A gas detection device based on a variable optical path multi-integrating sphere and its detection method

Abstract

The present invention discloses a gas detection device based on a variable optical path multi-integrating sphere and a detection method thereof. The device comprises: a multi-integrating sphere housing; a multi-integrating sphere, which is arranged in series in the multi-integrating sphere housing through a plurality of identical single integrating spheres, and an aperture is provided at the connection between each of the single integrating spheres; each of the single integrating spheres is provided with a light inlet and an air inlet hole, and the single integrating sphere located at the head end is also provided with a light outlet and an air outlet hole, and the inner wall of the single integrating sphere is provided with a diffuse reflection coating; a light source is arranged outside the light inlet; and a spectrometer is connected to the light outlet via an optical fiber; by arranging the multiple integrating spheres, the effective optical path during gas detection can be conveniently and stably changed, thereby solving the problem that the single integrating sphere cannot change the optical path when used as a gas pool, and improving its flexibility in detecting gases of different concentrations and types.

Description

Technical Field

[0001] The present invention relates to the fields of optical integrating spheres and optical gas detection, and in particular to a gas detection device based on a variable optical path multi-integrating sphere and a detection method thereof. Background Art

[0002] When a beam of light strikes a specific gas molecule, the light energy of a specific wavelength, corresponding to the energy required for translational, rotational, vibrational, and electronic transitions, is absorbed by the gas molecule, causing a change in the spectral curve, forming the absorption spectrum of the gas. By analyzing this spectral change using the Lambert-Beer theorem, the type and concentration of the gas molecule can be inferred. Optical gas detection methods that adhere to the Lambert-Beer theorem place high demands on the optical path length between light and gas. Traditional long-path gas cells include the Herriott cell and the White cell, which rely on multiple reflections. However, these cells all have challenges such as requiring high mirror finish precision, complex optical path adjustment, delicate operation, high cost, and limited portability.

[0003] A diffuse reflectance integrating sphere is a spherical cavity formed by coating the inner wall with a material with a high diffuse reflectance coefficient. Light entering the sphere is absorbed by the gas during multiple reflections from the inner wall coating, achieving the goal of achieving a longer effective optical path in a small space. Compared to other long-path gas cells, it is simple to manufacture, has good stability, and is relatively low in cost. However, because the optical path of an integrating sphere is only related to its inner diameter and the reflectivity of the diffuse reflection surface within the sphere, its optical path cannot be changed when a single integrating sphere is directly used as a gas detection chamber. This leads to two problems: for high-concentration gases, if the optical path is too long, the light energy of a specific wavelength will be completely absorbed by the gas in the gas cell prematurely during transmission, resulting in absorption saturation and inaccurate concentration measurements of high-concentration gases. Similarly, for low-concentration gases, if the optical path is too short, the gas will not absorb enough light, resulting in a poor signal-to-noise ratio and affecting the measurement results. Furthermore, for gases with different absorption characteristics, the optical path length must be adjusted to achieve more accurate detection results. For gases with a high absorptivity at a specific wavelength, a short optical path length is required, while for gases with a high absorptivity at a specific wavelength, a long optical path length is required. The inability to adjust the optical path length of a traditional single integrating sphere gas cell results in significant variations in measurement performance when measuring different types and concentrations of gases, complicating operation and impacting work efficiency. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the prior art, the present invention provides a gas detection device based on a variable optical path multi-integrating sphere. Compared with directly using an integrating sphere as a gas absorption cell, the device can be used to detect a wider range of gases and concentrations, and can ensure the performance stability of the multi-integrating sphere after adjusting the optical path.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a gas detection device based on a variable optical path multi-integrating sphere, comprising:

[0006] Multiple integrating sphere housings;

[0007] A multiple integrating sphere is provided in series within the multiple integrating sphere housing by connecting multiple identical single integrating spheres. An integrating sphere connection port is provided at the connection between each of the single integrating spheres. An aperture is provided on the integrating sphere connection port for controlling the opening and closing of the integrating sphere connection port. Each of the single integrating spheres is provided with a light inlet and an air inlet. The single integrating sphere at the head end is also provided with a light outlet and an air outlet. The opening direction of the light inlet is perpendicular to the opening direction of the light outlet. The opening direction of the integrating sphere connection port is in the same straight line as the opening direction of the light outlet. The inner wall of the single integrating sphere is provided with a diffuse reflection coating.

[0008] A light source is arranged outside the light inlet;

[0009] A spectrometer is connected to the light outlet via an optical fiber.

[0010] As a preferred embodiment of the present invention: the multiple integrating spheres include a first integrating sphere, a second integrating sphere, and a third integrating sphere arranged in series, the first integrating sphere is provided with the light outlet and the air outlet, a first aperture is provided between the first integrating sphere and the second integrating sphere, and a second aperture is provided between the second integrating sphere and the third integrating sphere.

[0011] As a preferred embodiment of the present invention, the opening direction of the air inlet and the opening direction of the air outlet are on the same straight line.

[0012] As a preferred embodiment of the present invention: an air valve is provided on the outside of the air inlet, and an air outlet valve is provided on the outside of the air outlet, for controlling the air inlet and outlet of the integrating sphere.

[0013] As a preferred embodiment of the present invention: the inner diameter of the integrating sphere is 40 mm, and the reflectivity of the diffuse reflection coating in the integrating sphere is 98%.

[0014] As a preferred embodiment of the present invention, the diffuse reflection coating coated on the inner wall of the multi-integrating sphere is a polytetrafluoroethylene coating.

[0015] A detection method for a gas detection device based on a variable optical path multi-integrating sphere comprises the following steps:

[0016] S1, according to the approximate concentration of the gas to be measured, decide the number of single integrating spheres to be used in the multi-integrating sphere, and adjust the corresponding aperture size to change the optical path of the multi-integrating sphere

[0017] S2, connect the air inlet of the corresponding integrating sphere to the gas container to be tested through the air valve, connect the air outlet to the exhaust device through the air outlet valve, and keep the air valve and air outlet valve closed;

[0018] S3, connect the light outlet of the multi-integrating sphere to the spectrometer through an optical fiber to obtain dark spectrum data;

[0019] S4: Align the light source with the light entrance of the corresponding integrating sphere, turn on the light source and adjust the light source, set the spectrometer integration time, and subtract the dark spectrum data from the measured data to obtain the original wavelength data S;

[0020] S5, open the gas valve and introduce the gas to be measured into the integrating sphere cavity. After the spectrum curve stabilizes, record the gas absorption wavelength data Sd;

[0021] S6, obtain the absorbance data A(λ) of the gas according to the formula A(λ)=log(S / Sd), where λ is the wavelength. Based on the known absorption cross-section data, the effective optical path length L of the integrating sphere and the experimentally measured absorbance data A(λ), the concentration of the gas is calculated according to the formula c=A(λ) / σ(λ)L, where c is the gas concentration, λ is the wavelength, A(λ) is the absorbance of the gas at the wavelength λ, σ(λ) is the absorption cross-section of the gas at the wavelength λ, and L is the effective optical path length;

[0022] S7, open the air outlet valve to discharge the gas in the integrating sphere.

[0023] As a preferred embodiment of the present invention, step 1 specifically includes the following steps:

[0024] S11, if the concentration of the gas to be measured is known in its approximate range,

[0025] Gases with concentrations above 400 ppm are detected using an integrating sphere;

[0026] Gases with a concentration range of 50-400 ppm were detected using two integrating spheres;

[0027] Gases with concentrations below 50 ppm are detected using three integrating spheres.

[0028] S12: When the concentration of the gas to be measured is uncertain, use a single integrating sphere to test and observe the degree of decrease in the spectrum curve;

[0029] S13, test the absorption wavelength position of the gas. If the test shows that the light intensity after gas absorption is less than 10% of the light intensity before gas absorption, the decrease is considered not significant and an integrating sphere is added to test again, with a maximum of three integrating spheres.

[0030] S14, repeat step S13 until the light intensity at the absorption wavelength position decreases by more than 10%, then it is considered that the decrease in the spectrum curve is obvious, and the number of integrating spheres used is maintained for detection.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention sets up a multi-integrating sphere group so that light can be reflected multiple times inside the multiple integrating spheres, pass through the gas in the multi-integrating sphere cavity and be absorbed, and enter the spectrometer through the optical fiber at the light outlet to obtain the spectral absorption data of the gas. The gas concentration information can be obtained through concentration inversion.

[0033] (2) Setting up a multi-integrating sphere group as a gas pool can realize optical measurements from a short optical path of several meters to a long optical path of tens of meters using only a very small space, which greatly compresses the volume of the equipment for long optical path measurement and has portability, greatly improving the current situation that long optical path gas pools can basically only be used for laboratory measurements.

[0034] (3) The use of the multiple integrating spheres as a variable optical path gas cell has the advantages of simple manufacturing process, low cost, and no need for complex optical path adjustment compared with the currently commonly used variable optical path gas cells such as the White cell and the Herriott cell. By changing the number of integrating spheres used and fine-tuning the aperture size at the connection of the integrating spheres, the function of conveniently and stably changing the effective optical path during gas detection can be achieved.

[0035] (4) The use of multiple integrating spheres solves the problem that a single integrating sphere cannot change the optical path when used as a gas pool. For high-concentration gases and gases with a high absorption rate at a specific absorption wavelength, only one integrating sphere can be used to achieve short optical path measurement, avoiding the problem of gas oversaturation absorption of light energy at a specific wavelength. For low-concentration gases and gases with a low absorption rate at a specific absorption wavelength, multiple integrating spheres can be used to achieve long optical path measurement, increasing the proportion of light energy at a specific wavelength absorbed by the gas and improving the signal-to-noise ratio of the spectral signal. Therefore, compared with a single integrating sphere gas pool, the variable optical path multi-integrating sphere device significantly improves the flexibility of the integrating sphere as a gas pool in detecting gases of different concentrations and types. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of the gas detection device of the present invention;

[0037] Figure 2 Schematic diagram of the structure of the multi-integrating sphere in the present invention;

[0038] Figure numerals: 1 is the light source; 2 is the multi-integrating sphere; 21 is the multi-integrating sphere housing; 22 is the third integrating sphere; 23 is the second integrating sphere; 24 is the first integrating sphere; 25 is the aperture; 26 is the light inlet; 27 is the light outlet; 28 is the air inlet; 29 is the air outlet; 211 is the air valve; 3 is the optical fiber; 4 is the spectrometer; 5 is the computer. DETAILED DESCRIPTION

[0039] The present invention is further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, modifications of various equivalent forms of the present invention made by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0040] like Figure 1 The figure shows a gas detection device based on a variable optical path multi-integrating sphere, comprising: a light source 1, a multi-integrating sphere 2, an optical fiber 3, a spectrometer 4, and a computer 5. The multi-integrating sphere is arranged in series within the multi-integrating sphere housing 21 through a plurality of identical single integrating spheres, an integrating sphere connection port is provided at the connection between each of the single integrating spheres, and an aperture 25 is provided on the integrating sphere connection port for controlling the opening and closing of the integrating sphere connection port; each of the single integrating spheres is provided with a light inlet and an air inlet 28, and the single integrating sphere at the head end is also provided with a light outlet 27 and an air outlet 29, the opening direction of the light inlet is perpendicular to the opening direction of the light outlet 27, the opening direction of the integrating sphere connection port is on the same straight line as the opening direction of the light outlet 27, and the inner wall of the single integrating sphere is provided with a diffuse reflection coating;

[0041] The diffuse reflection coating of the integrating sphere is a polytetrafluoroethylene coating with a reflectivity of 98%. The inner diameter of the integrating sphere is 40 mm.

[0042] A light source is arranged outside the light inlet;

[0043] A spectrometer connected to the light outlet 27 via an optical fiber;

[0044] A computer is connected to the spectrometer.

[0045] According to the optical path requirements, the number of working integrating spheres is selected, the aperture 25 of the unused integrating sphere connection port is closed, and the light output position of the light source 1 is aligned and parallel to the corresponding integrating sphere light inlet 26. When the light source 1 is working, it will emit light within a certain wavelength range, enter the multiple integrating spheres 2 and be reflected multiple times, and be absorbed multiple times by the gas to be measured in the cavity of the multiple integrating spheres 2; the spectrometer 4 receives the light signal after reflection in the multiple integrating spheres 2 through the optical fiber 3, and connects to the computer 5 with a USB to obtain the absorption spectrum information of the gas; the air inlet valve of the corresponding integrating sphere is connected to the gas container to be measured, and the air outlet valve is connected to the exhaust device.

[0046] A detection method for a gas detection device based on a variable optical path multi-integrating sphere comprises the following steps:

[0047] S1, based on the approximate concentration of the gas to be measured, determine the number of single integrating spheres to be used in the multi-integrating sphere, and adjust the corresponding aperture size to change the optical path of the multi-integrating sphere;

[0048] S11, if the concentration of the gas to be measured is known in its approximate range,

[0049] Gases with concentrations above 400 ppm are detected using an integrating sphere;

[0050] Gases with a concentration range of 50-400 ppm were detected using two integrating spheres;

[0051] Gases with concentrations below 50 ppm are detected using three integrating spheres.

[0052] S12: When the concentration of the gas to be measured is uncertain, use a single integrating sphere to test and observe the degree of decrease in the spectrum curve;

[0053] S13, test the absorption wavelength position of the gas. If the test shows that the light intensity after gas absorption is less than 10% of the light intensity before gas absorption, the decrease is considered not significant and an integrating sphere is added to test again, with a maximum of three integrating spheres.

[0054] S14, repeat step S13 until the light intensity at the absorption wavelength position decreases by more than 10%, then it is considered that the decrease in the spectrum curve is obvious, and the number of integrating spheres used is maintained for detection.

[0055] S2, connect the gas inlet 28 of the corresponding integrating sphere to the gas container to be measured through the gas valve 211, connect the gas outlet 29 to the exhaust device through the gas valve 211, and keep the gas valve 211 closed;

[0056] S3, connecting the light outlet 27 in the multi-integrating sphere to the spectrometer via an optical fiber to obtain dark spectrum data;

[0057] S4: Align the light source with the light entrance of the corresponding integrating sphere, turn on the light source and adjust the light source, set the spectrometer integration time, and subtract the dark spectrum data from the measured data to obtain the original wavelength data S;

[0058] S5, open the gas valve 211, introduce the gas to be measured into the integrating sphere cavity, and record the gas absorption wavelength data Sd after the spectrum curve stabilizes;

[0059] S6, obtain the absorbance data A(λ) of the gas according to the formula A(λ)=log(S / Sd), where λ is the wavelength, obtain the absorption cross section data of the gas from the data on the spectral database website hitran, and based on the known absorption cross section data, the effective optical path length L of the integrating sphere and the experimentally measured absorbance data A(λ), calculate the concentration of the gas according to the formula c=A(λ) / σ(λ)L, where c is the gas concentration, λ is the wavelength, A(λ) is the absorbance of the gas at the wavelength λ, σ(λ) is the absorption cross section of the gas at the wavelength λ, and L is the effective optical path length;

[0060] S7, open the gas valve 211 to discharge the gas in the integrating sphere.

[0061] The method of changing the optical path of multiple integrating spheres is to first determine the number of single integrating spheres used as gas pools, open the iris at the connection of the integrating spheres in use, close the iris at the connection of the integrating spheres in use, open the light inlet and air inlet of the corresponding integrating spheres, keep the other light inlets and air inlets closed, and then fine-tune the optical path by adjusting the iris size between the integrating spheres used as gas pools.

[0062] The present invention sets up a multi-integrating sphere group so that light can be reflected multiple times inside the multiple integrating spheres, pass through the gas in the multiple integrating sphere cavities and be absorbed, and enter the spectrometer through the optical fiber at the light outlet to obtain spectral absorption data of the gas. Gas concentration information can be obtained through concentration inversion.

[0063] Setting up a multi-integrating sphere group as a gas pool can realize optical measurements from short optical path of several meters to long optical path of tens of meters using only a very small space, greatly compressing the volume of equipment for long optical path measurement while being portable, greatly improving the current situation where long optical path gas pools can basically only be used for laboratory measurements.

[0064] Compared with the currently commonly used variable optical path gas cells such as the White cell and the Herriott cell, the use of this multi-integrating sphere as a variable optical path gas cell has the advantages of simple manufacturing process, low cost, and no need for complex optical path adjustment. By changing the number of integrating spheres used and fine-tuning the aperture size at the connection between the integrating spheres, the function of conveniently and stably changing the effective optical path during gas detection can be achieved.

[0065] The use of a multi-integrating sphere assembly solves the long-standing problem of a single integrating sphere as a gas cell being unable to change the optical pathlength. For high-concentration gases and gases with high absorptivity at specific absorption wavelengths, a single integrating sphere can be used to achieve short optical pathlength measurements, avoiding the problem of the gas's oversaturated absorption of light energy at a specific wavelength. For low-concentration gases and gases with low absorptivity at specific absorption wavelengths, multiple integrating spheres can be used to achieve long optical pathlength measurements, increasing the proportion of light energy at a specific wavelength absorbed by the gas and improving the signal-to-noise ratio of the spectral signal. Therefore, compared to a single integrating sphere gas cell, the variable optical pathlength multi-integrating sphere assembly significantly increases the flexibility of the integrating sphere as a gas cell for detecting gases of varying concentrations and types.

[0066] The present invention proposes a gas detection device and detection method based on a variable optical path multi-integrating sphere. The device effectively solves the problem that the optical path cannot be changed when a single integrating sphere is used as a gas detection gas pool. It can be applied to the absorption spectrum measurement of gases of more types and concentration ranges, and effectively ensures the stability of the system during the adjustment of the optical path.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A gas detection device based on a variable optical path multi-integrating sphere, characterized in that: include: Multiple integrating sphere housings; A multiple integrating sphere is provided in series within the multiple integrating sphere housing by connecting a plurality of identical single integrating spheres. An integrating sphere connection port is provided at the connection between each of the single integrating spheres. An aperture is provided on the integrating sphere connection port for controlling the opening and closing of the integrating sphere connection port, including opening the aperture at the connection of the integrating spheres in use, closing the aperture at the connection of the integrating spheres in unuse, and adjusting the aperture size between the integrating spheres serving as gas pools to fine-tune the optical path. Each of the single integrating spheres is provided with a light inlet and an air inlet hole. The single integrating sphere at the head end is also provided with a light outlet and an air outlet hole. The opening direction of the light inlet is perpendicular to the opening direction of the light outlet. The opening direction of the integrating sphere connection port is in the same straight line as the opening direction of the light outlet. The inner wall of the single integrating sphere is provided with a diffuse reflection coating. A light source is arranged outside the light inlet; A spectrometer is connected to the light outlet via an optical fiber.

2. The gas detection device based on a variable optical path multi-integrating sphere according to claim 1, characterized in that: The multiple integrating spheres include a first integrating sphere, a second integrating sphere, and a third integrating sphere arranged in series. The first integrating sphere is provided with the light outlet and the air outlet. A first aperture is provided between the first integrating sphere and the second integrating sphere. A second aperture is provided between the second integrating sphere and the third integrating sphere.

3. The gas detection device based on a variable optical path multi-integrating sphere according to claim 2, characterized in that: The opening direction of the air inlet and the opening direction of the air outlet are on the same straight line.

4. The gas detection device based on a variable optical path multi-integrating sphere according to claim 2, characterized in that: An air valve is provided on the outside of the air inlet, and an air outlet valve is provided on the outside of the air outlet, for controlling the air inlet and outlet of the integrating sphere.

5. The gas detection device based on a variable optical path multi-integrating sphere according to claim 2, characterized in that: The inner diameter of the integrating sphere is 40 mm, and the reflectivity of the diffuse reflection coating in the integrating sphere is 98%.

6. The gas detection device based on a variable optical path multi-integrating sphere according to claim 2, characterized in that: The diffuse reflection coating coated on the inner wall of the multi-integrating sphere is a polytetrafluoroethylene coating.

7. The detection method based on the gas detection device based on the variable optical path multi-integrating sphere according to claim 2 is characterized in that: The following steps are involved: S1, based on the approximate concentration of the gas to be measured, determine the number of single integrating spheres to be used in the multi-integrating sphere, and adjust the corresponding aperture size to change the optical path of the multi-integrating sphere; S2, connect the air inlet of the corresponding integrating sphere to the gas container to be tested through the air valve, connect the air outlet to the exhaust device through the air outlet valve, and keep the air valve and air outlet valve closed; S3, connect the light outlet of the multi-integrating sphere to the spectrometer through an optical fiber to obtain dark spectrum data; S4: Align the light source with the light entrance of the corresponding integrating sphere, turn on the light source and adjust the light source, set the spectrometer integration time, and subtract the dark spectrum data from the measured data to obtain the original wavelength data S; S5, open the gas valve and introduce the gas to be measured into the integrating sphere cavity. After the spectrum curve stabilizes, record the gas absorption wavelength data Sd; S6, obtain the absorbance data A(λ) of the gas according to the formula A(λ) = log(S / Sd), where λ is the wavelength. Based on the known absorption cross-section data, the effective optical path length L of the integrating sphere and the experimentally measured absorbance data A(λ), the concentration of the gas is calculated by the formula c=A(λ) / σ(λ)L, where c is the gas concentration, λ is the wavelength, A(λ) is the absorbance of the gas at wavelength λ, σ(λ) is the absorption cross-section of the gas at wavelength λ, and L is the effective optical path length; S7, open the air outlet valve to discharge the gas in the integrating sphere.

8. The detection method according to claim 7, characterized in that The step S1 specifically includes the following steps: S11, if the concentration of the gas to be measured is within a known range, then Gases with concentrations above 400 ppm are detected using an integrating sphere; Gases with a concentration range of 50-400 ppm were detected using two integrating spheres; Gases with a concentration range below 50 ppm are detected using three integrating spheres; S12: When the concentration of the gas to be measured is uncertain, use a single integrating sphere to test and observe the degree of decrease in the spectrum curve; S13: At the absorption wavelength of the gas to be tested, if the test shows that the decrease in light intensity after gas absorption is within 10% compared to the light intensity before gas absorption, the decrease is considered insignificant and an integrating sphere is added for retesting, with a maximum of three integrating spheres required for testing. S14, repeat step S13 until the decrease in the spectrum curve exceeds 10%, and keep using the number of integrating spheres for detection.

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