A differential optical fiber temperature sensor

Abstract

The application provides a differential optical fiber temperature sensor, characterized in that it comprises temperature sensitive ends, a protective sleeve, a brancher, an optical fiber connecting line and an optical fiber joint; the temperature sensitive ends are connected through the protective sleeve; the brancher is installed at the end of the protective sleeve and is used for dividing the optical fiber connecting line into two paths; and the optical fiber joint is installed at the end of the optical fiber connecting line.

Description

Technical Field

[0001] This invention belongs to the field of thermal parameter measurement, specifically relating to a differential fiber optic temperature sensor and its calibration method. Background Technology

[0002] In scientific research, industrial production, and other fields, environmental and structural temperature is a crucial thermal parameter. High-precision real-time temperature monitoring can reflect the operating status of systems and structures, aiding in decision-making. Traditional temperature measurement methods utilize thermocouples for point-based measurement. While thermocouple temperature measurement is technically mature, it has significant drawbacks for large structures and spaces. To increase the coverage area of ​​temperature measurement, the number of thermocouples needs to be increased. Each measuring point requires two metal wires to form a sensitive unit and a measurement circuit, and increasing the number of measuring points significantly increases the amount of cabling.

[0003] Fiber Bragg grating (FBG) sensors, as a novel sensing and measurement method, are characterized by their small size, light weight, resistance to electromagnetic interference, and ease of networking, making them ideal for extreme environments and scenarios requiring a large number of measurement points. However, due to the instability of the light source and the sensing end, FBG sensors are theoretically only suitable for measuring temperature changes and cannot achieve absolute temperature measurements like thermocouples and platinum resistance thermometers. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of fiber optic grating sensor temperature measurement technology and provide a differential fiber optic temperature sensor and calibration method. This sensor is not affected by the light source fluctuation of the demodulation system. After calibration, it can perform absolute temperature measurement and has high sensing stability and temperature sensitivity.

[0005] This invention provides a differential fiber optic temperature sensor, comprising a plurality of temperature-sensitive ends, a protective sleeve, a splitter, fiber optic connectors, and fiber optic connectors; the temperature-sensitive ends are connected through the protective sleeve; the splitter is installed at the end of the protective sleeve to split the fiber optic connectors into two paths; and the fiber optic connectors are installed at the end of the fiber optic connectors.

[0006] Furthermore, the temperature-sensitive end includes an encapsulation shell, a high-expansion metal sheet, a first fiber grating, a low-expansion metal sheet, a second fiber grating, and a cover plate; both the high-expansion metal sheet and the low-expansion metal sheet are fixed to the bottom plate of the encapsulation shell; the first fiber grating is attached to the high-expansion metal sheet, and the pigtail passes through the through-hole; the second fiber grating is attached to the low-expansion metal sheet, and the pigtail passes through the through-hole; the cover plate is fixed above the encapsulation shell to form a closed structure.

[0007] Furthermore, both the high-expansion metal sheet and the low-expansion metal sheet are fixed to the bottom plate of the packaging shell by bolts.

[0008] Furthermore, the cover plate is fixed above the encapsulation shell via threaded holes.

[0009] Furthermore, the substrate of the encapsulation shell is a high thermal conductivity metal with a thin base plate to improve thermal conductivity; the surface of the encapsulation shell is chrome-plated to enhance rigidity and hardness.

[0010] Furthermore, the high-expansion metal sheet is an aluminum alloy, and the low-expansion metal sheet is an Invar alloy; the metal sheet has a small thickness to ensure a tight fit with the bottom plate of the packaging shell.

[0011] Furthermore, the fiber grating and the metal sheet are connected by an adhesive, and the elastic modulus of the adhesive changes little with temperature.

[0012] Furthermore, a calibration method for a differential fiber optic temperature sensor includes the following steps: A differential fiber optic temperature sensor is placed inside a constant temperature chamber, and a fiber optic connector is led out from the chamber and connected to a signal demodulator to acquire wavelength signals. The temperature of the constant temperature chamber is set at equal intervals, and the temperature is maintained for several minutes after each preset temperature is reached. The difference in center wavelength between the two fiber gratings in the same enclosure is calculated to obtain the wavelength difference, and a corresponding relationship is established with the absolute temperature of the constant temperature chamber at that moment. A mathematical model of wavelength difference-temperature is obtained through curve fitting.

[0013] The advantages of this invention compared to the prior art are as follows: 7. This invention provides a differential fiber optic temperature sensor. Compared with thermocouple temperature measurement, which requires an electrical circuit and involves numerous cables when deploying a large number of measurement points, the fiber optic temperature sensor uses a single optical fiber for transmission, greatly improving the network measurement capability and saving time and space.

[0014] 8. This invention provides a differential fiber optic temperature sensor. Traditional fiber optic temperature measurement requires manual calibration of the initial temperature each time it is used before absolute temperature measurement can be performed; the differential fiber optic temperature sensor does not require initial temperature calibration and achieves plug-and-play functionality.

[0015] 9. This invention provides a differential fiber optic temperature sensor. The center wavelength of a traditional fiber optic temperature sensor may be affected by the light source of the demodulation device, which is particularly noticeable when the demodulation system uses a scanning light source. The differential fiber optic temperature sensor cancels out the influence of the light source by using wavelength difference.

[0016] 10. This invention provides a differential fiber optic temperature sensor. Existing fiber optic temperature measurement technologies mostly use a suspended grating method to avoid temperature / strain coupling effects, but the center wavelength may be unstable due to local micro-bending. The differential fiber optic temperature sensor improves stability by using a hard coupling method and cancels the coupling effect through differential coupling. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a diagram showing the internal structure of a single measuring point of a differential fiber optic temperature sensor according to an embodiment of the present invention. Figure 2 This is a schematic diagram of a multi-point series network of a differential fiber optic temperature sensor according to an embodiment of the present invention.

[0018] Wherein: 1-Encapsulation shell; 2-High expansion metal sheet; 3-Fiber Bragg grating one; 4-Pass-through hole; 5-Low expansion metal sheet; 6-Fiber Bragg grating two; 7-Threaded hole; 8-Temperature sensitive end; 9-Protective sleeve; 10-Splitter; 11-Fiber optic connector; 12-Fiber optic connector Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0020] Example 1 The present invention provides a differential fiber optic temperature sensor, comprising a plurality of temperature-sensitive ends 8, a protective sleeve 9, a splitter 10, an optical fiber connector 11, and an optical fiber connector 12; the temperature-sensitive ends 8 are connected through the protective sleeve 9; the splitter 10 is installed at the end of the protective sleeve 9 and is used to split the optical fiber connector 11 into two paths; the optical fiber connector 12 is installed at the end of the optical fiber connector 11. The temperature-sensitive end includes a housing 1, a high-expansion metal sheet 2, a fiber grating 1 3, a low-expansion metal sheet 5, a fiber grating 2 6, and a cover plate; the high-expansion metal sheet 2 and the low-expansion metal sheet 5 are both fixed to the bottom plate of the housing 1; the fiber grating 1 3 is attached to the high-expansion metal sheet 2, and the pigtail passes through the through hole 4; the fiber grating 2 6 is attached to the low-expansion metal sheet 5, and the pigtail passes through the through hole 4; the cover plate is fixed on top of the housing 1 to form a closed structure.

[0021] Both the high-expansion metal sheet 2 and the low-expansion metal sheet 5 are fixed to the bottom plate of the encapsulation shell 1 by bolts.

[0022] The cover plate is fixed to the top of the encapsulation shell 1 through the threaded hole 7.

[0023] The substrate of the encapsulation shell 1 is a high thermal conductivity metal with a thin base plate to improve thermal conductivity; the surface of the encapsulation shell 1 is chrome-plated to enhance rigidity and hardness.

[0024] The high-expansion metal sheet 2 is made of aluminum alloy, and the low-expansion metal sheet 5 is made of Invar alloy; the metal sheets are thin and are used to fit tightly against the base plate of the packaging shell 1.

[0025] The fiber grating and the metal sheet are connected by an adhesive, and the elastic modulus of the adhesive changes little with temperature.

[0026] A calibration method for a differential fiber optic temperature sensor includes the following steps: A differential fiber optic temperature sensor is placed inside a constant temperature chamber. Fiber optic connector 5 is led out from the constant temperature chamber and connected to a signal demodulator to acquire wavelength signals. The temperature of the constant temperature chamber is set at equal intervals, and the temperature is maintained for several minutes after each preset temperature is reached. The difference in center wavelength between the two fiber optic gratings inside the same encapsulation shell 1 is calculated to obtain the wavelength difference, and a corresponding relationship is established between the wavelength difference and the absolute temperature of the constant temperature chamber at that moment. A mathematical model of wavelength difference-temperature is obtained through curve fitting.

[0027] Example 2 A differential fiber optic temperature sensor, comprising Figure 1 The package consists of an inner encapsulation shell 1, a high-expansion metal sheet 2, a fiber Bragg grating (FBG) I 3, a cable pass-through hole 4, a low-expansion metal sheet 5, a fiber Bragg grating II 6, and a threaded hole 7. FBG I 3 is attached to the high-expansion metal sheet 2, and the fiber pigtail exits through the cable pass-through hole 4. FBG II 6 is attached to the low-expansion metal sheet 5, and the fiber pigtail exits through the cable pass-through hole 4. One end of each metal sheet is bolted to the base plate of the encapsulation shell 1. A cover plate is fixed through the threaded hole 7 to cover the encapsulation shell 1, forming... Figure 2 The temperature-sensitive end 8 is encapsulated in the middle; the protective sleeve 9 connects multiple temperature-sensitive end encapsulation shells, and the transmission optical fibers between multiple fiber Bragg gratings are located inside the protective sleeve; at the end, the protective sleeve is divided into two optical fiber connection lines 11 by a splitter 10, and the ends of the optical fiber connection lines are equipped with optical fiber connectors 12.

[0028] The substrate of the encapsulation shell is made of a metal with high thermal conductivity, and the thickness of the base plate is as small as possible (<0.2mm, depending on the processing capability). The smaller the thickness, the better the thermal conductivity. The surface of the encapsulation shell is chrome-plated to enhance rigidity and hardness.

[0029] The high-expansion metal sheet 2 can be made of aluminum alloy, and the low-expansion metal sheet 5 can be made of Invar alloy. The thickness of the metal sheet should be as small as possible, and it should have a high degree of flatness to ensure that it fits tightly with the bottom plate of the packaging shell when laid flat.

[0030] Fiber Bragg gratings can be selected from excimer gratings or femtosecond gratings depending on the actual operating temperature; the adhesive used to bond the fiber Bragg gratings should be selected according to the actual operating temperature, requiring that the elastic modulus changes little with temperature.

[0031] A calibration method for a differential fiber optic temperature sensor, comprising the following steps: 1) Place the sensor in the constant temperature chamber, lead the fiber optic cable out from the outlet, and seal the outlet with heat insulation cotton; 2) Set the temperature of the constant temperature chamber at equal intervals, and maintain the temperature for 10 minutes after each preset temperature is reached; 3) The fiber optic temperature sensor is connected to the signal demodulator to acquire wavelength signals; 4) The difference between the center wavelengths of the two fiber gratings in the same package is obtained to obtain the wavelength difference Δλ, and a corresponding relationship is formed with the absolute temperature T at that moment. The temperature model of Δλ-T is obtained by curve fitting.

[0032] Example 3 like Figure 1 As shown, a differential fiber optic temperature sensor includes... Figure 1 The package consists of an inner casing 1, a high-expansion metal sheet 2, a fiber Bragg grating (FBG) I 3, a cable pass-through hole 4, a low-expansion metal sheet 5, a fiber Bragg grating II 6, and a threaded hole 7. FBG I 3 is attached to the high-expansion metal sheet 2, with a pigtail passing through the cable pass-through hole 4. FBG II 6 is attached to the low-expansion metal sheet 5, with a pigtail passing through the cable pass-through hole 4. One end of each metal sheet is bolted to the base plate of the inner casing 1. A cover plate is then fixed through the threaded hole 7 to cover the inner casing, forming... Figure 2 The temperature-sensitive end 8 is encapsulated in the middle; multiple temperature-sensitive ends are connected by a protective sleeve 9, and the end is split by a splitter 10 to divide the protective sleeve 9 into two optical fiber connection lines 11, which are connected to optical fiber connectors 12.

[0033] A calibration method for a differential fiber optic temperature sensor is described below: Based on temperature measurement requirements, determine the number of gratings on each fiber, the pigtail spacing, and the center wavelength of each grating; according to… Figure 1 After assembly, the structure shown forms Figure 2The differential fiber optic temperature sensor shown is placed in a constant temperature chamber. Fiber optic connector 12 leads out from the chamber and connects to a signal demodulator to acquire wavelength signals. The chamber temperature is set at equal intervals, and maintained at each preset temperature for 10 minutes. The center wavelengths of the two differential fiber gratings within the same enclosure are subtracted to obtain the wavelength difference Δλ, which corresponds to the absolute temperature T of the chamber at that moment. A temperature model of Δλ-T is obtained through curve fitting. To improve calibration accuracy, a platinum resistance thermometer can be placed at each temperature-sensitive point of the fiber grating as a temperature calibration source.

[0034] In subsequent applications, the differential fiber optic temperature sensor can be mounted on the structural surface using methods such as welding or bonding, ensuring a tight fit between the bottom surface of the encapsulation shell and the structural surface. Thermally conductive adhesive can be used to fill gaps to improve thermal conductivity. Additionally, it must be ensured that the transmission fiber lengths of the two fiber optic connectors 5 are equal. After the system connection is complete, the absolute temperature can be obtained in real time through the wavelength difference based on the Δλ-T temperature conversion model.

[0035] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A differential fiber optic temperature sensor, characterized in that, It includes several temperature-sensitive terminals (8), protective sleeves (9), splitters (10), optical fiber connectors (11), and optical fiber connectors (12); the temperature-sensitive terminals (8) are connected through the protective sleeves (9); the splitters (10) are installed at the end of the protective sleeves (9) to split the optical fiber connectors (11) into two paths; the optical fiber connectors (12) are installed at the end of the optical fiber connectors (11). The temperature-sensitive end includes a package shell (1), a high-expansion metal sheet (2), a fiber grating one (3), a low-expansion metal sheet (5), a fiber grating two (6), and a cover plate; the high-expansion metal sheet (2) and the low-expansion metal sheet (5) are both fixed on the bottom plate of the package shell (1); the fiber grating one (3) is pasted on the high-expansion metal sheet (2), and the pigtail passes through the through hole (4); the fiber grating two (6) is pasted on the low-expansion metal sheet (5), and the pigtail passes through the through hole (4); the cover plate is fixed above the package shell (1) to form a closed structure.

2. The differential fiber optic temperature sensor according to claim 1, characterized in that, Both the high-expansion metal sheet (2) and the low-expansion metal sheet (5) are fixed to the bottom plate of the encapsulation shell (1) by bolts.

3. The differential fiber optic temperature sensor according to claim 1, characterized in that, The cover plate is fixed above the encapsulation shell (1) through a threaded hole (7).

4. The differential fiber optic temperature sensor according to claim 1, characterized in that, The substrate of the encapsulation shell (1) is a high thermal conductivity metal with a small base plate thickness to improve thermal conductivity; the surface of the encapsulation shell (1) is chrome plated to enhance rigidity and hardness.

5. The differential fiber optic temperature sensor according to claim 1 or 2, characterized in that, The high-expansion metal sheet (2) is an aluminum alloy, and the low-expansion metal sheet (5) is an Invar alloy; the metal sheet has a small thickness and is used to fit tightly against the bottom plate of the packaging shell (1).

6. The differential fiber optic temperature sensor according to claim 1, characterized in that, The fiber grating and the metal sheet are connected by an adhesive, and the elastic modulus of the adhesive changes little with temperature.

7. A calibration method for the differential fiber optic temperature sensor according to claim 1, characterized in that, Includes the following steps: Place the differential fiber optic temperature sensor into the constant temperature chamber, and lead the fiber optic connector (5) out from the constant temperature chamber and connect it to the signal demodulator to collect the wavelength signal; set the temperature of the constant temperature chamber at equal intervals, and maintain the constant temperature for several minutes after reaching a preset temperature; calculate the difference in the center wavelength of the two fiber optic gratings in the same encapsulation shell (1), obtain the wavelength difference, and form a corresponding relationship with the absolute temperature of the constant temperature chamber at that moment. Obtain the mathematical model of wavelength difference-temperature through curve fitting.

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