Gas detection device and method based on V-type wavelength tuning and modulation technology

Abstract

The invention discloses a gas detection device based on a V-shaped wavelength tuning and modulation technology. The gas detection device comprises a V-shaped waveform modulator, a tunable laser, a parabolic mirror, a gas sample cell, a semi-reflecting and semi-transmitting mirror, an etalon, a total reflecting mirror, a dual-channel photoelectric detector, a signal demodulation and analysis module and a signal display and output module which are sequentially connected in series. The invention also discloses a gas detection method based on the V-type wavelength tuning and modulation technology. According to the invention, the dependence characteristic of the output power and wavelength of the tunable semiconductor laser on the scanning current or voltage is utilized, and the symmetry of the V-shaped waveform is combined, 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 in spectral signal processing and concentration inversion can be effectively reduced. Compared with a traditional wide-range wavelength scanning and modulation mode, the device has the advantages of being high in response speed, high in stability and measurement precision, more compact in overall structure and high in general practicability in practical application.

Description

Technical Field

[0001] The present invention relates to the field of laser spectroscopy and gas detection technology, in particular to a gas detection device and method based on V-type wavelength tuning and modulation technology. Background Art

[0002] Direct absorption spectroscopy is a spectral analysis technique based on the Lambert-Beer law. By measuring the light intensity of the incident laser before and after passing through the gas absorption medium, combined with known molecular spectral line parameters and experimental condition parameters (such as temperature, pressure and optical path), and 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 change in light intensity in direct absorption spectroscopy is the absorbance representing the molecular absorption strength. Due to the influence of various noises, its detection sensitivity is usually within 10 -3 Order of magnitude. In view of the 1 / f dependence of typical noise, the wavelength modulation spectroscopy technology developed in combination with the phase-locked demodulation principle has a good noise suppression effect, thereby achieving higher sensitivity. The technical principle is mainly divided into fixed wavelength modulation spectroscopy and scanning wavelength modulation spectroscopy. Among them, the fixed wavelength modulation spectroscopy method mainly fixes the laser output wavelength at the absorption spectrum of the gas molecule to be measured, and directly measures the gas absorption signal at the specific wavelength. The implementation process is relatively simple, but in practical applications, although the output wavelength of the laser can be regulated by feedback, it is difficult to ensure long-term stability, which in turn affects the accuracy of the measurement results. Relatively speaking, scanning wavelength modulation spectroscopy obtains the full spectrum information of the molecular absorption signal by tuning the laser output wavelength. During the signal processing process, its center position can be monitored and corrected in real time. The measurement results have higher accuracy and are widely used. However, the tunable semiconductor laser commonly used in wavelength modulation spectroscopy technology has a significant dependence on its emission wavelength and output power on its operating current or voltage, and with the increase of the tuning current or voltage range, the nonlinear effect of the emission wavelength and output power becomes more and more significant, thereby causing the so-called residual amplitude effect. Existing studies have shown that these effects have a non-negligible impact on the detection of trace gas concentrations by wavelength modulation spectroscopy. In addition, as an indirect analytical technique, wavelength modulation spectroscopy first requires the establishment of a system calibration model before the concentration inversion of the measurement signal can be performed, and the reliability of the calibration model is easily affected by the long-term stability of the spectral system. Summary of the invention

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

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] A gas detection device based on V-type wavelength tuning and modulation technology comprises: a V-type waveform modulator, a tunable laser, a parabolic mirror, a gas sample pool, a half-reflecting half-mirror, an etalon, a full-reflecting mirror, a dual-channel photoelectric detector, a signal demodulation and analysis module, and a signal display and output module which are sequentially connected in series; the V-type voltage or current waveform signal output by the V-type waveform modulator is input into the laser beam output by the tunable laser, is focused and reflected by the parabolic mirror, and is then directly coupled into the gas sample pool, and the reflected beam through the half-reflecting half-mirror and the beams sequentially projected through the half-reflecting half-mirror, transmitted through the etalon, and reflected by the full-reflecting mirror are all input into the dual-channel photoelectric detector, and then demodulated and analyzed by the signal demodulation and analysis module, and finally input into the signal display and output module for display and output.

[0006] Preferably, the half-reflecting, half-mirror mirror divides the incident light beam into two vertical light beams: a reflected light beam and a transmitted light beam. The reflected light beam through the half-transparent, half-reflecting mirror is directly reflected to the dual-channel photodetector and is marked as a first channel signal; while the transmitted light beam through the half-transparent, half-reflecting mirror is transmitted by the standard device and reflected by the full-reflecting mirror to the dual-channel photodetector and is marked as a second channel signal.

[0007] Preferably, the signal demodulation and analysis module comprises a signal demodulation module and a signal analysis module. The signal demodulation module combines the V-shaped waveform modulation signal output by the V-shaped waveform modulator (1) to demodulate the first channel signal into a second harmonic signal with gas absorption, and then transmits it and the interference signal of the standard tool (6) in the second channel to the signal analysis module for analysis and processing.

[0008] Preferably, 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.

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

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

[0011] First, preliminarily estimate the minimum position P of the second harmonic signal obtained from the first channel; secondly, select a data set D(P-10, P+10) with 10 points around the minimum position P, and then smooth the data set D(P-10, P+10); then, solve the precise minimum position P of the filtered data set, and use it as the optimal center position to perform similar correction and filtering on each measurement signal; finally, average all signals of the first channel according to the defined signal averaging times to obtain the original spectral signal with a higher signal-to-noise ratio.

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

[0013] Used for the analysis and processing of the interference signal of the standard instrument (6), firstly, the position corresponding to each peak in the interference fringe signal is calculated, then, with the peak position as the horizontal coordinate and the integer sequence [1, 2, ..., N] established with the total number of peaks N 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; then, the integer sequence [1, 2, ..., N] corresponding to the total number of peaks N is substituted into the obtained polynomial fitting formula, and then multiplied by the free spectrum range FSR value of the standard instrument, the relative wave number range of the laser emission wavelength can be calculated. Finally, the relative center position of the absorption spectrum of the gas molecule to be analyzed when the relative wave number is the horizontal coordinate and the absolute position of the corresponding spectrum line in the database are combined to calculate the difference between the relative wave number and the absolute wave number, and then the difference is added to the relative wave number, so as to realize the wave number correction of the laser wavelength tuning range.

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

[0015] 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, the concentration of the gas to be analyzed is c, and the solution function is defined as ξ. The specific expression is as follows:

[0016]

[0017] 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:

[0018]

[0019] Linear fitting algorithm: According to different molecular characteristics, hard collision linear shape H(x,y) and soft collision linear shape G(x,y,z) are used. Their theoretical expressions can be described by the following function models:

[0020]

[0021] in: M is the confluence hypergeometric function, D is the Dicke narrowing coefficient and η is the optical diffusion coefficient, π is the circumference of ... D and γ L denote the Doppler linewidth and the Lorentz linewidth, respectively.

[0022] Using the above two linear functions, the integral area A of the absorption signal in the molecular absorption spectrum is fitted and calculated:

[0023]

[0024] Among them, α(v) represents the absorption coefficient, L represents the absorption path length, v represents the integral variable wave number, v0 represents the wave number of the center position of the molecular spectral line, 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.

[0025] Combined with the linear function to meet the normalization conditions, the above formula can be simplified to:

[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, when the relevant experimental conditions, including temperature T, pressure P, optical path L and 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 number or concentration of the absorbing molecules; conversely, the spectral line parameters of the molecules can be calculated.

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

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

[0031] 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 pool 4, where it undergoes a mutual absorption process with the gas medium to be detected, and finally emits a beam;

[0032] S3, the emitted light beam is reflected and transmitted by the half-reflecting mirror 5, and the reflected light beam by the half-transparent mirror 5 is directly reflected to the dual-channel photodetector 8, which is marked as the first channel signal; and the transmitted light beam by the half-transparent mirror 5 is further transmitted by the etalon 6 to generate an interference signal for laser output wavelength correction, and finally incident on the total reflection mirror 7 to be reflected to the dual-channel photodetector 8, which is marked as the second channel signal;

[0033] S4, the light beam signal marked by the dual-channel photoelectric detector 8 is then input into the signal demodulation and analysis module 9, and the first channel signal is demodulated into a second harmonic signal with gas absorption by the demodulation module in combination with the V-shaped waveform modulation signal output by the V-shaped waveform modulator 1, and then the interference signal of the second channel standard 6 is simultaneously transmitted to the signal analysis module for analysis and processing;

[0034] S5. The inverted gas concentration signal to be analyzed after the 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.

[0035] The beneficial effects of the present invention are:

[0036] (1) The gas detection device and method based on V-type wavelength tuning and modulation technology of the present invention drives a tunable semiconductor laser through an ultra-narrow range V-type wave signal, which not only improves the system response time, but also effectively reduces the influence of the laser nonlinear effect on the spectral signal; through the signal demodulation and analysis module, the center position correction algorithm, signal filtering and denoising and signal averaging algorithm are adopted to effectively solve the signal distortion phenomenon after spectral averaging caused by the drift of the laser center wavelength; by adopting a multidimensional linear regression algorithm and a least mean square algorithm to perform concentration analysis on the spectral signal, the measurement precision and accuracy of the measurement result can be effectively improved.

[0037] (2) The gas detection device and method based on the V-type wavelength tuning and modulation technology of the present invention utilizes the dependence of the output power and wavelength of the tunable semiconductor laser on the scanning current or voltage, combined with the symmetry of the V-type waveform, to realize the wavelength scanning and modulation of the laser in an ultra-narrow range, which can effectively reduce the influence of the laser nonlinear effect in spectral signal processing and concentration inversion. Compared with the traditional wide-range wavelength scanning and modulation method, the present invention has fast response speed, high stability and measurement accuracy, more compact overall structure, and high universal practicability in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0039] Figure 2The nonlinear effect diagram of the emission spectrum range and driving voltage of a typical tunable semiconductor laser is shown;

[0040] Figure 3 A comparison diagram of the scanning modulation signal of the conventional ramp wave and the V waveform of the present invention and their corresponding second harmonic signals;

[0041] Figure 4 It is the standard tool interference signal and peak position calibration diagram of the present invention;

[0042] Figure 5 It is a schematic diagram of the concentration inversion process based on the multidimensional linear regression algorithm and the least mean square algorithm of the present invention;

[0043] Figure 6 It is a schematic diagram of the integral area A fitting based on the linear fitting algorithm of the present invention. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the embodiments. It should be noted that these are merely examples and illustrations of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should be deemed to fall within the protection scope of the present invention.

[0045] Embodiment 1:

[0046] Figure 1 The following is a structural diagram of a gas detection device based on V-type wavelength tuning and modulation technology. Figure 1 As shown, a gas detection device based on V-type wavelength tuning and modulation technology includes: a V-type waveform modulator 1, a tunable laser 2, a parabolic mirror 3, a gas sample cell 4, a semi-reflective and semi-mirror 5, an etalon 6, a fully reflective mirror 7, a dual-channel photodetector 8, a signal demodulation and analysis module 9, and a signal display and output module 10 connected in series.

[0047] The V-shaped waveform modulator 1 is adjusted according to the load working parameters and outputs a V-shaped voltage or current waveform signal.

[0048] The V-shaped voltage or current waveform signal output by the V-shaped waveform modulator 1 is input into the tunable laser 2 to drive the tunable laser 2 to output a laser beam within a certain wavelength range.

[0049] The parabolic mirror 3 can focus and reflect the laser beam output by the tunable laser 2 .

[0050] The gas sample pool 4 contains the gas medium to be detected. The reflected light beam of the parabolic mirror 3 is directly coupled into the gas sample pool 4, undergoes a mutual absorption process with the gas medium to be detected in the gas sample pool 4, and finally emits the light beam.

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

[0052] The demodulation and analysis module 9 includes a signal demodulation module and a signal analysis module. The signal demodulation module combines the V-shaped waveform modulation signal output by the V-shaped waveform modulator 1 to demodulate the first channel signal into a second harmonic signal with gas absorption, and then transmits it to the signal analysis module for analysis and processing at the same time as the interference signal of the standard device 6 in the second channel.

[0053] The signal display and output module 10 includes: an LCD liquid crystal display unit, a signal output unit, and the signal output unit has a Bluetooth wireless communication output function and a wired serial communication output and an Ethernet communication output interface to meet the needs of different display terminals. The inverted gas concentration signal to be analyzed after demodulation and analysis processing by the signal demodulation and analysis module 9 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.

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

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

[0056] In this embodiment, the central wavelength is 6046.5cm -1 The following example describes the method of measuring methane gas molecules using a semiconductor laser. However, by selecting a laser light source that matches other molecules, it is possible to measure and analyze different gas components with high precision.

[0057] Figure 2 Figure 2 is a typical nonlinear effect diagram of the emission spectrum range and driving voltage of a tunable semiconductor laser. Figure 2 Shown is a methane (CH4) molecule at 6046.5 cm -1There are strong absorption spectral characteristics, and the wavelength tuning characteristics of semiconductor lasers commonly used in this band have significant nonlinear effects, as shown in the polynomial fitting results in the figure.

[0058] Figure 3 : is a comparison diagram of the scanning modulation signal of the conventional ramp wave and the V waveform of the present invention and their corresponding second harmonic signals, wherein: Figure 3 (a) is the scanning modulation signal diagram of the traditional ramp wave. Figure 3 (b) is a scanning modulation signal diagram of the V waveform of the present invention, Figure 3 (c) is the second harmonic signal diagram corresponding to the traditional ramp wave. Figure 3 (d) is a second harmonic signal diagram corresponding to the V waveform of the present invention. Figure 3 As shown, the traditional ramp tuning and modulation mode requires a resolution of about 1.0 points to obtain a complete second harmonic signal spectrum, while the V waveform tuning and modulation mode proposed in the present invention only requires a resolution of about 0.4 points to obtain a complete second harmonic signal spectrum.

[0059] S2. The output laser beam is focused and reflected by the parabolic mirror 3. The reflected beam is directly coupled into the gas sample pool 4, where it undergoes a mutual absorption process with the gas medium to be detected, and finally emits the beam.

[0060] 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 photodetector 8, and is marked as the first channel signal; and the transmitted light beam by the semi-transparent mirror 5 is then transmitted by the standard device 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 photodetector 8, and is marked as the second channel signal.

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

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

[0063] Among them, the spectral signal center position correction algorithm, signal filtering and denoising, and signal averaging algorithm are specifically as follows: first, preliminarily estimate the minimum position P of the second harmonic signal obtained in the first channel; secondly, select a data set D(P-10, P+10) with 10 points on the left and right sides of the minimum position P, and then perform smoothing filtering on the data set D(P-10, P+10); then, solve the precise minimum position P of the filtered data set, and use it as the optimal center position to perform similar correction and filtering processing on each measurement signal; finally, average all signals in the first channel according to the defined signal averaging times to obtain the original spectral signal with a higher signal-to-noise ratio.

[0064] The wavelength correction algorithm is mainly used for analyzing and processing the interference signal of the etalon (6) in the second channel signal. Figure 4 This is a calibration diagram of the interference signal and peak position of the standard tool of the present invention. Figure 4 As shown in the figure, the wavelength correction algorithm is as follows:

[0065] First, calculate the position corresponding to each peak in the interference fringe signal; then, use the peak position as the horizontal coordinate and the integer sequence [1, 2, ..., N] established by the total number of peaks N as the vertical coordinate, establish the corresponding curve and perform a high-order polynomial fitting on it to obtain the polynomial fitting formula; then, use the integer sequence [1, 2, ..., N] corresponding to the total number of peaks N as the independent variable, substitute it into the obtained polynomial fitting formula, and then multiply it by the free spectrum region FSR value of the standard tool 6 to calculate the relative wave number range of the laser. Finally, combine the relative center position of the absorption spectrum of the gas molecule to be analyzed when the relative wave number is the horizontal coordinate and the absolute position of the corresponding spectrum line in the database, calculate the difference between the relative wave number and the absolute wave number, and then add the difference to the relative wave number to achieve the wave number correction of the laser wavelength tuning range.

[0066] Among them, the concentration inversion algorithm mainly includes two methods: multidimensional linear regression algorithm and linear fitting algorithm, which are as follows:

[0067] 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, the concentration of the gas to be analyzed is c, and the solution function is defined as ξ. The specific expression is as follows:

[0068]

[0069] Figure 5 The concentration inversion process diagram based on the multidimensional linear regression algorithm and the least mean square algorithm of the present invention is shown in FIG. Figure 5As shown in the figure, 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:

[0070]

[0071] Linear fitting algorithm: According to different molecular characteristics, hard collision linear shape H(x,y) and soft collision linear shape G(x,y,z) are used. Their theoretical expressions can be described by the following function models:

[0072]

[0073] in: M is the confluence hypergeometric function, D is the Dicke narrowing coefficient and η is the optical diffusion coefficient, π is the circumference of ... D and γ L denote the Doppler linewidth and the Lorentz linewidth, respectively.

[0074] 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 path length, v represents the integral variable wave number, v0 represents the wave number of the center position of the molecular spectral line, 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 linear function to meet the normalization conditions, the above formula can be simplified to:

[0078] A=S(T)·N·L,

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

[0080] Finally, when the relevant experimental conditions (such as temperature T, pressure P, optical path L and 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 number or concentration of the absorbing molecules; conversely, the spectral line parameters of the molecules (such as line intensity) can be calculated. Figure 6 FIG. 1 is a schematic diagram of the integral area A fitting based on the linear fitting algorithm of the present invention, as shown in FIG. Figure 6 As shown, the fitting residuals of the two linear models are less than 8×10 -5 , which shows that the linear model has a very high match with the experimental data and can achieve high-precision concentration inversion.

[0081] Finally, when the relevant experimental conditions, including temperature T, pressure P, optical path L and 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 number or concentration of the absorbing molecules; conversely, the spectral line parameters of the molecules can be calculated.

[0082] S5. The inverted gas concentration signal to be analyzed after the 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.

[0083] The gas detection device and method based on V-type wavelength tuning and modulation technology of the present invention drives a tunable semiconductor laser through an ultra-narrow range V-type 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 spectral signal; through a signal demodulation and analysis module, a center position correction algorithm, a signal filtering and denoising, and a signal averaging algorithm are adopted to effectively solve the signal distortion phenomenon after spectral averaging caused by the drift of the laser center wavelength; by adopting a multidimensional linear regression algorithm and a least mean square algorithm to perform concentration analysis on the spectral signal, the measurement precision and accuracy of the measurement result can be effectively improved.

[0084] The gas detection device and method based on V-type wavelength tuning and modulation technology of the present invention utilizes the dependence of the output power and wavelength of the tunable semiconductor laser on the scanning current or voltage, combined with the symmetry of the V-type waveform, to realize the wavelength scanning and modulation of the laser in an ultra-narrow range, which can effectively reduce the influence of the nonlinear effect of the laser in spectral signal processing and concentration inversion. Compared with the traditional wide-range wavelength scanning and modulation method, the present invention has fast response speed, high stability and measurement accuracy, more compact overall structure, and high universal practicability in practical applications.

[0085] The above is an exemplary description of the invention. Obviously, the specific implementation of the present invention is not limited to the above-mentioned method. As long as such non-substantial improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

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 projected by the half-reflecting half-mirror (5), transmitted by the etalon (6), and reflected by 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.

2. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 1 is characterized in that: The semi-reflective mirror (5) divides the incident light beam into two vertical light beams: a reflected light beam and a transmitted light beam. The reflected light beam through the semi-transparent and semi-reflective mirror (5) is directly reflected to the dual-channel photoelectric detector (8) and is marked as a first channel signal; while the transmitted light beam through the semi-transparent and semi-reflective mirror (5) is transmitted through the etalon (6) and reflected by the full-reflective mirror (7) to the dual-channel photoelectric detector (8) and is marked as a second channel signal.

3. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 2 is characterized in that: The signal demodulation and analysis module (9) comprises a signal demodulation module and a signal analysis module. The signal demodulation module combines the V-shaped waveform modulation signal output by the V-shaped waveform modulator (1) to demodulate the first channel signal to obtain a second harmonic signal with gas absorption, and then transmits the interference signal of the standard tool (6) in the second channel to the signal analysis module for analysis and processing.

4. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 3 is characterized in that: The signal analysis module performs analysis and processing, and the methods adopted include spectral signal center position correction algorithm, signal filtering denoising and signal averaging algorithm, wavelength correction algorithm, and concentration inversion algorithm.

5. 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.

6. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 4 is characterized in that: The spectral signal center position correction algorithm, signal filtering and denoising, and signal averaging algorithm are as follows: First, preliminarily estimate the minimum position P of the second harmonic signal obtained in the first channel; secondly, select a data set D(P-10, P+10) with 10 points around the minimum position P, and then smooth the data set D(P-10, P+10); then, solve the precise minimum position P of the filtered data set, and use it as the optimal center position to perform similar correction and filtering processing on each measurement signal; finally, average all signals in one channel according to the defined signal averaging times to obtain the original spectral signal with a higher signal-to-noise ratio.

7. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 6 is characterized in that: The wavelength correction algorithm is as follows: Used for analyzing and processing the interference signal of the standard instrument (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, ..., N] established by the total number of peaks N 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, ..., N] corresponding to the total number of peaks N 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 standard instrument, the relative emission wave number range of the laser can be calculated.

8. The gas detection device based on V-type wavelength tuning and modulation technology according to claim 7, characterized in that: The concentration inversion algorithm includes two methods: a multidimensional linear regression algorithm and a linear fitting algorithm, which are specifically 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, the concentration of the gas to be analyzed is c, and 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 linear shape H(x,y) and soft collision linear shape G(x,y,z) are used. Their theoretical expressions can be described by the following function models: in: M is the confluence hypergeometric function, D is the Dicke narrowing coefficient and 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: Among them, α(v) represents the absorption coefficient, L represents the absorption path length, v represents the integral variable wave number, v0 represents the wave number of the center position of the molecular spectral line, 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. Combined with the linear function to meet the normalization conditions, the above formula can be simplified to: A=S(T)·N·L, Wherein, S(T) and L are defined as above, and N represents the number of molecules of the absorption medium to be measured. Finally, when the relevant experimental conditions, including temperature T, pressure P, optical path L and 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 number or concentration of the absorbing molecules; conversely, the spectral line parameters of the molecules can be calculated.

9. A gas detection method based on V-type wavelength tuning and modulation technology, according to the gas detection device based on V-type wavelength tuning and modulation technology according to any one of claims 1 to 8, characterized in that: The steps include: S1, adjusting and outputting a V-shaped voltage or current waveform signal according to load working parameters through a V-shaped waveform modulator (1); then inputting the signal 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 pool (4), where it undergoes a mutual absorption process with the gas medium to be detected, and finally emits a beam; S3, the emitted light beam is reflected and transmitted by the half-reflecting mirror (5), and the reflected light beam by the half-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 half-transparent mirror (5) is further transmitted by the standard tool (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 first channel signal is demodulated into a second harmonic signal with gas absorption by the demodulation module in combination with the V-shaped waveform modulation signal, and then transmitted to the signal analysis module for analysis and processing together with the second channel signal; S5. The inverted gas concentration signal to be analyzed after the analysis 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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