Fiber grating pressure sensor

Abstract

The utility model relates to the technical field of sensors, in particular to a fiber bragg grating pressure sensor. Comprising an optical fiber, an elastic membrane, a dowel bar and a mounting seat, one end of the dowel bar is connected with the elastic membrane, and the other end of the dowel bar is in sliding connection with the mounting seat through a sliding block; the optical fiber is provided with a first grating section and a second grating section, one end of the first grating section is fixedly connected with the mounting seat, and the other end of the first grating section is fixedly connected with the sliding block; one end of the second grating section is fixedly connected with the sliding block, and the other end of the second grating section is fixedly connected with the mounting seat; and the elastic diaphragm generates axial deformation under external pressure to drive the dowel bar and the sliding block to move axially so as to drive the first grating section to perform stretching motion and simultaneously drive the second grating section to perform compression motion. According to the utility model, temperature compensation is realized by using a differential compensation principle, and errors caused by temperature change are offset, so that the measurement precision of the sensor is effectively improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to sensor technical field more specifically, relate to a kind of fiber grating pressure sensor. BACKGROUND

[0002] Seawater pressure is one of the important parameters of ocean observation, which has important significance for marine disaster warning, oceanography research, marine environmental protection and development. At the same time, in the study of the profile of marine chemical and physical parameters, seawater pressure is also an important index that cannot be ignored; especially for monitoring tsunami waves. At present, China's marine environmental monitoring depth equipment is usually based on acoustic, mechanical and electrical sensing technology to measure. Mechanical solutions such as float sensors are not easily affected by atmospheric pressure and seawater density, and are low in equipment cost. However, mechanical resolution is low, and they are easily damaged mechanically and cause high maintenance costs. Radar-based sensors (using radio frequency or ultrasonic waves) are a common solution, as the sensor head does not come into direct contact with the liquid, dust and steam are mixed in the medium, and temperature changes will interfere with the reflected waves, reducing sensor performance. Waveguide radar can control wave propagation and overcome problems related to environmental influences, but the liquid level probe will produce accumulation or coating in use. Although electronic pressure sensors such as piezoresistive sensors have good performance, mature manufacturing process and easy integration, they are generally complex in structure, difficult to deploy, susceptible to electromagnetic interference, and cannot meet the requirements of extreme environment monitoring.

[0003] With the rapid development of optical fiber sensing technology, many optical fiber sensors have been developed for ocean sensing and detection. The fiber grating-based seabed pressure sensor is a sensor for monitoring seabed depth and pressure changes. Its principle is to use the sensitivity of fiber grating to light wavelength to detect changes in pressure. Specifically, fiber grating uses the periodic refractive index change structure in the optical fiber to form the reflection and diffraction of optical wavelength, and this periodic change in refractive index can be changed by external pressure and other factors. When the fiber grating is subjected to external pressure, its periodic structure will change, causing the reflected light wavelength to shift. By measuring the change in light wavelength, the size of the external pressure can be determined. However, the fiber grating is also affected by the external environment temperature when it is subjected to external stress changes, resulting in a large difference in the detected stress results and affecting the accuracy of the sensor. Utility model content

[0004] The utility model aims at overcoming the deficiency that the existing technology fiber grating sensor is easily affected by temperature and affects the measurement accuracy, and provides a kind of fiber grating pressure sensor, which can effectively reduce the influence of temperature, thereby improving the measurement accuracy of the sensor.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0006] A fiber Bragg grating pressure sensor is provided, comprising: an optical fiber, an elastic diaphragm, a force transmission rod, and a mounting base; one end of the force transmission rod is connected to the elastic diaphragm, and the other end is slidably connected to the mounting base via a slider; the optical fiber has a first grating segment and a second grating segment, one end of the first grating segment is fixedly connected to the mounting base, and the other end is fixedly connected to the slider; one end of the second grating segment is fixedly connected to the slider, and the other end is fixedly connected to the mounting base; the elastic diaphragm undergoes axial deformation under external pressure, driving the force transmission rod and the slider to move axially, thereby causing the first grating segment to achieve tensile motion and simultaneously causing the second grating segment to achieve compressive motion.

[0007] This utility model provides a fiber Bragg grating pressure sensor. One side of the elastic diaphragm is in contact with the outside environment to receive pressure from the outside, while the other side is connected to a force transmission rod. Under external pressure, the diaphragm undergoes axial elastic deformation, which is transmitted to the force transmission rod, causing it to move axially, thus moving the slider accordingly. Since the two ends of the optical fiber are fixed to the two ends of the mounting base, and the middle of the optical fiber is fixedly connected to the slider (i.e., the first and second grating segments are located on opposite sides of the slider), when the slider moves, it stretches the first grating segment and compresses the second grating segment. The first grating segment converts the axial deformation of the stretched optical fiber into a change in optical signal, and the second grating segment converts the axial deformation of the compressed optical fiber into a change in optical signal. Because the first and second grating segments are located at the same ambient temperature, the drift caused by temperature is also the same. Therefore, the first and second grating segments can utilize the differential compensation principle to achieve temperature compensation, offsetting errors caused by temperature changes, thereby effectively improving the measurement accuracy of the sensor.

[0008] Furthermore, both the first and second grating segments are suspended in the air. This suspension avoids contact with other structures that could cause friction and thus affect deformation.

[0009] Furthermore, the length values ​​of the first grating segment and the second grating segment are the same.

[0010] Furthermore, the first grating segment and the second grating segment have the same temperature sensitivity and pressure sensitivity. Both the first and second grating segments are simultaneously affected by strain and temperature, and the temperature sensitivity coefficients of the two grating segments are consistent. The first grating segment measures positive strain, and the second grating segment measures negative strain. The two strains are equal in magnitude and opposite in direction.

[0011] Further, the force transmission rod is arranged perpendicularly to the elastic diaphragm, and the force transmission rod is connected to the center of the elastic diaphragm; and the optical fiber is arranged in parallel to the force transmission rod. When the elastic diaphragm is subjected to pressure, the deformation is the largest at the center; the force transmission rod is parallel to the optical fiber, and the axial deformation of the elastic diaphragm can be converted into the axial deformation of the optical fiber.

[0012] Further, the utility model further includes the shell that is internally equipped with containing cavity, one end of shell is equipped with first through -hole, the other end is equipped with second through -hole for optical fiber passes through, the elastic diaphragm is sealedly installed in first through -hole, first grating section, second grating section, force transmission rod, mounting seat are all encapsulated in the shell, the elastic diaphragm is installed at one end of shell, and one side of elastic diaphragm is located in the shell for contacting with outside, and one side is located in the shell and contacts with force transmission rod, and first grating section, second grating section, force transmission rod and mounting seat are all encapsulated in the shell interior, and the influence of outside environment is avoided, and the other end of optical fiber passes out from second through -hole and is connected with detection device.

[0013] Further, the utility model further includes the mounting ring, the elastic diaphragm is coaxially sealedly installed in the ring of mounting ring, and the mounting ring is sealedly installed in first through -hole, the elastic diaphragm is circular structure, and the elastic diaphragm is installed in the ring of mounting ring and is sealedly connected with mounting ring, and mounting ring is sealedly connected with shell, in the utility model, first through -hole is circular structure, and is equipped with internal thread structure in first through -hole, and is equipped with external thread structure in mounting ring, and mounting ring is threadedly connected with shell, when connecting, and is sleeved with sealing washer, realizes the sealed connection of mounting ring and shell.

[0014] Further, the utility model further includes the clamping flange, the clamping flange is fixedly installed on mounting ring, one end of mounting seat is fixedly installed in shell through clamping flange, and the clamping flange is equipped with third through -hole for force transmission rod passes through, the clamping flange is fixed in shell, and one end of mounting seat is fixedly connected with clamping flange, and realizes the installation and fixed of mounting seat through clamping flange, and is equipped with the fourth through -hole that is coaxial with third through -hole on mounting seat, and force transmission rod is connected with slider after passing through third through -hole and fourth through -hole in sequence.

[0015] Further, the utility model further includes the mounting seat on being equipped with recess, the recess bottom is equipped with guide rail, the slider is slidably connected with the guide rail, and first grating section and second grating section are both suspended and arranged in the recess, and are equipped with recess on mounting seat, realize the fixed of first grating section and second grating section, and can also guarantee the suspended arrangement, and the slider is located in the middle position of recess, and the guide rail is located in the position corresponding to second grating section, so that the recess is divided into two chambers: left chamber and right chamber by the slider, left chamber corresponds first grating section, right chamber corresponds second grating section, and the guide rail is located at the bottom of right chamber, and when the slider slides, moves to right chamber, so as to realize the stretching movement of first grating section and the compression movement of second grating section.

[0016] Further, the shell is internally provided with a mounting platform with a planar structure, the bottom of the mounting seat is a planar structure, the mounting seat is placed on the mounting platform, and the bottom of the mounting seat is in contact with the mounting platform. The bottom of the mounting seat is connected with the shell, which not only provides stable support, but also realizes rapid and uniform distribution of the internal temperature of the left and right cavities, effectively reduces the measurement error caused by temperature inconsistency of the two grating segments under different temperature fields, and further improves the precision of differential measurement and temperature compensation capability.

[0017] Compared with the prior art, the utility model has the advantages that:

[0018] The fiber grating pressure sensor of the utility model, the first grating segment converts the axial deformation of the fiber elongation into the change of the optical signal, the second grating segment converts the axial deformation of the fiber compression into the change of the optical signal, because the environment temperature of the first grating segment and the second grating segment is same, the drift caused by temperature influence is same, therefore, the first grating segment and the second grating segment can realize temperature compensation by using differential compensation principle, offset the error caused by temperature change, can effectively reduce the influence caused by temperature, thereby improve the measurement precision of the sensor. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is the whole structure schematic view of the fiber grating pressure sensor in example 1;

[0020] Figure 2 It is the three-dimensional schematic view of the fiber grating pressure sensor in example 1;

[0021] Figure 3 It is the internal structure schematic view of the fiber grating pressure sensor in example 1;

[0022] Figure 4 It is the change curve diagram of grating ambient temperature with time in example 2;

[0023] Figure 5 It is the change curve diagram of FBG1 and FBG2 ambient temperature difference with time in example 2;

[0024] Figure 6 It is the change curve diagram of FBG1 and FBG2 center wavelength with pressure in example 3;

[0025] Figure 7 It is the change curve diagram of FBG1 and FBG2 center wavelength with temperature in example 4.

[0026] In the attached diagram: 1. Optical fiber; 2. Elastic diaphragm; 3. Force transmission rod; 4. Mounting base; 5. First grating segment; 6. Second grating segment; 7. Slider; 8. Mounting ring; 9. Clamping flange; 10. Guide rail; 11. First through hole; 12. Housing. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only, representing schematic diagrams rather than actual physical objects, and should not be construed as limiting the present invention. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0028] In the accompanying drawings of this utility model, the same or similar reference numerals correspond to the same or similar components. In the description of this utility model, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing this utility model and simplifying the description, 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, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this utility model. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0029] Example 1

[0030] This embodiment is a first embodiment of a fiber optic grating pressure sensor, such as... Figures 1 to 3 As shown, it includes: an optical fiber 1, an elastic diaphragm 2, a force transmission rod 3, and a mounting base 4; one end of the force transmission rod 3 is connected to the elastic diaphragm 2, and the other end is slidably connected to the mounting base 4 via a slider 7; the optical fiber 1 is provided with a first grating segment 5 and a second grating segment 6, one end of the first grating segment 5 is fixedly connected to the mounting base 4, and the other end is fixedly connected to the slider 7; one end of the second grating segment 6 is fixedly connected to the slider 7, and the other end is fixedly connected to the mounting base 4; the elastic diaphragm 2 undergoes axial deformation under external pressure, driving the force transmission rod 3 and the slider 7 to move axially, thereby driving the first grating segment 5 to achieve tensile motion, and simultaneously driving the second grating segment 6 to achieve compressive motion.

[0031] like Figures 1 to 3As shown, the device also includes a housing 12 with a receiving cavity, a mounting ring 8, and a clamping flange 9. One end of the housing 12 is provided with a first through hole 11, and the other end is provided with a second through hole through which the optical fiber 1 passes. The elastic diaphragm 2 is sealingly mounted in the first through hole 11, and the first grating segment 5, the second grating segment 6, the transmission rod 3, and the mounting seat 4 are all encapsulated in the housing 12. The elastic diaphragm 2 is coaxially sealingly mounted in the annular ring of the mounting ring 8, and the mounting ring 8 is sealingly mounted in the first through hole 11. The clamping flange 9 is fixedly mounted in the housing 12, and one end of the mounting seat 4 is fixedly mounted in the housing 12 through the clamping flange 9. The clamping flange 9 is provided with a third through hole through which the transmission rod 3 passes. The elastic diaphragm 2 is circular in structure, and is mounted in the annular ring of the mounting ring 8 and sealingly connected with the mounting ring 8. The mounting ring 8 is also sealingly connected with the housing 12. One side of the elastic diaphragm 2 is located outside the housing 12 for contact with the outside world, and the other side is located inside the housing 12 and in contact with the transmission rod 3. The first grating segment 5, the second grating segment 6, the transmission rod 3, and the mounting seat 4 are all encapsulated inside the housing 12 to avoid the influence of the external environment. The other end of the optical fiber 1 passes out of the housing 12 from the second through hole and is connected with a detection device. The first through hole 11 is circular in structure and is provided with an internal thread structure. An external thread structure is provided on the mounting ring 8, and the mounting ring 8 is threadedly connected with the housing 12. When connected, a sealing gasket is sleeved to achieve the sealing connection of the mounting ring 8 and the housing 12. The sealing gasket can be a Teflon gasket, and the material is fluorine rubber. It is mainly used to make the space between the elastic diaphragm 2 and the optical fiber 1 element a sealed environment, and to achieve dustproof and waterproof inside the sensor. The specific parameters of the Teflon gasket can be adjusted according to actual use. In this embodiment, when the optical fiber 1 passes into the housing 12 from the second through hole, it is connected and fixed through a gland joint. The gland joint is threadedly connected with the housing 12. In this embodiment, a stainless steel gland joint of M8 is used, which is mainly used to connect the optical cable and has the characteristics of dustproof and waterproof. The specific parameters of the gland joint can be adjusted according to actual use.

[0032] As shown in Figure 1 and Figure 2 , the clamping flange 9 is fixed in the housing 12, and one end of the mounting seat 4 is fixedly connected with the clamping flange 9 to achieve the installation and fixation of the mounting seat 4 through the clamping flange 9. A fourth through hole coaxial with the third through hole is provided on the mounting seat 4, and the transmission rod 3 is connected with the sliding block 7 after passing through the third through hole and the fourth through hole in sequence. The clamping flange 9 is made of 316 stainless steel, and can be used to screw and fix the mounting seat 4. As shown, the clamping flange 9 is also an annular structure, which is fixed on the mounting ring 8 through bolts, and the other side is provided with clamping pieces protruding to one side. The mounting seat 4 is clamped between the two clamping pieces and fixed through screws.

[0033] As shown in Figure 3As shown, the shell 12 is a cylindrical structure, the material is 316L stainless steel, the outer of the cylinder is provided with a thread, facilitating the subsequent pressure gauge connection and fixation The force transmission rod 3 is a cylindrical long rod, the material is carbon fiber, mainly used for transmitting the axial stress of the diaphragm to the slider 7, so that the moving distance of the slider 7 is equal to the axial displacement of the diaphragm.

[0034] As shown in Figure 1 The first grating section 5 and the second grating section 6 are both provided with Bragg gratings FBG, the first grating section 5 is provided with Bragg grating FBG1, and the second grating section 6 is provided with Bragg grating GBG2; the grating is an optical element, and its manufacturing principle is based on the diffraction and interference effect of periodic structure on light. The commonly used methods for making gratings include mechanical etching, photolithography, electron beam exposure and interference lithography technology, etc. By laser etching on part of the fiber, there are multiple reflection surfaces with equal intervals inside the fiber. Among them, the Bragg grating is a special type of grating, and its manufacturing principle is based on the Bragg diffraction law. The Bragg diffraction law indicates that when light waves with a specific incident angle and wavelength are incident on a periodic structure, diffraction will occur in a specific direction, and only when the incident angle is equal to the Bragg angle, the diffraction wave will satisfy the coherence condition. The Bragg grating is usually formed by exposing the photosensitive material (such as optical fiber 1, optical waveguide, etc.) to the light beam formed by interference fringes, and then performing photo-induced refractive index change or local modification of the photosensitive material, to form a periodic refractive index or equivalent refractive index structure.

[0035] As shown in Figure 1 And Figure 2 The first grating section 5 and the second grating section 6 are both suspended. The first grating section 5 and the second grating section 6 are suspended, which can avoid friction caused by contact with other structures, thereby affecting the deformation amount. The Bragg grating structure parameters of the first grating section 5 and the second grating section 6 are the same, including temperature sensitivity, pressure sensitivity and length value. The first grating section 5 and the second grating section 6 are both affected by strain and temperature, and the temperature sensitivity coefficients of the two grating sections are consistent. The first grating section 5 measures positive strain, and the second grating section 6 measures negative strain, and the two strains are equal in size and opposite in direction.

[0036] As shown in Figure 2As shown, the mounting seat 4 is provided with a groove, and the groove is provided with a guide rail 10 at the bottom, and the sliding block 7 is in sliding connection with the guide rail 10; the first grating segment 5 and the second grating segment 6 are both suspended in the groove. The groove is arranged on the mounting seat 4, so that the first grating segment 5 and the second grating segment 6 are fixed, and at the same time, it can be ensured that they can be suspended. The sliding block 7 is located at the middle position of the groove, and the guide rail 10 is located at the corresponding position of the second grating segment 6, so that the sliding block 7 divides the groove into two chambers: a left chamber and a right chamber. The left chamber corresponds to the first grating segment 5, and the right chamber corresponds to the second grating segment 6. The guide rail 10 is located at the bottom of the right chamber, and when the sliding block 7 slides, it moves to the right chamber, so as to realize the stretching movement of the first grating segment 5 and the compression movement of the second grating segment 6.

[0037] As shown in Figure 1 The mounting seat 4 is placed on the mounting platform, and the bottom of the mounting seat 4 is in contact with the mounting platform. The bottom of the mounting seat 4 is connected with the shell 12, which not only provides stable support, but also realizes the rapid and uniform distribution of the internal temperature of the left and right cavities, effectively reduces the measurement error of the two grating segments caused by the inconsistency of the temperature in different temperature fields, and further improves the accuracy of the difference measurement and the temperature compensation capability.

[0038] As shown in Figure 1 The force transmission rod 3 is vertically arranged with the elastic diaphragm 2, and the center of the force transmission rod 3 is connected with the elastic diaphragm 2; the optical fiber 1 is arranged in parallel with the force transmission rod 3. When the elastic diaphragm 2 is subjected to pressure, the deformation amount at the center is the largest; the force transmission rod 3 is parallel with the optical fiber 1, and the axial deformation of the elastic diaphragm 2 can be converted into the axial deformation of the optical fiber 1.

[0039] In this embodiment, the optical fiber 1 uses a Corning single-mode optical fiber 1G.652D, which is mainly used for transmission of optical signals. The specific parameters of the optical fiber 1 can be adjusted according to actual use. The material of the elastic diaphragm 2 is 316L stainless steel, the thickness is 1.9 mm, and the diameter is Φ42 mm. It mainly serves as a pressure-bearing element of the sensor, which converts the external water pressure into the axial deformation of the diaphragm to cause the axial strain of the grating. The specific parameters of the pressure-bearing elastic diaphragm 2 can be adjusted according to actual use.

[0040] In this embodiment, the first grating segment 5 is used to convert the axial deformation of the elongated optical fiber 1 into a change in optical signal. It is initially fixed by bonding after applying a large prestress. In this embodiment, a 1535nm band grating is used, with an initial wavelength of 1535.0351nm and an ambient temperature of 25℃. After stretching, the wavelength is 1537.4623nm, and the stretching amount is 2.4272nm. The specific parameters of the elongated end grating segment can be adjusted according to actual usage. The second grating segment 6 is used to convert the axial deformation of the compressed optical fiber 1 into a change in optical signal. Initially, a prestress slightly smaller than that of the first grating segment 5 is applied before bonding, ensuring that the tension of the first grating segment 5 is greater than that of the second grating segment 6 to guarantee that the force transmission rod 3 can directly contact the diaphragm. The grating of the second grating segment 6 is a 1540nm band grating, with an initial wavelength of 1555.0351nm and an ambient temperature of 25℃. After stretching, the wavelength is 1542.2789nm, and the stretching amount is 2.2432nm. The specific parameters of the second grating segment 6 can be adjusted according to actual usage.

[0041] Bragg Wavelength Determined by the following formula:

[0042]

[0043] In the formula: The effective refractive index for laser propagation within the optical fiber; The period of the Bragg grating.

[0044] When the strain exerted on the FBG by external forces is zero, the change in ambient temperature When light wavelengths change, the amount of this shift is related to the temperature change as follows:

[0045]

[0046] In the formula: The coefficient of thermal expansion of FBG material; The thermo-optic coefficient of FBG material; Let be the temperature change. Therefore, the temperature sensitivity coefficient of FBG is... .

[0047] Ignoring temperature changes, we only consider the strain generated by axial tension or compression of the FBG. Time-to-grating period Due to the influence of the grating period, the change is as follows:

[0048]

[0049] Meanwhile, considering the influence of the elasto-optic effect, the effective refractive index of FBG will change with the deformation of the fiber core, and the corresponding relationship is as follows:

[0050]

[0051] The effective photoelastic coefficient of the optical fiber can be obtained from the formula

[0052]

[0053] In the formula, is the photoelastic coefficient, is the Poisson ratio.

[0054] Substituting the formula into the formula, the wavelength shift and pressure change relationship formula is obtained as

[0055]

[0056] Therefore, when the strain and temperature act on the FBG at the same time, the wavelength shift amount is

[0057]

[0058] Differential compensation method:

[0059] The differential compensation method uses two FBGs to compensate for temperature. Both FBGs are affected by strain and temperature at the same time, and the temperature sensitivity coefficients of the two gratings are consistent. In this embodiment, one Bragg grating FBG measures positive strain, that is, the Bragg grating FBG1 of the first grating section measures positive strain, and the other Bragg grating FBG measures negative strain, that is, the Bragg grating FBG2 of the second grating section measures negative strain, and the two strains are equal in size and opposite in direction.

[0060]

[0061] In the formula, and are the wavelength shift amounts of FBG1 and FBG2, respectively, and are the center wavelengths of the gratings of the first grating section and the second grating section, respectively, is and are approximate values. Since the compression end grating section and the elongation end grating section are in the same temperature environment, the drift amounts caused by temperature effects are the same, so the compression end grating and the elongation end grating can mutually compensate for temperature and offset the errors caused by temperature changes.

[0062] ​The optical fiber 1 grating pressure sensor provided by the embodiment has one side of the elastic diaphragm 2 in contact with the outside world to receive pressure from the outside world, and the other side connected with the force transmission rod 3 to produce axial elastic deformation under the external pressure, and transmit the elastic deformation to the force transmission rod 3 to drive the force transmission rod 3 to move axially, so that the slider 7 moves together. Since the two ends of the optical fiber 1 are fixed with the two ends of the mounting seat 4 respectively, and the middle part of the optical fiber 1 is fixedly connected with the slider 7, that is, the first grating section 5 and the second grating section 6 are respectively located on the two sides of the slider 7, therefore, when the slider 7 moves, the first grating section 5 is stretched, and the second grating section 6 is compressed. The first grating section 5 converts the axial deformation amount of the elongation of the optical fiber 1 into the change amount of the optical signal, and the second grating section 6 converts the axial deformation amount of the compression of the optical fiber 1 into the change amount of the optical signal. Since the first grating section 5 and the second grating section 6 are in the same environment, the drift amount caused by temperature influence is the same, therefore, the first grating section 5 and the second grating section 6 can realize temperature compensation by using the differential compensation principle, offset the error caused by the temperature change, and effectively improve the measurement accuracy of the sensor.

[0063] The optical fiber 1 grating pressure sensor provided by the embodiment has one side of the elastic diaphragm 2 in contact with the outside world to receive pressure from the outside world, and the other side connected with the force transmission rod 3 to produce axial elastic deformation under the external pressure, and transmit the elastic deformation to the force transmission rod 3 to drive the force transmission rod 3 to move axially, so that the slider 7 moves together. Since the two ends of the optical fiber 1 are fixed with the two ends of the mounting seat 4 respectively, and the middle part of the optical fiber 1 is fixedly connected with the slider 7, that is, the first grating section 5 and the second grating section 6 are respectively located on the two sides of the slider 7, therefore, when the slider 7 moves, the first grating section 5 is stretched, and the second grating section 6 is compressed. The first grating section 5 converts the axial deformation amount of the elongation of the optical fiber 1 into the change amount of the optical signal, and the second grating section 6 converts the axial deformation amount of the compression of the optical fiber 1 into the change amount of the optical signal. Since the first grating section 5 and the second grating section 6 are in the same environment, the drift amount caused by temperature influence is the same, therefore, the first grating section 5 and the second grating section 6 can realize temperature compensation by using the differential compensation principle, offset the error caused by the temperature change, and effectively improve the measurement accuracy of the sensor.

[0064] The sensor is integrated with two optical fiber 1 gratings of the same specification, adopts a push-pull grating structure to realize the differential method of the grating, FBG1 is bonded between the mounting seat 4 and the slider 7 after a pre-stretching amount (about 2.5nm wavelength shift) is applied, and is used for sensing the positive displacement change converted by the pressure; FBG2 is bonded between the slider 7 and the mounting seat 4 after a pre-stretching amount (about 2.3nm wavelength shift) is applied, and is used for sensing the negative displacement change converted by the pressure. When the environmental pressure changes, the elastic diaphragm 2 of the sensor will drive the slider 7 to reciprocate, since the two optical fibers 1 are fixed on the slider 7, the length change amounts of the two gratings are the same, the displacement amounts are equal, the strain amounts of the first grating section 5 and the second grating section 6 are equal, the two gratings are in the same environment, can be self-compensated for temperature, and can double the sensitivity of the sensor, and improve the measurement accuracy and precision.

[0065] Embodiment two

[0066] The embodiment verifies the temperature consistency of the first grating segment 5 and the second grating segment 6 in the sensor provided in Embodiment One through finite element thermal simulation. In the fiber 1 grating sensing system, environmental temperature changes will cause grating wavelength drift, thereby affecting the accuracy of the submarine water pressure measurement. To reduce the influence of temperature on the measurement results, the push-pull type sensing probe adopts a differential measurement method, and temperature compensation is achieved through two Bragg gratings (FBG1 and FBG2) in the same environment. However, the effectiveness of this compensation method depends on whether the two Bragg gratings are in the same temperature environment, otherwise the error of temperature drift may still affect the measurement results.

[0067] To verify the temperature consistency of the environment in which the gratings are located, transient heat transfer simulation is performed on the sensor to simulate the process of temperature changing from 297 K to 298 K, and to analyze the temperature distribution and its effect on grating compensation. Since the fiber 1 can reach temperature equilibrium within 180 s, here we take 2 s as the step size, and record the temperature change of the fiber 1 within 0-1800 s under the condition that the external temperature is 1 K higher than the initial temperature of the sensing probe. When reaching 90% of the external temperature, it is considered that the temperature has reached a stable state. The temperature change of the fiber 1 obtained by simulation calculation is shown in Figure 4 The simulation results show that the temperature at the positions of the two gratings changes relatively slowly with the environment, and tends to be stable within 180 s. Among them, the FBG1 environmental temperature tends to be stable at about 157 s, and the FBG2 environmental temperature tends to be stable at about 163 s. Therefore, the temperature consistency of the environment in which the two gratings are located can be judged by analyzing the temperature data within 250 s.

[0068] Further calculation of the temperature difference between the two gratings is shown in Figure 5 The simulation results show that during the entire temperature stabilization process, the maximum temperature difference is only 0.01398 K, and the average temperature of the absolute value of the temperature difference is 0.00927978 K, which is extremely small relative to the temperature change of 1 K. This indicates that the two gratings are basically in the same temperature environment, which can ensure the conditions of the differential measurement method.

[0069] Embodiment Three

[0070] The sensor provided in Example One was tested for sensitivity. The sensor was connected to a hydraulic pump via a high-pressure hose. One end of the armored optical cable of the sensor was connected to an optical fiber 1 grating demodulator. The ambient temperature during the test was 25°C. In the experiment, the test was performed in steps of 0.1 MPa, from 0 MPa to 2 MPa. Each pressure measurement point was maintained for 10-15 s. The reflected wavelengths of the first grating segment Bragg grating FBG1 and the second grating segment Bragg grating FBG2 were recorded by the optical fiber 1 grating demodulation software, and the reflection spectra of FBG1 and FBG2 at each pressure measurement point were recorded.

[0071] As shown in Figure 6 FIG. 1 shows the changes in the wavelengths of FBG1 and FBG2 with pressure during the three pressure tests. As can be seen, the wavelengths of FBG1 and FBG2 showed good linear response and repeatability to pressure. The average pressure sensitivity of FBG1 was 914.17 pm / MPa, and the average linear correlation coefficient was 0.99995. The average pressure sensitivity of FBG2 was 905.88 pm / MPa, and the average linear correlation coefficient was 0.99996. Thus, the sensitivity of the sensor within the working range of 2 MPa was (914.17 + 905.88) pm / MPa = 1820.05 pm / MPa.

[0072] Example Four

[0073] The sensor provided in Example One was tested for temperature sensitivity. The sensor was placed in a temperature-controlled oven, and one end of the armored optical cable of the sensor was connected to an optical fiber 1 grating demodulator. In the experiment, the test was performed in steps of 5°C, from 10°C to 70°C. Each temperature measurement point was maintained for 10 min. The reflected wavelengths of the first grating segment Bragg grating FBG1 and the second grating segment Bragg grating FBG2 were recorded by the optical fiber 1 grating demodulation software, and the reflection spectra of FBG1 and FBG2 at each temperature point were recorded.

[0074] As shown in Figure 7 FIG. 1 shows the changes in the wavelengths of FBG1 and FBG2 with temperature during the temperature test. As can be seen, the wavelengths of FBG1 and FBG2 showed good linear response to temperature. The temperature sensitivity of FBG1 was 0.0370 nm / °C, and the linear correlation coefficient was 0.9998. The temperature sensitivity of FBG2 was 0.0376 nm / °C, and the linear correlation coefficient was 0.9999. Thus, the temperature sensitivity of the sensor after temperature compensation was 0.0006 nm / °C, which was 60 times lower than the temperature sensitivity when FBG was used alone (0.0370 nm / °C and 0.0376 nm / °C). This means that the water pressure sensor described herein is almost no longer disturbed by temperature changes.

[0075] In the specific contents of the above specific embodiments, each technical feature can be combined arbitrarily without contradiction, and in order to make the description simple, all possible combinations of the above technical features are not described, however, as long as the combination of the technical features does not exist contradiction, it should be considered as the scope of the description.

[0076] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to enumerate all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A fiber Bragg grating pressure sensor, characterized in that, include: An optical fiber (1), an elastic diaphragm (2), a force transmission rod (3), and a mounting base (4) are provided. One end of the force transmission rod (3) is connected to the elastic diaphragm (2), and the other end is slidably connected to the mounting base (4) via a slider (7). The optical fiber (1) is provided with a first grating segment (5) and a second grating segment (6). One end of the first grating segment (5) is fixedly connected to the mounting base (4), and the other end is fixedly connected to the slider (7). One end of the second grating segment (6) is fixedly connected to the slider (7), and the other end is fixedly connected to the mounting base (4). The elastic diaphragm (2) is subjected to external pressure and undergoes axial deformation, which drives the force transmission rod (3) and the slider (7) to move axially, thereby driving the first grating segment (5) to perform a stretching motion and simultaneously driving the second grating segment (6) to perform a compressing motion.

2. The fiber Bragg grating pressure sensor according to claim 1, characterized in that, Both the first grating segment (5) and the second grating segment (6) are suspended.

3. The fiber Bragg grating pressure sensor according to claim 1, characterized in that, The length of the first grating segment (5) is the same as that of the second grating segment (6).

4. The fiber Bragg grating pressure sensor according to claim 2, characterized in that, The first grating segment (5) has the same temperature sensitivity and pressure sensitivity as the second grating segment (6).

5. The fiber Bragg grating pressure sensor according to claim 3, characterized in that, The force transmission rod (3) is arranged perpendicularly to the elastic diaphragm (2), and the force transmission rod (3) is connected to the center of the elastic diaphragm (2); the optical fiber (1) is arranged parallel to the force transmission rod (3).

6. The fiber Bragg grating pressure sensor according to any one of claims 1 to 5, characterized in that, It also includes a housing (12) with an internal cavity, one end of which has a first through hole (11) and the other end has a second through hole for the optical fiber (1) to pass through; the elastic diaphragm (2) is sealed and installed in the first through hole (11), and the first grating segment (5), the second grating segment (6), the force transmission rod (3), and the mounting base (4) are all encapsulated in the housing (12).

7. The fiber Bragg grating pressure sensor according to claim 6, characterized in that, It also includes a mounting ring (8), in which the elastic diaphragm (2) is coaxially and sealed within the ring of the mounting ring (8), and the mounting ring (8) is sealed within the first through hole (11).

8. The fiber Bragg grating pressure sensor according to claim 7, characterized in that, It also includes a clamping flange (9), which is fixedly installed inside the housing (12). One end of the mounting base (4) is fixedly installed inside the housing (12) through the clamping flange (9). The clamping flange (9) is provided with a third through hole through which the force transmission rod (3) passes.

9. The fiber Bragg grating pressure sensor according to claim 6, characterized in that, The mounting base (4) has a groove, and a guide rail (10) is provided at the bottom of the groove. The slider (7) is slidably connected to the guide rail (10). The first grating segment (5) and the second grating segment (6) are both suspended in the groove.

10. The fiber Bragg grating pressure sensor according to claim 6, characterized in that, The housing (12) is provided with a mounting platform with a planar surface. The bottom of the mounting base (4) is a planar structure. The mounting base (4) is placed on the mounting platform and the bottom of the mounting base (4) is in contact with the mounting platform.

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