and filtering of the analog signal, the AD698 demodulates it into a direct current voltage, and then inputs it into a multi-channel synchronous sampling ADC for data acquisition. In practice, the multi-channel synchronous sampling ADC can use the AD7606 chip, which supports 16-bit resolution and a maximum sampling rate of 200kSPS, has oversampling filtering, input protection and channel balancing functions, and realizes high-precision, low-noise multi-channel parallel sampling. The sampled data is transmitted to the main control unit through the SPI interface, providing a high-quality data basis for subsequent digital signal processing and defect identification.

[0099] To verify the detection consistency of the system under multi-channel configuration, Figure 6 The comparison results of the multi-channel eddy current detection output signals in a certain test are shown. From the figure, it can be seen that the waveforms output by each detection channel under the same detection conditions maintain a high degree of consistency in amplitude and phase, indicating that the multi-channel hardware structure of the invention has good channel consistency and synchronization.

[0100] Figure 7 to Figure 9 Further, the response characteristics of the system in detecting different types of defects (including changes in defect length, inclination angle and depth, etc.) are shown. Figure 7 For cracks of different lengths, Figure 8 For cracks of different inclination angles, Figure 9 For cracks of different depths; the (a) figures of the three figures are real samples, and the (b) figures are the response characteristics detected by the corresponding scheme; from the figure, it can be clearly seen that when the system faces changes in defect size and geometric characteristics, the output signal shows obvious distinguishability, which can effectively identify the type of defect and quantitatively evaluate its geometric characteristics, showing high detection sensitivity.

[0101] Figure 10 ​The detection response of the scheme to typical cluster cracks is demonstrated. The results show that the scheme can effectively distinguish cluster cracks with different spatial distribution characteristics, and the detection signals show significant differences in waveform structure and amplitude change. This fully verifies the adaptability and accuracy of the system in complex defect recognition, and has good application prospect, especially for quantitative detection and early diagnosis of structural damage such as stress corrosion cracks.

[0102] Although the present application has been disclosed in the preferred embodiments as above, they are not intended to limit the present application, and any skilled person in the art can make various changes or modifications without departing from the spirit and scope of the present application, so the protection scope of the present application should be defined by the protection scope of the claims of the present application.

Claims

1. A method for detecting arrayed eddy currents based on differential and amplitude decoupling, applied to non-destructive testing of cracks using a differential arrayed eddy current probe; characterized in that: The AD698 chip is used to realize multi-channel control of the differential array eddy current probe. The excitation signal of the excitation coil of the differential array eddy current probe is connected to the B terminal of the primary end of the AD698 chip. The signal of one channel of the multiple channels of the receiving coil is transmitted to the A terminal of the secondary end according to a preset order. The AD698 chip outputs the change in the ratio of the secondary end receiving signal to the primary end excitation signal. The change in the ratio of different channels is used as the basis for whether there is damage at the workpiece position corresponding to that channel.

2. The array eddy current detection method based on differential and amplitude decoupling according to claim 1, characterized in that: The multi-channel control of the differential array eddy current probe using the AD698 chip is specifically achieved through an AD698-based signal conditioning module. This module includes the AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, a preamplifier, and a filter circuit. The phase lag / lead network performs phase compensation on the received signal at the secondary end of the AD698 chip, aligning it with the phase of the primary end excitation signal. The compensated signal then enters the amplitude decoupling and demodulation circuit, outputting an amplitude signal that reflects defect information. Before the received signal enters the AD698 chip, it is sequentially amplified and noise suppressed by the preamplifier and filter circuit, improving the signal-to-noise ratio and amplitude stability of the received signal. The preamplifier is a low-noise, high-precision operational amplifier, and the filter circuit is an RC passive filter network.

3. The array eddy current detection method based on differential and amplitude decoupling according to claim 1, characterized in that: The excitation coil and the detection coil are connected to the AD698 chip via their respective analog switch chips; the switching channels of the analog switch chips are controlled by a microcontroller to achieve synchronous switching of multi-channel excitation and reception.

4. The array eddy current detection method based on differential and amplitude decoupling according to claim 2, characterized in that: The amplitude signal output by the AD698-based signal conditioning module, which reflects defect information, is used to adjust its excitation frequency and demodulation bandwidth through external capacitors. The first capacitor connected to pins 6 and 7 of the AD698 chip is used to set the excitation frequency, while the second capacitor connected to pins 8 and 9, the third capacitor connected to pins 16 and 17, and the fourth capacitor connected to pins 18 and 19 are used to adjust the demodulation bandwidth, so that the output excitation signal can adapt to the spectral characteristics of different defect response signals.

5. The array eddy current detection method based on differential and amplitude decoupling according to claim 1, characterized in that: Specifically, the following steps are included: Step 1: Construct a multi-channel eddy current detection platform; the multi-channel eddy current detection platform includes a differential array eddy current probe, an AD698-based signal conditioning module, an analog switch chip, a microcontroller, a data acquisition module, and a host computer processing system; the AD698-based signal conditioning module includes an AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, and a preamplifier and filter circuit; Step 2: Arrange the excitation coil and receiving coil of the differential array eddy current probe in multiple detection areas on the surface of the workpiece to be tested according to the specific working conditions. The microcontroller controls the analog switch chip to realize the channel switching of the excitation and receiving coils. The multiple received signals are sequentially connected to the AD698 chip for signal conditioning. Step 3: Preprocess the voltage signal received by the receiving coil; after the signal from the receiving coil is amplified by a low-noise, high-precision operational amplifier, high-frequency interference and power supply noise are suppressed by an RC passive filter network, and the phase of the detection signal is adjusted by a phase compensation circuit to align it with the phase of the excitation signal. Subsequently, the amplitude decoupling and demodulation circuit of the AD698-based signal conditioning module performs synchronous demodulation and outputs the amplitude signal. Data acquisition is completed by an analog-to-digital converter, and time-domain features including peak value, peak-to-peak value and signal width are extracted. Step 4: Input the extracted time-domain features into the preset defect identification and prediction model in the host computer processing system, and analyze and predict the angle, length and depth parameters of the defect based on the crack response change law; Step 5: Visualize the output of the detection results in the host computer interface for online status assessment and engineering decision support.

6. An array eddy current detection system based on differential and amplitude decoupling, wherein the detection is achieved using the method described in any one of claims 1-5; characterized in that: It includes a differential array eddy current probe, an AD698-based signal conditioning module, an analog switch chip, a microcontroller, a data acquisition module, and a host computer processing system; The excitation coil and receiving coil of the differential array eddy current probe are deployed on the surface of the test piece. The received signal is transmitted to the AD698-based signal conditioning module through an analog switch chip. The analog switch chip is controlled by a microcontroller to realize the synchronous switching of the excitation coil and the receiving coil. The AD698-based signal conditioning module includes an AD698 chip, a phase lag / lead network, an amplitude decoupling and demodulation circuit, and a preamplifier and filter circuit. The multi-channel received signals enter the AD698 chip after passing through the preamplifier and filter circuit. The phase lag / lead network adjusts the phase of the received signal to ensure strict alignment with the phase of the excitation signal. The amplitude decoupling and demodulation circuit synchronously demodulates the received signals input to the AD698 chip and outputs the amplitude signal. The data acquisition module converts the amplitude signal output by the AD698-based signal conditioning module into a digital output. The host computer processing system extracts the time-domain features of peak value, peak-to-peak value and signal width for crack identification, and presets a defect identification and prediction model. The extracted time-domain features are input into the defect identification and prediction model to analyze and predict the angle, length and depth parameters of the defect, and the results are displayed in a visual manner.

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