Methane gas detection system and method based on cavity ring-down spectroscopy

Abstract

The invention provides a methane gas detection system and method based on cavity ring-down spectroscopy, and the system comprises a laser emission module which is used for emitting a laser with a preset wavelength to a to-be-detected methane gas in a resonant cavity module; the resonant cavity module is used for receiving the methane gas to be detected and reacting with the input laser to cause gradual weakening of the laser intensity; the gas path module is used for inputting and outputting methane gas to be detected in the resonant cavity module; the signal acquisition and processing module is used for acquiring ring-down optical signals of the laser emitted by the laser emission module, wherein the ring-down optical signals are gradually weakened through the methane gas; performing baseline correction and de-noising on the collected ring-down optical signal, and performing fitting processing based on the de-noised ring-down optical signal to obtain an exponential decay function; and extracting ring-down time when the function value is 1 / e of the maximum value based on the obtained exponential decay function, obtaining the methane gas concentration based on the ring-down time in combination with the methane gas absorption cross section and the AvoGamdeo constant inversion, and obtaining a methane gas detection result.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas detection, and in particular relates to a methane gas detection system and method based on cavity ring-down spectroscopy. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Methane (CH4) is an important greenhouse gas, and its impact on global climate change has attracted increasing attention. In the atmospheric environment, even a small change in methane concentration may have a significant impact on the climate system. Accurately measuring methane concentration is of vital importance for studying greenhouse gas emission sources and sinks, assessing climate change trends, and formulating emission reduction strategies.

[0004] Traditional methane detection methods include gas chromatography and non-dispersive infrared methods. Although gas chromatography has high accuracy, the equipment is complex, the operation is cumbersome, and it requires professional personnel to maintain and operate. The analysis cycle is long, and it is difficult to achieve real-time and rapid detection. The non-dispersive infrared method is easily affected by interference factors such as water vapor, and has limited sensitivity when detecting low-concentration methane. These traditional methods have obvious shortcomings when meeting the needs of high-precision, high-sensitivity, and rapid real-time detection of methane concentrations.

[0005] Cavity ring-down spectroscopy (CRDS) technology has emerged as a new type of high-sensitivity absorption spectroscopy detection technology. CRDS technology uses multiple reflections of light in a high-reflectivity resonant cavity to form an ultra-long optical path, thereby significantly improving the detection sensitivity of trace gases. However, the current methane concentration detection method based on CRDS is affected by factors such as the cavity mirror reflectivity of the resonant cavity, wavelength detection accuracy, cavity mirror position adjustment accuracy, and system stability, resulting in insufficient detection accuracy and reliability; and the existing methane concentration detection method based on CRDS lacks consideration of environmental factors in terms of concentration calculation, that is, fluctuations in temperature and pressure will affect the absorption characteristics of the gas, thereby interfering with the accurate calculation of methane concentration. Summary of the invention

[0006] The embodiments of the present invention provide a methane gas detection system and method based on cavity ring-down spectroscopy to solve the problem that the traditional method requires professional personnel to operate and is easily affected by external interference factors, and the methane concentration detection method based on CRDS is affected by factors such as the cavity mirror reflectivity of the resonant cavity, wavelength detection accuracy, cavity mirror position adjustment accuracy and system stability, resulting in insufficient detection accuracy and reliability.

[0007] According to a first aspect of an embodiment of the present invention, there is provided a methane gas detection system based on cavity ring-down spectroscopy, comprising:

[0008] A laser emission module, which is used to emit a laser of a preset wavelength to the methane gas to be measured in the resonant cavity module; wherein the preset wavelength is the wavelength at which the methane gas has the highest absorption intensity;

[0009] A resonant cavity module, which is used to receive the methane gas to be measured and react with the input laser to cause the laser intensity to gradually weaken;

[0010] A gas path module, which is used for inputting and outputting the methane gas to be measured in the resonant cavity module;

[0011] The signal acquisition and processing module is used to acquire the ring-down light signal of the laser emitted by the laser emission module which is gradually weakened by methane gas; and to perform baseline correction and denoising on the acquired ring-down light signal, and to obtain an exponential decay function by fitting the denoised ring-down light signal; based on the obtained exponential decay function, the ring-down time when the function value is 1 / e of the maximum value is extracted, and based on the ring-down time, the methane gas concentration is obtained by inversion in combination with the methane gas absorption cross section and the Avogadro constant, so as to obtain the methane gas detection result.

[0012] Furthermore, the methane gas concentration is determined by the following formula:

[0013]

[0014] Where c is the light speed in the ring-down cavity, σ(λ) is the absorption cross section of methane gas, and N A is Avogadro's constant, τ(λ) is the ring-down time when the function value is 1 / e of the maximum value, and τ0(λ) is the ring-down time when the function value is 1 / e of the maximum value when the resonant cavity is empty.

[0015] Furthermore, the collected ring-down light signal is subjected to baseline correction and denoising, specifically: a digital signal processing technique is used to remove a DC offset in the signal, so that the baseline of the ring-down light signal is adjusted to near zero, and a wavelet transform filtering algorithm is used to perform denoising on the ring-down light signal.

[0016] Furthermore, the preset wavelength is determined by: drawing a relationship diagram between the absorption intensity and wavelength of methane gas based on the methane gas data in the molecular spectrum database; and selecting the corresponding wavelength with the highest absorption intensity of methane gas through the relationship diagram as the output laser wavelength of the laser module.

[0017] Furthermore, the gas path module includes an inlet gas path pipeline, an exhaust gas path pipeline and an air pump, wherein the inlet gas path pipeline is sequentially provided with a filter and an intake proportional valve, one end of the inlet gas path pipeline is connected to the resonance cavity module, and the other end is used for the input of the methane gas to be tested; one end of the exhaust gas path pipeline is connected to the resonance cavity module, and the other end is used for the output of the methane gas.

[0018] Furthermore, the signal acquisition and processing module is also used for laser emission control of the laser module. When the transmitted light intensity signal reaches a preset threshold, the laser is controlled to stop laser emission.

[0019] Furthermore, the laser module adopts a DFB laser, and the resonant cavity adopts a ring-down cavity based on a plano-concave high-reflection mirror.

[0020] According to a second aspect of an embodiment of the present invention, a methane gas detection method based on cavity ring-down spectroscopy is provided, which is based on the above-mentioned methane gas detection system based on cavity ring-down spectroscopy, and includes:

[0021] The ring-down optical signal of the laser emitted by the laser emission module which is gradually weakened by the methane gas is collected;

[0022] Baseline correction and denoising are performed on the collected ring-down light signal, and an exponential decay function is obtained by fitting the denoised ring-down light signal;

[0023] The ring-down time when the function value is 1 / e of the maximum value is extracted based on the obtained exponential decay function. Based on the ring-down time, the methane gas concentration is obtained by combining the methane gas absorption cross section and the Avogadro constant to obtain the methane gas detection result.

[0024] According to a third aspect of an embodiment of the present invention, there is provided an electronic device, comprising a memory, a processor, and a computer program stored and running on the memory, wherein when the processor executes the program, the method for detecting methane gas based on cavity ring-down spectroscopy is implemented.

[0025] According to a fourth aspect of an embodiment of the present invention, a non-transitory computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the methane gas detection method based on optical cavity ring-down spectroscopy is implemented.

[0026] One or more of the above technical solutions have the following beneficial effects:

[0027] The present invention provides a methane gas detection system and method based on cavity ring-down spectroscopy. The scheme adopts CRDS (cavity ring-down spectroscopy) technology, and by virtue of its ultra-long effective absorption optical path, combined with the calculation strategy of methane gas concentration, realizes ultra-high sensitivity detection of methane concentration, and the detection accuracy can reach ppb (concentration unit) level or even higher, and can accurately detect extremely low concentration methane changes in the atmospheric environment, providing a powerful means for greenhouse gas monitoring.

[0028] The solution of the present invention significantly improves the stability and reliability of the detection system by adding a filter and performing baseline correction and denoising on the collected ring-down light signal, reduces the influence of external environmental factors (such as temperature, air pressure, vibration, etc.) on the detection results, ensures the accuracy and repeatability of methane concentration detection, and is suitable for long-term continuous monitoring.

[0029] The scheme of the present invention is easy to operate, can realize automatic, real-time continuous measurement, and has low professional requirements for operators. The scheme of the present invention has a fast detection speed and can complete a methane concentration measurement in a short time (such as within a few seconds), meeting the needs of rapid monitoring and dynamic change tracking of methane emission sources, such as industrial waste gas emission monitoring, landfill methane leakage monitoring and other fields, and has broad application prospects;

[0030] The solution of the present invention does not require a complicated sample pretreatment process, thus avoiding errors and contamination introduced by the pretreatment process, achieving non-contact, non-destructive detection of methane gas, protecting the integrity of the sample, and reducing detection costs and operational difficulty.

[0031] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0033] Figure 1 Schematic diagram of the structure of a methane gas detection system based on cavity ring-down spectroscopy described in an embodiment of the present invention;

[0034] Figure 2 Schematic diagram of the ring-down optical signal acquisition process described in an embodiment of the present invention;

[0035] Figure 3 Schematic diagram of the methane concentration calculation process described in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0037] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0038] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0039] like Figure 1 As shown, an embodiment of the present invention provides a methane gas detection system based on cavity ring-down spectroscopy, comprising:

[0040] A laser emission module, which is used to emit a laser of a preset wavelength to the methane gas to be measured in the resonant cavity module; wherein the preset wavelength is the wavelength at which the methane gas has the highest absorption intensity;

[0041] The laser emission module uses a DFB laser, whose emission wavelength is precisely set to 1653.7nm, output power is stable at 20mW, has narrow linewidth characteristics, linewidth <2MHz, side mode suppression ratio (SMSR) up to 40dB, working current is 80mA, and wavelength tolerance is ±1nm. This laser can provide a stable, monochromatic and precisely adjustable wavelength laser source, laying the foundation for high-precision detection of methane gas.

[0042] A resonant cavity module, which is used to receive the methane gas to be measured and react with the input laser to cause the laser intensity to gradually weaken;

[0043] Among them, the resonant cavity module adopts a carefully designed ring-down cavity with a cavity length of 50cm. The inner wall of the cavity is plated with a quartz layer, which effectively reduces the adsorption of gas molecules by the inner wall of the cavity and reduces the measurement error. The cavity mirror uses two plano-concave high-reflection mirrors with a diameter of 25.4mm and a curvature radius of 100cm. Its reflectivity is as high as 99.9963% in the wavelength range of 1600-1700nm. The cavity mirror is installed on a high-precision adjustable three-dimensional mirror frame. The mechanical parallelism of the optical cavity can be accurately adjusted by fine-tuning the mirror frame to ensure the perfect match between the laser mode and the cavity mode, and improve the coupling efficiency and resonance effect of light in the cavity.

[0044] In a specific implementation, the signal acquisition and processing module is also used for laser emission control of the laser module. When the transmitted light intensity signal reaches a preset threshold, the laser is controlled to stop laser emission.

[0045] A gas path module, which is used for inputting and outputting the methane gas to be measured in the resonant cavity module;

[0046] Among them, the gas path module includes an inlet gas path pipeline, an exhaust gas path pipeline and an air pump, wherein the inlet gas path pipeline is sequentially provided with a filter and an intake proportional valve, one end of the inlet gas path pipeline is connected to the resonance cavity module, and the other end is used for the input of the methane gas to be tested; one end of the exhaust gas path pipeline is connected to the resonance cavity module, and the other end is used for the output of methane gas.

[0047] Specifically, the gas circuit module includes an intake proportional valve, an air pump, a thermometer, a pressure gauge, and an air circuit pipeline with an inlet and an exhaust port. The intake proportional valve is used to accurately control the gas flow rate entering the resonant cavity to ensure a stable supply of gas samples. The air pump maintains the air pressure in the gas circuit system stable and evenly distributes the gas in the cavity. The thermometer and pressure gauge monitor the temperature and pressure changes in the gas circuit in real time, providing the necessary correction parameters for subsequent concentration calculations.

[0048] The signal acquisition and processing module is used to acquire the ring-down light signal of the laser emitted by the laser emission module which is gradually weakened by methane gas; and to perform baseline correction and denoising on the acquired ring-down light signal, and to obtain an exponential decay function by fitting the denoised ring-down light signal; based on the obtained exponential decay function, the ring-down time when the function value is 1 / e of the maximum value is extracted, and based on the ring-down time, the methane gas concentration is obtained by inversion in combination with the methane gas absorption cross section and the Avogadro constant, so as to obtain the methane gas detection result.

[0049] Among them, the signal acquisition and processing module includes a photoelectric detector, a high-speed and high-precision data acquisition card and an industrial computer. The photoelectric detector is selected to have a high sensitivity response to the 1653.7nm wavelength, which is used to accurately receive the transmitted light signal. When the transmitted light intensity signal reaches the preset threshold, the photoelectric detector immediately sends a shutdown signal to the trigger board to stop the laser from emitting the laser. At this time, the light signal in the cavity begins to attenuate. The data acquisition card has a high sampling rate and high resolution, and can accurately collect the attenuated light signal output by the photoelectric detector. The industrial computer has a built-in specially developed data processing software, which is responsible for real-time processing, analysis and calculation of the collected data, and finally obtains the methane concentration value.

[0050] In a specific implementation, the methane gas concentration is determined by using the following formula:

[0051]

[0052] Where c is the speed of light in the ring-down cavity, σ(λ) is the absorption cross section of methane gas, NA is Avogadro's constant, τ(λ) is the ring-down time when the function value is 1 / e of the maximum value, and τ0(λ) is the ring-down time when the function value is 1 / e of the maximum value when the resonant cavity is empty.

[0053] In a specific implementation, the baseline correction and denoising of the collected ring-down light signal is specifically: using digital signal processing technology to remove the DC offset in the signal, adjusting the baseline of the ring-down light signal to near zero, and using a wavelet transform filtering algorithm to perform denoising on the ring-down light signal.

[0054] In a specific implementation, the preset wavelength is determined by: drawing a relationship diagram between the absorption intensity and wavelength of methane gas based on the methane gas data in the molecular spectrum database; and selecting the corresponding wavelength with the highest absorption intensity of methane gas through the relationship diagram as the output laser wavelength of the laser module.

[0055] Specifically, the molecular spectral database uses HITRAN spectral data to simulate the absorption wavelength range of methane gas. In a specific implementation, the HITRAN spectral data simulation can be performed on PyCharm, and the real-time calculation of methane concentration can be performed on Visual Studio.

[0056] In one or more embodiments, a methane gas detection method based on cavity ring-down spectroscopy is provided, which is based on the above-mentioned methane gas detection system based on cavity ring-down spectroscopy, including:

[0057] The ring-down optical signal of the laser emitted by the laser emission module which is gradually weakened by the methane gas is collected;

[0058] Baseline correction and denoising are performed on the collected ring-down light signal, and an exponential decay function is obtained by fitting the denoised ring-down light signal;

[0059] The ring-down time when the function value is the maximum value 1 / e is extracted based on the obtained exponential decay function. Based on the ring-down time, the methane gas concentration is obtained by combining the methane gas absorption cross section and the Avogadro constant to obtain the methane gas detection result.

[0060] Furthermore, the solution of this embodiment is described in detail from the perspective of specific implementation as follows:

[0061] like Figure 1 and Figure 2 As shown, the scheme described in this embodiment utilizes the gas in the resonant cavity to cause the gradual attenuation of the light intensity, obtains the ring-down light signal and performs data analysis and processing. The specific processing process of the scheme includes: collecting the ring-down light signal and calculating the methane concentration based on the ring-down light signal. Specifically:

[0062] (I) Collection of light swing signals

[0063] The specific steps include:

[0064] Step (1): using HITRAN spectrum data to simulate the absorption wavelength range of methane gas;

[0065] Wherein, the step (1) comprises:

[0066] Step (1-1): Draw a graph of the absorption intensity of methane gas versus wavelength based on the HITRAN spectral database to ensure that there is no interference from other gases near the wavelength;

[0067] Step (1-2): Through the image, select the corresponding wavelength with high absorption intensity of methane gas and determine that the wavelength of the laser is 1653.7nm.

[0068] Step (2): Start building a methane detection system based on the wavelength of the DFB laser;

[0069] Wherein, the step (2) comprises:

[0070] Step (2-1): Install the laser on a bracket with good heat dissipation performance to ensure that its operating temperature is stable;

[0071] Step (2-2): selecting a resonant cavity composed of a plano-concave high reflective mirror with a reflectivity of 99.9963% in the wavelength range of 1600-1700 nm to achieve optimal matching between the laser mode and the cavity mode;

[0072] Step (2-3): Connect a photodetector to the output end of the resonant cavity to receive the transmitted light signal after methane gas absorption;

[0073] Step (2-4): Connect the output signal of the photodetector to a high-speed and high-precision data acquisition card to monitor and save the signal in real time;

[0074] Step (2-5): The data acquisition card is installed in the industrial computer, and the software can be run to process and analyze the signal;

[0075] Step (2-6): Assemble the air intake filter, air intake proportional valve, flow meter, vacuum pump and connecting pipes to construct an air path system to ensure smooth airflow during operation and remove particulate matter, moisture and organic impurities in the methane gas.

[0076] Step (3): Initialize and debug the environmental parameters of the CRDS system to ensure that the system is operating normally;

[0077] Wherein, the step (3) comprises:

[0078] Step (3-1): preheat the DFB laser, monitor the temperature change, and adjust it to the normal operating range;

[0079] Step (3-2): Use a wavelength meter to adjust the output wavelength of the laser to 1653.7 nm;

[0080] Step (3-3): Open the data acquisition card control software on the industrial computer and set the sampling rate to 1 GHz;

[0081] Step (3-4): Calibrate the acquisition card to ensure the accuracy of the acquired signal;

[0082] Step (3-5): Calibrate the gas system using standard gas (methane gas with known concentration);

[0083] Step (3-6): Check data preservation to prevent data loss;

[0084] Step (4): preparation of the gas path system and monitoring of the intracavitary environment, debugging of the signal triggering and acquisition system;

[0085] Wherein, the step (4) comprises:

[0086] Step (4-1): Before formally testing the methane gas in the environment, fill the cavity with nitrogen and adjust the flow rate and pressure of the gas flow;

[0087] Step (4-2): During the intake process, the gas flow rate and gas pressure are monitored in real time, and the intake proportional valve is adjusted through feedback to stabilize the flow rate within the range of ±5% of the set value and the pressure fluctuation within the range of ±0.001atm;

[0088] Step (4-3): Use an oscilloscope to debug the trigger signal of the laser driver to ensure normal control of the laser;

[0089] Step (4-4): In the cavity state, collect the output signal of the photodetector to determine the size of the trigger threshold;

[0090] Step (4-5): Monitor the photodetector signal in real time, trigger data acquisition when the threshold is reached, and record and analyze the trigger signal to ensure that the trigger is accurate and without abnormalities.

[0091] Step (5): Monitor the methane gas in the environment in real time, and save the ring-down light signal in a .bin file in real time;

[0092] Wherein, the step (5) comprises:

[0093] Step (5-1): first fill the cavity space with nitrogen, collect and save the ring-down light signal at this time;

[0094] Step (5-2): Turn on the exhaust device to allow the methane gas in the environment to enter the resonant cavity;

[0095] Step (5-3): Turn on the laser driver through the industrial computer to generate a trigger signal;

[0096] Step (5-4): Observe the collected ring-down optical signal to see if there is obvious interference and distortion;

[0097] Step (5-5): Check the .bin file to ensure that the ring-down light signal is saved normally.

[0098] Step (6): Acquisition of the ring-down light signal is completed by using the cavity ring-down spectroscopy technique and detecting the transmitted light signal.

[0099] (II) Calculation of methane concentration based on ring-down light signal

[0100] The specific steps include:

[0101] Step (1): The above ring-down light signal is collected and saved in a .bin file. First, the ring-down light signal is preprocessed, that is, baseline correction and denoising are performed on each ring-down light signal;

[0102] Wherein, the step (1) comprises:

[0103] Step (1-1): using digital signal processing technology to remove the DC offset in the signal, so that the baseline of the ring-down optical signal is adjusted to near zero;

[0104] Step (1-2): Use wavelet transform filtering algorithm to perform noise reduction on the ring-down light signal.

[0105] Step (2): Establish a fitting model for the ring-down light signal and use an extraction algorithm to extract the decay time when the maximum value is 1 / e;

[0106] Wherein, the step (2) comprises:

[0107] Step (2-1): using a fitting algorithm to perform fitting processing on the filtered and denoised ring-down light signal;

[0108] Step (2-2): using the least squares method, fitting the signal data to the exponential decay function;

[0109] Step (2-3): by optimizing the extraction algorithm, extract the ring-down time τ value when the value is 1 / e of the maximum value;

[0110] It should be noted here that for the maximum value 1 / e, the maximum value at this time is changing dynamically, which represents the intensity of the light intensity signal. Among them, based on the fitting function, the time corresponding to the horizontal axis value corresponding to the maximum value 1 / e is the ring-down time.

[0111] In a specific implementation, the optimization extraction algorithm is specifically: using wavelet transform filtering to reduce noise, then using least squares fitting, and then using a convolutional neural network to extract the required eigenvalues ​​of the signal, for example: extracting purer signal eigenvalues ​​through CNN.

[0112] Step (2-4): Through the above operations, the same baseline correction and denoising are performed on the cavity ring-down light signal;

[0113] Step (2-5): Through the fitting extraction algorithm, extract the ring-down time τ0 value when the cavity value is 1 / e of the maximum value.

[0114] It should be noted here that for the 1 / e of the maximum value in the cavity, step (2-3) is for the case where methane gas exists. In this step, the cavity ring-down time is first collected, and the cavity is filled with nitrogen, and then the measurement is performed. This cavity represents that there is almost no methane gas inside; when detecting methane gas, first use the suction device to inflate for a period of time to allow the ambient gas to circulate in the cavity, so that the ring-down time is measured.

[0115] Step (3): Calculate the methane gas concentration according to the concentration calculation formula and perform corrections for temperature and pressure;

[0116] Wherein, the step (3) comprises:

[0117] Step (3-1): Determine the absorption cross section σ(λ) of methane gas at wavelength λ = 1653.7 nm to be 3.5×10 - 21 cm 2 / mol, and the light speed c in the ring-down cavity is determined to be 2.99792458×10 10 cm / s, Avogadro constant N A is 6.02214076×10 23 ;

[0118] Step (3-2): According to The concentration value C of methane gas is calculated using the formula and the two ring-down times extracted;

[0119] Step (3-3): After completing one measurement, the system will enter the next measurement to achieve continuous monitoring of methane concentration;

[0120] Step (2-3-4): Correct the concentration data by combining the temperature and pressure data measured by the thermometer and pressure gauge in the gas path module.

[0121] Step (4): Display the methane concentration in real time on the PC interface and save it in a .txt file together with the detection time;

[0122] Wherein, the step (4) comprises:

[0123] Step (4-1): The collected methane concentration data is displayed in real time on the software interface of the industrial computer;

[0124] Step (4-2): The visualization interface will display the change curve of methane concentration over time - concentration trend chart;

[0125] Step (4-3): The processed data is stored in .txt format in another folder named after the date and the file is named after the measurement time;

[0126] Step (4-4): Create a data index file to record the storage location, measurement time and related parameter information of each measurement data.

[0127] In the specific implementation, in view of the problems of the existing CRCS-based methane concentration detection method in concentration calculation, the scheme described in this embodiment introduces environmental factors, that is, considering that the fluctuations of temperature and pressure will affect the absorption characteristics of the gas, thereby interfering with the accurate calculation of the methane concentration, the scheme described in this embodiment takes environmental factors into account and adds temperature and pressure calibration functions to ensure the accuracy of the concentration calculation; secondly, the scheme described in this embodiment can achieve calibration-free use, ensuring the long-term stability of the system; thirdly, considering the limitations of the detection range of traditional methods, that is, when calculating the concentration, the signal intensity of low-concentration methane is weak during detection, the scheme described in this embodiment uses a more sensitive detector to improve the detection sensitivity.

[0128] In further embodiments, there is also provided:

[0129] An electronic device includes a memory and a processor and computer instructions stored in the memory and executed on the processor, wherein the computer instructions, when executed by the processor, perform the method described in the above embodiment. For the sake of brevity, no further description is given here.

[0130] It should be understood that in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general-purpose processors, digital signal processors DSP, application-specific integrated circuits ASIC, off-the-shelf programmable gate arrays FPGA or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0131] The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A portion of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the device type.

[0132] A computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the method described in the above embodiment is completed.

[0133] The method in the above embodiment can be directly embodied as being executed by a hardware processor, or can be executed by a combination of hardware and software modules in the processor. The software module can be located in a mature storage medium in the art such as a random access memory, a flash memory, a read-only memory, a programmable read-only memory, or an electrically erasable programmable memory, a register, etc. The storage medium is located in the memory, and the processor reads the information in the memory and completes the steps of the above method in combination with its hardware. To avoid repetition, it will not be described in detail here.

[0134] Those skilled in the art will appreciate that the units, i.e., algorithm steps, of the various examples described in the present embodiment can be implemented in electronic hardware or in 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 the present invention.

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A methane gas detection system based on cavity ring-down spectroscopy, characterized in that: include: A laser emission module, which is used to emit a laser of a preset wavelength to the methane gas to be measured in the resonant cavity module; wherein the preset wavelength is the wavelength at which the methane gas has the highest absorption intensity; A resonant cavity module, which is used to receive the methane gas to be measured and react with the input laser to cause the laser intensity to gradually weaken; A gas path module, which is used for inputting and outputting the methane gas to be measured in the resonant cavity module; The signal acquisition and processing module is used to acquire the ring-down light signal of the laser emitted by the laser emission module which is gradually weakened by methane gas; and to perform baseline correction and denoising on the acquired ring-down light signal, and to obtain an exponential decay function by fitting the denoised ring-down light signal; based on the obtained exponential decay function, the ring-down time when the function value is 1 / e of the maximum value is extracted, and based on the ring-down time, the methane gas concentration is obtained by inversion in combination with the methane gas absorption cross section and the Avogadro constant, so as to obtain the methane gas detection result.

2. A methane gas detection system based on cavity ring-down spectroscopy as claimed in claim 1, characterized in that: The methane gas concentration is determined by the following formula: Where c is the light speed in the ring-down cavity, σ(λ) is the absorption cross section of methane gas, and N A is Avogadro's constant, τ(λ) is the ring-down time when the function value is 1 / e of its maximum value, and τ0(λ) is the ring-down time when the function value is 1 / e of its maximum value when the resonant cavity is empty.

3. A methane gas detection system based on cavity ring-down spectroscopy as claimed in claim 1, characterized in that: The baseline correction and denoising of the collected ring-down light signal is specifically performed by: using digital signal processing technology to remove the DC offset in the signal, adjusting the baseline of the ring-down light signal to near zero, and using a wavelet transform filtering algorithm to perform denoising on the ring-down light signal.

4. A methane gas detection system based on cavity ring-down spectroscopy as claimed in claim 1, characterized in that: The preset wavelength is determined by: drawing a relationship diagram between the absorption intensity and wavelength of methane gas based on the methane gas data in the molecular spectrum database; and selecting the corresponding wavelength with the highest absorption intensity of methane gas through the relationship diagram as the output laser wavelength of the laser module.

5. The methane gas detection system based on cavity ring-down spectroscopy as claimed in claim 1, characterized in that: The gas path module includes an inlet gas path pipeline, an exhaust gas path pipeline and an air pump, wherein the inlet gas path pipeline is sequentially provided with a filter and an intake proportional valve, one end of the inlet gas path pipeline is connected to the resonance cavity module, and the other end is used for the input of the methane gas to be tested; one end of the exhaust gas path pipeline is connected to the resonance cavity module, and the other end is used for the output of the methane gas.

6. A methane gas detection system based on cavity ring-down spectroscopy as claimed in claim 1, characterized in that: The signal acquisition and processing module is also used for laser emission control of the laser module. When the transmitted light intensity signal reaches a preset threshold, the laser is controlled to stop laser emission.

7. A methane gas detection system based on cavity ring-down spectroscopy as claimed in claim 1, characterized in that: The laser module adopts a DFB laser, and the resonant cavity adopts a ring-down cavity based on a plano-concave high-reflection mirror.

8. A methane gas detection method based on cavity ring-down spectroscopy, which is based on a methane gas detection system based on cavity ring-down spectroscopy as claimed in any one of claims 1 to 7, characterized in that: include: The ring-down optical signal of the laser emitted by the laser emission module which is gradually weakened by the methane gas is collected; Baseline correction and denoising are performed on the collected ring-down light signal, and an exponential decay function is obtained by fitting the denoised ring-down light signal; The ring-down time when the function value is 1 / e of the maximum value is extracted based on the obtained exponential decay function. Based on the ring-down time, the methane gas concentration is obtained by combining the methane gas absorption cross section and the Avogadro constant to obtain the methane gas detection result.

9. An electronic device, comprising a memory, a processor, and a computer program stored and running on the memory, wherein when the processor executes the program, the methane gas detection method based on cavity ring-down spectroscopy as claimed in claim 8 is implemented.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the methane gas detection method based on cavity ring-down spectroscopy as described in claim 8 is implemented.

Images