CN115993346A - Atmospheric quality monitoring method and system based on TDLAS and temperature compensation - Google Patents
Atmospheric quality monitoring method and system based on TDLAS and temperature compensation Download PDFInfo
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- 238000012544 monitoring process Methods 0.000 title claims abstract description 35
- 238000000034 method Methods 0.000 title claims abstract description 30
- 238000000041 tunable diode laser absorption spectroscopy Methods 0.000 title claims abstract 12
- 238000010521 absorption reaction Methods 0.000 claims abstract description 22
- 238000012937 correction Methods 0.000 claims abstract description 17
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- NAWXUBYGYWOOIX-SFHVURJKSA-N (2s)-2-[[4-[2-(2,4-diaminoquinazolin-6-yl)ethyl]benzoyl]amino]-4-methylidenepentanedioic acid Chemical compound C1=CC2=NC(N)=NC(N)=C2C=C1CCC1=CC=C(C(=O)N[C@@H](CC(=C)C(O)=O)C(O)=O)C=C1 NAWXUBYGYWOOIX-SFHVURJKSA-N 0.000 description 1
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Abstract
The invention provides an atmosphere quality monitoring method and system based on TDLAS and temperature compensation, which relate to the technical field of gas quality monitoring and comprise the steps of collecting a low-frequency sawtooth signal continuously emitted by a signal generator in gas to be detected; the low-frequency sawtooth signal is overlapped with a high-frequency sinusoidal signal, a semiconductor laser is driven, and scanning of laser wavelength near the center of a gas absorption spectrum line is achieved; extracting gas to be detected to fill the gas chamber, scanning the gas chamber to be detected, focusing after gas absorption, and extracting second harmonic peak-to-peak information after pre-amplification; and constructing a mathematical model of harmonic signals and temperature, selecting a secondary function for fitting, and carrying the measured second harmonic peak values at each temperature into a quadratic polynomial fitting equation for temperature correction to obtain corrected gas concentration values. The method is simple in algorithm and high in data processing efficiency. The adaptability of the monitoring equipment on the vehicle-mounted application is enhanced.
Description
Technical Field
The disclosure relates to the technical field of gas quality monitoring, in particular to an atmosphere quality monitoring method and system based on tunable semiconductor laser absorption spectroscopy (TDLAS) and temperature compensation.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The vehicle-mounted gas detection device is an atmosphere quality monitoring device which is used for installing the monitoring device on a motor vehicle and realizing navigation monitoring along with the running of the vehicle, can be used for measuring the content of specific gas in the atmosphere in real time and is usually applied to an environment monitoring station for measuring the average air quality in a local area.
Because the working environment of the detection equipment is complex and changeable, the temperature can be changed in a huge variety along with the different application scenes, regions and time. The change of the ambient temperature during the operation of the device directly affects the measurement of the concentration by the monitoring device, so that the existing vehicle-mounted gas detection device on the market has the defect of low precision generally, and the gas concentration measurement error caused by the change of the external inlet air temperature during the operation of the vehicle-mounted gas detection device is overlarge, so that the atmospheric monitoring precision has larger error and the overall monitoring effect is affected.
Disclosure of Invention
In order to solve the problems, the method and the system for monitoring the air quality based on TDLAS and temperature compensation are provided, the characteristics of harmonic signals of a tunable semiconductor laser absorption spectrum are analyzed, a mathematical model of the harmonic signals and the temperature is established, interference caused by environmental temperature change to a detection result is restrained, and high-sensitivity real-time monitoring of certain gases in the air is realized.
According to some embodiments, the present disclosure employs the following technical solutions:
the atmosphere quality monitoring method based on TDLAS and temperature compensation comprises the following steps:
collecting low-frequency sawtooth signals continuously emitted by a signal generator in the gas to be detected;
the low-frequency sawtooth signal is overlapped with a high-frequency sinusoidal signal, a semiconductor laser is driven, and scanning of laser wavelength near the center of a gas absorption spectrum line is achieved;
extracting gas to be detected to fill the gas chamber, scanning the gas chamber to be detected, focusing after gas absorption, and extracting second harmonic peak-to-peak information after pre-amplification; and constructing a mathematical model of harmonic signals and temperature, selecting a secondary function for fitting, and carrying the measured second harmonic peak values at each temperature into a quadratic polynomial fitting equation for temperature correction to obtain corrected gas concentration values.
According to some embodiments, the present disclosure employs the following technical solutions:
an atmospheric quality monitoring system based on TDLAS and temperature compensation, comprising:
the signal acquisition module is used for acquiring a low-frequency sawtooth signal continuously emitted by the signal generator in the gas to be detected; the low-frequency sawtooth signal is overlapped with a high-frequency sinusoidal signal to drive the laser to send out a signal in the gas to be detected, and the absorption peak of the gas is continuously scanned;
the signal processing module is used for extracting gas to be detected to fill the gas chamber, scanning the gas chamber to be detected, focusing the gas after the gas is absorbed, and extracting second harmonic peak-peak information after the gas is amplified in advance;
the temperature correction module is used for temperature compensation, a mathematical model of harmonic signals and temperature is constructed, a quadratic function is selected to be used for fitting, and a second harmonic peak value measured at each temperature is brought into a quadratic polynomial fitting equation to carry out temperature correction, so that a corrected gas concentration value is obtained.
According to some embodiments, the present disclosure employs the following technical solutions:
a computer readable storage medium having stored therein a plurality of instructions adapted to be loaded by a processor of a terminal device and to perform the TDLAS and temperature compensation based atmospheric quality monitoring method.
According to some embodiments, the present disclosure employs the following technical solutions:
a terminal device comprising a processor and a computer readable storage medium, the processor configured to implement instructions; the computer readable storage medium is for storing a plurality of instructions adapted to be loaded by a processor and to perform the TDLAS and temperature compensation based atmospheric quality monitoring method.
Compared with the prior art, the beneficial effects of the present disclosure are:
the temperature compensation is utilized, the compensation effect is obvious, the measurement error of the system is reduced within 3%, and the accuracy of measuring the gas concentration of the TDLAS sensor in practical environment application is improved. The algorithm is simple, and the data processing efficiency is high. The adaptability of the monitoring equipment on the vehicle-mounted application is enhanced.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate and explain the exemplary embodiments of the disclosure and together with the description serve to explain the disclosure, and do not constitute an undue limitation on the disclosure.
FIG. 1 is a flowchart of a method overall process according to an embodiment of the present disclosure;
FIG. 2 is a graph of a fit of the results of a 1000ppm CH4 standard gas temperature variation experiment in an embodiment of the present disclosure;
FIG. 3 is a graph showing concentration values after compensation in a 1000ppm CH4 standard gas temperature variation experiment in accordance with an embodiment of the present disclosure;
FIG. 4 is a graph of the absorption spectra of methane at 1.33 μm and 1.66 μm for the examples of the present disclosure.
The specific embodiment is as follows:
the disclosure is further described below with reference to the drawings and examples.
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments in accordance with the present disclosure. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Example 1
An embodiment of the present disclosure provides an atmospheric quality monitoring method based on TDLAS and temperature compensation, including:
collecting low-frequency sawtooth signals continuously emitted by a signal generator in the gas to be detected;
the low-frequency sawtooth signal is overlapped with a high-frequency sinusoidal signal, a semiconductor laser is driven, and scanning of laser wavelength near the center of a gas absorption spectrum line is achieved;
extracting gas to be detected to fill the gas chamber, scanning the gas chamber to be detected, focusing after gas absorption, and extracting second harmonic peak-to-peak information after pre-amplification; and constructing a mathematical model of harmonic signals and temperature, selecting a secondary function for fitting, and carrying the measured second harmonic peak values at each temperature into a quadratic polynomial fitting equation for temperature correction to obtain corrected gas concentration values.
As an example, when the gas to be measured is CH 4 The monitoring method comprises the following steps:
firstly, a signal generator sends out sawtooth waves, and then a high-frequency sinusoidal signal is superimposed to enable a laser to work, so that an absorption peak of gas to be detected is scanned. The gas outlet is connected with a gas pump to pump gas to fill the gas chamber, the emergent light enters the gas chamber to be detected after passing through the collimator, laser is focused and transmitted into the photoelectric detector after being absorbed by the gas, the required frequency is selectively extracted by the phase-locked amplifier after being amplified, and data processing is carried out on the microprocessor.
1000ppm methane gas is sealed in a thermal cycle chamber, the temperature of a temperature cycle test box is controlled, and the application scene that the temperature of the interior of a cruising vehicle is constant when the cruising vehicle works and the temperature of the external environment changes is simulated. And a methane bag in the thermal cycle chamber is led out of the temperature cycle test box through a soft air pipe and is connected into a system at room temperature. By adjusting the internal temperature of the incubator, the experimental temperature ranges from 233K to 343K, and the test temperature point per 10K is set. After each temperature point was stable for 10 minutes, a constant temperature test was started for one hour. The PC records the second harmonic peak-peak information processed by the system microprocessor module, then carries out average processing on the measured second harmonic peak-peak information, and simultaneously collects the second harmonic waveforms at different temperatures from the host. As the ambient temperature increases, the second harmonic peak-to-peak value tested by the monitoring system gradually decreases, which requires temperature compensation of the entire waveform.
As an embodiment, the gas detection method of the TDLAS technology includes:
from Lambert-Beer law, when the frequency is v, the intensity is I 0 The single-color laser of (2) passes through a methane gas tank filled with a certain concentration, and the output light intensity can be written as
Wherein α (v) is expressed as molar absorption coefficient, unit: square centimeter per mole (cm) 2 ·mol -1 ) P is expressed as gas pressure, unit: atm, L represents the optical length, unit: cm, C represents the concentration of the gas to be measured, unit: mol cm -3 ·atm -1 . In the near infrared band, the absorption coefficient of the gas is very small, and when the gas absorption light path is short or the gas concentration is low, alpha (v) CL < 1 is generally satisfied, and the formula (1) can be rewritten as:
I(v)＝I 0 (v)[1-α(v)PCL] (2)
α(v)＝S(T)g(v，v 0 ) (3)
wherein S (T) is the spectrum intensity at a certain temperature, unit: atm of (1) -1 ·cm -2 ，g(v，v 0 ) Represented as a gas line linear absorption function. The combination of the formulas (1) (2) can be obtained:
I(v)＝I 0 (v)[1-S(T)g(v，v 0 )PCL] (4)
the system environment is mainly collisional broadening under normal pressure experimental conditions, so that the Lorentzian line type can be used for fitting.
The lorentz line type is caused by the mutual collision between particles, and depends not only on the pressure P, but also on the collision cross section of molecules, and the function expression is as follows:
wherein Deltav C The full line width of the linear function is calculated as follows:
wherein, gamma and P are the pressure broadening coefficient and pressure of the gas to be detected, n isTemperature coefficient, gamma i And P i Expressed as the pressure broadening coefficient and the pressure of the impinging gas, respectively.
In order to improve the detection precision and sensitivity, a Wavelength Modulation Spectroscopy (WMS) technology is adopted, a high-frequency sinusoidal current signal is superimposed with a low-frequency sawtooth current signal, a semiconductor laser is driven, the laser wavelength is scanned near the center of a gas absorption spectrum line, the light source frequency and the output light intensity are correspondingly modulated, and the power v of the light source of the laser is:
v＝v 0 +v m cos2πft (7)
wherein v is 0 For the laser centre frequency, v m For modulation amplitude, f is frequency and t is time. In order to eliminate the influence of light intensity, the second harmonic wave of gas absorption is obtained by demodulating the second harmonic wave by using frequency doubling of a modulation signal, the formula (4) is subjected to Fourier expansion, and the second harmonic wave signal is in direct proportion to the concentration of the measured gas, namely:
I 2f ∝I 0 (v)S(T)g(v)PCL (8)
the test result shows that the amplitude of the second harmonic has obvious linear relation with the temperature change, the second harmonic peak value measured at each temperature is carried into a quadratic polynomial fitting equation by selecting a quadratic function for fitting, and the parameter A, B, C is obtained.
And temperature correction is performed by the formula (10)
To ensure T 0 The reliability of the gas concentration to be measured at the moment is selected as a constant T by 293K 0 Carry-in (10), N mea For the uncorrected gas concentration, all the concentrations after that are calibrated by the formula to obtain corrected concentration values
CH 4 The absorption peak wavelengths of the gas in the near infrared band are 1330nm and 1650nm, respectively, and FIG. 4 shows the absorption spectra of methane in the 1.33 μm and 1.66 μm regions, CH 4 The absorption intensity of the gas at 1650nm is not only an order of magnitude higher than that of 1330nm wave band, but also the interference of water vapor on gas detection can be eliminated, so that CH is selected 4 The absorption line of the gas at 1650nm was used as a characteristic absorption line for gas concentration inversion.
According to the HITRAN2008 database (the HITRAN2008molecular spectroscopic database), line intensity is a function of temperature; thus, CH 4 The estimation of gas concentration requires knowledge of CH 4 Gas temperature of the gas. The experiment simulates the temperature change from 233 to 343K, as this corresponds to the ambient temperature change, and FIG. 2 shows that the amplitude of the second harmonic has a significant linear relationship with temperature change. Thus, a function is used to fit, as shown in the following equation.
(11) In the method, in the process of the invention,
is CH 4 Is strong, T is CH 4 The temperature of the gas. The second harmonic peak values measured at each temperature are brought into a quadratic polynomial fit equation to obtain a=640.8691, b=4.8487, c= -0.0114, thus the quadratic polynomial fit equation and CH are in the temperature range of 233-343K 4 The second harmonic peak variation has a good fit. It can be seen that this equation is in the temperature range of 233-243K and CH 4 The correlation of the actual concentration is very good, and the equation (12) can be fully utilized for CH 4 The gas undergoes temperature correction. Will->
NL brings in (7) to get +.>
(12) Wherein I is 0 For initial intensity, T is the temperature of the molecule being measured, g (v) is a linear function, N is the absorption number concentration, and L is the optical path. If in a closed vessel, when the temperature is changed, the pressure is changed and causes line broadening, g (v) is changed. Let the initial measured temperature be T 0 Concentration before correction is N mea ，
Corrected methane concentration, then CH 4 The empirical formula of the concentration temperature correction is that
To ensure T 0 The reliability of the gas concentration to be measured at the moment is selected as a constant T by 293K 0 Bringing into equation (13), all concentrations thereafter are calibrated by the equation to obtain corrected concentration values. By CH at normal temperature 4 The temperature compensation experiments of 233 to 343K were performed by the formula (13) with the gas concentration of 1080ppm as a true value. The curve fitting the normalized concentration with temperature is shown in fig. 2 below.
Methane gas with concentration of 1000ppm is measured at different temperatures, the collected second harmonic wave is subjected to data pretreatment to obtain a corresponding second harmonic wave peak value, and the corresponding second harmonic wave peak value is substituted into a corresponding conventional concentration inversion and temperature parameter prediction database, and the obtained measured value and relative error are shown in table 1.
TABLE 1 concentration detection data and analysis at different temperatures
The experimental result shows that the compensation effect of the temperature compensation algorithm is obvious, the relative error of the temperature compensation algorithm is reduced compared with the uncompensated concentration, the amplitude of the second harmonic signal and the concentration of methane in the concentration range show a good linear relation, and the experimental scheme can eliminate the influence of temperature fluctuation and realize trace methane gas concentration detection.
Example 2
In one embodiment of the present disclosure, an atmospheric quality monitoring system based on TDLAS and temperature compensation is provided, comprising:
the signal acquisition module is used for acquiring a low-frequency sawtooth signal continuously emitted by the signal generator in the gas to be detected; the low-frequency sawtooth signal is overlapped with a high-frequency sinusoidal signal to drive the laser to send out a signal in the gas to be detected, and the absorption peak of the gas is continuously scanned;
the signal processing module is used for extracting gas to be detected to fill the gas chamber, scanning the gas chamber to be detected, focusing the gas after the gas is absorbed, and extracting second harmonic peak-peak information after the gas is amplified in advance;
the temperature correction module is used for temperature compensation, a mathematical model of harmonic signals and temperature is constructed, a quadratic function is selected to be used for fitting, and a second harmonic peak value measured at each temperature is brought into a quadratic polynomial fitting equation to carry out temperature correction, so that a corrected gas concentration value is obtained.
The signal acquisition module comprises a laser, the signal processing module comprises a photoelectric detector, a pre-amplifying circuit, a lock-in amplifier and a temperature correction module comprises a microcontroller. Firstly, a signal generator sends out sawtooth waves to enable a laser to work, and then a high-frequency sinusoidal signal is overlapped to scan an absorption peak of gas to be detected so as to generate harmonic signals. The gas outlet is connected with a gas pump to pump gas to fill the gas chamber, the emergent light enters the gas chamber to be detected after passing through the collimator, laser is focused and transmitted into the photoelectric detector after being absorbed by the gas, the required frequency is selectively extracted by the phase-locked amplifier after being amplified, and data processing is carried out on the microprocessor.
1000ppm methane gas is sealed in a thermal cycle chamber, the temperature of a temperature cycle test box is controlled, and the application scene that the temperature of the interior of a cruising vehicle is constant when the cruising vehicle works and the temperature of the external environment changes is simulated. And a methane bag in the thermal cycle chamber is led out of the temperature cycle test box through a soft air pipe and is connected into a system at room temperature. By adjusting the internal temperature of the incubator, the experimental temperature ranges from 233K to 343K, and the test temperature point per 10K is set. After each temperature point was stable for 10 minutes, a constant temperature test was started for one hour. The PC records the second harmonic peak-peak information processed by the system microprocessor module, then carries out average processing on the measured second harmonic peak-peak information, and simultaneously collects the second harmonic waveforms at different temperatures from the host. As the ambient temperature increases, the peak-to-peak value of the second harmonic wave detected by the monitoring system gradually decreases, and the temperature compensation of the whole waveform is required.
Example 3
In one embodiment of the present disclosure, a computer readable storage medium is provided in which a plurality of instructions are stored, the instructions being adapted to be loaded by a processor of a terminal device and to perform the TDLAS and temperature compensation based atmospheric quality monitoring method.
Example 4
In one embodiment of the disclosure, a terminal device is provided, including a processor and a computer readable storage medium, where the processor is configured to implement instructions; the computer readable storage medium is for storing a plurality of instructions adapted to be loaded by a processor and to perform the TDLAS and temperature compensation based atmospheric quality monitoring method.
The present disclosure is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the disclosure. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While the specific embodiments of the present disclosure have been described above with reference to the drawings, it should be understood that the present disclosure is not limited to the embodiments, and that various modifications and changes can be made by one skilled in the art without inventive effort on the basis of the technical solutions of the present disclosure while remaining within the scope of the present disclosure.
Claims (10)
1. The atmosphere quality monitoring method based on TDLAS and temperature compensation is characterized by comprising the following steps:
collecting low-frequency sawtooth signals continuously emitted by a signal generator in the gas to be detected;
the low-frequency sawtooth signal is overlapped with a high-frequency sinusoidal signal, a semiconductor laser is driven, and scanning of laser wavelength near the center of a gas absorption spectrum line is achieved;
extracting gas to be detected to fill the gas chamber, scanning the gas chamber to be detected, focusing after gas absorption, and extracting second harmonic peak-to-peak information after pre-amplification; and constructing a mathematical model of harmonic signals and temperature, selecting a secondary function for fitting, and carrying the measured second harmonic peak values at each temperature into a quadratic polynomial fitting equation for temperature correction to obtain corrected gas concentration values.
2. The method for monitoring the atmospheric quality based on TDLAS and temperature compensation according to claim 1, wherein the mode of generating the harmonic signal by superposing the low frequency sawtooth signal with a high frequency sinusoidal signal is as follows: the wavelength modulation spectrum technology is adopted, and a high-frequency sinusoidal current signal is overlapped with a low-frequency sawtooth current signal to drive a semiconductor laser, so that the laser wavelength scans near the center of a gas absorption spectrum line.
3. The TDLAS and temperature compensation based atmosphere quality monitoring method of claim 1, wherein the process of selectively extracting second harmonic peak-to-peak information after focusing through gas absorption and pre-amplification comprises: and (3) selecting an absorption spectrum line of the gas to be detected at a set value as a characteristic absorption line, and reflecting the concentration value of the gas to be detected by using a second harmonic signal of the gas to be detected and the gas concentration in direct proportion through a second harmonic peak-to-peak value.
4. The method for monitoring the atmospheric quality based on TDLAS and temperature compensation according to claim 1, wherein the process of constructing a mathematical model of harmonic signals and temperature, selecting a quadratic function for fitting, and bringing the measured second harmonic peak values at each temperature into a quadratic polynomial fitting equation for temperature correction, and obtaining corrected gas concentration values is as follows: firstly, sealing the gas to be tested in a thermal cycle chamber, controlling the temperature of a temperature cycle test box, controlling the upper and lower limit values of the temperature by adjusting the internal temperature of the test box, setting test temperature points, and starting constant-temperature test after each temperature point is stable for a certain time.
5. The method for monitoring the atmospheric quality based on TDLAS and temperature compensation according to claim 4, wherein Lorentz line type is used as the absorption line type of the gas, and the influence of the pressure broadening coefficient and the pressure of the gas to be measured is analyzed.
6. The TDLAS and temperature compensation based atmosphere quality monitoring method of claim 4 wherein second harmonic peak-to-peak information is obtained, the measured second harmonic peak-to-peak information is averaged, and at the same time, second harmonic waveforms at different temperatures are collected.
7. The TDLAS and temperature compensation based atmosphere quality monitoring method of claim 6 wherein the amplitude of the second harmonic varies with temperature, has a linear relationship, chooses to fit using a quadratic function, and brings the measured second harmonic peaks at each temperature into a quadratic polynomial fit equation, obtains parameters, and performs temperature correction.
8. Atmospheric quality monitoring system based on TDLAS and temperature compensation, characterized by comprising:
the signal acquisition module is used for acquiring a low-frequency sawtooth signal continuously emitted by the signal generator in the gas to be detected; the low-frequency sawtooth signal is overlapped with a high-frequency sinusoidal signal to drive the laser to send out a signal in the gas to be detected, and the absorption peak of the gas is continuously scanned;
the signal processing module is used for extracting gas to be detected to fill the gas chamber, scanning the gas chamber to be detected, focusing the gas after the gas is absorbed, and extracting second harmonic peak-peak information after the gas is amplified in advance;
the temperature correction module is used for temperature compensation, a mathematical model of harmonic signals and temperature is constructed, a quadratic function is selected to be used for fitting, and a second harmonic peak value measured at each temperature is brought into a quadratic polynomial fitting equation to carry out temperature correction, so that a corrected gas concentration value is obtained.
9. A computer readable storage medium, characterized in that a plurality of instructions are stored, which instructions are adapted to be loaded by a processor of a terminal device and to perform the TDLAS and temperature compensation based atmospheric quality monitoring method of any one of claims 1-7.
10. A terminal device comprising a processor and a computer readable storage medium, the processor configured to implement instructions; a computer readable storage medium for storing a plurality of instructions adapted to be loaded by a processor and to perform the TDLAS and temperature compensation based atmospheric quality monitoring method of any one of claims 1-7.
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