Distributed optical fiber temperature and humidity sensor and preparation method thereof
By using distributed fiber optic temperature and humidity sensors and a series of fiber optic gratings and support structures, the problems of low sensor reliability and insufficient monitoring density in grain storage environments have been solved, enabling accurate and stable monitoring of temperature and humidity inside grain piles.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- LASER RES INST OF SHANDONG ACAD OF SCI
- Filing Date
- 2026-04-09
- Publication Date
- 2026-05-12
AI Technical Summary
Existing sensors used for grain mold monitoring suffer from low reliability and limited monitoring coverage in complex storage environments. In particular, cable connections are prone to corrosion and line resistance increases in humid and dusty environments, leading to signal attenuation or communication failures. Furthermore, the real-time performance of data acquisition and processing by point-deployed sensors is reduced.
A distributed fiber optic temperature and humidity sensor is used, which is formed by connecting fiber optic gratings in series to form a sensing unit. The surface of the fiber optic grating is coated with a humidity-sensitive material. Combined with the support structure and protection unit, including armored spiral sleeve, steel wire, PE sheath and sensing protection unit, it can realize multi-point synchronous monitoring and is fixed inside the grain pile by steel wire rope lock.
It achieves accurate sensing of temperature and humidity inside the grain pile, simultaneous monitoring at multiple points, more comprehensive data, and high stability of the sensor in complex environments, avoiding signal attenuation and data processing delay, thus improving the reliability and coverage density of monitoring.
Smart Images
Figure CN122015976A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of fiber optic sensor technology, and provides a distributed fiber optic temperature and humidity sensor and its fabrication method. Background Technology
[0002] Maintaining suitable storage conditions is crucial to preventing grain quality deterioration during the storage process. Due to the large scale and long storage period, significant losses can easily occur during storage and distribution if storage conditions are not properly controlled or post-harvest monitoring technology is outdated.
[0003] In temperature and humidity monitoring, existing systems mostly use digital sensors, such as thermistors and humidity-sensitive capacitors, to transmit signals to the monitoring terminal via cables. However, the humidity, dust, and fumigation in warehousing environments can easily lead to corrosion of cable connections and increased line resistance, causing signal attenuation or communication failures, thus affecting system reliability. Furthermore, sensors are typically deployed in a point-like manner, requiring the system to collect data point by point. As the number of monitoring points increases, the real-time performance of data acquisition and processing decreases.
[0004] Therefore, the sensors used for existing grain mold monitoring have problems such as low reliability and limited monitoring coverage density in complex storage environments. Summary of the Invention
[0005] This application addresses the problems of low reliability and limited monitoring coverage density of existing sensors used for grain mold monitoring in complex storage environments. One solution is to provide a distributed fiber optic temperature and humidity sensor, comprising: The sensing unit is composed of multiple fiber gratings connected in series by optical fibers. The fiber gratings are arranged at intervals along the direction of the optical fibers. Each fiber grating surface is coated with a humidity-sensitive material, which is thermo-cured to form a distributed temperature and humidity sensing string, used to sense temperature and humidity through changes in grating wavelength. A support structure, the support structure comprising an optical cable unit and a knotting structure; The optical cable unit is composed of an armored spiral sleeve, steel wire, and PE sheath. The sensing unit is embedded inside the armored spiral sleeve, the steel wire is composited on the outside of the armored spiral sleeve, the PE sheath covers the outside of the steel wire, and the PE sheath is made of polyethylene material. The knotting structure is located at the end of the steel wire and is configured to be inserted into an external steel rod to fix the sensor inside the grain pile by the implantation force of the external steel rod.
[0006] In one feasible implementation, a coating device is also included; The coating device is a cuboid substrate made of hydrophobic material, and multiple grating grooves are etched side by side in the top middle area of the cuboid substrate. Each of the grating grooves is used to accommodate a single fiber grating, and fiber grooves are engraved on both sides of the grating groove. The optical fiber is laid in the fiber groove and fixed with tape. The humidity-sensitive material is filled into the surface of the fiber grating within the grating groove and then thermo-cured to form the sensing unit.
[0007] In one feasible implementation, the armored spiral sleeve is matched with the outer diameter of the optical fiber, and the steel wire is integrally formed with the armored spiral sleeve and the PE sheath through an integrated molding process. The PE sheath is provided with peeling areas at preset intervals, and the peeling areas are used to expose the armored spiral sleeve and steel wire. The stripped area is provided with a sensing protection unit, which is used to house the fiber grating.
[0008] In one feasible implementation, the sensing protection unit includes a stainless steel sleeve, a dust filter, and a waterproof connector. The stainless steel sleeve has a cylindrical structure with air exchange holes on its outer wall, and the dust filter is attached to the inner wall of the stainless steel sleeve. The waterproof connectors are located at both ends of the stainless steel sleeve and are used to connect the optical cable unit and the stainless steel sleeve. The fiber grating of the sensing unit is located inside the stainless steel sleeve and is fixed by the armored spiral sleeve.
[0009] In one feasible implementation, the knotting structure is a wire rope lock, configured to be inserted into the U-shaped structure at the front end of the external steel rod, for implanting the sensor into the grain pile through the external steel rod.
[0010] In one feasible implementation, the stainless steel sleeve has an outer diameter of 12mm, an inner diameter of 10mm, and a length of 80mm; the air exchange hole has a diameter of 1.5mm; and the dust filter has a mesh size of 100 mesh.
[0011] Another aspect of this application provides a method for fabricating a distributed optical fiber temperature and humidity sensor, used to fabricate the distributed optical fiber temperature and humidity sensor described in any of the above claims, comprising: Multiple fiber gratings are fabricated on the optical fiber and spaced apart along its length to form a grating string; Multiple grating grooves are formed on a substrate, fiber gratings in the grating string are placed in the corresponding grating grooves, and a humidity-sensitive material is coated on the surface of the fiber gratings in the grating grooves. After curing, a distributed sensing unit is formed. The sensing unit is implanted inside the optical cable unit, which is composed of an armored spiral sleeve, steel wire and PE sheath. The sensing unit is inserted into the armored spiral sleeve of the optical cable unit, the steel wire is attached to the outside of the armored spiral sleeve, and the PE sheath covers the outside of the armored spiral sleeve. A sensing protection unit is installed on the optical cable unit. The sensing protection unit is sleeved on the outside of the optical cable unit and houses the fiber grating of the sensing unit. The optical cable unit and the sensing protection unit are encapsulated, and multiple optical cable units are connected in series to obtain a distributed optical fiber temperature and humidity sensor.
[0012] In one feasible implementation, the step of forming multiple grating grooves on the substrate includes: Multiple grating grooves are etched side-by-side on the top of a cuboid substrate, and fiber grooves are etched on both sides of each grating groove; the cuboid substrate is made of a hydrophobic material.
[0013] In one feasible implementation, the step of placing the fiber Bragg gratings in the grating string correspondingly in the grating groove includes: The fiber Bragg gratings in the grating string are placed one by one into the grating groove, and the fiber portions connecting adjacent fiber Bragg gratings are laid in the corresponding fiber grooves and fixed.
[0014] In one feasible implementation, the step of installing the sensing protection unit on the optical cable unit includes: Stripping areas are set at predetermined intervals on the PE sheath of the optical cable unit to expose the internal armored spiral sleeve and steel wire; A sensing protection unit is installed in the stripped area. The sensing protection unit includes a stainless steel sleeve, a dust filter attached to the inner wall of the stainless steel sleeve, and waterproof connectors at both ends of the stainless steel sleeve. The waterproof connectors are used to connect multiple optical cable units in series.
[0015] The distributed fiber optic temperature and humidity sensor and its preparation method provided in this application achieve accurate sensing of temperature and humidity in grain piles through fiber optic sensing principle; the distributed grating design enables multi-point synchronous monitoring, resulting in more comprehensive data; the steel wire composite structure of the optical cable unit enhances strength, the PE sheath is resistant to PH3 corrosion, and the sensing protection unit can filter dust, making it suitable for complex grain storage environments; a dedicated coating device enables batch and precise coating of the grating, the overall preparation process is standardized, and the sensor implantation and maintenance are convenient, effectively reducing grain storage losses. Attached Figure Description
[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the implementation of the invention and, together with the description, serve to explain the principles of the embodiments of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.
[0017] Figure 1 This is a schematic diagram of the structure of a sensing unit shown in an exemplary embodiment of this application; Figure 2 This is a schematic diagram of the coating apparatus shown in an exemplary embodiment of this application; Figure 3 This is a schematic diagram of the structure of an optical cable unit shown in an exemplary embodiment of this application; Figure 4 This is a schematic diagram of the structure of a stainless steel sleeve shown in an exemplary embodiment of this application; Figure 5 This is a schematic diagram of the structure of a sensing protection unit shown in an exemplary embodiment of this application; Figure 6 This is a schematic diagram of the structure of a distributed optical fiber temperature and humidity sensor, which is an exemplary embodiment of this application.
[0018] Figure label: 1-Sensing unit; 2-Supporting structure; 3-Coating device; 11-Fiber grating; 12-Fiber optic cable; 21-Optical cable unit; 22-Sensing protection unit; 23-Knotting structure; 31-Cuboid substrate; 32-Grate groove; 33-Fiber optic groove; 211-Armored spiral sleeve; 212-Steel wire; 213-PE sheath; 221-Stainless steel sleeve; 222-Dust filter screen; 223-Waterproof connector; 224-Air exchange port. Detailed Implementation
[0019] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the embodiments of the invention will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of how embodiments of the invention are carried out.
[0020] When grain is stored safely, its temperature and humidity remain at a relatively stable and suitable level. However, once grain is exposed to a humid environment, the situation changes significantly. When grain becomes damp, its metabolic process accelerates rapidly, continuously generating respiration heat. This accumulation of respiration heat causes localized temperature increases within the grain, which is a key factor in causing grain to heat up and mold growth.
[0021] Therefore, to effectively inhibit the growth and reproduction of microorganisms in grain and thus reduce grain loss, it is essential to ensure that the temperature and humidity inside the grain warehouse are in a proper balance. Only in this way can a relatively stable storage environment be provided for the grain, avoiding the decline in grain quality and quantity loss caused by excessive microbial growth.
[0022] Existing monitoring systems mostly use digital sensors to transmit signals to the monitoring terminal via cables. However, the humidity, dust, and fumigation conditions in storage environments can easily cause corrosion at cable joints and increase line resistance, leading to signal attenuation or communication failures, thus affecting system reliability. Furthermore, the point-based deployment of sensors and the system's point-by-point data collection can reduce the real-time performance of data acquisition and processing as the number of monitoring points increases. Therefore, existing grain mold monitoring sensors suffer from low reliability and limited monitoring coverage density in complex storage environments.
[0023] To address the aforementioned issues, in conjunction with Figures 1-6 As shown, this application proposes a distributed fiber optic temperature and humidity sensor for monitoring the temperature and humidity inside a grain silo. Its components include a sensing unit 1 and a support structure 2.
[0024] The sensing unit 1 consists of multiple fiber gratings 11 and optical fibers 12. The multiple fiber gratings 11 are arranged at intervals along the extension direction of the optical fibers 12. The surface of each fiber grating 11 is completely coated with a humidity-sensitive material. After the coating is completed, the whole is treated by a thermosetting process to form a distributed temperature and humidity sensing string. This distributed temperature and humidity sensing string is the core sensing component of the sensor. It can sense the temperature and humidity parameters inside the grain warehouse through the wavelength change of the fiber grating 11 itself. It is the basic structure for the sensor to realize temperature and humidity monitoring.
[0025] The support structure 2 provides the installation carrier, structural support, and on-site implantation conditions for the sensing unit 1. The support structure 2 includes an optical cable unit 21 and a knotting structure 23. The optical cable unit 21 is composed of an armored spiral sleeve 211, a steel wire 212, and a PE sheath 213. The sensing unit 1 is implanted into the internal cavity of the armored spiral sleeve 211. The armored spiral sleeve 211 provides a suitable installation space for the sensing unit 1 and avoids direct contact between the sensing unit 1 and the outside environment, which could cause structural damage. The steel wire 212 is attached to the outside of the armored spiral sleeve 211 and forms a composite support structure with the armored spiral sleeve 211, providing structural strength support for the entire optical cable unit 21.
[0026] The PE sheath 213 is made of polyethylene material and completely covers the outside of the steel wire 212, forming the outer protective structure of the optical cable unit 21. Polyethylene material has strong resistance to PH3 corrosion, effectively preventing PH3 gas from corroding the sensor during grain fumigation, thus isolating the internal armored spiral sleeve 211 and steel wire 212 from external environmental corrosion. The knotted structure 23 is located at the end of the steel wire 212, serving as a connection structure between the sensor and the external implantation tool. Its overall configuration allows for insertion with an external steel rod. With the implantation force applied by the external steel rod, the entire sensor can be stably fixed in the preset monitoring position inside the grain pile, ensuring that the sensor will not shift in the complex environment of the grain pile and guaranteeing monitoring stability.
[0027] In the actual application of temperature and humidity monitoring in grain warehouses, the use of this sensor requires first completing the cooperation with the external steel rod. The front end of the external steel rod is inserted into the knotted structure 23 set at the end of the steel wire 212. The entire sensor is implanted into the monitoring point inside the grain pile by using the operating force of the external steel rod. After implantation, the knotted structure 23 is separated from the external steel rod, and the sensor is kept in the preset position by the stability of its own support structure 2.
[0028] In this embodiment, the sensor is implanted inside the armored spiral sleeve 211 of the support structure 2. The support structure 2 is used to achieve stable implantation of the sensor unit 1 inside the grain pile, which solves the problem that conventional fiber optic sensing devices cannot directly penetrate into the grain pile for monitoring. At the same time, the sensor unit 1 adopts a series structure of multiple spaced fiber optic gratings 11, which can realize distributed temperature and humidity sensing inside the grain pile, breaking through the limitations of single temperature and humidity monitoring. It can acquire temperature and humidity data at different locations in the grain pile, and the fiber optic gratings 11 sense temperature and humidity through wavelength changes, which can directly capture subtle changes in temperature and humidity inside the grain pile.
[0029] In some embodiments of this application, a coating device 3 is also included. The coating device 3 is used to provide a precise positioning and mounting carrier for coating the moisture-sensitive material on the surface of the fiber optic grating 11, ensuring the uniformity and stability of the moisture-sensitive material coating, thereby ensuring the temperature and humidity sensing accuracy of the sensing unit 1.
[0030] The core of the coating device 3 is a cuboid substrate 31, which is made of a hydrophobic material. The hydrophobic properties of the material can effectively prevent the moisture-sensitive material from sticking or spreading unevenly during the coating process, providing a good substrate condition for the film formation of the moisture-sensitive material. In the top center region of the cuboid substrate 31, multiple grating grooves 32 are etched side by side along a straight line. The number of grating grooves 32 matches the number of fiber Bragg gratings 11 in the sensing unit 1. The internal space of each grating groove 32 can accommodate a single fiber Bragg grating 11, achieving precise positioning of the fiber Bragg grating 11 and preventing displacement of the fiber Bragg grating 11 during the coating process.
[0031] On both sides of each grating groove 32, there is a corresponding fiber groove 33. The extension direction of the fiber groove 33 is consistent with the arrangement direction of the grating groove 32. The fiber 12 in the sensing unit 1 can be laid inside the fiber groove 33. The fiber groove 33 plays a role in limiting and fixing the fiber 12. After the fiber 12 is laid in the fiber groove 33, it is further fixed by high temperature tape so that the fiber 12 and the fiber grating 11 maintain a relatively fixed positional relationship during the coating process.
[0032] During the fabrication of sensing unit 1, the humidity-sensitive material is directly filled into the grating groove 32 containing the fiber grating 11, so that the humidity-sensitive material can completely and uniformly cover the surface of the fiber grating 11. After the humidity-sensitive material is coated, the entire coating device 3, together with the fiber grating 11 and the optical fiber 12 placed therein, is subjected to a thermosetting process. After curing, the humidity-sensitive material and the surface of the fiber grating 11 form a stable bond, and finally form a stable and accurate sensing unit 1.
[0033] Specifically, in the actual fabrication process of the sensing unit 1, firstly, fiber gratings 11 are placed one by one inside the grating grooves 32 of the cuboid substrate 31, ensuring that each fiber grating 11 is at the center of the grating groove 32. Then, the optical fibers 12 connecting each fiber grating 11 are laid in the optical fiber grooves 33 on both sides of the grating groove 32. After laying, high-temperature tape is used to press and fix the optical fibers 12 in the optical fiber grooves 33 to prevent displacement of the optical fibers 12 or fiber gratings 11 during the subsequent coating process. Then, the humidity-sensitive material is quantitatively filled into the grating grooves 32 so that the humidity-sensitive material completely covers the surface of the fiber grating 11, ensuring the uniformity of the coating. Finally, the coating device 3, which has been filled with humidity-sensitive material, is placed in a thermosetting device for thermosetting treatment. After the humidity-sensitive material has been cured and formed, the fiber gratings 11 and optical fibers 12 are removed from the grooves of the coating device 3, thus forming the sensing unit 1 in the form of a distributed temperature and humidity sensing string.
[0034] In this embodiment, by adding a coating device 3, the fiber grating 11 and the fiber optic cable 12 are precisely positioned by using the grating groove 32 and the fiber optic groove 33 on the cuboid substrate 31, respectively. Combined with the fixing effect of the high-temperature tape, the displacement problem of the fiber grating 11 and the fiber optic cable 12 during the coating process is avoided from the structure. At the same time, the cuboid substrate 31 made of hydrophobic material improves the film formation effect of the moisture-sensitive material.
[0035] In this embodiment, the coating apparatus 3 is designed based on the film-forming characteristics of the moisture-sensitive material and the processing requirements of the fiber Bragg grating. The cuboid substrate 31 made of hydrophobic material reduces the adhesion between the moisture-sensitive material and the substrate, preventing the moisture-sensitive material from sticking to the substrate surface. It also reduces the diffusion of the moisture-sensitive material, allowing it to remain more within the grating groove 32 and adhere to the surface of the fiber Bragg grating 11, thus improving the film-forming efficiency and quality. The etching design of the grating groove 32 and the fiber groove 33 is based on the principle of mechanical positioning. The physical structure limits the precise fixation of the fiber Bragg grating 11 and the optical fiber 12, ensuring the positional stability of each component during the coating process. The coating apparatus 3 achieves precise positioning of the fiber Bragg grating 11 and the optical fiber 12 during the coating process, effectively ensuring the uniformity of the moisture-sensitive material coating and improving the consistency of the sensing performance of each fiber Bragg grating 11 in the sensing unit 1.
[0036] In some embodiments of this application, the internal cavity size of the armored spiral sleeve 211 is matched with the outer diameter of the optical fiber 12, so that the optical fiber 12 can be arranged in close contact with the inner wall of the armored spiral sleeve 211, avoiding shaking or displacement of the sensing unit 1 inside the armored spiral sleeve 211, and ensuring the structural stability of the sensing unit 1.
[0037] The steel wire 212, the armored spiral sleeve 211, and the PE sheath 213 are compositely processed using an integrated molding process. This integrated molding process creates a seamless and firm bond between the steel wire 212, the armored spiral sleeve 211, and the PE sheath 213, preventing relative movement among the three components. This effectively improves the overall structural strength and stability of the optical cable unit 21 and avoids damage to the sensing unit 1 caused by relative displacement among the three components.
[0038] On the surface of the PE sheath 213, there are peeling areas set at preset distances. The peeling area is a local removal area of the PE sheath 213. After the PE sheath 213 in this area is peeled off, the armored spiral sleeve 211 and steel wire 212 inside can be directly exposed to the external environment, providing the sensing component of the sensing unit 1 with the conditions for interaction with the external temperature and humidity environment.
[0039] At the stripped area of the PE sheath 213, a corresponding sensing protection unit 22 is provided. The sensing protection unit 22 is an independent protective structure, which is completely covered by the armored spiral sleeve 211 and steel wire 212 exposed in the stripped area. The internal space of the sensing protection unit 22 is specifically used to accommodate the fiber optic grating 11 in the sensing unit 1, so that the fiber optic grating 11 is within the protection range of the sensing protection unit 22. This ensures effective interaction between the fiber optic grating 11 and the external temperature and humidity environment, and also provides targeted protection for the fiber optic grating 11.
[0040] In the overall assembly process of the sensor, the sensing unit 1, prepared by the coating device 3, is first inserted into the armored spiral sleeve 211. Utilizing the matching diameter between the armored spiral sleeve 211 and the outer diameter of the optical fiber 12, the sensing unit 1 remains stable inside the armored spiral sleeve 211 without significant shaking. Then, a steel wire 212 is integrally molded onto the outside of the armored spiral sleeve 211, forming a composite structure of the armored spiral sleeve 211 and the steel wire 212. Finally, a PE sheath 213 is completely wrapped around the outside of this composite structure. The initial assembly of the optical cable unit 21 is performed. Then, according to the location requirements of the distributed monitoring of the grain warehouse, a stripping area is opened on the PE sheath 213 at a preset distance, and the PE sheath 213 in this area is stripped to expose the internal armored spiral sleeve 211 and steel wire 212. Finally, the sensing protection unit 22 is installed in the stripping area of the PE sheath 213, and the fiber grating 11 in the sensing unit 1 is precisely housed inside the sensing protection unit 22, thus completing the cooperative assembly of the sensing protection unit 22 with the optical cable unit 21 and the sensing unit 1.
[0041] In this embodiment, by limiting the matching of the outer diameter of the armored spiral sleeve 211 and the optical fiber 12, the shaking of the sensing unit 1 inside the armored spiral sleeve 211 is avoided. The steel wire 212 and the armored spiral sleeve 211 are combined through an integral molding process, which solves the problem of relative displacement between the two and improves the structural stability of the optical cable unit 21. At the same time, by setting a stripping area on the PE sheath 213 and correspondingly arranging the sensing protection unit 22, the fiber optic grating 11 can effectively interact with the external environment in the stripping area, ensuring the sensitivity of temperature and humidity sensing. Furthermore, the sensing protection unit 22 provides targeted protection for the fiber optic grating 11, solving the technical problem of the difficulty in balancing protection and sensing sensitivity.
[0042] In some embodiments of this application, the sensing protection unit 22 is composed of three parts: a stainless steel sleeve 221, a dust filter 222, and a waterproof connector 223. The three parts form an integrated protection and interaction structure, which together realizes the protection of the fiber optic grating 11, the exchange of temperature and humidity gases, and the connection with the optical cable unit 21.
[0043] The stainless steel sleeve 221 has a cylindrical structure with a hollow internal space. This space provides the main installation and protection area for the fiber optic grating 11. Multiple air exchange holes 224 are evenly distributed on the outer wall of the stainless steel sleeve 221. The air exchange holes 224 penetrate the wall thickness of the stainless steel sleeve 221, connecting the internal cavity of the stainless steel sleeve 221 with the external environment, and providing an interaction channel for the temperature and humidity of the gas inside the grain silo and the fiber optic grating 11 inside the stainless steel sleeve 221.
[0044] The dust filter 222 is a flexible filter structure. It is attached to the inner wall surface of the stainless steel sleeve 221 and completely covers the opening of the air exchange hole 224 in the inner wall of the stainless steel sleeve 221, thereby filtering the gas passing through the air exchange hole 224.
[0045] The waterproof connector 223 is a rigid connection structure, and there are two of them, which are respectively set at the two ends of the stainless steel sleeve 221. One end of the waterproof connector 223 is sealed to the end of the stainless steel sleeve 221, and the other end is fixedly connected to the optical cable unit 21. The waterproof connector 223 completes the seamless connection between the optical cable unit 21 and the stainless steel sleeve 221, and at the same time achieves waterproof and sealed protection of the connection part.
[0046] The fiber grating 11 in the sensing unit 1 is located in the hollow cavity inside the stainless steel sleeve 221, and the fiber grating 11 is fixedly connected to the armored spiral sleeve 211. The armored spiral sleeve 211 passes through the waterproof connector 223 and the stainless steel sleeve 221, which not only provides structural support for the fiber grating 11, but also ensures the integrated connection between the sensing unit 1 and the optical cable unit 21.
[0047] The assembly process of the sensing protection unit 22 is as follows: First, the dust filter 222 is completely attached to the inner wall surface of the stainless steel sleeve 221, ensuring that the dust filter 222 completely covers all the air exchange holes 224 openings on the inner wall of the stainless steel sleeve 221. After attachment, the dust filter 222 is fixed to the stainless steel sleeve 221 by welding to prevent it from falling off during use. Then, two waterproof connectors 223 are installed at both ends of the stainless steel sleeve 221 to achieve a sealed connection between the waterproof connectors 223 and the stainless steel sleeve 221. After that, the sensing unit 1 is inserted into the sleeve. The armored spiral sleeve 211 is inserted into the end of one of the waterproof connectors 223, passes through the internal cavity of the stainless steel sleeve 221, and exits from the end of the other waterproof connector 223. At the same time, the fiber optic grating 11 in the sensing unit 1 is precisely positioned and fixed in the internal cavity of the stainless steel sleeve 221, ensuring that the fiber optic grating 11 is in the corresponding area of the air exchange hole 224, so as to facilitate interaction with the external temperature and humidity gas. Finally, the waterproof connector 223 is fixedly connected to the corresponding part of the optical cable unit 21, completing the overall assembly of the sensing protection unit 22, the optical cable unit 21, and the sensing unit 1.
[0048] Understandably, temperature and humidity sensors used in grain silos are susceptible to the effects of dust, impurities, and moisture inside the grain pile during use. Dust and impurities can easily adhere to the surface of the sensing components, affecting the sensing accuracy, while moisture can easily penetrate the sensor and cause structural damage. At the same time, slight vibrations and shaking inside the grain pile can also interfere with the wavelength sensing of the fiber optic grating, leading to deviations in the monitoring data.
[0049] In this embodiment, air exchange holes 224 are provided on the outer wall of the stainless steel sleeve 221 to ensure effective interaction of temperature and humidity gases. A dust filter screen 222 is attached to the inner wall of the stainless steel sleeve 221 to filter dust and impurities, solving the problem of dust and impurities affecting sensing accuracy. Waterproof joints 223 are provided at both ends of the stainless steel sleeve 221 to achieve waterproof sealing of the connection points, solving the problem of structural damage caused by moisture intrusion. Simultaneously, the armored spiral sleeve 211, which fixes the fiber optic grating 11, avoids interference from grain pile vibration and shaking on the fiber optic grating 11, solves the problem of monitoring data deviation caused by external vibration, and avoids the impact of the grain pile environment on the sensor's monitoring performance and structural stability.
[0050] In some embodiments of this application, the knot structure 23 is specifically configured as a wire rope buckle. The wire rope buckle is a standardized metal connection structure with an openable insertion chamber. The structure is highly stable after insertion and is not easily detached. The wire rope buckle is firmly connected to the end of the wire 212. Its overall structure is configured to precisely engage with the U-shaped structure at the front end of the external steel rod. The U-shaped structure at the front end of the external steel rod can be directly embedded into the insertion chamber of the wire rope buckle, forming a stable connection. During sensor implantation, the implantation force applied to the external steel rod can be stably transmitted to the wire 212 through the wire rope buckle, thereby driving the entire sensor to move into the grain pile, achieving precise implantation of the sensor inside the grain pile.
[0051] In this embodiment, by setting the knotted structure 23 as a wire rope buckle, the standardized plug-in structure of the wire rope buckle achieves precise and stable cooperation with the U-shaped structure at the front end of the external steel rod. This solves the problems of low cooperation accuracy and easy detachment between the implanted structure and the external steel rod, ensuring efficient transmission of implantation force and enabling the sensor to accurately reach the preset monitoring point. Furthermore, the metallic structural characteristics of the wire rope buckle make its structure strong enough to withstand external forces during the implantation process, solving the problem of easy damage to simple implantation structures and improving the stability and reliability of the sensor implantation process.
[0052] In some embodiments of this application, the stainless steel sleeve 221 in the sensing protection unit 22 adopts a cylindrical structure of fixed size, with an outer diameter of 12mm, an inner diameter of 10mm, and an axial length of 80mm. This size design allows the stainless steel sleeve 221 to have a moderate internal accommodating space, which can fully accommodate the optical cable unit 21 without causing the optical cable unit 21 to shift inside due to excessive space. At the same time, the moderate external size allows the stainless steel sleeve 221 to adapt to the spatial environment inside the grain pile and will not be subjected to excessive squeezing resistance during the implantation process.
[0053] The air exchange hole 224 opened on the outer wall of the stainless steel sleeve 221 has a uniform radial diameter of 1.5mm. This size design allows the air exchange hole 224 to have a moderate gas flow area, which can ensure the rapid and effective exchange of temperature and humidity gas inside the grain silo with the inside of the stainless steel sleeve 221, and also prevent large particles of dust and impurities inside the grain pile from directly entering the sleeve through the air exchange hole 224 due to excessively large hole size, thus helping to improve the filtration and protection effect.
[0054] The dust filter screen 222, which is attached to the inner wall of the stainless steel sleeve 221, has a pore size of 100 mesh. The 100 mesh pore size gives the dust filter screen 222 high-precision filtration performance, which can effectively filter the tiny particles of dust and impurities inside the grain pile. At the same time, it will not affect the normal flow of gas due to the small pore size, thus achieving the dual effect of filtration and protection and gas exchange.
[0055] It is understandable that if the air exchange hole diameter is too large, dust and impurities will easily enter; if the diameter is too small, it will affect gas exchange. If the mesh count of the dust filter is too low, the filtration accuracy will be insufficient; if the mesh count is too high, it will hinder gas flow. If the sleeve size is unreasonable, it will affect the positioning and protection effect of the fiber optic grating. In this embodiment, by precisely limiting the specific dimensional parameters of the stainless steel sleeve 221, the air exchange hole 224, and the dust filter 222, the accommodating space of the stainless steel sleeve 221 is adapted to the fiber optic grating 11, the aperture of the air exchange hole 224 takes into account both gas exchange efficiency and primary filtration effect, and the 100-mesh aperture of the dust filter 222 achieves high-precision filtration protection without affecting gas flow, making the performance of the sensing protection unit 22 more suitable for the actual needs of grain warehouse temperature and humidity monitoring.
[0056] This embodiment relates to a method for fabricating a distributed fiber optic temperature and humidity sensor, used to fabricate the distributed fiber optic temperature and humidity sensor described in the above embodiment. The method includes the following steps: S100: A plurality of fiber gratings are prepared on the optical fiber at intervals along its length to form a grating string.
[0057] Specifically, optical fibers are selected, and fiber gratings are etched along the length of the optical fiber using fiber grating lithography. This results in multiple fiber gratings being spaced out along the fiber's extension direction, with a preset length of fiber connection segment remaining between each fiber grating. After lithography, a grating string is formed, consisting of optical fibers and multiple spaced fiber gratings. The overall structure of the grating string is adapted to the requirements of subsequent moisture-sensitive material coating and encapsulation processes.
[0058] This step is used to form the basic sensing structure of the sensor, laying the structural foundation for subsequent coating of humidity-sensitive materials to achieve temperature and humidity sensing. Multiple spaced fiber optic gratings can realize distributed temperature and humidity monitoring inside the grain pile, breaking through the limitations of single-point monitoring.
[0059] S200: Multiple grating grooves are formed on the substrate, fiber gratings in the grating string are placed in the corresponding grating grooves, and a humidity-sensitive material is coated on the surface of the fiber gratings in the grating grooves. After curing, a distributed sensing unit is formed.
[0060] Specifically, a suitable substrate is selected and multiple grating grooves are processed on its surface to match the number and spacing of fiber gratings in the grating string. The prepared grating string is positioned so that each fiber grating is precisely placed in a corresponding grating groove, ensuring that the fiber grating remains stable and without displacement within the groove. Subsequently, a coating process is used to uniformly fill the surface of the fiber grating in the grating groove with a moisture-sensitive material, so that the moisture-sensitive material completely covers the surface of the fiber grating. After coating, the substrate and the grating string are cured together. After the moisture-sensitive material is stably bonded to the surface of the fiber grating, it is removed from the substrate to form a distributed sensing unit.
[0061] This step achieves precise positioning of the fiber Bragg grating through the grating grooves on the substrate, ensuring the uniformity of the humidity-sensitive material coating. The curing process enables the humidity-sensitive material and the fiber Bragg grating to form a stable integrated structure. The resulting sensing unit is the core temperature and humidity sensing component of the sensor, which can achieve temperature and humidity sensing through the synergistic effect of the fiber Bragg grating and the humidity-sensitive material.
[0062] S300: The sensing unit is implanted inside the optical cable unit, which is composed of an armored spiral sleeve, steel wire and PE sheath, wherein the sensing unit is inserted into the armored spiral sleeve of the optical cable unit, the steel wire is attached to the outside of the armored spiral sleeve, and the PE sheath covers the outside of the armored spiral sleeve.
[0063] Specifically, firstly, an optical cable unit composed of an armored spiral sleeve, steel wire, and a PE sheath is prepared. The optical fiber end of the sensing unit is inserted into one end of the armored spiral sleeve, so that the entire sensing unit is inserted into the armored spiral sleeve along its length, ensuring that the sensing unit does not move significantly inside the armored spiral sleeve. Then, the steel wire is composited on the outside of the armored spiral sleeve to provide structural strength support. Finally, the PE sheath is completely wrapped around the outside of the steel wire to form an outer layer of protection for the internal structure, completing the implantation operation of the sensing unit into the optical cable unit.
[0064] This step provides the sensor unit with an installation carrier and multi-layered structural protection. The armored spiral sleeve can prevent the sensor unit from being damaged by direct contact with the outside world. The steel wire can improve the overall structural strength of the optical cable unit, enabling the sensor to adapt to the complex environment inside the grain pile, such as compression and collision. The PE sheath can isolate the internal structure from external corrosive substances, water vapor, etc., and realize the integrated packaging of the sensor unit and the optical cable unit.
[0065] S400: A sensing protection unit is installed on the optical cable unit, the sensing protection unit being sleeved outside the optical cable unit and housing the fiber Bragg grating of the sensing unit.
[0066] Specifically, based on the spacing of the fiber Bragg gratings in the grating string, the sensor protection unit is installed at the corresponding position of the optical cable unit. The sensor protection unit is then fitted over the optical cable unit, and its position is adjusted so that each fiber Bragg grating in the sensor unit is precisely housed inside its corresponding sensor protection unit. This ensures that the fiber Bragg gratings are within the effective protection range of the sensor protection unit, thus completing the assembly and coordination between the sensor protection unit and the optical cable unit.
[0067] This step provides targeted protection for the fiber Bragg grating, the core sensing component of the sensing unit, to prevent external factors such as dust, impurities, and vibration inside the grain pile from interfering with the temperature and humidity sensing of the fiber Bragg grating. At the same time, it ensures effective interaction between the fiber Bragg grating and the external temperature and humidity gases, thus ensuring the sensitivity and accuracy of temperature and humidity sensing.
[0068] S500: The optical cable unit and the sensing protection unit are encapsulated, and multiple optical cable units are connected in series to obtain a distributed optical fiber temperature and humidity sensor.
[0069] The optical cable unit with the completed sensing and protection unit installation is then encapsulated. The connection points between the sensing and protection unit and the optical cable unit are sealed and reinforced to ensure no gaps or looseness at any connection point. After encapsulation, multiple encapsulated optical cable units are connected sequentially according to the designed series connection method. During connection, the fiber Bragg grating sensing paths of adjacent optical cable units are ensured to be continuous, and the ends of the optical cable units are treated to ensure their structural integrity. Simultaneously, the entire device undergoes light transmission testing to confirm that each fiber Bragg grating can normally achieve optical signal transmission and temperature and humidity sensing. After passing the test, the overall encapsulation operation is completed, resulting in the finished distributed optical fiber temperature and humidity sensor.
[0070] This step forms a robust and sealed integrated structure for all components of the sensor, ensuring the sensor's structural stability and sealing, and preventing problems such as structural loosening and moisture intrusion during use. Light transmission testing ensures that the sensor's sensing performance meets the standards, guaranteeing the reliability of the finished sensor.
[0071] The fabrication method in this embodiment employs a step-by-step, standardized process design. First, it prepares a series of spaced fiber gratings. Then, it precisely coats and cures the humidity-sensitive material through substrate positioning, forming a stable distributed sensing unit. This solves the problem of the difficulty in precisely fabricating distributed sensing structures. Subsequently, the sensing unit is embedded into an optical cable unit composed of an armored spiral sleeve, steel wire, and PE sheath, providing multi-layered structural support and protection for the sensing unit and solving the problem of the sensing component being susceptible to environmental influences. Finally, by installing a sensing protection unit on the optical cable unit and precisely accommodating the fiber gratings, targeted protection for the sensing component is achieved, solving the problem of decreased sensing accuracy caused by insufficient protection.
[0072] In some embodiments of this application, step S200, which involves setting multiple grating grooves on the substrate, specifically includes: S210: A plurality of grating grooves are etched side by side on the top of a cuboid substrate, and fiber grooves are etched on both sides of each grating groove; the cuboid substrate is made of a hydrophobic material.
[0073] A hydrophobic material is selected as the substrate and formed into a rectangular substrate. The structural dimensions of the rectangular substrate are adapted to the requirements of fiber grating and fiber optic cable layout, and also to the requirements of subsequent moisture-sensitive material coating process.
[0074] Based on the spacing and size of the fiber Bragg gratings in the grating string, multiple grating grooves are etched side by side along a straight line in the middle area of the top surface of the cuboid substrate using an etching process. The number of grating grooves is consistent with the number of fiber Bragg gratings in the grating string, and the inner dimensions of the grating grooves are adapted to the outer dimensions of the fiber Bragg gratings, so as to achieve precise placement of the fiber Bragg gratings.
[0075] After etching each grating groove, fiber grooves are simultaneously etched on both sides of the grating groove as the center. The extension direction of the fiber groove matches the arrangement direction of the grating groove, and the inner dimensions of the fiber groove are adapted to the outer diameter of the connecting fiber, so as to realize the close-fitting laying of the connecting fiber. The etching depth and width of all grating grooves and fiber grooves are kept uniform to ensure etching accuracy.
[0076] This embodiment uses a hydrophobic material to fabricate a cuboid substrate, which reduces the adhesion between the moisture-sensitive material and the substrate surface, preventing adhesion and uneven diffusion of the moisture-sensitive material during coating. This provides a good substrate for the film formation of the moisture-sensitive material on the fiber Bragg grating surface, improving the film formation effect and coating success rate. Parallel etching of grating grooves on the top of the cuboid substrate enables precise positioning and independent placement of multiple fiber Bragg gratings, ensuring stable position and uniform spacing of each grating during coating. Etching fiber grooves on both sides of each grating groove limits the fiber placement connecting adjacent gratings, preventing fiber displacement and stacking during coating. This further ensures the overall structural stability of the grating string, maintaining a preset relative position between the fiber Bragg gratings and fibers. The orderly fiber arrangement also prevents interference from fibers during the moisture-sensitive material coating process, ensuring smooth coating operation. Furthermore, the cuboid substrate structure facilitates placement and operation, adapting to batch coating process requirements and enabling synchronous positioning of multiple fiber Bragg gratings, improving the fabrication efficiency of the sensing unit.
[0077] This embodiment uses a hydrophobic material to make a cuboid substrate, and specifically etches grating grooves and fiber grooves on the substrate. The properties of the hydrophobic material solve the problem of adhesion and diffusion of the moisture-sensitive material. The grating grooves enable the synchronous and precise positioning of multiple fiber gratings, and the fiber grooves enable the regular and limited positioning of the connecting fibers. This lays a good structural foundation for the uniform coating and curing of the moisture-sensitive material, and ensures the fabrication quality of the distributed sensing unit.
[0078] In some embodiments of this application, step S200, which involves placing the fiber gratings in the grating string into the corresponding grating grooves, specifically includes: S220: Place the fiber Bragg gratings in the grating string one by one into the grating groove, and lay the fiber portion connecting the adjacent fiber Bragg gratings in the corresponding fiber groove and fix it.
[0079] Using the arrangement of grating grooves and fiber grooves on the cuboid substrate as a reference, the fiber gratings in the grating string are aligned one by one to make the outer contour of each fiber grating match the inner dimensions of the corresponding grating groove. The fiber grating is then smoothly placed into the corresponding grating groove, ensuring that the fiber grating is completely within the accommodating space of the grating groove without any offset, and ensuring that the position of each fiber grating corresponds one-to-one with the grating groove.
[0080] After inserting a single fiber Bragg grating, the fiber portion connecting the adjacent fiber Bragg gratings is laid in the fiber grooves on both sides of the corresponding grating groove, so that the outer contour of the fiber fits the inner dimensions of the fiber groove, ensuring that the fiber fits completely in the fiber groove without bending or stacking.
[0081] After all fiber gratings and fiber optic components have been laid, a fixing process is used to fix the fiber optics laid in the fiber optic grooves, so that the relative position of the fiber optics and the fiber optic grooves remains stable, and to prevent the fiber optics from shifting or loosening during the subsequent coating and curing of moisture-sensitive materials.
[0082] By placing fiber Bragg gratings (FBGs) one by one, precise alignment of each FBG with its corresponding groove can be achieved, ensuring the accuracy and consistency of the FBG's position during coating and curing processes. This avoids grating misalignment and other issues that can occur with overall placement. Laying the connecting optical fibers within their corresponding grooves helps to regulate and limit their movement, preventing displacement, tangling, or stacking during the coating process and ensuring the overall structural stability of the grating string. Fixing the optical fibers within the grooves further locks the grating string's position, maintaining a fixed relative position between the FBGs and fibers throughout the process. This effectively prevents uneven coating of the moisture-sensitive material and FBG sensing position deviations caused by displacement, ensuring the fabrication accuracy of the sensing unit and the consistency of the sensing performance of each FBG.
[0083] In some embodiments of this application, step S400, installing the sensing protection unit on the optical cable unit, specifically includes: S410 sets stripping areas at preset intervals on the PE sheath of the optical cable unit to expose the internal armored spiral sleeve and steel wire.
[0084] Specifically, based on the spacing of the fiber Bragg gratings in the grating string, the PE sheath of the optical cable unit is stripped at a preset distance. A suitable stripping tool is used to cut open a local area of the PE sheath along the length of the optical cable unit. The stripping depth is based on completely removing the PE sheath in that area, exposing the internal armored spiral sleeve and steel wire. It is ensured that the length of the stripped area matches the axial length of the sensing protection unit, and that the position of the stripped area corresponds one-to-one with the position of the corresponding fiber Bragg grating.
[0085] By setting stripping zones at preset intervals on the PE sheath, the armored spiral sleeve and steel wire inside the optical cable unit can be exposed, providing installation space for the sensor protection unit. At the same time, the sheath layer at the location of the fiber optic grating is removed, ensuring that the fiber optic grating can effectively interact with the external temperature and humidity environment, avoiding the problem of insufficient sensing sensitivity caused by the PE sheath blocking the transmission of temperature and humidity signals.
[0086] S420: Install a sensing protection unit in the stripped area. The sensing protection unit includes a stainless steel sleeve, a dust filter attached to the inner wall of the stainless steel sleeve, and waterproof connectors at both ends of the stainless steel sleeve. The waterproof connectors are used to connect multiple optical cable units in series.
[0087] Select the sensor protection unit, first cut the dust filter according to the inner wall size of the stainless steel sleeve, so that the size of the dust filter completely fits the inner wall contour of the stainless steel sleeve. Then, tightly attach the cut dust filter to the inner wall surface of the stainless steel sleeve, ensuring that the dust filter is wrinkle-free, not warped, and completely covers the corresponding area of the air exchange hole on the inner wall of the stainless steel sleeve, thus completing the assembly of the dust filter and the stainless steel sleeve. Next, put the stainless steel sleeve with the dust filter on the stripping area of the optical cable unit, adjust the axial position of the stainless steel sleeve, so that the center area of the stainless steel sleeve is aligned with the center position of the stripping area, ensuring that the armored spiral sleeve and steel wire are completely covered by the stainless steel sleeve.
[0088] The sensing protection unit adopts a combination structure of stainless steel sleeve, dust filter and waterproof connector. The stainless steel sleeve provides robust structural protection for the fiber Bragg grating, which can resist external forces such as squeezing and collision inside the grain pile, and avoid damage to the fiber Bragg grating caused by external impact. The dust filter can effectively filter dust, impurities and other particulate matter inside the grain pile, and prevent dust and impurities from adhering to the moisture-sensitive material on the surface of the fiber Bragg grating and affecting the accuracy of temperature and humidity sensing. The waterproof connector can achieve a sealed connection between the stainless steel sleeve and the optical cable unit, preventing moisture and corrosive gases inside the grain pile from entering the sensor from the connection point, avoiding internal structure moisture and corrosion, and extending the service life of the sensor.
[0089] S430: The fiber grating coated with moisture-sensitive material is installed inside the stainless steel sleeve, and the two ends of the stainless steel sleeve are connected to the optical cable unit through the waterproof connector.
[0090] Specifically, two waterproof connectors are installed at both ends of the stainless steel sleeve to achieve a sealed fit between the waterproof connectors and the stainless steel sleeve. Then, the end of the waterproof connector furthest from the stainless steel sleeve is fixedly connected to the PE sheaths extending from both ends of the optical cable unit to ensure that the two adjacent optical cable units form a firm and sealed connection, thus completing the overall installation of the distributed fiber optic temperature and humidity sensor.
[0091] This embodiment exposes the internal structure by setting a stripping area on the PE sheath, adopts a sensing protection unit including a stainless steel sleeve, a dust filter and a waterproof connector, and designs standardized installation and connection steps for the fiber optic grating. This ensures that the protection, interaction and sealing functions of the sensing protection unit are fully utilized, thereby improving the overall monitoring performance and environmental adaptability of the sensor.
[0092] As can be seen from the above embodiments, the distributed fiber optic temperature and humidity sensor for grain storage and its preparation method provided in this application include: forming a sensing unit by etching a grating string, accurately positioning the grating using a hydrophobic cuboid substrate, coating it with a humidity-sensitive material and thermally curing it, then implanting the sensing unit into an armored spiral sleeve, composite steel wire, and covering it with a PE sheath to form an optical cable unit, installing a sensing protection unit containing a stainless steel sleeve, a dust filter, and a waterproof connector in a preset stripping area of the PE sheath, setting a steel wire rope lock at the end, and encapsulating and testing the entire sensor to complete the preparation of the sensor.
[0093] The sensor is inserted into the pre-set monitoring point of the grain pile by connecting it to the external steel rod through the steel wire rope lock. It can realize real-time distributed monitoring of temperature and humidity in the grain pile by connecting it to the signal acquisition equipment. It does not need to be disassembled during fumigation. In case of failure, the sensor can be removed by pulling the steel wire at the end of the sensor and re-inserted after maintenance.
[0094] This application provides a distributed fiber optic temperature and humidity sensor for grain storage, which achieves accurate sensing of temperature and humidity in grain piles through fiber optic sensing principles; the distributed grating design enables synchronous monitoring at multiple points, resulting in more comprehensive data; the steel wire composite structure of the optical cable unit enhances strength, the PE sheath is resistant to PH3 corrosion, and the sensing protection unit can filter dust, making it suitable for the complex environment of grain storage; a dedicated coating device enables precise batch coating of the grating, the overall manufacturing process is standardized, and the sensor implantation and maintenance are convenient, effectively reducing grain storage losses.
[0095] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the disclosure in the specification and the embodiments. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein.
Claims
1. A distributed fiber optic temperature and humidity sensor, characterized in that, include: The sensing unit (1) is composed of multiple fiber gratings (11) connected in series through optical fibers (12). The fiber gratings (11) are arranged at intervals along the direction of the optical fibers (12). Each fiber grating (11) is coated with a humidity-sensitive material and forms a distributed temperature and humidity sensing string after being thermo-cured. It is used to sense temperature and humidity through changes in grating wavelength. Support structure (2), the support structure (2) includes optical cable unit (21) and knot structure (23); The optical cable unit (21) is composed of an armored spiral sleeve (211), steel wire (212), and PE sheath (213); The sensing unit (1) is implanted inside the armored spiral sleeve (211), the steel wire (212) is composited on the outside of the armored spiral sleeve (211), the PE sheath (213) is wrapped around the outside of the steel wire (212), and the PE sheath (213) is made of polyethylene material. The knotting structure (23) is located at the end of the steel wire (212). The knotting structure (23) is configured to be inserted into an external steel rod so as to fix the sensor inside the grain pile by the implantation force of the external steel rod.
2. The distributed fiber optic temperature and humidity sensor according to claim 1, characterized in that, It also includes a coating device (3); The coating device (3) is a cuboid substrate (31) made of hydrophobic material, and a plurality of grating grooves (32) are etched side by side in the middle area of the top of the cuboid substrate (31). Each of the grating grooves (32) is used to accommodate a single fiber grating (11), and fiber grooves (33) are engraved on both sides of the grating groove (32). The optical fiber (12) is laid in the fiber groove (33) and fixed by tape. The humidity-sensitive material is filled into the surface of the fiber grating (11) in the grating groove (32) and then thermo-cured to form the sensing unit (1).
3. The distributed fiber optic temperature and humidity sensor according to claim 2, characterized in that, The armored spiral sleeve (211) matches the outer diameter of the optical fiber (12), and the steel wire (212), the armored spiral sleeve (211), and the PE sheath (213) are integrally formed by a molding process. The PE sheath (213) has a peeling area at a preset distance, which is used to expose the armored spiral sleeve (211) and the steel wire (212). The stripped area is provided with a sensing protection unit (22), which is used to accommodate the fiber grating (11).
4. The distributed fiber optic temperature and humidity sensor according to claim 3, characterized in that, The sensing protection unit (22) includes a stainless steel sleeve (221), a dust filter (222), and a waterproof connector (223). The stainless steel sleeve (221) has a cylindrical structure and an air exchange hole (224) on its outer wall. The dust filter (222) is attached to the inner wall of the stainless steel sleeve (221). The waterproof connector (223) is disposed at both ends of the stainless steel sleeve (221) and is used to connect the optical cable unit (21) and the stainless steel sleeve (221). The fiber grating (11) of the sensing unit (1) is located inside the stainless steel sleeve (221) and is fixed by the armored spiral sleeve (211).
5. The distributed fiber optic temperature and humidity sensor according to claim 4, characterized in that, The knotted structure (23) is a wire rope lock, configured to be inserted into the U-shaped structure at the front end of the external steel rod, for implanting the sensor into the grain pile through the external steel rod.
6. The distributed fiber optic temperature and humidity sensor according to claim 4, characterized in that, The stainless steel sleeve (221) has an outer diameter of 12mm, an inner diameter of 10mm, and a length of 80mm; the air exchange hole (224) has a diameter of 1.5mm; and the dust filter (222) has a pore size of 100 mesh.
7. A method for fabricating a distributed optical fiber temperature and humidity sensor, used to fabricate the distributed optical fiber temperature and humidity sensor according to any one of claims 1-6, characterized in that, include: Multiple fiber gratings are fabricated on the optical fiber and spaced apart along its length to form a grating string; Multiple grating grooves are formed on a substrate, fiber gratings in the grating string are placed in the corresponding grating grooves, and a humidity-sensitive material is coated on the surface of the fiber gratings in the grating grooves. After curing, a distributed sensing unit is formed. The sensing unit is implanted inside the optical cable unit, which is composed of an armored spiral sleeve, steel wire and PE sheath. The sensing unit is inserted into the armored spiral sleeve of the optical cable unit, the steel wire is attached to the outside of the armored spiral sleeve, and the PE sheath covers the outside of the armored spiral sleeve. A sensing protection unit is installed on the optical cable unit. The sensing protection unit is sleeved on the outside of the optical cable unit and houses the fiber grating of the sensing unit. The optical cable unit and the sensing protection unit are encapsulated, and multiple optical cable units are connected in series to obtain a distributed optical fiber temperature and humidity sensor.
8. The method for preparing a distributed optical fiber temperature and humidity sensor according to claim 7, characterized in that, The step of setting multiple grating grooves on the substrate includes: Multiple grating grooves are etched side-by-side on the top of a cuboid substrate, and fiber grooves are etched on both sides of each grating groove; the cuboid substrate is made of a hydrophobic material.
9. The method for preparing a distributed optical fiber temperature and humidity sensor according to claim 8, characterized in that, The step of placing the fiber Bragg gratings in the grating string into the corresponding grooves of the grating includes: The fiber Bragg gratings in the grating string are placed one by one into the grating groove, and the fiber portions connecting adjacent fiber Bragg gratings are laid in the corresponding fiber grooves and fixed.
10. The method for preparing a distributed optical fiber temperature and humidity sensor according to claim 9, characterized in that, The step of installing the sensing protection unit on the optical cable unit includes: Stripping areas are set at predetermined intervals on the PE sheath of the optical cable unit to expose the internal armored spiral sleeve and steel wire; A sensing protection unit is installed in the stripped area. The sensing protection unit includes a stainless steel sleeve, a dust filter attached to the inner wall of the stainless steel sleeve, and waterproof connectors at both ends of the stainless steel sleeve. The waterproof connectors are used to connect multiple optical cable units in series.