JP2009192250A - Fiber optic sensor cable - Google Patents

Abstract

An optical fiber sensor cable capable of measuring a temperature change with high accuracy is provided.
An optical fiber is attached to a strip-shaped tensile member having a linear expansion coefficient larger than that of the optical fiber, and the optical fiber and the tensile member are continuously or intermittently along the longitudinal direction of the tensile member. An optical fiber sensor cable comprising a fixed portion integrated so as to be in direct contact with each other, and measuring a laying environment temperature from a frequency shift amount of Brillouin scattered light accompanying a temperature change.
[Selection] Figure 1

Description

  The present invention relates to an optical fiber sensor cable for measuring a laying environment temperature from a frequency shift amount of Brillouin scattered light accompanying a temperature change using a high resolution BOTDA (Brillouin Optical Time Domain Analysis).

  Conventionally, an optical fiber sensor cable that measures strain (pressure) and temperature change applied to an optical fiber by installing an optical fiber in a measurement target area and monitoring changes in backscattered light and Brillouin scattered light of the optical fiber. For example, techniques disclosed in Patent Documents 1 to 5 have been proposed.

Patent Document 1 discloses a strain detection optical fiber sensor in which an optical fiber is continuously fixed in the longitudinal direction of a central member using a protective layer such as a heat shrinkable tube. This strain detection optical fiber sensor uses a multimode fiber sensitive to bending and detects compressive strain.
Patent Document 2 discloses an optical fiber sensor that measures the amount of strain by embedding an optical fiber sensor in the wall thickness of the tube or fixing the optical fiber to the inner wall and outer wall of the tube in the longitudinal direction.
Patent Document 3 discloses that strain is detected by BOTDR using an optical fiber sensor in which a long optical fiber is embedded in the thickness of a tubular resin strip.
Patent Document 4 discloses an optical fiber sensor in which an optical fiber is embedded in an elastomer tube wall having a larger coefficient of thermal expansion, and pressure, temperature, elongation, bending, and the like are measured.
Patent Document 5 discloses an optical fiber cable having a structure in which a plurality of optical fibers are fixed with a hot melt resin on an outer periphery of a core such as an FRP rod.
Japanese Utility Model Publication No. 2-120008 JP 2002-48518 A JP 2004-101414 A US Patent Application Publication No. 2006/71158 US Pat. No. 6,167,179

However, Patent Documents 1 to 5 have the following problems.
In Patent Document 1, since an increase in transmission loss caused by bending is converted into distortion, only compression distortion can be detected. In addition, since a multimode fiber sensitive to bending is used, there is a high possibility that measurement will become impossible due to an increase in loss when subjected to a large compressive strain that causes macrobending.

  In Patent Document 2, the stress applied to the optical fiber through the outer tube is detected as a strain. However, since the tube also expands and contracts due to a temperature change, it is difficult to separate the strain caused by the stress from the strain caused by the temperature change. is there.

  In Patent Document 3, the stress applied to the jacket sensor is detected as a strain. However, since the tube also expands and contracts due to a temperature change, it is difficult to separate the strain caused by the stress from the strain caused by the temperature change.

  In patent document 4, the heat resistance of the elastomer tube used is 100 to 120 ° C., 140 ° C. for styrene elastomers and 175 ° C. for polyester elastomers. The optical fiber sensor cable of Patent Document 4 is applied in a high temperature environment of 200 ° C. or higher. When an elastomer is used as a support for optical fiber, it melts and cannot function as a support.

  The cable disclosed in Patent Document 5 is not a sensor using an optical fiber. Even if the sensor cable is used, the external stress cannot be sufficiently transmitted to the optical fiber because the optical fiber is not in contact with the central core. Therefore, the detection sensitivity is low, and there is a possibility that the intended distortion change cannot be detected.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical fiber sensor cable capable of measuring a temperature change with high accuracy.

  In order to achieve the above object, the present invention provides an optical fiber attached to a strip-shaped tensile member having a linear expansion coefficient larger than that of the optical fiber, and continuously or intermittently along the longitudinal direction of the tensile member. An optical fiber sensor comprising a fixed portion integrated so that the optical fiber and the tensile body are in direct contact with each other, and measuring the installation environment temperature from the frequency shift amount of the Brillouin scattered light accompanying the temperature change Provide cables.

  In the optical fiber sensor cable of the present invention, at least one optical fiber is spirally wound along the longitudinal direction of the strength member, and the strength member and the optical fiber are directly or intermittently fixed by a fixing agent. It is preferable to provide an integrated fixing portion so as to be in contact with the surface.

  In the optical fiber sensor cable of the present invention, at least one or more optical fibers spirally wound along the longitudinal direction of the strength member are used as a middle core, and the middle core is covered with a strength fiber as a buffer material. In addition, it may be fixed intermittently or entirely with a fixing agent, and further has a fixing portion in which the cable jacket is covered and the middle core and the cable jacket are integrated with the fixing agent through tensile strength fibers. it can.

  In the optical fiber sensor cable of the present invention, when a tensile body is coated with a resin coating made of heat-resistant plastic, the optical fiber is spirally wound on the outer surface of the resin coating, and the optical fiber is integrated only with the tensile body It is also possible to adopt a configuration in which the amount of change in strain per 1 ° C. of temperature change is increased.

  In the optical fiber sensor cable of the present invention, it is preferable that the optical fiber has a strain change amount in a range of 20 με / ° C. to 100 με / ° C. with respect to a temperature change.

The optical fiber sensor cable of the present invention integrates an optical fiber intermittently or entirely fixed to a tensile body having a higher linear expansion coefficient than that of the optical fiber, thereby integrating the amount of strain change with respect to a temperature change with a high resolution BOTDA. As a result, it is possible to narrow the temperature detection error range and improve the temperature measurement accuracy. In addition, the presence of the tensile body can prevent a decrease in measurement reproducibility due to cable sheath shrinkage due to temperature changes.
In the optical fiber sensor cable of the present invention, the inner core, in which the optical fiber and the tensile body are integrated, and the cable jacket are integrated via the fixing agent, thereby causing the cable jacket to contract due to temperature change. It is possible to prevent a decrease in measurement reproducibility. By wrapping the cable jacket and the inner core with tensile strength fibers, the tensile strength fibers act as a cushioning material, and the cable jacket does not adhere directly to the optical fiber, reducing the increase in loss that affects strain measurement. It became possible to do.

Hereinafter, embodiments of the optical fiber sensor cable of the present invention will be described with reference to the drawings.
1A and 1B show a first embodiment of an optical fiber sensor cable according to the present invention, in which FIG. 1A is a longitudinal sectional view, FIG. 1B is a transverse sectional view of a fixed portion 6, and FIG. FIG. In FIG. 1, reference numeral 1A denotes an optical fiber sensor cable, 2 denotes an optical fiber, 3 denotes a strength member, 4 denotes a fixing agent, 5 denotes a cable jacket, 6 denotes a fixing portion, and 7 denotes a non-fixing portion.

  The optical fiber sensor cable 1 </ b> A of the present embodiment spirally winds two optical fibers 2 around a strip-shaped tensile member 3 having a larger linear expansion coefficient than the optical fiber 2. From the frequency shift amount of the Brillouin scattered light accompanying the temperature change, the fixing unit 6 integrated with the fixing agent 4 is provided so that the optical fiber 2 and the strength member 3 are in direct contact with each other along the longitudinal direction. It is characterized by measuring the laying environment temperature.

  In the optical fiber sensor cable 1A of the present embodiment, the optical fiber 2 is high when the strain caused by the linear expansion of the tensile body 3 is added in accordance with the temperature change in a state of being wound around the tensile body 3. There is no particular limitation as long as the laying environment temperature can be measured from the frequency shift amount of the Brillouin scattered light using the resolution BOTDA. However, in order to measure the temperature range from room temperature to about 300 ° C. with high accuracy, It is preferable to use a silica glass-based optical fiber having a coating. The number of the optical fibers 2 may be one or more, and is not limited to the two illustrated.

  In the optical fiber sensor cable 1A of the present embodiment, a high-strength material having a linear expansion coefficient higher than that of the optical fiber 2 is used as the tensile body 3, for example, carbon steel wire, aluminum wire, brass, etc. Copper alloy wire, zinc alloy wire, stainless steel wire such as SUS403, and the like.

  In the optical fiber sensor cable 1A of the present embodiment, examples of the fixing agent 4 include an adhesive such as an ultraviolet curable adhesive, a thermosetting adhesive, and a hot melt. The fixing agent is applied to the tensile body 3 and the optical fiber 2 of the predetermined fixing portion 6 in an uncured state, and the fixing portion 6 is formed by curing it.

  2A and 2B show a second embodiment of the optical fiber sensor cable of the present invention, wherein FIG. 2A is a longitudinal sectional view, and FIG. 2B is a transverse sectional view of a fixing portion 6. The optical fiber sensor cable 1B of the present embodiment is configured to include substantially the same components as the optical fiber sensor cable 1A of the first embodiment described above, and continuously forms the fixing portion 6 in the longitudinal direction of the strength member 3. It is characterized by that.

  3A and 3B show a third embodiment of the optical fiber sensor cable of the present invention, in which FIG. 3A is a longitudinal sectional view, FIG. 3B is a transverse sectional view of a fixed portion 6, and FIG. FIG. The optical fiber sensor cable 1 </ b> C of the present embodiment is configured to include substantially the same components as the optical fiber sensor cable 1 </ b> A of the first embodiment described above, and the two optical fibers 2 along the longitudinal direction of the strength member 3. Is formed as a middle core, and the middle core is covered with tensile strength fibers 8 serving as cushioning materials, intermittently fixed with a fixing agent 4, and further covered with a cable jacket 5 to fix the fixing agent. 4 has a fixing portion 6 in which the middle core and the cable jacket 5 are integrated through the tensile strength fiber 8.

  4A and 4B show a fourth embodiment of the optical fiber sensor cable of the present invention, in which FIG. 4A is a longitudinal sectional view, and FIG. 4B is a transverse sectional view of a fixing portion 6. The optical fiber sensor cable 1D of the present embodiment is configured to include substantially the same components as the optical fiber sensor cable 1C of the third embodiment described above, and the middle core and the cable jacket 5 are interposed via the tensile strength fibers 8. The integrated fixing part 6 is characterized in that it is continuously formed in the longitudinal direction of the strength member 3.

  5A and 5B show a fifth embodiment of the optical fiber sensor cable of the present invention, in which FIG. 5A is a longitudinal sectional view, FIG. 5B is a transverse sectional view of a fixed portion 6, and FIG. FIG. The optical fiber sensor cable 1E of the present embodiment is configured to include substantially the same components as the optical fiber sensor cable 1A of the first embodiment described above, and has a tensile strength with a resin coating 9 made of a heat-resistant plastic having a high linear expansion coefficient. The body 3 is covered, and the optical fiber 2 is spirally wound horizontally on the outer surface of the resin coating 9.

  The optical fiber sensor cables 1 </ b> A to 1 </ b> E according to the embodiments of the present invention described above include at least one or more optical fibers 2 in the longitudinal direction so that the temperature-measuring optical fiber 2 is in direct contact with the tensile body 3. The amount of strain caused by the linear expansion of the tensile body 3 is integrated by intermittently or entirely integrating the tensile body 3 and the optical fiber 2 by applying a fixing agent 4 such as an adhesive. Is added to the optical fiber 2 so that the amount of change in strain of the optical fiber with respect to temperature change can be increased.

In the optical fiber sensor cables 1A to 1E, the optical fiber 2 is spirally wound around the strength member 3 and is directly in contact with the fixing portion 6, so that the expansion and contraction of the strength member 3 with respect to a temperature change is suppressed by a hoop stress. Directional stress) can be transmitted uniformly and reliably over the entire length of the optical fiber 2. As a result, the optical fiber 2 can measure not only the Brillouin frequency shift due to the temperature change but also the strain amount due to the linear expansion of the strength member 3, and can increase the strain change amount per 1 ° C. It becomes. That is, as the strain measurement amount of the sensor itself increases, the temperature detection error can be reduced with respect to the measurement accuracy ± 25 με of the high resolution BOTDA used for strain measurement of this sensor. For example, when the strain change amount is about 25 με / ° C. which is the same as that of the conventional structure, the temperature detection error can be estimated to be ± 1 ° C. in view of the measurement accuracy of high resolution BOTDA ± 25 με. On the other hand, when the strain change amount is 50 με / ° C. by employing the sensor structure of the present invention, the temperature detection error is ± 0.5 ° C., and when it is 100 με, the temperature detection error is ± 0. .Improved to 25 ° C.
Hereinafter, the present invention will be described more specifically with reference to examples.

  The optical fiber sensor cable prototyped in this example uses a polyimide-coated fiber with sufficient heat resistance for the optical fiber, polyimide for the fixing agent, PFA for the cable jacket, and carbon steel wire and aluminum wire for the tensile body. Two types of structures were used. When the carbon steel wire was used as the tensile body, the amount of change in strain was 40 με / ° C., and when aluminum was used, it was 50 με / ° C. In addition to carbon steel and aluminum, brass, zinc, SUS403, or the like having a large linear expansion coefficient may be used as the strength member.

  The installation environment temperature range to which this sensor is to be applied is assumed to be room temperature to 300 ° C. With respect to the fixing agent, if it is a polyimide, the glass transition point was applied at 310 ° C. and 300 ° C., since almost no weight reduction was observed. Of course, the material need not be limited to polyimide as long as the material can be used in the temperature range of the installation environment. Examples of fixing adhesives include thermosetting heat-resistant epoxies and ceramic heat-resistant adhesives.

In this example, optical fiber sensor cables having the following structures (1) and (2) were produced.
(1) As shown in FIG. 3, a spiral core of two optical fibers 2 extending in the longitudinal direction so as to be in direct contact with the strength member 3 is used as a middle core, and this middle core is a cushioning material. The optical fiber sensor cable 1C was covered with the tensile strength fiber 8 to be, coated with an adhesive and intermittently integrated, and further covered with a cable jacket 5.
(2) As shown in FIG. 4, with respect to the strength member 3, two optical fibers 2 spirally wound in the longitudinal direction are used as a middle core, and the middle core serves as a cushioning material 8. Then, an adhesive was applied and integrated as a whole, and the cable jacket 5 was covered to obtain an optical fiber sensor cable 1D.

For the optical fiber sensor cables of the above (1) and (2) and the conventional loose-contained temperature detection fiber, the amount of strain change due to the environmental temperature change was examined and compared.
In the conventional loose-contained temperature detection fiber, the strain change amount due to temperature change is 20 με / ° C., but by using the optical fiber sensor cable manufactured in this example, the strain change amount 40 with respect to temperature change is 40. It became possible to set it to ˜100 με / ° C.
Therefore, considering the measurement accuracy of the measuring instrument ± 15 to 25 με, the temperature detection accuracy of ± 0.15 to .0. The measurement accuracy was improved by 6 ° C, that is, 2 to 5 times. In addition, cable sheath shrinkage due to temperature changes can be suppressed, and distortion waveform distortion and measurement reproducibility deterioration due to sheath shrinkage can be prevented.

  Further, as shown in FIG. 5, the temperature change is 1 ° C. as compared with the case where the optical fiber 2 is integrated with only the strength member 3 by coating the strength member 3 with a plastic resin such as PFA, PTFE, polyimide, polyimide amide or the like. It is possible to increase the amount of change in distortion per hit. Of course, a resin such as polyamide or polyolefin may be used as long as it has heat resistance in the target temperature range. By optimizing the outer diameter, linear expansion coefficient, elastic modulus, covering pressure, etc. of the constituent materials, it became possible to make the strain change amount 40 to 100 με / ° C. with respect to the temperature change.

1A and 1B show a first embodiment of an optical fiber sensor cable of the present invention, in which FIG. 1A is a longitudinal sectional view, FIG. 1B is a transverse sectional view of a fixing portion, and FIG. The 2nd Embodiment of the optical fiber sensor cable of this invention is shown, (a) is a longitudinal cross-sectional view, (b) is a cross-sectional view of a fixing | fixed part. 3A and 3B show a third embodiment of the optical fiber sensor cable of the present invention, in which FIG. 5A is a longitudinal sectional view, FIG. 5B is a transverse sectional view of a fixing portion, and FIG. The 4th Embodiment of the optical fiber sensor cable of this invention is shown, (a) is a longitudinal cross-sectional view, (b) is a cross-sectional view of a fixing | fixed part. 5 shows a fifth embodiment of the optical fiber sensor cable of the present invention, wherein (a) is a longitudinal sectional view, (b) is a transverse sectional view of a fixed portion, and (c) is a transverse sectional view of an unfixed portion.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1A-1E ... Optical fiber sensor cable, 2 ... Optical fiber, 3 ... Tensile body, 4 ... Fixing agent, 5 ... Cable jacket, 6 ... Fixed part, 7 ... Non-fixed part, 8 ... Tensile fiber, 9 ... Resin coating .

Claims (5)

  The optical fiber is attached to a strip-shaped tensile member having a larger linear expansion coefficient than that of the optical fiber, and the optical fiber and the tensile member are directly or continuously along the longitudinal direction of the tensile member. An optical fiber sensor cable comprising a fixed portion integrated so as to be in contact with each other, and measuring a laying environment temperature from a frequency shift amount of Brillouin scattered light accompanying a temperature change.   A fixing portion in which at least one optical fiber is spirally wound along the longitudinal direction of the strength member and integrated so that the strength material and the optical fiber are in direct contact with each other intermittently or entirely by a fixing agent. The optical fiber sensor cable according to claim 1, wherein the optical fiber sensor cable is provided.   At least one or more optical fibers spirally wound along the longitudinal direction of the tensile strength member are used as a middle core, and the middle core is covered with a tensile strength fiber that serves as a cushioning material. 2. The optical fiber sensor according to claim 1, further comprising: a fixing portion that is fixed to the cable and further covers the cable jacket and integrates the middle core and the cable jacket with the fixing agent via a tensile strength fiber. cable.   The strain per 1 ° C of temperature change is higher than when a tensile strength body is coated with a resin coating made of heat-resistant plastic, the optical fiber is spirally wound horizontally on the outer surface of the resin coating, and the optical fiber is integrated with the tensile strength body alone. The optical fiber sensor cable according to claim 1, wherein the amount of change is increased.   The optical fiber sensor cable according to any one of claims 1 to 4, wherein the optical fiber has a strain change amount in a range of 20 µε / ° C to 100 µε / ° C with respect to a temperature change.

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