CN111474138B - Gas concentration measuring device and method based on high-frequency reference optical frequency division multiplexing technology - Google Patents
Gas concentration measuring device and method based on high-frequency reference optical frequency division multiplexing technology Download PDFInfo
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Abstract
The invention discloses a gas concentration measuring device based on a high-frequency reference optical frequency division multiplexing technology and a gas concentration measuring method based on the high-frequency reference optical frequency division multiplexing technology. The high-frequency reference light path is coupled with the wavelength modulation measuring light path, so that the extraction of interference signals and the correction of detection light intensity are realized, the harmonic signals of the detection light intensity are accurately extracted, the accuracy of gas parameter measurement is improved, and the application range of a spectral absorption method is expanded; the method has the characteristics of good applicability, wide application scene and the like, so the method has important application value for detecting the flame temperature and the component concentration in the complex environments such as an aerospace engine combustion chamber and the like.
Description
Technical Field
The invention relates to a gas concentration measuring device based on a high-frequency reference optical frequency division multiplexing technology, and also relates to a gas concentration measuring method based on the high-frequency reference optical frequency division multiplexing technology, belonging to the technical field of optical measurement.
Background
An aircraft engine is a complex and precise thermal machine that directly impacts the performance, reliability, and economy of an aircraft. The combustion chamber is an essential important part of the engine, and chemical energy in fuel is released through combustion, so that the chemical energy is converted into heat energy, high-temperature and high-pressure fuel gas is generated, and the working capacity of the engine is improved. When designing the combustion chamber, need to guarantee that combustion stability is good, combustion efficiency is high, and the emission pollution is few. The combustion products are mainly composed of residual air (O) 2 And N 2 ) Carbon oxides (CO and CO) 2 ) Nitrogen oxides (NO and NO) 2 ) Gases such as unburned hydrocarbons (TCH) and solid fine particles. Wherein the characteristic gas is an important indicator gas reflecting the combustion characteristics. Its presence indicates that the fuel is not completely combusted and combustion efficiency is to be improved. The detection of the characteristic gas parameters is beneficial to the optimization of combustion efficiency and the acquisition of important data of combustion chamber design and fuel equivalence ratio selection.
Gas detection techniques are mainly classified into two categories according to the measurement principle: spectroscopic and non-spectroscopic methods. The non-spectroscopic method mainly includes a chemical analysis method and an electrical gas detection method. Chemical analysis methods can separate mixed gases efficiently, but have slow response times. The electrical gas detection method has high sensitivity and wide detection range, but needs to be in contact with a measurement environment and has poor capability of identifying the gas type. The spectroscopy can detect various types of gases by measuring the target gas spectrum related parameters and inverting the gas concentration information, has the advantages of non-contact measurement, quick response time and the like, and is a research hotspot of the current gas detection. The spectroscopy is mainly fourier transform infrared absorption spectroscopy (FTIR), tunable semiconductor laser absorption spectroscopy (TDLAS), and the like. The FTIR technology is mainly based on the Michelson interferometer principle, and the infrared light source sends the parallel light after collimating by collimating lens, is received by the telescope system after the gaseous absorption of awaiting measuring, assembles the detector through the interferometer again to obtain the interference signal of the gaseous of awaiting measuring, can obtain the absorption spectrum information of gaseous under the different concentrations after Fourier transform, thereby calculate gaseous concentration. However, FTIR devices are bulky, have relatively slow response speed and are relatively expensive, and therefore, certain development is required in the future. The TDLAS technology is a spectral measurement method based on the narrow linewidth characteristic of a semiconductor laser, can realize simultaneous measurement of multiple components and multiple parameters of mixed gas, has very strong universality and high measurement resolution, and can measure the concentration of trace gas by selecting a combined characteristic absorption spectrum line of gas to be measured. Among them, wavelength Modulation Spectroscopy (WMS) based on TDLAS has the advantages of high signal-to-noise ratio and high measurement sensitivity, and has been widely used in the fields of trace gas detection in the infrared band and detection of combustion flame temperature and component concentration in aerospace engines.
In the gas parameter detection under the complex environment, due to the influence of disturbance factors such as turbulence, strong vibration and the like in the environment, a signal measured by the traditional WMS method is distorted and cannot be used for extracting useful information. For example, in the combustion diagnosis process of an aeroengine, strong vibration of the ignition and combustion stages of the engine and strong turbulence of a combustion flow field bring serious interference to the transmitted light intensity, and the combustion diagnosis measurement accuracy of the engine is influenced. In this regard, when processing the experimental signal, the noise can be suppressed by averaging the light intensity in multiple periods. The wavelength modulation technology separates a high-frequency absorption signal from low-frequency noise on a frequency domain by superposing the high-frequency modulation signal, and demodulates the absorption signal at a specific frequency doubling position by means of a phase-locked filtering technology, thereby effectively inhibiting the interference of the low-frequency noise. However, the modulation frequencies currently used for aircraft engine combustion diagnostics are still low, mostly below 200 kHz. The modulation frequency of the traditional WMS method is improved, and the problems that a laser controller is unstable in controlling a laser light emitting center, the bandwidth of a detector is insufficient, a collection facility cannot meet requirements and the like are easily caused. In addition, in the measurement environments with serious mechanical vibration and flame jitter, especially for the transient flow field of the scramjet, the interference frequency is equivalent to the modulation frequency, crosstalk is easily generated, the separation of interference and absorption signals on the frequency domain cannot be realized, and the measurement accuracy is seriously influenced.
Disclosure of Invention
The invention aims to: the invention aims to provide a gas concentration measuring device based on a high-frequency reference light frequency division multiplexing technology.
The invention also aims to solve the technical problem of providing a gas concentration measuring method based on a high-frequency reference optical frequency division multiplexing technology, and the measuring method can greatly improve the accuracy of gas parameter measurement in a complex environment by extracting effective information from an original light intensity signal.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a gas concentration measuring device based on a high-frequency reference optical frequency division multiplexing technology sequentially comprises a signal generating module, a gas parameter measuring module, a signal receiving module and a signal processing module; the signal generation module comprises a function generator, a laser controller, a distributed feedback laser and an optical fiber beam splitter; the gas parameter measuring module comprises an optical etalon and a measuring cell; the signal receiving module consists of three photoelectric detectors; the measuring cell is filled with gas to be measured; the function generator inputs scanning superposition modulation signals into a laser controller I, and the laser controller I tunes the output wavelength and light intensity of the distributed feedback laser I; meanwhile, the function generator inputs a modulation signal into the laser controller II, and the laser controller II tunes the output wavelength and the light intensity of the distributed feedback laser II; two beams of laser are coupled and then are divided into three beams of optical signals through two optical fiber beam splitters in sequence, wherein one beam of optical signal passes through a measuring cell from a laser emitting end, is received by a photoelectric detector I after being absorbed by gas to be measured and is converted into an electric signal, and a transmitted light intensity signal is obtained; the other beam of optical signal is received by a photoelectric detector II after passing through an optical etalon to obtain an etalon signal for time frequency conversion; and the last beam of optical signal is directly received by the photoelectric detector III to obtain a background signal, and the three beams of signals are transmitted to the signal processing module by the corresponding photoelectric detectors to be processed.
A gas concentration measuring method based on a high-frequency reference optical frequency division multiplexing technology specifically comprises the following steps:
(1) The function generator sets the scanning frequency to f s Signal superposition modulation frequency f m The signal is input into a laser controller I through a first channel in the signal, and the laser controller I tunes the output wavelength and the light intensity of the DFB laser I;
(2) Function generator modulates frequency f ref The signal is input into a laser controller II through a second channel inside the laser controller II, and the laser controller II tunes the output wavelength and the light intensity of the DFB laser II;
(3) Coupling the modulated light in the step (1) with the modulated light in the step (2), dividing the coupled modulated light into three light signals by an optical fiber beam splitter, enabling one light signal to pass through a measuring cell from a laser emitting end, absorbing the light signal by gas to be measured, receiving the light signal by a photoelectric detector I, converting the light signal into an electric signal, and obtaining a transmitted light intensity signal I t (t); one beam passes through the optical etalon and is used for collecting etalon signal I by the photoelectric detector II v (t); the other beam is directly collected by a photoelectric detector III to obtain a background light intensity signal I 0 (t)；
(4) From etalon signal I v (t) obtaining a time-frequency response characteristic v (t);
(5) Transmitted light intensity signal I t (t) performing digital phase locking and low-pass filtering, wherein parameters of the digital phase locking and the low-pass filtering are based on the reference frequency f in the processing process ref Setting to obtain a first harmonic signal S 1f Will transmit the light intensity signal I t (t) dividing by the first harmonic signal
Then the corrected light intensity signal is obtained>
(6) For background light intensity signal I 0 (t) and the corrected intensity signal
Respectively carrying out digital phase locking and low-pass filtering treatment, wherein the parameters of the digital phase locking and the low-pass filtering are based on the modulation frequency f in the treatment process m Setting to obtain corresponding first harmonic signal and second harmonic signal; />
(7) According to Beer-Lambert law, further processing the first harmonic signal and the second harmonic signal of the light intensity signal obtained in the step (6) to obtain a normalized second harmonic signal, and utilizing a background light intensity signal I 0 And (t) obtaining a simulated normalized second harmonic signal according to the time frequency response characteristics obtained in the step (4), finally fitting an integral absorption area A by using a least square algorithm according to the obtained normalized second harmonic and the simulated normalized second harmonic signal, and calculating the concentration value of the gas to be detected through the integral absorption area A.
Wherein, in step (5), the corrected light intensity signal
Calculated by the following formula:
in the formula (1), the reaction mixture is,
for transmitting a light intensity signal I t (t) corresponding reference frequency f ref The first harmonic component and the second harmonic component are x component and y component, and F is a low-pass filter;
in the formula (2), the reaction mixture is,
for transmitting a light intensity signal I t (t) corresponding reference frequency f ref A next first harmonic signal;
in the formula (3), the reaction mixture is,
is the corrected light intensity signal.
Wherein, in step (6), the background light intensity signal I 0 (t) first and second harmonic signals and modified intensity signal
The first harmonic signal and the second harmonic signal are calculated by the following formula:
in the formula (4), the reaction mixture is,
as background light intensity signal I 0 (t) the corresponding first and second harmonic x-and y-components, < >, in a manner that is based on the value of the harmonic>
Respectively is the corrected light intensity signal>
Corresponding first harmonic x component and second harmonic y component, F is low-pass filter;
in the formula (5), the reaction mixture is,
as a background light intensity signal I 0 (t) first and second harmonic signal->
For the corrected light intensity signal->
First and second harmonic signals.
Wherein, in step (7), the background light intensity signal I is subtracted 0 (t) normalized second harmonic signal S 2f/1f Expressed as:
the algorithm widens the integral absorption area A and the line collision by delta v C Doppler spread Deltav D And the laser center frequency v0 as a fitting parameter participates in the pair S 2f/1f The least square fitting of (2) is carried out, digital phase-locking low-pass filtering and background-deducting normalization processing are carried out on simulated (etalon) and experimental light intensity signals, and background-deducting normalization harmonic signals of simulated light intensity are obtained
Background-subtracted normalized harmonic signal S of sum experimental light intensity 2f/1f (ii) a Fitting the spectral absorbance using a least squares algorithm, according to which the absorbance is based on ≥ i>
And S 2f/1f Converging when the residual error is minimum to obtain the best fitting parameter A;
the relationship between the integrated absorption area a and the gas concentration is expressed as follows according to Beer-Lambert's law:
in the formula (7), X is the concentration of the gas to be measured, P is the total pressure of the gas, S (T) is the linear intensity of the transition spectral line, T is the temperature of the gas, and X is gas Is the gas concentration, L is the optical path length, and A is the integral absorption area.
Has the advantages that: compared with the existing wavelength modulation spectrum technology, the invention couples the high-frequency reference light path with the wavelength modulation measurement light path, realizes the extraction of interference signals and the correction of detection light intensity, further accurately extracts harmonic signals of the detection light intensity, improves the accuracy of gas parameter measurement, and expands the application range of a spectrum absorption method; the method has the characteristics of good applicability, wide application scene and the like, and therefore, the method can be applied to the detection of the flame temperature and the component concentration in the complex environments such as an aerospace engine combustion chamber and the like.
Drawings
FIG. 1 is a schematic diagram of a system of a gas concentration measuring apparatus according to the present invention;
FIG. 2 is a flow chart of a gas concentration measurement method according to the present invention;
FIG. 3 is a schematic diagram of a built verification system;
FIG. 4 is a graph of methane concentration results obtained when the prior art method does not employ a reference light signal to correct the light intensity signal;
fig. 5 shows the result of methane concentration obtained by the method of the present invention using the reference optical signal to perform the optical intensity correction on the WMS signal.
Detailed Description
The technical solutions of the present invention are further described below with reference to the accompanying drawings, but the scope of the claimed invention is not limited thereto.
As shown in fig. 1, the gas concentration measuring apparatus based on the high-frequency reference optical frequency division multiplexing technology of the present invention can measure the gas concentration under strong interference, and the measuring apparatus sequentially includes a signal sending module 1, a gas parameter measuring module 2, a signal receiving module 3 and a signal processing module 4; the signal generating module 1 comprises a function generator 5, a laser controller I6, a laser controller II7, a distributed feedback laser (DFB) I8, a distributed feedback laser (DFB) II9 and a fiber beam splitter 10; the gas parameter measuring module 2 comprises an optical etalon 12 and a measuring cell 11; the signal receiving module 3 consists of three photoelectric detectors 13; introducing gas to be measured into the measuring cell 11; the function generator 5 inputs scanning superposition modulation signals into a laser controller I6 through a first internal channel, the laser controller I6 tunes the output wavelength and the light intensity of a DFB laser I8, meanwhile, the function generator 5 inputs the modulation signals into a laser controller II7 through a second internal channel, the laser controller II7 tunes the output wavelength and the light intensity of a DFB laser II9, laser emitted by the DFB laser I8 is coupled with laser emitted by the DFB laser II9 and is divided into three light signals through two optical fiber beam splitters 10, one light signal penetrates through a measuring cell 11 from a laser emitting end, light with gas absorption signals is received by a photoelectric detector 13 and converted into electric signals, and transmission light intensity signals are obtained; one beam passes through the optical etalon 12 and is received by the photoelectric detector 13 to obtain an etalon signal; the other light signal is directly received by the photoelectric detector 13 to obtain a background signal; the three signals are all transmitted to the signal processing module 4 for processing. The distributed feedback laser can continuously emit stable laser light, and the wavelength of the stable laser light depends on the gas to be measured.
As shown in fig. 2, the gas concentration measuring method based on the high-frequency reference optical frequency division multiplexing technology of the present invention specifically includes the following steps:
step 3, coupling the modulated light of the step 1 with the modulated light of the step 2, dividing the coupled light into three beams by an optical fiber beam splitter 10, enabling one beam to pass through a measuring cell 11 from a laser emitting end, absorbing the gas to be measured, receiving the gas by a photoelectric detector 13, and converting the gas into electricitySignal to obtain transmitted light intensity signal I t (t); one beam passes through the optical etalon 12 and is collected by the photoelectric detector 13 to obtain an etalon signal I v (t); the other beam is directly collected by the photoelectric detector 13 to obtain a background light intensity signal I 0 (t)；
Corrected light intensity signal
Calculated by the following formula:
in the formula (1), the reaction mixture is,
for transmitting a light intensity signal I t (t) corresponding reference frequency f ref The next one and the secondA subharmonic x-component and y-component, F being a low pass filter;
in the formula (2), the reaction mixture is,
for transmitting a light intensity signal I t (t) corresponding reference frequency f ref A next first harmonic signal;
in the formula (3), the reaction mixture is,
is the corrected light intensity signal;
background light intensity signal I 0 (t) first and second harmonic signals and modified intensity signal
The first and second harmonic signals are calculated by the following formula: />
In the formula (4), the reaction mixture is,
as background light intensity signal I 0 (t) the corresponding first and second harmonic x-and y-components, < >, in a manner that is based on the value of the harmonic>
Respectively is the corrected light intensity signal>
Corresponding first harmonic x component and second harmonic y component, F is low-pass filter;
in the formula (5), the reaction mixture is,
as a background light intensity signal I 0 (t) first and second harmonic signal->
For the corrected light intensity signal->
First, second harmonic signals;
and 7, further processing the first harmonic signal and the second harmonic signal of the light intensity signal obtained in the step 6 according to the Beer-Lambert law to obtain a normalized second harmonic signal, and utilizing a background light intensity signal I 0 (t) obtaining a simulated normalized second harmonic signal according to the time-frequency response characteristics obtained in the step (4), fitting an integral absorption area A by using a least square algorithm according to the obtained normalized second harmonic signal and the simulated normalized second harmonic signal, and calculating a concentration value of the gas to be detected through the integral absorption area A;
background-subtracted intensity signal I 0 (t) normalized second harmonic signal S 2f/1f Can be expressed as:
the algorithm widens the integral absorption area A and the line collision by delta v C Doppler spread Deltav D And the laser center frequency v0 as a fitting parameter participates in the pair S 2f/1f The least square fitting of (1) is to carry out digital phase-locking low-pass filtering and background-deduction normalization processing on simulated and experimental light intensity signals to obtain simulated light intensityBackground-subtracted normalized harmonic signal
Background-subtracted normalized harmonic signal S of sum experimental light intensity 2f/1f (ii) a Fitting the spectral absorbance using a least squares algorithm, according to which the absorbance is based on ≥ i>
And S 2f/1f Converging when the residual error is minimum, and obtaining the optimal fitting parameter A;
in the formula (7), X is the concentration of the gas to be measured, P is the total pressure of the gas, S (T) is the linear intensity of the transition spectral line, T is the temperature of the gas, and X is gas Is the gas concentration, L is the optical path length, and A is the integral absorption area.
As shown in fig. 3, fig. 3 is a built verification system, which emits 50 sets of filtering white gaussian noises with cut-off frequencies from 200Hz to 10kHz on a first path of light path through a loudspeaker to interfere light intensity, and the method of the present invention is compared with the method of the prior art under such interference, so as to demonstrate that the method of the present invention can effectively suppress the influence of interference signals on gas detection.
The verification system is as follows: inputting a sinusoidal modulation signal generated by a first channel of a function generator 5 into a laser controller I6 to tune the output wavelength of a DFB laser I8; and a second channel of the function generator 5 generates a sinusoidal signal and inputs the sinusoidal signal into the laser controller II7 to tune the output wavelength of the DFB laser II 9. Wherein the central wave number of the DFB laser I8 is selected as the center of a methane absorption spectral line (6046.95 cm-1), and the central wave number of the DFB laser II9 is selected as a methane non-absorption part (6050.45 cm-1); two beams of laser are divided into two paths after passing through the optical fiber coupler: the first path of laser passes through a gas absorption cell 11 with the length of 20cm, is reflected by a reflecting film fixed on a loudspeaker 14 (LS 77W-35F-R8), and is finally received by a photoelectric detector 13 and converted into an electric signal to obtain the transmission light intensity; wherein the loudspeaker 14 is used for generating interference signals with different frequencies and different amplitudes; the second path of laser is divided into two paths by the optical fiber beam splitter, wherein one path of laser is directly received by the photoelectric detector 13 to obtain incident light intensity; the other path of laser passes through an optical etalon 12 (the free spectrum distance is 0.01cm < -1 >) and is received by a photoelectric detector 13 to obtain an etalon signal, and the frequency response characteristic relation of the laser is obtained; the light intensity is disturbed by emitting 50 sets of filtered white gaussian noise with cut-off frequencies from 200Hz to 10kHz through the loudspeaker 14.
FIG. 4 is a graph of methane concentration calculated by a verification system using a prior art method without using a reference light signal to correct the light intensity signal. When the interference frequency range is below 5kHz, the variance of the methane concentration is below 0.06%, and the fluctuation is small. When the interference frequency range reaches above 5kHz, the fluctuation of the methane concentration is increased; and along with the increase of the interference frequency range, the error of the methane concentration is larger and larger, and the fluctuation of the concentration is also larger and larger.
FIG. 5 shows the result of the methane concentration calculated by the verification system after the WMS signal is subjected to light intensity correction by using the method of the present invention and the reference light signal. The errors of the corrected methane concentration are within +/-1%, the variance is below 0.02%, and the fluctuation is small. Experiments verify that under different interference conditions, harmonic signals before and after correction and methane concentration calculation results are analyzed, so that the interference signals are extracted through the high-frequency reference optical signals, the method for correcting the WMS signals is feasible, and the influence of the interference signals on gas detection can be effectively inhibited.
Claims (4)
1. A gas concentration measuring device based on a high-frequency reference optical frequency division multiplexing technology is characterized in that: the gas parameter measuring device sequentially comprises a signal generating module, a gas parameter measuring module, a signal receiving module and a signal processing module; the signal generation module comprises a function generator, a laser controller, a distributed feedback laser and an optical fiber beam splitter; the gas parameter measuring module comprises an optical etalon and a measuring cell; the signal receiving module consists of three photoelectric detectors; the measuring cell is filled with gas to be measured; the function generator inputs scanning superposition modulation signals into a laser controller I, and the laser controller I tunes the output wavelength and light intensity of the distributed feedback laser I; meanwhile, the function generator inputs a modulation signal into the laser controller II, and the laser controller II tunes the output wavelength and the light intensity of the distributed feedback laser II; two beams of laser are coupled and then are divided into three beams of optical signals through two optical fiber beam splitters in sequence, wherein one beam of optical signal passes through a measuring cell from a laser emitting end, is received by a photoelectric detector I after being absorbed by gas to be measured and is converted into an electric signal, and a transmitted light intensity signal is obtained; the other beam of optical signal is received by a photoelectric detector II after passing through an optical etalon to obtain an etalon signal for time frequency conversion; the last beam of optical signal is directly received by the photoelectric detector III to obtain a background signal, and three paths of signals are transmitted to the signal processing module by the corresponding photoelectric detectors to be processed;
the measuring method of the gas concentration measuring device based on the high-frequency reference light frequency division multiplexing technology specifically comprises the following steps:
(1) The function generator will scan at frequency f s Signal superposition modulation frequency f m The signal is input into a laser controller I through a channel I in the DFB laser, and the laser controller I tunes the output wavelength and the light intensity of the DFB laser I;
(2) Function generator modulates frequency f ref The signal is input into a laser controller II through a channel II in the laser controller II, and the laser controller II tunes the output wavelength and the light intensity of the DFB laser II;
(3) Coupling the modulated light in the step (1) with the modulated light in the step (2), dividing the coupled modulated light into three light signals by an optical fiber beam splitter, enabling one light signal to pass through a measuring cell from a laser emitting end, absorbing the light signal by gas to be measured, receiving the light signal by a photoelectric detector I, converting the light signal into an electric signal, and obtaining a transmitted light intensity signal I t (t); one beam passes through the optical etalon and is used for collecting etalon signal I by the photoelectric detector II υ (t); the other beam is directly collected by a photoelectric detector III to obtain a background light intensity signal I 0 (t)；
(4) From etalon signal I υ (t) obtaining a time-frequency response characteristic v (t);
(5) Transmitted light intensity signal I t (t) performing digital phase-locking, low-passFiltering, in the course of which the parameters of digital phase-locked and low-pass filtering are based on reference frequency f ref Setting to obtain a first harmonic signal S 1f Will transmit the light intensity signal I t (t) dividing by the first harmonic signal
Then obtain the corrected light intensity signal>
(6) For background light intensity signal I 0 (t) and the corrected intensity signal
Respectively carrying out digital phase locking and low-pass filtering treatment, wherein in the treatment process, the parameters of the digital phase locking and the low-pass filtering are based on the modulation frequency f m Setting to obtain the corresponding first harmonic signal and second harmonic signal:
(7) According to Beer-Lambert law, further processing the first harmonic signal and the second harmonic signal of the light intensity signal obtained in the step (6) to obtain a normalized second harmonic signal, and utilizing a background light intensity signal I 0 And (t) obtaining a simulated normalized second harmonic signal according to the time frequency response characteristics obtained in the step (4), fitting an integral absorption area A by using a least square algorithm according to the obtained normalized second harmonic signal and the simulated normalized second harmonic signal, and calculating the concentration value of the gas to be detected through the integral absorption area A.
2. The gas concentration measuring apparatus based on the high-frequency reference optical frequency division multiplexing technique as set forth in claim 1, wherein: in step (5), the corrected light intensity signal
Calculated by the following formula:
in the formula (1), the reaction mixture is,
for transmitting a light intensity signal I t (t) corresponding reference frequency f ref The first harmonic component and the second harmonic component are x component and y component, and F is a low-pass filter;
in the formula (2), the reaction mixture is,
for transmitting a light intensity signal I t (t) corresponding reference frequency f ref A lower first harmonic signal;
in the formula (3), the reaction mixture is,
is the corrected light intensity signal.
3. The gas concentration measuring apparatus based on the high-frequency reference optical frequency division multiplexing technique as set forth in claim 1, wherein: in step (6), the background light intensity signal I 0 (t) first and second harmonic signals and modified intensity signal
The first harmonic signal and the second harmonic signal are calculated by the following formula:
in the formula (4), the reaction mixture is,
as a background light intensity signal I 0 (t) the corresponding first and second harmonic x-and y-components, < >, in a manner that is based on the value of the harmonic>
Respectively is the corrected light intensity signal>
Corresponding first harmonic x component and second harmonic y component, F is low-pass filter;
in the formula (5), the reaction mixture is,
as a background light intensity signal I 0 (t) first and second harmonic signal->
For the corrected light intensity signal->
First and second harmonic signals.
4. The gas concentration measuring apparatus based on the high-frequency reference optical frequency division multiplexing technique as set forth in claim 1, wherein: in step (7), the background light intensity signal I is subtracted 0 (t) normalized second harmonic signal S 2f/1f Expressed as:
the algorithm widens the integral absorption area A and the spectral line collision by delta v C Doppler broadening Deltav D And the laser center frequency v0 is used as a fitting parameter to participate in the pair S 2f/1f The least square fitting is carried out, digital phase-locked low-pass filtering and background-deduction normalization processing are carried out on the simulated and experimental light intensity signals, and background-deduction normalization harmonic signals of the simulated light intensity are obtained
Background-subtracted normalized harmonic signal S of sum experimental light intensity 2f/1f (ii) a Fitting the spectral absorbance using a least squares algorithm, according to which the absorbance is based on ≥ i>
And S 2f/1f Converging when the residual error is minimum to obtain the best fitting parameter A;
according to Beer-Lambert's law, the relationship between the integrated absorption area a and the gas concentration is expressed as:
in the formula (7), X is the concentration of the gas to be measured, P is the total pressure of the gas, S (T) is the linear intensity of the transition spectral line, T is the temperature of the gas, and X is gas Is the gas concentration, L is the optical path length, and A is the integral absorption area.
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