JP2002062213A - Optical fiber wettness sensor and wettness measuring device using this sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber wettness sensor capable of measuring the vertical directional wettness distribution and the horizontal directional wettness distribution with the simple constitution. SOLUTION: A liquid expansible fiber holding member 34 is stuck to a measuring object part arranged in at least a wettness measuring part of an optical fiber 33 to constitute this optical fiber wettness sensor 32. The pulse light is made incident from one end of the optical fiber 33 in this optical fiber wettness sensor 32. The backward scattered light returned in the optical fiber 33 is detected by a light detecting part, and the strain distribution of the measuring object part in the optical fiber 33 is calculated and outputted on the basis of this backward scattered light. Thus, a wettness of a wettness measuring part for arranging the measuring object part of the optical fiber 33 is measured from the outputted strain distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber wetness sensor used for measuring the wetness distribution of a bank, soil, etc., and detecting water leakage from a wall surface of a tunnel, an underground pipe, and the like, and using this sensor. To a wetness measuring device.

[0002]

2. Description of the Related Art Conventionally, there has been known an optical fiber wetness sensor which detects a change in soil heat capacity due to a difference in wetness, thereby measuring a vertical wetness distribution in a bank.

FIG. 7 shows a configuration of a wetness measuring device using the optical fiber wetness sensor. In this apparatus, an optical fiber wetness sensor 4 having a structure in which a heater-combined optical fiber cable 2 is wound around a cylinder 3 is vertically embedded in a wetness measurement portion 1a of a bank body 1. Then, the heater of the optical fiber wetness sensor 4 is heated by the heater power supply 5, and the temperature distribution of the optical fiber during the heating is measured by the wetness measuring unit 6. Further, the temperature distribution of the optical fiber at the time of cooling without heating the heater is also measured in advance by the wetness degree measuring unit 6. In the wetness measuring section 6, the wetness measuring portion 1a of the embankment body 1 is determined based on the temperature change width of the optical fiber during heating and cooling.
Is used to calculate the vertical wetting degree distribution.

[0004]

However, in this type of conventional wetness measuring device, a heater power supply 5 for heating the heater of the optical fiber wetness sensor 4 and a power supply line from the heater power supply 5 are provided. Was needed. Moreover, conventionally, since the local measurement was performed in the vertical direction with respect to the embankment 1, to measure the wetness distribution over the entire length of the embankment,
A plurality of locations must be set at predetermined intervals as wettability measurement sites, and the optical fiber wetness sensor 4 must be buried in each of them for measurement. For this reason, the heater power supply 5 is prepared for each of the wetness degree measurement parts, or even if the heater power supply 5 can be commonly used in each of the wetness degree measurement parts, the power supply line is connected from the heater power supply 5 to each of the wetness degree measurement parts. The trouble was that it had to be laid long.

The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide an optical fiber wetness sensor capable of realizing local measurement of the wetness distribution with a simple configuration and an optical fiber wetness sensor. An object of the present invention is to provide a wetness measuring device using a sensor. A second object of the present invention is to provide an optical fiber wetness sensor capable of continuously measuring the wetness distribution over a long distance with a simple structure and a wetness measuring device using the sensor. is there.

[0006]

SUMMARY OF THE INVENTION According to the present invention, backscattered light which has been returned by inputting pulse light from one end of an optical fiber is detected, and distortion generated in the optical fiber based on the backscattered light is detected. The object is solved by measuring the degree of wetness using a technique for measuring the distribution. That is, the invention corresponding to claim 1 of the present application is an optical fiber wetness sensor in which a fiber holding member having liquid expandability or liquid contraction is attached to a measurement target portion installed at least at a wetness measurement site of an optical fiber. .

According to a second aspect of the present invention, a liquid holding member having a liquid swelling property is attached to a portion to be measured which is installed at least in a wetness measuring portion of an optical fiber, and the optical fiber is attached to the fiber holding member. An optical fiber wetness sensor is provided in which a surface other than the surface is closely fitted to an inner surface of a groove formed in a restraining member. In addition, the invention corresponding to claim 3 of the present application is a method in which at least a portion to be measured which is installed at a wettability measurement site of an optical fiber is spirally formed on the outer peripheral surface of a rod-shaped or cylindrical fiber holding member having liquid expansion or contraction. The optical fiber wetness sensor is wound around. Further, the invention corresponding to claim 4 of the present application embeds a fiber holding member having liquid expandability in a spirally formed groove on the outer peripheral surface of a rod-shaped or cylindrical core member,
An optical fiber wetness sensor is formed by attaching an optical fiber to a surface of a fiber holding member and spirally winding a measurement target portion provided at least at a wetness measurement site of the optical fiber around an outer peripheral surface of a core member.

Further, the invention corresponding to claim 5 of the present invention is the optical fiber wetness sensor according to each of the above-described inventions 1 to 4, and the pulse light is incident from one end of the optical fiber in the optical fiber wetness sensor and returned. Light detecting means for detecting the backscattered light that has come, and strain distribution output means for calculating and outputting the strain distribution of the measured portion in the optical fiber based on the backscattered light detected by the light detecting means. There is provided a wetness measuring device configured to measure a wetness of a wetness measuring portion where a measured portion of an optical fiber is installed from a strain distribution output by a distribution output unit.

Here, as the fiber holding member having liquid expandability or liquid contraction, a member such as rubber or plastic is used.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment suitable for local measurement of the degree of wetness in soil such as an embankment or a cliff will be described with reference to FIGS. In the first embodiment, the case where the vertical wetness distribution in the embankment is measured is shown, but the same applies to the case where the vertical wetness distribution in the soil is measured.

FIG. 1 is a configuration diagram of a wetness measuring device according to a first embodiment.
a, an optical fiber cable 12 is connected to a cylindrical core member 13;
Fiber wetness sensor 14 having a spirally wound structure
Is buried vertically. One end of the optical fiber cable 12 is connected to an optical fiber strain distribution measuring device 15.

The strain distribution measuring device 15 is a pulse light source 1
From 6, the pulse light is incident on the optical fiber in the optical fiber cable 12 while varying the optical frequency, and the Brillouin scattered light of the backscattered light returning from the optical fiber is detected by the light detection unit 17. Then, the signal processing unit 1 uses the Brillouin scattered light of each optical frequency detected by the light detection unit 17.
At 8, measure the spectrum distribution of Brillouin scattered light,
Further, a Brillouin frequency shift in the length direction of the optical fiber is obtained from the spectrum distribution, a strain distribution in the length direction of the optical fiber is obtained from the Brillouin frequency shift, and can be confirmed on the monitor 18.

Here, the light detecting section 17 constitutes a light detecting means for detecting the back scattered light which has entered the pulse light from one end of the optical fiber in the optical fiber wetness sensor and returned, and has a signal processing section 18 and a monitor. Reference numeral 19 constitutes a strain distribution output unit that calculates and outputs a strain distribution of the measured portion in the optical fiber based on the backscattered light detected by the light detection unit (the light detection unit 17). Incidentally, as the strain distribution measuring device 15, a commercially available single-ended optical fiber strain distribution measuring device can be used.

FIG. 2A is a perspective view of the optical fiber wetness sensor 14 used in the first embodiment, and FIG.
Is a part of the longitudinal section of the optical fiber wetness sensor 14.
As shown in the figure, the optical fiber wetness sensor 14 has a fiber holding tube 21 as a fiber holding member made of a rubber material having a water-swelling property which expands by absorbing water on the outer periphery of a cylindrical core member 13 made of a metal. And fix it. The optical fiber cable 12 is spirally wound around and attached to the outer peripheral surface of the fiber holding tube 21.

In the first embodiment, the optical fiber wetness sensor 14 having the above structure is buried vertically in the bank body 11 to measure the wetness of the wetness measuring portion 11a. . Then, in a location where the degree of wetness is high, the volume of the water-swellable fiber holding tube 21 expands due to moisture adsorption, and the optical fiber cable 12 wound on the surface thereof is bent. When the optical fiber cable 12 bends, a new strain is generated in the bent portion, so that the strain distribution in the length direction of the optical fiber measured by the strain distribution measuring device 15 changes. By evaluating the change in the strain distribution, it is possible to measure the wetness of the wetness measuring portion 11a where the measured portion of the optical fiber cable 12 is installed.

For example, suppose that the strain distribution in the longitudinal direction of the optical fiber, which can be confirmed by the monitor 19, has changed from FIG. 3A to FIG. 3B. Then, the wetness measurement part 11 where the measured part of the optical fiber cable 12 is installed is set.
It can be seen that the distortion distribution changes at point X in a. That is, before the point X, the fiber holding tube 21
It can be seen that the volume has expanded due to moisture adsorption.

As described above, according to the first embodiment, since the local measurement of the wetness distribution can be performed without heating by the heater, the heater power supply for heating the heater or the heater power supply can be used. Power supply line from the
The configuration can be simplified. In particular, in the case of setting as a plurality of wetness measurement sites at a certain interval, and burying the optical fiber wetness sensor 14 for each measurement,
The effect is great.

FIG. 4 shows a modification of the optical fiber wetness sensor 14 used in the first embodiment, and FIG.
1 is a perspective view, and FIG. 1B is a part of a vertical section. As shown in the figure, the optical fiber wetness sensor 14 'has a spiral groove 20 formed on the outer peripheral surface of a cylindrical core member 13, and a fiber holding member made of a rubber material having water expandability is formed in the groove 20. By embedding the member 22 and attaching the optical fiber cable 12 to the surface of the fiber holding member 22, at least the portion to be measured installed at the wetness measurement site 11 a of the optical fiber is spirally wound on the outer peripheral surface of the core member 13. It is wound in a shape.

Even when the optical fiber wetness sensor 14 'having such a configuration is used, the volume of the water-swellable fiber holding member 22 expands due to moisture adsorption at the location where the wetness of the wetness measuring portion 11a is high. As a result, the strain distribution in the length direction of the optical fiber measured by the strain distribution measuring device 15 changes, and the change in the strain distribution is evaluated, whereby the covering of the optical fiber cable 12 is evaluated. It is possible to measure the wetness of the wetness measurement site 11a in which the measurement unit is installed.

Also in this case, since the heater power supply and the power supply line are unnecessary as described above, the configuration can be simplified. In addition, since the fiber holding member 21 is in close contact with the groove 20 except for the surface to which the optical fiber cable 12 is attached, the coefficient of expansion of the optical fiber attachment surface is large, and the precision is higher than that of the optical fiber wetness sensor 14 shown in FIG. Has the advantage that the wetness distribution can be measured.

The optical fiber wetness sensors used in the wetness measuring apparatus according to the first embodiment are not limited to the optical fiber wetness sensors 14 and 14 'shown in FIGS. For example, in the optical fiber wetness sensor 14 shown in FIG. 2, even if the core member 13 itself is formed of a rubber material having water expandability, and the core member functions as a fiber holding member, the first embodiment is also applicable. The same operation and effect as those of the embodiment can be obtained.

Further, the periphery of the optical fiber wetness sensors 14, 14 'shown in FIGS. 2 and 4 may be covered with a tubular member configured to allow only permeated water to flow. By doing so, the optical fiber cable 12 can be protected when the optical fiber cable 12 is buried in the wetness measurement site 11a.

Further, as the fiber holding tube 21 and the fiber holding member 22, it is possible to use a member having a water shrinkage property which shrinks by absorbing water. In this case as well, in a location where the wetness of the wetness measurement part 11a is high, the fiber holding tube 21 or the fiber holding member 22 having water shrinkage contracts in accordance with the wetness and deflects the optical fiber cable 12, so that distortion is caused. The strain distribution in the length direction of the optical fiber measured by the distribution measuring device 15 changes, and by evaluating the change in the strain distribution, the wetness measuring portion 11a where the measured portion of the optical fiber cable 12 is installed is measured. Wetness can be measured.

Next, a second embodiment suitable for detecting a water leak or the like by continuously measuring the wetness distribution in the inner wall surface of a tunnel or an underground pipe or the like in the horizontal direction. This will be described with reference to FIGS. In the second embodiment, the case where the horizontal wetness distribution of the inner wall surface of the tunnel is measured is shown. However, the case where the horizontal wettability distribution of the inner wall surface such as an underground pipeline or the soil is measured. Can be similarly applied.

FIG. 5 is a configuration diagram of a wetness measuring device according to the second embodiment. An optical fiber wetness sensor 32 is buried in a horizontal direction at a wetness measuring portion 31a along the inner wall surface of a tunnel 31. I have. Further, one end of the optical fiber cable 33 extended from the optical fiber wetness sensor 32 is connected to the optical fiber strain distribution measuring device 15 which functions in the same manner as in the first embodiment.

FIG. 6A is a perspective view of the optical fiber wetness sensor 32, and FIG.
It is arrow A sectional drawing. As shown in the figure, the optical fiber wetness sensor 32 includes a plate made of a rubber material having a water swelling property, at least in a portion to be measured installed at the wetness measurement portion 31 in the tunnel in the entire length of the optical fiber cable 33. The fiber holding member 34 is adhered, and the surface of the fiber holding member 34 other than the optical fiber attachment surface is closely fitted to the inner surface of the groove 36 formed in the restraining member 35 made of metal or the like. .

In the second embodiment, the optical fiber wetness sensor 32 having the above structure is mounted horizontally along the inner wall surface of the tunnel 31, and the wetness measuring portion 31a is provided.
Is measured. As a method of mounting the sensor, the bottom surface of the restraining member 35 is fixed to the wall surface, or a groove is formed in the wall surface so that the restraining member 35 can be accommodated in the horizontal direction. And attach it.

Then, in a location having a high degree of wetness (a location where water is leaking), the fiber holding member 3 having water swellability is used.
4 swells due to moisture adsorption, and deflects the optical fiber cable 33 wound around its surface. When the optical fiber cable 33 bends, a new strain is generated in the bent portion, so that the strain distribution measuring device 15 is used similarly to the first embodiment.
The strain distribution in the length direction of the optical fiber measured by the above changes. By evaluating the change in the strain distribution, it is possible to measure the wetness of the wetness measuring portion 11a where the measured portion of the optical fiber cable 12 is installed.

As described above, also in the second embodiment,
Since the local measurement of the wetness distribution can be performed without heating by the heater, a heater power supply for heating the heater and a power supply line from the heater power supply can be eliminated, and the configuration can be simplified. Of course, the wetting degree distribution in the horizontal direction can be measured in the length direction of the optical fiber cable 33, so that the wetting degree distribution can be continuously measured over a long distance (wide range) according to the length of the optical fiber cable 33. become.

Further, since the fiber holding member 34 is in close contact with the groove 36 of the restraining member 35 except for the surface to which the optical fiber cable 33 is attached, the expansion coefficient of the optical fiber attachment surface is large, and the degree of horizontal wetting is accurately determined. The distribution can be measured.

The fiber holding member 34 is directly fixed to the inner wall surface of the tunnel 31 without using the restraining member 35,
It is also possible to measure the wetness of the wetness measurement site 31a. Alternatively, the optical fiber cable 12 may be protected by covering the periphery of the optical fiber wetness sensor 32 with a tubular member configured to allow only permeated water to flow.

As the fiber holding member 34, a member having water shrinkage can be used. Further, by using a member that expands or contracts by sucking a liquid other than water, for example, oil, as the fiber holding member 34, it is possible to use the fiber holding member 34 as an oil leak sensor. In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0033]

As described in detail above, according to the present invention,
An optical fiber wetness sensor capable of realizing local measurement of the wetness distribution with a simple configuration and a wetness measuring device using the sensor can be provided. Further, it is possible to provide an optical fiber wetness sensor capable of continuously measuring the wetness distribution over a long distance with a simple configuration and a wetness measuring device using the sensor.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a wetness measuring device according to a first embodiment of the present invention.

FIG. 2 is a structural diagram of an optical fiber wetness sensor used in the first embodiment.

FIG. 3 is a diagram showing a measurement result of wetness in the first embodiment.

FIG. 4 is a view showing a modification of the optical fiber wetness sensor used in the first embodiment.

FIG. 5 is a configuration diagram of a wetness measuring device according to a second embodiment of the present invention.

FIG. 6 is a structural diagram of an optical fiber wetness sensor used in the second embodiment.

FIG. 7 is a configuration diagram of a conventional wetness measuring device.

[Explanation of symbols]

 11 ... embankment body 12, 33 ... optical fiber cable 13 ... core member 14, 14 ', 32 ... optical fiber wetness sensor 15 ... strain distribution measuring instrument 21 ... fiber holding tube (fiber holding member) 22, 34 ... fiber holding member 35 ... restraint member

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Eiji Nagai Inventor F-term (reference) 2G040 AB01 AB07 BA29 BB04 CA02 CA12 CA23 FA09 FA10 GA01 HA11 3-18-10 Motoasakusa, Taito-ku, Tokyo ZA05 2G067 AA11 BB16 CC02 DD27 EE08 EE09

Claims (5)

[Claims] 1. An optical fiber wetness sensor comprising: a liquid holding member having liquid expandability or liquid contraction attached to a measurement target portion provided at least in a wetness measurement portion of an optical fiber. 2. A liquid holding member having a liquid swelling property is attached to a measurement target portion of the optical fiber which is installed at least at a wetness measurement site, and a surface of the fiber holding member other than the optical fiber attachment surface is restricted. An optical fiber wetness sensor characterized by being fitted in close contact with an inner surface of a groove formed in the optical fiber. 3. An optical fiber in which at least a portion to be measured installed at a wetness measurement site is spirally wound around an outer peripheral surface of a rod-shaped or cylindrical fiber holding member having liquid expandability or liquid contraction. An optical fiber wetness sensor characterized by the above-mentioned. 4. A fiber holding member having liquid expandability is embedded in a spirally formed groove on the outer peripheral surface of a rod-shaped or cylindrical core member, and an optical fiber is attached to the surface of the fiber holding member. An optical fiber wetness sensor, wherein a part to be measured installed at least at a wetness measurement part of the optical fiber is spirally wound around the outer peripheral surface of the core member. 5. An optical fiber wetness sensor according to claim 1, wherein the backscattered light that has entered pulse light from one end of the optical fiber and returned from the optical fiber in the optical fiber wetness sensor. Light detecting means for detecting, and a strain distribution output means for calculating and outputting a strain distribution of the measured portion in the optical fiber based on the backscattered light detected by the light detecting means, wherein the strain distribution output means Measuring the wetness of the wetness measurement site where the measured portion of the optical fiber is installed from the strain distribution output by the method.