Gas detection method and device capable of automatically calibrating central wavelength of laser

Abstract

The invention relates to a gas detection method and device capable of self-calibrating the central wavelength of a laser, and the method comprises the steps: finding out a non-toxic and non-corrosive interference gas in a target associated wave band, and replacing a target gas to be filled into a reference light path; adjusting the wavelength sweep frequency range of the laser, then adjusting the laser to enable the central wavelength of the laser to coincide with the strongest absorption peak of the target gas, recording the initial absorption peak information of the interference gas at the moment, and analyzing and constructing gas absorption peak reference data; comparing gas absorption peak reference data, and adjusting the central wavelength of the laser based on negative feedback of the change of the interference gas absorption peak during operation detection so as to maintain the central wavelength to coincide with the corresponding wavelength of the strongest absorption peak of the target gas; and analyzing a measurement light path signal to determine the type and concentration of the gas. Target gas is replaced by non-toxic and non-corrosive interference gas, so that the safety risk of toxic and corrosive gas is avoided; the wavelength drift is corrected in real time through negative feedback adjustment, so that the detection stability is ensured, and safe and accurate laser gas detection and self-calibration are realized.

Description

Technical Field

[0001] This invention relates to the field of gas detection technology, and more specifically, to a gas detection method and apparatus that can self-calibrate the center wavelength of a laser. Background Technology

[0002] Laser gas sensors are based on Tunable Diode Laser Absorption Spectroscopy (TDLAS). Their working principle is that each analyte gas has inherent molecular vibrational and rotational frequencies, thus exhibiting absorption of infrared laser signals of specific frequencies or wavelengths. This characteristic is known as the gas's characteristic absorption spectrum. When the laser signal emitted by the laser passes through the analyte gas, if the laser wavelength coincides with the gas's characteristic absorption spectrum, the laser signal will be absorbed by the gas. The relationship between light absorption intensity and gas molecule concentration follows the Lambert-Beer law. For effective gas detection, the laser's center wavelength, i.e., the position of the gas absorption peak, must remain stable. However, in practical applications, the laser's center wavelength can be affected by environmental factors such as temperature, air pressure, laser operating time, and system electrical parameter drift, leading to a decrease in the sensitivity and accuracy of laser detection.

[0003] To address the issue of laser center wavelength offset, various methods for automatic laser center wavelength calibration have been proposed. For example, patent publication CN113670832A discloses a method for retrieving the center profile of a gas absorption peak in a reference chamber, and patent publication CN116448704A discloses a gas detection self-calibration method based on TDLAS. Both methods employ a reference chamber and introduce target gas into it. By detecting the position of the gas absorption peak, which is the laser center wavelength position, an adjustment algorithm is used to automatically adjust the gas absorption peak position, i.e., the laser center wavelength, to ensure the sensitivity and accuracy of laser detection.

[0004] However, existing methods have the following drawbacks: 1. When the target gas is a toxic or corrosive gas, introducing such gas into the reference chamber or using a reference chamber filled with such gas poses a high safety risk to both operators and users. 2. Prolonged contact between corrosive gases and the reference chamber leads to corrosion of the reference chamber, affecting its airtightness and posing a risk of corrosive gas leakage.

[0005] The above problems are worth solving. Summary of the Invention

[0006] To overcome the safety risks of corrosion and damage to the reference gas chamber caused by filling it with toxic or corrosive target gases in existing technologies, which affects airtightness and thus the adjustment, this invention provides a gas detection method and device that can self-calibrate the center wavelength of a laser.

[0007] The technical solution of this invention is as follows: A gas detection method with a self-calibrating laser center wavelength includes the following steps: Query the absorption band of the target gas, define the target correlation band based on the absorption band of the target gas, and find the interfering gas to replace the target gas within the target correlation band. The interfering gas is used to replace the target gas and fill the reference optical path of the laser; The wavelength sweep range of the laser is adjusted to cover the absorption spectrum of the interfering gas. After fixing the wavelength sweep range, the center wavelength of the laser is adjusted to coincide with the wavelength corresponding to the strongest absorption peak of the target gas. Measure and record the initial absorption peak information of the interfering gas at this time, and construct gas absorption peak reference data; During device operation and testing, based on the changes in the absorption peak of the interfering gas and the reference data of the gas absorption peak, the center wavelength of the laser is adjusted by negative feedback to maintain its overlap with the wavelength corresponding to the strongest absorption peak of the target gas. The laser signal in the optical path is analyzed to extract the absorption peak information of the gas, determine the gas type, and calculate the gas concentration.

[0008] As a preferred embodiment of the present invention, the bandwidth of the target correlation band is ±0.6nm; the absorption intensity of the interfering gas is greater than 1 / 20 of the absorption intensity of the target gas.

[0009] As a preferred embodiment of the present invention, the gas absorption peak reference data includes at least the initial absorption peak information of the interfering gas, the absorption peak information of the target gas, and the absorption peak spacing between the interfering gas and the target gas; wherein, the absorption peak information includes the absorption peak position, light absorption intensity, and different absorption peak spacings.

[0010] As a preferred embodiment of the present invention, the specific steps for adjusting the wavelength sweep range of the laser are as follows: Set the laser drive current waveform; The current driving circuit is adjusted to change the range of laser driving current, thereby adjusting the wavelength sweep range so that the wavelength sweep range covers at least two absorption lines of interfering gases. The range of laser drive current is fixed to fix the wavelength sweep range.

[0011] As a preferred technical solution of the present invention, the specific steps for recording the initial absorption peak information of the interfering gas are as follows: sequentially recording the position and intensity information of several absorption peaks of the interfering gas.

[0012] As a preferred embodiment of the present invention, the step of negative feedback adjustment of the laser center wavelength based on the change of the interfering gas absorption peak and the gas absorption peak reference data includes the following steps: By comparing the gas absorption peak reference data, the consistency of the measured absorption peak information of the interfering gas is determined, including the number of absorption peaks, the spacing between adjacent absorption peaks, and the intensity ratio. If they are inconsistent, the laser temperature is adjusted until the absorption peak information is consistent to complete the coarse adjustment. The absorption peak information refers to the number of absorption peaks, the spacing between adjacent absorption peaks, and the intensity ratio. By comparing the gas absorption peak reference data, the consistency between the measured absorption peak position of the interfering gas and the position recorded in the initial absorption peak information is determined. If they are inconsistent, the laser temperature is adjusted to bring the measured absorption peak position of the interfering gas back to the position recorded in the initial absorption peak information to complete the fine adjustment.

[0013] Furthermore, during coarse adjustment, the temperature adjustment amount and the number of adjustments are set. The laser temperature is adjusted bidirectionally, and the measured data of the interfering gas are compared with the initial absorption peak information one by one until the number of absorption peaks of the interfering gas, the spacing between adjacent absorption peaks, and the intensity ratio all correspond, thus completing the coarse adjustment.

[0014] Furthermore, during fine-tuning, the position of the first absorption peak of the interfering gas is used as a reference to calculate the offset between the position of the first absorption peak recorded in the initial absorption peak information of the interfering gas and the position of the first absorption peak. The initial adjustment amount of the laser temperature is determined based on the offset. The offset is dynamically adjusted to gradually reduce the offset until the measured position of the first absorption peak of the interfering gas returns to the position of the first absorption peak recorded in its initial absorption peak information, so that the overall absorption peak position matches the initial recorded state, and the fine-tuning is completed.

[0015] As a preferred technical solution of the present invention, negative feedback regulation is performed at intervals after each power-on preheating of the device and during normal operation.

[0016] The present invention also provides a gas detection device capable of self-calibrating the center wavelength of a laser, for implementing the gas detection method capable of self-calibrating the center wavelength of a laser described above, including an MCU, a laser and an optical fiber beam splitter, and further including a temperature control circuit, a current driving circuit and two amplification and filtering circuits electrically connected to the MCU. The temperature control circuit is used to adjust the center wavelength of the laser, and the current drive circuit is used to adjust the wavelength sweep range of the center wavelength. The fiber beam splitter is located at the output end of the laser and is used to split the laser beam into two paths; the first laser beam is emitted to the reference optical path, which includes a reference gas chamber, a first photodetector and a first amplification and filtering circuit; the reference gas chamber is filled with an interfering gas to replace the target gas, the interfering gas is located near the absorption band of the target gas, and the interfering gas is a non-toxic and non-corrosive gas.

[0017] The second laser beam passes through an optical fiber collimator and enters the measurement optical path, which includes a measurement gas chamber or open space, a second photodetector, and a second amplification and filtering circuit.

[0018] Furthermore, the MCU stores the absorption peak information of the target gas and the interfering gas. The MCU can compare the measured data collected by the first photodetector with the reference data, and adjust the laser through the negative feedback of the temperature control circuit to achieve self-calibration. The MCU can also analyze the type of gas to be tested and calculate the gas concentration based on the signal collected by the second photodetector.

[0019] As a preferred embodiment of the present invention, the splitting ratio of the fiber optic beam splitter is such that the intensity ratio of the measurement optical path is greater than that of the reference optical path.

[0020] Preferably, the ratio of light intensity between the measurement optical path and the reference optical path is 9.0:1.0 to 9.9:0.1.

[0021] Optionally, the second photodetector receives laser signals via direct illumination, single reflection, or multiple reflections, and the detection method of the second photodetector includes fixed, through-beam, reflective, or telemetry.

[0022] According to the above-described solution, the beneficial effects of this invention are as follows: This invention uses an interfering gas to replace the target gas in the reference optical path, which can avoid the safety hazards of toxic or corrosive gases in the reference optical path by using a non-toxic and non-corrosive interfering gas, and significantly improve the safety and stability of the device operation. This invention first fixes the laser wavelength sweep range and then adjusts the center wavelength. It combines the initial absorption peak of the interfering gas recorded by measurement to construct reference data, making wavelength calibration more targeted. By comparing the changes in the absorption peak of the interfering gas with the reference data, negative feedback adjustment is achieved. Even without dependence on the target gas, the laser center wavelength can still be accurately aligned with the strongest absorption peak of the target gas, ensuring detection accuracy. The present invention analyzes and measures the optical path signal and extracts absorption peak information by combining it with reference data. This can effectively distinguish between target gas and interfering gas, achieve accurate gas type identification and concentration calculation, break through the limitations of single gas detection, expand detection functions, improve the adaptability and practicality of the device to multiple scenarios, and resist the influence of absorption peak shift and other interfering gases, ensuring the high precision and high stability of the laser gas sensor. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the structure of the present invention; Figure 3 This is a schematic diagram of negative feedback regulation under the condition of a single interfering gas; Figure 4 This is a schematic diagram of negative feedback regulation under two interfering gas conditions. Detailed Implementation

[0024] To better understand the purpose, technical solution, and technical effects of this invention, the invention will be further explained and described below in conjunction with the accompanying drawings and embodiments. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. It is also stated that the embodiments described below are only for explaining this invention and are not intended to limit this invention.

[0025] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The term "several" means two or more, unless otherwise explicitly specified.

[0026] This invention provides a gas detection method for self-calibrating the center wavelength of a laser based on the principle of tunable laser absorption spectroscopy. Its core logic involves selecting a safe interfering gas to replace the target gas in a reference gas chamber, and then combining this with constructed gas absorption peak reference data to achieve self-calibration and accurate detection of the laser wavelength. The specific technical solution is as follows: like Figure 1 As shown, a gas detection method with a self-calibrating laser center wavelength includes the following steps: Step 1: Locate the absorption band of the target gas, define the target correlation band based on this absorption band, and find a non-toxic and non-corrosive gas as the interfering gas within the target correlation band; analyze the absorption characteristics of the target gas and the interfering gas, such as the absorption peak position, intensity, spectral spacing, etc.; this step provides a basis for comparison for subsequent calibration and testing.

[0027] The specific steps for defining the target correlation band are as follows: First, determine the absorption band of the target gas, and then define the target correlation band with a bandwidth of ±0.6nm, using the target gas's absorption band as a reference. In this way, the interfering gas and the target gas are located near the same absorption band, ensuring that the absorption characteristics of the interfering gas are highly correlated with those of the target gas.

[0028] Step 2: The selected interfering gas is filled into the reference optical path of the laser (i.e., the reference gas chamber of the laser) to replace the toxic or corrosive target gas, thus solving the problems of corrosion and leakage caused by contact with toxic or corrosive gases in the reference gas chamber.

[0029] Step 3: Adjust the wavelength sweep range of the laser to cover the absorption spectrum of the interfering gas. After fixing the wavelength sweep range, adjust the center wavelength of the laser to coincide with the wavelength corresponding to the strongest absorption peak of the target gas. At the same time, measure and record the initial absorption peak information of the interfering gas. Construct gas absorption peak reference data and store the data information in the MCU to establish a benchmark for subsequent calibration.

[0030] Step 4: During device operation and testing, by monitoring changes in the absorption peaks of interfering gases in the reference optical path, such as position shifts and intensity ratio changes, and combining the gas absorption peak reference data, the center wavelength of the laser is adjusted using a negative feedback mechanism to maintain the matching state between the center wavelength of the laser and the strongest absorption peak of the target gas, that is, to maintain the overlap between the two.

[0031] Step 5: Analyze the laser signal in the measurement optical path to extract the gas absorption peak information, compare it with the gas absorption peak reference data, determine the gas type, and calculate the gas concentration according to Lambert-Beer Law to complete the detection.

[0032] The above technical solution stems from the synergistic effect of each step. First, a mismatch gas is identified within the target-related wavelength band to replace the target gas. This gas is ensured to be non-toxic and non-corrosive, and possesses distinguishable characteristics from the target gas within the related wavelength band. This serves as an effective calibration reference, providing a precise theoretical basis for indirectly calibrating the laser's center wavelength to match the target gas wavelength. Initially, the laser wavelength sweep range is fixed, and then the center wavelength is adjusted to coincide with the target gas's strongest absorption peak. Simultaneously, the initial absorption peak information of the mismatch gas is recorded. The negative feedback adjustment mechanism compares the current mismatch gas absorption peak with the initial peak, combines this with gas absorption peak reference data, and uses temperature adjustment to correct the laser's center wavelength in real time, accurately and indirectly maintaining the alignment between the laser's center wavelength and the target gas's strongest absorption peak. The signal processing in the measurement optical path, based on gas absorption peak characteristic matching, achieves accurate gas type identification and quantitative concentration calculation, ultimately realizing safe, stable, and accurate self-calibration and gas detection.

[0033] Therefore, in terms of safety, this invention avoids the risk of operators coming into contact with hazardous gases by using a non-toxic, non-corrosive interfering gas instead of the potentially toxic or corrosive target gas in the reference optical path. It also reduces the possibility of corrosion of the reference gas chamber, extends the device's lifespan, and lowers the risk of leakage. Regarding stability, the negative feedback adjustment mechanism based on the changes in the interfering gas absorption peak can calibrate the laser's center wavelength in real time, ensuring it always coincides with the strongest absorption peak of the target gas, avoiding problems such as decreased detection sensitivity or failure. In terms of detection accuracy, the gas absorption peak reference data records the detailed absorption peak characteristics of the target gas and the interfering gas, allowing the absorption peak information extracted from the measurement optical path to accurately distinguish between the target gas and the interfering gas through comparison. Even in environments with multiple gases coexisting, the position and intensity of different absorption peaks can be used to identify gas types and accurately calculate concentrations, achieving multi-gas detection functionality.

[0034] In step 1, the interfering gas searched within the target correlation band meets the following criteria: absorption intensity greater than 1 / 20 of the target gas's absorption intensity, and non-toxic and non-corrosive. This step limits the absorption intensity threshold of the interfering gas, ensuring that it generates a sufficiently significant absorption signal in the reference optical path. This makes the absorption peak of the interfering gas easily captured and identified by the photodetector, providing a clear reference for subsequent wavelength calibration and avoiding the indistinguishability of characteristic peaks due to weak absorption signals. Since the interfering gas and the target gas are located near the same absorption band and their absorption intensities meet the aforementioned threshold, their absorption characteristics are effectively correlated with those of the target gas. Combined with the gas absorption peak reference data, the shift in the laser's center wavelength can be accurately reflected by monitoring changes in the position, spacing, and intensity ratio of the interfering gas's absorption peaks, providing a reliable quantitative basis for negative feedback adjustment.

[0035] In this invention, the gas absorption peak reference data includes at least the initial absorption peak information of the interfering gas, the absorption peak information of the target gas, and the absorption peak spacing between the interfering gas and the target gas; wherein, the absorption peak information includes the absorption peak position P, the light absorption intensity I, and the different absorption peak spacings ΔP.

[0036] In this invention, the specific steps for adjusting the wavelength sweep range of the laser are as follows: The first step is to set the laser drive current waveform, such as a sawtooth wave or a sawtooth wave superimposed with a sine wave, to ensure that the wavelength can be continuously and uniformly swept. The second step is to adjust the current driving circuit to change the range of the laser driving current, and then adjust the wavelength sweep range so that the sweep range covers at least two absorption lines of the interfering gas. Step 3: Fix the laser drive current range to fix the wavelength sweep range.

[0037] When the laser wavelength sweep range covers at least two absorption lines of the interfering gas, it can simultaneously cover the absorption spectra of both the interfering and target gases. The principle is that the interfering gas is selected within a target-related band with a bandwidth of ±0.6 nm, based on the target gas's absorption band. Since the absorption spectra of both are in highly similar bands, the sweep range inevitably includes the target gas's absorption spectrum. Furthermore, after adjusting the laser wavelength sweep range, the laser's center wavelength is initially aligned with the target gas's strongest absorption peak, ensuring that the sweep range revolves around that center wavelength.

[0038] In addition, the scanning wavelength range completely covers the absorption spectrum of at least two interfering gases, providing sufficient feature references for coarse adjustment. This is because coarse adjustment is achieved by comparing the number of absorption peaks, the spacing between adjacent peaks, and the intensity ratio. Two or more interfering gas absorption spectra can provide multiple feature points, avoiding misjudgments caused by a single absorption peak and ensuring more accurate judgment of absorption feature matching during coarse adjustment.

[0039] During coarse adjustment, the temperature adjustment amount and the number of adjustments are set. The temperature adjustment amount is related to the two absorption peaks of the interfering gas. The coarse adjustment amount should not be too large to avoid missing the two absorption peaks of the interfering gas; the coarse adjustment amount should not be too small to avoid low adjustment efficiency. By adjusting the laser temperature bidirectionally (i.e., adjusting the temperature in both directions of increasing and decreasing), and comparing the number of absorption peaks, the spacing between adjacent absorption peaks, and the ratio of absorption peak intensities, based on the absorption characteristics of the interfering gas recorded in the gas absorption peak reference data, the coarse adjustment is only considered complete when the measured number of absorption peaks, the spacing between adjacent absorption peaks, and the ratio of absorption peak intensities are all consistent with the reference data, ensuring that the core characteristics of the interfering gas absorption peaks match the baseline state after coarse adjustment.

[0040] During fine-tuning, the position of the first absorption peak of the interfering gas is used as a reference to calculate the offset of the first absorption peak position in the initial absorption peak information. The initial adjustment amount of the laser temperature is determined based on the offset. The offset is gradually reduced through dynamic adjustment until the position of the first absorption peak of the interfering gas returns to the initial position. At this time, the overall position of the interfering gas absorption peak matches the initial state, thereby ensuring that the center wavelength of the laser always coincides with the wavelength corresponding to the strongest absorption peak of the target gas.

[0041] To better understand the adjustment process, the following two operational examples are provided: Case 1: Adjustment process for a single interfering gas (containing two absorption peaks) Reference Figure 3In diagrams a), b), and c), the horizontal axis represents wavelength in nm, and the vertical axis represents absorption peak intensity, which is the ratio of light intensity before and after gas absorption and is dimensionless. Within a fixed wavelength sweep range, this range is set based on the target associated band defined by the target gas absorption band and must cover at least two absorption lines of the interfering gas. When the target gas absorption spectrum initially coincides with the laser center wavelength, only one interfering gas exists in the reference gas cell, and this interfering gas has two absorption peaks (A01, A02). Initially, the initial absorption peak information of the interfering gas is recorded sequentially: the position of absorption peak (A01) is P(A01), and its intensity is I(A01); the position of absorption peak (A02) is P(A02), and its intensity is I(A02). The spacing between adjacent absorption peaks, D1 = P(A02) - P(A01), and the intensity ratio K1 = I(A02) / I(A01) are calculated. Simultaneously, the distance between the strongest absorption peaks of the interfering gas and the target gas is recorded. All of these parameters are stored in the gas absorption peak reference data. Figure 3 (a) in the middle.

[0042] When the center wavelength of the laser shifts, the interference gas absorption peak (A11) detected by the first photodetector does not match the reference data (A01, A02) of the gas absorption peak. Figure 3 In step b), the number, spacing, and intensity ratio of the interfering gas absorption peaks are all different. This triggers coarse adjustment. Set the temperature adjustment amount and limit the number of adjustments N. N can be 10, 20, 30, etc., and is not limited here. The adjustment amount remains constant during the adjustment process. First, lower the laser temperature. After adjustment, compare the number, spacing, and intensity ratio of the current absorption peak with the reference data of the gas absorption peak. If a consistent state is not achieved within the limited number of adjustments, adjust the temperature back to the initial value, and then increase the laser temperature in the opposite direction with the same adjustment amount. Compare again until the number, spacing, and intensity ratio of the absorption peaks in the measured results are consistent with the reference data of the gas absorption peak. Specifically, the interfering gas absorption peak changes from only one absorption peak (A11) to two absorption peaks (A21, A22), and the absorption peak spacing P(A22)-P(A21) equals P(A02)-P(A01), and the intensity ratio I(A22) / I(A21) equals I(A02) / I(A01). Figure 3 (c) in the text, coarse adjustment ends.

[0043] After coarse adjustment, proceed to fine adjustment: Using the first absorption peak (A21) of the interfering gas as a reference, calculate its position offset ΔP = P(A21) - P(A01) from the first absorption peak (A01) in the initial absorption peak information. Determine the initial adjustment amount based on the offset; specifically, the offset change corresponding to the initial adjustment amount is equal to half of the offset ΔP.

[0044] During the initial adjustment, if the absolute value of the offset ΔP increases, it indicates that the absorption peak (A21) is moving away from the absorption peak (A01), and the adjustment needs to be reversed. If the absolute value of the offset ΔP decreases, it indicates that the absorption peak (A21) is moving closer to the absorption peak (A01). Continue adjusting while maintaining the initial adjustment amount. If the positions of the absorption peaks (A21) and (A01) coincide, the fine-tuning is complete. If the absolute value of the offset ΔP increases after a certain adjustment while decreasing, it indicates that the initial adjustment amount does not meet the adjustment accuracy requirements. Reduce the initial adjustment amount to obtain a correction adjustment amount. Use the correction adjustment amount β for reverse adjustment, causing the absolute value of the offset ΔP to decrease again until the positions of the absorption peaks (A21) and (A01) coincide, completing the fine-tuning. At this point, all absorption peaks are matched to the initial state, and the center wavelength of the laser coincides with the wavelength corresponding to the strongest absorption peak of the target gas.

[0045] Case 2: Adjustment process for multiple interfering gases (containing multiple absorption peaks) Reference Figure 4 Within a fixed wavelength sweep range, when the absorption spectrum of the target gas initially coincides with the center wavelength of the laser, two interfering gases exist in the reference gas cell: the first gas has three absorption peaks (A01, A02, A03), and the second gas has one absorption peak (B). Initially, the initial absorption peak information of each interfering gas is recorded sequentially: the position and intensity of each peak, the spacing between different absorption peaks of the interfering gas, and the spacing between the absorption peaks of the interfering gas and the target gas. Simultaneously, the intensity ratio is calculated. All these parameters are stored in the gas absorption peak reference data. Figure 4 (a) in the middle.

[0046] When the center wavelength of the laser shifts, a comparison between the absorption peak detected by the first photodetector and the reference data of the gas absorption peak reveals that the number of absorption peaks and the ratio of absorption peak intensities remain consistent, with only the overall position shifting. Figure 4 Therefore, since we can directly proceed to fine-tuning without coarse adjustment (as shown in b) and c), we can skip coarse adjustment and go directly to fine adjustment. Figure 4 b) and c) represent two offset scenarios where the target gas absorption spectrum does not coincide with the center wavelength of the laser.

[0047] Fine-tuning is performed using the first absorption peak (A21) or (A31) of the first interfering gas as a reference. The position offset P(A21) - P(A01) or P(A31) - P(A01) from the corresponding absorption peak (A01) in the initial absorption peak information is calculated. Following the same fine-tuning steps, the position offset P(A21) - P(A01) or P(A31) - P(A01) is gradually reduced until the absorption peak (A21) or (A31) returns to the position of the absorption peak (A01). At this point, all absorption peaks are matched with the initial state, achieving the coincidence of the laser center wavelength with the wavelength corresponding to the strongest absorption peak of the target gas, thus completing self-calibration.

[0048] In this invention, negative feedback adjustment is performed after each power-on preheating of the device, which can effectively correct the cumulative wavelength shift caused by changes in ambient temperature and static drift of device parameters after the device has been stored for a long time. If the shift is not calibrated in time, the center wavelength of the laser will deviate from the strongest absorption peak of the target gas in the initial stage of power-on, directly affecting the detection accuracy.

[0049] In addition, because the slow drift of the laser gas sensor accumulates to a certain extent during long-term operation, it can lead to a decrease in the detection sensitivity of the absorption peak or even an error in the identification of the characteristic peak. Therefore, negative feedback adjustment is performed at regular intervals during normal operation of the device, for example, after 1 hour, 2 hours, ..., 24 hours of operation. Periodic calibration can capture and correct the offset in a timely manner, avoiding the gradual wavelength shift caused by factors such as continuous heat generation of the laser, fluctuations in ambient temperature and humidity, and real-time drift of electrical parameters during operation.

[0050] In step 5, the signal received by the second photodetector is analyzed to extract the position and intensity of the gas absorption peaks. The reference data for gas absorption peaks is compared with the actual tested gas absorption peaks. The gas type (target gas or interfering gas) is determined by the position of the actual tested gas absorption peaks, and the gas concentration is calculated by the intensity of the actual tested gas absorption peaks. If both target gas and interfering gas are present in the measurement chamber / open space, a sawtooth waveform will have multiple gas absorption peaks. The corresponding gas concentration is calculated by matching the position and intensity of each absorption peak, thus achieving multi-gas detection functionality.

[0051] like Figure 2 As shown, the present invention also provides a gas detection device capable of self-calibrating the center wavelength of a laser, which mainly consists of a microcontroller (MCU), a current driving circuit, a temperature control circuit, a laser, an optical fiber beam splitter, an optical fiber collimator, a reference gas chamber, a first photodetector (i.e., photodetector 1), a second photodetector (i.e., photodetector 2), and two amplification and filtering circuits. The components work together to realize the above-mentioned gas detection method.

[0052] The MCU, as the core control and data processing unit, drives the laser by controlling the temperature control circuit and the current drive circuit, thereby adjusting the center wavelength and wavelength sweep range of the emitted laser. The temperature control circuit is mainly responsible for precisely adjusting the center wavelength of the laser, while the current drive circuit is used to adjust the wavelength sweep range to ensure that the laser can cover the absorption spectrum of both the target gas and the interfering gas. The laser emitted by the laser is first split into two beams by an optical fiber beam splitter located at its output end. The beam splitting ratio is designed so that the intensity of the measurement optical path is greater than that of the reference optical path. Specifically, ratios such as 9.0:1.0, 9.2:0.8, 9.3:0.7, 9.4:0.6, 9.9:0.1, or other similar ratios can be used. This is because the measurement optical path, as an external optical path, requires stronger light intensity to cope with possible light loss, while the reference optical path, as an internal optical path, has lower light intensity requirements. This ratio setting can ensure that the reference optical path signal is stable while ensuring that the measurement optical path has sufficient light intensity for accurate detection.

[0053] The first laser beam after splitting is directed towards a reference gas chamber, which is filled with an interfering gas selected from a target correlation band of ±0.6nm, based on the target gas's absorption band. This interfering gas is non-toxic and non-corrosive, replacing the toxic or corrosive target gas. This not only prevents the reference gas chamber from being corroded and extends its service life, but also eliminates the safety hazards of production and operation personnel coming into contact with dangerous gases. The laser beam passing through the reference gas chamber is received by the first photodetector, and its output signal is processed by the corresponding first amplification and filtering circuit before being transmitted to the MCU. The MCU analyzes the signal to obtain the current absorption peak information of the interfering gas and compares it with the stored initial absorption peak information and gas absorption peak reference data to determine whether the laser's center wavelength has drifted. If a drift exists, negative feedback adjustment is performed through the temperature control circuit to ensure that the laser's center wavelength always coincides with the wavelength corresponding to the strongest absorption peak of the target gas, thus achieving a self-calibration function.

[0054] The second laser beam, after being collimated by an optical fiber collimator, is directed towards the measurement gas chamber or open space. This beam has a flexible transmission path; the second photodetector can receive the laser signal via direct beam, single reflection, or multiple reflections. The second photodetector can be fixed, through-beam, reflective, or telemetry-based, adapting to different detection scenarios. The laser beam passing through the measurement area is received by the second photodetector, and its output signal is processed by the second amplification and filtering circuit before being transmitted to the MCU. The MCU, combined with stored gas absorption peak reference data, analyzes the absorption peaks in the signal, determines the gas type by the absorption peak position, and calculates the gas concentration based on the Lambert-Beer law using the absorption peak intensity. Even if both target gas and interfering gas are present in the measurement area, accurate detection of multiple gases can be achieved by extracting their respective strongest absorption peaks.

[0055] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A gas detection method with a self-calibrating laser center wavelength, characterized in that, Includes the following steps: Query the absorption band of the target gas, define the target correlation band based on the absorption band of the target gas, and find the interfering gas to replace the target gas within the target correlation band. The interfering gas is used to replace the target gas and fill the reference optical path of the laser; The wavelength sweep range of the laser is adjusted to cover the absorption spectrum of the interfering gas. After fixing the wavelength sweep range, the center wavelength of the laser is adjusted to coincide with the wavelength corresponding to the strongest absorption peak of the target gas. Measure and record the initial absorption peak information of the interfering gas at this time, and construct gas absorption peak reference data; During device operation and testing, based on the changes in the absorption peak of the interfering gas and the reference data of the gas absorption peak, the center wavelength of the laser is adjusted by negative feedback to maintain its overlap with the wavelength corresponding to the strongest absorption peak of the target gas. The laser signal in the optical path is analyzed to extract the absorption peak information of the gas, determine the gas type, and calculate the gas concentration.

2. The gas detection method for a self-calibrating laser center wavelength according to claim 1, characterized in that, The bandwidth of the target associated band is ±0.6 nm; the absorption intensity of the interfering gas is greater than 1 / 20 of the absorption intensity of the target gas.

3. The gas detection method for a self-calibrating laser center wavelength according to claim 1, characterized in that, The gas absorption peak reference data includes at least the initial absorption peak information of the interfering gas, the absorption peak information of the target gas, and the absorption peak spacing between the interfering gas and the target gas; wherein, the absorption peak information includes the absorption peak position, light absorption intensity, and different absorption peak spacings.

4. The gas detection method for a self-calibrating laser center wavelength according to claim 1, characterized in that, The specific steps for adjusting the wavelength sweep range of the laser are as follows: Set the laser drive current waveform; The current driving circuit is adjusted to change the range of laser driving current, thereby adjusting the wavelength sweep range so that the wavelength sweep range covers at least two absorption lines of interfering gases. The range of laser drive current is fixed to fix the wavelength sweep range.

5. The gas detection method for a self-calibrating laser center wavelength according to claim 1, characterized in that, The specific steps for recording the initial absorption peak information of the interfering gas are as follows: sequentially record the position and intensity information of several absorption peaks of the interfering gas.

6. The gas detection method for a self-calibrating laser center wavelength according to claim 1, characterized in that, The steps for adjusting the center wavelength of the laser based on the changes in the absorption peak of the interfering gas and the reference data of the gas absorption peak include the following steps: By comparing the gas absorption peak reference data, the consistency of the measured absorption peak information of the interfering gas is determined, including the number of absorption peaks, the spacing between adjacent absorption peaks, and the intensity ratio. If they are inconsistent, the laser temperature is adjusted until the above absorption peak information is consistent to complete the coarse adjustment. By comparing the gas absorption peak reference data, the consistency between the measured absorption peak position of the interfering gas and the position recorded in the initial absorption peak information is determined. If they are inconsistent, the laser temperature is adjusted to bring the measured absorption peak position of the interfering gas back to the position recorded in the initial absorption peak information to complete the fine adjustment.

7. The gas detection method for a self-calibrating laser center wavelength according to claim 6, characterized in that, During coarse adjustment, the temperature adjustment amount and the number of adjustments are set. The laser temperature is adjusted bidirectionally, and the measured data of the interfering gas are compared with the initial absorption peak information one by one until the number of interfering gas absorption peaks, the spacing between adjacent absorption peaks, and the intensity ratio all correspond. Then the coarse adjustment is completed.

8. The gas detection method for a self-calibrating laser center wavelength according to claim 6, characterized in that, During fine-tuning, the position of the first absorption peak of the interfering gas is used as a reference. The offset between the position of the first absorption peak recorded in the initial absorption peak information of the interfering gas and the position of the first absorption peak is calculated. The initial adjustment amount of the laser temperature is determined based on the offset. The offset is dynamically adjusted to gradually reduce the offset until the measured position of the first absorption peak of the interfering gas returns to the position of the first absorption peak recorded in the initial absorption peak information. This achieves the matching of the overall absorption peak position with the initial recorded state, and the fine-tuning is then completed.

9. The gas detection method for a self-calibrating laser center wavelength according to claim 1 or 6, characterized in that, Negative feedback regulation is performed periodically after each power-on preheating and during normal operation.

10. A gas detection device capable of self-calibrating the center wavelength of a laser, characterized in that, A gas detection method for implementing the self-calibrating laser center wavelength as described in any one of claims 1 to 9 includes an MCU, a laser, and an optical fiber beam splitter, and further includes a temperature control circuit, a current drive circuit, and two amplification and filtering circuits electrically connected to the MCU. The temperature control circuit is used to adjust the center wavelength of the laser, and the current drive circuit is used to adjust the wavelength sweep range of the center wavelength. The fiber beam splitter is located at the output end of the laser and is used to split the laser beam into two paths; the first laser path is emitted to the reference optical path, which includes a reference gas chamber, a first photodetector, and a first amplification and filtering circuit; the reference gas chamber is filled with an interfering gas to replace the target gas; The second laser beam is collimated by an optical fiber and then enters the measurement optical path, which includes a measurement gas chamber or open space, a second photodetector, and a second amplification and filtering circuit.

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