A methane gas concentration detection algorithm and its integrated laser methane detection device

Abstract

This invention relates to a methane gas concentration detection algorithm and its integrated laser methane detection device, belonging to the field of gas detection. It employs an MCU signal processing circuit module with AD and DA functions to convert an analog signal containing gas absorption signals into a digital signal, and to convert the laser drive digital signal into an analog signal, driving the laser to emit a laser of a specific wavelength. After methane gas absorbs the specific wavelength of the laser, the signal is converted into an electrical signal by a photodetector, amplified by a preamplifier circuit, and then processed by the MCU signal processing circuit to obtain the methane gas concentration in the environment. The detection algorithm integrates the gas path, optical path, circuit, and structure of the laser methane detection into a highly integrated laser methane detection device. This solves the problems of existing methane detection devices, such as large size, high power consumption, low measurement sensitivity, poor stability, and weak anti-interference. It has wide applications in urban utility tunnels, coal mines, and household gas leak detection.

Description

Technical Field

[0001] This invention belongs to the field of gas detection, and more specifically to the field of methane gas detection. In particular, it relates to a methane gas concentration detection algorithm and its integrated laser methane detection device. Background Technology

[0002] Traditional methane detection methods primarily utilize carrier catalysis, pyroelectricity, and infrared principles. Carrier catalysis-based methane detection suffers from susceptibility to other gases, narrow detection range, and poor stability. Pyroelectric methane detection is highly susceptible to ambient temperature fluctuations, has low accuracy, and poor stability. Infrared methane detection is prone to interference from alkane gases, is greatly affected by water vapor, and exhibits poor stability. Compared to traditional methane detection, laser-based methane detection offers advantages such as high measurement sensitivity, good stability, and strong anti-interference capabilities, and is increasingly being applied to methane concentration detection in environments such as coal mines and urban utility tunnels. However, current laser-based methane sensors generally employ fiber optic transmission or multiple spatial reflections, resulting in large size, high power consumption, and poor measurement stability.

[0003] A search of the Chinese patent database revealed over 360 patents related to laser methane and laser gas detection. For example, CN200520071347.1, "Optical Structure of an Online Monitoring Instrument for Atmospheric Methane Concentration Based on Laser Absorption Spectroscopy," proposes a spatial multiple-reflection cavity structure, which suffers from large size and complex structure. CN201620380595.2, "A Methane Detection Device for Mining Based on TDLAS," proposes a fiber optic transmission laser methane detection device, which also suffers from large size and complex structure. CN202110178920.2, "Laser Gas Detector and Laser Gas Detection System," proposes a gas detector designed with a large-aperture through-beam optical system. CN202122826683.4, "A Non-Contact Laser Methane Sensor," is a utility model patent that proposes a structural design applicable to coal mine drainage pipelines. The vast majority of these are utility model patent applications related to laser methane sensors; there are currently no applications for highly integrated miniaturized laser gas detection devices and optimized detection algorithms.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the issues of large size, high power consumption, low measurement sensitivity, poor stability, and weak anti-interference in existing methane detection devices.

[0006] The inventive concept of the present application is: adopting an MCU signal processing circuit module with multi-channel AD and DA functions, the AD function converts the analog signal with a gas absorption signal into a digital signal, the DA function converts the laser driver digital signal stored in the chip into an analog signal to drive the laser to emit laser of a specific wavelength. Through the absorption of the laser specific wavelength light wave by the methane gas, the laser of the specific wavelength emitted by the laser is modulated by light absorption, and then converted into an electrical signal by a PD photodetector, amplified by a preamplifier circuit, and then processed by the MCU signal processing circuit. The methane gas concentration in the environment is obtained by inversion. The optimized detection algorithm is combined to integrate the gas path, optical path, circuit, and structure of the laser methane detector in one. The non-airtight packaging components are used for dustproof, waterproof, and shockproof protection. The gas diffusion channel of the non-airtight packaging component is used as the gas path. The optical channel cavity structure is made on the component mounting surface of the optical module base to form the optical path. The internal optical components, optoelectronic devices, and semiconductor components are assembled without leads to form a highly integrated laser methane detector integrating the gas path, optical path, circuit, and structure, so as to realize the high integration, low power consumption, and high stability of the laser methane device, thereby solving the problems of large volume, high power consumption, and poor measurement stability of most existing laser methane sensors. It will play an important role in promoting the wide application of laser methane devices in coal mines and urban pipe corridors.

[0007] Therefore, the present application provides a methane gas concentration laser detection algorithm as shown in Figure 3 . The specific algorithm is as follows:

[0008] (1) Adopting an MCU signal processing circuit module with multi-channel AD and DA functions, the AD function converts the analog signal with a gas absorption signal into a digital signal, the DA function converts the laser driver digital signal stored in the chip into an analog signal to drive the laser to emit laser of a specific wavelength;

[0009] (2) Through the absorption of the laser specific wavelength light wave by the methane gas, the laser of the specific wavelength emitted by the laser is modulated by light absorption, and then converted into an electrical signal by a PD photodetector, and then amplified by a preamplifier circuit;

[0010] (3) The AD function of the MCU is triggered synchronously to sample the photoelectric signal of the PD photodetector after the preamplifier circuit, and the average power signal P 均 is obtained after high-frequency multiple sampling;

[0011] (4) The digital signal P 均 after high-frequency sampling is convoluted with a high-pass filter function F(X) to obtain a digital high-pass filtered digital signal Q=F(X)*P 均 after removing the low-frequency scanning signal;

[0012] (5) Harmonic signal extraction: the digital signal Q is multiplied by the laser sine wave driving signal F1(Y) (as a reference signal) and its second harmonic signal F2(Y) respectively, to obtain the first harmonic signal W1=F1(Y) x Q and the second harmonic signal W2=F2(Y) x Q;

[0013] (6) Digital low-pass filtering: the second harmonic signal W2 is convolved with a low-pass filtering function F(Z) to obtain the digital signal E after removing the high-frequency scanning signal. E1=F(Z)*W1, E2=F(Z)*W2, after high-pass and low-pass digital filtering, only the signal corresponding to the frequency of the laser driving signal is retained;

[0014] (7) Digital smoothing filtering: the obtained signal E is subjected to multi-point averaging of adjacent points to obtain the digital signal E(N, M) after smoothing filtering, E1'=E1(N,M), E2'=E2(N,M);

[0015] (8) Concentration signal: the integral areas of the second harmonic signal E2(N, M) and the first harmonic signal E1(N, M) after smoothing filtering are calculated respectively, and the methane gas concentration value C in the environment is calculated as C=∑E2'(N) / ∑E1'(N), which has a one-to-one positive linear relationship with ΣE2(N, M) / ΣE1(N, M);

[0016] (9) Multi-point smoothing filtering of adjacent points for concentration signal C: the gas concentration signal value C obtained by solving is subjected to multi-point averaging filtering of adjacent points to remove the maximum and minimum values, and the average value is obtained to improve the stability of the measurement.

[0017] (10) True gas concentration: by introducing a standard methane gas sample, the corresponding concentration value and concentration signal value C are recorded to obtain a calibration function F(C), and then the concentration of methane gas in the environment is obtained by combining the concentration signal C obtained by solving with the calibration function F(C).

[0018] (11) Temperature compensation: the temperature change of the environment will affect the absorption rate of methane gas to light waves. The correlation function F(C, T) of temperature T and concentration signal value C is obtained by fitting a large amount of experimental test data, the concentration signal C is compensated for temperature, to obtain the compensated concentration signal C'=F(C, T), to eliminate the influence of environmental temperature change on the measurement;

[0019] (12) Pressure compensation: the change of gas pressure in the environment will also affect the absorption rate of methane gas to light waves. The correlation function F(C', P) of pressure P and concentration signal value C is obtained by fitting a large amount of experimental test data, the concentration signal C' is compensated for pressure, to obtain the compensated concentration signal C"=F(C', P), to eliminate the influence of environmental pressure change on the measurement.

[0020] The integrated laser methane detection device of the methane gas concentration laser detection algorithm is shown in Figure 1 、 Figure 2 The composition structure of the detection device includes a shell assembly, an internal component, a non-airtight packaging component, a gas path, and an optical path.

[0021] The shell assembly includes a device shell 10, a dustproof and breathable mesh 11, and a screw ring 12, which provide dustproof, waterproof, and anti-vibration protection for the internal component.

[0022] The internal component includes an optical module base 1, a TO laser 2, a left reflective prism 3, a right reflective prism 4, a PD photodetector 5, a temperature and pressure integrated chip 6, a preamplifier circuit module 7, an MCU signal processing circuit module 8, and a connection ribbon 9, which are the functional implementation parts of the device.

[0023] The non-airtight packaging component includes a non-airtight packaging material.

[0024] The optical module base 1 is integrally formed and provides a cavity structure for the optical path.

[0025] The entire device is packaged with the non-airtight packaging component, and the gas diffusion channels of the non-airtight packaging component form the gas path. The gas path and the optical path exchange with the environment gas through gas diffusion.

[0026] The TO laser 2 has a back light detection PD photodetector. According to the PD photodetector signal, the light wave emitted by the laser can be monitored in real time, and the methane detection absorption peak wavelength can be aligned in real time by adjusting the temperature of the laser. After adjusting the optical path on the optical platform, fill the gap with insulating heat-conducting material, and weld and fix the laser and the optical module base.

[0027] After adjusting the optical path on the optical platform, the right reflective prism 3 and the left reflective prism 4 are fixed on the optical module base.

[0028] The PD photodetector 5 is used to convert the received laser light wave signal into an electrical signal. After adjusting the optical path on the optical platform, the PD photodetector is welded and fixed with the optical module base.

[0029] The laser 2 and the PD photodetector 5 in the optical component are connected to the preamplifier circuit module 7 through the self-provided multi-PIN metal pin.

[0030] The preamplifier circuit module 7 performs analog signal filtering and amplification processing on the weak electrical signal converted by the PD photodetector.

[0031] The temperature and pressure integrated chip 6 is used for temperature measurement and pressure measurement, and is connected and communicated with the main control chip through the ribbon.

[0032] The preamplifier circuit module 7 and the MCU signal processing circuit module 8 are connected through a plurality of PIN metal pins for signal transmission.

[0033] The MCU signal processing circuit module 8 is provided with a plurality of AD and DA functions, and the AD function converts the analog signal with the gas absorption signal into a digital signal.

[0034] The connecting flat cable 9 is used for connecting an external system to provide a direct current power supply and signal transmission for the device.

[0035] The device shell 10 comprises a shell lower cover 1001 and a shell upper cover 1002, the shell lower cover 1001 is in a cylindrical structure, internally assembled with internal components, and the upper part is a cylindrical step with a thickness decreasing inward, used for sleeving the shell upper cover 1002, and the bottom is connected with a dustproof and breathable net 11; the shell upper cover 1002 is a reversed T-shaped cylinder, the lower end is sleeved on the upper part of the shell lower cover 1001, the upper end is provided with an external thread, and is used in cooperation with a screw ring 12 to fix the methane detection device on an application device, and meanwhile, the upper end is used for penetrating the connecting flat cable 9.

[0036] The working principle of the device is briefly described as follows:

[0037] The gas path and the light path of the integrated laser methane detection device are exchanged with the ambient gas through gas diffusion, the TO laser 2 monitors the light wave emitted by the laser in real time according to the PD signal of the back light detection, and then adjusts the laser temperature in real time to align the methane detection absorption peak wavelength, and the methane gas modulates the light wave emitted by the TO laser 2 on the light path. The light wave emitted by the TO laser 2 is emitted in parallel through the right reflecting prism 3, and then reaches the light PD electric detector 5 through a left reflecting prism 4, the PD photoelectric detector 5 converts the light signal into an electric current signal in a linear proportion, then the analog signal is filtered and amplified through the preamplifier circuit module 7, and then the processed analog signal is converted into a digital signal through AD, and the relevant digital signal processing is performed by the MCU signal processing circuit module 8, and finally the methane gas concentration in the environment to be detected is obtained by inversion. The device is powered and externally communicated by the connecting flat cable 9.

[0038] The technical effects of the present application are as follows:

[0039] The photoelectric device, the light path and the circuit are designed in a small integrated design, which greatly reduces the volume of the device.

[0040] A TO type collimating laser filled with methane and having high sealing performance is adopted, which can align the methane absorption center wavelength in real time, and improve the detection precision and reliability of the device.

[0041] The harmonic detection algorithm is optimized to improve the processing speed and stability of the device.

[0042] The application is widely applied to the fields of urban pipe corridors, coal mines and household gas leakage, is particularly suitable for the field of small-sized methane gas leakage monitoring, and has wide market prospect and application space. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is a schematic diagram of an optical module principle.

[0044] Figure 2 It is a schematic diagram of an integrated laser methane detection device structure.

[0045] Figure 3 It is a schematic diagram of a gas concentration detection algorithm flow of an integrated laser methane detection device.

[0046] In the figure: 1 is an optical module base, 2 is a TO laser, 3 is a right reflecting prism, 4 is a left reflecting prism, 5 is a PD photodetector, 6 is a temperature and pressure integrated chip, 7 is a preamplifier circuit module, 8 is an MCU signal processing circuit module, 9 is a connecting flat cable, 10 is a device shell, 1001 is a shell lower cover, 1002 is a shell upper cover, 11 is a dustproof and breathable mesh, and 12 is a screw ring. DETAILED DESCRIPTION

[0047] As shown in Figures 1-2 , the specific embodiment of the integrated laser methane detection device is as follows:

[0048] The optical module base 1 is integrally formed and provides a cavity structure for an optical path, and is made of 314 stainless steel.

[0049] The TO laser 2 is a TO60 laser sealed with pure methane, and is provided with a back light detection PD. According to the PD signal, the light wave emitted by the laser can be monitored in real time, and the wavelength 1653.7 nm of the methane detection absorption peak can be aligned in real time by adjusting the temperature of the laser. The TO60 laser is provided with an aspheric collimating lens at the front end, and emits a light wave of approximately parallel light. After adjusting the optical path on the optical platform, the gap is filled with heat-conducting silicone grease, and the TO60 laser and the optical module base are fixed by laser welding at the top.

[0050] The right reflecting prism 3 and the right reflecting prism 4 are both 45° reflecting prisms. The 45° reflecting mirror is based on Si02, and the emitting surface is plated with gold (or multi-layer dielectric film), and is used for 90° direction deflection of a vertically incident laser beam. After adjusting the optical path on the optical platform, the 3535D high-temperature curing glue is glued on the optical module base at 100 DEG C.

[0051] PD photodetector 5 is a TO56 type InGaAs PD photodetector, the sensing wavelength range is 800~1700nm, the responsivity is about 1mA / mW, and the front end is provided with a focusing lens for converting the received laser light wave signal into an electric signal. After adjusting the optical path on the optical platform, the TO56 type PD photodetector is fixed with the optical module base by laser welding at the top.

[0052] The TO60 laser 2 and the TO56 PD photodetector 5 in the optical component are connected with the preamplifier circuit module 7 by welding through the self-provided multi-PIN metal pin.

[0053] The preamplifier circuit module 7 performs filtering and amplification processing on the weak electric signal converted by the PD photodetector.

[0054] The temperature and pressure integrated chip 6 adopts a PT300 type high-precision temperature and pressure chip, the temperature measurement range is-30℃~60℃, the pressure range is 80~130kpa, and the chip is connected and communicated with the main control chip through a wire.

[0055] The preamplifier circuit module 7 and the main control MCU signal processing circuit module 8 are connected through multi-PIN metal pins for signal transmission.

[0056] The main control MCU signal processing circuit module 8 selects an STM32F405 chip as the main control chip, the chip is provided with multi-channel AD and DA functions, and the AD function converts the analog signal with the gas absorption signal into a digital signal.

[0057] The connecting wire 9 is a multi-core connecting wire, which is used for external connection of a signal transmitter or a computer and other supporting equipment, and provides direct current power supply and signal transmission for the device.

[0058] The entire device includes a shell part and an internal component part, the shell design includes a device shell 10, a dustproof and breathable net 11, a shell lower cover 1001, a shell upper cover 1002 and a hexagonal screw ring 12, and after the internal core components are detected and qualified, the entire device is filled and sealed with epoxy resin and other curing glue, the gas path and the optical path are exchanged with the environment gas through gas diffusion, and the entire shell design provides dustproof, waterproof and anti-vibration protection for the internal device core components for field industrial application.

[0059] As shown in Figures 1-3 The specific implementation manner is as follows:

[0060] (1) The DA function and the AD function of the main control chip in the MCU signal processing circuit module are controlled by the crystal clock synchronous signal, the DA function converts the laser driver digital signal stored in the chip into an analog signal, and drives the laser to emit light waves with a specific wavelength of 1653.7nm±0.1nm.

[0061] (2) Under the control of the synchronization signal, the AD function on the chip samples the voltage signal carrying the gas concentration signal after the light wave emitted by the laser and absorbed by the gas in the light path is converted into an electric current signal by the PD photodetector and processed by the preamplification circuit. The average value is obtained by using high-frequency repeated sampling at each sampling point to eliminate the white noise of the circuit and improve the accuracy of the measurement.

[0062] (3) The digital signal P 均 is convoluted with the high-pass filter function F(X) to obtain the digital signal Q after the low-frequency scanning signal is removed. The high-pass filter function F(X) is a FIR filter function, and the specific function value is designed according to the laser sawtooth wave scanning frequency.

[0063] (4) The digital signal Q is multiplied with the laser sinusoidal wave driving signal F1(Y) (as a reference signal) and its second frequency doubling signal F2(Y) respectively to obtain the first harmonic signal W1 and the second harmonic signal W2.

[0064] (5) The second harmonic signal W2 is convoluted with the low-pass filter function F(Z) to obtain the digital signal E after the high-frequency scanning signal is removed. The low-pass filter function F(Z) is a FIR filter function, and the specific function value is designed according to the laser sinusoidal wave scanning frequency. After high-pass and low-pass digital filtering, only the signal corresponding to the laser driving signal frequency is retained.

[0065] (6) The obtained signal E is subjected to multi-point averaging of adjacent points to obtain the digital signal E(N, M) after smoothing filtering.

[0066] (7) The integral areas of the second harmonic signal E2(N, M) and the first harmonic signal E1(N, M) after smoothing filtering are obtained. The methane gas concentration value C in the environment has a one-to-one positive linear relationship with ΣE2(N, M) / ΣE1(N, M), and the gas concentration C in the environment can be solved by fitting the calibration function.

[0067] (8) The gas concentration signal value C obtained by solving is subjected to multiple average filtering of adjacent points to remove the maximum and minimum values to obtain the average value to improve the stability of the measurement.

[0068] (9) The standard methane gas sample is introduced, the corresponding concentration value and signal value C are recorded, the calibration function F(C) is obtained, and then the methane gas concentration in the environment is obtained by combining the solved signal C with the calibration function F(C).

[0069] (10) In practical application, the temperature change of the environment will affect the absorption rate of the methane gas to the light wave. The correlation function F(C, T) of the temperature T and the concentration signal value C is obtained by fitting a large amount of experimental test data, and the temperature compensation is performed according to the detected temperature T of the actual environment, so as to eliminate the influence of the temperature change of the environment on the measurement.

[0070] (11) In practical application, the gas pressure change of the environment will also affect the absorption rate of the methane gas to the light wave. The correlation function F(C, P) of the pressure P and the concentration signal value C is obtained by fitting a large amount of experimental test data, and the pressure compensation is performed according to the detected pressure P of the actual environment, so as to eliminate the influence of the pressure change of the environment on the measurement.

[0071] The above detection algorithm greatly improves the accuracy and stability of the laser methane device in the detection of the actual environment application.

[0072] Finally, it should be noted that: the above examples are only examples for clearly illustrating the present application, the present application includes but is not limited to the above examples, all the embodiments need not and can not be exhausted here. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made. Any implementation scheme meeting the requirements of the present application shall fall within the scope of protection of the present application.

Claims

1. A methane gas concentration laser detection algorithm, characterized by, The algorithm comprises the following steps: (1) The MCU signal processing circuit module with multi-channel AD and DA functions is adopted, the AD function converts the analog signal with gas absorption signal into digital signal, and the DA function converts the laser driver digital signal stored in the chip into analog signal to drive the laser to emit laser of specific wavelength; (2) The laser of specific wavelength is modulated by the absorption of methane gas, and then the laser is converted into electric signal by the PD photodetector and enters the preamplifier circuit for signal amplification; (3) The AD function of the MCU is triggered synchronously to sample the photoelectric signal of the PD photodetector after the preamplification circuit, and the average power signal P is obtained after high-frequency multiple sampling 均 ; (4) the digital signal P after high-frequency sampling 均 convolution processing with the high-pass filter function F(X), to obtain the digital high-pass filtered digital signal Q=F(X)*P after removing the low-frequency scanning signal 均 ; (5) Harmonic signal extraction: the digital signal Q is multiplied with the laser sinusoidal wave driving signal F1(Y) and the twice frequency signal F2(Y) of the laser sinusoidal wave driving signal F1(Y) respectively to obtain the first harmonic signal W1=F1(Y)×Q and the second harmonic signal W2=F2(Y)×Q; (6) Digital low-pass filtering: the second harmonic signal W2 is convolved with the low-pass filtering function F(Z) to obtain the digital signal E after removing the high-frequency scanning signal, E1=F(Z)*W1, E2=F(Z)*W2, and only the signal corresponding to the laser driving signal frequency is reserved after high-pass and low-pass digital filtering; (7) Digital smoothing filtering: the adjacent point multiple point average of the digital signal E is obtained to obtain the digital signal E(N, M) after smoothing filtering, E1'=E1(N,M), E2'=E2(N,M); (8) Concentration signal: the integral areas of the second harmonic signal E2(N, M) and the first harmonic signal E1(N, M) after smoothing filtering are obtained, and the methane gas concentration value C in the environment is C=∑E2'(N) / ∑E1'(N), which is in a one-to-one corresponding positive linear relationship with ΣE2(N, M) / ΣE1(N, M); (9) Adjacent point multiple smoothing filtering of the concentration signal C: the gas concentration signal value C obtained by solving is subjected to adjacent point multiple average filtering to remove the maximum and minimum values to obtain the average value, so as to improve the stability of measurement; (10) Real gas concentration: the standard methane gas sample is introduced, the corresponding concentration value and concentration signal value C are recorded, the calibration function F(C) is obtained, and then the concentration signal C obtained by solving is combined with the calibration function F(C) to obtain the methane gas concentration in the environment; (11) Temperature compensation: the temperature change of the environment will affect the absorption rate of methane gas to light wave, the correlation function F(C, T) of the temperature T and the concentration signal value C is obtained by fitting a large amount of experimental test data, the concentration signal C is compensated for temperature, the compensated concentration signal C'=F(C, T) is obtained, and the influence of the change of the environment temperature on the measurement is eliminated; (12) Pressure compensation: the change of the gas pressure of the environment will also affect the absorption rate of methane gas to light wave, the correlation function F(C', P) of the pressure P and the concentration signal value C is obtained by fitting a large amount of experimental test data, the concentration signal C' is compensated for pressure, the compensated concentration signal C''=F(C', P) is obtained, and the influence of the change of the environment pressure on the measurement is eliminated.

2. An integrated laser methane detection device, characterized by: The methane gas concentration laser detection algorithm comprises a shell assembly, an internal component, a non-airtight packaging component, a gas path, and a light path. The shell assembly comprises a device shell (10), a dustproof air-permeable net (11), and a screw ring (12). The internal component comprises an optical module base (1), a TO laser (2), a left reflective prism (3), a right reflective prism (4), a PD photodetector (5), a temperature and pressure integrated chip (6), a preamplification circuit module (7), an MCU signal processing circuit module (8), and a connection cable (9). The non-airtight packaging component comprises a non-airtight packaging material. The light path is made on the upper surface of the integrally formed optical module base (1) and is a cavity structure. The gas path is formed by the gas diffusion channel of the non-airtight packaging component, the entire device is packaged with the non-airtight packaging component, and the gas path and the light path exchange with ambient gas through gas diffusion. The TO laser (2) is provided with a back light detection PD photodetector, the light wave emitted by the laser is monitored in real time according to the PD photodetector signal, the laser is real-time aligned with the methane detection absorption peak wavelength by adjusting the temperature of the laser, the gap is filled with an insulating heat-conducting material after the light path is adjusted on an optical platform, and the laser and the optical module base are welded and fixed. The right reflective prism (3) and the left reflective prism (4) are fixed on the optical module base after the light path is adjusted on the optical platform. The PD photodetector (5) is used for converting the received laser light wave signal into an electric signal, and the PD photodetector and the optical module base are welded and fixed after the light path is adjusted on the optical platform. The laser (2) and the PD photodetector (5) in the optical component are welded and connected with the preamplification circuit module (7) through the self-provided multi-PIN metal pins. The preamplification circuit module (7) performs analog signal filtering and amplification processing on the weak electric signal converted by the PD photodetector. The temperature and pressure integrated chip (6) is used for temperature measurement and pressure measurement and is connected and communicated with the main control chip through the cable. The preamplification circuit module (7) and the MCU signal processing circuit module (8) are welded and connected through the multi-PIN metal pins for signal transmission. The MCU signal processing circuit module (8) is provided with multi-channel AD and DA functions, the AD function converts the analog signal with the gas absorption signal into a digital signal. The connection cable (9) is used for connecting an external system and providing direct current power supply and signal transmission for the device. The device shell (10) comprises a shell lower cover (1001) and a shell upper cover (1002), the shell lower cover (1001) is in a cylindrical structure, internally assembled with internal components, and has a cylindrical step with a thickness decreasing inward at the upper part, used for sleeving with the shell upper cover (1002), and is connected with a dustproof and breathable mesh (11) at the bottom; the shell upper cover (1002) is a reverse T-shaped cylinder, the lower end of which is sleeved on the upper part of the shell lower cover (1001), and the upper end is provided with external threads, used in cooperation with a screw ring (12) for fixing the methane detection device on an application device, and the upper end is used for penetrating through a connecting wire (9).

3. The integrated laser methane detection device of claim 2, wherein: The material of the optical module base (1) is 314 stainless steel.

4. The integrated laser methane detection device of claim 2, wherein: The TO laser (2) is a TO60 laser sealed with pure methane, provided with a non-spherical collimating lens at the front end, emitting approximately parallel light waves, and provided with a back light detection PD photodetector for monitoring the light waves emitted by the laser in real time according to the PD photodetector signal, and then adjusting the temperature of the laser to align the methane detection absorption peak wavelength 1653.7 nm in real time.

5. The integrated laser methane detection device of claim 4, wherein: After adjusting the optical path of the TO60 laser on an optical platform, the gap is filled with heat-conducting silicone grease, and the TO60 laser and the optical module base are fixed by laser welding at the top.

6. The integrated laser methane detection device of claim 2, wherein: The right reflective prism (3) and the left reflective prism (4) are both 45° reflective prisms, the 45° reflective prisms are based on Si02, the emission surface is plated with gold or multi-layer dielectric film, and are used for deflecting a vertically incident laser beam by 90°; after adjusting the optical path on an optical platform, the 3535D high-temperature curing glue is used to glue the optical module base in a 100℃ environment.

7. The integrated laser methane detection device as described in claim 2, characterized in that: The PD photodetector (5) is a TO56 type InGaAs PD photodetector, the sensing wavelength range is 800-1700 nm, the front end is provided with a focusing lens, and is used for converting the received laser signal into an electrical signal; after adjusting the optical path on an optical platform, the TO56 type PD photodetector and the optical module base are fixed by laser welding at the top.

8. The integrated laser methane detection device of claim 2, wherein: The temperature and pressure integrated chip (6) adopts a PT300 type high-precision temperature and pressure chip, the temperature measurement range is -30-60℃, the pressure range is 80-130kpa, and the chip is connected and communicated with an MCU main control chip through a wire.

9. The integrated laser methane detection device as described in claim 2, characterized in that: The MCU signal processing circuit module (8) selects an STM32F405 chip as the main control chip, the chip is provided with multi-channel AD and DA functions, and the AD function converts an analog signal with a gas absorption signal into a digital signal.

10. The integrated laser methane detection device as described in claim 2, characterized in that: The connecting wire (9) is a multi-core connecting wire, used for connecting an external signal transmitter or a computer supporting device, and providing direct current power supply and signal transmission for the device.

11. The integrated laser methane detection device as described in claim 2, characterized in that: The screw ring (12) is a hexagonal screw ring.

12. The integrated laser methane detection device of claim 2, wherein: The material of the non-gas-tight packaging component is epoxy resin.

13. An integrated laser methane detection device as claimed in one of the claims 2-12, characterized in that, The specific algorithm of the laser methane detection device is as follows: (1) MCU signal processing circuit module in the main control chip DA function and AD function of the crystal clock synchronization signal control, DA function will chip storage laser drive digital signal into analog signal, drive laser to emit specific wavelength of 1653.7 nm ± 0.1 nm light wave; (2) under the control of synchronization signal, the AD function on the chip to laser emission light wave after the gas absorption in the optical path, again by PD photodetector into current signal, again by preamplifier processing after carrying gas concentration signal voltage signal high frequency digital sampling, each sampling point all use high frequency multiple repeated sampling to obtain the average value method, to eliminate the white noise of the circuit, improve the accuracy of measurement; (3) the digital signal P after high-frequency sampling 均 convolution processing with a high-pass filter function F(X) to obtain a digital signal Q after removing the low-frequency scanning signal; the high-pass filter function F(X) is a FIR filter function, and specific function values are designed according to the laser sawtooth wave scanning frequency; (4) digital signal Q respectively with laser sinusoidal drive signal F1(Y) and F1(Y) of the second frequency doubling signal F2(Y) corresponding multiplication, get the first harmonic signal W1 and second harmonic signal W2; (5) second harmonic signal W2 again with low pass filter function F(Z) convolution, get after the removal of high frequency scanning signal digital signal E, the low pass filter function F(Z) is FIR filter function, the specific function value according to the laser sinusoidal scanning frequency design, after high pass and low pass digital filter, only keep down the laser drive signal frequency corresponding signal; (6) to the signal E obtained by adjacent point multiple point average, get the digital signal E(N, M) after smoothing filter; (7) respectively to obtain the integral area of the second harmonic signal E2(N, M) and the first harmonic signal E1(N, M) after smoothing filter, the methane gas concentration value C in the environment and ΣE2(N, M) / ΣE1(N, M) corresponding to the positive linear relationship, through the fitting calibration function to solve the gas concentration C in the environment; (8) to the gas concentration signal value C obtained by solving the adjacent point multiple average filter, remove the maximum and minimum value, get the average value, to improve the stability of measurement; (9) by passing into the standard methane gas sample, record the corresponding concentration value and signal value C, get the calibration function F(C), then by the signal C combined with the calibration function F(C) to get the methane gas concentration in the environment; (10) compensation of environmental temperature change: the temperature change of the environment affects the absorption rate of methane gas to light wave, through a large number of experimental test data fitting to get the correlation function F(C, T) of temperature T and concentration signal value C, according to the actual environment detection temperature T temperature compensation, to eliminate the influence of environmental temperature change on measurement; (11) compensation of environmental gas pressure change: the change of environmental gas pressure affects the absorption rate of methane gas to light wave, through a large number of experimental test data fitting to get the correlation function F(C, P) of pressure P and concentration signal value C, according to the actual environment detection pressure P pressure compensation, to eliminate the influence of environmental pressure change on measurement.

Images