Doped gas concentration detection method and system based on gas analyzer

Abstract

The invention relates to the technical field of gas detection, and provides a doped gas concentration detection method and system based on a gas analyzer. The method comprises the following steps: constructing a standard spectrum database under the same pressure and temperature as a to-be-measured site; the method comprises the following steps: introducing sample gas into an optical absorption cell, carrying out wavelength scanning through a tunable diode laser in a plurality of adjacent absorption spectral line intervals containing target gas and interference gas, superposing a high-frequency sinusoidal modulation signal on a driving current, and synchronously detecting a second harmonic component of transmission laser to generate an actual measurement spectrum; fitting the actually measured spectrum with a synthetic spectrum generated on the basis of a standard spectrum database, and outputting a target gas concentration ratio as a detection result when a residual error meets a threshold value, so as to solve the technical problem that the detection precision is reduced due to spectrum overlapping caused by interference gas, and achieve the purpose that the detection precision is reduced by constructing the standard spectrum database and second harmonic spectrum fitting analysis. And the accuracy and the anti-interference capability of gas detection are improved.

Description

Technical Field

[0001] This application relates to the field of gas detection technology, specifically to a method and system for detecting the concentration of doped gases based on a gas analyzer. Background Technology

[0002] With the continuous development of industrial production, environmental monitoring, and energy utilization, the demand for online, rapid, and high-precision detection of gas components is increasing. Especially in scenarios such as petrochemicals, natural gas transportation, coal mine safety, environmental monitoring, and semiconductor manufacturing, mixed gases often contain both the target gas and multiple interfering gases. Accurate detection of the concentration of dopant gases is of great significance for process control, safety protection, and pollution emission monitoring.

[0003] Existing gas detection technologies include chemical sensing, electrochemical analysis, infrared absorption, and tunable diode laser absorption spectroscopy (TDLAS). Among these, TDLAS is widely used in trace gas detection due to its advantages such as high sensitivity, high selectivity, fast response speed, and suitability for harsh environments. However, in practical applications, the environment in which the gas to be measured usually contains multiple components, and the absorption lines of different gases may overlap in adjacent wavelength regions, leading to interference components in the measurement signal and affecting the accuracy of target gas concentration retrieval. Furthermore, changes in environmental pressure and temperature can cause broadening and frequency shift effects on gas absorption lines, further increasing the difficulty of detection under complex conditions. In existing technologies, most detection methods use single target gas fitting or simple background interference subtraction, which is insufficient to effectively handle the complex spectral characteristics of multiple interfering gases simultaneously, easily causing concentration calculation errors and resulting in unstable detection results. Summary of the Invention

[0004] This application provides a method and system for detecting the concentration of doped gases based on a gas analyzer, aiming to solve the technical problem of decreased detection accuracy caused by spectral overlap due to interfering gases.

[0005] The first aspect disclosed in this application provides a method for detecting dopant gas concentration based on a gas analyzer. The method includes: pre-measuring and constructing a standard spectral database under the same pressure and temperature conditions as the test site; passing a sample gas into an optical absorption cell, performing wavelength scanning within a spectral range containing multiple adjacent absorption lines of the target gas and interfering gas using a tunable diode laser, while simultaneously superimposing a high-frequency sinusoidal modulation signal onto the laser driving current, and synchronously detecting the second harmonic component of the transmitted laser to generate a measured second harmonic spectrum; fitting the measured second harmonic spectrum with a synthetic spectrum generated based on the standard spectral database, and generating a target gas concentration ratio as the dopant gas detection result when the residual between the synthetic spectrum and the measured second harmonic spectrum meets a preset threshold; wherein the synthetic spectrum is a linear superposition of the standard second harmonic spectra of the target gas and the interfering gas at different concentration ratios.

[0006] Another aspect of this application discloses a dopant gas concentration detection system based on a gas analyzer. The system includes: a standard library construction module: pre-measuring and constructing a standard spectral database under the same pressure and temperature conditions as the test site; a synchronous detection module: introducing a sample gas into an optical absorption cell, performing wavelength scanning within a spectral range containing multiple adjacent absorption lines of the target gas and interfering gases using a tunable diode laser, and simultaneously superimposing a high-frequency sinusoidal modulation signal onto the laser driving current to synchronously detect the second harmonic component of the transmitted laser, generating a measured second harmonic spectrum; and a spectral fitting module: fitting the measured second harmonic spectrum with a synthesized spectrum generated based on the standard spectral database. When the residual between the synthesized spectrum and the measured second harmonic spectrum meets a preset threshold, a target gas concentration ratio is generated as the dopant gas detection result; wherein the synthesized spectrum is a linear superposition of the standard second harmonic spectra of the target gas and the interfering gas at different concentration ratios.

[0007] One or more technical solutions provided in this application have at least the following technical effects or advantages: The aforementioned method for detecting dopant gas concentration based on a gas analyzer first establishes a standard spectral database by pre-measuring standard spectra of different gases under pressure and temperature conditions consistent with those at the field site. Next, the sample gas is passed into an optical absorption cell. In multiple absorption spectral regions containing both the target gas and interfering gases, a tunable diode laser is used for wavelength scanning. A high-frequency sinusoidal modulation signal is superimposed on the laser current to obtain the second harmonic component of the transmitted light, forming a measured spectrum. Finally, the measured spectrum is fitted with a synthesized spectrum generated from the database. The fitting accuracy is determined based on the residual. When a threshold condition is met, the concentration ratio of the target gas is output, effectively eliminating the influence of interfering gases and improving the accuracy and reliability of dopant gas concentration detection.

[0008] The above description is merely an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic flowchart of a dopant gas concentration detection method based on a gas analyzer in one embodiment.

[0011] Figure 2 This is a schematic diagram of a doped gas concentration detection system based on a gas analyzer in one embodiment.

[0012] Figure labeling: Standard library construction module 11, synchronous detection module 12, spectral fitting module 13. Detailed Implementation

[0013] This application provides a method and system for detecting the concentration of doped gases based on a gas analyzer, thereby solving the technical problem of decreased detection accuracy caused by spectral overlap due to interfering gases.

[0014] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0015] It should be noted that the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or server that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or modules that are not explicitly listed or that are inherent to such process, method, product, or device.

[0016] Example 1, as Figure 1 As shown, this application provides a method for detecting the concentration of doped gas based on a gas analyzer, the method comprising: Under the same pressure and temperature conditions as the test site, a standard spectral database is pre-measured and constructed.

[0017] In this embodiment, firstly, under the same pressure and temperature conditions as the test site, high-purity gas samples are selected based on the types of target and interfering gases that may be present at the test site. Then, standard mixed samples of each gas are precisely prepared using a gas mixing device at different volume fractions to ensure their concentration covers the expected detection range. Subsequently, the standard mixed samples are sequentially introduced into the optical absorption cell, and the pressure and temperature within the absorption cell are stably maintained to match the test site. Next, a tunable diode laser is used to perform a fine wavelength scan of the target spectral range. The second harmonic signals of each gas under different conditions are obtained through synchronous phase-locked loop detection. Each set of experimental data is then repeatedly measured and averaged to reduce the influence of random noise, and normalization processing is used to eliminate errors caused by laser intensity fluctuations. Subsequently, the obtained high-resolution second harmonic spectral signals are classified and stored according to parameters such as gas type, concentration, temperature, and pressure, and a standard spectral database is established in the form of data files. This standard spectral database records the standard spectral characteristic parameters of each gas under different physical conditions, including absorption peak position, peak width, peak shape, and corresponding harmonic response values, providing a basic data source for subsequent spectral fitting and concentration inversion, and ensuring the stability and reliability of the doped gas detection results.

[0018] Furthermore, this application provides a standard spectral database that stores the standard second harmonic spectra of the target gas and a variety of known interfering gases.

[0019] Preferably, the standard spectral database stores standard second harmonic spectral data of the target gas and various known interfering gases under different physical conditions. This data is typically stored in a hierarchical structure or multidimensional matrix format to ensure rapid retrieval and access. Each record in the standard spectral database corresponds to a complete set of experimental conditions and spectral response data, reflecting the standard absorption characteristics of the gas under specific physical conditions. This provides a reliable basis for subsequent linear superposition and fitting calculations of synthesized spectra, thereby enabling accurate concentration analysis and detection of dopant gases in multi-component mixed gas environments.

[0020] The sample gas is introduced into an optical absorption cell. Within the spectral range containing multiple adjacent absorption lines of the target gas and interfering gas, a tunable diode laser is used for wavelength scanning. At the same time, a high-frequency sinusoidal modulation signal is superimposed on the laser driving current, and the second harmonic component of the transmitted laser is detected simultaneously to generate a measured second harmonic spectrum.

[0021] In one embodiment, the sample gas mixture to be tested is introduced into an optical absorption cell. This optical absorption cell is a closed gas channel structure equipped with a high-reflectivity window material to ensure transmission stability and low loss of the laser during propagation in the gas sample. The sample gas mixture is introduced into the absorption cell after pressure stabilization and temperature control, keeping the gas pressure and temperature constant, thereby reducing the impact of environmental fluctuations on spectral measurements. During the scanning process, the system drives a tunable diode laser to continuously fine-tune the selected wavelength range, ensuring that its output wavelength covers the absorption spectral regions of both the target gas and interfering gases. To improve detection sensitivity and suppress low-frequency noise, a high-frequency sinusoidal modulation signal is superimposed on the laser's drive current. The modulation frequency of this high-frequency sinusoidal modulation signal is typically set in the range of 1MHz to 10MHz, with the specific frequency determined based on the laser's response characteristics and the system bandwidth. High-frequency modulation causes a small periodic shift in the laser output wavelength near the center wavelength, resulting in the transmission signal containing higher harmonic components related to the gas absorption characteristics. After the transmitted laser light is absorbed by the gas, its intensity varies with wavelength, generating a periodic modulation signal. The system converts the transmitted light into an electrical signal using a photodetector, and then uses a lock-in amplifier to extract the second harmonic component of the signal at twice the modulation frequency, thereby obtaining a high signal-to-noise ratio second harmonic response curve. Finally, the acquired harmonic signal is converted from analog to digital to form digitized wavelength-harmonic intensity relationship data. After synchronous sampling, a complete measured second harmonic spectrum is generated. This measured second harmonic spectrum can accurately reflect the absorption characteristics of each component in the sample gas, providing fundamental data support for subsequent spectral fitting and concentration inversion calculations.

[0022] Furthermore, this application provides a step for selecting the modulation amplitude of the high-frequency sinusoidal modulation signal, including: For the absorption spectrum of the target gas within the specified spectral range, the peak response data of the second harmonic signal under different modulation amplitudes are measured; for the absorption spectrum of the target gas within the specified spectral range, the signal-to-noise ratio (SNR) variation data under different modulation amplitudes are verified through experimental measurements; based on the peak response data and SNR variation data, the modulation amplitude that achieves the preset optimal balance between peak response and SNR is selected.

[0023] Preferably, to obtain optimal second harmonic detection sensitivity and signal stability, a spectral range containing representative strong absorption peaks is first selected from a standard spectral database based on the absorption characteristics of the target gas as the experimental test range, ensuring that the measured peak values ​​are representative and have a good signal response. Then, keeping the laser center wavelength and modulation frequency constant, the sinusoidal modulation amplitude superimposed on the laser driving current is gradually changed, for example, increasing from a small amplitude to the maximum allowable amplitude. Under each modulation amplitude condition, the second harmonic signal is extracted through a lock-in amplifier, and the peak response amplitude of the corresponding absorption peak is recorded as the peak response data. Subsequently, under the same experimental conditions, the obtained harmonic signal is repeatedly measured multiple times, and the ratio of the signal peak amplitude to the baseline noise amplitude is statistically analyzed and recorded as the signal-to-noise ratio (SNR). This baseline noise is obtained by selecting a wavelength range in the region without absorption peaks and calculating the standard deviation of the signal intensity within that range, ensuring the comparability of the SNR calculation. As the modulation amplitude increases, the peak response gradually strengthens within a certain range, but excessively large modulation amplitudes introduce linear distortion, leading to a decrease in the SNR. Therefore, it is necessary to find an optimal balance between the peak response amplitude and the SNR. During the search process, the peak response and signal-to-noise ratio (SNR) change curves corresponding to different modulation amplitudes are compared and analyzed. The position where the peak response reaches a high value and the SNR does not decrease significantly is selected as the optimal modulation amplitude. This optimal modulation amplitude can effectively suppress noise interference while ensuring sensitivity, providing a reliable guarantee for the stable acquisition and concentration inversion of the subsequent second harmonic signal, thereby enabling the system to maintain high detection sensitivity and stability in complex gas environments.

[0024] Furthermore, this application provides wavelength scanning using a tunable diode laser, including: From the standard spectral database, select a spectral window containing at least one strong absorption line of the target gas and one strong absorption line of the interfering gas as the scanning interval; control the laser temperature and current to ensure that the laser output wavelength stably covers the selected scanning interval, and perform wavelength scanning according to the preset sampling density.

[0025] Optionally, based on the standard absorption characteristics of each gas recorded in the standard spectral database, a spectral window containing at least one strong absorption line of the target gas and one strong absorption line of the interfering gas is selected as the scanning interval. Within this scanning interval, both the target signal and the interfering signal can be obtained simultaneously, providing sufficient information for subsequent spectral superposition fitting and concentration inversion, avoiding system complexity and error accumulation caused by multi-segment scanning. Subsequently, the operating temperature and driving current of the tunable diode laser are stably controlled by a precise temperature control and current drive unit, ensuring that its output wavelength continuously and smoothly covers the selected spectral interval. The temperature control unit is used to suppress wavelength drift caused by temperature fluctuations, and the current drive unit enables fine-tuning of the wavelength scan. During wavelength scanning, to ensure that the acquired data accurately describes the harmonic signal changes, the sampling frequency must satisfy the Nyquist sampling theorem, i.e., the sampling frequency must be greater than twice the highest frequency component of the signal. By setting a sufficiently high sampling density, aliasing effects can be avoided, ensuring that the reconstructed harmonic signal shape is consistent with the true absorption characteristics, thereby guaranteeing fitting accuracy. Subsequently, within a preset wavelength range, the laser wavelength is controlled to vary at a constant scanning rate, and the harmonic components of the transmitted signal are acquired at a high frequency. The acquired time signal is then synchronized with the laser wavelength. Finally, the acquired high-resolution wavelength-harmonic intensity data is stored as a set of continuous spectral data, providing the basic input for subsequent spectral fitting and target gas concentration calculation.

[0026] Furthermore, this application provides a method for simultaneously detecting the second harmonic component of transmitted laser light and generating a measured second harmonic spectrum, including: The component of the transmitted laser signal at the second harmonic of the frequency of the high-frequency sinusoidal modulation signal is extracted by a lock-in amplifier; the extracted second harmonic signal is converted from analog to digital to obtain a digital harmonic signal sequence; according to the synchronization signal of wavelength scanning, the harmonic signal sequence is matched one-to-one with the laser wavelength to form a measured spectrum of wavelength-harmonic intensity relationship, and the measured second harmonic spectrum is generated.

[0027] Optionally, when the modulated laser beam passes through an optical absorption cell containing both the target gas and interfering gases, its transmission intensity will periodically change with the wavelength scanning and gas absorption characteristics. A photodetector converts the transmitted laser into an electrical signal, which includes a fundamental frequency component, harmonic components, and random noise. At this point, based on the narrowband filtering characteristics of the lock-in amplifier, the reference signal is set to twice the laser modulation frequency to synchronously demodulate the transmitted laser signal, suppressing uncorrelated frequency noise and retaining only the frequency components corresponding to the second harmonic, significantly improving the signal-to-noise ratio. The second harmonic signal, after demodulation by the lock-in amplifier, is converted into an analog electrical signal. This signal needs to be sampled by a high-speed, high-precision analog-to-digital converter (ADC) to convert the analog signal into a digital signal sequence. The sampling frequency of this ADC is determined according to the preset sampling density and modulation frequency to ensure that the amplitude and phase information of the harmonic signal are completely preserved. Then, based on the synchronous trigger signal generated during wavelength scanning, the change in the current output wavelength of the laser is recorded. The sampling time of the harmonic signal is then precisely paired with the change information of the laser wavelength to achieve a one-to-one correspondence between the harmonic signal and the scanning wavelength. Finally, by processing the digital harmonic signal and matching it with the corresponding wavelength value according to the sampling order, a complete wavelength-second harmonic intensity relationship curve is constructed. This wavelength-second harmonic intensity relationship curve is the measured second harmonic spectrum, which truly reflects the absorption characteristics of the target gas and interfering gas in the sample gas and is the basis for subsequent spectral fitting and concentration inversion calculation.

[0028] Furthermore, this application provides an integrated pressure sensor and temperature sensor inside the optical absorption cell to monitor the pressure and temperature of the gas environment in real time. When the pressure and temperature of the gas environment deviate from the conditions when constructing the standard spectral database beyond the tolerance limit, the standard second harmonic spectrum retrieved from the standard spectral database is numerically corrected according to a preset spectral correction model to generate a corrected standard spectrum that matches the current actual environmental conditions, which is then used in the generation and fitting process of the synthesized spectrum.

[0029] Optionally, to ensure the accuracy of subsequent spectral fitting and the reliability of detection results, high-precision pressure and temperature sensors are integrated inside the optical absorption cell to monitor pressure and temperature changes of the sample gas in real time during the detection process. Subsequently, a set of pressure and temperature deviation tolerances is preset. When the deviation between the current detection environment's pressure or temperature and the corresponding reference value in the standard spectral database exceeds this tolerance, the standard second harmonic spectrum of the corresponding gas in the standard spectral database is numerically corrected according to a preset spectral correction model. This spectral correction model is built on a multilayer perceptron and has been iteratively trained using pressure, temperature, gas type encoding, the original standard spectrum, and the corrected standard spectrum through forward propagation, loss calculation, backpropagation, and parameter optimization. Upon receiving the called standard second harmonic spectrum and the actual pressure and temperature, the spectral correction model calculates and corrects the spectral linewidth, peak position, and shape parameters of the standard second harmonic spectrum based on learned knowledge, obtaining a corrected standard second harmonic spectrum that matches the current actual detection environment. The corrected spectrum more accurately reflects the gas absorption characteristics under actual measurement conditions, avoiding fitting errors caused by temperature and pressure deviations. Finally, the system will call the corrected standard second harmonic spectrum and the measured second harmonic spectrum to generate and fit the subsequent synthetic spectrum, so as to improve the accuracy and stability of spectral matching and ensure that high-precision doping gas concentration detection can still be achieved under different operating conditions.

[0030] The measured second harmonic spectrum is fitted with the synthetic spectrum generated based on the standard spectral database. When the residual between the synthetic spectrum and the measured second harmonic spectrum meets a preset threshold, the target gas concentration ratio is generated as the doping gas detection result. The synthetic spectrum is a linear superposition of the standard second harmonic spectra of the target gas and the interfering gas at different concentration ratios.

[0031] In one embodiment, standard second harmonic (HH) spectra of the target gas and various known interfering gases corresponding to the current detection wavelength range are first extracted from a standard spectral database. The system uses the standard HH spectra as basis functions and performs weighted linear superposition according to the concentration ratio of each gas to establish a synthetic spectrum. Subsequently, the measured HH spectra are used as reference data and least-squares fitted to the synthetic spectrum. By continuously adjusting the concentration ratio of each gas, the sum of squared residuals between the synthetic spectrum and the measured HH spectra across the entire wavelength range is gradually reduced, thereby finding the concentration combination closest to the measured result. If the calculated residual value is less than a preset threshold across the entire spectral range, the fitting result is considered convergent and reliable. At this point, the concentration value of the target gas is output based on the final concentration ratio as the detection result of the doping gas. Conversely, if the calculated residual value exceeds the preset threshold, it indicates that the current gas combination or concentration ratio fails to accurately describe the characteristics of the measured spectrum, and the concentration parameters are automatically readjusted, and the fitting process is repeated. Through the above process, the target gas and interfering gas spectra can be separated and identified in complex mixed gas environments, effectively eliminating the interference caused by spectral line overlap and improving the accuracy and reliability of dopant gas concentration detection.

[0032] Furthermore, this application provides a method for fitting the measured second harmonic spectrum with a synthesized spectrum generated based on the standard spectral database, including: The standard second harmonic spectra of the target gas and each interfering gas are extracted from the standard spectral database to form an initial spectral matrix. Principal component analysis is performed on the initial spectral matrix to extract the first k principal components that best characterize the spectral matrix. The measured second harmonic spectra are projected onto the subspace formed by the first k principal components. Based on the projection coefficients, preliminary matching and concentration estimation are performed in the standard spectral database to determine the types and initial concentration ranges of key interfering gases. Using the initial concentration range as the initial value, and only for the key interfering gases, the standard second harmonic spectra of the target gas and interfering gases are retrieved from the standard spectral database as basis functions. The concentration ratios are iteratively adjusted and linearly superimposed to calculate the sum of squared residuals between the iteratively synthesized spectrum and the measured second harmonic spectrum. When the sum of squared residuals is less than the preset threshold, the iteration is stopped and the current target gas concentration ratio is output.

[0033] Preferably, to achieve high-precision inversion of target gas concentration in complex multi-component gas environments, standard second harmonic spectral data of the target gas and each known interfering gas corresponding to the target spectral range are first extracted from a standard spectral database. These spectra are then arranged into a matrix according to wavelength sampling points, with each column representing the standard spectrum of a gas and each row representing the spectral response at a specific wavelength, forming an initial spectral matrix. Subsequently, the initial spectral matrix is ​​standardized to ensure comparability of the gas spectral data at the same numerical scale. The covariance matrix of the initial spectral matrix is ​​then calculated to reflect the correlation between different spectral variables. Next, eigenvalue decomposition or singular value decomposition is performed on the covariance matrix to obtain a set of eigenvectors and their corresponding eigenvalues. The magnitude of the eigenvalues ​​reflects the amount of spectral information contained in each eigenvector. Based on the magnitude of the eigenvalues, the top k principal components with the largest variance contribution rate are extracted. These principal components can retain most of the spectral information in fewer dimensions, reducing computational complexity and effectively eliminating redundant interference information, laying the foundation for subsequent fitting calculations. Subsequently, the acquired measured second harmonic spectra underwent the same preprocessing operations as the standard second harmonic spectra data to ensure consistent scale and characteristics with the data in the principal component space. The preprocessed measured second harmonic spectra were then projected onto a feature subspace composed of the first k principal components, and the inner product of the measured second harmonic spectrum with each principal component vector was calculated to obtain k projection coefficients. These projection coefficients represent the position and characteristic distribution of the measured second harmonic spectrum in the principal component space. After obtaining the k projection coefficients, these coefficients were compared with the principal component projection coefficients of each gas in the standard spectral database, and their Euclidean distances were calculated to identify the gas feature combinations closest to the measured second harmonic spectrum. This determined the key interfering gas types affecting the measured second harmonic spectrum, and combined with the concentration information corresponding to the standard spectra, the initial concentration range of each interfering gas was given. Then, using the initial concentration range as the initial value, and only for the key interfering gases and target gases, the corresponding standard second harmonic spectra were retrieved from the standard spectral database as basis functions. The gas concentration ratios were iteratively adjusted and linearly superimposed to form the synthetic spectrum. In each iteration, the system calculates the sum of squared residuals between the synthesized and measured spectra, and continuously reduces the residuals using least squares or nonlinear optimization methods. Finally, when the sum of squared residuals is less than a preset threshold, the iteration process stops, and the system outputs the target gas concentration ratio at this point as the detection result. If the residuals do not meet the threshold, the parameters are adjusted until the preset threshold is met. Through these steps, the computational load can be significantly reduced while preserving spectral feature information, thereby quickly identifying key interfering components and achieving high-precision inversion and detection of target gas concentrations in multi-component mixed gases.

[0034] Furthermore, this application provides, before linear superposition by iteratively adjusting the concentration ratio, the following steps are also included: After fitting the data using the initial concentration range as the initial value, the residual spectrum is calculated and analyzed. Characteristic peaks are identified in the residual spectrum; if a residual peak with an amplitude exceeding the noise level is found, it is determined that an unknown interfering gas not included in the fitting is present. The residual spectrum is then correlated with the standard spectra of all gases in the standard spectral database to screen out candidate gases with the highest matching degree to the residual spectrum characteristics. The standard second harmonic spectrum of the candidate gas is used as a new basis function for refitting until no characteristic peaks with amplitudes exceeding the noise level exist in the residual spectrum.

[0035] Optionally, after completing the spectral fitting starting from the initial concentration range, the system calculates the difference between the measured second harmonic spectrum and the synthesized spectrum, i.e., the residual spectrum. This residual spectrum reflects components in the measured signal that are not explained by the current fitting model, typically including measurement noise and absorption characteristics of possible unknown gases. Subsequently, after smoothing and baseline correction of the residual spectrum, its characteristic peak positions and amplitudes are identified. If a significant absorption peak signal appears in the residual spectrum, and its amplitude is significantly higher than the system noise level, such as exceeding three times the standard deviation of the background noise, it is determined that the peak may be caused by an unknown interfering gas that has not yet been included in the fitting. Then, the standard second harmonic spectra of all gases in the standard spectral database are called up, and correlation matching analysis is performed one by one with the residual spectrum. By calculating the Pearson correlation coefficient between the residual spectrum and each standard spectrum, the similarity of their spectral shape, peak position, and intensity is evaluated. Then, based on the calculated matching score, the candidate gas that is closest to the residual spectrum characteristics is selected. Then, the standard second harmonic spectrum of the selected candidate gases is used as a new basis function, which, together with the existing target gas and interfering gas spectra from the original fitting, forms a new spectral combination. Using the previous concentration estimates as initial conditions, linear superposition and iterative fitting are performed again to optimize the concentration ratios of each gas, further reducing the sum of squared residuals between the new synthesized spectrum and the measured spectrum. After refitting, the system recalculates the residual spectrum. If the amplitudes of all characteristic peaks are below the set noise threshold, the fitting is considered to have fully converged and includes all significant gas components. At this point, the final target gas concentration ratio is output as the detection result. If residual peaks still exist that exceed the threshold, the above correlation matching and refitting process is repeated until the residual spectrum meets the convergence condition, thereby further improving the comprehensiveness and accuracy of dopant gas concentration detection.

[0036] Furthermore, this application provides a step for setting the preset threshold, including: Against a background of pure interfering gas without a target gas, the residual between the synthesized spectrum and the measured spectrum is repeatedly measured and calculated to obtain the background noise level; based on the statistical distribution of the background noise level, an upper limit for the residual is set to generate the preset threshold.

[0037] Optionally, to scientifically and rationally determine the criteria for residual judgment during spectral fitting, firstly, only interfering gas without the target gas is introduced into the optical absorption cell, and the pressure and temperature conditions of the gas are strictly controlled to maintain consistency with the actual detection environment. At this point, there is no absorption signal from the target gas in the system, and the measured spectral signal should only contain background interference and system noise. Subsequently, under the same experimental conditions, multiple repeated scanning measurements are performed on the pure interfering gas environment. A tunable diode laser is used for wavelength scanning and modulation detection to obtain multiple sets of measured second harmonic spectra. Each set of data is fitted with the theoretical synthesized spectrum under the corresponding conditions, and the residual distribution between the two is calculated. Then, the residual data obtained from multiple measurements are normalized, the amplitude distribution characteristics of the residuals are statistically analyzed, and an appropriate confidence level, such as 95% or 99%, is selected as the judgment criterion. The mean residual is added to a certain number of standard deviations, such as 3σ or 5σ, and set as the upper limit of the residual. This upper limit of the residual is the maximum acceptable residual range of the system under pure interference conditions. Finally, the determined upper limit of the residual is defined as a preset threshold for subsequent spectral fitting and concentration inversion processes, thereby realizing the quantification and objectification of residual judgment and effectively improving the fitting reliability and detection accuracy.

[0038] In summary, the embodiments of this application have at least the following technical effects: This application first establishes a standard spectral database under the same pressure and temperature conditions as the test site. Then, the sample gas is introduced into an optical absorption cell. Within the spectral range containing multiple adjacent absorption lines of the target gas and interfering gases, a tunable diode laser performs wavelength scanning. Simultaneously, a high-frequency sinusoidal modulation signal is superimposed on the laser driving current, and the second harmonic component of the transmitted laser is detected synchronously, generating a measured second harmonic spectrum. Finally, the measured second harmonic spectrum is fitted with a synthetic spectrum generated based on the standard spectral database. When the residual between the synthetic spectrum and the measured second harmonic spectrum meets a preset threshold, the target gas concentration ratio is generated as the doping gas detection result. The synthetic spectrum is a linear superposition of the standard second harmonic spectra of the target gas and the interfering gas at different concentration ratios. These technical effects collectively solve the technical problem of decreased detection accuracy due to spectral overlap caused by interfering gases, achieving the technical effect of improving the accuracy and anti-interference capability of gas detection through the construction of a standard spectral database and second harmonic spectrum fitting analysis.

[0039] Example 2 is based on the same inventive concept as the doped gas concentration detection method based on a gas analyzer in the previous examples, such as... Figure 2As shown, this application provides a dopant gas concentration detection system based on a gas analyzer. The system includes: a standard library construction module 11: pre-measuring and constructing a standard spectral database under the same pressure and temperature conditions as the test site; a synchronous detection module 12: passing the sample gas into an optical absorption cell, performing wavelength scanning in the spectral range containing multiple adjacent absorption lines of the target gas and interfering gas using a tunable diode laser, and simultaneously superimposing a high-frequency sinusoidal modulation signal on the laser driving current to synchronously detect the second harmonic component of the transmitted laser and generate a measured second harmonic spectrum; and a spectral fitting module 13: fitting the measured second harmonic spectrum with a synthetic spectrum generated based on the standard spectral database, and generating a target gas concentration ratio as the dopant gas detection result when the residual between the synthetic spectrum and the measured second harmonic spectrum meets a preset threshold; wherein the synthetic spectrum is a linear superposition of the standard second harmonic spectra of the target gas and the interfering gas at different concentration ratios.

[0040] Furthermore, the standard library construction module 11 is also used to perform the following methods: The standard spectral database stores the standard second harmonic spectra of the target gas and a variety of known interfering gases.

[0041] Furthermore, the synchronization detection module 12 is also used to perform the following method: For the absorption spectrum of the target gas within the specified spectral range, the peak response data of the second harmonic signal under different modulation amplitudes are measured; for the absorption spectrum of the target gas within the specified spectral range, the signal-to-noise ratio (SNR) variation data under different modulation amplitudes are verified through experimental measurements; based on the peak response data and SNR variation data, the modulation amplitude that achieves the preset optimal balance between peak response and SNR is selected.

[0042] Furthermore, the synchronization detection module 12 is also used to perform the following method: From the standard spectral database, select a spectral window containing at least one strong absorption line of the target gas and one strong absorption line of the interfering gas as the scanning interval; control the laser temperature and current to ensure that the laser output wavelength stably covers the selected scanning interval, and perform wavelength scanning according to the preset sampling density.

[0043] Furthermore, the synchronization detection module 12 is also used to perform the following method: The component of the transmitted laser signal at the second harmonic of the frequency of the high-frequency sinusoidal modulation signal is extracted by a lock-in amplifier; the extracted second harmonic signal is converted from analog to digital to obtain a digital harmonic signal sequence; according to the synchronization signal of wavelength scanning, the harmonic signal sequence is matched one-to-one with the laser wavelength to form a measured spectrum of wavelength-harmonic intensity relationship, and the measured second harmonic spectrum is generated.

[0044] Furthermore, the synchronization detection module 12 is also used to perform the following method: The optical absorption cell integrates pressure and temperature sensors to monitor the pressure and temperature of the gas environment in real time. When the pressure and temperature of the gas environment deviate from the conditions when constructing the standard spectral database beyond the tolerance limit, the standard second harmonic spectrum retrieved from the standard spectral database is numerically corrected according to the preset spectral correction model to generate a corrected standard spectrum that matches the current actual environmental conditions, which is then used in the generation and fitting process of the synthesized spectrum.

[0045] Furthermore, the spectral fitting module 13 is also used to perform the following method: The standard second harmonic spectra of the target gas and each interfering gas are extracted from the standard spectral database to form an initial spectral matrix. Principal component analysis is performed on the initial spectral matrix to extract the first k principal components that best characterize the spectral matrix. The measured second harmonic spectra are projected onto the subspace formed by the first k principal components. Based on the projection coefficients, preliminary matching and concentration estimation are performed in the standard spectral database to determine the types and initial concentration ranges of key interfering gases. Using the initial concentration range as the initial value, and only for the key interfering gases, the standard second harmonic spectra of the target gas and interfering gases are retrieved from the standard spectral database as basis functions. The concentration ratios are iteratively adjusted and linearly superimposed to calculate the sum of squared residuals between the iteratively synthesized spectrum and the measured second harmonic spectrum. When the sum of squared residuals is less than the preset threshold, the iteration is stopped and the current target gas concentration ratio is output.

[0046] Furthermore, the spectral fitting module 13 is also used to perform the following method: After fitting the data using the initial concentration range as the initial value, the residual spectrum is calculated and analyzed. Characteristic peaks are identified in the residual spectrum; if a residual peak with an amplitude exceeding the noise level is found, it is determined that an unknown interfering gas not included in the fitting is present. The residual spectrum is then correlated with the standard spectra of all gases in the standard spectral database to screen out candidate gases with the highest matching degree to the residual spectrum characteristics. The standard second harmonic spectrum of the candidate gas is used as a new basis function for refitting until no characteristic peaks with amplitudes exceeding the noise level exist in the residual spectrum.

[0047] Furthermore, the spectral fitting module 13 is also used to perform the following method: Against a background of pure interfering gas without a target gas, the residual between the synthesized spectrum and the measured spectrum is repeatedly measured and calculated to obtain the background noise level; based on the statistical distribution of the background noise level, an upper limit for the residual is set to generate the preset threshold.

[0048] It should be noted that the order of the embodiments described above is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, the above description focuses on specific embodiments of this specification. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired results. In some implementations, multitasking and parallel processing are possible or may be advantageous.

[0049] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0050] This specification and accompanying drawings are merely illustrative examples of this application and are intended to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Therefore, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. A method for detecting doped gas concentration based on a gas analyzer, characterized in that, include: Under the same pressure and temperature conditions as the test site, a standard spectral database was pre-measured and constructed. The sample gas is introduced into the optical absorption cell. Within the spectral range containing multiple adjacent absorption lines of the target gas and interfering gas, a tunable diode laser is used for wavelength scanning. At the same time, a high-frequency sinusoidal modulation signal is superimposed on the laser driving current, and the second harmonic component of the transmitted laser is detected simultaneously to generate the measured second harmonic spectrum. The measured second harmonic spectrum is fitted with the synthetic spectrum generated based on the standard spectral database. When the residual between the synthetic spectrum and the measured second harmonic spectrum meets a preset threshold, the target gas concentration ratio is generated as the doping gas detection result. The synthesized spectrum is a linear superposition of the standard second harmonic spectra of the target gas and the interfering gas at different concentration ratios.

2. The method for detecting doped gas concentration based on a gas analyzer as described in claim 1, characterized in that, The steps for selecting the modulation amplitude of the high-frequency sinusoidal modulation signal include: For the absorption spectrum of the target gas within the spectral range, the peak response data of the second harmonic signal under different modulation amplitudes were measured; For the absorption spectral lines of the target gas within the spectral range, the signal-to-noise ratio variation data under different modulation amplitudes were verified through experimental measurements. Based on peak response data and signal-to-noise ratio (SNR) variation data, the modulation amplitude that achieves the preset optimal balance between peak response and SNR is selected.

3. The method for detecting doped gas concentration based on a gas analyzer as described in claim 1, characterized in that, Wavelength scanning using a tunable diode laser includes: From the standard spectral database, select a spectral window containing at least one strong absorption line of the target gas and one strong absorption line of the interfering gas as the scanning interval; The laser temperature and current are controlled to ensure that the laser output wavelength stably covers the selected scanning range, and wavelength scanning is performed according to the preset sampling density.

4. The method for detecting doped gas concentration based on a gas analyzer as described in claim 1, characterized in that, The second harmonic component of the transmitted laser is detected simultaneously to generate a measured second harmonic spectrum, including: The component of the transmitted laser signal at the second harmonic of the frequency of the high-frequency sinusoidal modulation signal is extracted using a lock-in amplifier. The extracted second harmonic signal is converted from analog to digital to obtain a digital harmonic signal sequence; Based on the synchronization signal of wavelength scanning, the harmonic signal sequence is matched one-to-one with the laser wavelength to form a measured spectrum of wavelength-harmonic intensity relationship, and the measured second harmonic spectrum is generated.

5. The method for detecting doped gas concentration based on a gas analyzer as described in claim 1, characterized in that, Fitting the measured second harmonic spectrum with the synthesized spectrum generated based on the standard spectral database includes: The standard second harmonic spectra of the target gas and each interfering gas are extracted from the standard spectral database to form an initial spectral matrix; Principal component analysis was performed on the initial spectral matrix to extract the top k principal component components that best characterize the spectral matrix. The measured second harmonic spectrum is projected onto the subspace formed by the forward k principal components. Based on the projection coefficients, preliminary matching and concentration estimation are performed in the standard spectral database to determine the types and initial concentration ranges of key interfering gases. Using the initial concentration range as the initial value, and targeting only the key interfering gas, the standard second harmonic spectra of the target gas and the interfering gas are retrieved from the standard spectral database as the basis function. The concentration ratio is adjusted iteratively and linearly superimposed to calculate the sum of squared residuals between the iteratively synthesized spectrum and the measured second harmonic spectrum. When the sum of squared residuals is less than the preset threshold, the iteration stops and the current target gas concentration ratio is output.

6. The method for detecting doped gas concentration based on a gas analyzer as described in claim 5, characterized in that, Before performing linear superposition by iteratively adjusting the concentration ratio, the following steps are also included: After fitting the data using the initial concentration range as the initial value, the residual spectrum was calculated and analyzed. The residual spectrum is subjected to characteristic peak identification. If a residual peak with an amplitude exceeding the noise level is found, it is determined that there is an unknown interfering gas that has not been included in the fitting. The residual spectrum is correlated with the standard spectra of all gases in the standard spectral database to screen out the candidate gas with the highest matching degree with the residual spectral characteristics. The standard second harmonic spectrum of the candidate gas is used as a new basis function and refitted until there are no characteristic peaks in the residual spectrum with amplitudes exceeding the noise level.

7. The method for detecting doped gas concentration based on a gas analyzer as described in claim 1, characterized in that, The standard spectral database stores the standard second harmonic spectra of the target gas and a variety of known interfering gases.

8. The method for detecting doped gas concentration based on a gas analyzer as described in claim 5, characterized in that, The steps for setting the preset threshold include: In a background of pure interfering gas without a target gas, the residual between the synthesized spectrum and the measured spectrum was repeatedly measured and calculated to obtain the background noise level. Based on the statistical distribution of the background noise level, an upper limit for the residual is set, and the preset threshold is generated.

9. The method for detecting doped gas concentration based on a gas analyzer as described in claim 1, characterized in that, The optical absorption cell integrates pressure and temperature sensors to monitor the pressure and temperature of the gas environment in real time. When the pressure and temperature of the gas environment deviate from the conditions when constructing the standard spectral database beyond the tolerance limit, the standard second harmonic spectrum retrieved from the standard spectral database is numerically corrected according to the preset spectral correction model to generate a corrected standard spectrum that matches the current actual environmental conditions, which is then used in the generation and fitting process of the synthesized spectrum.

10. A doped gas concentration detection system based on a gas analyzer, characterized in that, The system is used to perform the dopant gas concentration detection method based on a gas analyzer as described in any one of claims 1-9, including: Standard library construction module: Under the same pressure and temperature conditions as the test site, a standard spectral database is pre-measured and constructed; Synchronous detection module: The sample gas is introduced into the optical absorption cell. Within the spectral range containing multiple adjacent absorption lines of the target gas and interfering gas, a tunable diode laser is used for wavelength scanning. At the same time, a high-frequency sinusoidal modulation signal is superimposed on the laser driving current to synchronously detect the second harmonic component of the transmitted laser and generate a measured second harmonic spectrum. Spectral fitting module: Fits the measured second harmonic spectrum with the synthetic spectrum generated based on the standard spectral database. When the residual between the synthetic spectrum and the measured second harmonic spectrum meets a preset threshold, the target gas concentration ratio is generated as the doping gas detection result. The synthesized spectrum is a linear superposition of the standard second harmonic spectra of the target gas and the interfering gas at different concentration ratios.

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