Gas detection apparatus and method based on v-shaped wavelength tuning and modulation techniques

Abstract

The application discloses a gas detection device based on V-shaped wavelength tuning and modulation technology, comprising a V-shaped wave modulator, a tunable laser, a parabolic mirror, a gas sample cell, a half-reflection half-transmission lens, a standard device, a full-reflection mirror, a double-channel photoelectric detector, a signal demodulation and analysis module, a signal display and output module which are connected in series. The application also discloses a gas detection method based on V-shaped wavelength tuning and modulation technology. The application utilizes the dependence of the output power and wavelength of the tunable semiconductor laser on the scanning current or voltage, and combines the symmetry of the V-shaped wave, so that the wavelength scanning and modulation of the laser are realized in an ultra-narrow range, and the influence of the nonlinear effect of the laser on the spectrum signal processing and concentration inversion can be effectively reduced. Compared with the traditional wide-range wavelength scanning and modulation mode, the application has the advantages of fast response speed, high stability and measurement precision, and the overall structure is more compact, and has high universal practicality in actual application.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser spectroscopy and gas detection, and particularly to a gas detection device and method based on V-shaped wavelength tuning and modulation technology. BACKGROUND

[0002] Direct absorption spectroscopy is a kind of spectroscopic analysis technology based on Lambert-Beer law. By measuring the light intensity before and after the incident laser passes through the gas absorption medium, combining the known molecular spectral line parameters and experimental condition parameters (such as temperature, pressure and optical path), and the spectral line function, the concentration of the analyzed gas and other parameter information can be directly calculated. However, the physical quantity obtained by analyzing the light intensity change in the direct absorption spectroscopy technology is the absorbance representing the strength of molecular absorption, which is affected by various noises, and its detection sensitivity is usually in the order of 10 -3 The wavelength modulation spectroscopy technology developed for the 1 / f dependent characteristics of typical noise has good noise suppression effect combined with the lock-in demodulation principle, thereby realizing higher sensitivity. The technical principle is mainly divided into fixed wavelength modulation spectroscopy and scanning wavelength modulation spectroscopy. The fixed wavelength modulation spectroscopy method mainly measures the gas absorption signal at a specific wavelength by fixing the output wavelength of the laser at the molecular absorption spectrum line of the gas to be measured, and the implementation process is relatively simple. However, in practical application, although the output wavelength of the laser can be adjusted through feedback, it is difficult to ensure long-term stability, thereby affecting the accuracy of the measurement results. In comparison, the scanning wavelength modulation spectroscopy obtains the full spectral information of the molecular absorption signal by tuning the output wavelength of the laser, and the center position can be monitored and corrected in real time in the signal processing process, so that the measurement results have higher accuracy and are widely used. However, the emission wavelength and output power of the commonly used tunable semiconductor laser in the wavelength modulation spectroscopy technology have significant dependence on the working current or voltage, and with the increase of the tuning current or voltage range, the non-linear effects of the emission wavelength and output power become more and more significant, thereby causing the so-called residual amplitude effect. Existing research shows that these effects have a non-negligible influence on the concentration of trace gases detected by the wavelength modulation spectroscopy technology. In addition, as an indirect analysis technology, the wavelength modulation spectroscopy needs to establish a correction model before the measurement signal can be inverted for concentration, and the reliability of the correction model is easily affected by the long-term stability of the spectroscopic system. SUMMARY

[0003] The purpose of the present application is to provide a gas detection device and method based on V-shaped wavelength tuning and modulation technology to solve the above defects.

[0004] In order to achieve the above purpose, the present application provides the following technical scheme:

[0005] A kind of gas detection device based on V-type wavelength tuning and modulation technique, comprising: V-type wave modulator, tunable laser, parabolic mirror, gas sample cell, half-reflection half-transmission lens, etalon, full reflection mirror, double-channel photodetector, signal demodulation and analysis module, signal display and output module in series successively;The V-type voltage or current waveform signal output by the V-type wave modulator is input to tunable laser to output laser beam, is focused and reflected by parabolic mirror, is directly coupled into gas sample cell, the reflected beam of half-reflection half-transmission lens and the beam that is projected in turn by half-reflection half-transmission lens, transmitted by etalon, reflected by full reflection mirror are all input to double-channel photodetector, then are demodulated and analyzed by signal demodulation and analysis module, finally are input to signal display and output module to display and output.

[0006] Preferably, the half-reflection half-transmission lens divides the incident beam into two perpendicular beams: reflected beam and transmitted beam, the reflected beam of half-reflection half-transmission lens is directly reflected to double-channel photodetector and is marked as first channel signal, and the transmitted beam of half-reflection half-transmission lens is transmitted by etalon and reflected by full reflection mirror to double-channel photodetector and is marked as second channel signal.

[0007] Preferably, the signal demodulation and analysis module comprises signal demodulation module and signal analysis module, the signal demodulation module demodulates the first channel signal to second harmonic signal with gas absorption in combination with the V-type waveform modulation signal output by V-type wave modulator (1), and simultaneously sends the second channel signal and etalon (6) interference signal to the signal analysis module for analysis and processing.

[0008] Preferably, the signal analysis module adopts the method comprising spectrum signal center position correction algorithm, signal filtering denoising and signal averaging algorithm, wavelength correction algorithm and concentration inversion algorithm for analysis and processing.

[0009] Preferably, the signal display and output module comprises LCD liquid crystal display unit and signal output unit, and the signal output unit has Bluetooth wireless communication output function and wired serial communication output and network communication output interface.

[0010] Preferably, the spectrum signal center position correction algorithm, signal filtering denoising and signal averaging algorithm are as follows:

[0011] Firstly, the minimum position P of the second harmonic signal obtained from the first channel is preliminarily estimated; secondly, a data set D(P-10, P+10) in a range of 10 points around the minimum position P is selected, and then the data set D(P-10, P+10) is subjected to smoothing filtering; then, the accurate minimum position P of the data set after filtering is solved, and each measurement signal is subjected to similar correction and filtering processing with the accurate minimum position P as the best center position; finally, all signals of the first channel are subjected to average processing according to the defined average number of signals, so as to obtain the original spectral signal with a higher signal-to-noise ratio.

[0012] Preferably, the wavelength correction algorithm is specifically as follows:

[0013] For the analysis and processing of the etalon (6) interference signal, firstly, the positions corresponding to each peak value in the interference fringe signal are calculated, then a corresponding curve is established with the peak value positions as the horizontal coordinates and the integer sequence [1, 2, …, N] established with the total number N of peak values as the vertical coordinates, and a polynomial fitting formula is obtained by performing high-order polynomial fitting on the corresponding curve; then, the integer sequence [1, 2, …, N] corresponding to the total number N of peak values is taken as the independent variable, substituted into the obtained polynomial fitting formula, and multiplied by the free spectral range FSR value of the etalon, so that the relative wave number range of the laser emission wavelength can be calculated. Finally, the difference between the relative center position of the absorption spectrum of the gas to be analyzed in the relative wave number as the horizontal coordinate and the absolute position of the corresponding spectral line in the database is calculated, and then the difference is added to the relative wave number, so as to realize the wavelength correction of the laser wavelength tuning range.

[0014] Preferably, the concentration inversion algorithm includes two methods: a multi-dimensional linear regression algorithm and a linear fitting algorithm, which are specifically as follows:

[0015] The multi-dimensional linear regression algorithm: assuming that the number of spectral signal sampling points is n, n is a natural number, the measurement signal is Amb, the background signal is Bgr, the calibrated signal after background correction is Cal, the concentration of the gas to be analyzed is c, and the solving function definition is ξ, the specific expression is as follows:

[0016]

[0017] The concentration inversion calculation process combines the multi-dimensional linear regression algorithm and the least square algorithm, and the best c value is obtained by solving the minimum value of the function ξ. The differential calculation formula is as follows:

[0018]

[0019] The linear fitting algorithm: for different molecular characteristics, the hard collision linear type H(x, y) and the soft collision linear type G(x, y, z) are adopted, and the theoretical expressions thereof can be described by the following function models respectively:

[0020]

[0021] wherein: M is the confluent hypergeometric function, D is the Dicke narrowing coefficient and η is the optical diffusion coefficient, π represents the circular constant; S represents the spectral line intensity, w(u) represents a complex function with respect to the variable u, i represents the imaginary unit of the complex number, γ D and γ L respectively represent the Doppler line width and the Lorentz line width.

[0022] By using the above two line shape functions, the integral area A of the absorption signal in the molecular absorption spectrum is fitted and calculated:

[0023]

[0024] wherein, α(v) represents the absorption coefficient, L represents the absorption optical path; v represents the integral variable wave number, v0 represents the wave number of the center position of the molecular spectrum, S(T) represents the spectral line intensity related to the temperature T, and N(T, P) represents the number of molecules related to the temperature T and the pressure P.

[0025] In combination with the normalized condition of the line shape function, the above formula can be simplified as:

[0026] A = S(T) · N · L,

[0027] wherein, S(T) and L are defined as above, and N represents the number of molecules of the absorption medium to be measured.

[0028] Finally, under the known conditions of the related experiments, including the temperature T, the pressure P, the optical path L and the spectral line intensity S of the molecules to be measured, the integral absorption area A of the molecules calculated by the above fitting can be used to inversely calculate the number or concentration of the absorption molecules; conversely, the spectral line parameters of the molecules can be calculated.

[0029] Preferably, a gas detection method based on V-shaped wavelength tuning and modulation technology comprises the following steps:

[0030] S1, a V-shaped wave modulator 1 is used to adjust and output a V-shaped voltage or current wave signal according to the load working parameters; and then the V-shaped voltage or current wave signal is input into a tunable laser 2 to drive the tunable laser 2 to output a laser beam in a certain wavelength range;

[0031] S2, the output laser beam is focused and reflected by a parabolic mirror 3, and the reflected beam is directly coupled into a gas sample cell 4, and then interacts with the gas medium to be detected in the gas sample cell 4, and finally the beam is emitted;

[0032] S3, the emitted light beam is reflected and transmitted by the half-reflection half-transmission lens 5, the reflected light beam of the half-reflection half-transmission lens 5 is directly reflected to the double-channel photodetector 8 and is marked as a first channel signal, and the transmitted light beam of the half-reflection half-transmission lens 5 is transmitted by the etalon 6 again to generate an interference signal for laser output wavelength correction and is finally reflected to the double-channel photodetector 8 by the full reflection mirror 7 and is marked as a second channel signal;

[0033] S4, the light beam signal marked by the double-channel photodetector 8 is input into the signal demodulation and analysis module 9, the first channel signal is demodulated to a second harmonic signal with gas absorption by the demodulation module combined with the V-shaped waveform modulator 1, and the second channel etalon 6 interference signal is simultaneously transmitted to the signal analysis module for analysis and processing;

[0034] S5, the analyzed and inverted gas concentration signal is input into the signal display and output module 10 for display and output, so that the gas detection based on the V-shaped wavelength tuning and modulation technology is realized.

[0035] The present application has the following advantages:

[0036] (1) The gas detection device and method based on the V-shaped wavelength tuning and modulation technology of the present application drive the tunable semiconductor laser by the super-narrow range V-shaped wave signal, which not only improves the system response time, but also effectively reduces the influence of the nonlinear effect of the laser on the spectrum signal; by using the center position correction algorithm, signal filtering and denoising and signal averaging algorithm in the signal demodulation and analysis module, the spectrum signal distortion phenomenon after signal averaging caused by the center wavelength drift of the laser can be effectively solved, and by using the multi-dimensional linear regression algorithm and the least square algorithm for concentration analysis of the spectrum signal, the measurement accuracy and precision of the measurement result can be effectively improved.

[0037] (2) The gas detection device and method based on the V-shaped wavelength tuning and modulation technology of the present application utilize the dependence of the output power and wavelength of the tunable semiconductor laser on the scanning current or voltage, and combine the symmetry of the V-shaped wave to realize the wavelength scanning and modulation of the laser in a super-narrow range, which can effectively reduce the influence of the nonlinear effect of the laser on the spectrum signal processing and concentration inversion. Compared with the traditional wide-range wavelength scanning and modulation method, the present application has the advantages of fast response speed, high stability and measurement precision, and the overall structure is more compact, which has high universal practicality in actual application. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a structural framework diagram of the gas detection device based on the V-shaped wavelength tuning and modulation technology of the present application;

[0039] Figure 2The figure of non-linear effect of emission spectrum range and driving voltage for typical tunable semiconductor laser;

[0040] Figure 3 The figure of scanning modulation signal and its corresponding second harmonic signal of traditional ramp wave and V wave of the present application;

[0041] Figure 4 The figure of etalon interference signal and peak position calibration of the present application;

[0042] Figure 5 The figure of concentration inversion process based on multi-dimensional linear regression algorithm and least square algorithm of the present application;

[0043] Figure 6 The figure of integral area A fitting based on linear fitting algorithm of the present application. DETAILED DESCRIPTION

[0044] The present application is further described below in conjunction with embodiments. It should be noted that the embodiments are only examples of the present application and the skilled in the art can make various modifications or supplements or use similar ways to replace the described embodiments without departing from the concept of the present application or exceeding the scope defined by the present claims, which should be considered as falling within the protection scope of the present application.

[0045] Embodiment 1:

[0046] Figure 1 The figure of structural framework of gas detection device based on V-type wavelength tuning and modulation technology. As shown in Figure 1 The gas detection device based on V-type wavelength tuning and modulation technology comprises V-type wave modulator 1, tunable laser 2, parabolic mirror 3, gas sample cell 4, half-mirror 5, etalon 6, full mirror 7, double-channel photodetector 8, signal demodulation and analysis module 9, signal display and output module 10 connected in series.

[0047] V-type wave modulator 1, which outputs V-type voltage or current waveform signal according to the adjustment of load working parameters.

[0048] Tunable laser 2, which inputs the V-type voltage or current waveform signal output by V-type wave modulator 1 to drive tunable laser 2 to output laser beam in a certain wavelength range.

[0049] Parabolic mirror 3, which can focus and reflect the laser beam output by tunable laser 2.

[0050] Gas sample cell 4, which contains the gas medium to be detected. The reflected beam of parabolic mirror 3 is directly coupled into gas sample cell 4, and the interaction between the reflected beam and the gas medium to be detected occurs in gas sample cell 4, and finally the light beam is emitted.

[0051] Half-transmission half-reflection mirror 5 divides the incident light beam into two perpendicular beams: a reflected beam and a transmitted beam. The reflected beam passing through half-transmission half-reflection mirror 5 is directly reflected into dual-channel photodetector 8, and is marked as the first channel signal; while the transmitted beam passing through half-transmission half-reflection mirror 5 is transmitted through etalon 6, reflected by full-reflection mirror 7, and then input into dual-channel photodetector 8, and is marked as the second channel signal.

[0052] Demodulation and analysis module 9 includes a signal demodulation module and a signal analysis module. The signal demodulation module demodulates the first channel signal to obtain a second harmonic signal with gas absorption in combination with the V-shaped waveform modulation signal output by V-shaped waveform modulator 1, and simultaneously transmits the second harmonic signal and the etalon 6 interference signal in the second channel to the signal analysis module for analysis and processing.

[0053] Signal display and output module 10 includes an LCD liquid crystal display unit and a signal output unit. The signal output unit has Bluetooth wireless communication output function and wired serial communication output and network communication output interfaces to meet the needs of different display terminals. The gas concentration signal obtained by inversion after demodulation and analysis by signal demodulation and analysis module 9 is input into signal display and output module 10 for display and output, thereby realizing gas detection based on V-shaped wavelength tuning and modulation technology.

[0054] A gas detection method based on V-shaped wavelength tuning and modulation technology, comprising the following steps:

[0055] S1, through V-shaped waveform modulator 1, adjust and output V-shaped voltage or current waveform signal according to load working parameters; then input into tunable laser 2 to drive tunable laser 2 to output laser beam in a certain wavelength range.

[0056] In this embodiment, a semiconductor laser with a center wavelength of 6046.5 cm -1 nearby and a methane gas molecule measurement method are taken as examples for illustration. If other laser light sources matched with other molecules are selected, high-precision measurement and analysis of different gas components can be realized.

[0057] Figure 2 A typical tunable semiconductor laser emission spectrum range and driving voltage nonlinear effect diagram is shown in FIG. 2. Figure 2 As shown in FIG. 3, the methane (CH4) molecule has a center wavelength of 6046.5 cm -1There is a strong absorption spectrum characteristic, while this band out of the commonly used semiconductor laser wavelength tuning characteristics, there are significant non-linear effects, such as the polynomial fitting results in the figure.

[0058] Figure 3 For the traditional ramp and the V waveform of the present invention scanning modulation signal and its corresponding second harmonic signal contrast chart, wherein, Figure 3 (a) is the traditional ramp scanning modulation signal diagram, Figure 3 (b) is the V waveform of the present invention scanning modulation signal diagram, Figure 3 (c) is the traditional ramp corresponding second harmonic signal diagram, Figure 3 (d) is the V waveform of the present invention corresponding second harmonic signal diagram. As Figure 3 The traditional ramp tuning and modulation mode needs about 1.0 point resolution to obtain the complete second harmonic signal spectrum, while the V waveform tuning and modulation mode proposed in the present invention only needs about 0.4 point resolution to obtain the complete second harmonic signal spectrum.

[0059] S2, the output laser beam is focused and reflected by the parabolic mirror 3, and the reflected beam is directly coupled into the gas cell 4, and the gas medium to be detected occurs in the gas cell 4. Interacting absorption process, finally the light beam is emitted.

[0060] S3, the emitted light beam is reflected and transmitted by the half-reflection half-transmission lens 5, the reflected light beam of the half-transmission half-reflection lens 5 is directly reflected to the double-channel photodetector 8, and is marked as the first channel signal; while the transmitted light beam of the half-transmission half-reflection lens 5, again transmitted by the etalon 6, generates an interference signal for laser output wavelength correction, and finally enters the full reflection mirror 7 to reflect to the double-channel photodetector 8, which is marked as the second channel signal.

[0061] S4, the light beam signal marked by the double-channel photodetector 8 is input into the signal demodulation and analysis module 9, and the first channel signal is demodulated to have a second harmonic signal with gas absorption by the demodulation module combined with the V-type waveform modulation signal output by the V-type waveform modulator 1., and the second channel signal is simultaneously transmitted to the signal analysis module for analysis and processing.

[0062] The signal analysis module performs analysis and processing, and the methods include spectral signal center position correction algorithm, signal filtering and denoising and signal averaging algorithm, wavelength correction algorithm, and concentration inversion algorithm.

[0063] The spectrum signal center position correction algorithm, signal filtering and denoising and signal averaging algorithm are as follows: firstly, the minimum position P of the second harmonic signal obtained by the first channel is preliminarily estimated; secondly, the data set D(P-10, P+10) in the range of 10 points around the left and right of the minimum position P is selected, and then the data set D(P-10, P+10) is subjected to smoothing filtering; then, the accurate minimum position P of the data set after filtering is solved, and each measurement signal is subjected to similar correction and filtering processing with the accurate minimum position P as the best center position; finally, all the signals in the first channel are subjected to average processing according to the defined signal average times, so as to obtain the original spectrum signal with a higher signal-to-noise ratio.

[0064] The wavelength correction algorithm is mainly used for the standard device (6) interference signal analysis processing in the second channel signal. Figure 4 The wavelength correction algorithm is mainly used for the standard device (6) interference signal analysis processing in the second channel signal. Figure 4 The wavelength correction algorithm is mainly used for the standard device (6) interference signal analysis processing in the second channel signal.

[0065] Firstly, the positions corresponding to each peak (Peak) in the interference fringe signal are calculated; then, the peak positions are taken as the abscissa, and the integer column [1, 2,..., N] established by the total number N of peaks is taken as the ordinate, a corresponding curve is established, and high-order polynomial fitting is performed on the curve to obtain a polynomial fitting formula; then, the integer column [1, 2,..., N] corresponding to the total number N of peaks is taken as the independent variable, substituted into the obtained polynomial fitting formula, and multiplied by the free spectral range FSR value of the standard device 6, so that the relative wave number range of the laser can be calculated. Finally, the difference between the relative center position of the absorption spectrum of the gas to be analyzed in the relative wave number as the abscissa and the absolute position of the corresponding spectral line in the database is calculated, and the difference is added to the relative wave number, so that the wavelength tuning range of the laser is corrected.

[0066] The concentration inversion algorithm mainly includes two methods: a multi-dimensional linear regression algorithm and a linear fitting algorithm, and the specific steps are as follows:

[0067] The multi-dimensional linear regression algorithm: assuming that the number of spectrum signal sampling points is n, n is a natural number, the measurement signal is Amb, the background signal is Bgr, the calibrated signal after background correction is Cal, the concentration of the gas to be analyzed is c, and the solving function definition is ξ, and the specific expression is as follows:

[0068]

[0069] Figure 5 The concentration inversion flowchart based on the multi-dimensional linear regression algorithm and the least square algorithm is as follows: Figure 5As shown, the concentration inversion calculation process, combined with a multi-dimensional linear regression algorithm and a least square algorithm, the algorithm calculation process obtains the best c value by solving the minimum value of the function ξ, combined with the differential calculation formula as follows:

[0070]

[0071] Linear fitting algorithm: for different molecular characteristics, hard collision linear H(x, y) and soft collision linear G(x, y, z) are adopted, and the theoretical expression can be described by the following function model respectively:

[0072]

[0073] Among them: M is the confluent hypergeometric function, D is the Dicke narrowing coefficient and η is the optical diffusion coefficient, π represents the circular constant; S represents the spectral line intensity, w(u) represents the complex function about the variable u, i represents the imaginary unit of the complex number, γ D and γ L respectively represent the Doppler line width and the Lorentz line width.

[0074] By using the above two linear functions, the integral area A of the absorption signal in the molecular absorption spectrum is fitted and calculated:

[0075]

[0076] Among them, α(v) represents the absorption coefficient, L represents the absorption optical path; v represents the integral variable wave number, v0 represents the molecular spectral line center position wave number, S(T) represents the spectral line intensity related to temperature T, and N(T, P) represents the number of molecules related to temperature T and pressure P.

[0077] Combined with the normalization condition of the linear function, the above formula can be simplified as:

[0078] A=S(T)·N·L,

[0079] Among them, S(T) and L are defined as above, and N represents the number of molecules of the absorption medium to be measured.

[0080] Finally, under the condition that the related experimental conditions (such as: temperature T, pressure P, optical path L and spectral line intensity S of the measured molecule) are known, the integral absorption area A of the molecule calculated by the above fitting can be used to inverse the number of molecules or the concentration of the absorption molecule; on the contrary, the spectral line parameters (such as: line intensity) of the molecule can be calculated. Figure 6 The integral area A fitting schematic diagram based on the linear fitting algorithm of the present application is shown as Figure 6 As shown, the fitting residual of the two linear models is less than 8×10 -5 , thereby embodying that the linear model has very high matching degree with the experimental data, and high-precision concentration inversion can be realized.

[0081] Finally, in the relevant experimental conditions, including temperature T, pressure P, optical path L and the line intensity S of the spectrum of the molecule to be measured, the integral absorption area A of the molecule calculated by the above fitting can be used to inverse the number or concentration of the absorbing molecule.

[0082] S5, the analyzed and processed concentration signal of the gas to be analyzed is input into the signal display and output module 10 for display and output, thereby realizing gas detection based on V-shaped wavelength tuning and modulation technology.

[0083] The gas detection device and method based on V-shaped wavelength tuning and modulation technology of the present application drives the tunable semiconductor laser by the super-narrow-range V-shaped wave signal, which not only improves the system response time, but also effectively reduces the influence of the nonlinear effect of the laser on the spectrum signal; through the signal demodulation and analysis module, the center position correction algorithm, signal filtering and denoising and signal averaging algorithm are adopted, which can effectively solve the spectrum signal distortion phenomenon after signal averaging caused by the center wavelength drift of the laser; through the use of multi-dimensional linear regression algorithm and least square algorithm for concentration analysis of the spectrum signal, the measurement precision and accuracy of the measurement result can be effectively improved.

[0084] The gas detection device and method based on V-shaped wavelength tuning and modulation technology of the present application utilizes the dependence of the output power and wavelength of the tunable semiconductor laser on the scanning current or voltage, and combines the symmetry of the V-shaped wave, to realize wavelength scanning and modulation of the laser in a super-narrow range, which can effectively reduce the influence of the nonlinear effect of the laser on the spectrum signal processing and concentration inversion. Compared with the traditional wide-range wavelength scanning and modulation method, the present application has the advantages of fast response speed, high stability and measurement precision, and compact overall structure, and has high universal practicality in actual application.

[0085] The above is an exemplary description of the present application, and it is obvious that the specific implementation of the present application is not limited by the above method. As long as the method concept and technical solution of the present application are used for such non-essential improvement, or the concept and technical solution of the present application are directly applied to other occasions without improvement, they are all within the protection scope of the present application.

Claims

1. A gas detection device based on V-type wavelength tuning and modulation technology, characterized in that: include: A V-shaped waveform modulator (1), a tunable laser (2), a parabolic mirror (3), a gas sample pool (4), a half-reflecting half-mirror (5), an etalon (6), a full-reflecting mirror (7), a dual-channel photoelectric detector (8), a signal demodulation and analysis module (9), and a signal display and output module (10) are sequentially connected in series; the V-shaped voltage or current waveform signal output by the V-shaped waveform modulator (1) is input into the laser beam output by the tunable laser (2), is focused and reflected by the parabolic mirror (3), and is then directly coupled into the gas sample pool (4); the reflected beam through the half-reflecting half-mirror (5) and the beams sequentially transmitted through the half-reflecting half-mirror (5), the etalon (6), and the full-reflecting mirror (7) are all input into the dual-channel photoelectric detector (8), then demodulated and analyzed by the signal demodulation and analysis module (9), and finally input into the signal display and output module (10) for display and output; The semi-reflective mirror (5) splits the incident light beam into two perpendicular light beams: a reflected light beam and a transmitted light beam. The reflected light beam is directly reflected by the semi-transparent and semi-reflective mirror (5) to the dual-channel photodetector (8) and is marked as a first channel signal. The transmitted light beam is then transmitted by the etalon (6) and reflected by the full-reflective mirror (7) to the dual-channel photodetector (8) and is marked as a second channel signal. The signal demodulation and analysis module (9) includes a signal demodulation module and a signal analysis module. The signal demodulation module demodulates the first channel signal into a second harmonic signal with gas absorption in combination with the V-shaped waveform modulation signal output by the V-shaped waveform modulator (1), and then transmits the interference signal of the etalon (6) in the second channel to the signal analysis module for analysis and processing. The signal analysis module performs analysis and processing using methods including a spectral signal center position correction algorithm, a signal filtering and denoising and signal averaging algorithm, a wavelength correction algorithm, and a concentration inversion algorithm.

2. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 1, characterized in that: The signal display and output module (10) comprises: an LCD liquid crystal display unit and a signal output unit, wherein the signal output unit has a Bluetooth wireless communication output function and wired serial port communication output and network port communication output interfaces.

3. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 1, characterized in that: The spectral signal center position correction algorithm, signal filtering and denoising, and signal averaging algorithm are as follows: First, the minimum position P of the second harmonic signal obtained in the first channel is preliminarily estimated. Second, a data set D(P-10, P+10) with 10 points on each side near the minimum position P is selected, and the data set D(P-10, P+10) is smoothed and filtered. Then, the precise minimum position P is solved for the filtered data set, and similar correction and filtering processing is performed on each measurement signal using it as the optimal center position. Finally, all signals in a channel are averaged according to the defined number of signal averaging times to obtain the original spectral signal with a higher signal-to-noise ratio.

4. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 3, characterized in that: The wavelength correction algorithm is as follows: For analyzing and processing the interference signal of the etalon (6), firstly, the position corresponding to each peak in the interference fringe signal is calculated, then the peak position is used as the horizontal coordinate, and the integer sequence [1, 2, ..., K] established by the total number of peaks K is used as the vertical coordinate, a corresponding curve is established and a high-order polynomial fitting is performed on it to obtain the polynomial fitting formula; finally, the integer sequence [1, 2, ..., K] corresponding to the total number of peaks K is used as the independent variable, substituted into the obtained polynomial fitting formula, and then multiplied by the free spectrum range FSR value of the etalon, the relative emission wave number range of the laser can be calculated.

5. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 4, characterized in that: The concentration inversion algorithm includes two methods: multidimensional linear regression algorithm and line fitting algorithm, which are as follows: Multidimensional linear regression algorithm: Assume that the number of spectral signal sampling points is N, where N is a natural number, the measured signal is Amb, the background signal is Bgr, the calibration signal after background correction is Cal, and the concentration of the gas to be analyzed is c. The solution function is defined as ξ. The specific expression is as follows: The concentration inversion calculation process combines the multidimensional linear regression algorithm and the least mean square algorithm. The algorithm calculation process obtains the optimal c value by solving the minimum value of the function ξ. The differential calculation formula is as follows: Linear fitting algorithm: According to different molecular characteristics, hard collision line shape H(x,y) and soft collision line shape G(x,y,z) are used. Their theoretical expressions can be described by the following function models: in: M is the confluent hypergeometric function, v is the integral variable wave number, v0 is the wave number at the center of the molecular spectral line, D is the Dicke narrowing coefficient, η is the optical diffusion coefficient, π is the circumference of ... D and γ L denote the Doppler linewidth and the Lorentz linewidth, respectively; Using the above two linear functions, the integral area A of the absorption signal in the molecular absorption spectrum is fitted and calculated: Where α(v) represents the absorption coefficient, L represents the absorption path length, S(T) represents the intensity of the spectral line related to temperature T, and N(T,P) represents the number of molecules related to temperature T and pressure P. Combined with the linear function to meet the normalization conditions, the above formula can be simplified to: A=S(T)·N(T,P)·L, Wherein, S(T) and L are defined as above; Finally, when the relevant experimental conditions, including temperature T, pressure P, optical path L and the line intensity S of the molecular spectral line to be measured, are known, the molecular integrated absorption area A calculated by the above fitting can be used to invert the molecular number or concentration of the absorbing molecules; conversely, the spectral line parameters of the molecules can be calculated.

6. A gas detection method based on V-type wavelength tuning and modulation technology, using the gas detection device based on V-type wavelength tuning and modulation technology according to any one of claims 1 to 5, characterized in that: The steps include: S1, through a V-shaped waveform modulator (1), adjusting according to load operating parameters and outputting a V-shaped voltage or current waveform signal; then inputting it into a tunable laser (2), driving the tunable laser (2) to output a laser beam within a certain wavelength range; S2, the output laser beam is focused and reflected by the parabolic mirror (3), and the reflected beam is directly coupled into the gas sample cell (4), where it undergoes a mutual absorption process with the gas medium to be detected, and finally emits the beam; S3, the emitted light beam is reflected and transmitted by the half-reflecting mirror (5), and the reflected light beam by the semi-transparent mirror (5) is directly reflected to the dual-channel photoelectric detector (8), and is marked as the first channel signal; and the transmitted light beam by the semi-transparent mirror (5) is further transmitted by the etalon (6) to generate an interference signal for laser output wavelength correction, and finally enters the total reflection mirror (7) and is reflected to the dual-channel photoelectric detector (8), and is marked as the second channel signal; S4, the light beam signal marked by the dual-channel photoelectric detector (8) is input into the signal demodulation and analysis module (9), and the demodulation module combines the V-shaped waveform modulation signal to demodulate the first channel signal into a second harmonic signal with gas absorption, and then transmits it and the second channel signal to the signal analysis module for analysis and processing; S5. The inverted gas concentration signal to be analyzed after analysis and processing is input into the signal display and output module (10) for display and output, thereby realizing gas detection based on V-type wavelength tuning and modulation technology.

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