A portable impulse eddy current detection device for grounding grid of transformer substation

Abstract

This utility model relates to a convenient pulse eddy current detection device for grounding grids suitable for various terrains in substations, belonging to the field of power equipment testing. It includes a trolley chassis, an extension section, and a platform. The trolley chassis is connected to the platform via the extension section. The trolley chassis is connected to a front wheel assembly, and the extension section is connected to a rear wheel assembly. The trolley chassis has a concentric coil with a nested magnetic core. The concentric coil includes a concentric transmitting coil, a receiving coil, and a ring-shaped magnetic core nested inside the receiving coil. The platform has a transmitter-receiver integrated box. The transmitter-receiver integrated box is connected to the concentric coil via a cable, realizing signal excitation of the transmitting coil and signal acquisition and processing of the receiving coil. This solution has strong sensitivity and anti-interference capabilities, adapts to complex terrains, and features modularity and efficient, flexible signal processing.

Description

Technical Field

[0001] This utility model belongs to the field of power equipment testing and relates to a convenient detection device for pulsed eddy currents in grounding grids suitable for various terrains in substations. Background Technology

[0002] In power systems, substation grounding grids serve as core facilities for ensuring the safe operation of equipment and the safety of personnel, undertaking critical functions such as safely conducting fault currents to the ground, maintaining system potential balance, and preventing lightning overvoltage. Their performance directly affects the lightning protection of power equipment, the accuracy of relay protection devices, and the stable operation of the entire power grid. However, with the extension of the service life of power equipment and the intensification of environmental corrosion, grounding grids are prone to defects such as corrosion, breakage, and poor contact, leading to increased grounding resistance, protection failure, and even potentially causing serious safety accidents (such as equipment breakdown and electric shock). Therefore, regular, efficient, and accurate testing of grounding grids is an urgent engineering requirement.

[0003] Traditional grounding grid testing methods mostly rely on contact or semi-contact equipment, which suffers from low testing efficiency, complex operation, and poor adaptability to complex terrain. For example, the conventional DC resistance method requires manual excavation or the use of probes to contact the soil, which is not only time-consuming and labor-intensive but may also damage the grounding grid structure. In addition, existing equipment is difficult to move and maneuver in complex terrain (such as gravel roads and dirt roads), limiting its application scope in practical scenarios. Utility Model Content

[0004] In view of this, the purpose of this utility model is to provide a convenient detection device for grounding grid pulse eddy currents suitable for various terrains in substations. Through differentiated wheel layout, composite detection structure design and functional integration scheme, it effectively solves the above-mentioned technical problems.

[0005] To achieve the above objectives, this utility model provides the following technical solution:

[0006] A convenient pulse eddy current detection device for grounding grids suitable for various terrains in substations includes a trolley chassis, an extension section, and a platform. The trolley chassis is connected to the platform via the extension section. The trolley chassis is connected to a front wheel assembly, and the extension section is connected to a rear wheel assembly. The trolley chassis is equipped with a concentric coil with nested magnetic cores. The concentric coil includes a concentric transmitting coil, a receiving coil, and a ring-shaped magnetic core nested inside the receiving coil. The platform is equipped with a transmitter-receiver integrated box. The transmitter-receiver integrated box is connected to the concentric coil via a cable to realize signal excitation of the transmitting coil and signal acquisition and processing of the receiving coil.

[0007] Furthermore, the concentric coil of the nested magnetic core includes a coil frame, which is composed of two concentric rings; wherein the outer ring is provided with a receiving coil composed of multiple turns of winding, and an annular magnetic core is embedded inside the receiving coil, and the inner ring is provided with a transmitting coil composed of multiple turns of winding.

[0008] Furthermore, the integrated transmitter-receiver box includes a main control module, a signal acquisition and processing module, a pulse excitation module, a power supply, and a host computer; the main control module is connected to the signal acquisition and processing module, the pulse excitation module, and the host computer, and the signal acquisition and processing module is connected to the receiving coil and the main control module; the power supply provides power to the signal acquisition and processing module, the pulse excitation module, the power supply, and the host computer.

[0009] Furthermore, the main control module includes a main control unit, which is connected to an internal buffer, a control circuit, and a communication circuit. The internal buffer receives sampling signals from the transmitting coil and the receiving coil and transmits them to the main control unit. The control circuit receives control commands from the main control unit and controls the drive circuit according to the control commands issued by the main control unit. The communication circuit is connected to a host computer to realize communication control.

[0010] Furthermore, the signal acquisition and processing module includes a preamplifier module, a Butterworth low-pass filter, a programmable amplifier module, an ADC driver module, and a first ADC acquisition module; the receiving coil is sequentially connected to the preamplifier module, the Butterworth low-pass filter, the programmable amplifier module, the first ADC acquisition module, and an internal buffer; the control circuit of the main control module is connected to the programmable amplifier module to adjust its gain; the control circuit of the main control module is also connected to the first ADC acquisition module through the ADC driver module to adjust the front-end impedance and protect the circuit.

[0011] Furthermore, the pulse excitation module includes a driving circuit and a transmitting main circuit; the main control unit is sequentially connected to the control circuit, the driving circuit, the transmitting main circuit, and the transmitting coil; the driving circuit is used to receive control signals and convert them into driving signals for the switching transistors in the transmitting main circuit; the transmitting main circuit is based on an H-bridge circuit, receives driving signals, and converts DC signals into pulse signals;

[0012] The transmitting coil is also connected in sequence to a current transformer, a second ADC acquisition module, and an internal buffer. The voltage signal in the transmitting coil is acquired by the current transformer and the second ADC acquisition module and stored in the internal buffer.

[0013] Furthermore, it also includes a detection circuit connecting the main transmission circuit and the main control unit, as well as a memory and a real-time clock connecting the main control unit. The memory stores the acquired data, and the real-time clock provides time alignment calibration for the first ADC acquisition module, the second ADC acquisition module, and the main control module.

[0014] Furthermore, the power supply includes a battery, a boost regulator circuit, and a power supply circuit; the battery directly supplies power to the main transmitting circuit; the battery supplies power to the signal acquisition and processing module through the power supply circuit; and the battery, after passing through the boost regulator circuit, supplies power to the detection circuit and the main control module.

[0015] Furthermore, the extension is a hollow column, and the hollow column has a cable channel inside for accommodating the cable, and the cable has a shielding layer.

[0016] Furthermore, the front wheel assembly includes two solid rubber wheels with annular anti-slip grooves on their surfaces and a metal frame inside. The rear wheel assembly includes two omnidirectional self-locking rollers, each consisting of an omnidirectional roller and a self-locking mechanism. The self-locking mechanism includes a pedal and a ratchet latch locked by the pedal.

[0017] The beneficial effects of this utility model are as follows:

[0018] Non-contact testing: This solution does not require damaging the grounding grid structure, enabling non-destructive testing of defects such as corrosion and fracture.

[0019] High sensitivity and anti-interference capability: This solution adopts a concentric coil + magnetic core nested structure, which significantly improves the acquisition efficiency of shallow defect signals, while reducing the interference of the primary magnetic field on the secondary signal;

[0020] Adaptable to complex terrain: The combination of the front wheel rubber buffer design and the rear wheel universal self-locking mechanism in this solution solves the problem of jamming and positioning of traditional trolleys in gravel, dirt roads and other scenarios.

[0021] Modular and efficient signal processing: The cable channel and integrated box design of this solution improves detection efficiency and system reliability, while facilitating flexible and efficient signal processing.

[0022] Other advantages, objectives, and features of this invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination and study, or may be learned from practice of this invention. The objectives and other advantages of this invention can be realized and obtained through the following description. Attached Figure Description

[0023] To make the objectives, technical solutions, and advantages of this utility model clearer, the preferred embodiments of this utility model will be described in detail below with reference to the accompanying drawings, wherein:

[0024] Figure 1 A schematic diagram of the overall structure of a convenient pulse eddy current detection device for grounding grids suitable for various terrains in substations.

[0025] Figure 2 Top view of a convenient pulse eddy current detection device for grounding grids suitable for various terrains in substations;

[0026] Figure 3 The diagram shows a concentric coil structure with nested magnetic cores, where (a) is a three-dimensional view and (b) is a top view.

[0027] Figure 4 This is a diagram showing the internal connections of the integrated transmitter-receiver box.

[0028] Figure 5 This is a flowchart of the testing process;

[0029] Figure 6 This is the receiving coil induced signal without the introduction of a magnetic core;

[0030] Figure 7 This is the induced signal after the magnetic core is introduced.

[0031] Reference numerals in the attached diagram: 1-Rubber buffer wheel; 2-Concentric coil; 3-Universal self-locking roller; 4-Extension; 5-Transmitter-receiver integrated box; 6-Tabletop; 7-Universal wheel self-locking device; 8-Ring magnetic core; 9-Transmitting coil; 10-Coil frame; 11-Receiving coil. Detailed Implementation

[0032] The following specific examples illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this utility model. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0033] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the present invention. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0034] In the accompanying drawings of this utility model, the same or similar reference numerals correspond to the same or similar components. In the description of this utility model, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this utility model. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0035] Example 1:

[0036] Please see Figures 1-3 This utility model provides a convenient pulse eddy current detection device for grounding grids suitable for various terrains in substations. It includes a trolley chassis, an extension 4, and a platform 6. The trolley chassis is connected to the platform 6 via the extension 4. The trolley chassis is connected to a front wheel assembly, and the extension 4 is connected to a rear wheel assembly. A concentric coil 2 with a nested magnetic core is mounted on the trolley chassis. The concentric coil 2 includes a concentric transmitting coil, a receiving coil, and a ring-shaped magnetic core nested inside the receiving coil. A transmitter-receiver integrated box 5 is mounted on the platform 6. The transmitter-receiver integrated box 5 is connected to the concentric coil 2 via a cable, enabling signal excitation of the transmitting coil and signal acquisition and processing of the receiving coil.

[0037] In this embodiment, the front wheel assembly consists of rubber buffer wheels 1, which are large-sized solid rubber wheels with a diameter of 15-30cm. The surface is machined with annular anti-slip grooves to increase friction with the ground. An aluminum frame is embedded inside the wheel, and a high-elasticity rubber layer is wrapped around it, effectively absorbing vibrations and preventing wheel deformation. The rear wheel assembly consists of omnidirectional self-locking rollers 3, which are 360° omnidirectional rollers with foot brakes. The rollers are made of a nylon-coated composite structure. The self-locking mechanism uses a ratchet latch, and the mechanical locking device is driven by stepping on the pedal to achieve roller rotation and fixation. The large-sized rubber material of the front wheels adapts to complex terrain, reducing the risk of the cart getting stuck. The omnidirectional design of the rear wheels with brakes facilitates quick positioning and stability of the device at detection points. The modular installation of the wheel assembly supports quick replacement, improving equipment maintenance efficiency.

[0038] In this embodiment, the extension 4 is a hollow plastic column, with the top of the column connected to the horizontal platform surface 6. The column is made of high-strength PVC material and has a square cross-section. The column has an internal cable channel to accommodate shielded cables. The cables have a twisted-pair shielded structure and a core cross-sectional area of ​​0.3 mm². 2 The shielding layer is an aluminum foil + copper mesh composite layer, and the outer layer is wrapped with a corrugated metal flexible tube with a tensile strength of ≥200N; both ends of the cable are equipped with aviation connectors, supporting IP67 protection level, ensuring stable connection in humid environments.

[0039] To address the problems of low sensitivity and significant primary magnetic field interference in traditional eddy current detection devices for shallow grounding grid defects, this invention proposes a composite detection structure consisting of a concentric coil and a nested magnetic core. The coil structure is as follows: Figure 3 As shown. The receiving coil consists of multi-turn windings with a diameter of 50-80cm, forming a ring-shaped detection area around the transmitting coil; the transmitting coil consists of multi-turn windings with a diameter of 10-20cm. A 5mm thick toroidal magnetic core, made of manganese-zinc ferrite (permeability 2000-3000), is embedded inside the receiving coil and fixed to the coil frame via a slot. The concentric coil structure optimizes the magnetic field distribution through the magnetic core, significantly improving the sensitivity for detecting shallow defects: because the receiving coil is located outside the transmitting coil and its radius is much larger than that of the transmitting coil, when a magnetic core is placed inside the receiving coil, the magnetic reluctance difference introduced by the core produces a symmetrical cancellation effect on the primary magnetic field directly coupled to the transmitting coil, increasing the proportion of the secondary magnetic field (from grounding grid defects) by 30%-50%.

[0040] To achieve a compact and efficient pulse eddy current detection system, as well as efficient and flexible pulse eddy current signal processing, this invention integrates a transmitter-receiver box 5 on the tabletop to realize signal excitation of the transmitting coil and signal processing and acquisition of the receiving coil.

[0041] Example 2:

[0042] In this embodiment, the transmitter-receiver integrated box 5 consists of a main control module, a signal acquisition and processing module, an H-bridge-based pulse excitation module, a power supply, and a host computer. The circuit composition is as follows: Figure 4 As shown.

[0043] The main control module includes a main control unit and internal buffers, control circuits, and communication circuits connected to the main control unit, as well as a memory and a real-time clock connected to the main control unit. The signal acquisition and processing module includes a preamplifier module, a Butterworth low-pass filter, a programmable amplifier module, an ADC driver module, and a first ADC acquisition module. The receiving coil is sequentially connected to the preamplifier module, the Butterworth low-pass filter, the programmable amplifier module, the first ADC acquisition module, and the internal buffer. The control circuit of the main control module is connected to the programmable amplifier module to adjust its gain. To ensure accurate sampling by the first ADC acquisition module, an ADC driver module needs to be installed before it. This ADC driver module is connected to the main control module to adjust the front-end impedance, avoid sampling errors, and also provide circuit protection. The pulse excitation module includes a driver circuit and a transmitting main circuit. The main control unit is sequentially connected to the control circuit, the driver circuit, the transmitting main circuit, and the transmitting coil. The transmitting coil is also sequentially connected to a current transformer, a second ADC acquisition module, and the internal buffer. The voltage signal in the transmitting coil is acquired by the current transformer and the second ADC acquisition module and stored in the internal buffer. It also includes a detection circuit connecting the main transmitting circuit and the main control unit, as well as a memory and real-time clock connecting the main control unit. Due to the high sampling rate of the ADC and the limited capacity of its internal buffer, the internal buffer is only used for data buffering. The data acquired by the ADC is first quickly written to the internal buffer, and then subsequently read and transferred to the external memory. The external memory, with its larger capacity, is used to store all acquired data. The real-time clock provides a time alignment reference for the two ADCs and the entire main control system. The power supply includes a battery, a boost regulator circuit, and a power supply circuit. The battery directly powers the main transmitting circuit; the battery powers the signal acquisition and processing module through the power supply circuit; and the battery, after passing through the boost regulator circuit, powers the detection circuit and the main control module.

[0044] The main control unit, composed of an FPGA and an ARM processor, generates corresponding control commands based on pulse width and frequency settings configured by the user on the host computer. This precisely controls the timing of the entire detection process, including when to activate the drive circuit, when to trigger sampling, and the sampling duration and frequency. The main control unit receives digital signals stored in its internal buffer and performs storage and processing. The control circuit acts as a bridge between the main control unit and the drive circuit, translating commands and converting levels. It receives control signals from the main control unit and converts them into signals sufficient to drive the drive circuit. Upon receiving a rising-edge pulse control command from the main control unit, the control circuit outputs a corresponding pulse control signal to the drive circuit via its internal circuitry. The drive circuit receives signals from the control circuit, converts them into drive signals for the controllable switch, and provides sufficient current and voltage to quickly and reliably switch the transmitting main circuit. The transmitting main circuit is the core component generating a powerful pulse current and is directly connected to the transmitting coil and the power supply. In this embodiment, an H-bridge-based transmitting main circuit is used, consisting of four basic switching elements. It converts DC signals into pulse signals via control signals to generate the pulse signals. Before the drive signal arrives, the battery charges the large-capacity capacitor to saturation. When the drive signal turns on the internal power switch, the large capacitor releases the stored energy. At this time, the large capacitor provides a stable DC voltage to the transmitting coil. The current in the coil first rises and then stabilizes, forming the rising edge and flat segment of the pulse current signal. After the set pulse width time is reached, the switch is turned off instantaneously, the voltage applied to the transmitting coil is cut off, and the battery starts charging the large-capacity capacitor again. At this time, the current in the coil drops rapidly, forming the falling edge of the pulse current signal, thus completing the application of the pulse signal to the coil. According to Faraday's law of electromagnetic induction, the changing current in the transmitting coil will induce a transient pulse magnetic field in the surrounding space. The change in the magnetic field will cause eddy currents to be generated in the grounding grid. By measuring and analyzing the secondary magnetic field generated by the eddy currents, the grounding grid can be detected. The detection circuit detects the drive signal from the drive circuit, acquires different moments of the drive signal, and controls the corresponding working time of the acquisition module. After acquiring the pulse turn-off moment, it controls the ADC acquisition module to start signal acquisition and ends acquisition at the corresponding moment when the next pulse begins. Before the next pulse turn-off moment, the signal is stored, thus realizing the acquisition of the effective signal period and the storage of the remaining period, completing the acquisition and storage control. It also includes a current transformer connected to the transmitting coil and a second ADC sampling module connected to the current transformer. The current transformer measures the current signal in the transmitting coil and converts the current signal into a voltage signal proportionally. The second ADC sampling module acquires the voltage signal from the current transformer, thereby obtaining the waveform and magnitude of the proportionally scaled transmitting coil current signal, which is then input into the internal buffer of the main control module.

[0045] On the other hand, the receiving coil induces a weak, varying secondary magnetic field generated by the attenuated eddy currents in the grounding grid and converts this magnetic field signal into a measurable induced voltage signal. Since the receiving coil is located outside the transmitting coil and its radius is much larger, when a magnetic core is placed inside the receiving coil, the magnetic reluctance difference introduced by the core causes a symmetrical cancellation effect on the primary magnetic field directly coupled to the transmitting coil, increasing the proportion of the secondary magnetic field. Because the voltage signal induced by the receiving coil is very weak and easily drowned out by environmental noise, the preamplifier amplifies this weak signal by a high factor with low noise, improving the signal-to-noise ratio. Then, a Butterworth low-pass filter is used to filter the amplified signal, removing high-frequency noise and retaining the useful low-frequency signal. The Butterworth filter is a specific type of filter with the flattest frequency response within its passband. While filtering noise, it does not significantly distort the waveform of the useful signal. It has a cutoff frequency; signals above this frequency are significantly attenuated. Due to differences in the burial depth of the grounding grid, soil conductivity, and the severity of defects, the received signal strength may vary considerably. If a fixed-gain amplifier is used, strong signals may cause amplifier saturation, while weak signals may still be too weak after amplification. Therefore, this invention also includes a programmable amplifier. Based on the signal strength, the main control unit dynamically adjusts its amplification factor via digital signals to ensure that the signal amplitude ultimately output to the first ADC acquisition module is always within an optimal range. The first ADC acquisition module converts the analog voltage signal processed by all previous modules into a digital signal that can be recognized and processed by the main control module and the host computer. The host computer is used for data calculation, analysis, and display.

[0046] like Figure 5 As shown, the specific implementation process of the device described in this embodiment is as follows:

[0047] (1) Equipment assembly and calibration: Fix the transmitter-receiver box on the table, connect the cable and ensure that the cable channel is unobstructed.

[0048] (2) Terrain adaptation and movement: Push the device to the testing area, with the front rubber buffer wheel in contact with the ground and the rear universal self-locking roller locked by the foot brake to ensure the stability of the equipment.

[0049] (3) Movement and positioning: After the test is completed, release the rear wheel brake and move the device to the next measurement area by using the anti-slip grooves of the front wheel and the flexible steering of the universal roller.

[0050] (4) Pulse eddy current detection: Start the device, the pulse power supply supplies power to the transmitting coil to generate a transient magnetic field; after the magnetic field penetrates the soil, it generates an eddy current response with the grounding grid defect, and the receiving coil collects the secondary magnetic field signal.

[0051] Select a suitable measurement area based on the tower grounding electrode design drawings, and plan a reasonable measurement route based on the site conditions; conduct a rough test on the preliminary plan to obtain the approximate topological information of the grounding electrode, and select the final measurement line based on the results; measure the burial depth parameters of the detection device along the measurement line; compare the comprehensive measured structural parameters with the actual grounding electrode structure after excavation.

[0052] First, introducing a magnetic core through a concentric coil structure weakens the signal strength generated by the primary magnetic field and increases the proportion of the secondary magnetic field response signal. Without a magnetic core, the signal induced by the receiving coil is mostly generated by the primary magnetic field and is primarily determined by the magnetic flux inside the transmitting coil. The magnetic flux in the region from the outside of the transmitting coil to the inside of the receiving coil cancels out the primary magnetic field signal. With the introduction of a magnetic core, the magnetic flux canceling out the primary magnetic field response signal increases, thus reducing the induced signal generated by the primary magnetic field and increasing the proportion of the secondary magnetic field response signal. The difference in the induced signal generated at the receiving coil with and without a magnetic core is significant. Figure 6 and Figure 7 As shown, the introduction of a magnetic core can reduce the intensity of the primary magnetic field induced signal and increase the proportion of the receiving coil response signal.

[0053] The induced voltage of the receiving coil is transmitted to the transmitting and receiving integrated box via cable. The signal processing module in the transmitting and receiving integrated box filters, amplifies, and performs programmable amplification on the acquired signal, adjusts the amplitude of the signal to a suitable value, and converts it into a digital signal.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from the spirit and scope of this technical solution, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A convenient detection device for pulsed eddy currents in grounding grids suitable for various terrains in substations, characterized in that: The device includes a trolley chassis, an extension, and a platform. The trolley chassis is connected to the platform via the extension. The trolley chassis is connected to a front wheel assembly, and the extension is connected to a rear wheel assembly. The trolley chassis has a concentric coil with nested magnetic cores. The concentric coil includes a concentric transmitting coil, a receiving coil, and a ring-shaped magnetic core nested inside the receiving coil. The platform has a transmitter-receiver integrated box. The transmitter-receiver integrated box is connected to the concentric coil via a cable to realize signal excitation of the transmitting coil and signal acquisition and processing of the receiving coil. The concentric coil of the nested magnetic core includes a coil frame, which is composed of two concentric rings; wherein the outer ring is provided with a receiving coil composed of multiple turns of winding, and a ring magnetic core is embedded inside the receiving coil, and the inner ring is provided with a transmitting coil composed of multiple turns of winding. The transmitter-receiver integrated box includes a main control module, a signal acquisition and processing module, a pulse excitation module, a power supply, and a host computer; the main control module is connected to the signal acquisition and processing module, the pulse excitation module, and the host computer; the signal acquisition and processing module is connected to the receiving coil and the main control module; the pulse excitation module is connected to the transmitting coil; the power supply provides power to the signal acquisition and processing module, the pulse excitation module, the power supply, and the host computer; The main control module includes a main control unit, which is connected to an internal buffer, a control circuit, and a communication circuit. The internal buffer receives sampling signals from the transmitting coil and the receiving coil and transmits them to the main control unit. The control circuit receives control commands from the main control unit and converts them into control signals. The communication circuit is connected to a host computer to achieve communication control. The signal acquisition and processing module includes a preamplifier module, a Butterworth low-pass filter, a programmable amplifier module, an ADC driver module, and a first ADC acquisition module. The receiving coil is sequentially connected to the preamplifier module, the Butterworth low-pass filter, the programmable amplifier module, the first ADC acquisition module, and an internal buffer. The control circuit of the main control module is connected to the programmable amplifier module to adjust its gain. The control circuit of the main control module is also connected to the first ADC acquisition module through the ADC driver module to adjust the front-end impedance and protect the circuit. The pulse excitation module includes a drive circuit and a main transmitting circuit; the main control unit is connected in sequence to the control circuit, the drive circuit, the main transmitting circuit and the transmitting coil; the drive circuit is used to receive control signals and convert them into drive signals for the main transmitting circuit; the main transmitting circuit is based on an H-bridge circuit, receives drive signals and converts DC signals into pulse signals; The transmitting coil is also connected in sequence to a current transformer, a second ADC acquisition module and an internal buffer. The voltage signal in the transmitting coil is acquired by the current transformer and the second ADC acquisition module and stored in the internal buffer. It also includes a detection circuit connecting the main transmission circuit and the main control unit, as well as a memory and a real-time clock connecting the main control unit. The memory stores the acquired data, and the real-time clock provides time alignment calibration for the first ADC acquisition module, the second ADC acquisition module, and the main control module. The power supply includes a battery, a boost regulator circuit, and a power supply circuit; the battery directly supplies power to the main transmitting circuit; the battery supplies power to the signal acquisition and processing module through the power supply circuit; and the battery supplies power to the detection circuit and the main control module after passing through the boost regulator circuit. The extension is a hollow column, and the hollow column has a cable channel inside for accommodating the cable, and the cable has a shielding layer; The front wheel assembly includes two solid rubber wheels with annular anti-slip grooves on their surfaces and a metal frame inside. The rear wheel assembly includes two omnidirectional self-locking rollers, each consisting of an omnidirectional roller and a self-locking mechanism. The self-locking mechanism includes a pedal and a ratchet latch locked by the pedal.

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