High-precision laser gas detection system

Abstract

The invention discloses a high-precision laser gas detection system, and belongs to the technical field of laser spectrum gas detection. According to the invention, the reference signal feedback drives the laser to realize the locking of the laser output central wavelength. By arranging a half-optical-path sampling hole, double-path acquisition of half-optical-path and full-optical-path interference signals is realized, and when an absorption signal of a full-optical-path digital signal is smaller than a set threshold value, laser fluctuation noise, front half-optical-path interference noise and photoelectric detector noise are eliminated by adopting a double-path signal comparison method; and the interference waveform of the absorption region of the rear half optical path is fitted by combining the light interference Airy model function through the interference signals of the two-wing non-absorption region of the double-path comparison signal, so that the interference noise of the rear half optical path is eliminated, and the measurement precision of the to-be-measured gas at low concentration can be further improved. When the absorption signal of the full-optical-path digital signal is larger than or equal to a set threshold value, the measurement range can be directly and effectively increased by adopting the half-optical-path signal, and the wide-range measurement range is achieved while high-precision measurement is met.

Description

Technical Field

[0001] The invention relates to the technical field of laser spectrum gas detection, in particular to a high-precision laser gas detection system. Background Art

[0002] Tunable semiconductor laser absorption spectroscopy (TDLAS) is an important technical means of gas detection. It has the advantages of high detection accuracy, no calibration, no zero drift, and no gas cross-interference. It has been maturely applied to safety, environmental protection, industrial processes, metallurgy, chemical industry, electricity, medical and aerospace fields. According to the Beer-Lambert law, the intensity of gas molecule spectral absorption is related to gas concentration, absorption optical path length, air pressure and temperature. Therefore, in order to improve the accuracy and sensitivity of TDLAS gas detection, the commonly used methods include: selecting spectral lines with stronger absorption, increasing the absorption optical path, noise suppression, etc. However, if a far-infrared laser with stronger absorption is used, the cost will increase significantly; increasing the absorption optical path has higher requirements on the stability and cost of the system, and the optical path cannot be increased indefinitely; noise suppression to improve the signal-to-noise ratio of the absorption spectrum signal is the most fundamental, flexible and economical solution. In the TDLAS system, the noise sources include: white noise, laser light source fluctuation noise, optical interference noise, photoelectric detection noise, and circuit noise. Summary of the invention

[0003] In view of the above problems, a high-precision laser gas detection method is provided. The present invention fits the interference noise of the gas absorption interval band through the phase and intensity law of the interference signal to remove most of the interference noise, thereby achieving high-precision TDLAS gas concentration measurement. At the same time, combined with the half-path absorption signal, the maximum detection range of the gas to be measured can be multiplied to achieve a wide range of gas concentration measurement.

[0004] To achieve the above object, the technical solution adopted by the present invention is.

[0005] A high-precision laser gas detection system comprises a laser, a beam splitter, a reference gas pool, a photoelectric detector 1, a reference signal processing module, a multiple reflection pool, a measurement signal processing module, an MCU and a laser driving module; the multiple reflection pool comprises a high-reflection concave mirror 1, a high-reflection concave mirror 2, a sampling hole, a photoelectric detector 2 and a photoelectric detector 3; the high-reflection concave mirror 1 is arranged at the upper end of the multiple reflection pool, and is symmetrical with the high-reflection concave mirror 2 arranged at the lower end of the multiple reflection pool along the middle horizontal position; a pinhole window 1, a sampling hole and a pinhole window 2 are arranged on the left side, the middle and the right side of the high-reflection concave mirror 1 in sequence.

[0006] Preferably, the laser output by the laser is split into measurement light and reference light by a beam splitter; after the reference light is absorbed by the standard concentration gas in the reference gas cell, it is received by a photodetector and converted into a reference electrical signal, the reference electrical signal is processed by a reference signal processing module to obtain the absorption peak position corresponding to the standard concentration gas in the reference gas cell, and the absorption peak position is output to the MCU, and the MCU feedback controls the laser driving module to lock the central wavelength of the laser output laser.

[0007] Preferably, the measuring light enters the multiple reflection pool through pinhole window 1, is reflected multiple times by high-reflection concave mirror 2 and high-reflection concave mirror 1 and is absorbed by the gas to be measured in the multiple reflection pool, and then is output to photodetector 2 and photodetector 3 through the sampling hole of the middle half-optical path of the high-reflection concave mirror 1 and pinhole window 2 of the full-optical path on the right side respectively, is synchronously converted into half-optical path electrical signals and full-optical path electrical signals by photodetector 2 and photodetector 3, and then is output to the measurement signal processing module, is synchronously converted into half-optical path digital signals and full-optical path digital signals by the measurement signal processing module, and is output to the MCU, and the MCU calculates the concentration of the gas to be measured according to the noise reduction algorithm and the Lambert-Beer gas absorption theorem.

[0008] Preferably, the splitting ratio of the measurement signal to the reference signal is 19:1.

[0009] Preferably, an air inlet and an air outlet for the gas to be tested are respectively provided at the upper end and the lower end on the left side of the multiple reflection pool.

[0010] Preferably, the multiple reflection pool further includes a collimator for collimating the laser spot.

[0011] Preferably, the Lambert-Beer gas absorption theorem is as follows: in, I 0 is the incident light intensity, I t is the transmitted light intensity, α ( n ) is the absorbance, k ν is the spectral absorption coefficient, S (T) is the temperature-dependent absorption line intensity, ϕ( n ) is the normalized absorption line function, P is the pressure, X is the concentration of the gas, and L is the absorption path length.

[0012] Preferably, the noise reduction algorithm comprises the following steps: Step 1: The MCU synchronously acquires the half-light-path digital signal and the full-light-path digital signal output by the measurement signal processing module, and performs multi-cycle signal averaging on the half-light-path digital signal and the full-light-path digital signal to eliminate white noise; Step 2: Perform peak normalization processing on the half-light-path digital signal and the full-light-path digital signal after white noise reduction in step 1 to ensure that the amplitudes of the half-light-path digital signal and the full-light-path digital signal are the same; Step 3: Perform FIR filtering on the half-light-path digital signal and the full-light-path digital signal after the peak normalization processing in step 2; Step 4: Determine whether the absorption signal of the full optical path digital signal after FIR filtering in step 3 exceeds a set threshold; Step 5: If the absorption signal of the full optical path digital signal is greater than or equal to the set threshold, the absorption signal corresponding to the half optical path digital signal is used, and the concentration of the gas to be measured is calculated in combination with the Lambert-Beer gas absorption theorem; Step 6: If the absorption signal of the full optical path digital signal is less than the set threshold, a dual-path signal comparison method is used to eliminate the laser fluctuation noise, the first half optical path interference noise and the photodetector noise to obtain a dual-path comparison signal; Step 7: The interference signals of the non-absorption areas on both wings of the dual-path comparison signal in step 6 are combined with the light interference Airy model function to fit the interference waveform of the absorption area in the second half of the optical path, and finally the interference noise in the second half of the optical path is eliminated. Then, the absorption signal corresponding to the full optical path digital signal is used, combined with the Lambert-Beer gas absorption theorem, to calculate the concentration of the gas to be measured.

[0013] Preferably, the set threshold is 5% Vol.

[0014] Preferably, the two-way signal comparison method comprises the following steps: Step S1: The half-optical path interference signal D1 detected by the second photodetector and the full-optical path interference signal D2 detected by the third photodetector are as follows:

[0015] Among them, S L is the gas absorption signal intensity of the full optical path interference signal; S L / 2 is the gas absorption signal intensity of the half-path interference signal; n 激光器 is the laser fluctuation noise; n 前半光程干涉 is the interference noise of the first half of the optical path; n 后半光程干涉 is the interference noise of the second half of the optical path; n 光电探测器 represents the noise of photodetector 2 or photodetector 3; Step S2: When the absorption signal of the full optical path digital signal is less than the set threshold, the gas absorption signal intensity S of the full optical path interference signal L Gas absorption signal intensity 2S approximated with half-path interference signal L / 2 If they are equal, the dual comparison signal 2 (D2-D1) is: Among them, S L is the gas absorption signal intensity of the full optical path interference signal; n 后半光程干涉 is the interference noise of the second half of the optical path.

[0016] Preferably, the light interference Airy model function is as follows: in, R is the distance between the high-reflection concave mirror 1 and the high-reflection concave mirror 2; I r An interference signal formed by a half-optical-path interference signal and a full-optical-path interference signal; d is the phase of the half-optical path interference signal or the full-optical path interference signal.

[0017] Due to the adoption of the above technical solution, the present invention has the following beneficial effects.

[0018] (1) The present invention drives the laser through reference signal feedback to achieve locking of the laser output center wavelength. By setting a tiny half-optical path sampling hole, dual-path collection of half-optical path and full-optical path interference signals is achieved. When the absorption signal of the full-optical path digital signal is less than the set threshold, the dual-path signal comparison method is used to eliminate the laser fluctuation noise, the first half-optical path interference noise and the photoelectric detector noise to remove the laser light source fluctuation noise and photoelectric detection noise. The dual-path comparison signal can greatly eliminate white noise, laser light source fluctuation noise, light interference noise, photoelectric detector and other noise signals, greatly improving the accuracy of ultra-low concentration laser gas monitoring.

[0019] (2) The present invention uses the interference signals of the non-absorption areas on both wings of the dual-path comparison signal, and combines the light interference Airy model function to fit the interference waveform of the absorption area in the second half of the optical path, and finally eliminates the interference noise in the second half of the optical path, which can further improve the measurement accuracy of the gas to be measured at low concentrations.

[0020] (3) The present invention can directly and effectively increase the measurement range by using a half-optical path signal when the absorption signal of the full-optical path digital signal is ≥ the set threshold, that is, when the gas absorption intensity corresponding to the sampled interference light is high, thereby achieving a wide range of measurement while meeting high-precision measurement.

[0021] (4) The present invention fits the interference noise of the gas absorption interval band through the phase and intensity law of the interference signal, which can effectively remove the laser light source fluctuation noise and photoelectric detection noise, and achieve high-precision measurement of the concentration of the gas to be measured. At the same time, the present invention combines the half-path absorption signal to multiply the detection upper limit of the gas concentration to be measured, achieving a wide-range gas concentration detection technology effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The following is a detailed discussion of the making and application of the preferred embodiments of the present invention. However, it should be understood that the present invention provides many applicable inventive concepts that can be embodied in various specific environments. The specific embodiments discussed are only for the purpose of illustrating the specific ways of making and using the present invention, and do not limit the scope of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work.

[0023] Figure 1 It is a structural diagram of the present invention.

[0024] Among them, 1-laser; 2-beam splitter; 3-reference gas pool; 4-photodetector 1; 5-pinhole window 1; 6-collimator; 7-sampling hole; 8-photodetector 2; 9-photodetector 3; 10-air inlet; 11-high reflection concave mirror 1; 12-pinhole window 2; 13-multiple reflection pool; 14-air outlet; 15-high reflection concave mirror 2; 16-reference signal processing module; 17-laser driving module; 18-MCU; 19-measurement signal processing module. DETAILED DESCRIPTION

[0025] The following is a detailed discussion of the making and application of the preferred embodiments of the present invention. However, it should be understood that the present invention provides many applicable inventive concepts that can be embodied in various specific environments. The specific embodiments discussed are only intended to illustrate specific ways to make and use the present invention and do not limit the scope of the present invention.

[0026] The present invention fits the interference noise of the gas absorption interval band through the phase and intensity law of the interference signal, which can effectively remove the laser light source fluctuation noise and photoelectric detection noise, and achieve high-precision measurement of the concentration of the gas to be measured. At the same time, the present invention combines the half-path absorption signal to multiply the detection upper limit of the gas concentration to be measured, achieving a wide-range gas concentration detection technology effect.

[0027] The following is combined with Figure 1 Further elaboration.

[0028] A high-precision laser gas detection system comprises a laser 1, a beam splitter 2, a reference gas pool 3, a photodetector 14, a reference signal processing module 16, a multiple reflection pool 13, a measurement signal processing module 19, an MCU 18 and a laser driving module 17; the multiple reflection pool 13 comprises a high-reflection concave mirror 11, a high-reflection concave mirror 2 15, a sampling hole 7, a collimator 6 for collimating the laser spot, a photodetector 2 8 and a photodetector 3 9; the upper and lower ends of the left side of the multiple reflection pool 13 are respectively provided with an inlet 10 and an outlet 14 for the inlet and outlet of the gas to be measured, the high-reflection concave mirror 11 is arranged at the upper end of the multiple reflection pool 13, and is symmetrical with the high-reflection concave mirror 2 15 arranged at the lower end of the multiple reflection pool 13 along the middle horizontal position; the left, middle and right sides of the high-reflection concave mirror 11 are sequentially provided with a pinhole window 15, a sampling hole 7 and a pinhole window 2 12.

[0029] The laser output by the laser 1 is split into measurement light and reference light by the beam splitter 2, and the splitting ratio of the measurement signal to the reference signal is 19:1. After the reference light is absorbed by the standard concentration gas in the reference gas pool 3, it is received by the photodetector 4 and converted into a reference electrical signal. After the reference electrical signal is processed by the reference signal processing module 16, the absorption peak position corresponding to the standard concentration gas in the reference gas pool 3 is obtained, and the absorption peak position is output to the MCU 18, and the MCU 18 feedback controls the laser driving module 17 to lock the central wavelength of the laser output by the laser 1.

[0030] The measuring light enters the multiple reflection pool 13 through the pinhole window 15, is reflected multiple times by the high-reflection concave mirror 2 15 and the high-reflection concave mirror 1 1 and is absorbed by the gas to be measured in the multiple reflection pool 13, and then is output to the photodetector 2 8 and the photodetector 3 9 through the sampling hole 7 of the middle half-light path of the high-reflection concave mirror 1 1 and the pinhole window 2 12 of the full-light path on the right side, respectively. The photodetector 2 8 and the photodetector 3 9 are synchronously converted into half-light path electrical signals and full-light path electrical signals, and then output to the measurement signal processing module 19, which are synchronously converted into half-light path digital signals and full-light path digital signals by the measurement signal processing module 19 and output to the MCU 18. The MCU 18 calculates the concentration of the gas to be measured according to the noise reduction algorithm and the Lambert-Beer gas absorption theorem.

[0031] The Lambert-Beer gas absorption theorem is as follows: in, I 0 is the incident light intensity, I t is the transmitted light intensity, α ( n ) is the absorbance, k ν is the spectral absorption coefficient, S(T) is the temperature-dependent absorption line intensity, ϕ( n ) is the normalized absorption line function, P is the pressure, X is the concentration of the gas, and L is the absorption path length.

[0032] The noise reduction algorithm includes the following steps: Step 1: The MCU 18 synchronously obtains the half-optical path digital signal and the full-optical path digital signal output by the measurement signal processing module 19, and performs multi-cycle signal averaging on the half-optical path digital signal and the full-optical path digital signal to reduce white noise.

[0033] Step 2: Perform peak normalization processing on the half-light-path digital signal and the full-light-path digital signal after white noise reduction in step 1 to ensure that the amplitudes of the half-light-path digital signal and the full-light-path digital signal are the same.

[0034] Step 3: Perform FIR filtering on the half-light-path digital signal and the full-light-path digital signal after the peak normalization processing in step 2.

[0035] Step 4: Determine whether the absorption signal of the full optical path digital signal after FIR filtering in step 3 exceeds a set threshold, wherein the set threshold is 5% Vol.

[0036] Step 5: If the absorption signal of the full optical path digital signal is greater than or equal to the set threshold, the absorption signal corresponding to the half optical path digital signal is used, and the concentration of the gas to be measured is calculated in combination with the Lambert-Beer gas absorption theorem.

[0037] Step 6: If the absorption signal of the full optical path digital signal is less than the set threshold, a dual-path signal comparison method is used to eliminate the laser 1 fluctuation noise, the first half optical path interference noise and the photodetector noise to obtain a dual-path comparison signal.

[0038] The dual-path signal comparison method comprises the following steps: Step S1: the half-optical path interference signal D1 detected by the photoelectric detector 2 8 and the full-optical path interference signal D2 detected by the photoelectric detector 3 9 are as follows: Among them, S L is the gas absorption signal intensity of the full optical path interference signal; S L / 2 is the gas absorption signal intensity of the half-path interference signal; n 激光器 is the laser 1 fluctuation noise; n 前半光程干涉 is the interference noise of the first half of the optical path; n 后半光程干涉 is the interference noise of the second half of the optical path; n 光电探测器 represents the noise of photodetector two 8 or photodetector three; Step S2: When the absorption signal of the full optical path digital signal is less than the set threshold, the gas absorption signal intensity S of the full optical path interference signalL Gas absorption signal intensity 2S approximated with half-path interference signal L / 2 If they are equal, the dual comparison signal 2 (D2-D1) is: Among them, S L is the gas absorption signal intensity of the full optical path interference signal; n 后半光程干涉 is the interference noise of the second half of the optical path.

[0039] Step 7: The interference waveform of the absorption region in the second half of the optical path is fitted by combining the interference signals of the non-absorption regions on both wings of the two-way comparison signal in step 6 with the light interference Airy model function. The light interference Airy model function is as follows: in, R is the distance between the high-reflection concave mirror 11 and the high-reflection concave mirror 2 15; I r An interference signal formed by a half-optical-path interference signal and a full-optical-path interference signal; d is the phase of the half-path interference signal or the full-path interference signal. Finally, the interference noise of the second half of the path is eliminated, and then the absorption signal corresponding to the full-path digital signal is used, combined with the Lambert-Beer gas absorption theorem to calculate the concentration of the gas to be measured.

[0040] Specifically, Figure 1 The high-precision laser gas detection system not only ensures the high-precision performance of the laser gas monitoring system, but also ensures a wide range of gas measurement. The present invention adopts the TDLAS technology in the field of laser spectral gas absorption detection. The laser 1 is a semiconductor laser 1 commonly used in TDLAS, which can emit laser light of a specific wavelength. The laser driving module 17 is used for high-frequency current modulation to drive the laser 1. The beam splitter 2 is a 5%:95% ratio optical beam splitter 2 for light splitting. The reference gas pool 3 is used to emit and receive reference lasers, and is filled with standard sample gas. The absorption position of the standard sample gas is used as the reference position of the output center wavelength of the laser 1.

[0041] The photoelectric detector 4 is a reference light receiver of the reference gas pool 3, which can realize the photoelectric conversion of the reference light. The reference signal processing module 16 is used to convert and process the reference electrical signal and feedback control the laser 1 driving module, thereby locking the output center wavelength of the laser 1. The multi-reflection pool 13 samples the fully sealed metal warehouse to isolate the external air to prevent the gas in the external air from interfering with the detection of the gas sample to be measured. The air inlet 10 is used to introduce the gas sample to be measured. The air outlet 14 is used to export the gas sample to be measured.

[0042] The laser driving module 17 controls the output of the laser 1 through high-frequency current modulation to measure the laser of a specific wavelength of the gas to be measured. The laser is input to the 5%:95% beam splitter 2 after optical fiber coupling. The 5% reference light output after beam splitting by the beam splitter 2 is used to monitor and lock the output center wavelength of the laser 1. The reference light is input into the reference absorption optical path filled with standard sample gas, passes through the reference gas and is absorbed, and is received by the photoelectric detector 4. After photoelectric conversion by the photoelectric detector 4, a reference electrical signal is formed and output to the reference signal processing module 16. After calculation and processing by the reference signal processing module 16, the absorption peak position of the standard sample gas can be obtained, so that the feedback control adjusts the center wavelength of the laser 1 to a fixed position, thereby improving the reliability and stability of the measurement system.

[0043] 95% of the measurement light is input into the multiple reflection absorption chamber, and the measurement light is reflected multiple times in the chamber body of the multiple reflection pool 13. After multiple absorption by the gas to be measured in the absorption chamber, the reflected laser carrying the spectral information of the gas to be measured forms a half-optical path interference signal and a full-optical path interference signal at the sampling hole 7 at the half-optical path and the pinhole window 2 12 at the full-optical path, respectively. The half-optical path interference signal and the full-optical path interference signal are received by the photoelectric detector 2 8 and the photoelectric detector 3 9 in two paths, respectively. The photoelectric detector 2 8 and the photoelectric detector 3 9 form a half-optical path electrical signal and a full-optical path electrical signal output value measurement signal processing module 19 after photoelectric conversion, and are processed by the measurement signal processing module 19 and output as a half-optical path digital signal and a full-optical path digital signal to MCU18. After MCU18 obtains the half-optical path digital signal and the full-optical path digital signal, the MCU18 calculates the concentration of the gas to be measured according to the noise reduction algorithm and the Lambert-Beer gas absorption theorem.

[0044] The Lambert-Beer gas absorption theorem is as follows: in, I 0 is the incident light intensity, I t is the transmitted light intensity, α ( n ) is the absorbance, k ν is the spectral absorption coefficient, S (T) is the temperature-dependent absorption line intensity, ϕ( n ) is the normalized absorption line function, P is the pressure, X is the concentration of the gas, and L is the absorption path length.

[0045] The noise reduction algorithm comprises the following steps: Step 1: The MCU 18 synchronously acquires the half-optical path digital signal and the full-optical path digital signal output by the measurement signal processing module 19, and performs multi-cycle signal averaging on the half-optical path digital signal and the full-optical path digital signal to eliminate white noise.

[0046] Step 2: Perform peak normalization processing on the half-light-path digital signal and the full-light-path digital signal after white noise reduction in step 1 to ensure that the amplitudes of the half-light-path digital signal and the full-light-path digital signal are the same.

[0047] Step 3: Perform FIR filtering on the half-light-path digital signal and the full-light-path digital signal after the peak normalization processing in step 2.

[0048] Step 4: Determine whether the absorption signal of the full optical path digital signal after FIR filtering in step 3 exceeds a set threshold.

[0049] Step 5: If the absorption signal of the full optical path digital signal is greater than or equal to the set threshold, the absorption signal corresponding to the half optical path digital signal is used, and the concentration of the gas to be measured is calculated in combination with the Lambert-Beer gas absorption theorem.

[0050] Step 6: If the absorption signal of the full optical path digital signal is less than the set threshold, a dual-path signal comparison method is used to eliminate the laser 1 fluctuation noise, the first half optical path interference noise and the photodetector noise to obtain a dual-path comparison signal.

[0051] Step 7: The interference signals of the non-absorption areas on both wings of the dual-path comparison signal in step 6 are combined with the light interference Airy model function to fit the interference waveform of the absorption area in the second half of the optical path, and finally the interference noise in the second half of the optical path is eliminated. Then, the absorption signal corresponding to the full optical path digital signal is used, combined with the Lambert-Beer gas absorption theorem, to calculate the concentration of the gas to be measured.

[0052] The two-way signal comparison method comprises the following steps: Step S1: The half-optical path interference signal D1 detected by the second photodetector 8 and the full-optical path interference signal D2 detected by the third photodetector 9 are as follows: Among them, S L is the gas absorption signal intensity of the full optical path interference signal; S L / 2 is the gas absorption signal intensity of the half-path interference signal; n 激光器 is the laser 1 fluctuation noise; n 前半光程干涉 is the interference noise of the first half of the optical path; n 后半光程干涉 is the interference noise of the second half of the optical path; n 光电探测器 Represents the noise of photodetector two 8 or photodetector three.

[0053] Step S2: When the absorption signal of the full optical path digital signal is less than the set threshold, the gas absorption signal intensity S of the full optical path interference signal L Gas absorption signal intensity 2S approximated with half-path interference signal L / 2If they are equal, the dual comparison signal 2 (D2-D1) is: Among them, S L is the gas absorption signal intensity of the full optical path interference signal; n 后半光程干涉 is the interference noise of the second half of the optical path.

[0054] The light interference Airy model function is as follows: in, R is the distance between the high-reflection concave mirror 11 and the high-reflection concave mirror 2 15; I r An interference signal formed by a half-optical-path interference signal and a full-optical-path interference signal; d is the phase of the half-optical path interference signal or the full-optical path interference signal.

[0055] The present invention discloses a high-precision laser gas detection system, which belongs to the technical field of laser spectrum gas detection. The present invention drives the laser 1 through reference signal feedback to achieve locking of the laser output center wavelength. By setting a half-optical path sampling hole 7, dual-path collection of half-optical path and full-optical path interference signals is achieved. When the absorption signal of the full-optical path digital signal is less than the set threshold, a dual-path signal comparison method is used to eliminate the laser 1 fluctuation noise, the first half-optical path interference noise and the photodetector noise, and the interference signal of the non-absorption area on both wings of the dual-path comparison signal is combined with the light interference Airy model function to fit the interference waveform of the absorption area in the second half-optical path to eliminate the interference noise in the second half-optical path, which can further improve the measurement accuracy of the gas to be measured at low concentrations. When the absorption signal of the full-optical path digital signal is greater than or equal to the set threshold, the half-optical path signal is used to directly and effectively increase the measurement range, and while meeting the high-precision measurement, a wide range of measurement is achieved.

[0056] Although the specification has been described in detail, it should be understood that various changes, substitutions and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. In addition, the specific embodiments described are not intended to limit the scope of the invention, and those of ordinary skill in the art can easily understand based on the present invention that currently existing or later to be developed processes, machines, manufactures, material compositions, means, methods, or steps can perform substantially the same functions as the embodiments of the present invention or obtain substantially the same results. Therefore, the appended claims are intended to include such processes, machines, manufactures, material compositions, means, methods or steps within their scope.

Claims

1. A high-precision laser gas detection system, characterized in that: It includes a laser, a beam splitter, a reference gas pool, a photoelectric detector 1, a reference signal processing module, a multiple reflection pool, a measurement signal processing module, an MCU and a laser driving module; the multiple reflection pool includes a high-reflection concave mirror 1, a high-reflection concave mirror 2, a sampling hole, a photoelectric detector 2 and a photoelectric detector 3; the high-reflection concave mirror 1 is arranged at the upper end of the multiple reflection pool, and is symmetrical with the high-reflection concave mirror 2 arranged at the lower end of the multiple reflection pool along the middle horizontal position; the left side, the middle part and the right side of the high-reflection concave mirror 1 are provided with a pinhole window 1, a sampling hole and a pinhole window 2 in sequence; The laser output by the laser is split into measurement light and reference light by a beam splitter; the reference light is absorbed by the standard concentration gas in the reference gas pool, and then received by a photodetector 1 and converted into a reference electrical signal; the reference electrical signal is processed by a reference signal processing module to obtain the absorption peak position corresponding to the standard concentration gas in the reference gas pool, and the absorption peak position is output to the MCU, and the MCU feedback controls the laser driving module to lock the central wavelength of the laser output laser; The measuring light enters the multiple reflection pool through the pinhole window 1, is reflected multiple times by the high-reflection concave mirror 2 and the high-reflection concave mirror 1 and is absorbed by the gas to be measured in the multiple reflection pool, and then is output to the photodetector 2 and the photodetector 3 through the sampling hole of the middle half optical path of the high-reflection concave mirror 1 and the pinhole window 2 of the full optical path on the right side respectively, is synchronously converted into a half-optical path electrical signal and a full-optical path electrical signal by the photodetector 2 and the photodetector 3, and then is output to the measurement signal processing module, is synchronously converted into a half-optical path digital signal and a full-optical path digital signal by the measurement signal processing module, and is output to the MCU, and the MCU calculates the concentration of the gas to be measured according to the noise reduction algorithm and the Lambert-Beer gas absorption theorem.

2. A high-precision laser gas detection system as claimed in claim 1, characterized in that: The splitting ratio of the measurement signal to the reference signal is 19:

1.

3. A high-precision laser gas detection system as claimed in claim 1, characterized in that: An air inlet and an air outlet for the gas to be measured are respectively arranged at the upper end and the lower end of the left side of the multiple reflection pool.

4. A high-precision laser gas detection system as claimed in claim 3, characterized in that: The multiple reflection pool further includes a collimator for collimating the laser spot.

5. A high-precision laser gas detection system as claimed in claim 1, characterized in that: The Lambert-Beer gas absorption theorem is as follows: in, I 0 is the incident light intensity, I t is the transmitted light intensity, α ( ν ) is the absorbance, k ν is the spectral absorption coefficient, S (T) is the temperature-dependent absorption line intensity, ϕ( ν ) is the normalized absorption line function, P is the pressure, X is the concentration of the gas, and L is the absorption path length.

6. A high-precision laser gas detection system as claimed in claim 1, characterized in that: The noise reduction algorithm comprises the following steps: Step 1: The MCU synchronously acquires the half-light-path digital signal and the full-light-path digital signal output by the measurement signal processing module, and performs multi-cycle signal averaging on the half-light-path digital signal and the full-light-path digital signal to eliminate white noise; Step 2: Perform peak normalization processing on the half-light-path digital signal and the full-light-path digital signal after white noise reduction in step 1 to ensure that the amplitudes of the half-light-path digital signal and the full-light-path digital signal are the same; Step 3: Perform FIR filtering on the half-light path digital signal and the full-light path digital signal after the peak normalization processing in step 2; Step 4: Determine whether the absorption signal of the full optical path digital signal after FIR filtering in step 3 exceeds a set threshold; Step 5: If the absorption signal of the full optical path digital signal is greater than or equal to the set threshold, the absorption signal corresponding to the half optical path digital signal is used, and the concentration of the gas to be measured is calculated in combination with the Lambert-Beer gas absorption theorem; Step 6: If the absorption signal of the full optical path digital signal is less than the set threshold, a dual-path signal comparison method is used to eliminate the laser fluctuation noise, the first half optical path interference noise and the photodetector noise to obtain a dual-path comparison signal; Step 7: The interference signals of the non-absorption areas on both wings of the dual-path comparison signal in step 6 are combined with the light interference Airy model function to fit the interference waveform of the absorption area in the second half of the optical path, and finally the interference noise in the second half of the optical path is eliminated. Then, the absorption signal corresponding to the full optical path digital signal is used, combined with the Lambert-Beer gas absorption theorem, to calculate the concentration of the gas to be measured.

7. A high-precision laser gas detection system as claimed in claim 6, characterized in that: The set threshold is 5% Vol.

8. A high-precision laser gas detection system as claimed in claim 6, characterized in that: The two-way signal comparison method comprises the following steps: Step S1: The half-optical path interference signal D1 detected by the second photodetector and the full-optical path interference signal D2 detected by the third photodetector are as follows: Among them, S L is the gas absorption signal intensity of the full optical path interference signal; S L / 2 is the gas absorption signal intensity of the half-path interference signal; n 激光器 is the laser fluctuation noise; n 前半光程干涉 is the interference noise of the first half of the optical path; n 后半光程干涉 is the interference noise of the second half of the optical path; n 光电探测器 represents the noise of photodetector 2 or photodetector 3; Step S2: When the absorption signal of the full optical path digital signal is less than the set threshold, the gas absorption signal intensity S of the full optical path interference signal L Gas absorption signal intensity 2S approximated with half-path interference signal L / 2 If they are equal, the dual comparison signal 2 (D2-D1) is: Among them, S L is the gas absorption signal intensity of the full optical path interference signal; n 后半光程干涉 is the interference noise of the second half of the optical path.

9. A high-precision laser gas detection system as claimed in claim 1, characterized in that: The light interference Airy model function is as follows: in, R is the distance between the high-reflection concave mirror 1 and the high-reflection concave mirror 2; I r An interference signal formed by a half-optical-path interference signal and a full-optical-path interference signal; δ is the phase of the half-optical path interference signal or the full-optical path interference signal.

Images