Multi-point detection fiber bragg grating sensor for soil moisture content

Abstract

The utility model discloses a multi-point detection fiber bragg grating sensor for soil moisture content. The multi-point detection fiber bragg grating sensor comprises an optical fiber protection tube and a measuring tube assembly, one end of the optical fiber protection tube is connected with the head end of the measuring tube assembly; the measuring pipe assembly comprises a plurality of measuring pipes, and every two adjacent measuring pipes are connected through a heat insulation pipe. Densely distributed optical fibers are arranged in the measuring tube assembly, and optical fiber grating regions are arranged at the positions, corresponding to the measuring tubes, of the densely distributed optical fibers respectively; a heating resistance wire is arranged in each measuring tube; and densely distributed optical fibers led out from the measuring tube assembly and a lead connected with the heating resistance wire are fixed in the optical fiber protection tube. The soil moisture detector can be inserted into soil to detect the moisture content of different positions of the soil at one time, the detected soil cannot be damaged, the measurement precision is high, and the detection process is convenient and fast.

Description

Technical Field

[0001] This utility model relates to the field of fiber optic grating sensor technology, specifically to a fiber optic grating sensor for multi-point detection of soil moisture content. Background Technology

[0002] Since their invention, fiber Bragg gratings (FBGs) have been widely used in fiber optic sensing. Due to their advantages such as resistance to electromagnetic interference, corrosion resistance, electrical insulation, high sensitivity, low cost, and good compatibility with ordinary optical fibers, FBG sensors are attracting increasing attention. Because the resonant wavelength of FBGs is sensitive to changes in stress, strain, and temperature, they are mainly used for measuring temperature, stress, and strain. Densely distributed optical fibers not only possess the above advantages but also have the following characteristics: for continuous multi-point monitoring, a single densely distributed optical fiber can run through all sensor branches, eliminating the need for fusion splicing, reducing energy loss, and enabling simultaneous monitoring of moisture content at multiple points over a wider range.

[0003] Fiber Bragg grating (FBG) moisture content detection technology, originating from the development of fiber optic sensing technology, is an emerging method for monitoring soil moisture content. This technology utilizes the sensitivity of fiber optic gratings to changes in environmental parameters, indirectly measuring soil moisture content by measuring changes in the grating's reflectance spectrum. First proposed in the 1970s, FBG technology has been widely applied in structural health monitoring and geological disaster early warning after decades of development. In recent years, with the increasing demand for precision agricultural management and the growing importance of water resource management, FBG technology has shown great potential in soil moisture content monitoring. With the intensification of global climate change and water scarcity, accurate soil moisture content monitoring is becoming increasingly important for optimizing agricultural irrigation, water resource management, and ecological environmental protection. The development trends of FBG moisture content detection technology are mainly reflected in the following aspects: first, optimization of the probe design to improve measurement accuracy and spatial resolution; second, improvement of signal processing algorithms to enhance anti-interference capabilities and data reliability; and third, structural optimization to facilitate rapid on-site installation, reduce construction difficulty, and minimize damage to the original soil moisture content during construction. Current moisture content probes all use corundum tubes, which are hard but brittle and easily break when inserted into the soil. Therefore, these probes require excavation before placement, making construction difficult and disrupting the soil's moisture content. Existing moisture content sensors also require waiting for the moisture content in the excavated area to return to normal before monitoring can begin, resulting in lengthy detection times. Furthermore, existing moisture content sensors struggle to simultaneously detect moisture content at different locations in the soil.

[0004] Therefore, there is a need to develop a sensor that can be quickly installed for monitoring without damaging the soil moisture content during installation, and can be used to monitor the moisture content of different locations in the soil. Utility Model Content

[0005] To solve the above-mentioned technical problems, the purpose of this utility model is to provide a fiber optic grating sensor for multi-point detection of soil moisture content. It can detect the moisture content of different locations in the soil at one time by inserting it into the soil without damaging the soil being measured. It has high measurement accuracy and the detection process is convenient and fast.

[0006] To achieve the above-mentioned technical objectives and effects, this utility model is implemented through the following technical solution:

[0007] A fiber Bragg grating sensor for multi-point detection of soil moisture content includes an optical fiber protection tube and a measuring tube assembly; one end of the optical fiber protection tube is connected to the head end of the measuring tube assembly; the measuring tube assembly includes multiple measuring tubes, with adjacent measuring tubes connected by a heat insulation tube; the measuring tube assembly is provided with densely distributed optical fibers, and each densely distributed optical fiber has an optical fiber grating area at the position corresponding to each measuring tube; each measuring tube is also provided with a heating resistance wire; the densely distributed optical fibers leading out from the measuring tube assembly and the wires connecting the heating resistance wires are fixed inside the optical fiber protection tube.

[0008] Furthermore, the tail end of the measuring tube assembly is connected to a tail cone.

[0009] Furthermore, the interior of the optical fiber protection tube is filled with glue to secure the densely distributed optical fibers leading out from the measuring tube assembly and the wires connecting the heating resistance wire.

[0010] Furthermore, the other end of the optical fiber protection tube is connected to a fixed outlet bracket.

[0011] Furthermore, the fixed cable outlet is connected to a wire lead clamp and an optical fiber lead clamp. The optical fiber lead clamp is used to clamp and fix the passing optical fiber lead, and the wire lead clamp is used to clamp and fix the passing wire lead.

[0012] Furthermore, the measuring tube is provided with a plurality of through holes evenly distributed on the circumference, wherein two through holes are respectively used to arrange the heating resistance wire and the densely distributed optical fiber.

[0013] Furthermore, the measuring tube is a stainless steel tube.

[0014] Furthermore, the heat insulation pipe is a bakelite pipe.

[0015] Furthermore, both the optical fiber lead and the conductor lead are armored optical cables.

[0016] Furthermore, the measuring tube and the heat insulation tube, as well as the measuring tube and the optical fiber protection tube, are all connected by threads.

[0017] The beneficial effects of this utility model are:

[0018] This invention can be directly inserted into the soil being tested, and the heating resistance wire power supply is turned on to begin real-time monitoring of the fiber optic grating. This invention uses multiple measuring tubes, isolated by heat-insulating tubes, ensuring that the temperatures within each measuring tube are independent of each other. Therefore, when detecting soil moisture content, after heating, the temperature of the soil near the sensor rises. Since the moisture content varies at different locations, the temperature rise differs, resulting in different wavelength changes in the fiber optic grating region at different locations within the densely distributed optical fiber. Since moisture content is directly proportional to temperature, and temperature has a linear relationship with the wavelength change of the fiber optic grating, the wavelength change within the densely distributed optical fiber ultimately reflects the moisture content of the soil being tested. Each optical fiber in each measuring tube reflects the moisture content of its corresponding soil layer, thus enabling more accurate monitoring of soil moisture content at different locations.

[0019] This utility model has a simple overall structure, high strength, and quick installation. It can be directly inserted into the soil during use without damaging the moisture content of the soil being tested. The moisture content at different locations in the soil can be reflected by the wavelength changes of the densely distributed optical fibers.

[0020] This invention features high measurement sensitivity, high measurement accuracy and precision, long service life, and strong structural reliability. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the fiber optic grating sensor for multi-point detection of soil moisture content in Embodiment 1 of this utility model;

[0022] Figure 2 This is a cross-sectional view of the fiber optic grating sensor for multi-point detection of soil moisture content according to Embodiment 1 of this utility model;

[0023] Figure 3 This is a schematic diagram of the structure of the fiber optic grating sensor for multi-point detection of soil moisture content in Embodiment 2 of this utility model;

[0024] Figure 4 This is a schematic cross-sectional view of the measuring tube in this utility model;

[0025] Figure 5 This is a cross-sectional schematic diagram of the heat insulation pipe in this utility model.

[0026] In the diagram, 1: Tail cone; 2: Heating resistance wire; 3: Densely distributed optical fiber; 4: Measuring tube; 5: Heat insulation tube; 6: Optical fiber protection tube; 7: Fixed outlet socket; 8: Conductor lead crimping tube; 9: Optical fiber lead crimping tube. Detailed Implementation

[0027] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the scope of protection of the present invention.

[0028] Example 1

[0029] like Figure 1 and Figure 2 The soil moisture content multi-point detection fiber optic grating sensor shown includes an optical fiber protection tube 6 and a measuring tube assembly; in this embodiment 1, the measuring tube assembly includes two measuring tubes 4.

[0030] The optical fiber protection tube 6 has a hollow structure with internal threads at both ends. Each measuring tube 4 has threads at both ends. The first measuring tube 4 is connected to the optical fiber protection tube 6 by engaging its external thread with the internal thread. Adjacent measuring tubes 4 are connected by a heat insulation tube 5. Specifically, the heat insulation tube 5 has external threads at both ends, and the corresponding measuring tube 4 has internal threads at its ends. Thus, the heat insulation tube 5 and the measuring tube 4 are connected by threads, splicing the two measuring tubes 4 into a whole.

[0031] The measuring tube assembly is provided with a densely distributed optical fiber 3 running through it; the densely distributed optical fiber 3 is provided with an optical fiber grid area at the position corresponding to each measuring tube 4. Figure 2 Only the fiber grating region of the densely distributed optical fiber is shown. Each measuring tube also contains a heating resistance wire; the heating resistance wires are connected by wires. The heating resistance wire 2 is used for heating by electricity, and the fiber grating region of the densely distributed optical fiber 3 is used for temperature monitoring, thereby measuring the soil moisture content by measuring the temperature change. The densely distributed optical fiber 3 and the wires are led out from the measuring tube assembly and enter the optical fiber protection tube 6. The inside of the optical fiber protection tube 6 is filled with glue to fix the led-out densely distributed optical fiber and wires.

[0032] Specifically, such as Figure 4 As shown, the measuring tube 4 has four through holes evenly distributed around its circumference, two of which are used to arrange the heating resistance wire 2 and the densely distributed optical fiber 3, respectively. Correspondingly, as... Figure 5 As shown, the heat insulation pipe 5 also has four corresponding through holes.

[0033] The measuring tube assembly is connected to a tail cone 1 at its tail end; specifically, the tail cone 1 is threadedly connected to the end of the last measuring tube 4.

[0034] One end of the fiber optic protection tube 6, away from the measuring tube, is connected to a fixed cable outlet 7. The fixed cable outlet 7 has two threaded through holes for fixing and connecting the wire lead clamp 8 and the fiber optic lead clamp 9. The densely distributed optical fiber 3 is connected to an optical fiber lead, which passes through the fiber optic lead clamp 9 and extends outward to extract the signal measured by the densely distributed optical fiber 3; the heating resistance wire 2 is connected to a wire lead, which passes through the wire lead clamp 8 and extends outward; the fiber optic lead clamp 9 is used to press and fix the passing optical fiber lead, and the wire lead clamp 8 is used to press and fix the passing wire lead.

[0035] In this invention, the measuring tube 4 is made of stainless steel, ensuring the strength and toughness of the sensor and facilitating direct insertion into the ground for moisture content monitoring. The heat insulation tube 5 is made of bakelite, effectively isolating the temperatures within the two measuring tubes and preventing temperature interference. The bakelite heat insulation tube provides long-term waterproofing and corrosion resistance, ensuring its long-term use in the soil. Both the fiber optic lead and the conductor lead are armored optical cables. The tail cone 1, fiber optic protection tube 6, fixed cable outlet 7, fiber optic lead clamp 9, and conductor lead clamp 8 are all made of stainless steel.

[0036] Example 2

[0037] like Figure 1 As shown, the difference between this embodiment 2 and embodiment 1 is that the measuring tube assembly includes four measuring tubes 4.

[0038] In other embodiments, the measuring tube assembly may be provided with an additional number of measuring tubes 4 as needed.

[0039] In use, the fiber Bragg grating sensor is first inserted into the soil being tested using its tail cone 1. The power supply to the heating resistance wire 2 is then turned on, initiating real-time monitoring of the fiber Bragg grating. As the sensor heats up, the temperature of the soil near the sensor increases. However, due to varying moisture content at different locations, the degree of temperature increase differs. This results in different wavelength changes in the fiber Bragg grating region at different locations of the densely distributed optical fibers 3. Since moisture content is directly proportional to temperature, and temperature has a linear relationship with the wavelength change of the fiber Bragg grating, the wavelength change within the densely distributed optical fibers ultimately reflects the moisture content of the soil being tested. Each optical fiber in the measuring tube 4 reflects the moisture content of its corresponding soil layer, thus enabling more accurate monitoring of soil moisture content at different locations.

[0040] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention.

[0041] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A fiber optic grating sensor for multi-point detection of soil moisture content, characterized in that, The device includes an optical fiber protection tube and a measuring tube assembly; one end of the optical fiber protection tube is connected to the head end of the measuring tube assembly; the measuring tube assembly includes multiple measuring tubes, with adjacent measuring tubes connected by a heat insulation tube; the measuring tube assembly contains densely distributed optical fibers, each with an optical fiber grid region corresponding to each measuring tube; each measuring tube also contains a heating resistance wire; the optical fiber protection tube contains the densely distributed optical fibers leading out from the measuring tube assembly and the wires connecting the heating resistance wires.

2. The fiber optic grating sensor for multi-point detection of soil moisture content according to claim 1, characterized in that, The measuring tube assembly is connected to a tail cone at its tail end.

3. The fiber optic grating sensor for multi-point detection of soil moisture content according to claim 1, characterized in that, The fiber optic protective tube is filled with glue to secure the densely distributed optical fibers leading out from the measuring tube assembly and the wires connecting the heating resistance wire.

4. A fiber optic grating sensor for multi-point detection of soil moisture content according to claim 1, characterized in that, The other end of the fiber optic protection tube is connected to a fixed outlet bracket.

5. A fiber optic grating sensor for multi-point detection of soil moisture content according to claim 4, characterized in that, The fixed cable outlet is connected to a wire lead clamp and an optical fiber lead clamp. The optical fiber lead clamp is used to clamp and fix the passing optical fiber lead, and the wire lead clamp is used to clamp and fix the passing wire lead.

6. A fiber optic grating sensor for multi-point detection of soil moisture content according to claim 1, characterized in that, The measuring tube has multiple through holes evenly distributed around its circumference, two of which are used to arrange a heating resistance wire and a densely distributed optical fiber, respectively.

7. A fiber optic grating sensor for multi-point detection of soil moisture content according to claim 1, characterized in that, The measuring tube is made of stainless steel.

8. A fiber optic grating sensor for multi-point detection of soil moisture content according to claim 1, characterized in that, The insulation pipe is a bakelite pipe.

9. A fiber optic grating sensor for multi-point detection of soil moisture content according to claim 5, characterized in that, Both the optical fiber leads and the conductor leads are armored optical cables.

10. A fiber optic grating sensor for multi-point detection of soil moisture content according to claim 1, characterized in that, The measuring tube and the heat insulation tube, as well as the measuring tube and the optical fiber protection tube, are all connected by threads.

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