A non-metal pipeline metal marking detection method and device based on an eddy current effect

Abstract

The application provides a non-metal pipeline metal marker detection method and device based on an eddy current effect, and relates to the technical field of non-metal pipeline detection. The method installs a metal marker carrying binary code on a pipeline, excites the eddy current effect of the metal marker by applying an alternating magnetic field, and picks up an induced magnetic field signal. The device adopts a double-D-shaped anti-phase series differential eddy current probe combined with a four-stage signal conditioning chain to improve the anti-interference ability and signal quality, and then extracts multi-domain features of the marker in the amplitude, phase and frequency spectrum. By matching the extracted features with a preset database, the device accurately analyzes the binary code and spatial position of the metal marker, thereby uniquely determining the identity information of the pipeline, including the ownership, material, burial depth and direction, etc. The application realizes high-precision positioning, large-capacity identity code and strong anti-interference detection, and effectively solves the problems of weak anti-interference, small code capacity and limited detection depth and precision in the existing non-metal pipeline positioning technology.

Description

Technical Field

[0001] This invention relates to the field of intelligent detection and identification technology for underground pipelines, and in particular to a method for accurate positioning and identification of non-metallic pipelines such as PE / PVC in scenarios such as municipal water supply and drainage and gas transmission. Background Technology

[0002] Polyethylene (PE) pipes, widely used in urban gas and water supply systems, face significant challenges in locating and identifying pipelines in complex underground environments due to their non-conductive properties. Existing technologies have serious limitations: ground-penetrating radar (GPR) is constrained by soil dielectric properties and completely fails to identify pipelines; electromagnetic tracing relies on fragile pre-buried wires, and under strong electromagnetic interference, positioning drift often exceeds 1.2 meters, lacking coding and identification capabilities; acoustic detection methods are impractical due to implementation limitations and shallow-buried wave aliasing issues, and lack identification mechanisms. To fundamentally overcome the dilemma of simultaneously meeting the three major requirements of "identity recognition," "high-precision positioning," and "strong anti-interference" for non-metallic pipelines, eddy current detection technology based on pre-embedded binary coded metal tags has emerged. By pre-installing coded metal markers on the pipe wall and integrating highly robust signal processing and multi-domain feature (amplitude, phase, spectrum) joint analysis, this technology provides a solution for simultaneously achieving centimeter-level spatial coordinate positioning and accurate identification of a complete digital identity including ownership, pipe diameter, material, and medium, laying the core technological foundation for smart pipeline networks.

[0003] Existing technical solutions include the electromagnetic-tracer line method and the acoustic detection method. The electromagnetic-tracer line method is a traditional pipeline positioning technology. This method involves pre-burying a metal tracer line during pipeline laying, using a ground transmitter to inject an alternating current of a specific frequency into the tracer line, and a receiver to detect the electromagnetic field signal radiated by the tracer line. The pipeline trajectory is located by calculating the field strength attenuation gradient. However, the electromagnetic-tracer line method is too dependent on pre-buried infrastructure. The renovation of old pipelines requires excavation and laying of tracer lines along the entire line. Furthermore, electromagnetic interference from nearby cables can cause the positioning signal to drift. At the same time, this method cannot provide pipeline identification functionality.

[0004] Acoustic detection is a novel detection technology that uses a seismic source to generate an acoustic excitation signal. The signal propagates to the surface of the pipeline and generates a reflected wave signal. A signal receiving device receives the reflected wave signal and processes it through translation, superposition, and other methods to locate the buried pipeline. However, the acoustic reflection method has high requirements for the seismic source equipment, requiring a high-power seismic source to ensure signal strength. Furthermore, the reflected wave signal and the direct wave signal must be completely separated, making it difficult to apply in sensitive areas such as residential areas. In addition, the reflected wave and the direct wave of shallow buried pipelines are prone to overlap, which seriously affects the positioning accuracy. Summary of the Invention

[0005] This invention aims to address the shortcomings of the existing technology and provides a method and device for detecting metal markers on non-metallic pipelines based on the eddy current effect. This solution integrates differential eddy current sensing, multi-domain feature analysis, and binary encoding parsing technology to achieve centimeter-level positioning and accurate identification of buried non-metallic pipelines.

[0006] The present invention adopts the following technical solution: This invention addresses three major technical bottlenecks in non-metallic pipeline positioning: weak anti-interference, insufficient coding capacity, and limited detection depth. It provides a method and device for detecting metal markers based on the eddy current effect. The device includes a power module, an excitation signal generator, an excitation coil, a dual-D-shaped differential eddy current probe, a signal conditioning and acquisition module, a signal analyzer, and an embedded main control system. The power module supplies power to all components. The excitation signal generator receives instructions from the embedded main control system and generates an excitation current with a specific frequency and amplitude. The excitation coil converts the current into an alternating magnetic field, exciting eddy currents in the metal markers embedded in the pipeline. The dual-D-shaped differential eddy current probe uses an anti-phase series structure, externally covered with a permalloy magnetic shielding layer and internally with a copper foil electrostatic shielding layer for high-sensitivity capture of the secondary magnetic field signal generated by the eddy currents. The signal conditioning and acquisition module is sequentially connected to a high common-mode rejection ratio (CMRR) amplifier, an instrumentation amplifier, a center-frequency adjustable bandpass filter, a programmable gain amplifier, and a 24-bit... The analog-to-digital converter enables anti-interference conditioning and high-precision digitization of the signal; the signal analyzer is responsible for extracting key feature parameters from the digitized signal, including amplitude attenuation, phase shift, and spectral response; the embedded main control system controls the operating parameters of the excitation signal generator through the data bus, accesses the preset metal mark feature-encoding mapping database for feature matching, and finally parses out the 64-bit binary code sequence and its three-dimensional spatial coordinates carried by the metal mark.

[0007] A method for detecting metal marks on non-metallic pipes based on the eddy current effect, comprising the following steps: Step 1: Set the excitation frequency and amplitude, and the moving device emits an alternating magnetic field; First, based on the material properties of the metal markers and the estimated pipeline burial depth, the excitation frequency range is preset to 5 to 50 kHz and the reference current is 200 mA. Then, the handheld detection device moves at a constant speed along the preset trajectory of the pipeline. The built-in sensor of the device monitors the ambient background noise intensity in real time. When the noise exceeds the 10 mV threshold, the system automatically increases the excitation current by 20% to 50% and activates the anti-interference mode. Finally, the excitation coil emits an alternating magnetic field into the soil, which penetrates the soil and excites the metal markers embedded in the non-metallic pipe wall to generate an eddy current effect.

[0008] Step 2 involves acquiring the induced signal through a differential coil, followed by amplification, bandpass filtering, and adaptive gain adjustment. The noise calibration program is initiated in an unmarked area 1 meter to the side of the pipeline track. The device automatically collects 10 seconds of ambient electromagnetic noise and calculates the root mean square (RMS) value. Based on this, the system sets a noise threshold of three times the RMS value. Subsequently, a dual-D differential eddy current probe captures the secondary magnetic field signal of the metal marker and performs real-time amplification through a three-stage processing chain. First, a high-gain instrumentation amplifier amplifies the signal by 90 dB to suppress common-mode interference. Second, a bandpass filter with a center frequency matched to the excitation frequency removes out-of-band noise. Finally, a programmable gain module dynamically boosts the weak signal by 1000 times while limiting the output amplitude to the measurable range. The conditioned signal is compared with the noise threshold in real time, and invalid data below the threshold is automatically discarded.

[0009] Step 3: Calculate the amplitude attenuation rate and phase shift, and generate a binary ID based on the threshold to determine the existence of the marker; S301. Signal Acquisition and Transmission The embedded main control system sends control commands to the excitation signal generator, driving it to generate an excitation current signal of a specific frequency. This current is transmitted to the excitation coil to generate the target alternating magnetic field, which in turn excites the buried metal marker to form eddy currents and a secondary magnetic field. After the dual D-shaped differential eddy current probe captures the secondary magnetic field signal, the signal is amplified and filtered by the conditioning module, and finally the digital signal is uploaded to the embedded main control system by the acquisition system.

[0010] S302. Multi-domain Feature Processing and Judgment The embedded main control system performs synchronous dual-channel analysis on the received signal: first, it calculates the attenuation rate of the signal peak relative to the reference value and quantifies it in decibels; second, it accurately extracts the phase offset between the excitation signal and the received signal through a cross-correlation algorithm; based on the preset amplitude attenuation threshold and phase offset threshold, the system integrates dual features to determine the existence of the metal mark.

[0011] Step 4: Locate the horizontal position based on the peak signal strength, calculate the burial depth using the attenuation model, and map the pipe attributes using the ID sequence. The system identifies the peak curvature point of the signal attenuation curve and determines the horizontal coordinate of this point as the center position of the metal marker. The measured positioning accuracy reaches ±3 cm. The burial depth calculation adopts a dual-frequency cross-verification strategy. First, the initial depth is calculated with a 10 kHz excitation signal, and then the soil attenuation coefficient is calibrated with a 30 kHz signal. Finally, the embedded main control system inputs the 64-bit binary code sequence into the preset pipeline database, automatically parses and outputs the pipeline physical attributes, including pipe diameter, material and service life, ownership unit and contact information, and safety level of the transported medium, and simultaneously generates a three-dimensional pipeline trajectory map.

[0012] The beneficial effects of this invention are: 1. It realizes the unique identification information of non-metallic pipelines (ownership, material, pipe diameter, burial depth, direction, medium, etc.). Through the pre-embedded binary code metal mark, it can meet the identification requirements of one pipe for one identity in a massive urban pipeline network, and completely solve the historical problem of inaccurate identification of non-metallic pipelines.

[0013] 2. Based on the horizontal positioning algorithm of signal strength gradient peak and the burial depth calculation strategy based on dual-frequency excitation + attenuation model, combined with the high spatial resolution of the dual D-shaped anti-phase series differential eddy current probe, ultra-high precision positioning of the buried metal marker center position at ±3 cm level was achieved, which is far superior to the existing technology.

[0014] 3. A dual-D-shaped anti-phase series differential eddy current probe design is proposed. Combining permalloy magnetic shielding, copper foil electrostatic shielding, and a three-stage high-robust signal conditioning chain, it can maintain an ultra-high signal-to-noise ratio even in strong electromagnetic interference environments, which can effectively solve the problem of positioning drift or failure caused by interference in existing technologies.

[0015] 4. A dynamic optimization mechanism for excitation parameters based on the skin depth model and soil attenuation law is proposed. Combined with a dual-frequency cross-validation depth calculation strategy, the influence of soil electrical property changes on detection sensitivity and depth is significantly reduced, and the effective detection depth and reliability under complex soil conditions are greatly improved, with strong depth adaptability.

[0016] 5. The binary encoding scheme of this invention supports a very large identifier capacity, providing a scalable technical foundation for the massive data management of smart pipeline networks. Attached Figure Description

[0017] Figure 1 This is a time-domain schematic diagram of the eddy current detection pulse of the present invention; Figure 2 This is a graph showing the time-domain eddy current attenuation curve of the eddy current detection pulse of the present invention. Figure 3 This is a schematic diagram of the continuous wave frequency domain principle for eddy current detection in this invention. Figure 4 This is a diagram showing the phase shift results of continuous wave excitation for eddy current detection according to the present invention. Figure 5 This is a magnetic flux density diagram of each tag for eddy current detection in this invention; Figure 6 This is a schematic diagram of the module layout of the device of the present invention; Figure 7 This is an external view of the portable detection device of the present invention; Figure 8 This is an interface diagram of the pipeline identification system of the present invention.

[0018] In the diagram: 1-Vehicle body, 2-Waterproof data interface, 3-LCD display screen, 4-Support column, 5-Embedded main control system, 6-Push handle, 7-Universal wheel. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings; for example... Figure 1-4 As shown, this device employs a dual-mode approach of transient and transient detection to enhance detection robustness. The transient detection mode is as follows: Figure 1 , Figure 2 In this process, the excitation signal generator produces a high-voltage narrow pulse, which induces eddy currents in the metal mark through a transient magnetic field generated by the excitation coil. These induced eddy currents decay exponentially: where the time constant ( (where is the relative permeability, is the electrical conductivity, and d is the burial depth). A dual-D-shaped probe captures the secondary magnetic field generated by this decaying eddy current, measured within a specific sampling time window. to The integral value of the differential signal within can be used to calculate the mark depth and material properties in transient detection modes, such as... Figure 3 , Figure 4 The middle part uses continuous sinusoidal excitation. This causes the metal marker to generate eddies with the same frequency but a phase shift. This phase offset Distance from marker Satisfying the relation ,in The equivalent resistance decreases exponentially with increasing distance.

[0020] like Figure 6 As shown, the non-metallic pipe metal marking detection device based on the eddy current effect of the present invention includes a power supply module, an excitation signal generator, an excitation coil, a dual D-shaped differential eddy current probe, a signal conditioning and acquisition module, a signal analyzer, and an embedded main control system. All components are integrated into a portable vehicle body 1, with an LCD screen 3 on the top and a waterproof data interface 2 on the side. The power supply module provides 24V DC power to the system and connects to each subsystem through an internal bus.

[0021] The embedded main control system connects to the excitation signal generator control terminal via data interface 2 and sends frequency modulation commands. Upon receiving the commands, the excitation signal generator generates an excitation current, which is transmitted to the excitation coil via a copper core cable. The excitation coil employs a multi-turn flat spiral structure and is installed in the probe area at the bottom of the housing, converting the current into a vertically downward alternating magnetic field. The eddy current is generated by penetrating the soil layer and exciting the metal markings buried in the PE pipe wall.

[0022] like Figure 6 As shown, the double-D-shaped differential eddy current probe is located 20mm to the right of the excitation coil and adopts a double-D-shaped anti-phase series structure. The coil frame is made of ceramic substrate, covered with a 1mm thick permalloy magnetic shielding layer on the outside, and a 0.1mm copper foil electrostatic shielding layer on the inside. The coil is wound with 200 turns of 800 strands of 0.05mm excitation wire.

[0023] The signal conditioning and acquisition module comprises a four-stage processing chain: a high-precision instrumentation amplifier pre-amplifies the differential signal; a programmable fourth-order Chebyshev bandpass filter with a center frequency removes out-of-band noise; an automatic gain amplifier dynamically adjusts the gain based on signal strength; and a 24-bit... The ADC performs digital conversion at a sampling rate of 10 times the excitation frequency. The processed data is transmitted to the signal analyzer via the SPI bus.

[0024] like Figure 7 As shown, the embedded main control system has a built-in metal marker feature database and executes the core algorithm: Real-time calculation of amplitude attenuation rate Solving for phase offset Existence determination of markers Implementation of the automatic vehicle trajectory correction algorithm: The correction coil system collects the magnetic field strength signals from both the left and right sides in real time. and The signal is then transmitted to the embedded main control system. The system first normalizes the signal and calculates the real-time horizontal deviation. This processing eliminates the influence of absolute signal amplitude, making the deviation comparable. The embedded main control system's built-in PID controller adjusts this deviation accordingly. The control output of the steering servo is dynamically calculated. The core of the PID controller lies in three working components: the proportional term (P) is responsible for the immediate response to the current deviation. Quickly correct vehicle orientation; the integral term (I) accumulates historical deviations. (in The sampling period is used to eliminate long-standing path offsets; the differential term (D) is calculated by measuring the rate of change of the deviation. It predicts future trends and effectively suppresses oscillations during steering. Combining these three functions, the steering angle... The output is determined by the following discretized PID formula: This PID control algorithm addresses instantaneous vehicle body deviation through a proportional term, corrects long-term trajectory drift through an integral term, suppresses steering overshoot through a derivative term, and deeply couples eddy current signal intensity detection, significantly improving the automatic tracking stability of the detection device in complex terrain. The measured path tracking error can be controlled within 5 centimeters.

[0025] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting metal markings on non-metallic pipes based on the eddy current effect, characterized in that, The steps are as follows: Step 1. Parameter initialization and excitation application; Set the frequency and amplitude of the excitation current and determine the preset attribute parameters of the metal marker; apply an alternating magnetic field of a specific frequency and amplitude to the target detection position to excite the metal marker buried on the non-metallic pipe; S101. Set the excitation parameters and excitation frequency according to the characteristics of the metallic marking material and the soil attenuation characteristics. Based on the skin depth of metallic marker materials Sure: in To label conductivity, The relative permeability, Permeability of free space; Excitation amplitude By detection depth Sure: S102. Apply excitation by moving the excitation coil above the pipe to generate a time-varying magnetic field that excites eddy currents in the metal marker. : in The magnitude of the magnetic flux density. The excitation frequency, It is the direction vector; Step 2. Differential signal acquisition and conditioning; The eddy current induced magnetic field signal generated by the excitation of a metal mark is detected by a geometrically symmetrical and anti-phase series dual D-shaped differential eddy current probe; the induced signal is pre-amplified, bandpass filtered and gain adaptively adjusted, wherein the center frequency of the bandpass filter is matched with the excitation frequency; S201. Eddy current induction signal, eddy current density generated by a metal marker. satisfy: in Electrical conductivity, its secondary magnetic field Captured by the differential coil; S202. Differential anti-interference design, the output potential difference of the two coils : in , The area vector of the coil. To sense the magnetic field strength, a symmetrical layout minimizes environmental interference. ; S203. Signal Conditioning Chain Design: Preamplifier Instrumentation Amplifier Gain : The transfer function of a fourth-order Chebyshev bandpass filter is as follows: Center frequency , bandwidth , Gain adaptive, dynamically adjusting the PGA gain based on the signal RMS value. : Step 3. Signal digitization and feature extraction; The conditioned analog signal is converted into a high-resolution digital signal, and feature parameters related to the properties of the metal mark are extracted from the digital signal, including amplitude attenuation, phase shift and spectral response characteristics. Step 4. Metal marker identification and information analysis; The extracted signal feature parameters are matched with a preset metal marker feature-encoding mapping database. Based on the matching results, the binary identification code of the metal marker and its spatial location are analyzed. Combined with the encoding rules and location distribution of the metal marker, the direction, burial depth and preset identification information of the non-metallic pipeline are determined.

2. The method for detecting metal marks on non-metallic pipes based on the eddy current effect according to claim 1, characterized in that, The step S201 describes the use of a dual D-shaped anti-phase series differential eddy current probe to directly capture the secondary magnetic field induced by the metal tag. The anti-phase series structure outputs a potential difference, which helps to suppress environmental common-mode interference and improve the ability to detect weak eddy current signals from metal tags. By employing four-level robust signal conditioning, multi-domain feature (amplitude attenuation, phase shift, spectral Q value) joint analysis, and identity reconstruction based on a feature-encoding mapping database (binary ID sequence and three-dimensional coordinate positioning), a high-precision detection process is achieved throughout the entire process, from eddy current excitation optimization, specific acquisition of metal tag signals, feature extraction to intelligent reconstruction of complete pipeline identity information. The output signal of the four-level signal conditioning chain provides a high signal-to-noise ratio input for subsequent multi-domain joint analysis of amplitude, phase, and spectrum. Feature parameter extraction: Amplitude attenuation: in For amplitude attenuation, The acquired voltage signal. Excitation magnetic field amplitude; Phase shift: in For phase shift, For the excitation current signal, For excitation frequency; Spectral response: Q represents the quality factor.

3. The method for detecting metal marks on non-metallic pipes based on the eddy current effect according to claim 1, characterized in that, Using metal tags as precise excitation targets for the eddy current effect, the identification and positioning of pipelines can be achieved by receiving the electromagnetic signals induced by the metal tags and analyzing the binary code sequence they carry. Binary encoding and decoding: Along the axial position of the pipe Existence determination of the marker: Generate encoded sequence .

4. According to claim 3, the characteristic is: The metallic markings are designed with gradient electromagnetic properties. High-conductivity materials such as copper and aluminum are used in shallow pipelines. d ≤1.5m) to maximize eddy current density, high permeability alloys such as permalloy are used for deep pipelines ( d To compensate for magnetic field attenuation (>1.5m), or to use a copper-permalloy composite structure to synergistically optimize penetration and signal strength; and to carry binary codes through preset shape combinations (rings, crosses or rectangular arrays), where the ring has a spectral Q value that is more than 40% higher than the cross under 20kHz excitation. Anti-aliasing coding is achieved by utilizing the separability of phase shift and spectral response. This design breaks through the single signal limitation of existing homogeneous metal sheet technology. Through the coupling of material gradient, geometric size and shape features, a single mark can simultaneously transmit the three-in-one identity information of material type, geometric properties and binary code.

5. A non-metallic pipe metal marking detection device based on the eddy current effect, characterized in that, include: The vehicle body, power supply, excitation signal generator, excitation coil, dual D-shaped differential eddy current probe, signal conditioning and acquisition module, signal analyzer, embedded main control system, step control unit and correction coil system; The bottom of the vehicle body is equipped with casters and a drive motor, and the top is equipped with an LCD screen and a push handle. The step distance control unit is integrated into the embedded main control system and is used to receive preset step distance commands and control the vehicle body to start and stop periodically according to the step distance. The correction coil system includes detection coils symmetrically arranged on the left and right sides of the vehicle body, which collect the magnetic field strength on both sides in real time and transmit it to the embedded main control system; the power supply is used to power the excitation signal generator, signal conditioning and acquisition module, signal analyzer and embedded main control system; The output terminal of the excitation signal generator is connected to the excitation coil and is used to generate a pulse current of a specific frequency and amplitude according to the control command of the embedded main control system, so as to drive the excitation coil to generate an excitation alternating magnetic field. The output end of the dual D-shaped differential eddy current probe is connected to the input end of the signal conditioning and acquisition module, and is used to detect the induced magnetic field signal generated by the eddy current induced by the metal mark under the action of the excitation alternating magnetic field. The output of the signal conditioning and acquisition module is connected to the input of the signal analyzer for conditioning and digital acquisition of the induced magnetic field signal. The signal analyzer is used to perform feature analysis on digitally acquired signals; The embedded main control system is communicatively connected to the control terminal of the excitation signal generator and the signal analyzer, respectively. It is used to send control commands to the excitation signal generator to set its working parameters, receive signal feature analysis results from the signal analyzer, and identify the position of the metal mark and the binary identification code information it carries according to the preset metal mark signal feature and encoding rule database.

6. The apparatus according to claim 5, characterized in that: When performing a detection task, the step distance control unit drives the vehicle to move automatically along the preset pipeline trajectory, and automatically stops to collect data after reaching the preset step distance. After the data collection is completed, it automatically cruises again to perform measurements.

7. The apparatus according to claim 5, characterized in that: The signal conditioning and acquisition module includes, in sequence, an instrumentation amplifier, a bandpass filter, a programmable gain amplifier, and... A type of analog-to-digital converter; wherein the instrumentation amplifier has high input impedance and high common-mode rejection ratio, and the center frequency of the bandpass filter matches the operating frequency of the excitation signal generator.

8. The apparatus according to claim 5, characterized in that: The dual D-shaped differential eddy current probe includes two coil units with the same geometric dimensions, number of turns, and inductance. The two coil units are connected in series in opposite phases, with a symmetry axis spacing of ≤10mm and a mutual inductance deviation of <5%.

9. The apparatus according to claim 5, characterized in that: The dual D-shaped differential eddy current probe is covered with a magnetic shielding layer made of high magnetic permeability material on the outside and has an electrostatic shielding layer inside. The coil unit is wound with excitation wire.

10. The apparatus according to claim 5, characterized in that: The correction coil system collects the magnetic field strength on both sides in real time. , And transmit it to the embedded main control system; The embedded main control system has a built-in PID controller that dynamically controls the vehicle's steering servo based on the deviation in left and right signal strength, calculating the real-time horizontal deviation. The steering angle is output through the PID control algorithm. ,when At that time, the steering servo is driven by pressing Adjust the wheel deflection angle to make the vehicle body converge toward the side with higher signal strength. The difference in eddy current signal intensity can be used as the direct input source of the PID controller to achieve closed-loop tracking of the vehicle body to the center line of the pipeline, breaking through the limitation of traditional mechanical guide wheels relying on the flatness of the terrain.

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