A gas detection method and device capable of self-calibrating the central wavelength of a laser

Abstract

The present application relates to a kind of gas detection method and device of self-calibration laser center wavelength, find non-toxic non-corrosive interference gas in target correlation waveband, replace target gas and fill reference light path;Adjust the wavelength sweep range of laser, adjust laser again to make its center wavelength coincide with the strongest absorption peak of target gas, record the initial absorption peak information of interference gas at this time, analyze and construct gas absorption peak reference data;Compare gas absorption peak reference data, based on the change of interference gas absorption peak when running detection, adjust the center wavelength of laser by negative feedback to maintain its coincidence with the wavelength corresponding to the strongest absorption peak of target gas;Analysis measurement light path signal, determine gas type and concentration.The present application replaces target gas by non-toxic non-corrosive interference gas, avoids the safety risk of toxic and corrosive gas;Negative feedback regulation real-time correction wavelength drift, ensure detection stability, realize safe, accurate laser gas detection and self-calibration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas detection, in particular to a gas detection method and device capable of self-calibrating the central wavelength of a laser. BACKGROUND

[0002] A laser gas sensor is based on tunable diode laser absorption spectroscopy (TDLAS), and its working principle is that each type of gas to be detected has inherent molecular vibration and rotation frequency, so it has absorption effect on infrared laser signals of specific frequency or wavelength. This characteristic is called the characteristic absorption spectrum of the gas. When the laser signal emitted by the laser passes through the gas to be detected, if the laser wavelength coincides with the characteristic absorption spectrum of the gas to be detected, the laser signal will be absorbed by the gas to be detected, and the relationship between the light absorption intensity and the concentration of gas molecules follows the Lambert-Beer law. When the laser gas sensor detects gas, it needs to ensure that the central wavelength of the laser, i.e., the position of the gas absorption peak, remains stable to ensure the effect of gas detection. However, in actual use, the central wavelength of the laser will be affected by factors such as temperature and pressure of the use environment, running time of the laser, and drift of electrical parameters of the system itself, resulting in a shift in the central wavelength of the laser, which reduces the sensitivity and accuracy of laser detection.

[0003] To solve the problem of shift in the central wavelength of the laser, different methods for automatic calibration of the central wavelength of the laser have been proposed. For example, a reference gas chamber gas absorption peak profile center retrieval method disclosed in patent publication CN113670832A and a gas detection self-calibration method based on TDLAS disclosed in patent publication CN116448704A both use a reference gas chamber and introduce target gas into it. By detecting the position of the gas absorption peak, i.e., the position of the central wavelength of the laser, and using an adjustment algorithm, the position of the gas absorption peak, i.e., the central wavelength of the laser, is automatically adjusted to ensure the sensitivity and accuracy of laser detection.

[0004] However, the existing methods have the following defects:

[0005] 1. When the target gas is a toxic or corrosive gas, introducing such gas into the reference gas chamber and using a reference gas chamber filled with such gas pose a high safety risk to the operators and users.

[0006] 2. The corrosive gas is in contact with the reference gas chamber for a long time, which causes the reference gas chamber to be corroded, affecting the gas tightness of the chamber, and there is a risk of leakage of the corrosive gas.

[0007] The above problems need to be solved. SUMMARY

[0008] In order to overcome the safety risk of corrosion and damage to the reference gas chamber and the influence on the air tightness in the prior art by filling the reference gas chamber with a toxic or corrosive target gas, thereby affecting the adjustment, the present application provides a gas detection method and device capable of self-calibrating the center wavelength of a laser.

[0009] The technical scheme of the present application is as follows:

[0010] A gas detection method capable of self-calibrating the center wavelength of a laser, comprising the following steps:

[0011] querying the absorption band of the target gas, defining a target correlation band based on the absorption band of the target gas, and finding an interference gas for replacing the target gas in the target correlation band;

[0012] filling the reference light path of the laser with the interference gas to replace the target gas;

[0013] adjusting the wavelength sweep range of the laser to cover the absorption spectrum of the interference gas, and then adjusting the center wavelength of the laser to coincide with the wavelength corresponding to the strongest absorption peak of the target gas after fixing the wavelength sweep range;

[0014] measuring and recording the initial absorption peak information of the interference gas at this time, and constructing gas absorption peak reference data;

[0015] based on the change of the absorption peak of the interference gas and the gas absorption peak reference data, the center wavelength of the laser is adjusted by negative feedback to maintain the coincidence state with the wavelength corresponding to the strongest absorption peak of the target gas during the detection of the device operation;

[0016] analyzing the laser signal in the measurement light path to extract the absorption peak information of the gas, determining the type of the gas and calculating the concentration of the gas.

[0017] As a preferred technical scheme of the present application, the bandwidth of the target correlation band is ±0.6nm; the absorption intensity of the interference gas is greater than 1 / 20 of the absorption intensity of the target gas.

[0018] As a preferred technical scheme of the present application, the gas absorption peak reference data at least includes the initial absorption peak information of the interference gas, the target gas absorption peak information, and the absorption peak spacing between the interference gas and the target gas; wherein the absorption peak information includes the absorption peak position, the light absorption intensity, and the spacing between different absorption peaks.

[0019] As a preferred technical scheme of the present application, the specific steps of adjusting the wavelength sweep range of the laser are as follows:

[0020] setting the laser drive current waveform;

[0021] Adjusting the current driving circuit to change the laser driving current range to adjust the wavelength sweep range to cover at least the absorption spectral lines of two interfering gases;

[0022] Fixing the laser driving current range to fix the wavelength sweep range.

[0023] As a preferred technical solution of the present application, the specific steps of recording the initial absorption peak information of the interfering gas are: sequentially recording the position and intensity information of several absorption peaks of the interfering gas.

[0024] As a preferred technical solution of the present application, based on the change of the absorption peak of the interfering gas and the gas absorption peak reference data, the step of negative feedback adjusting the center wavelength of the laser includes the following steps:

[0025] Comparing the gas absorption peak reference data to judge the consistency of the measured absorption peak information of the interfering gas, including the number of absorption peaks, the interval of adjacent absorption peaks and the intensity ratio, and if they are inconsistent, adjusting the laser temperature to the above absorption peak information to complete the coarse adjustment; wherein the absorption peak information refers to the number of absorption peaks, the interval of adjacent absorption peaks and the intensity ratio;

[0026] Comparing the gas absorption peak reference data to judge the consistency of the measured absorption peak position of the interfering gas and the position recorded in the initial absorption peak information, and if they are inconsistent, adjusting the laser temperature to make the measured absorption peak position of the interfering gas return to the position recorded in the initial absorption peak information to complete the fine adjustment.

[0027] Further, during the coarse adjustment, the temperature adjustment amount and the adjustment times are set, the laser temperature is adjusted in both directions, and the measured data of the interfering gas and the initial absorption peak information are compared in sequence until the number of absorption peaks of the interfering gas, the interval of adjacent absorption peaks and the intensity ratio are all matched, and then the coarse adjustment is completed.

[0028] Further, during the fine adjustment, the first absorption peak position of the interfering gas is taken as a reference to calculate the offset amount of the first absorption peak position of the interfering gas from the first absorption peak position recorded in the initial absorption peak information of the interfering gas, and the initial adjustment amount of the laser temperature is determined according to the offset amount; the offset amount is dynamically adjusted to gradually decrease until the measured first absorption peak position of the interfering gas returns to the first absorption peak position recorded in the initial absorption peak information, and the overall absorption peak position is matched with the initial recorded state, and then the fine adjustment is completed.

[0029] As a preferred technical solution of the present application, the negative feedback adjustment is performed after each preheating of the device and at regular intervals during normal operation.

[0030] The application further provides a gas detection device capable of self-calibrating the central wavelength of a laser, which is used to implement the gas detection method capable of self-calibrating the central wavelength of a laser.

[0031] The temperature control circuit is used to adjust the central wavelength of the laser, and the current driving circuit is used to adjust the wavelength sweep range of the central wavelength.

[0032] The fiber splitter is arranged at the light emitting end of the laser and is used to split the laser into two paths.

[0033] The second path laser is emitted into a measurement light path after passing through a fiber collimator, and the measurement light path comprises a measurement gas chamber or an open space, a second photodetector and a second amplification filter circuit.

[0034] Further, the MCU stores the absorption peak information of the target gas and the interference gas, the MCU can compare the actual measurement data collected by the first photodetector with the reference data, and realize self-calibration through negative feedback adjustment of the laser by the temperature control circuit, and the MCU can also analyze the type of the to-be-measured gas and calculate the gas concentration according to the signal collected by the second photodetector.

[0035] As a preferred technical scheme of the application, the light splitting ratio of the fiber splitter is that the light intensity of the measurement light path accounts for more than that of the reference light path.

[0036] Preferably, the light intensity ratio of the measurement light path to the reference light path is 9.0:1.0 to 9.9:0.1.

[0037] Optionally, the second photodetector receives the laser signal in a straight-through, one-time reflection or multiple reflection manner, and the second photodetector detects in a fixed, opposite, reflective or remote manner.

[0038] The application according to the above scheme has the following advantages:

[0039] The application uses an interference gas to replace a target gas to fill the reference light path, which can avoid the safety hazard of the existence of toxic or corrosive gas in the reference light path by using a non-toxic and non-corrosive interference gas, and significantly improves the safety and stability of the device operation.

[0040] The present application first fixes the wavelength sweep range of the laser, then adjusts the central wavelength, combines the initial absorption peak of the interference gas measured and recorded to construct reference data, makes the wavelength calibration more targeted, realizes negative feedback adjustment by comparing the change of the interference gas absorption peak with the reference data, can still accurately maintain the alignment of the central wavelength of the laser and the strongest absorption peak of the target gas even if it is independent of the target gas, and guarantees the detection accuracy;

[0041] The present application analyzes the measurement light path signal and extracts the absorption peak information in combination with the reference data, can effectively distinguish the target gas and the interference gas, realizes accurate identification of the gas type and concentration calculation, breaks through the limitation of single gas detection, expands the detection function, improves the adaptability and practicality of the device to multiple scenes, and can resist the influence of absorption peak shift and other interference gases, and guarantees the high precision and high stability of the laser gas sensor. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The present application is a method flowchart;

[0043] Figure 2 The present application is a structural schematic diagram;

[0044] Figure 3 The present application is a negative feedback adjustment schematic diagram under the condition of single interference gas;

[0045] Figure 4 The present application is a negative feedback adjustment schematic diagram under the condition of two kinds of interference gas. DETAILED DESCRIPTION

[0046] In order to better understand the purpose, technical scheme and technical effect of the present application, the present application will be further explained in combination with the drawings and examples. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. At the same time, it is declared that the following described examples are only for explaining the present application, and are not used to limit the present application.

[0047] It should be noted that when an element is referred to as "fixed to" or "provided on" another element, it can be directly on another element or there can be a middle element, and when an element is considered to be "connected" to another element, it can be directly connected to another element or there can be a middle element. The term "several" means two or more, unless otherwise specifically and specifically limited.

[0048] The application provides a gas detection method based on a tunable laser absorption spectrum principle, which can self-calibrate the center wavelength of a laser, and the core logic is to replace the target gas filled in the reference gas chamber with a safe interference gas, and to realize the self-calibration and accurate detection of the wavelength of the laser by combining the constructed gas absorption peak reference data.

[0049] As shown in Figure 1 A gas detection method capable of self-calibrating the center wavelength of a laser, comprising the following steps:

[0050] Step 1: Query the absorption band of the target gas, define the target correlation band based on the absorption band, and find a non-toxic and non-corrosive gas as the interference gas in the target correlation band; analyze the absorption characteristics of the target gas and the interference gas, such as absorption peak position, intensity, spectral spacing, etc.; this step provides a basis for comparison for subsequent calibration and detection.

[0051] 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 ±0.6 nm based on the absorption band of the target gas. In this way, the interference gas and the target gas are in the vicinity of the same absorption band, ensuring that the absorption characteristics of the interference gas are highly correlated with the target gas.

[0052] Step 2: Fill the selected interference gas into the reference light path of the laser (i.e. the reference gas chamber of the laser) to replace the toxic or corrosive target gas, solving the problems of corrosion and leakage caused by the contact of the reference gas chamber with toxic or corrosive gases.

[0053] Step 3: Adjust the wavelength sweep range of the laser to cover the absorption spectrum of the interference gas, and then adjust the center wavelength of the laser to coincide with the corresponding wavelength of the strongest absorption peak of the target gas after fixing the wavelength sweep range; at the same time, measure and record the initial absorption peak information of the interference gas; construct the gas absorption peak reference data and store the data information in the MCU to establish a reference for subsequent calibration.

[0054] Step 4: During the detection of the device, the changes in the absorption peak of the interference gas in the reference light path, such as position shift and intensity ratio change, are monitored, and the gas absorption peak reference data is combined to adjust the center wavelength of the laser using a negative feedback mechanism to maintain the matching state of the center wavelength of the laser and the strongest absorption peak of the target gas, i.e. to maintain their coincidence.

[0055] Step 5: Analyze the laser signal in the measurement light path to extract the absorption peak information of the gas, compare it with the gas absorption peak reference data, determine the type of gas, and calculate the concentration of the gas according to the Lambert-Beer law to complete the detection.

[0056] The implementation of the above technical solution is derived from the synergistic effect of each step. First, the interfering gas that can replace the target gas is found in the target correlation band to ensure that it is non-toxic and non-corrosive and can have distinguishable characteristics with the target gas in the correlation band, serving as an effective calibration reference. The indirect calibration of the laser center wavelength matching the target gas wavelength by the interfering gas provides a precise theoretical basis. In the initial state, the laser wavelength sweep range is first fixed, then the center wavelength is adjusted to coincide with the strongest absorption peak of the target gas, and the initial absorption peak information of the interfering gas at this moment is recorded. The negative feedback adjustment mechanism compares the difference between the current interfering gas absorption peak and the initial peak, combines the gas absorption peak reference data, and uses temperature adjustment to correct the laser center wavelength in real time, accurately and indirectly maintaining the alignment of the laser center wavelength and the strongest absorption peak of the target gas. The signal processing of the measurement light path is based on gas absorption peak characteristic matching, which realizes accurate identification of gas type and quantitative calculation of concentration, and finally realizes safe, stable and accurate self-calibration and gas detection.

[0057] It can be seen that, in terms of safety, the use of non-toxic and non-corrosive interfering gas to replace the target gas that may be toxic or corrosive fills the reference light path, avoiding the risk of operators contacting dangerous gas, reducing the possibility of reference gas chamber corrosion, prolonging the service life of the device, and reducing the risk of leakage. In terms of stability, the negative feedback adjustment mechanism based on the change of the absorption peak of the interfering gas can calibrate the laser center wavelength in real time, ensuring that it always coincides with the strongest absorption peak of the target gas, avoiding the problem of decreased or failed detection sensitivity. 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, so that the absorption peak information extracted in the measurement light path can accurately distinguish the target gas and the interfering gas by comparison. Even in a multi-gas coexisting environment, the position and intensity of the different absorption peaks can be used to identify the gas type and accurately calculate the concentration, realizing the function of multi-gas detection.

[0058] In step 1, the interfering gas found in the target correlation band satisfies: the absorption intensity is greater than 1 / 20 of the target gas absorption intensity and is non-toxic and non-corrosive. This step limits the absorption intensity threshold of the interfering gas to ensure that the interfering gas produces a sufficiently significant absorption signal in the reference light path, making the absorption peak of the interfering gas easy to be accurately captured and identified by the photodetector, providing a clear reference benchmark for subsequent wavelength calibration, and avoiding the difficulty in distinguishing the characteristic peak due to weak absorption signal. Since the interfering gas and the target gas are in the same absorption band, and the absorption intensity satisfies the above threshold, the absorption characteristics of the interfering gas and the target gas form an effective correlation, and combined with the gas absorption peak reference data, the position, spacing and intensity ratio of the interfering gas absorption peak can be monitored to accurately reflect the deviation of the laser center wavelength, providing a reliable quantitative basis for negative feedback adjustment.

[0059] In the present application, the gas absorption peak reference data at least includes initial absorption peak information of the interference gas, target gas absorption peak information and absorption peak interval between the interference gas and the target gas; wherein the absorption peak information includes absorption peak position P, light absorption intensity I, and different absorption peak interval ΔP.

[0060] In the present application, the specific steps of adjusting the wavelength sweep range of the laser are as follows:

[0061] The first step is to set the laser drive current waveform, such as sawtooth wave or sawtooth wave superimposed on sine wave, to ensure that the wavelength can be continuously and uniformly swept;

[0062] The second step is to adjust the current drive circuit to change the laser drive current range, and then adjust the wavelength sweep range, so that the sweep range covers at least two absorption lines of the interference gas;

[0063] The third step is to fix the laser drive current range to fix the wavelength sweep range.

[0064] When the laser wavelength sweep range covers at least two absorption lines of the interference gas, the absorption spectrum of the interference gas and the target gas can be covered at the same time, and the principle is that the interference gas is selected in the target correlation waveband with a bandwidth of ±0.6 nm based on the target gas absorption waveband, and the absorption spectra of the two are in highly similar wavebands. The sweep range must contain the absorption spectrum of the target gas at the same time. At the same time, after adjusting the laser wavelength sweep range, the initial center wavelength of the laser is aligned with the strongest absorption peak of the target gas, so that the sweep range is an interval around the center wavelength.

[0065] In addition, the scanned wavelength interval completely covers at least two absorption lines of the interference gas, providing enough characteristic reference for coarse adjustment, because coarse adjustment needs to be realized by comparing the number of absorption peaks, adjacent intervals and intensity ratio, and the absorption spectrum of two or more interference gases can provide multiple characteristic points, avoiding misjudgment caused by a single absorption peak, and ensuring more accurate judgment of absorption characteristic matching during coarse adjustment.

[0066] During coarse adjustment, the temperature adjustment amount and the adjustment times are set, and the temperature adjustment amount is related to the two absorption peaks of the interference gas. The coarse adjustment amount cannot be too large to avoid missing the two absorption peaks of the interference gas; and the coarse adjustment amount cannot be too small to avoid low adjustment efficiency. By adjusting the laser temperature in two directions (i.e. temperature increasing and decreasing) and comparing the number of absorption peaks, the interval between adjacent absorption peaks and the absorption peak intensity ratio successively, according to the interference gas absorption characteristics recorded in the gas absorption peak reference data, only when the measured number of absorption peaks, the interval between adjacent absorption peaks and the absorption peak intensity ratio are consistent with the reference data, the coarse adjustment is completed, and it is ensured that the core characteristics of the interference gas absorption peak after coarse adjustment match the reference state.

[0067] Fine adjustment, based on the position of the first absorption peak of the interference gas, calculate the offset of the corresponding first absorption peak position in the initial absorption peak information, and determine the initial adjustment amount of the laser temperature according to the offset; through dynamic adjustment, the offset gradually decreases until the position of the first absorption peak of the interference gas returns to the initial position, at this time the overall position of the interference gas absorption peak matches the initial state, and then ensures that the center wavelength of the laser always coincides with the wavelength corresponding to the strongest absorption peak of the target gas.

[0068] In order to better understand the adjustment process, the following two operation examples are provided

[0069] Case 1: Adjustment process of a single interference gas (containing 2 absorption peaks)

[0070] Referring to Figure 3 , the abscissa represents the wavelength, in nm; the ordinate represents the absorption peak intensity, which is the ratio of light intensity before and after gas absorption, dimensionless. In the fixed wavelength sweep range, the range is set based on the target correlation wavelength defined by the target gas absorption wavelength, and at least covers 2 absorption lines of the interference gas; when the target gas absorption spectrum is initially coincided with the center wavelength of the laser, there is only one interference gas in the reference gas chamber, and the interference gas has two absorption peaks (A01, A02). In the initial state, the initial absorption peak information of the interference gas is recorded in sequence: the position of the absorption peak (A01) is P(A01), the intensity is I(A01), the position of the absorption peak (A02) is P(A02), the intensity is I(A02), and the distance D1 between adjacent absorption peaks is calculated P(A02)-P(A01), the intensity ratio K1 is I(A02) / I(A01), and the distance between the interference gas and the strongest absorption peak of the target gas is recorded. The above parameters are stored in the gas absorption peak reference data, refer to Figure 3 a).

[0071] When the center wavelength of the laser is offset, the interference gas absorption peak (A11) detected by the first photodetector does not match the gas absorption peak reference data (A01, A02), refer to Figure 3 b), which is that the number, distance and intensity ratio of the interference gas absorption peak are all different. At this time, the coarse adjustment is triggered:

[0072] Set the temperature adjustment amount, limit the number of adjustments N, N can be 10 times, 20 times, 30 times, etc., not limited here, the adjustment amount is fixed during the adjustment. First, lower the laser temperature, and after adjustment, compare the number of absorption peaks, the distance and the intensity ratio of the absorption peaks in the current absorption peak and the gas absorption peak reference data. If it does not reach a consistent state within the limited number of adjustments, the temperature will be adjusted back to the initial value, and the same adjustment amount will be used to reverse the adjustment of the laser temperature. Re-comparison until the number of absorption peaks, the distance and the intensity ratio in the measured results are consistent with the gas absorption peak reference data, specifically, the interference gas absorption peak has two absorption peaks (A21, A22) from only one absorption peak (A11), and the absorption peak distance P(A22)-P(A21) is equal to P(A02)-P(A01), and the intensity ratio I(A22) / I(A21) is equal to I(A02) / I(A01). Referring to Figure 3 c) in the reference

[0073] After coarse adjustment, fine adjustment is entered: taking the first absorption peak (A21) of the interference gas as the reference, calculate the position offset ΔP=P(A21)-P(A01) of the first absorption peak (A01) corresponding to the initial absorption peak information. According to the offset, determine the initial adjustment amount of fine adjustment, specifically, the offset change amount corresponding to the initial adjustment amount is equal to half of the offset ΔP.

[0074] First adjustment, if the absolute value of the offset ΔP increases, it means that the absorption peak (A21) is far from the position of the absorption peak (A01), and needs to be adjusted in the opposite direction; if the absolute value of the offset ΔP decreases, it means that the absorption peak (A21) is approaching the position of the absorption peak (A01), and the initial adjustment amount is maintained to continue adjustment, if the position of the absorption peak (A21) and the absorption peak (A01) can be overlapped, the fine adjustment is completed. If the absolute value of the offset ΔP increases after a certain adjustment in the process of decreasing, it means that the initial adjustment amount does not meet the adjustment accuracy requirement, reduce the initial adjustment amount to get the modified adjustment amount, use the modified adjustment amount β to adjust in the opposite direction, make the absolute value of the offset ΔP decrease again, until the position of the absorption peak (A21) and the absorption peak (A01) coincide, the fine adjustment is completed. At this time, all absorption peaks match the initial state as a whole, and the center wavelength of the laser coincides with the wavelength corresponding to the strongest absorption peak of the target gas.

[0075] Case 2: Adjustment process of multiple interference gases (containing multiple absorption peaks)

[0076] Referring to Figure 4In the fixed wavelength sweep range, when the target gas absorption spectrum initially coincides with the laser center wavelength, there are two interfering gases in the reference gas chamber: the first gas has three absorption peaks (A01, A02, A03), and the second gas has one absorption peak (B). In the initial state, the initial absorption peak information of each interfering gas is recorded in sequence: the position, intensity of each peak, and the distance between different absorption peaks of the interfering gas, the distance between the absorption peaks of the interfering gas and the target gas, and the intensity ratio are calculated, and the above parameters are stored in the gas absorption peak reference data. Figure 4 a) in the reference.

[0077] When the laser center wavelength deviates, the absorption peaks detected by the first photodetector are compared with the gas absorption peak reference data, and it is found that the number of absorption peaks and the intensity ratio of absorption peaks remain unchanged, and only the overall position deviates, referring to b) and c) in the reference. Figure 4 b) and c) in the reference, so no coarse adjustment is needed, and fine adjustment is directly entered. Figure 4 b) and c) in the reference are two deviation cases of the target gas absorption spectrum and the laser center wavelength.

[0078] The fine adjustment takes the first absorption peak (A21) or (A31) of the first interfering gas as the reference to calculate the position deviation P(A21) - P(A01) or P(A31) - P(A01) of the corresponding absorption peak (A01) in the initial absorption peak information. As in the above fine adjustment step, the position deviation 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 which point all absorption peaks match the initial state, the laser center wavelength coincides with the wavelength corresponding to the strongest absorption peak of the target gas, and the self-calibration is completed.

[0079] In the present application, the negative feedback regulation is performed after the device is powered on and preheated each time, which can effectively correct the cumulative wavelength deviation caused by changes in environmental temperature, static drift of device parameters, etc. If the deviation is not corrected in time, the laser center wavelength will deviate from the strongest absorption peak of the target gas in the initial stage of power-on, directly affecting the detection accuracy.

[0080] In addition, because the laser gas sensor slowly drifts during long-term operation, if the cumulative drift reaches a certain level, it will cause a decrease in absorption peak detection sensitivity or even a characteristic peak recognition error. Therefore, the negative feedback regulation is performed at regular intervals during normal operation of the device, for example, after the device has been running for 1 hour, 2 hours, …, 24 hours. Periodic calibration can timely capture and correct the deviation, avoiding progressive wavelength deviation caused by factors such as continuous heating of the laser, fluctuations in environmental temperature and humidity, real-time drift of electrical parameters, etc. during operation.

[0081] In step 5, the signal received by the second photodetector is analyzed to extract the position and intensity of the gas absorption peak; the reference data of the gas absorption peak is compared and analyzed with the actual test gas absorption peak, the type of gas (target gas or interfering gas) is determined by the position of the actual test gas absorption peak, and the concentration of the gas is calculated by the intensity of the actual test gas absorption peak. If the target gas and the interfering gas exist at the same time in the measurement cell / open space, a sawtooth waveform has multiple gas absorption peaks, and the corresponding gas concentration is calculated by the position and intensity of different absorption peaks one by one to realize the multi-gas detection function.

[0082] As shown in Figure 2 The application also provides a gas detection device capable of self-calibrating the central wavelength of the laser, mainly composed of a single-chip microcomputer (MCU), a current driving circuit, a temperature control circuit, a laser, a fiber beam splitter, a fiber collimator, a reference cell, a first photodetector (i.e. photodetector 1), a second photodetector (i.e. photodetector 2), and two amplification and filtering circuits. Each component works together to realize the above-mentioned gas detection method.

[0083] Among them, the MCU serves as the core control and data processing unit, which drives the laser through controlling the temperature control circuit and the current driving circuit, and then adjusts the central wavelength and wavelength sweep range of the laser emitted laser. The temperature control circuit is mainly responsible for accurately adjusting the central wavelength of the laser, and the current driving circuit is used to adjust the wavelength sweep range to ensure that the laser can cover the absorption spectrum of the target gas and the interfering gas. The laser emitted by the laser is first split into two paths by the fiber beam splitter arranged at the light emitting end of the laser, and the splitting ratio is designed to be that the light intensity of the measurement light path accounts for more than the reference light path, which can be 9.0:1.0, 9.2:0.8, 9.3:0.7, 9.4:0.6, 9.9:0.1 or other similar ratios. Because the measurement light path is an external light path, it needs stronger light intensity to cope with possible light loss, while the reference light path is an internal light path with lower light intensity requirement. This ratio setting can ensure the stability of the reference light path signal while ensuring that the measurement light path has enough light intensity for accurate detection.

[0084] The first laser after beam splitting is directed to the reference gas chamber, the reference gas chamber is filled with an interference gas selected from the target correlation wave band of ±0.6 nm based on the target gas absorption wave band, the interference gas is non-toxic and non-corrosive, and replaces the toxic or corrosive target gas, which not only avoids corrosion of the reference gas chamber and prolongs the service life, but also eliminates the safety hazard of contact with dangerous gas for production and operation personnel; the laser passing through the reference gas chamber is received by the first photodetector, and the output signal of the first photodetector is transmitted to the MCU after being processed by the corresponding first amplification filter circuit, the MCU obtains the current absorption peak information of the interference gas by analyzing the signal, and compares the signal with the stored initial absorption peak information and the gas absorption peak reference data to determine whether the center wavelength of the laser drifts, and if the center wavelength of the laser drifts, the temperature control circuit is used to perform negative feedback adjustment to ensure that the center wavelength of the laser always coincides with the wavelength corresponding to the strongest absorption peak of the target gas, thereby realizing the self-calibration function.

[0085] The second laser after beam splitting is collimated by the optical fiber collimator and then directed to the measurement gas chamber or open space, the transmission path of the second laser is flexible, the second photodetector can receive the laser signal in a straight-through mode, a one-time reflection mode or a multiple reflection mode, and the second photodetector can be in a fixed mode, a reflection mode or a remote mode, thereby adapting to different detection scenarios; the laser passing through the measurement area is received by the second photodetector, and the output signal of the second photodetector is transmitted to the MCU after being processed by the second amplification filter circuit, the MCU analyzes the absorption peak in the signal in combination with the stored gas absorption peak reference data, determines the type of gas according to the position of the absorption peak, and calculates the concentration of the gas according to the Lambert-Beer law according to the intensity of the absorption peak, so that even if the target gas and the interference gas exist in the measurement area at the same time, the accurate detection of multiple gases can be realized by extracting the strongest absorption peak of each gas.

[0086] The technical features of the above embodiments can be combined in any manner, and to make the description concise, not all possible combinations of the technical features in the above embodiments are described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the description.

[0087] The above embodiments only express several implementation manners of the present application, the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled persons in the art, some modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to 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. The steps for adjusting the center wavelength of the laser using negative feedback include: 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.

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, 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.

7. The gas detection method for a self-calibrating laser center wavelength according to claim 1, 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.

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

9. 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 8 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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