Temperature difference compensation pressure sensor

Abstract

The invention relates to the technical field of pressure sensors, in particular to a temperature difference compensation pressure sensor. Axial deformation of the corrugated pipe is used for driving the first Bragg grating to stretch and the second Bragg grating to compress, positive strain is measured through the first Bragg grating, negative strain is measured through the second Bragg grating, the two strains are equal in magnitude and opposite in direction, temperature compensation can be achieved through a differential compensation method, and therefore the influence caused by temperature is effectively reduced, and the measurement accuracy is improved. The measurement precision of the sensor is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure sensors, and more particularly to a temperature difference compensation pressure sensor. Background Art

[0002] Ocean level monitoring is also a key tool for Earth observation. By continuously observing ocean levels, scientists can study important issues such as global climate change and sea level fluctuations. These findings are of great significance for the development of environmental protection policies and responses to climate change. Long-term monitoring of ocean levels can help us understand the fundamental laws governing global climate change, providing a scientific basis for addressing global climate change. Subsea level monitoring refers to the use of various techniques to monitor and measure subsea level in real time. Currently, conventional ocean level monitoring methods suffer from numerous limitations, including significant influences from meteorological conditions and atmospheric pressure fluctuations, making them unsuitable for precise level measurement; high equipment costs, requiring a stable power supply and data storage and processing facilities; significant influences from water quality, temperature, and target objects, making them unsuitable for use in areas prone to interference; significant influences from atmospheric conditions and aerosols, making them unsuitable for monitoring oceans with high atmospheric humidity; and relatively low resolution, which, due to limitations in remote sensing equipment performance and weather conditions, prevents high-precision level measurement.

[0003] With the rapid development of fiber optic sensing technology, various countries have developed a number of fiber optic sensors for use in ocean sensing and detection. A fiber Bragg grating (FBG)-based submarine pressure sensor is a sensor used to monitor changes in seabed depth and pressure. Its principle is to detect changes in pressure by leveraging the FBG's sensitivity to light wavelength. Specifically, the FBG utilizes the periodic refractive index variation structure in the optical fiber to form reflection and diffraction of the optical wavelength, and this periodic variation in refractive index can be altered by factors such as external pressure. When the FBG is subjected to external pressure, its periodic structure changes, causing the reflected light wavelength to shift. By measuring this change in light wavelength, the magnitude of the external pressure can be determined. However, in addition to being affected by external stress changes, the FBG is also affected by the external ambient temperature, resulting in large differences in the stress detection results, thereby affecting the sensor's accuracy. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art fiber Bragg grating sensors that are easily affected by temperature and thus affect the measurement accuracy, and to provide a temperature difference compensation pressure sensor that can effectively reduce the impact of temperature, thereby improving the measurement accuracy of the sensor.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A temperature differential compensation pressure sensor is provided, comprising a housing having a cavity therein, and an optical fiber, a bellows, and a movable block disposed within the housing; the housing being provided with a first through hole, one end of the bellows being fixedly mounted within the encapsulated housing and communicating with the first through hole, the other end of the bellows being sealed and connected to the movable block; both ends of the optical fiber being fixedly mounted within the housing, the middle portion of the optical fiber being fixedly connected to the movable block; the optical fiber and the bellows being coaxially arranged; the bellows being axially displaced by external pressure, pushing the movable block to slide, thereby causing one section of the optical fiber to undergo tensile deformation and the other section to undergo compressive deformation; a first Bragg grating being provided in the tensile deformation section, and a second Bragg grating being provided in the compressive deformation section; the pressure sensor achieves temperature differential compensation by:

[0007] The first Bragg grating and the second Bragg grating are affected by strain and temperature at the same time, and the temperature sensitivity coefficients of the first Bragg grating and the second Bragg grating are consistent. The first Bragg grating measures positive strain, and the second Bragg grating measures negative strain. The two strains are equal in magnitude and opposite in direction:

[0008]

[0009]

[0010] Δλ1-Δλ2=2λ(1-P e )ε

[0011] Where Δλ1 and Δλ2 are the wavelength shifts of the first and second Bragg gratings, λ1 and λ2 are the central wavelengths of the first and second Bragg gratings, and λ is the approximate value of λ1 and λ2. α is the thermal expansion coefficient of the materials of the first and second Bragg gratings. ξ is the thermo-optic coefficient of the materials of the first and second Bragg gratings. ΔT is the temperature change. P e is the effective elastic-optical coefficient of the optical fiber;

[0012] The axial displacement of the bellows is calculated using the following formula:

[0013]

[0014] The strain ε experienced by the optical fiber is:

[0015]

[0016] Where ρ is the density of seawater; g is the acceleration due to gravity; A is the straight cross-sectional area of ​​the bellows; k is the elastic modulus of the bellows; Δx is the change in the length of the bellows; Δh is the change in the water level of the bellows immersed in seawater; x is the effective length of the optical fiber;

[0017] Combining the above formulas we get:

[0018]

[0019] Then the water pressure sensitivity K of the pressure sensor is:

[0020]

[0021] The present invention provides a temperature-difference-compensated pressure sensor. Seawater flows into a bellows from a first through hole in a housing. One end of the bellows is sealed. Upon receiving the impact force of the seawater, the bellows moves axially, that is, the bellows stretches, thereby pushing a movable block to move. Since the optical fiber is coaxially arranged with the bellows, and both ends of the optical fiber are fixed, with the middle portion connected to the movable block, movement of the movable block causes one section of the optical fiber to stretch and the other end of the optical fiber to compress. A first Bragg grating is provided on the tensile deformation section, and a second Bragg grating is provided on the compressive deformation section. The first Bragg grating measures positive strain, while the second Bragg grating measures negative strain. The two strains are equal in magnitude and opposite in direction. Temperature compensation can be achieved through a differential compensation method, thereby effectively reducing the influence of temperature and improving the measurement accuracy of the sensor.

[0022] Furthermore, when fixing the tensile deformation section and the compressive deformation section, prestress is set, and the prestress of the compressive deformation section is greater than the prestress of the tensile deformation section. During installation, in order to ensure that the first Bragg grating and the second Bragg grating can respond to the water pressure in a timely manner, prestress needs to be set in advance. The bellows will stretch axially under the action of water pressure and drive the first Bragg grating to stretch. Therefore, when the water pressure increases, the wavelength of light of the first Bragg grating will redshift; the bellows will stretch axially under the action of water pressure and compress the second Bragg grating. Therefore, when the water pressure increases, the wavelength of light of the second Bragg grating will blueshift. However, since the second Bragg grating is compressed, in order to ensure that it can respond within the measurement range, the prestress setting must be much larger than that of the first Bragg grating.

[0023] Furthermore, the device further includes a first fixing member having a second through-hole. The first fixing member is fixed to the interior of the housing, the corrugated tube is mounted on the first fixing member, and one end of the second through-hole is connected to the first through-hole, and the other end is connected to the tube opening of the corrugated tube. The first fixing member is used to fix the corrugated tube and the optical fiber; on the other hand, it is also used to connect the first through-hole and the corrugated tube. Seawater flows in from the first through-hole, flows through the second through-hole, and then enters the corrugated tube.

[0024] Furthermore, the invention further comprises a second fixing member, which is fixed within the housing and spaced apart from the first fixing member. The two ends of the optical fiber are fixedly connected to the first fixing member and the second fixing member, respectively, and the movable block is located between the first fixing member and the second fixing member. The second fixing member is used to fix the other end of the optical fiber. The two ends of the optical fiber are fixed to the first fixing member and the second fixing member, respectively, and the middle portion is fixed to the movable block. The optical fiber segment between the first fixing member and the movable block is a tensile deformation segment, and the optical fiber segment between the movable block and the second fixing member is a compressive deformation segment. Through the fixation of the first fixing member, the movable block, and the second fixing member, the optical fiber is in a straight state without bending.

[0025] Furthermore, the optical fiber is bonded to the first fixing member, the second fixing member and the movable block respectively.

[0026] Furthermore, the two ends of the second through hole are sealedly connected to the first through hole and the mouth of the bellows, respectively, and the first through hole, the second through hole, and the bellows together constitute a pressure channel. Seawater enters from the first through hole, flows through the second through hole, and then enters the bellows. Since the other end of the bellows is blocked, the bellows is pressed by the seawater and deforms axially, driving the movable block to move toward the second fixed block, thereby stretching the first Bragg grating and compressing the second Bragg grating. The first through hole, the second through hole, and the bellows together constitute a sealed pressure channel. On the one hand, this prevents seawater from entering the interior of the housing and causing damage to parts such as the grating. On the other hand, it also ensures that the pressure of the seawater can eventually act on the bellows, causing it to deform axially.

[0027] Furthermore, the tensile deformation section and the compressive deformation section are both suspended. The tensile deformation section and the compressive deformation section are both suspended to avoid contact with other structures causing friction, thereby affecting the deformation amount.

[0028] Furthermore, the tensile deformation segment and the compressive deformation segment have the same length. They also have the same temperature sensitivity and pressure sensitivity. Both the tensile deformation segment and the compressive deformation segment are affected by both strain and temperature, and the temperature sensitivity coefficients of the two grating segments are consistent. The tensile deformation segment measures positive strain, while the compressive deformation segment measures negative strain, and the two strains are equal in magnitude and opposite in direction.

[0029] Furthermore, the housing is provided with a third through-hole, through which one end of the optical fiber passes. The third through-hole is located on a side opposite the first through-hole. After passing through the third through-hole, the optical fiber passes through the second fixing member, the movable block, and the first fixing member in sequence. The end of the optical fiber is fixed to the first fixing member, and the end that passes through is fixed to the second fixing member. The end that passes through is used to connect to other detection equipment.

[0030] Furthermore, a gland connector is provided at the third through hole. Connecting the optical fiber via the gland connector can fix the optical fiber on the one hand, and also play a sealing role on the other hand, preventing seawater from entering the interior of the housing through the third through hole.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] A temperature-compensated pressure sensor of the present invention utilizes the axial deformation of a bellows to drive the stretching of a first Bragg grating and the compression of a second Bragg grating. The positive strain is measured by the first Bragg grating, while the negative strain is measured by the second Bragg grating. The two strains are equal in magnitude and opposite in direction. Temperature compensation can be achieved through a differential compensation method, thereby effectively reducing the influence of temperature and improving the measurement accuracy of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic structural diagram of a temperature difference compensation pressure sensor in Example 1;

[0034] Figure 2 This is the stress cloud diagram of the bellows in Example 1;

[0035] Figure 3 This is the displacement cloud diagram of the bellows in Example 1;

[0036] Figure 4 This is a temperature difference curve diagram of the first Bragg grating and the second Bragg grating at 1K temperature change in Example 1.

[0037] In the accompanying drawings: 1. housing; 2. optical fiber; 3. bellows; 4. movable block; 5. first through hole; 6. first Bragg grating; 7. second Bragg grating; 8. first fixing member; 9. second through hole; 10. second fixing member; 11. third through hole. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only and are schematic, not actual, representations. They 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 in size, and do not represent the actual dimensions of the products. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted from the drawings.

[0039] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "up", "down", "left", "right", etc. indicate directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0040] Example 1

[0041] This embodiment is the first embodiment of a temperature difference compensation pressure sensor. Figure 1 As shown, it includes a shell 1 with a cavity inside, and an optical fiber 2, a bellows 3, and a movable block 4 arranged inside the shell 1; a first through hole 5 is provided on the shell 1, one end of the bellows 3 is fixedly installed in the packaging shell 1 and communicates with the first through hole 5, and the other end of the bellows 3 is blocked and connected to the movable block 4; the two ends of the optical fiber 2 are respectively fixedly installed in the shell, and the middle part of the optical fiber 2 is fixedly connected to the movable block 4; the optical fiber 2 and the bellows 3 are coaxially arranged; the bellows 3 is axially displaced by external pressure, pushing the movable block 4 to slide, so as to drive one section of the optical fiber 2 to produce tensile deformation and the other section to produce compressive deformation; a first Bragg grating 6 is provided in the tensile deformation section, and a second Bragg grating 7 is provided in the compressive deformation section. The pressure sensor realizes temperature difference compensation in the following way:

[0042] The first Bragg grating 6 and the second Bragg grating 7 are affected by strain and temperature at the same time, and the temperature sensitivity coefficients of the first Bragg grating 6 and the second Bragg grating 7 are consistent. The first Bragg grating 6 measures positive strain, and the second Bragg grating 7 measures negative strain. The two strains are equal in magnitude and opposite in direction:

[0043]

[0044]

[0045] Δλ1-Δλ2=2λ(1-P e )ε

[0046] Wherein, Δλ1 and Δλ2 are the wavelength shifts of the first Bragg grating 6 and the second Bragg grating 7, respectively; λ1 and λ2 are the central wavelengths of the first Bragg grating 6 and the second Bragg grating 7, respectively; λ is the approximate value of λ1 and λ2; α is the thermal expansion coefficient of the materials of the first Bragg grating 6 and the second Bragg grating 7; ξ is the thermo-optical coefficient of the materials of the first Bragg grating 6 and the second Bragg grating 7; ΔT is the temperature change; Pe is the effective elastic-optical coefficient of optical fiber 2;

[0047] The axial displacement of the bellows 3 is calculated using the following formula:

[0048]

[0049] The strain ε of fiber 2 is:

[0050]

[0051] Wherein, ρ is the density of seawater; g is the acceleration due to gravity; A is the straight cross-sectional area of ​​the bellows 3; k is the elastic modulus of the bellows 3; Δx is the change in the length of the bellows 3; Δh is the change in the water level of the bellows 3 immersed in seawater; x is the effective length of the optical fiber 2;

[0052] Combining the above formulas we get:

[0053]

[0054] Then the water pressure sensitivity K of the pressure sensor is:

[0055]

[0056] This embodiment provides a temperature-compensated pressure sensor that utilizes the axial deformation of a bellows to stretch a first Bragg grating and compress a second Bragg grating. Positive strain is measured by the first Bragg grating, while negative strain is measured by the second Bragg grating. The two strains are equal in magnitude and opposite in direction. Temperature compensation can be achieved through differential compensation, effectively reducing the effects of temperature and improving the sensor's measurement accuracy.

[0057] In this embodiment, the bellows 3 is mainly used to isolate the grating from the outside world, protect the grating and provide elastic support; under the action of water pressure, the bellows 3 will stretch axially, driving the movable block 4 to move axially, and at the same time stretching the first Bragg grating 6 and compressing the second Bragg grating 7. In this embodiment, a vacuum bellows 3 is used, the bellows 3 has a wall thickness of 1.5mm, an inner diameter of Φ20mm, a length of 35mm, and is made of 316L. The movable block 4 is axially connected to the bellows, can transmit the axial deformation of the bellows 3, and fix the common end of the first Bragg grating 6 and the second Bragg grating 7. In addition, water pressure will also act on the Φ20mm area of ​​the movable block 4, increasing a portion of the axial deformation of the bellows 3. The movable block 4 has a diameter of Φ50mm and is a solid part made of 316L. The shell 1 is a hollow columnar structure, which is mainly used to isolate the grating and the outer wall of the bellows 3 from contact with external water pressure and protect the grating. In this embodiment, it is a cylindrical structure with an outer diameter of Φ80mm and an inner diameter of Φ70mm, and is made of 316L.

[0058] This embodiment further includes a first fixing member 8 and a second fixing member 10. The first fixing member 8 is provided with a second through hole 9 and is fixed within the housing 1. The corrugated tube 3 is mounted on the first fixing member 8. One end of the second through hole 9 is connected to the first through hole 5, and the other end is connected to the opening of the corrugated tube 3. The second fixing member 10 is fixed within the housing and spaced apart from the first fixing member 8. The ends of the optical fiber 2 are fixedly connected to the first fixing member 8 and the second fixing member 10, respectively. The movable block 4 is located between the first fixing member 8 and the second fixing member 10. The first fixing member 8 is used to securely mount the corrugated tube 3 and also to secure the optical fiber 2. It also connects the first through hole 5 and the corrugated tube 3. Seawater flows from the first through hole 5, passes through the second through hole 9, and then enters the corrugated tube 3. In this embodiment, the first fixing member 8 is made of stainless steel, and the inner diameter of the second through hole 9 is Φ10 mm. The second fixture 10 is used to secure the other end of the optical fiber 2. The ends of the optical fiber 2 are fixed to the first fixture 8 and the second fixture 10, respectively, while the middle portion is fixed to the movable block 4. The section of the optical fiber 2 between the first fixture 8 and the movable block 4 is a tensile deformation section, while the section between the movable block 4 and the second fixture 10 is a compressive deformation section. The fixation of the optical fiber 2 by the first fixture 8, the movable block 4, and the second fixture 10 maintains a straight line without any bends. During installation, prestressing is required to ensure that the first and second Bragg gratings 6 and 7 respond promptly to water pressure. The bellows 3 stretches axially under water pressure, causing the first Bragg grating 6 to stretch. Therefore, the wavelength of the light from the first Bragg grating 6 redshifts as the water pressure increases. The bellows 3 also stretches axially under water pressure, compressing the second Bragg grating 7. Therefore, the wavelength of the light from the second Bragg grating 7 blueshifts as the water pressure increases. However, since the second Bragg grating 7 is compressed, the prestressing force must be significantly greater than that of the first Bragg grating 6 to ensure responsiveness within the measurement range. For example, a 1535nm band grating can be used as the first Bragg grating 6, and the initial wavelength after prestressing is 1555.0351nm; the second Bragg grating 7 uses the 1555 band, and the wavelength after prestressing is 1558.8656, with a stretching amount of 3.8655nm. The specific parameters of the grating segment can be adjusted according to actual usage.

[0059] The two ends of the second through hole 9 are sealed with the first through hole 5 and the mouth of the bellows 3, respectively. The first through hole 5, the second through hole 9, and the bellows 3 together constitute a pressure channel. Seawater enters through the first through hole 5, flows through the second through hole 9, and then enters the bellows 3. Because the other end of the bellows 3 is blocked, the bellows 3 is pressed by the seawater and deforms axially, driving the movable block 4 to move toward the second fixed block, thereby stretching the first Bragg grating 6 and compressing the second Bragg grating 7. The first through hole 5, the second through hole 9, and the bellows 3 together constitute a sealed pressure channel. On the one hand, this prevents seawater from entering the interior of the housing 1 and causing damage to the grating and other parts. On the other hand, it also ensures that the pressure of the seawater can ultimately act on the bellows 3, causing it to deform axially.

[0060] In this embodiment, the tensile deformation segment and the compressive deformation segment are both suspended. The lengths of the tensile deformation segment and the compressive deformation segment are the same. The temperature sensitivity and pressure sensitivity of the tensile deformation segment and the compressive deformation segment are the same. The tensile deformation segment and the compressive deformation segment are both suspended to avoid friction caused by contact with other structures, thereby affecting the deformation amount. The tensile deformation segment and the compressive deformation segment are both affected by strain and temperature at the same time, and the temperature sensitivity coefficients of the two grating segments are consistent. The tensile deformation segment measures positive strain, and the compressive deformation segment measures negative strain. The two strains are equal in magnitude and opposite in direction.

[0061] In this embodiment, the housing 1 is provided with a third through hole 11, through which one end of the optical fiber 2 passes. The third through hole 11 is located on the side opposite the first through hole 5. After passing through the third through hole 11, the optical fiber 2 passes through the second fixing member 10, the movable block 4, and the first fixing member 8 in sequence. The end of the optical fiber 2 is fixed to the first fixing member 8, and the end that passes through is fixed to the second fixing member 10. The end that passes through is used to connect to other detection equipment. The optical fiber 2 is sealed and connected to the third through hole 11 to prevent seawater from entering the interior of the housing 1 through the third through hole 11.

[0062] Working principle:

[0063] A grating is an optical element that uses a periodic structure to produce diffraction and interference effects on light. A typical grating is usually composed of parallel grooves or protrusions, and the spacing and shape of these grooves or protrusions determine the performance of the grating. Common methods for making gratings include mechanical etching, photolithography, electron beam exposure, and interference lithography. Among them, the Bragg grating is a special type of grating, and its production principle is based on the Bragg diffraction law. The Bragg diffraction law states that when a light wave is irradiated on a periodic structure at a specific incident angle and wavelength, it will diffract in a specific direction, and only when the incident angle is equal to the Bragg angle will the diffracted wave meet the coherence condition. Bragg gratings are usually formed by exposing a photosensitive material (such as an optical fiber, optical waveguide, etc.) to a light beam formed by interference fringes, and then performing photoinduced refractive index changes or local modification of the photosensitive material to form a periodic refractive index or equivalent refractive index structure.

[0064] Bragg wavelength λ B Determined by the following formula:

[0065] λ B =2n eff Λ

[0066] Where: n eff is the effective refractive index of light propagating in the optical fiber; Λ is the period of the Bragg grating.

[0067] When the strain acting on the Bragg grating is zero and the ambient temperature changes by ΔT, the wavelength of light will drift. The relationship between the drift and the temperature change is:

[0068] Δλ B =λ B (α+ξ)ΔT

[0069] Where, α = 5.5 × 10 -7 / ℃ is the thermal expansion coefficient of the Bragg grating material; ξ=8.3×10 -6 / ℃ is the thermo-optic coefficient of the Bragg grating material; △T is the temperature change. Therefore, the temperature sensitivity coefficient of the Bragg grating is K T =α+ξ.

[0070] Without considering the temperature change, only the effect of the strain ε on the grating period Λ caused by the axial tension or compression of the Bragg grating is considered. The change of the grating period is:

[0071] ΔΛ=εΛ

[0072] At the same time, considering the influence of the elastic-optical effect, the effective refractive index of the Bragg grating will change with the deformation of the fiber core, and the corresponding relationship is:

[0073]

[0074] The effective elastic coefficient P of the optical fiber can be obtained from the formula e for:

[0075]

[0076] Where, P ij (i=1,j=1,2) is the elastic-optical coefficient, and ν is the Poisson's ratio.

[0077] Then the relationship between wavelength drift and pressure change can be obtained as follows:

[0078] Δλ B =λ B (1-P e )ε

[0079] Therefore, when strain and temperature act on the Bragg grating simultaneously, the wavelength shift is:

[0080] Δλ=λ B (1-P e )ε+λ B (α+ξ)ΔT

[0081] Differential compensation uses two Bragg gratings for temperature compensation. Specifically, the two Bragg gratings are simultaneously affected by strain and temperature, and their temperature sensitivity coefficients are identical. One Bragg grating, the first Bragg grating, measures positive strain, while the other, the second Bragg grating, measures negative strain. The two strains are equal in magnitude and opposite in direction.

[0082]

[0083]

[0084] Δλ1-Δλ2=2λ(1-P e )ε

[0085] Since the compression end grating segment and the extension end grating segment are in the same temperature environment, the drift caused by the temperature effect is the same, so the compression end grating and the extension end grating can compensate each other for temperature changes and offset the error caused by temperature changes.

[0086] The buoyancy is proportional to the volume of the bellows 3 immersed in the seawater. Since the bellows 3 has a constant right circular cross-section, the volume depends only on the height of the bellows 3 immersed in the water, so the buoyancy can be expressed as:

[0087] F=ρgAΔh=PA=kΔx

[0088] Where ρ is the density of seawater; g is the acceleration due to gravity; A is the cross-sectional area of ​​the bellows 3; k is the elastic modulus of the bellows 3; Δx is the change in length of the bellows 3 or optical fiber 2; and Δh is the change in the water level of the bellows 3 immersed in seawater. Therefore, the change in the length of the optical fiber 2 can be expressed as:

[0089]

[0090] The longitudinal strain suffered by optical fiber 2 can be expressed as:

[0091]

[0092] Where x is the effective length of optical fiber 2. Combining the deformation characteristics of the corrugated tube 3 and the differential mode of optical fiber 2, we have:

[0093]

[0094] Therefore, the water pressure sensitivity K of the push-pull bellows structure can be expressed as:

[0095]

[0096] After the design is completed, the sensor is subjected to stress and thermal simulation tests. As can be seen from the stress cloud diagram, Figure 2 As shown in the figure, the maximum stress of the bellows 3 is 1.658N / mm2 under a water pressure of 2MPa, which is less than the yield stress of 316L stainless steel 1.73N / mm2, ensuring that the deformation of the bellows 3 is within the linear elastic range. Figure 3 As shown, the bellows 3 achieves axial elongation under the action of water pressure, enabling a push-pull structure with the first Bragg grating 6 stretched and the second Bragg grating 7 compressed, consistent with theoretical design. Since the displacement is 0.06073 mm at 2 MPa and the effective length of the grating is 35 mm, the theoretical sensitivity of the sensor is 2 * 1.0441 nm / MPa = 2.0882 nm / MPa. The temperature difference curve of the two gratings under a 1 K temperature change shows that the maximum difference in ambient temperature between the two gratings is 0.0411 K when the ambient temperature changes by 1 K. This temperature difference is sufficiently small to meet the requirement that both gratings in the push-pull structure maintain the same ambient temperature.

[0097] In a temperature-compensated pressure sensor of the present embodiment, seawater flows into the bellows 3 from the first through hole 5 of the housing 1. One end of the bellows 3 is blocked. When subjected to the impact force of the seawater, the bellows 3 moves axially, that is, the bellows 3 stretches, thereby pushing the movable block 4 to move. Since the optical fiber 2 is coaxially arranged with the bellows 3, and the two ends of the optical fiber 2 are fixed and the middle part is connected to the movable block 4, the movement of the movable block 4 will cause one section of the optical fiber 2 to stretch and the other end of the optical fiber 2 to compress; a first Bragg grating 6 is provided on the tensile deformation section, and a second Bragg grating 7 is provided on the compressive deformation section. The positive strain is measured by the first Bragg grating 6, and the negative strain is measured by the second Bragg grating 7. The two strains are equal in magnitude and opposite in direction. Temperature compensation can be achieved through the differential compensation method, thereby effectively reducing the influence of temperature and improving the measurement accuracy of the sensor.

[0098] This embodiment utilizes a grating etched on an optical fiber 2 as a sensing element to form a sensor probe, achieving a passive, all-optical sensing terminal, offering the advantages of safety and reliability for use in electromagnetically sensitive environments. The pressure information sensed by the fiber grating temperature and pressure sensor 2 is reflected by changes in its central wavelength. This wavelength change is converted into a wavelength change in the laser light input to the probe from a remote light source. The laser light carrying the pressure information is then transmitted back to a remote signal processing device via the transmission fiber 2 for pressure data interpretation. The sensor integrates two identical Bragg gratings, employing a push-pull configuration. One Bragg grating senses positive displacement changes associated with pressure conversion, while the other senses negative displacement changes. When the ambient pressure changes, the movable block 4 within the sensor undergoes reciprocating motion, causing the gratings to stretch and compress, resulting in equal displacements. The strain of the second Bragg grating 7 in the compression deformation section and the first Bragg grating 6 in the extension deformation section are equal. The two gratings are exposed to the same temperature environment, providing temperature compensation for each other, improving measurement accuracy and precision. Furthermore, the bellows 3 provides enhanced sensitivity, enabling greater water pressure sensitivity.

[0099] Example 2

[0100] This embodiment is a second embodiment of a temperature difference compensation pressure sensor. This embodiment is similar to the first embodiment, except that in this embodiment, the optical fiber 2 is bonded to the first fixing member 8, the second fixing member 10, and the movable block 4, respectively, for example, by glue.

[0101] Example 3

[0102] This third embodiment of a temperature-compensated pressure sensor is similar to the first embodiment, differing in that a gland connector is provided at the third through-hole 11. Connecting the optical fiber 2 with the gland connector not only secures the optical fiber 2 but also provides a seal, preventing seawater from entering the housing 1 through the third through-hole 11. The gland connector primarily connects the optical cable to the housing 1 and is dustproof and waterproof. This embodiment uses an M8 stainless steel gland connector.

[0103] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0104] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A temperature differential compensation pressure sensor, characterized in that: The invention comprises a shell (1) with a cavity therein, an optical fiber (2), a corrugated tube (3), and a movable block (4) arranged inside the shell (1); the shell (1) is provided with a first through hole (5); one end of the corrugated tube (3) is fixedly installed in the shell (1) and communicates with the first through hole (5); the other end of the corrugated tube (3) is blocked and connected to the movable block (4); both ends of the optical fiber (2) are respectively fixedly installed in the shell (1), and the middle part of the optical fiber (2) is fixedly connected to the movable block (4); the optical fiber (2) and the corrugated tube (3) are coaxially arranged; the corrugated tube (3) is axially displaced by external pressure, pushing the movable block (4) to slide, thereby driving one section of the optical fiber (2) to generate tensile deformation and the other section to generate compressive deformation; a first Bragg grating (6) is provided in the tensile deformation section, and a second Bragg grating (7) is provided in the compressive deformation section; the pressure sensor realizes temperature difference compensation in the following manner: The first Bragg grating (6) and the second Bragg grating (7) are affected by strain and temperature at the same time, and the temperature sensitivity coefficients of the first Bragg grating (6) and the second Bragg grating (7) are consistent. The first Bragg grating (6) measures positive strain, and the second Bragg grating (7) measures negative strain. The two strains are equal in magnitude and opposite in direction: Δλ1-Δλ2=2λ(1-P e )e Wherein, Δλ1 and Δλ2 are the wavelength shifts of the first Bragg grating (6) and the second Bragg grating (7), respectively; λ1 and λ2 are the central wavelengths of the first Bragg grating (6) and the second Bragg grating (7), respectively; λ is the approximate value of λ1 and λ2; α is the thermal expansion coefficient of the materials of the first Bragg grating (6) and the second Bragg grating (7); ξ is the thermo-optical coefficient of the materials of the first Bragg grating (6) and the second Bragg grating (7); ΔT is the temperature change; P e is the effective elastic-optical coefficient of the optical fiber (2); The axial displacement of the bellows (3) is calculated by the following formula: The strain ε of the optical fiber (2) is: Wherein, ρ is the density of seawater; g is the acceleration due to gravity; A is the straight cross-sectional area of ​​the bellows (3); k is the elastic coefficient of the bellows (3); Δx is the change in the length of the bellows (3); Δh is the change in the water level of the bellows (3) immersed in seawater; x is the effective length of the optical fiber (2); Combining the above formulas we get: Then the water pressure sensitivity K of the pressure sensor is:

2. The temperature difference compensated pressure sensor according to claim 1, characterized in that: When the tensile deformation section and the compressive deformation section are fixed, prestress is provided on both sections, and the prestress of the compressive deformation section is greater than the prestress of the tensile deformation section.

3. The temperature difference compensated pressure sensor according to claim 1, characterized in that: The invention also includes a first fixing member (8), wherein the first fixing member (8) is provided with a second through hole (9), the first fixing member (8) is fixed inside the housing (1), the bellows (3) is mounted on the first fixing member (8), and one end of the second through hole (9) is connected to the first through hole (5), and the other end is connected to the pipe mouth of the bellows (3).

4. The temperature difference compensated pressure sensor according to claim 3, characterized in that: The invention also includes a second fixing member (10), which is fixed in the housing (1) and spaced apart from the first fixing member (8). The two ends of the optical fiber (2) are fixedly connected to the first fixing member (8) and the second fixing member (10), respectively. The movable block (4) is located between the first fixing member (8) and the second fixing member (10).

5. The temperature difference compensated pressure sensor according to claim 4, characterized in that: The optical fiber (2) is bonded to the first fixing member (8), the second fixing member (10) and the movable block (4) respectively.

6. The temperature difference compensated pressure sensor according to claim 4, characterized in that: The two ends of the second through hole (9) are sealedly connected to the first through hole (5) and the pipe opening of the bellows (3), respectively; the first through hole (5), the second through hole (9) and the bellows (3) together constitute a pressure channel.

7. The temperature difference compensated pressure sensor according to any one of claims 1 to 6, characterized in that: The tensile deformation section and the compressive deformation section are both suspended.

8. The temperature difference compensated pressure sensor according to claim 7, characterized in that: The lengths of the tensile deformation section and the compressive deformation section are the same.

9. The temperature difference compensated pressure sensor according to claim 8, characterized in that: The housing (1) is provided with a third through hole (11), and one end of the optical fiber (2) passes through the third through hole (11).

10. The temperature difference compensated pressure sensor according to claim 9, characterized in that: A gland joint is provided at the third through hole (11).

Images