Closed-loop mixed gas flux measurement system

Abstract

The invention discloses a closed-loop type mixed gas flux measurement system, and relates to the technical field of flux measurement, a gas path structure of a gas analyzer in the measurement system is designed by combining serial gas pools with a sucking pump, and a group of TDLAS sensors are arranged at a phosgene gas path of each gas pool respectively; the specifications of the phosgene paths of the gas pools and the TDLAS sensors are matched and designed according to the characteristics of various to-be-detected gases, and in the gas extraction process of the gas extraction pump, the measurement host performs concentration calculation by using data of the TDLAS sensors and then completes transmission time delay compensation with the three-dimensional ultrasonic wind, so that the concentration measurement results of the various to-be-detected gases can be obtained through calculation. Cross interference of different gases is avoided, and synchronous measurement of various to-be-measured gases can be basically realized in an error range, so that the accuracy, reliability and efficiency of flux measurement are improved, and all-day and all-weather measurement of flux can be realized.

Description

Technical Field

[0001] The present application relates to the technical field of flux measurement, and in particular to a closed-circuit mixed gas flux measurement system. Background Art

[0002] Accurate estimation of greenhouse gas emissions is crucial to the study of global material cycles and climate change. In order to achieve the "quantification, execution and evaluation" of greenhouse gas emissions and absorption, the micrometeorological methods for measuring fluxes mainly include aerodynamics, heat balance and eddy covariance (EC) methods. Currently, the eddy covariance method is the mainstream in the world.

[0003] The eddy covariance method is based on a flux observation system composed of a three-dimensional ultrasonic anemometer and a gas analyzer. It can serve as a bridge between remote sensing (global or regional scale) and leaf scale greenhouse gas observations, verify the accuracy of remote sensing greenhouse gas observations, and provide regional scale (10 2 m~10 3 m) high-frequency, continuous, and non-interference measurement data of material exchange and energy cycle.

[0004] The gas analyzers in the current mainstream flux observation systems are implemented using NDIR (Non-Dispersive InfraRed) sensors. NDIR sensors have the advantages of high sensitivity, high accuracy and the ability to quickly perform gas analysis. When applied, dual-wavelength infrared light measurement technology is often used: a wide-frequency infrared light source (that is, it includes all the absorption wavelengths of the target gas) is used to modulate the infrared light it emits into two beams of infrared light, namely a measurement beam at the measurement wavelength (the wavelength at which the gas has the strongest absorption capacity in this band) and a reference beam at the reference wavelength (the wavelength at which the gas has no absorption capacity in this band). The infrared detector can determine the true concentration of the target gas by comparing the difference between the reference signal and the measurement signal.

[0005] The most common application of flux observation systems is to measure the gas concentrations of CO2 and H2O. Therefore, existing gas analyzers are equipped with motors, which drive the filter to rotate to select the spectrum, and thus the concentrations of different target gases can be measured. However, NDIR technology uses a wide-wavelength light source, which results in cross-interference between different gas measurements. The use of motors to switch spectrum selection also results in limited life of moving parts and high power consumption. The maximum measurement frequency is also limited by the motor speed, resulting in unsatisfactory flux measurement results for mixed systems. Summary of the invention

[0006] In view of the above problems and technical requirements, this application proposes a closed-circuit mixed gas flux measurement system. The technical solution of this application is as follows:

[0007] A closed-circuit mixed gas flux measurement system, wherein a gas analyzer in the closed-circuit mixed gas flux measurement system comprises N gas cells, N groups of TDLAS sensors and an air pump, wherein each gas cell is connected in series in sequence through its own optical gas path air inlet and optical gas path air outlet, wherein the optical gas path air inlet of the first gas cell is connected to the air inlet of the gas analyzer and obtains the mixed gas to be measured, and the optical gas path air outlet of the last gas cell is connected to the air pump; the specification of the optical gas path of the i-th gas cell connected in series in sequence matches the i-th gas to be measured in the mixed gas to be measured; wherein the integer parameter N≥2, and the integer parameter 1≤i≤N;

[0008] The laser and the receiver in any i-th group of TDLAS sensors are respectively arranged at the two ends of the light-passing gas path of the i-th gas pool, and the laser emission path of the laser is along the gas transmission direction inside the gas pool; the i-th group of TDLAS sensors matches the i-th gas to be measured in the mixed gas to be measured, and the absorption intensity of the wavelength of the laser in the i-th group of TDLAS sensors for the i-th gas to be measured reaches the upper limit intensity threshold and the absorption intensity for other gases to be measured is lower than the lower limit intensity threshold;

[0009] The measuring host in the closed-loop mixed gas flux measurement system is connected to N groups of TDLAS sensors. During the vacuum pumping process, the measuring host uses any i-th group of TDLAS sensors to obtain the original concentration data of the i-th gas to be measured in the mixed gas to be measured based on the TDLAS technology, and obtains the basic delay of the i-th gas to be measured by dividing the pipeline volume from the air inlet of the optical gas path of the i-th gas cell to the air inlet of the gas analyzer by the gas flow rate of the mixed gas to be measured, and obtains the concentration measurement result of the i-th gas to be measured after the transmission delay compensation is performed on the original concentration data of the i-th gas to be measured according to the transmission delay of the i-th gas to be measured.

[0010] A further technical solution is that obtaining the concentration measurement result of the i-th gas to be measured includes:

[0011] Every average time period T, the delay error correction is performed on the original concentration data of the i-th gas to be measured after transmission delay compensation based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor in the closed-loop mixed gas flux measurement system, and the concentration measurement result of the i-th gas to be measured that is synchronously matched with the wind measurement data is obtained.

[0012] A further technical solution is to perform delay error correction on the original concentration data of the i-th gas to be measured after transmission delay compensation based on the wind measurement data, including:

[0013] At any calibration time t, a vertical wind speed time series is extracted from the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the last averaging time T, wherein the vertical wind speed time series includes M vertical wind speed data arranged in chronological order;

[0014] A plurality of different original concentration time series consisting of M original concentration data of the i-th gas to be tested are extracted respectively at different delay offsets at the current correction time t, and at the j-th delay offset τ at the current correction time t j The jth original concentration time series extracted below includes: the most recent original concentration data obtained at the correction time t is offset by τ according to the jth delay offset j The original concentration data after the data point and the M-1 consecutive original concentration data before it; among them, the delay offset τ j When it is less than 0, it indicates a deviation to the previous calibration time, and the delay offset τ j Greater than 0 indicates a shift in the direction of the next correction moment; integer parameter 1≤j≤J, integer parameter J≥2;

[0015] Calculate the covariance between the jth original concentration time series and the vertical wind speed time series, and determine the delay offset corresponding to the original concentration time series with the largest covariance between the jth original concentration time series and the vertical wind speed time series as the target delay offset;

[0016] After the original concentration data of the i-th gas to be measured after transmission delay compensation is time-shifted according to the target delay offset to complete the delay error correction, the concentration measurement result of the i-th gas to be measured that is synchronously matched with the wind measurement data is obtained.

[0017] A further technical solution is that, based on the wind measurement data, the original concentration data of the i-th gas to be measured after the transmission delay compensation is performed delay error correction further includes:

[0018] At any calibration time t, the theoretical offset τ at the calibration time t is determined based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time T and the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer in the closed-loop mixed gas flux measurement system. δ ; Among them, the theoretical offset τ δ is an integer parameter;

[0019] According to the theoretical offset τ at the correction time t δ In τ j ∈[τ δ -τ max , τ δ +τ max ] range to extract J = 2τ max +1 original concentration time series, where the positive integer τ max Indicates the maximum delay offset.

[0020] A further technical solution is to determine the theoretical offset τ at the correction time t δ include:

[0021] According to the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer, determine the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer;

[0022] Determine the stable wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer at the calibration time t according to the wind direction and wind speed in the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the last average time length T at the calibration time t;

[0023] According to the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer and the stable wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer at the calibration time t, the theoretical offset τ at the calibration time t is determined. δ ; Among them, the greater the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer, the smaller the wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer, and the theoretical offset τ δ The bigger.

[0024] A further technical solution is that the flow rate of the vacuum pump is not less than L max *F, where L max is the gas path capacity of the largest gas cell among all N gas cells, and F is the frequency of the gas signal of the closed-loop mixed gas flux measurement system.

[0025] A further technical solution is that the specifications of the light path of each gas cell include the aperture and optical path of the light path, the optical path of the i-th gas cell matches the gas absorption characteristics of the i-th gas to be measured, and the apertures of the light paths of N gas cells are equal and match the maximum spot of the laser in all N groups of TDLAS sensors.

[0026] A further technical solution is that each gas pool is provided with a curved temperature-conducting gas path in front of the air inlet of the optical gas path, and the temperature-conducting gas path is made of heat-conducting material. The mixed gas to be measured enters the optical gas path after heat transfer through the temperature-conducting gas path.

[0027] A further technical solution is that a temperature sensor and a pressure sensor are arranged at the air inlet of the light-passing gas path of each gas pool, and the measuring host in the closed-circuit mixed gas flux measurement system is also connected to each temperature sensor and pressure sensor;

[0028] The measuring host detects and obtains the original concentration data of the i-th gas to be measured, including: using any i-th group of TDLAS sensors based on TDLAS technology, combined with the temperature data collected by the temperature sensor at the air inlet of the optical gas path of the i-th gas pool and the pressure data collected by the pressure sensor, to detect and obtain the original concentration data of the i-th gas to be measured.

[0029] A further technical solution is that a particle filter is arranged at the air inlet of the gas analyzer, and an air filter is arranged between the light gas path outlet of the last gas pool and the air pump.

[0030] The beneficial technical effects of this application are:

[0031] The present application discloses a closed-loop mixed gas flux measurement system, in which the gas path structure of the gas analyzer is designed by connecting gas cells in series and combining an air pump. The specifications of the optical gas paths of each gas cell and each group of TDLAS sensors are matched and designed according to the characteristics of various gases to be measured, so that multiple groups of TDLAS sensors can be used to achieve synchronous measurement of multiple gases to be measured based on TDLAS technology. The transmission delay introduced by the series gas cells can be compensated by performing transmission delay compensation on the original concentration data of each gas to be measured. Thanks to the characteristics of the TDLAS measurement technology, cross-interference of different gases is avoided, which is conducive to improving the accuracy, reliability and efficiency of flux measurement. In addition, the gas analyzer uses an air pump to obtain sample gas to avoid the analyzer being exposed to the air, avoid pollution of the optical lens, reduce the frequency of maintenance, and avoid the influence of precipitation and snowfall, so that the flux can be measured all day and all weather.

[0032] This application is also based on the fact that the wind measurement data of the three-dimensional ultrasonic wind sensor is consistent with the changing characteristics of the concentration measurement results. The wind measurement data of the three-dimensional ultrasonic wind sensor that comes with the closed-loop mixed gas flux measurement system is used as a benchmark to perform time delay correction on the measurement results of the TDLAS sensor, thereby further improving the accuracy of the concentration measurement results without the need to add additional correction devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a system structure block diagram of a closed-loop mixed gas flux measurement system according to an embodiment of the present application.

[0034] Figure 2 It is a schematic diagram of the series structure of two gas cells in an example of the present application.

[0035] Figure 3 It is a schematic diagram of the structure of a gas analyzer in another embodiment of the present application.

[0036] Figure 4It is a flow chart of a method for obtaining the concentration measurement result of the i-th gas to be measured in one embodiment of the present application.

[0037] Figure 5 It is a schematic diagram of the original concentration time series extracted at different delay offsets in an example of the present application. DETAILED DESCRIPTION

[0038] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0039] This application discloses a closed-circuit mixed gas flux measurement system, please refer to Figure 1 As shown in the structural schematic diagram, the closed-circuit mixed gas flux measurement system includes a gas analyzer, a three-dimensional ultrasonic wind sensor and a measurement host. The present application optimizes the traditional NDIR-based gas analyzer. The gas analyzer in the present application includes N gas cells, N groups of TDLAS sensors and a vacuum pump, wherein the integer parameter N≥2, and the value of N is determined according to the number of types of gases to be measured. For example, the closed-circuit mixed gas flux measurement system is commonly used to measure the flux of carbon dioxide and water vapor in the air, then N=2. When more types of gases need to be measured at the same time, the number of gas cells and TDLAS sensors is increased accordingly.

[0040] Each gas pool includes a light-passing gas path, and the direction from the gas inlet to the gas outlet of the light-passing gas path in each gas pool is the gas transmission direction inside the gas pool.

[0041] Each gas cell is connected in series through its own optical gas path inlet and optical gas path outlet. The optical gas path inlet of the first gas cell is connected to the gas inlet of the gas analyzer to obtain the mixed gas to be measured, and the optical gas path outlet of the last gas cell is connected to the vacuum pump. During the vacuum pump pumping process, the mixed gas to be measured enters the gas analyzer from the gas inlet of the entire gas analyzer and is transmitted through the optical gas path of each gas cell in turn. The optical gas path is formed inside the gas cell. In actual application, the gas cell and TDLAS sensor are encapsulated in the shell to form a closed-loop structure, which prevents the optical path measurement process from being affected by environmental factors such as precipitation and snowfall, and can also effectively reduce the maintenance frequency. Please refer to Figure 1 and Figure 2 Taking the series structure of gas pool 1 and gas pool 2 as an example, the dotted part inside gas pool 1 is the light-passing gas path 11 of gas pool 1, and the dotted part inside gas pool 2 is the light-passing gas path 21 of gas pool 2. The gas outlet of the light-passing gas path 21 of gas pool 2 is connected to the vacuum pump 3, and the gas transmission direction inside the two gas pools is shown by the arrows.

[0042] N groups of TDLAS sensors are respectively arranged at N gas cells, and any i-th group of TDLAS sensors is arranged at the i-th gas cell connected in series, and the laser and the receiver in the i-th group of TDLAS sensors are respectively arranged at the two ends of the light-passing gas path of the i-th gas cell, and the laser emission path of the laser is along the gas transmission direction inside the gas cell. Figure 1 In the figure, the laser 12 and the receiver 13 of the first group of TDLAS sensors are arranged at both ends of the optical gas path 11 of the gas cell 1, and the laser 22 and the receiver 23 of the second group of TDLAS sensors are arranged at both ends of the optical gas path 21 of the gas cell 2. In the figure, the integer parameter 1≤i≤N.

[0043] When it is necessary to measure the flux of N gases in the mixed gas to be measured, the structure of the optical gas path of each gas cell and the TDLAS sensor arranged at each gas cell should be designed according to the type of gas to be measured, including:

[0044] (1) The specification of the optical gas path of the ith gas cell connected in series matches the ith gas to be measured in the mixed gas to be measured. It should be noted that the ith gas to be measured in the present application is used to refer to any gas to be measured in the mixed gas to be measured. This representation does not mean that the gases to be measured in the mixed gas to be measured should be arranged in a specific order. In fact, since the mixed gas to be measured is transmitted through each gas cell in sequence, the series connection order of the gas cells can be set arbitrarily, as long as the gas cells and the gases to be measured correspond one to one.

[0045] In one embodiment, the optical gas path of each gas pool adopts a cylindrical structure, and the specifications of the optical gas path of each gas pool include the aperture along the radial direction of the cylindrical structure and the optical path in the length direction of the cylindrical structure. Since the laser emission path of the laser passes through the optical gas path along the gas transmission direction inside the gas pool and is received by the receiver, the optical path of the optical gas path of the ith gas pool matches the gas absorption characteristic of the ith gas to be measured. The gas absorption characteristic of the ith gas to be measured is the spectral absorption peak of the ith gas to be measured, and the detection range of its absorption intensity and gas concentration is determined by the Lambert-Beer law. For example, Figure 2 In the example, gas cell 1 corresponds to water vapor, and the optical path L1 of the optical gas path of gas cell 1 matches the gas absorption characteristics of water vapor, while gas cell 2 corresponds to carbon dioxide, and the optical path L2 of the optical gas path of gas cell 2 matches the gas absorption characteristics of carbon dioxide. Since the gas absorption characteristics of different gases to be measured are inconsistent, the optical path lengths of the optical gas paths of different gas cells may be different.

[0046] In order to ensure the transmission stability of the mixed gas to be measured in each gas cell and the same gas flow rate in each gas cell, the apertures of the light paths of the N gas cells are set to be equal. The aperture of the light path of each gas cell needs to be determined according to the spot size of the laser at the gas cell. Therefore, the aperture that matches the maximum spot of the laser in all N groups of TDLAS sensors is selected as the aperture of the light path of each gas cell. Generally, the aperture of the light path of the gas cell is slightly larger than the maximum spot of all N lasers. When the light output of the laser is not parallel, the spot of the laser in the i-th group of TDLAS sensors is related to the optical path of the light path of the i-th gas cell, and the spot size can also be adjusted by an optical lens.

[0047] (2) The i-th group of TDLAS sensors matches the i-th gas to be measured in the mixed gas to be measured. The mixed gas to be measured will be transmitted through each gas pool in turn, and the i-th group of TDLAS sensors is used to measure the i-th gas to be measured. Therefore, the wavelength of the laser in the i-th group of TDLAS sensors has an absorption intensity of the i-th gas to be measured that reaches the upper intensity threshold and the absorption intensity of other gases to be measured is lower than the lower intensity threshold. That is, the laser in the i-th group of TDLAS sensors selects a wavelength that has a strong absorption for the i-th gas to be measured and a negligible absorption for the other N-1 gases to be measured. The absorption intensity of various gases can be determined by referring to the absorption peaks of various gases in the HITRAN database.

[0048] The measuring host in the closed-loop mixed gas flux measurement system is connected to N groups of TDLAS sensors in the gas analyzer. During the air pumping process, the mixed gas to be measured passes through the optical gas path of each gas pool in turn, and in the optical gas path of any i-th gas pool, the laser of the i-th group of TDLAS sensors emits a laser with a wavelength matching the i-th gas to be measured and is received by the corresponding receiver. The original concentration data of the i-th gas to be measured can be measured using the TDLAS technology. Since the TDLAS measurement technology with a narrow linewidth laser light source is used, cross-interference of different gases to be measured is avoided. In addition, in the process of the mixed gas to be measured passing through each gas pool in turn, the original concentration data of various gases to be measured can be obtained using each group of TDLAS sensors. Within the error range, it can be considered that the synchronous measurement of multiple gases to be measured is achieved, and there is no need to switch filters to measure separately like NDIR, so the measurement efficiency is also higher. The specific measurement results of the original concentration data of the gas to be measured using the signal of each group of TDLAS sensors can refer to the existing single gas flux measurement method, and this embodiment will not be repeated.

[0049] In order to reduce the effect of temperature on flux measurement, in one embodiment, Figure 3As shown, each gas pool is also provided with a curved temperature-conducting gas path in front of the light-passing gas path inlet, and the temperature-conducting gas path is made of heat-conducting material. The mixed gas to be measured passes through the temperature-conducting gas path for heat transfer before entering the light-passing gas path. The aperture of the temperature-conducting gas path may be consistent with or inconsistent with the light-passing gas path. The length of the temperature-conducting gas path is designed based on the actual heat transfer effect to ensure that the gas temperature is consistent with the gas pool temperature. In actual applications, the entire gas pool is generally designed to be made of metal materials, which have the characteristics of heat conductivity, corrosion resistance and non-adsorption. For example Figure 3 In the embodiment, a temperature-conducting gas path 14 is provided in front of the air inlet of the light-conducting gas path 11 of the gas pool 1, and a temperature-conducting gas path 24 is provided in front of the air inlet of the light-conducting gas path 21 of the gas pool 2. Figure 3 As shown, a temperature sensor and a pressure sensor are also arranged at the air inlet of the optical gas path of each gas pool, and the measuring host in the closed-loop mixed gas flux measurement system is also connected to each temperature sensor and pressure sensor. When the measuring host uses the i-th group of TDLAS sensors to detect and obtain the original concentration data of the i-th gas to be measured based on the TDLAS technology, the temperature data collected by the temperature sensor at the air inlet of the optical gas path of the i-th gas pool and the pressure data collected by the pressure sensor are also applied to the TDLAS algorithm. The specific content of the TDLAS algorithm is not described in detail in this application.

[0050] In the above measurement process, the gas update rate in the gas pool and the measurement rate of the gas analyzer determine the maximum measurement rate of the entire closed-loop mixed gas flux measurement system. The gas pools are connected in series, so the update rate of the gas in the maximum gas pool determines the update rate of the gas in the entire gas analyzer. Therefore, in one embodiment, the flow rate of the air pump is not less than L max *F, where L max is the gas path capacity of the largest gas cell among all N gas cells, and F is the frequency of the gas signal of the closed-loop mixed gas flux measurement system.

[0051] As can be seen from the above introduction, this application uses a vacuum pump to extract the mixed gas to be measured into the gas analyzer, and adopts a closed-circuit structure, which can effectively prevent the gas analyzer from being exposed to the air, avoid the contamination of the optical lens, and help reduce the frequency of maintenance. In addition, in order to further reduce the contamination of the optical lens, such as Figure 3 As shown, a particle filter 4 is arranged at the air inlet of the gas analyzer, and an air filter 5 is arranged between the light gas path outlet of the last gas pool and the air pump.

[0052] However, due to the use of this closed-loop structure, even if the vacuum pump flowmeter is increased to increase the gas update rate, there will still be an unavoidable time delay in the transmission of the measured mixed gas to the optical gas path of each gas pool. Therefore, the original concentration data of the i-th gas to be measured directly detected based on the TDLAS technology is not directly used as the concentration measurement result, but the basic time delay of the i-th gas to be measured is obtained by dividing the pipeline volume from the air inlet of the optical gas path of the i-th gas pool to the air inlet of the gas analyzer by the gas flow rate of the mixed gas to be measured. After the gas pool structure design is determined, the pipeline volume from the air inlet of the optical gas path of the i-th gas pool to the air inlet of the gas analyzer is known, and the gas flow rate is also known during the vacuum pump vacuuming process. The basic time delay of the i-th gas to be measured is the time delay for the mixed gas to be measured to be transmitted from the gas inlet of the gas analyzer to the gas inlet of the optical gas path of the i-th gas cell, and is also the time delay for the original concentration data of the i-th gas to be measured. Then, the original concentration data of the i-th gas to be measured is compensated for the transmission delay of the i-th gas to be measured, and the concentration measurement result of the i-th gas to be measured is obtained, thereby compensating for the transmission delay introduced by the series-connected gas cells.

[0053] For a closed-circuit mixed gas flux measurement system, the obtained concentration measurement results need to be used in conjunction with the wind measurement data. However, in practice, since the air inlet of the gas analyzer and the probe position of the three-dimensional ultrasonic wind sensor are often physically separated, it is still difficult to ensure the synchronization of the original concentration data after the transmission delay compensation based on the delay after transmission in the gas pool with the wind measurement data. Therefore, in one embodiment, after the original concentration data of the i-th gas to be measured after the transmission delay compensation is obtained by using any i-th group of TDLAS sensors based on the TDLAS technology, it is not directly used as the final concentration measurement result. Instead, the original concentration data of the i-th gas to be measured after the transmission delay compensation is corrected for delay errors based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor in the closed-circuit mixed gas flux measurement system at average time lengths T, so as to obtain the concentration measurement result of the i-th gas to be measured that is synchronized with the wind measurement data. Since the three-dimensional ultrasonic wind sensor adopts an open-circuit structure, it can be considered that the wind measurement data of the three-dimensional ultrasonic wind sensor does not have time delay, and the wind measurement data of the three-dimensional ultrasonic wind sensor is consistent with the changes in the concentration measurement results of the gas to be measured. Therefore, this embodiment uses the wind measurement data as a reference to perform delay error correction on the original concentration data to correct the time delay introduced by the closed-circuit structure. Moreover, the three-dimensional ultrasonic wind sensor is a structure originally included in the closed-circuit mixed gas flux measurement system, so this approach does not require additional hardware. The average duration T can be customized to take into account the stability of the ambient wind. For example, the average duration T can be set to half an hour.

[0054] The method for correcting the delay error of the original concentration data of various gases to be measured is the same. The delay error correction of the original concentration data of the i-th gas to be measured based on the wind measurement data includes the following steps, please refer to Figure 4 The flowchart shown:

[0055] Step 1: At any calibration time t, obtain the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the last average time T, where the last average time T is the period from the last calibration time to the current calibration time t. The obtained wind measurement data includes the wind speed and wind direction at M wind measurement times. Since the wind measurement frequency of the three-dimensional ultrasonic wind sensor is known, the number M of wind measurement times included in each average time T is also fixed and known. For example, the common average time T is half an hour. According to the common wind measurement frequency of the three-dimensional ultrasonic wind sensor, the three-dimensional ultrasonic wind sensor can obtain wind measurement data at 18,000 wind measurement times within one average time T.

[0056] Step 2, at any calibration time t, extract the vertical wind speed time series from the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous averaging time T. After obtaining the wind speed and wind direction at each wind measurement moment, the vertical wind speed data at each wind measurement moment can be solved, thereby extracting the vertical wind speed time series including M vertical wind speed data arranged in chronological order.

[0057] Step 3: extracting M original concentration data of the i-th gas to be tested detected at different delay offsets at the current correction time t to form a plurality of different original concentration time series.

[0058] The jth delay offset τ at the current correction time t j The jth original concentration time series extracted below includes: the most recent original concentration data obtained at the correction time t is offset by τ according to the jth delay offset j The original concentration data after the data point and the M-1 consecutive original concentration data before it, that is, each original concentration time series extracted also includes M original concentration data arranged in chronological order.

[0059] Among them, the delay offset τ j When it is less than 0, it indicates a deviation to the previous calibration time, and the delay offset τ j A value greater than 0 indicates a shift toward the next calibration moment.

[0060] For example, in one instance, based on Figure 5 The schematic diagram of the discrete points of the original concentration data of the i-th type arranged in time sequence is shown. In this example, the 10 original concentration data arranged in time sequence in the black dotted box are the delay offset τ j= 0, the 10 original concentration data arranged in chronological order in the red dotted box are the delay offset τ j = -2, the original concentration time series extracted, the 10 original concentration data arranged in chronological order in the green dotted box are the delay offset τ j =4. It should be noted that, Figure 5 For the convenience of illustration, M=10 is taken as an example, but in fact, as mentioned above, the value of M is relatively large.

[0061] Through the above method, J different original concentration time series can be extracted, the integer parameter J≥2, the above integer parameter 1≤j≤J, and the specific value of J can be customized.

[0062] Step 4, calculate the covariance between the jth original concentration time series and the vertical wind speed time series, and determine the delay offset corresponding to the original concentration time series with the largest covariance between the J original concentration time series and the vertical wind speed time series as the target delay offset. The original concentration time series with the largest covariance between the original concentration time series and the vertical wind speed time series is the original concentration time series with the highest consistency in changes with the vertical wind speed time series.

[0063] Step 5: according to the target delay offset, the original concentration data of the i-th gas to be tested after the transmission delay compensation is time-shifted to complete the delay error correction, that is, to determine the latest original concentration data detected at the correction time t to be offset by the j-th delay offset τ j The original concentration data after the data points is the original concentration data actually corresponding to the correction time t, so as to obtain the concentration measurement result of the i-th gas to be measured that is synchronously matched with the wind measurement data.

[0064] In another embodiment, in order to improve the correction efficiency, at any correction time t, firstly, according to the wind measurement data obtained by the three-dimensional ultrasonic wind sensor in the previous average time T, combined with the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer in the closed-loop mixed gas flux measurement system, the theoretical offset τ at the correction time t is determined. δ , then the final target delay offset should be within the current theoretical offset τ δ Then according to the theoretical offset τ at the correction time t δ In τ j ∈[τ δ -τ max , τ δ +τ max ] range to extract J = 2τ max +1 original concentration time series, where the positive integer τ maxIndicates that the maximum delay offset can be customized. Since the gas in the gas pool is updated quickly, the time delay introduced by the closed-loop structure will not be too large, so the positive integer τ here max Generally, 5 to 10 is sufficient.

[0065] Among them, since the probe position of the three-dimensional ultrasonic wind sensor is not at the same position as the air inlet of the gas analyzer, there is an inherent error and time delay between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer due to the physical separation input. In addition, when the structural design is fixed, when the ambient wind is different, the time delay between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer is also different, so the theoretical offset τ at the correction time t δ Dynamic adjustments are required based on wind measurement data, including:

[0066] At any calibration time t, the theoretical offset τ at the calibration time t is determined based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time T and the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer in the closed-loop mixed gas flux measurement system. δ . It includes: determining the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer according to the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer, and determining the stable wind speed from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer at the calibration time t according to the wind direction and wind speed in the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the last average time length T at the calibration time t. The wind measurement data actually obtained by the three-dimensional ultrasonic wind sensor is dynamic discrete data, and the stable wind speed at the calibration time t can be calculated using existing methods.

[0067] Then, according to the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer and the stable wind speed from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer at the calibration time t, the theoretical offset τ at the calibration time t is determined. δ The layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer is fixed, that is, the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer is fixed, but the wind measurement data changes dynamically. δ When the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer is larger, the wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer is smaller, and the theoretical offset τ δ The larger the value, the more customizable the value setting method can be.

[0068] The above is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A closed-circuit mixed gas flux measurement system, characterized in that: The gas analyzer in the closed-loop mixed gas flux measurement system includes N gas cells, N groups of TDLAS sensors and a vacuum pump, each gas cell is connected in series in sequence through its own optical gas path inlet and optical gas path outlet, the optical gas path inlet of the first gas cell is connected to the gas inlet of the gas analyzer and obtains the mixed gas to be measured, and the optical gas path outlet of the last gas cell is connected to the vacuum pump; the specification of the optical gas path of the i-th gas cell connected in series in sequence matches the i-th gas to be measured in the mixed gas to be measured; wherein, the integer parameter N≥2, and the integer parameter 1≤i≤N; The laser and the receiver in any i-th group of TDLAS sensors are respectively arranged at two ends of the light-passing gas path of the i-th gas pool, and the laser emission path of the laser is along the gas transmission direction inside the gas pool; the i-th group of TDLAS sensors matches the i-th gas to be measured in the mixed gas to be measured, and the absorption intensity of the wavelength of the laser in the i-th group of TDLAS sensors for the i-th gas to be measured reaches the upper limit intensity threshold and the absorption intensity for other gases to be measured is lower than the lower limit intensity threshold; The measuring host in the closed-loop mixed gas flux measurement system is connected to N groups of TDLAS sensors. During the vacuum pumping process, the measuring host uses any i-th group of TDLAS sensors to obtain the original concentration data of the i-th gas to be measured in the mixed gas to be measured based on the TDLAS technology, and divides the pipeline volume from the air inlet of the optical gas path of the i-th gas pool to the air inlet of the gas analyzer by the gas flow rate of the mixed gas to be measured to obtain the basic delay of the i-th gas to be measured, and performs transmission delay compensation on the original concentration data of the i-th gas to be measured according to the transmission delay of the i-th gas to be measured to obtain the concentration measurement result of the i-th gas to be measured.

2. The closed-circuit mixed gas flux measurement system according to claim 1, characterized in that: Obtaining the concentration measurement result of the i-th gas to be measured also includes: At average time intervals of T, the original concentration data of the i-th gas to be measured after transmission delay compensation is corrected based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor in the closed-loop mixed gas flux measurement system, so as to obtain a concentration measurement result of the i-th gas to be measured that is synchronously matched with the wind measurement data.

3. The closed-circuit mixed gas flux measurement system according to claim 2, characterized in that: The delay error correction of the original concentration data of the i-th gas to be measured after the transmission delay compensation is completed based on the wind measurement data includes: Extracting a vertical wind speed time series from wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the last averaging time T at any calibration time t, wherein the vertical wind speed time series includes M vertical wind speed data arranged in chronological order; A plurality of different original concentration time series consisting of M original concentration data of the i-th gas to be tested are extracted respectively at different delay offsets at the current correction time t, and at the j-th delay offset τ at the current correction time t j The jth original concentration time series extracted below includes: the most recent original concentration data obtained at the correction time t is offset by τ according to the jth delay offset j The original concentration data after the data point and the M-1 consecutive original concentration data before it; among them, the delay offset τ j When it is less than 0, it indicates a deviation to the previous calibration time, and the delay offset τ j Greater than 0 indicates a shift in the direction of the next correction moment; integer parameter 1≤j≤J, integer parameter J≥2; Calculate the covariance between the jth original concentration time series and the vertical wind speed time series, and determine the delay offset corresponding to the original concentration time series with the largest covariance between the jth original concentration time series and the vertical wind speed time series as the target delay offset; After the original concentration data of the i-th gas to be measured after transmission delay compensation is time-shifted according to the target delay offset to complete delay error correction, a concentration measurement result of the i-th gas to be measured that is synchronously matched with the wind measurement data is obtained.

4. The closed-circuit mixed gas flux measurement system according to claim 3, characterized in that: The delay error correction of the original concentration data of the i-th gas to be measured after the transmission delay compensation is completed based on the wind measurement data also includes: At any calibration time t, the theoretical offset τ at the calibration time t is determined based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the last average time T and the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer in the closed-loop mixed gas flux measurement system. δ ; Among them, the theoretical offset τ δ is an integer parameter; According to the theoretical offset τ at the correction time t δ In τ j ∈[τ δ -τ max , τ δ +τ max ] range to extract J = 2τ max +1 original concentration time series, where the positive integer τ max Indicates the maximum delay offset.

5. The closed-circuit mixed gas flux measurement system according to claim 4, characterized in that: Determine the theoretical offset τ at the correction time t δ include: According to the layout structure of the three-dimensional ultrasonic wind sensor and the gas analyzer, determining the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer; Determine the stable wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer at the calibration time t according to the wind direction and wind speed in the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the last average time length T at the calibration time t; According to the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer and the stable wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer at the calibration time t, the theoretical offset τ at the calibration time t is determined. δ ; Among them, the greater the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer, the smaller the wind speed in the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer, and the theoretical offset τ δ The bigger.

6. The closed-circuit mixed gas flux measurement system according to claim 1, characterized in that: The flow rate of the vacuum pump is not less than L max *F, where L max is the light path capacity of the largest gas cell among all N gas cells, and F is the frequency of the gas signal of the closed-loop mixed gas flux measurement system.

7. The closed-circuit mixed gas flux measurement system according to claim 1, characterized in that: The specifications of the optical gas path of each gas cell include the aperture and optical path of the optical gas path. The optical path of the optical gas path of the ith gas cell matches the gas absorption characteristics of the ith gas to be measured. The apertures of the optical gas paths of N gas cells are equal and match the maximum spot of the laser in all N groups of TDLAS sensors.

8. The closed-circuit mixed gas flux measurement system according to claim 1, characterized in that: Each gas pool is also provided with a curved temperature-conducting gas path in front of the gas inlet of the optical gas path, and the temperature-conducting gas path is made of heat-conducting material. The mixed gas to be measured enters the optical gas path after heat transfer through the temperature-conducting gas path.

9. The closed-circuit mixed gas flux measurement system according to claim 1, characterized in that: A temperature sensor and an air pressure sensor are also arranged at the air inlet of the light-passing air path of each gas pool, and the measuring host in the closed-circuit mixed gas flux measurement system is also connected to each temperature sensor and air pressure sensor; The measuring host detects and obtains the original concentration data of the i-th gas to be measured, including: using any i-th group of TDLAS sensors based on TDLAS technology, combined with the temperature data collected by the temperature sensor at the light gas path inlet of the i-th gas pool and the pressure data collected by the pressure sensor, to detect and obtain the original concentration data of the i-th gas to be measured.

10. The closed-circuit mixed gas flux measurement system according to claim 1, characterized in that: A particle filter is arranged at the air inlet of the gas analyzer, and an air filter is arranged between the light gas path outlet of the last gas pool and the air pump.

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