CN109270027A - A kind of gas absorptivity On-line Measuring Method based on the fitting of Sine Modulated time domain - Google Patents
A kind of gas absorptivity On-line Measuring Method based on the fitting of Sine Modulated time domain Download PDFInfo
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- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
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- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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Abstract
A kind of gas absorptivity On-line Measuring Method based on the fitting of Sine Modulated time domain, belongs to tunable diode laser absorption spectroscopy (TDLAS) technical field.This method is modulated semiconductor laser with tunable electric current using sinusoidal signal, while realizing laser wavelength Sine Modulated, it is ensured that incident intensity laser intensity (baseline) has clear expression formula；By converting absorptivity between frequency domain and time domain, in conjunction with specific baseline expression formula, baseline on-line measurement synchronous with gas absorptivity is realized by being fitted in the time domain to transmission laser intensity.This method is easy to operate, it efficiently solves traditional directly absorption process (triangle or serrated signal scanning) baseline fitting and is affected by human factors the problems such as big, Optical thin film precision is low, temporal resolution is low, data processing complex, it is contemplated that measurement means can be provided for gas parameter on-line monitoring in line parameters high-precision calibrating, complex industrial scene.
Description
Technical field
The present invention relates to a kind of gas absorptivity On-line Measuring Methods, more particularly to one kind to be based on tunable diode laser
Absorption spectrum directly absorbs the Optical thin film method of law technology, belongs to laser spectrum and gas measurement technique field.
Background technique
T unable filter (Tunable diode laser absorption
Spectroscopy, TDLAS) due to the advantages that its is non-contact, measurement sensitivity is high, strong antijamming capability, it has been developed as
One of high-precision gas parameter diagnosis main means.This method is composed using narrow-band tunable semiconductor laser scanning molecule absorption
Line calculates molecule absorption rate in conjunction with Bill-Lambert (Beer-Lambert) law, so determine gas temperature, concentration,
The information such as pressure, spectral line physical parameter.
TDLAS, which has formed directly to absorb by the development of many years, modulates two kinds of main measurement methods with wavelength.Directly absorb
Method utilize low frequency triangular wave or sawtooch sweep molecular absorption line, by incident light in conjunction with the relationship between transmitted light than
That-Lambert (Beer-Lambert) law directly calculates molecule absorption rate, and clear physics conception is easy to operate；Wavelength tune
Preparation method loads high frequency sinusoidal modulation on the basis of low-frequency sweep, and it is strong that particulate matter, laser in experiment is effectively reduced by harmonic detecting
The noise jammings such as degree fluctuation, have higher sensitivity, and robustness is preferable, have in adverse circumstances such as complex industrial scenes significant excellent
Gesture.Although wavelength modulation method has been obtained extensively using harmonic detecting technique and calibration experiment in terms of gas temperature and measurement of concetration
Concern, but directly absorption process is occupied in TDLAS technology due to the advantages that capable of directly measuring molecule absorption rate, non-calibrating
Critical role.
In direct absorption process, precise measurement incident laser (baseline) intensity is the key that accurate measurement Optical thin film,
Traditional directly absorption process generally uses multinomial to be fitted transmission laser intensity two sides without absorption region, obtains baseline expression
Formula, and then be absorbed rate according to Beer-Lambert law and Calibration of Laser wavelength.There are following problems for this method: (1) by
Higher in bandwidth requirement of the radio-frequency component of triangular wave or sawtooth wave to detection system, scan frequency is usually restricted
100Hz-10kHz seriously constrains the temporal resolution of this method；(2) due to broadening of spectral lines, the interference of adjacent spectral line and laser wave
Factors, the no absorption regions such as long scan range is limited are difficult to obtain in actual measurement, and such as under atmospheric pressure environment, collision broadening is accounted for
Leading factor, even if absorption intensity is about peak there is also certain absorption at ten times from absorption line central wavelength halfwidths
1 the percent of value.Therefore, by the way that without absorbing or absorbing weaker area fitting baseline, there are biggish uncertainties, such as 1%
Under the conditions of (peak value) weak absorbing, 1% baseline fitting error may bring 100% measurement error.
In view of baseline fitting uncertainty bring measurement error, researcher is frequently with following methods to reduce base
Line error: (1) being measured respectively by timesharing without transmission laser intensity when absorbing and having an absorption, will be without the laser measured when absorbing
Intensity is as baseline, the environment that this method is suitable for having closed chamber, as laboratory line parameters are demarcated, but for open space
Measure helpless, such as combustion diagnosis, flue gas analysis；In addition, timesharing measurement can not eliminate the shadow of laser intensity itself fluctuation
It rings, while small variation can also occur for optical path.(2) reference laser intensity is measured by beam splitting and is considered as baseline, the party
Method is suitable for the near-infrared measuring of optical fiber technology maturation, and in infrared free space output laser answered using beam splitting measuring system
It is miscellaneous；In addition, beam splitting measurement easily causes optical path interference, simultaneously because the difference between reference path and optical path to refer to
Light can not strictly represent baseline, and then lead to measurement error.
Summary of the invention
In order to solve the problems such as direct absorption process baseline fitting is uncertain big, temporal resolution is low, the present invention provides one kind
Based on the gas absorptivity On-line Measuring Method of Sine Modulated time domain fitting, to further increase gas Optical thin film precision,
Simplify measurement process.Technical scheme is as follows:
1) its core wavelength v is determined in spectra database for spectral line to be measured0；
2) wave of semiconductor laser with tunable output laser is controlled by adjusting laser controller central current and temperature
It grows in v0Near, the sinusoidal signal that frequency is ω is generated by signal generator, laser controller is inputed to, to modulate laser
The output electric current of controller, and then modulate the wavelength of semiconductor laser with tunable output laser；
3) laser that semiconductor laser with tunable generates is divided into two-way by fiber optic splitter, all the way after collimation
Across gas chamber to be measured, transmission laser intensity is received by the first photodetector；Another way laser injects interferometer, passes through second
Photodetector detects the shoot laser intensity of interferometer, and the first and second photodetectors convert optical signals to electric signal biography
Enter computer 10；
4) semiconductor laser with tunable 3 is enabled to export laser transient wave long are as follows:
To the collected signal of the second photodetector 8, it is fitted to obtain the coefficient in formula (1) using Matlab program
a1,ω,η1,a2,η2；T is detection time in formula,For laser center wavelength, a1、a2It is respectively linear and non-thread
Property wavelength modulation amplitude, η1、η2Respectively linear and nonlinear wavelength phase modulation angle；
5) it enables and is incident on the instantaneous incident laser intensity before gas chamber 5 are as follows:
In formula:For laser intensity average value, i1、i2Respectively linear and nonlinear intensity modulation amplitude, θ1、θ2Respectively
Linear and nonlinear intensity modulation phase angle；
6) according to Bill-Lambert (Beer-Lambert) law, across the instantaneous transmission laser intensity of gas chamber 5 are as follows:
Wherein, α (v) is line absorption rate to be measured, and A is integral area,For spectral line linear function to be measured, Raution is used
Function representation, by spectral line Gauss line width γ to be measuredD, Lorentz line width γLAnd Dick convergence coefficient β is determined；
7) formula (1) and (2) are substituted into formula (3), obtains the pass between instantaneous transmission laser intensity and detection time t
It is formula, the instantaneous transmission that the second photodetector receives is swashed using the FIT function in Matlab program by the relational expression
Luminous intensity is fitted in the time domain, obtains instantaneous incident laser intensity I0, integral area A, spectral line Gauss line width γ to be measuredD, Lip river
Human relations hereby line width γLAnd Dick convergence coefficient β；
8) by spectral line Gauss line width γ to be measuredD, Lorentz line width γLAnd Dick convergence coefficient β is substituted into Raution function,
Calculate spectral line linear function to be measuredIn conjunction with gained integral area A in 7), formula is utilizedCalculate spectrum to be measured
Line absorption rate α (v).
The present invention has the following advantages that and the technical effect of high-lighting: the method for the present invention is directed to traditional triangular wave or sawtooth
Wave modulation direct absorption process there are the problem of, propose it is a kind of based on Sine Modulated time domain fitting Optical thin film method, no
Only be conducive to the raising of modulating frequency, and baseline fitting can be effectively eliminated in traditional directly absorption process by human factor shadow
Sound is big, fitting uncertainty is big, big problem is influenced on Optical thin film result, while this method data processing repeatability is very
Height may be implemented software and automatically process.
Detailed description of the invention
Fig. 1 is gas absorption rate measurement system structure principle chart of the invention.
Fig. 2 is that present invention experiment measures resulting instantaneous transmission laser strength signal and interferometer signal, and passes through dry
The Wavelength calibration result that interferometer signal obtains.
Fig. 3 is the instantaneous incident laser intensity I being fitted in the time domain through the invention0With instantaneous transmission laser intensity
ItAnd instantaneous transmission laser intensity regression criterion.
Fig. 4 is gained absorptivity and Raution Function Optimization fitting result through the invention.
In figure: 1- signal generator；2- laser controller；3- semiconductor laser with tunable；4- optical fiber score device；5- gas
Room；The first photodetector of 6-；7- interferometer；The second photodetector of 8-；9- oscillograph；10- computer.
Specific embodiment
The present invention will be further described below with reference to the drawings.
Fig. 1 be gas absorption rate measurement system structure principle chart of the invention, the measuring system include signal generator 1,
Laser controller 2, semiconductor laser with tunable 3, optical fiber score device 4, gas chamber 5, the first photodetector 6, interferometer 7,
Two photodetectors 8, oscillograph 9 and computer 10.Signal generator 1 generates the sinusoidal signal that frequency is ω, inputs to laser
Controller 2 to modulate the output electric current of laser controller 2, and then modulates the wave that semiconductor laser with tunable 3 exports laser
It is long；Laser that semiconductor laser with tunable 3 generates is divided by fiber optic splitter 4 for two-way, is passed through after collimation all the way
Gas chamber 5 receives transmission laser intensity by the first photodetector 6；Another way laser injects interferometer 7), pass through the second photoelectricity
Detector 8 detects the shoot laser intensity of interferometer 7, and the first and second photodetectors convert optical signals to electric signal through showing
Computer 10 is passed to after wave device 9.
Based on above-mentioned measuring system, the present invention provides a kind of gas absorptivity on-line measurement side based on laser absorption spectrum
Method, this method include following steps:
1) its core wavelength v is determined in spectra database for spectral line to be measured0；
2) it controls semiconductor laser with tunable 3 by adjusting 2 central current of laser controller and temperature and exports laser
Wavelength is in v0Near, the sinusoidal signal that frequency is ω is generated by signal generator 1, laser controller 2 is inputed to, to modulate
The output electric current of laser controller 2, and then modulate the wavelength that semiconductor laser with tunable 3 exports laser；
3) laser that semiconductor laser with tunable 3 generates is divided by fiber optic splitter 4 for two-way, all the way by collimation
Gas chamber 5 to be measured is passed through afterwards, and transmission laser intensity is received by the first photodetector 6；Another way laser injects interferometer 7, leads to
The shoot laser intensity of the second photodetector 8 detection interferometer 7 is crossed, the first and second detectors convert optical signals to telecommunications
Number incoming computer 10；Shown in the signal that second photodetector 8 detects such as Fig. 2 " "；" o " is Wavelength calibration point in Fig. 2,
Its coordinate is defined as follows: each time to peak of Fig. 2 " " being denoted as to the abscissa of Wavelength calibration point, certainly according to experiment interferometer used
The ordinate of each Wavelength calibration point, i.e. relative wavelength are successively defined as 1 × FSR, 2 × FSR ... by spectral regions FSR value,
(n-1) × FSR, n × FSR, (n-1) × FSR ..., 2 × FSR, 1 × FSR, wherein n be half period in " " number, when
M- relative wavelength coordinate takes out lower each wavelength points of drafting, as shown in " o " in Fig. 2；
4) semiconductor laser with tunable 3 is enabled to export laser transient wave long are as follows:
T is detection time in formula,For laser center wavelength, a1, a2Respectively linear and nonlinear wavelength modulation amplitude,
η1, η2Respectively linear and nonlinear wavelength phase modulation angle utilizes the fitting of Matlab program for the Wavelength calibration point in 3)
Obtain the coefficient in formula (1)a1,ω,η1,a2,η2；
5) it enables and is incident on the instantaneous incident laser intensity before gas chamber 5 are as follows:
In formulaFor laser intensity average value, i1、i2Respectively linear and nonlinear intensity modulation amplitude, θ1、θ2Respectively line
Property and non-linear intensity modulation phase angle；
6) according to Bill-Lambert (Beer-Lambert) law, across the instantaneous transmission laser intensity of gas chamber 5 are as follows:
Wherein, α (v) is line absorption rate to be measured, and A is integral area,For spectral line linear function to be measured, Raution is used
Function representation, is defined as:
By spectral line Gauss line width γ to be measuredD, Lorentz line width γLAnd Dick convergence coefficient β is determined；X, y, z are intermediate changes
Amount, k is integrated form variable；Spectral line linear function to be measured except using in addition to Raution, also can be used Fu Yite (Voigt) and
Galatry function representation；
7) formula (1) and (2) are substituted into formula (3), obtains the pass between instantaneous transmission laser intensity and detection time t
It is formula, instantaneous transmission laser intensity is by I0、γD、γL, β and A determine, pass through the FIT letter in Matlab program using the relational expression
It is several that the instantaneous transmission laser intensity that second photodetector 8 receives is fitted in the time domain, obtain instantaneous incident laser
Intensity I0, integral area A, spectral line Gauss line width γ to be measuredD, Lorentz line width γLAnd Dick convergence coefficient β；
8) by spectral line Gauss line width γ to be measuredD, Lorentz line width γLAnd Dick convergence coefficient β substitutes into formula (4) Raution
In function, spectral line linear function to be measured is calculatedIn conjunction with gained integral area A in 7), formula is utilizedIt calculates
Line absorption rate α (v) to be measured.
Embodiment:
1) embodiment measures its absorptivity, its center is chosen from spectra database by taking R (11) spectral line for measuring CO as an example
Wavelength v0=4300.699cm-1；
2) by adjusting 32.07 DEG C of control semiconductor laser with tunable of 2 central current 100mA of laser controller and temperature
The wavelength of 3 output laser is in wavelength v0=4300.699cm-1Near, frequencies omega=2 × π × 100 are generated by signal generator
Sinusoidal signal, input to laser controller 2, to modulate the output electric current of laser controller 2, and then modulate and tunable partly lead
The wavelength of the output laser of body laser 3；
3) laser that semiconductor laser with tunable 3 generates is divided by fiber optic splitter 4 for two-way, all the way by collimation
Gas chamber 5 to be measured is passed through afterwards, and transmission laser intensity is received by the first photodetector 6；Another way laser injects interferometer 7, leads to
The shoot laser intensity of the second photodetector 8 detection interferometer 7 is crossed, the first and second detectors convert optical signals to telecommunications
Number incoming computer 10；Experiment gained interferometer signal and instantaneous transmission laser strength signal respectively as in Fig. 2 " " and
Shown in " ▲ ", " o " is Wavelength calibration point in Fig. 2；" " each time to peak is denoted as to the abscissa of Wavelength calibration point, due to selected
Interferometer free spectral range (FSR) is 0.05cm-1, each Wavelength calibration point ordinate is successively defined as 0.05,0.1,
0.15 ..., 1.15,1.2,1.15 ... 0.1,0.05, when m- relative wavelength coordinate take out under draw each Wavelength calibration point, such as scheme
In 2 shown in " o "；
4) semiconductor laser with tunable 3 is enabled to export laser transient wave long are as follows:
T is detection time in formula,For laser center wavelength, a1, a1For linear and nonlinear wavelength modulation amplitude, η1, η2
It is fitted for Wavelength calibration point shown in Fig. 2 " o " using Matlab program for linear and nonlinear wavelength phase modulation angle
To the coefficient in formula (1)a1=0.598, η1=0.421 π, a2=-0.138, η2=0.082 π, fitting result
As shown in Fig. 2 solid black lines, wavelength regression criterion is as shown in below Fig. 2；
5) it enables and is incident on the instantaneous incident laser intensity before gas chamber 5 are as follows:
In formulaFor laser intensity average value, i1、i2Respectively linear and nonlinear intensity modulation amplitude, θ1、θ2Respectively
Linear and nonlinear intensity modulation phase angle；
6) according to Bill-Lambert (Beer-Lambert) law, across the instantaneous transmission laser intensity of gas chamber 5 are as follows:
Wherein, α (v) is line absorption rate to be measured, and A is integral area,For spectral line linear function to be measured, Raution is used
Function representation；
7) formula (1) and (2) are substituted into formula (3), obtains the pass between instantaneous transmission laser intensity and detection time t
It is formula, instantaneous transmission laser intensity is by I0、γD、γL, β and A determine, pass through the FIT letter in Matlab program using the relational expression
It is several that the instantaneous transmission laser intensity that second photodetector 8 receives is fitted in the time domain, obtain integral area A=
0.0361, spectral line Gauss line width γ to be measuredD=5.0 × 10-3cm-1, Lorentz line width γL=5.77 × 10-3cm-1And Dick is received
Hold back factor beta=0.02, instantaneous incident laser intensity
I0=1.635+0.2798cos (2 π × 100t+1.379 π) -0.00847cos [(4 π × 100t+0.885 π)]；Its
Middle optimal fitting I0And ItAs shown in figure 3, being wherein instantaneous transmission laser intensity regression criterion below Fig. 3；
8) by spectral line Gauss line width γ to be measuredD, Lorentz line width γLAnd Dick convergence coefficient β substitutes into formula (4) Raution
In function, spectral line linear function to be measured is calculatedIn conjunction with gained integral area A in 7), formula is utilizedMeter
Line absorption rate α (v) to be measured is calculated, as shown in Figure 4.
Claims (1)
1. a kind of gas absorptivity On-line Measuring Method based on the fitting of Sine Modulated time domain, it is characterized in that this method includes as follows
Step:
1) its core wavelength v is determined in spectra database for spectral line to be measured0；
2) laser is exported by adjusting laser controller (2) central current and temperature control semiconductor laser with tunable (3)
Wavelength is in v0Near, the sinusoidal signal that frequency is ω is generated by signal generator (1), inputs to laser controller (2), to
The output electric current of laser controller (2) is modulated, and then modulates the wavelength of semiconductor laser with tunable (3) output laser；
3) laser that semiconductor laser with tunable (3) generate is divided into two-way by fiber optic splitter (4), all the way by collimation
Gas chamber to be measured (5) are passed through afterwards, receive transmission laser intensity by the first photodetector (6)；Another way laser injects interferometer
(7), by the shoot laser intensity of the second photodetector (8) detection interferometer (7), the first and second photodetectors are by light
Signal is converted to electric signal and is passed to computer (10)；
4) enable semiconductor laser with tunable (3) output laser transient wave long are as follows:
To the second photodetector (8) collected signal, it is fitted to obtain the coefficient in formula (1) using Matlab programa1,
ω,η1,a2,η2；Wherein t is detection time,For laser center wavelength, a1、a2Respectively linear and nonlinear wavelength modulated amplitude
Value, η1、η2Respectively linear and nonlinear wavelength phase modulation angle；
5) it enables and is incident on the instantaneous incident laser intensity before gas chamber (5) are as follows:
In formula:For laser intensity average value, i1、i2Respectively linear and nonlinear intensity modulation amplitude, θ1、θ2It is respectively linear
With non-linear intensity modulation phase angle；
6) according to Beer Lambert law, the instantaneous transmission laser intensity of gas chamber (5) is passed through are as follows:
In formula: α (v) is line absorption rate to be measured, and A is integral area,For spectral line linear function to be measured, with Raution function
It indicates, by spectral line Gauss line width γ to be measuredD, Lorentz line width γLAnd Dick convergence coefficient β is determined；
7) formula (1) and (2) are substituted into formula (3), obtains the relationship between instantaneous transmission laser intensity and detection time t
Formula swashs the instantaneous transmission that the second photodetector (8) receives using the FIT function in Matlab program by the relational expression
Luminous intensity is fitted in the time domain, obtains instantaneous incident laser intensity I0, integral area A, spectral line Gauss line width γ to be measuredD, Lip river
Human relations hereby line width γLAnd Dick convergence coefficient β；
8) by spectral line Gauss line width γ to be measuredD, Lorentz line width γLAnd Dick convergence coefficient β is substituted into Raution function, is calculated
Spectral line linear function to be measuredIn conjunction with gained integral area A in 7), formula is utilizedSpectral line to be measured is calculated to inhale
Yield α (v).
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| CN109991189A (en) * | 2019-04-04 | 2019-07-09 | 东南大学 | A kind of fixed point wavelength modulation gas concentration measuring apparatus and its measurement method based on wave number drift correction |
| CN111122496A (en) * | 2019-12-20 | 2020-05-08 | 清华大学 | Calibration-free gas concentration measuring device and method |
| CN112461785A (en) * | 2020-09-30 | 2021-03-09 | 北京工业大学 | Aviation oxygen monitoring system based on TDLAS combined Fabry-Perot optical chamber |
| CN113612859A (en) * | 2021-09-18 | 2021-11-05 | 中国科学院长春光学精密机械与物理研究所 | Mine environment monitoring system and monitoring method thereof |
| CN113899703A (en) * | 2021-09-29 | 2022-01-07 | 安徽农业大学 | Linear broadening eliminating method under wavelength deviation |
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109991189A (en) * | 2019-04-04 | 2019-07-09 | 东南大学 | A kind of fixed point wavelength modulation gas concentration measuring apparatus and its measurement method based on wave number drift correction |
| CN109991189B (en) * | 2019-04-04 | 2021-09-28 | 东南大学 | Fixed point wavelength modulation gas concentration measuring device based on wave number drift correction and measuring method thereof |
| CN111122496A (en) * | 2019-12-20 | 2020-05-08 | 清华大学 | Calibration-free gas concentration measuring device and method |
| CN111122496B (en) * | 2019-12-20 | 2021-03-23 | 清华大学 | Calibration-free gas concentration measuring device and method |
| CN112461785A (en) * | 2020-09-30 | 2021-03-09 | 北京工业大学 | Aviation oxygen monitoring system based on TDLAS combined Fabry-Perot optical chamber |
| CN113612859A (en) * | 2021-09-18 | 2021-11-05 | 中国科学院长春光学精密机械与物理研究所 | Mine environment monitoring system and monitoring method thereof |
| CN113899703A (en) * | 2021-09-29 | 2022-01-07 | 安徽农业大学 | Linear broadening eliminating method under wavelength deviation |
| CN113899703B (en) * | 2021-09-29 | 2022-07-05 | 安徽农业大学 | Linear broadening eliminating method under wavelength deviation |
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