A gas concentration detection method and device, a terminal device and a medium

Abstract

The application provides a gas concentration detection method and device, terminal equipment and medium, comprising controlling a laser to output a laser signal covering a characteristic absorption spectral line of a to-be-detected gas, and converting the laser signal into an original electric signal after passing through the to-be-detected gas via a standard-free light path; demodulating the original electric signal to extract first-order and second-order harmonic signals, and calculating a multi-dimensional harmonic characteristic ratio; obtaining temperature and pressure, introducing a spectral line broadening correction coefficient to construct a physical temperature and pressure model, and correcting the multi-dimensional harmonic characteristic ratio; extracting a waveform feature of a non-absorption reference region, performing nonlinear waveform distortion self-calibration on the corrected harmonic characteristic ratio, and obtaining a final harmonic characteristic ratio; establishing a theoretical mapping relationship between the final harmonic characteristic ratio and a to-be-detected gas concentration based on the Lambert-Beer law, and substituting the final harmonic characteristic into the to-be-detected gas to obtain a gas concentration detection result of the to-be-detected gas. The application can improve the accuracy and robustness of gas concentration detection.

Description

Technical Field

[0001] This invention belongs to the field of gas concentration detection technology, specifically relating to a gas concentration detection method, device, terminal equipment, and medium. Background Technology

[0002] TDLAS gas detection technology, with its advantages of high spectral resolution, high sensitivity, and non-contact detection, has become the mainstream technology for gas concentration detection. The core of this technology is based on Beer-Lambert's law, which calculates concentration by analyzing the light intensity attenuation or harmonic signals after laser absorption by the gas.

[0003] However, existing TDLAS concentration retrieval methods generally have certain drawbacks. Traditional techniques heavily rely on on-site calibration with standard gases, a process that is extremely cumbersome and requires professionals to carry the standard gases to the site, resulting in high long-term maintenance costs. Furthermore, environmental factors such as temperature and pressure fluctuations and optical path losses can easily invalidate the original calibration relationships, leading to a significant increase in measurement errors. Additionally, each device requires individual calibration, resulting in poor batch consistency.

[0004] To address the shortcomings of traditional calibration methods, some calibration-free solutions have been proposed in existing technologies, but they still have significant drawbacks: First, some existing solutions (such as patent CN107219190A) require fitting an etalon signal to obtain the laser's time-frequency response model. This technique relies on an additional etalon optical path, greatly increasing the complexity of the hardware structure and the computational load. Second, some solutions (such as patent CN103868885A) use the ratio of the second to fourth (or higher) harmonics to calculate the concentration. Phase-locked demodulation of higher harmonics requires extremely complex Fourier series fitting, resulting in very high computational complexity, making it difficult to run on lightweight embedded platforms such as FPGAs or STM32.

[0005] Furthermore, existing temperature and pressure correction and waveform drift compensation are mostly simple linear models (such as patent WO2013096396A1, which only uses the non-absorption region for simple background subtraction compensation). When high turbidity and high scattering occur in actual working conditions, resulting in severe nonlinear waveform distortion, simple linear compensation will completely fail and cannot cope with harsh working conditions. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a gas concentration detection method, device, terminal equipment and medium to solve the problems of existing TDLAS calibration-free schemes, such as dependence on standard instruments for additional hardware, excessive system computation due to high harmonic extraction, failure of waveform distortion correction under harsh conditions of high turbidity and high attenuation due to reliance on linear baseline compensation alone, single characteristic amplitude extraction and inaccurate temperature and pressure correction physical model, thereby improving the accuracy and robustness of gas concentration detection.

[0007] In a first aspect, the present invention provides a method for detecting gas concentration, the method comprising the following steps: The laser output is controlled to cover the characteristic absorption spectrum of the gas to be tested, and the laser signal is converted into the original electrical signal after passing through the gas to be tested via a standardless optical path; the laser signal is modulated by superposition of low-frequency triangular wave and high-frequency sine wave; The original electrical signal is demodulated by phase-locked loop to extract the first-order and second-order harmonic signals. The characteristic amplitudes of the first-order and second-order harmonic signals are adaptively selected according to the detection conditions to calculate the multi-dimensional harmonic characteristic ratio. The characteristic amplitudes include peak amplitude, full width at half maximum (FWHM) amplitude, or integral area. The temperature and pressure of the detection environment are obtained, and a physical temperature and pressure model is constructed by introducing a pre-calibrated spectral broadening correction coefficient. The physical temperature and pressure model is used to correct the multi-dimensional harmonic characteristic ratio to obtain the corrected harmonic characteristic ratio. Waveform features of the non-absorbing reference region are extracted, and nonlinear waveform distortion self-calibration is performed on the corrected harmonic characteristic ratio based on the waveform features to obtain the final harmonic characteristic ratio. The waveform features include waveform kurtosis, waveform skewness, and phase features. Based on Beer-Lambert's law, a theoretical mapping relationship is established between the final harmonic characteristic ratio and the concentration of the gas to be measured. By substituting the final harmonic characteristic ratio into the theoretical mapping relationship, a calibration-free concentration inversion is achieved, and the gas concentration detection result of the gas to be measured is obtained.

[0008] Optionally, after performing phase-locked demodulation on the original electrical signal to extract the first-order harmonic signal and the second-order harmonic signal, the method further includes: The extracted first-order and second-order harmonic signals were preprocessed. The preprocessing included extracting the baseline of the non-absorbing region to eliminate DC drift, and using Butterworth low-pass filtering and Savitzky Gore smoothing cascade filtering to suppress noise signals.

[0009] Optionally, based on the detection conditions, the characteristic amplitudes of the first-order and second-order harmonic signals are adaptively selected to calculate the multi-dimensional harmonic characteristic ratio, including: Under normal concentration detection conditions, the peak amplitudes of the first-order harmonic signal and the second-order harmonic signal are extracted to calculate the harmonic characteristic ratio. Under trace detection conditions, the full width at half maximum (FWHM) values ​​of the first-order and second-order harmonic signals are extracted to calculate the harmonic characteristic ratio. Under spectral distortion conditions, the integral area of ​​the first-order harmonic signal and the second-order harmonic signal is extracted to calculate the harmonic characteristic ratio.

[0010] Optionally, the expression for the physical temperature and pressure model is:

[0011] in, This represents the corrected harmonic characteristic ratio; This represents the ratio of extracted multidimensional harmonic features; This indicates the real-time temperature of the monitored environment, expressed in Kelvin. This indicates the real-time pressure of the detection environment, expressed in standard atmospheres. Indicates the nominal temperature under standard conditions; Indicates the nominal pressure under standard conditions; This represents the spectral broadening correction factor for a specific gas to be measured, based on a pre-calibrated HITRAN database.

[0012] Optionally, waveform features of the non-absorbing reference region are extracted, and nonlinear waveform distortion self-calibration is performed on the corrected harmonic characteristic ratio based on the waveform features to obtain the final harmonic characteristic ratio, including: The region where no gas to be measured is absorbed is selected as the non-absorption reference region, and the waveform kurtosis, waveform skewness, and phase characteristics of the signal in the non-absorption reference region are extracted. A nonlinear mapping relationship between waveform characteristics and correction coefficients is established based on polynomial fitting. When the deviation between the baseline ratio in the non-absorbing reference region and the initial baseline ratio exceeds one percent, the nonlinear mapping relationship is used to perform nonlinear self-calibration on the corrected harmonic characteristic ratio to output the final harmonic characteristic ratio.

[0013] Optionally, a theoretical mapping relationship between the final harmonic characteristic ratio and the concentration of the gas to be measured is established based on the Lambert-Beer law. The final harmonic characteristic ratio is substituted into the theoretical mapping relationship to achieve calibration-free concentration inversion. The theoretical model used is configured as follows: the concentration value of the gas to be measured is a mapping function of the final harmonic characteristic ratio, spectral line intensity, optical path length, and normalized spectral line shape function. Among them, the spectral line intensity is determined by the inherent properties of the measured spectral line, the optical path length represents the physical distance of the laser passing through the gas to be measured, and the normalized spectral line shape function is used to characterize the profile distribution of the absorption spectral line of the gas to be measured, and its integral value satisfies the normalization condition. The normalized spectral line shape function also depends on the real-time temperature and real-time pressure of the detection environment.

[0014] Optionally, the method further includes a multi-component gas expansion detection step; the step includes: The laser is controlled to scan the non-cross-interference characteristic spectral lines of multiple test gases in a time-division manner, and the harmonic signal extraction, multi-dimensional harmonic characteristic ratio calculation, temperature and pressure correction, waveform distortion nonlinear calibration, and calibration-free concentration inversion are performed independently for each test gas, so as to simultaneously output the concentration detection results of multiple gases.

[0015] In a second aspect, the present invention provides a gas concentration detection device, comprising: The acquisition module is configured to control the laser to output a laser signal covering the characteristic absorption spectral lines of the gas to be measured, and convert it into a raw electrical signal after passing through the gas to be measured via a standardless optical path; the laser signal is modulated by superimposing a low-frequency triangular wave and a high-frequency sine wave. The demodulation and extraction module is configured to perform phase-locked demodulation on the original electrical signal to extract the first-order harmonic signal and the second-order harmonic signal, and adaptively select the characteristic amplitudes of the first-order harmonic signal and the second-order harmonic signal according to the detection conditions to calculate the multi-dimensional harmonic characteristic ratio; the characteristic amplitudes include peak amplitude, full width at half maximum (FWHM) amplitude or integral area; The temperature and pressure correction module is configured to acquire the temperature and pressure of the detection environment, and introduce a pre-calibrated spectral broadening correction coefficient to construct a physical temperature and pressure model. The physical temperature and pressure model is used to correct the multi-dimensional harmonic characteristic ratio to obtain the corrected harmonic characteristic ratio. The nonlinear calibration module is configured to extract waveform features from the non-absorbing reference region, perform nonlinear waveform distortion self-calibration on the corrected harmonic characteristic ratio based on the waveform features, and obtain the final harmonic characteristic ratio; the waveform features include waveform kurtosis, waveform skewness, and phase features. The concentration inversion module is configured to establish a theoretical mapping relationship between the final harmonic characteristic ratio and the concentration of the gas to be measured based on the Lambert-Beer law. By substituting the final harmonic characteristic ratio into the theoretical mapping relationship, calibration-free concentration inversion is achieved, and the gas concentration detection result of the gas to be measured is obtained.

[0016] Thirdly, the present invention provides a terminal device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-described method.

[0017] Fourthly, the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0018] The present invention has at least the following beneficial effects: The method provided by this invention extracts first- and second-order harmonic signals by employing a standard-free etalon optical path and superimposing low-frequency triangular waves and high-frequency sine waves, directly eliminating the dependence on expensive additional hardware in traditional schemes and significantly reducing system computational complexity. By adaptively extracting multi-dimensional feature ratios, including peak amplitude, full width at half maximum (FWHM) amplitude, or integral area, it effectively overcomes the instability of single-feature extraction under trace or complex spectra, significantly improving the robustness of detection across all scenarios. Combining a pre-calibrated spectral broadening correction coefficient with a physical model for temperature and pressure correction eliminates the impact of extreme environmental fluctuations on detection accuracy. Furthermore, using the waveform kurtosis, waveform skewness, and phase characteristics of the non-absorption reference region for nonlinear waveform distortion self-calibration overcomes the limitations of traditional linear baseline compensation, maintaining high-precision correction capabilities even when facing waveform distortion caused by high turbidity and high scattering conditions. Finally, through physical mapping, calibration-free concentration inversion is achieved, eliminating the cumbersome process and maintenance costs of on-site calibration and ensuring measurement consistency and accuracy of the equipment under complex conditions. Attached Figure Description

[0019] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0020] Figure 1 This is a flowchart of a gas concentration detection method in one embodiment of this application; Figure 2 This is one embodiment of the present application. Waveform diagram of the 1f / 2f harmonic signal after preprocessing; Figure 3 This is a structural diagram of a gas concentration detection device in another embodiment of this application; Figure 4 This is a structural diagram of a terminal device in another embodiment of this application. Detailed Implementation

[0021] The technical solution of the present invention will now be described in detail and completely with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0023] Existing technologies often rely on etalon structures, involve complex high-order harmonic calculations, and depend solely on simple linear background subtraction, resulting in high equipment costs and a sharp decline in accuracy or even complete failure of compensation functions under harsh operating conditions with high dust levels and large temperature differences. To address these issues, embodiments of the present invention provide a gas concentration detection method, apparatus, terminal equipment, and medium. Specific embodiments are described below.

[0024] Example 1 This embodiment uses hydrogen sulfide ( Taking gas concentration detection as an example, the specific implementation of this step of the present invention will be described in detail. It should be noted that this is only for illustrative purposes and does not constitute a limitation on the gas concentration detection method provided by the present invention. In specific implementations, depending on the actual application scenario, the gas concentration detection method provided by the present invention can also be used for gases including sulfur hexafluoride (SF6). Detection of decomposition products, detection of dissolved gases in transformer oil (mainly including hydrogen, methane, acetylene, ethylene, ethane, carbon dioxide, etc.), monitoring of power plant flue gas, monitoring of chemical tail gas, detection of flammable and explosive gases (mainly including methane, hydrogen, acetylene), detection of corrosive gases, and detection of air pollutants (e.g., carbon monoxide). ), nitrogen oxides ( ), sulfur dioxide ( Monitoring of volatile organic compounds (VOCs) Applications include: detection of indoor air quality, detection of industrial furnace exhaust gas, detection of gas turbine exhaust gas, detection of coalbed methane, and detection of coal mine gas (mainly composed of ethane).

[0025] like Figure 1 As shown, the gas concentration detection method provided by the present invention includes steps 11 to 15.

[0026] Step 11: Control the laser to output a laser signal that covers the characteristic absorption spectrum of the gas to be tested, and convert it into a raw electrical signal after passing through the gas to be tested via a standardless optical path.

[0027] In one feasible implementation, a distributed feedback (DFB) semiconductor laser with a center wavelength of approximately 1.39 μm is selected as the light source. The tunable range of this laser can precisely cover... Characteristic absorption spectral lines of gas in the near-infrared band (center wavenumber of absorption line approximately 7180) Up to 7190 The laser drive circuit modulates the laser current according to preset scanning parameters.

[0028] In this embodiment of the invention, the laser signal is modulated by superimposing a low-frequency triangular wave and a high-frequency sine wave.

[0029] Specifically, the low-frequency triangular wave frequency is set to 10Hz, and the scanning amplitude corresponds to a wavenumber range covering ±0.5 of the absorption peak center. This ensures that the laser wavelength can completely and linearly scan the entire absorption peak of the gas under test and the non-absorption regions on both sides; the high-frequency sinusoidal modulation frequency is 5kHz, and the modulation depth (corresponding to wavenumber modulation amplitude) is approximately 0.1. This enables effective wavelength modulation spectrum (WMS) harmonic generation. The two modulation signals drive the laser together through a superposition circuit, forming a laser signal that simultaneously contains slow wavelength scanning and fast wavelength modulation.

[0030] The laser signal is directly incident into the gas detection chamber through a standard-free optical path (i.e., without the need for an additional standard or reference cell). The chamber is made of stainless steel with quartz windows installed at both ends. The optical path length is fixed at 0.5m. The chamber is filled with the gas to be measured. Gas (concentration range 0 to 100 ppm, background gas is nitrogen or air).

[0031] After the laser passes through the gas being tested, part of the light intensity is... Molecular selective absorption occurs, and the transmitted light is received and converted into a weak current signal by a tail-end photodetector (InGaAs photodiode, response band 1.0µm to 1.7µm). This current signal is immediately amplified by a preamplifier circuit (40dB gain, low-noise operational amplifier), and then filtered by a bandpass filter (center frequency 5kHz, bandwidth 2kHz) to remove DC components and high-frequency noise, resulting in a raw electrical signal with moderate amplitude and a signal-to-noise ratio suitable for subsequent processing. This raw electrical signal directly enters the subsequent phase-locked demodulation stage, without requiring any etalon hardware to participate in the entire signal acquisition process.

[0032] Step 12: Perform phase-locked demodulation on the original electrical signal to extract the first-order harmonic signal and the second-order harmonic signal, and adaptively select the characteristic amplitude of the first-order harmonic signal and the second-order harmonic signal according to the detection conditions to calculate the multi-dimensional harmonic characteristic ratio.

[0033] In this embodiment of the invention, the process of performing phase-locked demodulation on the original electrical signal to extract the first-order harmonic signal and the second-order harmonic signal includes steps 12.1.1 to 12.1.4: Step 12.1.1: Synchronously acquire a high-frequency sinusoidal modulation signal (frequency 5kHz) from the laser driving circuit as a reference, and first generate two orthogonal reference signals.

[0034] In this embodiment of the invention, the two orthogonal reference signals include a first-order reference signal and a second-order reference signal. The first-order reference signal is a sine and cosine component (5kHz) with the same modulation frequency, and the second-order reference signal is a sine and cosine signal of the harmonic component (10kHz) of the same frequency.

[0035] Step 12.1.2: Perform multiplication and mixing operations (phase-sensitive detection) on the original electrical signal with the first-order reference signal and the second-order reference signal respectively to obtain the mixed signal.

[0036] Step 12.1.3: Extract the DC component using a low-pass filter (4th-order Butterworth filter, cutoff frequency 20Hz, time constant approximately 50ms) to obtain the in-phase component of the first-order harmonic signal. Orthogonal components and the in-phase component of the second harmonic signal Orthogonal components .

[0037] Step 12.1.4, using the calculation formula

[0038]

[0039] Obtain the complete first-order harmonic signal and second harmonic signals .

[0040] Fixed phase compensation or dynamic phase tracking can be added during demodulation to ensure maximum amplitude extraction. The entire demodulation process is completed in real time within one laser scanning cycle (100ms), and the output first-order and second-order harmonic signals have smooth waveforms and significant noise suppression (e.g., Figure 2 As shown), first-order harmonic signals (such as...) Figure 2 The 1f in the image mainly reflects background light intensity information, while the second harmonic signal (such as...) reflects background light intensity information. Figure 2 2f) in The absorption peak position exhibits a distinct second harmonic peak, providing high-quality input for subsequent characteristic ratio calculation.

[0041] The above implementation uses only a phase-locked demodulation strategy for 1f / 2f low-order harmonics, completely avoiding the complex calculations required for additional demodulation of 4th-order and other high-order harmonics in existing technologies (such as CN103868885A). This significantly reduces the computational load. Furthermore, it works closely with the aforementioned etalonless triangular wave combined with high-frequency sine wave superposition modulation method, allowing for the direct establishment of a reliable harmonic ratio analytical model without any etalon or Fourier series fitting. This direct analytical method for low-order harmonics effectively overcomes the computational complexity and embedded resource bottlenecks caused by high-order harmonic demodulation, laying a core foundation for subsequent lightweight, all-scenario adaptable calibration-free concentration inversion.

[0042] The following explains the process of adaptively selecting the characteristic amplitudes of the first-order and second-order harmonic signals based on the detection conditions to calculate the multi-dimensional harmonic characteristic ratio.

[0043] The aforementioned characteristic amplitudes include peak amplitude, half-width at half-maximum (FWHM) amplitude, or integral area.

[0044] In this embodiment of the invention, the criteria for determining the operating condition include: real-time calculation. The baseline standard deviation (noise level), absorption peak signal-to-noise ratio (SNR), waveform symmetry (preliminary assessment of kurtosis / skewness), and continuity with the concentration estimate from the previous scan cycle are considered. If the SNR is greater than 20 dB and the waveform is symmetrical, it is determined to be a normal concentration; if the SNR is less than 10 dB or the concentration estimate is extremely low, it switches to trace mode; if the waveform kurtosis deviation is greater than 15% or the baseline fluctuation is significant, it is determined to be a spectral distortion mode. The above adaptive switching is completed within one laser scan cycle (100 ms), and the switching threshold can be optimized according to the factory calibration of the specific gas.

[0045] In one feasible implementation, under conventional concentration detection conditions, the peak amplitudes of the first-order and second-order harmonic signals are extracted to calculate the harmonic characteristic ratio. At this point, the harmonic characteristic ratio... .

[0046] Under trace detection conditions, the full width at half maximum (FWHM) values ​​of the first-order and second-order harmonic signals are extracted to calculate the harmonic characteristic ratio. At this point, the harmonic characteristic ratio... .

[0047] Under spectral distortion conditions, the harmonic characteristic ratio is calculated by extracting the integral area of ​​the first and second harmonic signals. Here, the integral area refers to the numerical integration over the region containing the absorption peak. The harmonic characteristic ratio is then calculated. .

[0048] by For example, gas detection (see Figure 2Under normal concentrations, the peak amplitude is clear (the 2f peak is about 150), and K is directly calculated using the peak value. In trace scenarios, the peak value is submerged in noise, so the half-width amplitude is switched to improve the signal-to-noise ratio. When the waveform is distorted in a high turbidity environment, the integral area can effectively suppress the influence of local distortion and ensure the stability of the K value.

[0049] In the above embodiments, the adaptive selection mechanism of multi-dimensional harmonic characteristic amplitudes completely solves the problems of insufficient trace detection sensitivity and measurement instability in spectral distortion scenarios caused by the existing technology that only uses the peak amplitude. Through real-time condition judgment and dynamic switching of peak value / half-width at half maximum / integral area, the detection accuracy and robustness in all scenarios are significantly improved. In contrast, the existing TDLAS harmonic ratio method generally relies on a single peak feature and does not consider the differences in optimal features under different concentrations and conditions. It is necessary to establish dynamic decision rules by combining signal statistical characteristics (signal-to-noise ratio, kurtosis, etc.) to achieve full-scenario adaptation.

[0050] Step 13: Obtain the temperature and pressure of the detection environment, and introduce a pre-calibrated spectral broadening correction coefficient to construct a physical temperature and pressure model. Use the physical temperature and pressure model to correct the multi-dimensional harmonic characteristic ratio to obtain the corrected harmonic characteristic ratio.

[0051] In this embodiment of the invention, a temperature and pressure integrated sensor is integrated near the gas detection chamber (temperature measurement uses a PT1000 platinum resistance sensor, pressure measurement uses a MEMS piezoresistive sensor, with measurement ranges covering -40℃ to 85℃ and 0.1 atm to 2 atm, and accuracies of ±0.1K and ±0.005 atm, respectively). This sensor... The digital interface or ADC channel communicates with the main control unit (FPGA or STM32 processor) in real time, synchronously acquiring the temperature T (K, Kelvin) and pressure P (atm, standard atmosphere) of the current detection environment once per laser scanning cycle (100ms). For example, in In gas detection, the sensor may read the data in real time. (50℃) ATM data.

[0052] The main control unit immediately calls up the factory-set parameters based on the HITRAN spectral database for... Specific absorption line (approximately 7195.5) Pre-calibrated and stored spectral broadening correction factors (The typical value is 1.05. This coefficient is obtained through standard gas calibration experiments combined with theoretical calculations and requires no on-site adjustment.) In one feasible implementation, during the factory calibration stage, the gas concentration detection device can be placed in a precision temperature and pressure controlled environmental test chamber, and gases of known accurate concentrations can be sequentially introduced into the gas detection chamber. Certification standard gases (concentrations of 10 ppm, 30 ppm, and 50 ppm, with uncertainty ≤ ±1%) were used. Under combined conditions at multiple temperature points (-40℃, 0℃, 25℃, 50℃, and 85℃) and pressure points (0.5 atm, 1.0 atm, 1.5 atm, and 2.0 atm) covering the operating range, after the temperature and pressure had fully stabilized, multiple sets (no fewer than 50 sets) of first-order / second-order multidimensional harmonic characteristic ratio K data were collected. Simultaneously, the characteristic absorption spectral line (center wavenumber approximately 7195.5) was queried using the HITRAN spectral database. spectral line intensity Air saturation coefficient Self-expansion coefficient Using parameters such as the temperature dependence index n, and combining them with the Voigt linear function theoretical model, the theoretical harmonic ratio under the corresponding temperature and pressure conditions is calculated. The optimal spectral broadening correction coefficient was determined using the least squares optimization fitting method. In practice, once the coefficient is determined, it is permanently written into the non-volatile memory of the device's main control unit for direct retrieval during subsequent field testing, without requiring any on-site calibration by the user.

[0053] Subsequently, based on the ideal gas law and the physical model of TDLAS spectral detection (pressure P mainly determines collisional broadening, i.e., Lorentz broadening, and temperature T mainly determines Doppler broadening, i.e., Gaussian broadening), a physical thermo-pressure model was constructed, and the multi-dimensional harmonic eigenvalue ratio K was normalized and corrected in real time to obtain the corrected harmonic eigenvalue ratio. The specific expression is:

[0054] in, This indicates the nominal temperature under standard conditions. ; This represents the nominal pressure under standard conditions. .

[0055] In practice, the correction calculation is rapidly completed by the main control unit within one laser scanning cycle, and the resulting corrected harmonic characteristic ratio is obtained. It is directly passed to the subsequent nonlinear waveform distortion self-calibration stage.

[0056] In the above embodiments, the band line broadening correction factor The physical temperature and pressure model completely solves the problems of coarse temperature and pressure corrections and simple linear compensation in existing technologies, achieving accurate compensation with relative errors ≤ ±2% over a wide range of -40°C to 85°C and 0.1 atm to 2 atm. In contrast, most existing calibration-free schemes neglect the precise physical mechanisms of spectral line broadening or rely solely on empirical formulas, failing to introduce dedicated correction coefficients pre-calibrated based on the HITRAN database. However, this model cannot accurately compensate for the impact of temperature and pressure fluctuations on the harmonic ratio and linear function. This physical model, combined with the aforementioned adaptive extraction of multi-dimensional feature amplitudes, significantly improves the measurement stability and accuracy of the system under extreme temperature and pressure fluctuation conditions, providing a crucial guarantee for robust, calibration-free inversion across all scenarios.

[0057] Step 14: Extract the waveform features of the non-absorbing reference region, and perform nonlinear waveform distortion self-calibration on the corrected harmonic characteristic ratio based on the waveform features to obtain the final harmonic characteristic ratio.

[0058] In one feasible implementation, within each laser scanning cycle, the regions without H2S characteristic absorption in the start and end segments of the laser scanning are first selected as non-absorption reference regions (see...). Figure 2 The "non-absorbing reference region" marked in the image typically occupies about 20% to 30% of the entire scan cycle, ensuring that there are no absorption peaks and the baseline is stable within this region. Statistical features of the 1f and 2f harmonic signal waveforms within this reference region are extracted.

[0059] In this embodiment of the invention, the waveform features include waveform kurtosis, waveform skewness, and phase features. Waveform kurtosis measures the sharpness of the waveform and the impact of outliers; waveform skewness is used to assess the degree of left-right asymmetry of the waveform; and phase features characterize the phase offset of the 1f or 2f signal relative to the high-frequency sinusoidal modulation reference signal (which can be directly obtained from the phase output of the phase-locked demodulation stage, in radians).

[0060] In one feasible implementation, the three characteristic values ​​mentioned above are compared with the initial reference characteristic values ​​(reference kurtosis, reference skewness, and reference phase) pre-stored under clean operating conditions during factory calibration, and the relative deviation between the current reference area baseline ratio and the initial baseline ratio is calculated. When this deviation does not exceed ±1%, it is directly... As the final harmonic characteristic ratio When the deviation exceeds ±1% (typically occurring under conditions of high turbidity, high scattering, or optical path contamination), the factory-pre-established nonlinear mapping model based on experimental data is invoked. This model employs a second or third-order polynomial fitting, using the extracted kurtosis, skewness, and phase deviation as input variables, and outputs a correction coefficient. ( Typically in the range of 0.95 to 1.05). Finally, for Apply nonlinear calibration: .

[0061] In the above embodiments, the nonlinear self-calibration method based on the waveform kurtosis, skewness, and phase characteristics of the non-absorbing reference region completely solves the industry pain point of the complete failure of waveform distortion compensation under high turbidity and high scattering conditions caused by the existing technology that only uses linear baseline subtraction. It can still control the relative error within ±2% in harsh environments. Existing calibration-free schemes (such as WO2013096396A1) only perform simple linear background subtraction and do not utilize higher-order statistical features (kurtosis, skewness, phase) to establish a polynomial nonlinear mapping relationship. It is necessary to combine the actual harmonic waveform distortion physical mechanism for targeted modeling to achieve effective compensation for the drift of complex systems. This innovation, together with the aforementioned multi-dimensional feature extraction and physical temperature and pressure correction, constitutes the core of highly robust calibration-free inversion, significantly improving the stability and accuracy of the system in all scenarios.

[0062] Step 15: Based on Beer-Lambert's law, establish a theoretical mapping relationship between the final harmonic characteristic ratio and the concentration of the gas to be measured. Substitute the final harmonic characteristic ratio into the theoretical mapping relationship to achieve calibration-free concentration inversion and obtain the gas concentration detection result of the gas to be measured.

[0063] Specifically, the first step is to call the factory-preset firmware. Specific absorption spectral parameters (center wavelength approximately 1.39 μm, corresponding wavenumber 7195.5). ), spectral line intensity Real-time temperature data from the HITRAN database Optical path length obtained by down-interpolation calculation Set a fixed physical distance between the gas chambers (0.5m in this example); normalize the spectral line shape function. Based on real-time temperature T and pressure P, the Voigt linear model (Gaussian + Lorentz broadened convolution) is obtained through numerical calculation or a pre-stored lookup table, satisfying the normalization condition. .

[0064] Based on TDLAS-WMS theory, the 2f / 1f harmonic ratio With gas concentration There is a strict theoretical mapping relationship (no on-site standard gas calibration required): ,in The analytical inversion function derived from the Lambert-Beer law has the following approximate form:

[0065] in, This represents the peak value of the linear function at the absorption peak. The modulation coefficient (derived from the modulation depth of the high-frequency sine wave) (The factory calibration is fixed). All parameters are derived from the HITRAN database, real-time temperature and pressure sensors, and factory modulation parameters, requiring no on-site calibration. Taking testing as an example, under normal operating conditions (T=298K, P=1atm), when At that time, the inversion yielded Temperature and pressure fluctuations or slight distortions still maintain high accuracy after the aforementioned corrections.

[0066] In the above implementation, the theoretical mapping inversion based on Lambert-Beer's law and the TDLAS physical model completely overcomes the limitations of existing calibration-free schemes, which generally remain at the level of linear or empirical fitting and do not fully utilize the spectral line intensity S(T) and normalized line type function provided by the HITRAN database. The physical temperature and pressure correction with spectral broadening coefficient is used to construct an accurate theoretical mapping. Only by organically combining the aforementioned low-order harmonic analysis without standard etalon, adaptive extraction of multi-dimensional features, nonlinear waveform distortion calibration and physical temperature and pressure model can a closed-loop, high-precision theoretical inversion system be formed, which significantly improves the accuracy in all scenarios.

[0067] Example 2 In this embodiment of the invention, the gas concentration detection method provided by the present invention can be further extended to the scenario of simultaneous detection of multiple components of gas based on Example 1, realizing the simultaneous output of the concentration of multiple gases to be measured (taking H2S and CO as examples) without calibration. Specific implementation methods are as follows: Based on pre-configured characteristic absorption spectral information of various gases to be tested ( The center wavelength of the characteristic spectral line is approximately 1.39 μm, corresponding to a wavenumber of approximately 7195.5 cm. The characteristic spectral lines have a center wavelength of approximately 1.57 μm and a corresponding wavenumber of approximately 6360 cm⁻¹ (with no spectral cross-interference between the two), which controls the DFB laser to scan the characteristic spectral lines of each gas in a time-division manner.

[0068] Within a complete detection cycle (e.g., 500ms), 100ms are allocated sequentially to Spectral line scan, 100ms input The spectral scanning is performed, and the remaining time is used for laser wavelength switching and stabilization (switching time is less than 10ms, achieved through rapid, oscillatory wavelength switching via combined current and temperature control). The laser drive circuit independently generates superimposed modulation signals according to the low-frequency triangular wave frequency (10Hz), high-frequency sine wave modulation frequency (5kHz), and modulation depth parameters corresponding to each gas, ensuring that the laser signal covers the characteristic absorption spectral lines of the corresponding gas within each scanning cycle.

[0069] During each time-division scan, for the current gas (first... ,back Independently and completely perform the following operations: control the laser to pass through the same gas detection chamber (optical path 0.5m, mixed gas environment) via a standard-free optical path; perform phase-locked demodulation on the original electrical signal to extract the 1f and 2f harmonic signals; adaptively select the peak amplitude, half-width at half-maximum amplitude, or integral area according to the real-time operating conditions to calculate the multi-dimensional harmonic characteristic ratio K; obtain the real-time temperature T and pressure P through an integrated temperature and pressure sensor, and introduce a spectral broadening correction coefficient. A physical temperature and pressure model was constructed to obtain the corrected ratio. Extract the waveform kurtosis, skewness, and phase characteristics of the non-absorbing reference region, and then... Perform nonlinear waveform distortion self-calibration to obtain the final harmonic characteristic ratio. Based on the Lambert-Beer law and the corresponding HITRAN spectral parameters (S(T) of the gas), (L), will By substituting the theoretical mapping relationship, the concentration inversion without calibration can be achieved, and the concentration detection result of the gas can be obtained.

[0070] The inversion results for both gases are output synchronously at the end of the same detection cycle (e.g., sent simultaneously via serial port or Ethernet interface). The concentration is 8.2 ppm, and the CO concentration is 25 ppm. The entire multi-component process can be seamlessly extended to more gases (such as methane, sulfur dioxide, etc.) by simply adding the corresponding spectral parameters and scanning timing, without any additional hardware modifications.

[0071] Example 3 In this embodiment of the invention, a gas concentration detection device is also disclosed, such as... Figure 3 As shown, the gas concentration detection device 300 includes: The acquisition module 301 is configured to control the laser to output a laser signal covering the characteristic absorption spectrum of the gas to be measured, and convert it into a raw electrical signal after passing through the gas to be measured via a standardless optical path; the laser signal is modulated by superposition of low-frequency triangular wave and high-frequency sine wave; The demodulation and extraction module 302 is configured to perform phase-locked demodulation on the original electrical signal to extract the first-order harmonic signal and the second-order harmonic signal, and adaptively select the characteristic amplitudes of the first-order harmonic signal and the second-order harmonic signal according to the detection conditions to calculate the multi-dimensional harmonic characteristic ratio; the characteristic amplitudes include peak amplitude, full width at half maximum (FWHM) amplitude or integral area; The temperature and pressure correction module 303 is configured to acquire the temperature and pressure of the detection environment, and to introduce a pre-calibrated spectral broadening correction coefficient to construct a physical temperature and pressure model. The physical temperature and pressure model is used to correct the multi-dimensional harmonic characteristic ratio to obtain the corrected harmonic characteristic ratio. The nonlinear calibration module 304 is configured to extract waveform features of the non-absorbing reference region, perform nonlinear waveform distortion self-calibration on the corrected harmonic characteristic ratio based on the waveform features, and obtain the final harmonic characteristic ratio; the waveform features include waveform kurtosis, waveform skewness and phase features. The concentration inversion module 305 is configured to establish a theoretical mapping relationship between the final harmonic characteristic ratio and the concentration of the gas to be measured based on the Lambert-Beer law. By substituting the final harmonic characteristic ratio into the theoretical mapping relationship, the concentration inversion without calibration is achieved, and the gas concentration detection result of the gas to be measured is obtained.

[0072] It should be noted that the information interaction and execution process between the above-mentioned devices / units are based on the same concept as the method embodiments of this application. Their specific functions and technical effects can be found in the method embodiments section, and will not be repeated here. Those skilled in the art will understand that, for the sake of convenience and brevity, the division of the above-mentioned functional units and modules is only used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0073] like Figure 4 As shown, embodiments of the present invention provide a terminal device, such as... Figure 4 As shown, the terminal device D10 of this embodiment includes: at least one processor D100 ( Figure 4 The diagram shows only one processor, a memory D101, and a computer program D102 stored in the memory D101 and executable on the at least one processor D100, wherein the processor D100 executes the computer program D102 to implement the steps in any of the above method embodiments.

[0074] Specifically, when the processor D100 executes the computer program D102, it controls the laser to output a laser signal covering the characteristic absorption spectrum of the gas to be tested. This signal passes through the gas via a standard-free optical path and is converted into a raw electrical signal. The raw electrical signal is then subjected to phase-locked demodulation to extract the first and second harmonic signals. Based on the detection conditions, the characteristic amplitudes of the first and second harmonic signals are adaptively selected to calculate the multi-dimensional harmonic characteristic ratio. The temperature and pressure of the detection environment are acquired, and a pre-calibrated spectral broadening correction coefficient is introduced to construct a physical temperature and pressure model. This model is used to correct the multi-dimensional harmonic characteristic ratio, resulting in a corrected harmonic characteristic ratio. Waveform features of the non-absorption reference region are extracted, and nonlinear waveform distortion self-calibration is performed on the corrected harmonic characteristic ratio based on these features to obtain the final harmonic characteristic ratio. A theoretical mapping relationship between the final harmonic characteristic ratio and the concentration of the gas to be tested is established based on Beer-Lambert's law. The final harmonic characteristic ratio is then substituted into the theoretical mapping relationship to achieve calibration-free concentration inversion, yielding the gas concentration detection result of the gas to be tested. The method employs a standard-free etalon optical path and superimposed modulation of low-frequency triangular waves and high-frequency sine waves to extract first- and second-order harmonic signals, directly eliminating the reliance on expensive additional hardware found in traditional solutions and significantly reducing system computational complexity. By adaptively extracting multi-dimensional feature ratios, including peak amplitude, full width at half maximum (FWHM) amplitude, or integral area, it effectively overcomes the instability of single-feature extraction under trace or complex spectra, significantly improving the robustness of detection across all scenarios. Combining pre-calibrated spectral broadening correction coefficients to construct a physical model for temperature and pressure correction eliminates the impact of extreme environmental fluctuations on detection accuracy. Furthermore, utilizing the waveform kurtosis, waveform skewness, and phase characteristics of the non-absorption reference region for nonlinear waveform distortion self-calibration overcomes the limitations of traditional linear baseline compensation, maintaining high-precision correction capabilities even when facing waveform distortion caused by high turbidity and high scattering conditions. Finally, physical mapping enables calibration-free concentration inversion, eliminating the cumbersome process and maintenance costs of on-site calibration and ensuring measurement consistency and accuracy under complex conditions.

[0075] The processor D100 can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0076] In some embodiments, the memory D101 may be an internal storage unit of the terminal device D10, such as a hard disk or memory of the terminal device D10. In other embodiments, the memory D101 may be an external storage device of the terminal device D10, such as a plug-in hard disk, smart media card (SMC), secure digital card (SD), flash card, etc., equipped on the terminal device D10. Furthermore, the memory D101 may include both internal and external storage units of the terminal device D10. The memory D101 is used to store the operating system, applications, bootloader, data, and other programs, such as the program code of the computer program. The memory D101 can also be used to temporarily store data that has been output or will be output.

[0077] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps described in the various method embodiments above.

[0078] This application provides a computer program product that, when run on a terminal device, enables the terminal device to implement the steps described in the various method embodiments above.

[0079] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0080] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A method for detecting gas concentration, characterized in that, include: The laser output is controlled to cover the characteristic absorption spectrum of the gas to be tested, and the laser signal is converted into the original electrical signal after passing through the gas to be tested via a standardless optical path; the laser signal is modulated by superposition of low-frequency triangular wave and high-frequency sine wave; The original electrical signal is demodulated by phase lock to extract the first-order harmonic signal and the second-order harmonic signal, and the characteristic amplitude of the first-order harmonic signal and the second-order harmonic signal is adaptively selected according to the detection conditions to calculate the multi-dimensional harmonic characteristic ratio. The characteristic amplitude includes peak amplitude, full width at half maximum (FWHM) amplitude, or integral area; The temperature and pressure of the detection environment are obtained, and a physical temperature and pressure model is constructed by introducing a pre-calibrated spectral broadening correction coefficient. The multi-dimensional harmonic characteristic ratio is corrected using the physical temperature and pressure model to obtain the corrected harmonic characteristic ratio. Waveform features of the non-absorbing reference region are extracted, and nonlinear waveform distortion self-calibration is performed on the corrected harmonic characteristic ratio based on the waveform features to obtain the final harmonic characteristic ratio; the waveform features include waveform kurtosis, waveform skewness, and phase features. Based on Beer-Lambert's law, a theoretical mapping relationship is established between the final harmonic characteristic ratio and the concentration of the gas to be measured. The final harmonic characteristic ratio is substituted into the theoretical mapping relationship to achieve calibration-free concentration inversion and obtain the gas concentration detection result of the gas to be measured.

2. The gas concentration detection method according to claim 1, characterized in that, After performing phase-locked demodulation on the original electrical signal to extract the first-order harmonic signal and the second-order harmonic signal, the method further includes: The extracted first-order harmonic signal and the second-order harmonic signal are preprocessed; the preprocessing includes extracting the baseline of the non-absorption region to eliminate DC drift, and using Butterworth low-pass filtering and Savitzky Gore smoothing cascade filtering to suppress noise signals.

3. The gas concentration detection method according to claim 2, characterized in that, The step of adaptively selecting the characteristic amplitudes of the first-order and second-order harmonic signals based on the detection conditions to calculate the multi-dimensional harmonic characteristic ratio includes: Under normal concentration detection conditions, the peak amplitudes of the first-order harmonic signal and the second-order harmonic signal are extracted to calculate the harmonic characteristic ratio. Under trace detection conditions, the half-width at half maximum (FWHM) values ​​of the first-order harmonic signal and the second-order harmonic signal are extracted to calculate the harmonic characteristic ratio. Under spectral distortion conditions, the harmonic characteristic ratio is calculated by extracting the integral area of ​​the first-order harmonic signal and the second-order harmonic signal.

4. The gas concentration detection method according to claim 3, characterized in that, The expression for the physical temperature and pressure model is: in, This represents the corrected harmonic characteristic ratio; This represents the extracted ratio of the multidimensional harmonic features; This indicates the real-time temperature of the monitored environment, expressed in Kelvin. This indicates the real-time pressure of the detection environment, expressed in standard atmospheres. Indicates the nominal temperature under standard conditions; Indicates the nominal pressure under standard conditions; This represents the spectral broadening correction factor for a specific gas to be measured, based on a pre-calibrated HITRAN database.

5. The gas concentration detection method according to claim 4, characterized in that, The process of extracting waveform features from the non-absorbing reference region, and performing nonlinear waveform distortion self-calibration on the corrected harmonic characteristic ratio based on these waveform features to obtain the final harmonic characteristic ratio includes: The region where no gas to be measured is absorbed is selected as the non-absorption reference region, and the waveform kurtosis, waveform skewness, and phase characteristics of the signal within the non-absorption reference region are extracted. A nonlinear mapping relationship between the waveform characteristics and the correction coefficients is established based on polynomial fitting. When the deviation between the baseline ratio of the non-absorbing reference region and the initial baseline ratio exceeds one percent, the nonlinear mapping relationship is used to perform nonlinear self-calibration on the corrected harmonic characteristic ratio to output the final harmonic characteristic ratio.

6. The gas concentration detection method according to claim 5, characterized in that, The method establishes a theoretical mapping relationship between the final harmonic characteristic ratio and the concentration of the gas to be measured based on the Lambert-Beer law. Substituting the final harmonic characteristic ratio into this theoretical mapping relationship enables calibration-free concentration inversion. The theoretical model used is configured as follows: the concentration of the gas to be measured is a mapping function of the final harmonic characteristic ratio, spectral line intensity, optical path length, and normalized spectral line shape function. The spectral line intensity is determined by the inherent properties of the measured spectral line; the optical path length represents the physical distance the laser travels through the gas to be measured; the normalized spectral line shape function characterizes the profile distribution of the absorption spectral line of the gas to be measured, and its integral value satisfies the normalization condition. The normalized spectral line shape function also depends on the real-time temperature and real-time pressure of the detection environment.

7. The gas concentration detection method according to claim 1, characterized in that, The method further includes a multi-component gas extended detection step; the step includes: The laser is controlled to scan the non-cross-interference characteristic spectral lines of multiple test gases in a time-division manner, and the operation of harmonic signal extraction, multi-dimensional harmonic characteristic ratio calculation, temperature and pressure correction, waveform distortion nonlinear calibration, and calibration-free concentration inversion is performed independently for each test gas, so as to simultaneously output the concentration detection results of multiple gases.

8. A gas concentration detection device, characterized in that, include: The acquisition module is configured to control the laser to output a laser signal covering the characteristic absorption spectral lines of the gas to be tested, and convert it into a raw electrical signal after passing through the gas to be tested via a standard-free optical path; the laser signal is modulated by superimposing a low-frequency triangular wave and a high-frequency sine wave. The demodulation and extraction module is configured to perform phase-locked demodulation on the original electrical signal to extract the first-order harmonic signal and the second-order harmonic signal, and adaptively select the characteristic amplitude of the first-order harmonic signal and the second-order harmonic signal according to the detection conditions to calculate the multi-dimensional harmonic characteristic ratio. The characteristic amplitude includes peak amplitude, full width at half maximum (FWHM) amplitude, or integral area; The temperature and pressure correction module is configured to acquire the temperature and pressure of the detection environment, and to construct a physical temperature and pressure model by introducing a pre-calibrated spectral broadening correction coefficient. The physical temperature and pressure model is used to correct the multi-dimensional harmonic characteristic ratio to obtain the corrected harmonic characteristic ratio. The nonlinear calibration module is configured to extract waveform features of the non-absorbing reference region, and perform nonlinear waveform distortion self-calibration on the corrected harmonic characteristic ratio based on the waveform features to obtain the final harmonic characteristic ratio; the waveform features include waveform kurtosis, waveform skewness, and phase features. The concentration inversion module is configured to establish a theoretical mapping relationship between the final harmonic characteristic ratio and the concentration of the gas to be measured based on the Lambert-Beer law. The final harmonic characteristic ratio is substituted into the theoretical mapping relationship to achieve calibration-free concentration inversion and obtain the gas concentration detection result of the gas to be measured.

9. A terminal device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1 to 7.

Images