A low-cost two-dimensional measurement method and system for potassium atomic concentration in flames based on an electronic rolling shutter camera

Abstract

The present invention discloses a low-cost two-dimensional measurement method and system for potassium atom concentration field. The method combines tunable semiconductor laser absorption spectroscopy technology with electronic rolling shutter camera imaging technology to achieve two-dimensional measurement of potassium atom concentration. The light source module provides a stable signal light for the detection system. After the signal light is shaped and expanded by the beam shaping module, it passes through the combustion area to be measured, and is then collected and imaged by the signal acquisition module. Finally, the captured image signal is processed on the computer host data processing module to obtain the absorption spectra of different spatial positions of the potassium atom concentration field, and finally the two-dimensional measurement of the potassium atom concentration field is achieved.

Description

Technical Field

[0001] The invention relates to the field of optical detection technology, and in particular to a low-cost two-dimensional measurement method and system for potassium atom concentration in flames based on an electronic rolling shutter camera. Background Art

[0002] The two-dimensional measurement of the potassium atom concentration field in flames is of great significance for combustion diagnosis and alkali metal detection. At present, the commonly used non-contact optical detection methods for alkali metal concentration include chemiluminescence, laser-induced fluorescence, Rayleigh scattering, Raman scattering and laser absorption tomography. However, these methods generally have problems such as low spatial resolution, complex system structure and high cost. Tunable diode laser absorption spectroscopy (TDLAS) is widely used in gas flow field detection in various environments due to its advantages such as non-invasive and disturbance-free detection, high temporal resolution, simple measurement system and simultaneous measurement of multiple components and multiple parameters. When facing non-uniform combustion flow fields, traditional single-point measurement methods often require a lot of time and manpower to measure point by point, which is inefficient. In recent years, domestic and foreign scholars have conducted a lot of research on TDLAS two-dimensional measurement technology. Foreign two-dimensional measurement technology research mainly focuses on scanning TDLAS, fan beam TDLAS and tomographic TDLAS, while domestic research mainly focuses on CT-TDLAS, fiber TDLAS array and other technologies.

[0003] Despite this, the existing TDLAS two-dimensional measurement technology still faces problems such as high system complexity and high cost. Although the TDLAS two-dimensional measurement technology based on high-speed cameras can achieve high spatial resolution, the equipment cost is expensive, and there are problems such as large data volume and complex processing in practical applications. Therefore, it is necessary to develop a low-cost method and system that can achieve two-dimensional measurement of potassium atomic concentration to overcome the high cost of existing technologies and meet practical application needs. Summary of the invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a low-cost two-dimensional measurement method and system for potassium atom concentration based on an electronic rolling shutter camera. Compared with the solution using a high-speed camera, the present invention can achieve two-dimensional measurement by cleverly utilizing the exposure characteristics of the electronic rolling shutter camera, using a low-cost electronic rolling shutter camera (the price is about one hundredth of that of a high-speed camera), while solving the problems of complex system and high cost existing in the prior art. To achieve the above purpose, the present invention provides a low-cost two-dimensional measurement method for potassium atom concentration, which comprises the following steps:

[0005] (1) Use a signal generator to generate a triangular wave signal, load the triangular wave signal to a current controller, and use the current controller to tune the current of a laser diode that generates a laser wavelength of 769.9 nm to generate a laser with appropriate power. If the laser output power is too large, it may cause the electronic rolling shutter camera to be oversaturated or even damage the camera. If the laser output power is too small, the signal-to-noise ratio of the image will be low;

[0006] (2) collimating the point light source generated by the tunable laser using a collimator to ensure that the collimated laser is a parallel light beam; the collimated parallel laser beam diverges when passing through a plano-concave lens, and then is converged into a parallel light beam by a plano-convex lens and then emitted, so that it covers the potassium atom concentration field to be measured;

[0007] (3) After passing through the potassium atomic concentration field, the laser beam first passes through a filter. The filter is a filter with cutoff bands adjacent to both sides of the transmission band of the spectral characteristic curve. The purpose is to filter out light waves in other spectral bands that may interfere with the detection results, improve the image signal-to-noise ratio, and thus improve the measurement accuracy. The bandpass filter must be placed in front of the camera lens to ensure that light waves in other bands do not enter the CMOS image sensor inside the camera through the gap between the filter and the camera. Then an electronic rolling shutter camera is used to perform spatiotemporal sampling of the laser beam after passing through the potassium atomic concentration field to obtain the original image data;

[0008] (4) Process the obtained raw image data and extract the laser wavelength scanning signal. First, the region of interest is selected. In the field of machine vision, the region of interest (RoI) of an image generally refers to a part of the image containing key information selected from the image captured by the camera. Therefore, before processing the image data, the RoI must be selected first. The RoI is the image area containing the potassium atom absorption information, that is, the location of the light spot. However, since the laser output light spot is Gaussian distributed, the light intensity at the edge of the light spot distribution is weak, which may cause excessive errors when inverting the potassium atom concentration field. Therefore, when selecting RoI, the area with weak light intensity should be eliminated first. In order to extract the wavelength scanning signal containing absorption information from the RoI, the following steps are used to process the RoI image array: First, the RoI is divided into 5 independent parts according to the wavelength scanning period rule, and 1 400×2000, 2 400×1500 and 2 400×100 are obtained respectively. 0 two-dimensional array; process each area separately; extract the grayscale information of all pixels in each array area to obtain a 400×2000 grayscale value array, and then process the array; decompose the 400×2000 grayscale value array into 2000 400×1 one-dimensional arrays, normalize the grayscale values ​​in each one-dimensional array in turn and arrange them in order on the coordinate axis, and obtain multiple transmission wavelength scanning period signals with absorption information; finally, repeat steps 1 to 4 for the remaining part of the RoI until all pixel information is extracted, and then obtain the transmission light intensity signal contained in the entire RoI;

[0009] (5) According to the extracted laser wavelength scanning signal, the two-dimensional distribution of potassium atomic concentration is calculated. The horizontal coordinate corresponding to the absorption peak is the number of row pixels (sampling points). According to the principle of potassium atomic concentration measurement, the integral absorbance of the absorption line must be solved, so the sampling points need to be converted into wave numbers. The present invention does not use the traditional calibration method using the FB standard tool, but uses the half-width at half maximum (FWHM) of a single absorption line for wave number calibration based on the characteristic that only one absorption line is included in the wavelength scanning signal range. The specific method of wave number calibration is as follows: First, find the corresponding absorption peak from the HITRAN spectral library, and find the wave number corresponding to the FWHM position; then, use the experimentally measured absorbance curve information to find the absorbance curve, the sampling point corresponding to the FWHM position, and the relationship between the wave number and the sampling point can be obtained; finally, use the sampling point and wave number obtained in the previous step to fit the measured gas absorption spectrum to the Voigt standard line type, and finally obtain the value of the integral absorbance by calculation. According to the concentration inversion algorithm, the light intensity signals containing absorption information obtained from all sub-images in the RoI are processed separately to obtain the integrated absorbance of each sub-image in the entire RoI. Then, they are combined according to their original positions to obtain the two-dimensional distribution of the potassium atom concentration field.

[0010] Compared with the prior art, the advantages of the present invention are:

[0011] 1. Innovatively utilize the exposure characteristics of low-cost electronic rolling shutter cameras to achieve two-dimensional measurement of potassium atomic concentration without the use of expensive high-speed cameras;

[0012] 2. The system has a simple structure, reduces costs by more than 90%, is easy to implement, has high measurement efficiency, and is suitable for two-dimensional measurement of potassium atomic concentration during combustion;

[0013] 3. Compared with high-speed camera solutions, it has small data volume and simple processing, making it more suitable for industrial field applications.

[0014] The present invention combines tunable semiconductor laser absorption spectroscopy technology with electronic rolling shutter camera imaging technology to achieve two-dimensional measurement of potassium atom concentration field, which has important application prospects in the fields of combustion diagnosis, alkali metal concentration detection, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1A diagram of a two-dimensional measurement system for potassium atom concentration field based on an electronic rolling shutter camera provided in an embodiment of the present invention.

[0017] Figure 2 A two-dimensional measurement optical path diagram of potassium atom concentration field based on an electronic rolling shutter camera provided in an embodiment of the present invention.

[0018] Figure 3 A data processing flow chart of a two-dimensional measurement method of potassium atom concentration field based on an electronic rolling shutter camera provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0020] Figure 1 FIG. 4 is a schematic diagram of a measurement system according to an embodiment of the present invention.

[0021] (1) Light source module: The light source module provides stable and reliable signal light for the detection system. The signal generator generates a triangle wave signal with 100% symmetry and loads it to the current controller. The current of the laser diode is controlled by adjusting the current controller, and the triangle wave signal is transmitted to the laser diode.

[0022] (2) Beam shaping module: The signal light is shaped and expanded by the beam shaping module. The laser emitted by the laser diode is collimated into a parallel laser beam by a laser collimator. The parallel laser beam is diverged by a plano-concave lens and converged into a parallel laser beam after passing through a plano-convex lens. The combination of the plano-concave lens and the plano-convex lens realizes the function of light spot amplification, in order to cover the combustion environment to be detected.

[0023] (3) Image signal module: The signal light passes through the combustion area to be tested and is then collected by the signal acquisition module. The amplified laser beam passes through the area to be tested and then passes through a filter to eliminate interference from other wavelengths. The laser beam finally reaches the electronic rolling shutter camera, and the host computer uses software to collect and save images with absorption information.

[0024] Figure 2 FIG. 4 is a schematic diagram of an optical path of a measurement system according to an embodiment of the present invention.

[0025] The laser emitted by the laser diode 1 is collimated into a parallel laser beam by the laser collimator 2. The parallel laser beam is diverged by the plano-concave lens 3 and converged into a parallel laser beam after passing through the plano-convex lens 4. The combination of the plano-concave lens 3 and the plano-convex lens 4 realizes the function of amplifying the light spot, so as to cover the combustion environment to be detected. The laser beam after imaging and amplification passes through the area to be detected and passes through the filter 5 to eliminate the interference of light of other wavelengths. The laser beam finally reaches the electronic rolling shutter camera 6.

[0026] Figure 3 FIG. 4 is a data processing flow chart according to an embodiment of the present invention.

[0027] First, the region of interest is selected (the image captured by the camera contains a large amount of data information, and a single image contains millions of pixel information, but not all of this information is useful, and only some areas contain the data required for gas flow field detection). At the same time, in order to obtain the laser wavelength scanning signal from the original image, after the region of interest is selected, its image array needs to be processed. In addition, since the laser wavelength scanning signal directly obtained from the region of interest usually contains more serious noise, further filtering and noise reduction processing is required to finally achieve the concentration inversion of potassium atoms at different spatial positions.

[0028] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A low-cost two-dimensional measurement method for potassium atomic concentration, characterized in that: The following steps are involved: A signal generator is used to generate a triangular wave signal, and the triangular wave signal is added to a current controller. The current controller is used to tune the current of a laser diode that generates a laser wavelength of 769.9 nm to generate laser; a collimator is used to collimate the laser to obtain a parallel light beam, and the parallel light beam is sequentially diverged by a plano-concave lens and then converged into a parallel light beam by a plano-convex lens to cover a potassium atom flow field to be measured; the parallel light beam passes through a potassium atom concentration field and then passes through an optical filter, and the optical filter is an optical filter with cutoff bands adjacent to both sides of a transmission band of a spectral characteristic curve, and an electronic rolling shutter camera is used to perform spatiotemporal sampling on the laser beam after passing through the potassium atom concentration field to obtain original image data.

2. The method according to claim 1, characterized in that: The original image data is subjected to region of interest selection, and the region of interest is divided into five independent parts according to the wavelength scanning period rule, and one 400×2000, two 400×1500 and two 400×1000 two-dimensional arrays are obtained respectively; each region is processed, and the grayscale information of all pixels in each array region is extracted to obtain a 400×2000 grayscale value array; Decomposing the 400×2000 grayscale value array into 2000 400×1 one-dimensional arrays, normalizing the grayscale values ​​in each one-dimensional array and arranging them in order on the coordinate axis, and obtaining a transmission wavelength scanning period signal with absorption information; The two-dimensional distribution of potassium atom concentration is calculated according to the transmission wavelength scanning periodic signal, including: using the half-width of a single absorption spectrum line to perform wave number calibration, performing Voigt standard line fitting on the measured potassium atomic absorption spectrum, calculating the value of the integrated absorbance, processing the light intensity signals containing absorption information obtained in all sub-images in the region of interest according to the concentration inversion algorithm, obtaining the integrated absorbance of each sub-image in the entire region of interest, and combining them according to their original positions to obtain the two-dimensional distribution of the potassium atom concentration field.

3. The method according to claim 1, characterized in that: The specific steps of wavenumber calibration include: finding the wavenumber corresponding to the corresponding absorption peak and its half-maximum full width position from the HITRAN spectral library; finding the sampling point corresponding to the half-maximum full width position according to the experimentally measured absorbance curve information, and obtaining the relationship between the wavenumber and the sampling point.

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