CN105067564B - A kind of optical fiber gas concentration detection method with temperature compensation capability - Google Patents

A kind of optical fiber gas concentration detection method with temperature compensation capability Download PDF

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CN105067564B
CN105067564B CN201510413838.8A CN201510413838A CN105067564B CN 105067564 B CN105067564 B CN 105067564B CN 201510413838 A CN201510413838 A CN 201510413838A CN 105067564 B CN105067564 B CN 105067564B
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temperature
gas
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detection
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CN105067564A (en
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阎毓杰
王楠
陈佳
耿伟智
杨云涛
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719th Research Institute of CSIC
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Abstract

The present invention provides a kind of optical fiber gas concentration detection method with temperature compensation capability, and process is:One, laser produces the optical signal that two centre wavelengths are λ 1 and λ 2;Two, optical signal is divided into after two beams after being transmitted through optical fiber by optical splitter, passes through the reference gas chamber and the detection air chamber for the under test gas that is stored with of the reference gas that is stored with respectively;Three, repeatedly measurement is by reference gas chamber and the intensity of spectral line for detecting air chamber emergent light;Step 4, linear fit is carried out to described the intensity of spectral line, obtains the temperature influence fitting coefficient of the monochromatic absorption coefficient of light of two kinds of wavelength;Five, according to fitting coefficient, calculate the gas concentration after temperature-compensating.This method establishes the model of temperature compensation of fiber-optic fiber gas detecting system, realize the fiber-optic fiber gas detecting system for considering temperature change factor, suppressed by way of temperature-compensating variation of ambient temperature to detection band come interference, reduce the accuracy of detection that system is improved due to the measurement error that variation of ambient temperature is introduced.

Description

A kind of optical fiber gas concentration detection method with temperature compensation capability
Technical field
The present invention relates to a kind of gas concentration detection method, and in particular to a kind of gas concentration with temperature compensation capability Detection method, belongs to technical field of optical fiber detection.
Background technology
Industry spot operation be typically under the environmental condition of high temperature, high-moisture, high dust, severe corrosive and high flow rate, The detection that reliable, safety development depends particularly on rapidly and accurately progress gas concentration that continues to field operation.
Although traditional non-optical gas detecting instrument can reach relatively low test limit, it is easy to by other gases The intersection of composition is sensitive, and its response speed is slower, and repeatable utilization rate is low, and service life is shorter, it is difficult to which real-time continuous is examined Survey.To overcome these defects, Diode Laser Absorption Spectroscopy (TDLAS technologies) employs " single line spectrum " technology of uniqueness With modulated spectrum technology, it can not be disturbed by background gas cross jamming and dust, form pollution, therefore will can test and analyze Equipment is directly installed on measure field, realizes that the live on-line continuous gas that other spectral absorption technologies can not or be difficult to realize is surveyed Amount.
Currently for industry spot fiber-optic fiber gas detection, typically using under test gas fiber transparent window (0.8~ 1.7 μm) in absworption peak, measure by gas absorb produce light intensity attenuation, so as to deduce out the concentration of under test gas.Specifically adopt With the method for harmonic detecting, noise spectra of semiconductor lasers light source carries out sinusoidal signal (or triangular wave) and modulated, and modulated optical signal Harmonic components are directly proportional after being absorbed through gas to gas concentration, by detecting that these harmonic components just can obtain the dense of under test gas Spend information.The influence for the absorption coefficient change that the change that above-mentioned detection method have ignored under test gas environment temperature is brought.It is real On border, in actual measuring environment, the change of under test gas environment temperature produces shadow to processes such as rotation, the vibrations of gas molecule Ring, so as to cause the change of absorption coefficient, influence the detection of gas concentration.Therefore, needed while gas concentration is detected true Determine the residing environment temperature of gas, the concentration to correct tested gas.How to determine gaseous absorption line with measuring environment temperature The characteristic of degree change makes it possible to measure the concentration of gas in the environment of temperature change, fails solution very well always.
The content of the invention
In view of this, the present invention provides a kind of optical fiber gas concentration detection method with temperature compensation capability, using this Method can be directed to traditional dual-wavelength difference gas detection mode, set up the mathematical modeling of temperature-compensating to remove temperature factor Influence to absorption coefficient, so as to eliminate the error of the introduced gas concentration detection of temperature change, obtains higher detection essence Degree.
Realize that technical scheme is as follows
A kind of optical fiber gas concentration detection method with temperature compensation capability, detailed process is:
Step one, laser produces the optical signal that two centre wavelengths are λ 1 and λ 2, the suction of wherein λ 1 correspondence under test gas Receive peak, the absworption peak of the correspondence reference gases of λ 2;
Step 2, optical signal is divided into after two beams after being transmitted through optical fiber by optical splitter, passes through the reference gas that is stored with respectively Reference gas chamber and the detection air chamber of under test gas of being stored with;
Step 3, repeat step two, repeatedly measurement is by reference gas chamber and the intensity of spectral line for detecting air chamber emergent light;
Step 4, linear fit is carried out using formula (1) to described the intensity of spectral line, is obtained monochromatic absorb of wavelength X 1 and is Number temperature influence fitting coefficient a1, b1, c1, obtain the monochromatic absorption coefficient temperature influence fitting coefficient a of wavelength X 22, b2, c2
S=a+bT-1+cT-2 (1)
Wherein, T is the environment temperature in air chamber;
Step 5, according to fitting coefficient, the gas concentration after temperature-compensating is calculated using formula (2);
Wherein, l represents light path, and n is temperature coefficient, and I (λ 1) is the monochromatic harmonic wave light intensity of wavelength X 1, and I (λ 2) is wavelength X 2 monochromatic harmonic wave light intensity, T0For reference temperature 296k, γ0For temperature T0Half high half-breadth of lower Absorption Line, k is that Boltzmann is normal Amount, P is the pressure of under test gas.
Beneficial effect
This method establishes the model of temperature compensation of fiber-optic fiber gas detecting system, realizes the light for considering temperature change factor Fine gas concentration detection system, suppressed by way of temperature-compensating variation of ambient temperature to gas concentration detection band come it is dry Disturb, reduce the accuracy of detection that system is improved due to the measurement error that variation of ambient temperature is introduced.
The detection method can effectively suppress interference of stray light and signal noise, eliminate the light such as source device output optical power shakiness The interference of temperature factor is also eliminated while the factor influence of road.
Brief description of the drawings
Fig. 1 is the flow chart of detection method;
Fig. 2 is the schematic diagram of this example detection process;
Fig. 3 is the schematic diagram of this example temperature compensation procedure.
Embodiment
The present invention will now be described in detail with reference to the accompanying drawings and examples.
The present embodiment provides a kind of optical fiber gas concentration detection method with temperature compensation capability, by being absorbed to gas The intensity of spectral line of line is fitted, on carrying out temperature-compensating, suppression because of the gas concentration detection error influence that temperature change is brought The interference that variation of ambient temperature processed is come to detection band, so as to accurately obtain the concentration of tested gas.
As shown in figure 1, a kind of optical fiber gas concentration detection method with temperature compensation capability of the present invention, detailed process For:
Step one, laser produces the optical signal that two centre wavelengths are λ 1 and λ 2, the suction of wherein λ 1 correspondence under test gas Receive peak, the absworption peak of the correspondence reference gases of λ 2;
Step 2, optical signal is divided into after two beams after being transmitted through optical fiber by optical splitter, passes through the reference gas that is stored with respectively Reference gas chamber and the detection air chamber of under test gas of being stored with;
Step 3, repeat step two, repeatedly measurement is by reference gas chamber and the intensity of spectral line for detecting air chamber emergent light;
Step 4, linear fit is carried out using formula (1) to described the intensity of spectral line, is obtained monochromatic absorb of wavelength X 1 and is Number temperature influence fitting coefficient a1, b1, c1, obtain the monochromatic absorption coefficient temperature influence fitting coefficient a of wavelength X 22, b2, c2
S=a+bT-1+cT-2 (1)
Wherein, T is the environment temperature in air chamber;
Step 5, according to fitting coefficient, the gas concentration after temperature-compensating is calculated using formula (2);
Wherein, l represents light path, and n is temperature coefficient, and I (λ 1) is the monochromatic harmonic wave light intensity of wavelength X 1, and I (λ 2) is wavelength X 2 monochromatic harmonic wave light intensity, T0For reference temperature 296k, γ0For temperature T0Half high half-breadth of lower Absorption Line, k is that Boltzmann is normal Amount, P is the pressure of under test gas.
Influence of the temperature to absorption coefficient is taken into full account in formula (2) of the present invention, by the mathematics for setting up temperature-compensating Model is to remove influence of the temperature factor to absorption coefficient, compared to existing detection method, the gas that the inventive method is detected Concentration has higher accuracy of detection.
The derivation to formula (1) and formula (2) is described in detail below:
Be separated by with two wavelength Xs 1 and λ 2 extremely closely (has very big difference on absorption coefficient:Wherein λ 1 absorbs under test gas On peak, and under test gas absorbs very weak to λ 2 or not absorbed, while also to avoid the absorption of other non-under test gas molecules etc.) Monochromatic light is simultaneously or difference very short time is interior by under test gas, and light intensity, which is divided by, to be obtained:
Wherein, l represents light path;
Under wavelength X 1, λ 2, such as the absorption coefficient (λ 1) of gas, α (λ 2) can be obtained by calibrating gas measurement, Then under the conditions of of the same race, the concentration of under test gas can just be obtained by measuring harmonic wave light intensity I (λ 1) and I (λ 2).
However, according to the broadening principle of spectrum line, absorption coefficient changes as ambient temperature changes.Therefore, merely By measuring the intensity of second harmonic, if not considering the influence of temperature change, it is impossible to accurately obtain surveyed gas concentration.By In the method using second-harmonic detection, mainly need to consider the compensation effect of second harmonic when carrying out temperature-compensating, its is right The dependence of temperature can directly result in the deviation of measurement result, it is thus necessary to determine that dependence of the second harmonic for temperature.
Utilization index Function Fitting absorption coefficient:
Density of gas molecules, the line strength of Absorption Line in absorption coefficient and unit volume at gaseous absorption line centre frequency It is relevant with half high half-breadth of Absorption Line, it can be expressed as:
In formula, N is the density of gas molecules (mol/cm in unit volume3), S is the intensity of spectral line (cm of Absorption Line-1/ (mol·cm3)), γ is half high half-breadth (cm of Absorption Line-1)。
According to the pressure formula of perfect gas, the analytic density of the under test gas in unit volume is:
In formula, P is the pressure of under test gas, and k is Boltzmann constant, and T is thermodynamic temperature.
Pressure does not change during due to detection, and half high half-breadth of Absorption Line is relevant with temperature, and the half of different temperatures Absorption Line High half-breadth can be expressed as:
In formula, T0、γ0Temperature value and the high half-breadth of Absorption Line half during respectively reference temperature 296k;N is temperature coefficient.
Have:
Variation with temperature, gas absorption spectrum line strength also changes, and gas absorption spectrum line strength can be expressed as into temperature The function of degree:
NcFor Loschmidt constants, unit is cm-3;E and meRespectively quantities of charge and quality;C is the light velocity;Q (T) is Molecular partition function;H is Planck (Planck) constant;K is Boltzmann constant;G, W, f be respectively decay factor, energy and Oscillation intensity.
The intensity of spectral line in view of Absorption Line reduces with the rise of temperature, is fitted, obtained with second order polynomial:
S=a+bT-1+cT-2 (1)
Wherein, a, b, c are fitting coefficient respectively.It can be marked by repeatedly measuring the intensity of spectral line with the numerical relation of temperature Surely the coefficient is fitted.
Then absorption coefficient temperature influence model is represented by:
α=∈ (aTn-1+bTn-2+cTn-3)
Wherein,For a constant.
Then, it is considered to which the gas concentration (namely model of temperature compensation) after temperature factor of influence is:
Wherein, a1, b1, c1Fitting coefficient is influenceed for the monochromatic absorption coefficient temperature of wavelength X 1;
a2, b2, c2Fitting coefficient is influenceed for the monochromatic absorption coefficient temperature of wavelength X 2;
Due to a1, a2, b1, b2, c1, c2, it is known that being therefore that can obtain temperature by the above-mentioned formula with temperature-compensating Gas concentration after compensation.
When under test gas is influenceed by variation of ambient temperature, it is the concentration of accurate measurement under test gas, need to be mended by temperature Repay and suppress the interference that variation of ambient temperature is come to detection band.System gathers gas indoor environment temperature using temperature sensor, to not The synthermal lower obtained gas concentration that measures carries out temperature-compensating.
Example:
Based on existing bipolar electrode DFBLD Difference Absorption detecting system, as shown in Fig. 2 signal generator produces sine Ripple, is modulated by the Injection Current for adjusting laser to its output wavelength.By changing two electrodes of semiconductor laser The current ratio of input, produces the optical signal that two centre wavelengths are λ 1 and λ 2, and λ 2 is reference light, and the correspondence gas molecules of λ 1 Absworption peak, intensity approximately equal.From the light of DFBLD outgoing through optoisolator to fiber coupler, be coupled to light in optical fiber by Beam splitter is divided into two beams, and light beam is by reference to air chamber to PIN detector, after PIN output signals are mutually amplified through lock, for feeding back Control the Injection Current of laser, the output frequency of stable laser;Another light beam is by detecting air chamber, to another photodetection Device, output signal lock is used for the concentration for obtaining under test gas after mutually amplifying.The output light of detection air chamber and reference gas chamber is through photoelectricity Detector is converted into electric signal, extracts their second harmonic signal by differential mode with lock-in amplifier, then by two Second harmonic signal feeding divider carries out ratio output, and output quantity carries the gas concentration information containing temperature factor of influence. According to the model of temperature compensation for above setting up gas concentration, the interference shadow of temperature fluctuation can be eliminated by the method for temperature-compensating Ring, while also eliminating due to the measurement error that light source fluctuation and external environment influence are caused.
As shown in figure 3, detailed process is:
1. gather the environment temperature in air chamber with temperature sensor;
2. many measurement the intensity of spectral line;
3. second order polynomial fit is carried out to the intensity of spectral line using formula (1)
4. λ 1 is obtained, the temperature influence fitting coefficient of the wavelength of λ 2;
5. gas concentration C (T) is calculated by model of temperature compensation;
The signal of reacting gas concentration through above-mentioned processing is admitted to signal processing device and postponed, at input computer Reason, display and printing.
In summary, presently preferred embodiments of the present invention is these are only, is not intended to limit the scope of the present invention. Within the spirit and principles of the invention, any modification, equivalent substitution and improvements made etc., should be included in the present invention's Within protection domain.

Claims (1)

1. a kind of optical fiber gas concentration detection method with temperature compensation capability, it is characterised in that detailed process is:
Step one, the optical signal that two centre wavelengths of laser generation are λ 1 and λ 2, the absworption peak of wherein λ 1 correspondence under test gas, The absworption peak of the correspondence reference gases of λ 2;
Step 2, optical signal is divided into after two beams after being transmitted through optical fiber by optical splitter, passes through the ginseng for the reference gas that is stored with respectively Examine the detection air chamber of air chamber and the under test gas that is stored with;
Step 3, repeat step two, repeatedly measurement is by reference gas chamber and the intensity of spectral line for detecting air chamber emergent light;
Step 4, linear fit is carried out using formula (1) to described the intensity of spectral line, obtains the temperature of the monochromatic absorption coefficient of light of wavelength X 1 Degree influence fitting coefficient a1, b1, c1, obtain the temperature influence fitting coefficient a of the monochromatic absorption coefficient of light of wavelength X 22, b2, c2
S=a+bT-1+cT-2 (1)
Wherein, T is the environment temperature in air chamber;
Step 5, according to fitting coefficient, the gas concentration after temperature-compensating is calculated using formula (2);
<mrow> <mi>C</mi> <mrow> <mo>(</mo> <mi>T</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <mrow> <mo>&amp;lsqb;</mo> <mrow> <mo>(</mo> <msub> <mi>&amp;alpha;</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>&amp;alpha;</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <msup> <mi>T</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mo>+</mo> <mrow> <mo>(</mo> <msub> <mi>b</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>b</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <msup> <mi>T</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>2</mn> </mrow> </msup> <mo>+</mo> <mrow> <mo>(</mo> <msub> <mi>c</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>c</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <msup> <mi>T</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>3</mn> </mrow> </msup> <mo>&amp;rsqb;</mo> <mo>&amp;Element;</mo> <mi>l</mi> </mrow> </mfrac> <mfrac> <mrow> <mi>I</mi> <mrow> <mo>(</mo> <mi>&amp;lambda;</mi> <mn>2</mn> <mo>)</mo> </mrow> <mo>-</mo> <mi>I</mi> <mrow> <mo>(</mo> <mi>&amp;lambda;</mi> <mn>1</mn> <mo>)</mo> </mrow> </mrow> <mrow> <mi>I</mi> <mrow> <mo>(</mo> <mi>&amp;lambda;</mi> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow>
<mrow> <mo>&amp;Element;</mo> <mo>=</mo> <mfrac> <mi>P</mi> <mrow> <msub> <mi>k&amp;pi;&amp;gamma;</mi> <mn>0</mn> </msub> <msup> <mrow> <mo>(</mo> <msub> <mi>T</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mi>n</mi> </msup> </mrow> </mfrac> </mrow>
Wherein, l represents light path, and n is temperature coefficient, and I (λ 1) is the monochromatic harmonic wave light intensity of wavelength X 1, and I (λ 2) is that wavelength X 2 is single The harmonic wave light intensity of coloured light, T0For reference temperature 296k, γ0For temperature T0Half high half-breadth of lower Absorption Line, k is Boltzmann constant, P is the pressure of under test gas.
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CN109946231B (en) * 2019-03-13 2021-04-27 上海交通大学 Differential photoacoustic measurement system and method with temperature compensation
CN110132808A (en) * 2019-04-08 2019-08-16 中国船舶重工集团公司第七一九研究所 A kind of thorax mouth smoke density detection method
CN110531032A (en) * 2019-09-20 2019-12-03 哈尔滨学院 Pollutant testing apparatus for mathematical modeling and the unmanned plane with it
CN110927346A (en) * 2019-12-24 2020-03-27 中国航空工业集团公司西安飞机设计研究所 Gas concentration test system calibration method and device

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