阅读说明：本技术 大范围激光诱导荧光浓度测量系统 (Large-range laser-induced fluorescence concentration measuring system ) 是由 阮哲伟 廖谦 孙圣舒 刘上瑜 管磊 何良 刘中奎 曹淼 卢晶晶 程千文 于 2021-08-09 设计创作，主要内容包括：本发明大范围激光诱导荧光浓度测量系统,属于环境试验测量领域。本系统包含以下装置：激光光源,激光扫描单元,图像采集单元和时钟同步单元,以上四种装置通过电缆进行星形连接,其中时钟同步单元为中心节点,信号电缆分别连接激光光源、激光扫描单元和图像采集单元。作为端节点的激光光源,激光扫描单元和图像采集单元在时钟同步单元的控制下协同工作。本发明的优点在于：构造了采用激光诱导荧光方法测量大面积液体浓度分布的系统；安装简单；能迅速获得大面积离散点的浓度。(The invention discloses a large-range laser-induced fluorescence concentration measuring system, and belongs to the field of environmental test measurement. The system comprises the following devices: the system comprises a laser light source, a laser scanning unit, an image acquisition unit and a clock synchronization unit, wherein the four devices are in star connection through cables, the clock synchronization unit is a central node, and a signal cable is respectively connected with the laser light source, the laser scanning unit and the image acquisition unit. And as a laser light source of the end node, the laser scanning unit and the image acquisition unit work cooperatively under the control of the clock synchronization unit. The invention has the advantages that: a system for measuring the concentration distribution of the large-area liquid by adopting a laser-induced fluorescence method is constructed; the installation is simple; the concentration of large-area discrete points can be rapidly obtained.)

1. Large-scale laser-induced fluorescence concentration measurement system, its characterized in that: comprises the following devices: the system comprises a laser light source, a laser scanning unit, an image acquisition unit and a clock synchronization unit, wherein the four devices are in star connection through cables, the clock synchronization unit is a central node, and signal cables are respectively connected with the laser light source, the laser scanning unit and the image acquisition unit;

and as a laser light source of the end node, the laser scanning unit and the image acquisition unit work cooperatively under the control of the clock synchronization unit.

2. The broad laser-induced fluorescence concentration measurement system of claim 1, wherein: the installation mode of the device is as follows:

(1) the included angle between the laser emitted by the laser scanning unit and the plumb line is +/-30 degrees;

(2) the projection of the laser scanning unit vertical to the measuring plane is positioned at the geometric center of the measuring range;

(3) the image acquisition unit and the laser scanning unit are arranged on the same elevation, and the relation between the installation distance d and the installation height H of the image acquisition unit and the laser scanning unit is that H/d is more than or equal to 50;

(4) the energy stability of the laser is less than or equal to 1 percent, and the divergence angle is less than 1.5 mrad;

(5) the working frequency of the laser scanning unit is as follows:

3. the broad laser-induced fluorescence concentration measurement system of claim 1, wherein: the working mode of the device is as follows:

(1) during a measurement period: the laser light source flashes for 400-10000 times accurately under the control of a synchronous signal of a clock synchronization unit, the flashing time of each time is accurately controlled by the synchronous signal, the time control precision is nanosecond, and the measurement period is 1-9 s;

(2) the laser scanning unit scans a laser beam by 400-10000 point positions line by line under the control of a synchronous signal of the clock synchronization unit, the position precision of a repeated period is millimeter level, the line by line scanning is a square area, and the number of lines is equal to the number of points;

(3) the image acquisition unit completes multiple exposures under the control of a synchronization signal of the clock synchronization unit, one line of image information is recorded in each exposure, and the clock precision of the exposure time is in a nanosecond level.

Technical Field

The invention relates to a large-range concentration field measuring system, in particular to a water concentration field measuring method based on laser-induced fluorescence, and belongs to the field of environmental measurement.

Background

The Laser Induced Fluorescence (LIF) technology is a new measuring method. The laser-induced fluorescence refers to the fluorescence emitted by a fluorescent substance such as fluorescein sodium which absorbs photons with characteristic frequency under the induction of laser, and the concentration can be measured by detecting the fluorescence intensity because the fluorescence intensity and the concentration are in a linear relationship at low concentration.

PLIF technology illuminates the area of interest with a laser sheet to obtain planar two-dimensional information. Laser sheet light is generally obtained by expanding a very thin laser beam through a semi-cylindrical lens, which brings two problems affecting measurement accuracy for a given measurement: firstly, along the optical path direction of the laser, the laser intensity is attenuated along the way due to the absorption of the laser by the fluorescent substance, so that the corresponding attenuation of the fluorescence intensity is caused; secondly, the light intensity of the sheet light has uneven distribution, for example, the laser TEM mode is Gaussian distribution, thereby causing uneven distribution of fluorescence intensity.

LIF is suitable for a large number of molecules and atoms for combustion, spraying, and various fluid mechanical flow studies. LIF detection of atomic species is also known as Laser Excited Atomic Fluorescence (LEAF). Flame radicals and most fuel species can be visualized directly using LIF.

The LIF emission is distributed over many wavelengths (emission spectrum), with most of the emission red-shifted from the laser line. Due to such spectral shifts emitted by the LIF, harmful interference caused by stray light or mie scattering can be effectively suppressed.

The LIF concentration measurements of the prior art are based on sheet light source measurements. Since the Gaussian distribution characteristic of the sheet light source is obvious, the maximum measurement area is generally not more than 30 x 30 cm. There has been no effective method for large scale concentration field measurements in model experiments.

Disclosure of Invention

The invention aims to provide a system for measuring a concentration field in a large-scale water body based on an LIF (limiting LIF) method, and solves the problem that the large-scale water body synchronous measurement cannot be carried out in a pollutant diffusion model test.

Specifically, the system comprises the following devices: the three devices are connected in a star shape through cables, wherein the clock synchronization unit is a central node, and a signal cable is respectively connected with the laser light source, the laser scanning unit and the image acquisition unit. And as a laser light source of the end node, the laser scanning unit and the image acquisition unit work cooperatively under the control of the clock synchronization unit.

The installation mode of the device is as follows:

(3) the included angle between the laser emitted by the laser scanning unit and the plumb line is +/-30 degrees;

(4) the projection of the laser scanning unit vertical to the measuring plane is positioned at the geometric center of the measuring range;

(3) the image acquisition unit and the laser scanning unit are arranged on the same elevation, and the relation between the installation distance d and the installation height H of the image acquisition unit and the laser scanning unit is that H/d is more than or equal to 50;

the inventor finds through a large number of experiments that when the installation relationship between the image acquisition unit and the laser scanning unit does not meet the above conditions, the image acquisition unit acquires a part of the light column unit instead of a plane image obtained from the same incident angle, and the image cannot be subjected to density calibration.

(4) The energy stability of the laser is less than or equal to 1 percent, and the divergence angle is less than 1.5 mrad;

the inventor finds out through a large number of laser tests that: when the divergence angle of the laser is larger than or equal to 1.5mrad, the laser forms an elliptical light spot on the water surface, even if the condition (2) can be met, the acquired return image still can not obtain accurate concentration calibration due to the elliptical light spot, and the divergence angle of the laser can not be considered only when the image acquisition unit and the laser scanning unit are completely overlapped.

(5) The working frequency of the laser scanning unit is as follows:

the inventor respectively adopts laser progressive scanning and laser interlaced scanning, and simultaneously uses the synchronous interlaced scanning of double lasers, and finally finds that the working effect of progressive scanning by adopting a single laser is optimal.

The specific working mode is as follows:

during a measurement period: the laser light source flashes for 400-10000 times accurately under the control of a synchronous signal of a clock synchronization unit, the flashing time of each time is accurately controlled by the synchronous signal, the time control precision is nanosecond, and the measurement period is 1-9 s;

the laser scanning unit scans a laser beam by 400-10000 point positions line by line under the control of a synchronous signal of the clock synchronization unit, the position precision of a repeated period is millimeter level, the line by line scanning is a square area, and the number of lines is equal to the number of points;

the image acquisition unit completes multiple exposures under the control of a synchronization signal of the clock synchronization unit, one line of image information is recorded in each exposure, and the clock precision of the exposure time is in a nanosecond level.

The image processing and calibration working method comprises the following steps:

the inventors have found that there is a linear relationship between the image grey value and the density value over a range of densities. Through calibration tests, the inventor finds that the gray value of each laser point at the concentration is calibrated by using a solution with a standard concentration, the gray value of the central area is large, the gray value of the edge area is small, and Gaussian distribution is presented. In order to obtain accurate relation between gray level and concentration, the invention adopts the following method to calibrate the point concentration:

(1) calibration of laser line scanning gray value and standard solution

Preparing 50L of a standard concentration fluorescein sodium solution with the concentration of 0.05ppm, placing the solution into a transparent acrylic water tank 8 with the area of 50cm x 50cm, enabling the water depth to be 20cm and be consistent with the water depth of a model, preparing the corresponding number of water tanks according to the number of points scanned on one line, placing the water tanks in the line, collecting the water tanks line by line, collecting pictures of three periods in each line, and taking the maximum gray value of the point in the three periods as the fluorescence brightness of the standard solution.

(2) Calibration of concentration curves

Preparing standard concentration fluorescein sodium solution with the concentrations of 0.05ppm, 0.04ppm, 0.03ppm, 0.02ppm, 0.01ppm, 0.005ppm and 0.002ppm in a gradient manner, placing the solution in a transparent acrylic cylinder, taking the vertical downward projection of a laser scanning unit as the center and a region of 1m multiplied by 1m around the laser scanning unit, selecting two adjacent fixed points, collecting pictures for 60 seconds, taking the average value of the laser points, and obtaining a relation curve of the fluorescein sodium concentration and the gray value by using least square fitting.

(3) And (3) comparing and converting the measured gray value data with the concentration curve obtained in the step (2) to obtain a concentration value on the model.

(4) When the included angle between the laser emitted by the laser scanning unit and the vertical line is larger than 15 degrees and smaller than 30 degrees, the cosine value of the angle is adopted as a correction coefficient for the concentration value, namely: actual concentration is measured/cos (a), where a is the angle between the laser and the vertical.

Specifically, the benefits of the present invention are as follows:

the invention constructs a system for measuring the concentration distribution of large-area liquid by adopting a laser-induced fluorescence method;

2, the system firmware constructed by the invention is simple to install;

3, the invention adopts a laser line-by-line scanning mode to obtain the concentration of large-area discrete points, and provides a new calibration method of the relationship between the gray value and the concentration, which is suitable for the system;

4, the invention provides a concentration correction method suitable for the system.

Drawings

FIG. 1 is a schematic view of a measured quantity apparatus and method of the present invention;

FIG. 2 is a schematic diagram of adjacent fixed points selected during the calibration process of the present invention;

FIG. 3 is a schematic plan view of data points obtained by the progressive scan of the present invention;

FIG. 4 is a schematic diagram showing the results of the concentration calibration step (1) of the present invention;

FIG. 5 is a graph showing the results of the calibration step (2) according to the present invention;

FIG. 6 is a schematic diagram of the concentration values on the model obtained in the calibration step (3) of the present invention;

FIG. 7 is a graph showing the gray scale measurement results of the present invention.

Detailed Description

The present invention is further described with reference to the accompanying drawings, and the following examples are only for clearly illustrating the technical solutions of the present invention, and should not be taken as limiting the scope of the present invention.

Example 1

Specifically, the system comprises the following devices: the system comprises a laser light source 2, a laser scanning unit 4, an image acquisition unit 3 and a clock synchronization unit 1, wherein the four devices are in star connection through cables, the clock synchronization unit 1 is a central node, and a signal cable 5 is respectively connected with the laser light source 2, the laser scanning unit 4 and the image acquisition unit 3. The laser light source 2 as the end node, the laser scanning unit 4 and the image acquisition unit 3 work cooperatively under the control of the clock synchronization unit 1.

The installation mode of the device is as follows:

(1) the included angle between the laser 7 emitted by the laser scanning unit 4 and the plumb line is +/-30 degrees;

(2) the projection of the laser scanning unit 4 perpendicular to the measuring plane is positioned at the geometric center of the measuring range;

(3) the image acquisition unit 3 and the laser scanning unit 4 are installed on the same elevation, and the relation between the installation distance d and the installation height H of the image acquisition unit 3 and the laser scanning unit 4 is that H/d is more than or equal to 50;

(4) the energy stability of the laser is less than or equal to 1 percent, and the divergence angle is less than 1.5 mrad;

(5) the working frequency of the laser scanning unit is as follows:

the specific working mode is as follows:

during a measurement period: the laser light source flickers for 400 times accurately under the control of a synchronous signal of a clock synchronization unit, the flickering time of each time is accurately controlled by the synchronous signal, the time control precision is in a nanosecond level, and the measurement period is 1 s;

the laser scanning unit scans the laser beam line by line for 400 point positions under the control of a synchronous signal of the clock synchronization unit, the position precision of a repeated period is millimeter level, the line by line scanning is a square area, and the number of lines is equal to the number of points;

the image acquisition unit completes multiple exposures under the control of a synchronization signal of the clock synchronization unit, one line of image information is recorded in each exposure, and the clock precision of the exposure time is in a nanosecond level.

The image processing and calibration working method comprises the following steps:

(1) calibration of laser line scanning gray value and standard solution

Preparing 50L of a standard concentration fluorescein sodium solution with the concentration of 0.05ppm, placing the solution into a transparent acrylic water tank with the area of 50cm x 50cm, enabling the water depth to be 20cm and be consistent with the water depth of a model, preparing the corresponding number of water tanks according to the number of points scanned on one line, placing the water tanks in the line, collecting the water tanks line by line, collecting pictures of three periods in each line, and taking the maximum gray value of the point in the three periods as the fluorescence brightness of the standard solution. The device layout is shown in fig. 1 and the various points acquired are shown in fig. 3.

(2) Calibration of concentration curves

Preparing standard concentration fluorescein sodium solution with the concentrations of 0.05ppm, 0.04ppm, 0.03ppm, 0.02ppm, 0.01ppm, 0.005ppm and 0.002ppm in a gradient manner, placing the solution in a transparent acrylic cylinder, taking the vertical downward projection of a laser scanning unit as the center and a region of 1m multiplied by 1m around the laser scanning unit, selecting two adjacent fixed points, collecting pictures for 60 seconds, taking the average value of the laser points, and obtaining a relation curve of the fluorescein sodium concentration and the gray value by using least square fitting. The arrangement of the device is shown in fig. 2, the obtained pixel-to-gray scale relationship measurement result is shown in fig. 4, and the fitted concentration-to-gray scale relationship is shown in fig. 5.

(3) Gray scale density conversion

And (3) comparing and converting the measured gray value data with the concentration curve obtained in the step (2) to obtain a concentration value on the model. Fig. 6 shows the concentration values on the converted model.

(4) Concentration correction

When the included angle between the laser emitted by the laser scanning unit and the vertical line is larger than 15 degrees and smaller than 30 degrees, the cosine value of the angle is adopted as a correction coefficient for the concentration value, namely: actual concentration is measured/cos (a), where a is the angle between the laser and the vertical. FIG. 7 is a corrected model concentration value.

Example 2

Specifically, the system comprises the following devices: the system comprises a laser light source 2, a laser scanning unit 4, an image acquisition unit 3 and a clock synchronization unit 1, wherein the four devices are in star connection through cables, the clock synchronization unit 1 is a central node, and a signal cable 5 is respectively connected with the laser light source 2, the laser scanning unit 4 and the image acquisition unit 3. The laser light source 2 as the end node, the laser scanning unit 4 and the image acquisition unit 3 work cooperatively under the control of the clock synchronization unit 1.

The installation mode of the device is as follows:

(3) the included angle between the laser 7 emitted by the laser scanning unit 4 and the plumb line is +/-30 degrees;

(4) the projection of the laser scanning unit 4 perpendicular to the measuring plane is positioned at the geometric center of the measuring range;

(3) the image acquisition unit 3 and the laser scanning unit 4 are installed on the same elevation, and the relation between the installation distance d and the installation height H of the image acquisition unit 3 and the laser scanning unit 4 is that H/d is more than or equal to 50;

(4) the energy stability of the laser is less than or equal to 1 percent, and the divergence angle is less than 1.5 mrad;

(5) the working frequency of the laser scanning unit is as follows:

the specific working mode is as follows:

during a measurement period: the laser light source flickers for 900 times accurately under the control of a synchronous signal of a clock synchronization unit, the flickering time of each time is accurately controlled by the synchronous signal, the time control precision is nanosecond, and the measurement period is 3 s;

the laser scanning unit scans 900 point positions line by the laser beam under the control of a synchronous signal of the clock synchronization unit, the position precision of a repeated period is millimeter level, the line by line scanning is a square area, and the number of lines is equal to the number of points;

the image acquisition unit completes multiple exposures under the control of a synchronization signal of the clock synchronization unit, one line of image information is recorded in each exposure, and the clock precision of the exposure time is in a nanosecond level.

The image processing and calibration working method comprises the following steps:

(1) calibration of laser line scanning gray value and standard solution

Preparing 50L of a standard concentration fluorescein sodium solution with the concentration of 0.05ppm, placing the solution into a transparent acrylic water tank 8 with the area of 50cm x 50cm, enabling the water depth to be 20cm and be consistent with the water depth of a model, preparing the corresponding number of water tanks according to the number of points scanned on one line, placing the water tanks in the line, collecting the water tanks line by line, collecting pictures of three periods in each line, and taking the maximum gray value of the point in the three periods as the fluorescence brightness of the standard solution. The device layout is shown in fig. 1 and the various points acquired are shown in fig. 3.

(2) Calibration of concentration curves

Preparing standard concentration fluorescein sodium solution with the concentrations of 0.05ppm, 0.04ppm, 0.03ppm, 0.02ppm, 0.01ppm, 0.005ppm and 0.002ppm in a gradient manner, placing the solution in a transparent acrylic cylinder, taking the vertical downward projection of a laser scanning unit as the center and a region of 1m multiplied by 1m around the laser scanning unit, selecting two adjacent fixed points, collecting pictures for 60 seconds, taking the average value of the laser points, and obtaining a relation curve of the fluorescein sodium concentration and the gray value by using least square fitting. The arrangement of the device is shown in fig. 2, the obtained pixel-to-gray scale relationship measurement result is shown in fig. 4, and the fitted concentration-to-gray scale relationship is shown in fig. 5.

(3) Gray scale density conversion

And (3) comparing and converting the measured gray value data with the concentration curve obtained in the step (2) to obtain a concentration value on the model. Fig. 6 shows the concentration values on the converted model.

(4) Concentration correction

When the included angle between the laser emitted by the laser scanning unit and the vertical line is larger than 15 degrees and smaller than 30 degrees, the cosine value of the angle is adopted as a correction coefficient for the concentration value, namely: actual concentration is measured/cos (a), where a is the angle between the laser and the vertical. FIG. 7 is a corrected model concentration value.

Example 3

Specifically, the system comprises the following devices: the system comprises a laser light source 2, a laser scanning unit 4, an image acquisition unit 3 and a clock synchronization unit 1, wherein the four devices are in star connection through cables, the clock synchronization unit 1 is a central node, and a signal cable 5 is respectively connected with the laser light source 2, the laser scanning unit 4 and the image acquisition unit 3. The laser light source 2 as the end node, the laser scanning unit 4 and the image acquisition unit 3 work cooperatively under the control of the clock synchronization unit 1.

The installation mode of the device is as follows:

(5) the included angle between the laser 7 emitted by the laser scanning unit 4 and the plumb line is +/-30 degrees;

(6) the projection of the laser scanning unit 4 perpendicular to the measuring plane is positioned at the geometric center of the measuring range;

(3) the image acquisition unit 3 and the laser scanning unit 4 are installed on the same elevation, and the relation between the installation distance d and the installation height H of the image acquisition unit 3 and the laser scanning unit 4 is that H/d is more than or equal to 50;

(4) the energy stability of the laser is less than or equal to 1 percent, and the divergence angle is less than 1.5 mrad;

(5) the working frequency of the laser scanning unit is as follows:

the specific working mode is as follows:

during a measurement period: the laser light source flashes 10000 times accurately under the control of a synchronous signal of a clock synchronization unit, the flashing time of each time is controlled accurately by the synchronous signal, the time control precision is nanosecond, and the measuring period is 5 s;

the laser scanning unit scans 900 point positions line by the laser beam under the control of a synchronous signal of the clock synchronization unit, the position precision of a repeated period is millimeter level, the line by line scanning is a square area, and the number of lines is equal to the number of points;

the image acquisition unit completes multiple exposures under the control of a synchronization signal of the clock synchronization unit, one line of image information is recorded in each exposure, and the clock precision of the exposure time is in a nanosecond level.

The image processing and calibration working method comprises the following steps:

(1) calibration of laser line scanning gray value and standard solution

Preparing 50L of a standard concentration fluorescein sodium solution with the concentration of 0.05ppm, placing the solution into a transparent acrylic water tank 8 with the area of 50cm x 50cm, enabling the water depth to be 20cm and be consistent with the water depth of a model, preparing the corresponding number of water tanks according to the number of points scanned on one line, placing the water tanks in the line, collecting the water tanks line by line, collecting pictures of three periods in each line, and taking the maximum gray value of the point in the three periods as the fluorescence brightness of the standard solution. The device layout is shown in fig. 1 and the various points acquired are shown in fig. 3.

(2) Calibration of concentration curves

Preparing standard concentration fluorescein sodium solution with the concentrations of 0.05ppm, 0.04ppm, 0.03ppm, 0.02ppm, 0.01ppm, 0.005ppm and 0.002ppm in a gradient manner, placing the solution in a transparent acrylic cylinder, taking the vertical downward projection of a laser scanning unit as the center and a region of 1m multiplied by 1m around the laser scanning unit, selecting two adjacent fixed points, collecting pictures for 60 seconds, taking the average value of the laser points, and obtaining a relation curve of the fluorescein sodium concentration and the gray value by using least square fitting. The arrangement of the device is shown in fig. 2, the obtained pixel-to-gray scale relationship measurement result is shown in fig. 4, and the fitted concentration-to-gray scale relationship is shown in fig. 5.

(3) Gray scale density conversion

And (3) comparing and converting the measured gray value data with the concentration curve obtained in the step (2) to obtain a concentration value on the model. Fig. 6 shows the concentration values on the converted model.

(4) Concentration correction

When the included angle between the laser emitted by the laser scanning unit and the vertical line is larger than 15 degrees and smaller than 30 degrees, the cosine value of the angle is adopted as a correction coefficient for the concentration value, namely: actual concentration is measured/cos (a), where a is the angle between the laser and the vertical. FIG. 7 is a corrected model concentration value.