Temperature self-compensated fiber grating strain sensor

Abstract

The utility model relates to temperature self -compensating's fiber grating strain sensor technical field, especially a kind of temperature self -compensating's fiber grating strain sensor, a kind of temperature self -compensating's fiber grating strain sensor, including monitoring grating, the both ends of monitoring grating are connected with transmission optical fiber, it is characterized by: the both ends of monitoring grating are sleeved and installed with two inner layer hollow thin-walled pipe on transmission optical fiber, the outer side of the end of two inner layer hollow thin-walled pipe is sleeved and installed with middle layer hollow thin-walled pipe.The utility model is extruded by inner layer hollow thin-walled pipe, weakens the influence of temperature to center wavelength, obtains the strain size by directly calculating center wavelength offset of monitoring grating, sensor response speed is fast, adopts tubular design, and good sealing property and waterproof property are realized by epoxy resin layer and 704 silicone rubber layer, improve the survival rate of sensor in construction.

Description

Technical Field

[0001] This utility model relates to the field of temperature-compensated fiber optic strain sensor technology, and in particular to a temperature-compensated fiber optic strain sensor. Background Technology

[0002] Fiber Bragg grating sensors are the preferred sensing element for structural health monitoring, with advantages such as low mass, high sensitivity, and strong resistance to electromagnetic interference. They are widely used in intelligent monitoring of large structures such as tunnels and bridges.

[0003] The working principle is that the strain of the sensor causes the center wavelength of the grating to change, and the amount of wavelength change is linearly related to the strain. Based on this characteristic, the amount of strain change of the measured substrate can be obtained from the amount of wavelength change, and both positive and negative strain can be measured.

[0004] In terms of packaging methods, fiber Bragg grating sensors include substrate packaging, embedded packaging, direct measurement with bare fiber, and tubular packaging. Fiber Bragg gratings have low shear strength; compared to the other three packaging methods, tubular packaging provides better protection for the fiber Bragg grating and reduces the risk of shear damage.

[0005] Existing fiber Bragg grating (FBG) sensors exhibit wavelength changes under the combined effects of temperature and strain. When measuring substrate strain, an additional bare FBG sensor is required for temperature self-compensation. However, the survival rate of bare optical fibers is low, making it impossible to achieve temperature self-compensation over a long period, thus hindering the long-term measurement of accurate strain.

[0006] Therefore, it is essential to provide a temperature-self-compensated fiber Bragg grating strain sensor to address the shortcomings of existing technologies. Utility Model Content

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a temperature-compensated fiber optic strain sensor. This fiber optic strain sensor reduces the influence of temperature on the center wavelength by squeezing the inner hollow thin-walled circular tubes together.

[0008] The technical means employed by this utility model to achieve the above objectives are as follows:

[0009] A temperature-compensated fiber Bragg grating strain sensor includes a monitoring grating with transmission optical fibers connected to both ends of the monitoring grating. The sensor is characterized in that two inner hollow thin-walled circular tubes are sleeved and installed on the transmission optical fibers at both ends of the monitoring grating, and a middle hollow thin-walled circular tube is sleeved and installed on the outer side of the ends of the two inner hollow thin-walled circular tubes.

[0010] An outer hollow thin-walled round tube is sleeved on the outer side of the middle layer hollow thin-walled round tube; an outer end clamping sleeve is sleeved on both outer sides of the outer and middle hollow thin-walled round tubes.

[0011] The other end of the outer layer end clamping sleeve is sleeved on the outside of the inner layer hollow thin-walled round tube.

[0012] The preferred technical solution is that a first epoxy resin layer is filled between the transmission optical fiber and the inner hollow thin-walled circular tube.

[0013] The preferred technical solution is that a second epoxy resin layer is filled between the inner hollow thin-walled circular tube and the middle hollow thin-walled circular tube.

[0014] The preferred technical solution is that a second 704 silicone rubber layer is filled between the outer layer hollow thin-walled circular tube and the middle layer hollow thin-walled circular tube.

[0015] The preferred technical solution is that the outer end clamping sleeve and the outer middle hollow thin-walled round tube are connected by a first 704 silicone rubber layer.

[0016] The preferred technical solution is that a third epoxy resin layer is filled between the outer end clamping sleeve and the inner hollow thin-walled round tube and the middle hollow thin-walled round tube.

[0017] The preferred technical solution is that the inner hollow thin-walled tube, the middle hollow thin-walled tube, and the outer end clamping sleeve are all symmetrically installed on both sides of the monitoring grating.

[0018] The preferred technical solution is that the middle hollow thin-walled circular tube is formed by joining two sections together.

[0019] The preferred technical solution is that the monitoring grating is a Bragg grating.

[0020] Compared with the prior art, the advantages of this utility model are as follows: This utility model reduces the influence of temperature on the center wavelength by extruding the inner hollow thin-walled circular tubes together. The actual strain can be measured by the change of the center wavelength alone. It has high monitoring sensitivity, is resistant to electromagnetic interference and corrosion. The strain magnitude can be directly calculated by obtaining the center wavelength shift of the monitoring grating. There are no extra transmission devices. The sensor has a fast response speed. It adopts a tubular design and achieves good sealing and waterproof performance through epoxy resin layer and 704 silicone rubber layer. It can be directly deployed to the required monitoring location or pre-embedded in prefabricated components, improving the survival rate of the sensor during construction. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the main structure of this utility model.

[0022] Figure 2This is an exploded view of this utility model.

[0023] Figure 3 yes Figure 1 A schematic diagram of section AA in the diagram.

[0024] Figure 4 yes Figure 1 A schematic diagram of the BB section.

[0025] Figure 5 This is a utility model Figure 1 A schematic diagram of the CC section.

[0026] The corresponding component names in the attached drawings are as follows:

[0027] 1. Monitoring grating; 2. Transmission optical fiber; 3. Inner hollow thin-walled cylindrical tube; 4. Middle hollow thin-walled cylindrical tube; 5. Outer hollow thin-walled cylindrical tube in the middle; 6. Outer end clamping sleeve; 7. First epoxy resin layer; 8. Second epoxy resin layer; 9. Third epoxy resin layer; 10. First 704 silicone rubber layer; 11. Second 704 silicone rubber layer. Detailed Implementation

[0028] The present invention will be further described in conjunction with the following embodiments. Figure 1-3 As shown, a temperature-compensated fiber optic strain sensor includes a monitoring grating 1, with transmission optical fibers 2 connected to both ends of the monitoring grating 1. Two inner hollow thin-walled circular tubes 3 are sleeved on the transmission optical fibers 2 at both ends of the monitoring grating 1. Two middle hollow thin-walled circular tubes 4 are sleeved on the outside of the two inner hollow thin-walled circular tubes 3. One end of the two middle hollow thin-walled circular tubes 4 is connected to each other. An outer middle hollow thin-walled circular tube 5 and two outer end clamping sleeves 6 are sleeved on the outside of the middle hollow thin-walled circular tubes 4.

[0029] This application is used for monitoring structures. First, the outer end clamping sleeve 6 is clamped and fixed to the structure, such as a structural column, by the clamping support. The actual strain is measured by the wavelength shift of the monitoring grating 1. The transmission optical fiber 2 and the monitoring grating 1 pass through the centroid of the inner hollow thin-walled circular tube 3. Epoxy resin is bonded layer by layer from the inside out, only in the area of ​​the outer end clamping sleeve 6. When the temperature rises, the inner hollow thin-walled circular tube 3 and the monitoring grating 1 are squeezed against each other to achieve low-temperature sensitivity. The wavelength shift of the monitoring grating 1 is not affected by temperature, but only by strain. The actual strain is measured by the wavelength shift.

[0030] The inner hollow thin-walled circular tube 3, the middle hollow thin-walled circular tube 4, the middle hollow thin-walled circular tube and the outer end clamping sleeve 6 are all miniature hollow thin-walled circular tubes with annular cross-sections, and the coefficient of thermal expansion of the hollow thin-walled circular tubes decreases sequentially from the inside to the outside.

[0031] During installation, there are limitations imposed by the clamping support. The miniature hollow thin-walled cylindrical tube expands inward and squeezes the outer end clamping sleeve 6, squeezing layer by layer until the fiber is squeezed, which causes the fiber to generate a certain compressive strain. The center wavelength shift caused by the compressive strain cancels out the center wavelength shift caused by the temperature, thereby realizing a low-temperature sensitive fiber optic grating strain sensor.

[0032] The outer end clamping sleeve 6 is located at both ends of the outer middle hollow thin-walled circular tube 5. The transmission optical fiber 2 and the inner hollow thin-walled circular tube 3 are filled with a first epoxy resin layer 7. The inner hollow thin-walled circular tube 3 and the middle hollow thin-walled circular tube 4 are filled with a second epoxy resin layer 8. The outer end clamping sleeve 6 is filled with a third epoxy resin layer 9 between the inner hollow thin-walled circular tube 3 and the middle hollow thin-walled circular tube 4. The outer end clamping sleeve 6 and the outer middle hollow thin-walled circular tube 5 are connected by a first 704 silicone rubber layer 10. The outer middle hollow thin-walled circular tube 5 and the middle hollow thin-walled circular tube 4 are filled with a second 704 silicone rubber layer 11.

[0033] The 704 silicone rubber filler provides airtightness and waterproofing.

[0034] The inner hollow thin-walled circular tube 3, the middle hollow thin-walled circular tube 4, and the outer end clamping sleeve 6 are all symmetrically installed at both ends of the monitoring grating 1.

[0035] Monitoring grating 1 is a Bragg grating.

[0036] The outer end clamping sleeve 6 moves collaboratively under the clamping support. The support is only related to the deformation of the base. Under the single-factor effect of temperature, the two ends of the clamping support are fixed. Therefore, only the temperature self-compensation of the hollow thin-walled circular tube of the clamping section for the monitoring grating 1 is considered. The loss of strain transmission between the hollow thin-walled circular tubes and the adhesive is ignored. Taking the temperature rise as an example, when the temperature rises, the hollow thin-walled circular tube of the clamping section expands due to heat, and the deformation satisfies the linear thermal expansion formula:

[0037]

[0038] In the formula, This indicates the deformation length of the hollow thin-walled circular tube under heat in the single-sided clamping section. This indicates the initial length of the hollow thin-walled circular tube clamped on one side. This represents the coefficient of thermal expansion of the hollow thin-walled circular tube in the clamping section. It represents the amount of temperature change.

[0039] The magnitude of the compressive strain generated by the expansion of the clamping section on the monitoring grating 1 is:

[0040]

[0041] In the formula, This indicates the strain value of segment 1 of the monitoring grating. This indicates the initial length of segment 1 of the monitoring grating. Based on the basic principles of fiber optic gratings:

[0042]

[0043] In the formula, This indicates the change in wavelength of monitoring grating 1. This indicates the initial wavelength of monitoring grating 1. To monitor the strain sensitivity coefficient of grating 1, To monitor the temperature sensitivity coefficient of grating 1, we can obtain:

[0044]

[0045] The thermal expansion coefficients of the inner hollow thin-walled circular tube 3, the middle hollow thin-walled circular tube 4, and the outer end clamping sleeve 6 satisfy the above formula, thus achieving temperature self-compensation.

[0046] This invention utilizes the mutual compression of inner hollow thin-walled circular tubes 3 to reduce the influence of temperature on the center wavelength. The actual strain can be measured solely by the change in the center wavelength, resulting in high monitoring sensitivity, resistance to electromagnetic interference, and corrosion resistance. The strain magnitude is directly calculated by acquiring the center wavelength shift of the monitoring grating 1, eliminating unnecessary transmission devices and ensuring a fast sensor response. The tubular design, combined with epoxy resin and 704 silicone rubber layers, achieves excellent sealing and waterproofing. It can be directly installed at the required monitoring location or pre-embedded in prefabricated components, improving the sensor's survival rate during construction.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model and are not intended to limit the scope of protection of this utility model. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this utility model without departing from the essence and scope of the technical solutions of this utility model.

Claims

1. A temperature-compensated fiber optic strain sensor, comprising a monitoring grating (1), wherein both ends of the monitoring grating (1) are connected to transmission optical fibers (2), characterized in that: The monitoring grating (1) has two inner hollow thin-walled round tubes (3) sleeved on the transmission optical fiber (2) at both ends, and a middle hollow thin-walled round tube (4) sleeved on the outer side of the ends of the two inner hollow thin-walled round tubes (3). An outer layer hollow thin-walled round tube (5) is sleeved on the outer side of the middle layer hollow thin-walled round tube (4); an outer layer end clamping sleeve (6) is sleeved on both outer sides of the outer layer hollow thin-walled round tube (5) and the middle layer hollow thin-walled round tube (4). The other end of the outer layer end clamping sleeve (6) is sleeved on the outside of the inner layer hollow thin-walled round tube (3).

2. The temperature-self-compensated fiber optic strain sensor according to claim 1, characterized in that: The first epoxy resin layer (7) is filled between the transmission optical fiber (2) and the inner hollow thin-walled circular tube (3).

3. The temperature-self-compensated fiber optic strain sensor according to claim 1, characterized in that: A second epoxy resin layer (8) is filled between the inner hollow thin-walled tube (3) and the middle hollow thin-walled tube (4).

4. The temperature-self-compensated fiber optic strain sensor according to claim 1, characterized in that: A second 704 silicone rubber layer (11) is filled between the outer layer hollow thin-walled tube (5) and the middle layer hollow thin-walled tube (4).

5. A temperature-self-compensated fiber optic strain sensor according to claim 1, characterized in that: The outer end clamping sleeve (6) and the outer middle hollow thin-walled round tube (5) are connected by a first 704 silicone rubber layer (10).

6. The temperature-self-compensated fiber optic strain sensor according to claim 1, characterized in that: A third epoxy resin layer (9) is filled between the outer end clamping sleeve (6), the inner hollow thin-walled round tube (3), and the middle hollow thin-walled round tube (4).

7. A temperature-self-compensated fiber optic strain sensor according to claim 1, characterized in that: The inner hollow thin-walled tube (3), the middle hollow thin-walled tube (4), and the outer end clamping sleeve (6) are all symmetrically installed on both sides of the monitoring grating.

8. A temperature-self-compensated fiber optic strain sensor according to claim 1, characterized in that: The middle layer hollow thin-walled circular tube (4) is formed by joining two sections together.

9. A temperature-self-compensated fiber optic strain sensor according to claim 1, characterized in that: The monitoring grating (1) is a Bragg grating.

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