Power transmission tower angle steel defect detection method and system based on electromagnetic induction

Abstract

This application relates to the field of electromagnetic nondestructive testing technology, specifically providing a method and system for detecting defects in the angle steel of transmission towers based on electromagnetic induction. The method includes: when an AC excitation source flows through the entire angle steel under test, a differential eddy current probe that continuously scans along the moving direction acquires the dynamic differential signal of the angle steel in real time; the differential eddy current probe includes a first detection coil and a second detection coil, which are differentially connected to output a dynamic differential signal; the dynamic differential signal is conditioned to obtain a conditioned low-frequency analog characteristic signal; the digital signal corresponding to the low-frequency analog characteristic signal is logically judged, and when a zero-crossing characteristic time-domain waveform is captured during the logical judgment process, the true defect result based on the defect coordinates is determined. This application penetrates the excitation current deep into the interior of the angle steel under test and captures the zero-crossing characteristic time-domain waveform of the angle steel under test, enabling rapid detection and location of corrosion and crack defects in the angle steel.

Description

Technical Field

[0001] This application relates to the field of electromagnetic nondestructive testing technology, and in particular to a method and system for detecting defects in the angle steel of transmission towers based on electromagnetic induction. Background Technology

[0002] Angle steel for transmission towers is a large outdoor metal structure. Its defects are mostly surface and near-surface corrosion and cracks. Because angle steel is exposed to wind, sun, rain, snow, and pollution for extended periods, it is prone to corrosion thinning, pitting, and cracking. Accumulated defects reduce component strength and affect the safe operation of the tower. Current inspection methods for angle steel defects mostly involve manual visual inspection, tapping and listening, or traditional contact testing after grinding away the surface coating. However, the severe rust, anti-corrosion coating, and dirt on the angle steel surface significantly disrupt the signal stability of contact testing, making it difficult to meet the needs of large-scale inspections.

[0003] Furthermore, conventional high-frequency localized eddy current testing methods are insufficient to cover the entire angle steel, and the strong skin effect of high-frequency signals makes them unsuitable for detecting shallow defects near the surface of the angle steel. They are also extremely insensitive to early-stage micro-cracks and hidden corrosion within the matrix, resulting in a significant risk of missed detections. Summary of the Invention To address the aforementioned issues, this application provides a method and system for detecting defects in the angle steel of transmission towers based on electromagnetic induction. By applying low-frequency AC excitation to the angle steel under test and using a differential eddy current probe to scan changes in the magnetic field, rapid detection, location, and early warning of corrosion and crack defects in the angle steel can be achieved.

[0004] To achieve the objectives of this application, the following technical solution is provided: In a first aspect, this application provides a method for detecting defects in the angle steel of transmission towers based on electromagnetic induction, comprising: When current is passed through the entire angle steel under test by an AC excitation source, the dynamic differential signal of the angle steel under test is acquired in real time by a differential eddy current probe that continuously scans along the moving direction; the differential eddy current probe includes a first detection coil and a second detection coil, and the first detection coil and the second detection coil are differentially connected to output the dynamic differential signal; The dynamic differential signal is conditioned to obtain a conditioned low-frequency analog characteristic signal; Logical discrimination is performed on the digital signal corresponding to the low-frequency analog characteristic signal, and the zero-crossing characteristic time-domain waveform is captured during the logical discrimination process to determine the true defect result based on the defect coordinates.

[0005] A further improvement of this application is that the method of acquiring the dynamic differential signal of the angle steel under test in real time using a differential eddy current probe that continuously scans along the moving direction includes: placing the differential eddy current probe above the surface of the angle steel under test and maintaining a constant lift-off distance under handheld sliding scanning conditions, continuously scanning along a preset moving trajectory to obtain a dynamic differential signal based on the moving trajectory; wherein, the moving trajectory is a longitudinal path along the global flow path of the angle steel under test.

[0006] A further improvement of this application is that the conditioning of the dynamic differential signal to obtain the conditioned low-frequency analog characteristic signal includes: after low-noise amplification of the dynamic differential signal, locking the characteristic frequency band and filtering out high-frequency electromagnetic interference from the environment and extremely low-frequency baseline drift caused by hand-held shaking; extracting the envelope features of the dynamic differential waveform and converting the envelope features into the low-frequency analog characteristic signal.

[0007] A further improvement of this application is that the actual defect result is at least one of crack defects and corrosion pit defects; the step of performing logical discrimination on the digital signal corresponding to the low-frequency analog feature signal, and capturing a zero-crossing feature time-domain waveform during the logical discrimination process, to determine the actual defect result based on the defect coordinates includes: converting the low-frequency analog feature signal into a digital signal via AD conversion; determining the low-frequency analog feature signal as a pseudo-defect signal when the waveform characteristics of the digital signal only show monotonically slow fluctuations, and masking the pseudo-defect signal; determining the low-frequency analog feature signal as a real defect signal when the waveform characteristics of the digital signal contain a zero-crossing feature time-domain waveform that conforms to alternating positive and negative jumps; and determining the defect coordinates of the angle steel to be tested based on the scanning spatial position corresponding to the zero-crossing feature time-domain waveform; and then analyzing the zero-crossing feature time-domain waveform to determine the defect data based on the defect coordinates, wherein the defect data is the morphological characteristics of the crack defect or the corrosion pit defect.

[0008] A further improvement of this application is that the scanning spatial position is the instantaneous spatial position coordinate of the probe; the step of determining the defect coordinate of the angle steel to be tested based on the scanning spatial position corresponding to the zero-crossing characteristic time-domain waveform includes: during the continuous scanning process of the differential eddy current probe, the captured signal feature mutation points based on the time series are synchronously matched with the instantaneous spatial displacement coordinate of the probe calculated by the encoder to complete the mapping from the time axis to the spatial axis, thereby determining the defect coordinate.

[0009] A further improvement of this application is that the output frequency of the AC excitation source is continuously adjustable in the range of 100Hz to 5000Hz, and the lift-off distance is 2mm to 5mm.

[0010] Secondly, this application provides a defect detection system for angle steel of transmission towers based on electromagnetic induction, used to implement the above-mentioned defect detection method for angle steel of transmission towers based on electromagnetic induction, including: An AC excitation source is used to electrically connect to both ends of the angle steel under test and output a low-frequency AC current to the interior of the angle steel under test, so as to form an alternating magnetic field around the angle steel under test. A differential eddy current probe is used to closely approach the surface of the angle steel to be tested and continuously scan along the moving direction to acquire the dynamic differential signal of the angle steel to be tested in real time; the differential eddy current probe includes a first detection coil and a second detection coil, and the first detection coil and the second detection coil are differentially connected to output the dynamic differential signal; The signal conditioning module is connected to the output terminal of the differential eddy current probe and is used to condition the dynamic differential signal to obtain a conditioned low-frequency analog characteristic signal. An AD conversion module is connected to the output of the signal conditioning module and is used to convert the low-frequency analog characteristic signal into a digital signal. The control module, connected to the AD conversion module, is used to receive the digital signal and perform logical discrimination on the digital signal. In the process of logical discrimination, if the zero-crossing characteristic time-domain waveform is captured, the actual defect result based on the defect coordinates is determined.

[0011] A further improvement of this application is that the first detection coil and the second detection coil are fixedly encapsulated in the probe housing of the differential eddy current probe, and the center distance between the first detection coil and the second detection coil is 5mm to 10mm; the bottom of the probe housing near the angle steel to be tested maintains a constant lifting distance from the surface of the angle steel to be tested, and the lifting distance is 2mm to 5mm.

[0012] A further improvement of this application is that the signal conditioning module includes: a preamplifier unit for low-noise amplification of the dynamic differential signal excited when the differential balance is broken; a bandpass filter unit for locking the characteristic frequency band and filtering out high-frequency electromagnetic interference from the environment and extremely low-frequency baseline drift caused by hand shake; and a detector / demodulation unit for extracting the envelope features of the dynamic differential waveform and converting the envelope features into the low-frequency analog characteristic signal.

[0013] A further improvement of this application is that it also includes: The display and early warning module is connected to the control module and is used to display the detection results and output early warning information when it is determined that there are real defects.

[0014] Compared with the prior art, this application has the following beneficial effects: The electromagnetic induction-based method and system for detecting defects in the angle steel of transmission towers provided in this application utilizes an AC excitation source to conduct current through the entire angle steel under test. A differential eddy current probe, continuously scanning along the moving direction, is used to acquire the dynamic differential signal of the angle steel in real time. The dynamic differential signal is then conditioned to obtain a conditioned low-frequency analog characteristic signal. Logical discrimination is then performed on the digital signal corresponding to this low-frequency analog characteristic signal. If a zero-crossing characteristic time-domain waveform is captured during the logical discrimination process, the true defect result of the angle steel under test based on the defect coordinates is determined. In this way, the excitation current is penetrated deep into the angle steel under test, capturing the zero-crossing characteristic time-domain waveform of the angle steel. This effectively distinguishes defect signals from interference signals, realizes the effective excitation of deep corrosion and cracks in the angle steel, and finally obtains true and reliable defect detection results based on defect coordinates, avoiding misjudgment and missed detection. At the same time, the closed-loop constant current drive architecture effectively overcomes the contact impedance fluctuation interference caused by the anti-corrosion layer and rust on the surface of the angle steel, ensuring the high fidelity and stability of the detection signal. It can meet the needs of efficient and high-precision defect detection of angle steel of transmission towers under complex outdoor working conditions. Attached Figure Description

[0015] The accompanying drawings are provided to further understand this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof. Figure 1 A schematic flowchart of an optional method for detecting defects in angle steel of transmission towers based on electromagnetic induction, provided in an embodiment of this application; Figure 2 This is a schematic diagram of the differential eddy current probe structure provided in the embodiments of this application; Figure 3 A schematic diagram of a defect detection system for angle steel of transmission towers based on electromagnetic induction provided in an embodiment of this application; Figure 4 This is a schematic diagram of the detection process for the electromagnetic induction-based angle steel defect detection method for transmission towers provided in this application embodiment.

[0016] Figure label: 1. Angle steel under test; 2. Differential eddy current probe; 3. AC excitation source; 4. Signal conditioning module; 5. Controller; 6. Display and warning; 7. Movement direction; 8. Differential connection; 9. Probe housing; 10. Lift-off distance g; 11. Magnetic field change at the defect; 12. Preamplifier; 13. Bandpass filter; 14. Detection / demodulation; 15. AD conversion. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this application, unless otherwise stated, "multiple" means two or more.

[0019] Transmission towers mostly use angle steel components as the main load-bearing structure. Angle steel is exposed to wind, sun, rain, snow, and pollution for a long time, which can easily lead to defects such as corrosion thinning, pitting, and cracks. The accumulation of defects will reduce the strength of the components and affect the safe operation of the tower.

[0020] Currently, conventional inspection methods for defects in angle steel mostly rely on manual visual inspection, tapping and listening, or traditional contact inspection after grinding off the surface coating. These methods have the following shortcomings: (1) Insufficient sensitivity and reliability: It is not sensitive to early fine cracks and hidden corrosion inside the matrix, and there is a large risk of missed detection; (2) Poor environmental adaptability and efficiency: The severe rust layer, anti-corrosion coating and dirt on the surface of the angle steel will seriously damage the signal stability of the contact detection, making it difficult to meet the needs of large-scale inspection. (3) Conventional high-frequency local excitation eddy current detection method is difficult to cover the entire angle steel, and the high-frequency signal has a strong skin effect, which is not targeted enough for the detection of shallow defects near the surface of the angle steel, and is extremely insensitive to early micro cracks and hidden corrosion inside the matrix.

[0021] To address the aforementioned technical problems, this application proposes the following technical solutions and corresponding embodiments.

[0022] The following is combined Figures 1 to 4 The embodiments shown illustrate the technical solutions of this application: Example 1 This application provides an embodiment of a method for detecting defects in the angle steel of transmission towers based on electromagnetic induction, referring to... Figure 1 As shown, the steps include S101 to S103 as follows: Step S101: When the AC excitation source is applied to the entire angle steel under test, the dynamic differential signal of the angle steel under test is acquired in real time using a differential eddy current probe that continuously scans along the moving direction; the differential eddy current probe includes a first detection coil and a second detection coil, and the first detection coil and the second detection coil are differentially connected to output the dynamic differential signal.

[0023] In this embodiment, the output frequency of the AC excitation source is configured to be continuously adjustable from 100Hz to 5000Hz to flexibly match the complex electromagnetic interference environment on site and meet different detection sensitivity requirements. As a feasible implementation method, the excitation source can specifically be a programmable frequency converter power supply composed of a DDS (Direct Digital Synthesizer) module and a high-power constant current amplifier circuit cascaded together to achieve overall current flow to the angle steel under test.

[0024] Considering the physical characteristics of angle steel in transmission towers as thick-walled ferromagnetic components, the excitation frequency is limited to the low-to-medium frequency band of 100Hz to 5000Hz. On the one hand, this effectively overcomes the problem of insufficient penetration depth caused by the strong skin effect in high-frequency eddy current detection, ensuring that the excitation current can penetrate deep into the angle steel to effectively excite deep corrosion and cracks. On the other hand, compared with extremely low frequencies (such as below 100Hz), this frequency band ensures that the induction coils at both ends of the differential probe can cut out an induced electromotive force with a sufficient signal-to-noise ratio.

[0025] In this embodiment, an AC excitation source is connected to both ends of the angle steel under test, and a low-frequency AC current is passed into the angle steel to generate an alternating magnetic field around it. It should be noted that, to adapt to the actual working conditions of transmission tower angle steel being relatively thick and having surfaces often covered with rust or coatings, this embodiment directly connects the low-frequency AC excitation source to both ends of the angle steel under test, making the angle steel as a whole a current-carrying conductor to generate an alternating magnetic field. The detection is then performed based on the macroscopic magnetic field distortion caused when the low-frequency current flows around a defect.

[0026] In this embodiment, a differential eddy current probe is placed above the surface of the angle steel to be tested and kept at a constant lift-off distance, and continuously scanned along a preset moving direction. Specifically, the moving trajectory of the differential eddy current probe is a longitudinal path scan along the entire current-carrying path of the angle steel, enabling the probe to accurately cut and pick up the longitudinal spatial magnetic field distortion gradient caused by the physical flow around the defect when the current encounters it. As a feasible implementation, a constant lift-off distance is maintained during handheld sliding scanning, and continuous scanning is performed along this moving trajectory to obtain a dynamic differential signal based on the moving trajectory. Here, the dynamic differential signal is the difference signal output in real time by the two detection coils of the differential eddy current probe during continuous scanning along the moving direction, which changes continuously with the moving position and the defect.

[0027] In the embodiments of this application, reference is made to Figure 2 As shown, the differential eddy current probe contains a first detection coil (coil C1) and a second detection coil (coil C2), which are differentially connected to output a weak dynamic differential signal. The differential eddy current probe uses a probe housing to fix and physically protect the internal coil assembly (coil C1 and coil C2). During the detection operation, the bottom of the probe (near the bottom of the angle steel to be tested) maintains a constant lift-off distance g from the angle steel to be tested (10). As a feasible implementation, the center distance between the first detection coil and the second detection coil is 5mm to 10mm, and the lift-off distance is 2mm to 5mm, to ensure that the preamplifier can capture an induced electromotive force with a sufficient signal-to-noise ratio.

[0028] Here, based on the signal excitation principle of differential eddy current effect, when there is no defect, the induced current path on the surface of the angle steel is uniformly distributed, and the local magnetic field picked up by the two coils in the probe is basically the same, and the differential output approaches zero, thus effectively suppressing common mode background interference; when the probe slides over the area of ​​corrosion pit defect or crack defect, the defect forces the local current path to undergo flow distortion, causing a sudden change in the magnetic field, resulting in a difference in the induced electromotive force of the two coils, which in turn excites a significant alternating differential fluctuation characteristic signal.

[0029] Therefore, when the probe is located in a defect-free area, the magnetic field distribution induced by the first detection coil and the second detection coil is approximately the same, and the differential output approaches zero; when the probe passes through an area with corrosion or cracks, the defect causes the current path to change and generates a change in the magnetic field at the defect location, and the first detection coil and the second detection coil are not in sync, thus forming a clear differential output signal to indicate the location of the defect.

[0030] Step S102: Condition the dynamic differential signal to obtain a conditioned low-frequency analog characteristic signal.

[0031] In this embodiment, the signal conditioning module employs an amplification preamplifier unit, a bandpass filter unit, and a detection / demodulation unit to sequentially perform low-noise amplification, high-frequency interference filtering, and waveform envelope feature extraction on the dynamic differential signal acquired by the differential eddy current probe. Specifically, after the signal conditioning module performs low-noise amplification on the dynamic differential signal, it locks the characteristic frequency band determined by the probe's moving speed and the physical size of the defect, filters out high-frequency electromagnetic interference from the environment and extremely low-frequency baseline drift caused by hand-held shaking; then, it extracts the envelope features of the dynamic differential waveform and converts these envelope features into a high signal-to-noise ratio low-frequency analog characteristic signal.

[0032] Random hand tremors (i.e., lift-off distance fluctuations) are usually extremely low-frequency (below several hertz) and slowly changing unipolar interference, which manifests as a slowly changing low-frequency baseline drift on the detection curve. The bandpass filter unit can effectively remove this lift-off noise.

[0033] Step S103: Perform logical discrimination on the digital signal corresponding to the low-frequency analog feature signal, and if the zero-crossing feature time-domain waveform is captured during the logical discrimination process, determine the real defect result based on the defect coordinates.

[0034] In this embodiment, an AD conversion module is used to convert the conditioned low-frequency analog feature signal into a high-precision digital signal, and then feature recognition and logical discrimination are performed based on the digital signal to identify the real defect signal.

[0035] Specifically, if the waveform characteristics of the monitored digital signal only exhibit monotonous, slowly fluctuating patterns, the signal is determined to be a false defect signal caused by material inhomogeneity or residual lift-off, and this false defect signal is masked. If the monitored digital signal waveform characteristics contain a time-domain waveform that conforms to the alternating positive and negative zero-crossing characteristics, it is determined to be a real defect signal. In other words, the alternating positive and negative polarity dynamic waveform characteristics generated by the probe successively cutting across the defect are extracted, and only when a time-domain waveform that conforms to the alternating positive and negative zero-crossing characteristics is captured is it determined that there is a real crack or corrosion pit defect at the scanning location.

[0036] In this embodiment, the defect coordinates of the angle steel under test are determined based on the scanning spatial position corresponding to the zero-crossing characteristic time-domain waveform. Specifically, during the continuous scanning process of the differential eddy current probe, the captured signal feature mutation points (zero-crossing characteristic time-domain waveform) based on the time series are synchronously mapped with the instantaneous spatial displacement coordinates of the probe calculated by the encoder, completing the mapping from the time axis to the spatial axis, thereby determining the defect coordinates. That is, during the continuous scanning process of the probe, the system dynamically maps the signal feature mutation points captured on the time series with the instantaneous spatial displacement coordinates of the probe calculated by the encoder or a known speed, ultimately achieving high-precision calibration of the defect position. For example, if the time point corresponding to the mutation point of the zero-crossing characteristic time-domain waveform is 1.256 seconds, and the number of pulses output by the encoder is the 1264th, then the probe at that time point is at 126.4 mm on the moving trajectory.

[0037] In this embodiment, the zero-crossing characteristic time-domain waveform is analyzed to determine defect data based on defect coordinates, wherein the defect data represents the morphological characteristics of crack defects or corrosion pit defects. As a feasible implementation, the defect data is the crack depth; here, the peak value of the zero-crossing characteristic time-domain waveform is highly positively correlated with the crack depth.

[0038] In this embodiment, when the probe passes over a real defect, the spatially separated dual coils in the differential probe successively cut through the locally distorted magnetic field, thereby exciting a high-frequency abrupt change and a zero-crossing double-peak waveform with alternating positive and negative polarities within an extremely short spatiotemporal scale. The alternating positive and negative polarities (zero-crossing) AC dynamic waveform characteristics generated when the probe successively passes over the defect are retained and extracted. By distinguishing this temporal characteristic and combining it with the mapping to the scanning spatial position, the system can effectively differentiate between the real defect signal and the low-frequency baseline drift caused by handheld detection due to lift-off distance fluctuations (hand tremors).

[0039] The electromagnetic induction-based method for detecting defects in the angle steel of transmission towers provided in this embodiment involves supplying current to the angle steel under test through an AC excitation source, and using a differential eddy current probe that continuously scans along the moving direction to acquire the dynamic differential signal of the angle steel under test in real time. The dynamic differential signal is then conditioned to obtain a conditioned low-frequency analog characteristic signal. The digital signal corresponding to the low-frequency analog characteristic signal is then logically judged. If a zero-crossing characteristic time-domain waveform is captured during the logical judgment process, the true defect result of the angle steel under test based on the defect coordinates is determined. In this way, the excitation current is penetrated deep into the angle steel under test, capturing the zero-crossing characteristic time-domain waveform of the angle steel. This effectively distinguishes defect signals from interference signals, realizes the effective excitation of deep corrosion and cracks in the angle steel, and finally obtains true and reliable defect detection results based on defect coordinates, avoiding misjudgment and missed detection. At the same time, the closed-loop constant current drive architecture effectively overcomes the contact impedance fluctuation interference caused by the anti-corrosion layer and rust on the surface of the angle steel, ensuring the high fidelity and stability of the detection signal. It can meet the needs of efficient and high-precision defect detection of angle steel of transmission towers under complex outdoor working conditions.

[0040] Example 2 Based on the above embodiments, this embodiment also provides a defect detection system for angle steel of transmission towers based on electromagnetic induction, used to implement the above-mentioned defect detection method for angle steel of transmission towers based on electromagnetic induction, referring to... Figure 3 , Figure 4 As shown, the system in this embodiment includes: The AC excitation source 3 is used to be electrically connected to both ends of the angle steel 1 under test, and to output a low-frequency AC current to the interior of the angle steel 1 under test, so as to form an alternating magnetic field around the angle steel 1 under test. The differential eddy current probe 2 is used to closely approach the surface of the angle steel 1 under test and continuously scan along the moving direction 7 to acquire the dynamic differential signal of the angle steel 1 under test in real time; the differential eddy current probe 2 includes a first detection coil C1 and a second detection coil C2, and the first detection coil and the second detection coil are differentially connected to output the dynamic differential signal; The signal conditioning module 4 is connected to the output terminal of the differential eddy current probe 2 and is used to condition the dynamic differential signal to obtain a conditioned low-frequency analog characteristic signal. AD conversion module 15 is connected to the output terminal of the signal conditioning module 4 and is used to convert the low-frequency analog characteristic signal into a digital signal. The controller 5, connected to the AD conversion module 15, is used to receive the digital signal and perform logical discrimination on the digital signal. In the process of logical discrimination, if the zero-crossing characteristic time-domain waveform is captured, the controller determines the true defect result based on the defect coordinates.

[0041] The display and early warning unit 6 is used to intuitively present the test results and trigger an audible and visual alarm or an operation interface prompt when the system determines that a defect exists.

[0042] Reference Figure 3 As shown, the AC excitation source 3 is connected to both ends of the angle steel 1 under test, and a low-frequency AC current is passed into the angle steel 1 to form an alternating magnetic field around it. The differential eddy current probe 2 is placed above the surface of the angle steel 1 under test and scans along the moving direction 7. The output signal of the differential eddy current probe 2 is sent to the signal conditioning module 4, processed, and then sent to the controller 5. The controller 5 outputs the result to the display and early warning unit 6 to realize the display of the detection result and the defect alarm.

[0043] Reference Figure 2 As shown, the differential eddy current probe 2 includes a probe housing 9, inside which a first detection coil C1 and a second detection coil C2 are disposed, and the two coils are differentially connected 8 for output. The bottom of the differential eddy current probe 2 maintains a lifting distance g10 from the surface of the angle steel 1 to be measured.

[0044] When the probe is located in a defect-free area, the magnetic field distribution induced by the two coils is approximately the same, and the differential output approaches zero. When the probe passes through an area with corrosion or cracks, the defect causes the current path to change and generates a change in the magnetic field at the defect location. The two coils are not induced in a consistent manner, thus forming a significant differential output signal to indicate the location of the defect.

[0045] Reference Figure 4 As shown, the AC excitation source 3 acts on the angle steel 1 under test. During actual continuous scanning, when the differential eddy current probe 2 smoothly glides over a defect-free, intact area, a stable background magnetic field is formed inside the angle steel 1 under test. Relying on the hardware differential subtraction mechanism inside the probe, the background signal, as common-mode interference, is instantly canceled out, and the initial signal sent to the preamplifier 12 exhibits a smooth baseline close to zero potential. If hand-held shaking during operation causes slow fluctuations in the lift-off distance, the resulting extremely low-frequency drift will be effectively isolated by the subsequent bandpass filter 13, thereby ensuring the absolute stability of the system's reference zero point.

[0046] As the differential eddy current probe 2 continues scanning and crosses defects such as cracks or corrosion pits, it causes a change in the magnetic field at the defect location 11. This spatiotemporal misalignment momentarily disrupts the differential balance, generating a weak dynamic AC differential voltage. The preamplifier 12 then amplifies this transient weak signal with low noise, and the signal subsequently enters the bandpass filter 13 and the detection / demodulation module 14 in sequence. The bandpass filter 13 accurately locks the characteristic frequency band and completely filters out high-frequency electromagnetic interference. The detection / demodulation module 14 extracts the envelope characteristics of the dynamic differential waveform and converts it into a low-frequency analog signal, which is then converted into a digital signal by the AD converter 15.

[0047] The characteristic signal, after complete link conditioning, is finally sent to controller 5 for logical judgment. At this stage, the controller performs pattern recognition based on the "alternating positive and negative polarity (zero crossing)" AC dynamic waveform characteristics generated when the differential eddy current probe 2 successively crosses the defect. If the input signal only shows monotonous slow fluctuations, the controller treats it as a spurious signal and blocks it; only when the "zero crossing" characteristic waveform that conforms to the alternating positive and negative polarity is accurately captured, the controller determines it as a real defect and outputs the defect information to display and warning 6 to trigger an alarm.

[0048] Thus, the entire signal link works in effective coordination, enabling high-sensitivity defect pickup under complex operating conditions.

[0049] Example 3 Based on the above embodiments, the physical testing platform and hardware configuration of this embodiment are specifically as follows: Test object (angle steel): Q235 standard angle steel commonly used in transmission towers is selected, and artificial pre-fabricated cracks of different depths (e.g., 1mm, 2mm, 3mm) and widths of 0.5mm, as well as flat-bottomed blind holes of different diameters are processed on the surface using wire EDM technology to simulate localized corrosion pits. AC excitation source configuration: A combination of an arbitrary waveform signal generator and a broadband power amplifier is used as the AC excitation source. In actual implementation, the signal generator outputs a continuous sine wave signal from 100Hz to 5000Hz, which, after being amplified by the power amplifier, is directly injected into both ends of the angle steel under test with a low-frequency AC constant current excitation of 100mA. Due to the direct current transmission method, the alternating current is conducted inside the angle steel under test and a stable circumferential alternating background magnetic field is generated on the surface of the angle steel under test and above the anti-corrosion coating.

[0050] In this embodiment, the differential eddy current probe is specifically configured as follows (corresponding to...). Figure 2 The differential coil is made of tightly wound enameled wire, and the center distance between the two coils (C1 and C2) is set to 5mm to 10mm according to the target defect size. During the scanning process, the probe maintains a constant lift distance of g=2mm to 5mm from the surface of the angle steel to be tested through the non-metallic wear-resistant shell, simulating the actual non-contact detection conditions with coatings or dirt.

[0051] Testing revealed that when the probe smoothly glided over a defect-free Q235 angle steel area, the alternating current flowing through the angle steel was uniformly distributed, generating a stable background magnetic field. Because the two coils inside the probe were connected differentially (in reverse series), the induced background voltages, reaching several volts, canceled each other out. The common-mode residual voltage fed into the preamplifier was suppressed to the millivolt level, demonstrating the extremely strong suppression effect of the differential structure on the background magnetic field.

[0052] When the probe crosses a pre-existing crack with a width of 0.5 mm, the crack cuts off the conduction path of the alternating current inside the angle steel, forcing the current to physically bypass the crack and generating a distorted magnetic field above the defect. As the two detection coils inside the probe pass through this distorted magnetic field sequentially, an oscilloscope or host computer interface clearly captures a voltage waveform with alternating positive and negative jumps and a "zero-crossing" characteristic. The peak-to-peak value of this waveform is highly positively correlated with the crack depth, and the signal-to-noise ratio is typically above 15 dB.

[0053] In summary, the proposed solution does not require complex surface grinding pretreatment. By configuring a conventional direct current excitation source and differential induction probe according to the above platform parameters, and utilizing the unique spatial misalignment response of the differential coil to extract the zero-crossing characteristic waveform, the defect signal of the angle steel under test can be stably and sensitively picked up even under conditions where there is a lift-off distance (such as anti-corrosion coating), making it suitable for rapid on-site inspection.

[0054] This application also provides a computer-readable storage medium storing a computer program. When executed by a processor, the computer program implements the method in any of the embodiments of this application. Specifically, a system or apparatus equipped with a storage medium may be provided, on which software program code implementing the functions of any of the above embodiments is stored, and the computer (or CPU (Central Processing Unit) or MPU (Microprocessor Unit) of the system or apparatus may read and execute the program code stored in the storage medium.

[0055] Specifically, according to embodiments of this application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of this application include a computer program product comprising a computer program carried on a computer-readable storage medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication component, and / or installed from a removable medium. When the computer program is executed by a central processing unit (CPU), it performs the functions defined above in the system of this application.

[0056] It should be noted that the computer-readable storage medium shown in this application can be a computer-readable signal medium or a computer-readable storage medium, or any combination thereof. A computer-readable storage medium can be, for example, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of a computer-readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) or flash memory, optical fiber, portable compact disc read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this application, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. In this application, a computer-readable signal medium can include a data signal propagated in baseband or as part of a carrier wave, carrying computer-readable program code. The transmitted data signal can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. The computer-readable signal medium can also be any computer-readable storage medium other than a computer-readable storage medium, which can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the computer-readable storage medium can be transmitted using any suitable medium, including but not limited to: wireless, wire, optical fiber, RF (Radio Frequency), etc., or any suitable combination thereof.

[0057] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram or flowchart, and combinations of blocks in a block diagram or flowchart, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0058] The units described in the embodiments of this application can be implemented in software or hardware, and the described units can also be located in a processor. The names of these units do not necessarily limit the specific unit itself.

[0059] It should be noted that although several modules or units for the device used to perform actions have been mentioned in the detailed description above, this division is not mandatory. In fact, according to the embodiments of this application, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided and embodied by multiple modules or units.

[0060] In the several embodiments provided in this application, it should be understood that the disclosed systems, modules, and methods can be implemented in other ways. For example, the module embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between modules or units, and may be electrical, mechanical, or other forms.

[0061] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. This application is not limited to the exact structures described above and illustrated in the accompanying drawings, and it should not be considered that the specific implementation of this application is limited to these descriptions. For those skilled in the art, various changes and modifications made without departing from the concept of this application should be considered to fall within the protection scope of this application.

Claims

1. A method for detecting defects in angle steel of transmission towers based on electromagnetic induction, characterized in that, include: When current is passed through the entire angle steel under test by an AC excitation source, the dynamic differential signal of the angle steel under test is acquired in real time by a differential eddy current probe that continuously scans along the moving direction; the differential eddy current probe includes a first detection coil and a second detection coil, and the first detection coil and the second detection coil are differentially connected to output the dynamic differential signal; The dynamic differential signal is conditioned to obtain a conditioned low-frequency analog characteristic signal; Logical discrimination is performed on the digital signal corresponding to the low-frequency analog characteristic signal, and the zero-crossing characteristic time-domain waveform is captured during the logical discrimination process to determine the true defect result based on the defect coordinates.

2. The method for detecting defects in angle steel of transmission towers based on electromagnetic induction according to claim 1, characterized in that, The method of acquiring the dynamic differential signal of the angle steel under test in real time using a differential eddy current probe that continuously scans along the moving direction includes: The differential eddy current probe is placed above the surface of the angle steel to be tested and a constant lift-off distance is maintained under handheld sliding scanning conditions. Continuous scanning is performed along a preset movement trajectory to obtain a dynamic differential signal based on the movement trajectory. The movement trajectory is the longitudinal path along the global flow path of the angle steel to be tested.

3. The method for detecting defects in angle steel of transmission towers based on electromagnetic induction according to claim 2, characterized in that, The conditioning of the dynamic differential signal to obtain the conditioned low-frequency analog characteristic signal includes: After low-noise amplification of the dynamic differential signal, the characteristic frequency band is locked, and high-frequency electromagnetic interference from the environment and extremely low-frequency baseline drift caused by hand shake are filtered out. Extract the envelope features of the dynamic differential waveform and convert the envelope features into the low-frequency analog feature signal.

4. The method for detecting defects in angle steel of transmission towers based on electromagnetic induction according to claim 3, characterized in that, The actual defect result is at least one of crack defects and corrosion pit defects; the step of performing logical discrimination on the digital signal corresponding to the low-frequency analog feature signal, and capturing the zero-crossing feature time-domain waveform during the logical discrimination process, to determine the actual defect result based on the defect coordinates includes: The low-frequency analog characteristic signal is converted into a digital signal using an AD converter; If the waveform characteristics of the digital signal are found to be only monotonically fluctuating, the low-frequency analog characteristic signal is determined to be a false defect signal, and the false defect signal is shielded. If the waveform characteristics of the digital signal show a zero-crossing time-domain waveform with alternating positive and negative transitions, the low-frequency analog characteristic signal is determined to be a real defect signal. Based on the scanning spatial position corresponding to the zero-crossing time-domain waveform, the defect coordinates of the angle steel under test are determined. Then, the zero-crossing time-domain waveform is analyzed to determine the defect data based on the defect coordinates. The defect data is the morphological characteristics of the crack defect or the corrosion pit defect.

5. The method for detecting defects in angle steel of transmission towers based on electromagnetic induction according to claim 4, characterized in that, The scanning spatial position is the instantaneous spatial position coordinate of the probe; determining the defect coordinates of the angle steel under test based on the scanning spatial position corresponding to the zero-crossing characteristic time-domain waveform includes: During the continuous scanning process of the differential eddy current probe, the captured signal feature abrupt change points based on the time series are synchronously correlated with the instantaneous spatial displacement coordinates of the probe calculated by the encoder, thus completing the mapping from the time axis to the spatial axis and determining the defect coordinates.

6. The method for detecting defects in angle steel of transmission towers based on electromagnetic induction according to any one of claims 2-5, characterized in that, The output frequency of the AC excitation source is continuously adjustable within the range of 100Hz to 5000Hz, and the lift-off distance is 2mm to 5mm.

7. A defect detection system for angle steel of transmission towers based on electromagnetic induction, used to implement the defect detection method for angle steel of transmission towers based on electromagnetic induction as described in any one of claims 1-6, characterized in that, The system includes: An AC excitation source is used to electrically connect to both ends of the angle steel under test and output a low-frequency AC current to the interior of the angle steel under test, so as to form an alternating magnetic field around the angle steel under test. A differential eddy current probe is used to closely approach the surface of the angle steel to be tested and continuously scan along the moving direction to acquire the dynamic differential signal of the angle steel to be tested in real time; the differential eddy current probe includes a first detection coil and a second detection coil, and the first detection coil and the second detection coil are differentially connected to output the dynamic differential signal; The signal conditioning module is connected to the output terminal of the differential eddy current probe and is used to condition the dynamic differential signal to obtain a conditioned low-frequency analog characteristic signal. An AD conversion module is connected to the output of the signal conditioning module and is used to convert the low-frequency analog characteristic signal into a digital signal. The control module, connected to the AD conversion module, is used to receive the digital signal and perform logical discrimination on the digital signal. In the process of logical discrimination, if the zero-crossing characteristic time-domain waveform is captured, the actual defect result based on the defect coordinates is determined.

8. The electromagnetic induction-based defect detection system for angle steel of transmission towers according to claim 7, characterized in that, The first detection coil and the second detection coil are fixedly encapsulated in the probe housing of the differential eddy current probe, and the center distance between the first detection coil and the second detection coil is 5mm to 10mm; The bottom of the probe housing near the angle steel to be tested maintains a constant lifting distance from the surface of the angle steel to be tested, and the lifting distance is 2mm to 5mm.

9. The electromagnetic induction-based defect detection system for angle steel of transmission towers according to claim 7, characterized in that, The signal conditioning module includes: The preamplifier unit is used to amplify the dynamic differential signal excited when the differential balance is broken with low noise. The bandpass filter unit is used to lock the characteristic frequency band and filter out high-frequency electromagnetic interference from the environment and extremely low-frequency baseline drift caused by hand shake. The detection / demodulation unit is used to extract the envelope features of the dynamic differential waveform and convert the envelope features into the low-frequency analog feature signal.

10. The electromagnetic induction-based defect detection system for angle steel of transmission towers according to any one of claims 7-9, characterized in that, Also includes: The display and early warning module is connected to the control module and is used to display the detection results and output early warning information when it is determined that there are real defects.

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