Dust concentration and temperature monitoring system based on fiber bragg grating
By combining fiber Bragg grating technology, especially sensing fiber Bragg gratings and thermal regeneration fiber Bragg gratings, synchronous and real-time monitoring of dust concentration and temperature in high-temperature and flammable and explosive environments has been achieved, solving the applicability and safety issues of existing technologies and providing a highly integrated and reliable monitoring system.
Patent Information
- Application Number
- CN202511793991.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-02
- Publication Date
- 2026-02-24
AI Technical Summary
Existing dust concentration and temperature monitoring technologies face challenges in terms of applicability and safety in environments with strong electromagnetic interference, flammable and explosive materials, and high temperatures. Traditional methods cannot achieve synchronous, real-time, and online monitoring.
Employing fiber Bragg grating technology, combining the sensing fiber Bragg grating in the dust concentration monitoring module and the thermal regeneration fiber Bragg grating in the temperature monitoring module, data processing is achieved through a fiber Bragg grating demodulator and a computer host. It features high integration, strong anti-interference capability, and can simultaneously monitor dust concentration and temperature in harsh environments.
It enables synchronous, real-time, and online monitoring in high-temperature and flammable/explosive environments, improving system integration and flexibility, reducing costs, and making it suitable for industrial environments with explosive hazards, strong electromagnetic interference, high temperatures, and high corrosion.
Smart Images
Figure CN121558587A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of industrial safety and environmental monitoring technology, specifically relating to a dust concentration and temperature monitoring system based on fiber Bragg gratings. Its temperature monitoring function is achieved by replacing the sensing fiber Bragg grating in the concentration monitoring module with a thermally regenerated fiber Bragg grating. Background Technology
[0002] In many industrial sectors such as petrochemicals, aerospace, military energetic materials production, and coal mining, dust explosions and equipment overheating are two major safety hazards. Dust can easily explode when it reaches a certain concentration and encounters an ignition source; at the same time, equipment in the production process (such as reaction vessels, pipelines, and heating furnaces) is often under high temperature and high pressure, and temperature runaway may lead to equipment damage, fire, or even explosion.
[0003] Existing dust concentration monitoring technologies are mainly based on laser scattering and beta-ray methods. However, the applicability and safety of these sensors face challenges in environments with strong electromagnetic interference and flammable / explosive conditions. For temperature monitoring, traditional methods such as thermocouples, while offering a wide temperature range, suffer from susceptibility to electromagnetic interference, poor corrosion resistance, short lifespan at extreme temperatures, and difficulty in achieving multi-point measurements. Non-contact infrared thermometry cannot measure temperatures inside enclosed spaces or equipment and is easily affected by environmental factors.
[0004] Fiber Bragg grating (FBG) sensing technology has shown great potential in the field of safety monitoring due to its advantages such as resistance to electromagnetic interference, intrinsic safety (electrical insulation), corrosion resistance, small size, light weight, and ease of implementation of quasi-distributed measurements. Ordinary fiber Bragg gratings (FBGs) can be used to measure parameters such as strain and temperature, but their refractive index modulation structure will experience thermal degradation in high-temperature environments above 300°C, leading to sensing failure and greatly limiting their application in high-temperature environments. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a dust concentration and temperature monitoring system based on fiber Bragg grating. This system has high integration, strong anti-interference ability, and high temperature resistance, and can realize synchronous, real-time, and online monitoring of dust concentration and equipment temperature.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] A dust concentration and temperature monitoring system based on fiber Bragg gratings includes a dust concentration monitor and a temperature monitor. Both the dust concentration monitor and the temperature monitor are connected to a fiber Bragg grating demodulator and a computer host via fiber optic patch cords. The fiber Bragg grating demodulator is used for demodulation and analysis of optical signals, and the computer host is used for final data processing and display.
[0008] When used for dust concentration monitoring, it also includes an optical measurement chamber. A fiber optic collimator is installed on each side of the optical measurement chamber, and the fiber optic collimator is connected to a transmission fiber. The transmission fiber is connected to a fiber optic patch cord, and a coupler is installed on the fiber optic patch cord. The optical measurement chamber is connected to an air compressor through a dust pipe. The air compressor outlet is sequentially equipped with a pressure regulating valve, a timed solenoid valve, and a dust diffusion switch. The air compressor is used to generate a controllable airflow to blow the dust to be measured into the optical measurement chamber. The dust concentration monitor includes a fiber Bragg grating, used to monitor dust concentration based on the principle of light transmission.
[0009] When used for temperature monitoring, the temperature monitor includes a thermally regenerated fiber Bragg grating with an encapsulated tube. The thermally regenerated fiber Bragg grating is connected to a fiber optic demodulator via a coupler and a fiber optic patch cord, and is used to achieve long-distance temperature measurement by monitoring its Bragg wavelength drift.
[0010] The fiber optic demodulator uses 1550nm, 20mw infrared light.
[0011] The computer host calculates the dust mass concentration based on the light intensity attenuation data from the dust concentration monitoring module according to Lambert-Beer's law.
[0012] Based on the Bragg wavelength drift of the thermally regenerated fiber Bragg grating in the temperature monitoring module, combined with its temperature sensitivity coefficient, the temperature of the measured point is calculated; thus realizing the functions of real-time data display, historical data query, over-limit alarm, and trend analysis.
[0013] The system includes a dust concentration monitoring module and a temperature monitoring module, with both modules sharing a core optical platform and signal processing unit. These shared components include: a fiber optic demodulator that provides the probe light and is used for optical signal demodulation and analysis; fiber optic patch cords for optical signal transmission; and a computer host for final data processing and display.
[0014] The dust concentration monitoring function is achieved by introducing a fiber optic dust concentration sensing unit. This unit, based on a shared platform, adds an optical measurement chamber, fiber optic collimators positioned on both sides of the chamber, a transmission fiber, and a fiber Bragg grating (FBG) with low sensitivity to temperature crosstalk. Its working principle is based on the optical transmission method (extinction method): light emitted from the demodulator is collimated and passes parallel to the dust-laden chamber. The transmitted light is then guided into the FBG via another fiber optic collimator. The intensity of the light signal reflected by the FBG is attenuated due to scattering and absorption by the dust. By measuring this attenuation using the demodulator, the dust concentration can be deduced using the Lambert-Beer law.
[0015] Temperature monitoring is achieved by introducing a temperature fiber optic sensing unit: this unit adds a thermally regenerated fiber Bragg grating (RFBG) to the shared platform. The RFBG is deployed at the high-temperature point to be monitored and connected to the system via fiber optic patch cords. When the ambient temperature changes, the Bragg wavelength of the RFBG drifts. By accurately measuring this wavelength drift using the same fiber optic demodulator, the temperature value of the measured point can be calculated. The RFBG is prepared by high-temperature annealing of a type I FBG, enabling it to operate stably for extended periods in high-temperature environments above 1000℃.
[0016] In this way, the system can simultaneously monitor two different parameters on the same hardware platform, greatly improving the system's integration, flexibility, and economy.
[0017] The fabrication method of the thermally regenerated fiber Bragg grating includes the following steps:
[0018] S1: Type I fiber Bragg gratings (FBGs) are etched onto hydrogen-loaded germanium-silicon optical fibers using the phase mask method; axial prestress is applied to the type I fiber Bragg gratings (FBGs), with the prestress range from 0 to 80% of the theoretical tensile strength of this type of fiber, to enhance the performance of thermally regenerated fiber Bragg gratings (RFBGs).
[0019] S2: The inscribed Type I fiber Bragg grating (FBG) is encapsulated in a high-temperature resistant encapsulation tube (16) and placed in a high-temperature tube furnace for high-temperature treatment. The high-temperature tube furnace is heated to a preset temperature of 950°C at a rate of 15°C / min and kept at the temperature for 60 minutes. The encapsulation tube (16) is made of corundum ceramic and stainless steel and has an inner diameter of 2mm to 10mm.
[0020] S3: During the regeneration process, the erasure process of the Type I Fiber Bragg Grating (FBG) spectrum and the spectral regeneration process of the thermally regenerated Fiber Bragg Grating (RFBG) are monitored in real time using a fiber optic demodulator.
[0021] S4: The temperature sensitivity and mechanical properties of the prepared thermally regenerated fiber Bragg grating (RFBG) are calibrated.
[0022] Thermally regenerated fiber Bragg gratings (RFBGs) are highly stable gratings that are regrown at higher temperatures after the initial grating has been erased by a specific high-temperature annealing process on a type I FBG. RFBGs can operate stably for extended periods in high-temperature environments above 1000°C and have advantages such as high side-mode suppression ratio, good spectral quality, and easy coupling with ordinary optical fibers, making them ideal high-temperature sensing elements.
[0023] Therefore, there is an urgent need to develop an integrated monitoring system capable of simultaneously, at the same point, or in a distributed manner, and adaptable to harsh industrial environments. Combining the dust concentration monitoring advantages of FBG with the high-temperature tolerance of RFBG to construct a complete and highly reliable safety monitoring system is of great significance for preventing industrial accidents and protecting life and property.
[0024] Compared with the prior art, the beneficial effects of the present invention are:
[0025] 1. Functional Integration: It is the first to integrate FBG dust concentration monitoring and RFBG high temperature monitoring into one system, solving two major safety monitoring problems, reducing costs and simplifying wiring.
[0026] 2. Superior Performance: The system fully leverages the inherent advantages of fiber optic sensing technology, including resistance to electromagnetic interference, intrinsic safety, corrosion resistance, and excellent long-term stability. In particular, the introduction of RFBG extends the temperature monitoring range to over 1000℃, breaking through the temperature limitations of ordinary FBG.
[0027] 3. High level of intelligence: Based on a computer data processing platform, it can realize in-depth data mining, intelligent alarm and trend prediction, providing support for preventive maintenance and safety decision-making.
[0028] 5. Strong environmental adaptability: It is particularly suitable for harsh industrial environments with explosive hazards, strong electromagnetic interference, high temperature and high corrosion, such as explosive production lines, petrochemical reaction units, aerospace engine test benches, etc. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the overall structure of the system of the present invention (integrating dust concentration and temperature monitoring).
[0030] Figure 2 This is a schematic diagram of the gas path and optical path principle of the dust concentration monitoring module of the present invention.
[0031] Figure 3 This is a schematic diagram of the optical path principle of the temperature monitoring module of the present invention.
[0032] Figure 4 This is a flowchart illustrating the fabrication process of RFBG in the temperature monitoring module of this invention.
[0033] Figure 5 This is a schematic diagram of thermal regeneration of RFBG under different prestresses.
[0034] Figure 6 This is a schematic diagram of the initial FBG encapsulation. Detailed Implementation
[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0036] Example 1
[0037] like Figure 1 As shown, the core of the system is the fiber optic grating demodulator 9 and the computer host 10.
[0038] When dust concentration monitoring is required, such as Figure 2 Configure the system in the first mode: connect the fiber optic sensing unit, which includes an optical measurement gas chamber 6, a collimator 5, a transmission fiber optic cable 7, and a fiber Bragg grating 4. Start the gas path unit (if equipped) and the optical unit to perform concentration measurements.
[0039] When temperature monitoring is required, such as Figure 3 The system is configured in the second mode: a fiber optic sensing unit with a thermally regenerated fiber Bragg grating (RFBG) 15 is connected. This RFBG 15 is installed at the high-temperature point to be measured, allowing the system to measure temperature by monitoring wavelength drift.
[0040] In practical applications, the two sets of sensing units can be connected in parallel to different channels of the demodulator, and synchronous or selective monitoring can be achieved by switching them through software.
[0041] Example 2
[0042] This embodiment focuses on describing the fabrication and optimization method of the thermally regenerated fiber Bragg grating (RFBG) 15. For example... Figure 4 As shown, the RFBG preparation process is as follows:
[0043] S1. High-temperature treatment: Carefully place the initial FBG17 in the center of the constant temperature zone of the high-temperature tube furnace 18. Under air atmosphere, perform the heating program: raise the temperature from room temperature to 950°C at a rate of 15°C / min, and then hold at 950°C for 60 minutes.
[0044] S2. Real-time monitoring: During the heating process, the changes in the FBG reflection spectrum are monitored in real time using a fiber optic grating demodulator 9. It can be observed that the reflectivity of the initial FBG gradually decreases with increasing temperature until it is erased (approximately 800-950℃). Subsequently, within 60 minutes of holding at 950℃, the reflection spectrum reappears and gradually increases, which is the RFBG regeneration process.
[0045] S3. Cooling and Performance Testing: After the program is completed, the furnace is rapidly cooled to room temperature (the furnace power is turned off and the furnace is quickly removed). Temperature sensing characteristics of the prepared RFBG are tested, and the results show that it has good linear response and repeatability in the range of 200-1000℃.
[0046] like Figure 5 To optimize the mechanical properties (such as tensile strength) of the RFBG, before step S1, the initial FBG is fixed on a precision displacement platform, including a displacement platform 19 and a tension gauge 20. A constant axial prestress (less than 80% of the mechanical strength of the fiber grating) is applied by the displacement of the platform, followed by annealing. The prestressed RFBG exhibits significantly higher fracture strength than the unstressed RFBG.
[0047] like Figure 6 To investigate the impact of encapsulation, before step S1, the initial FBG was inserted into encapsulation tubes 16 with inner diameters of 2mm, 4mm, 6mm, 8mm, and 10mm, respectively. Both ends were sealed with high-temperature inorganic adhesive, followed by annealing. Within a certain range, a larger encapsulation space volume is more conducive to improving the final reflectivity and regeneration efficiency of the RFBG.
[0048] Example 3 This example demonstrates the application of the system of the present invention in a complex industrial scenario requiring synchronous, remote, and integrated monitoring of dust concentration in a specific area and the temperature of key equipment nodes within that area. In a large chemical plant's enclosed material conveying trestle, two major safety hazards exist: first, the dust concentration within the trestle may reach the explosion limit due to material conveying; second, the drive motor bearings located in the middle section of the trestle, far from the control room, are at risk of overheating due to long-term high-load operation. In implementation, the system is deployed as follows:
[0049] Dust Concentration Monitoring: The optical measurement chamber 6 of the dust concentration monitoring module is directly installed at a representative location inside the trestle. The air generation unit operates periodically, injecting air into the chamber to blow up the dust, ensuring uniform and stable dispersion of the dust within the dust pipe. The entire module is connected to the system host located in the remote control room via an ultra-low loss single-mode optical fiber as a fiber optic patch cord.
[0050] Temperature monitoring: The thermally regenerated fiber Bragg grating 15 of the temperature monitoring module is tightly mounted to the bearing housing of the drive motor to be monitored using a high-temperature resistant metal clamp. Then, an ultra-low loss single-mode fiber is used as a fiber optic patch cord to connect the thermally regenerated fiber Bragg grating 15 to the fiber optic demodulator 9 located in the same remote control room.
[0051] System integration: The dust concentration monitoring module and the temperature monitoring module share the same fiber Bragg grating demodulator 9 and computer host 10. The demodulator synchronously calculates the light intensity signal (for concentration) from fiber Bragg grating 4 and the wavelength signal (for temperature) from thermally regenerated fiber Bragg grating 15 through different channels or timing sequences. The software platform on the computer host displays the dust concentration curve within the stack and the temperature curve of the drive motor bearing in real time.
Claims
1. A dust concentration and temperature monitoring system based on fiber Bragg gratings, characterized in that, It includes a dust concentration monitor and a temperature monitor, both of which are connected to a fiber optic grating demodulator (9) and a computer host (10) via fiber optic patch cords; the fiber optic grating demodulator (9) is used for demodulation and analysis of optical signals; the computer host (10) is used for final data processing and display. When used for dust concentration monitoring, it also includes an optical measuring chamber (6), with an optical fiber collimator (5) on each side of the optical measuring chamber (6). The optical fiber collimator (5) is connected to a transmission optical fiber (7), and the transmission optical fiber (7) is connected to an optical fiber jumper. A coupler (8) is provided on the optical fiber jumper. The optical measuring chamber (6) is connected to an air compressor (1) through a dust pipe (12). The outlet of the air compressor (1) is provided with a pressure regulating valve (2), a timed solenoid valve (3), and a dust diffusion switch (14) in sequence. The air compressor (1) is used to generate a controllable airflow to blow the dust to be measured into the optical measuring chamber (6). The dust concentration monitor includes a fiber Bragg grating (4) for monitoring dust concentration based on the principle of light transmission. When used for temperature monitoring, the temperature monitor includes a thermally regenerated fiber Bragg grating (15) with a package tube (16). The thermally regenerated fiber Bragg grating (15) is connected to a fiber optic patch cord via a coupler (8) on a fiber optic demodulator (9) for remote temperature measurement by monitoring its Bragg wavelength drift.
2. The dust concentration and temperature monitoring system based on fiber Bragg grating according to claim 1, characterized in that: The optical measurement chamber (6) is composed of an optical flat plate (13), a dust stage (11), and a transparent dust tube (12) connected in a sealed manner.
3. The dust concentration and temperature monitoring system based on fiber Bragg grating according to claim 1, characterized in that: The fabrication method of the thermally regenerated fiber Bragg grating (15) includes the following steps: S1: Type I fiber Bragg gratings are etched onto hydrogen-loaded germanium-silicon optical fibers using the phase mask method; S2: The inscribed type I fiber Bragg grating is encapsulated in a high-temperature resistant encapsulation tube (16) and placed in a high-temperature tube furnace for high-temperature treatment. The high-temperature tube furnace is heated to a preset temperature of 950°C at a rate of 15°C / min and kept at that temperature for 60 minutes. S3: During the regeneration process, the erasure process of the Type I fiber Bragg grating spectrum and the spectral regeneration process of the thermally regenerated fiber Bragg grating are monitored in real time by a fiber grating demodulator. S4: The temperature sensitivity and mechanical properties of the prepared thermally regenerated fiber Bragg grating are calibrated.
4. The dust concentration and temperature monitoring system based on fiber Bragg grating according to claim 3, characterized in that: Before the high-temperature treatment in step S2, an axial prestress is applied to the type I fiber Bragg grating. The prestress ranges from 0 to 80% of the theoretical tensile strength of the fiber of this type, in order to enhance the performance of the thermally regenerated fiber Bragg grating.
5. The dust concentration and temperature monitoring system based on fiber Bragg grating according to claim 1, characterized in that: The encapsulation tube (16) is made of corundum ceramic and stainless steel, with an inner diameter of 2 mm to 10 mm.
6. The dust concentration and temperature monitoring system based on fiber Bragg grating according to claim 1, characterized in that: The fiber optic demodulator (9) uses infrared light of 1550nm and 20mw.
7. A dust concentration and temperature monitoring system based on fiber Bragg grating according to claim 1, characterized in that: The computer host (10) calculates the dust mass concentration based on the light intensity attenuation data of the dust concentration monitoring module according to Lambert-Beer's law; The temperature of the measured point is calculated based on the Bragg wavelength drift of the thermally regenerated fiber Bragg grating (15) of the temperature monitoring module and its temperature sensitivity coefficient. It enables real-time data display, historical data query, over-limit alarm, and trend analysis.