Measuring method and packaging structure of fiber bragg grating osmometer with built-in temperature compensation

Abstract

The invention discloses a fiber bragg grating osmometer measuring method with built-in temperature compensation and a packaging structure, and relates to the technical field of osmotic pressure measurement, and the key points of the technical scheme are that the fiber bragg grating osmometer comprises a protective shell, and an osmometer internal structure is formed in the protective shell; the packaging structure further comprises a structure head end connected with the pressure measuring part, a structure tail end connected with the temperature measuring part, an induction part arranged in the protective shell and used for transmitting deformation generated by osmotic pressure to the pressure measuring part, and the pressure measuring part arranged in the protective shell, and the pressure measuring part is of a suspension frame structure formed by coupling double bent frames. The two sides of the pressure measurement part are symmetrically provided with installation grooves for placing pressure measurement fiber gratings. The temperature measuring part is arranged in the protective shell, so that the problem that the measurement precision is obviously influenced by the environment temperature change due to the lack of a temperature compensation function of the existing sensor is solved, and the long-term measurement accuracy and reliability of the osmometer in a complex temperature environment are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of osmotic pressure measurement technology, and more specifically, to a measurement method and packaging structure for a fiber Bragg grating osmotic pressure gauge with built-in temperature compensation. Background Technology

[0002] In the field of civil engineering, long-term and stable seepage pressure monitoring of major infrastructure such as dams, slopes, and tunnels is a key link in ensuring their construction and operation safety. Achieving high-precision and high-reliability pressure measurement is of great significance for structural health monitoring.

[0003] Traditional resistance strain gauges or vibrating wire piezometers used in engineering, while technically mature, have inherent drawbacks such as weak electromagnetic interference resistance, susceptibility to lightning strikes, short signal transmission distance, and insufficient long-term stability. They are difficult to meet the high-reliability monitoring requirements in complex environments. Fiber optic grating sensing technology, with its advantages of electromagnetic interference resistance, corrosion resistance, lightning protection, long signal transmission distance, and suitability for multiplexing and networking, provides a new solution for piezometer monitoring.

[0004] However, existing fiber Bragg grating piezometers still have significant shortcomings: In terms of measurement accuracy, common fiber Bragg grating piezometers lack an effective temperature compensation mechanism. Fiber Bragg gratings are sensitive to both ambient temperature and strain. In actual working conditions, temperature changes will cause the grating center wavelength to shift. This shift is coupled with the wavelength change caused by pressure. If it is not distinguished and compensated, it will introduce significant measurement errors, reduce the reliability of the data, and fail to meet the requirements of high-precision long-term monitoring.

[0005] Therefore, in order to solve the above-mentioned technical problems, this application proposes a fiber optic grating piezometer measurement method and packaging structure with built-in temperature compensation. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a measurement method and packaging structure for a fiber Bragg grating piezometer with built-in temperature compensation.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for measuring piezometers with built-in temperature compensation, comprising the following steps: S1. Obtain the total wavelength offset by measuring the pressure of the fiber optic grating; S2. Obtain the center wavelength shift caused by temperature by measuring the fiber optic grating; S3. Subtract the center wavelength shift caused by temperature from the total wavelength shift to obtain the net wavelength shift caused only by osmotic pressure; S4. Calculate the osmotic pressure value based on the net wavelength offset.

[0008] Preferably, during the process of obtaining the total wavelength offset by the pressure measuring fiber grating, the pressure measuring fiber grating is in a pre-loaded stress state and is attached to the inner wall of the pressure measuring part of the fiber grating piezometer encapsulation structure, while the temperature measuring fiber grating is in a free state and is fixed to the temperature measuring part of the fiber grating piezometer encapsulation structure. The steps for fixing fiber Bragg gratings include the following: Pressure measurement fiber optic grating: An axial pre-tension force is applied to the pressure measurement fiber optic grating by a clamp, and while maintaining the axial pre-tension force, it is fixed to the inner wall of the suspension frame of the pressure measurement part using adhesive. Temperature measurement fiber optic grating: The temperature measurement fiber optic grating is fixed to the temperature measurement unit using adhesive under natural stress, so that it is in a mechanically decoupled state.

[0009] Preferably, the method for obtaining the total wavelength offset by measuring the pressure fiber grating is as follows: The permeable stone of the fiber optic piezometer encapsulation structure transmits external osmotic pressure to the pressure-sensing diaphragm. The osmotic pressure deformation generated by the pressure-sensing diaphragm is transmitted to the pressure measuring unit, which then undergoes synchronous deformation. The synchronous deformation is transmitted through the pressure measurement unit, causing the pressure measurement fiber grating, which is in a preloaded stress state, to produce a center wavelength shift, which is the total wavelength shift.

[0010] Preferably, the method for obtaining the center wavelength shift caused by temperature through the temperature measurement fiber optic grating is as follows: The temperature measurement fiber optic grating is in a mechanically decoupled state and is not affected by pressure deformation. Its center wavelength offset is caused only by changes in ambient temperature.

[0011] Preferably, the method for calculating the osmotic pressure value using the net wavelength offset is as follows: The pre-calibrated response relationship between the seepage pressure and the net wavelength offset of the pressure measurement fiber grating is invoked; The response relationship is the proportional relationship between the unit seepage pressure change and the net wavelength offset of the pressure measurement fiber grating; Based on the aforementioned response relationship, the net wavelength shift caused solely by osmotic pressure is converted into the corresponding osmotic pressure value using an external fiber optic grating demodulator. The conversion formula is as follows: P = ΔλP / kP; Wherein, P represents the osmotic pressure value to be determined, ΔλP represents the net wavelength shift caused by osmotic pressure, and the total wavelength shift minus the center wavelength shift caused by temperature; kP represents the pressure sensitivity coefficient of the pressure measurement fiber grating, which is the wavelength shift caused by a unit change in osmotic pressure, determined through pre-calibration.

[0012] A fiber Bragg grating piezometer packaging structure with built-in temperature compensation includes: Protective casing; Pressure measuring unit is installed inside the protective housing; Temperature measuring unit disposed within the protective housing; The sensing component installed inside the protective housing is used to transmit the deformation caused by seepage pressure to the pressure measuring unit; Some of the optical fibers are housed inside the protective housing; A pressure measurement fiber grating coupled to the pressure measurement unit for sensing the deformation of the pressure measurement unit; A temperature measurement fiber grating coupled to the temperature measurement unit for sensing temperature changes; The pressure measuring fiber grating and the temperature measuring fiber grating are fabricated on the optical fiber. The pressure measuring part is a suspension frame structure coupled by two bending frames. The pressure measuring part has mounting slots symmetrically opened on both sides to place the pressure measuring fiber grating.

[0013] Preferably, it further includes a structural head end connected to the pressure measuring unit and a structural tail end connected to the temperature measuring unit, wherein the structural tail end has a communication portion and the pressure-sensing diaphragm is disposed at the communication portion.

[0014] Preferably, the sensing element is a pressure-sensitive diaphragm that deforms in response to external seepage pressure.

[0015] Preferably, the tail end of the structure is provided with a permeable water-permeable element, which is connected to the pressure-sensitive membrane and transmits external osmotic pressure to the pressure-sensitive membrane. The water-permeable element is a permeable stone.

[0016] Preferably, the protective housing is provided with a tail sleeve terminal for connecting to an external device, and the optical fiber extends through the tail sleeve terminal to the outside of the protective housing.

[0017] Compared with the prior art, the present invention has the following beneficial effects: In this invention, by employing different packaging processes, the two gratings are placed in different mechanical states, with the pressure grating in a pre-stretched state and the temperature grating in a stress-decoupled state. Real-time compensation is performed using the pure temperature reference signal provided by the temperature grating, effectively distinguishing the optical response caused by pressure and temperature changes. This solves the problem that the measurement accuracy of existing sensors is significantly affected by changes in ambient temperature due to the lack of temperature compensation function, and significantly improves the long-term measurement accuracy and reliability of the piezometer in complex temperature environments. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the overall structure of the present invention; Figure 3 This is a schematic diagram of the overall internal structure of the present invention; Figure 4 This is a schematic diagram of the overall internal structure of the present invention from another perspective; Figure 5 This is a schematic diagram of the pressure measuring unit and temperature measuring unit in this invention.

[0019] 1. Protective casing; 20. Structural head end; 21. Structural tail end; 22. Pressure measuring unit; 23. Temperature measuring unit; 24. Mounting slot; 30. Optical fiber; 31. Pressure measurement fiber grating; 32. Temperature measurement fiber grating; 4. Permeable stone; 5. Pressure-sensitive diaphragm; 6. Tail sleeve terminal. Detailed Implementation

[0020] Example 1

[0021] like Figure 5 As shown, this invention provides a method for measuring fiber optic grating piezometers with built-in temperature compensation: It should be noted that the physical basis of this method is the sensing principle of gratings: when the strain on the grating or the ambient temperature changes, it will cause the grating pitch to change, which in turn causes the center wavelength of its reflection or transmission to shift. This wavelength shift is linearly related to the amount of strain and temperature change. The key innovation of this method lies in: Physical signal separation: By encapsulating the pressure measurement fiber grating 31 in a pre-loaded stress state on the pressure measurement unit 22, it can respond to both the strain caused by pressure and the change in ambient temperature. At the same time, the temperature measurement fiber grating 32 is encapsulated in a free state, i.e., a stress decoupled state, on the temperature measurement unit 23, so that its optical signal only responds to the change in ambient temperature and is independent of mechanical stress. Mathematical compensation algorithm: Using the "pure" temperature reference signal provided by the temperature measurement fiber optic grating 32, the interference caused by temperature change is subtracted from the mixed signal measured by the pressure measurement fiber optic grating 31, thereby solving for the true signal caused only by osmotic pressure.

[0022] Includes the following steps: S1. Obtain the total wavelength offset by measuring the pressure of the fiber optic grating 31; During the process of obtaining the total wavelength offset by the pressure measuring fiber grating 31, the pressure measuring fiber grating 31 is in a preloaded stress state and is attached to the inner wall of the pressure measuring part 22 of the fiber grating piezometer encapsulation structure, while the temperature measuring fiber grating 32 is in a free state and is fixed to the temperature measuring part 23 of the fiber grating piezometer encapsulation structure. The steps for fixing fiber Bragg gratings include the following: Pressure measuring fiber optic grating 31: An axial pre-tension force is applied to the pressure measuring fiber optic grating 31 by a clamp, and while maintaining the axial pre-tension force, it is fixed to the inner wall of the suspension frame of the pressure measuring part 22 using adhesive. Temperature measuring fiber optic grating 32: The temperature measuring fiber optic grating 32 is fixed to the temperature measuring part 23 with adhesive under natural stress, so that it is in a mechanically decoupled state; It should be noted that the following steps are involved in fixing the fiber Bragg grating: Pressure measuring fiber optic grating 31: The pressure measuring fiber optic grating 31 is bonded to the inner wall of the suspension frame of the pressure measuring unit 22 by high-temperature adhesive to form an integral unit. An axial pre-tension force is applied to the pressure measuring fiber optic grating 31 by a clamp, and while maintaining the axial pre-tension force, it is fixed to the inner wall of the suspension frame of the pressure measuring unit 22 by adhesive. Temperature measuring fiber optic grating 32: The temperature measuring fiber optic grating 32 is fixed to the surface of the temperature measuring part 23 without stress by high temperature glue. The temperature measuring fiber optic grating 32 is fixed to the temperature measuring part 23 by adhesive under natural stress, so that it is in a mechanically decoupled state. The total wavelength offset is obtained by measuring the pressure of fiber optic grating 31, as follows: The permeable stone 4 of the fiber optic piezometer encapsulation structure transmits the external osmotic pressure to the pressure-sensing diaphragm 5. The osmotic pressure deformation generated by the pressure-sensing diaphragm 5 is transmitted to the pressure measuring unit 22, and the pressure measuring unit 22 undergoes synchronous deformation. Synchronous deformation is transmitted through pressure measurement unit 22, causing the pressure measurement fiber optic grating 31, which is in a preloaded stress state, to produce a center wavelength shift, which is the total wavelength shift. It should be noted that the osmotic pressure in the environment under test is transmitted to the pressure-sensitive diaphragm 5 through the permeable stone 4. The pressure-sensitive diaphragm 5 undergoes slight deformation under the action of osmotic pressure. This deformation is transmitted to the pressure measuring unit 22 through the mechanical structure, causing the structure of the pressure measuring unit 22 to undergo corresponding elastic deformation. In this embodiment, the pressure-sensitive diaphragm 5 is made of a metal sheet or a polymer material sheet with good elasticity and high stability. It can undergo significant and recoverable deformation under external seepage pressure. It is sealed and fixed to the inner end face of the protective shell 1 by laser welding or high-temperature brazing process and is located inside the permeable stone 4. The pressure-sensitive diaphragm 5 has good elasticity and fatigue resistance characteristics and can generate recoverable deformation in response to changes in external seepage pressure.

[0023] S2. Obtain the center wavelength shift caused by temperature by measuring the fiber optic grating 32; The temperature-induced center wavelength shift is obtained by measuring the fiber optic grating 32, as follows: The temperature measurement fiber optic grating 32 is in a mechanically decoupled state and is not affected by pressure deformation. Its center wavelength shift is only caused by changes in ambient temperature. It should be noted that, almost simultaneously, the change in ambient temperature causes a shift in the center wavelength of the temperature measurement fiber optic grating 32. Since the grating is in a mechanically free state, its wavelength shift is purely caused by temperature changes, thus providing a pure temperature reference signal that is not affected by pressure. S3. Subtract the center wavelength shift caused by temperature from the total wavelength shift to obtain the net wavelength shift caused only by osmotic pressure; Using an external fiber optic demodulator, the center wavelength signals of the pressure measurement fiber optic grating 31 and the temperature measurement fiber optic grating 32 are synchronously acquired through the same fiber optic cable 30. Ambient temperature changes affect both the pressure measurement fiber grating 31 and the temperature measurement fiber grating 32. Since the temperature measurement fiber grating 32 is encapsulated in a stress-decoupled state, the offset of its center wavelength is caused only by temperature changes, and therefore it can be used as a pure temperature reference signal. The difference between the total center wavelength offset measured by the pressure measurement fiber grating 31 and the interference center wavelength offset calculated in the previous step, which is purely caused by temperature change, is the net wavelength offset caused only by osmosis pressure. It should be noted that this step is the key to temperature compensation. First, based on the center wavelength offset of the temperature measurement fiber grating 32 and its known temperature sensitivity characteristics, the current change in ambient temperature is calculated. Then, based on the sensitivity characteristics of the pressure measurement fiber grating 31 to temperature changes, the magnitude of the temperature change will cause a center wavelength offset in the pressure channel. This step essentially converts the temperature reference signal into an estimate of the interference to the pressure channel. S4. Calculate the seepage pressure value based on the net wavelength offset; The method for calculating the osmotic pressure value using net wavelength offset is as follows: The pre-calibrated pressure measurement fiber grating 31 is invoked to determine the response relationship between the seepage pressure and the net wavelength offset; The response relationship is the proportional relationship between the unit osmotic pressure change of the pressure measurement fiber grating 31 and the net wavelength offset. Based on the response relationship, the net wavelength shift caused solely by osmotic pressure is converted into the corresponding osmotic pressure value using an external fiber optic grating demodulator. The conversion formula is as follows: P = ΔλP / kP; Where P represents the osmotic pressure value to be determined, ΔλP represents the net wavelength shift caused by osmotic pressure, and the net wavelength shift is the total wavelength shift minus the center wavelength shift caused by temperature; kP represents the pressure sensitivity coefficient of the pressure measurement fiber grating 31, and the pressure sensitivity coefficient is the wavelength shift caused by a unit change in osmotic pressure, which is determined by pre-calibration. In this embodiment, an external fiber optic demodulator (an instrument used for fiber optic measurement in the prior art) synchronously acquires the center wavelengths of the pressure measuring fiber optic grating 31 and the temperature measuring fiber optic grating 32. The data processing of the fiber optic demodulator first calculates the current change in ambient temperature based on the center wavelength offset of the temperature measuring fiber optic grating 32 and its known temperature sensitivity coefficient. Then, based on the known temperature sensitivity coefficient of the pressure measuring fiber optic grating 31, it calculates the wavelength offset caused by the temperature change to the pressure channel. Finally, by subtracting the thermally induced offset from the total wavelength offset of the pressure channel, the true wavelength offset caused only by the change in osmotic pressure can be obtained. Then, the accurate external osmotic pressure value is calculated based on its pressure sensitivity coefficient. In addition, it includes a calibration step for pre-determining the temperature sensitivity coefficient of the temperature measurement fiber grating 32, the temperature sensitivity coefficient of the pressure measurement fiber grating 31, and the pressure sensitivity coefficient. In addition, to ensure measurement accuracy, a calibration step (existing technology) is required before implementing this method. The purpose of this step is to measure the temperature sensitivity of the temperature measuring fiber grating 32 and the temperature sensitivity coefficient and pressure sensitivity coefficient of the pressure measuring fiber grating 31 (the sensitivity coefficients are all pre-set known quantities). This step is used to accurately determine the temperature sensitivity of the temperature measuring fiber grating 32, the temperature sensitivity of the pressure measuring fiber grating 31, and the pressure sensitivity in advance. These calibration parameters will serve as the reference in the above calculation process.

[0024] Example 2

[0025] like Figures 2-5 As shown, the present invention provides a fiber Bragg grating piezometer packaging structure with built-in temperature compensation, comprising: The protective housing 1 contains an internal structure of a piezometer. The encapsulation structure also includes a structural head end 20 connected to the pressure measuring unit 22 and a structural tail end 21 connected to the temperature measuring unit 23. A sensing component is disposed within the protective housing 1 to transmit the deformation generated by osmosis to the pressure measuring unit 22. The structural tail end 21 has a communication point, and a pressure-sensing diaphragm 5 is disposed at the communication point. The end of the structural tail end 21 is provided with a permeable water-permeable element. The water-permeable element is made of porous material and is connected to the pressure-sensing diaphragm 5 to transmit external osmosis to the pressure-sensing diaphragm 5. The water-permeable element is a permeable stone 4, which can be a sintered metal permeable stone 4 or a ceramic permeable stone 4. The pressure measuring unit 22 is installed inside the protective housing 1. The pressure measuring unit 22 is a suspension frame structure formed by double bending frame coupling. The two sides of the pressure measuring unit 22 are symmetrically provided with mounting slots 24 for placing the pressure measuring fiber optic grating 31; the temperature measuring unit 23 is installed inside the protective housing 1. It should be noted that the deformation of the sensing diaphragm caused by the seepage pressure from the permeable stone 4 directly acts on the temperature measuring unit 23. The temperature measuring unit 23 and the pressure measuring unit 22 are coupled. Due to its robust structure, the temperature measuring unit 23 transmits the deformation pressure from the sensing diaphragm to the pressure measuring unit 22. Since the pressure measuring unit 22 is a double-bend suspension frame structure, the suspension frame structure also deforms when the sensing diaphragm deforms. It should be noted that in this embodiment, the protective shell 1 is made of stainless steel with precision machining. Its interior forms a sealed accommodating chamber. The whole has good mechanical strength and corrosion resistance, and is suitable for long-term installation in harsh engineering environments. One end of the protective shell 1 is provided with an installation interface for fixing the permeable stone 4. The permeable stone 4 is preferably a loose and porous structure made of sintered stainless steel or ceramic material, which can effectively filter impurities and allow the liquid or gas medium to be tested to permeate.

[0026] A pressure measuring fiber grating 31 is coupled to the pressure measuring unit 22 to sense the deformation of the pressure measuring unit 22; a temperature measuring fiber grating 32 is coupled to the temperature measuring unit 23 to sense temperature changes; the pressure measuring fiber grating 31 is encapsulated and bonded to the inner wall of the suspension frame of the pressure measuring unit 22 in a pre-loaded stress state, and the temperature measuring fiber grating 32 is encapsulated and fixed to the temperature measuring unit 23 in a free state; a high-temperature adhesive is provided on the inner wall of the suspension frame of the pressure measuring unit 22 to make the pressure measuring fiber grating 31 and the inner wall of the suspension frame adhere tightly to each other; a high-temperature adhesive is provided on the surface of the temperature measuring unit 23 to fix the stress-free temperature measuring fiber grating 32 to the surface of the temperature measuring unit 23. The pressure measurement fiber grating 31 is encapsulated and fixed in a preloaded stress state. The preloaded stress state of the pressure measurement fiber grating 31 is achieved by applying axial prestress to it during encapsulation to measure the pressure change. The temperature measurement fiber grating 32 is encapsulated and fixed in a stress decoupling state. The stress decoupling state of the temperature measurement fiber grating 32 is achieved by fixing it in a region inside the optical fiber that is not affected by mechanical deformation, so that its optical signal only responds to the change of ambient temperature. The pressure measurement fiber grating 31 is cured and encapsulated under pre-stress by a high-bonding epoxy resin adhesive, while the temperature measurement fiber grating 32 is cured and encapsulated under free state by a high-bonding epoxy resin adhesive. It should be noted that the pressure measuring fiber optic grating 31 measures pressure through optical signals. It does not directly receive pressure itself, but rather transforms physical quantities such as the deformation of the pressure-sensing diaphragm 5 and the prestress applied by the pressure measuring fiber optic grating 31 itself into strain that it can sense, and finally presents it through changes in optical signals. The packaging state of the pressure sensing component is different from that of the temperature reference component. The pressure sensing module acquires optical signals related to osmotic pressure, and the temperature compensation module acquires optical signals related to temperature. The two signals are processed together to eliminate errors and realize temperature self-compensation for osmotic pressure measurement. In the embodiments, the key packaging processes are described as follows: After the pressure measuring fiber optic grating 31 is placed in an axial pre-stretched state by a special fiber optic clamp, it is firmly bonded and fixed to the inside of the fiber optic and the temperature measuring part 23 by a high-strength epoxy resin adhesive, thereby sensitively receiving the strain transmitted by the pressure-sensitive diaphragm 5. The temperature measurement fiber grating 32 is fixed inside the fiber 30 under natural stress (i.e., free state) and is located in the non-stressed area of ​​the internal structure of the piezometer, so that its optical response is only sensitive to changes in ambient temperature and is decoupled from mechanical stress.

[0027] The protective housing 1 is provided with a tail sleeve terminal 6 for connecting to external devices, and an optical fiber extends through the tail sleeve terminal 6 to the outside of the protective housing 1; It should be noted that the pressure measuring fiber grating 31 and the temperature measuring fiber grating 32 are engraved on the same optical fiber 30. The optical fiber 30 passes through the tail sleeve terminal 6 located at the other end of the protective housing 1 and leads out to the outside. The tail sleeve terminal 6 is filled with sealant to ensure the airtightness of the housing.

[0028] Its specific working principle is as follows: External seepage pressure changes are transmitted to the pressure-sensing diaphragm 5 through the permeable stone 4. The diaphragm deforms under the pressure from the permeable stone 4, and this deformation directly acts on the temperature measuring unit 23. The temperature measuring unit 23 and the pressure measuring unit 22 are coupled. Due to its robust structure, the temperature measuring unit 23 transmits the deformation pressure from the diaphragm to the pressure measuring unit 22. Since the pressure measuring unit 22 is a double-bend suspension frame structure, the suspension frame structure also deforms when the diaphragm deforms. This deformation is further transmitted to the pressure measuring fiber optic grating 31 coupled with it, causing a change in its grating pitch, which in turn causes a shift in its center wavelength. This wavelength shift includes the optical response caused by both the actual seepage pressure change and the temperature change. Ambient temperature changes affect both the pressure measurement fiber grating 31 and the temperature measurement fiber grating 32. Since the temperature measurement fiber grating 32 is encapsulated in a stress-decoupled state, the offset of its center wavelength is caused only by temperature changes, and therefore it can be used as a pure temperature reference signal. An external fiber optic demodulator (an instrument used for fiber optic grating measurement in the prior art) synchronously acquires the center wavelengths of the pressure measuring fiber optic grating 31 and the temperature measuring fiber optic grating 32. The data processing of the fiber optic demodulator first calculates the current change in ambient temperature based on the center wavelength offset of the temperature measuring fiber optic grating 32 and its known temperature sensitivity coefficient. Then, based on the known temperature sensitivity coefficient of the pressure measuring fiber optic grating 31, it calculates the wavelength offset caused by the temperature change to the pressure channel. Finally, by subtracting the thermally induced offset from the total wavelength offset of the pressure channel, the true wavelength offset caused only by the change in osmotic pressure can be obtained. Then, the accurate external osmotic pressure value is calculated based on its pressure sensitivity coefficient.

[0029] All parts not covered in this invention are the same as or can be implemented using existing technologies.

[0030] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the description above. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for measuring piezometers with built-in temperature compensation, characterized in that, Includes the following steps: S1. Obtain the total wavelength offset by measuring the pressure of the fiber optic grating (31); S2. Obtain the center wavelength shift caused by temperature by measuring the fiber optic grating (32); S3. Subtract the center wavelength shift caused by temperature from the total wavelength shift to obtain the net wavelength shift caused only by osmotic pressure; S4. Calculate the osmotic pressure value based on the net wavelength offset.

2. The method for measuring fiber optic grating piezometers with built-in temperature compensation according to claim 1, characterized in that: During the process of obtaining the total wavelength offset by the pressure measuring fiber grating (31), the pressure measuring fiber grating (31) is in a preloaded stress state and is attached to the inner wall of the pressure measuring part (22) of the fiber grating piezometer encapsulation structure, while the temperature measuring fiber grating (32) is in a free state and is fixed to the temperature measuring part (23) of the fiber grating piezometer encapsulation structure. The steps for fixing fiber Bragg gratings include the following: Pressure measuring fiber optic grating (31): An axial pre-tension force is applied to the pressure measuring fiber optic grating (31) by a clamp, and while maintaining the axial pre-tension force, it is fixed to the inner wall of the suspension frame of the pressure measuring part (22) using an adhesive. Temperature measuring fiber optic grating (32): The temperature measuring fiber optic grating (32) is fixed to the temperature measuring part (23) with adhesive under natural stress, so that it is in a mechanically decoupled state.

3. The method for measuring fiber optic grating piezometers with built-in temperature compensation according to claim 2, characterized in that: The total wavelength offset is obtained by measuring the pressure of the fiber optic grating (31) as follows: The external osmotic pressure is transmitted to the pressure-sensing diaphragm (5) through the permeable stone (4) of the fiber optic piezometer encapsulation structure. The osmotic pressure deformation generated by the pressure-sensing diaphragm (5) is transmitted to the pressure measuring unit (22), and the pressure measuring unit (22) undergoes synchronous deformation. The synchronous deformation is transmitted through the pressure measuring unit (22), causing the pressure measuring fiber grating (31) in the preloaded stress state to produce a center wavelength shift, which is the total wavelength shift.

4. The method for measuring fiber optic grating piezometers with built-in temperature compensation according to claim 2, characterized in that: The temperature-induced center wavelength shift is obtained by measuring the fiber optic grating (32) using the temperature measurement method as follows: The temperature measurement fiber grating (32) is in a mechanically decoupled state and is not affected by pressure deformation. Its center wavelength offset is caused only by changes in ambient temperature.

5. The method for measuring fiber optic grating piezometers with built-in temperature compensation according to claim 4, characterized in that: The method for calculating the osmotic pressure value using the net wavelength offset is as follows: The response relationship between the seepage pressure and the net wavelength offset of the pre-calibrated pressure measurement fiber grating (31) is invoked; Based on the aforementioned response relationship, the net wavelength shift caused solely by osmotic pressure is converted into the corresponding osmotic pressure value using an external fiber optic grating demodulator. The conversion formula is as follows: P = ΔλP / kP; Where P represents the osmotic pressure value to be determined, ΔλP represents the net wavelength offset caused by osmotic pressure, and kP represents the pressure sensitivity coefficient of the pressure measurement fiber grating (31).

6. A fiber Bragg grating piezometer encapsulation structure with built-in temperature compensation, applied to the measurement method of a fiber Bragg grating piezometer with built-in temperature compensation as described in any one of claims 1-5, characterized in that, include: Protective casing (1); Pressure measuring unit (22) is installed inside the protective housing (1); Temperature measuring unit (23) is installed inside the protective housing (1); The sensing component installed inside the protective housing (1) is used to transmit the deformation caused by seepage pressure to the pressure measuring unit (22). Optical fiber (30) partially disposed inside the protective housing (1); A pressure measurement fiber grating (31) is coupled to the pressure measurement unit (22) for sensing the deformation of the pressure measurement unit (22); A temperature measurement fiber grating (32) is coupled to the temperature measurement unit (23) for sensing temperature changes. The pressure measuring fiber grating (31) and the temperature measuring fiber grating (32) are fabricated on the optical fiber (30). The pressure measuring part (22) is a suspension frame structure formed by double bending frame coupling. The pressure measuring part (22) has mounting slots (24) symmetrically opened on both sides for placing the pressure measuring fiber grating (31).

7. The packaging structure of a fiber Bragg grating piezometer with built-in temperature compensation according to claim 6, characterized in that: It also includes a structural head end (20) connected to the pressure measuring unit (22) and a structural tail end (21) connected to the temperature measuring unit (23), the structural tail end (21) having a communication point, and the pressure-sensing diaphragm (5) being disposed at the communication point.

8. The fiber Bragg grating piezometer packaging structure with built-in temperature compensation according to claim 6, characterized in that: The sensing component is a pressure-sensitive diaphragm (5) that deforms in response to external seepage pressure.

9. The packaging structure of a fiber Bragg grating piezometer with built-in temperature compensation according to claim 7, characterized in that: The end of the tail end (21) of the structure is provided with a permeable water-permeable element. The water-permeable element is connected to the pressure-sensitive membrane (5) and transmits external osmosis pressure to the pressure-sensitive membrane (5). The water-permeable element is a permeable stone (4).

10. The packaging structure of a fiber Bragg grating piezometer with built-in temperature compensation according to claim 6, characterized in that: The protective housing (1) is provided with a tail sleeve terminal (6) for connecting to external devices, and the optical fiber (30) extends through the tail sleeve terminal (6) to the outside of the protective housing (1).

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