Fiber grating soil pressure sensor and monitoring system

Abstract

The application relates to a fiber grating soil pressure sensor and a monitoring system, which comprises a shell, a top cover, a spring piece combination, a measuring fiber and an optical cable, the shell comprises a shell body, and the spring piece combination is fixed in the inner cavity of the shell body; the middle part of the measuring fiber is provided with a grating, and both ends are fixedly connected with the spring piece combination; the top cover comprises a cover plate and a force transmission block, the cover plate is fixed on the top of the shell body and is used for closing the inner cavity of the shell body; the force transmission block is used for being in contact with the spring piece combination to transmit pressure, when the pressure is transmitted, the spring piece combination respectively transmits tensile forces in different directions to both ends of the measuring fiber; the inside of the optical cable is wrapped with a transmission fiber, the transmission fiber is integrally fused with the fiber core of the measuring fiber, and when the shell, the top cover, the spring piece combination, the measuring fiber and the optical cable are assembled, an external thermal insulation coating with a thickness not less than 2mm is sprayed on the outer surfaces of the shell and the top cover. The technical scheme effectively avoids the influence of temperature on the measurement result, and the measurement precision is high.

Description

Technical Field

[0001] This invention belongs to the field of soil pressure monitoring technology, specifically relating to a fiber Bragg grating soil pressure sensor and a fiber Bragg grating soil pressure monitoring system including the sensor. Background Technology

[0002] Earth pressure monitoring technology has been widely used both domestically and internationally. Its technical methods are relatively mature, allowing for the acquisition of static conditions at different media contact surfaces (interfaces) or within the soil mass using earth pressure sensors. Current earth pressure sensors include electronic and fiber Bragg grating types.

[0003] Electronic earth pressure sensors are mainly divided into resistance strain gauge type and vibrating wire type, and can be installed horizontally, vertically or at any angle. Electronic sensors have the following defects: (1) Electronic sensors require power supply. If used for a long time, errors such as zero drift will occur. They may also be affected by environmental electromagnetic interference. Small errors will lead to a significant decrease in the accuracy of measurement data after long-term superposition, affecting the earth pressure monitoring effect. (2) Electronic earth pressure sensors are easily affected by ambient temperature. Tests have shown that even without pressure, changing the ambient temperature can still detect significant numerical changes, thus affecting the reliability of the monitoring results.

[0004] In recent years, the gradual maturation of fiber optic sensing technology has provided a new approach to earth pressure monitoring. Fiber optic sensing technology has advantages such as no power supply required, high sensitivity, and resistance to electromagnetic interference, and has developed rapidly in the field of soil and rock condition monitoring. Fiber Bragg grating earth pressure sensors have been widely used. To address the influence of temperature, a temperature-measuring grating unaffected by external forces is typically added for temperature compensation. However, due to the nonlinearity of the temperature compensation coefficient and the inconsistency of the compensation coefficient when the temperature rises or falls, the measurement error caused by temperature changes remains unresolved.

[0005] To achieve high-sensitivity and high-precision measurement of earth pressure and reduce or even avoid the influence of ambient temperature, it is urgent to develop new types of earth pressure sensors. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a fiber Bragg grating earth pressure sensor and a fiber Bragg grating earth pressure monitoring system including the sensor.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] A fiber optic earth pressure sensor includes a housing, a top cover, a spring assembly, a measuring optical fiber, and an optical cable.

[0009] The outer casing includes a bottomless shell with optical cable access holes on the side.

[0010] The spring clip assembly is fixedly connected to the outer shell and is located inside the cavity of the shell;

[0011] A grating of length Lg is provided in the middle of the measuring optical fiber along its length direction, and the two ends of the measuring optical fiber are respectively fixedly connected to the spring plate combination.

[0012] The top cover includes a cover plate and a force transmission block. The cover plate is fixed to the top of the housing by screws and is used to seal the inner cavity of the housing. The force transmission block is used to contact the spring assembly to transmit pressure. The position of the force transmission block corresponds to the middle position of the grating. When the force transmission block transmits pressure to the spring assembly, the spring assembly transmits tensile forces in different directions to both ends of the measuring optical fiber.

[0013] The optical cable is internally wrapped with transmission optical fibers, and the cores of the transmission optical fibers and the measurement optical fibers are fused together. The outer end of the optical cable is placed outside the shell through an optical cable through-hole, and the optical cable is fixedly connected to the optical cable through-hole through a connector.

[0014] After the outer shell, top cover, spring assembly, measuring optical fiber and optical cable are assembled, an external thermal insulation coating with a thickness of not less than 2mm is sprayed on the outer surface of the outer shell and top cover.

[0015] Furthermore, the bottom and side surfaces of the inner cavity of the housing are coated with an internal thermal insulation coating of not less than 1 mm.

[0016] Furthermore, both the outer and inner insulation coatings are made of nano-insulation materials.

[0017] Furthermore, a support block A and a support block B are fixedly provided on the bottom surface of the inner cavity of the housing. The distance between the opposite faces of the support block A and the support block B is Lb, and the distance between their opposite back faces is La.

[0018] The spring assembly includes a spring and a pair of fiber optic fixing blocks. The length of the spring is LA, the distance between the opposite faces of the pair of fiber optic fixing blocks is LC, and the distance between the opposite faces of the pair of fiber optic fixing blocks is LB; LA=La, LB<Lb, LC>Lg; the two fiber optic fixing blocks are respectively fixedly connected to the two ends of the measuring fiber. The two ends of the spring are respectively fixedly connected to support block A and support block B by screws. Support block B is provided with fiber optic through holes for the optical cable to pass through.

[0019] Furthermore, both support block A and support block B are provided with V-shaped grooves, and the two ends of the measuring optical fiber are placed in the corresponding V-shaped grooves and bonded and fixed to the V-shaped grooves.

[0020] Furthermore, the joint between the cover plate and the housing is sealed by applying sealant; the joint between the connector and the optical cable through hole is also sealed by applying sealant, thereby sealing the inner cavity of the housing.

[0021] Furthermore, the outer shell is made of steel, and its Brinell hardness is not less than 200 N / mm². 2 The cover plate is made of beryllium bronze or spring steel.

[0022] A fiber Bragg grating earth pressure monitoring system includes several fiber Bragg grating earth pressure sensors as described above. The optical cables in the fiber Bragg grating earth pressure sensors are connected to a fiber Bragg grating demodulator, the fiber Bragg grating demodulator is connected to a switch, and the switch is connected to a server.

[0023] Furthermore, the installation method of the fiber optic grating earth pressure monitoring system is as follows:

[0024] Includes the following steps:

[0025] S1: Foundation leveling

[0026] Select the installation location W for the fiber Bragg grating earth pressure sensor and level the foundation at that location;

[0027] S2: Laying the subbase

[0028] Lay a layer of soil or fine sand with a thickness of T1 on the foundation at the installation location W. The particle diameter of the soil and fine sand should not be greater than 10mm. Then compact and level the surface.

[0029] S3: Placement of thermal insulation nano-aerogel felt

[0030] The heat-insulating nano-aerogel felt is prepared into an open cube, and through holes T are left on the side of the open cube to allow optical cables to pass through. The open cube is then placed on the padding layer.

[0031] S4: Install sensors and backfill.

[0032] Lay soil or fine sand into the open cube to a thickness of T2 and compact it. Then place the fiber optic grating soil pressure sensor on the soil or fine sand in the open cube. Lead the optical cable out from the through hole T on the side of the open cube and seal the gap between the optical cable and the through hole T with sealant. Continue to lay soil or fine sand into the open cube and compact it. After the soil or fine sand is laid to the opening of the open cube, cover the opening of the open cube with a cover made of heat-insulating nano-aerogel felt and completely seal the cover to the opening of the open cube with sealant. Then backfill with soil or fine sand to meet the construction parameter requirements.

[0033] Furthermore, in step S2, T1 is 150mm to 200mm; in step S4, T2 is 20mm to 30mm.

[0034] The beneficial effects that this invention can achieve are as follows:

[0035] (1) In this technical solution, the fiber optic grating earth pressure sensor is equipped with an insulation layer, which blocks the heat convection, heat conduction and heat radiation inside and outside the sensor, effectively avoiding the influence of temperature on the measurement results and achieving high measurement accuracy.

[0036] (2) Compared with the existing technology of sensors that use temperature gratings for temperature compensation, it has a lower cost.

[0037] (3) By further spraying an inner heat insulation coating into the inner cavity of the housing, the heat convection, heat conduction and heat radiation inside and outside the sensor are further blocked.

[0038] (4) By laying heat-insulating nano-aerogel felt during the on-site installation process, the influence of external temperature on the sensor is effectively reduced. Attached Figure Description

[0039] Figure 1 This is a perspective view of an embodiment of the present invention.

[0040] Figure 2 This is a top view of an embodiment of the present invention.

[0041] Figure 3 yes Figure 2 AA sectional view.

[0042] Figure 4 This is a perspective view of an embodiment of the present invention (with the outer insulation coating removed).

[0043] Figure 5 This is an exploded view of an embodiment of the present invention (with the external temperature coating removed).

[0044] Figure 6 This is a perspective view of the outer shell in an embodiment of the present invention.

[0045] Figure 7 This is a cross-sectional view of the outer casing in an embodiment of the present invention.

[0046] Figure 8 This is a perspective view of the top cover in an embodiment of the present invention.

[0047] Figure 9 This is a front view of the top cover in an embodiment of the present invention.

[0048] Figure 10 This is a perspective view of the spring assembly in an embodiment of the present invention.

[0049] Figure 11 This is a front view of the spring assembly in an embodiment of the present invention.

[0050] Figure 12 This is a bottom view of the spring assembly in an embodiment of the present invention.

[0051] Figure 13This is a side view of the spring assembly in an embodiment of the present invention.

[0052] Figure 14 This is a connection structure diagram of the fiber optic grating earth pressure monitoring system in the embodiment of the invention.

[0053] In the diagram: 1-External insulation coating, 2-Outer shell, 201-Shell, 202-Support block A, 203-Step, 204-Support block B, 205-Fiber optic via, 206-Fiber optic cable via; 3-Internal insulation coating, 4-Top cover, 401-Cover plate, 402-Force transmission block; 5-Spring assembly, 501-Spring, 502-Fiber optic fixing block, 503-V-groove; 6-Measuring fiber, 601-Grate; 7-Transmission fiber, 8-Fiber optic cable, 9-Connector, 10-Fiber Bragg grating earth pressure sensor; 11-Fiber Bragg grating demodulator; 12-Switch; 13-Server. Detailed Implementation

[0054] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0055] like Figures 1-5 As shown, a fiber optic grating earth pressure sensor 10 includes a housing 2, a top cover 4, a spring assembly 5, a measuring fiber optic cable 6, and an optical cable 8.

[0056] like Figures 6-7 As shown, the outer shell 2 includes a cylindrical shell 201 with a bottom but no top. A fiber optic cable through-hole 206 with a diameter of 6 mm is provided on the side of the shell 201. The inner diameter of the shell 201 is 68 mm, and the depth of the inner cavity is H = 16 mm. Support block A202 and support block B204 are fixedly provided on the bottom surface of the inner cavity of the shell 201. Support block B204 is close to the fiber optic cable through-hole 206. The distance between the opposing surfaces of support block A202 and support block B204 is Lb = 44 mm, and the distance between their opposing back surfaces is La = 56 mm. The height of support block A202 and support block B204 is Hb = 6 mm. An optical fiber through-hole 205 is provided on support block B204 for the optical cable 8 to pass through. A step 203 is provided at the opening of the shell 201. The inner diameter of step 203 is R = 76 mm, and the height of step 203 is Ha = 3 mm. For shell 2, the Brinell hardness should be no less than 200 N / mm. 2 The steel material can remain stable and undeformed even under strong forces; the bottom and sides of the inner cavity of the shell 201 are coated with an inner insulation coating of not less than 1 mm.

[0057] like Figures 10-13As shown, the spring assembly 5 includes a spring 501 and a pair of fiber optic fixing blocks 502. The length of the spring 501 is LA=56mm, the thickness of the spring 501 is Hd=2mm, and the height of the fiber optic fixing blocks 502 is He=4mm, satisfying He<Hb. The distance between the opposite faces of the pair of fiber optic fixing blocks 502 is LC=24mm, and the distance between the back faces of the pair of fiber optic fixing blocks 502 is LB=40mm. Both support blocks A202 and support blocks B204 are provided with V-grooves 503. The two ends of the spring 501 are fixedly connected to support blocks A202 and support blocks B204 respectively by screws. The spring 501, support blocks A202 and support blocks B204 form a simply supported beam.

[0058] A grating 601 is provided in the middle of the measuring fiber 6 along its length direction. The length of the grating 601 is Lg=10mm. The two ends of the measuring fiber 6 are fixed in the corresponding V-grooves 503 on the support block A202 and the support block B204, respectively. The fixing method is as follows: peel off the coating layer at the contact point between the measuring fiber 6 and the V-groove 503. After peeling off the coating layer, the fiber core is exposed. The exposed fiber core is then glued into the V-groove 503 with epoxy resin.

[0059] The optical cable 8 internally encases a transmission optical fiber 7, which is fused together with the core of the measurement optical fiber 6. The outer end of the optical cable 8 is located outside the housing 201 through an optical cable through-hole 206, and the optical cable 8 is fixedly connected to the optical cable through-hole 206 through a connector 9. The optical cable 8 is a PE-coated armored optical cable with excellent temperature and corrosion resistance, and a minimum bending radius of not less than 100mm; the connector 9 is a Gaggle connector.

[0060] like Figures 8-9 As shown, the top cover 4 includes a cover plate 401 and a force transmission block 402. The outer diameter of the cover plate 401 is r=76mm, the thickness of the cover plate 401 is HA=3mm, and the height of the force transmission block 402 is Hc=5mm, satisfying HA=Ha and HA+HC+Hd+Hb=H. The cover plate 401 is fixed to the step 203 at the opening of the housing 201 by screws, and is used to close the inner cavity of the housing 201. The force transmission block 402 is used to contact the spring assembly 5 to transmit pressure. The position of the force transmission block 402 corresponds to the middle position of the grating 601. When the force transmission block 402 transmits pressure to the spring assembly 5, the spring assembly 5 transmits tension in different directions to both ends of the measuring optical fiber 6.

[0061] The cover plate 401 and the spring sheet 501 are both made of beryllium bronze or spring steel, which are high in strength, elastic and fatigue-resistant, and can withstand large stress and maintain long-term stability.

[0062] After the outer shell 2, top cover 4, spring assembly 5, measuring optical fiber 6 and optical cable 8 are assembled together, the joint between the cover plate 401 and the shell 201 is sealed by applying polyurethane sealant; the joint between the connector 9 and the optical cable through hole 206 is also sealed by applying sealant; so that the inner cavity of the shell 201 is sealed; an outer thermal insulation coating 1 with a thickness of not less than 2mm is sprayed on the outer surface of the outer shell 2 and the top cover 4, and both the outer thermal insulation coating 1 and the inner thermal insulation coating 3 are nano aerogel thermal insulation coatings.

[0063] A fiber optic grating earth pressure monitoring system includes several (the number is set according to project needs) fiber optic grating earth pressure sensors as described above, such as... Figure 14 As shown, the optical cable 8 in the fiber optic earth pressure sensor is connected to the fiber optic demodulator 11, the fiber optic demodulator 11 is connected to the switch 12, and the switch 12 is connected to the server 13.

[0064] The installation method includes the following steps:

[0065] S1: Foundation leveling

[0066] Select the installation location W for the fiber Bragg grating earth pressure sensor and level the foundation at that location.

[0067] S2: Laying the subbase

[0068] Lay a 175mm thick layer of soil or fine sand on the foundation at the installation location W. The particle diameter of both soil and fine sand should not exceed 10mm. Then compact and level the surface.

[0069] S3: Placement of thermal insulation nano-aerogel felt

[0070] The heat-insulating nano-aerogel felt is prepared into an open cube, with a 6mm diameter through hole T left on the side of the open cube for the optical cable 8 to pass through, and the open cube is placed on the pad layer.

[0071] S4: Install sensors and backfill.

[0072] Lay soil or fine sand to a thickness of 25mm in the open cube and compact it. Then place the fiber optic grating soil pressure sensor on the soil or fine sand in the open cube. Lead the optical cable 8 out from the through hole T on the side of the open cube and seal the gap between the optical cable 8 and the through hole T with sealant. Continue to lay soil or fine sand in the open cube and compact it. After the soil or fine sand is laid to the opening of the open cube, cover the opening of the open cube with a cover made of heat-insulating nano aerogel felt and completely seal the cover to the opening of the open cube with sealant. Then backfill with soil or fine sand to meet the construction parameter requirements.

[0073] During use, the fiber Bragg grating demodulator 11 is powered on to acquire data from the monitoring system. After the server 13 completes the IP address setting, the data acquired by the fiber Bragg grating demodulator 11 is synchronously transmitted to the server 13. The fiber Bragg grating soil pressure sensor 10 converts the soil pressure on the top cover 4 into a change in the wavelength of the internal sensing fiber Bragg grating. The soil pressure causes a shift in the resonant wavelength of the fiber Bragg grating through the elastic-optical effect, and then the pressure value is obtained by demodulation by the fiber Bragg grating demodulator.

[0074] In the description of this invention, terms such as "inner," "outer," "upper," "lower," "front," and "rear," which indicate orientation or positional relationship, are used only for the convenience of describing this invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0075] The above description is only one embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A fiber optic grating earth pressure sensor, characterized in that: It includes an outer shell (2), a top cover (4), a spring assembly (5), a measuring optical fiber (6), and an optical cable (8). The outer casing (2) includes a bottomless shell (201), and the side of the shell (201) is provided with an optical cable through hole (206). The spring assembly (5) is fixedly connected to the outer shell (2) and is disposed in the inner cavity of the shell (201); A grating (601) of length Lg is provided in the middle of the measuring fiber (6) along the length direction, and the two ends of the measuring fiber (6) are fixedly connected to the spring assembly (5). The top cover (4) includes a cover plate (401) and a force transmission block (402). The cover plate (401) is fixed to the top of the housing (201) by screws and is used to close the inner cavity of the housing (201). The force transmission block (402) is used to contact the spring assembly (5) to transmit pressure. The position of the force transmission block (402) corresponds to the middle position of the grating (601). When the force transmission block (402) transmits pressure to the spring assembly (5), the spring assembly (5) transmits tension in different directions to both ends of the measuring optical fiber (6). The optical cable (8) is wrapped with a transmission optical fiber (7), and the core of the transmission optical fiber (7) and the measurement optical fiber (6) are fused together. The outer end of the optical cable (8) is placed outside the housing (201) through the optical cable through hole (206). The optical cable (8) is fixedly connected to the optical cable through hole (206) through the connector (9). After the outer shell (2), top cover (4), spring assembly (5), measuring fiber (6) and optical cable (8) are assembled, an external heat insulation coating (1) with a thickness of not less than 2mm is sprayed on the outer surface of the outer shell (2) and top cover (4). Support block A (202) and support block B (204) are fixedly provided on the bottom surface of the inner cavity of the housing (201). The distance between the opposite surfaces of support block A (202) and support block B (204) is Lb, and the distance between their opposite back surfaces is La. The spring assembly (5) includes a spring (501) and a pair of fiber fixing blocks (502). The length of the spring (501) is LA, the distance between the opposite faces of the pair of fiber fixing blocks (502) is LC, and the distance between the opposite faces of the pair of fiber fixing blocks (502) is LB. LA=La, LB<Lb, LC>Lg. The two fiber fixing blocks (502) are respectively fixedly connected to the two ends of the measuring fiber (6). The two ends of the spring (501) are fixedly connected to the support block A (202) and the support block B (204) respectively by screws. The support block B (204) is provided with a fiber optic through hole (205). The fiber optic through hole (205) is used to allow the optical cable (8) to pass through. The joint between the cover plate (401) and the housing (201) is sealed by applying sealant; the joint between the connector (9) and the optical cable through hole (206) is also sealed by applying sealant; thus sealing the inner cavity of the housing (201).

2. The fiber optic grating earth pressure sensor according to claim 1, characterized in that: The bottom and side surfaces of the inner cavity of the housing (201) are coated with an inner thermal insulation coating (3) of not less than 1 mm.

3. The fiber optic grating earth pressure sensor according to claim 2, characterized in that: The outer insulation coating (1) and the inner insulation coating (3) are both made of nano-insulation materials.

4. The fiber optic grating earth pressure sensor according to claim 1, characterized in that: Both support block A (202) and support block B (204) are provided with V-grooves (503). The two ends of the measuring optical fiber (6) are placed in the corresponding V-grooves (503) and are bonded and fixed to the V-grooves (503).

5. The fiber optic grating earth pressure sensor according to claim 1, characterized in that: The outer shell (2) is made of steel, and its Brinell hardness is not less than 200 N / mm². 2 The cover plate (401) is made of beryllium bronze or spring steel.

6. A fiber optic grating earth pressure monitoring system, characterized in that: It includes several fiber Bragg grating earth pressure sensors as described in any one of claims 1-5, wherein the optical cable (8) of the fiber Bragg grating earth pressure sensor is connected to the fiber Bragg grating demodulator (11), the fiber Bragg grating demodulator (11) is connected to the switch (12), and the switch (12) is connected to the server (13).

7. The fiber optic grating earth pressure monitoring system according to claim 6, characterized in that: The installation method is as follows: Includes the following steps: S1: Foundation leveling Select the installation location W for the fiber Bragg grating earth pressure sensor and level the foundation at that location; S2: Laying the subbase Lay a layer of soil or fine sand with a thickness of T1 on the foundation at the installation location W. The particle diameter of the soil and fine sand should not be greater than 10mm. Then compact and level the surface. S3: Placement of thermal insulation nano-aerogel felt The heat-insulating nano-aerogel felt is prepared into an open cube, and a through hole T is left on the side of the open cube for the optical cable (8) to pass through. The open cube is then placed on the pad. S4: Install sensors and backfill. Lay soil or fine sand in the open cube to a thickness of T2 and compact it. Then place the fiber optic grating soil pressure sensor on the soil or fine sand in the open cube. Lead the optical cable (8) out from the through hole T on the side of the open cube and seal the gap between the optical cable (8) and the through hole T with sealant. Continue to lay soil or fine sand in the open cube and compact it. After the soil or fine sand is laid to the opening of the open cube, cover the opening of the open cube with a cover made of heat-insulating nano aerogel felt and seal the cover and the opening of the open cube completely with sealant. Then backfill with soil or fine sand to meet the construction parameter requirements.

8. The fiber optic grating earth pressure monitoring system according to claim 7, characterized in that: In step S2, T1 is 150mm to 200mm; in step S4, T2 is 20mm to 30mm.

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