System and method for real-time monitoring of gas concentration based on wavelength modulation spectroscopy technology

Abstract

A system for monitoring gas concentration, comprising a distributed feedback laser, a signal generation module, a corner cube prism, an off-axis parabolic mirror, a photoelectric detection module, a signal transmission module, a lock-in amplifier module, and a signal processing module, wherein: the laser output by the distributed feedback laser is collimated and then passes through the central hole of the off-axis parabolic mirror and the area to be measured of the target gas, and is reflected back to the off-axis parabolic mirror by the corner cube prism, and the returned laser is focused on the photosensitive area of the photoelectric detection module; the signal transmission module transmits the electrical signal collected by the photoelectric detection module to the lock-in amplifier module; the lock-in amplifier module demodulates the electrical signal collected by the photoelectric detection module by using the reference signal provided by the signal generation module; the signal processing module extracts the 2f signal through a filter, and uses the filter to smooth and filter the extracted signal, so as to provide the 2f signal and the DC signal for subsequent algorithm processing.

Description

Technical Field

[0001] The present invention relates to the field of tail gas emissions, and particularly to a system and method for real-time monitoring of gas concentration based on wavelength modulation spectroscopy technology. Background Art

[0002] Tunable laser absorption spectroscopy technology can realize in-situ online measurement of parameters such as component concentration, temperature, pressure, and velocity of the components in the measured gas by using the laser absorption characteristics of the components. Compared with other technologies, laser absorption spectroscopy technology has the advantages of accurate measurement, fast response speed, non-invasive sensing, etc., and has broad application prospects in the field of atmospheric environment detection. Tunable laser absorption spectroscopy technology is mainly divided into two methods: direct absorption spectroscopy technology and wavelength modulation spectroscopy technology.

[0003] The working principle of direct absorption spectroscopy technology is to inject a certain scanning current into the laser to drive the laser to emit a laser band that completely covers the absorption peak band of the gas. The laser passes through the absorption path containing the gas to be measured and is absorbed by the gas at a specific position. The photodetector converts the absorbed optical signal into an electrical signal, and the characteristics of the absorption peak are obtained by means of baseline fitting, etc. The direct absorption spectroscopy technology system is simple and easy to implement, but the measurement result is easily affected by the output light intensity of the laser, etc., and the measurement result has poor stability. Therefore, the wavelength modulation spectroscopy technology is often used to improve the stability and measurement accuracy of the system.

[0004] The working principle of wavelength modulation spectroscopy is to modulate a high-frequency sine signal with a frequency of f on the scanning current of the laser. The laser emitted by the laser is absorbed by the gas to be measured, and then the photodetector converts the optical signal into an electrical signal. The lock-in amplifier performs phase-sensitive detection processing by using the non-correlation between the input signal and the noise signal, demodulates the electrical signal by using the same-frequency (1f) or double-frequency (nf) signal, and extracts the complete useful signal from the noise. The concentration of the gas to be measured can be obtained through the relationship between the amplitude of the harmonic signal and the concentration of the gas to be measured. The value of the frequency f is from several tens of kHz to several hundreds of kHz. By changing the frequency and amplitude of the high-frequency sine modulation signal, the optical noise in the direct absorption spectroscopy technology can be effectively reduced. At the same time, the wavelength modulation spectroscopy technology moves the information to be detected to the high-frequency band, effectively suppresses the 1 / f low-frequency noise in the system, and obtains higher detection accuracy.

[0005] In actual measurement, the laser intensity is easily affected by temperature, dust, vibration, etc., resulting in changes in intensity. Inverting the concentration only based on the 2f signal has a large error. Generally, a reference optical path is set by adding a reference cell, etc. to eliminate the influence of light intensity change on the measurement result, and the system complexity is high. Summary of the Invention

[0006] In view of this, the main object of the present invention is to provide a system and method for monitoring gas concentration, so as to at least partially solve at least one of the above technical problems.

[0007] To achieve the above object, as one aspect of the present invention, there is provided a system for monitoring gas concentration, including a distributed feedback laser, a signal generation module, a corner cube prism, an off-axis paraboloid mirror, a photoelectric detection module, a signal transmission module, a lock-in amplifier module, and a signal processing module, wherein:

[0008] The laser output by the distributed feedback laser is collimated and then passes through the central hole of the off-axis paraboloid mirror and the area to be measured of the target gas, and is reflected back to the off-axis paraboloid mirror by the corner cube prism, and the returned laser is focused on the photosensitive area of the photoelectric detection module;

[0009] The signal transmission module transmits the electrical signal collected by the photoelectric detection module to the lock-in amplifier module;

[0010] The lock-in amplifier module demodulates the electrical signal collected by the photoelectric detection module by using the reference signal provided by the signal generation module;

[0011] The signal processing module extracts the 2f signal through a filter and smooths and filters the extracted signal by using the filter, so as to provide the 2f signal and the DC signal for subsequent algorithm processing.

[0012] Wherein, the signal generation module generates a sawtooth signal and a sine signal, and modulates the sine signal onto the sawtooth signal as the driving signal of the distributed feedback laser;

[0013] The photoelectric detection module is used to convert the received optical signal into an electrical signal containing gas concentration information to obtain a direct absorption signal.

[0014] Wherein, the system further includes a temperature control module, and the temperature control module is used to control the operating temperature of the distributed feedback laser. The internal secondary temperature control can accurately control the temperature at the required temperature with an error of ±0.001 °C, effectively ensuring the stability of the output wavelength of the distributed feedback laser;

[0015] The system further includes a current driving module, and the current driving module converts the modulated voltage signal into a current signal and tunes the current of the distributed feedback laser to ensure that the wavelength range of the laser emitted by the distributed feedback laser completely covers the absorption wavelength of the target gas.

[0016] Wherein, the system normalizes the 2f signal by using the DC signal, and there is no need to set a reference gas chamber and a reference optical path inside, and the system complexity is low.

[0017] Among them, the signal processing module extracts the absorption spectral line of the gas by using an FIR filter.

[0018] Among them, the signal processing module normalizes the 2f signal by using a DC signal, and quickly inversely calculates the concentration by establishing a second-order relationship between the peak value of the normalized 2f signal and the concentration.

[0019] Among them, the specific steps of the inversion are as follows:

[0020] Pre-collect 2f signals and direct absorption signals with different concentrations in the area of the gas to be measured, and perform the following processing:

[0021] Extract the maximum value of the 2f peak at the position known as the absorption peak, and extract the left minimum value and the right minimum value of the 2f valley at the positions on both wings of the absorption peak. Subtract the average value of the left minimum value and the right minimum value from the maximum value to obtain the peak value of the 2f absorption peak, denoted as 2fpeak;

[0022] Since the number of points of the direct absorption signal is known to be equal to the number of points of the 2f signal, select a certain section of the direct absorption signal at the position without an absorption peak, and calculate the average value of this section of the direct absorption signal, denoted as dcmean;

[0023] Normalize the peak value 2fpeak of the 2f absorption peak by using the average value dcmean of the direct absorption signal to obtain the normalized 2f value, denoted as 2fmean;

[0024] Establish a non-linear relationship between the concentration and 2fmean;

[0025] Fill the gas with the concentration to be measured into the area of the gas to be measured, calculate the obtained normalized 2f value, and substitute this value into the established non-linear relationship, and then the true value of the concentration of the gas to be measured can be obtained.

[0026] Among them, the signal generation module, the signal transmission module, the lock-in amplifier module and the signal processing module are integrated on the same circuit board.

[0027] Among them, the temperature control module and the current drive module are integrated on the same circuit board.

[0028] As another aspect of the present invention, a method for monitoring the gas concentration is also provided, including the following steps:

[0029] Power on and self-start the system. The signal generation module generates a voltage of a waveform, and the current drive module converts the voltage signal into a current to drive the laser to generate a laser signal;

[0030] The laser signal passes through the central hole of the off-axis paraboloid mirror, passes through the target area of the gas to be measured, and the corner cube prism reflects the laser signal to the off-axis paraboloid mirror;

[0031] The off-axis parabolic mirror focuses the laser on the photoelectric detection module. The photoelectric detection module converts the optical signal into a voltage signal. The signal transmission module collects the voltage signal and transmits it to the lock-in amplifier module. The lock-in amplifier module analyzes the 2f signal;

[0032] Judge whether the light intensity meets the requirements. If it does not meet the requirements, an alarm will be given and whether the light intensity meets the requirements will be judged again. If it meets the requirements, the 2f signal will be collected, and the gas concentration can be obtained by using the fast inversion step.

[0033] Among them, the fast inversion includes the following steps:

[0034] Pre-collect the 2f signals and direct absorption signals of different concentrations in the area of the gas to be measured, and perform the following processing:

[0035] Extract the maximum value of the 2f peak at the position known as the absorption peak, and extract the left minimum value and right minimum value of the 2f valley at the positions on both wings of the absorption peak. Subtract the average value of the left minimum value and right minimum value from the maximum value to obtain the peak value of the 2f absorption peak, denoted as 2fpeak;

[0036] Since the number of points of the direct absorption signal is known to be equal to the number of points of the 2f signal, select a certain section of the direct absorption signal at the position without an absorption peak, and calculate the average value of this section of the direct absorption signal, denoted as dcmean;

[0037] Use the average value dcmean of the direct absorption signal to normalize the peak value 2fpeak of the 2f absorption peak to obtain the normalized 2f value, denoted as 2fmean;

[0038] Establish a non-linear relationship between the concentration and 2fmean;

[0039] Fill the gas with the concentration to be measured into the area of the gas to be measured, calculate the obtained normalized 2f value, and substitute this value into the established non-linear relationship to obtain the true value of the concentration of the gas to be measured.

[0040] Based on the above technical solutions, the system and method for monitoring gas concentration of the present invention have at least one of the following beneficial effects compared with the prior art:

[0041] 1. The method of the present invention uses the absorption signal of the ambient gas collected in real time as the background curve to be deducted, without setting a reference gas chamber inside the system, avoiding the influence of the airtightness of the gas chamber and the adsorption of the gas on the measurement result;

[0042] 2. The system of the present invention selects appropriate filtering coefficients and uses a FIR filter to extract the absorption spectrum line of the gas to reduce the interference of noise;

[0043] 3. The present invention uses a DC signal to normalize the 2f signal, eliminates the influence of laser light intensity jitter and dust on the light intensity, and quickly retrieves the concentration by establishing a second-order linear relationship between the peak value of the normalized 2f signal and the concentration;

[0044] 4. In this system, the functions of the signal generation module, the lock-in amplifier module, the signal processing module, etc. are integrated on one circuit board, and the functions of the current drive module and the temperature control module of the laser are integrated on one circuit board, which is convenient for the modularization and integration of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is the working flow chart of the hardware system according to the embodiment of the present invention;

[0046] Figure 2 is the flow chart of the monitoring method according to the embodiment of the present invention;

[0047] Figure 3 is the spectrogram of the CO absorption peak and concentration in Embodiment 1 of the present invention;

[0048] Figure 4 is the second-order non-linear fitting graph of the CO concentration and 2fmean in Embodiment 1 of the present invention;

[0049] Figure 5 is the spectrogram of the CO2 absorption peak and concentration in Embodiment 2 of the present invention;

[0050] Figure 6 is the second-order non-linear fitting graph of the CO2 concentration and 2fmean in Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following further elaborates on the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0052] The present invention discloses a system and method for real-time monitoring of gas concentration based on wavelength modulation spectroscopy technology. By integrating the functions of the signal generation module, the lock-in amplifier module, the signal processing module, etc. on one circuit board, and integrating the functions of the current drive module and the temperature control module of the laser on one circuit board, it is convenient for the modularization and integration of the system; by real-time collecting the absorption signal of the ambient gas as the background curve to be deducted, there is no need to set a reference gas chamber inside the system, avoiding the influence of the airtightness of the gas chamber and the adsorption of the gas on the measurement result; the system of the present invention extracts the absorption spectral line of the gas by selecting an appropriate filtering coefficient using an FIR filter to reduce the interference of noise; uses a DC signal to normalize the 2f signal, eliminates the influence of laser light intensity jitter, etc. on the light intensity, and quickly retrieves the concentration by establishing a second-order relationship between the peak value of the normalized 2f signal and the concentration.

[0053] Specifically, as Figure 1 shown, it is the working flowchart of the hardware system of the embodiment of the present invention. The present invention discloses a system for monitoring gas concentration, including a distributed feedback laser, a signal generation module, a corner cube prism, an off-axis paraboloid mirror, a photoelectric detection module, a signal transmission module, a lock-in amplifier module, and a signal processing module, wherein:

[0054] The laser output by the distributed feedback laser is collimated and then passes through the central hole of the off-axis paraboloid mirror and the area to be measured of the target gas, and is reflected back to the off-axis paraboloid mirror by the corner cube prism, and the returned laser is focused on the photosensitive area of the photoelectric detection module;

[0055] The signal transmission module transmits the electrical signal collected by the photoelectric detection module to the lock-in amplifier module;

[0056] The lock-in amplifier module demodulates the electrical signal collected by the photoelectric detection module by using the reference signal provided by the signal generation module;

[0057] The signal processing module extracts the 2f signal through a filter and smooths and filters the extracted signal by using the filter, so as to provide the 2f signal and the DC signal for subsequent algorithm processing.

[0058] Among them, the signal generation module generates a sawtooth signal and a sine signal, and modulates the sine signal onto the sawtooth signal as the driving signal of the distributed feedback laser;

[0059] The photoelectric detection module is used to convert the received optical signal into an electrical signal containing gas concentration information to obtain a direct absorption signal.

[0060] Among them, the system further includes a temperature control module, and the temperature control module is used to control the working temperature of the distributed feedback laser. The internal secondary temperature control can accurately control the temperature at the required temperature with an error of ±0.001 °C, effectively ensuring the stability of the output wavelength of the distributed feedback laser;

[0061] The system further includes a current driving module, and the current driving module converts the modulated voltage signal into a current signal and performs current tuning on the distributed feedback laser to ensure that the wavelength range of the laser emitted by the distributed feedback laser completely covers the absorption wavelength of the target gas.

[0062] Among them, the system uses the DC signal to normalize the 2f signal, and there is no need to set a reference gas chamber and a reference optical path inside the system, and the system complexity is low.

[0063] Among them, the signal processing module uses a FIR filter to extract the absorption spectral line of the gas.

[0064] Among them, the signal processing module normalizes the 2f signal using a DC signal, and quickly inversely calculates the concentration by establishing a second-order relationship between the peak value of the normalized 2f signal and the concentration.

[0065] Among them, the specific steps of the inversion are as follows:

[0066] Pre-collect 2f signals and direct absorption signals of different concentrations in the area of the gas to be measured, and perform the following processing:

[0067] Extract the maximum value of the 2f peak at the position known as the absorption peak, and extract the left minimum value and the right minimum value of the 2f valley at the positions on both wings of the absorption peak. Subtract the average value of the left minimum value and the right minimum value from the maximum value to obtain the peak value of the 2f absorption peak, denoted as 2fpeak;

[0068] Since the number of points of the direct absorption signal is known to be equal to the number of points of the 2f signal, select a certain section of the direct absorption signal at the position without an absorption peak, and calculate the average value of this section of the direct absorption signal, denoted as dcmean;

[0069] Normalize the peak value 2fpeak of the 2f absorption peak using the average value dcmean of the direct absorption signal to obtain the normalized 2f value, denoted as 2fmean;

[0070] Establish a non-linear relationship between the concentration and 2fmean;

[0071] Flush the gas with the concentration to be measured into the area of the gas to be measured, calculate the obtained normalized 2f value, and substitute this value into the established non-linear relationship, then the true value of the concentration of the gas to be measured can be obtained.

[0072] Among them, the signal generation module, the signal transmission module, the lock-in amplifier module and the signal processing module are integrated on the same circuit board.

[0073] Among them, the temperature control module and the current drive module are integrated on the same circuit board.

[0074] As Figure 2 shown, it is the flow chart of the monitoring method of the embodiment of the present invention. This method includes the following steps:

[0075] Power on and self-start the system. The signal generation module generates a voltage of a waveform, and the current drive module converts the voltage signal into a current to drive the laser to generate a laser signal;

[0076] The laser signal passes through the central hole of the off-axis paraboloid mirror, passes through the target area of the gas to be measured, and the corner cube prism reflects the laser signal to the off-axis paraboloid mirror;

[0077] The off-axis parabolic mirror focuses the laser on the photoelectric detection module. The photoelectric detection module converts the optical signal into a voltage signal. The signal transmission module collects the voltage signal and transmits it to the lock-in amplifier module. The lock-in amplifier module analyzes the 2f signal;

[0078] Judge whether the light intensity meets the requirements. If it does not meet the requirements, alarm and judge whether the light intensity meets the requirements. If it meets the requirements, collect the 2f signal, and the gas concentration can be obtained by using the fast inversion step.

[0079] Among them, the fast inversion includes the following steps:

[0080] Pre-collect 2f signals and direct absorption signals with different concentrations in the area of the gas to be measured, and perform the following processing:

[0081] Extract the maximum value of the 2f peak at the position known as the absorption peak, and extract the left minimum value and the right minimum value of the 2f valley at the positions on both wings of the absorption peak. Subtract the average value of the left minimum value and the right minimum value from the maximum value to obtain the peak value of the 2f absorption peak, denoted as 2fpeak;

[0082] Since the number of points of the direct absorption signal is known to be equal to the number of points of the 2f signal, select a certain section of the direct absorption signal at the position without an absorption peak, and calculate the average value of this section of the direct absorption signal, denoted as dcmean;

[0083] Normalize the peak value 2fpeak of the 2f absorption peak by using the average value dcmean of the direct absorption signal to obtain the normalized 2f value, denoted as 2fmean;

[0084] Establish a non-linear relationship between the concentration and 2fmean;

[0085] Fill the gas with the concentration to be measured into the area of the gas to be measured, calculate the obtained normalized 2f value, and substitute this value into the established non-linear relationship to obtain the true value of the concentration of the gas to be measured.

[0086] The technical solution of the present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0087] Embodiment 1

[0088] Example 1 is to monitor the change in the concentration of CO (carbon monoxide) in the air. The following analyzes the specific implementation.

[0089] First, select a DFB laser with a central wavelength of 2326.8 nm, set the operating temperature of the laser to 29 °C, and the output wavelength of the laser is 2326.56 nm to 2327.21 nm, which completely covers the absorption peak of CO at the position of 2326.823 nm.

[0090] Adjust the optical path so that the absorption light intensity voltage range of the detector is between 2V and 5V to ensure the accuracy of the measurement results.

[0091] Before measurement, non-linear calibration of the measured concentration of CO is required. Set the maximum measured concentration to 1000 ppm. Starting from 1000 ppm as the initial concentration, select a point every 1000 ppm, and a total of 9 points are selected for calibration. The relationship between the absorption peak and the concentration is as Figure 3 shown;

[0092] Establish a non-linear relationship between the concentration and the ratio, as Figure 4 shown;

[0093] Measure CO with concentrations of 2000 ppm, 5000 ppm, and 10000 ppm again for verification. The measurement results are shown in Table 1. The maximum error is about 1%, and the measurement accuracy is high, meeting the measurement requirements.

[0094] Table 1 Measurement errors in Example 1

[0095]

[0096] Example 2

[0097] Example 2 is to monitor the concentration change of CO2 (carbon dioxide) in the air. The following is an analysis of the specific implementation.

[0098] Select a DFB laser with a central wavelength of 2004 nm, set the operating temperature of the laser to 30 °C, and the output wavelength of the laser is 2003.61 nm to 2004.41 nm, fully covering the absorption peak of CO2 at the position of 2004.019 nm.

[0099] Adjust the optical path so that the maximum voltage value range of the absorption light intensity of the detector is between 2V and 5V to ensure the accuracy of the measurement results.

[0100] Before measurement, non-linear calibration of the measured concentration of CO2 is required. Set the maximum measured concentration to 50000 ppm. Starting from 10000 ppm as the initial concentration, select a point every 10000 ppm, and a total of 5 points are selected for calibration. The relationship between the absorption peak and the concentration is as Figure 5 shown;

[0101] Establish a non-linear relationship between the concentration and the ratio, as Figure 6 shown;

[0102] Select CO2 with concentrations of 10000 ppm, 30000 ppm, and 50000 ppm again for verification. The measurement results are shown in Table 2. It can be seen that the error between the two is very small, and the maximum error is within 7%, meeting the measurement requirements.

[0103] Table 2 Measurement errors in Example 2

[0104]

[0105] The specific embodiments described above further elaborate on the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A system for monitoring gas concentration, characterized in that, It includes a distributed feedback laser, a signal generation module, a corner cube prism, an off-axis paraboloid mirror, a photoelectric detection module, a signal transmission module, a lock-in amplifier module, and a signal processing module, where: The laser output by the distributed feedback laser is collimated and passes through the central hole of the off-axis paraboloid mirror and the area to be measured of the target gas, and is reflected back to the off-axis paraboloid mirror by the corner cube prism. The returned laser is focused on the photosensitive area of the photoelectric detection module; The signal transmission module transmits the electrical signal collected by the photoelectric detection module to the lock-in amplifier module; The lock-in amplifier module demodulates the electrical signal collected by the photoelectric detection module by using the reference signal provided by the signal generation module; The signal processing module extracts the 2f signal through a filter and smooths and filters the extracted signal by using the filter, so as to provide a 2f signal and a DC signal for subsequent algorithm processing; The specific steps for the signal processing module to quickly invert the concentration are as follows: Pre-collect 2f signals and direct absorption signals with different concentrations in the area of the gas to be measured, and perform the following processing: Extract the maximum value of the 2f wave peak at the position known as the absorption peak, and extract the left minimum value and the right minimum value of the 2f wave valley at the positions on both wings of the absorption peak. Subtract the average value of the left minimum value and the right minimum value from the maximum value to obtain the peak value of the 2f absorption peak, denoted as 2fpeak; Since the number of points of the direct absorption signal is known to be equal to the number of points of the 2f signal, select a certain section of the direct absorption signal at the position without an absorption peak, and calculate the average value of this section of the direct absorption signal, denoted as dcmean; Normalize the peak value 2fpeak of the 2f absorption peak by using the average value dcmean of the direct absorption signal to obtain the normalized 2f value, denoted as 2fmean; Establish a non-linear relationship between the concentration and 2fmean; Fill the gas with the concentration to be measured into the area of the gas to be measured, calculate the obtained normalized 2f value, and substitute this value into the established non-linear relationship, and then the true value of the concentration of the gas to be measured can be obtained.

2. The system for monitoring gas concentration according to claim 1, characterized in that, The signal generation module generates a sawtooth signal and a sine signal, and modulates the sine signal onto the sawtooth signal as the drive signal of the distributed feedback laser; The photoelectric detection module is used to convert the received optical signal into an electrical signal containing gas concentration information to obtain a direct absorption signal.

3. The system for monitoring gas concentration according to claim 1, wherein The system further includes a temperature control module. The temperature control module is used to control the operating temperature of the distributed feedback laser. The internal secondary temperature control can accurately control the temperature at the required temperature, with an error of ±0.001 °C, effectively ensuring the stability of the output wavelength of the distributed feedback laser; The system further includes a current drive module. The current drive module converts the modulated voltage signal into a current signal and performs current tuning on the distributed feedback laser to ensure that the wavelength range of the laser emitted by the distributed feedback laser completely covers the absorption wavelength of the target gas.

4. The system for monitoring gas concentration according to claim 1, wherein The system normalizes the 2f signal by using the DC signal, and there is no need to set a reference gas chamber and a reference optical path inside, and the system complexity is low.

5. The system for monitoring gas concentration according to claim 1, characterized in that, The signal processing module extracts the absorption spectral line of the gas by using a FIR filter.

6. The system for monitoring gas concentration according to claim 1, wherein The signal processing module normalizes the 2f signal using a DC signal, and quickly inverses the concentration by establishing a second-order relationship between the peak value of the normalized 2f signal and the concentration.

7. The system for monitoring gas concentration according to claim 1, characterized in that, The signal generation module, signal transmission module, lock-in amplifier module, and signal processing module are integrated on the same circuit board.

8. The system for monitoring gas concentration according to claim 3, characterized in that, The temperature control module and current drive module are integrated on the same circuit board.

9. A method for monitoring gas concentration using the system for monitoring gas concentration according to any one of claims 1 to 8, characterized in that, It includes the following steps: Power on and self-start the system. The signal generation module generates a voltage of a waveform, and the current drive module converts the voltage signal into a current to drive the laser to generate a laser signal. The laser signal passes through the central hole of the off-axis paraboloid mirror, passes through the target area of the gas to be measured, and the corner cube prism reflects the laser signal to the off-axis paraboloid mirror. The off-axis paraboloid mirror focuses the laser on the photoelectric detection module. The photoelectric detection module converts the optical signal into a voltage signal. The signal transmission module collects the voltage signal and transmits it to the lock-in amplifier module, and the lock-in amplifier module analyzes the 2f signal. Judge whether the light intensity meets the requirements. If it does not meet the requirements, alarm and judge whether the light intensity meets the requirements. If it meets the requirements, collect the 2f signal, and the gas concentration can be obtained by using the fast inversion step. Among them, the fast inversion includes the following steps: Pre-collect the 2f signals and direct absorption signals of different concentrations in the area of the gas to be measured, and perform the following processing: Extract the maximum value of the 2f wave peak at the position known as the absorption peak, and extract the left minimum value and right minimum value of the 2f wave valley at the positions on both wings of the absorption peak. Subtract the average value of the left minimum value and the right minimum value from the maximum value to obtain the peak value of the 2f absorption peak, denoted as 2fpeak. Since the number of points of the direct absorption signal is known to be equal to the number of points of the 2f signal, select a certain section of the direct absorption signal at the position without an absorption peak, and calculate the average value of this section of the direct absorption signal, denoted as dcmean. Normalize the peak value 2fpeak of the 2f absorption peak using the average value dcmean of the direct absorption signal to obtain the normalized 2f value, denoted as 2fmean. Establish a non-linear relationship between the concentration and 2fmean. Flush the gas with the concentration to be measured into the area of the gas to be measured, calculate the obtained normalized 2f value, and substitute this value into the established non-linear relationship to obtain the true value of the concentration of the gas to be measured.

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