A method and system for locating a cable fault by combining microphone and infrared thermal imaging positioning

Abstract

The present application relates to a kind of microphone and infrared thermal imaging combined positioning cable fault positioning method and system.The present application detects heat source due to abnormal discharge by infrared thermal imager.Infrared radiation all carries the characteristic information of object, after the power signal radiated by the heating site of object is converted into electric signal by photoelectric infrared detector, imaging device can simulate the spatial distribution of object surface temperature, finally, after system processing, form thermal image video signal, just obtain the thermal image corresponding to object surface heat distribution.The system is composed of infrared thermal imager and display two parts, infrared thermal imager is by non-contact detection infrared energy, and it is converted into electric signal after signal amplification and processing, generates thermal image, shows temperature distribution in space in the form of image, obtains spatial infrared thermal imaging chart.The present application reduces imaging range, reduces calculation amount;Make the accuracy of detection greatly improve real-time performance, system is simple and easy to realize.

Description

Technical Field

[0001] This invention relates to a cable fault location method and its system implementation that combines microphone array sound source localization with infrared thermal imager (infrared camera) localization, and particularly to a two-dimensional spatial localization algorithm and its corresponding system implementation. Background Technology

[0002] Currently, there are two methods for detecting power cable faults: coarse fault detection and precise fault location. Coarse fault detection uses the bridge method or pulse-echo method, which can only detect fault types under limited conditions and cannot locate the fault point.

[0003] Precise fault location methods mainly include acoustic detection and audio induction. Acoustic detection is the most basic and accurate fault location method for cables, but it is easily interfered with by external vibration and noise. Audio induction is generally used to detect low-resistance faults with a fault resistance of less than 10Ω. It can achieve satisfactory results for two-phase-to-ground short circuits and three-phase short circuits, but this method is only applicable to a small number of low-resistance faults and open-circuit faults, and its versatility is poor.

[0004] The detection methods mentioned above have drawbacks such as limited detection range, susceptibility to external noise, and high equipment costs. Therefore, a cable fault detection and location method combining microphone array and infrared thermal imaging is considered. Summary of the Invention

[0005] High-voltage signals passing through a fault point in a cable will cause a discharge phenomenon. Acoustic imaging can provide a fast and accurate distribution map of the sound source target; infrared thermal imagers can accurately quantify the detected heat, enabling not only observation of thermal images but also accurate identification and rigorous analysis of the heated fault area. Therefore, this invention employs a combination of these two methods for fault point detection and location.

[0006] This invention uses a microphone array for sound source localization. By measuring the phase difference of sound waves arriving at each microphone in space, the location of the sound source is determined based on the phased array principle. The distribution of the sound source in space is displayed as an image, obtaining a spatial sound field distribution cloud map (acoustic image), where the color and brightness of the image represent the intensity of the sound. The system consists of three parts: a microphone array unit, a data acquisition card unit, and a host computer unit. The microphone array unit is required to consist of several (16-64) microphones with identical performance. The microphone array unit is responsible for collecting and processing the sound source signal. The data acquisition card performs multi-channel synchronous data transmission and storage. The host computer processes and displays the data transmitted by the data acquisition card. In operation, the microphone array first converts the sound source signal into an electrical signal and amplifies the target sound source signal. Then, the data acquisition card performs multi-channel synchronous data acquisition and outputs the data through the display of the host computer system's peripheral devices. The hardware components of the microphone array unit and the acoustic data acquisition card unit are interconnected by wires.

[0007] This invention uses an infrared thermal imager to detect heat sources generated by abnormal discharges. Infrared thermal imaging works by utilizing the infrared radiation emitted by objects with temperatures above absolute zero. This infrared radiation carries characteristic information about the object. A photoelectric infrared detector converts the power signal radiated by the object's heat-generating parts into an electrical signal. The imaging device then simulates the spatial distribution of the object's surface temperature. Finally, the system processes this data to form a thermal image video signal, resulting in a thermal image corresponding to the object's surface heat distribution. The system consists of an infrared thermal imager and a display. The infrared thermal imager detects infrared energy non-contactly, converts it into an electrical signal, amplifies and processes the signal to generate a thermal image, and displays the spatial distribution of temperature as a visual representation, thus obtaining a spatial infrared thermal image. The grayscale of the image represents the temperature level, with bright areas indicating high temperatures and dark areas indicating low temperatures, or warm and dark colors representing different temperatures. The colors, from high to low, are marked with red, yellow, blue, and green, respectively. The infrared thermal imager transmits the image data to a host computer unit via a Universal Serial Bus (USB) interface.

[0008] In summary, when a high-voltage signal passes through a faulty cable, it generates sound and infrared signals. A microphone array can be used to obtain a spatial sound field map and locate the sound source. An infrared thermal imager can be used to obtain an infrared thermal image of the cable and determine the location of the abnormal infrared heat source generated by the electrical spark caused by the high-voltage discharge.

[0009] Based on the field of view of the infrared camera, the resolution of the acoustic image is determined, and a sound field map with the same size as the infrared image is obtained. Then, the average fusion method is used to perform image fusion. If the fault point pointed to by the acoustic image coincides with the fault point pointed to by the infrared image, the detection and location of the cable fault point are realized.

[0010] The advantages of this invention are:

[0011] First, this invention innovates in acoustic imaging methods by determining the range of the sound field map based on the size of the infrared image, thereby reducing the imaging range and computational load. In addition, the combined detection using microphone array and infrared thermal imaging technology greatly improves detection accuracy and real-time performance. The technology is relatively mature, the system is simple, and it is easy to implement. Attached Figure Description

[0012] Figure 1 This is a schematic diagram showing the placement of the infrared camera and microphone;

[0013] Figure 2 This is a schematic diagram of the system implementation;

[0014] Figure 3 This is an example of imaging using a circular microphone array. Detailed Implementation

[0015] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] like Figure 1 As shown, multiple microphones form a microphone array, and an infrared detector is placed at the physical center of the array.

[0017] like Figure 1 As shown, the physical center point of the entire microphone array is used as the center of the spatial coordinate system to achieve coordinate system transformation.

[0018] Figure 2 The diagram shows a system diagram of the combined method of microphone sound source localization and infrared thermal imaging technology. The system consists of five parts: a microphone array unit, an infrared thermal imager, a data acquisition card unit, a host computer unit, and a display. The microphone array unit is required to be composed of several microphones with completely identical performance assembled in a certain order.

[0019] The following description uses a circular array as an example to illustrate the process of microphone array beamforming:

[0020] like Figure 3 As shown, M identical microphones are evenly distributed on a circle of radius R on a plane XY. The spatial coordinate system is established with the center of the entire array model, i.e., the reference element, as the center of the circle, and the X-axis of the coordinate system as the line connecting the reference element and the first element. θ is the elevation angle between the sound source and the center of the circle, and Φ is the azimuth angle between the sound source and the center of the circle.

[0021] Frequency domain beamforming algorithms address the issue of high computational complexity in traditional time domain beamforming algorithms by incorporating FFT technology into beamforming, thereby improving computational speed.

[0022] First, the cross-spectral matrix (CSM) between the microphones in the array needs to be determined. The time-domain data signals acquired by the microphones are divided into blocks and converted into frequency-domain signals using Fast Fourier Transform (FFT) to obtain the M×M cross-spectral matrix of the microphones.

[0023]

[0024] The matrix elements in the formula are:

[0025]

[0026] In the formula: C mn In (f), f is the center frequency of the 1 / 3 octave band in the Fast Fourier Transform, K is the number of array signal data blocks, M represents the number of microphones in the array, and P... mk (f) represents the frequency domain signal of the k-th data block of the m-th microphone, P nk (f) represents the frequency domain signal of the k-th data block of the n-th microphone, W S The data window function factor T selected for spectral analysis B The bandwidth is given by the superscript T, which indicates conjugation. The lower triangular elements of the cross-spectral matrix are obtained by complex conjugation of the corresponding upper triangular matrix elements.

[0027] In acoustic experiments, a scanning region is typically established at the sound source, where the sound power at any scanning point is denoted by A. Let... The steering vector is M-dimensional and consists of the microphone sound pressure amplitudes excited by a set of point sound sources at the scanning point. Because it contains phase, it can exponentially cancel out the phase shift associated with sound propagation.

[0028] If the (m,n) combination is a subset of S, then the acoustic power A can be obtained by minimizing the following equation.

[0029]

[0030] Where g m and g n These represent the steering vectors of the m-th and n-th microphones, respectively.

[0031] The solution is as follows:

[0032]

[0033] The key to fusing sound field maps and infrared thermal images is to set the sound field map and the infrared thermal image to the same size and align their resolutions so that the same pixel in the sound field map and the infrared thermal image corresponds to the same position.

[0034] The method adopted in this invention is as follows: for a selected infrared camera, its image size, resolution, viewing angle and other parameters can be obtained. The viewing angle can be calculated by physical parameters of the lens such as focal length and flange distance.

[0035] Imaging of the microphone array is achieved using both pitch angle θ and azimuth angle. This means that, assuming the size of an infrared image generated by the camera is k×l (length multiplied by width), and the camera's field of view is [-γ, γ]. Generally, the field of view of the microphone array imaging exceeds that of the camera. Therefore, in this invention, the angular resolution of the microphone array imaging is set to [2γ / k, 2γ / l]. Then, the step size of the acoustic image generated by formula (4) is [2γ / k, 2γ / l], so that the pixels of the acoustic image and the infrared image can correspond one-to-one.

[0036] Then, this invention employs an average fusion method for image fusion. The weighted average fusion method linearly weights the grayscale values ​​of pixels in two source images to generate a new fused image. It is a simple and direct image fusion method. The fusion process is as follows:

[0037] F(x,y)=aA(x,y)+bB(x,y)#(5)

[0038] Where A and B represent the original images to be fused, F is the fused image, and a and b are weighting coefficients. In this invention, the weighting coefficients used are a = b = 0.5. In this fusion method, the images participating in the fusion provide redundant information, which can improve the reliability of detection and also improve the signal-to-noise ratio.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

[0040] In the test sample, the present invention applies a high voltage (250V~1000V) pulse signal to the cable under test. The pulse signal propagates along the cable under test and generates an electric spark at the fault point, while also generating light and sound.

Claims

1. A cable fault location method using a combination of microphone and infrared thermal imaging, characterized in that: M identical microphones are evenly distributed on a circle of radius R on the plane XY; the center of the entire array model, i.e. the reference element, is taken as the center of the spatial coordinate system, and the X-axis of the coordinate system is the line connecting the reference element and the first element, thus establishing the spatial coordinate system for acoustic imaging; θ is the pitch angle between the sound source and the center of the circle, and Φ is the azimuth angle between the sound source and the center of the circle. First, the cross-spectral matrix between each microphone in the array must be determined; then, the time-domain data signals acquired by the microphones are divided into blocks and converted into frequency-domain signals using a Fast Fourier Transform to obtain the microphone's... Cross-spectral matrix; The matrix elements in the formula are: In the formula: In The center frequency of the 1 / 3 octave band in the Fast Fourier Transform is given by K, where K is the number of array signal data blocks and M represents the number of microphones in the array. This represents the frequency domain signal of the k-th data block from the m-th microphone. This represents the frequency domain signal of the k-th data block from the n-th microphone. The data window function factor selected for spectrum analysis The bandwidth is given by the superscript T, which indicates conjugation. The lower triangular elements of the cross-spectral matrix are obtained by complex conjugation of the corresponding upper triangular matrix elements. In acoustic experiments, a scanning region is established at the sound source, where the sound power at any scanning point is denoted by A; let... It is an M-dimensional steering vector, composed of the microphone sound pressure amplitudes excited by a set of point sound sources at the scanning point; If the combination is a subset of S, then the acoustic power A is obtained by minimizing the following equation: in and They represent the first The microphone and the first The steering vector of each microphone; The solution is as follows: Set the sound field map and the infrared thermal image to the same size and align their resolutions so that the same pixel in the sound field map and the infrared thermal image corresponds to the same position. For a selected infrared camera, obtain its image size, resolution, and field of view. Imaging of the microphone array at pitch angle and azimuth This means that, assuming the size of an infrared image generated by the camera is... That is, length multiplied by width, the camera's field of view is ; The field of view of a microphone array image exceeds that of a camera; therefore, the angular resolution of the microphone array image is set to [value missing]. Then the step size for generating the acoustic image using formula (4) is In this way, the pixels of the acoustic image and the infrared image correspond one-to-one; Then, the image fusion method is used. The weighted average fusion method is to linearly weight the gray values ​​of the pixels in the two source images to generate a new fused image. The fusion process is as follows: Where A and B represent the original images to be fused, F is the fused image, and a and b are weighting coefficients, with the weighting coefficients being a = b = 0.5.

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