JP2009103496A - Fiber optic sensor cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber optic sensor cable which distributes local strain/stress such as cracks and allows sensing. <P>SOLUTION: The fiber optic sensor cable 10 is formed by tightly integrally covering at least one strain detection optical fiber 11, a loose tube 14 which accommodates at least one temperature compensation optical fiber 12, and at least a pair of tensile strength bodies 15. The strain detection optical fiber 11 is covered with a low hardness layer 17 with a Shore A hardness of less than 90. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical fiber sensor cable used by being embedded in soil such as a concrete structure such as a building, a bridge, or a tunnel, a mortar structure, a river bank, a mountain slope, or the like.

  In recent years, fiber optic cables have been embedded in soil such as concrete structures such as buildings, bridges and tunnels, mortar structures, river embankments, mountain slopes, etc., in a straight line or in a loop, and BOTDA is used. A method has been developed for measuring the strain of each structure online by propagating light through the optical fiber.

For example, Patent Literature 1 describes an optical fiber sensor cable including a strain detection optical fiber and a temperature compensation optical fiber.
Further, Patent Document 2 discloses an optical fiber sensor cable having a coating layer with unevenness, and thereby it is disclosed that the adhesion with a strained object can be improved and more accurate strain measurement can be performed. Has been.
JP 2001-304822 A JP 2002-023030 A

  An example of the structure of a conventional optical fiber sensor cable is shown in FIG. In this optical fiber sensor cable 20, a strain detection optical fiber 21, a loose tube 24 that houses a temperature compensation optical fiber 22 in a tensile strength fiber 23, and a pair of tensile strength members 25, 25 include a sheath resin layer 26. Thus, the film is tightly covered in a lump, embedded in a structure such as mortar, and the occurrence of distortion and cracks in the structure is monitored. When the crack C occurs, as shown in FIG. 5B, the crack generation portion of the embedded optical fiber sensor cable 20 has a local elongation strain (indicated by a white arrow in FIG. 5B). The location can be detected.

  However, if the strain detection optical fiber 21 is locally strained more than the elongation at break of the optical fiber or is left for a long time with a large elongation strain applied, the optical fiber breaks and functions as a sensor. The problem of disappearing occurred.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the optical fiber sensor cable which disperse | distributes local distortion stress, such as a crack, and enables sensing.

  In order to solve the above-described problems, the present invention provides a tightly integrated package of at least one strain detection optical fiber, a loose tube that houses at least one temperature compensation optical fiber, and at least one pair of strength members. An optical fiber sensor cable is provided, wherein the strain detection optical fiber is covered with a low hardness layer having a Shore A hardness of less than 90.

  According to the optical fiber sensor cable of the present invention, by providing a low hardness layer around the strain detection optical fiber, it is possible to disperse the stress at the time of crack occurrence and reduce the amount of strain applied to the strain detection optical fiber. Can do.

The present invention will be described below with reference to the drawings based on the best mode.
As shown in FIG. 1, the optical fiber sensor cable 10 of this embodiment includes at least one strain detection optical fiber 11, a loose tube 14 that houses at least one temperature compensation optical fiber 12, and at least one. The pair of tensile strength members 15 and 15 are tightly covered together, and the periphery of the strain detection optical fiber 11 is covered with a low hardness layer 17 having a Shore A hardness of less than 90.

  The strain detection optical fiber 11 uses OTDR (Optical Time Domain Reflectometry), BOTDA (Brillouin Optical Time Domain Analysis), or the like to measure changes in Rayleigh scattered light and Brillouin scattered light when strain is applied to the optical fiber. Therefore, when a distortion occurs in an object such as a concrete structure, a mortar structure, or soil, the distortion is applied to the strain detection optical fiber 11 when the distortion occurs in the object. The

  The temperature compensating optical fiber 12 is housed in the loose tube 14 together with the tensile fiber 13 in a loose manner. As a result, even if the cable (sheath or the like) does not depend on the temperature change, the temperature compensating optical fiber 12 is hardly affected by an external force or the like, and more reliable temperature compensation is possible. By providing the strain detection optical fiber 11 and the temperature compensation optical fiber 12 in the same optical fiber sensor cable, it is possible to obtain strain and temperature data collectively, and to perform accurate strain compensation with temperature compensation. Can do.

  In the present embodiment, the strain detecting optical fiber 11 and the temperature compensating optical fiber 12 are not particularly limited with respect to the material, core diameter, cladding diameter, coating structure, and the like, and can be appropriately selected and used. In particular, it is preferable to use an optical fiber, an optical fiber core, or the like in which a silica glass optical fiber is coated with one or more layers because it is excellent in strength and stability and has good transmission characteristics. The number of the strain detection optical fibers 11 and the temperature compensation optical fibers 12 is not limited to one, and one or a plurality of them can be provided.

  The tensile strength fiber 13 in the present embodiment is vertically attached to the temperature compensating optical fiber 12, and supports the temperature compensating optical fiber 12 loosely. Thus, by storing the temperature compensating optical fiber 12 in the hollow tube 14 having a hollow structure, accurate temperature compensation becomes possible. Further, regarding temperature compensation, as shown in FIG. 1A, it is desirable that the periphery of the loose tube 14 that houses the temperature compensating optical fiber 12 in the loose is covered with a low hardness layer 17.

  Although it does not specifically limit as the tensile strength fiber 13, For example, high strength fiber reinforced plastics (FRP), such as an aramid fiber (aromatic polyamide fiber), is mentioned. The temperature compensating optical fiber 12 and the tensile strength fiber 13 may be loosely accommodated in the loose tube 14 to constitute a temperature compensating optical fiber cord. In this case, the loose tube 14 is formed of the temperature compensating optical fiber cord. As the coating, the temperature compensating optical fiber 12 and the tensile fiber 13 are integrated.

  Further, a tension member such as a metal wire such as a steel wire is provided as the strength member 15 of the cable. The tension member is not limited to a metal wire, and high strength fiber reinforced plastic (FRP) such as aramid fiber (aromatic polyamide fiber) can also be used. The tensile body 15 is provided with at least one pair (two). For example, as shown in FIG. 1 (a) and FIG. 2, if the cable has a circular cross section, it may be a pair with one pair on the both sides in the diameter direction, or a cable with a rectangular cross section as shown in FIG. For example, a mode in which one pair is formed on each side of the long side direction can be exemplified. Also, two or more pairs of strength members 15 can be provided.

  It is desirable that the sheath resin used for batch coating of the optical fiber sensor cable 10 has alkali resistance in order to resist strong alkali of concrete or mortar. Moreover, in order to prevent permeation of earth and sand and moisture contained therein, it is desirable to have water resistance. Examples of such resins include polyethylene resins, fluorine resins, polyolefin resins, polystyrene resins, polypropylene resins, polyurethane resins, polyamide resins, polyethylene terephthalate (PET) resins, polyvinyl chloride (PVC) resins. Resins, acrylonitrile butadiene styrene (ABS) resins, and elastomer materials incorporating these materials. The resin for the sheath is not too low in fluidity of the resin so that the formation of irregularities can be easily realized at the time of extrusion of the sheath, and is not too high so that the cable shape can be easily maintained. The melt flow rate (MFR) is preferably in the range of 0.2 to 20 g / 10 min.

  In the optical fiber sensor cable 10 shown in FIG. 1, the sheath that collectively covers the optical fiber and the tensile body is composed of two layers of a low hardness layer 17 having a Shore A hardness of less than 90 and a protective layer 16 that covers the periphery thereof. . Examples of the low hardness layer 17 include polyurethane, polyurethane elastomer, polyolefin elastomer, polyester elastomer, rubber resin, olefin resin, and the like, and those having a Shore A hardness of less than 90 can be selected and used. In this embodiment, one low hardness layer is coated, but the present invention is not particularly limited to this, and two or more low hardness layers can be coated.

  The protective layer 16 is provided on the outer periphery of the cable in order to impart alkali resistance, ultraviolet resistance, water resistance, and the like. Such an optical fiber sensor cable 10 includes, for example, a strain detecting optical fiber 11, a temperature compensating optical fiber cord in which the temperature compensating optical fiber 12 is housed in a loose tube 14, and a tensile body 15 in the longitudinal direction. Can be manufactured by a method in which the low-hardness layer 17 is extrusion-molded around these and collectively covered, and the protective layer 16 is formed around the low-hardness layer 17.

  The optical fiber sensor cable 10 of this embodiment can be embedded in a structure such as mortar and used to monitor the occurrence of distortion or cracks in the structure. When the crack C occurs, as shown in FIG. 1B, the crack generation portion of the embedded optical fiber sensor cable 20 has a local elongation strain (indicated by a white arrow in FIG. 1B). The location can be detected.

  Furthermore, according to the optical fiber sensor cable 10 of the present embodiment, since the low hardness layer 17 is provided around the strain detecting optical fiber 11, when a crack or the like occurs in the structure around the cable, The stress is applied to the strain detecting optical fiber 11 after passing through the low hardness layer 17. As schematically shown in FIG. 1B, the stress at the time of crack generation can be dispersed and the elongation strain applied to the strain detection optical fiber 11 can be reduced, so that the strain detection optical fiber 11 is broken. And the like can be prevented, and the life of the sensor can be extended.

  Further, by adjusting the Shore A hardness, material, thickness, etc. of the low hardness layer 17, the ratio of the magnitude of strain generated around the cable and the amount of strain applied to the strain detecting optical fiber 11 can be changed. Can do. As a result, in the strain detection sensor that detects a strain application amount that is greater than or equal to a predetermined value, it is possible to detect the strain according to the strain application amount that is obtained by reducing the strain generated around the cable with the low hardness layer 17. Can be controlled. For example, when the strain reduction rate by the low-hardness layer 17 is large, the lower limit threshold value for detecting strain can be increased, and detection of strain less than the threshold value can be suppressed.

  As mentioned above, although this invention has been demonstrated based on suitable embodiment, this invention is not limited to the above-mentioned example, Various modifications are possible in the range which does not deviate from the summary of this invention.

  For example, in the optical fiber sensor cable 10A shown in FIG. 2, the low hardness layer 17 is provided so as to cover the strain detection optical fiber 11 alone, and the low hardness layer 17 that covers the strain detection optical fiber 11 and the temperature compensation are provided. The loose tube 14 in which the optical fiber 12 is housed and the strength member 15 are collectively covered with the protective layer 16. It is considered that the same effect as that of the optical fiber sensor cable 10 shown in FIG. In the present embodiment, one low-hardness layer is coated around the strain detection optical fiber 11, but the present invention is not limited to this, and two or more low-hardness layers can be covered.

  The cable structure is not limited to the round shape as shown in FIGS. 1 and 2, but is a cable having a square shape (rectangular cross-section) or other cross-sectional shapes such as the optical fiber sensor cable 10B shown in FIG. It is also possible to apply.

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, this invention is not limited only to these Examples.

  As shown in FIG. 1 (a), a strain detecting optical fiber 11, a temperature compensating optical fiber cord in which a temperature compensating optical fiber 12 and an aramid fiber 13 are housed loosely inside a loose tube 14, and 2 Tensile strength members 15 and 15 are arranged in parallel, and a resin having a Shore A hardness of less than 90 is coated thereon to have a diameter of 3.5 mm, and a protective layer (alkali resistance, ultraviolet resistance, water resistance, etc.) is further formed thereon. An optical fiber sensor cable having a diameter of 4.0 mm was manufactured by coating polyethylene having a Shore D hardness of 50 (hereinafter abbreviated as “Polyethylene of Shore D50”).

(Example 1)
In Example 1, an optical fiber core of φ0.25 mm is used as the strain detection optical fiber 11, an optical fiber cord of φ1.5 mm is used as the temperature compensating optical fiber cord, and a φ0.4 mm steel wire is used as the tensile body. The outer diameter was φ3.5 mm by coating a polystyrene elastomer having a Shore A hardness of 30 on the top, and the outer diameter of the cable was set to φ4.0 mm by coating Shore D50 polyethylene as a protective layer.

(Example 2)
In Example 2, an optical fiber core of φ0.25 mm is used as the strain detection optical fiber 11, an optical fiber cord of φ1.5 mm is used as the temperature compensation optical fiber cord, and a φ0.4 mm steel wire is used as the tensile body. The outer diameter was 3.5 mm by coating a polystyrene elastomer having a Shore A hardness of 60 on the top, and the outer diameter of the cable was set to 4.0 mm by covering with polyethylene of Shore D50 as a protective layer.

(Example 3)
In Example 3, a φ0.25 mm optical fiber core wire is used as the strain detection optical fiber 11, a φ1.5 mm optical fiber cord is used as the temperature compensation optical fiber cord, and a φ0.4 mm steel wire is used as the tensile body. The outer diameter was 3.5 mm by covering with a polystyrene elastomer having a Shore A hardness of 90, and the outer diameter of the cable was 4.0 mm by covering with polyethylene of Shore D50 as a protective layer.

(Example 4)
In Example 4, an optical fiber core of φ0.25 mm is used as the strain detection optical fiber 11, an optical fiber cord of φ1.5 mm is used as the temperature compensation optical fiber cord, and a φ0.4 mm steel wire is used as the tensile body. The outer diameter of the cable was set to φ4.0 mm by covering with Shore D50 polyethylene.

  The above four types of optical fiber sensor cables were prepared, and each cable was embedded in mortar, and the strain detection sensitivity at the time of crack occurrence was compared.

  The optical fiber sensor cables of Examples 1 to 4 were embedded in mortar to generate a crack of 1.5 mm, and the strain applied to the strain detection optical fiber in the cable was measured using BOTDA. The measurement results are shown in FIG.

As shown in the graph of FIG. 4, in Example 1 in which the hardness around the strain detection optical fiber is Shore A hardness 30, the strain peak value is about 2000 μStrain, and in Example 2 where the Shore A hardness is 60, the strain peak value is about In Example 3 with 3500 μStrain and Shore A hardness 90, the strain peak value was about 5000 μStrain, and in Example 4 with Shore D hardness 50, the strain peak value was about 7500 μStrain.
That is, as the Shore hardness decreases, the strain peak value of the strain detecting optical fiber at the crack occurrence site decreases. In other words, the amount of strain applied to the optical fiber can be controlled by the Shore hardness around the strain detecting optical fiber.

  Further, transmission loss characteristics were measured for each of the optical fiber sensor cables of Examples 1 to 4. The results are shown in Table 1.

  As shown in Table 1, even when a low hardness layer having a Shore A hardness of less than 90 is provided around the strain detection optical fiber (Examples 1 and 2), it is inferior to the conventional structure (Example 4). No transmission loss was observed, and all were good results.

  The optical fiber sensor cable of the present invention can be suitably used for strain sensing in soil such as concrete structures such as buildings, bridges, and tunnels, mortar structures, river dikes, and mountain slopes.

It is the cross-sectional view showing the structure in (a) structure in one example of the optical fiber sensor cable of the present invention, and (b) a partial vertical cross-sectional view for explaining the operation. It is a cross-sectional view showing the 2nd example of an optical fiber sensor cable of the present invention. It is a cross-sectional view showing the 3rd example of an optical fiber sensor cable of the present invention. It is a graph showing the crack generation | occurrence | production part distortion in a test example. It is a cross-sectional view showing an example of a conventional optical fiber sensor cable.

Explanation of symbols

C: Crack, 10, 10A, 10B: Optical fiber sensor cable, 11: Strain detection optical fiber, 12: Temperature compensation optical fiber, 13: Tensile fiber, 14: Loose tube, 15: Tensile body, 16 ... Protective layer (Sheath), 17 ... low hardness layer.

Claims (1)

  An optical fiber sensor cable in which at least one strain detecting optical fiber, a loose tube containing at least one temperature compensating optical fiber, and at least one pair of strength members are collectively covered with tight. An optical fiber sensor cable, wherein the strain detecting optical fiber is covered with a low hardness layer having a Shore A hardness of less than 90.

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