A high-pressure resistant optical fiber Fabry-Perot sensor

Abstract

The present invention discloses a high-pressure-resistant optical fiber Fabry-Perot sensor, characterized in that it comprises a cylindrical protective tube body and an optical fiber Fabry-Perot sensing assembly arranged in the protective tube body along the length direction, end cap assemblies are provided at both ends of the protective tube body in a closed manner, the optical fiber Fabry-Perot sensing assembly comprises a sensing optical fiber passing through one of the end cap assemblies along the axial direction and a pigtail installed at the inner end of the other end cap assembly, a sleeve is coaxially provided at one end of the sensing optical fiber and the pigtail opposite to each other, and a Fabry-Perot cavity structure is formed between the two. The present invention has the advantages of strong pressure bearing capacity, not easy to be damaged, and conducive to extending the service life.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, and in particular to a high-pressure resistant optical fiber Fabry-Perot sensor. Background Art

[0002] Fiber optic sensing is one of the important applications of modern fiber optic technology. It has the advantages of small size, simple structure, high sensitivity, strong anti-electromagnetic interference ability, and long-distance transmission. It can be used to detect a variety of physical quantities, such as strain, temperature, pressure, sound field, electric field, vibration, acceleration, etc. Fiber optic Fabry-Perot sensor is one of them. It is widely used in real-time health detection of large engineering structures such as bridges, balance structures, and oil pipelines. Fiber optic Fabry-Perot strain sensor usually encapsulates optical fiber and Fabry-Perot cavity on a deformable strain gauge. When in use, the strain gauge is installed on the structure to be measured. The deformation of the structure to be measured causes the deformation of the strain gauge, and finally the measurement result is obtained.

[0003] When in use, the fiber optic Fabry-Perot strain sensor is often used in a high temperature and high pressure environment, with the pressure reaching 17.5MPa. The existing fiber optic Fabry-Perot strain sensor is often unable to withstand the external pressure, causing damage to the sensor and failing to achieve the detection purpose. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is: how to provide an optical fiber Fabry-Perot sensor which has a strong pressure bearing capacity, is not easily damaged, and is conducive to extending the service life.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A high-pressure resistant fiber Fabry-Perot sensor, characterized in that it comprises a cylindrical protective tube body and a fiber optic Fabry-Perot sensing assembly arranged in the protective tube body along the length direction, end cap assemblies are provided at both ends of the protective tube body in a closed manner, the fiber optic Fabry-Perot sensing assembly comprises a sensing optical fiber axially passing through one of the end cap assemblies and a pigtail installed at the inner end of the other end cap assembly, the sensing optical fiber and the pigtail are coaxially sleeved at the opposite ends thereof, and a Fabry-Perot cavity structure is formed between the two.

[0007] When in use, the two ends of the protective tube are fixed on the surface of the object to be measured. Once the surface of the object to be measured is deformed, the length of the protective tube will change, and then the length of the Fabry-Perot cavity between the sensing optical fiber and the pigtail will change, thereby achieving the measurement of strain. Since the protective tube is cylindrical, when measuring in a fluid, the pressure exerted by the fluid on the surface of the protective tube acts on the protective tube in the radial direction of the protective tube. Since the same pressure is evenly distributed along the circumference, a balance is formed between them, thereby preventing the protective tube from being deformed in the radial direction and damaged. It has a strong pressure-bearing capacity, which is beneficial to protect the internal optical fiber Fabry-Perot sensing component, avoid damage, and extend the service life of the sensor.

[0008] Furthermore, the protective tube body is made of a metal capillary.

[0009] Furthermore, the surface of the protection tube body has a weakened groove arranged along the circumferential direction, the weakened groove is spiral or annular, and the maximum depth of the weakened groove is less than the minimum thickness of the protection tube body.

[0010] In this way, the pressure on the surface of the protective tube body can be balanced in the circumferential direction, and the axial strength of the protective tube body can be reduced, so that the deformation of the surface of the object to be measured can be more reliably transmitted to the protective tube body, thereby ensuring the sensing accuracy.

[0011] Furthermore, the weakening groove is made by laser, electric spark or corrosion processing.

[0012] Furthermore, the outer diameter of the protective tube body is 2 mm to 5 mm, and the wall thickness is 0.1 to 0.2 mm.

[0013] Furthermore, the end cover assembly includes an elongated base and a cylindrical end cover, the end cover is connected to the base along the width direction of the base, and one end of the end cover has a circular groove or boss for sealing the protective tube body.

[0014] Furthermore, the distance between the bottom of the base and the axial center of the end cover is greater than the radius of the protective tube body.

[0015] In this way, when the protective tube body is fixed to the surface of the object to be tested through the base, a gap can be ensured between the protective tube body and the surface of the object, allowing the fluid to fully surround the protective tube body, avoiding unbalanced pressure on the protective tube body and causing pressure damage to the protective tube body.

[0016] Furthermore, a strain gauge in the form of a rectangular sheet is connected between the two end cover assemblies, and the strain gauge includes a pigtail substrate, a Fabry-Perot cavity substrate and a sensing optical fiber substrate which are arranged in sequence and spaced apart along the length direction; an annular elastic deformation ring is connected between the pigtail substrate and the Fabry-Perot cavity substrate, and between the Fabry-Perot cavity substrate and the sensing optical fiber substrate, and the elastic deformation ring includes two arc-shaped semi-rings symmetrically arranged along the width direction of the strain gauge; the sensing optical fiber, pigtail and sleeve are respectively fixed on the sensing optical fiber substrate, the pigtail substrate and the Fabry-Perot cavity substrate.

[0017] Furthermore, the strain gauge has an optical fiber groove extending along the axial direction of the protective tube body, and the sensing optical fiber, pigtail and sleeve are respectively fixed in the optical fiber grooves of the sensing optical fiber substrate, pigtail substrate and Fabry-Perot cavity substrate.

[0018] Furthermore, the pigtail substrate, Fabry-Perot cavity substrate and sensing optical fiber substrate all have glue dripping grooves connected to the optical fiber grooves, and the pigtail, sleeve and sensing optical fiber are fixed in the corresponding optical fiber grooves by glue; both ends of the sleeve are filled with silicone.

[0019] In summary, the present invention has the advantages of strong pressure bearing capacity, not easy to be damaged, and being conducive to extending the service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall structure of this embodiment.

[0021] Figure 2 It is a structural schematic diagram of the end cover assembly.

[0022] Figure 3 It is a schematic diagram of the structure of the protective tube body.

[0023] Figure 4 and Figure 5 Schematic diagram of the structure of the strain gauge. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with embodiments.

[0025] When implementing: Figure 1 to Figure 5 As shown, a high-pressure resistant optical fiber Fabry-Perot sensor comprises a cylindrical protective tube body 1 and an optical fiber Fabry-Perot sensing assembly 2 arranged in the protective tube body 1 along the length direction, end cover assemblies 3 are closed at both ends of the protective tube body 1, and a rectangular sheet-shaped strain gauge 4 is connected between the two end cover assemblies 3.

[0026] When in use, the two ends of the protective tube are fixed on the surface of the object to be measured. Once the surface of the object to be measured is deformed, the length of the protective tube will change, and then the length of the Fabry-Perot cavity between the sensing optical fiber and the pigtail will change, thereby achieving the measurement of strain. Since the protective tube is cylindrical, when measuring in a fluid, the pressure exerted by the fluid on the surface of the protective tube acts on the protective tube in the radial direction of the protective tube. Since the same pressure is evenly distributed along the circumference, a balance is formed between them, thereby preventing the protective tube from being deformed in the radial direction and damaged. It has a strong pressure-bearing capacity, which is beneficial to protect the internal optical fiber Fabry-Perot sensing component, avoid damage, and extend the service life of the sensor.

[0027] The optical fiber Fabry-Perot sensing assembly 2 comprises a coaxially arranged sensing optical fiber 21, a pigtail 22 and a sleeve 23. The opposite ends of the sensing optical fiber 21 and the pigtail 22 extend into the sleeve 23 to form a Fabry-Perot cavity structure. The sensing optical fiber 21 passes through one of the end cap assemblies 3, and the pigtail 22 is arranged at the inner end of the other end cap assembly 3. The two ends of the sleeve 23 are filled with sealing silicone. The sealing silicone is used to ensure the original cavity length of the Fabry-Perot cavity between the sensing optical fiber 21 and the pigtail 22. During detection, the sensing optical fiber 21 and the pigtail 22 move relative to each other under the action of an external force, changing the cavity length of the Fabry-Perot cavity, so that the optical signal in the sensing optical fiber 21 changes, thereby measuring the strain size. Once the external deformation is eliminated, the sealing silicone can also restore the Fabry-Perot cavity between the two to its original cavity length.

[0028] like Figure 4 As shown, the strain gauge 4 includes a pigtail substrate 41, a Fabry-Perot cavity substrate 42 and a sensing optical fiber substrate 43 which are arranged in sequence along the length direction. An annular elastic deformation ring 44 is connected between the pigtail substrate 41 and the Fabry-Perot cavity substrate 42, and between the Fabry-Perot cavity substrate 42 and the sensing optical fiber substrate 43. The elastic deformation ring 44 includes two arc-shaped semi-rings symmetrically arranged along the width direction of the strain gauge 4. The strain gauge 4 has an optical fiber groove extending along the axial direction of the protective tube body 1, and the sensing optical fiber 21, the pigtail 22 and the sleeve 23 are respectively fixed in the optical fiber grooves of the sensing optical fiber substrate 43, the pigtail substrate 41 and the Fabry-Perot cavity substrate 42.

[0029] Specifically, the pigtail substrate 41, the Fabry-Perot cavity substrate 42 and the sensing optical fiber substrate 43 are all provided with glue dripping grooves connected with the optical fiber grooves, and the pigtail, the sleeve and the sensing optical fiber are fixed in the corresponding optical fiber grooves by adhesive.

[0030] In this way, the pigtail and the sensing optical fiber are fixed on the pigtail substrate and the sensing optical fiber substrate respectively by adhesive, the sleeve is fixed on the Fabry-Perot cavity substrate 42, and the opposite ends of the pigtail and the sensing optical fiber extend into the sleeve and are free ends. After the end cap assemblies 3 at both ends are subjected to force, the pigtail substrate 41 and the sensing optical fiber substrate 43 move relative to the Fabry-Perot cavity substrate 42, pulling the pigtail and the sensing optical fiber, changing the cavity length of the Fabry-Perot cavity between the two, thereby realizing detection. When the pigtail substrate 41 and the sensing optical fiber substrate 43 move relative to the Fabry-Perot cavity substrate 42, the elastic deformation ring 44 undergoes elastic deformation. Once the external force is eliminated, the elastic deformation ring can reset the pigtail and the sensing optical fiber.

[0031] The end cap assembly 3 includes a long strip base 31 and a cylindrical end cap 32, wherein the end cap 32 is connected to the base 31 along the width direction of the base 31, and one end of the end cap 32 has a circular groove or boss for sealing the protection tube body 1. The distance between the bottom of the base 31 and the axial center of the end cap 32 is greater than the radius of the protection tube body 1.

[0032] In this way, when the protective tube body is fixed to the surface of the object to be tested through the base, a gap can be ensured between the protective tube body and the surface of the object, allowing the fluid to fully surround the protective tube body, avoiding unbalanced pressure on the protective tube body and causing pressure damage to the protective tube body.

[0033] In this embodiment, both ends of the strain gauge 4 are connected to a cylindrical base, the diameter of the base matches the inner diameter of the protection tube body 1, and both ends of the protection sleeve 1 are sleeved on the base.

[0034] The base 31 and the end cap 32 are integrally formed, and one side of the end cap 32 has a circular groove, the inner diameter of which is consistent with the diameter of the base, and is sleeved on the base. The bottom of the base 31 has two positioning holes, and the positioning holes are distributed along the length direction of the base 31. In this way, during calibration, corresponding positioning holes can be set at corresponding positions on the standard body to be measured, and the optical fiber Fabry-Perot sensor to be calibrated can be connected to the standard body to be measured by a pin, so as to improve the efficiency of calibration.

[0035] In addition, in this embodiment, the protective sleeve 1 is filled with high temperature resistant soft glue. In this way, the high temperature resistant soft glue is used to wrap the middle strain ring (elastic deformation ring 44) and the suspended optical fiber of the strain ring to prevent the suspended optical fiber from being shattered under the external vibration, thereby achieving a shockproof effect. High temperature resistant soft glue is a mature existing product. High temperature resistant soft glue products are vulcanized into elastomers by contacting moisture in the air. The vulcanized rubber can be used for a long time in the temperature range of -60~+2000C, has excellent electrical insulation performance and chemical stability, is resistant to water, ozone, and weather aging, and has good adhesion to a variety of metal and non-metal materials.

[0036] In addition, the high temperature resistant soft glue fills the inner cavity of the protective sleeve 1, providing certain support for the protective sleeve from the inside. At the same time, once the protective sleeve is damaged, the high temperature resistant soft glue can also completely wrap the strain gauge 4 and the optical fiber Fabry-Perot sensor component 2 installed on the strain gauge to provide protection, thereby preventing high pressure from damaging the optical fiber Fabry-Perot sensor component 2 and improving the reliability of the sensor.

[0037] In this embodiment, the protective tube body 1 is made of a stainless steel capillary (it can also be made of other metal capillaries). Considering that the overall deformation ability of the sensor in the axial direction is weakened after adding the protective tube body 1, in order to ensure sufficient detection accuracy, in this embodiment, the surface of the protective tube body 1 has a weakened groove arranged along the circumferential direction (such as Figure 3 As shown in the figure), the weakening groove is spiral or annular, and the maximum depth of the weakening groove is less than the minimum thickness of the protective tube body 1.

[0038] In this way, the pressure on the surface of the protective tube body can be balanced in the circumferential direction, and the axial strength of the protective tube body can be reduced, so that the deformation of the surface of the object to be measured can be more reliably transmitted to the protective tube body, thereby ensuring the sensing accuracy.

[0039] In this embodiment, the outer diameter of the protection tube body 1 is 2.5 mm, and the wall thickness is 0.1 mm. Since the wall thickness of the protection tube body 1 is very thin, the weakening groove can be made by laser, electric spark or corrosion processing.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-pressure resistant optical fiber Fabry-Perot sensor, characterized in that: The invention comprises a cylindrical protective tube body (1) and an optical fiber Fabry-Perot sensor assembly (2) arranged in the protective tube body (1) along the length direction, end cap assemblies (3) are provided at both ends of the protective tube body (1) in a sealed manner, the optical fiber Fabry-Perot sensor assembly (2) comprises a sensing optical fiber (21) passing through one of the end cap assemblies (3) along the axial direction and a pigtail (22) installed at the inner end of the other end cap assembly (3), a sleeve (23) is coaxially sleeved at the opposite ends of the sensing optical fiber (21) and the pigtail (22), and a Fabry-Perot cavity structure is formed between the two ends; the protective tube body (1) is made of a metal capillary, and the protective sleeve (1) is filled with high-temperature resistant soft glue; the outer diameter of the protective tube body (1) is 2 mm to 5 mm, and the wall thickness is 0.1 mm to 0.2 mm.

2. The high-pressure resistant optical fiber Fabry-Perot sensor according to claim 1, characterized in that: The surface of the protective tube body (1) has a weakened groove arranged along the circumferential direction, the weakened groove is spiral or annular, and the maximum depth of the weakened groove is less than the minimum thickness of the protective tube body (1).

3. The high-pressure-resistant optical fiber Fabry-Perot sensor according to claim 2, characterized in that: The weakened groove is made by laser, electric spark or corrosion processing.

4. The high-pressure-resistant optical fiber Fabry-Perot sensor according to claim 1, characterized in that: The end cover assembly (3) comprises a long strip-shaped base (31) and a cylindrical end cover (32), wherein the end cover (32) is connected to the base (31) along the width direction of the base (31), and one end of the end cover (32) has a circular groove or a boss for sealing the protective tube body (1).

5. The high-pressure-resistant optical fiber Fabry-Perot sensor according to claim 4, characterized in that: The distance between the bottom of the base (31) and the axial center of the end cover (32) is greater than the radius of the protective tube body (1).

6. The high-pressure-resistant optical fiber Fabry-Perot sensor according to claim 1, characterized in that: A strain gauge (4) in the form of a rectangular sheet is connected between the two end cover assemblies (3); the strain gauge (4) comprises a pigtail substrate (41), a Fabry-Perot cavity substrate (42) and a sensing optical fiber substrate (43) which are arranged in sequence and spaced apart along the length direction; an annular elastic deformation ring (44) is connected between the pigtail substrate (41) and the Fabry-Perot cavity substrate (42), and between the Fabry-Perot cavity substrate (42) and the sensing optical fiber substrate (43); the elastic deformation ring (44) comprises two arc-shaped half rings which are symmetrically arranged along the width direction of the strain gauge (4); and the sensing optical fiber (21), the pigtail (22) and the sleeve (23) are respectively fixed on the sensing optical fiber substrate (43), the pigtail substrate (41) and the Fabry-Perot cavity substrate (42).

7. The high-pressure-resistant optical fiber Fabry-Perot sensor according to claim 6, characterized in that: The strain gauge (1) has an optical fiber groove extending along the axial direction of the protective tube body (1), and the sensing optical fiber (21), the pigtail fiber (22) and the sleeve (23) are respectively fixed in the optical fiber grooves of the sensing optical fiber substrate (43), the pigtail fiber substrate (41) and the Fabry-Perot cavity substrate (42).

8. The high-pressure-resistant optical fiber Fabry-Perot sensor according to claim 7, characterized in that: The pigtail substrate (41), the Fabry-Perot cavity substrate (42) and the sensing optical fiber substrate (43) are all provided with glue dripping grooves which are in communication with the optical fiber grooves; the pigtail, the sleeve and the sensing optical fiber are fixed in the corresponding optical fiber grooves by means of adhesive; and both ends of the sleeve are filled with silica gel.

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