CN111474138B - Gas concentration measuring device and method based on high-frequency reference optical frequency division multiplexing technology - Google Patents

Abstract

The invention discloses a gas concentration measurement device based on the high-frequency reference light frequency division multiplexing technology, and also discloses a gas concentration measurement method based on the high-frequency reference light frequency division multiplexing 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 the detection light intensity, and then accurately extracts the harmonic signals of the detection light intensity, improves the accuracy of gas parameter measurement, and expands the spectrum The scope of application of the absorption method; the method of the present invention has the characteristics of good applicability and wide application scenarios, so the method of the present invention has important application value for the detection of flame temperature and component concentration in complex environments such as aerospace engine combustion chambers.

Description

A gas concentration measurement device and measurement method based on high-frequency reference optical frequency division multiplexing technology

Technical Field

The invention relates to a gas concentration measuring device based on high-frequency reference light frequency division multiplexing technology, and also to a gas concentration measuring method based on high-frequency reference light frequency division multiplexing technology, belonging to the technical field of optical measurement.

Background Art

Aircraft engines are complex and sophisticated thermal machines that directly affect the performance, reliability and economy of aircraft. The combustion chamber is an indispensable and important component of the engine. It releases the chemical energy in the fuel through combustion, converts the chemical energy into thermal energy, produces high-temperature, high-pressure combustion gas, and improves the engine's work capacity. When designing the combustion chamber, it is necessary to ensure good combustion stability, high combustion efficiency, and low emission pollution. The combustion products mainly include residual air ( _O2 and _N2 ), carbon oxides (CO and _CO2 ), nitrogen oxides (NO and _NO2 ), unburned hydrocarbon compounds (TCH) and other gases and solid fine particles. Among them, characteristic gases are important indicative gases that reflect combustion characteristics. Its presence indicates that the fuel is not completely burned and the combustion efficiency needs to be improved. The detection of characteristic gas parameters is conducive to the optimization of combustion efficiency and the acquisition of important data for combustion chamber design and fuel equivalence ratio selection.

Gas detection technology is mainly divided into two categories according to the measurement principle: spectroscopy and non-spectroscopy. Non-spectroscopy mainly includes chemical analysis and electrical gas detection. Chemical analysis can effectively separate mixed gases, but the response time is slow. Electrical gas detection has high sensitivity and wide detection range, but it needs to contact the measurement environment and has poor ability to identify gas types. Spectroscopy measures the relevant parameters of the target gas spectrum and inverts the gas concentration information. It can detect many types of gases and has the advantages of non-contact measurement and fast response time. It is currently a hot research topic in gas detection. Spectroscopy mainly includes Fourier transform infrared absorption spectroscopy (FTIR) and tunable semiconductor laser absorption spectroscopy (TDLAS). FTIR technology is mainly based on the principle of Michelson interferometer. The infrared light source is collimated by a collimating lens to emit parallel light, which is absorbed by the gas to be measured and received by the telescope system. Then it is converged to the detector through the interferometer to obtain the interference signal of the gas to be measured. After Fourier transform, the absorption spectrum information of the gas at different concentrations can be obtained, so as to calculate the concentration of the gas. However, FTIR equipment is relatively large, has a relatively slow response speed, and is relatively expensive, so it will need some development in the future. TDLAS technology is a spectral measurement method based on the narrow linewidth characteristics of semiconductor lasers. It can achieve multi-component and multi-parameter simultaneous measurement of mixed gases. It has strong versatility and high measurement resolution. The concentration of trace gases can be measured by selecting the appropriate characteristic absorption spectrum of the 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. It has been widely used in trace gas detection in the infrared band and aerospace engine combustion flame temperature, component concentration detection and other aspects.

In the detection of gas parameters in complex environments, due to the influence of interference factors such as turbulence and strong vibration in the environment, the signal measured by the traditional WMS method will be distorted and cannot be used to extract useful information. For example, in the process of aircraft engine combustion diagnosis, the strong vibration of the engine ignition and combustion stage and the strong turbulence of the combustion flow field will cause serious interference to the transmitted light intensity, affecting the measurement accuracy of engine combustion diagnosis. In this regard, when processing the experimental signal, the multi-cycle averaging method of light intensity can be used to suppress the noise. The wavelength modulation technology separates the high-frequency absorption signal from the low-frequency noise in the frequency domain by superimposing the high-frequency modulation signal, and demodulates the absorption signal at a specific frequency with the help of phase-locked filtering technology, thereby effectively suppressing the low-frequency noise interference. However, the modulation frequency currently used for aircraft engine combustion diagnosis is still relatively low, mostly below 200kHz. Increasing the modulation frequency of the traditional WMS method is likely to cause problems such as unstable control of the laser light output center by the laser controller, insufficient detector bandwidth, and inability of the acquisition facilities to meet the requirements. In addition, in measurement environments with severe mechanical vibration and flame jitter, especially for the transient flow field of a scramjet engine, the interference frequency and the modulation frequency are equivalent, which easily causes crosstalk and makes it impossible to separate the interference and absorption signals in the frequency domain, seriously affecting the measurement accuracy.

Summary of the invention

Purpose of the invention: The technical problem to be solved by the present invention is to provide a gas concentration measurement device based on high-frequency reference optical frequency division multiplexing technology.

Another technical problem to be solved by the present invention is to provide a gas concentration measurement method based on high-frequency reference optical frequency division multiplexing technology, which can greatly improve the accuracy of gas parameter measurement in complex environments by extracting effective information from the original light intensity signal.

In order to solve the above technical problems, the technical solution adopted by the present invention is:

A gas concentration measuring device based on high-frequency reference optical frequency division multiplexing technology comprises a signal generating module, a gas parameter measuring module, a signal receiving module and a signal processing module in sequence; wherein the signal generating 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 standard tool and a measuring cell; the signal receiving module consists of three photodetectors; the measuring cell is filled with a gas to be measured; the function generator inputs a scanning superposition modulation signal into a laser controller I, and the laser controller I tunes the output wavelength and light intensity of the distributed feedback laser I; and at the same time, the function generator inputs the modulation signal into the laser controller I. The laser controller II is input into the laser controller II, which tunes the output wavelength and light intensity of the distributed feedback laser II; after the two laser beams are coupled, they are divided into three light signals through two optical fiber splitters in turn, one of which passes through the measuring cell from the laser emission end, is received by the photodetector I after being absorbed by the gas to be measured and converted into an electrical signal to obtain a transmitted light intensity signal; another light signal is received by the photodetector II after passing through the optical standard, and the standard signal is obtained for time-frequency conversion; the last light signal is directly received by the photodetector III to obtain the background signal, and the three signals are transmitted by the corresponding photodetectors to the signal processing module for processing.

A gas concentration measurement method based on high-frequency reference optical frequency division multiplexing technology specifically comprises the following steps:

(1) The function generator superimposes the signal with the scanning frequency _fs with the modulation frequency _fm and inputs it into the laser controller I through its internal channel 1. The laser controller I tunes the output wavelength and light intensity of the DFB laser I;

(2) The function generator inputs the modulation frequency f _ref signal into the laser controller II through its internal channel 2, and the laser controller II tunes the output wavelength and light intensity of the DFB laser II;

(3) The modulated light of step (1) is coupled with the modulated light of step (2), and is divided into three light signals through an optical fiber beam splitter. One light signal is transmitted from the laser emission end through the measuring cell, and is received by the photodetector I after being absorbed by the gas to be measured and converted into an electrical signal to obtain a transmitted light intensity signal I _t (t); one light signal is transmitted through an optical standard, and the standard signal I _v (t) is collected by the photodetector II; and the other light signal is directly collected by the photodetector III to obtain a background light intensity signal I ₀ (t);

(4) Obtain the time-frequency response characteristic υ(t) from the etalon signal I _v (t);

后得到修正后的光强信号

(5) The transmitted light intensity signal I _t (t) is subjected to digital phase locking and low-pass filtering. During the processing, the parameters of the digital phase locking and low-pass filtering are set according to the reference frequency f _ref to obtain the first harmonic signal S _1f . The transmitted light intensity signal I _t (t) is divided by the first harmonic signal

Then the corrected light intensity signal is obtained

分别进行数字锁相、低通滤波处理，在处理过程中，数字锁相、低通滤波的参数依据调制频率f_m进行设置，得到各自对应的一、二次谐波信号；(6) Background light intensity signal I ₀ (t) and corrected light intensity signal

Digital phase locking and low-pass filtering are performed respectively. During the processing, the parameters of digital phase locking and low-pass filtering are set according to the modulation frequency f _m to obtain the first and second harmonic signals corresponding to each other;

(7) According to the Beer-Lambert law, the first and second harmonic signals of the light intensity signal obtained in step (6) are further processed to obtain a normalized second harmonic signal. The simulated normalized second harmonic signal is obtained using the background light intensity signal I ₀ (t) and the time-frequency response characteristics obtained in step (4). Finally, the integral absorption area A is fitted based on the obtained normalized second harmonic and the simulated normalized second harmonic signal using a least squares algorithm, and the concentration value of the gas to be measured is calculated using the integral absorption area A.

由如下公式计算得到：Among them, in step (5), the corrected light intensity signal

It is calculated by the following formula:

为透射光强信号I_t(t)对应的参考频率f_ref下的一、二次谐波x分量和y分量，F为低通滤波器；In formula (1),

are the first and second harmonic x and y components at the reference frequency f _ref corresponding to the transmitted light intensity signal I _t (t), and F is a low-pass filter;

为透射光强信号I_t(t)对应的参考频率f_ref下的一次谐波信号；In formula (2),

is the first harmonic signal at the reference frequency f _ref corresponding to the transmitted light intensity signal I _t (t);

为修正后的光强信号。In formula (3),

is the corrected light intensity signal.

的一、二次谐波信号由如下公式计算得到：In step (6), the first and second harmonic signals of the background light intensity signal I ₀ (t) and the corrected light intensity signal

The first and second harmonic signals are calculated by the following formula:

为背景光强信号I₀(t)对应的一、二次谐波x分量和y分量，

分别为修正后的光强信号

对应的一、二次谐波x分量和y分量，F为低通滤波器；In formula (4),

are the first and second harmonic x and y components corresponding to the background light intensity signal I ₀ (t),

are the corrected light intensity signals

The corresponding first and second harmonic x and y components, F is a low-pass filter;

为背景光强信号I₀(t)的一、二次谐波信号，

为修正后的光强信号

的一、二次谐波信号。In formula (5),

are the first and second harmonic signals of the background light intensity signal I ₀ (t),

is the corrected light intensity signal

The first and second harmonic signals.

Wherein, in step (7), the normalized second harmonic signal S _2f/1f after deducting the background light intensity signal I ₀ (t) is expressed as:

和实验光强的扣除背景归一化谐波信号S_2f/1f；使用最小二乘算法对光谱吸收率进行拟合，根据最小二乘拟合算法，当

和S_2f/1f残差最小时收敛，得到最佳拟合参数A；The algorithm uses the integrated absorption area A, spectral line collision broadening Δv _C , Doppler broadening Δv _D and laser center frequency v0 as fitting parameters to participate in the least squares fitting of S _2f/1f , performs digital phase-locked low-pass filtering and background-subtracting normalization processing on the simulated (etalon) and experimental light intensity signals, and obtains the background-subtracting normalized harmonic signal of the simulated light intensity.

and the background-deducted normalized harmonic signal S _2f/1f of the experimental light intensity; the spectral absorbance is fitted using the least squares algorithm. According to the least squares fitting algorithm, when

The convergence occurs when the residual of S _2f/1f is the smallest, and the best fitting parameter A is obtained;

According to the Beer-Lambert law, the relationship between the integrated absorption area A and the gas concentration is expressed as:

In formula (7), X is the concentration of the gas to be measured, P is the total pressure of the gas, S(T) is the line intensity of the transition spectrum, T is the gas temperature, X _gas is the gas concentration, L is the optical path length, and A is the integrated absorption area.

Beneficial effects: Compared with the existing wavelength modulation spectroscopy technology, the present invention couples the high-frequency reference optical path with the wavelength modulation measurement optical path, realizes the extraction of interference signals and the correction of detection light intensity, and then accurately extracts the harmonic signal of the detection light intensity, improves the accuracy of gas parameter measurement, and expands the application scope of spectral absorption method; the method of the present invention has the characteristics of good applicability and wide application scenarios. Therefore, the method of the present invention can be applied to the detection of flame temperature and component concentration in complex environments such as aerospace engine combustion chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a system schematic diagram of a gas concentration measuring device according to the present invention;

FIG2 is a flow chart of a gas concentration measurement method according to the present invention;

FIG3 is a schematic diagram of the constructed verification system;

FIG4 is a methane concentration result obtained when the prior art method does not use a reference light signal to correct the light intensity signal;

FIG5 shows the methane concentration result obtained after the light intensity correction of the WMS signal using the reference light signal according to the method of the present invention.

DETAILED DESCRIPTION

The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but the scope of protection claimed by the present invention is not limited thereto.

As shown in FIG1 , the gas concentration measuring device based on the high-frequency reference optical frequency division multiplexing technology of the present invention can measure the gas concentration under strong interference. The measuring device comprises a signal sending module 1, a gas parameter measuring module 2, a signal receiving module 3 and a signal processing module 4 in sequence; 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 standard 12 and a measuring cell 11; the signal receiving module 3 is composed of three photodetectors 13; the gas to be measured is introduced into the measuring cell 11; the function generator 5 inputs the scanning superposition modulation signal into the laser controller I6 through its internal channel 1, and the laser controller I6 The output wavelength and light intensity of the DFB laser I8 are tuned, and at the same time, the function generator 5 inputs the modulation signal into the laser controller II7 through its internal channel 2. The laser controller II7 tunes the output wavelength and light intensity of the DFB laser II9. The laser emitted by the DFB laser I8 is coupled with the laser emitted by the DFB laser II9, and is divided into three light signals through two optical fiber beam splitters 10. One light signal passes through the measuring cell 11 from the laser emission end, and the light with the gas absorption signal is received by the photodetector 13 and converted into an electrical signal to obtain a transmitted light intensity signal; one light signal passes through the optical standard 12 and is received by the photodetector 13 to obtain the standard signal; another light signal is directly received by the photodetector 13 to obtain the background signal; all three signals are transmitted to the signal processing module 4 for processing. Among them, the distributed feedback laser can continuously emit stable laser light, and its wavelength is determined according to the gas to be measured.

As shown in FIG. 2 , the gas concentration measurement method based on high-frequency reference optical frequency division multiplexing technology of the present invention specifically includes the following steps:

Step 1, the function generator 5 inputs the scanning frequency _fs signal superimposed with the modulation frequency _fm signal into the laser controller I6 through channel 1, and the laser controller I6 tunes the output wavelength and light intensity of the DFB laser I8;

Step 2, the function generator 5 inputs the modulation frequency f _ref signal into the laser controller II2 through the channel 2, and the laser controller II6 tunes the output wavelength and light intensity of the DFB laser II9;

Step 3, the modulated light of step 1 is coupled with the modulated light of step 2, and is divided into three beams by the optical fiber beam splitter 10, one beam passes through the measuring cell 11 from the laser emission end, is received by the photodetector 13 and converted into an electrical signal after being absorbed by the gas to be measured, and a transmitted light intensity signal I _t (t) is obtained; one beam passes through the optical etalon 12 and is collected by the photodetector 13 to obtain an etalon signal I _v (t); the other beam is directly collected by the photodetector 13 to obtain a background light intensity signal I ₀ (t);

Step 4, obtaining the time-frequency response characteristic υ(t) from the etalon signal I _v (t);

后得到修正后的光强信号

Step 5: The transmitted light intensity signal I _t (t) is subjected to digital phase locking and low-pass filtering. During the processing, the parameters of the digital phase locking and low-pass filtering are set according to the reference frequency f _ref to obtain the first harmonic signal S _1f . The transmitted light intensity signal I _t (t) is divided by the first harmonic signal

Then the corrected light intensity signal is obtained

由如下公式计算得到：Corrected light intensity signal

It is calculated by the following formula:

为透射光强信号I_t(t)对应的参考频率f_ref下的一、二次谐波x分量和y分量，F为低通滤波器；In formula (1),

are the first and second harmonic x and y components at the reference frequency f _ref corresponding to the transmitted light intensity signal I _t (t), and F is a low-pass filter;

为透射光强信号I_t(t)对应的参考频率f_ref下的一次谐波信号；In formula (2),

is the first harmonic signal at the reference frequency f _ref corresponding to the transmitted light intensity signal I _t (t);

为修正后的光强信号；In formula (3),

is the corrected light intensity signal;

分别进行数字锁相、低通滤波处理，在处理过程中，数字锁相、低通滤波的参数依据调制频率f_m进行设置，得到各自对应的一、二次谐波信号；Step 6: The background light intensity signal I ₀ (t) and the corrected light intensity signal

Digital phase locking and low-pass filtering are performed respectively. During the processing, the parameters of digital phase locking and low-pass filtering are set according to the modulation frequency f _m to obtain the first and second harmonic signals corresponding to each other;

的一、二次谐波信号由如下公式计算得到：The first and second harmonic signals of the background light intensity signal I ₀ (t) and the corrected light intensity signal

The first and second harmonic signals are calculated by the following formula:

为背景光强信号I₀(t)对应的一、二次谐波x分量和y分量，

分别为修正后的光强信号

对应的一、二次谐波x分量和y分量，F为低通滤波器；In formula (4),

are the first and second harmonic x and y components corresponding to the background light intensity signal I ₀ (t),

are the corrected light intensity signals

The corresponding first and second harmonic x and y components, F is a low-pass filter;

为背景光强信号I₀(t)的一、二次谐波信号，

为修正后的光强信号

的一、二次谐波信号；In formula (5),

are the first and second harmonic signals of the background light intensity signal I ₀ (t),

is the corrected light intensity signal

The first and second harmonic signals;

Step 7, according to the Beer-Lambert law, further process the first and second harmonic signals of the light intensity signal obtained in step (6) to obtain a normalized second harmonic signal, use the background light intensity signal I ₀ (t) and the time-frequency response characteristics obtained in step (4) to obtain a simulated normalized second harmonic signal, and finally fit the integral absorption area A according to the obtained normalized second harmonic and the simulated normalized second harmonic signal using a least squares algorithm, and calculate the concentration value of the gas to be measured by the integral absorption area A;

The normalized second harmonic signal S _2f/1f after deducting the background light intensity signal I ₀ (t) can be expressed as:

和实验光强的扣除背景归一化谐波信号S_2f/1f；使用最小二乘算法对光谱吸收率进行拟合，根据最小二乘拟合算法，当

和S_2f/1f残差最小时收敛，可得到最佳拟合参数A；The algorithm uses the integrated absorption area A, spectral line collision broadening Δv _C , Doppler broadening Δv _D and laser center frequency v0 as fitting parameters to participate in the least squares fitting of S _2f/1f , performs digital phase-locked low-pass filtering and background-subtracting normalization processing on the simulated and experimental light intensity signals, and obtains the background-subtracting normalized harmonic signal of the simulated light intensity

and the background-deducted normalized harmonic signal S _2f/1f of the experimental light intensity; the spectral absorbance is fitted using the least squares algorithm. According to the least squares fitting algorithm, when

The convergence occurs when the residual of S _2f/1f is the smallest, and the best fitting parameter A can be obtained;

In formula (7), X is the concentration of the gas to be measured, P is the total pressure of the gas, S(T) is the line intensity of the transition spectrum, T is the gas temperature, X _gas is the gas concentration, L is the optical path length, and A is the integrated absorption area.

As shown in FIG3 , FIG3 is a verification system that has been constructed. The verification system emits 50 groups of filtered Gaussian white noises with cutoff frequencies ranging from 200 Hz to 10 kHz through a speaker on the first optical path to interfere with the light intensity. Under such interference, the method of the present invention is compared with the prior art method, thereby illustrating that the method of the present invention can effectively suppress the influence of interference signals on gas detection.

The verification system is as follows: a sinusoidal modulation signal is generated by channel 1 of function generator 5 and input into laser controller I6 to tune the output wavelength of DFB laser I8; a sinusoidal signal is generated by channel 2 of function generator 5 and input into laser controller II7 to tune the output wavelength of DFB laser II9. The center wave number of DFB laser I8 is selected as the center of the methane absorption spectrum (6046.95cm-1), and the center wave number of DFB laser II9 is selected as the non-absorption point of methane (6050.45cm-1); the two laser beams are divided into two paths after passing through the fiber coupler: the first laser beam passes through the gas absorption cell 11 with a length of 20cm and then reflects through the reflective film fixed on the speaker 14 (LS77W-35F-R8), and is finally received by the photodetector 13 and converted into an electrical signal to obtain the transmitted light intensity; the speaker 14 is used to generate interference signals of different frequencies and amplitudes; the second laser beam is first divided into two paths through the fiber beam splitter, one of which is directly received by the photodetector 13 to obtain the incident light intensity; the other laser beam passes through the optical standard 12 (the free spectrum spacing is 0.01cm-1) and is received by the photodetector 13 to obtain the standard signal, and the laser frequency response characteristic relationship is obtained; 50 groups of filtered Gaussian white noise with cutoff frequencies ranging from 200Hz to 10kHz are emitted through the speaker 14 to interfere with the light intensity.

Figure 4 shows the methane concentration calculated by the verification system using the existing technical method without using the 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 volatility is small. When the interference frequency range reaches above 5kHz, the volatility of the methane concentration becomes larger; and as the interference frequency range increases, the error of the methane concentration becomes larger and the volatility of the concentration becomes larger.

Figure 5 is a verification system that uses the method of the present invention to calculate the methane concentration result after using a reference light signal to correct the light intensity of the WMS signal. The error of the corrected methane concentration is within ±1%, and the variance is below 0.02%, with low volatility. Through experimental verification under different interference conditions, the harmonic signals before and after correction and the calculation results of methane concentration are analyzed. It can be seen that the method of extracting interference signals through high-frequency reference light signals and then correcting the WMS signal is feasible and can effectively suppress the influence of interference signals on gas detection.

Claims (4)

1. A gas concentration measurement device based on high-frequency reference optical frequency division multiplexing technology, characterized in that: it comprises a signal generating module, a gas parameter measuring module, a signal receiving module and a signal processing module in sequence; wherein the signal generating 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 standard tool and a measuring cell; the signal receiving module consists of three photodetectors; the measuring cell is filled with a gas to be measured; the function generator inputs a scanning superposition modulation signal into the laser controller I, and the laser controller I tunes the output wavelength and light intensity of the distributed feedback laser I; and at the same time, the function generator modulates the The control signal is input into the laser controller II, and the laser controller II tunes the output wavelength and light intensity of the distributed feedback laser II; after the two laser beams are coupled, they are divided into three light signals through two optical fiber beam splitters in turn, one of which passes through the measuring cell from the laser emission end, is received by the photodetector I after being absorbed by the gas to be measured and converted into an electrical signal, and a transmitted light intensity signal is obtained; another light signal is received by the photodetector II after passing through the optical standard tool, and the standard tool signal is obtained for time-frequency conversion; the last light signal is directly received by the photodetector III to obtain the background signal, and the three signals are transmitted by the corresponding photodetectors to the signal processing module for processing; The above-mentioned gas concentration measurement method based on high-frequency reference optical frequency division multiplexing technology specifically includes the following steps: (1) The function generator superimposes the signal with the scanning frequency _fs with the modulation frequency _fm and inputs it into the laser controller I through its internal channel 1. The laser controller I tunes the output wavelength and light intensity of the DFB laser I; (2) The function generator inputs the modulation frequency f _ref signal into the laser controller II through its internal channel 2, and the laser controller II tunes the output wavelength and light intensity of the DFB laser II; (3) The modulated light of step (1) is coupled with the modulated light of step (2), and is divided into three light signals through an optical fiber beam splitter. One light signal is transmitted from the laser emission end through the measuring cell, and is received by the photodetector I after being absorbed by the gas to be measured and converted into an electrical signal to obtain a transmitted light intensity signal I _t (t); one light signal is transmitted through an optical standard, and the standard signal I _υ (t) is collected by the photodetector II; and the other light signal is directly collected by the photodetector III to obtain a background light intensity signal I ₀ (t); (4) Obtaining the time-frequency response characteristic υ(t) from the etalon signal I _υ (t); (5) The transmitted light intensity signal I _t (t) is subjected to digital phase locking and low-pass filtering. During the processing, the parameters of the digital phase locking and low-pass filtering are set according to the reference frequency f _ref to obtain the first harmonic signal S _1f . The transmitted light intensity signal I _t (t) is divided by the first harmonic signal

Then the corrected light intensity signal is obtained

(6) Background light intensity signal I ₀ (t) and corrected light intensity signal

Digital phase locking and low-pass filtering are performed respectively. During the processing, the parameters of digital phase locking and low-pass filtering are set according to the modulation frequency f _m to obtain the first and second harmonic signals corresponding to each other: (7) According to the Beer-Lambert law, the first and second harmonic signals of the light intensity signal obtained in step (6) are further processed to obtain a normalized second harmonic signal. The simulated normalized second harmonic signal is obtained using the background light intensity signal I ₀ (t) and the time-frequency response characteristics obtained in step (4). Finally, the integral absorption area A is fitted based on the obtained normalized second harmonic and the simulated normalized second harmonic signal using a least squares algorithm, and the concentration value of the gas to be measured is calculated using the integral absorption area A. 2. The gas concentration measurement device based on high-frequency reference light frequency division multiplexing technology according to claim 1 is characterized in that: in step (5), the corrected light intensity signal

It is calculated by the following formula:

In formula (1),

are the first and second harmonic x and y components at the reference frequency f _ref corresponding to the transmitted light intensity signal I _t (t), and F is a low-pass filter; In formula (2),

is the first harmonic signal at the reference frequency f _ref corresponding to the transmitted light intensity signal I _t (t); In formula (3),

is the corrected light intensity signal. 3. The gas concentration measurement device based on high-frequency reference light frequency division multiplexing technology according to claim 1 is characterized in that: in step (6), the first and second harmonic signals of the background light intensity signal I ₀ (t) and the corrected light intensity signal

The first and second harmonic signals are calculated by the following formula:

In formula (4),

are the first and second harmonic x and y components corresponding to the background light intensity signal I ₀ (t),

are the corrected light intensity signals

The corresponding first and second harmonic x and y components, F is a low-pass filter; In formula (5),

are the first and second harmonic signals of the background light intensity signal I ₀ (t),

is the corrected light intensity signal

The first and second harmonic signals. 4. The gas concentration measuring device based on high-frequency reference light frequency division multiplexing technology according to claim 1 is characterized in that: in step (7), the normalized second harmonic signal S _2f/1f after deducting the background light intensity signal I ₀ (t) is expressed as:

The algorithm uses the integrated absorption area A, spectral line collision broadening Δν _C , Doppler broadening Δν _D and laser center frequency ν0 as fitting parameters to participate in the least squares fitting of S _2f/1f , performs digital phase-locked low-pass filtering and background-subtracting normalization processing on the simulated and experimental light intensity signals, and obtains the background-subtracting normalized harmonic signal of the simulated light intensity

and the background-deducted normalized harmonic signal S _2f/1f of the experimental light intensity; the spectral absorbance is fitted using the least squares algorithm. According to the least squares fitting algorithm, when

The convergence occurs when the residual of S _2f/1f is the smallest, and the best fitting parameter A is obtained; According to the Beer-Lambert law, the relationship between the integrated absorption area A and the gas concentration is expressed as:

In formula (7), X is the concentration of the gas to be measured, P is the total pressure of the gas, S(T) is the line intensity of the transition spectrum, T is the gas temperature, X _gas is the gas concentration, L is the optical path length, and A is the integrated absorption area.

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