Strain and displacement sensing optical cable

Abstract

The invention discloses a strain and displacement sensing optical cable, and belongs to the field of optical fiber sensing technology and communication optical cable engineering. The optical cable comprises an FRP central reinforcing core coated with EAA, six strain sensing optical fibers which are annularly and symmetrically distributed and bonded around the central reinforcing core, a PA12 tight sleeve layer, a PA12 sheath and a double-layer galvanized steel wire armor layer. Through unique structural design and application of high-performance materials and in combination with the phi-OTDR technology, synchronous acquisition and decoupling of multiple parameters such as vibration, strain, displacement and temperature are realized, the positioning precision is improved, the signal redundancy is improved, and the false alarm rate is reduced. Meanwhile, the optical cable has excellent low temperature resistance, corrosion resistance, high tensile strength and compression resistance, is suitable for complex and severe environments and various laying scenes, has good industrial practicability and economic benefits, and particularly shows unique characteristics in complex environments such as cement grouting and the like.

Description

Technical Field

[0001] The present invention relates to the fields of optical fiber sensing technology and communication optical cable engineering, and in particular to a strain and displacement sensing optical cable for distributed optical fiber sensing. Background Art

[0002] In the field of distributed fiber optic sensing, existing sensing cables suffer from numerous technical deficiencies, limiting their application in complex environments and high-precision monitoring scenarios. The fiber optic vibration sensing cable disclosed in patent CN208173298U utilizes a single-core strain gauge fiber structure, enabling only single-channel vibration signal acquisition and failing to simultaneously decouple multiple parameters such as strain, temperature, and displacement. This single-core structure cannot capture multi-dimensional vibration vector information through spatial distribution differences, resulting in a high false alarm rate in complex scenarios and failing to meet the demand for coordinated multi-parameter monitoring in complex environments such as bridges, oil and gas pipelines, and building structures. The distributed fiber optic strain sensing cable disclosed in patent CN204143943U utilizes a traditional PVC sheath and a single-layer metal reinforcement. Its compressive strength is only 200 N / cm², and its temperature resistance is limited to -20°C to +60°C. In direct burial or cement-cast environments, the fiber core is susceptible to breakage due to external pressure. The sheath material is prone to cracking in corrosive oil and gas environments, causing fiber displacement and slippage, leading to signal distortion. Furthermore, the adhesion between its reinforcement and optical fiber is poor, making relative displacement easily occur under external forces, further reducing monitoring stability. Although patent CN109870780B utilizes a three-core strain gauge optical fiber, its arrangement is asymmetrical, making it impossible to achieve spatial decoupling of vibration signals. Its protective layer and sheath materials (such as polyimide coatings and ceramic fiber braids) focus on high-temperature resistance but fail to address multi-core signal interference and mechanical stability in complex environments. In summary, there is an urgent need for a new type of sensing optical cable that can overcome these drawbacks, enable simultaneous multi-parameter monitoring, possess high compressive strength, environmental adaptability, and high structural reliability. Summary of the Invention

[0003] In view of the above problems in the prior art, the present invention is proposed.

[0004] Therefore, the present invention provides a strain and displacement sensing optical cable that can realize multi-parameter synchronous monitoring, has high pressure resistance and environmental adaptability, and has high structural reliability.

[0005] To solve the above technical problems, the present invention provides the following technical solutions: a strain and displacement sensing optical cable, comprising: a central strengthening core, wherein the central strengthening core is a fiber reinforced plastic (FRP) coated with ethylene acrylic acid copolymer (EAA); and six strain sensing optical fibers, which are evenly distributed in a ring shape around the central strengthening core, and the angle between adjacent strain sensing optical fibers is 60°; the strain sensing optical fiber includes a single-mode optical fiber located in the center, and a layer of flexible steel armor is provided outside the single-mode optical fiber, and the flexible steel armor is covered with a tight jacket layer on the outside, and the tight jacket layer material is PA12; the central strengthening core is tightly bonded to the tight jacket layer on the outer surface of the six strain sensing optical fibers through the coating of ethylene acrylic acid copolymer (EAA) to form an integrated structure; the strain sensing optical fibers and the central strengthening core are covered with a PA sheath; the material of the PA sheath is PA12; the PA sheath is wrapped with a double-layer galvanized steel wire armor layer, and the double-layer galvanized steel wire armor layer includes an inner layer of galvanized high-strength steel wire and an outer layer of galvanized high-strength steel wire.

[0006] In some embodiments, the PA sheath is formed by an extrusion process, in which PA12 is filled into the gaps between adjacent strain-sensing optical fibers, and the PA sheath is extruded and wrapped around the six strain-sensing optical fibers and the central reinforcing core to thereby fix the six strain-sensing optical fibers and the central reinforcing core.

[0007] In some embodiments, the single-mode optical fiber and the flexible steel armor are bonded by ethylene acrylic acid copolymer (EAA), and the ethylene acrylic acid copolymer (EAA) is uniformly distributed on the surface of the single-mode optical fiber in the form of a coating. The ethylene acrylic acid copolymer (EAA) is a transparent grade ethylene acrylic acid copolymer (EAA), and the thickness of the ethylene acrylic acid copolymer (EAA) coating is 10-30 microns.

[0008] In some embodiments, the diameter of the central reinforcement core is 1.5-2.5 mm, the diameter of the single-mode optical fiber is 125 μm, the thickness of the tight sleeve layer is 0.3-0.5 mm, the thickness of the PA sheath is 1-2 mm, and the diameters of the inner layer galvanized high-strength steel wire and the outer layer galvanized high-strength steel wire are both 0.1-0.3 mm.

[0009] In some embodiments, the inner layer of galvanized high-strength steel wire, the outer layer of galvanized high-strength steel wire and the flexible steel armor are all wrapped in a spiral manner with a gap of 0.05-0.5 mm, forming a spring-like retractable structure.

[0010] Beneficial effects of the present invention: The strain and displacement sensing optical cable of the present invention effectively solves the technical difficulties of existing sensing optical cables and performs excellently in multi-parameter monitoring, pressure resistance, environmental adaptability and structural reliability.

[0011] Six strain-sensing optical fibers are evenly distributed in a ring, breaking through the limitations of a single core and enabling simultaneous monitoring of multiple parameters. They can simultaneously decouple parameters such as strain, temperature, and displacement, significantly reducing the false alarm rate in complex scenarios and meeting the needs of monitoring complex environments.

[0012] The double-layer galvanized steel wire armor layer adopts intermittent spiral wrapping, which has strong compressive resistance and avoids damage to the fiber core during direct burial or cement pouring, which is superior to the traditional single metal reinforcement structure.

[0013] PA12, used as the tight-buffer layer and PA sheath material, is resistant to low temperatures and corrosion, broadening the operating temperature range; EAA adhesive maintains elasticity at low temperatures, blocks external corrosion, enhances the stability of the optical cable, and has high environmental adaptability.

[0014] EAA achieves tight bonding of the central reinforcement core, strain-sensing optical fiber, single-mode optical fiber and flexible steel armor to form an integrated structure, eliminating relative sliding between components, improving positioning accuracy, high structural reliability, and reasonable size design to further optimize structural performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 A schematic diagram of the cross-sectional structure of a strain and displacement sensing optical cable provided in one embodiment of the present invention; In the figure: 1. Single-mode optical fiber; 2. Flexible steel armor; 3. Tight-buffered layer; 4. Central reinforcing core; 5. PA sheath; 6. Inner layer of galvanized high-strength steel wire; 7. Outer layer of galvanized high-strength steel wire. DETAILED DESCRIPTION

[0017] like Figure 1As shown, an embodiment of the present invention provides a strain and displacement sensing optical cable, comprising a central reinforcing core 4, which is a fiber-reinforced plastic (FRP) coated with ethylene acrylic acid copolymer (EAA); and six strain-sensing optical fibers, evenly distributed in a circular pattern around the central reinforcing core 4, with adjacent strain-sensing optical fibers forming a 60° angle. This unique design of six evenly distributed strain-sensing optical fibers overcomes the limitation of existing single-core structures that can only acquire single-channel vibration signals. Multi-dimensional vibration vector information can be acquired through spatial distribution differences, thereby simultaneously decoupling multiple parameters such as strain, temperature, and displacement. This significantly reduces the false alarm rate in complex scenarios and meets the demand for coordinated multi-parameter monitoring in complex environments such as bridges, oil and gas pipelines, and building structures. The strain-sensing optical fiber comprises a central single-mode optical fiber 1 covered with a flexible steel armor 2, which is then covered with a tight jacket 3 made of PA12 (nylon 12). A central strength member 4 is tightly bonded to the tight jacket 3 on the outer surfaces of the six strain-sensing optical fibers via a coating of ethylene acrylic acid copolymer (EAA), forming an integrated structure. The PA jacket 5 is wrapped with a double-layer galvanized steel wire armor, comprising an inner layer of galvanized high-strength steel wire 6 and an outer layer of galvanized high-strength steel wire 7. The strain-sensing optical fiber and central strength member 4 are covered with a PA12 jacket 5. This EAA bonding method enhances the overall cable structure, eliminates relative slippage between components (traditional non-bonded structures can experience slippage of up to ±50μm), ensures accurate acquisition of distributed sensing signals (such as Φ-OTDR vibration signals), and significantly improves monitoring stability and accuracy.

[0018] In some embodiments, the PA sheath 5 is formed through an extrusion process, in which PA12 is filled into the gaps between adjacent strain-sensing optical fibers. The PA sheath 5 is then extruded over the six strain-sensing optical fibers and the central reinforcing core 4 to secure them. PA12 exhibits excellent low-temperature and corrosion resistance, broadening the cable's operating temperature range to withstand long-term temperature fluctuations from -40°C to +85°C. This addresses the limitations of existing optical cables' temperature resistance and the susceptibility of the sheath material to cracking in corrosive oil and gas environments.

[0019] In some embodiments, the single-mode optical fiber 1 and the flexible steel armor 2 are bonded via an ethylene acrylic acid copolymer (EAA) coating, which is evenly distributed on the surface of the single-mode optical fiber 1. The EAA is a transparent-grade EAA, and the EAA coating thickness ranges from 10 to 30 microns. This EAA bonding method stabilizes the entire cable structure, eliminates relative slip between components (traditional non-bonded structures can experience slip displacements of up to ±50 μm), ensures accurate acquisition of distributed sensing signals (such as Φ-OTDR vibration signals), and significantly improves monitoring stability and accuracy. Furthermore, the EAA maintains its elasticity at -40°C, preventing interfacial cracking at low temperatures. It also prevents moisture, oil, and gas from coming into direct contact with the optical fiber / steel armor, enhancing the cable's stability and reliability in complex environments.

[0020] Furthermore, in some embodiments, the diameter of the central reinforcing core 4 is 1.5-2.5 mm, the diameter of the single-mode optical fiber 1 is 125 μm, the thickness of the tight jacket 3 is 0.3-0.5 mm, the thickness of the PA jacket 5 is 1-2 mm, and the diameters of the inner and outer galvanized high-strength steel wires 6 and 7 are both 0.1-0.3 mm. This precise dimensional design optimizes the structural performance of the optical cable and further enhances its overall reliability.

[0021] In some embodiments, the inner layer of galvanized high-strength steel wire 6, the outer layer of galvanized high-strength steel wire 7, and the flexible steel armor 2 are all wrapped with galvanized steel wire in a spiral wrapping pattern with a wrapping gap of 0.05-0.5 mm, forming a spring-like, retractable structure. This structure allows the armor layer to undergo relative displacement without breaking when bent, significantly improving the cable's compressive strength and avoiding the problem of fiber core breakage caused by external pressure in existing optical cables in high-pressure environments such as direct burial or cement pouring.

[0022] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0023] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A strain and displacement sensing optical cable, characterized in that: include: A central reinforcing core, wherein the central reinforcing core is a fiber reinforced plastic (FRP) coated with ethylene acrylic acid copolymer (EAA); it also includes six strain-sensing optical fibers, which are evenly distributed in a ring shape around the central reinforcing core, and the angle between adjacent strain-sensing optical fibers is 60°; the strain-sensing optical fibers include a single-mode optical fiber located in the center, and a layer of flexible steel armor is provided outside the single-mode optical fiber. The flexible steel armor is covered with a tight sleeve layer on the outside, and the tight sleeve layer is made of PA12; the central reinforcing core is tightly bonded to the tight sleeve layer on the outer surface of the six strain-sensing optical fibers through the ethylene acrylic acid copolymer (EAA) coating to form an integrated structure; the strain-sensing optical fibers and the central reinforcing core are covered with a PA sheath; the material of the PA sheath is PA12; the PA sheath is wrapped with a double-layer galvanized steel wire armor layer, and the double-layer galvanized steel wire armor layer includes an inner layer of galvanized high-strength steel wire and an outer layer of galvanized high-strength steel wire.

2. The strain and displacement sensing optical cable according to claim 1, characterized in that: The PA sheath is formed by an extrusion process, in which PA12 is filled into the gaps between adjacent strain sensing optical fibers, and the PA sheath is extruded and wrapped around the six strain sensing optical fibers and the central reinforcing core, thereby fixing the six strain sensing optical fibers and the central reinforcing core.

3. The strain and displacement sensing optical cable according to claim 1, characterized in that: The single-mode optical fiber and the flexible steel armor are bonded by ethylene acrylic acid copolymer (EAA). The ethylene acrylic acid copolymer (EAA) is evenly distributed on the surface of the single-mode optical fiber in the form of a coating. The ethylene acrylic acid copolymer (EAA) is a transparent grade ethylene acrylic acid copolymer (EAA). The thickness of the ethylene acrylic acid copolymer (EAA) coating is 10-30 microns.

4. The strain and displacement sensing optical cable according to claim 1, characterized in that: The diameter of the central reinforcing core is 1.5-2.5 mm, the diameter of the single-mode optical fiber is 125 μm, the thickness of the tight sleeve layer is 0.3-0.5 mm, the thickness of the PA sheath is 1-2 mm, and the diameters of the inner layer galvanized high-strength steel wire and the outer layer galvanized high-strength steel wire are both 0.1-0.3 mm.

5. The strain and displacement sensing optical cable according to claim 1, characterized in that: The inner layer of galvanized high-strength steel wire, the outer layer of galvanized high-strength steel wire and the flexible steel armor are all wrapped in a spiral manner with gaps of galvanized steel wire, with a wrapping gap of 0.05-0.5mm, to form a spring-like retractable structure.

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