CN215338638U

CN215338638U - Fiber bragg grating high-temperature sensor for on-line monitoring of wall temperature of spiral heating tube

Info

Publication number: CN215338638U
Application number: CN202121386748.1U
Authority: CN
Inventors: 张桂林
Original assignee: Wuhan Leishier Photoelectric Information Engineering Co ltd
Current assignee: Wuhan Leishier Photoelectric Information Engineering Co ltd
Priority date: 2021-06-22
Filing date: 2021-06-22
Publication date: 2021-12-28
Anticipated expiration: 2031-06-22

Abstract

The utility model provides a fiber bragg grating high-temperature sensor for monitoring the wall temperature of a spiral heating tube on line. The high-temperature sensor comprises a multi-core optical fiber, a connector, an optical fiber jumper head and an optical fiber coupler arranged in the connector; the multi-core optical fiber comprises an armored shell, a plurality of optical fiber temperature measuring tubes which are dispersedly arranged in the armored shell, a heat conducting medium filled in gaps between the optical fiber temperature measuring tubes and the armored shell, and an optical fiber grating arranged in each optical fiber temperature measuring tube, wherein protective gas is filled in each optical fiber temperature measuring tube; the armored shell is a hollow metal tube with one closed end, the open end of the metal tube is hermetically connected with the connector, the plurality of fiber gratings are respectively connected with the plurality of input ends of the fiber coupler, and the fiber jumper head is connected with the output end of the fiber coupler through the connector. The positions and the number of the measuring points can be freely designed, the damage of each measuring point is not interfered with each other, and the problems of limited installation space and distortion stress/strain interference of the wall temperature on-line monitoring of the spiral heating tube are solved.

Description

Fiber bragg grating high-temperature sensor for on-line monitoring of wall temperature of spiral heating tube

Technical Field

The utility model relates to a quasi-distributed fiber bragg grating high-temperature sensor for on-line monitoring of wall temperature of a spiral heating tube in the fields of aerospace, weaponry, nuclear industry and the like, and belongs to the technical field of optical fiber sensing measurement.

Background

In the fields of aerospace, weaponry, nuclear industry and the like, the temperatures of a plurality of positions on the surface of a structural member need to be accurately and reliably measured, safety accidents caused by the overtemperature of the surface of the structural member are prevented, and the structural member has various forms, such as a spiral heating tube, an arc-shaped plate and the like, the heating temperature of the structural member is usually higher than 300 ℃, and the temperature of certain special parts, such as an engine, a reactor and the like, nearby the structural member even exceeds more than 1000 ℃; meanwhile, due to the limitations of measurement and installation space and application environment, the temperature sensor is required to have the characteristics of miniaturization, quasi-distributed online monitoring, strong electromagnetic interference resistance, radiation resistance, corrosion resistance and the like, so that the traditional temperature sensors such as a thermocouple, a thermal imager, an electronic pyrometer and the like are generally difficult to apply.

The optical fiber temperature sensor senses the external temperature change through an optical signal by taking an optical fiber as a medium. The optical fiber is generally made of quartz or sapphire with a higher melting point and other crystal materials, has the characteristics of no electricity, small volume, radiation resistance, high and low temperature resistance and the like, and is particularly suitable for being used in dangerous (inflammable and explosive), radiation, space-limited and other severe environments, so that the optical fiber temperature sensor has wide application prospects in the fields of aerospace, weaponry, nuclear industry and the like.

The core component of the optical fiber temperature sensor is an optical fiber grating, the periodic variation of the refractive index along the axial direction of the fiber core is generated in the fiber core of the optical fiber by adopting a laser writing technology to form a phase grating of a permanent space, when broadband light enters the grating, the light meeting the Bragg condition is reflected, the peak wavelength appears on the reflection spectrum, and the working mechanism is that the environmental temperature variation causes the drift of the peak wavelength. Currently, a great deal of research on fiber grating high-temperature sensors has been carried out at home and abroad, such as: congratulations et al propose an ultra-high temperature sensor based on FBG, which is packaged in a stainless steel tube with small holes by a type ii fiber grating engraved by a femtosecond laser, and the stainless steel tube is fixed on a carbon-carbon composite substrate by a high-temperature ceramic glue block [ patent application number: 201711431759.5'; amir Azhari et al propose an optical fiber temperature sensor based on fiber grating and zirconia ceramic tube, the use temperature of the sensor is above 600 ℃; chenshuang et al propose a capillary fiber grating high temperature sensor and a manufacturing method thereof, which integrally package a fiber grating and a non-metal capillary by adopting a welding mode, and can realize temperature measurement of-55 to 1100 ℃ (patent application number: 201710353372.6 ].

However, for a spiral heating tube wall temperature quasi-distributed online monitoring scene, the existing fiber bragg grating high-temperature sensor has a large armored size and cannot be installed on the surface of a spiral or bent structural member in an embedded manner for direct measurement; in addition, single-core cable structures are mostly adopted among measuring points of the existing sensor, and all fiber gratings are easily subjected to stress interference and are only suitable for the application environment of linear installation; in addition, a single-core structure or a series connection mode of the existing sensor has the defect that a certain measuring point is damaged, and all measuring points far away from the demodulator end cannot work. In the aspect of packaging, a larger air gap is arranged between the fiber grating of the conventional sensor and an external metal or ceramic tube, so that the real-time property of the temperature response of the sensor is influenced to a certain extent, and O in the air exists in severe environments such as high temperature, radiation and the like for a long time₂、H₂The molecules such as O and the like accelerate the aging of the optical fiber coating, and simultaneously can generate hydrolysis and stress corrosion at the micro-crack and external force scratch part on the surface of the optical fiber, so that the optical fiber is subjected to fatigue fracture, and the service life of the optical fiber high-temperature sensor is greatly shortened.

Disclosure of Invention

In order to solve the problems of limited installation space, distortion stress/strain interference, non-mutual influence of multipoint measurement and the like of the wall temperature online monitoring of the spiral heating tube, the utility model provides a quasi-distributed fiber bragg grating high-temperature sensor which has the characteristics of no stress/strain interference, small structural size, high temperature resistance, high reliability, quasi-distributed measurement and the like.

The technical scheme adopted by the utility model for solving the technical problems is as follows: the utility model provides a fiber grating high temperature sensor for spiral heating tube wall temperature on-line monitoring which characterized in that: the high-temperature sensor comprises a multi-core optical fiber, a connector, an optical fiber coupler and an optical fiber jumper head, wherein the optical fiber coupler is an all-in-one optical fiber coupler with a plurality of input ends and an output end, the optical fiber coupler is embedded in the connector, the multi-core optical fiber is connected with the plurality of input ends of the optical fiber coupler through the connector, and the optical fiber jumper head is connected with the output end of the optical fiber coupler through the connector;

the multi-core optical fiber comprises an armored shell, a plurality of optical fiber temperature measuring tubes which are dispersedly arranged in the armored shell, a heat conducting medium filled in gaps between the optical fiber temperature measuring tubes and the armored shell, and an optical fiber grating arranged in each optical fiber temperature measuring tube, wherein protective gas is filled in each optical fiber temperature measuring tube; the armored shell is a hollow metal tube with one open end and one closed end, the open end of the metal tube is hermetically connected with the connector, and the tail fiber ends of the optical fiber temperature measuring tubes respectively extend out of the open end of the armored shell and are connected with a plurality of input ends of the optical fiber couplers in the connector.

The utility model has the following excellent technical scheme: the connector is of a hollow tubular structure, a multi-core optical fiber mounting hole is formed in one end of the connector, an optical fiber jumper mounting hole is formed in the other end of the connector, the open end of an armor shell of a multi-core optical fiber extends into the connector from the multi-core optical fiber mounting hole, the outer wall of the armor shell of the multi-core optical fiber is connected with the inner wall of the multi-core optical fiber mounting hole in a sealing mode, and the optical fiber grating of each optical fiber temperature measuring tube is connected with the corresponding input end of the optical fiber coupler in an optical fiber fusion mode; the optical fiber jumper head extends into the connector from an optical fiber jumper head mounting hole of the connector, the tail fiber of the optical fiber jumper head is connected with the output end of the optical fiber coupler in an optical fiber fusion mode, and the connecting part of the optical fiber jumper head and the connector is sealed.

The utility model has the following excellent technical scheme: the optical fiber temperature measuring tube is a metal capillary tube with an opening at one end and a closed end, one end of the fiber bragg grating is positioned in the optical fiber temperature measuring tube, and the tail fiber at the other end extends out of the opening end of the optical fiber temperature measuring tube and is connected with the corresponding input end of the optical fiber coupler; the part of the fiber grating arranged in the fiber temperature measuring tube is sealed and fixed with the fiber temperature measuring tube by adopting a metal welding, glass bead welding or high-temperature sealant bonding mode.

The further technical scheme of the utility model is as follows: the multi-core optical fiber is bent into a spiral shape matched with the spiral heating tube; the central wavelengths of the fiber gratings in the multiple fiber temperature measuring tubes of the multi-core fiber are different, the beam combination integration of the multiple fiber gratings is realized through the fiber coupler, and the number of the input ends of the fiber coupler is not less than that of the fiber gratings; the fiber grating is a II-type fiber grating which is engraved by a femtosecond laser, the maximum tolerant temperature reaches 1100 ℃, a grid region is engraved at one end of the fiber, and the length of the grid region is far less than the spiral radius of the heating tube to be subjected to temperature measurement.

The utility model has the following excellent technical scheme: the optical fiber jumper head is an optical fiber connector with an armored jacket and comprises an FC optical fiber connector, an LC optical fiber connector or an SC optical fiber connector with the armored jacket.

The utility model has the following excellent technical scheme: the metal fixed connection mode among the armor shell, the optical fiber temperature measuring tube, the connector and the sheath of the optical fiber jumper head can adopt metal welding, threaded connection or high-temperature structural adhesive bonding.

The utility model has the following excellent technical scheme: the armored shell and the optical fiber temperature measuring tube are stainless steel tubes, copper tubes or nickel alloy tubes; the heat-conducting medium adopts carbon powder, magnesium oxide powder, quartz powder or silicone oil; the protective gas is any one inert gas of nitrogen, helium or argon.

The utility model has the following excellent technical scheme: the optical fiber coupler is a single-mode C-band all-in-one optical fiber coupler provided with a plurality of input ends and an output end, and the number of the input ends is two or four or eight or sixteen.

The utility model has the following excellent technical scheme: the connector is internally provided with a coupler slot, an output tail fiber slot and a plurality of input tail fiber slots, the optical fiber coupler is embedded into the coupler slot, the output tail fiber slot is arranged at the output joint end of the optical fiber coupler, and the plurality of input tail fiber slots are arranged at the input joint end of the optical fiber coupler; the fusion joints of the fiber bragg grating, the fiber jumper head tail fiber and the fiber coupler are protected by recoating, and the fusion joints are correspondingly arranged in an output tail fiber groove and an input tail fiber groove of the connector respectively.

The utility model has the following excellent technical scheme: the connector is formed by butt joint of an upper half pipe and a lower half pipe, the outer parts of two ends of the connector are respectively provided with a threaded connection structure, and when the two half pipes are butt jointed into a complete metal pipe, the two ends are connected through a fastening nut.

According to the fiber bragg grating high-temperature sensor, the number of the fiber bragg grating temperature measuring tubes and the number of the fiber bragg grating are prepared according to the requirement of the number of the wall temperature measuring points of the spiral heating tube, the fiber bragg grating high-temperature sensor is numbered in a one-to-one correspondence manner, the inner wall surface and the outer wall surface of the prepared fiber bragg grating temperature measuring tubes are cleaned, and drying treatment is carried out; according to the requirement of the temperature measurement point position of the wall of the spiral heating pipe, the fiber bragg gratings sequentially penetrate into the correspondingly numbered fiber temperature measurement pipes respectively, the measurement point positions of the fiber bragg gratings are marked on the fiber temperature measurement pipes, and the sealed fixed positions are marked on the fibers. Placing the optical fiber temperature measuring tube penetrated with the optical fiber grating in a vacuum operation box, pumping out air in the optical fiber temperature measuring tube, filling protective gas after the vacuum degree meets the requirement, and then carrying out adhesive dispensing, sealing and fixing at the optical fiber sealing and fixing mark position; before the optical fiber temperature measuring tube penetrates into the armored shell, cleaning and drying the inner wall surface and the outer wall surface of the armored shell, filling a heat-conducting medium after the optical fiber temperature measuring tube penetrates into the armored shell, and then carrying out metal welding, sealing and fixing on the optical fiber temperature measuring tube and the armored shell; the optical fiber grating, the optical fiber jumper wire head tail fiber and the optical fiber coupler are welded; the output end optical fiber of the optical fiber coupler is welded with the tail fiber of the optical fiber jumper wire head, the welding length is properly longer than the length of an optical fiber groove in the connector, and the melting point position is subjected to recoating protection; installing the welded optical fiber coupler in a coupler groove in the middle of the connector, filling glue for fixing, installing tail fibers at two ends of the optical fiber coupler in the tail fiber groove, and properly fixing a melting point part; the upper and lower lamella structures of the connector are fixedly installed through the lock nut, then the armor shell and the optical fiber jumper wire head sheath are respectively installed in the installation holes at the two ends of the connector, and are sealed and fixed through metal welding or high-temperature structural adhesive bonding, so that the optical fiber high-temperature sensor is manufactured.

According to the technical scheme, the utility model has the following beneficial effects:

(1) the grating area is carved at the tail end of the optical fiber, the length of the grating area is far smaller than the spiral radius of the heating tube, and the grating area is sealed and fixed by the optical fiber temperature measuring tube, so that the grating is always in a free state and is not interfered by spiral stress/strain;

(2) the armored shell of the multi-core optical fiber is internally provided with a plurality of optical fiber temperature measuring tubes, different fiber bragg grating measuring points in the optical fiber temperature measuring tubes are integrated through the all-in-one optical fiber coupler, quasi-distributed temperature measurement is achieved, the optical fiber temperature measuring tubes are not affected with one another, the heat conduction speed is improved, and rapid response of temperature is achieved;

(3) the long-term reliability of the fiber bragg grating high-temperature environment is improved by pumping air out of the fiber temperature measuring tube and filling protective gas into the fiber temperature measuring tube; meanwhile, a heat-conducting medium is filled between the optical fiber temperature measuring tube and the armored shell, so that the temperature response speed is improved;

(4) through the connector integrated design, effectively connect and protect outside armor shell, coupler and optic fibre jumper wire head and tail optical fiber melting point, improved the reliability of sensor in abominable service environment.

The utility model has the characteristics of small structure size, high temperature resistance and high reliability, the positions and the number of the measuring points can be freely designed, the damage of each measuring point is not interfered with each other, and the problems of limited installation space, distortion stress/strain interference, non-interference of multi-point measurement and the like of the wall temperature on-line monitoring of the spiral heating tube are solved.

Drawings

FIGS. 1 and 2 are structural design diagrams of the sensor of the present invention

FIG. 3 is a schematic view showing an external structure of the connector according to the present invention;

FIG. 4 is a transverse cross-sectional view of the connector of the present invention;

fig. 5 is a cross-sectional view of a multi-core optical fiber according to the present invention.

In the figure: 1-multi-core fiber, 100-armor shell, 101-fiber temperature measuring tube, 102-fiber grating, 103-heat conducting medium, 2-connector, 200-multi-core fiber mounting hole, 201-fiber jumper wire head mounting hole, 202-coupler groove, 203-output tail fiber groove, 204-input tail fiber groove, 3-fiber coupler and 4-fiber jumper wire head.

Detailed Description

The utility model is further illustrated by the following figures and examples. Fig. 1 to 5 are drawings of embodiments, which are drawn in a simplified manner and are only used for the purpose of clearly and concisely illustrating the embodiments of the present invention. The following claims presented in the drawings are specific to embodiments of the utility model and are not intended to limit the scope of the claimed invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it is to be understood that the terms "upper", "lower", "inner", "outer", "left", "right", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, or the orientations or positional relationships that the products of the present invention are conventionally placed in use, or the orientations or positional relationships that are conventionally understood by those skilled in the art, and are used for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the equipment or elements referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.

In an embodiment, a quasi-distributed fiber grating high temperature sensor for online monitoring of wall temperature of a spiral heating tube is provided, as shown in fig. 1 and fig. 2, and includes a multi-core fiber 1, a connector 2, a fiber coupler 3, and a fiber jumper 4, where the fiber coupler 3 is a multi-in-one fiber coupler with multiple input ends and one output end, and may be a single-mode C-band multi-in-one fiber coupler such as 1 × 2/1 × 4/1 × 8/1 × 16. The optical fiber jumper head 4 is an optical fiber connector with an armored jacket, and comprises an FC optical fiber connector, an LC optical fiber connector or an SC optical fiber connector with the armored jacket. The optical fiber coupler 3 is embedded in the connector 2, the multi-core optical fiber 1 is connected with a plurality of input ends of the optical fiber coupler 3 through the connector 2, and the optical fiber jumper 4 is connected with the output end of the optical fiber coupler 3 through the connector 2.

In the quasi-distributed fiber bragg grating high-temperature sensor for online monitoring of the wall temperature of the spiral heating tube provided in the embodiment, the connector 2 is a hollow tubular structure as shown in fig. 3 and 4, a multi-core fiber mounting hole 200 is formed in one end of the connector, a fiber jumper mounting hole 201 is formed in the other end of the connector, the connector 2 is formed by butting an upper half tube and a lower half tube, threaded connection structures are arranged outside two ends of the connector 2, and when the two half tubes are butted to form a complete metal tube, the two ends are connected through fastening nuts. The connector 2 is provided with a coupler slot 202, an output pigtail slot 203 and a plurality of input pigtail slots 204, the optical fiber coupler 3 is embedded in the coupler slot 202, the output pigtail slot 203 is arranged at the output connector end of the optical fiber coupler 3, and the plurality of input pigtail slots 204 are arranged at the input connector end of the optical fiber coupler 3. As shown in fig. 5, the multi-core optical fiber 1 includes an armor shell 100, a plurality of optical fiber temperature measuring tubes 101 dispersed in the armor shell 100, a heat conducting medium 103 filled in gaps between the optical fiber temperature measuring tubes 101 and the armor shell 100, and an optical fiber grating 102 disposed in each optical fiber temperature measuring tube 101, and a protective gas is filled in each optical fiber temperature measuring tube 101; the armored shell 100 and the optical fiber temperature measuring tube 101 are stainless steel tubes, copper tubes or nickel alloy tubes; the heat-conducting medium 103 adopts carbon powder, magnesium oxide powder, quartz powder or silicone oil; the protective gas is any one inert gas of nitrogen, helium or argon. A plurality of optical fiber temperature measuring tubes 101 are arranged in the armored shell 100, quasi-distributed temperature measurement is realized, multi-point measurement is not influenced mutually, a heat conducting medium 103 is filled in a gap between the optical fiber temperature measuring tubes 101 and the armored shell 100 to improve the heat conduction speed, and real-time response of temperature is realized; the optical fiber temperature measuring tube 101 is a metal capillary tube with an opening at one end and a closed end, protective gas and the optical fiber grating 102 are arranged in the optical fiber temperature measuring tube, and long-term reliability of the optical fiber grating 102 in a high-temperature environment is realized by adopting protective gas atmosphere. The armored shell 100 is a hollow metal tube with an opening at one end and a closed end, the optical fiber temperature measuring tube 101 is a metal capillary tube with an opening at one end and a closed end, the open end of the armored shell 100 of the multi-core optical fiber 1 extends into the multi-core optical fiber mounting hole 201 of the connector 2, the outer wall of the armored shell is hermetically connected with the inner wall of the multi-core optical fiber mounting hole 200, one end of each fiber bragg grating 102 is located inside the optical fiber temperature measuring tube 101, and tail fibers at the other end extend out of the open end of the optical fiber temperature measuring tube 101 and respectively extend out of the open end of the armored shell 100 and are connected with the input end corresponding to the optical fiber coupler 3 in an optical fiber fusion mode; the optical fiber jumper head 4 extends into the optical fiber jumper head mounting hole 201 of the connector 2, the tail fiber of the optical fiber jumper head 4 is connected with the output end of the optical fiber coupler 3 in an optical fiber fusion mode, and the connecting part of the optical fiber jumper head 4 and the connector 2 is sealed. The fusion-spliced parts of the fiber bragg grating 102, the tail fiber of the fiber jumper head 4 and the optical fiber of the optical fiber coupler 3 are protected by recoating, and the fusion-spliced points are respectively and correspondingly arranged in an output tail fiber groove 203 and an input tail fiber groove 204 of the connector 2.

In the embodiment, the part of the fiber bragg grating 102, which is arranged in the fiber temperature measuring tube 101, is sealed and fixed with the fiber temperature measuring tube 101 by adopting a metal welding, glass bead welding or high-temperature sealant bonding mode. The metal fixed connection mode among the armor shell 100, the optical fiber temperature measuring tube 101, the connector 2 and the sheath of the optical fiber jumper head 4 can adopt metal welding, threaded connection or high-temperature structural adhesive bonding.

In the embodiment, the central wavelengths of the fiber gratings 102 in the multiple fiber temperature measuring tubes 101 are different, the beam combination integration of the multiple fiber gratings 102 is realized through the fiber coupler 3, and the number of the input ends of the fiber coupler 3 is not less than the number of the fiber gratings 102; the fiber grating 102 is a II-type fiber grating which is engraved by a femtosecond laser, the maximum tolerant temperature reaches 1100 ℃, a grid region is engraved at one end of the fiber, and the length of the grid region is far less than the spiral radius of the heating tube to be subjected to temperature measurement.

In the embodiment, when the fiber bragg grating high-temperature sensor is used, as shown in fig. 1 and 2, the multi-core optical fiber 1 is bent into a spiral shape matched with the spiral heating tube.

The preparation method of the present invention is further described with reference to the specific embodiment, in this embodiment, the metal fixing connection manner among the armored case 100, the optical fiber temperature measuring tube 101, the connector 2, and the sheath of the optical fiber jumper head 4 is metal welding; the fiber grating 102 and the fiber temperature measuring tube 101 can be bonded by high-temperature sealant in a sealing and fixing manner; the fiber bragg grating 102, the tail fiber of the fiber jumper head 4 and the fiber coupler 3 are connected in a fusion mode, the melting point positions of the fiber bragg grating and the tail fiber are protected by recoating, and the melting points are arranged in the fiber grooves of the connector 2; the fiber grating 102 is a II-type fiber grating which is engraved on a polyimide-coated pure quartz fiber by adopting a femtosecond laser, the maximum tolerant temperature reaches 1100 ℃, the distance from the center of a grid region to the tail end of the fiber is 2mm, and the length of the grid region is 2 mm; the number of the wall temperature measuring points of the spiral heating tube is 8, the working temperature range is room temperature-600 ℃, the radius of the spiral is 200mm, and the thread pitch is 50 mm; the central wavelength of each fiber grating 102 is 1520nm, 1530nm, 1540nm, 1550nm, 1560nm, 1570nm, 1580nm and 1590nm, the bandwidth is less than 0.3nm, and the reflectivity is more than 30%; the armored shell 100 is made of stainless steel pipes, and the length, the inner diameter and the outer diameter of the armored shell are 2000mm, 2mm and 3mm respectively; the heat-conducting medium 103 is magnesium oxide powder; the optical fiber temperature measuring tube 101 is made of stainless steel capillary tubes, the length, the inner diameter and the outer diameter of the optical fiber temperature measuring tube are 2020mm, 0.3mm and 0.5mm respectively, and the optical fiber temperature measuring tube has the advantages of small volume, fast heat transfer, corrosion resistance and the like; the protective gas is nitrogen, and the performance of the protective gas is stable in a high-temperature and radiation environment, so that the fiber bragg grating 102 can be reliably protected for a long time; the optical fiber jumper head 4 is an FC/APC optical fiber connector with a stainless steel screwed pipe sheath, the outer diameter of the sheath is 3.5mm, and the length of the sheath is 500 mm; the optical fiber coupler 3 is a 1-8 single-mode C-waveband optical fiber coupler, the size of the middle coupler part is 4mm multiplied by 40mm, the input and output optical fibers are bare fibers with coating layers, and the length and the outer diameter of the input and output optical fibers are 0.5m and 0.25mm respectively; the connector 2 is a metal tube cut along the axis, the outer diameter of the metal tube is 7mm, the length of the metal tube is 140mm, and fastening nuts of M5 are arranged at two ends of the metal tube; a coupler groove with the diameter of 4.1mm multiplied by 42mm is formed in the center of the metal pipe, and an armored shell mounting hole with the outer diameter of 3.2mm and the depth of 20mm and an optical fiber jumper head sheath mounting hole with the outer diameter of 3.8mm and the depth of 8mm are formed in two ends of the coupler groove respectively; one end of the coupler groove is provided with an input tail fiber groove with the thickness of 1mm multiplied by 3.5mm multiplied by 35mm, and the other end of the coupler groove is provided with an output tail fiber groove with the thickness of 1mm multiplied by 35 mm. The manufacturing method of the quasi-distributed fiber bragg grating high-temperature sensor for online monitoring of the wall temperature of the spiral heating tube in the embodiment comprises the following steps:

(1) cutting 8 optical fiber temperature measuring tubes 101 with the diameter of 2.02m and optical fiber gratings 102 with the diameter of 2.5m in advance, numbering the optical fiber temperature measuring tubes one by one, cleaning the inner and outer wall surfaces of the prepared optical fiber temperature measuring tubes 101, drying the optical fiber temperature measuring tubes, polishing the opening ends of the optical fiber temperature measuring tubes to be flat, and performing leak detection test on the closed ends of the optical fiber temperature measuring tubes; according to the requirement of the position of the temperature measurement point of the wall of the spiral heating pipe, the fiber bragg gratings 102 are respectively penetrated into the correspondingly numbered fiber temperature measurement pipes 101 in sequence, the position of the measurement point of the fiber bragg gratings is marked on the fiber temperature measurement pipes 101, and a sealing fixed position is marked on the fibers;

(2) the optical fiber temperature measuring tube 101 penetrated with the optical fiber grating 102 is placed in a vacuum operation box, air in the optical fiber temperature measuring tube 101 is pumped out, normal-pressure nitrogen is filled after the vacuum degree meets the requirement, and then dispensing, sealing and fixing are carried out at the optical fiber sealing and fixing mark position.

(3) Cutting a 2m armored shell 100, cleaning and drying the inner wall surface and the outer wall surface of the armored shell, polishing the opening end of the armored shell to be flat, and performing leak detection test on the closed end of the armored shell; sequentially penetrating the manufactured optical fiber temperature measuring tubes 101 into the armored shell 100, and marking the positions of grating measuring points on the armored shell 100; then, magnesium oxide powder is filled in a gap between the optical fiber temperature measuring tube 101 and the armored shell 100, and then the optical fiber temperature measuring tube 101 and the armored shell 100 are fixed in a metal welding and sealing manner.

(4) The fiber grating 102, the tail fiber of the fiber jumper head 4 and the fiber coupler 3 are welded; and sequentially welding the tail fiber of the fiber bragg grating 102 in each optical fiber temperature measuring tube 101 with the input end optical fiber of the optical fiber coupler 3, welding the output end optical fiber of the optical fiber coupler 3 with the tail fiber of the optical fiber jumper wire head 4, wherein the welding length is 38mm, and recoating and protecting the melting point position.

(5) Installing the welded optical fiber coupler 3 in the coupler slot 202 in the middle of the connector 2, and fixing by filling glue; and installing the tail fibers at two ends of the optical fiber coupler 3 in a tail fiber groove, and fixing the melting point part by adopting adhesive dispensing.

(6) The upper half structure and the lower half structure of the connector 2 are fixedly installed through locking nuts, then the armor shell 100 and the sheaths of the optical fiber jumper heads 4 are respectively installed in the installation holes at the two ends of the connector 2, and sealing and fixing are carried out through metal welding, so that the optical fiber high-temperature sensor is manufactured.

In summary, the present invention is described as an embodiment, but the present invention is not limited to the above embodiment, and any similar or identical means may be used to achieve the technical effects of the present invention, and all such means should fall within the protection scope of the present invention.

Claims

1. The utility model provides a fiber grating high temperature sensor for spiral heating tube wall temperature on-line monitoring which characterized in that: the high-temperature sensor comprises a multi-core optical fiber (1), a connector (2), an optical fiber coupler (3) and an optical fiber jumper head (4), wherein the optical fiber coupler (3) is an all-in-one optical fiber coupler with a plurality of input ends and an output end, the optical fiber coupler (3) is embedded into the connector (2), the multi-core optical fiber (1) is connected with the plurality of input ends of the optical fiber coupler (3) through the connector (2), and the optical fiber jumper head (4) is connected with the output end of the optical fiber coupler (3) through the connector (2);

the multi-core optical fiber (1) comprises an armored shell (100), a plurality of optical fiber temperature measuring tubes (101) which are dispersedly arranged in the armored shell (100), a heat conducting medium (103) filled in gaps between the optical fiber temperature measuring tubes (101) and the armored shell (100), and an optical fiber grating (102) arranged in each optical fiber temperature measuring tube (101), wherein protective gas is filled in each optical fiber temperature measuring tube (101); the armored shell (100) is a hollow metal tube with an opening at one end and a closed end, the opening end of the hollow metal tube is hermetically connected with the connector (2), and tail fiber ends of the optical fiber temperature measuring tubes (101) respectively extend out of the opening end of the armored shell (100) and are connected with a plurality of input ends of the optical fiber couplers (3) in the connector (2).

2. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 1, wherein: the connector (2) is of a hollow tubular structure, one end of the connector is provided with a multi-core optical fiber mounting hole (200), the other end of the connector is provided with an optical fiber jumper mounting hole (201), the open end of an armored shell (100) of the multi-core optical fiber (1) extends into the connector from the multi-core optical fiber mounting hole (200) of the connector (2), the outer wall of the armored shell is hermetically connected with the inner wall of the multi-core optical fiber mounting hole (200), and the optical fiber grating (102) of each optical fiber temperature measuring tube (101) is connected with the corresponding input end of the optical fiber coupler (3) in an optical fiber fusion mode; the optical fiber jumper (4) extends into the connector from an optical fiber jumper mounting hole (201) of the connector (2), the tail fiber of the optical fiber jumper (4) is connected with the output end of the optical fiber coupler (3) in an optical fiber fusion mode, and the connecting part of the optical fiber jumper (4) and the connector (2) is sealed.

3. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 1 or 2, wherein: the optical fiber temperature measuring tube (101) is a metal capillary tube with an opening at one end and a closed end, one end of the optical fiber grating (102) is positioned in the optical fiber temperature measuring tube (101), and the tail fiber at the other end extends out of the opening end of the optical fiber temperature measuring tube (101) and is connected with the corresponding input end of the optical fiber coupler (3); the part of the fiber bragg grating (102) arranged in the fiber temperature measuring tube (101) is hermetically fixed with the fiber temperature measuring tube (101) by adopting a metal welding, glass bead welding or high-temperature sealant bonding mode.

4. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 1 or 2, wherein: the multi-core optical fiber (1) is bent into a spiral shape matched with the spiral heating tube; the central wavelengths of the fiber gratings (102) in the multiple fiber temperature measuring tubes (101) of the multi-core fiber (1) are different, the combination integration of the multiple fiber gratings (102) is realized through the fiber coupler (3), and the number of the input ends of the fiber coupler (3) is not less than the number of the fiber gratings (102); the fiber grating (102) is a II-type fiber grating which is engraved by a femtosecond laser, the maximum tolerant temperature reaches 1100 ℃, a grid region is engraved at one end of the optical fiber, and the length of the grid region is far less than the spiral radius of the heating tube to be subjected to temperature measurement.

5. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 1 or 2, wherein: the optical fiber jumper (4) is an optical fiber connector with an armored jacket, and comprises an FC optical fiber connector, an LC optical fiber connector or an SC optical fiber connector with the armored jacket.

6. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 1 or 2, wherein: the metal fixed connection mode among the armor shell (100), the optical fiber temperature measuring tube (101), the connector (2) and the sheath of the optical fiber jumper head (4) can adopt metal welding, threaded connection or high-temperature structural adhesive bonding.

7. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 1 or 2, wherein: the armored shell (100) and the optical fiber temperature measuring tube (101) are stainless steel tubes, copper tubes or nickel alloy tubes; the heat-conducting medium (103) adopts carbon powder, magnesium oxide powder, quartz powder or silicone oil; the protective gas is any one inert gas of nitrogen, helium or argon.

8. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 1 or 2, wherein: the optical fiber coupler (3) is a single-mode C-band all-in-one optical fiber coupler provided with a plurality of input ends and an output end, and the number of the input ends is two or four or eight or sixteen.

9. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 2, wherein: a coupler slot (202), an output pigtail slot (203) and a plurality of input pigtail slots (204) are arranged in the connector (2), the optical fiber coupler (3) is embedded in the coupler slot (202), the output pigtail slot (203) is arranged at the output joint end of the optical fiber coupler (3), and the plurality of input pigtail slots (204) are arranged at the input joint end of the optical fiber coupler (3); the fusion splicing parts of the fiber bragg grating (102), the tail fiber of the fiber jumper head (4) and the fiber coupler (3) are protected by recoating, and fusion splicing points are respectively and correspondingly installed in an output tail fiber groove (203) and an input tail fiber groove (204) of the connector (2).

10. The fiber bragg grating high-temperature sensor for the online monitoring of the wall temperature of the spiral heating tube according to claim 2, wherein: the connector (2) is formed by butt joint of an upper half pipe and a lower half pipe, the outer parts of two ends of the connector (2) are respectively provided with a threaded connection structure, and when the two half pipes are butt jointed into a complete metal pipe, the two ends are connected through fastening nuts.