Gas concentration inversion method based on radiation transmission channel switching

Abstract

The present application relates to the technical field of imaging spectrum, in particular to a kind of gas concentration inversion method based on radiation transmission channel switching.The above-mentioned gas concentration inversion method mainly includes temperature calibration, concentration calibration and concentration inversion three steps, by carrying out temperature calibration and concentration calibration, the calibration coefficient of gas concentration and temperature is obtained, by switching transmission spectrum channel, the background image can be obtained without the influence of the gas to be measured, the concentration length product of the gas to be measured is inverted combined with calibration curve, the influence of background radiation and stray light etc. on the inversion of the concentration of the gas column to be measured is reduced, and the inversion precision is improved;At the same time, because the present application uses multiple filters, the concentration inversion of multiple gases to be measured can be realized.

Description

Technical Field

[0001] This invention relates to the field of imaging spectroscopy, and in particular to a gas concentration inversion method based on switching of radiation transmission channels. Background Technology

[0002] Gas concentration detection technology is crucial in modern industrial production. Currently, the main optical gas detection methods include spectral imaging and spectral analysis. Spectral analysis can analyze the physical structure and chemical composition of targets at specific points. Spectral imaging, based on the principle that most industrial gases have specific absorption peaks in the infrared band, uses filters to image specific wavelengths, achieving gas imaging. It has a large imaging range, is more intuitive, and has a more significant long-distance detection capability. It can detect a wide range of spectra and a variety of gases, and has now become the focus of gas concentration detection research.

[0003] Spectroscopic analysis is a commonly used gas concentration detection technique. The basic principle of the representative TDLAS technique is the Lambert-Beer law. A modulation signal is applied to the gas being tested using a semiconductor laser. When the laser beam carrying the modulation signal passes through the gas, the gas interacts with the laser signal molecules, generating an absorption spectrum. This allows information about the gas to be obtained. TDLAS technology has strong anti-interference capabilities, eliminating the influence of current noise in experimental equipment on weak signals. It can obtain accurate atmospheric concentrations even in harsh environments and when gas concentrations are very low. Laser-induced breakdown spectroscopy (LIBS) involves focusing a pulsed laser onto the sample surface and interacting with it. The power density of the pulsed laser on the sample surface is increased sufficiently to generate plasma. When the laser pulse ends, atoms and ions in the plasma in excited states transition from high energy levels to low energy levels or the ground state, simultaneously releasing emission spectra at characteristic frequencies. Based on these characteristic emission spectra, the qualitative and quantitative relationships of elements in the sample can be obtained. Cavity ring-down spectroscopy (CRDS) is based on the Lambert-Beer law. It involves sending a laser beam back and forth through a resonant cavity filled with a homogeneous medium, recording the time it takes for the light intensity to decay to 1 / e of its initial value. This time is called the ring-down time. By combining the ring-down time with the cavity ring-down time and the absorption cross-section of the medium at the laser wavelength λ, the medium concentration can be determined. This allows for highly sensitive and accurate detection of trace gases at extremely low concentrations. Besides spectral analysis, gas infrared spectral imaging is also widely used in gas detection. It utilizes the characteristic spectral absorption of infrared radiation by gases to detect them. Most existing spectral imaging gas detection devices only image the target gas, clearly showing the gas distribution and leakage location in the output image, but not the gas concentration. Existing gas concentration detection algorithms mainly calculate the concentration based on the gas's absorption characteristics. When infrared radiation passes through a gas, it attenuates due to gas absorption. The amount of attenuation is related to the gas concentration and the optical path length. According to the Lambert-Beer law, the column concentration of the gas is inferred by calculating the gas transmittance.

[0004] While gas spectral analysis can accurately determine gas concentration, it can only perform single-point detection, making it difficult to obtain gas concentration data over a wide area. It cannot visually represent the gas concentration distribution or pinpoint the location of a leak. TDLAS technology, although having a low detection limit, suffers from system complexity and poor stability. LIBS technology, while capable of distinguishing the components and concentrations of mixed gases, is significantly affected by environmental pressure and exhibits poor stability. CRDS technology requires not only a homogeneous test medium but also multiple reflections of the laser light within a resonant cavity.

[0005] Most existing gas detection technologies based on spectral imaging rely on the Lambert-Beer law. When retrieving gas concentration, a grayscale image of the background is required. However, due to the absorption of the gas being measured, an accurate grayscale image of the background cannot be obtained. Existing methods for obtaining the background image include: ① obtaining a grayscale image of the background beforehand without the gas being measured; ② selecting locations in the image where the gas being measured does not absorb as the background grayscale. Both of these methods are difficult to implement in practical applications because the application scenarios are complex, the uniformity of background radiation is poor, and it may change over time. Therefore, how to accurately obtain a grayscale image of the background is a key problem to be solved in gas concentration retrieval. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a gas concentration inversion method based on radiation transmission channel switching, which can achieve high-precision inversion of the concentration of the gas to be measured.

[0007] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0008] The gas concentration inversion method based on radiation transmission channel switching provided by this invention includes the following steps:

[0009] S1. Temperature calibration: Heat the surface source blackbody, acquire grayscale images of the surface source blackbody at different temperatures through an infrared detector, and fit the grayscale value-temperature calibration curve.

[0010] S2. Concentration calibration: By adjusting the concentration of the gas to be tested, grayscale images of the gas to be tested at different concentrations are obtained, and the absorbance-gas column concentration calibration curve is obtained by fitting.

[0011] S3. Concentration Inversion: First, calibrate the temperature of the transmission spectral channels of the first and second filters of the infrared detector based on the grayscale value-temperature calibration curves, obtaining the temperature calibration curves for the first and second filters' transmission spectral channels. The transmission band of the first filter coincides with the absorption peak of the gas to be measured, while the transmission band of the second filter does not coincide with the absorption peak of the gas to be measured. Second, obtain the grayscale image of the gas to be measured and the grayscale image of the background by switching between the first and second filters. Third, based on... The background temperature is determined based on the grayscale image of the background and the temperature calibration curve of the transmission spectrum channel of the second filter; the background grayscale image under the transmission spectrum channel of the first filter is determined based on the background temperature and the temperature calibration curve of the transmission spectrum channel of the first filter; the radiance of the gas to be tested is determined based on the background grayscale image under the transmission spectrum channel of the first filter and the temperature of the gas to be tested; the absorbance of the gas to be tested is calculated based on the radiance of the gas to be tested; and the column concentration of the gas to be tested is obtained based on the absorbance of the gas to be tested and the absorbance-gas column concentration calibration curve.

[0012] Furthermore, the specific calculation process for temperature calibration in step S1 is as follows:

[0013] According to Planck's radiation law, the infrared radiation of a target is expressed as:

[0014]

[0015] Where S(λ) is the output signal of the infrared detector, A d Let T be the pixel area of ​​the infrared detector, F be the F-number of the temperature calibration system, η(λ) be the quantum efficiency of the infrared detector, and T be the T pixel area. int L is the integration time of the infrared detector, and L(λ, T) is the spectral radiance entering the temperature calibration system.

[0016] Within the wavelength range λ1~λ2 corresponding to the first and second filters, multiple images of a blackbody at different temperatures are performed, and the temperature T of the blackbody is considered. i and the output signal S of the infrared detector i The calibration function can then be obtained:

[0017]

[0018] After fitting, three parameters, B, R, and F, are obtained. Based on these parameters, the corresponding temperature is obtained from the output signal of an infrared detector in the wavelength range of λ1 to λ2.

[0019] Furthermore, in step S2, the specific operation process for concentration calibration is as follows:

[0020] First, the blackbody is heated and kept at a constant temperature. The gas cell between the blackbody and the infrared detector is evacuated to a vacuum to obtain a grayscale image of the blackbody under vacuum. Then, the concentration of the gas to be tested is adjusted by diluting the gas. Different concentrations of the gas to be tested are introduced into the gas cell, and grayscale images of the gas to be tested at different concentrations are obtained by the infrared detector. The grayscale values ​​of the grayscale images of the gas to be tested at different concentrations are then divided by the grayscale values ​​of the grayscale images under vacuum to obtain the transmittance of the gas to be tested, which is then converted into the absorbance of the gas to be tested. After fitting, an absorbance-gas column concentration calibration curve is obtained.

[0021] Furthermore, the expression for the radiance received by the infrared detector is:

[0022] DN s =τ gas DN(λ, T) B )+(1-τ gas )DN(λ,T gas (3);

[0023] In the formula, DN s DN(λ, T) represents the radiance received by the infrared detector. B ) represents the radiance of the blackbody source, DN(λ, T) gas τ represents the radiance of the gas being measured. gas T represents the transmittance of the gas being measured. B T is the equivalent temperature of the surface-source blackbody. gas The equivalent temperature of the gas to be measured;

[0024] The transmittance τ of the gas to be measured is obtained. gas :

[0025]

[0026] According to the Lambert-Beer Law, the relationship between the spectral transmittance of a gas and the concentration of the gas column is as follows:

[0027] τ gas =exp(-a gas c gas L) (5);

[0028]

[0029] In the formula, a gas Let c be the spectral absorption coefficient of the gas to be measured. gas Where L is the concentration of the gas to be measured, and L is the optical path length of the gas to be measured to the infrared detector.

[0030] By measuring the gas absorbance at different column concentrations within the transmission band λ1 to λ2 of the filter, the absorbance A of the gas to be tested and the column concentration c can be obtained. gas The relationship between them is defined by the calibration function:

[0031]

[0032] After fitting, three parameters a, b, and c are obtained. Based on the above formula, the column concentration can be obtained from the gas absorbance.

[0033] The present invention can achieve the following technical effects:

[0034] This invention obtains calibration coefficients for gas concentration and temperature by performing temperature and concentration calibration. By switching transmission spectral channels, it can acquire background images regardless of the influence of the gas to be measured. Combined with the calibration curve, the concentration-range product of the gas to be measured is inverted, reducing the influence of background radiation and stray light on the inversion of the concentration of the gas column to be measured, thus improving the inversion accuracy. At the same time, because this invention uses multiple filters, it can realize the inversion of the concentration of multiple gases to be measured. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a temperature calibration device provided according to an embodiment of the present invention.

[0036] Figure 2 This is a schematic diagram of the grayscale value-temperature calibration curve provided according to an embodiment of the present invention.

[0037] Figure 3 This is a schematic diagram of the concentration calibration device provided according to an embodiment of the present invention.

[0038] Figure 4 This is a schematic diagram of the absorbance-gas column concentration calibration curve provided in an embodiment of the present invention.

[0039] Figure 5 This is a schematic diagram of the concentration inversion process provided in an embodiment of the present invention.

[0040] The reference numerals in the figures include:

[0041] 1. Surface source blackbody; 2. Infrared detector; 3. Gas cell; 4. Constant temperature bath; 5. Vacuum pump; 6. Gas mixer; 7. Gas to be tested; 8. Diluent gas. Detailed Implementation

[0042] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0044] This invention provides a gas concentration inversion method based on radiation transmission channel switching, which mainly includes the following steps:

[0045] S1. Temperature calibration: Heat the surface source blackbody, obtain grayscale images of the surface source blackbody at different temperatures through an infrared detector, and fit the grayscale value-temperature calibration curve.

[0046] Figure 1 The equipment used for temperature calibration is shown, such as... Figure 1 As shown, the system includes a blackbody 1 and an infrared detector 2. The blackbody 1 serves as a standard radiation source, and the infrared detector 2 is used to image the blackbody. The image obtained by the infrared detector 2 is a grayscale image of the target. In this embodiment of the invention, the blackbody 1 is used to convert the grayscale values ​​of the image into the temperature values ​​of the target, as detailed below:

[0047] According to Planck's radiation law, the infrared radiation of a target is expressed as:

[0048]

[0049] In the formula, S(λ) is the output signal of infrared detector 2, and A d Let T be the pixel area of ​​infrared detector 2, F be the F-number of the temperature calibration system, η(λ) be the quantum efficiency of infrared detector 2, and T be the quantum efficiency of infrared detector 2. int L is the integration time of infrared detector 2, and L(λ, T) is the spectral radiance entering the optical system.

[0050] The infrared detector 2 includes a first filter channel and a second filter channel. The transmission band of the first filter corresponds to the absorption peak of the gas to be measured, while the transmission band of the second filter does not coincide with the absorption peak of the gas to be measured. Multiple images of the blackbody 1 at different temperatures are performed within the corresponding wavelength range λ1 to λ2 of the filters, and the results are combined with the temperature T of the blackbody 1. i and the output signal S of infrared detector 2 i The calibration function can then be obtained:

[0051]

[0052] After fitting, three parameters, B, R, and F, are obtained. Figure 2 The grayscale value-temperature calibration curve is shown, which can be used to obtain the corresponding temperature value from the output signal with a wavelength in the range of λ1 to λ2.

[0053] S2. Concentration calibration: By adjusting the concentration of the gas to be tested, grayscale images of the gas to be tested at different concentrations are obtained, and the absorbance-gas column concentration calibration curve is obtained by fitting.

[0054] Figure 3 The equipment used for concentration calibration is shown, such as... Figure 3 As shown, the system includes a blackbody 1, an infrared detector 2, a gas cell 3, a thermostatic bath 4, a vacuum pump 5, a gas mixer 6, a gas to be tested 7, and a dilution gas 8. The blackbody 1 is a standard radiation source. The infrared detector 2 is used to image the blackbody. The gas cell 3 is used to contain the gas to be tested. The thermostatic bath 4 is used to maintain the temperature of the gas to be tested. The vacuum pump 5 is used to extract the gas from the gas cell 3. The gas mixer 6 is used to control the gas to be tested 7 and the dilution gas 8 to adjust the concentration of the gas to be tested in the gas cell 3.

[0055] In this embodiment of the invention, infrared detector 2 is selected. It is a passive infrared optical system. When the working distance of the gas detection system is relatively short, the influence of the atmosphere on the gas transmission process can be ignored. Therefore, the infrared radiation received by infrared detector 2 mainly includes two parts: the radiation from the background blackbody 1 and the radiation from the gas to be measured. The expression for the radiance received by infrared detector 2 is as follows:

[0056] DN s =τ gas DN(λ, T) B )+(1-τ gas )DN(λ,T gas (3);

[0057] In the formula, DN s DN(λ, T) is the radiance received by infrared detector 2. B ) represents the radiance of the blackbody 1, DN(λ, T) gas τ represents the radiance of the gas being measured. gas T represents the transmittance of the gas being measured. B T is the equivalent temperature of the surface source blackbody 1. gas The equivalent temperature of the gas to be measured;

[0058] The transmittance τ of the gas to be measured can be obtained. gas :

[0059]

[0060] According to the Lambert-Beer Law, the relationship between the spectral transmittance of a gas and the concentration of the gas column is as follows:

[0061] τ gas =exp(-a gas c gas L) (5);

[0062]

[0063] In the formula, a gas Let c be the spectral absorption coefficient of the gas to be measured. gas Where L is the concentration of the gas to be measured, and L is the optical path length of the gas to be measured to the infrared detector.

[0064] By measuring the gas absorbance at different gas column concentrations within the transmission band λ1 to λ2 of the filter, the absorbance A of the gas to be measured and the column concentration c can be obtained. gas The relationship between them is defined by the calibration function:

[0065]

[0066] After fitting, three parameters a, b, and c are obtained. Figure 4 The absorbance-gas column concentration calibration curve is shown, from which the column concentration of the gas can be obtained based on the gas absorbance.

[0067] S3. Concentration Inversion: First, calibrate the temperature of the transmission spectral channels of the first and second filters of the infrared detector based on the grayscale value-temperature calibration curve, obtaining the temperature calibration curves for the first and second filters' transmission spectral channels. The transmission band of the first filter coincides with the absorption peak of the gas to be measured, while the transmission band of the second filter does not coincide with the absorption peak of the gas to be measured. Second, obtain the grayscale image of the gas to be measured and the grayscale image of the background by switching between the first and second filters. Third, based on... The background temperature is determined based on the grayscale image of the background and the temperature calibration curve of the transmission spectrum channel of the second filter; the background grayscale image under the transmission spectrum channel of the first filter is determined based on the background temperature and the temperature calibration curve of the transmission spectrum channel of the first filter; the radiance of the gas to be tested is determined based on the background grayscale image under the transmission spectrum channel of the first filter and the temperature of the gas to be tested; the absorbance of the gas to be tested is calculated based on the radiance of the gas to be tested; and the column concentration of the gas to be tested is obtained based on the absorbance of the gas to be tested and the absorbance-gas column concentration calibration curve.

[0068] Figure 5 The concentration inversion process in an embodiment of the present invention is shown below:

[0069] After obtaining the grayscale value-temperature calibration curve and absorbance-gas column concentration calibration curve according to steps S1 and S2, the gas column concentration is inverted. The principle of gas column concentration inversion provided in this embodiment of the invention is to switch the transmission spectral channel by switching filters to eliminate the influence of gas on background radiation, obtain accurate background radiation, and achieve accurate inversion of gas column concentration. The concentration inversion process is as follows:

[0070] An image of the gas to be tested is obtained by imaging the gas through a first filter corresponding to the gas to be tested, acquiring a grayscale image of the first filter channel. By switching the first filter to a second filter whose transmission band does not coincide with the absorption peak of the gas to be tested, a grayscale image is obtained in the second filter channel. Since most gases have specific absorption peaks in the infrared band, and the transmission band of the second filter does not coincide with the absorption peak of the gas to be tested, the absorption rate of the gas to be tested in the band corresponding to the second filter is almost 0. The gas to be tested will not absorb background blackbody radiation in this band, and the radiation emitted by the gas to be tested itself will not pass through the second filter. Therefore, the grayscale image acquired by the infrared detector is a background blackbody image in the band corresponding to the second filter, which has basically eliminated interference from the gas to be tested.

[0071] In the temperature calibration process described above, grayscale value-temperature calibration curves for corresponding bands under different spectral channels were obtained. By substituting the obtained background grayscale image under the second filter channel into the corresponding temperature calibration curve, the temperature distribution T of the background can be obtained. B Based on the temperature calibration relationship of the first filter channel, an inverse operation is performed to obtain the background grayscale image DN under the corresponding band of the first filter. B Because the image is obtained through a background temperature T B The calculated value is equivalent to the grayscale image obtained under the first filter channel without the influence of the gas being measured. The radiance DN(T) of the gas being measured is determined based on its temperature. gas Combined with the absorbance formula (7) above, determine the absorbance A of the gas to be tested, and then calculate the path length product c of the gas to be tested by inverting the absorbance-gas column concentration calibration curve. gas L, to obtain the concentration c of the gas to be measured. gas .

[0072] In the above inversion process, by switching filters, an image of the background blackbody that is not affected by the gas to be measured is obtained. Therefore, the absorbance of the gas to be measured can be accurately obtained, thereby obtaining the column concentration of the gas. If other gases are to be detected, it is only necessary to switch the filter to the band where the gas has an absorption peak to realize the concentration inversion of multiple gases.

[0073] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0074] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0075] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A gas concentration inversion method based on radiation transmission channel switching, characterized in that, Includes the following steps: S1. Temperature calibration: Heat the surface source blackbody, acquire grayscale images of the surface source blackbody at different temperatures through an infrared detector, and fit the grayscale value-temperature calibration curve. S2. Concentration calibration: By adjusting the concentration of the gas to be tested, grayscale images of the gas to be tested at different concentrations are obtained, and the absorbance-gas column concentration calibration curve is obtained by fitting. S3. Concentration Inversion: First, calibrate the temperature of the transmission spectral channels of the first and second filters of the infrared detector based on the grayscale value-temperature calibration curves, obtaining the temperature calibration curves for the first and second filters' transmission spectral channels. The transmission band of the first filter coincides with the absorption peak of the gas to be measured, while the transmission band of the second filter does not coincide with the absorption peak of the gas to be measured. Second, obtain the grayscale image of the gas to be measured and the grayscale image of the background by switching between the first and second filters. Third, based on... The background temperature is determined based on the grayscale image of the background and the temperature calibration curve of the transmission spectrum channel of the second filter; the background grayscale image under the transmission spectrum channel of the first filter is determined based on the background temperature and the temperature calibration curve of the transmission spectrum channel of the first filter; the radiance of the gas to be tested is determined based on the background grayscale image under the transmission spectrum channel of the first filter and the temperature of the gas to be tested; the absorbance of the gas to be tested is calculated based on the radiance of the gas to be tested; and the column concentration of the gas to be tested is obtained based on the absorbance of the gas to be tested and the absorbance-gas column concentration calibration curve.

2. The gas concentration inversion method based on radiation transmission channel switching according to claim 1, characterized in that, In step S1, the specific calculation process for temperature calibration is as follows: According to Planck's radiation law, the infrared radiation of a target is expressed as: Where S(λ) is the output signal of the infrared detector, A d Let T be the pixel area of ​​the infrared detector, F be the F-number of the temperature calibration system, η(λ) be the quantum efficiency of the infrared detector, and T be the T pixel area. int L is the integration time of the infrared detector, and L(λ, T) is the spectral radiance entering the temperature calibration system. Within the wavelength range λ1~λ2 corresponding to the first and second filters, multiple images of a blackbody at different temperatures are performed, and the temperature T of the blackbody is considered. i and the output signal S of the infrared detector i The calibration function can then be obtained: After fitting, three parameters, B, R, and F, are obtained. Based on these parameters, the corresponding temperature is obtained from the output signal of an infrared detector in the wavelength range of λ1 to λ2.

3. The gas concentration inversion method based on radiation transmission channel switching according to claim 1, characterized in that, In step S2, the specific operation process for concentration calibration is as follows: First, the blackbody is heated and kept at a constant temperature. The gas cell between the blackbody and the infrared detector is evacuated to a vacuum to obtain a grayscale image of the blackbody under vacuum. Then, the concentration of the gas to be tested is adjusted by diluting the gas. Different concentrations of the gas to be tested are introduced into the gas cell, and grayscale images of the gas to be tested at different concentrations are obtained by the infrared detector. The grayscale values ​​of the grayscale images of the gas to be tested at different concentrations are then divided by the grayscale values ​​of the grayscale images under vacuum to obtain the transmittance of the gas to be tested, which is then converted into the absorbance of the gas to be tested. After fitting, an absorbance-gas column concentration calibration curve is obtained.

4. The gas concentration inversion method based on radiation transmission channel switching according to claim 3, characterized in that, The expression for the radiance received by the infrared detector is: DN s =t gas DN(λ,T B )+(1-τ gas )DN(λ,T gas ) (3); In the formula, DN s DN(λ, T) represents the radiance received by the infrared detector. B ) represents the radiance of the blackbody source, DN(λ, T) gas τ represents the radiance of the gas being measured. gas T represents the transmittance of the gas being measured. B T is the equivalent temperature of the surface-source blackbody. gas The equivalent temperature of the gas to be measured; The transmittance τ of the gas to be measured is obtained. gas : According to the Lambert-Beer Law, the relationship between the spectral transmittance of a gas and the concentration of the gas column is as follows: τ gas <exp(-a gas c gas L) (5); In the formula, a gas Let c be the spectral absorption coefficient of the gas to be measured. gas Where L is the concentration of the gas to be measured, and L is the optical path length of the gas to be measured to the infrared detector. By measuring the gas absorbance at different column concentrations within the transmission band λ1 to λ2 of the filter, the absorbance A of the gas to be tested and the column concentration c can be obtained. gas The relationship between them is defined by the calibration function: After fitting, three parameters a, b, and c are obtained. Based on the above formula, the column concentration can be obtained from the gas absorbance.

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