Cable insulation layer defect detection equipment and method based on infrared thermal wave phase locking

Abstract

The invention discloses cable insulation layer defect detection equipment and method based on infrared thermal wave phase locking. The equipment comprises an infrared thermal imager, a rotating bracket, a photo-thermal excitation source, a transmission guide rail, a mode knob and a data processing upper computer, the thermal infrared imager and the photo-thermal excitation source are both installed on the rotating support through the test equipment connecting block, the rotating support is movably installed on the transmission guide rail, the mode knob is installed on the test equipment connecting block and used for selecting axial detection or circumferential detection, and the thermal infrared imager, the photo-thermal excitation source and the mode knob are all connected with the data processing upper computer. Based on a phase analysis method, extremely high anti-interference capability is achieved, and accurate detection of early tiny defects is achieved for phase delay with statistical significance caused by uneven internal microstructures.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of non-destructive testing of cables, and particularly relates to a cable insulation layer defect detection device and method based on infrared thermal wave phase locking. BACKGROUND

[0002] During the manufacturing process of the cross-linked polyethylene (XLPE) power cable insulation layer, due to melt flow, material performance and other reasons, situations such as glue lines, uneven cross-linking, uneven crystallization and the like are prone to occur, thereby causing insulation material defects, which can seriously affect the electrical performance and mechanical strength of the cable and threaten the safety of the power system.

[0003] The existing non-destructive testing methods include ultrasonic wave, X-ray and ultraviolet fluorescence detection. Ultrasonic wave detection relies on the difference in acoustic impedance and has advantages in detecting cracks and serious delamination, but since ultrasonic waves cannot effectively propagate in air, water or gel must be applied as a coupling agent on the surface of the probe and the insulation layer during detection, which is extremely cumbersome to use on the cable production line or at the user end and is prone to introduce contamination. At the same time, due to the very small difference in acoustic impedance between the uneven cross-linking or slightly density variation region and the normal material, the reflected signal is weak and the signal-to-noise ratio is low, which is not sensitive and obvious. Most importantly, the cross-linked polyethylene material has strong attenuation to sound waves, and often the resolution needs to be sacrificed to ensure the penetration depth. X-ray detection mainly relies on the difference in material density and is sensitive to the cross-linked polyethylene density variation region, but X-ray (industrial CT) requires high equipment cost and complex radiation protection measures when used, which makes it difficult to achieve large-scale and continuous detection at the production end and the user end. Most importantly, it can only reflect the difference in density and is not sensitive to key performance such as material cross-linking difference and crystallization state difference. Ultraviolet fluorescence detection mainly uses the fluorescence intensity emitted by specific products in the insulation layer material under ultraviolet fluorescence irradiation for detection, but it has very poor penetration and can only detect the surface of the power cable insulation layer and cannot detect deep defects, while unevenness in the insulation layer usually occurs in a relatively deep place. At the same time, it has very high requirements for the material and has little effect on the detection of density difference and unevenness.

[0004] However, traditional infrared detection methods, whether passive or active, heavily rely on temperature differences, are easily affected by surface conditions, and require high emissivity from the material. Even slight changes in ambient temperature can impact detection efficiency and accuracy, making it difficult to extract crucial information. Most importantly, they place extremely high demands on the active excitation source, requiring highly uniform heating of the insulated cable. Even slight differences can lead to significant variations in the thermal imaging, sometimes more noticeable than the defect itself, making this difficult to achieve at both the cable production and user ends. Therefore, traditional methods struggle to detect deep-seated non-uniformity within the insulation. Thus, an improved infrared thermal wave detection method and equipment specifically for XLPE materials are needed. Summary of the Invention

[0005] The purpose of this invention is to provide a cable insulation layer defect detection device and method based on infrared thermal wave phase lock, which solves the problems of insufficient detection depth, poor anti-interference ability, and lack of intuitiveness of existing technologies for uneven material defects inside power cable insulation layers.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A cable insulation layer defect detection device based on infrared thermal wave phase-locked loop includes an infrared thermal imager, a rotating bracket, a photothermal excitation source, a transmission guide rail, a mode knob, and a data processing host computer. Both the infrared thermal imager and the photothermal excitation source are mounted on the rotating bracket via the test equipment connecting block. The rotating bracket is movably mounted on the transmission guide rail. The mode knob is mounted on the test equipment connecting block and is used to select axial or circumferential detection. The infrared thermal imager, the photothermal excitation source, and the mode knob are all connected to the data processing host computer.

[0007] Furthermore, it also includes a cable bracket, which is a U-shaped groove bracket, with the cable to be tested placed in the groove of the cable bracket.

[0008] Furthermore, both the infrared thermal imager and the photothermal excitation source are fixedly mounted on the test equipment connection block, and the infrared thermal imager and the photothermal excitation source are located on the same side of the cable under test.

[0009] Furthermore, the rotating support is a ring-shaped track support, and the test equipment connecting block can be movably installed within the ring-shaped track of the rotating support.

[0010] Furthermore, the inner diameter of the rotating bracket is larger than the diameter of the cable under test.

[0011] Furthermore, an insulation layer is movably installed on the transmission guide rail. The insulation layer is a box or cover, and it surrounds the outside of the detection area.

[0012] Furthermore, the transmission guide rail is mounted on the base. The transmission guide rail is a precision linear guide rail and is set along the axial direction of the cable to be tested.

[0013] Furthermore, the photothermal excitation source is a high-power halogen lamp or a laser.

[0014] A method for detecting cable insulation defects based on infrared thermal wave phase-locked loop in the device, comprising: The photothermal excitation source applies periodic thermal excitation at different excitation frequencies to the surface of the cable under test. The heat wave propagates inside the material and is reflected when it encounters a defect. The surface temperature time series of the cable under test is acquired using an infrared thermal imager, and the acquired temperature time series and the thermal wave sequence of the photothermal excitation source are transmitted to the data processing host computer. The data processing host computer performs a fast Fourier transform on each pixel in the temperature time series, converting the time domain signal into a frequency domain signal, extracting the phase information in the frequency domain signal, and generating phase maps at different detection depths. The phase information of the pixel is compared with the phase information of the thermal wave sequence to obtain the phase difference. The grayscale of the phase difference map is used to identify whether the pixel defect is reliable, and a pixel defect map is generated to realize the location of non-uniform defects at different depths inside the insulating layer.

[0015] Furthermore, defect detection includes circumferential detection mode and axial detection mode; When using the circumferential detection mode, the mode knob is used to select the circumferential detection mode. The photothermal excitation source applies circumferential thermal excitation at different excitation frequencies to the surface of the cable under test. The rotating bracket drives the infrared thermal imager and the photothermal excitation source to rotate at a constant speed around the central axis of the cable under test. During the rotation, the infrared thermal imager acquires thermal image sequences, obtains the temperature change of each point on the circumference of the cable under test over time, records the temperature time series, and transmits it to the data processing host computer for processing to generate a pixel defect map. When using the axial detection mode, the mode knob is used to select the axial detection mode. The test equipment connecting block is parallel to the axis of the cable under test. The photothermal excitation source applies periodic thermal excitation at different excitation frequencies to the surface of the cable under test. The transmission guide rail drives the entire test equipment to move along the axis of the cable under test. The infrared thermal imager records the temperature time series under its field of view during the translation process and transmits it to the data processing host computer for processing to generate a pixel defect map.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a cable insulation defect detection device based on infrared thermal wave phase-locked loop. An infrared thermal imager and a photothermal excitation source are both mounted on a rotating bracket via a test equipment connecting block. The rotating bracket is movably mounted on a transmission guide rail. The rotation function of the rotating bracket allows the infrared thermal imager and photothermal excitation source to perform 360-degree omnidirectional detection around the cable, ensuring that no potential defects in any part of the cable insulation layer are missed. The movement function of the transmission guide rail enables continuous axial detection of the cable. A mode knob mounted on the test equipment connecting block is used to select axial or circumferential detection, allowing flexible switching of the detection direction according to different characteristics of cable insulation defects and detection requirements. The infrared thermal imager, photothermal excitation source, and mode knob are all connected to a data processing host computer, realizing real-time data transmission and efficient processing, enabling timely and accurate determination of the existence, type, location, and severity of defects in the cable insulation layer. The integrated design of this invention results in a simple device structure, convenient operation, and a reasonable layout, suitable for online detection in industrial fields. It not only improves detection efficiency but also provides a scientific basis for subsequent maintenance and decision-making, helping to take timely measures to ensure the safe operation of cables.

[0017] This invention also provides a method for detecting defects in cable insulation based on infrared thermal wave phase-locked loop. A photothermal excitation source applies periodic thermal excitation at different frequencies to the surface of the cable under test. The thermal wave propagates within the material and reflects when it encounters a defect. A same-side detection layout and high-frequency thermal excitation are employed to adapt to the low thermal conductivity of XLPE material, improving the detection depth. An infrared thermal imager collects the temperature time series of the cable surface under test. The collected temperature time series and the thermal wave sequence from the photothermal excitation source are transmitted to a data processing host computer. The host computer performs a fast Fourier transform on each pixel in the temperature time series, converting the time-domain signal into a frequency-domain signal. Phase information is extracted from the frequency-domain signal to generate phase maps at different detection depths. The phase information of this pixel is compared with the phase information of the thermal wave sequence to obtain the phase difference. Based on the grayscale of the phase difference map, the confidence level of the pixel defect is determined, generating a pixel defect map, thus enabling the localization of non-uniform defects at different depths within the insulation layer. This invention utilizes phase analysis instead of amplitude analysis, offering strong resistance to surface condition interference and a high signal-to-noise ratio. Furthermore, frequency domain feature imaging allows for the differentiation of defects at different depths, resulting in high detection accuracy. It can be used for both axial and circumferential inspection. This invention is based on… "The statistical threshold phase analysis method perfectly solves all the pain points of traditional infrared detection. For infrared thermal wave phase-locked loop technology, its phase response..." It will still fall Within the normal statistical distribution, it achieves extremely high anti-interference capability. This invention targets the statistically significant phase delay caused by internal microstructural inhomogeneity. This phase signal is hidden under amplitude noise and can be clearly extracted through FFT and statistical criteria, thereby achieving accurate detection of early-stage minute defects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the circumferential inspection structure of the cable insulation layer defect detection equipment based on infrared thermal wave phase-locked loop according to the present invention.

[0020] Figure 2 This is a schematic diagram of the axial detection structure of the cable insulation layer defect detection equipment based on infrared thermal wave phase-locked loop according to the present invention.

[0021] Among them: 1-Infrared thermal imager, 2-Rotating bracket, 3-Photothermal excitation source, 4-Cable bracket, 5-Insulation layer, 6-Heat wave, 7-Infrared radiation, 8-Cable under test, 9-Hypothetical defect, 10-Transmission guide rail, 11-Test equipment connection block, 12-Mode knob, 13-Data processing host computer. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention 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, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0027] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0028] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1 This invention provides a cable insulation defect detection device based on infrared thermal wave phase-locked loop, including an infrared thermal imager 1, a rotating bracket 2, a photothermal excitation source 3, a cable bracket 4, an insulation layer 5, a transmission rail 10, a test equipment connecting block 11, a mode knob 12, and a data processing host computer 13. The infrared thermal imager 1 and the photothermal excitation source 3 are arranged on the same side. The rotating bracket 2 is used to rotate the infrared thermal imager 1 and the photothermal excitation source 3. The cable bracket 4 supports and fixes the cable 8 under test. The insulation layer 5 reduces environmental heat loss. The mode knob 12 is used to select axial or circumferential detection. The transmission rail 10 is used for axial detection. The test equipment connecting block 11 connects the photothermal excitation source 3 and the infrared thermal imager 1. The photothermal excitation source 3 generates a periodic sinusoidal thermal excitation with an adjustable frequency. The infrared thermal imager 1 acquires temperature sequence images at a high sampling rate. The data processing host computer 13 collects the infrared thermal wave sequences from the photothermal excitation source 3 and the infrared thermal imager 1, and calculates and outputs a defect cloud map using a built-in algorithm.

[0029] The infrared thermal imager 1 is rigidly fixed to the test equipment connecting block 11 and is located on the same side as the photothermal excitation source 3 on the cable under test 8. This same-side arrangement ensures convenient and consistent signal acquisition. The infrared thermal imager 1 is a high-speed, high-sensitivity infrared thermal imager with a sampling rate ≥100 Hz, continuously acquiring 512~1024 frames of thermal images. Its core function is to non-contactly acquire the infrared radiation 7 emitted from the surface of the cable under test 8, extract the temperature response sequence of each pixel through fast Fourier transform, and generate a phase difference map. To ensure the capture of the transient response of the infrared radiation 7, its sampling rate should be much higher than the thermal excitation frequency 3.

[0030] The rotating bracket 2 is a ring-shaped track bracket with an inner diameter larger than that of the cable under test 8, allowing it to surround the cable. The main function of the rotating bracket 2 is to support the test equipment connecting block 11 and, in circumferential detection mode, drive the infrared thermal imager 1 and the photothermal excitation source 3 to rotate and scan around the central axis of the cable under test 8.

[0031] The photothermal excitation source 3 and the infrared thermal imager 1 are fixed together on the test equipment connection block 11 to ensure synchronization and spatial alignment of thermal excitation and temperature acquisition. The photothermal excitation source 3 is preferably a high-power halogen lamp or laser, capable of generating a periodically sinusoidally modulated heat wave 6 with a frequency range of 0.01~10 Hz. Its most critical function is frequency adjustability, injecting the heat wave 6 into the insulation layer by actively and periodically heating the surface of the cable under test 8. The penetration depth μ of the heat wave 6 is related to the excitation frequency. Inversely proportional to the square root Therefore, by adjusting the frequency It can directly control the depth of detection, using low frequency to detect deep defects and high frequency to detect shallow defects.

[0032] The cable bracket 4 is a U-shaped groove bracket, which is used to accurately position and firmly support the cable under test 8, ensuring that the cable under test 8 maintains a constant focal length and relative position with the infrared thermal imager 1 and the photothermal excitation source 3 in both detection methods.

[0033] The insulation layer 5 is a box or cover that surrounds the entire detection area. Its core function is to isolate environmental thermal noise. It effectively prevents interference from ambient airflow, background thermal radiation, and other factors on the weak temperature field of the cable under test 8, while reducing the cable's own heat loss. This greatly improves the signal-to-noise ratio and is a key structure for solving the problem of traditional infrared detection being susceptible to environmental interference in background technologies.

[0034] The drive rail 10 is a precision linear guide located on the equipment base. The rotating bracket 2 and the insulation layer 5 are both mounted on the moving platform of the drive rail 10. The drive rail 10 operates in axial detection mode, driving the entire detection system along the axis of the cable 8 under test at a constant speed. Perform a translation scan.

[0035] The test equipment connecting block 11 is used to connect and fix the infrared thermal imager 1 to the photothermal excitation source 3, forming a rigid bracket. The mode knob 12, mounted on the test equipment connecting block 11, is a mechanical locking and rotation mechanism that allows switching between two detection modes. Circumferential pattern (e.g.) Figure 1 As shown): The mode knob 12 fixes the test equipment connection block 11 on the circular track of the rotating bracket 2, so that it can rotate around the cable under test 8.

[0036] Axial mode (e.g.) Figure 2 As shown): Rotate the mode knob 12, the posture of the test equipment connecting block 11 is adjusted and locked with the rotating bracket 2, so that it no longer rotates, but is parallel to the axis of the cable under test 8, ready for axial translation scanning.

[0037] The data processing host computer 13 is fixed on the test equipment connection block 11. It collects infrared thermal wave data from the infrared thermal imager 1 and the photothermal excitation source 3 through the built-in data cable of the test equipment connection block 11 via the mode knob 12, and processes the data according to the built-in algorithm to obtain a defect cloud map. The cloud map can be copied via the USB interface.

[0038] This invention also provides a method for detecting defects in cable insulation based on infrared thermal wave phase-locked loop, comprising the following steps: Step 1: Photothermal excitation source 3 applies periodic thermal excitation to the cable surface, and thermal wave 6 propagates inside the material and is reflected by defects.

[0039] Step 2: Use infrared thermal imager 1 to collect surface temperature time series. The collected time series and the thermal wave sequence of the photothermal excitation source are transmitted to the data processing host computer 13.

[0040] Step 3: Data Processing The host computer 13 performs a Fast Fourier Transform (FFT) on the temperature signal, converts it to the frequency domain, extracts the frequency domain phase information, compares it with the periodic thermal excitation frequency to generate a phase difference map, identifies whether the pixel defect is reliable based on the grayscale of the phase difference map, and generates a pixel defect map.

[0041] This invention provides a quantitative, high signal-to-noise ratio, and highly interference-resistant defect discrimination standard. It extracts the temperature response sequence of each pixel using Fast Fourier Transform and generates a phase difference map. Specifically, it includes the following steps: Before defect detection, this invention requires a calibration step, preferably performed on a qualified cable, specifically on a section of XLPE insulation layer that has been confirmed as having acceptable manufacturing processes through other means. The data processing host computer 13 operates at a set excitation frequency. Next, a reference phase map of the qualified area is collected and generated.

[0042] Subsequently, the data processing host computer 13 processed all data on the reference phase diagram. Phase angle of each pixel Statistical analysis was performed to calculate two key baseline parameters: Mean phase angle : Represents the phase delay of characteristic thermal wave propagation of this batch of qualified insulation materials at the current excitation frequency.

[0043] Standard deviation This represents the acceptable fluctuation range for the qualified material.

[0044] After establishing the average phase angle and standard deviation of a qualified power cable insulation layer, the device of this invention enters continuous detection mode: The cable under test is monitored in real time, and the phase angle of each pixel (i,j) is generated accordingly. ; Some non-uniform defects physically manifest as local thermal diffusivity The anomaly acts as a barrier to heat wave propagation, causing the heat wave to travel more slowly at that point, thus creating a significantly larger [temperature / effect]. Phase delay.

[0045] This invention sets a statistically based defect determination threshold. A defect determination threshold is set if and only if the phase angle of a pixel... A point is considered a "non-uniform defect" if the following conditions are met:

[0046] in, It is a confidence factor that can be preset according to the detection accuracy requirements. The possible values ​​are 2, 3, or higher. At this point, statistically, the deviation of the phase delay from the normal mean reached 99.7% significance, allowing for high-confidence identification as a defect. Furthermore, due to the relative nature of the standard, almost all random noise interference was eliminated. Finally, a defect cloud map was generated from the pixels identified as non-uniform defects and normal pixels, clearly showing the continuous defect locations.

[0047] This invention has two independent operating modes, selectable by mode knob 12: Working mode 1: Circumferential inspection (e.g.) Figure 1 (As shown) Preparation: Place the cable 8 to be tested on the cable bracket 4. Select the circumferential testing mode.

[0048] Excitation and Acquisition: Photothermal excitation source 3 starts working at the set frequency. A sinusoidal heat wave 6 is applied to the surface of the cable, and the heat wave 6 propagates inside the material.

[0049] Mechanical action: The rotating bracket 2 starts, driving the infrared thermal imager 1 and the photothermal excitation source 3 on the test equipment connecting block 11 to rotate at a constant speed around the central axis of the cable under test 8.

[0050] Data Acquisition: During rotation, the infrared thermal imager 1 continuously acquires thermal image sequences at a high sampling rate, obtaining the temperature change over time at each point on the circumference of the cable under test 8. If there are material inhomogeneities, such as in the case of bonded wires, part of the heat wave 6 is reflected, causing a delay in the phase angle of the reflected heat wave. The infrared thermal imager 1 records the temperature time series and transmits it to the data processing host computer 13 for processing.

[0051] Principle and Effect: After this process is completed, the data processing host computer 13 obtains complete data of the circumference of the cable cross-section. An FFT is performed on the temperature signal of each pixel to obtain the frequency domain response.

[0052] Where T(k) is the discrete temperature signal, L is the data length, and Fs is the sampling frequency. Extract the phase angle of the complex number F(n):

[0053] Pixel phases are generated. Areas with material inhomogeneity show significant phase delays and are identified as defect pixel locations. All pixels are then combined into a defect cloud map.

[0054] Working mode two: Axial detection (e.g.) Figure 2 (As shown) Preparation: Place the cable 8 to be tested on the cable bracket 4. Rotate the mode knob 12 to switch to the axial detection mode, making the test equipment connecting block 11 parallel to the cable 8 under test. At this time, the infrared thermal imager 1 and the photothermal excitation source 3 are locked, pointing towards the surface of the cable 8 under test, and parallel to the axial direction of the cable 8 under test.

[0055] Excitation and Acquisition: Photothermal excitation source 3 at a set frequency A sinusoidal heat wave 6 is continuously applied, and the infrared thermal imager 1 continuously acquires a sequence of thermal images.

[0056] Mechanical action: The transmission guide rail 10 starts, driving the entire testing equipment along the axial direction (length direction) of the cable under test 8 at a constant speed. During scanning, the cable under test 8 remains stationary via the cable bracket 4.

[0057] Data acquisition: During the translation process, the infrared thermal imager 1 continuously records the temperature sequence below its field of view.

[0058] Principle and Effect: The data processing host computer 13 stitches together the acquired continuous data frames and performs the same phase-locked loop and statistical analysis. Finally, it generates a phase cloud map unfolding along the cable length, which can intuitively display the distribution of longitudinal defects. Through application... Statistical judgment methods can be used to identify longitudinal non-uniform defects distributed along the cable length.

[0059] This invention utilizes the physical principle of thermal waves, namely, thermal diffusion length. With excitation frequency The result is inversely proportional to the square root, enabling controllable detection of defect depth. To distinguish and locate defects of different depths, this invention employs a frequency scanning implementation, repeatedly executing the detection steps described above at at least two or more different excitation frequencies: For XLPE materials (thermal conductivity 0.2~0.4 W / (m·K), density 0.92~0.95 g / cm³), 3 Specific heat capacity 2.0~2.5 J / (g·K)), thermal diffusivity α is 0.84×10 -6 ~38.26×10 -6 m 2 / s. The thermal diffusion length μ is related to the frequency f:

[0060] During operation, the detection depth of the material of the cable under test (8) can be controlled by adjusting the excitation frequency. In-depth material testing of cable 8 under test: Preparation: Adjust the photothermal excitation source 3 and the infrared thermal imager 1 to low frequency mode (0.01~0.1 Hz); Excitation and Acquisition: Photothermal excitation source 3 at a set frequency When a sinusoidal heat wave is continuously applied at this frequency, the thermal diffusion length is... The thermal wave 6 is relatively large, allowing it to penetrate deeper into the insulation layer. The infrared thermal imager 1 continuously acquires a sequence of thermal images. It can be used in both operating modes one and two to test axial depth detection and circumferential depth detection. The host computer 13 generates a deep phase map for data processing. The deep non-uniform defect map is obtained based on the decision algorithm.

[0061] Shallow material testing of cable 8 under test: Preparation: Adjust the photothermal excitation source 3 and the infrared thermal imager 1 to high frequency mode (1~10 Hz); Excitation and Acquisition: Photothermal excitation source 3 at a set frequency When a sinusoidal heat wave is continuously applied at this frequency, the thermal diffusion length is... The thermal wave 6 is very small, propagating only in the shallow surface layer of the insulation. The infrared thermal imager 1 continuously acquires a sequence of thermal images. It can be used in both operating modes one and two to test deep axial detection and shallow circumferential detection. The data processing host computer 13 generates a shallow phase map. The shallow non-uniform defect map is obtained based on the decision algorithm.

[0062] By comparing and analyzing these two (or more) defect images at different frequencies, the depth information of the defect can be determined. If a defect is clearly visible in both the shallow and deep non-uniform defect images, it indicates that the defect is close to the surface or penetrates to a considerable depth. If a defect is visible only in the deep non-uniform defect image and not in the shallow non-uniform defect image, it can be determined with high confidence that the defect is an internal deep defect.

[0063] Working principle of the invention: Healthy and uniform XLPE material has a low thermal diffusivity. It is consistent that the phase delay of thermal wave 6 propagating within it is consistent. It is consistent. When heat wave 6 encounters hypothetical defect 9, the area... The change hinders the propagation of the heat wave, causing a change in the reflection time of heat wave 6, which in turn affects the phase angle. The delay.

[0064] Then, this phase angle is extracted using FFT. ,take Based on the judgment criteria, a non-uniform defect diagram is generated.

[0065] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cable insulation defect detection device based on infrared thermal wave phase-locked loop, characterized in that, It includes an infrared thermal imager (1), a rotating bracket (2), a photothermal excitation source (3), a transmission guide rail (10), a mode knob (12), and a data processing host computer (13). The infrared thermal imager (1) and the photothermal excitation source (3) are both mounted on the rotating bracket (2) via the test equipment connecting block (11). The rotating bracket (2) is movably mounted on the transmission guide rail (10). The mode knob (12) is mounted on the test equipment connecting block (11) and is used to select axial detection or circumferential detection. The infrared thermal imager (1), the photothermal excitation source (3), and the mode knob (12) are all connected to the data processing host computer (13).

2. The cable insulation defect detection device based on infrared thermal wave phase-locked loop as described in claim 1, characterized in that, It also includes a cable bracket (4), which is a U-shaped groove bracket, and the cable to be tested (8) is placed in the groove of the cable bracket (4).

3. The cable insulation defect detection device based on infrared thermal wave phase-locked loop as described in claim 1, characterized in that, The infrared thermal imager (1) and the photothermal excitation source (3) are both fixedly installed on the test equipment connection block (11), and the infrared thermal imager (1) and the photothermal excitation source (3) are located on the same side of the cable (8) under test.

4. The cable insulation defect detection device based on infrared thermal wave phase-locked loop as described in claim 1, characterized in that, The rotating bracket (2) is a ring track bracket, and the test equipment connecting block (11) is movable and installed in the ring track of the rotating bracket (2).

5. The cable insulation defect detection device based on infrared thermal wave phase-locked loop as described in claim 1, characterized in that, The inner diameter of the rotating bracket (2) is larger than the diameter of the cable (8) to be tested.

6. The cable insulation defect detection device based on infrared thermal wave phase-locked loop according to claim 1, characterized in that, A heat insulation layer (5) is movably installed on the transmission guide rail (10). The heat insulation layer (5) is a box or cover, and the heat insulation layer (5) surrounds the outside of the detection area.

7. The cable insulation defect detection device based on infrared thermal wave phase-locked loop according to claim 1, characterized in that, The transmission guide (10) is mounted on the base. The transmission guide (10) is a precision linear guide and is set along the axial direction of the cable (8) to be tested.

8. The cable insulation defect detection device based on infrared thermal wave phase-locked loop according to claim 1, characterized in that, The photothermal excitation source (3) is a high-power halogen lamp or a laser.

9. A method for detecting cable insulation defects based on infrared thermal wave phase-locked loop using the equipment described in any one of claims 1 to 8, characterized in that, include: The photothermal excitation source (3) applies periodic thermal excitation at different excitation frequencies to the surface of the cable under test (8). The thermal wave (6) propagates inside the material and is reflected when it encounters a defect. The infrared thermal imager (1) is used to collect the surface temperature time series of the cable (8) under test, and the collected temperature time series and the thermal wave sequence of the photothermal excitation source (3) are transmitted to the data processing host computer (13). The data processing host computer (13) performs a fast Fourier transform on each pixel in the temperature time series, converts the time domain signal into a frequency domain signal, extracts the phase information in the frequency domain signal, and generates phase maps at different detection depths. The phase information of the pixel is compared with the phase information of the thermal wave sequence to obtain the phase difference. The grayscale of the phase difference map is used to identify whether the pixel defect is reliable, and a pixel defect map is generated to realize the location of non-uniform defects at different depths inside the insulating layer.

10. The cable insulation layer defect detection method based on infrared thermal wave phase-locked loop according to claim 9, characterized in that, Defect detection includes circumferential detection mode and axial detection mode; When using the circumferential detection mode, the mode knob (12) is used to select the circumferential detection mode. The photothermal excitation source (3) applies circumferential thermal excitation with different excitation frequencies to the surface of the cable (8) under test. The rotating bracket (2) drives the infrared thermal imager (1) and the photothermal excitation source (3) to rotate at a constant speed around the central axis of the cable (8) under test. During the rotation, the infrared thermal imager (1) collects thermal image sequences, obtains the temperature change of each point on the circumference of the cable (8) under test over time, records the temperature time sequence, and transmits it to the data processing host computer (13) for processing to generate a pixel defect map. When using the axial detection mode, the mode knob (12) is used to select the axial detection mode. The test equipment connecting block (11) is parallel to the axis of the cable under test (8). The photothermal excitation source (3) applies periodic thermal excitation with different excitation frequencies to the surface of the cable under test (8). The transmission guide rail (10) drives the entire test equipment to move along the axis of the cable under test (8). The infrared thermal imager (1) records the temperature time series under its field of view during the translation process and transmits it to the data processing host computer (13) for processing to generate a pixel defect map.

Images