A cable seal eddy current detection system and method with magnetic field focusing function

Abstract

The present invention discloses a cable seal eddy current detection system and method with a magnetic field focusing function. The present invention belongs to the field of nondestructive detection technology of cable seals. The detection system includes an excitation module; the excitation module includes an inner core, a shielding layer and an excitation coil; the inner core is located in the innermost layer, and is an inverted truncated cone structure with a groove in the middle; the shielding layer is located in the outer layer of the inner core, which is used to mechanically limit the inner core and prevent the magnetic field from leaking out; the copper wire is tightly wound on the outer layer of the shielding layer to form an excitation coil; the excitation coil generates a time-varying magnetic field at the groove in the middle of the inner core under the action of the excitation signal, and the time-varying magnetic field induces eddy currents in the cable seal to be inspected, thereby realizing the internal detection of the cable seal to be inspected. The present invention adopts an inverted truncated cone structure with a groove in the middle of the inner core, which can converge the magnetic field generated by the excitation coil inside the groove, improve the intensity of the induced eddy current, and effectively realize the detection of internal defects of the cable seal, expand the detection range, and improve the detection accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive detection of cable seals, and in particular relates to a cable seal eddy current detection system and method with a magnetic field focusing function. Background Art

[0002] As an important sealing component to ensure the waterproofness of cable joints and the grounding of the metal outer layer of the cable, it is necessary to perform non-destructive testing on cable seals to evaluate their structural integrity.

[0003] The existing cable seal eddy current detection technology has an excitation coil in the shape of a cylinder or square. The magnetic field generated by the time-varying current signal is scattered in the circular or square cross-section of the excitation coil, and the magnetic field energy cannot be concentrated. As a result, the existing cable seal eddy current detection technology can only detect defects on the surface or near the surface of the seal, and it is difficult to effectively detect internal defects of the cable seal. Summary of the invention

[0004] In order to solve the problem in the existing cable seal eddy current detection technology that, due to the shape of the excitation coil being cylindrical or square, the magnetic field generated by the time-varying current signal is scattered in the circular or square cross-section of the excitation coil, and the magnetic field energy cannot be concentrated, resulting in only being able to detect surface or near-surface defects of the seal, and being unable to effectively detect internal defects of the cable seal, the present invention provides a cable seal eddy current detection system and method with a magnetic field focusing function, which can realize the detection of internal defects of the cable seal, expand the detection range, and improve the reliability of the detection.

[0005] The present invention is achieved through the following technical solutions:

[0006] A cable seal eddy current detection system and method with magnetic field focusing function, the detection system includes an excitation module;

[0007] The excitation module comprises an inner core, a shielding layer and an excitation coil;

[0008] The inner core is located in the innermost layer and is an inverted truncated cone structure with a groove in the middle;

[0009] The shielding layer is located on the outer layer of the inner core and is used to mechanically limit the inner core and prevent the magnetic field from leaking out;

[0010] Copper wire is tightly wound on the outer layer of the shielding layer to form the excitation coil;

[0011] The excitation coil generates a time-varying magnetic field at the groove in the middle of the inner core under the action of the excitation signal, and the time-varying magnetic field induces eddy currents in the cable seal to be inspected, thereby realizing internal inspection of the cable seal to be inspected.

[0012] The traditional lead seal eddy current detection technology can only detect the surface or near-surface defects of the lead seal due to the dispersion of the magnetic field, which makes the magnetic field energy unable to be concentrated, and cannot effectively detect the internal defects of the lead seal. The cable lead seal eddy current detection system proposed by the present invention adopts an inverted truncated cone structure with a groove in the middle of the inner core, which can gather the magnetic field generated by the excitation coil inside the groove, avoid the problem of energy non-concentration caused by the dispersion of the magnetic field, and improve the induced eddy current intensity, so as to effectively realize the detection of internal defects of the cable lead seal, expand the detection range, and improve the detection accuracy.

[0013] As a preferred embodiment, the inner core of the present invention is composed of two D-shaped metal bodies with grooves in the middle, and the distance between the two D-shaped metal bodies is the same as the width of the grooves in the middle. The present invention is easy to process and manufacture by using two D-shaped metal bodies with grooves in the middle.

[0014] As a preferred embodiment, the material of the D-shaped metal body of the present invention is aluminum.

[0015] As a preferred embodiment, the magnetic permeability of the shielding layer of the present invention is 1500 H / m. The present invention adopts a high magnetic permeability shielding layer to effectively prevent the magnetic field from leaking out.

[0016] As a preferred embodiment, the excitation module of the present invention further includes a waveform generator, a power amplifier and a controller;

[0017] The controller controls the waveform generator to output a sinusoidal excitation signal to the power amplifier;

[0018] The power amplifier amplifies the input sinusoidal excitation signal and outputs the amplified signal to the excitation coil.

[0019] As a preferred embodiment, the preferred frequency of the sinusoidal excitation of the present invention is:

[0020] f=1 / (πμσd 2 )

[0021] Among them, μ is the magnetic permeability of the seal, σ is the electrical conductivity of the seal, and d is the depth of the defect.

[0022] As a preferred embodiment, the detection system of the present invention further includes a detection module;

[0023] The detection module includes a detection coil and a data acquisition card;

[0024] The detection coil is wound with copper wire, is located at the lower side of the inner core and is coaxially arranged with the inner core, and is used to detect eddy current signals;

[0025] The data acquisition card is used to collect the voltage signal generated by the detection coil.

[0026] As a preferred embodiment, the detection coil of the present invention has an inner radius of 1 mm, an outer radius of 2 mm, a height of 2 mm, and 800 turns of the coil.

[0027] As a preferred embodiment, the detection system of the present invention further includes a signal analysis module;

[0028] The signal analysis module includes a denoising unit and an analysis unit;

[0029] The denoising unit performs denoising on the voltage signal collected by the data acquisition card using a wavelet denoising method, and transmits the denoised voltage signal to the analysis unit;

[0030] The analysis unit determines whether the amplitude of the voltage signal after the denoising process is greater than a threshold value. If it is greater than the threshold value, it is determined that there is a defect inside the cable seal.

[0031] On the other hand, the present invention proposes a cable seal eddy current detection method, which is implemented based on the above detection system of the present invention and includes the following steps:

[0032] Applying an excitation signal to the excitation coil to generate a time-varying magnetic field at the groove in the middle of the inner core, the time-varying magnetic field inducing eddy currents in the cable seal to be inspected;

[0033] The eddy current signal is detected and analyzed to identify whether there are defects inside the cable seal to be inspected.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] The cable eddy current detection system provided by the present invention adopts an excitation structure with an inner core shape of an inverted truncated cone with a groove in the middle, which can gather the magnetic field generated by the excitation coil inside the groove, avoid the problem of unconcentrated magnetic field capacity caused by the dispersion of magnetic field lines, and improve the induced eddy current intensity, thereby effectively realizing the internal defect detection of cable seals and expanding the detection range. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0037] Figure 1 4 is a diagram of the detection system architecture of an embodiment of the present invention.

[0038] Figure 2 Schematic diagram of the inner core structure of the excitation module according to an embodiment of the present invention.

[0039] Reference numerals and corresponding component names:

[0040] 100-inner core, 101-excitation coil, 102-shielding layer, 103-detection coil, 201-D-type high conductivity metal body. DETAILED DESCRIPTION

[0041] Hereinafter, the term "include" or "may include" used in various embodiments of the present invention indicates the presence of the invented function, operation or element, and does not limit the addition of one or more functions, operations or elements. In addition, as used in various embodiments of the present invention, the terms "include", "have" and their cognates are intended only to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be understood as first excluding the presence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0042] In various embodiments of the present invention, the expression "or" or "at least one of A or / and B" includes any combination or all combinations of the words listed at the same time. For example, the expression "A or B" or "at least one of A or / and B" may include A, may include B, or may include both A and B.

[0043] The expressions (such as "first", "second", etc.) used in various embodiments of the present invention may modify the various constituent elements in various embodiments, but may not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used for the purpose of distinguishing an element from other elements. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, without departing from the scope of various embodiments of the present invention, the first element may be referred to as the second element, and similarly, the second element may also be referred to as the first element.

[0044] It should be noted that if it is described that one component element is “connected” to another component element, the first component element may be directly connected to the second component element, and a third component element may be “connected” between the first component element and the second component element. Conversely, when one component element is “directly connected” to another component element, it can be understood that there is no third component element between the first component element and the second component element.

[0045] The terms used in various embodiments of the present invention are only used for the purpose of describing specific embodiments and are not intended to limit various embodiments of the present invention. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. Unless otherwise limited, all terms used here (including technical terms and scientific terms) have the same meaning as the meaning generally understood by those of ordinary skill in the art to which the various embodiments of the present invention belong. The terms (such as the terms defined in the dictionary generally used) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or an overly formal meaning, unless clearly defined in various embodiments of the present invention.

[0046] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0047] Embodiment 1:

[0048] In the existing lead seal eddy current detection technology, most of the excitation coils used are cylindrical or square in shape. The magnetic field generated by the time-varying current signal is scattered in the circular or square cross-section of the excitation coil, and the magnetic field energy cannot be concentrated, resulting in only being able to detect defects on the surface or near the surface of the lead seal, and being unable to effectively detect defects inside the lead seal. In view of the above problems existing in the prior art, this embodiment proposes a cable lead seal eddy current detection system with a magnetic field focusing function. The inner core shape of the excitation module of the cable lead seal eddy current detection system proposed in this embodiment is an inverted truncated cone with a groove in the middle, which can gather the magnetic field generated by the excitation coil inside the groove, avoid the problem of non-concentration of magnetic field energy caused by the dispersion of magnetic field lines, and improve the induced eddy current intensity, so as to effectively realize the detection of internal defects of cable lead seals, expand the detection range, and improve the detection accuracy.

[0049] Specific as Figure 1 As shown, the cable seal eddy current detection system proposed in this embodiment includes an excitation module, a detection module and a signal analysis module.

[0050] The excitation module includes an inner core 100, a shielding layer 102, an excitation coil 101, a waveform generator, a power amplifier and a controller.

[0051] The inner core 100 is a high conductivity (≥1×10 7 The inner core is located in the innermost layer and is an inverted truncated cone structure. Preferably, the height of the inverted truncated cone structure is 10 mm, the top radius is 10 mm, and the bottom radius is 2 mm. Specifically, Figure 2As shown, the inner core 100 can be composed of two D-shaped high-conductivity metal bodies 201 with grooves in the middle. The spacing between the two D-shaped high-conductivity metal bodies 201 is consistent with the width of the middle groove, both of which are l. Preferably, l can be 0.2-0.5mm, and the D-shaped high-conductivity metal body 201 can be made of aluminum material.

[0052] The shielding layer 102 is a high magnetic permeability shielding layer, which is located on the outer layer of the high conductivity inner core. The magnetic permeability of the shielding layer is 1500H / m, and it is used to mechanically limit the inner core and prevent the magnetic field from leaking out. The copper wire is tightly wound on the outer layer of the high magnetic permeability shielding layer to form an excitation coil 101. The copper wire diameter is preferably 0.3mm, and the number of winding turns is 300.

[0053] The controller controls the waveform generator to output a sinusoidal excitation signal to the power amplifier. The sinusoidal excitation signal frequency f is f = 1 / (πμσd 2 ), μ is the magnetic permeability of the seal, σ is the electrical conductivity of the seal, and d is the depth of the defect. Specifically, the waveform generator uses Tektronix AFG31021, and the power amplifier uses Aigtek ATA-3000.

[0054] The power amplifier amplifies the input sinusoidal excitation signal and outputs it to the excitation coil 101, which is used to generate a time-varying magnetic field at the groove in the middle of the high-conductivity inner core, and further induce eddy currents in the cable seal to be inspected. For example, when inspecting a seal defect with a burial depth of 6 mm, that is, d is 6 mm, and μ is 4π×10 -7 H / m, σ is 4.67MS / m, so the frequency of the sinusoidal excitation signal is f set to 1500Hz, and the amplitude is set to 5V; the power amplifier amplifies the input pulse excitation signal by 10 times and outputs it to the excitation coil, which is used to generate a time-varying magnetic field in the middle groove of the high-conductivity inner core, and further induce eddy currents in the lead seal to be inspected.

[0055] Since the inner core of the excitation module is in the shape of an inverted cone with a groove in the middle, the magnetic field generated by the excitation coil can be gathered inside the groove, avoiding the problem of unconcentrated magnetic field capacity caused by the dispersion of magnetic field lines, and improving the intensity of induced eddy currents, thereby effectively realizing the detection of internal defects of cable seals.

[0056] The detection module includes a detection coil 103 and a high-frequency data acquisition card. The detection coil 103 is wound with ultra-fine copper wire, located at the lower side of the high-conductivity inner core 100, and coaxially arranged with the inner core 100, for detecting eddy current signals; the high-frequency data acquisition card is used to collect the voltage signal generated by the detection coil 103 and transmit it to the signal analysis module. Preferably, the inner radius of the detection coil can be set to 1mm, the outer radius to 2mm, the height to 2mm, the number of coil turns to 800 turns, and the high-frequency data acquisition card can use Altai Technology PXIe8912.

[0057] The signal analysis module includes a denoising unit and an analysis unit. The denoising unit uses a wavelet denoising method to denoise the voltage signal collected by the high-frequency data acquisition card, and transmits the denoised voltage signal to the analysis unit; the analysis unit is used to identify the internal defects of the cable seal according to the denoised voltage signal. Specifically, the analysis unit determines whether the amplitude of the denoised voltage signal is greater than a preset threshold. If it is greater than the preset threshold, there is a defect inside the cable seal.

[0058] The working process of the above detection system proposed in this embodiment is as follows:

[0059] The controller controls the frequency and amplitude of the sinusoidal excitation signal output by the waveform generator, and transmits the sinusoidal excitation signal output by the waveform generator to the power amplifier;

[0060] The sinusoidal excitation signal output by the waveform generator is amplified by the power amplifier and then transmitted to the excitation coil, thereby generating a time-varying magnetic field at the groove in the middle of the high-conductivity inner core, and the time-varying magnetic field induces eddy currents in the cable seal to be inspected;

[0061] The eddy current signal is converted into a voltage signal by the detection coil, collected by a high-frequency data acquisition card and transmitted to the signal analysis module;

[0062] Finally, the collected signals are processed and analyzed through the signal analysis module to detect the internal defects of the cable seal.

[0063] Embodiment 2:

[0064] This embodiment uses the cable seal eddy current detection system proposed in the above embodiment and the traditional detection system to perform defect detection on a 50mm×50mm×10mm metal plate (the material is the same as the cable seal). A 2mm×2mm×4mm groove is processed at the center of the bottom of the metal plate to simulate a seal defect with a buried depth of 6mm. The detection system proposed in the embodiment of the present invention uses a high conductivity core ( Figure 2 The conventional detection system uses a cylindrical excitation coil (radius of 2 mm, height of 10 mm). The excitation signals in both detection systems are sinusoidal signals with a frequency of 1500 Hz and an amplitude of 5 V. The structures and installation positions of the detection coils are the same. The maximum amplitude of the detection signal obtained by the conventional detection system is 0.8 V, while the maximum amplitude of the detection signal obtained by the detection system proposed in the embodiment of the present invention is 1.2 V, an increase of nearly 50%.

[0065] It can be seen that the cable seal eddy current detection system proposed in the embodiment of the present invention utilizes the magnetic field focusing function of the groove in the middle to gather the magnetic field generated by the excitation coil inside the groove, thereby avoiding the problem of magnetic field energy non-concentration caused by the dispersion of magnetic field lines, and improving the induced eddy current intensity and the sensitivity of cable seal defect detection.

[0066] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cable seal eddy current detection system with magnetic field focusing function, characterized in that: The detection system includes an excitation module; The excitation module comprises an inner core, a shielding layer and an excitation coil; The inner core is located in the innermost layer and is an inverted truncated cone structure with a groove in the middle, which gathers the magnetic field generated by the excitation coil inside the groove; The shielding layer is located on the outer layer of the inner core and is used to mechanically limit the inner core and prevent the magnetic field from leaking out; Copper wire is tightly wound on the outer layer of the shielding layer to form the excitation coil; The excitation coil generates a time-varying magnetic field at the groove in the middle of the inner core under the action of the excitation signal, and the time-varying magnetic field induces eddy currents in the cable seal to be inspected, thereby realizing internal inspection of the cable seal to be inspected; The inner core has an electrical conductivity greater than or equal to 1×10 7 The invention discloses a high conductivity inner core with a conductivity of 0.1447 W / m, wherein the height of the inverted truncated cone structure is 10 mm, the top radius is 10 mm and the bottom radius is 2 mm; the inner core is composed of two D-shaped metal bodies with grooves in the middle, and the spacing between the two D-shaped metal bodies is the same as the width of the groove in the middle, and the spacing and width are 0.2-0.5 mm.

2. The cable seal eddy current detection system with magnetic field focusing function according to claim 1, characterized in that: The material of the D-shaped metal body is aluminum.

3. The cable seal eddy current detection system with magnetic field focusing function according to claim 1, characterized in that: The magnetic permeability of the shielding layer is 1500 H / m.

4. A cable seal eddy current detection system with magnetic field focusing function according to any one of claims 1 to 3, characterized in that: The excitation module also includes a waveform generator, a power amplifier and a controller; The controller controls the waveform generator to output a sinusoidal excitation signal to the power amplifier; The power amplifier amplifies the input sinusoidal excitation signal and outputs the amplified signal to the excitation coil.

5. The cable seal eddy current detection system with magnetic field focusing function according to claim 4, characterized in that: The preferred frequency of the sinusoidal excitation is: f=1 / (πμσd 2 ) Among them, μ is the magnetic permeability of the seal, σ is the electrical conductivity of the seal, and d is the depth of the defect.

6. The cable seal eddy current detection system with magnetic field focusing function according to claim 4, characterized in that: The detection system also includes a detection module; The detection module includes a detection coil and a data acquisition card; The detection coil is wound with copper wire, is located at the lower side of the inner core and is coaxially arranged with the inner core, and is used to detect eddy current signals; The data acquisition card is used to collect the voltage signal generated by the detection coil.

7. The cable seal eddy current detection system with magnetic field focusing function according to claim 6, characterized in that: The inner radius of the detection coil is 1 mm, the outer radius is 2 mm, the height is 2 mm, and the number of turns of the coil is 800.

8. The cable seal eddy current detection system with magnetic field focusing function according to claim 6, characterized in that: The detection system also includes a signal analysis module; The signal analysis module includes a denoising unit and an analysis unit; The denoising unit performs denoising on the voltage signal collected by the data acquisition card using a wavelet denoising method, and transmits the denoised voltage signal to the analysis unit; The analysis unit determines whether the amplitude of the voltage signal after the denoising process is greater than a threshold value. If it is greater than the threshold value, it is determined that there is a defect inside the cable seal.

9. A cable seal eddy current detection method, characterized in that: The method is implemented based on the detection system according to any one of claims 1 to 8, and comprises the following steps: Applying an excitation signal to the excitation coil to generate a time-varying magnetic field at the groove in the middle of the inner core, the time-varying magnetic field inducing eddy currents in the cable seal to be inspected; The eddy current signal is detected and analyzed to identify whether there are defects inside the cable seal to be inspected.

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