A Sensitivity-Enhanced FBG Pressure Sensor Based on Circumferential Deformation and Measurement Method

Abstract

The present invention discloses a sensitivity-enhanced FBG pressure sensor based on circumferential deformation and a measurement method, which includes a pressure cell, a spindle, and an optical fiber grating. A spindle is disposed inside the pressure cell, and an optical fiber grating is wound between the pressure cell and the spindle. The optical fiber grating includes a pressure measurement grating and a temperature compensation grating. Among them, the pressure measurement grating is disposed on the spindle, and the temperature compensation grating is disposed on the pressure cell. When the pressure cell is subjected to a normal pressure, the spindle is deformed under the action of bending, and the circumferential perimeter changes. By means of the built-in thin-walled spindle structure, the present invention converts the change in the normal pressure of the sealing cover into the change in the circumferential perimeter of the middle part of the thin-walled spindle. Compared with the linear structural deformation of other sensor structures, especially the diameter-based structural deformation of circular structures, the structural deformation of the pressure sensor of the present invention is Π times that of the diameter-based structural deformation, thereby increasing the strain value of the optical fiber grating and improving the sensitivity of the pressure sensor.

Description

Technical Field

[0001] The present invention relates to an FBG pressure sensor and a measurement method, and particularly to a sensitivity-enhanced FBG pressure sensor based on circumferential deformation and a measurement method. Background Art

[0002] Optical fiber grating pressure sensors have been widely used in various fields due to their good corrosion resistance, electromagnetic interference resistance, and transmission performance. When the FBG (fiber Bragg grating) pressure sensor is subjected to external forces and temperature, the optical fiber grating generates strain, resulting in a change in its central wavelength. Therefore, during pressure measurement, the change value of the grating wavelength can be measured, and then the strain value of the pressure sensor structure can be obtained according to the relationship between strain and wavelength change value. Finally, the actual pressure value can be obtained according to the relationship between strain and pressure corresponding to the pressure sensor structure form. Although there are currently various sensor structure forms, the grating is fixed in a simply supported form at both ends, and the grating generates axial strain through the structural deformation at both ends. According to different structural forms, the pressure sensitivities of each pressure sensor are also different. However, the strength of the grating is not high, and the grating is extremely prone to damage when pulled at both ends, resulting in a low survival rate of the sensor. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to propose a sensitivity-enhanced FBG pressure sensor based on circumferential deformation and a measurement method, so that the grating is subjected to centripetal force, generates circumferential strain, enhances the survival rate of the grating, and at the same time, can effectively improve the sensitivity of the pressure sensor and perform temperature compensation for the measurement environment.

[0004] Technical Solution: The present invention includes a pressure box, a spindle, and an optical fiber grating. A spindle is provided inside the pressure box, and an optical fiber grating is wound between the pressure box and the spindle. The optical fiber grating includes a pressure measurement grating and a temperature compensation grating. Among them, the pressure measurement grating is arranged on the spindle, and the temperature compensation grating is arranged on the pressure box. When the pressure box is subjected to a normal pressure, the spindle is bent and deformed, and the circumferential perimeter changes.

[0005] The spindle adopts a symmetric structure. A pipe groove is provided on one side of the middle part of the spindle, and a groove is provided on the spindle between the two pipe grooves. The pressure measurement grating is arranged in this groove.

[0006] The pressure box includes a box body and a sealing cover. A groove is provided on the inner wall of the box body, and the temperature compensation grating is arranged in this groove. Through holes are provided at both ends of the groove opposite to each other.

[0007] The pressure measurement grating and the temperature compensation grating are connected in series on the optical fiber.

[0008] The optical fiber passes through the through hole on the side wall of the box body, winds around the groove of the box body and the spindle, and then passes out through the through hole on the other side.

[0009] The sealing cover is subjected to normal pressure.

[0010] The top of the spindle is connected to the inner side of the sealing cover, and the bottom is connected to the bottom surface of the box body.

[0011] A measurement method of a FBG pressure sensor with enhanced sensitivity based on annular deformation comprises the following steps:

[0012] (1) Measure the initial wavelength of the pressure measurement grating and the temperature compensation grating;

[0013] (2) When the spindle is subjected to pressure P, the circumference change △C and strain change △ε in the middle part can be expressed as:

[0014]

[0015]

[0016] Wherein, P is the pressure on the thin-walled spindle, t is the wall thickness of the thin-walled spindle, θ is the tilt angle of the thin-walled spindle, R is the inner diameter of the pressure box, r is the radius of the top of the thin-walled spindle, d is the diameter of the middle of the thin-walled spindle, μ is the Poisson's ratio of the thin-walled spindle, and E is the elastic modulus of the thin-walled spindle;

[0017] (3) The relationship between fiber Bragg grating wavelength, strain and temperature is expressed as:

[0018] Δλ=(1-P e )Δε+(α+ξ)ΔT (8)

[0019] Among them, Δλ is the change of FBG wavelength, △ε is the strain change of FBG, P e , α, ξ are the effective photoelastic coefficient, thermal expansion coefficient and thermo-optic coefficient of the optical fiber respectively;

[0020] (4) From the above equations, the relationship between pressure and the actual change in grating wavelength can be obtained as follows:

[0021]

[0022]

[0023] Among them, K P is the pressure sensitivity coefficient of the FBG fiber Bragg grating sensor based on annular deformation.

[0024] Beneficial effects: By means of the built-in thin-walled spindle structure, the present invention converts the change in the normal pressure of the sealing cover into the change in the circumferential perimeter in the middle of the thin-walled spindle. Compared with the linear structural deformation of other sensor structures, especially the structural deformation based on the diameter of the circular structure, the structural deformation of the pressure sensor of the present invention is Π times that of the diameter-based structural deformation, thereby increasing the strain value of the fiber grating and improving the sensitivity of the pressure sensor. A temperature compensation grating is bonded to the inner wall groove of the box body. Since the inner wall of the box body is thick and the circumferential deformation is small, it can effectively reflect the temperature of the measurement environment of the pressure sensor, so as to perform temperature compensation during pressure measurement. The pressure sensor of the present invention can make the grating subject to centripetal force, generate circumferential strain, and enhance the survival rate of the grating. Brief Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0026] Figure 2 It is a schematic diagram of the spindle structure of the present invention;

[0027] Figure 3 It is a schematic diagram of the fiber grating arrangement of the present invention;

[0028] Figure 4 It is a schematic diagram of the box body structure of the present invention;

[0029] Figure 5 It is a schematic diagram of the sealing cover structure of the present invention. Detailed Embodiment

[0030] The present invention will be further described below with reference to the accompanying drawings.

[0031] As Figure 1 shown, the present invention includes a pressure box 1, a spindle 2, and a fiber grating 3. A spindle 2 is provided inside the pressure box 1, and a fiber grating 3 is wound between the pressure box 1 and the spindle 2. The pressure box 1 includes a box body 11 and a sealing cover 12. The box body 11 and the sealing cover 12 are sealed and glued. A groove is provided on the inner wall of the box body 11 to facilitate the bonding of the grating. The groove in this embodiment is a semi-circle with a radius of 1 mm, and a set of through holes are provided through the two opposite ends of the groove, as Figure 4 shown; a circumferentially distributed triangular convex flange is provided in the center of the sealing cover 12, as Figure 5 shown; the spindle 2 adopts a thin-walled structure, as Figure 2 shown, and is a vertically symmetric structure. Its top is adapted to the convex flange on the inner side of the sealing cover 12, and the two are glued and connected. The bottom is glued to the bottom surface of the pressure box 1. A pipe groove is provided on one side of the middle part of the spindle 2, and a groove is provided on the spindle 2 between the two pipe grooves. In this embodiment, pipe grooves are provided at 0° - 90° and 180° - 270° in the middle of the spindle 2 for winding the optical fiber; grooves are provided at 90° - 180° and 270° - 360° for bonding the grating.

[0032] When the sealing cover 12 is under the action of normal pressure, the box body 11 and the top of the spindle 2 make the sealing cover 12 in a continuous simply supported state. The spindle 2 is deformed under the action of bending, and the middle part shows a tendency to expand outwards, and the circumferential perimeter changes. In the present invention, by arranging a thin-walled spindle in the pressure box, the change of the normal pressure of the sealing cover is transformed into the change of the circumferential perimeter of the middle part of the thin-walled spindle, thereby increasing the strain value of the fiber Bragg grating and improving the sensitivity of the pressure sensor.

[0033] As Figure 3 shown, the fiber Bragg grating 3 includes a pressure measurement grating 31 and a temperature compensation grating 32. The pressure measurement grating 31 and the temperature compensation grating 32 are connected in series on the optical fiber. The center wavelength interval between the pressure measurement grating 31 and the temperature compensation grating 32 is 2 nm to 3 nm. The pressure measurement grating 31 is pasted at the middle groove of the spindle 2, and the temperature compensation grating 32 is bonded in the groove on the inner wall of the box body 11. Since the inner wall of the box body 11 is thick and the circumferential deformation is small, it can effectively reflect the measurement ambient temperature of the pressure sensor, so as to perform temperature compensation during pressure measurement. During measurement, the optical fiber passes through one of the through holes on the side wall of the box body 11, winds around the groove of the box body 11 and the spindle 2, and then passes out from the through hole on the other side. Among them, the pressure measurement grating 31 is bonded to the optical fiber at the middle groove of the spindle 2, and the temperature compensation grating 32 is bonded to the optical fiber in the groove of the box body 11.

[0034] A measurement method of a sensitivity-enhanced FBG pressure sensor based on circumferential deformation includes the following steps:

[0035] (1) Measure the initial wavelengths of the pressure measurement grating and the temperature compensation grating;

[0036] (2) By arranging a thin-walled spindle structure in the box body, the normal pressure P received by the sealing cover is transformed into the change of the circumferential perimeter ΔC of the middle part of the thin-walled spindle, so that the fiber Bragg grating wound around the middle part is tensioned to generate a strain Δε = ΔC / C, and the corresponding wavelength change Δλ is recorded. When the thin-walled spindle is under the pressure P, the perimeter change value ΔC and the strain change value Δε occurring in the middle part can be respectively expressed as:

[0037]

[0038]

[0039] Among them, P is the pressure received by the thin-walled spindle, t is the wall thickness of the thin-walled spindle, θ is the inclination angle of the thin-walled spindle, R is the inner diameter of the pressure box, r is the top radius of the thin-walled spindle, d is the middle diameter of the thin-walled spindle, μ is the Poisson's ratio of the thin-walled spindle, and E is the elastic modulus of the thin-walled spindle.

[0040] (3) The relationship expression between the wavelength of the fiber Bragg grating and strain and temperature is as follows:

[0041] Δλ=(1 - P e )Δε+(α + ξ)ΔT (13)

[0042] where Δλ is the change in the wavelength of the FBG, △ε is the change in the strain of the FBG, and P e , α, and ξ are the effective photoelastic coefficient, thermal expansion coefficient, and thermo - optic coefficient of the optical fiber, respectively.

[0043] (4) For the sensitivity - enhanced FBG fiber grating sensor considering the circumferential deformation, a pressure - measuring grating and a temperature - compensating grating are arranged. By subtracting the wavelength change values of the two gratings, the wavelength change value under pressure can be obtained. From the above formulas, the relationship expression between pressure and the actual wavelength change value of the grating is as follows:

[0044]

[0045]

[0046] where K P is the pressure sensitivity coefficient of the sensitivity - enhanced FBG fiber grating sensor based on circumferential deformation.

Claims

1. A measurement method for a sensitivity-enhanced FBG pressure sensor based on circumferential deformation, characterized in that, Including a sensitivity-enhanced FBG pressure sensor based on circumferential deformation, the sensitivity-enhanced FBG pressure sensor includes a pressure cell, a thin-walled spindle, and a fiber Bragg grating. A thin-walled spindle is provided inside the pressure cell, and a fiber Bragg grating is wound between the pressure cell and the thin-walled spindle. The fiber Bragg grating includes a pressure measurement grating and a temperature compensation grating. Among them, the pressure measurement grating is arranged on the thin-walled spindle, and the temperature compensation grating is arranged on the pressure cell. When the pressure cell is subjected to a normal pressure, the thin-walled spindle is deformed by the bending action, and the circumferential perimeter changes; The thin-walled spindle adopts a symmetric structure. A tube groove is provided on one side of the middle part of the thin-walled spindle, and a groove is provided on the thin-walled spindle between the two tube grooves. The pressure measurement grating is arranged in this groove. The pressure cell includes a cell body and a sealing cover. A groove is opened on the inner wall of the cell body, and the temperature compensation grating is arranged in this groove. Through holes are penetrated through the two opposite ends of the groove. The top of the thin-walled spindle is connected to the inner side of the sealing cover, and the bottom is connected to the bottom surface of the cell body; The measurement method includes the following steps: (1) Measure the initial wavelengths of the pressure measurement grating and the temperature compensation grating; (2) When the spindle is subjected to a pressure P, the perimeter change value △C and the strain change value △ε occurring in the middle can be respectively expressed as: where P is the pressure applied to the thin-walled spindle, t is the wall thickness of the thin-walled spindle, θ is the inclination angle of the thin-walled spindle, R is the inner diameter of the pressure cell, r is the top radius of the thin-walled spindle, d is the middle diameter of the thin-walled spindle, μ is the Poisson's ratio of the thin-walled spindle, and E is the elastic modulus of the thin-walled spindle; (3) The relationship expression between the wavelength of the fiber Bragg grating and the strain and temperature is: Δλ=(1 - P e )Δε+(α + ξ)ΔT (3) where Δλ is the change in the wavelength of the FBG, △ε is the strain change value of the FBG, and P e , α, and ξ are the effective photoelastic coefficient, thermal expansion coefficient, and thermo-optic coefficient of the optical fiber, respectively; (4) From the above formulas, the relationship expression between the pressure and the actual change value of the grating wavelength can be obtained as: Among them, K P is the pressure sensitivity coefficient of the sensitivity-enhanced FBG fiber grating sensor based on circumferential deformation.

2. The measuring method of a sensitivity-enhanced FBG pressure sensor based on circumferential deformation according to claim 1, characterized in that The pressure measurement grating and the temperature compensation grating are connected in series on the optical fiber.

3. The measuring method of a sensitivity-enhanced FBG pressure sensor based on circumferential deformation according to claim 2, characterized in that The optical fiber passes through the through hole on the side wall of the cell body, winds around the groove of the cell body and the spindle, and then passes out through the through hole on the other side.

4. The measuring method of a sensitivity-enhanced FBG pressure sensor based on circumferential deformation according to claim 1, characterized in that The sealing cover is subjected to a normal pressure.

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