A dual optical path gas chamber, a dual optical path detection system and a gas concentration detection method

Abstract

A double optical path gas chamber, a double optical path detection system and a gas concentration detection method belong to the technical field of gas concentration detection. The gas chamber comprises first and second beam splitting prisms and first and second concave mirrors. The first and second concave mirrors are oppositely arranged and sealed to form a Helium gas cell. The center and the edge of the first concave mirror are respectively provided with a short optical path inlet hole and a long optical path inlet hole, and the center and the edge of the second concave mirror are respectively provided with a short optical path outlet hole and a long optical path outlet hole. A light beam is split by the first beam splitting prism. A short optical path light beam enters the gas cell through the short optical path inlet hole and is emitted from the short optical path outlet hole. A long optical path light beam enters the gas cell through the long optical path inlet hole and is emitted from the long optical path outlet hole after multiple reflections in the cell. The emitted long and short optical path light beams are combined by the second beam splitting prism and are emitted. The system comprises a light source, the above-mentioned gas chamber and a spectrometer. The method is realized based on the above-mentioned system. The present application simultaneously meets the detection needs of long and short optical paths, realizes ultra-low concentration detection and has an ultra-high range.

Description

Technical Field

[0001] This invention relates to the field of gas concentration detection technology, and in particular to a dual-path gas chamber, a dual-path detection system, and a gas concentration detection method. Background Technology

[0002] In the process of detecting the concentration of gaseous substances using a gas chamber, the optical path length directly affects the detection accuracy and range. A long optical path length results in a low detection limit, enabling the detection of low-concentration components but limiting the range; a short optical path length results in a large range but lower detection accuracy, making it impossible to detect low-concentration substances. In some applications (such as multi-component detection), some substances have high concentrations while others have low concentrations. Therefore, a single-path gas chamber cannot simultaneously meet the requirements for ultra-low concentration detection and large-range detection. Existing technologies address these issues by employing two sets of equipment: one with a long optical path gas chamber for detecting ultra-low concentration substances and the other with a short optical path gas chamber for detecting high-concentration substances. While this satisfies both high and low range detection requirements, it significantly increases equipment costs. Furthermore, after detection using two sets of equipment, gas concentration calculations need to be performed separately for the long-path and short-path signals, and existing concentration detection methods are based on gases with specific optical paths.

[0003] Invention patent application CN201511016831.9 discloses an adjustable optical path dual-absorption optical absorption device, specifically disclosing that the device includes an adjustable absorption cell formed by a left and right reflector arranged in the form of a Herriott-type absorption cell. The left reflector has a light-passing hole, and the right reflector has a semi-transparent, semi-reflective coated small truncated cone mounted on the through hole. When a light beam enters the absorption cell, it is reflected multiple times between the two reflectors. After a certain number of reflections, it is transmitted and reflected after passing through the semi-transparent, semi-reflective coated small truncated cone. The transmitted light produces a shorter absorption optical path, and the reflected light continues to reflect back and forth within the absorption cell, exiting from the light-passing hole of the left reflector, producing a longer absorption optical path. By rotating the reflector with the semi-transparent, semi-reflective coated small truncated cone, the ratio of the dual absorption optical path can be easily changed. Although the invention achieves two different absorption optical paths through a single optical absorption cell, it uses a semi-transparent and semi-reflective coated small truncated cone at one end of the device to split the beam, making it impossible to control the incident light angle of the long optical path. After beam splitting, the first absorption optical path exits from the right reflector and the second absorption optical path exits from the left reflector, so it is necessary to set a detector at each end of the device to detect and calculate the gas concentration for different absorption optical paths.

[0004] Utility model patent CN201721639266.6 discloses an optical fiber path length cell, specifically comprising two concave mirrors: a first concave mirror and a second concave mirror, and two optical fiber collimators: a first optical fiber collimator and a second optical fiber collimator. The two concave mirrors form the optical path length cell's reflecting cavity. The two optical fiber collimators are fixed on different mirrors or on the same mirror. A laser beam enters from one collimator, undergoes multiple reflections within the optical path length cell's reflecting cavity, and is finally collected by the other collimator. The two optical fiber collimators are optical fiber collimators with different Gaussian optical characteristics, forming an asymmetric optical path. This patent mainly solves the problem of excessive coupling loss caused by existing optical path length cells using optical fiber collimators with the same properties, and the optical path length cell used in this patent is only used for detecting a certain optical path, and cannot simultaneously meet the detection needs of different optical paths.

[0005] Invention patent application CN201710329903.8 discloses a detection device and method for trace CO gas concentration based on TDLAS, and invention patent application CN201911143830.9 discloses a method for detecting nitrogen dioxide gas by ultraviolet differential. Both of the above inventions are for detecting specific gases and cannot simultaneously meet the requirements of detecting ultra-low concentration and ultra-high range. Summary of the Invention

[0006] This invention aims to solve the problem that existing gas chamber structures cannot meet the requirements for long and short optical path detection and require two sets of equipment to detect gases. To this end, it is necessary to design a gas chamber that can simultaneously achieve long and short optical path detection in a single gas cell, and propose a detection method based on this gas chamber that can achieve zero calibration of dual optical path gas chambers and simultaneously meet the requirements for detection of ultra-low concentration and ultra-high range.

[0007] This invention provides a dual-optical-path gas chamber, comprising a first beam-splitting prism, a first concave mirror, a second concave mirror, and a second beam-splitting prism; the first and second concave mirrors are arranged opposite to each other and sealed to form a Heliot gas cell; the first beam-splitting prism is located at the front end of the first concave mirror, and the second beam-splitting prism is located at the rear end of the second concave mirror; a short-path inlet is formed at the center of the first concave mirror, and a long-path inlet is formed at the edge of the first concave mirror according to the design of the Heliot gas cell; the second... The center of the surface mirror has a short optical path exit hole, and the edge of the second concave mirror has a long optical path exit hole designed according to the Heliot gas cell. The light beam enters the dual optical path gas cell and is split by the first beam splitter. The short optical path beam enters the Heliot gas cell through the short optical path entrance hole and exits from the short optical path exit hole. The long optical path beam enters the Heliot gas cell through the long optical path entrance hole and returns multiple times in the Heliot gas cell before exiting from the long optical path exit hole. The short optical path beam and the long optical path beam exiting from the Heliot gas cell are combined by the second beam splitter and exit from the dual optical path gas cell.

[0008] Invention patent application CN201511016831.9 discloses an adjustable optical path dual-absorption optical absorption device. While this device can solve the problem that existing gas chambers cannot meet the needs of measuring long and short optical paths, it does not have beam-splitting prisms at both ends of the gas cell for beam splitting and combining, unlike the present invention. It cannot use beam-splitting prisms to control the incident angle of long optical paths, and its structural stability is inferior to the gas chamber in the present invention. Furthermore, because the present invention uses a semi-transparent, semi-reflective coated frustum located only in the right reflector for beam splitting, the two different optical paths exit at different ends of the device, requiring two detectors (such as spectrometers) for detection. Subsequently, gas concentration needs to be detected separately for each optical path, making the detection process cumbersome and failing to eliminate the differences in detection by different spectrometers.

[0009] In this invention, the gas chamber uses a first beam-splitting prism to split the light beam after it enters. The short-path beam passes through the centers of the first and second concave mirrors, ensuring its optical path matches the length of the gas cell. The long-path beam passes through the edges of the first and second mirrors, returning multiple times within the gas cell, resulting in its optical path being N times the length of the gas cell. Finally, the second beam-splitting prism combines the short-path and long-path beams into a single beam that exits the gas chamber. This gas chamber can simultaneously detect both short and long optical paths, eliminating the need for two separate detection systems. Furthermore, only one detector (such as a spectrometer) is required to detect the concentration of the sample gas passing through the chamber, significantly reducing the cost of existing detection equipment and improving detection efficiency.

[0010] Preferably, the dual-optical-path gas chamber further includes a first collimating lens and a second collimating lens; the first collimating lens is located at the front end of the first beam splitter, and the second collimating lens is located at the rear end of the second beam splitter; the light beam enters the dual-optical-path gas chamber, is collimated by the first collimating lens, and then enters the first beam splitter for beam splitting; the short-path beam and the long-path beam are combined by the second beam splitter, collimated by the second collimating lens, and finally exit from the dual-optical-path gas chamber.

[0011] Preferably, the first beam splitter has two surfaces: a reflective surface coated with an anti-reflective coating and a semi-reflective, semi-transparent surface. The wedge angle between the reflective surface and the semi-reflective, semi-transparent surface in the first beam splitter is half of the incident angle designed for the Heliot gas cell, so that the short-path beam is incident parallel to the Heliot gas cell, and the long-path beam enters the Heliot gas cell at the incident angle designed for the Heliot gas cell. The second beam splitter has two surfaces: a reflective surface coated with an anti-reflective coating and a semi-reflective, semi-transparent surface. The wedge angle between the reflective surface and the semi-reflective, semi-transparent surface in the second beam splitter is half of the exit angle designed for the Heliot gas cell, so that the short-path beam and the long-path beam are combined and exited.

[0012] Preferably, the first beam splitter has four faces, with the other two faces being transmission faces coated with antireflective coatings; the second beam splitter has four faces, with the other two faces being transmission faces coated with antireflective coatings.

[0013] Preferably, the transmittance-to-reflection ratio of the semi-reflective and semi-transparent surface is allocated according to the energy loss of the designed return gas chamber, so that the light intensity distribution of long and short optical paths is similar.

[0014] A dual-optical-path detection system includes a light source, the aforementioned dual-optical-path gas chamber, and a spectrometer; the light source is connected to the dual-optical-path gas chamber via an optical fiber, and the dual-optical-path gas chamber is connected to the spectrometer via an optical fiber.

[0015] A light beam emitted from the light source is coupled into an optical fiber, which then guides the beam into a dual-path gas chamber. The beam emitted from the dual-path gas chamber is then sent through an optical fiber to a spectrometer, which detects the spectral energy of sample gas (or standard gas) at different concentrations. This invention utilizes a dual-path gas chamber and a spectrometer to achieve detection of both long and short optical paths, simultaneously meeting the requirements for ultra-low concentration detection and large-range detection, while reducing equipment costs.

[0016] A gas concentration detection method, based on the above-mentioned dual optical path detection system, includes the following steps:

[0017] Step S01: Based on the path length ratio N of the dual-path gas chamber and the spectral energies of three sets of standard gases at specified concentrations, the formula of Lambert-Beer's Law is applied. Solve for long optical path light intensity I l and short optical path light intensity l s Among them, l sFor the short optical path length, l l For short optical path length, l l =Nl s c is the gas concentration;

[0018] Step S02, based on the long-to-short path ratio N of the dual-path gas chamber and the spectral energy I of a set of sample gases with unknown concentrations. c The long optical path intensity I obtained from step S01 l and short optical path light intensity I s According to the Lamb-Beer law formula Solving for the results Based on this formula, the absorption cross section α(λ) is calculated, and a polynomial fitting is performed on the absorption cross section α(λ) to obtain the slowly varying part α of the absorption cross section. s (λ), and thus obtain the differential absorption cross section σ(λ)=α(λ)-α s (λ);

[0019] Step S03, for the results obtained in step S02 Differential processing is performed to obtain differential optical thickness. And solve using the least squares algorithm or partial least squares algorithm. This allows us to obtain the concentration c of each component gas in the sample gas. i .

[0020] The method of this invention can be processed and calculated by a controller. It utilizes a dual-optical-path detection system to obtain spectral energy through multiple measurements, calculates the long-path and short-path light intensities based on Beer-Lambert's law, and then performs differential processing to calculate the gas concentrations of each component in the sample gas. This differential calculation method can effectively remove environmental noise and reduce interference from unknown gas components.

[0021] Preferably, step S01 specifically includes:

[0022] Step S11: N2, standard gas at concentrations c and 2c are sequentially introduced into the gas cell to obtain the spectral energy I under different concentrations of standard gas detected by the spectrometer. c I 2c And without introducing standard gas, the spectral energy I0 detected by the spectrometer was obtained;

[0023] Step S12, based on the path length ratio N of the dual-path gas chamber and the spectral energies of the three sets of standard gases at specified concentrations, according to the Lambert-Beer law formula:

[0024] I0(λ)=I1(λ)+I s (λ)

[0025]

[0026]

[0027] Solve for long optical path light intensity I l and short optical path light intensity I s .

[0028] Preferably, the method further includes: determining the long-path absorbance OD before step S03. l Not greater than the long-path absorbance threshold k1, and the short-path absorbance OD s If the absorbance is not less than the short-path absorbance threshold k2, proceed to step S03; otherwise, do not proceed to step S03, and calculate the concentration as follows: Determine the long-path absorbance OD. l When the absorbance is greater than the long-path absorbance threshold k1, assuming the optical path intensity I... l The value is 0, based on the Lamb-Beer law formula. Determine the concentrations of each component gas in the sample gas; determine the short-path absorbance (OD). s When the absorbance is less than the short-path absorbance threshold k2, it is assumed that only long-path absorption occurs, based on the Lambert-Beer law formula. Determine the concentrations of each component gas in the sample gas;

[0029] Among them, short optical path absorbance OD s =lnx, long-path absorbance is OD l =Nlnx.

[0030] Preferably, the method further includes step S04, based on Piecewise nonlinear compensation is applied to the concentrations of each component gas in the calculated sample gas; where, U i The concentration after compensation is given, and a1 and a2 are constant coefficients.

[0031] The present invention has the following beneficial effects:

[0032] This invention discloses a dual-optical-path gas chamber and a dual-optical-path detection system that can simultaneously achieve detection of two different optical paths (long and short) within a single gas cell, while simultaneously meeting the requirements for ultra-low concentration detection and large-range detection. This solves the problem of existing technologies requiring two separate sets of equipment for long and short optical path detection, significantly reducing equipment costs and improving detection efficiency. The gas concentration detection method of this invention, based on the aforementioned system, can eliminate environmental noise and reduce interference from unknown gas components, while avoiding nonlinearity. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the optical path of a dual-path gas chamber according to the present invention;

[0034] Figure 2 This is a system framework diagram of a dual optical path detection system according to the present invention;

[0035] Figure 3 This is a flowchart of a gas concentration detection method according to the present invention. Detailed Implementation

[0036] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0037] like Figure 1 This invention discloses a dual-optical-path gas chamber, comprising a first beam-splitting prism, a first concave mirror, a second concave mirror, and a second beam-splitting prism arranged sequentially according to the optical path. The first and second concave mirrors are arranged opposite each other and sealed to form a Heliot gas cell. Specifically, the first and second concave mirrors are placed at opposite ends of the sealed chamber, and the gas cell is designed according to a Heliot cell structure. The first and second concave mirrors have the same focal length. The first and second beam-splitting prisms are located at end caps outside the sealed chamber.

[0038] The first concave mirror has a short-path inlet at its center and a long-path inlet designed according to the Heliot gas cell at its edge. The second concave mirror has a short-path outlet at its center and a long-path outlet designed according to the Heliot gas cell at its edge. Since the Heliot gas cell's spot distribution on the lens is circular or elliptical, the central hole in the mirror does not affect multiple return paths. Light rays in the short-path path enter and exit through the center of the lens, while light rays in the long-path path enter and exit through the gas cell's designed inlet and outlet ports. In the short-path path (see the horizontal path emitted along the center in the figure), the optical path length is the same as the gas cell length; in the long-path path (see the multiple return paths in the figure), the beam returns multiple times, and the optical path is N times the length of the gas cell.

[0039] The first beam splitter is used for beam splitting, and the second beam splitter is used for beam combining. The first and second concave mirrors are used for multiple return paths of the beam. When the beam is emitted from the light source and enters the gas chamber, it is split into two beams by the first beam splitter. The short-path beam enters the Heliot gas cell through the short-path inlet and exits through the short-path outlet. The long-path beam enters the Heliot gas cell through the long-path inlet and, after multiple return paths within the Heliot gas cell, exits through the long-path outlet. The short-path beam and the long-path beam exiting the Heliot gas cell are combined by the second beam splitter into a single beam, which exits from the dual-path gas chamber.

[0040] The first and second beam-splitting prisms are polyhedral prisms. To achieve beam splitting and beam combining, two faces of the first beam-splitting prism are a reflective surface coated with an anti-reflective coating and a semi-reflective, semi-transparent surface. The wedge angle between the reflective surface and the semi-reflective, semi-transparent surface of the first beam-splitting prism is half the designed incident angle of the Heliot gas cell, ensuring that the short-path beam enters the Heliot gas cell parallel to the beam, while the long-path beam enters the Heliot gas cell at the designed incident angle. Similarly, two faces of the second beam-splitting prism are a reflective surface coated with an anti-reflective coating and a semi-reflective, semi-transparent surface. The wedge angle between the reflective surface and the semi-reflective, semi-transparent surface of the second beam-splitting prism is half the designed exit angle of the Heliot gas cell, ensuring that the short-path beam and the long-path beam are combined and emitted as a single beam. The parameters of the Heliot gas cell vary depending on the specific application requirements. For example, when the gas chamber length (distance between the two concave mirrors) is 400 mm, the focal length of the concave mirror is 1260 mm, the number of reflections is 10, and the incident light coordinates (relative to the center of the concave mirror) are (5,7), the calculated incident light direction vector is (-0.026,0,1). Therefore, based on the specific application requirements, a wedge angle is designed to meet the specific needs.

[0041] Furthermore, the other faces of the first and second beam-splitting prisms are transmission surfaces. For example, when the polyhedral prism is tetrahedral, the first beam-splitting prism has a reflective surface coated with an anti-reflective coating, a semi-reflective and semi-transparent surface, and two transmission surfaces; the second beam-splitting prism has a reflective surface coated with an anti-reflective coating, a semi-reflective and semi-transparent surface, and two transmission surfaces. The first and second beam-splitting prisms are preferably cubic prisms, but are not limited to other types of polyhedral prisms.

[0042] The transmittance / reflection ratio of the semi-reflective, semi-transparent surface is allocated according to the energy loss of the designed return gas chamber, resulting in similar light intensity distribution across long and short optical paths. Regarding energy distribution, energy is lost because the long optical path undergoes multiple reflections by the concave mirror. For example, a concave mirror with 95% reflectivity will retain 60% of its energy after 10 reflections. If the transmittance / reflection ratio of the semi-reflective, semi-transparent surface is used, where the short-path input energy is equal to the long-path input energy, and the long-path output energy is equal to 3 / 5, then the short-path output energy can be equal to the long-path output energy, and the long-path output energy can be equal to 1 / 1.

[0043] The dual-optical-path gas chamber of this invention further includes a first collimating lens and a second collimating lens. The first collimating lens is located at the front end of the first beam splitter, and the second collimating lens is located at the rear end of the second beam splitter. The collimating lenses serve to collimate and focus the light beam, allowing the light to propagate parallel within the gas chamber and couple into the optical fiber. Both the first and second collimating lenses are plano-convex lenses and can be placed at the end caps outside the sealed chamber. The light beam enters the dual-optical-path gas chamber, is collimated by the first collimating lens, and then enters the first beam splitter for beam splitting; the short-path and long-path beams are combined by the second beam splitter, collimated by the second collimating lens, and finally exit from the dual-optical-path gas chamber.

[0044] like Figure 2 The present invention also provides a dual-optical-path detection system, including a light source, the aforementioned dual-optical-path gas chamber, and a spectrometer. The light source is connected to the dual-optical-path gas chamber via an optical fiber, and the dual-optical-path gas chamber is connected to the spectrometer via an optical fiber. The light source is a laser source. When ultraviolet light is used, the ultraviolet light is emitted from the light source, coupled into the optical fiber, and then enters the dual-optical-path gas chamber. The light beam after passing through the dual-optical-path gas chamber is sent to the spectrometer via an optical fiber. The spectrometer measures the spectral energy of standard gas or sample gas at different concentrations.

[0045] This invention also provides a gas concentration detection method based on the above-described system. Multiple spectral energy measurements are performed within this system, and concentration calculations are performed using multiple sets of data. Specifically, as shown... Figure 3 The method of the present invention includes:

[0046] Step S01: Based on the path length ratio N of the dual-path gas chamber and the spectral energies of three sets of standard gases at specified concentrations, the formula of Lambert-Beer's Law is applied. Solve for long optical path light intensity I l and short optical path light intensity I s Among them, l s For the short optical path length, l l For short optical path length, l l =Nl s c is the gas concentration;

[0047] Step S02, based on the long-to-short path ratio N of the dual-path gas chamber and the spectral energy I of a set of sample gases with unknown concentrations. c The long optical path intensity I obtained from step S01 l and short optical path light intensity I s According to the Lamb-Beer law formula Solving for the results Based on this formula, the absorption cross section α(λ) is calculated, and a polynomial fitting is performed on the absorption cross section α(λ) to obtain the slowly varying part α of the absorption cross section. s (λ), and thus obtain the differential absorption cross section σ(λ)=α(λ)-α s (λ);

[0048] Step S03, for the results obtained in step S02 Differential processing is performed to obtain differential optical thickness. And solve using the least squares algorithm or partial least squares algorithm. This allows us to obtain the concentration c of each component gas in the sample gas. i .

[0049] Step S01 is the zeroing and calibration process. Specifically, step S01 is as follows:

[0050] Step S11: N2, standard gas at concentrations c and 2c are sequentially introduced into the gas cell to obtain the spectral energy I under different concentrations of standard gas detected by the spectrometer. c I 2c And without introducing standard gas, the spectral energy I0 detected by the spectrometer was obtained;

[0051] Step S12, based on the path length ratio N of the dual-path gas chamber and the spectral energies of the three sets of standard gases at specified concentrations, according to the Lambert-Beer law formula:

[0052] I0(λ)=I1(λ)+I s (λ)

[0053]

[0054]

[0055] Solve for long optical path light intensity I l and short optical path light intensity I s .

[0056] The number of return cycles, i.e., the ratio of the short optical path length to the long optical path length N, was determined at the initial design stage. Therefore, when the short optical path exits horizontally from the center of the reflector, its length is equal to the distance between the two reflecting lenses. The long optical path length can be obtained by converting the ratio of the short optical path length to the long optical path length. Let x be the value, and convert the formula in step S12 to:

[0057] I0(λ)=I1(λ)+I s (λ)

[0058] I c (λ)=I1(λ)x N +I s (λ)x

[0059] I 2c (λ)=I1(λ)x 2N +I s (λ)x 2

[0060] The light intensity at long and short optical paths is solved using three equations.

[0061] Step S02 is used to calculate the absorption cross section and perform differential processing on the absorption cross section. After obtaining... Then, the transformation yields α(λ) = -ln x / cl s To avoid the influence of Mie scattering and Rayleigh scattering during the detection process, a polynomial fitting is performed on the absorption cross section α(λ) to obtain the "slowly changing" part, denoted as: α s(λ), by subtracting the slowly varying value obtained from the fitting from the absorption cross section, we obtain the differential absorption cross section σ(λ) = α(λ) - α s (λ).

[0062] Step S03 is used to calculate the optical thickness and perform differential processing on the optical thickness. Then, the optical thickness formula after differential processing is solved using a less-squares algorithm or a partial least-squares algorithm to obtain the concentration of each component gas in the sample gas. Specifically, the optical thickness is obtained in step S02 based on the long-path ratio N of the dual-path gas chamber, the spectral energy of a set of sample gases with unknown concentrations, and the long-path and short-path light intensities calculated in step S01, using the Lambert-Beer law formula. The optical thickness is obtained by performing natural logarithmic processing, and the slowly varying portion is obtained by polynomial fitting of the natural logarithm. The differential optical thickness, denoted as ln[x(λ)], is obtained by subtracting the slowly varying portion from the natural logarithm of the absorbance. Finally, a formula based on the differential absorption cross-section is obtained. In addition, in order to remove various additive noises such as CCD electrical noise and optical noise such as stray light in the optical path, it is also necessary to perform low-pass filtering on the obtained differential optical thickness.

[0063] The above process is not limited to calculations based on short optical path parameters; calculations can also be based on long optical path parameters. Considering that the conversion between short and long optical paths can be performed using the long-to-short optical path ratio, calculations can be performed solely based on either the short or long optical path portion.

[0064] To improve computational efficiency, the calculation is performed in segments based on different absorbance values. At the beginning of the method, a long-path absorbance threshold of k1 and a short-path absorbance threshold of k2 are pre-set. Before step S03, segmented judgments are made for various absorbance cases. The method includes: before step S03, determining the long-path absorbance OD. l Not greater than the long-path absorbance threshold k1, and the short-path absorbance OD s If the absorbance is not less than the short-path absorbance threshold k2, proceed to step S03; otherwise, do not proceed to step S03, and calculate the concentration as follows: If the long-path absorbance OD1 is greater than the long-path absorbance threshold k1, the substance concentration is high, the long-path absorbance is completely absorbed, and the light intensity is approximately considered to be 0, leaving only short-path absorption. Then, assume the light intensity I is... l The value is 0, based on the Lamb-Beer law formula. Determine the concentrations of each component gas in the sample gas; determine the short-path absorbance (OD). s When the absorbance is less than the short-path absorbance threshold k2, the substance concentration is low, and the short-path absorption is weak and negligible, resulting in only long-path absorption. Therefore, it is assumed that only long-path absorption exists, based on the Lambert-Beer law formula. Determine the concentrations of each component gas in the sample gas; where the short-path absorbance OD is... s =lnx, long-path absorbance is ODl =Nlnx.

[0065] Knowing the optical path length ratio, the detected spectral energy, and the long-path and short-path light intensities obtained in step S01, the absorbance of both optical paths can be calculated. By determining whether the absorbance meets the absorbance threshold condition, the appropriate formula for gas concentration detection can be determined.

[0066] Considering that Beer-Lambert law has a certain linear applicability range, piecewise nonlinear compensation is needed for the calculated concentration. The method of this invention also includes step S04, based on... Piecewise nonlinear compensation is applied to the concentrations of each component gas in the calculated sample gas; where, U i The concentration is compensated, and a1 and a2 are constant coefficients. Based on nonlinear fitting experience, a1 is typically between 0.3 and 1.1, and a2 is typically < 0.3; the specific values ​​need to be determined based on the actual fitting conditions. The closer a1 is to 1, the better the linearity. This method can eliminate the interference from the calculation results of Lambert-Beer's law under offset linearity conditions.

[0067] Those skilled in the art should understand that the embodiments of the present invention described above and shown in the accompanying drawings are merely examples and do not limit the present invention. The objectives of the present invention have been fully and effectively achieved. The functions and structural principles of the present invention have been demonstrated and explained in the embodiments, and any modifications or variations of the implementation of the present invention may be made without departing from the stated principles.

Claims

1. A dual optical path gas chamber, characterized in that, The system includes a first beam splitter, a first concave mirror, a second concave mirror, and a second beam splitter. The first and second concave mirrors are arranged opposite each other and sealed to form a Heliot gas cell. The first beam splitter is located at the front end of the first concave mirror, and the second beam splitter is located at the rear end of the second concave mirror. A short-path inlet is formed at the center of the first concave mirror, and a long-path inlet designed according to the Heliot gas cell is formed at its edge. A short-path outlet is formed at the center of the second concave mirror, and a long-path outlet designed according to the Heliot gas cell is formed at its edge. A light beam enters the dual-path gas cell and is split by the first beam splitter. The short-path beam enters the Heliot gas cell through the short-path inlet and exits through the short-path outlet, while the long-path beam enters the Heliot gas cell through the long-path inlet and exits through the short-path outlet. After multiple back-and-forth movements within the Heliot gas cell, the beam exits through the long-path exit hole. The short-path and long-path beams exiting the Heliot gas cell are combined by the second beam splitter and then exit from the dual-path gas chamber to be sent to a spectrometer to detect the spectral energy of sample or standard gases at different concentrations. The first beam splitter has two surfaces: a reflective surface coated with an anti-reflective coating and a semi-reflective, semi-transparent surface. The wedge angle between the reflective surface and the semi-reflective, semi-transparent surface in the first beam splitter is half the designed incident angle of the Heliot gas cell, ensuring that the short-path beam enters the Heliot gas cell parallel to the ground, while the long-path beam enters the Heliot gas cell at the designed incident angle. The second beam splitter has two surfaces: a reflective surface coated with an anti-reflective coating and a semi-reflective, semi-transparent surface. The wedge angle between the reflective surface and the semi-reflective, semi-transparent surface in the second beam splitter is half the designed exit angle of the Heliot gas cell, ensuring that the short-path and long-path beams are combined and exited.

2. The dual optical path gas chamber according to claim 1, characterized in that, It also includes a first collimating lens and a second collimating lens; the first collimating lens is located at the front end of the first beam splitter, and the second collimating lens is located at the rear end of the second beam splitter; the light beam enters the dual-path gas chamber, is collimated by the first collimating lens, and then enters the first beam splitter to split the beam; the short-path beam and the long-path beam are combined by the second beam splitter, collimated by the second collimating lens, and finally exit from the dual-path gas chamber.

3. The dual optical path gas chamber according to claim 1, characterized in that, The first beam splitter has four faces, the other two of which are transmission faces coated with antireflective coatings; the second beam splitter has four faces, the other two of which are transmission faces coated with antireflective coatings.

4. A dual optical path gas chamber according to claim 1, characterized in that, The transmittance-to-reflection ratio of the semi-reflective and semi-transparent surface is allocated according to the energy loss of the designed return gas chamber, so that the light intensity distribution of long and short optical paths is similar.

5. A dual optical path detection system, characterized in that, It includes a light source, a dual-path gas chamber as described in claim 1 or 2, and a spectrometer; the light source is connected to the dual-path gas chamber via an optical fiber, and the dual-path gas chamber is connected to the spectrometer via an optical fiber.

6. A method for detecting gas concentration, characterized in that, Based on the dual optical path detection system described in claim 5, the method includes: Step S01: Based on the path length ratio N of the dual-path gas chamber and the spectral energies of three sets of standard gases at specified concentrations, the formula of Lambert-Beer's Law is applied. Solve for long optical path light intensity and short optical path light intensity ;in, For short optical paths, the optical path length is... The optical path length is the length of the long optical path. c is the gas concentration; Step S02, based on the long-to-short optical path ratio N of the dual-path gas chamber and the spectral energy of a set of sample gases with unknown concentrations. The long-path light intensity calculated in step S01 and short optical path light intensity According to the Lamb-Beer law formula Solving for the given information yields the following results. And the absorption cross section is calculated based on this formula. and the absorption cross section Polynomial fitting is used to obtain the slowly varying portion of the absorption cross section. Thus, the differential absorption cross section is obtained. ; Step S03, for the results obtained in step S02 Differential processing is performed to obtain differential optical thickness. And solve using the least squares algorithm or partial least squares algorithm. This allows us to obtain the concentrations of each component gas in the sample gas. .

7. The gas concentration detection method according to claim 6, characterized in that, The specific steps of S01 are as follows: Step S11: Introduce gas into the gas pool sequentially. ,concentration c With concentration 2c The standard gas was used to obtain the spectral energy of the standard gas at different concentrations detected by the spectrometer. , And without introducing standard gas, the spectral energy detected by the spectrometer was obtained. ; Step S12, based on the path length ratio N of the dual-path gas chamber and the spectral energies of the three sets of standard gases at specified concentrations, according to the Lambert-Beer law formula: , Solving for long optical path light intensity and short optical path light intensity .

8. The gas concentration detection method according to claim 6, characterized in that, The method further includes: determining the long-path absorbance before step S03. Not greater than the long optical path absorbance threshold And short optical path absorbance Not less than the short optical path absorbance threshold If the condition is met, proceed to step S03; otherwise, skip step S03 and calculate the concentration as follows: Determine the long-path absorbance. greater than the long optical path absorbance threshold At that time, assuming optical path and light intensity The value is 0, based on the Lamb-Beer law formula. Determine the concentrations of each component gas in the sample gas; determine the short-path absorbance. Less than the short optical path absorbance threshold At this time, assuming only long-path absorption, based on the Lamb-Beer law formula... Determine the concentrations of each component gas in the sample gas; among them, the short-path absorbance... Long optical path absorbance is .

9. A gas concentration detection method according to claim 6 or 8, characterized in that, The method also includes step S04, based on Piecewise nonlinear compensation is applied to the concentrations of each component gas in the calculated sample gas; among which, The concentration calculated in step S03, The concentration after compensation. , These are constant coefficients.

Images