Gas concentration and temperature two-parameter detection method and device based on TDLAS (Tunable Diode Laser Absorption Spectroscopy)

Abstract

The invention discloses a TDLAS (Tunable Diode Laser Absorption Spectroscopy)-based gas concentration and temperature dual-parameter detection method and device, and the detection method comprises the following steps: 1, obtaining an optical signal passing through an absorption cell filled with gas to be detected, and converting the obtained optical signal into a digital signal to be detected; step 2, obtaining a fundamental frequency harmonic phase signal according to the digital signal to be measured and the two fundamental frequency reference signals; obtaining a second harmonic signal according to the digital signal to be measured and the two paths of frequency doubling reference signals; and 3, establishing an equation set of the fundamental frequency harmonic phase signal, the second harmonic signal and the gas concentration and temperature, and solving the equation set to obtain the gas concentration and temperature. According to the invention, the gas concentration and temperature signals are obtained through a simple method, the method can be used for replacing a lock-in amplifier, and the cost of a detection device and the system complexity can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of tunable semiconductor laser absorption spectroscopy, and particularly relates to a method for detecting two parameters of gas concentration and temperature based on TDLAS. Background Art

[0002] With the development of industry and agriculture, a large number of various fossil energy sources used in production will generate many toxic, harmful, flammable and explosive gases. These gases will affect the atmospheric circulation, trigger acid rain, damage the ozone layer, and cause very serious environmental problems. Some greenhouse gases such as CO2 will also exacerbate the greenhouse effect, leading to global warming and affecting the living environment of humans. Therefore, it is of great significance to monitor the harmful gas components in the atmosphere and research and develop gas sensors. In the field of industrial safety, gas sensors can be used to monitor the CH4 concentration in mines, which can effectively prevent and avoid safety accidents caused by gas explosions. In the field of electric power, monitoring and analyzing the gases in transformer insulating oil can complete fault alarm and fault analysis. In the field of medical health, by detecting exhaled breath and analyzing the concentration changes of volatile organic compounds in it, diseases can be diagnosed.

[0003] Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology is an optical and spectroscopic measurement method that applies lasers to absorption spectroscopy measurement technology. It has advantages such as high measurement accuracy, high sensitivity, strong anti-interference ability, and a compact structure of the measurement device, and has been widely used in the field of gas parameter measurement. Traditional gas concentration detection systems based on the TDLAS principle include lasers, optical path structures, photodetectors, and lock-in amplifiers, which increase the cost and system complexity of the detection system. Under some special conditions, high-frequency modulation signals are required, and in this case, it is easily affected by noise and will affect the sensitivity. Summary of the Invention

[0004] The purpose of the present invention is to provide a device and method for detecting two parameters of gas concentration and temperature based on TDLAS.

[0005] To achieve the above object of the present invention, the following technical solutions are adopted:

[0006] The present invention first provides a method for detecting two parameters of gas concentration and temperature based on TDLAS, including:

[0007] Step 1, obtain an optical signal passing through an absorption cell filled with the gas to be measured, and convert the obtained optical signal into a digital signal to be measured (8);

[0008] Step 2: Obtain the fundamental harmonic phase signal based on the digital signal to be measured (8) and two fundamental frequency reference signals; obtain the second harmonic signal based on the digital signal to be measured and two second harmonic reference signals;

[0009] Step 3: Establish a system of equations for the fundamental harmonic phase signal, the second harmonic signal, the gas concentration, and the temperature, and solve the system of equations to obtain the gas concentration and the temperature. The established system of equations for the fundamental harmonic phase signal, the second harmonic signal, the gas concentration, and the temperature is as follows:

[0010]

[0011] where Y 2f is the peak value of the second harmonic signal; φ 1f is the peak-to-peak value of the fundamental harmonic phase signal; f1(C,T) is a function of the peak value of the second harmonic signal with respect to the gas temperature value C and the gas concentration value T, and f2(C,T) is a function of the peak value of the fundamental harmonic phase signal with respect to the gas temperature value C and the gas concentration value T.

[0012] The present invention also provides a dual-parameter detection device for gas concentration and temperature based on TDLAS, including: a signal generator, a temperature controller, a DFB laser, a collimator, a gas absorption cell, a photodetector, a data acquisition card, and a signal processor; the output ends of the signal generator and the temperature controller are connected to the DFB laser; the output end of the DFB laser is connected to the collimator; the gas absorption cell is arranged between the collimator and the photodetector; the output end of the photodetector is connected to the data acquisition card, and the data acquisition card converts the absorption signal received by the photodetector into a digital signal to be measured; the signal generator generates two fundamental frequency reference signals and two frequency-doubled reference signals; the signal processor receives the digital signal to be measured output by the data acquisition card, and the signal processor processes the digital signal to be measured according to the dual-parameter detection method for gas concentration and temperature based on TDLAS to obtain the gas concentration and the temperature.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] The detection device and method of the present invention can achieve the simultaneous calibration of gas concentration and temperature without using a lock-in amplifier, so as to reduce the cost of the gas detection system and simplify the system complexity.

[0015] Compared with the traditional TDLAS gas concentration detection method, under high-frequency modulation signal conditions, it can ensure high sensitivity while reducing the influence of noise on the detection results of concentration and temperature. Description of the Drawings

[0016] Figure 1 is a schematic diagram of the whole of the present invention;

[0017] Figure 2 Schematic diagram of the demodulation process of the present invention;

[0018] Figure 3 Comparison chart of the experimental results of the concentration of the present invention;

[0019] Figure 4 Linear fitting graph of the concentration of the present invention;

[0020] Figure 5 Temperature change graph of the present invention;

[0021] Figure 6 Two-dimensional simple schematic diagram of RBF. Specific implementation manners

[0022] The following further describes in detail the specific implementation manners of the present invention in conjunction with the accompanying drawings. The following embodiments are used to illustrate the present invention, but should not limit the protection scope of the present invention.

[0023] Figure 1 Overall schematic diagram of a gas concentration and temperature dual-parameter detection device provided by this embodiment based on TDLAS.

[0024] The gas concentration and temperature detection device includes:

[0025] First part: Select a Distributed Feedback (DFB) laser that conforms to the gas absorption spectrum according to the type of gas to be measured; use a signal generator to generate a low-frequency sawtooth scanning wave and a high-frequency sine modulation wave to drive the DFB laser, and modulate signal frequencies, intensities, etc. according to the laser parameters;

[0026] Second part: Design a semi-open gas absorption cell. Collimate the laser emitted by the laser and then pass it through the absorption cell filled with the gas to be measured, receive it by a photodetector, and then convert the absorption signal into a digital signal to be measured by a data acquisition card; process the acquired signal in a digital phase demodulation manner.

[0027] This embodiment takes carbon dioxide gas (CO2) as an example to provide a gas concentration and temperature dual-parameter detection method based on TDLAS, including:

[0028] The output end of the signal generator 1 and the output end of the temperature controller 2 are jointly connected to the DFB laser 3. The temperature controller 2 is used to adjust the operating temperature of the DFB laser 3 to prevent the spectral drift of the emitted light caused by excessive laser temperature; the output end of the DFB laser 3 is connected to the collimator 4, the output end of the collimator 4 is connected to the gas absorption cell 5, the other end of the gas absorption cell 5 is connected to the photodetector 6, and the output end of the photodetector 6 is connected to the data acquisition card 7. The data acquisition card 7 converts the signal into a digital signal to be measured 8.

[0029] The signal generator 1 generates two baseband reference signals and two second-harmonic reference signals; the two baseband reference signals are respectively a baseband sine reference signal 9 and a baseband cosine reference signal 10; the two second-harmonic reference signals are respectively a second-harmonic sine reference signal 15 and a second-harmonic cosine reference signal 16.

[0030] The signal processor receives the digital signal to be measured 8 output by the data acquisition card 7.

[0031] The signal processor processes the signal as follows:

[0032] The signal to be measured 8 is respectively multiplied by the baseband sine reference signal 9 and the baseband cosine reference signal 10, and then processed by a low-pass filter to obtain mutually orthogonal first baseband orthogonal signals 11 and second baseband orthogonal signals 12. After the first baseband orthogonal signals 11 and the second baseband orthogonal signals 12 are divided, a ratio signal 13 is obtained. After the ratio signal 13 is processed by an arctangent operation, a baseband harmonic phase signal 14 is obtained.

[0033] The digital signal to be measured 8 and the two second-harmonic reference signals are multiplied to obtain a first second-harmonic orthogonal signal 17 and a second second-harmonic orthogonal signal 18; the first second-harmonic orthogonal signal 17 and the second second-harmonic orthogonal signal 18 are squared and then square-rooted to obtain a second-harmonic signal 19.

[0034] Establish a system of equations for the baseband harmonic phase signal, the second-harmonic signal, the gas concentration, and the temperature, and solve the system of equations to obtain the gas concentration and the temperature. The system of equations established for the baseband harmonic phase signal, the second-harmonic signal, the gas concentration, and the temperature is as follows:

[0035]

[0036] Among them, Y 2f is the peak value of the second-harmonic signal; φ 1f is the peak-to-peak value of the baseband harmonic phase signal; f1(C, T) is a function of the peak value of the second-harmonic signal, the gas temperature value C, and the gas concentration value T, and f2(C, T) is a function of the peak value of the baseband harmonic phase signal, the gas temperature value C, and the gas concentration value T.

[0037] For the system of equations of the baseband harmonic phase signal, the second-harmonic signal, the gas concentration, and the temperature, a set of determined temperature values and concentration values corresponds to a set (the peak value Y of the second-harmonic 2f , the peak-to-peak value φ of the first-harmonic phase 1f ). Since the system of equations is non-linear, an exact relational expression cannot be directly obtained. In order to solve the system of equations, a 5×5 matrix can be simply established first (a 10×10, 15×15, etc. matrix can be established to increase the matrix data density and improve the detection accuracy. Here, a 5×5 matrix is taken as an example):

[0038]

[0039] Based on the above matrix, 25 sets of discrete points can be obtained. The radial basis function (RBF) interpolation algorithm is used to interpolate these discrete points to construct a non-linear continuous function. See Figure 6 , and the RBF interpolation method is to fit a non-linear function that conforms to all points for a series of discrete points. Thus, according to the constructed non-linear continuous function, the gas temperature value C and the gas concentration value T can be obtained.

[0040] In the actual process, multiple sets of temperature and concentration values are repeatedly set, and the peak value Y of the corresponding second harmonic is calculated 2f , and the peak-to-peak value of the primary harmonic phase Taking the above 5×5 matrix as an example, the data of the entire matrix is constructed.

[0041] Suppose a set of temperature is 660K and the concentration is 18% at this time. The two parameters of Y 2f (660, 18) and φ 1f (660, 18) are found at the closest positions in the database through RBF. If the corresponding temperature coordinate here is 655K and the concentration coordinate is 17.2%, which is an approximation of the original value, the simultaneous inversion of temperature and concentration for the two parameters is achieved in this way.

[0042] The dual-parameter detection method for gas concentration and temperature based on TDLAS of the present invention includes the following steps:

[0043] Step 1: According to the type of gas to be measured, the corresponding absorption spectral line is selected, and the central frequency of the absorption spectrum is v0;

[0044] Step 2: In order to make the output spectrum of the DFB laser cover the gas absorption spectrum, a low-frequency sawtooth signal sawtooth(t) needs to be generated by a signal generator to control the scanning of the DFB laser; in order to suppress the interference of background noise, a high-frequency sine wave signal sin(t) needs to be generated to modulate the output light of the DFB laser; the two signals are superimposed and applied to the DFB laser;

[0045] The laser signal frequency generated by the DFB laser in Step 2 is:

[0046] v(t) = v0 + Esin(2πf m t)

[0047] In the formula, v(t) is the laser output frequency, v0 is the laser center frequency, E is the modulation amplitude, f m is the modulation frequency, and t is the scanning time;

[0048] Step 3: The laser emitted by the laser passes through a collimator and then through an absorption cell filled with the gas to be measured, and is received by a photodetector. Then, the data acquisition card converts the analog absorption signal into a digital signal to be measured;

[0049] According to the Beer-Lambert law, the change in light intensity before and after a laser beam of a specific frequency enters the gas to be measured can be expressed as:

[0050] I(v) = I0exp[-α(v)CPL]

[0051] In the formula, I0 is the incident light intensity, I(v) is the light intensity at the receiving end after passing through the gas to be measured, L is the optical path length of the laser passing through the gas to be measured, C is the concentration of the gas to be measured, P is the pressure, α(ν) is the absorption coefficient of the gas to be measured for light at frequency v, which is a function of the gas temperature T, and the expression is as follows:

[0052]

[0053] In the formula, T0 represents the normal temperature of 298K, S(T0) represents the absorption line intensity at temperature T0, Q(T) represents the molar molecular weight function, h represents Planck's constant, c represents the speed of light, E’ represents the energy of the low energy level, K represents Boltzmann's constant, v c represents that the gas absorption center frequency is equal to the center frequency v0 of the absorption spectrum, and m represents the atomic mass.

[0054] The relationship between the light intensity generated by the absorption of the light signal by the gas to be measured in Step 3 and time is as follows:

[0055] I(v(t)) = I0exp{-α[v(t)]CPL} = I0exp{-α[v0 + Esin(2πf m t)]CPL}

[0056] Step 4: Process the collected digital signal by means of digital quadrature demodulation phase and digital quadrature phase-locking. The demodulation process is as Figure 2 shown. Let D[n] represent the signal to be measured (8), and the expression is as follows:

[0057]

[0058] In the formula, D0 is the DC component existing in the signal to be measured, A is the amplitude of the signal to be measured, n is the number of sampling points, is the phase difference between the modulation signal and the reference signal;

[0059] Use a data acquisition card to directly collect the fundamental frequency sine reference signal S[n] and fundamental frequency cosine reference signal C[n] generated by a signal generator, which have the same frequency as the signal to be measured, as well as the second harmonic frequency sine reference signal S2[n] and second harmonic frequency cosine reference signal C2[n], which are twice the frequency of the signal to be measured. The expressions are as follows:

[0060] S[n] = Bsin(2πf m n)

[0061] C[n] = Bcos(2πf m n)

[0062] S2[n] = Bsin(2 * 2πf m n)

[0063] C2[n] = Bcos(2 * 2πf m n)

[0064] In the formula, B is the amplitude of the reference signal;

[0065] After multiplying S[n] and C[n] with the signal to be measured D[n] respectively and then performing low-pass filtering, the high-frequency components can be filtered out, leaving the low-frequency DC part containing the amplitude and phase information of the original signal, and obtaining the mutually orthogonal signals Y[n] and X[n];

[0066] After multiplying S2[n] and C2[n] with the signal to be measured D[n] respectively and then performing low-pass filtering, the high-frequency components can be filtered out, leaving the low-frequency DC part containing the amplitude and harmonic information of the original signal, and obtaining the mutually orthogonal signals Y LPF [n] and X LPF [n];

[0067] Step 5: After performing a division operation on the mutually orthogonal signals Y[n] and X[n] and then performing an arctangent operation, obtain the fundamental frequency harmonic phase signal The expression is as follows:

[0068]

[0069] After performing a square sum and then a square root operation on the mutually orthogonal signals Y LPF [n] and X LPF [n], obtain the second harmonic signal Y 2f [n]. The expression is as follows:

[0070]

[0071] Step 6: For the fundamental harmonic phase signal, take the vertical coordinate phases of the maximum and minimum points at the sampling points near the gas absorption peak, calculate its peak-to-peak value, and obtain a parameter of the fundamental harmonic phase peak-to-peak value. This parameter has a positive linear variation relationship with the gas concentration and a negative non-linear variation relationship with the temperature.

[0072] For the second harmonic signal, take its peak value to obtain another parameter of the second harmonic peak value. This parameter has a positive linear variation relationship with the gas concentration and a negative non-linear variation relationship with the temperature.

[0073] Step 7: Establish a system of equations for the fundamental harmonic phase signal, the second harmonic signal, the gas concentration, and the temperature, and solve the system of equations to obtain the gas concentration and the temperature. The system of equations established for the fundamental harmonic phase signal, the second harmonic signal, the gas concentration, and the temperature is as follows:

[0074]

[0075] where, Y 2f is the peak value of the second harmonic signal; is the peak-to-peak value of the fundamental harmonic phase signal; f1(C,T) is the function of the second harmonic signal peak value with respect to the gas temperature value C and the gas concentration value T, and f2(C,T) is the function of the fundamental harmonic phase signal peak value with respect to the gas temperature value C and the gas concentration value T.

[0076] For the system of equations of the fundamental harmonic phase signal, the second harmonic signal, the gas concentration, and the temperature, a set of determined temperature values and concentration values corresponds to a set of (the peak value Y 2f of the second harmonic, and the peak-to-peak value φ 1f of the fundamental harmonic phase). Due to the non-linearity of the system of equations, an exact relationship cannot be directly obtained.

[0077] Step 8: Solve the system of equations, and a matrix of the concentration and temperature corresponding to the peak-to-peak value of the fundamental harmonic phase signal and the peak value of the second harmonic signal can be established. Based on the data in the matrix, use the Radial Basis Function (RBF) interpolation algorithm to interpolate these discrete points to construct a non-linear continuous function. Thus, according to the constructed non-linear continuous function, the gas temperature value C and the gas concentration value T can be obtained.

[0078] To illustrate the feasibility of the method of the present invention, actual experimental data is used for illustration as follows:

[0079] The gas to be measured is carbon dioxide (CO2). A DFB laser with a center wavelength of 1579.12 nm and an initial optical intensity of 10 mW is selected. The modulation signal amplitude is selected as 0.05 V, and the modulation signal frequency is selected as 10 kHz. A gas absorption cell with an optical path of 2 m is selected and filled with carbon dioxide gas in the range of 15000 ppm to 40000 ppm under normal temperature and pressure. The above method of the present invention is used for digital demodulation. With the sampling points as the abscissa and the fundamental harmonic phase φ[n] and the second harmonic Y 2f [n] as the ordinate, a two-dimensional curve image is plotted, as shown in Figure 3 panels (a) and (b); with the peak-to-peak value of the fundamental harmonic phase and the peak value of the second harmonic as the abscissa and the actual gas concentration as the ordinate, a two-dimensional curve image is plotted, as shown in Figure 4 panels (a) and (b). It can be observed that as the peak-to-peak value of the fundamental harmonic signal and the peak value of the second harmonic increase, the gas concentration also increases. Thus, it can be known that there is indeed a linear relationship change between the fundamental harmonic phase signal and the second harmonic and the gas concentration. Immediately afterwards, the temperature of the carbon dioxide gas at 10000 ppm under normal pressure is changed from 300 K to 1000 K. With the peak-to-peak value of the fundamental harmonic phase and the peak value of the second harmonic as the abscissa and the gas temperature as the ordinate, a two-dimensional curve image is plotted, as shown in Figure 5 panels (a) and (b). It can be observed that as the peak-to-peak value of the fundamental harmonic signal and the peak value of the second harmonic increase, the gas temperature decreases. There is a non-linear relationship change with a negative correlation between the fundamental harmonic phase signal and the second harmonic and the gas temperature. Then, different temperature and concentration values are given to obtain two parameters, namely the peak-to-peak value of the fundamental harmonic phase and the peak value of the second harmonic. Multiple sets of discrete point data are accumulated. Through the RBF interpolation method, as shown in Figure 6 , a non-linear function regarding temperature and concentration is constructed to realize the detection of unknown temperature and concentration.

[0080] This embodiment provides a device for detecting gas concentration and temperature dual parameters based on TDLAS. By means of digital quadrature phase-locking and digital quadrature demodulation phase method for the signal to be measured containing concentration information, two parameters, namely the second harmonic signal and the fundamental harmonic phase signal containing concentration and temperature information, can be obtained. Using multiple sets of discrete point data formed by these two parameters at different concentrations and temperatures, a non-linear function is constructed through the RBF interpolation method to realize the detection of unknown concentration and temperature. The present invention obtains signals containing gas concentration and temperature through a relatively simple method, replacing the function of the actual hardware phase-locked amplifier, which can effectively reduce the cost and system complexity of the detection device, and can ensure high sensitivity and reduce the influence of noise on the detection results of concentration and temperature in the case of high-frequency modulation signals.

[0081] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A dual-parameter detection method for gas concentration and temperature based on TDLAS, characterized in that, Including: Step 1: Obtain the optical signal passing through the absorption cell filled with the gas to be measured, and convert the obtained optical signal into a digital signal to be measured (8); Step 2: Obtain the fundamental harmonic phase signal (14) according to the digital signal to be measured (8) and two fundamental frequency reference signals; obtain the second harmonic signal (19) according to the digital signal to be measured (8) and two second harmonic reference signals; Step 3: Establish a system of equations of the fundamental harmonic phase signal, the second harmonic signal with the gas concentration and temperature, and solve the system of equations to obtain the gas concentration and temperature (20), where the established system of equations of the fundamental harmonic phase signal, the second harmonic signal with the gas concentration and temperature is: Among them, Y 2f is the peak value of the second harmonic signal; is the peak value of the fundamental harmonic phase signal; f1(C, T) is a function of the peak value of the second harmonic signal with respect to the gas temperature value C and the gas concentration value T, and f2(C, T) is a function of the peak value of the fundamental harmonic phase signal with respect to the gas temperature value C and the gas concentration value T.

2. The dual-parameter detection method for gas concentration and temperature based on TDLAS according to claim 1, wherein In Step 2, obtaining the fundamental harmonic phase signal (14) according to the digital signal to be measured (8) and two fundamental frequency reference signals includes: Performing a multiplication operation on the digital signal to be measured (8) and a fundamental frequency sine reference signal (9), and then processing through a low-pass filter to obtain mutually orthogonal first fundamental frequency orthogonal signals (11); performing a multiplication operation on the signal to be measured (8) and a fundamental frequency cosine reference signal (10), and then processing through a low-pass filter to obtain mutually orthogonal second fundamental frequency orthogonal signals (12); Performing a division operation on the first fundamental frequency orthogonal signal (11) and the second fundamental frequency orthogonal signal (12) to obtain a ratio signal (13), and after performing an arctangent operation on the ratio signal (13), obtaining the fundamental harmonic phase signal (14).

3. The dual-parameter detection method for gas concentration and temperature based on TDLAS according to claim 1, wherein, In Step 2, obtaining the second harmonic signal (19) according to the digital signal to be measured (8) and two second harmonic reference signals includes: Performing a multiplication operation on the digital signal to be measured (8) and a second harmonic sine reference signal (15), and then processing through a low-pass filter to obtain mutually orthogonal first second harmonic orthogonal signals (17); performing a multiplication operation on the signal to be measured (8) and a second harmonic cosine reference signal (16), and then processing through a low-pass filter to obtain mutually orthogonal second second harmonic orthogonal signals (18); Performing a square sum and square root operation on the first second harmonic orthogonal signal (17) and the second second harmonic orthogonal signal (18) to obtain the second harmonic signal (19).

4. The dual-parameter detection method for gas concentration and temperature based on TDLAS according to claim 2 or 3, characterized in that The frequency and intensity expressions of the digital signal to be measured (8) are as follows: v(t) = v0 + Esin(2πf m t) I(v(t)) = I0exp{-α[v(t)]CPL} Where, v(t) is the output frequency of the laser, v0 is the center frequency of the laser, E is the modulation amplitude, f m is the modulation frequency, t is the scanning time, I0 is the incident light intensity, I(v(t)) is the light intensity at the receiving end after passing through the gas to be measured, L is the optical path length of the laser passing through the gas to be measured, C is the concentration of the gas to be measured, P is the pressure, α[ν(t)] is the light absorption coefficient of the gas to be measured at the frequency v(t), which is a function of the gas temperature T, and the expression is as follows: In the formula, T0 represents the normal temperature of 298K, S(T0) represents the absorption spectral line intensity at temperature T0, Q(T) represents the molar molecular weight function, h represents the Planck constant, c represents the speed of light, E’ represents the low-level energy, K represents the Boltzmann constant, v c represents the gas absorption center frequency, and m represents the atomic mass.

5. The dual-parameter detection method for gas concentration and temperature based on TDLAS according to claim 4, wherein The collected digital signal to be measured is processed by means of digital orthogonal phase-locking and digital orthogonal demodulation phase. Represent the digital signal to be measured (8) with D[n], and the expression is as follows: where D0 is the DC component existing in the signal to be measured, A is the amplitude of the signal to be measured, n is the number of sampling points, is the phase difference between the modulation signal and the reference signal.

6. The dual-parameter detection method for gas concentration and temperature based on TDLAS according to claim 5, wherein The fundamental frequency sine reference signal (9) has the same frequency as the digital signal to be measured (8), and the fundamental frequency cosine reference signal (10) has the same frequency as the digital signal to be measured (8); The expressions of the fundamental frequency sine reference signal and the fundamental frequency cosine reference signal are as follows: S[n] = Bsin(2πf m n) C[n] = B cos(2πf m n) In the formula, S[n] is the fundamental frequency sine reference signal (9), C[n] is the fundamental frequency cosine reference signal (10), and B is the amplitude of the reference signal; S[n] and C[n] are respectively multiplied by the signal D[n] and then processed through low-pass filtering, leaving the low-frequency DC part containing the amplitude and phase information of the original signal, to obtain mutually orthogonal first fundamental frequency orthogonal signals (11) and second fundamental frequency orthogonal signals (12).

7. The dual-parameter detection method for gas concentration and temperature based on TDLAS according to claim 6, characterized in that, The expression of the fundamental frequency harmonic phase signal (14) is obtained by performing an arctangent operation on the result of dividing the first fundamental frequency quadrature signal (11) by the second fundamental frequency quadrature signal, as follows: wherein, is the fundamental harmonic phase signal (14), Y[n] is the first fundamental frequency quadrature signal, and X[n] is the second fundamental frequency quadrature signal.

8. The dual-parameter detection method for gas concentration and temperature based on TDLAS according to claim 5, characterized in that, The digital signal to be measured (8) obtained by the data acquisition card, the second harmonic sine reference signal (15), and the second harmonic cosine reference signal (16) are respectively: S2[n] = Bsin(2 * 2πf m n) C2[n] = B cos(2 * 2πf m n) Wherein, S2[n] is the double-frequency sine reference signal (15), C2[n] is the double-frequency cosine reference signal (16), A is the amplitude of the signal to be measured, B is the amplitude of the reference signal, n is the number of sampling points, is the phase difference between the modulation signal and the reference signal, D0 is the DC component existing in the signal to be measured, f m is the modulation frequency; To obtain the second harmonic, the modulation frequency of the reference signal is twice the frequency of the signal to be measured, i.e., 2 * 2πf m ; The output signals after the signal to be measured and the two reference signals are multiplied are After low-pass filtering, the high-frequency terms and the terms with D0 are filtered out, and two output signals of second-harmonic orthogonal X LPF and Y LPF are: The square root of the sum of the squares of the two quadrature signals is taken to obtain the second harmonic signal as: According to the second harmonic signal Y 2f Obtain the peak value of the second harmonic signal and obtain the amplitude A of the signal D0 to be measured.

9. The dual-parameter detection method for gas concentration and temperature based on TDLAS according to claim 5, characterized in that, The two fundamental frequency reference signals and the two second harmonic reference signals are all generated by the signal generator (1) and converted into digital reference signals by the data acquisition card (7).

10. The dual-parameter detection device for gas concentration and temperature based on TDLAS includes: A signal generator (1), a temperature controller (2), a DFB laser (3), a collimator (4), a gas absorption cell (5), a photodetector (6), a data acquisition card (7), and a signal processor; the output ends of the signal generator (1) and the temperature controller (2) are connected to the DFB laser (3); the output end of the DFB laser (3) is connected to the collimator (4); the gas absorption cell (5) is arranged between the collimator (4) and the photodetector (6); the output end of the photodetector (6) is connected to the data acquisition card (7), and the data acquisition card (7) converts the absorption signal received by the photodetector into a digital signal to be measured (8); characterized in that: The signal generator (1) generates two fundamental frequency reference signals and two second harmonic reference signals; the signal processor receives the digital signal to be measured (8) output by the data acquisition card (7), and the signal processor processes the digital signal to be measured (8) according to the dual-parameter detection method for gas concentration and temperature based on TDLAS described in any one of claims 1-9 to obtain the gas concentration and temperature.

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