Closed-circuit mixed-gas flux measurement system
By using a closed-loop mixed gas flux measurement system, which combines a series gas cell and a TDLAS sensor with a pump and a three-dimensional ultrasonic wind sensor, the problems of cross-interference and frequency limitation in NDIR technology are solved, and efficient and accurate gas flux measurement is achieved.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- AEROSPACE NEWSKY TECHNOLOGY CO LTD
- Filing Date
- 2025-09-08
- Publication Date
- 2026-07-23
AI Technical Summary
Existing NDIR technology suffers from cross-interference and limited lifespan of moving parts in gas flux measurement, resulting in limited measurement frequency and making it impossible to effectively measure the flux of mixed gases accurately.
A closed-loop mixed gas flux measurement system is adopted, which connects N gas cells and N sets of TDLAS sensors in series, combined with a vacuum pump and a three-dimensional ultrasonic wind sensor. The system uses TDLAS technology to measure gas concentration and achieves synchronous measurement of multiple gases through transmission delay compensation and delay error correction.
It improves the accuracy and efficiency of gas flux measurement, avoids optical lens contamination, reduces maintenance frequency, and enables all-day, all-weather gas flux measurement.
Smart Images
Figure CN2025119620_23072026_PF_FP_ABST
Abstract
Description
A closed-loop mixed gas flux measurement system Technical Field
[0001] This application relates to the field of flux measurement technology, and in particular to a closed-loop mixed gas flux measurement system. Background Technology
[0002] Against the backdrop of global warming, reducing atmospheric greenhouse gas concentrations, mitigating global warming trends, and slowing global environmental change are current international consensuses. Accurate estimation of greenhouse gas emissions is crucial for studying global material cycles and climate change. To achieve "quantifiable, actionable, and assessable" greenhouse gas emissions and absorption, micrometeorological methods for measuring fluxes mainly include aerodynamic methods, heat balance methods, and eddy covariance (EC) methods, with the eddy covariance method currently being the mainstream internationally.
[0003] 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, verifying the accuracy of remote sensing greenhouse gas observations and providing data on the underlying surface at a regional scale (10). 2 m~10 3 High-frequency, continuous, and interference-free measurement data of matter exchange and energy cycling (m).
[0004] Currently, mainstream flux monitoring systems use NDIR (Non-Dispersive Infrared) sensors for gas analysis. NDIR sensors have advantages such as high sensitivity, high accuracy, and rapid gas analysis. In application, dual-wavelength infrared light measurement technology is often used: a wide-frequency infrared light source (that is, one that includes all absorption wavelengths of the target gas) is used, and the emitted infrared light is modulated into two beams: a measurement beam at the measurement wavelength (the wavelength at which the gas absorbs the strongest light in this band) and a reference beam at the reference wavelength (the wavelength at which the gas does not absorb the light 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 also equipped with motors. By rotating the filters driven by the motors, spectral selection can be performed, thereby enabling the measurement of the concentrations of different target gases. Technical issues
[0006] NDIR technology uses a wide wavelength light source, which can cause cross-interference in the measurement of different gases. In addition, the use of motor-switched spectrum selection also has problems such as limited lifespan of moving parts and high power consumption. The maximum measurement frequency is also limited by the motor speed, resulting in less than ideal flux measurement results for mixed systems. Technical solutions
[0007] This application addresses the aforementioned problems and technical requirements by proposing a closed-loop mixed gas flux measurement system. The technical solution of this application is as follows:
[0008] A closed-loop mixed gas flux measurement system is disclosed. The gas analyzer in the closed-loop mixed gas flux measurement system includes N gas cells, N sets of TDLAS sensors, and a pump. Each gas cell is connected in series through its own light-transmitting gas path inlet and outlet. The light-transmitting gas path inlet of the first gas cell is connected to the gas analyzer inlet to acquire the mixed gas to be measured, and the light-transmitting gas path outlet of the last gas cell is connected to the pump. The specifications of the light-transmitting gas path of the i-th gas cell connected in series are matched with the i-th gas to be measured in the mixed gas. Wherein, the integer parameter N≥2, and the integer parameter 1≤i≤N.
[0009] In any i-th group of TDLAS sensors, the laser and receiver are respectively positioned facing each other at both ends of the light-transmitting 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; the i-th group of TDLAS sensors is matched with the i-th gas to be measured in the gas mixture to be measured, and 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 limit intensity threshold and an absorption intensity of the other gases to be measured that is lower than the lower limit intensity threshold;
[0010] In a closed-loop mixed gas flux measurement system, the measurement host is connected to N sets of TDLAS sensors. During the gas extraction process, the measurement host uses any i-th set of TDLAS sensors to detect the original concentration data of the i-th gas in the mixed gas to be measured based on TDLAS technology. The basic time delay of the i-th gas is obtained by dividing the pipeline volume from the inlet of the light-transmitting gas path of the i-th gas cell to the inlet of the gas analyzer by the gas flow rate of the mixed gas to be measured. The original concentration data of the i-th gas is then compensated for the transmission time delay of the i-th gas to obtain the concentration measurement result of the i-th gas.
[0011] A further technical solution involves obtaining the concentration measurement results of the i-th gas to be tested, including:
[0012] Every average time interval 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 the concentration measurement result of the i-th gas to be measured that is synchronously matched with the wind measurement data.
[0013] A further technical solution involves correcting the delay error of the original concentration data of the i-th gas to be measured after transmission delay compensation based on wind measurement data, including:
[0014] At any calibration time t, the vertical wind speed time series is extracted from the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average duration T. The vertical wind speed time series includes M vertical wind speed data arranged in chronological order.
[0015] At different delay offsets at the current correction time t, M raw concentration data of the i-th analyte gas are extracted to form multiple different raw concentration time series. delay offset The extracted first The original concentration time series includes: the most recent original concentration data obtained at correction time t, according to the... Delay offset The original concentration data after each data point and the preceding M-1 consecutive original concentration data points; where the delay offset is... A value less than 0 indicates a directional shift to the previous correction time, representing the delay shift. A value greater than 0 indicates a directional offset to the next correction time; integer parameters Integer parameters ;
[0016] Calculate the first The covariance between the original concentration time series and the vertical wind speed time series was determined. The delay offset corresponding to the original concentration time series with the largest covariance between the original concentration time series and the vertical wind speed time series is taken as the target delay offset;
[0017] After time offsetting the original concentration data of the i-th gas to be measured after completing the transmission delay compensation according to the target delay offset, and completing the delay error correction, the concentration measurement result of the i-th gas to be measured is synchronously matched with the wind measurement data.
[0018] A further technical solution involves correcting the delay error of the original concentration data of the i-th gas to be measured after compensation for transmission delay based on wind measurement data.
[0019] At any calibration time t, the theoretical offset at calibration time t is determined based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time period T, combined with the layout structure of the three-dimensional ultrasonic wind sensor and gas analyzer in the closed-loop mixed gas flux measurement system. Among them, theoretical offset The parameter is an integer.
[0020] Based on the theoretical offset at correction time t exist Extract within range _n ... This indicates the maximum delay offset.
[0021] A further technical solution involves determining the theoretical offset at correction time t. include:
[0022] Based on the layout of the three-dimensional ultrasonic wind sensor and the gas analyzer, the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer is determined.
[0023] Based on the wind direction and wind speed in the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time T before the calibration time t, determine the stable wind speed at the calibration time t from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer.
[0024] Based on the distance between the probe position of the 3D ultrasonic wind sensor and the air inlet of the gas analyzer, and the stable wind speed at calibration time t along the direction from the probe position of the 3D ultrasonic wind sensor to the air inlet of the gas analyzer, the theoretical offset at calibration time t is determined. 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 greater the theoretical offset. The larger.
[0025] A further technical solution is that the flow rate of the air pump is not less than L. max *F, where L max It is the light-transmitting 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.
[0026] The further technical solution is that the specifications of the light transmission path of each gas cell include the aperture and optical path length of the light transmission path. The optical path length of the light transmission path of the i-th gas cell is matched with the gas absorption characteristics of the i-th gas to be measured. The apertures of the light transmission paths of the N gas cells are all equal and are matched with the maximum spot size of the laser in all N groups of TDLAS sensors.
[0027] A further technical solution is that each gas cell is equipped with a curved temperature-conducting gas path before the light-conducting gas path inlet, and the temperature-conducting gas path is made of heat-conducting material. After the mixed gas to be measured passes through the temperature-conducting gas path, it undergoes heat transfer and then enters the light-conducting gas path.
[0028] The further technical solution is that a temperature sensor and a pressure sensor are also arranged at the air inlet of the light-transmitting gas path of each gas pool, and the measurement host in the closed-loop mixed gas flux measurement system is also connected to each temperature sensor and pressure sensor.
[0029] The measurement host detects the original concentration data of the i-th gas to be measured, which includes: 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 i-th gas pool and the air pressure data collected by the air pressure sensor, to detect the original concentration data of the i-th gas to be measured.
[0030] A further technical solution is that a particulate filter is installed at the air inlet of the gas analyzer, and an air filter is installed between the air outlet of the last gas cell and the air pump. Beneficial effects
[0031] This application discloses a closed-loop mixed gas flux measurement system. The gas analyzer in this system is designed with a gas path structure using a series gas cells combined with a pump. The specifications of the optical transmission paths of each gas cell and the sets of TDLAS sensors are matched to the characteristics of various analytes, enabling simultaneous measurement of multiple analytes using TDLAS technology. Transmission delay compensation for the raw concentration data of each analyte compensates for the transmission delay introduced by the series gas cells. Furthermore, thanks to the characteristics of TDLAS measurement technology, cross-interference between different gases is avoided, thus improving the accuracy, reliability, and efficiency of flux measurement. In addition, the gas analyzer uses a pump to obtain sample gas, avoiding exposure to the air, preventing contamination of the optical lens, reducing maintenance frequency, and avoiding the effects of precipitation and snowfall, enabling all-weather, 24 / 7 flux measurement.
[0032] This application also leverages the consistent variation characteristics between the wind measurement data and concentration measurement results of the three-dimensional ultrasonic wind sensor to perform time delay correction on the measurement results of the TDLAS sensor, based on the wind measurement data of the three-dimensional ultrasonic wind sensor integrated into the closed-loop mixed gas flux measurement system. This further improves the accuracy of the concentration measurement results without the need for additional correction devices. Attached Figure Description
[0033] Figure 1 is a system structure block diagram of a closed-loop mixed gas flux measurement system according to an embodiment of this application.
[0034] Figure 2 is a schematic diagram of the series connection structure of two gas cells in one example of this application.
[0035] Figure 3 is a schematic diagram of the structure of a gas analyzer in another embodiment of this application.
[0036] Figure 4 is a flowchart of a method for obtaining the concentration measurement result of the i-th gas to be tested in one embodiment of this application.
[0037] Figure 5 is a schematic diagram of the original concentration time series extracted under different delay offsets in an example of this application. Embodiments of the present invention
[0038] The specific embodiments of this application will be further described below with reference to the accompanying drawings.
[0039] This application discloses a closed-loop mixed gas flux measurement system. Referring to the structural schematic shown in Figure 1, the system includes a gas analyzer, a three-dimensional ultrasonic wind sensor, and a measurement host. This application optimizes traditional NDIR-based gas analyzers. The gas analyzer in this application includes N gas cells, N sets of TDLAS sensors, and a pump, where the integer parameter N ≥ 2. The value of N is determined based on the number and types of gases to be measured. For example, in a common closed-loop mixed gas flux measurement system used to measure the flux of carbon dioxide and water vapor in the air, N = 2. When more gases need to be measured simultaneously, the number of gas cells and TDLAS sensors is increased accordingly.
[0040] Each gas chamber contains a light-transmitting gas path, and the direction from the inlet to the outlet of the light-transmitting gas path within each gas chamber is the gas transmission direction inside the gas chamber.
[0041] Each gas cell is connected in series via its own optically oriented gas path inlet and outlet. The inlet of the first gas cell connects to the inlet of the gas analyzer to acquire the gas mixture to be measured, while the outlet of the last gas cell connects to a vacuum pump. During the vacuum pump's operation, the gas mixture to be measured enters the gas analyzer from the inlet and is sequentially transmitted through the optically oriented gas paths of each gas cell. The optically oriented gas paths are formed inside the gas cells. In practical applications, the gas cells and the TDLAS sensor are encapsulated in a housing, forming a closed-loop structure. This avoids the optical path measurement process being affected by environmental factors such as precipitation and snowfall, and also effectively reduces maintenance frequency. Please refer to Figures 1 and 2. Taking the series structure of gas pool 1 and gas pool 2 as an example, the dotted line inside gas pool 1 is the light-transmitting gas path 11 of gas pool 1, and the dotted line inside gas pool 2 is the light-transmitting gas path 21 of gas pool 2. The outlet of the light-transmitting gas path 21 of gas pool 2 is connected to the vacuum pump 3. The gas transmission direction inside the two gas pools is shown by the arrow.
[0042] N sets of TDLAS sensors are respectively set at N gas cells. The i-th set of TDLAS sensors is set at the i-th gas cell connected in series. The laser and receiver of the i-th set of TDLAS sensors are respectively positioned facing each other at both ends of the light-transmitting 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. As shown in Figure 1, the laser 12 and receiver 13 of the first set of TDLAS sensors are set at both ends of the light-transmitting gas path 11 of gas cell 1, and the laser 22 and receiver 23 of the second set of TDLAS sensors are set at both ends of the light-transmitting gas path 21 of gas cell 2. Wherein, the integer parameter 1 ≤ i ≤ N.
[0043] When it is necessary to measure the flux of N analytes in a gas mixture, the structure of the light transmission path of each gas cell and the TDLAS sensors placed at each gas cell must be designed according to the type of analyte gas, including:
[0044] (1) The specifications of the light-transmitting gas path of the i-th gas cell connected in series match the i-th gas to be measured in the gas mixture to be measured. It should be noted that the i-th gas to be measured in this application is used to refer to any one of the gas to be measured in the gas mixture to be measured. This representation does not mean that the gas to be measured in the gas mixture to be measured must be arranged in a specific order. In fact, since the gas mixture 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 correspond one-to-one with the gas to be measured.
[0045] In one embodiment, the optical path of each gas cell adopts a cylindrical structure. The specifications of the optical path for each gas cell include the aperture along the radial direction of the cylindrical structure and the optical path length along the length of the cylindrical structure. Since the laser emission path of the laser is received by the receiver after passing through the optical path along the gas transmission direction inside the gas cell, the optical path length of the optical path of the i-th gas cell matches the gas absorption characteristics of the i-th analyte gas. The gas absorption characteristics of the i-th analyte gas are the spectral absorption peak of the i-th analyte gas, its absorption intensity, and the detection range of its gas concentration. The optical path length of the optical path of the i-th gas cell is determined by Beer-Lambert's law. For example, in Figure 2, gas cell 1 corresponds to water vapor, so the optical path length L1 of the optical path of gas cell 1 matches the gas absorption characteristics of water vapor, while gas cell 2 corresponds to carbon dioxide, so the optical path length L2 of the optical path of gas cell 2 matches the gas absorption characteristics of carbon dioxide. Because the gas absorption characteristics of different analytes are inconsistent, the optical path lengths of the optical paths of different gas cells may differ.
[0046] To ensure the stability of the gas mixture's transmission within each gas cell and to maintain the same gas flow velocity in each cell, the apertures of the light-transmitting gas paths in the N gas cells are all equal. The aperture of the light-transmitting gas path in each gas cell needs to be determined based on the laser spot size at that cell. Therefore, an aperture matching the maximum laser spot size of all N TDLAS sensors is selected as the aperture of the light-transmitting gas path for each gas cell. Generally, the aperture of the light-transmitting gas path in each gas cell is slightly larger than the maximum laser spot size of all N lasers. When the laser beams are not parallel, the laser spot size in the i-th TDLAS sensor group is related to the optical path length of the light-transmitting gas path in the i-th gas cell. The spot size can also be adjusted using an optical lens.
[0047] (2) The i-th group of TDLAS sensors is matched with the i-th analyte gas in the gas mixture to be measured. The gas mixture to be measured will be transmitted sequentially through each gas cell, and the i-th group of TDLAS sensors is used to measure the i-th analyte gas. Therefore, the wavelength of the laser in the i-th group of TDLAS sensors has an absorption intensity of the upper limit threshold for the i-th analyte gas and an absorption intensity of the lower limit threshold for the other analyte gases. That is, the laser in the i-th group of TDLAS sensors is selected with a wavelength that has strong absorption for the i-th analyte gas and negligible absorption for the other N-1 analyte gases. The absorption intensity for each gas can be determined by referring to the absorption peaks of each gas in the HITRAN database.
[0048] In the closed-loop mixed gas flux measurement system, the main unit is connected to N sets of TDLAS sensors in the gas analyzer. During the gas extraction process, the gas mixture to be measured sequentially passes through the optical transmission paths of each gas cell. In the optical transmission path of any i-th gas cell, the laser emitted by the i-th set of TDLAS sensors emits a laser with a wavelength matching that of the i-th analyte gas, which is then received by the corresponding receiver. Using TDLAS technology, the raw concentration data of the i-th analyte gas can be measured. Because TDLAS measurement technology uses a narrow-linewidth laser source, cross-interference between different analytes is avoided. Furthermore, as the gas mixture passes through each gas cell sequentially, the raw concentration data of each analyte gas can be obtained using each set of TDLAS sensors. Within the error range, simultaneous measurement of multiple analytes can be considered achieved, eliminating the need to switch filters for separate measurements like with NDIR, thus resulting in higher measurement efficiency. The specific measurement results of obtaining the raw concentration data of the analyte gas using the signals from each set of TDLAS sensors can be referenced from existing single-gas flux measurement methods, which will not be elaborated upon in this embodiment.
[0049] To reduce the impact of temperature on flux measurement, in one embodiment, as shown in Figure 3, each gas cell is equipped with a curved temperature-conducting gas path before the inlet of the light-transmitting gas path. This temperature-conducting gas path is made of a thermally conductive material. The mixed gas to be measured passes through the temperature-conducting gas path for heat transfer before entering the light-transmitting gas path. The aperture of the temperature-conducting gas path can be the same as or different from that of the light-transmitting 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 remains consistent with the gas cell temperature. In practical applications, the entire gas cell is generally designed to be made of metal, which has the characteristics of thermal conductivity, corrosion resistance, and non-adsorption. For example, in Figure 3, a temperature-conducting gas path 14 is also provided before the inlet of the light-transmitting gas path 11 in gas cell 1, and a temperature-conducting gas path 24 is also provided before the inlet of the light-transmitting gas path 21 in gas cell 2. Additionally, as shown in Figure 3, temperature sensors and pressure sensors are also arranged at the inlet of the light-transmitting gas path in each gas cell. The measurement host in the closed-loop mixed gas flux measurement system is also connected to each temperature sensor and pressure sensor. When the measuring host obtains the original concentration data of the i-th gas to be measured by using the i-th group of TDLAS sensors based on TDLAS technology, it also applies the temperature data collected by the temperature sensor at the air inlet of the i-th gas pool and the pressure data collected by the pressure sensor to the TDLAS algorithm. The specific content of the TDLAS algorithm will not be elaborated in this application.
[0050] In the above measurement process, the gas renewal rate in the gas cell and the measurement rate of the gas analyzer determine the maximum measurement rate of the entire closed-loop mixed gas flux measurement system. Since the gas cells are connected in series, the gas renewal rate in the largest gas cell determines the gas renewal rate of the entire gas analyzer. Therefore, in one embodiment, the flow rate of the pump is not less than L. max *F, where L max It is the light-transmitting 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 description, this application uses a vacuum pump to draw the mixed gas to be measured into the gas analyzer, employing a closed-loop structure. This effectively prevents the gas analyzer from being exposed to the air, avoiding contamination of the optical lens and reducing maintenance frequency. Furthermore, to further reduce optical lens contamination, as shown in Figure 3, a particulate filter 4 is installed at the gas analyzer's inlet, and an air filter 5 is installed between the outlet of the light-transmitting gas path of the last gas cell and the vacuum pump.
[0052] However, due to this closed-loop structure, even if the gas exchange rate is increased by increasing the flow rate of the pump, there will still be an unavoidable time delay in the transmission of the gas mixture to be measured to the light-transmitting gas path of each gas cell. Therefore, the original concentration data of the i-th gas to be measured obtained directly based on TDLAS technology is not directly used as the concentration measurement result. Instead, the basic time delay of the i-th gas to be measured is obtained by dividing the pipeline volume from the inlet of the light-transmitting gas path of the i-th gas cell to the inlet of the gas analyzer by the gas flow rate of the gas mixture to be measured. After the gas cell structure design is determined, the pipeline volume from the inlet of the light-transmitting gas path of the i-th gas cell to the inlet of the gas analyzer is known, and the gas flow rate during the pumping process is also known. The base time delay of the i-th gas to be measured is the time delay of the gas mixture being measured from the inlet of the gas analyzer to the inlet of the light-transmitting gas path of the i-th gas cell, and it is also the time delay of the existence of 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 time delay according to the transmission time delay of the i-th gas to be measured to obtain the concentration measurement result of the i-th gas to be measured, thereby making up for the transmission time delay introduced by the series gas cells.
[0053] For closed-loop mixed gas flux measurement systems, the obtained concentration measurement results need to be used in conjunction with wind measurement data. However, in reality, due to the physical separation between the gas analyzer's inlet and the probe of the three-dimensional ultrasonic wind sensor, it is still difficult to guarantee the synchronization of the original concentration data after compensation for transmission delay based on the transmission delay within the gas pool with the wind measurement data. Therefore, in one embodiment, after obtaining the original concentration data of the i-th analyte gas after transmission delay compensation using any i-th group of TDLAS sensors based on TDLAS technology, it is not directly used as the final concentration measurement result. Instead, every average time interval T, the original concentration data of the i-th analyte gas after transmission delay compensation is corrected for delay error based on the wind measurement data obtained from the three-dimensional ultrasonic wind sensor in the closed-loop mixed gas flux measurement system, to obtain a concentration measurement result of the i-th analyte gas that is synchronized with the wind measurement data. Because the 3D ultrasonic wind sensor uses an open-circuit structure, its wind measurement data can be considered to have no time delay. Furthermore, the wind measurement data is consistent with the changes in the concentration measurement results of the gas being measured. Therefore, this embodiment uses the wind measurement data as a benchmark to correct the delay error in the original concentration data to offset the time delay introduced by the closed-circuit structure. Since the 3D ultrasonic wind sensor is an inherent component of the closed-circuit mixed gas flux measurement system, this approach requires no additional hardware. The average duration T can be customized, taking 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 raw concentration data of various gases to be measured is the same. The delay error correction of the raw concentration data of the i-th gas to be measured based on the wind measurement data includes the following steps, please refer to the flowchart shown in Figure 4:
[0055] Step 1: At any calibration time t, acquire the wind measurement data obtained by the 3D ultrasonic wind sensor within the previous average duration T. The previous average duration T is the time period between the previous calibration time and the current calibration time t. The acquired wind measurement data includes wind speed and direction at M measurement times. Since the wind measurement frequency of the 3D ultrasonic wind sensor is known, the number of wind measurement times M included in each average duration T is also fixed and known. For example, a common approach is to take the average duration T as half an hour. According to the commonly used wind measurement frequency of the 3D ultrasonic wind sensor, the 3D ultrasonic wind sensor can acquire wind measurement data at 18,000 measurement times within one average duration T.
[0056] Step 2: Extract the vertical wind speed time series from the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time T at any calibration time t. After obtaining the wind speed and wind direction at each wind measurement time, the vertical wind speed data at each wind measurement time can be calculated, thereby extracting the vertical wind speed time series including M vertical wind speed data arranged in chronological order.
[0057] Step 3: Extract M original concentration data of the i-th gas to be tested at different delay offsets at the current correction time t to form multiple different original concentration time series.
[0058] At the current correction time t, the first delay offset The extracted first The original concentration time series includes: the most recent original concentration data obtained at correction time t, according to the... Delay offset The original concentration data after each data point and the M-1 consecutive original concentration data points before it, that is, each extracted original concentration time series also includes M original concentration data points arranged in chronological order.
[0059] Among them, delay offset A value less than 0 indicates a directional shift to the previous correction time, representing the delay shift. A value greater than 0 indicates a directional shift towards the next correction time.
[0060] For example, in one instance, based on the discrete point diagram of the i-th type of raw concentration data arranged in chronological order as shown in Figure 5, the 10 raw concentration data points arranged sequentially in chronological order within the black dashed box represent the delay offset. The extracted raw concentration time series is shown below. The 10 raw concentration data points arranged in chronological order within the red dashed box represent the delay offset. The extracted raw concentration time series, with the 10 raw concentration data points arranged chronologically within the green dashed box representing the delay offset. The original concentration time series was extracted below. It should be noted that Figure 5 uses M=10 as an example for ease of illustration, but in reality, as mentioned above, the value of M is much larger.
[0061] The above method can be used to extract... A number of distinct original concentration time series, with integer parameters The above integer parameters ,specific The value can be customized.
[0062] Step 4, calculate the first... The covariance between the original concentration time series and the vertical wind speed time series was determined. The delay offset corresponding to the original concentration time series with the largest covariance with the vertical wind speed time series is taken as the target delay offset. The original concentration time series with the largest covariance with the vertical wind speed time series is the original concentration time series with the highest consistency with the change of the vertical wind speed time series.
[0063] Step 5: Time offset the original concentration data of the i-th gas after transmission delay compensation according to the target delay offset to complete the delay error correction. That is, determine the most recent original concentration data detected at correction time t according to the target delay offset. Delay offset The original concentration data after each data point is the original concentration data corresponding to the actual correction time t, thus obtaining 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, to improve calibration efficiency, at any calibration time t, the theoretical offset at calibration time t is first determined based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time period 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. Therefore, the final determined target delay offset should be the current theoretical offset. The surrounding area. Then, based on the theoretical offset at correction time t. exist Extract within range _n ... This indicates that the maximum delay offset can be customized. Because the gas in the gas pool is rapidly updated, the time delay introduced by the closed-loop structure will not be too large, hence the positive integer value here. A value of 5 to 10 is generally sufficient.
[0065] Because the probe of the 3D ultrasonic wind sensor is not located at the same position as the air inlet of the gas analyzer, there is an inherent time delay due to the physical separation of the inputs. Furthermore, with a fixed structural design, the time delay between the probe position and the air inlet varies depending on the ambient wind conditions, thus affecting the theoretical offset at calibration time t. It needs to be dynamically adjusted based on wind measurement data, including:
[0066] At any calibration time t, the theoretical offset at calibration time t is determined based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time period T, combined with the layout structure of the three-dimensional ultrasonic wind sensor and gas analyzer in the closed-loop mixed gas flux measurement system. This includes: determining the distance between the probe position of the 3D ultrasonic wind sensor and the air inlet of the gas analyzer based on the layout of the 3D ultrasonic wind sensor and the gas analyzer; and determining the stable wind speed at calibration time t from the probe position of the 3D ultrasonic wind sensor to the air inlet of the gas analyzer based on the wind direction and wind speed obtained from the wind measurement data within the previous average time period T of the calibration time t. The wind measurement data actually acquired by the 3D ultrasonic wind sensor is dynamic discrete data, and the stable wind speed at calibration time t can be calculated using existing methods.
[0067] Then, based on 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 at calibration time t along the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer, the theoretical offset at calibration time t is determined. The layout of the 3D ultrasonic wind sensor and gas analyzer is fixed; that is, the distance between the probe position of the 3D ultrasonic wind sensor and the air inlet of the gas analyzer is fixed. However, the wind measurement data changes dynamically. The theoretical offset is determined based on the distance and wind speed. At the same time, 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 greater the theoretical offset. The larger the value, the more customizable the specific numerical settings can be.
[0068] The above descriptions are merely preferred embodiments of this application, and this application is not limited to the above embodiments. It is understood that other improvements and variations that can be directly derived or conceived by those skilled in the art without departing from the spirit and concept of this application should be considered to be included within the protection scope of this application.
Claims
1. A closed-loop 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 sets of TDLAS sensors, and a pump. Each gas cell is connected in series through its own light-transmitting gas path inlet and outlet. The light-transmitting gas path inlet of the first gas cell is connected to the inlet of the gas analyzer to acquire the mixed gas to be measured, and the light-transmitting gas path outlet of the last gas cell is connected to the pump. The specifications of the light-transmitting gas path of the i-th gas cell connected in series are matched with the i-th gas to be measured in the mixed gas. Wherein, the integer parameter N≥2, and the integer parameter 1≤i≤N. In any i-th group of TDLAS sensors, the laser and receiver are respectively positioned facing each other at both ends of the light-transmitting 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; the i-th group of TDLAS sensors is matched with the i-th gas to be measured in the gas mixture to be measured, and 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 limit intensity threshold and an absorption intensity of the other gases to be measured that is lower than the lower limit intensity threshold; The measurement host in the closed-loop mixed gas flux measurement system is connected to N sets of TDLAS sensors. During the gas extraction process of the pump, the measurement host uses any i-th set of TDLAS sensors to detect the original concentration data of the i-th gas in the mixed gas to be measured based on TDLAS technology. The volume of the pipeline from the inlet of the light-transmitting gas path of the i-th gas cell to the inlet of the gas analyzer is divided by the gas flow rate of the mixed gas to be measured to obtain the basic time delay of the i-th gas. The original concentration data of the i-th gas is then compensated for the transmission time delay of the i-th gas to obtain the concentration measurement result of the i-th gas.
2. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, Obtaining the concentration measurement result of the i-th gas to be tested also includes: Every average time interval T, based on the wind measurement data obtained from the three-dimensional ultrasonic wind sensor in the closed-loop mixed gas flux measurement system, the original concentration data of the i-th gas to be measured after transmission delay compensation is corrected for delay error, 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.
3. The closed-loop mixed gas flux measurement system according to claim 2, characterized in that, The delay error correction for the original concentration data of the i-th gas under test after transmission delay compensation based on wind measurement data includes: 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 previous average duration T. The vertical wind speed time series includes M vertical wind speed data arranged in chronological order. At different delay offsets at the current correction time t, M raw concentration data of the i-th analyte gas are extracted to form multiple different raw concentration time series. delay offset The extracted first The original concentration time series includes: the most recent original concentration data obtained at correction time t, according to the... Delay offset The original concentration data after each data point and the preceding M-1 consecutive original concentration data points; where the delay offset is... A value less than 0 indicates a directional shift to the previous correction time, representing the delay shift. A value greater than 0 indicates a directional offset to the next correction time; integer parameters Integer parameters ； Calculate the first The covariance between the original concentration time series and the vertical wind speed time series is determined. The delay offset corresponding to the original concentration time series with the largest covariance to the vertical wind speed time series is taken as the target delay offset. After time offsetting the original concentration data of the i-th gas to be tested after transmission delay compensation according to the target delay offset, and completing the delay error correction, the concentration measurement result of the i-th gas to be tested is obtained and synchronized with the wind measurement data.
4. The closed-loop mixed gas flux measurement system according to claim 3, characterized in that, The delay error correction for the original concentration data of the i-th gas under test after transmission delay compensation based on wind measurement data also includes: At any calibration time t, the theoretical offset of calibration time t is determined based on the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time period T, combined with the layout structure of the three-dimensional ultrasonic wind sensor and gas analyzer in the closed-loop mixed gas flux measurement system. Among them, theoretical offset The parameter is an integer. Based on the theoretical offset at correction time t exist Extract within range _n ... This indicates the maximum delay offset.
5. The closed-loop mixed gas flux measurement system according to claim 4, characterized in that, Determine the theoretical offset at correction time t include: Based on the layout of the three-dimensional ultrasonic wind sensor and the gas analyzer, the distance between the probe position of the three-dimensional ultrasonic wind sensor and the air inlet of the gas analyzer is determined. Based on the wind direction and wind speed in the wind measurement data obtained by the three-dimensional ultrasonic wind sensor within the previous average time T before the calibration time t, determine the stable wind speed at the calibration time t from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer. Based on 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 at calibration time t along the direction from the probe position of the three-dimensional ultrasonic wind sensor to the air inlet of the gas analyzer, the theoretical offset at calibration time t is determined. 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 greater the theoretical offset. The larger.
6. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, The flow rate of the air pump is not less than L. max *F, where L max It is the light-transmitting 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.
7. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, The specifications of the optical path of each gas cell include the aperture and optical path length. The optical path length of the optical path of the i-th gas cell is matched with the gas absorption characteristics of the i-th gas to be measured. The apertures of the optical paths of the N gas cells are all equal and are matched with the maximum spot size of the laser in all N groups of TDLAS sensors.
8. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, Each gas chamber is equipped with a curved temperature-conducting gas path before the light-conducting gas path inlet. The temperature-conducting gas path is made of thermally conductive material. After the mixed gas to be measured passes through the temperature-conducting gas path, it undergoes heat transfer before entering the light-conducting gas path.
9. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, Temperature and pressure sensors are also arranged at the air inlet of each gas cell through the light-transmitting gas path. The measurement host in the closed-loop mixed gas flux measurement system is also connected to each temperature and pressure sensor. The measurement host detects the original concentration data of the i-th gas to be tested by: 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 i-th gas pool and the air pressure data collected by the air pressure sensor, to detect the original concentration data of the i-th gas to be tested.
10. The closed-loop mixed gas flux measurement system according to claim 1, characterized in that, A particulate filter is installed at the air inlet of the gas analyzer, and an air filter is installed between the air outlet of the last gas cell and the air pump.