JP2001012970A - Optical strain sensor cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an elongation or contraction due to a temperature change in an optical strain sensor cable capable of sensing in an overall lengthwise length without necessity of a power source at an observing site so that an optical fiber is scarcely disconnected. SOLUTION: In the optical strain sensor cable, an optical fiber 2 and a low thermal expansion wire material (invar wire 3) covered with a coating material 4. It is preferred to increase a diameter of the low thermal expansion wire material than that of the fiber 2 in view of a protection of the fiber. This cable is embedded in an object to be sensed such as a baserock or the like, connected with a strain measuring unit such as an OTDR or the like and to capture as an increase in the strain of the optical fiber at the strain as an omen of a cave-in. The wire 3 has extremely small elongation or contraction in the case of a temperature change of the wire 3 and the strain to sensed is easily distinguished from a strain of the elongation or contraction of the invar wire, and hence sensing accuracy can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of laying on a rock wall or embedding in the ground, a road, a dike, a large building, or the like.
The present invention relates to an optical distortion sensor cable for detecting distortion generated in these cables, and a distortion detection system using the cable.

[0002]

2. Description of the Related Art A point sensor method is used to observe and detect mechanical distortion that occurs on rock walls, ground, embankments, large buildings, and the like, which is a sign of an abnormal situation such as rock collapse, land subsidence, landslide, or depression. Is conventionally known. This is a method in which sensors that detect the occurrence of distortion as changes in electrical resistance or capacitance are scatteredly installed on a detection target.

Recently, it has been considered to use an optical fiber strain measuring technique by laying or burying an optical fiber so that observation and detection can be performed over the entire length of the detection object in the longitudinal direction.

[0004]

However, according to the point sensor method, an undetectable range occurs between the sensors, and uniform observation detection over the entire length of the detection target in the longitudinal direction cannot be performed. Further, a power source for driving the sensor and a transmission device for the detection information are required at the site where the observation and detection are performed, and there is a problem that maintenance and management are difficult.

Further, when an optical fiber is laid or buried and the strain is measured and detected uniformly over the entire length in the longitudinal direction, the cable using only the used optical fiber is liable to be disconnected and cannot be detected in many cases. There is a problem to say. On the other hand, there is a cable in which an optical fiber and a steel wire are integrated for the purpose of preventing disconnection.
However, since the steel wire greatly expands and contracts due to temperature, distortion occurs in the optical fiber due to expansion and contraction of the steel wire, not the detection target, and accurate detection of distortion of the detection target cannot be performed.

FIG. 4 shows an optical communication cable in which a steel wire 6 and an optical fiber 5 are integrated with a covering material 7 and is used for a part drawn from a telephone pole into a home. Since this cable is used for optical communication, even if the steel wire 6 expands and contracts due to temperature and causes distortion, it has little effect on communication, but for the above-mentioned reason, it cannot be used for strain measurement at all.

Accordingly, it is a primary object of the present invention to use an optical fiber strain measurement technique, observing over the entire length in the longitudinal direction without requiring a power source at an observation site, and making it possible to prevent the optical fiber from being disconnected, and furthermore, due to a temperature change. An object of the present invention is to provide an optical distortion sensor cable with little expansion and contraction and a distortion detection system using the cable.

[0008]

The present invention achieves the above object by combining an optical fiber and a low thermal expansion wire.

That is, the optical strain sensor cable of the present invention comprises:
The optical fiber and the low-thermal-expansion wire are collectively covered with a covering material.

Here, the low thermal expansion wire is a wire made of a material having a small coefficient of linear expansion. Most metallic materials have a linear expansion coefficient of 10 ⁻⁵ m / m ° C., but a material having a linear expansion coefficient of about half, more preferably about 1/10 can be used. For example, the coefficient of linear expansion is about 1/10 that of iron or nickel.
Is best. Fe-Ni for Invar
System, Fe-Pt system, Fe-Pd system, and any of them may be used. Typical standard composition in a typical Fe-Ni system is Mn: 0.4, C: 0.
2, Ni: 36, balance Fe (wt%).

The number of optical fibers and low thermal expansion wires is not particularly limited. It is sufficient that at least one of them is combined. Furthermore, the arrangement of the optical fiber and the low thermal expansion wire is not particularly limited, but it is preferable that the optical fiber is sandwiched between the low thermal expansion wires. Thereby, disconnection of the optical fiber is effectively suppressed. In particular, by making the diameter of the low-thermal-expansion wire larger than the diameter of the optical fiber, a structure in which an external load is hardly applied to the optical fiber can be obtained, which is more preferable.

On the other hand, the coating material is not particularly limited. For example, polyolefin-based plastics such as polyethylene and polypropylene can be used.

Such a cable is buried in an object to be detected, and further connected to a strain measuring device, whereby a strain detecting system can be constructed. Examples of the detection target include large structures such as buildings and bridges, in addition to rock walls, ground and embankments. And, rock detection, land subsidence, landslide,
Detects the occurrence of mechanical distortion that is a sign of an abnormal situation such as depression or cracking. OTDR as a strain measurement device
(Optical Time-Domain Reflectometer) and BOTDA
(Brillouin Optical-Fiber Time Domain Analysis).

The OTDR applies an optical pulse from one end of an optical fiber, detects distortion generated in the optical fiber from a change in transmission loss, and further detects distortion from the time until the backscattered light of the optical pulse returns to the incident end. This is a device for detecting the position where the occurrence has occurred.

BOTDA utilizes Brillouin scattering, sends out an optical pulse from one end of an optical fiber, measures the frequency shift of Brillouin scattered light returning from the middle of the optical fiber, and measures the shift in the longitudinal direction of the optical fiber. This is a device for measuring a change in distortion and a distance to a change point.

When an optical pulse is incident on an optical fiber, Rayleigh scattered light having the same frequency as the incident light is generated as backscattered light;
Brillouin scattered light whose frequency is shifted by the influence of the interstitial vibration is observed. Therefore, under the influence of the distortion, the interstitial vibration changes and the frequency of Brillouin scattering changes, so that the distortion can be basically determined by observing the frequency shift. Then, by observing the time waveform using the OTDR principle, it is possible to detect at which position the distortion has occurred.

[0017]

Embodiments of the present invention will be described below. FIG. 1 is an external view of a cable of the present invention, and FIG. 2 is a cross-sectional view of the same.

This optical strain sensor cable 1 has a structure in which one optical fiber 2 and two Invar wires 3 are integrated with a coating material 4. Here, a 36% Fe-Ni alloy is used as the invar wire 3. The coating material 4 used polyvinyl chloride.

Most metallic materials have a coefficient of thermal expansion of 10 ^−5.
At m / m ° C, a 1m rise in temperature at 1 ° C will stretch 0.01mm for a 1m substance. The thermal expansion coefficient of the Invar wire (Ni-36% Fe-Ni alloy) used in this example is 10 ⁻⁶ m / m ° C., and the elongation is 1/10 of that of a conventional metal.

For example, if a 100 m optical strain sensor cable is laid on a rock wall and the temperature difference per day is 10 ° C., when the cable shown in FIG. 4 is used, the steel wire will expand and contract by 10 mm, and Cannot be distinguished from the strain caused by the displacement of the steel wire due to the expansion and contraction of the steel wire. The expansion and contraction using the optical strain sensor cable of the present invention is 1/10, which enables more accurate observation and monitoring.

When the diameter of the invar wire is larger than that of the optical fiber, a load is prevented from being applied to the optical fiber, which is more effective in protecting the optical fiber. Furthermore, the arrangement of the optical fiber and the Invar wire is not limited, but FIG.
It is desirable that the optical fiber be sandwiched between invar wires as shown in FIG. Here, an example of one optical fiber and two Invar wires is shown, but one or a plurality of each may be used.

Next, FIG. 3 shows a configuration of a strain monitoring system using the optical strain sensor cable of the present invention. While the road 11 runs along the lower side of the slope 10, it is monitored that the embankment of the slope 10 has collapsed. The optical strain sensor cable 12 of the present invention is buried in the slope 10 and when the embankment falls, a strain is generated in the optical strain sensor cable, and a strain measuring device (for example, BOTDA)
The amount of distortion is measured by 13 and processing such as an alarm is performed by the personal computer 14.

[0023]

As described above, according to the optical strain sensor cable of the present invention, a sign of an abnormal situation such as a rock collapse, a land subsidence, a landslide, or a collapse that occurs on a rock wall, a ground, a levee, a large building, or the like. When observing and detecting the mechanical strain generated as above, it is possible to observe and detect over the entire length in the longitudinal direction without using a driving power source at the installation location. Further, more accurate strain detection can be performed even in an environment where the optical fiber is hardly broken and the temperature change is large.

[Brief description of the drawings]

FIG. 1 is an external view of an optical strain sensor cable of the present invention.

FIG. 2 is a cross-sectional view of the optical strain sensor cable of the present invention.

FIG. 3 is a configuration diagram of a strain detection system using the optical strain sensor cable of the present invention.

FIG. 4 is a sectional view of a conventional optical fiber cable for communication.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical strain sensor cable 2 Optical fiber 3 Invar wire 4 Coating material 5 Optical fiber 6 Steel wire 7 Coating material 10 Slope 11 Road 12 Optical strain sensor cable 13 Strain measuring device 14 Personal computer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Mitsuo Mukase 1-3-1 Shimaya, Konohana-ku, Osaka-shi Inside the Osaka Works, Sumitomo Electric Industries, Ltd. (72) Masakazu Miyauchi 1-chome, Shimaya, Konohana-ku, Osaka-shi No. 1-3 F-term in Sumitomo Electric Industries, Ltd. Osaka Works (reference) 2F065 AA65 CC00 CC14 CC40 DD16 EE02 FF12 FF46 LL02 SS09 2F076 BA11 BB08 BB09 BD01 BD06 2F103 BA00 BA02 EC09 GA14 2H038 AA05

Claims (4)

[Claims] 1. An optical strain sensor cable, wherein an optical fiber and a low thermal expansion wire are coated with a coating material. 2. The optical strain sensor cable according to claim 1, wherein the diameter of the low thermal expansion wire is larger than the diameter of the optical fiber. 3. The optical strain sensor cable according to claim 1, wherein the optical fiber is disposed so as to be sandwiched between a plurality of low thermal expansion wires. 4. An optical strain sensor cable embedded in a detection target, and a strain measuring device connected to the optical sensor cable, wherein the optical strain sensor cable includes an optical fiber, a low thermal expansion wire, A strain detection system, comprising: a coating material for collectively coating an optical fiber and a wire.