CN110927100B - System for measuring gas flux and method of measuring gas flux - Google Patents
System for measuring gas flux and method of measuring gas flux Download PDFInfo
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- CN110927100B CN110927100B CN201911198892.XA CN201911198892A CN110927100B CN 110927100 B CN110927100 B CN 110927100B CN 201911198892 A CN201911198892 A CN 201911198892A CN 110927100 B CN110927100 B CN 110927100B
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Abstract
The present disclosure relates to a system for measuring gas flux and a method of measuring gas flux. The system comprises: a laser that emits laser light; an absorption cell that accommodates a mixed gas including a gas to be measured and a reference gas, and through which laser light passes; a drive circuit coupled to the laser and providing a drive signal to scan and modulate a wavelength emitted by the laser, and the gas under test and the reference gas each have a characteristic absorption peak over a scan range of wavelengths; a detector that receives the laser light transmitted through the absorption cell and converts the laser light into an electrical signal; and a signal processing circuit receiving the electrical signal and extracting an absorption spectrum of the gas to be measured and an absorption spectrum of the reference gas, calculating a concentration of the gas to be measured and a concentration of the reference gas, respectively, from the extracted absorption spectra, and calculating a flux of the gas to be measured from the calculated concentrations, wherein the system further calibrates a wavelength emitted by the laser according to the absorption spectrum of the reference gas.
Description
Technical Field
The present disclosure relates to measurement of gas flux, and in particular, to a system for measuring gas flux and a method of measuring gas flux.
Background
In ecological monitoring, such as microclimate monitoring, it is often involved in the measurement of the flux of a certain gas. For example, monitoring of the nitrogen cycle process is an important component. In the nitrogen cycle, however, active nitrogen is usually present in the form of ammonia gas. Therefore, measurement of the flux of ammonia gas is often involved in ecological monitoring.
Disclosure of Invention
It is an object of the present disclosure to provide an improved system for measuring gas flux and a method of measuring gas flux.
According to an aspect of the present disclosure, there is provided a system for measuring gas flux, comprising: a laser configured to emit laser light; an absorption cell configured to contain a mixed gas including a gas to be measured and a reference gas, and through which laser light from a laser passes; a drive circuit coupled to the laser and configured to provide a drive signal to the laser so as to scan and modulate a wavelength of laser light emitted by the laser, and the gas to be measured and the reference gas each have a characteristic absorption peak within a scan range of the wavelength of the laser light; a detector configured to receive the laser light transmitted through the absorption cell and convert the laser light into an electrical signal representing an intensity of the received laser light; and a signal processing circuit configured to: receiving the electrical signal output by the detector and extracting an absorption spectrum of the gas to be measured and an absorption spectrum of the reference gas based on the electrical signal, calculating a concentration of the gas to be measured and a concentration of the reference gas from the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas, respectively, and calculating a flux of the gas to be measured from the calculated concentrations of the gas to be measured and the reference gas, wherein the system is further configured to calibrate a wavelength of laser light emitted by the laser according to the absorption spectrum of the reference gas.
According to another aspect of the present disclosure, there is provided a method of measuring gas flux, comprising: emitting laser light by a laser and passing the laser light through an absorption cell containing a mixed gas including a gas to be measured and a reference gas, wherein the laser is driven by a driving signal so as to scan and modulate a wavelength of the laser light emitted by the laser, and the gas to be measured and the reference gas each have a characteristic absorption peak in a scanning range of the wavelength of the laser light; receiving, by a detector, the laser light transmitted through the absorption cell and converting the laser light into an electrical signal representing an intensity of the received laser light; and receiving the electrical signal output by the detector and extracting an absorption spectrum of the gas to be measured and an absorption spectrum of the reference gas based on the electrical signal, calculating a concentration of the gas to be measured and a concentration of the reference gas from the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas, respectively, and calculating a flux of the gas to be measured from the calculated concentrations of the gas to be measured and the reference gas, wherein the method further comprises calibrating a wavelength of laser light emitted by the laser according to the absorption spectrum of the reference gas.
Other features of the present disclosure and advantages thereof will become more apparent from the following detailed description of exemplary embodiments thereof, which proceeds with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the principles of the disclosure.
The present disclosure may be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
fig. 1 shows a schematic block diagram of a system for measuring gas flux according to some exemplary embodiments of the present disclosure.
FIG. 2 shows absorption spectra of ammonia molecules and water molecules within a first wavelength band;
FIG. 3 shows absorption spectra of ammonia molecules and water molecules in a second wavelength band;
FIG. 4 shows an absorption spectrum of a mixed gas of ammonia and water vapor measured in some exemplary embodiments of the present disclosure;
FIG. 5 shows a schematic flow diagram of a method of measuring gas flux, according to some exemplary embodiments of the present disclosure;
fig. 6 illustrates an exemplary configuration diagram of a computing device in which embodiments in accordance with the present disclosure may be implemented.
Note that in the embodiments described below, the same reference numerals are used in common between different drawings to denote the same portions or portions having the same functions, and a repetitive description thereof will be omitted. In some cases, similar reference numbers and letters are used to denote similar items, and thus, once an item is defined in one figure, it need not be discussed further in subsequent figures.
For convenience of understanding, the positions, sizes, ranges, and the like of the respective structures shown in the drawings and the like do not sometimes indicate actual positions, sizes, ranges, and the like. Therefore, the present disclosure is not limited to the positions, dimensions, ranges, and the like disclosed in the drawings and the like. Moreover, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components.
Detailed Description
Various exemplary embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. It should be noted that: the following description of various exemplary embodiments is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. That is, the structures and methods herein are shown by way of example to illustrate different embodiments of the structures and methods of the present disclosure. Those skilled in the art will understand, however, that they are merely illustrative of exemplary ways in which the disclosure may be practiced and not exhaustive. Furthermore, the relative arrangement of the components and steps, the numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present disclosure unless specifically stated otherwise.
Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate.
For a more complete and clear understanding of the present disclosure, a system for measuring gas flux and a method of measuring gas flux according to the present disclosure will be described in detail below with reference to the accompanying drawings. It will be understood by those skilled in the art that the present disclosure is not limited to the structures and processes shown in the drawings, but can be adapted to other structures of systems for measuring gas flux and processes of methods of measuring gas flux according to the operating principle thereof. For example, the configuration, installation, and relative positional arrangement of the systems for measuring gas flux shown in the figures are exemplary only and not limiting, and the present disclosure may be adapted or adapted with simple modification to any suitable configuration, installation, and arrangement of systems for measuring gas flux.
The flux of the gas to be measured refers to the amount of the gas to be measured settled and released per unit area per unit time. The concentration of the gas to be measured is an important parameter in the calculation of the flux of the gas, and can be derived from the absorption spectrum of the gas for incident light. However, when measuring the absorption spectrum of a gas, a shift in the wavelength of incident light from a light source may affect the measurement result. In addition, the presence of other gases, such as moisture, can also affect the results of the flux measurements in calculating the flux.
In the related art of the present disclosure, some technical means have been adopted in order to reduce or eliminate the adverse effects caused by the above-mentioned factors. On the one hand, in order to reduce or eliminate the influence of the wavelength shift of the incident light on the measurement result, it is often necessary to additionally provide a reference optical path or the like, so as to implement peak locking on the wavelength of the laser light emitted by the laser. On the other hand, in order to correct the influence of other gases such as moisture on the measurement result, it is necessary to add an additional component to the concentration measurement apparatus of the gas to be measured or separately provide a gas analysis device for moisture in addition to measure the concentration of moisture or the like so as to correct the flux of the gas to be measured according to the concentration of moisture in the flux calculation process.
However, the above modifications all result in a more complicated system for measuring the gas flux, which is not favorable for reducing the measurement cost and improving the measurement flexibility. For example, peak locking using the reference optical path requires a complicated optical path to be provided, and optical interference may occur between the reference optical path and the measurement optical path, thereby affecting the measurement result. The use of the reference optical path also reduces the power of the incident light entering the measurement optical path, which is detrimental to the measurement result. In addition, adding additional components to the concentration measurement apparatus of the gas to be measured to measure the concentration of other gases increases the complexity and cost of the concentration measurement device, and reduces the efficiency of the concentration measurement of the gas to be measured. Furthermore, separately providing a gas analysis device for other gases to measure the concentration of the other gases obviously also increases the complexity and cost of the system. Moreover, the volume of the flux measurement system thus configured may increase significantly, which is detrimental to the transportation and deployment of the flux measurement system.
In view of the above problems, there is a need for a flux measurement system and method that has a simpler structure and lower cost to obtain better measurement results.
Hereinafter, a system for measuring a gas flux and a method for measuring a gas flux will be described in detail by taking ammonia gas as an example of a gas to be measured. It is to be noted that, although the system for measuring gas flux and the method for measuring gas flux of the present disclosure are mainly discussed below by taking flux measurement of ammonia as an example, it is understood by those skilled in the art that the present disclosure is not limited thereto, but can be applied to any other system for measuring gas flux and method for measuring gas flux having the same requirements, such as measuring carbon monoxide, carbon dioxide, nitric oxide, nitrous oxide, methane, etc., according to the working principle thereof.
Fig. 1 shows a schematic block diagram of a system 100 for measuring gas flux according to some exemplary embodiments of the present disclosure. It should be noted that other components may be present in the actual system 100 for measuring gas flux, and are not shown in the figures and discussed herein in order to avoid obscuring the points of the present disclosure.
As shown in fig. 1, the system 100 for measuring gas flux includes a laser 110, a drive circuit 150, an absorption cell 120, a detector 130, and a signal processing circuit 140. Note that solid arrows in the drawings indicate paths of light rays, and dashed arrows indicate electrical or mechanical couplings between circuits or modules.
In some embodiments, the system 100 for measuring gas flux may further include various optical components, such as lenses, mirrors, etc., positioned in the measurement optical path for passing laser light emitted by the laser 110 through the absorption cell 120 to the detector 130.
The laser 110 is configured to emit laser light having a wavelength and intensity that can be precisely controlled. The wavelength of the laser light emitted by the laser 110 is determined according to the types of the gas to be measured and the reference gas. In some embodiments, the laser 110 may be configured to emit laser light in the mid-infrared band. For example, the Laser 110 may include a continuous wave mid-infrared Quantum Cascade Laser (QCL). Further, the Continuous Wave mid-infrared QCL may comprise a Distributed Feedback Continuous Wave Quantum Cascade Laser (DFB-CW QCL) or an External Cavity Continuous Wave Quantum Cascade Laser (EC-CW QCL). Among them, DFB-CW QCLs can generally output a narrow spectrum; EC-CW QCLs are typically spectrally tunable, allowing rapid wavelength changes over a wide frequency range.
The drive circuit 150 coupled to the laser 110 may be configured to provide a drive signal to the laser 110 to scan and modulate the wavelength of the laser light emitted by the laser 110, thereby controlling the laser 110 to emit laser light having a desired wavelength and modulated. Furthermore, although not shown in fig. 1, a temperature control system may also be provided to the laser 110 according to embodiments of the present disclosure, thereby enabling real-time adjustment of the laser operating temperature. The drive circuit 150 may provide a drive signal to the temperature control system to control the operating temperature of the laser.
In the embodiments of the present disclosure, the gas to be measured and the reference gas each have a characteristic absorption peak in a scanning range of the wavelength of the laser light. In some examples, when the gas to be measured is ammonia, water vapor may be selected as the reference gas. The water vapor is widely existed in the environment, the water molecules have absorption peaks close to the ammonia molecules, and the concentration of the water vapor has a large variation range and has a large influence on the calculation result of the ammonia flux. For example, when the gas to be measured is ammonia gas and the reference gas is water vapor, the scanning wavelength of the laser emitted by the laser can be 8.89 to 8.95 microns or 9.04 to 9.09 microns.
FIG. 2 shows the line intensities of the absorption spectra of ammonia molecules and water molecules in the 8.89-8.95 micron band. FIG. 3 shows the line intensities of the absorption spectra of ammonia molecules and water molecules in the 9.04-9.09 micron band. As can be seen from fig. 2 and 3, in both of these two bands, the ammonia molecules and the water molecules have a plurality of absorption peaks, and the intensities of some absorption peaks of the ammonia molecules are several orders of magnitude higher than those of some absorption peaks of the water molecules. It will be appreciated by those skilled in the art that the above two bands are merely exemplary, and that other bands are conceivable as long as there are absorption peaks of both the gas to be measured and the reference gas within the band.
The laser light emitted from the laser 110 reaches the absorption cell 120. The absorption cell 120 is configured to contain a mixed gas including a gas to be measured and a reference gas, and the laser light from the laser 110 passes through the absorption cell 120.
In an embodiment of the present disclosure, the absorption cell 120 may be an open path absorption cell. For open cell, the cell has no side walls and is open to the environment, so that the gas in the environment can freely enter and exit the cell, and is therefore very sensitive to changes in the flux of the gas.
Additionally, in some embodiments, the absorption cell 120 of the present disclosure may be a long-path absorption cell, such that the laser is in sufficient contact with the mixed gas in the absorption cell to enhance the intensity of the absorption peak in the resulting absorption spectrum to improve the accuracy of subsequent laser wavelength correction and flux measurement. Specifically, the optical path of the laser light in the long-path absorption cell 120 may be up to 50m. For example, the optical length of the absorption cell can be increased by causing the laser light to reflect back and forth multiple times within the absorption cell.
The detector 130 is configured to receive the laser light transmitted through the absorption cell 120 and convert the laser light into an electrical signal, e.g., a voltage signal, representative of the intensity of the received laser light. The electrical signal represents information on absorption of laser light of the corresponding wavelength by the gas to be measured and the reference gas in the mixed gas. Since the concentration of the gas is proportional to its absorption of the laser light, the electrical signal can represent the respective concentrations of the gas to be measured and the reference gas in the mixed gas. In some embodiments, the detector 130 may include a photodiode or the like.
The signal processing circuit 140 is configured to receive the electrical signal output by the detector 130, and extract the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas from the electrical signal. And respectively calculating the concentration of the gas to be measured and the concentration of the reference gas according to the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas. In an embodiment of the present disclosure, the concentration of the gas to be measured and the concentration of the reference gas may be obtained simultaneously.
In some embodiments of the present disclosure, wavelength modulation spectroscopy techniques may be employed to detect gas concentration, which can improve the sensitivity and accuracy of gas concentration measurements. The basic principle of such gas concentration detection is briefly described as follows:
according to the Lambert-Beer law, after laser with frequency v passes through absorption gas to be detected, the transmitted light intensity is
I t (v)＝I 0 (v)exp(-Sφ v NL)＝I 0 (v)exp(-α(v))
In the above formula I 0 Is the incident light intensity, S is the absorption line transition intensity, phi v Is absorption lineShape function, N is gas molecule number density, L is absorption optical path, alpha = S phi v NL is absorbance. In order to tune the laser wavelength to cover the absorption line of the gas to be measured, the detection system according to some embodiments of the present invention uses a low frequency scanning signal superimposed with a high frequency modulation signal (modulation frequency f) to tune the drive current of the laser. For example, the low frequency scanning signal is a sawtooth wave, and the high frequency modulation signal is a high frequency sine/cosine wave signal. The laser modulated by high frequency enters the detector after passing through the gas absorption cell, and the harmonic wave can be obtained after the detector signal is demodulated by the phase-locked amplifier. The second harmonic signal (2 f) is typically used because the even harmonic component has a maximum at the resonance position to facilitate locking the wavelength of the laser to the absorption peak of the gas, and the value of each order harmonic component decreases as the order increases. The second harmonic signal is in direct proportion to the absorption of the gas, the second harmonic signal of the gas with the known concentration is used as a standard curve, and the second harmonic signal of the gas to be measured is fitted based on a least square method, so that the gas concentration can be calculated with high precision.
In an embodiment of the present disclosure, the current driving signal provided by the driving circuit 150 to the laser 110 may be a sawtooth signal superimposed with a signal modulated by a high-frequency sinusoidal signal, the sawtooth signal being used to change the output wavelength of the laser so as to cover a wavelength range including absorption peaks of the gas to be measured and the reference gas, the high-frequency sinusoidal signal being used to implement harmonic measurement of the phase-locked amplifying circuit. In actual measurement, in some cases, in order to obtain absorption spectra of a gas to be measured and a reference gas, the operating temperature of the laser may be set by a temperature control system not shown in fig. 1 so that the center wavelength of the laser output is located in the vicinity of the gas to be measured and the reference gas, and then a wavelength range covering the target absorption lines of the gas to be measured and the reference gas is obtained by tuning the laser drive current.
The signal processing circuit 140 demodulates the electrical signal received from the detector 130 and extracts a second harmonic signal, and filters the second harmonic signal. The second harmonic signal includes a second harmonic signal of the gas to be measured and a second harmonic signal of the reference gas. Then, the signal processing circuit 140 extracts the second harmonic signal of the gas to be measured and the second harmonic signal of the reference gas according to the characteristic peaks of the gas to be measured and the reference gas. And then, respectively aiming at the second harmonic signal of the gas to be detected and the second harmonic signal of the reference gas, obtaining a linear correlation coefficient by utilizing least square fitting according to the linear relation between the second harmonic signal of the corresponding gas with known standard concentration and the obtained second harmonic signal of the corresponding gas, and then calculating to obtain the concentration of the corresponding gas. The signal processing circuit 140 may include a lock-in amplifier, a data acquisition processing circuit, a filter, and the like to achieve the above-described functions. Although not shown, the system of the present invention may also include a display circuit for displaying the calculated gas concentration. The concentration of the gas to be detected can be calculated using various processes known in the art or developed in the future and will not be discussed in detail herein.
Fig. 4 is a second harmonic spectrum of a mixed gas of ammonia and water vapor measured with the flux measuring apparatus of the exemplary embodiment of the present disclosure. Second harmonic spectra of room air (typically with 11ppb ammonia) and mixed gas with 50ppb ammonia are shown in fig. 4, respectively. In addition, fig. 4 shows the second harmonic spectrum of the control gas when the ammonia gas concentration is zero. As can be seen from fig. 4, the concentration of ammonia gas is proportional to the intensity of the absorption peak of ammonia gas in the second harmonic spectrum, and therefore the concentration of ammonia gas can be determined from the second harmonic spectrum. Although the absorption line intensity of ammonia molecules is mostly higher than that of water molecules in fig. 2 and 3, since the concentration of ammonia gas is often much lower than that of water vapor in the environment, the absorption peak of ammonia gas and the absorption peak of water vapor do not overlap and the intensities of the two are substantially in the same order in the actually measured absorption spectrum shown in fig. 4, which facilitates accurate extraction of the absorption peak corresponding to ammonia gas and the absorption peak corresponding to water vapor, thereby facilitating accurate calculation of the concentrations of ammonia gas and water vapor, respectively.
Thus, in the embodiment of the present disclosure, the concentration of the gas to be measured and the concentration of the reference gas can be obtained simultaneously.
According to an embodiment of the present disclosure, signal processing circuit 140 may calibrate the wavelength of the laser light emitted by laser 110 according to the absorption spectrum of the reference gas, thereby ensuring that the laser light emitted by laser 110 has a desired wavelength. For example, in some embodiments, the signal processing circuit 140 may determine the wavelength shift of the laser light emitted by the laser from the amount of shift in the absorption spectrum (the position of the absorption peak) of the reference gas. A calibration signal based on the amount of drift is fed back to the drive circuit 150, thereby calibrating the wavelength of the laser light emitted by the laser 110. For example, the laser wavelength may be calibrated by controlling the operating current and/or operating temperature of the laser by a drive circuit controlling a drive signal provided to the laser 110 and/or a temperature controller. The calibration of the laser may be performed in real time or at predetermined intervals.
After the concentrations of the gas to be measured and the reference gas are obtained, the flux of the gas to be measured can be calculated based on the calculated concentrations of the gas to be measured and the reference gas. In one or more embodiments of the present disclosure, the signal processing circuit 140 may be configured to calculate the flux of the gas under test using an Eddy correlation (Eddy Covariance) method.
The whirl correlation method is a micrometeorological measurement method which can obtain the flux of a substance by calculating the covariance of the concentration of the substance and a vertical wind speed component. According to the whirl correlation method, the flux F of the substance C can be expressed as:
wherein w is the vertical wind speed, q c Is the concentration (mass density) of the gas C, wherein the upper-dashed line "_" represents time-averaging. Wind speed may be measured by an anemometer (e.g., an ultrasonic anemometer).
After Reynolds decomposition, the above equation is expressed as:
where the apostrophe "" represents the deviation of the instantaneous value from the mean value, i.e. the amount of pulsation.
In the whirl-related method calculation, a time average of the vertical wind speed is generally assumed
Is zero, so that
I.e. not taking into account the flux caused by the vertical mean flow. However, if the density of the gas is affected by other gas components such as moisture so as to pulsate, that is, expansion/contraction of the gas occurs, the result of the flux calculation needs to be corrected in consideration of the influence of the other gas components in the gas to be measured. At this time, the flux caused by the vertical average flow needs to be considered. An air density pulsation correction method considering water vapor is a WPL (Webb-Pearman-leaving) correction method. The flux calculation formula corrected by the WPL correction method is as follows:
wherein q is v As concentration (mass density) of water vapor, q d Mu is the molar mass ratio of the dry air to the water vapor molecules, sigma is the ratio of the water vapor concentration to the dry air concentration, and T is the temperature.
On the basis of this, the presence of other gases than the gas to be measured in the mixed gas also affects the calculation result of the concentration of the gas to be measured. Therefore, the calculation result of the concentration of the gas to be measured can also be corrected in consideration of the concentrations of other gases.
For example, when the wavelength modulation spectroscopy is used to detect the gas concentration, as the concentration of water vapor in the mixed gas increases, due to molecular collisions between the water vapor and the gas to be measured, the obtained spectrum of the gas to be measured may be broadened, so that the calculation result of the concentration of the gas to be measured is correspondingly reduced. The spectral broadening caused by the concentration of such other gases can be calculated by multiplying the calculated concentration of the gas to be measured by a correction factor k, which can be determined experimentally.
Corrected by the correction factor, the concentration of the gas to be measured can be expressed as: q. q.s c ＝q cm K is used. Wherein q is cm Is the detected concentration of the gas C to be measured, which is not corrected by the correction factor.
Further, when the calculation result of the concentration of the gas to be measured is corrected using this correction factor κ, it is also necessary to replace the measured gas pressure with the equivalent pressure of the gas. The equivalent pressure of a gas represents the sum of the products of the partial pressure of each gas in the mixed gas and the spectral broadening coefficient caused by that gas. In one embodiment of the present disclosure, water vapor is discussed as the only spectrally broadening gas, ignoring the spectral broadening caused by other gases as well as the gas to be measured itself. Thus, the equivalent pressure of the gas is expressed as:
P e ＝P(1+α v x v )，
wherein P is e Is an equivalent pressure, α v ＝a v -1，a v For spectral broadening coefficient, x, due to moisture v Is the mole fraction of water vapor. In one or more embodiments of the present disclosure, a v Experimentally determined to be 1.46.
Therefore, on the basis of the WPL correction, the flux calculation formula after accounting for the moisture-induced spectral broadening is:
the above parameters, calculation formulas and derivation processes are known to those skilled in the art and will not be described in detail herein.
Thereby, the flux of the gas to be measured can be measured quickly by the gas flux measuring system according to the embodiment of the present disclosure.
In the embodiment of the present disclosure, by measuring the absorption spectrum of the mixed gas of the gas to be measured such as ammonia and the reference gas such as water vapor, the wavelength of the laser light emitted by the laser can be corrected by the absorption spectrum of the reference gas. When the wavelength of the laser is corrected by using the absorption spectrum of the reference gas, a reference light path does not need to be additionally arranged to lock the peak of the wavelength of the laser. Meanwhile, the optical interference phenomenon possibly introduced in the peak locking process is also avoided. Since the laser emitted by the laser can substantially enter the absorption cell 120, it is helpful to improve the signal-to-noise ratio of the absorption spectrum under the limited laser emission power, so that the flux measurement is more accurate.
In addition, the concentration of the reference gas obtained by measuring the concentration of the gas to be measured simultaneously can be used for calculating the flux of the gas to be measured, no additional component or device is required to be provided for separately measuring the concentration of the reference gas in the environment, and the cost of the equipment is reduced. In addition, because the same system is used for simultaneously measuring the concentrations of the gas to be measured and the reference gas, the concentrations of the gas to be measured and the reference gas can be measured at the same frequency, and thus the real-time correction of the flux of the gas to be measured is realized. For example, in an embodiment in which the concentration of the gas is measured using a wavelength modulation method, it is possible to simultaneously measure the concentrations of the gas to be measured and the reference gas at a relatively fast frequency (> 5 Hz) and correct the flux of the gas to be measured in real time.
In addition, in the gas flux measurement system according to the embodiment of the present disclosure, sensors such as an anemometer, a thermometer, and a manometer, which provide data of parameters required for gas flux calculation, may be further included, and are not described in detail herein.
According to another aspect of the present disclosure, there is provided a method of measuring a gas flux, as shown in fig. 5, the method comprising:
step S100, emitting laser by a laser 110 and making the laser pass through an absorption cell 120, wherein the absorption cell 120 contains mixed gas comprising gas to be measured and reference gas, the laser 110 is driven by a driving signal so as to scan and modulate the wavelength of the laser emitted by the laser 110, and the gas to be measured and the reference gas respectively have characteristic absorption peaks in the scanning range of the wavelength of the laser;
step S200 of receiving the laser light transmitted through the absorption cell 120 by the detector 130 and converting the laser light into an electrical signal representing the intensity of the received laser light;
step S300, receiving the electric signal output by the detector 130 and extracting the absorption spectrum of the gas to be detected and the absorption spectrum of the reference gas based on the electric signal;
step S400, respectively calculating the concentration of the gas to be measured and the concentration of the reference gas according to the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas; and
step S500, calculating the flux of the gas to be measured according to the calculated concentration of the gas to be measured and the concentration of the reference gas.
In addition, as shown in fig. 5, the method further includes a step S600 of calibrating the wavelength of the laser light emitted by the laser according to the absorption spectrum of the reference gas.
By repeating the above steps, the measurement result of the gas flux can be obtained continuously. For example, in embodiments that employ a wavelength modulation method to measure the concentration of a gas, the concentrations of the test gas and the reference gas can be measured simultaneously at a faster frequency (> 5 Hz).
Although it is shown in fig. 5 that the step S600 is performed after the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas are extracted in the step S300, it can be understood by those skilled in the art that the step S600 can be performed after the step S400 or the step S500, or performed together with the steps S300, S400, and S500. Further, only steps S100-S500 may be performed without performing step S600 each time the method according to the embodiment of the present disclosure is repeatedly performed. In this case, step S600 may be performed as needed or at predetermined time intervals.
The method of measuring gas flux according to the embodiments of the present disclosure may achieve similar technical effects to those described above, and will not be repeated here.
In the embodiments of the present disclosure, the description is made using ammonia gas and water vapor as examples of the gas to be measured and the reference gas, respectively, because there is an absorption spectrum of water molecules in the vicinity of an absorption spectrum of ammonia molecules, the concentration of water vapor has a large influence on flux measurement of ammonia molecules, and water molecules are ubiquitous in the mixed gas. It will be understood by those skilled in the art that other gases may be selected for the test gas and the reference gas, as long as they have a similar relationship.
In the embodiments of the present disclosure, although the WPL correction is described as an example of the correction method of the gas flux, other flux correction methods may be conceived by those skilled in the art and applied alone or in combination with the WPL correction to correct the flux of the gas to be measured.
Fig. 6 illustrates an exemplary configuration of a computing device 2000 in which embodiments in accordance with the present disclosure may be implemented. Computing device 2000 is an example of a hardware device to which the above-described aspects of the disclosure may be applied. Computing device 2000 may be any machine configured to perform processing and/or computing. Computing device 2000 may be, but is not limited to, a Micro Controller Unit (MCU), a workstation, a server, a desktop computer, a laptop computer, a tablet computer, a Personal Data Assistant (PDA), a smart phone, an on-board computer, or a combination thereof. The laser 110, drive circuit 150, detector 130, and signal processing circuit 140 of the aforementioned system for measuring gas flux may all be implemented, in whole or at least in part, by the aforementioned computing device 2000 or a device or system similar thereto. The computing device 2000 may also simultaneously implement other functions of the signal processing circuit 140, such as the aforementioned operation of calculating the flux of the gas to be measured. In some embodiments, the computing device 2000 may also implement control functions for the driving circuit 150, such as controlling the waveform and amplitude of the current driving signal provided by the driving circuit 150, and/or adjusting the current driving signal provided by the driving circuit 150 based on feedback of wavelength shift information.
As shown in fig. 6, computing device 2000 may include one or more elements connected to or in communication with bus 2002, possibly via one or more interfaces. For example, computing device 2000 may include a bus 2002, one or more processors 2004, one or more input devices 2006, and one or more output devices 2008. Bus 2002 may include, but is not limited to, industry standard architecture (Industry Standard Architecture (ISA) bus, micro Channel Architecture (MCA) bus, enhanced ISA (EISA) bus, video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus. The one or more processing devices 2004 can be any kind of processor and can include, but are not limited to, one or more general-purpose processors or special-purpose processors (such as special-purpose processing chips). Input device 2006 may be any type of input device capable of inputting information to a computing device and may include, but is not limited to, a mouse, a keyboard, a touch screen, a microphone, and/or a remote control. Output device 2008 may be any type of device capable of presenting information and may include, but is not limited to, a display, speakers, a video/audio output terminal, a vibrator, and/or a printer. The computing device 2000 may also include or be connected to a non-transitory storage device 2010, which non-transitory storage device 2010 may be any non-transitory and may implement a data storage device, and may include, but is not limited to, a disk drive, an optical storage device, a solid state memory, a floppy disk, a flexible disk, a hard disk, a magnetic tape, or any other magnetic medium, a compact disk, or any other optical medium, a ROM (read only memory), a RAM (random access memory), a cache memory, and/or any other memory chip or module, and/or any other medium from which a computer may read data, instructions, and/or code. The non-transitory storage device 2010 may be removably connected with any interface. The non-transitory storage device 2010 may have data/instructions/code stored thereon for implementing the aforementioned methods and/or steps of measuring gas flux. Computing device 2000 may also include a communication device 2012, which communication device 2012 may be any kind of device or system capable of enabling communication with external apparatuses and/or networks and may include, but is not limited to, a modem, a network card, an infrared communication device, a wireless communication device, and/or a chipset (such as bluetooth) TM Equipment, 1302.11 equipment, wiFi equipment, wiMax equipment, cellular communications facilities, etc.).
The computing device 2000 may also include a working memory 2014. The working memory 2014 may be any type of working memory capable of storing instructions and/or data useful to the processor 2004 and may include, but is not limited to, random Access Memory (RAM) and Read Only Memory (ROM).
The software elements located on the above-described working memory may include, but are not limited to, an operating system 2016, one or more application programs 2018, drivers, and/or other data and code. The one or more applications 2018 may include instructions for performing the methods and steps for measuring gas flux as described above. The aforementioned components/units/elements of the system 100 for measuring gas flux may be implemented by a processor reading and executing one or more applications 2018. Executable code or source code of the instructions of the software elements may be stored in a non-transitory computer-readable storage medium (such as storage device 2010 as described above) and may be read into working memory 2014 by compilation and/or installation. Executable or source code for the instructions of the software elements may also be downloaded from a remote location.
It will be appreciated that variations may be made in accordance with specific requirements. For example, customized hardware might be used and/or particular elements might be implemented in hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. In addition, connections to other computing devices (such as network input/output devices) may be employed. For example, some or all of the methods and apparatus of the present disclosure may be implemented in accordance with the present disclosure using assembly language programming hardware (e.g., programmable logic circuits including Field Programmable Gate Arrays (FPGAs) and/or Programmable Logic Arrays (PLAs)) or hardware programming languages of logic and algorithms (e.g., VERILOG, VHDL, C + +).
It should be further understood that the elements of computing device 2000 may be distributed throughout a network. For example, some processes may be performed using one processor while other processes are performed using other remote processors. Other elements of the computer system 2000 may be similarly distributed. Thus, the computing device 2000 may be understood as a distributed computing system that performs processing at multiple sites.
The systems and methods of the present disclosure may be implemented in a number of ways. For example, the systems and methods of the present disclosure may be implemented by software, hardware, firmware, or any combination thereof. The order of the method steps described above is merely illustrative, and the method steps of the present disclosure are not limited to the order specifically described above unless explicitly stated otherwise. Further, in some embodiments, the present disclosure may also be embodied as a program recorded in a recording medium, which includes machine-readable instructions for implementing a method according to the present disclosure. Thus, the present disclosure also covers a recording medium storing a program for implementing the method according to the present disclosure.
The terms "front," "back," "top," "bottom," "over," "under," and the like in the description and in the claims are used for descriptive purposes only and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the disclosure described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
The word "exemplary" is used herein to mean "serving as an example, instance, or illustration," and not as a "model" that is to be reproduced exactly. Any implementation exemplarily described herein is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, the disclosure is not limited by any expressed or implied theory presented in the preceding technical field, background, brief summary or the detailed description.
The term "substantially" as used herein is intended to encompass any minor variation resulting from design or manufacturing imperfections, device or component tolerances, environmental influences and/or other factors. The word "substantially" also allows for differences from a perfect or ideal situation due to parasitics, noise, and other practical considerations that may exist in a practical implementation.
In addition, the foregoing description may refer to elements or nodes or features being "connected" or "coupled" together. As used herein, unless expressly stated otherwise, "connected" means that one element/node/feature is directly connected to (or directly communicates with) another element/node/feature, either electrically, mechanically, logically, or otherwise. Similarly, unless expressly stated otherwise, "coupled" means that one element/node/feature may be mechanically, electrically, logically, or otherwise joined to another element/node/feature in a direct or indirect manner to allow for interaction, even though the two features may not be directly connected. That is, to "couple" is intended to include both direct and indirect joining of elements or other features, including connection with one or more intermediate elements.
In addition, "first," "second," and like terms may also be used herein for reference purposes only, and thus are not intended to be limiting. For example, the terms "first," "second," and other such numerical terms referring to structures or elements do not imply a sequence or order unless clearly indicated by the context.
In the present disclosure, the term "providing" is used broadly to encompass all ways of obtaining an object, and thus "providing an object" includes, but is not limited to, "purchasing," "preparing/manufacturing," "arranging/setting," "installing/assembling," and/or "ordering" the object, and the like.
Those skilled in the art will appreciate that the boundaries between the above described operations merely illustrative. For example, multiple operations may be combined into a single operation, while a single operation may be distributed over multiple operations, and operations may be performed at least partially overlapping in time. Moreover, other embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments. Also, other modifications, variations, and alternatives are also possible. In addition, the various embodiments and examples described above may be combined arbitrarily as needed, for example, a particular operation or detail described in a certain embodiment may also be applied to other embodiments or examples.
Although some specific embodiments of the present disclosure have been described in detail by way of example, it should be understood by those skilled in the art that the foregoing examples are for purposes of illustration only and are not intended to limit the scope of the present disclosure. The various embodiments disclosed herein may be combined in any combination without departing from the spirit and scope of the present disclosure. It will also be appreciated by those skilled in the art that various modifications may be made to the embodiments without departing from the scope and spirit of the disclosure. The scope of the present disclosure is defined by the appended claims.
Claims (9)
1. A system for measuring gas flux, comprising:
a laser configured to emit laser light;
an absorption cell configured to accommodate a mixed gas including a gas to be measured and a reference gas, and through which laser light from a laser passes;
a drive circuit coupled to the laser and configured to provide a drive signal to the laser so as to scan and modulate a wavelength emitted by the laser, and the gas under test and the reference gas each have a characteristic absorption peak over a scan range of wavelengths;
a detector configured to receive the laser light transmitted through the absorption cell and convert the laser light into an electrical signal representing an intensity of the received laser light; and
a signal processing circuit configured to:
receiving the electrical signal output by the detector and extracting the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas based on the electrical signal,
calculating the concentration of the gas to be measured and the concentration of the reference gas from the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas, respectively, an
Calculating the flux of the gas to be measured according to the calculated concentration of the gas to be measured and the concentration of the reference gas by adopting a vorticity correlation method, correcting the flux of the gas to be measured in real time according to the concentration of the reference gas and the WPL correction,
wherein the gas to be measured is ammonia gas, the reference gas is water vapor, and
the system is further configured to determine a wavelength shift of the laser light emitted by the laser from an amount of drift of an absorption spectrum of the reference gas, and to feed back a calibration signal based on the amount of drift to the drive circuit, thereby calibrating the wavelength of the laser light emitted by the laser.
2. The system of claim 1, wherein,
the drive signal is a low-frequency scanning signal superimposed with a high-frequency modulation signal, and
and demodulating the absorption spectrum of the gas to be detected and the absorption spectrum of the reference gas to obtain a second harmonic spectrum of the gas to be detected and a second harmonic spectrum of the reference gas.
3. The system of claim 1 or 2, wherein the wavelength of the laser is swept in a range of 8.89-8.95 microns or 9.04-9.09 microns.
4. The system of claim 1 or 2, wherein the laser is a continuous wave mid-infrared quantum cascade laser.
5. The system of claim 4, wherein the continuous wave mid-infrared quantum cascade laser comprises a distributed feedback or external cavity continuous wave quantum cascade laser.
6. The system of claim 1 or 2, wherein the absorption cell is a long optical path absorption cell such that the optical path of the laser light within the absorption cell is up to 50m.
7. A method of measuring gas flux, comprising:
emitting laser light by a laser and passing the laser light through an absorption cell containing a mixed gas including a gas to be measured and a reference gas, wherein the laser is driven by a driving signal so as to scan and modulate a wavelength of the laser light emitted by the laser, and the gas to be measured and the reference gas each have a characteristic absorption peak in a scanning range of a laser wavelength;
receiving, by a detector, the laser light transmitted through the absorption cell and converting the laser light into an electrical signal representing an intensity of the received laser light; and
receiving the electrical signal output by the detector and extracting the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas based on the electrical signal,
calculating the concentration of the gas to be measured and the concentration of the reference gas from the absorption spectrum of the gas to be measured and the absorption spectrum of the reference gas, respectively, an
Calculating the flux of the gas to be measured according to the calculated concentration of the gas to be measured and the concentration of the reference gas by adopting a vorticity correlation method, correcting the flux of the gas to be measured in real time according to the concentration of the reference gas and WPL correction,
wherein the gas to be measured is ammonia gas, the reference gas is water vapor, and
the method further includes determining a wavelength shift of the laser light emitted by the laser from a drift amount of an absorption spectrum of the reference gas, and feeding back a calibration signal based on the drift amount to the drive circuit, thereby calibrating the wavelength of the laser light emitted by the laser.
8. The method of claim 7, wherein,
the drive signal is a low-frequency scanning signal superposed with a high-frequency modulation signal and is obtained by
And demodulating the absorption spectrum of the gas to be detected and the absorption spectrum of the reference gas to obtain a second harmonic spectrum of the gas to be detected and a second harmonic spectrum of the reference gas.
9. The method of claim 7 or 8, wherein the wavelength of the laser is scanned in a range of 8.89-8.95 microns or 9.04-9.09 microns.
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| CN112229805A (en) * | 2020-09-29 | 2021-01-15 | 苏州迈优医疗科技有限公司 | Medical gas detection system and method |
| CN113406082B (en) * | 2021-06-23 | 2023-07-28 | 湖州师范学院 | Soil carbon flux measurement system |
| CN115290599B (en) * | 2022-10-08 | 2023-01-24 | 青岛镭测创芯科技有限公司 | Laser radar system for measuring concentration of greenhouse gas |
| CN115684081B (en) * | 2023-01-04 | 2023-05-05 | 杭州泽天春来科技有限公司 | Laser gas analysis system |
| CN118501097A (en) * | 2024-07-17 | 2024-08-16 | 宁波海尔欣光电科技有限公司 | Semi-open type atmospheric ammonia concentration detection system and measurement method |
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