Gas concentration detection sensor based on dual-wavelength differential absorption and error compensation method

Abstract

The invention relates to a gas concentration detection sensor based on dual-wavelength differential absorption and an error compensation method, belongs to the field of gas pressure detection, and aims to solve the problem that temperature and humidity changes and equipment temperature drift cause significant errors to a gas concentration monitoring result in the prior art. The sensor comprises a laser module, a light beam combiner, a first optical system, a second optical system, a concentration error correction module, a concentration parameter time sequence control circuit and a data processing module. Two lasers with different wavelengths are adopted, a differential absorption principle is utilized to detect target gas, and concentration error correction is performed in combination with environment temperature and humidity information. A concentration error correction model containing a temperature item, a humidity item and a coupling item is introduced into the data processing module, and high-precision gas concentration inversion can be achieved in a complex environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of gas pressure detection and relates to a gas concentration detection sensor based on dual-wavelength differential absorption and an error compensation method. BACKGROUND

[0002] As the most important greenhouse gas, the concentration change of carbon dioxide (CO2) directly affects the global temperature rise trend. Therefore, how to accurately and stably measure the CO2 concentration in various complex environments is an important research direction of current gas detection technology.

[0003] The differential absorption laser radar (DIAL) technology has been widely used for remote sensing of gas concentration in the atmosphere due to its non-contact, high sensitivity and high spatial resolution. Among them, the dual-wavelength differential absorption method usually selects an absorption wavelength and a non-absorption wavelength, and realizes the inversion calculation of gas concentration through the difference of the return signal by virtue of the difference in gas absorption characteristics. It is the most critical core mechanism in current CO2 concentration detection.

[0004] However, in actual application, especially in areas with variable environmental conditions such as mines, atmospheric boundary layers and complex urban scenes, temperature, humidity and aerosol disturbance have a significant impact on the laser propagation path and signal attenuation, thereby introducing errors in gas concentration measurement. In addition, the stability of optical and electronic elements is reduced due to temperature drift during long-term continuous operation of the system, which further affects the accuracy of the concentration inversion result.

[0005] Existing technologies such as CN105510260A and CN114660573A optimize gas concentration monitoring from aspects such as path integral inversion model and dual-pulse frequency stabilization control, but still cannot effectively cope with dynamic interference and system temperature drift error in complex environments.

[0006] Therefore, there is an urgent need for a high-precision gas concentration detection technology that can consider external disturbance and system stability, integrate high-sensitivity differential absorption detection, temperature and humidity error compensation, power closed-loop control and optical optimization design, to meet the higher requirements for concentration data reliability in key application scenarios such as carbon emission monitoring and greenhouse gas tracking. SUMMARY

[0007] In the prior art, there are problems of large gas pressure detection error caused by temperature and humidity changes in the mine and serious temperature drift error during long-term operation. Therefore, the application provides a gas concentration detection sensor based on dual-wavelength differential absorption and an error compensation method to solve the above problems.

[0008] A gas concentration detection sensor based on dual-wavelength differential absorption, comprising:

[0009] The laser module comprises a first wavelength laser and a second wavelength laser, and is used for outputting laser pulses of different wavelengths.

[0010] A light beam combiner is used for combining the light beams output by the first wavelength laser and the second wavelength laser and realizing alternate emission.

[0011] The first optical system comprises, in sequence along an optical path, an expander, an axicon and a lens, the expander is used for expanding the light beam output by the light beam combiner, the axicon is used for converting the parallel light beam after expansion into a circular ring beam spot, and the lens is used for focusing the circular ring beam spot.

[0012] The second optical system comprises a Cassegrain telescope and a light barrier, the Cassegrain telescope is used for receiving the light beam focused by the first optical system and converting it into a parallel light beam, and the light barrier is arranged at a focal point of the Cassegrain telescope and is used for limiting an effective detection range.

[0013] The concentration error correction module comprises a temperature sensor and a humidity sensor, is used for monitoring the ambient temperature and relative humidity RH in real time, and generates a concentration error correction signal.

[0014] The concentration parameter time sequence control circuit is connected with the laser module and the concentration error correction module, is used for controlling the working parameters of the laser according to the received concentration error correction signal, and adopts a 20 ms periodic sampling frequency.

[0015] The data processing module is connected with the concentration parameter time sequence control circuit, comprises a signal acquisition board and a microcontroller, the signal acquisition board is used for receiving a detection signal, and the microcontroller is used for calculating the target gas concentration by using a concentration error correction model according to the detection signal and the concentration error correction signal, the model comprises a temperature term coefficient α, a humidity term coefficient β and a temperature and humidity coupling correction term γ, wherein α=0.035% / ℃, β=0.02% / %RH and γ=0.0015% / (℃·%RH).

[0016] The data processing module further comprises a storage unit, which stores, in a time sequence database structure and according to a time stamp, an original photon counting signal, temperature and humidity data, laser power adjustment records and a typical aerosol parameter reference table.

[0017] Further, the first wavelength laser is a 1064 nm laser, the second wavelength laser is a 1572 nm laser, and the emission wavelength of the second wavelength laser is fixed on an off wavelength in a non-absorption waveband.

[0018] Further, the beam expander, axicon and lens surface of the first optical system are coated with anti-reflection film of 770nm band.

[0019] Further, the Cassegrain telescope comprises a primary mirror and a secondary mirror, the size and position of the secondary mirror are configured to not block the emitted light beam output by the first optical system.

[0020] A gas concentration detection error compensation method based on dual-wavelength differential absorption is applied to the sensor, comprising the following steps:

[0021] S1: controlling the first wavelength laser and the second wavelength laser to alternately emit laser pulses through the beam combiner;

[0022] S2: using the first optical system to expand, convert into a circular ring beam spot and focus the combined laser pulses;

[0023] S3: using the second optical system to receive the focused light beam and convert it into a parallel light beam, and limiting the effective detection range through the diaphragm;

[0024] S4: using the concentration error correction module to monitor the ambient temperature t and the relative humidity h in real time, and generating a concentration error correction signal ΔC;

[0025] S5: using the concentration parameter time sequence control circuit to adjust the working parameters of the laser according to the concentration error correction signal ΔC;

[0026] S6: using the data processing module to collect the detection signal;

[0027] S7: using the microcontroller to obtain the gas concentration C based on the detection signal, and the corrected concentration C' = C + ΔC;

[0028] S8: storing the final concentration C' and the environmental parameters in the storage unit.

[0029] Further, in S5, the laser power adjustment adopts proportional-integral control logic; when ΔC>0, increase the power of 1064nm laser and reduce the power of 1572nm laser, and vice versa.

[0030] Further, in S1, the interval of the alternate emission of the laser is 500ms.

[0031] Further, in the inversion process, wavelength-dependent correction is introduced, and the value of the dynamic turbulence index k is calculated as 1.2-1.8 to improve the concentration inversion accuracy.

[0032] Further, the beam expander, axicon and lens surface of the first optical system are coated with anti-reflection film of 770nm band.

[0033] Further, the accuracy of the final output gas concentration C' is better than 0.05% VOL.

[0034] The beneficial effects of the present application are:

[0035] 1. The present application adopts a dual-wavelength laser alternating emission mechanism, combines the differential absorption principle and high-efficiency optical path design, and can accurately extract the concentration signal of CO2 and other target gases. By constructing a differential signal model between the absorption wavelength and the non-absorption wavelength, the background scattering and systematic deviation are effectively suppressed, and the accuracy of concentration inversion is significantly improved. The concentration detection accuracy is better than 0.05% VOL.

[0036] 2. The present application innovatively introduces a concentration error correction model composed of temperature terms, humidity terms and coupling terms, dynamically calculates the concentration error ΔC through real-time sampling of temperature and humidity, realizes the correction of the absorption characteristic deviation caused by the change of environmental temperature and humidity, effectively reduces the measurement error, and guarantees that the system can still output accurate concentration values in complex environments.

[0037] 3. The present application is based on a closed-loop control strategy, and automatically adjusts the power output of the dual-wavelength laser according to the concentration error correction signal, effectively overcomes the temperature drift problem of the laser source and the detection link in long-time operation, makes the system maintain sustained sensitivity and stability, and is suitable for long-period environmental monitoring tasks.

[0038] 4. By coating 770nm anti-reflection film on the surfaces of key optical devices such as beam expanders, axicon bodies and lenses, the light beam transmission efficiency and echo receiving strength are improved. At the same time, the Cassegrain telescope sub-mirror structure is precisely configured to avoid blocking the emission light beam, and the signal-to-noise ratio and energy utilization rate of the system during detection are significantly enhanced.

[0039] 5. The data processing module adopts a time series database structure, records the original detection signal, environmental parameters and laser power adjustment information according to the time stamp, and internally stores a typical aerosol parameter table, which is convenient for concentration inversion model iteration optimization and long-term data tracking analysis.

[0040] 6. The sensor system and compensation method proposed in the present application are suitable for online monitoring of gas concentration in various complex environments such as underground, atmospheric boundary layer and industrial park, and can be widely applied in the fields of carbon emission supervision, environmental gas tracking and underground safety, and has good engineering practicability and popularization value.

[0041] Other advantages, objects, and features of the present application will be apparent to those skilled in the art from the following specification, and will be learned from the practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the following specification. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred embodiments will be described in detail below with reference to the drawings, in which:

[0043] Figure 1 is a system structure block diagram;

[0044] Figure 2 is an optical path detail block diagram;

[0045] Figure 3 is a control and calculation flowchart. DETAILED DESCRIPTION

[0046] The embodiments of the present application will be described in detail below with reference to specific examples. Other advantages and effects of the present application can be easily understood by those skilled in the art from the content disclosed in the specification. The present application can also be implemented or applied in other different embodiments, and various modifications or changes can be made to the details in the specification based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following examples only schematically illustrate the basic concepts of the present application, and the features in the following examples and embodiments can be combined with each other without conflict.

[0047] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and should not be understood as a limitation on the present application. In order to better illustrate the embodiments of the present application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual size of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0048] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for exemplary illustration, and should not be understood as a limitation on the present application. For those skilled in the art, the specific meanings of the above terms can be understood according to the specific circumstances.

[0049] I. System structure composition

[0050] The present application comprises the following modules:

[0051] 1. Laser module

[0052] The system includes a first wavelength laser (1064nm) and a second wavelength laser (1572nm), which emit laser pulses alternately to form a differential absorption detection signal. The 1572nm is the absorption wavelength of CO2, and the 1064nm is the reference wavelength or off-wavelength.

[0053] 2. Beam combiner and first optical system

[0054] After the two laser beams are combined by the beam combiner, they pass through a beam expander (5 times), an axicon (converts parallel light into a ring-shaped beam), and a focusing lens (forms a beam spot) in sequence to be emitted to the detection area. All optical surfaces are coated with 770nm band antireflection film to reduce reflection loss.

[0055] 3. Second optical system

[0056] The system includes a Cassegrain telescope and an aperture, which are used to receive and collimate the return signal. The sub-mirror structure is optimally designed to not block the forward emission beam.

[0057] 4. Concentration error correction module

[0058] The system includes a temperature sensor (such as MLX90614) and a humidity sensor (such as AM2302), which are used to collect real-time environmental temperature t and humidity h, and are used for concentration error correction calculation.

[0059] 5. Concentration parameter timing control circuit

[0060] The sampling period is 20ms, and the concentration error signal ΔC calculated by the correction model is used to close-loop adjust the output power of the laser.

[0061] 6. Data processing module

[0062] The system includes a signal acquisition board (such as PCI-6115) and a microcontroller (such as STM32F407). After collecting the return signal, the differential absorption inversion algorithm is executed to calculate the CO2 concentration, and the output concentration is adjusted to C' = C + ΔC in combination with the correction model. The concentration correction model is as follows:

[0063] ΔC = (α·t + β·h + γ·t·h) × 100%

[0064] Where α = 0.035% / ℃, β = 0.02% / %RH, and γ = 0.0015% / (℃·%RH).

[0065] 7. Storage unit

[0066] The system stores concentration results, temperature and humidity data, power adjustment records, and preset aerosol parameter tables, and the data structure is a time series database.

[0067] II. Workflow

[0068] 1. Initialization:

[0069] The system loads the concentration error correction model parameters after power on, starts the dual-wavelength laser and each sensor module.

[0070] 2. Laser emission and detection:

[0071] The laser emits pulsed light beams at an interval of 500 ms. The laser is processed by the first optical system and enters the atmospheric detection area, and the return signal is received through the second optical system.

[0072] 3. Temperature and humidity sampling and error correction:

[0073] The temperature and humidity sensor collects environmental parameters in real time, and calculates the concentration error ΔC through the correction model and transmits it to the timing control module.

[0074] 4. Laser power regulation (closed loop control):

[0075] If ΔC>0, the system increases the power of the 1064nm laser and reduces the power of the 1572nm laser; if ΔC<0, the opposite adjustment is made. The power regulation adopts a PI control algorithm:

[0076] ΔP laser =K p ·|ΔC|+K i ·∫ΔCdt

[0077] Wherein, K p =0.8, K i =0.05.

[0078] 5. Signal inversion and concentration calculation:

[0079] The microcontroller uses the differential absorption algorithm and introduces the wavelength-dependent correction factor k (range 1.2-1.8), combines the atmospheric extinction coefficient and the backscattering characteristics to invert the CO2 concentration C, and superimposes ΔC to generate the final concentration C'.

[0080] 6. Result storage and output:

[0081] The system synchronously writes the final concentration value, environmental parameters and power regulation records into the storage unit.

[0082] III. Applicability and accuracy

[0083] The gas concentration detection system of the present application can operate stably in complex environments (such as mines, boundary layers, industrial sites). Experimental verification shows that the CO2 concentration inversion accuracy is better than 0.05% VOL, with excellent dynamic adaptability and long-term stability.

[0084] Figure 2 Focusing on the structure design of the core optical components:

[0085] 1. Beam expander:

[0086] The surface is marked with an anti-reflection film layer optimized for the 770nm wavelength band, achieving a 5-fold beam expansion and effectively improving the spatial distribution uniformity and transmission efficiency of laser energy.

[0087] 2. Axicon:

[0088] Receives the parallel light beam output by the beam expander and converts it into a ring-shaped light beam to form a circular ring-shaped spot suitable for differential absorption detection. The cross-sectional view shows the shape of the formed ring-shaped spot.

[0089] 3. Lens:

[0090] Focuses the ring-shaped light beam, with the final focused spot diameter being about 50μm, facilitating the improvement of spatial resolution and echo signal quality.

[0091] 4. Cassegrain telescope:

[0092] The primary mirror has a diameter of 200mm, the secondary mirror has a diameter of 50mm, and the distance between the primary and secondary mirrors is 100mm. The position of the secondary mirror is optimized to ensure that it does not block the emission light path. The structure design aims to enhance the reception capability of the echo signal and reduce energy loss.

[0093] 5. Diaphragm:

[0094] Located at the focal point of the Cassegrain telescope, it is used to limit the effective detection range to 100 meters, thereby enhancing the spatial filtering capability and suppressing the interference of background stray light.

[0095] Figure 3 Disclosed is the closed-loop control and data processing logic of the present invention:

[0096] 1. Input layer: environmental parameter acquisition

[0097] The temperature sensor acquires the environmental temperature t (unit: ℃) in real time;

[0098] The humidity sensor acquires the relative humidity h (unit: %RH) in real time.

[0099] 2. Error correction model calculation

[0100] The system calculates the concentration error correction amount ΔC based on the temperature and humidity inputs, and the correction model is:

[0101] ΔC = (0.035 × t + 0.02 × h + 0.0015 × t × h) × 100%

[0102] This model corrects the influence of environmental changes on the differential absorption results through linear and coupling terms.

[0103] 3. Control decision logic (power adjustment)

[0104] The decision block determines the direction of laser power adjustment according to the sign of ΔC:

[0105] If ΔC > 0: increase 1064 nm laser power, decrease 1572 nm laser power;

[0106] If ΔC < 0: decrease 1064 nm laser power, increase 1572 nm laser power.

[0107] The laser power adjustment amount is dynamically calculated by a PI controller:

[0108] ΔP laser = K p · |ΔC| + K i · ∫ΔCdt

[0109] Where K p = 0.8, K i = 0.05.

[0110] 4. Detection and signal acquisition

[0111] The laser alternately emits dual-wavelength pulsed laser at 500 ms intervals;

[0112] The signal acquisition board receives the echo signal after atmospheric absorption.

[0113] 5. Concentration inversion and correction

[0114] The microcontroller executes the differential absorption inversion algorithm to obtain the initial concentration value C, and outputs the final concentration value in combination with the correction amount:

[0115] C final = C + ΔC

[0116] A wavelength-dependent correction factor k is introduced in the inversion process to dynamically calculate the turbulence index (range 1.2-1.8), improving the accuracy of concentration calculation, especially suitable for environments with aerosol interference.

[0117] 6. Data storage

[0118] All key parameters and output results are written into the storage unit of the time series database structure according to the timestamp, including:

[0119] Original photon counting signal (sampling interval 20 ms);

[0120] Temperature and humidity sensor data (sampling frequency 1 Hz);

[0121] Laser power adjustment record;

[0122] The initial concentration value C and the corrected concentration value C final ;

[0123] The dynamically calculated turbulence parameter k;

[0124] The preset aerosol parameter table and the related control factor.

[0125] Embodiment one

[0126] The application provides a gas concentration detection sensor based on dual-wavelength differential absorption and an error compensation method. The sensor comprises a laser module, a first optical system, a second optical system, a concentration error correction module, a concentration parameter timing control circuit and a data processing module.

[0127] The laser module comprises a 1064nm laser and a 1572nm laser, and the 1064nm laser and the 1572nm laser alternately emit laser pulses through a beam combiner. The output beam of the beam combiner is expanded through a beam expander and then enters the atmospheric environment for detection through the first optical system. The beam expander expands the output beam of the laser, the axicon converts the parallel beam into a circular ring beam spot, and the lens focuses the converted beam. The surfaces of the beam expander, the axicon and the lens of the first optical system are coated with a 770nm band antireflection film for reducing the reverse transmission of the beam.

[0128] The second optical system comprises a Cassegrain telescope and a diaphragm, the Cassegrain telescope converts the focused beam into a parallel beam, and the diaphragm is arranged at the beam convergence point for limiting the effective detection range. The Cassegrain telescope of the second optical system comprises a primary mirror and a secondary mirror, and the size and position of the secondary mirror are optimized to not block the emitted beam.

[0129] The concentration error correction module comprises a temperature sensor and a humidity sensor for real-time monitoring of the ambient temperature and humidity to generate a concentration error correction signal. The concentration parameter timing control circuit controls the working parameters of the laser according to the environmental parameters, and adopts a periodic sampling frequency of 20ms.

[0130] The data processing module comprises a signal acquisition board and a microcontroller for receiving and processing the detection signal, and calculating the target gas concentration according to a concentration error correction model. The concentration error correction model comprises a temperature term coefficient a, a humidity term coefficient β and a temperature and humidity coupling correction term γ, wherein a = 0.035% / ℃, β = 0.02% / %RH, and γ = 0.0015% / (℃ %RH); the correction formula is: ΔC = (0.035 × t + 0.02 × h + 0.0015 × t × h) × 100%.

[0131] The data processing module further comprises a storage unit, and the storage unit adopts a time series database structure and stores the timestamp:

[0132] Raw photon count signal (20 ms interval);

[0133] 1Hz sampling data of temperature and humidity sensor;

[0134] Laser power adjustment history;

[0135] And prestore typical mine gas aerosol parameter table.

[0136] The output beams of the 1064nm laser and the 1572nm laser are alternately emitted through a beam combiner, and the emission wavelength of the 1572nm laser is fixed on the off wavelength to reduce the influence of atmospheric CO2 on the reference signal. During the detection process, the beams alternately emitted by the dual lasers are combined through the beam combiner, expanded and focused by the first optical system, and then enter the atmospheric environment for differential absorption detection. At the same time, the temperature sensor and the humidity sensor monitor the environmental parameters in real time to generate a concentration error correction signal, which is adjusted through the concentration parameter timing control circuit. The data processing module calculates the current gas concentration by using a concentration error correction model according to the detection signal and the environmental parameters, and stores the result in the storage unit.

[0137] Example two

[0138] The specific parameters of the gas concentration detection sensor provided by the application are as follows:

[0139] Laser module:

[0140] 1064nm laser: wavelength 1064nm, average power 100mW, pulse width 10ns, repetition frequency 100kHz;

[0141] 1572nm laser: wavelength 1572nm, average power 50mW, pulse width 8ns, repetition frequency 50kHz.

[0142] First optical system:

[0143] Beam expander: beam expansion ratio 5 times;

[0144] Axicon: radius 50mm, cone angle 30°;

[0145] Lens: focal length 500mm, numerical aperture 8mm.

[0146] Second optical system:

[0147] Primary mirror: diameter 200mm;

[0148] Secondary mirror: diameter 50mm;

[0149] Primary-secondary mirror spacing: 100mm.

[0150] Concentration error correction module:

[0151] Temperature sensor: model MLX90614, measurement range -40℃ to 125℃;

[0152] Humidity sensor: model AM2302, measurement range 0% to 100% RH.

[0153] Concentration parameter timing control circuit:

[0154] Sampling frequency: 20ms.

[0155] Data processing module:

[0156] Signal acquisition board: model PCI-6115, sampling rate 1MS / s, resolution 16 bits;

[0157] Microcontroller: model STM32F407, main frequency 168MHz.

[0158] Example three

[0159] The working principle of the gas concentration detection sensor of the application is as follows:

[0160] 1. The 1064nm laser and the 1572nm laser are alternately emitted by a beam combiner, and the interval between each emission is 500ms;

[0161] 2. After the emitted light beam is expanded and focused by the first optical system, a circular ring beam spot with a diameter of about 50μm is formed; after the beam spot is converged by the second optical system, it is converted into a parallel light beam with a diameter of about 10μm;

[0162] 3. After the parallel light beam is limited by the diaphragm, the effective detection range is controlled within the atmospheric path of 100 meters, which is used for differential absorption detection of target gases such as CO2;

[0163] 4. The temperature sensor and the humidity sensor monitor the ambient temperature t and the relative humidity h in real time, and calculate the concentration error correction signal ΔC:

[0164] ΔC=(0.035×t+0.02×h+0.0015×t×h)×100%

[0165] 5. The concentration parameter timing control circuit adjusts the working parameters of the laser according to ΔC:

[0166] The power adjustment adopts a PI controller, and the proportional coefficient K p =0.8, the integral coefficient K i =0.05, and the control output is:

[0167] ΔP laser= 0.8 * |AC| + 0.05 * integral AC dt

[0168] When AC > 0:

[0169] 1064nm laser power regulation is P 1064 * (1 + AP laser ) ;

[0170] 1572nm laser power regulation is P 1572 * (1 - 0.5AP laser ) ;

[0171] If AC < 0, then the average power of the two lasers is adjusted in the opposite direction.

[0172] 6. The data processing module collects the detection signal, uses the differential absorption inversion algorithm and the Fernald method to obtain the CO2 concentration on the target path, and outputs the final concentration value in combination with the correction term:

[0173] The initial concentration C is calculated by the inversion algorithm;

[0174] The final concentration C final = C + AC.

[0175] 7. The final concentration value C final , temperature, humidity, laser power and other operating parameters are stored in the storage unit of the data processing module, facilitating subsequent analysis and historical comparison.

[0176] Through the above parameter settings and working principles, the present application realizes high precision and high stability of gas concentration detection, meeting the practical application requirements of gas concentration monitoring in complex environments such as underground and atmospheric boundary layer.

[0177] Example Four

[0178] 1. System startup and initialization:

[0179] Start the gas concentration detection sensor.

[0180] The 1064nm laser and the 1572nm laser in the laser module complete preheating.

[0181] The microcontroller in the data processing module loads the preset concentration error correction model parameters:

[0182] Temperature term coefficient a = 0.035% / ℃

[0183] Humidity term coefficient b = 0.02% / %RH

[0184] Temperature and humidity coupling term coefficient g = 0.0015% / (℃ * %RH)

[0185] The concentration parameter timing control circuit is set to a 20 ms periodic sampling frequency.

[0186] 2. Dual-wavelength alternate emission and beam processing:

[0187] The concentration parameter timing control circuit issues control instructions, and the 1064 nm and 1572 nm lasers emit laser pulses alternately through a beam combiner at 500 ms intervals.

[0188] The 1572 nm laser emits at a fixed off-wavelength outside the CO2 absorption band.

[0189] The combined beam passes through the first optical system in turn: beam expander (expansion ratio 5 times) → axicon (converted to ring-shaped beam spot light) → lens (focusing to form a spot of about 50 μm).

[0190] The focused beam enters the second optical system: Cassegrain telescope (primary and secondary mirror structure) to convert it into parallel light, and the aperture stop limits the effective detection distance to 100 meters.

[0191] 3. Real-time monitoring of environmental parameters and generation of concentration error correction signals:

[0192] The temperature sensor collects the current temperature t (e.g. 30°C), and the humidity sensor collects the current humidity h (e.g. 60% RH).

[0193] The concentration error correction module calculates the correction amount:

[0194] ΔC = (0.035 × t + 0.02 × h + 0.0015 × t × h) × 100% = 4.35%

[0195] 4. Dynamic adjustment of laser parameters:

[0196] ΔC > 0, the concentration parameter timing control circuit issues control instructions within a 20 ms cycle:

[0197] Increase the average power of the 1064 nm laser

[0198] Reduce the average power of the 1572 nm laser

[0199] 5. Signal acquisition, inversion, and concentration calculation:

[0200] The signal acquisition board of the data processing module acquires the echo signal after atmospheric action, introduces a dynamic turbulence index k (range 1.2-1.8) during inversion, and performs wavelength-dependent correction.

[0201] The inversion calculation obtains the initial CO2 concentration value C, and combines the correction term to output the final concentration:

[0202] C final = C + ΔC

[0203] 6. Data storage:

[0204] Final concentration value C final , current temperature and humidity t, h, laser power control amount, etc. are written into the storage unit.

[0205] Example five

[0206] 1. Optical component processing:

[0207] All optical surfaces of the beam expander, axicon and lens of the first optical system are coated with antireflection film layers optimized for the 770 nm wavelength band.

[0208] The size (diameter 50 mm) and position (100 mm apart from the primary mirror) of the secondary mirror of the Cassegrain telescope are optimized to ensure that it does not block the path of the emitted light beam from the first optical system.

[0209] 2. Detection process:

[0210] The 1064 nm and 1572 nm laser alternately emit pulsed light beams, which are expanded by the surface-coated beam expander and then converted into a ring-shaped beam by the axicon.

[0211] The ring-shaped beam is focused by the lens and then enters the second optical system, which receives and collimates it into parallel light by the primary mirror and secondary mirror system. Subsequently, the entrance angle and detection depth are limited by the diaphragm.

[0212] The return signal carries gas absorption information and enters the signal acquisition module for processing.

[0213] 3. Subsequent processing flow:

[0214] Real-time monitoring of temperature and humidity, calculation of concentration error ΔC;

[0215] Adjusting the laser power in response to the concentration error;

[0216] Concentration inversion using differential absorption algorithm;

[0217] Output final concentration C final = C + ΔC;

[0218] All parameters are written into the storage unit (steps 3-6 in example four).

[0219] Example six

[0220] 1. System operation and control:

[0221] The system operates normally according to the process of example five.

[0222] The temperature sensor detects that the ambient temperature has risen to 35°C, and the humidity sensor detects that the relative humidity is 70% RH.

[0223] The concentration error correction module calculates:

[0224] AC = (0.035 x 35 + 0.02 x 70 + 0.0015 x 35 x 70) x 100% = 6.48%

[0225] 2. Closed-loop power regulation:

[0226] The concentration parameter timing control circuit determines that AC > 0, and immediately issues a closed-loop regulation command within a 20ms cycle:

[0227] Increase the power of the 1064nm laser;

[0228] Proportionally reduce the power of the 1572nm laser;

[0229] The adjustment value is output by the PI controller.

[0230] 3. Application of specific inversion algorithm:

[0231] The signal acquisition board receives the adjusted large air echo signal.

[0232] The microcontroller executes the Fernald differential absorption inversion algorithm, and uses the difference between the two wavelengths to invert the aerosol extinction coefficient and backscatter coefficient on the path, and further calculates the CO2 concentration.

[0233] Combined with the absorption cross section of CO2 at 1572nm wavelength and the corrected laser energy ratio, the average concentration value C is obtained.

[0234] 4. Concentration result synthesis and recording:

[0235] The preliminary concentration C is added to the correction term AC to obtain the final concentration value:

[0236] C final = C + AC

[0237] The final concentration value, current temperature and humidity, laser power and other operating data are recorded in the storage unit.

[0238] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A gas concentration detection sensor based on dual-wavelength differential absorption, characterized by: The application relates to a laser module, a light beam combiner, a first optical system, a second optical system, a concentration error correction module, a concentration parameter time sequence control circuit, and a data processing module. The laser module comprises a first wavelength laser and a second wavelength laser for outputting laser pulses of different wavelengths. The light beam combiner is used for combining the light beams output by the first wavelength laser and the second wavelength laser and realizing alternate emission. The first optical system comprises, sequentially arranged along an optical path, an expander, an axicon and a lens, the expander is used for expanding the light beam output by the light beam combiner, the axicon is used for converting the parallel light beam after expansion into circular ring beam spot light, and the lens is used for focusing the circular ring beam spot light. The second optical system comprises a Cassegrain telescope and a light barrier, the Cassegrain telescope is used for receiving the light beam focused by the first optical system and converting the light beam into parallel light beams, and the light barrier is arranged at a focal point of the Cassegrain telescope and is used for limiting an effective detection range. The concentration error correction module comprises a temperature sensor and a humidity sensor and is used for monitoring the ambient temperature and relative humidity RH in real time and generating a concentration error correction signal. The concentration parameter time sequence control circuit is connected with the laser module and the concentration error correction module and is used for controlling the working parameters of the laser according to the received concentration error correction signal, and the control circuit adopts a 20ms periodic sampling frequency. The data processing module is connected with the concentration parameter time sequence control circuit and comprises a signal acquisition board and a microcontroller, the signal acquisition board is used for receiving a detection signal, and the microcontroller is used for calculating the target gas concentration by using a concentration error correction model according to the detection signal and the concentration error correction signal, the model comprises a temperature term coefficient alpha, a humidity term coefficient beta and a temperature and humidity coupling correction term gamma, wherein alpha=0.035% / C, beta=0.02% / % RH and gamma=0.0015% / (C% RH). The data processing module further comprises a storage unit which stores, in a time stamp, the original photon counting signal, the temperature and humidity data, the laser power adjustment record and a typical aerosol parameter comparison table in a time sequence database structure.

2. The gas pressure detecting sensor according to claim 1, characterized by: The first wavelength laser is a 1064nm laser, the second wavelength laser is a 1572nm laser, and the emission wavelength of the second wavelength laser is fixed on a non-absorption waveband, namely an off wavelength.

3. The gas pressure detecting sensor according to claim 1 or 2, characterized by: The expander, the axicon and the lens of the first optical system are coated with an antireflection film of a 770nm waveband.

4. The gas pressure detecting sensor according to claim 1, characterized by: The Cassegrain telescope comprises a primary mirror and a secondary mirror, the size and position of the secondary mirror are configured to not shield the emission light beam output by the first optical system.

5. A method for compensating error of gas concentration detection based on dual-wavelength differential absorption, applied to the sensor of any one of claims 1-4, characterized in that: The application further discloses a method for detecting a target gas, comprising the following steps: S1: controlling the first wavelength laser and the second wavelength laser to alternately emit laser pulses through the light beam combiner; S2: expanding, converting into circular ring beam spot light and focusing the laser pulses after combination by using the first optical system; S3: receiving the focused light beam and converting the light beam into parallel light beams by using the second optical system, and limiting the effective detection range by using the light barrier; S4: monitoring the ambient temperature t and the relative humidity h in real time by using the concentration error correction module and generating a concentration error correction signal Delta C. S5: adjusting the working parameters of the laser according to the concentration error correction signal ΔC by using the concentration parameter timing control circuit; S6: collecting the detection signal by using the data processing module; S7: obtaining the gas concentration C by using the microcontroller based on the detection signal, and correcting the concentration C' = C + ΔC; S8: storing the final concentration C' and the environmental parameters in the storage unit.

6. The gas pressure detection error compensation method according to claim 5, characterized by: In S5, the laser power adjustment adopts proportional-integral control logic; when ΔC > 0, the 1064 nm laser power is increased and the 1572 nm laser power is decreased, and vice versa.

7. The gas pressure detection error compensation method according to claim 5 or 6, characterized by: In S1, the alternate emission interval of the laser is 500 ms.

8. The gas pressure detection error compensation method according to claim 5, characterized by: In the inversion process, the wavelength-dependent correction is introduced, and the value of the dynamic turbulence index k is calculated as 1.2-1.8 to improve the concentration inversion accuracy.

9. The gas pressure detection error compensation method according to claim 5, characterized by: The expander, axicon and lens of the first optical system are coated with anti-reflection film in the 770 nm band.

10. The gas pressure detection error compensation method according to claim 5, characterized by: The accuracy of the final output gas concentration C' is better than 0.05% VOL.

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