High-temperature-resistant diffuse reflection gas measuring device based on optical waveguide

Abstract

The invention discloses an optical waveguide-based high-temperature-resistant diffuse reflection gas measuring device, which comprises a diffuse reflection sheet, a first convex lens, an optical waveguide, an antireflection film optical window, a second convex lens, a collimator and a photoelectric detector, and is characterized in that the diffuse reflection sheet and the first convex lens are fixedly arranged at one end of the optical waveguide and form a TDLAS gas chamber; the anti-reflection film optical window, the second convex lens, the collimator and the photoelectric detector are fixedly arranged at the other end of the optical waveguide, the anti-reflection film optical window is fixedly arranged on the end face of the optical waveguide, a hole is formed in the middle of the second convex lens, the light beam output end of the collimator penetrates through the second convex lens from the hole, and the light beam input end of the collimator is connected with an output optical fiber of the TDLAS laser. The photoelectric detector is located at the light beam input end of the collimator. The high-temperature-resistant diffuse reflection gas measuring device based on the optical waveguide can stably measure gas for a long time under the environment working conditions of high temperature, corrosion, water vapor condensation and the like, and is simple in structure and low in cost.

Description

Technical Field

[0001] This application relates to the field of gas measurement technology, specifically to a high-temperature resistant diffuse reflection gas measurement device based on an optical waveguide. Background Technology

[0002] TDLAS (Tunable Diode Laser Absorption Spectroscopy) laser gas sensors are high-precision gas detection devices based on the principle of spectral absorption. The gas cell of a TDLAS laser gas sensor is composed of optical lenses. The function of the gas cell is to transmit the laser light from the laser source into the gas cell and convert it into a spatially propagating beam that illuminates the atmosphere to be measured. If the atmosphere contains the gas to be measured, the gas will absorb the corresponding wavelength energy from the laser light. The beam is then output through the gas cell to a photodetector, where the laser beam intensity signal is analyzed, the absorption curve intensity is determined, and the gas concentration is calculated accordingly.

[0003] However, traditional air chambers have poor durability, limited by the reliability of the adhesive used to fix the air chamber structure in terms of temperature resistance, corrosion resistance, and moisture resistance. They cannot bond when the adhesive material deforms or the adhesive carbonizes at high temperatures. In addition, they are limited by the temperature deformation of the air chamber fixing structure. For example, 316L stainless steel is generally used in industrial fields. Under high and low temperature changes, the deformation is large, which will damage the optical coupling and cause the signal to fail to return to the detector.

[0004] In practical applications, the gas chamber is placed in the environment to be measured. In industrial applications, measurements often encounter high temperatures, corrosion, and water vapor condensation, making the gas chamber measurement conditions quite harsh. To address this challenge, TDLAS industrial applications typically involve creating a pair of holes in the industrial pipeline and installing two optical observation windows. The TDLAS optical path passes through one of the observation windows, with the detector on the other side, forming the TDLAS measurement gas chamber. Because the added optical observation window is in contact with the outside environment, and the outside temperature is lower than the temperature inside the pipeline, the high-temperature water vapor inside the pipeline condenses on the observation window.

[0005] To address the issue of water vapor condensation, a heat tracing structure is required, complicating the system design. Furthermore, installing the heat tracing structure necessitates drilling pipes with precise precision, requiring production to be halted during drilling. Any adjustments also necessitate system shutdown for maintenance. To handle condensate and contaminants, heating and purging functions are added to the light-emitting window, increasing auxiliary equipment, costs, and reliability.

[0006] In summary, neither of the existing solutions can meet the requirements of TDLAS gas sensors for long-term, stable, and low-cost measurement under harsh operating conditions. Summary of the Invention

[0007] Therefore, this application provides a high-temperature resistant diffuse reflection gas measurement device based on optical waveguide to solve the problem that the existing TDLAS gas sensor cannot perform stable gas measurement for a long time under high temperature, corrosive and water vapor condensation environmental conditions.

[0008] To achieve the above objectives, this application provides the following technical solution:

[0009] A high-temperature resistant diffuse reflection gas measurement device based on an optical waveguide includes a diffuse reflector, a first convex lens, an optical waveguide, an anti-reflection optical window, a second convex lens, a collimator, and a photodetector. The optical waveguide is made of a high-temperature resistant material. The diffuse reflector and the first convex lens are fixedly disposed at one end of the optical waveguide, with the first convex lens close to the waveguide and the diffuse reflector away from it, forming a TDLAS gas chamber. The anti-reflection optical window, the second convex lens, the collimator, and the photodetector are fixedly disposed at the other end of the optical waveguide. The anti-reflection optical window is fixedly disposed on the end face of the optical waveguide. The second convex lens has an opening in the middle, through which the beam output end of the collimator passes. The beam input end of the collimator is connected to the output fiber of a TDLAS laser. The photodetector is located at the beam input end of the collimator and is at a certain distance from the collimator.

[0010] Preferably, the optical waveguide is a quartz optical waveguide.

[0011] Preferably, the length of the optical waveguide is at least 0.6m.

[0012] Preferably, the diameter of the antireflective film optical window is 1.5 times the collimated beam diameter.

[0013] Preferably, the antireflective optical window is bonded to the end face of the optical waveguide using transparent adhesive with a refractive index of 1.45.

[0014] Preferably, the diffuse reflective sheet is made of metal or glass.

[0015] Preferably, the system also includes a collimator fine-tuning fixing structure, which includes a fixing adjustment structure and a fixing structure. The collimator is disposed in the fixing adjustment structure and the fixing structure, fixed by a fixing screw, and adjusted by an adjusting screw.

[0016] Preferably, the system also includes a flange, which is fitted and circumferentially fixed to the axial center of the optical waveguide.

[0017] Compared with the prior art, this application has at least the following beneficial effects:

[0018] Based on further analysis and research of existing technical problems, this application proposes a high-temperature resistant diffuse reflection gas measurement device based on an optical waveguide. The device includes a diffuse reflector, a first convex lens, an optical waveguide, an anti-reflection optical window, a second convex lens, a collimator, and a photodetector. The diffuse reflector and the first convex lens are fixedly disposed at one end of the optical waveguide, with the first convex lens close to the waveguide and the diffuse reflector far from it. A certain distance exists between the first convex lens and the diffuse reflector, forming a TDLAS gas chamber. The anti-reflection optical window, the second convex lens, the collimator, and the photodetector are fixedly disposed at the other end of the optical waveguide. The anti-reflection optical window is fixedly disposed on the end face of the optical waveguide. The second convex lens has an opening in the middle, through which the beam output end of the collimator passes. The beam input end of the collimator is connected to the output fiber of the TDLAS laser. The photodetector is located at the beam input end of the collimator and is at a certain distance from the collimator. The high-temperature resistant diffuse reflection gas measurement device based on an optical waveguide provided by this application can perform gas measurement stably and for a long time under environmental conditions such as high temperature, corrosion, and water vapor condensation. It also has a simple structure and low cost. Attached Figure Description

[0019] To more intuitively illustrate the prior art and this application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concept disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, size ratios, etc. of certain units (components).

[0020] Figure 1 A schematic diagram of a high-temperature diffuse reflection gas measuring device based on an optical waveguide provided in this application;

[0021] Figure 2 This is a schematic diagram of the diameter structure of the antireflective coating optical window provided in this application;

[0022] Figure 3 A ZEMAX optical path simulation diagram of a high-temperature diffuse reflection gas measurement device based on an optical waveguide provided for this application;

[0023] Figure 4 A schematic diagram of the collimator fine-tuning and fixing structure provided in this application;

[0024] Figure 5 This application provides a schematic diagram of the installation structure of a high-temperature diffuse reflection gas measuring device based on an optical waveguide.

[0025] Explanation of reference numerals in the attached figures:

[0026] 1. Diffuse reflector; 2. First convex lens; 3. Optical waveguide; 4. Anti-reflective film optical window; 5. Second convex lens; 6. Collimator; 7. Photodetector; 8. Collimator fine-tuning fixing structure; 801. Fixing and adjusting structure; 802. Fixing structure; 803. Adjusting screw; 804. Fixing screw; 9. Flange. Detailed Implementation

[0027] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] In the description of this application: unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," "third," etc., in this application are intended to distinguish the objects referred to and do not have any special meaning in terms of technical connotation (e.g., they should not be construed as an emphasis on importance or order). Expressions such as "including," "comprising," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0029] The terms used in this application, such as "upper," "lower," "left," "right," and "middle," are generally used to indicate the general relative positional relationship for the purpose of intuitive understanding by referring to the accompanying drawings, and are not absolute limitations on the positional relationship in the actual product.

[0030] To expand the application range of TDLAS gas sensors and increase their application in high-temperature and highly corrosive industrial fields, such as gas boiler pipelines, high-temperature industrial process pipelines, and ovens, this application proposes a high-temperature resistant diffuse reflection gas measurement device based on optical waveguides. This device utilizes optical waveguides, diffuse reflection, and automatic gain adjustment of the photoelectric receiver circuit to create a gas measurement device suitable for complex and harsh working conditions.

[0031] Please see Figure 1This application provides a high-temperature resistant diffuse reflection gas measuring device based on an optical waveguide, comprising a diffuse reflector 1, a first convex lens 2, an optical waveguide 3, an anti-reflection optical window 4, a second convex lens 5, a collimator 6, and a photodetector 7. The optical waveguide 3 is made of a high-temperature resistant material, preferably a quartz waveguide. The diffuse reflector 1 and the first convex lens 2 are fixedly disposed at one end of the optical waveguide 3, with the first convex lens 2 close to the optical waveguide 3 and the diffuse reflector 1 far from the optical waveguide 3. A certain distance exists between the first convex lens 2 and the diffuse reflector 1. The antireflective optical window 4, the second convex lens 5, the collimator 6, and the photodetector 7 are fixedly disposed at the other end of the optical waveguide 3. The antireflective optical window 4 is fixedly disposed at the end face of the optical waveguide 3. The second convex lens 5 has an opening in the middle. The beam output end of the collimator 6 passes through the second convex lens 5 through the opening. The beam input end of the collimator 6 is connected to the output optical fiber of the TDLAS laser. The photodetector 7 is located at the beam input end of the collimator 6 and is at a certain distance from the collimator 6.

[0032] Prior to this application, in a high-temperature diffuse reflection gas measuring device based on an optical waveguide, the center points of the diffuse reflector 1, the first convex lens 2, the optical waveguide 3, the anti-reflection film optical window 4, the second convex lens 5, and the collimator 6 are located on the same optical axis to ensure efficient beam transmission and stable signal reception.

[0033] In the high-temperature diffuse reflection gas measurement device based on optical waveguide provided in this application, the output fiber optic pigtail of the TDLAS laser is connected to the collimator 6, which outputs a collimated spatial beam. The collimator 6 outputs a collimated spatial beam. The second convex lens 5 has a central opening with a diameter slightly larger than the diameter of the collimator 6. The collimator 6 passes through the central opening of the second convex lens 5. The output beam is transmitted to the optical waveguide 3 through the anti-reflection film optical window 4. The collimated beam passes through the optical waveguide 3 and the first convex lens 2, illuminating the diffuse reflector 1. The diffuse reflector 1 and the first convex lens 2 form a TDLAS gas cell. The f1 of the first convex lens 2 constitutes the optical path of the gas cell. The gas to be measured diffuses into the gas cell and absorbs the beam energy. The signal beam is diffusely reflected back to the first convex lens 2 by the diffuse reflector 1. The first convex lens 2 reflects the beam back to the optical waveguide 3, which transmits the beam to the second convex lens 5. The second convex lens 5 focuses the beam onto the photodetector 7. The photodetector 7 is placed at a distance of f1 to receive the reflected signal beam. After being demodulated by the back-end TDLAS system, the gas concentration in the diffuse reflector 1 and the first convex lens 2 can be calculated.

[0034] In the high-temperature diffuse reflection gas measuring device based on optical waveguide provided in this application, the first convex lens 2 and the second convex lens 5 expand the reflected signal beam and transmit it through the optical waveguide 3 before focusing it onto the photodetector 7. Because the optical waveguide 3 in this application is made of quartz, its refractive index is 1.45 for a beam with a wavelength of 1.3 μm and 1.44 for a beam with a wavelength of 1.6 μm. The refractive index of air is 1. Therefore, when the beam is transmitted through the quartz optical waveguide, it undergoes total internal reflection transmission, thus playing the role of waveguide transmission in this device.

[0035] Because the high-temperature diffuse reflection gas measuring device (i.e., sensor) based on optical waveguide provided in this application needs to be inserted into an industrial pipeline, the designed probe length is at least 0.6m, meaning the optical waveguide 3 is quite long. Therefore, it is impossible to coat the two end faces of the optical waveguide 3 with antireflection coatings. To avoid the beam output from the collimator 6 reflecting off the end faces of the optical waveguide 3 and forming interference fringes, this application attaches an antireflection film optical window 4 to the end face of the optical waveguide 3. The antireflection film optical window 4 is an optical window coated with an antireflection film to reduce interference. A key design detail is that the diameter of the antireflection film optical window 4 is 1.5 times the diameter of the collimated beam (e.g., ...). Figure 2 As shown in the figure, transparent adhesive with a refractive index close to 1.45 is used for bonding to ensure that no additional reflection is added to the bonding surface, thus avoiding the formation of new interference.

[0036] It should be noted that in this application, the length of the optical waveguide 3 can be customized according to the field application, and the diameter of the optical waveguide 3 and the beam diameter of the collimator 6 can be adjusted according to the actual situation.

[0037] The advantages of the high-temperature diffuse reflection gas measurement device based on optical waveguide provided in this application are as follows: The optical waveguide 3, as a high-temperature and corrosion-resistant optical waveguide device, serves to separate complex working conditions from the normal temperature environment (-40℃~70℃). The diffuse reflector 1 and the first convex lens 2 are located on the left side of the optical waveguide 3 and are used in high-temperature, corrosive, and condensation regions. The right side of the optical waveguide 3, namely the anti-reflection film optical window 4, the second convex lens 5, the collimator 6, and the photodetector 7, operates in the normal temperature environment. Simultaneously, the optical waveguide 3 plays a second important role in suppressing gas absorption generated in the non-gas chamber portion of the detection optical path. According to the TDLAS measurement principle, gas absorption will occur in the spatial light portion of the optical path if there is gas to be measured. However, the optical waveguide 3, as a transitional section, connects the two regions inside and outside the pipe. If this region is not filled with the optical waveguide 3 structure, the signal generated by the external gas entering the optical waveguide 3 will be superimposed on the signal of the gas chamber detection portion of the diffuse reflector 1 and the first convex lens 2, causing measurement interference. Therefore, by filling the optical path in this region with optical waveguide 3, the gas cannot generate absorption interference here.

[0038] In this application, to address condensation and prevent water droplets or mist from interfering with the optical path and refracting light beyond the detection area, thus rendering detection impossible, the diffuse reflector 1 uses a diffuse reflective mirror instead of an optical plane mirror. The diffuse reflective surface can be made of either metal or glass. The basic parameters of the two-dimensional profile surface roughness relevant to this device include the profile arithmetic mean deviation Ra < 1 mm and the maximum profile height RZ ≤ 100 μm. To reduce diffuse reflection optical interference, arbitrary surface waviness is not permitted on the diffuse reflective surface.

[0039] The high-temperature diffuse reflection gas measuring device based on optical waveguide provided in this application was simulated using ZEMAX software. After the collimated beam output from the right collimator 6 passes through the optical waveguide 3, it reaches the first convex lens 2, is focused by the diffuse reflector 1, and then returns along the original path to the right second convex lens 5, where it is focused onto the photodetector 7. Figure 3 As shown.

[0040] Because the output beam of the collimator 6 needs to be finely adjusted to the center of the optical waveguide 3 during production and debugging, a collimator fine-tuning fixing structure 8 is designed, as shown in the schematic diagram below. Figure 4 As shown: The collimator fine-tuning fixing structure 8 includes a fixing adjustment structure 801 and a fixing structure 802. The collimator 6 is disposed in the fixing adjustment structure 801 and the fixing structure 802 and fixed by a fixing screw 804, and adjusted by an adjusting screw 803. That is, in this application, the collimator 6 is inserted into the fixing adjustment structure 801 and the fixing structure 802, fixed by the fixing screw 804, and the beam coupling efficiency is maximized by adjusting the adjusting screw 803. Then, glue, generally epoxy polyurethane glue, is poured into the gaps between the fixing adjustment structure 801, the fixing structure 802 and the adjusting screw 803. The spherical structure of the fixing adjustment structure 801 generates the output beam angle adjustment, and it is fixed when the output beam illuminates the center of the optical waveguide 3.

[0041] In the high-temperature diffuse reflection gas measuring device based on optical waveguide provided in this application, when the light beam illuminates the photodetector 7, an automatic gain control circuit is designed at the back end to adjust the amplification factor through the resistance value of the transimpedance resistor. When the detected light intensity is ≤10% of the maximum value (the maximum value corresponding to the current range of resistance), the transimpedance resistor value is increased; when the detected light intensity is ≥90% of the maximum value (the maximum value corresponding to the current range of resistance), the transimpedance resistor value is decreased. Through the programmable automatic gain chip, the resistance value of different ranges is switched in the internal circuit of the automatic gain control to achieve the purpose of adjusting the amplification and reducing the gain.

[0042] It should be noted that in this application, the automatic gain switching parameters of 10% and 90% can be optimized and adjusted according to specific circumstances.

[0043] Please see Figure 5This application provides a high-temperature diffuse reflection gas measuring device based on an optical waveguide, which also includes a flange 9. The flange 9 is sleeved and circumferentially fixed to the axial center of the optical waveguide 3. Specifically, the flange 9 is placed at halfway point of the optical path structure. The left side of the flange 9 is for probing high-temperature, highly corrosive areas, such as gas boiler pipes, high-temperature industrial process pipes, and ovens. The right side of the flange 9 is for the ambient temperature environment, where the TDLAS laser, photodetector 7, and circuit board are placed. This device achieves long-term, stable, and reliable high-temperature gas concentration measurement.

[0044] The high-temperature diffuse reflection gas measurement device (i.e., TDLAS optical waveguide transmission structure) provided in this application adopts total internal reflection transmission, which has low loss and enables long-term reliable measurement in high-temperature and corrosive environments, eliminating gas interference generated in the optical path. In addition, when measuring diffuse reflection signals, it can suppress the inability to measure due to light refraction and deflection caused by condensation droplets, and can be applied in environments that are prone to condensation and condensation.

[0045] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

Claims

1. A high-temperature resistant diffuse reflection gas measuring device based on optical waveguide, characterized in that, The device includes a diffuse reflector, a first convex lens, an optical waveguide, an anti-reflection optical window, a second convex lens, a collimator, and a photodetector. The optical waveguide is made of a high-temperature resistant material. The diffuse reflector and the first convex lens are fixedly disposed at one end of the optical waveguide, with the first convex lens close to the waveguide and the diffuse reflector away from it. A certain distance exists between the first convex lens and the diffuse reflector, forming a TDLAS gas chamber. The anti-reflection optical window, the second convex lens, the collimator, and the photodetector are fixedly disposed at the other end of the optical waveguide. The anti-reflection optical window is fixedly disposed on the end face of the optical waveguide. The second convex lens has an opening in the middle. The beam output end of the collimator passes through the second convex lens through the opening. The beam input end of the collimator is connected to the output fiber of the TDLAS laser. The photodetector is located at the beam input end of the collimator and is at a certain distance from the collimator.

2. The high-temperature diffuse reflection gas measuring device based on optical waveguide according to claim 1, characterized in that, The optical waveguide is a quartz optical waveguide.

3. The high-temperature diffuse reflection gas measuring device based on optical waveguide according to claim 1, characterized in that, The length of the optical waveguide is at least 0.6m.

4. The high-temperature diffuse reflection gas measuring device based on optical waveguide according to claim 1, characterized in that, The diameter of the antireflective optical window is 1.5 times the diameter of the collimated beam.

5. The high-temperature diffuse reflection gas measuring device based on optical waveguide according to claim 1, characterized in that, The antireflective optical window is bonded to the end face of the optical waveguide with transparent adhesive of 1.

45.

6. The high-temperature diffuse reflection gas measuring device based on optical waveguide according to claim 1, characterized in that, The diffuse reflective sheet is made of metal or glass.

7. The high-temperature diffuse reflection gas measuring device based on optical waveguide according to claim 1, characterized in that, It also includes a collimator fine-tuning fixing structure, which includes a fixed adjustment structure and a fixed structure. The collimator is disposed in the fixed adjustment structure and the fixed structure, fixed by a fixing screw, and adjusted by an adjustment screw.

8. The high-temperature diffuse reflection gas measuring device based on optical waveguide according to claim 1, characterized in that, It also includes a flange, which is fitted and circumferentially fixed to the axial center of the optical waveguide.

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