A dual-wavelength detection system and method for CO2 gas concentration based on TDLAS-WMS

Abstract

The application relates to the technical field of gas spectrum detection, and discloses a CO2 gas concentration dual-wavelength detection system and method based on TDLAS-WMS, which comprises a main control upper computer, a signal generation and modulation module, a dual-channel laser module, an optical path module, a gas absorption cell, a photoelectric detection module and a signal acquisition and lock-in amplification module. The method comprises the following steps: initializing and loading parameters; generating a driving signal of superimposed scanning and modulation to drive a laser; extracting a second harmonic signal after the laser passes through the gas to be detected; realizing high signal-to-noise ratio concentration signal acquisition, automatically judging whether the current waveband is saturated or under-response, switching to another waveband, and realizing self-adaptive dynamic detection. Through dual-wavelength cooperation and self-adaptive switching, the technical problems of narrow dynamic range, easy saturation at high concentration, insufficient sensitivity at low concentration, and large error of a single-wavelength TDLAS system are solved, and wide-range, high-precision and continuous self-adaptive detection from low concentration to high concentration are realized.

Description

Technical Field

[0001] This invention belongs to the field of gas spectral detection technology, and particularly relates to the field of gas concentration measurement, specifically a dual-wavelength detection system and method for CO2 gas concentration based on TDLAS-WMS. Background Technology

[0002] In the field of gas detection using laser absorption spectroscopy, TDLAS (Tunable Diode Laser Absorption Spectroscopy) has become one of the most promising absorption spectroscopy technologies due to its advantages such as high sensitivity, high selectivity, non-contact operation, and fast response. Its basic principle is to use monochromatic light output from a tunable semiconductor laser to scan the absorption lines of gas molecules within a certain frequency range, and calculate the gas concentration by measuring the change in transmitted light intensity. However, in practical applications, traditional TDLAS systems have the following shortcomings:

[0003] 1. Limited Dynamic Range of Single-Wavelength Detection: With a fixed optical path length and a single detection wavelength, it is difficult for the detection system to simultaneously achieve both accurate measurement at low concentrations and reliable detection at high concentrations. In the low concentration range, gas molecules absorb laser light weakly, and the absorption peak of the scanning signal is easily overwhelmed by laser fluctuations, baseline drift, and optical interference, resulting in insufficient signal-to-noise ratio. In the high concentration range, gas molecules absorb laser light more strongly, significantly weakening the transmitted light intensity. At the corresponding absorption wavelength, the transmitted light intensity may drop to almost zero, and the absorption peak exhibits "pinching" (absorption tends to be complete), thus increasing the concentration detection error. Therefore, the single-wavelength scheme can only maintain optimal performance within a narrow concentration range.

[0004] 2. Significant impact from environmental interference and system noise: In addition to gas absorption information, the transmitted light intensity signal of the laser is also superimposed with various concentration-independent disturbance components such as laser intensity fluctuations, background light changes, detector noise, and optical fringe interference. These noises can seriously affect the measurement accuracy.

[0005] To address the aforementioned issues, a method combining WMS (Wavelength Modulation Spectroscopy) technology is proposed. Specifically, a high-frequency sinusoidal signal is superimposed on the low-frequency sawtooth wave scanning signal of the emitted laser to modulate the laser intensity and wavelength at a high frequency. The system then demodulates the absorption signal using a lock-in amplifier to obtain the harmonic signals, particularly the second harmonic (2). The amplitude of the signal is linearly related to the concentration, which can effectively suppress low-frequency noise and improve detection sensitivity. Existing gas concentration detection systems mostly use a single laser wavelength structure, which, while improving sensitivity, still struggles to cover a wide concentration detection range spanning multiple orders of magnitude in volume fraction. Therefore, there is an urgent need for a system that can simultaneously achieve adaptive detection of both high and low concentrations to address the shortcomings of existing technologies in terms of detection range and adaptability. Summary of the Invention

[0006] To address the problems of large differences in the absorption spectrum response of the same gas within different gas concentration ranges, severe limitations in detection dynamic range, signal saturation distortion, and insufficient detection sensitivity, and the inability to adaptively cover continuous measurement from low to high concentration ranges, this invention provides a dual-wavelength detection system and method for CO2 gas concentration based on TDLAS-WMS.

[0007] This invention is achieved using the following techniques:

[0008] This invention provides a dual-wavelength detection system for CO2 gas concentration based on TDLAS-WMS, comprising:

[0009] Main control host computer;

[0010] The signal generation and modulation module is connected to the main control host computer and is used to generate signals and output drive signals that are superimposed with low-frequency scanning signals and high-frequency sinusoidal modulation signals.

[0011] The dual-channel laser module is connected to the signal generation and modulation module through a dual-channel laser driver. It receives the driving signal and outputs wavelength-modulated light. The dual-channel laser module includes two tunable semiconductor lasers that emit modulated light of a first wavelength and a second wavelength, respectively. The tunable semiconductor lasers are DFB lasers, which are used to detect high-concentration and low-concentration regions, respectively. The first wavelength is 1572nm and the second wavelength is 2004nm.

[0012] The optical path combining and collimation module is connected to the dual-channel laser module and is used to perform optical path combining and collimation on the modulated light.

[0013] A gas absorption cell is located on the outgoing optical path of the optical beam combiner and collimator module to contain the gas to be measured.

[0014] The photoelectric detection module is set in the outgoing light path of the gas absorption cell to receive the light signal passing through the gas absorption cell and convert it into an electrical signal for output.

[0015] The signal acquisition and lock-in amplifier module is connected to the output of the photoelectric detection module. It is used to acquire electrical signals and perform synchronous demodulation, extract the second harmonic component in the modulated signal, and filter out low-frequency noise.

[0016] The output of the signal acquisition and phase-locked amplification module is connected to the host computer, which controls the switching between the first and second wavelengths based on the signal amplitude obtained from the second harmonic component and the preset threshold rules.

[0017] Furthermore, the main control host computer includes:

[0018] A wavelength switching control module is used to achieve adaptive switching and stable control between a first wavelength and a second wavelength.

[0019] The data processing and concentration inversion module is connected to the signal acquisition and lock-in amplification module and is used to invert the gas concentration based on the second harmonic component.

[0020] Furthermore, the signal generation and modulation module includes a direct digital synthesizer (DDS), a programmable waveform control unit, a dual-channel synchronous DAC output module, and an FPGA.

[0021] This invention also provides a detection method for CO2 gas concentration using a dual-wavelength detection system based on TDLAS-WMS, comprising the following steps:

[0022] S1, Parameter Loading and Preparatory Work

[0023] Initialize the system, load detection parameters, and set threshold rules;

[0024] Specifically, the center wavelength, scanning range, modulation amplitude, modulation frequency, and scanning frequency parameters corresponding to the first and second wavelengths are loaded, and the data acquisition time window is set.

[0025] The linear conversion relationship obtained from standard gas calibration converts the second harmonic signal amplitude into gas concentration, which is then used to invert the second harmonic amplitude into gas concentration.

[0026] Set threshold rules

[0027] Complete the hardware preparation for operation.

[0028] S2, Signal Generation and Wavelength Modulation

[0029] The signal generation and modulation module generates high-frequency sinusoidal modulation signals and low-frequency scanning signals. Specifically, the direct digital synthesizer (DDS) acts as the signal generation unit, generating high-frequency sinusoidal modulation signals, while the programmable waveform control unit generates low-frequency sawtooth or triangular scanning signals.

[0030] The scanning signal and the modulation signal are superimposed to form a driving signal, which is then output through a dual-channel synchronous DAC output module. Specifically, the phase difference between the output frequency and the phase-locked reference is monitored to perform automatic phase synchronization adjustment; and the amplitude of the modulation signal is automatically adjusted by measuring the amplitude of the second harmonic signal in real time to keep the modulation depth at the optimal state. Finally, the driving signal is sent to the dual-channel laser driver after digital-to-analog conversion to realize the modulation driving of the two-band light source.

[0031] One of the tunable semiconductor lasers is driven by a dual-channel laser driver to output modulated light.

[0032] S3, Optical Propagation and Signal Detection

[0033] After being combined and collimated by the optical path, the modulated light enters the gas absorption cell, passes through the gas to be measured, and the absorption by the gas causes the light intensity to change with wavelength.

[0034] The photoelectric detection module receives the optical signal passing through the gas absorption cell and converts it into an electrical signal for output.

[0035] S4, Phase-locked synchronous demodulation to extract the second harmonic.

[0036] The electrical signal enters the signal acquisition and lock-in amplifier module, where the lock-in amplifier synchronously demodulates the electrical signal, extracts the second harmonic component, and filters out low-frequency noise interference.

[0037] S5, Concentration Inversion and Parameter Calculation

[0038] The peak amplitude of the second harmonic component is acquired within a fixed time window, and the average peak amplitude and signal-to-noise ratio are calculated. The concentration measurement value is retrieved based on the average peak amplitude and calibration curve, and the concentration uncertainty is calculated based on the sensitivity coefficient obtained from the fitting.

[0039] S6, Threshold determination

[0040] Based on the obtained parameters and threshold rules, a decision is made to maintain the current band or switch bands. The threshold rules include a first threshold determination condition and a second threshold determination condition.

[0041] The first threshold determination condition is: the real-time signal-to-noise ratio is lower than the preset lower limit of the signal-to-noise ratio, or the real-time concentration measurement uncertainty is higher than the preset upper limit of uncertainty. The second threshold determination condition is: the amplitude of the real-time second harmonic component enters the saturation region, or the real-time concentration measurement value is higher than the preset upper limit of concentration.

[0042] If the first threshold condition is met, it is determined that the current signal quality does not meet the requirements for low concentration measurement, and the control switches to the second wavelength suitable for low concentration detection.

[0043] If the second threshold condition is met, it is determined that the current signal quality does not meet the requirements for high concentration measurement, and the control switches to the first wavelength suitable for high concentration detection.

[0044] If none of the conditions are met, the current operating band will be maintained, and the next detection cycle will begin.

[0045] If a band switching is detected, the host computer loads the switched band and locks the wavelength, then returns to step S2 for a loop. The system quickly relocks the second harmonic peak value through a phase-locked feedback mechanism and returns to the acquisition loop, achieving rapid re-acquisition.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] This invention provides a dual-wavelength CO2 gas concentration detection system and method based on TDLAS-WMS. By combining dual-wavelength laser collaborative detection with an automatic switching algorithm, it achieves accurate detection of CO2 gas concentration over a wide dynamic range. The range is wider and the accuracy is higher from low to high concentration, and adaptive detection is achieved. It overcomes the limitations of traditional single-wavelength TDLAS systems in terms of detection dynamic range, signal saturation distortion, and insufficient detection sensitivity. It is suitable for various occasions such as atmospheric carbon emission monitoring, industrial flue gas detection, and laboratory precision measurement.

[0048] This invention employs a signal acquisition and lock-in amplification module to extract the second harmonic and invert the concentration, effectively suppressing interference caused by factors such as laser intensity fluctuations, background light variations, detector noise, and optical fringe interference. This improves detection sensitivity, with a signal-to-noise ratio approximately 10-20 times higher than traditional TDLAS systems. It also effectively expands the detection range and reduces detection errors. Furthermore, this invention addresses the issues of single-wavelength systems easily saturating at excessively high concentrations and having insufficient signal-to-noise ratio at low concentrations through an automatic threshold switching algorithm, achieving seamless detection across high and low concentration ranges.

[0049] This invention achieves digital control of waveform generation and modulation depth, improving system stability; the overall system response time is fast, making it suitable for real-time monitoring of dynamic gas processes; by replacing lasers for different gas molecules, it can be widely used for high-precision online monitoring of gases such as CO2, CH4, and H2O. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the detection system structure of the present invention.

[0051] Figure 2 This is a schematic diagram of the inversion and band switching process of the present invention.

[0052] In the diagram: 1. Main control host computer; 2. Signal generation and modulation module; 3. Dual-channel laser driver; 4. Tunable semiconductor laser; 5. Optical path beam combining and collimation module; 6. Gas absorption cell; 7. Photoelectric detection module; 8. Signal acquisition and lock-in amplification module. Detailed Implementation

[0053] The specific embodiments of the present invention will be described in detail below.

[0054] Example 1

[0055] A dual-wavelength detection system for CO2 gas concentration based on TDLAS-WMS, such as Figure 1 As shown: including:

[0056] Main control host computer 1; preferably, the main control host computer 1 includes: a wavelength switching control module, used to realize adaptive switching and stable control between the first wavelength and the second wavelength;

[0057] The data processing and concentration inversion module is connected to the signal acquisition and lock-in amplification module 8, and is used to invert the gas concentration based on the second harmonic component.

[0058] The signal generation and modulation module 2, connected to the host computer 1, is used to generate signals and output a drive signal superimposed with a low-frequency scanning signal and a high-frequency sinusoidal modulation signal. Preferably, the signal generation and modulation module 2 includes a direct digital synthesizer (DDS), a programmable waveform control unit, a dual-channel synchronous DAC output module, and an FPGA.

[0059] The execution process is as follows:

[0060] ① Signal generation: A direct digital synthesizer (DDS) generates a high-frequency sine wave, with a modulation frequency of... The frequency range is 1~10kHz, i.e., a high-frequency sinusoidal modulation signal; the programmable waveform control unit generates a low-frequency sawtooth wave or triangular wave scanning signal, with a scanning frequency of... 10~100Hz;

[0061] ② Waveform superposition: The low-frequency scanning signal and the high-frequency sinusoidal modulation signal are digitally superimposed to form the driving signal. The following equation is satisfied:

[0062]

[0063] In the formula:

[0064] The driving voltage signal for the tunable semiconductor laser 4, i.e., the combined voltage input after scanning and modulation superposition, determines the output wavelength and power variation;

[0065] This is the DC bias voltage used to set the laser's operating point;

[0066] This is a low-frequency scanning waveform term, typically a sawtooth or triangular wave, where t is time. The period determines the scan rate. The amplitude determines the scanning range, which is used to achieve linear scanning of the absorption lines;

[0067] This is a high-frequency sinusoidal modulation term. For modulation frequency, This is for modulating the voltage amplitude.

[0068] ③ Synchronization control: Monitor the phase difference between the output frequency and the phase-locked reference signal to achieve automatic phase synchronization adjustment;

[0069] ④ Adaptive modulation depth adjustment: The amplitude of the modulation signal is automatically adjusted by measuring the 2f amplitude in real time. This ensures that the modulation depth remains at the optimal value.

[0070] ⑤ Output control: After the signal is converted by a dual-channel DAC, it drives the laser current input terminal to achieve synchronous modulation of two wavelengths.

[0071] The signal generation and modulation module 2 enables fully digital synchronous control of scanning and modulation signals, and features temperature compensation, phase correction, and adaptive modulation depth.

[0072] The dual-channel laser module is connected to the signal generation and modulation module 2 via the dual-channel laser driver 3. It receives the driving signal and outputs wavelength-modulated light. The dual-channel laser module includes two tunable semiconductor lasers 4 that emit modulated light of a first wavelength and a second wavelength, respectively. Preferably, the tunable semiconductor lasers 4 are DFB lasers, which detect high-concentration areas and low-concentration areas, respectively. The first wavelength is 1572nm and the second wavelength is 2004nm.

[0073] The optical path combining and collimation module 5 is connected to the dual-channel laser module and is used to perform optical path combining and collimation on the modulated light.

[0074] The gas absorption cell 6 is located on the outgoing optical path of the optical beam combiner and collimator module 5 and is used to contain the gas to be measured.

[0075] The photoelectric detection module 7 is located on the outgoing light path of the gas absorption cell 6 and is used to receive the light signal passing through the gas absorption cell 6 and convert it into an electrical signal for output.

[0076] The signal acquisition and lock-in amplifier module 8 is connected to the output of the photoelectric detection module 7. It is used to acquire electrical signals and perform synchronous demodulation, extract the second harmonic component in the modulated signal, and filter out low-frequency noise.

[0077] The output of the signal acquisition and phase-locked amplification module 8 is connected to the main control host computer 1. The main control host computer 1 is used to control the switching between the first wavelength and the second wavelength according to the signal amplitude obtained from the second harmonic component and the preset threshold rule.

[0078] Example 2

[0079] A dual-wavelength detection method for CO2 gas concentration based on TDLAS-WMS, such as Figure 2 As shown: Includes the following steps:

[0080] S1, Parameter Loading and Preparatory Work

[0081] Load the center wavelength, scanning range, modulation amplitude, modulation frequency, and scanning frequency parameters corresponding to the first and second wavelengths, and set the data acquisition time window.

[0082] The linear conversion relationship obtained from standard gas calibration converts the second harmonic signal amplitude into gas concentration, which is then used to invert the second harmonic amplitude into gas concentration.

[0083] Set threshold rules

[0084] Complete the hardware preparation for operation.

[0085] S2, Signal Generation and Wavelength Modulation

[0086] Signal generation and modulation module 2 generates a high-frequency sinusoidal modulation signal and a low-frequency scanning signal. Specifically, a direct digital synthesizer (DDS) acts as the signal generation unit, generating a high-frequency sinusoidal modulation signal with a modulation frequency of [missing information]. The programmable waveform control unit generates low-frequency sawtooth or triangular wave scanning signals ranging from 1 to 10 kHz, with a scanning frequency of... The frequency range is 10~100Hz.

[0087] The scanning signal and the modulation signal are superimposed to form the driving signal. Satisfy the following formula:

[0088]

[0089] In the formula:

[0090] The driving voltage signal for the laser, i.e., the combined voltage input after scanning and modulation, determines the output wavelength and power variation;

[0091] This is the DC bias voltage used to set the laser's operating point;

[0092] This is a low-frequency scanning waveform term, typically a sawtooth or triangular wave, where t is time. The period determines the scan rate. The amplitude determines the scanning range, which is used to achieve linear scanning of the absorption lines;

[0093] This is a high-frequency sinusoidal modulation term. For modulation frequency, This is for modulating the voltage amplitude.

[0094] The system monitors the phase difference between the output frequency and the phase-locked reference to perform automatic phase synchronization adjustment; and automatically adjusts the amplitude of the modulation signal by measuring the amplitude of the second harmonic signal (2f) in real time. This keeps the modulation depth at its optimal level.

[0095] The driving signal is converted from digital to analog and then sent to the dual-channel laser driver 3 to achieve modulation driving of two-band light sources.

[0096] Finally, one of the tunable semiconductor lasers 4 is driven by the dual-channel laser driver 3 to output modulated light.

[0097] S3, Optical Propagation and Signal Detection

[0098] After being combined and collimated by the optical path, the modulated light enters the gas absorption cell 6, passes through the gas to be measured, and the absorption by the gas causes the light intensity to change with wavelength.

[0099] The photoelectric detection module 7 receives the optical signal passing through the gas absorption cell 6 and converts it into an electrical signal for output.

[0100] S4, Phase-locked synchronous demodulation to extract the second harmonic.

[0101] The electrical signal enters the signal acquisition and lock-in amplifier module 8, where the lock-in amplifier synchronously demodulates the electrical signal, extracts the second harmonic component, and filters out low-frequency noise interference.

[0102] The principle and calculation basis for WMS second harmonic extraction are as follows:

[0103] By using a lock-in amplifier via WMS to extract the second harmonic (2f) signal, a high signal-to-noise ratio (SNR) signal can be obtained.

[0104] Drive current of tunable semiconductor laser 4 The superposition of the scanning signal and the modulation signal conforms to the following formula:

[0105]

[0106] In the formula:

[0107] This is the DC bias current, corresponding to the center wavelength of the laser. ;

[0108] It is a low-frequency sawtooth or triangular wave scanning current used for linear scanning of laser wavelength;

[0109] It is a high-frequency sinusoidal modulation component. For modulation frequency, The modulation amplitude is used to generate harmonic signals in WMS.

[0110] The wavelength changes with time according to the following formula:

[0111]

[0112] In the formula:

[0113] The instantaneous emission wavenumber or frequency of the laser;

[0114] The laser center wavenumber corresponds to the midpoint wavelength of the scan;

[0115] Linear tuning term (scan rate) caused by the scan signal Unit: cm -1 / s);

[0116] The modulation depth.

[0117] According to Beer-Lambert's law, the intensity of the laser light passing through the gas absorption cell 6 is represented by the detected light signal and satisfies the following equation:

[0118]

[0119] In the formula:

[0120] The light signal detected after absorption by the gas;

[0121] The light intensity when not absorbed.

[0122] For gas at frequency Absorption coefficient at [location], expressed in cm -1 The measurement reflects the absorption intensity;

[0123] This is the absorption optical path length.

[0124] The absorption coefficient is expanded into a Fourier series, synchronously demodulated by a lock-in amplifier, and the second harmonic (2f) component is extracted:

[0125]

[0126] In the formula:

[0127] The amplitude of the second harmonic (2f) signal extracted by lock-in amplification;

[0128] Let be a Bessel function, the first The absorption line response coefficient of each harmonic includes gas absorption characteristics, temperature, and pressure information;

[0129] Modulation depth;

[0130] This is the absorption coefficient term related to concentration;

[0131] This is for modulating the phase difference (the phase shift between laser modulation and detection).

[0132] The second-order modulation response intensity, reflecting the absorption line shape, is the most concentration-sensitive signal component in WMS technology. When When the "optimal modulation depth" is selected (approximately 2.2 to 2.4 times the linewidth), the signal strength is maximized and the noise impact is minimized.

[0133] Using standard gases, a linear relationship was obtained through calibration measurements, and a calibration curve was plotted:

[0134]

[0135] In the formula: This represents the theoretical value (target parameter) of gas volume fraction or concentration.

[0136] The sensitivity coefficient (determined by optical path length, absorption intensity, instrument gain, etc.);

[0137] Zero-point compensation term (considering background, drift, etc.);

[0138] With gas concentration Relationship, can Concentration is directly inverted using calibration constants. .

[0139] S5, Concentration Inversion and Parameter Calculation

[0140] The peak amplitude of the second harmonic component output in step S4 is collected within a fixed time window. And calculate the average peak amplitude within a fixed time window. With noise standard deviation Thus, the signal-to-noise ratio is obtained. It conforms to the following formula:

[0141]

[0142] In the formula:

[0143] for signal peak amplitude The average value within a fixed time window;

[0144] The noise standard deviation is obtained by sampling from the empty absorption area or the no-signal area.

[0145] Signal-to-noise ratio (SNR) reflects the quality of the current measurement signal.

[0146] Based on average peak amplitude and calibration curve Inversion concentration measurement value The concentration uncertainty was calculated based on the sensitivity coefficient obtained by fitting the calibration curve. It conforms to the following formula:

[0147]

[0148] In the formula:

[0149] Indicates the current concentration Sensitivity coefficient at the following levels This parameter can be obtained from the calibration curve. The results were obtained through fitting.

[0150] S6, Threshold determination

[0151] The real-time parameters calculated in step S5 are compared with preset threshold rules to determine whether to maintain the current band or switch bands. The threshold rules include a first threshold determination condition and a second threshold determination condition.

[0152] The first threshold determination condition is: ,or

[0153] Real-time signal-to-noise ratio The signal-to-noise ratio is lower than the preset lower limit. or real-time concentration measurement uncertainty Higher than the preset upper limit of uncertainty ;

[0154] The second threshold determination condition is: ,or

[0155] That is, the amplitude of the real-time second harmonic component Entering the saturation region or real-time concentration measurement value Higher than the preset concentration limit .

[0156] If the signal is too weak or the uncertainty is too large, and the first threshold judgment condition is met, it is determined that the current signal quality does not meet the requirements for low concentration measurement, and the control is switched to the second wavelength suitable for low concentration detection, namely the 2004nm band.

[0157] If the signal is too strong or the concentration is too high, and the second threshold judgment condition is met, it is determined that the current signal quality does not meet the requirements for high concentration measurement, and the control switches to the first wavelength suitable for high concentration detection, namely the 1572nm band.

[0158] If none of these conditions are met, that is If the signal is within the effective linear range, the current working band will be maintained, and the next detection cycle will begin.

[0159] If the switch band is determined, the main control computer 1 sends a control signal through the dual-channel laser driver 3 to achieve the switch, and automatically loads the center wavelength of the switched band. Scan range With modulation amplitude Then, the center 2f wavelength peak is locked and re-locked, and the process returns to step S2 to achieve rapid re-acquisition.

[0160] The scope of protection claimed by this invention is not limited to the specific embodiments described above. Moreover, for those skilled in the art, this invention can have various modifications and alterations. Any modifications, improvements, and equivalent substitutions made within the concept and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A dual-wavelength detection system for CO2 gas concentration based on TDLAS-WMS, characterized in that, include: Main control host computer (1); The signal generation and modulation module (2) is connected to the host computer (1) and is used to generate signals and output a drive signal superimposed with low-frequency scanning signals and high-frequency sinusoidal modulation signals. The driving signal is formed by digitally superimposing the low-frequency scanning signal and the high-frequency sinusoidal modulation signal. The following equation is satisfied: ； In the formula: The driving voltage signal for the tunable semiconductor laser, i.e., the combined voltage input after scanning and modulation, determines the output wavelength and power variation; This is the DC bias voltage used to set the laser's operating point; This is a low-frequency scanning waveform term, typically a sawtooth or triangular wave, where t is time. The period determines the scan rate. The amplitude determines the scanning range, which is used to achieve linear scanning of the absorption lines; This is a high-frequency sinusoidal modulation term. For modulation frequency, For modulating voltage amplitude; The dual-channel laser module is connected to the signal generation and modulation module (2) via a dual-channel laser driver (3), receives the driving signal and outputs wavelength-modulated light. The dual-channel laser module includes two tunable semiconductor lasers (4) that emit modulated light of the first wavelength and the second wavelength respectively. The optical path combining and collimation module (5) is connected to the dual-channel laser module and is used to perform optical path combining and collimation on the modulated light; The gas absorption cell (6) is set on the outgoing optical path of the optical path combining and collimating module (5) to contain the gas to be measured. The photoelectric detection module (7) is set on the outgoing light path of the gas absorption cell (6) to receive the light signal passing through the gas absorption cell (6) and convert it into an electrical signal for output. The signal acquisition and lock-in amplifier module (8) is connected to the output of the photoelectric detection module (7) and is used to acquire electrical signals and perform synchronous demodulation to extract the second harmonic component in the modulated signal. The output of the signal acquisition and phase-locked amplification module (8) is connected to the host computer (1), which is used to control the switching between the first wavelength and the second wavelength according to the signal amplitude obtained from the second harmonic component and the preset threshold rule.

2. The dual-wavelength CO2 gas concentration detection system based on TDLAS-WMS according to claim 1, characterized in that, The main control host computer (1) includes: A wavelength switching control module is used to achieve adaptive switching and stable control between a first wavelength and a second wavelength. The data processing and concentration inversion module is connected to the signal acquisition and lock-in amplification module (8) and is used to invert the gas concentration based on the second harmonic component.

3. The dual-wavelength CO2 gas concentration detection system based on TDLAS-WMS according to claim 1, characterized in that, The signal generation and modulation module (2) includes a direct digital synthesizer, a programmable waveform control unit, a dual-channel synchronous DAC output module, and an FPGA.

4. The dual-wavelength CO2 gas concentration detection system based on TDLAS-WMS according to claim 1, characterized in that, The tunable semiconductor laser (4) is a DFB laser; the first wavelength is 1572nm and the second wavelength is 2004nm.

5. A detection method using the dual-wavelength CO2 gas concentration detection system based on TDLAS-WMS as described in claim 3, characterized in that, Includes the following steps: S1, Parameter Loading and Preparatory Work Initialize the system, load detection parameters, and set threshold rules; S2, Signal Generation and Wavelength Modulation The signal generation and modulation module (2) generates a high-frequency sinusoidal modulation signal and a low-frequency scanning signal, which are superimposed to form a driving signal. The signal is output through the dual-channel synchronous DAC output module and drives one of the tunable semiconductor lasers (4) through the dual-channel laser driver (3) to output modulated light. S3, Optical Propagation and Signal Detection After being combined and collimated by the optical path, the modulated light enters the gas absorption cell (6) and passes through the gas to be measured. The photoelectric detection module (7) receives the light signal passing through the gas absorption cell (6) and converts it into an electrical signal for output; S4, Phase-locked synchronous demodulation to extract the second harmonic. The electrical signal enters the signal acquisition and lock-in amplifier module (8), where the lock-in amplifier synchronously demodulates the electrical signal, extracts the second harmonic component, and filters out low-frequency noise interference. S5, Concentration Inversion and Parameter Calculation The peak amplitude of the second harmonic component is collected within a fixed time window, and the average peak amplitude and signal-to-noise ratio are calculated. The concentration measurement value is retrieved based on the average peak amplitude and the calibration curve, and the concentration uncertainty is calculated based on the sensitivity coefficient obtained from the fitting. S6, Threshold determination Based on the obtained parameters and threshold rules, a decision is made to maintain the current band or switch bands. The threshold rules include a first threshold determination condition and a second threshold determination condition. The first threshold determination condition is: the real-time signal-to-noise ratio is lower than the preset lower limit of the signal-to-noise ratio, or the real-time concentration measurement uncertainty is higher than the preset upper limit of uncertainty. The second threshold determination condition is: the amplitude of the real-time second harmonic component enters the saturation region, or the real-time concentration measurement value is higher than the preset upper limit of concentration. If the first threshold condition is met, it is determined that the current signal quality does not meet the requirements for low concentration measurement, and the control switches to the second wavelength suitable for low concentration detection. If the second threshold condition is met, it is determined that the current signal quality does not meet the requirements for high concentration measurement, and the control switches to the first wavelength suitable for high concentration detection. If none of the conditions are met, the current operating band is maintained, and the next detection cycle begins; If it is determined that the band is switched, the host computer (1) loads the switched band and locks the wavelength, and returns to step S2 to loop.

6. The dual-wavelength detection method for CO2 gas concentration based on TDLAS-WMS according to claim 5, characterized in that, In step S2, the direct digital synthesizer generates a high-frequency sinusoidal modulation signal, with a modulation frequency of... The programmable waveform control unit generates low-frequency sawtooth or triangular wave scanning signals ranging from 1 to 10 kHz, with a scanning frequency of... 10~100Hz; The driving signal is formed by digitally superimposing the low-frequency scanning signal and the high-frequency sinusoidal modulation signal. The following equation is satisfied: ； In the formula: The driving voltage signal for the tunable semiconductor laser, i.e., the combined voltage input after scanning and modulation, determines the output wavelength and power variation; This is the DC bias voltage used to set the laser's operating point; This is a low-frequency scanning waveform term, typically a sawtooth or triangular wave, where t is time. The period determines the scan rate. The amplitude determines the scanning range, which is used to achieve linear scanning of the absorption lines; This is a high-frequency sinusoidal modulation term. For modulation frequency, This is for modulating the voltage amplitude.

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