A laser radar frequency locking method for gas detection

Abstract

The invention discloses a laser radar frequency locking method for gas detection, relates to the technical field of frequency locking, and is used to solve the problems of excessive collection and untimely adjustment of the locking range of the laser radar when the frequency is stroboscopic. The method collects the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference value, laser coverage gas concentration value difference and historical wavelength adjustment frequency calculated by the wavelength frequency change amplitude, obtains the locking evaluation coefficient and compares it with the locking threshold, obtains the comparison result and statistically analyzes it, sets the adjustment range rule by the number of comparison results analyzed by statistics and sorts all the locking evaluation coefficients from large to small, obtains the locking range adjustment result, and analyzes it with a PID control formula to obtain the PID gain coefficient difference and the degree of alignment of the wavelength with the target absorption peak position, uses fuzzy logic to determine the laser radar frequency adjustment result, reduces the necessity of frequent adjustment, and saves computing resources.

Description

Technical Field

[0001] The present invention relates to the technical field of frequency locking, and more specifically, to a laser radar frequency locking method for gas detection. Background Art

[0002] Differential absorption lidar is a lidar technology designed specifically for gas detection, in which laser frequency locking is crucial. The output wavelength of the laser needs to be precisely aligned with the absorption peak of the gas, and the lidar frequency is locked to ensure that the laser can effectively detect the presence and concentration of the gas.

[0003] The prior art has the following deficiencies:

[0004] At present, the frequency locking of the laser radar based on the gas pool method makes the frequency of the laser always keep consistent with the absorption peak of the gas in the gas pool. Since the absorption peak is a specific value, and the frequency flickers due to gas concentration and temperature, that is, the frequency jitters within a certain range of the absorption peak, it is not impossible to lock. Therefore, the limited locking range is adjusted, but multiple acquisitions and adjustments will waste computing resources, and too many subtle adjustments will also cause the frequency to flicker out of the set range of the absorption peak. Therefore, a laser radar frequency locking method for gas detection is proposed.

[0005] The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not constitute the prior art that is already known to one of ordinary skill in the art. Summary of the invention

[0006] In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides a laser radar frequency locking method for gas detection, which solves the problems raised in the above-mentioned background technology by applying different product inspection methods.

[0007] To achieve the above object, the present invention provides the following technical solution, a laser radar frequency locking method for gas detection, comprising:

[0008] S1: Collect laser wavelength change information, historical adjustment information and environmental information, and obtain the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference, laser coverage gas concentration value difference and historical wavelength adjustment frequency through data processing;

[0009] S2: Obtain the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference, laser coverage gas concentration value difference and historical wavelength adjustment frequency, establish a data weighted analysis model, and obtain the locking evaluation coefficient;

[0010] S3: Obtain the lock evaluation coefficient and compare it with the lock threshold, obtain the comparison result and perform statistical analysis, set the adjustment range rule by the number of comparison results analyzed statistically and the sorting of all the lock evaluation coefficients from large to small, obtain the lock range adjustment result, and set the radar frequency lock range according to the lock range adjustment result;

[0011] S4: Obtain the adjustment amplitude and PID control formula in the locking range adjustment result, collect the current frequency locking state data, and obtain the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position;

[0012] S5: Obtain the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position and use fuzzy logic to determine the lidar frequency adjustment result.

[0013] In a preferred embodiment, the laser wavelength change information includes the current frequency lock deviation and the absorption rate difference; the historical adjustment information includes the historical wavelength adjustment frequency; the environmental information includes the gas Doppler broadening difference value and the laser coverage gas concentration value difference; the current frequency lock deviation is obtained by calculating the ratio of the wavelength frequency change amplitude to the PID control formula ; Where i is the i-th collection point;

[0014] By calculating the absorbance of the two wavelengths, the absorbance difference is obtained by subtracting the absorbance of the offline wavelength from the absorbance of the online wavelength. ;

[0015] The Doppler broadening difference value of the gas is calculated according to the Doppler broadening formula based on the gas pool state at the previous acquisition point and the gas pool state at the current acquisition point. ;

[0016] According to the Lambert-Beer law, the laser coverage gas concentration value of the previous acquisition point and the laser coverage gas concentration value of the current acquisition point are obtained and subtracted to obtain the laser coverage gas concentration value difference ;

[0017] The historical wavelength adjustment frequency is calculated by calculating the ratio of the number of wavelength adjustments at each collection point to the time interval between the collection points. .

[0018] In a preferred embodiment, the current frequency lock deviation is obtained. , Absorption rate difference , gas Doppler broadening difference , Laser coverage gas concentration value difference and historical wavelength adjustment frequency , generate the lock assessment coefficient , according to the formula:

[0019]

[0020] In the formula, To lock the evaluation coefficient, , , , as well as are respectively the current frequency lock deviation, the absorption rate difference, the gas Doppler broadening difference value, the laser coverage gas concentration value difference and the preset proportional coefficient of the historical wavelength adjustment frequency, and , , , as well as Both are greater than 0.

[0021] In a preferred embodiment, after the locking evaluation coefficient is obtained, the locking evaluation coefficient is compared and analyzed with the continuously iterated locking threshold;

[0022] If the lock evaluation coefficient is greater than or equal to the lock threshold, the lidar frequency lock range of the current acquisition point is marked as a loose range, and a reduction signal is generated;

[0023] If the lock evaluation coefficient is less than the lock threshold, the lidar frequency lock range of the current acquisition point is marked as a relaxed range, and an increase signal is generated.

[0024] In a preferred embodiment, the number of comparison results of all locking evaluation coefficients and locking thresholds is counted, that is, the locking evaluation coefficients marked as "loose range" and "relaxed range", and all locking evaluation coefficient values ​​are sorted from large to small, and the maximum locking evaluation coefficient is ranked. Compare with the accumulated value of the remaining lock assessment coefficient, that is ;

[0025] Setting adjustment range rules, specifically, if the maximum value of the locking evaluation coefficient is greater than or equal to the accumulated value of the remaining locking evaluation coefficients, the current laser radar frequency locking range is reduced to a first reduced range;

[0026] If the maximum value of the locking evaluation coefficient is less than the accumulated value of the remaining locking evaluation coefficients, the current laser radar frequency locking range is reduced to the second reduced range or the third reduced range;

[0027] Further, if the number marked as "loose range" is greater than or equal to the number of "relaxed range", the current laser radar frequency locking range is narrowed to the second narrowed range; otherwise, the current laser radar frequency locking range is narrowed to the third narrowed range;

[0028] Furthermore, the minimum value of the evaluation coefficient will be locked Compare with the subtraction value of the remaining lock-in assessment coefficient, as well as the number of "loose range" and the number of "relaxed range", and set the corresponding "first increase range", "second increase range" and "third increase range".

[0029] In a preferred embodiment, the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position are obtained according to the adjustment amplitude in the locking range adjustment result and the PID control formula;

[0030] The PID gain coefficient difference is obtained by respectively subtracting the proportional gain coefficient, integral gain coefficient and differential gain coefficient in the PID control formula before the lock range adjustment from the proportional gain coefficient, integral gain coefficient and differential gain coefficient in the PID control formula after the change, and adding the proportional gain coefficient difference, integral gain coefficient difference and differential gain coefficient difference.

[0031] The degree of alignment between the wavelength and the target absorption peak position is obtained by subtracting the absolute value of the wavelength at which the gas has the maximum absorption capacity for laser of a specific wavelength from the wavelength actually emitted by the laser.

[0032] In a preferred embodiment, the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position are defined as input variables and divided into different fuzzy sets respectively;

[0033] The lidar frequency adjustment result is defined as the output variable and divided into fuzzy sets;

[0034] Fuzzy rules are formulated to describe the impact of the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position on the lidar frequency adjustment result;

[0035] Fuzzy reasoning is performed based on fuzzy rules to determine the lidar frequency adjustment plan.

[0036] Technical effects and advantages of the present invention:

[0037] 1. The present invention obtains the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference value, laser coverage gas concentration value difference and historical wavelength adjustment frequency by collecting the wavelength frequency change amplitude, obtains the locking evaluation coefficient and compares it with the locking threshold, obtains the comparison result and performs statistical analysis, sets the adjustment range rule through the number of comparison results obtained by statistical analysis and the sorting of all locking evaluation coefficients from large to small, obtains the locking range adjustment result, dynamically adjusts the locking range, reduces the number of laser radar frequency adjustment times to a certain extent, saves computing resources, and further enhances the adaptability of the feedback control system.

[0038] 2. The present invention obtains the adjustment amplitude and PID control formula in the locking range adjustment result, obtains the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position, and uses fuzzy logic to determine the laser radar frequency adjustment result, thereby reducing the necessity of frequent adjustments and the number of laser radar operations, which helps to improve the measurement accuracy of gas concentration while saving computing resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The present invention is a method flow chart of a laser radar frequency locking method for gas detection. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The system preparation includes a narrow linewidth laser, a gas pool (filled with the gas to be tested and ensuring that the gas concentration is within the measurable range), a highly sensitive photodetector to detect the change in light intensity after the laser passes through the gas pool, and a feedback control system that collects the above parameter configurations for feedback adjustment;

[0042] Based on the above feedback control system, the present invention develops a laser radar frequency locking method for gas detection, which re-divides the setting range of the absorption peak value according to the current frequency locking deviation and the degree of absorption peak change through the frequency change of the emitted laser wavelength and historical adjustment information; Example 1

[0043] See also Figure 1 , a lidar frequency locking method for gas detection, the specific operation process is as follows:

[0044] S1: Collect laser wavelength change information, historical adjustment information and environmental information, and obtain the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference, laser coverage gas concentration value difference and historical wavelength adjustment frequency through data processing;

[0045] Among them, the laser wavelength change information includes the current frequency locking deviation and the absorption rate difference; the historical adjustment information includes the historical wavelength adjustment frequency; the environmental information includes the gas Doppler broadening difference value and the laser coverage gas concentration value difference;

[0046] The current frequency lock deviation refers to the difference between the current output frequency of the laser and the absorption peak frequency of the target gas. The acquisition logic is to calculate the current frequency lock deviation by the ratio of the wavelength frequency change amplitude and the PID control formula. ;

[0047] Specifically, the wavelength-frequency variation amplitude refers to the offset range of the wavelength or frequency output by the laser relative to the target absorption peak position, that is, the variation of the laser frequency during the adjustment process. The acquisition logic is to determine the absorption peak wavelength of the target gas, use a wavelength meter to measure the laser output wavelength in real time, and subtract the absorption peak wavelength of the target gas from the laser output wavelength to obtain the wavelength-frequency variation amplitude. ; Where i is the i-th collection point;

[0048] There is no limit on the frequency of the real-time measurement of the wavelength meter. It is set by the experimenter based on the historical wavelength change frequency and its adjustment frequency, and is not limited here.

[0049] Specifically, the wavelength frequency change amplitude is calculated by ratio with the PID control formula, wherein the PID control formula is a feedback controller, which realizes comprehensive control of system behavior through three different control strategies (proportional, integral and differential). It can be understood by those skilled in the art that when the change amplitude is not transmitted to the calculation PID control formula through data, it is impossible to verify that the adjustment result and the change amplitude are the same, so the wavelength frequency change amplitude is calculated by ratio with the PID control formula to obtain the current frequency locking deviation; specifically, the PID control formula is:

[0050]

[0051] In the formula, Indicates the amount of adjustment made to the laser output wavelength, They are proportional gain coefficient, integral gain coefficient and differential gain coefficient respectively; is the error, is the rate of change of error with time or number of acquisitions, It is the accumulation of error values ​​at all times before the current time;

[0052] Absorption rate difference refers to the gas's ability to absorb light of different wavelengths when light passes through the gas. That is, for a specific gas, certain wavelengths of light (usually wavelengths corresponding to the gas's molecular vibration or rotation energy level) will be significantly absorbed, while other wavelengths of light will not. In differential absorption radar, two laser beams with different wavelengths are usually set, one of which is locked at the gas's absorption peak (called the online wavelength) and the other is deviated from the absorption peak (called the offline wavelength).

[0053] Specifically, the gas has obvious absorption of the laser at the online wavelength, but little or no absorption of the laser at the offline wavelength. The difference in absorption intensity after the laser passes through the gas at the two wavelengths (online and offline) is the difference in absorption rate. The logic for obtaining the difference is to calculate the absorption rates of the two wavelengths and subtract the absorption rate of the offline wavelength from the absorption rate of the online wavelength to obtain the absorption rate difference. ; The specific formula for calculating wavelength absorbance is as follows:

[0054]

[0055] in, is the absorption rate, is the incident light intensity, that is, the initial light intensity of the laser before passing through the gas medium, is the transmitted light intensity, i.e., the remaining light intensity after the laser passes through the gas;

[0056] The gas Doppler broadening difference value refers to the broadening phenomenon of the absorption spectrum line caused by the thermal motion of gas molecules. Specifically, the higher the temperature of the gas, the faster the molecular motion speed, the wider the absorption spectrum line, and the frequency locking of the laser deviates from the actual gas absorption peak. The acquisition logic is to calculate the gas Doppler broadening difference value according to the Doppler broadening formula through the gas pool state at the previous acquisition point and the gas pool state at the current acquisition point. ; The specific formula is as follows:

[0057]

[0058] in, is the gas Doppler broadening difference, is the center frequency of the laser, is the Boltzmann constant, is the gas temperature at the last sampling point, is the gas temperature at the current collection point, is the mass of the gas molecule, is the speed of light;

[0059] It should be noted that the gas Doppler broadening difference value expression is to further analyze the influence of gas state change on laser absorption characteristics by comparing the Doppler broadening of the gas under different acquisition points, so as to determine the locking status of the lidar frequency;

[0060] The difference in laser coverage gas concentration value refers to the change in gas concentration detected by the laser at different collection points. The acquisition logic is to obtain the laser coverage gas concentration value of the previous collection point and the laser coverage gas concentration value of the current collection point through the difference in absorption rate according to the Lambert-Beer law, and then subtract them to obtain the laser coverage gas concentration value difference. ;

[0061] Among them, the specific expression of Lambert-Beer law is:

[0062] In the formula, is the light intensity after passing through the medium, is the initial intensity of the incident light, is the absorption coefficient of the gas, which reflects the gas's ability to absorb light of a specific wavelength. is the gas concentration, is the optical path length;

[0063] Furthermore, according to the Lambert-Beer law, there is a linear relationship between the absorption rate and the gas concentration and the propagation path length of the light in the gas; therefore, by measuring the difference in absorption rate at the online and offline wavelengths, the gas concentration value can be inferred. The specific formula is as follows:

[0064]

[0065] in, is the path length through the gas, is the absorption coefficient of the target gas at the wavelength used, is the difference in absorption rate, that is, the difference in absorption rate ;

[0066] The historical wavelength adjustment frequency refers to the rate at which the wavelength is adjusted in order to maintain the locked state with the target absorption peak during the operation of the laser. The acquisition logic is to calculate the historical wavelength adjustment frequency by the ratio of the number of wavelength adjustments at each acquisition point to the time interval between the acquisition points. ;

[0067] Among them, the time interval of the collection points is determined by the experimenter according to the specific wavelength adjustment amplitude and its frequency locking time. Generally, the higher the frequency locking time, the longer the time interval of the collection points is to avoid wasting resources.

[0068] S2: Obtain the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference, laser coverage gas concentration value difference and historical wavelength adjustment frequency, establish a data weighted analysis model, and obtain the locking evaluation coefficient;

[0069] Among them, the data weighted analysis model refers to a weighted analysis model that generates a lock-in assessment coefficient through weighted calculation;

[0070] Get the current frequency lock deviation , Absorption rate difference , gas Doppler broadening difference , Laser coverage gas concentration value difference and historical wavelength adjustment frequency , generate the lock assessment coefficient , according to the formula:

[0071]

[0072] In the formula, To lock the evaluation coefficient, , , , as well as are respectively the current frequency lock deviation, the absorption rate difference, the gas Doppler broadening difference value, the laser coverage gas concentration value difference and the preset proportional coefficient of the historical wavelength adjustment frequency, and , , , as well as All are greater than 0;

[0073] Among them, the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference, laser coverage gas concentration value difference and historical wavelength adjustment frequency are all data manifestations that directly express the size of the laser radar locking range;

[0074] It can be seen from the above formula that the larger the current frequency locking deviation, the difference in gas Doppler broadening, the difference in laser coverage gas concentration value, and the historical wavelength adjustment frequency, the larger the frequency locking state of the system is, the more the frequency deviates from the target absorption peak, the larger the gas concentration changes, the significant Doppler effect, and the system frequently adjusts the wavelength. The larger the locking evaluation coefficient, the looser the locking range, and the need to narrow the locking range. Conversely, the greater the difference in absorption rate, the smaller the change evaluation coefficient.

[0075] S3: Obtain the lock evaluation coefficient and compare it with the lock threshold, obtain the comparison result and perform statistical analysis, set the adjustment range rule by the number of comparison results analyzed statistically and the sorting of all the lock evaluation coefficients from large to small, obtain the lock range adjustment result, and set the radar frequency lock range according to the lock range adjustment result;

[0076] The logic for obtaining the lock threshold is to collect a set of historical lidar frequency lock ranges, divide the data set into a training set and a test set, set the evaluation index and clustering algorithm, and in each round of cross-validation, train the model on the training set and evaluate the model performance on the test set. Then, adjust the lock threshold based on the performance of the validation set. Therefore, the lock threshold is constantly updated.

[0077] In the present invention, clustering algorithm is a type of unsupervised learning algorithm, which is used to divide the data points in the data set into groups or clusters with similarities; a common one is K-means clustering, which divides the data points in the data set into K clusters, so that the distance between the data point of each curve and the center point (centroid) of the cluster to which it belongs is minimized, and finally the effect of the adjusted locking threshold is measured by the Euclidean distance, so as to set the locking threshold;

[0078] After obtaining the lock assessment coefficient, compare and analyze the lock assessment coefficient with the continuously iterated lock threshold;

[0079] If the lock evaluation coefficient is greater than or equal to the lock threshold, the lidar frequency lock range of the current acquisition point is marked as a loose range, and a reduction signal is generated;

[0080] If the lock evaluation coefficient is less than the lock threshold, the lidar frequency lock range of the current acquisition point is marked as a relaxed range, and an increase signal is generated;

[0081] Count the number of comparison results of all lock assessment coefficients and lock thresholds, that is, the lock assessment coefficients marked as "loose range" and "relaxed range", sort all lock assessment coefficient values ​​from large to small, and put the maximum lock assessment coefficient Compare with the accumulated value of the remaining lock assessment coefficient, that is ;

[0082] Setting adjustment range rules, specifically, if the maximum value of the locking evaluation coefficient is greater than or equal to the accumulated value of the remaining locking evaluation coefficients, the current laser radar frequency locking range is reduced to a first reduced range;

[0083] If the maximum value of the locking evaluation coefficient is less than the accumulated value of the remaining locking evaluation coefficients, the current laser radar frequency locking range is reduced to the second reduced range or the third reduced range;

[0084] Further, if the number marked as "loose range" is greater than or equal to the number of "relaxed range", the current laser radar frequency locking range is narrowed to the second narrowed range; otherwise, the current laser radar frequency locking range is narrowed to the third narrowed range;

[0085] It should be noted that the above-mentioned "first reduction range", "second reduction range" and "third reduction range" are set by the experimenter based on the historical laser radar frequency locking range adjustment results. Specifically, for example, the "first reduction range" corresponds to a range reduction of 25%, the "second reduction range" corresponds to a range reduction of 18%, and the "third reduction range" corresponds to a range reduction of 8%;

[0086] Furthermore, the minimum value of the evaluation coefficient will be locked Compare with the subtraction value of the remaining lock assessment coefficient, as well as the number of "loose range" and the number of "relaxed range", set the "first increase range", "second increase range" and "third increase range" corresponding to the above, and no further details will be given here;

[0087] According to the set adjustment range rule, a locking range adjustment result is obtained, and the radar frequency locking range is set according to the locking range adjustment result;

[0088] The present invention collects the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference value, laser coverage gas concentration value difference and historical wavelength adjustment frequency calculated by wavelength frequency variation amplitude, obtains the locking evaluation coefficient and compares it with the locking threshold, obtains the comparison result and performs statistical analysis, sets the adjustment range rule through the number of comparison results of statistical analysis and the sorting of all locking evaluation coefficients from large to small, obtains the locking range adjustment result, dynamically adjusts the locking range, reduces the number of laser radar frequency adjustment times to a certain extent, saves computing resources, and further enhances the adaptability of the feedback control system.

[0089] Example 2

[0090] Embodiment 1 of the present invention focuses on the example of collecting the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference value, laser coverage gas concentration value difference and historical wavelength adjustment frequency calculated by the wavelength frequency change amplitude, obtaining the locking evaluation coefficient and comparing it with the locking threshold, obtaining the comparison result and statistically analyzing it, setting the adjustment range rule by the number of comparison results of the statistical analysis and the sorting of all the locking evaluation coefficients from large to small, and obtaining the operation strategy of the locking range adjustment result; however, in Embodiment 1, the number of laser radar frequency adjustments is reduced only from the perspective of limiting the locking range. Obviously, the number of laser radar frequency adjustments is usually set to be adjusted according to the locking deviation value, but due to the change of the locking range, too many laser radar frequency adjustments may cause the adjustment to be outside the locking range, thereby causing the laser radar frequency to be unable to be locked; in view of the above problems, Embodiment 2 of the present invention is further refined;

[0091] S4: Obtain the adjustment amplitude and PID control formula in the locking range adjustment result, collect the current frequency locking state data, and obtain the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position;

[0092] Specifically, the adjustment range in the locking range adjustment result includes the adjustment range of the locking range in the above-mentioned embodiment 1, such as "the first reduction range", "the second reduction range", "the third reduction range", etc. Due to the change of the locking range, the PID gain coefficient set in the PID controller is also changed accordingly, and there is a PID gain coefficient difference. The specific gain coefficients are the proportional gain coefficient, the integral gain coefficient and the differential gain coefficient. The PID controller and the locking range change have been described in embodiment 1 and will not be repeated here.

[0093] The logic for obtaining the PID gain coefficient difference is to subtract the PID gain coefficient changed with the lock range from the PID gain coefficient calculated by the PID control formula before the lock range is adjusted. Specifically, the proportional gain coefficient, integral gain coefficient and differential gain coefficient of the PID control formula before the lock range is adjusted are subtracted from the changed proportional gain coefficient, integral gain coefficient and differential gain coefficient, and the proportional gain coefficient difference, integral gain coefficient difference and differential gain coefficient difference are added to obtain the PID gain coefficient difference;

[0094] The degree of alignment between the wavelength and the target absorption peak position refers to the degree of deviation between the current output wavelength of the laser radar and the absorption peak wavelength of the target gas. The acquisition logic is to subtract the absolute value of the wavelength at which the gas has the maximum absorption capacity for a specific wavelength laser from the actual wavelength emitted by the laser to obtain the degree of alignment between the wavelength and the target absorption peak position. Specific influencing factors include environmental changes and changes in the locking range.

[0095] S5: Obtain the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position and use fuzzy logic to determine the laser radar frequency adjustment result;

[0096] For example, "High", "Low", and "Medium" are for high, medium, and low judgments of the PID gain coefficient difference, and "Many", "Less", and "Average" are for high, medium, and low judgments of the degree of alignment between the wavelength and the target absorption peak position;

[0097] Formulate a set of fuzzy rules to describe the impact of different input variables on output variables. The definition of rules can be based on professional knowledge or obtained through data analysis and experiments. For example:

[0098] The PID gain coefficient difference is marked as X, the degree of alignment between the wavelength and the target absorption peak position is marked as U, and the lidar frequency adjustment result is marked as C_results;

[0099] Then we can define:

[0100] Rule 1: IF (X is High) AND (U is Less) THEN (C_results is Low)

[0101] Rule 2: IF (U is Low) AND (U is Many) THEN (C_results is High) ...

[0103] Perform fuzzy reasoning based on fuzzy rules to determine the laser radar frequency adjustment plan;

[0104] It should be noted that the division of fuzzy sets can be adjusted according to actual conditions. For example, although this embodiment takes three fuzzy sets as an example, it can actually be divided into more than three sets to facilitate better accurate adjustment according to different similarities.

[0105] Specifically, when the LiDAR frequency adjustment result is calibrated as "High", the number of adjustments increases by 20% based on the current acquisition point. Conversely, when the LiDAR frequency adjustment result is calibrated as "Low", the number of adjustments decreases by 40% based on the current acquisition point.

[0106] Furthermore, for the judgment of the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position, the threshold can be set according to the actual situation for judgment. For example, when the PID gain coefficient difference exceeds 60%, it is marked as "High", and when the degree of alignment between the wavelength and the target absorption peak position is higher than 76%, it is marked as "Many", etc., which will not be elaborated here;

[0107] The present invention obtains the adjustment amplitude and PID control formula in the locking range adjustment result, obtains the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position, and uses fuzzy logic to determine the laser radar frequency adjustment result, thereby reducing the necessity of frequent adjustments and the number of laser radar operations, which helps to improve the measurement accuracy of gas concentration while saving computing resources.

[0108] The above formulas are all dimensionless and numerical calculations. The formula is a formula for the most recent real situation obtained by collecting a large amount of data and performing software simulation. The preset parameters in the formula are set by technicians in this field according to actual conditions.

[0109] The above embodiments can be implemented in whole or in part by software, hardware, firmware or any other combination. When implemented by software, the above embodiments can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from one website site, computer, server or data center to another website site, computer, server or data center by wired or wireless (e.g., infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that contains one or more available media sets. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium. The semiconductor medium can be a solid-state hard disk.

[0110] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0111] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0112] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0113] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0114] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0115] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0116] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage media include: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROM), random access memories (RAM), magnetic disks or optical disks.

[0117] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A laser radar frequency locking method for gas detection, characterized in that: include: S1: Collect laser wavelength change information, historical adjustment information and environmental information, and obtain the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference, laser coverage gas concentration value difference and historical wavelength adjustment frequency through data processing; S2: Obtain the current frequency locking deviation, absorption rate difference, gas Doppler broadening difference, laser coverage gas concentration value difference and historical wavelength adjustment frequency, establish a data weighted analysis model, and obtain the locking evaluation coefficient; S3: Obtain the lock evaluation coefficient and compare it with the lock threshold, obtain the comparison result and perform statistical analysis, set the adjustment range rule by the number of comparison results analyzed statistically and the sorting of all the lock evaluation coefficients from large to small, obtain the lock range adjustment result, and set the radar frequency lock range according to the lock range adjustment result; S4: Obtain the adjustment amplitude and PID control formula in the locking range adjustment result, collect the current frequency locking state data, and obtain the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position; S5: Obtain the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position and use fuzzy logic to determine the lidar frequency adjustment result.

2. A laser radar frequency locking method for gas detection according to claim 1, characterized in that: Laser wavelength change information includes the current frequency lock deviation and absorption rate difference; historical adjustment information includes historical wavelength adjustment frequency; environmental information includes gas Doppler broadening difference value and laser coverage gas concentration value difference; the current frequency lock deviation is obtained by calculating the ratio of wavelength frequency change amplitude and PID control formula ; Where i is the i-th collection point; By calculating the absorbance of the two wavelengths, the absorbance difference is obtained by subtracting the absorbance of the offline wavelength from the absorbance of the online wavelength. ; The Doppler broadening difference value of the gas is calculated according to the Doppler broadening formula based on the gas pool state at the previous acquisition point and the gas pool state at the current acquisition point. ; According to the Lambert-Beer law, the laser coverage gas concentration value of the previous acquisition point and the laser coverage gas concentration value of the current acquisition point are obtained and subtracted to obtain the laser coverage gas concentration value difference ; The historical wavelength adjustment frequency is calculated by calculating the ratio of the number of wavelength adjustments at each collection point to the time interval between the collection points. .

3. A laser radar frequency locking method for gas detection according to claim 2, characterized in that: Get the current frequency lock deviation , Absorption rate difference , gas Doppler broadening difference , Laser coverage gas concentration value difference and historical wavelength adjustment frequency , generate the lock assessment coefficient , according to the formula: ； In the formula, To lock the evaluation coefficient, , , , as well as are respectively the current frequency lock deviation, the absorption rate difference, the gas Doppler broadening difference value, the laser coverage gas concentration value difference and the preset proportional coefficient of the historical wavelength adjustment frequency, and , , , as well as Both are greater than 0.

4. A laser radar frequency locking method for gas detection according to claim 3, characterized in that: After obtaining the lock assessment coefficient, compare and analyze the lock assessment coefficient with the continuously iterated lock threshold; If the lock evaluation coefficient is greater than or equal to the lock threshold, the lidar frequency lock range of the current acquisition point is marked as a loose range, and a reduction signal is generated; If the lock evaluation coefficient is less than the lock threshold, the lidar frequency lock range of the current acquisition point is marked as a relaxed range, and an increase signal is generated.

5. A laser radar frequency locking method for gas detection according to claim 4, characterized in that: Count the number of comparison results of all lock assessment coefficients and lock thresholds, that is, the lock assessment coefficients marked as "loose range" and "relaxed range", sort all lock assessment coefficient values ​​from large to small, and put the lock assessment coefficient with the maximum value Compare with the accumulated value of the remaining lock assessment coefficient, that is ; Setting adjustment range rules, specifically, if the maximum value of the locking evaluation coefficient is greater than or equal to the accumulated value of the remaining locking evaluation coefficients, the current laser radar frequency locking range is reduced to a first reduced range; If the maximum value of the locking evaluation coefficient is less than the accumulated value of the remaining locking evaluation coefficients, the current laser radar frequency locking range is reduced to the second reduced range or the third reduced range; Further, if the number marked as "loose range" is greater than or equal to the number of "relaxed range", the current laser radar frequency locking range is narrowed to the second narrowed range; otherwise, the current laser radar frequency locking range is narrowed to the third narrowed range; Furthermore, the minimum value of the evaluation coefficient will be locked Compare with the subtraction value of the remaining lock assessment coefficient, as well as the number of "loose range" and the number of "relaxed range", and set the corresponding "first increase range", "second increase range" and "third increase range".

6. The laser radar frequency locking method for gas detection according to claim 1, characterized in that: According to the adjustment amplitude in the locking range adjustment result and the PID control formula, the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position are obtained; The PID gain coefficient difference is obtained by respectively subtracting the proportional gain coefficient, integral gain coefficient and differential gain coefficient in the PID control formula before the lock range adjustment from the proportional gain coefficient, integral gain coefficient and differential gain coefficient in the PID control formula after the change, and adding the proportional gain coefficient difference, integral gain coefficient difference and differential gain coefficient difference. The degree of alignment between the wavelength and the target absorption peak position is obtained by subtracting the absolute value of the wavelength at which the gas has the maximum absorption capacity for laser of a specific wavelength from the wavelength actually emitted by the laser.

7. The laser radar frequency locking method for gas detection according to claim 1, characterized in that: The PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position are defined as input variables and divided into different fuzzy sets respectively; The lidar frequency adjustment result is defined as the output variable and divided into fuzzy sets; Fuzzy rules are formulated to describe the impact of the PID gain coefficient difference and the degree of alignment between the wavelength and the target absorption peak position on the lidar frequency adjustment result; Fuzzy reasoning is performed based on fuzzy rules to determine the lidar frequency adjustment plan.

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