Cable based on distributed optical fiber temperature measurement and temperature measurement method thereof

Abstract

The invention relates to the technical field of temperature measurement optical fiber cables, and discloses a cable based on distributed optical fiber temperature measurement and a temperature measurement method thereof.The cable comprises a laid cable, the laid cable comprises a conductor, an insulating layer, a coating layer and a protective layer from inside to outside, temperature measurement optical fibers are arranged in the coating layer, the number of the temperature measurement optical fibers is at least two, and the number of the temperature measurement optical fibers is an even number; every two temperature measuring optical fibers form a group and are arranged around the conductor in a spiral symmetrical mode, a laser emitting module for emitting pulses to the temperature measuring optical fibers and a signal demodulation unit for collecting and analyzing data are arranged at the end of the laid cable, a sunken layer is arranged on the outer side of each temperature measuring optical fiber, the sunken layer is of a porous structure as a whole, and the temperature measuring optical fibers are arranged in the sunken layer. The refractive index of the concave layer is lower than that of the temperature measuring optical fiber, a circular air hole is formed in the concave layer, after different laid cables are connected, the outer sheath wraps the outer part, a magnetic attraction ring is arranged on one side of the outer sheath, and the two outer sheaths are attracted at the joint of the laid cables through magnetic attraction of the magnetic attraction ring.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature-measuring optical fiber cables, and specifically to a cable based on distributed optical fiber temperature measurement and a temperature measurement method therefor. Background Art

[0002] A cable based on distributed optical fiber temperature measurement is an innovative design that combines optical fiber sensing technology with power cables, enabling real-time, continuous, and long-distance monitoring of the temperature distribution along the cable. The core of this cable is the integration of an optical fiber sensing unit in a traditional power cable. The optical fiber serves both as a temperature sensor and a signal transmission medium. Distributed optical fiber temperature measurement is based on optical time domain reflectometry (OTDR) and Raman scattering effect, and the temperature distribution is retrieved by analyzing the characteristics of the backward scattered light in the optical fiber.

[0003] When the optical fiber detects the temperature of the cable, it is restricted by its set distribution position. Due to manufacturing costs, multiple optical fibers are usually not arranged in a circumferential array around the conductor in the cable for omnidirectional temperature detection. Therefore, the temperature measurement position and accuracy are limited. At the same time, in some usage scenarios, such as underwater use, due to the action of water flow, the cable will bend slightly, resulting in possible deviation of the laser propagation in the optical fiber and causing errors. Summary of the Invention

[0004] (1) Technical problems to be solved: Aiming at the deficiencies of the prior art, the present invention provides a cable based on distributed optical fiber temperature measurement and a temperature measurement method therefor, which have the advantages of multi-position detection and strong anti-bending ability, and solve the problem of inaccurate cable temperature measurement.

[0005] (2) Technical solutions: To achieve the above purposes of multi-position detection and strong anti-bending ability, the present invention provides the following technical solutions: A cable based on distributed optical fiber temperature measurement and a temperature measurement method therefor, including a laid cable. The laid cable includes a conductor, an insulating layer, a coating layer, and a protective layer from the inside to the outside. The coating layer is provided with temperature-measuring optical fibers. There are at least two and an even number of temperature-measuring optical fibers. Every two temperature-measuring optical fibers form a group and are arranged around the conductor in a helical symmetric manner, and the pitch of the temperature-measuring optical fibers is greater than 3 meters. The end of the laid cable is provided with a laser emission module for emitting pulses to the temperature-measuring optical fibers and a signal demodulation unit for collecting and analyzing data. The outside of the temperature-measuring optical fibers is provided with a recessed layer. The recessed layer is a porous structure as a whole, and the refractive index of the recessed layer is lower than that of the temperature-measuring optical fibers. The recessed layer is provided with circular air holes. After the connection of different laid cables is completed, an outer sheath is wrapped outside. One side of the outer sheath is provided with a magnetic attraction ring, and the two outer sheaths are attracted and joined at the connection of the laid cables through the magnetic force of the magnetic attraction ring.

[0006] The outer sheath is composed of a flexible pressure guiding cavity, a braided layer, and a drag reduction layer from the inside to the outside. The flexible pressure guiding cavity is filled with fluid. The braided layer has a structure imitating nacre, and carbon fibers are orthogonally braided at 90°, with epoxy resin embedded between layers. The surface of the drag reduction layer is provided with V-shaped notches.

[0007] An oil injection channel is provided in the outer sheath. One end of the oil injection channel communicates with the flexible pressure guiding cavity, and the other end extends outside the drag reduction layer. The oil injection channel is in a closed state under normal conditions.

[0008] A sealing ring is provided on the side of the outer sheath away from the magnetic attraction ring. The sealing ring communicates with the flexible pressure guiding cavity, and the degree of pressure-induced deformation of the sealing ring is less than that of the flexible pressure guiding cavity.

[0009] The circular air holes are in a non-uniform array in the recessed layer.

[0010] There are two temperature measurement optical fibers, and the included angle between the connecting lines of their positions in the cross-section of the cable is 180°.

[0011] There are four temperature measurement optical fibers, divided into two groups. The included angle between the connecting lines of the positions of the two temperature measurement optical fibers in each group in the cross-section of the cable is 180°, and the distances between different groups of temperature measurement optical fibers and the conductor are different.

[0012] The included angle between the connecting lines of the positions of the temperature measurement optical fibers in one of the two groups and the temperature measurement optical fibers in the other group in the cross-section of the cable is 90°.

[0013] (3) Beneficial effects: Compared with the prior art, the present invention provides a cable based on distributed optical fiber temperature measurement and its temperature measurement method, having the following beneficial effects: 1. For the cable based on distributed optical fiber temperature measurement and its temperature measurement method, by arranging two temperature measurement optical fibers in the cable's coating layer to surround the conductor in a helical symmetric manner and ensuring that the pitch is greater than 3 meters, such a design not only realizes periodic sampling along the circumferential direction of the cable, effectively avoiding the monitoring blind spots that may be generated by linear arrangement, but also provides data redundancy. When one of the optical fibers breaks due to a fault, the other optical fiber can still continue to work, ensuring at least 50% of the monitoring ability, greatly improving the reliability and stability of the system. The recessed layer provided on the outside of the temperature measurement optical fiber adopts a porous structure of fluorine-doped quartz or air gap, and its refractive index is lower than that of the temperature measurement optical fiber itself. This design enhances the optical waveguide effect and effectively reduces the leakage of light when the optical fiber is bent. Especially in an underwater environment, when the cable is bent by the action of water flow, although the light field will shift outward due to centrifugal force, the low-refractive-index recessed layer can effectively block the leakage of light, significantly reducing the bending loss and protecting the quality of the temperature measurement signal. The circular air hole design in the recessed layer not only further reduces the overall density of the structure, improves the buoyancy of the cable, making it more suitable for submarine laying, but also enhances the anti-bending ability of the cable, avoiding excessive deformation caused by complex submarine terrain and water flow impact, thereby protecting the temperature measurement optical fiber from damage. A magnetic attraction ring is provided on the outer sheath wrapped around the cable, facilitating the quick connection and fixation between cables. Especially in underwater operations, this magnetic attraction connection method simplifies the installation process and reduces the difficulty and risk of underwater operations.

[0014] 2. For the cable based on distributed optical fiber temperature measurement and its temperature measurement method, the flexible pressure guiding cavity inside the outer sheath is filled with fluid. This design enables the cable to dynamically balance the overall deformation through the fluidity of the fluid when it is under water pressure, which helps to reduce the local excessive deformation of the cable caused by uneven water pressure, protect the internal temperature measurement optical fiber, especially the optical fiber at the connection between cables from damage, and at the same time maintain the overall structure and performance stability of the cable. The braided layer is orthogonally braided with carbon fiber at 90° and embedded with epoxy resin. This structure mimics the nacre of a shell in nature and has excellent mechanical properties and durability. It can effectively resist mechanical stresses from all directions, especially the tensile, compressive, and shear forces in a complex underwater environment, thereby extending the service life of the cable. The circular air holes in the recessed layer are arranged in a non-uniform array. This design, while ensuring the anti-bending ability of the cable, effectively reduces the production cost by reducing the number of air holes and / or adjusting their distribution. This is of great significance for large-scale production and application and helps to promote the commercialization process of this technology.

[0015] 3. The cable based on distributed optical fiber temperature measurement and its temperature measurement method inject compressible silicone oil into the flexible pressure guiding cavity through the oil injection channel, which not only fixes the installation position of the outer sheath, but also enhances the overall stability and sealing performance of the outer sheath. The injection of silicone oil enables the flexible pressure guiding cavity to better balance deformation when subjected to water pressure. At the same time, the compressibility of silicone oil also provides a certain buffering effect for the outer sheath, helping to resist external pressure. The sealing ring is connected to the flexible pressure guiding cavity, and its deformation degree under pressure is less than that of the flexible pressure guiding cavity. When the outer sheath is subjected to water pressure, the silicone oil in the flexible pressure guiding cavity will flow into the sealing ring. Since the deformation degree of the sealing ring is small, the fluid concentrates in the sealing ring, effectively closing one side of the outer sheath. This design not only improves the underwater adaptability of the outer sheath, but also helps to extend its service life. Especially in the long-term underwater environment, the oil injection channel is not only used to inject silicone oil, but also strengthens the connection between the layers of the outer sheath. This design helps to prevent the separation between the layers of the outer sheath during long-term underwater use, maintaining the integrity and stability of the outer sheath.

[0016] 4. The cable based on distributed optical fiber temperature measurement and its temperature measurement method are provided with four temperature measurement optical fibers, which are divided into two groups. The included angle between the connecting lines of the positions of the two temperature measurement optical fibers in each group on the cross-section of the cable is 180°, and the distances between the temperature measurement optical fibers in different groups and the conductor are different. This four-quadrant sampling layout can capture the temperature distribution around the cable more comprehensively. Especially in three-dimensional space, it can provide more detailed and accurate data, which helps to improve the modeling accuracy of the three-dimensional thermal field and make the temperature monitoring results more reliable. Through the cooperation of the temperature measurement optical fibers and the recessed layer, a mesh support structure is formed. This structure not only enhances the overall bending resistance of the cable, but also effectively protects the temperature measurement optical fibers from external stress. In complex environments, such as when submarine cables are affected by external forces such as water flow scouring and submarine terrain changes, the mesh support structure can maintain the stability and accuracy of the temperature measurement optical fibers, ensuring high-precision acquisition. Compared with using only one or a small number of temperature measurement optical fibers, the setting of four temperature measurement optical fibers provides higher data acquisition reliability and redundancy. Even if one or several of the optical fibers fail or are damaged, the remaining optical fibers can still continue to work, ensuring the continuity and integrity of data acquisition. This is particularly important for long-term monitoring tasks and can reduce the risk of monitoring interruption caused by optical fiber failures. Brief Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the optical fiber distribution in the present invention.

[0018] Figure 2 It is a schematic cross-section diagram of the cable in Embodiment 1 of the present invention.

[0019] Figure 3 It is a schematic diagram of the outer sheath structure in the present invention Figure 1 .

[0020] Figure 4 Schematic diagram of the outer sheath structure in the present invention Figure 2 。

[0021] Figure 5 Schematic cross-sectional view of the concave layer in the present invention.

[0022] Figure 6 Schematic cross-sectional view of the outer sheath in the present invention.

[0023] Figure 7 Schematic cross-sectional view of the cable in the second embodiment of the present invention.

[0024] In the figure: 1, laid cable; 2, outer sheath; 11, conductor; 12, insulating layer; 13, coating layer; 14, temperature-measuring optical fiber; 15, protective layer; 21, flexible pressure-conducting cavity; 22, braided layer; 23, drag-reducing layer; 141, concave layer; 142, circular air hole; 201, magnetic attraction ring; 202, sealing ring; 211, oil injection channel; 231, notch. Specific embodiments

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] Embodiment 1: Please refer to Figures 1-5 , a cable based on distributed optical fiber temperature measurement and its temperature measurement method, including a laid cable 1, the laid cable 1 from the inside to the outside is respectively a conductor 11, an insulating layer 12, a coating layer 13 and a protective layer 15, a temperature-measuring optical fiber 14 is arranged in the coating layer 13, at least two temperature-measuring optical fibers 14 are provided and are even in number, every two temperature-measuring optical fibers 14 are in a group, and are arranged around the conductor 11 in a helical symmetric manner, and the pitch of the temperature-measuring optical fiber 14 is greater than 3 meters, a laser emission module for emitting pulses to the temperature-measuring optical fiber 14 and a signal demodulation unit for collecting and analyzing data are arranged at the end of the laid cable 1, a concave layer 141 is arranged outside the temperature-measuring optical fiber 14, the concave layer 141 is a porous structure as a whole, and the refractive index of the concave layer 141 is lower than that of the temperature-measuring optical fiber 14, circular air holes 142 are arranged in the concave layer 141, after the connection between different laid cables 1 is completed, an outer sheath 2 is wrapped outside, a magnetic attraction ring 201 is arranged on one side of the outer sheath 2, and the two outer sheaths 2 are attracted and combined at the connection of the laid cable 1 through the magnetic attraction of the magnetic attraction ring 201.

[0027] Two temperature-measuring optical fibers 14 that are arranged in a spiral-symmetrical manner around the conductor 11 are provided in the coating layer 13 of the laid cable 1, and the pitch is fixed. Pulses of 1550 nm and 1310 nm are emitted into the temperature-measuring optical fiber 14 through the laser emission module at the cable end to activate Raman and Brillouin scattering respectively. According to the speed of light and the refractive index of the optical fiber, the position of the event point is located. By pre-storing the spiral parameters of the pitch and diameter, the linear distance is converted into three-dimensional space coordinates. The Raman signal is used to calculate the temperature, the Brillouin signal is used to solve the strain, and the cross-sensitivity of temperature to strain is eliminated to generate a temperature-strain distribution map of the cable axis. When there is an over-limit area, that is, a temperature anomaly area, an alarm is triggered. The spiral path ensures that the temperature-measuring optical fiber 14 samples periodically along the circumferential direction of the cable to avoid the monitoring blind area caused by a straight-line arrangement. The two optical fibers are backup to each other, and 50% monitoring ability is still retained when a single optical fiber is broken. The outside of the temperature-measuring optical fiber 14 is wrapped with a depression layer 141. The depression layer 141 is a porous structure of fluorine-doped quartz or air gap, and the refractive index is less than that of the temperature-measuring optical fiber 14. The depression layer 141 forms a stronger optical waveguide effect by increasing the effective refractive index difference between the core and the outer cladding. When the cable is laid underwater and the optical fiber is bent under the action of water flow, the light field shifts outward due to centrifugal force, but the low refractive index of the depression layer will block the light leakage and significantly reduce the bending loss. Circular air holes 142 are provided in the depression layer 141. The circular air holes 142 can improve the anti-bending ability of the entire laid cable 1 in the seabed and avoid excessive deformation that may damage the temperature-measuring optical fiber 14.

[0028] Refer to Figure 6 , the outer sheath 2 is composed of a flexible pressure-conducting cavity 21, a braided layer 22, and a drag-reducing layer 23 from the inside to the outside. The flexible pressure-conducting cavity 21 is filled with fluid. Through the fluidity of the fluid, when the cable is underwater and under the action of water pressure, the overall deformation can be dynamically balanced. The braided layer 22 imitates the nacre structure of a shell, and carbon fibers are orthogonally braided at 90°, and epoxy resin is embedded between layers to form a mechanical support. The surface of the drag-reducing layer 23 is provided with V-shaped notches 231 to reduce the water flow resistance and suppress vortex vibration.

[0029] The outer sheath 2 is provided with an oil injection channel 211. One end of the oil injection channel 211 is communicated with the flexible pressure guiding cavity 21, and the other end extends out of the drag reduction layer 23. The oil injection channel 211 is in a closed state under normal conditions. After the construction personnel complete the connection and the installation of the outer sheath 2, compressible silicone oil is injected into the flexible pressure guiding cavity 21 through the oil injection channel 211, so that the installation position of the outer sheath 2 is fixed. A sealing ring 202 is provided on one side of the outer sheath 2 away from the magnetic attraction ring 201. The sealing ring 202 is communicated with the flexible pressure guiding cavity 21, and the degree of compression deformation of the sealing ring 202 is less than that of the flexible pressure guiding cavity 21. When the compressed silicone oil in the flexible pressure guiding cavity 21 is affected by the water pressure, it will flow into the sealing ring 202. At the same time, the deformation degree of the sealing ring 202 is small. Under the same pressure, the fluid will concentrate in the sealing ring 202 to realize the sealing of one side of the outer sheath 2. At the same time, the setting of the oil injection channel 211 strengthens the connection between the layers of the outer sheath 2 and avoids separation when it is underwater for a long time.

[0030] Refer to Figure 5 , the circular air holes 142 are in a non-uniform array in the recessed layer 141. On the premise of ensuring a certain anti-bending property, the non-uniform array greatly reduces the production cost.

[0031] Refer to Figure 2 , two temperature-measuring optical fibers 14 are provided, and the included angle of the connection lines of the positions where they are located in the cross-section of the cable is 180°. It is simple to process, has a low manufacturing cost, and is symmetrically distributed, improving the anti-interference ability to unilateral compressive stress without excessively increasing the production cost.

[0032] Embodiment 2: Please refer to Figure 1 , Figures 3-5 and Figure 7 , a cable based on distributed optical fiber temperature measurement and its temperature measurement method, including a laid cable 1. The laid cable 1 from the inside to the outside is respectively a conductor 11, an insulating layer 12, a covering layer 13 and a protective layer 15. A temperature-measuring optical fiber 14 is provided in the covering layer 13. At least two and an even number of temperature-measuring optical fibers 14 are provided. Every two temperature-measuring optical fibers 14 form a group and are arranged around the conductor 11 in a helical symmetric manner, and the pitch of the temperature-measuring optical fiber 14 is greater than 3 meters. A laser emission module for emitting pulses to the temperature-measuring optical fiber 14 and a signal demodulation unit for collecting and analyzing data are provided at the end of the laid cable 1. A recessed layer 141 is provided outside the temperature-measuring optical fiber 14. The recessed layer 141 is a porous structure as a whole, and the refractive index of the recessed layer 141 is lower than that of the temperature-measuring optical fiber 14. Circular air holes 142 are provided in the recessed layer 141. After the connection of different laid cables 1 is completed, an outer sheath 2 is wrapped outside. A magnetic attraction ring 201 is provided on one side of the outer sheath 2. Through the magnetic attraction of the magnetic attraction ring 201, the two outer sheaths 2 are attracted and combined at the connection of the laid cables 1.

[0033] Two temperature-measuring optical fibers 14 that are arranged in a helical symmetry manner around the conductor 11 are provided in the coating layer 13 of the laid cable 1, and the pitch is fixed. Pulses of 1550 nm and 1310 nm are emitted into the temperature-measuring optical fiber 14 through the laser emission module at the cable end to activate Raman and Brillouin scattering respectively. According to the speed of light and the refractive index of the optical fiber, the position of the event point is located. By pre-storing the helical parameters of the pitch and diameter, the linear distance is converted into three-dimensional space coordinates. The Raman signal is used to calculate the temperature, and the Brillouin signal is used to solve the strain, and the cross-sensitivity of temperature to strain is eliminated to generate the axial temperature-strain distribution map of the cable. When there is an over-limit area, that is, a temperature anomaly area, an alarm is triggered. The helical path ensures that the temperature-measuring optical fiber 14 samples periodically along the circumferential direction of the cable to avoid the monitoring blind area caused by a straight arrangement. The two optical fibers are backup to each other, and 50% monitoring ability is still retained when a single optical fiber is broken. The outside of the temperature-measuring optical fiber 14 is wrapped with a recessed layer 141. The recessed layer 141 is a porous structure of fluorine-doped quartz or air gap, and the refractive index is less than that of the temperature-measuring optical fiber 14. The recessed layer 141 forms a stronger optical waveguide effect by increasing the effective refractive index difference between the core and the outer cladding. When the cable is arranged underwater and the optical fiber is bent under the action of water flow, the light field shifts outward due to centrifugal force, but the low refractive index of the recessed layer will block the light leakage and significantly reduce the bending loss. Circular air holes 142 are provided in the recessed layer 141. The circular air holes 142 can improve the anti-bending ability of the entire laid cable 1 on the seabed and avoid excessive deformation that may damage the temperature-measuring optical fiber 14.

[0034] See Figure 6 , the outer sheath 2 is composed of a flexible pressure-conducting cavity 21, a braided layer 22 and a drag-reducing layer 23 from the inside to the outside. The flexible pressure-conducting cavity 21 is filled with fluid. Through the fluidity of the fluid, when the cable is underwater and affected by water pressure, the overall deformation can be dynamically balanced. The braided layer 22 imitates the nacre structure of a shell, and carbon fibers are orthogonally braided at 90°, and epoxy resin is embedded between layers to form a mechanical support. The surface of the drag-reducing layer 23 is provided with V-shaped notches 231 to reduce the water flow resistance and suppress the vortex vibration.

[0035] An oil injection channel 211 is provided in the outer sheath 2. One end of the oil injection channel 211 is communicated with the flexible pressure-conducting cavity 21, and the other end extends out of the drag-reducing layer 23. The oil injection channel 211 is in a closed state under normal conditions. After the construction personnel complete the connection and the installation of the outer sheath 2, compressible silicone oil is injected into the flexible pressure-conducting cavity 21 through the oil injection channel 211 to fix the installation position of the outer sheath 2. A sealing ring 202 is provided on the side of the outer sheath 2 away from the magnetic attraction ring 201. The sealing ring 202 is communicated with the flexible pressure-conducting cavity 21, and the compression deformation degree of the sealing ring 202 is less than that of the flexible pressure-conducting cavity 21, so that the compressed silicone oil in the flexible pressure-conducting cavity 21 will flow into the sealing ring 202 under the action of water pressure. At the same time, the deformation degree of the sealing ring 202 is small, and under the same pressure, the fluid will concentrate in the sealing ring 202 to realize the sealing of one side of the outer sheath 2.

[0036] Refer to Figure 5 , the circular air holes 142 are in a non-uniform array in the recessed layer 141. On the premise of ensuring a certain bending resistance, the non-uniform array greatly reduces the production cost.

[0037] Refer to Figure 7 , there are four temperature-measuring optical fibers 14. Every two are divided into a group. The included angle between the connecting lines of the positions of the two temperature-measuring optical fibers 14 in each group on the cross-section of the cable is 180°. And the distances between the temperature-measuring optical fibers 14 in different groups and the conductor 11 are different. The included angle between the connecting lines of the positions of the temperature-measuring optical fibers 14 in one of the two groups and the temperature-measuring optical fibers 14 in the other group on the cross-section of the cable is 90°. Through sampling in four quadrants, the modeling accuracy of the three-dimensional thermal field is greatly improved. And through cooperation with the recessed layer 141, a reticular support is formed, and the bending resistance is greatly improved, so that the temperature-measuring optical fibers 141 can also achieve high-precision acquisition in a complex environment.

[0038] Working principle: There are two temperature-measuring optical fibers 14 wound around the conductor 11 in a spiral symmetric manner in the coating layer 13 of the laid cable 1, and the pitch is fixed. Pulses of 1550 nm and 1310 nm are emitted into the temperature-measuring optical fibers 14 through the laser emission module at the cable end to activate Raman and Brillouin scattering respectively. According to the speed of light and the refractive index of the optical fiber, the position of the event point is located. By pre-storing the spiral parameters of the pitch and diameter, the linear distance is converted into three-dimensional space coordinates. The Raman signal calculates the temperature, and the Brillouin signal resolves the strain, and eliminates the cross-sensitivity of temperature to strain, generating the axial temperature-strain distribution map of the cable. When there is an over-limit area, that is, a temperature anomaly area, an alarm is triggered. The spiral path ensures that the temperature-measuring optical fibers 14 perform periodic sampling along the circumferential direction of the cable to avoid the monitoring blind area caused by a straight-line arrangement. The two optical fibers are backup to each other. When a single optical fiber is broken, 50% of the monitoring ability is still retained. The outside of the temperature-measuring optical fibers 14 is wrapped with a recessed layer 141. The recessed layer 141 is a porous structure of fluorine-doped quartz or air gap, and the refractive index is less than that of the temperature-measuring optical fibers 14. The recessed layer 141 forms a stronger optical waveguide effect by increasing the effective refractive index difference between the core and the outer cladding. When the optical fiber is bent, the optical field shifts outward due to the centrifugal force, but the low refractive index of the recessed layer will block the light leakage, significantly reducing the bending loss. The recessed layer 141 is provided with circular air holes 142. The circular air holes 142 can improve the bending resistance of the whole laid cable 1 in the seabed and avoid damage to the temperature-measuring optical fibers 14 caused by excessive deformation.

[0039] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0040] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A cable based on distributed optical fiber temperature measurement, comprising a laid cable (1), wherein the laid cable (1) includes a conductor (11), an insulating layer (12), a coating layer (13), and a protective layer (15) from inside to outside, and is characterized in that: A temperature-measuring optical fiber (14) is provided in the coating layer (13). There are at least two and an even number of the temperature-measuring optical fibers (14). Every two temperature-measuring optical fibers (14) form a group and are arranged around the conductor (11) in a helical symmetric manner. The pitch of the temperature-measuring optical fiber (14) is greater than 3 meters. At the end of the laid cable (1), there are a laser emission module for emitting pulses to the temperature-measuring optical fiber (14) and a signal demodulation unit for collecting and analyzing data. A recessed layer (141) is provided outside the temperature-measuring optical fiber (14). The recessed layer (141) is a porous structure as a whole, and the refractive index of the recessed layer (141) is lower than that of the temperature-measuring optical fiber (14). Circular air holes (142) are provided in the recessed layer (141). After the different laid cables (1) are connected, an outer sheath (2) is wrapped outside. A connecting ring is provided on one side of the outer sheath (2). The two outer sheaths (2) are connected through the connecting ring.

2. The cable based on distributed optical fiber temperature measurement according to claim 1, wherein: The outer sheath (2) is composed of a flexible pressure-conducting cavity (21), a braided layer (22), and a drag-reducing layer (23) from the inside to the outside. The flexible pressure-conducting cavity (21) is filled with a fluid. The braided layer (22) is a structure imitating nacre. Carbon fibers are orthogonally braided at 90°, and epoxy resin is embedded between layers. V-shaped notches (231) and magnetic attraction rings (201) are provided on the surface of the drag-reducing layer (23). The two outer sheaths (2) are attracted and joined at the connection of the laid cable (1) by the magnetic attraction of the magnetic attraction rings (201).

3. The cable based on distributed optical fiber temperature measurement and its temperature measurement method according to claim 2, characterized in that: An oil injection channel (211) is provided in the outer sheath (2). One end of the oil injection channel (211) is communicated with the flexible pressure-conducting cavity (21), and the other end extends outside the drag-reducing layer (23). The oil injection channel (211) is in a closed state under normal conditions.

4. The cable based on distributed optical fiber temperature measurement according to claim 3, wherein: A sealing ring (202) is provided on the side of the outer sheath (2) away from the magnetic attraction ring (201). The sealing ring (202) is communicated with the flexible pressure-conducting cavity (21), and the degree of pressure deformation of the sealing ring (202) is less than that of the flexible pressure-conducting cavity (21).

5. The cable based on distributed optical fiber temperature measurement according to claim 1, characterized in that: The circular air holes (142) are in a non-uniform array in the recessed layer (141).

6. The cable based on distributed optical fiber temperature measurement according to claim 1, characterized in that: There are two temperature-measuring optical fibers (14), and the included angle between the connecting lines of the positions where they are located in the cross-section of the cable is 180°.

7. The cable based on distributed optical fiber temperature measurement according to claim 1, characterized in that: There are four temperature-measuring optical fibers (14). Every two form a group. The included angle between the connecting lines of the positions where the two temperature-measuring optical fibers (14) in each group are located in the cross-section of the cable is 180°, and the distances between different groups of temperature-measuring optical fibers (14) and the conductor (11) are different.

8. The cable based on distributed optical fiber temperature measurement according to claim 7, characterized in that: The included angle between the connecting lines of the positions where the temperature-measuring optical fibers (14) in the two groups are located in the cross-section of the cable and those of the temperature-measuring optical fibers (14) in the other group is 90°.

9. The temperature measurement method of the cable based on distributed optical fiber temperature measurement described in claim 1, characterized in that: Step 1: There are two temperature-measuring optical fibers that are spirally symmetrically wound around the conductor in the cable's cladding, and the pitch is fixed. Pulses of 1550 nm and 1310 nm are emitted into the temperature-measuring optical fibers through the laser emission module at the cable end to activate Raman and Brillouin scattering respectively. Step 2: Locate the position of the event point according to the speed of light and the refractive index of the optical fiber, and convert the linear distance into three-dimensional space coordinates by pre-storing the spiral parameters of pitch and diameter. Step 3: Calculate the temperature with the Raman signal, solve the strain with the Brillouin signal, and eliminate the cross-sensitivity of temperature to strain. Step 4: Analyze the data to generate a temperature-strain distribution map of the cable axis. When there is an over-limit area, an alarm is triggered.

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