Gas-chamber-free self-calibration system based on laser gas detection and detection method

Abstract

The invention relates to the technical field of gas detection, and discloses a gas-chamber-free self-calibration system based on laser gas detection and a detection method, the system comprises a laser emission module, an optical system, a signal processing module and an environment detection assembly; the laser transmitting module comprises a laser; the optical system is used for receiving laser signals and is in signal connection with the signal processing module; the environment detection assembly is in signal connection with the signal processing module; the signal processing module is used for signal acquisition, processing and self-calibration. The whole structure is simple, a physical air chamber is not needed, and the problem of dependence on the physical air chamber in the prior art is solved. The method comprises a calibration stage and a measurement stage, wherein the calibration stage comprises the steps of introducing standard gas with known concentration, recording incident light intensity and absorption peak height or area and calculating a calibration ratio; in the measurement stage, self-calibration is realized through an algorithm based on a calibration ratio, the problem of result drift caused by environmental interference and laser aging in the prior art is solved, and the gas measurement precision is high.

Description

Technical Field

[0001] This invention relates to the field of gas detection technology, and in particular to a chamberless self-calibration system and detection method based on laser gas detection. Background Technology

[0002] Traditional laser gas detection systems typically require a built-in reference gas chamber for real-time calibration of laser fluctuations and optical path attenuation. However, the reference gas chamber increases system complexity and cost, and long-term use may lead to chamber leakage or contamination.

[0003] In addition, in open optical path detection, environmental factors (such as temperature, pressure, and humidity) and background noise (such as dust and absorption by other gases) can affect the detection accuracy; the laser output light intensity gradually decreases over time, causing the detection results to drift and resulting in low detection accuracy.

[0004] Therefore, it is necessary to provide a new detection method to solve the above-mentioned technical problems. Summary of the Invention

[0005] The main objective of this invention is to provide a chamberless self-calibration system and detection method based on laser gas detection, which aims to solve the problems of result drift caused by gas chamber dependence, environmental interference and laser aging in traditional technologies.

[0006] To achieve the above objectives, the present invention provides a chamberless self-calibration system based on laser gas detection, comprising a laser emission module, an optical system, a signal processing module, and an environmental detection component; The laser emitting module includes a laser for emitting a wavelength that matches the absorption peak of the target gas; The optical system is used to receive laser signals and is connected to the signal processing module. The environmental detection component is connected to the signal processing module and is used to measure the temperature of the laser, the pressure of the environment, and the humidity of the environment. The signal processing module is used for signal acquisition, processing, and self-calibration.

[0007] Preferably, the laser is a tunable diode laser.

[0008] Preferably, the optical system includes a photodetector and a emitting lens, a refractor, and a receiving lens arranged along the optical path.

[0009] Preferably, the signal processing module includes an analog-to-digital converter, a digital-to-analog converter, and a microprocessor; the microprocessor reads the laser temperature, ambient pressure, and ambient humidity through the analog-to-digital converter; the microprocessor controls the laser temperature by adjusting the TEC through PWM; and the microprocessor adjusts the laser current through the digital-to-analog converter.

[0010] Preferably, the environmental detection component includes a temperature sensor, a pressure sensor, and a humidity sensor. The temperature sensor is used to measure the temperature of the laser, the pressure sensor is used to measure the temperature of the environment, and the humidity sensor is used to measure the humidity of the environment.

[0011] The present invention also provides a laser gas detection method, which uses the above-mentioned self-calibration system without a gas chamber based on laser gas detection for self-calibration. The laser gas detection method includes a calibration stage and a measurement stage. The calibration phase includes the following steps: Step 1.1: Introduce a standard gas of known concentration; Step 1.2: Record the incident light intensity and absorption peak height or area ; Step 1.3: Calculate the calibration ratio. : or ; The measurement phase includes the following steps: Step 2.1: Measure the current effective incident light intensity. and absorption peak height or area ; Step 2.2: Calculate the current ratio as follows: or ; Step 2.3: Based on the calibration ratio and standard gas concentration Calculate the current concentration ,as follows: .

[0012] Preferably, in step 2.1: based on statistical moment theory, the area is... Defined as absorbance function of The weighted moments are calculated as follows: ; in: for Generalized absorbance moment; , Let be the order of the moment; This refers to the frequency or wavenumber of light. The center frequency or center wavenumber of the target gas absorption spectral line; The starting frequency of the integration interval; is the termination frequency of the integration interval.

[0013] Preferably, in step 2.2, the functional relationship between the incident light intensity and the laser's time-domain parameters is established as follows: ; in: The effective incident light intensity within a single scan cycle; For a complete wavelength scan cycle; The average output power is represented by the DC power component. For power fluctuations; For scanning functions; () represents the laser line shape function; The instantaneous center frequency of the laser; The half-width of the laser spectral line shape function; For time.

[0014] Preferably, it also includes environmental parameter compensation, specifically including the following steps: Step 3.1: Monitor environmental parameters in real time; Step 3.2: Correct the absorption coefficient based on the environmental parameters obtained in Step 3.1.

[0015] Preferably, the absorption coefficient in step 3.2 The following formula is used for calculation: ; in: This refers to the frequency or wavenumber of light. To detect the actual temperature of the environment; To detect the actual temperature of the environment; To detect the actual humidity of the environment; This is the absorbance function under standard operating conditions; The room temperature is 25℃; Standard atmospheric pressure; This is a humidity function.

[0016] The effect of applying the technical solution of this invention is: 1. The chamberless self-calibration system based on laser gas detection disclosed in this invention includes a laser emission module, an optical system, a signal processing module, and an environmental detection component. The laser emission module includes a laser for emitting wavelengths that match the absorption peak of the target gas. The optical system receives the laser signal and is connected to the signal processing module. The environmental detection component is connected to the signal processing module and measures the temperature of the laser, the pressure of the environment, and the humidity of the environment. The signal processing module is used for signal acquisition, processing, and self-calibration. The overall structure is simplified, eliminating the need for a physical gas chamber and solving the dependence of existing technologies on physical gas chambers.

[0017] 2. The laser gas detection method disclosed in this invention includes a calibration stage and a measurement stage. The calibration stage includes introducing a standard gas of known concentration and recording the incident light intensity. and absorption peak height or area It also calculates the calibration ratio; during the measurement stage, self-calibration is achieved through an algorithm based on the calibration ratio, which solves the problem of result drift caused by environmental interference and laser aging in traditional technologies, resulting in high gas measurement accuracy. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of a chamberless self-calibration system based on laser gas detection in an embodiment of the present invention. Figure 2 This is a schematic diagram of the calibration stage in the laser gas detection method of this invention. Figure 3 This is a schematic diagram of the measurement stage in the laser gas detection method according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the absorption spectrum in an embodiment of the present invention.

[0020] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example: A chamberless self-calibration system based on laser gas detection includes a laser emitting module, an optical system, a signal processing module, and an environmental detection component. The laser emitting module includes a laser for emitting wavelengths that match the absorption peak of a target gas. The optical system receives the laser signal and is connected to the signal processing module. The environmental detection component is connected to the signal processing module and measures the temperature of the laser, the pressure of the environment, and the humidity of the environment. The signal processing module is used for signal acquisition, processing, and self-calibration.

[0023] In this embodiment, the laser is a tunable diode laser (TDL).

[0024] In this embodiment, the optical system includes a photodetector and a emitting lens, a refractor, and a receiving lens arranged along the optical path.

[0025] In this embodiment, the signal processing module includes an analog-to-digital converter, a digital-to-analog converter, and a microprocessor; the microprocessor reads the laser temperature, ambient pressure, and ambient humidity through the analog-to-digital converter; the microprocessor controls the laser temperature by adjusting the TEC through PWM; and the microprocessor adjusts the laser current through the digital-to-analog converter.

[0026] In this embodiment, the environmental detection component includes a temperature sensor, a pressure sensor, and a humidity sensor. The temperature sensor is used to measure the temperature of the laser, the pressure sensor is used to measure the temperature of the environment, and the humidity sensor is used to measure the humidity of the environment.

[0027] After calibration using the aforementioned chamberless self-calibration system based on laser gas detection, laser gas detection is performed. This laser gas detection method includes a calibration phase and a measurement phase. The calibration phase includes the following steps: Step 1.1: Introduce a standard gas of known concentration; Step 1.2: Record the incident light intensity and absorption peak height or area ; Step 1.3: Calculate the calibration ratio. : or .

[0028] In this embodiment, the preferred embodiment is as follows: Figure 2The specific steps are as follows: Begin by placing the detector at room temperature, standard atmospheric pressure, 60% humidity, and 0% LEL for hardware initialization; read the laser temperature, ambient pressure, and ambient humidity using the ADC; adjust the TEC via PWM to control the laser temperature and stabilize the laser wavelength at the absorption peak; adjust the laser current via the DAC to scan near the absorption peak and record the 0% LEL intensity scan data; introduce 50% LEL standard gas; adjust the laser current via the DAC to scan near the absorption peak and record the 50% LEL intensity scan data. When recalibration is required, return directly to the steps of placing the detector at room temperature, standard atmospheric pressure, 60% humidity, and 0% LEL and performing hardware initialization.

[0029] In this embodiment, the absorbance moment and the effective incident light intensity are defined with high fidelity as follows: First, the redefinition of absorbance moment: To address the sensitivity of traditional integrals to baseline drift and noise, this embodiment utilizes statistical moment theory to integrate the area... Defined as absorbance function of The weighted moments are calculated as follows: ; in: for Generalized absorbance moment; , Let be the order of the moment; This refers to the frequency or wavenumber of light. The center frequency or center wavenumber of the target gas absorption spectral line; The starting frequency of the integration interval; is the termination frequency of the integration interval. Step Moment Degenerates to a traditional normalized area. Preferably, adopts... Step Moment It effectively suppresses low-frequency drift and high-frequency noise of the baseline by using second-order central moments weighting, providing a more robust area estimate.

[0030] Second, the dynamic reconstruction model of effective incident light intensity: This embodiment negates the static average. The functional relationship between it and the laser's time-domain parameters is established as follows: ; in: The effective incident light intensity within a single scan cycle; For a complete wavelength scan cycle; The average output power is represented by the DC power component. For power fluctuations; For scanning functions; () represents the laser line shape function; The instantaneous center frequency of the laser; The half-width of the laser spectral line shape function; For time. The model uses Kalman filtering. Real-time estimation and The variance is used to dynamically reconstruct the optimal estimate that is free from noise contamination within the current scanning cycle. .

[0031] In this embodiment, the path invariance theorem and the first-principles calibration coefficients are as follows: The core of this embodiment lies in constructing and proving the ratio. The path invariance is investigated, and its intrinsic connection with first-principles constants is revealed.

[0032] The statement and proof of the path invariance theorem in this embodiment are as follows: Consider a measurement system with non-uniform attenuation (dust scattering), whose total transmittance is calculated using the following formula: ; in, This represents the total transmittance. For dust scattering transmittance, This refers to the transmittance of the window due to pollution.

[0033] Apparent absorbance moment measured by the detector With the real moments The relationship is as follows: ; Under weak absorption, the attenuation has a negligible effect on the linearity.

[0034] Apparent incident light intensity measured by the detector Compared with ideal light intensity The relationship is as follows: .

[0035] Then, the ratio for: .

[0036] However, according to Lambert-Beer's law, the true absorbance moment... Proportional to the density of gas molecular columns and line strength The following relationship exists: ; in: This is a constant related to the line type.

[0037] Meanwhile, ideal light intensity Proportional to the average power of the laser With detector responsivity as follows: .

[0038] Therefore, we have the following formula: .

[0039] The key insight in this embodiment is: for slowly varying path decay Its value is constant within a single measurement cycle. However, the molecular column density... With average laser power Detector responsivity Physically, they are decoupled. Therefore, The changes directly reflect The changes, and with The slow change is irrelevant. Total transmittance As a common scaling factor, it is canceled out when calculating relative concentration changes; when calculating absolute concentrations, it can be... It is incorporated into a long-term stable system constant.

[0040] The measurement phase includes the following steps: Step 2.1: Measure the current effective incident light intensity. and absorption peak height or area (like Figure 4 (Illustration) Step 2.2: Calculate the current ratio as follows: or ; Step 2.3: Based on the calibration ratio and standard gas concentration Calculate the current concentration ,as follows: .

[0041] In this embodiment, see Figure 3 The process includes: startup; hardware initialization; reading laser temperature, ambient pressure, and ambient humidity via ADC; adjusting the TEC via PWM to control the laser temperature and stabilize the laser wavelength at the absorption peak; adjusting the laser current via DAC to scan near the absorption peak; reading the received light intensity via ADC and calculating the concentration of the detected gas according to the algorithm. If re-detection is required, the process returns directly to the hardware initialization steps.

[0042] In this embodiment, the current concentration The calculation formula describes a kind of "attenuation invariance" or "equivalent attenuation principle," which is unique in that: no matter how complex the physical mechanism causing the light intensity attenuation is (whether it is absorption by the target gas or scattering by dust), as long as the total generalized attenuation rate of the system remains constant... The logarithmic ratio of the changes Changes in target gas concentration There exists a definite and universal mapping relationship.

[0043] The detection method in this embodiment also includes environmental parameter compensation, specifically including the following steps: Step 3.1: Monitor environmental parameters in real time; Step 3.2: Correct the absorption coefficient based on the environmental parameters obtained in Step 3.1.

[0044] In this embodiment, the preferred absorption coefficient is calculated using the following formula: ; in: The frequency (or wavenumber) of the laser corresponds to the characteristic absorption spectral lines of the target gas. To detect the actual temperature of the environment (in °C); To detect the actual temperature of the environment (in Pa); To detect the actual humidity of the environment; This is the absorbance function under standard operating conditions; The room temperature is 25℃; Standard atmospheric pressure; It is a function of humidity, representing humidity. The function is used to correct the interference of ambient humidity on the absorption coefficient (such as scattering of water vapor molecules or cross-absorption with other targets). The specific form needs to be pre-calibrated according to the target gas and humidity range (which can be obtained by those skilled in the art using existing technical means).

[0045] Traditional laser gas detectors are typically calibrated under standard operating conditions (25°C, 101 kPa). However, in practical applications, these devices are often deployed in industrial environments with wide temperature and pressure ranges, resulting in significant deviations between their operating conditions and the calibration benchmark. To ensure measurement accuracy across all operating conditions, this embodiment performs real-time correction for absorption coefficient drift caused by changes in environmental parameters, thereby improving detection accuracy.

[0046] The uniqueness of the technical solution applied in this embodiment lies in: ① Cellless design, specifically: self-calibration is achieved through algorithms, eliminating the need for a physical reference cell, thus reducing system complexity and cost; ② Light intensity normalization, specifically: by saving the calibration ratio, the influence of light intensity attenuation caused by laser aging is eliminated; ③ Environmental compensation, specifically: by combining environmental sensor data, the absorption coefficient is corrected in real time according to environmental parameters. As the temperature increases, the absorption coefficient decreases. If not corrected, the temperature will inevitably deviate further from room temperature, and the greater the deviation, the greater the difference. The method of this embodiment corrects this deviation, improving detection accuracy.

[0047] The methane detection method of this embodiment is performed as follows: Calibration phase: Step 1.1: Introduce 2.5% methane standard gas.

[0048] Step 1.2: Record the incident light intensity =1000arb.units and absorption peak height =200arb.units.

[0049] Step 1.3: Calculate the calibration ratio: .

[0050] Measurement phase: Step 2.1: Measure the current incident light intensity =800arb.units and absorption peak height =160arb.units.

[0051] Step 2.2: Calculate the current ratio: ; Step 2.3: Calculate the current concentration: .

[0052] In addition, it can also detect a variety of gases (such as methane and carbon dioxide).

[0053] The above description is only a preferred embodiment of the present invention and does not limit the scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the protection scope of the present invention.

Claims

1. A chamberless self-calibration system based on laser gas detection, characterized in that, It includes a laser emission module, an optical system, a signal processing module, and environmental detection components; The laser emitting module includes a laser for emitting a wavelength that matches the absorption peak of the target gas; The optical system is used to receive laser signals and is connected to the signal processing module. The environmental detection component is connected to the signal processing module and is used to measure the temperature of the laser, the pressure of the environment, and the humidity of the environment. The signal processing module is used for signal acquisition, processing, and self-calibration.

2. The chamberless self-calibration system based on laser gas detection as described in claim 1, characterized in that, The laser is a tunable diode laser.

3. The chamberless self-calibration system based on laser gas detection as described in claim 1, characterized in that, The optical system includes a photodetector and a emitting lens, a refractor, and a receiving lens arranged along the optical path.

4. The chamberless self-calibration system based on laser gas detection as described in any one of claims 1-3, characterized in that, The signal processing module includes an analog-to-digital converter, a digital-to-analog converter, and a microprocessor; the microprocessor reads the laser temperature, ambient pressure, and ambient humidity through the analog-to-digital converter; the microprocessor controls the laser temperature by adjusting the TEC through PWM; and the microprocessor adjusts the laser current through the digital-to-analog converter.

5. The chamberless self-calibration system based on laser gas detection as described in claim 4, characterized in that, The environmental detection component includes a temperature sensor, a pressure sensor, and a humidity sensor. The temperature sensor is used to measure the temperature of the laser, the pressure sensor is used to measure the pressure of the environment, and the humidity sensor is used to measure the humidity of the environment.

6. A laser gas detection method, characterized in that, Self-calibration is performed using the chamberless self-calibration system based on laser gas detection as described in any one of claims 1-5, wherein the laser gas detection method includes a calibration stage and a measurement stage; The calibration phase includes the following steps: Step 1.1: Introduce a standard gas of known concentration; Step 1.2: Record the incident light intensity and absorption peak height or area ; Step 1.3: Calculate the calibration ratio. : or ; The measurement phase includes the following steps: Step 2.1: Measure the current effective incident light intensity. and absorption peak height or area ; Step 2.2: Calculate the current ratio as follows: or ; Step 2.3: Based on the calibration ratio and standard gas concentration Calculate the current concentration ,as follows: 。 7. The laser gas detection method as described in claim 6, characterized in that, In step 2.1: based on the statistical moments theory, the area is... Defined as absorbance function of The weighted moments are calculated as follows: ； in: for Generalized absorbance moment; , Let be the order of the moment; This refers to the frequency or wavenumber of light. The center frequency or center wavenumber of the target gas absorption spectral line; The starting frequency of the integration interval; is the termination frequency of the integration interval.

8. The laser gas detection method as described in claim 7, characterized in that, In step 2.2: the functional relationship between the incident light intensity and the laser's time-domain parameters is established as follows: ； in: The effective incident light intensity within a single scan cycle; For a complete wavelength scan cycle; The average output power is represented by the DC power component. For power fluctuations; For scanning functions; () represents the laser line shape function; The instantaneous center frequency of the laser; The half-width of the laser spectral line shape function; For time.

9. The laser gas detection method as described in claim 6, characterized in that, It also includes environmental parameter compensation, specifically including the following steps: Step 3.1: Monitor environmental parameters in real time; Step 3.2: Correct the absorption coefficient based on the environmental parameters obtained in Step 3.

1.

10. The laser gas detection method as described in claim 9, characterized in that, The absorption coefficient in step 3.2 The following formula is used for calculation: ； in: This refers to the frequency or wavenumber of light. To detect the actual temperature of the environment; To detect the actual temperature of the environment; To detect the actual humidity of the environment; This is the absorbance function under standard operating conditions; The room temperature is 25℃; Standard atmospheric pressure; This is a humidity function.

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