JP2008164352A - Distributed water pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distributed water pressure sensor capable of more accurately measuring distortion and reducing cost by commonly using one optical fiber for water pressure measuring and for temperature compensating. <P>SOLUTION: A distributed water pressure sensor is provided with a tubular body having a groove capable of installing optical fibers continuously or intermittently along the longitudinal direction and the optical fibers stranded at the outer periphery of the tubular body. The stranded parts where the optical fibers are stranded at the outer periphery of the tubular body and the linear parts where the optical fibers are installed in the tubular body are arranged alternately along the longitudinal direction of the tubular body. The folding part is set at the tip side of the stranded part to fold and introduce the tip side of the stranded part or the linear part of the optical fibers to inside of the tubular body, and the temperature compensating part is formed with linearly installing the optical fibers, which run from the folding part to the distal end side of the tubular body, inside the tubular body. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention detects a water pressure or a change thereof as a strain, and separates and detects strains in an axial direction and a radial direction depending on how the single fiber is wound in an optical cable or the like that plays a role as a sensor for detecting a water pressure distribution abnormality. In addition, the present invention relates to a distributed water pressure sensor that can accurately measure strain due to water pressure by performing temperature compensation.

  In order to ensure air tightness in underground storage tanks for water and oil, etc., the water pressure distribution in the reservoir tank or in the vicinity of the storage tank is measured and the water sealing function is constantly monitored. There is a need to. At present, a distributed optical fiber pressure gauge is one of measuring methods related to the water pressure distribution.

  Distributed fiber optic water pressure gauge is an optical fiber (or optical fiber cable) that functions as a water pressure gauge. By using BOTDR (Brillouin Optical Time Domain Reflectmetry), BOTDA (Brillouin Optical Time Domain Analysis) methods, etc. It is used as a water pressure gauge by measuring the amount of strain on the optical fiber.

To date, with respect to distributed optical fiber strain sensors, for example, techniques disclosed in Patent Documents 1 to 5 have been proposed.
In Patent Document 1, a high-voltage power cable having an inner semiconductive layer, an insulating layer, an outer semiconductive layer, a shielding layer, and a cable sheath in order on the outer periphery of the central conductor is formed on a part of the shielding layer. A distributed strain sensor having a structure in which at least one optical fiber along the longitudinal direction and spirally wound or SZ wound is provided is disclosed.
Patent Document 2 discloses an optical fiber sensor having a configuration in which a sensing coil is spirally wound around the outer periphery of a cylinder, and a reference optical fiber for temperature compensation is housed in a groove.
Patent Document 3 discloses a strain sensor having a configuration in which a sensing optical fiber is fixed between an inner cylinder and an outer cylinder with a resin, while an optical fiber for temperature compensation is housed loosely in the inner cylinder.
In Patent Document 4, a temperature distribution of an optical fiber core is measured in a strain distribution measurement system that uses an optical fiber core as a sensor and measures the strain distribution of an optical fiber cable using Brillouin scattered light in the optical fiber. A measurement system for deriving the strain distribution of an optical fiber cable by correcting the temperature of the Brillouin scattered light distribution measurement result of the optical fiber core wire is disclosed.
Patent Document 5 discloses an optical fiber sensor configured to eliminate the influence of temperature by fixing the strain-measuring optical fiber while fixing the temperature-compensating optical fiber unfixed.
Japanese Patent No. 2746424 US Pat. No. 5,475,216 US Pat. No. 5,094,527 Japanese Patent Laid-Open No. 11-173943 JP 2002-156215 A

However, the above-described conventional technique has the following problems.
1 and 2 show an outline of a conventional distributed water pressure sensor, FIG. 1 is a schematic sectional view of the distributed sensor, and FIG. 2 is a partially enlarged view thereof. This conventional strain sensor 1 has a structure in which one or more optical fibers 3 are twisted on the outer surface of a polyamide tube 2 and these are accommodated in a sheath 4. As shown in FIG. 2, the strain applied to the optical fiber 3 under the installation environment is a strain due to water pressure plus an elongation strain due to its own weight in the sensor radial direction. In the case of the conventional structure shown in FIG. 1, the strain measurement value obtained cannot separate the strain due to water pressure and the elongation strain in the longitudinal direction, and it is impossible to obtain only the intended water pressure distribution as strain information. In order to obtain the strain distribution accompanying the change in water pressure, it was necessary to install another optical fiber for strain measurement and measure the elongation strain due to the sensor's own weight.

  Furthermore, in order to perform temperature compensation of the measured value, it is necessary to mount another optical fiber 5 for temperature compensation separately.

  The present invention has been made in view of the above circumstances, enables more accurate strain measurement, and is a distributed type capable of reducing costs by combining water pressure measurement and temperature compensation with a single optical fiber. The purpose is to provide a water pressure sensor.

In order to achieve the above object, the present invention provides a tubular body provided with a groove capable of accommodating an optical fiber continuously or intermittently along the longitudinal direction, and an optical fiber twisted around the outer periphery of the tubular body. A twisted portion in which an optical fiber is twisted around the outer periphery of the tubular body, and a straight portion in which the optical fiber is housed in the tubular body are alternately provided along the longitudinal direction of the tubular body, There is provided a folded portion that folds the optical fiber on the distal end side of the twisted portion or linear portion provided at the distal end portion of the body and introduces it into the tubular body, and the optical fiber directed from the folded portion toward the proximal end side is straight in the tubular body. And a temperature compensation part is formed.
The strain in the longitudinal direction of the optical fiber is measured, and the amount of strain due to water pressure can be measured by subtracting the amount of strain measured in the linear portion from the amount of strain measured in the twisted portion, and the temperature compensation unit The distributed water pressure sensor is characterized in that the strain change due to the temperature of the strain amount due to the water pressure can be corrected by the measured strain amount.

As described above, the distributed water pressure sensor of the present invention can measure the strain due to the sensor's own weight and the strain due to the water pressure separately, and the strain amount measured at the linear portion can be calculated from the strain amount measured at the twist portion. By subtracting, the amount of strain due to water pressure can be accurately measured.
In addition, a single optical fiber can also serve as three measurement optical fibers: strain due to water pressure, strain due to the sensor's own weight, and temperature compensation, and a low-cost distributed water pressure sensor can be provided.

Hereinafter, embodiments of a distributed water pressure sensor of the present invention will be described with reference to the drawings.
FIG. 3 is a diagram showing an embodiment of the distributed water pressure sensor of the present invention, FIG. 3 (a) is a longitudinal sectional view of the distributed water pressure sensor 10, and FIG. 3 (b) is a transverse sectional view of the twisted portion 13. (C) is a cross-sectional view of the straight portion 14.

  The distributed water pressure sensor 10 of the present embodiment is twisted on the outer periphery of the tubular body 11 provided with a groove 18 capable of accommodating an optical fiber continuously or intermittently along the longitudinal direction. An optical fiber 12, a twisted portion in which the optical fiber 12 is twisted around the outer periphery of the tubular body 11, and a straight portion 14 in which the optical fiber 12 is accommodated in the tubular body 11. The sensing portions 16 are formed alternately along the direction, and the optical fiber 12 on the distal end side of the twisted portion 13 or the straight portion 14 provided at the distal end portion of the tubular body 11 is folded back into the tubular body 11. A folded portion 15 to be introduced is provided, and the optical fiber 12 from the folded portion 15 toward the proximal end side is linearly accommodated in the tubular body 11 to form a temperature compensating portion 17. It has become overturned structure.

  In the present embodiment, the cylindrical body 11 uses a synthetic resin tube having a C-shaped cross section in which a groove 18 in which a part of the circumference of the cylindrical body is cut is continuously formed along the longitudinal direction. Examples of the material of the cylindrical body 11 include polyethylene resin, polystyrene resin, fluororesin, polypropylene resin, polyamide resin, and silicone resin.

  In addition, the shape of the cylindrical body 11 is not limited to this illustration, What is necessary is just the structure where the optical fiber 12 arrange | positioned in the linear part 14 does not receive the pressure from the circumference | surroundings. That is, only the straight portion 14 may have a C-shaped cross section, and the twisted portion 13 may have an annular shape with no groove 18. Moreover, the tubular body 11 should just have the groove | channel more than the number of the optical fibers for a measurement only in the linear part 14 at least.

  The distributed water pressure sensor 10 of this embodiment can serve as three optical fibers for measurement, ie, strain due to water pressure, strain due to the sensor's own weight, and temperature compensation. The optical fiber 12 used for this is not particularly limited as long as the strain applied to the optical fiber can be detected by BOTDR (Brillouin Optical Time Domain Reflectmetry) or the like, and is not limited to a single mode light used as an optical fiber for optical communication. A fiber or a multimode optical fiber can be used. Further, the coating of the optical fiber 12 is not particularly limited as long as it can sufficiently protect the bare optical fiber and has a thickness that does not affect the strain sensing.

  The sheath 19 that covers the sensor main body portion composed of the cylindrical body 11 and the optical fiber 12 is preferably a synthetic resin thin-walled coating having a thickness that can directly transmit the water pressure applied from the outside to the sensing unit 16. Examples thereof include polyethylene resin, polystyrene resin, fluorine resin, polypropylene resin, polyamide resin, and silicone resin.

  In the distributed water pressure sensor 10 of the present embodiment, the lengths of the straight line portion 14 and the twisted portion 13 are longer than the minimum resolution distance of a strain measuring instrument such as BOTDR. As a result, the linear portion 14 is not affected by the external water pressure, and can simply measure only the elongation strain due to the sensor's own weight.

  By adopting the configuration described above, the distributed water pressure sensor 10 of the present embodiment can measure the strain due to the sensor's own weight and the strain due to the water pressure separately, and from the strain amount measured at the twist portion, By subtracting the measured strain amount, the strain amount due to water pressure can be accurately measured.

  FIG. 4 is a diagram illustrating an example of a water pressure measurement result in the distributed water pressure sensor 10 of the present embodiment. In FIG. 4, A part is strain at the twisted part 13 on the upper side of the sensing part 16, B part is strain at the straight part 14 immediately below it (denoted as strain (2)), and C part is the next stage of A. Strain at the twisted portion 13 (denoted as strain (1)), D portion is a strain at the straight portion 14 immediately below the C portion (denoted as strain (3)), and E portion is the next twist of the C portion. The distortion of the part 13 is shown.

  As shown in the graph on the left side of FIG. 4, the strain (1) measured at the central twisted portion 13 is the total amount of strain due to water pressure + elongation due to the sensor's own weight. Only the elongation due to the sensor's own weight was measured in the B part and D part which are the linear parts 14 on both the upper and lower sides. Further, the difference between the strain (2) at the straight portion 14 (B portion) immediately above the C portion and the strain (3) at the straight portion 14 (D portion) immediately below the C portion (strain (2) −distortion ( 3)) corresponds to elongation due to the sensor's own weight. Therefore, by subtracting [elongation due to the sensor's own weight] from [strain due to the water pressure + elongation due to the sensor's own weight], which is measured in the portion C, the strain due to the water pressure can be accurately measured.

  Further, in the distributed water pressure sensor 10 of the present embodiment, the optical fiber 12 in which the sensing unit 16 is folded is introduced into the tube of the tubular body 11 and used as the temperature compensation unit 17 so that the strain change due to temperature can be corrected. The temperature compensation unit 17 is capable of measuring only the strain caused by the temperature change because the optical fiber 12 is housed in the loose together with the tensile strength fiber such as the aramid fiber and the strain due to the water pressure or the sensor's own weight is not added.

  By correcting the [strain due to water pressure] measured by the sensing unit 16 with the amount of strain caused by the temperature change measured by the temperature compensation unit 17, the water pressure applied to the sensor can be measured more accurately. . In addition, the above-described water pressure measurement at one twisted portion 13 is performed on each twisted portion 13 along the sensor longitudinal direction, so that an accurate water pressure can be obtained over the entire length of the distributed water pressure sensor 10 installed at the water pressure measurement location. Can be measured.

It is the longitudinal cross-sectional view which illustrates schematic structure of the conventional sensor, and a cross-sectional view. It is a principal part enlarged view for demonstrating the distortion concerning the optical fiber in the conventional sensor shown in FIG. It is a figure which shows one Embodiment of the distributed water pressure sensor of this invention, (a) is a longitudinal cross-sectional view of a distributed water pressure sensor, is a cross-sectional view of the twist part, (c) is a cross-sectional view of a straight part. is there. It is a figure which shows the water pressure measurement result by the distributed water pressure sensor of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Distributed type water pressure sensor, 11 ... Tubular body, 12 ... Optical fiber, 13 ... Twist part, 14 ... Straight part, 15 ... Folding part, 16 ... Sensing part, 17 ... Temperature compensation part, 18 ... Groove, 19 ... Sheath .

Claims (1)

A tubular body provided with a groove capable of accommodating an optical fiber continuously or intermittently along the longitudinal direction, and an optical fiber twisted around the outer periphery of the tubular body, and the optical fiber on the outer periphery of the tubular body Are twisted together, and straight portions in which the optical fiber is housed in the tubular body are alternately provided along the longitudinal direction of the tubular body, and the twisted portion provided at the distal end portion of the tubular body or A folding portion is provided to fold back the optical fiber on the distal end side of the straight portion and introduce it into the tubular body, and the optical fiber from the folded portion toward the proximal end is linearly stored in the tubular body to form a temperature compensation portion. And
The strain in the longitudinal direction of the optical fiber is measured, and the amount of strain due to water pressure can be measured by subtracting the amount of strain measured in the linear portion from the amount of strain measured in the twisted portion, and the temperature compensation unit A distributed water pressure sensor characterized in that a strain change due to temperature of a strain amount due to the water pressure can be corrected by the measured strain amount.

Images