JPH01189541A - Optical fiber water leakage detection sensor - Google Patents

Abstract

PURPOSE:To accurately and rapidly detect the generation of a water leakage accident and the accident position thereof, by measuring the reflected light such as back scattering light of the light incident from the input terminal of an optical fiber and detecting an increase in the loss of transmission light due to the bending of the optical fiber. CONSTITUTION:A sensor 1 is constituted by forming a water leakage sensor part 3 to a part of an optical fiber 2. This water leakage sensor part 3 is constituted by mounting a water absorbing tube 4 composed of a water absorbable resin to a part of the optical fiber 2 and winding a string 5 around the outer periphery of the water absorbing tube 4 at a definite pitch and further fixing the water absorbing tube 4 in such a state that the mount part thereof is wound by several turns in a predetermined radius (r) of curvature. In a water leakage accident, the water absorbing tube 4 absorbs the moisture penetrated in a container to expand in its volume and the bent part of the optical fiber 2 to which bending stress is preliminarily applied is further bent. The loss increase of transmission light due to the bending of the optical fiber 2 is detected by measuring the reflected light such a back scattering light of the light incident from the input terminal of the optical fiber 2, and the generation of a water leakage accident and the accident position thereof can be detected accurately and rapidly.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention provides an optical fiber flood detection sensor that is disposed inside, for example, a telecommunications cable, and is capable of accurately and quickly detecting a flood accident in this type of cable. Regarding.

"Prior Art and its Problems" Generally, electric communication cables such as power cables and communication cables are laid within transmission lines within and outside cities, on the ocean floor, and the like.

A warning wire such as a bare wire, paper insulated wire, or plastic insulated wire is wired inside such a cable along its length, and water intrusion is detected by a partial short circuit of this warning wire. It is being

However, waterproof cables constructed by wiring this alarm wire use the above alarm wire, so
There was a problem in that it was not possible to accurately and quickly detect flooded areas. Another problem was that the warning wire had low sensitivity for detecting flooding.

Another problem is that warning wires using metal conductors cannot be used in sections where electromagnetic induction exists.

Further, in recent optical fiber cables, the relay interval is long, so there is a problem that the alarm line itself cannot be used.

Under these circumstances, there has been a desire for the development of a water intrusion detection sensor that can be installed inside telecommunications cables and the like as described above.

The optical fiber water immersion detection sensor according to the present invention includes a single-mode optical fiber, in which a bending stress is applied to the optical fiber at least at one location in advance, and the optical fiber is bent. A water immersion sensor part is provided with a water absorbent resin that expands in volume when absorbing water, and an expansion suppressing material that suppresses the expansion of the water absorbent resin is placed outside the bent part and the water absorbent resin. It was formed and structured and used as a means of solving problems.

"Function" The optical fiber water immersion detection sensor of the present invention, having the above-described configuration, exhibits the following function.

That is, in the event of a flooding accident, the water-swellable material absorbs moisture that has penetrated into the container and expands in volume, thereby further pushing and bending the bent portion of the optical fiber to which bending stress has been applied in advance. Therefore, the increased loss of transmitted light due to bending of the optical fiber can be detected by measuring reflected light such as backscattered light of the light incident from the input end of the optical fiber, and it is possible to accurately and accurately determine the occurrence and location of flooding accidents. Can be detected quickly.

"Example" Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention, and reference numeral 1 in the figure indicates an optical fiber water immersion detection sensor (hereinafter simply referred to as sensor). This sensor I is constructed by forming a water immersion sensor section 3 on three parts of an optical fiber 2.

In this water immersion sensor section 3, a water absorption duplex 4 made of water absorbent resin is attached to a part of the optical fiber 2, and a string 5 is wound around the outer circumference of the water absorption tube 4 at a constant pitch. It is constructed by fixing a portion wrapped around it several turns with a predetermined radius of curvature r. Although not shown, a plurality of water immersion sensor sections 3 are formed on the optical fiber 2 at appropriate intervals.

As the optical fiber 2, a single mode optical fiber such as a quartz single mode optical fiber, a multi-component single mode optical fiber, or a plastic songle mode optical fiber is used. )<Optical fiber strands in which the R wire is coated with one or more layers of thermosetting silicone, urethane, ultraviolet curable polymer, etc., and optical fiber cores in which this strand is coated with nylon, etc. Preferably used.

The material of the water absorption tube 4 has a volume of 5 when water is absorbed.
Examples of suitable materials include polyvinyl chloride, polyethylene, EVA resin,
Thermoplastics such as EEA resin, polyester resin, polyurethane, styrene-based thermoplastic elastomer (hereinafter abbreviated as TPE), olefin-based TPE, ester-based TPE, vinyl chloride-based TPE, amide-based TPE, tsene-based TPE, ionomer-based TPE, etc. Resin or rubber such as 1,3 diene rubber, polyacrylate-polyacrylic acid copolymer, polyvinyl alcohol-vinyl acetate copolymer,
Mixtures of water-absorbing materials such as polyurethane, polyethylene oxide, starch graft copolymers, and carboxymethyl cellulose (CMC) are preferably used. Further, the thickness of the water absorption tube 4 is appropriately set in consideration of the water absorption capacity and volumetric expansion coefficient of the water absorbent resin.

The string 5 is made of a material that does not expand when submerged in water, such as a string made of synthetic resin such as polyester, a string made of natural fibers such as cotton or silk, or a metal material.

Furthermore, the radius of curvature r of the water immersion sensor section 3 is
The transmission loss (initial loss value) is set to be about 0.01 to IdB, and it is particularly preferable that the initial loss value is about 0.1 dB.

This sensor l is manufactured, for example, as follows.

First, the water absorption duplex 4 is attached to a predetermined position of the optical fiber 2. The water-absorbing tube 4 can be attached by forming a water-absorbing resin into a tube shape and inserting this tube into the optical fiber 2, or by inserting a molten water-absorbing resin into a predetermined position of the optical fiber 2. A method is used in which the coating is applied to a certain thickness. Next, a string 5 is wound around the outer periphery of this water absorption tube 4. Next, the water absorption tube 4 is manufactured by winding it around several turns so that the transmission loss is about 0.1 dB, and fixing it in this state by applying adhesive to a part thereof.

The sensor I configured as described above detects the occurrence of a flooding accident in the following manner. First, a flooding accident occurs at a location where one of the water immersion sensor sections 3 is installed, and this moisture permeates into the water absorption tube 4. The water absorbing duplex 4 expands in volume by absorbing this permeated moisture, and on the other hand, the water absorbing tube 4 is in contact with the string 5 wound around the outer periphery of the water absorbing tube 4.
As a result, the water immersion sensor section 3 is deformed, and a portion with a radius of curvature smaller than the preset radius of curvature r is generated, and the loss of transmitted light transmitted through the optical fiber 2 occurs in this portion. By sensing this increase in the loss of transmitted light, it is possible to detect the occurrence of a flooding accident.

Next, an example of a water immersion detection system using this sensor 1 will be explained with reference to FIG. 2. The sensor 1 shown in this figure is
It is constructed by providing a plurality of water immersion sensor sections 3 on an optical fiber 2. At the end of this sensor 1, there is a device that measures the time delay of the reflected light of the light that enters the sensor 1, and
A water immersion detection device 6 is connected which measures changes in the level of received light and detects the position where bending of the optical fiber occurs. This water immersion detection device 6 includes a light emitting unit 9 consisting of a pulse generator 7 which inputs a light pulse from the input end of an optical fiber 2, a light emitting element 8 such as an LD (laser diode) or an LED (light emitting diode), and an optical fiber 2. a light detection unit IO having a light emitting element such as an APD (avalanche photodiode) that receives reflected light pulses such as backscattered light from the light emitting unit 9;
an optical directional coupler II that controls the flow of the optical pulses from the optical fiber 2 and the reflected optical pulses from the optical fiber 2, and an operation that calculates the time delay of the reflected optical pulses received by the photodetector IO. part I2 and display part 1 that displays the processing results.
It consists of 3.

Next, a method of operating the flood detection system having such a configuration will be explained. First, one end of the sensor 1 is connected to the water intrusion detection device 6, and then the other end of the sensor 1 is installed throughout each floor of a building or the like housing communication equipment. This completes the flood detection system.

For example, if a flooding accident occurs in the X area shown in this figure, moisture will penetrate into the water immersion sensor section 3 disposed within this X area, and the water absorption tube 4 of this water immersion sensor section 3 will absorb water and swell. and causes volumetric expansion. With this,
In the submersion sensor section 3 in the area, the radius of curvature of the optical fiber 2 becomes smaller than the initial setting value, resulting in an increase in transmission loss.

The increase in loss due to the bending of the optical fiber 2 is detected by the water immersion detection device 6 based on the time delay of reflected light pulses such as backscattered light returning to the input end of the optical fiber 2 and changes in the light reception level. Then, the calculation unit 12 of the water immersion detection device 6 analyzes the measurement data of the reflected light pulses to determine the distance from the input end of the optical fiber 2 to the location where water immersion has occurred. Next, by displaying this data on the display unit 13, a flooding accident in area X can be detected.

Next, in response to the occurrence of this flooding accident, immediate measures will be taken to deal with the flooding accident in Area X.

In such a flood detection system, at the position of the display unit 13 of the flood detection device 6, a flood accident in an area where the flood sensor unit 3 is installed in advance, such as the X area, can be accurately and quickly detected. Is possible. In addition, this flood detection system is not limited to the above example; for example, a sensor inside a telecommunications cable can be used. It is also possible to have a configuration in which the cable is installed together with other telecommunications lines or optical fibers.

In this case, the sensor 1 is constructed by attaching a water absorption tube 4 that expands in volume when water is absorbed to the optical fiber 2.
A string 5 is wound around the outer periphery of the optical fiber 2, and the water absorption duplex 4 is further wound several turns with a predetermined radius of curvature r to form a water immersion sensor section 3 at multiple locations on the optical fiber 2. The water absorption tube 4 expands in volume due to the penetration of moisture into the water absorption tube 4, while the string 5 on the outer periphery of the water absorption tube 4 suppresses the expansion of the water absorption tube 4 and sets the radius of curvature of the optical fiber 2 of the water immersion sensor section 3 to the initial setting value. Since the water intrusion detection means is made smaller than the above and increases the transmission loss of the optical fiber 2, it can be installed over a longer distance than conventional water intrusion detectors using metal conductors, and can be installed in areas where there is electromagnetic induction. It is also possible to adapt it to the situation.

By the way, in a sensor that determines whether a flooding accident has occurred based on an increase in the loss of the optical fiber 2 as in this example, it is possible to determine the amount of increase in the loss of the optical fiber 2 when water is detected so that it can be installed over a long distance. It is desirable that the value be as small as possible. Therefore, it is necessary to be able to control the amount of increase in transmission loss due to bending of the optical fiber within a certain range. and,
In general, the bending loss of a single mode optical fiber is determined by the refractive index difference between the core and the cladding, the core diameter, and the core profile, and even a slight change in these factors causes a large change in the bending loss. Therefore, in single-mode optical fibers, transmission loss due to bending is poorly controlled; for example, if the optical fiber is pressed against a mandrel with a fixed bending radius to cause bending, loss will not increase due to variations in fiber parameters. There may be cases where the increase in losses becomes extremely large. Therefore, as in the above example, by bending the optical fiber 2 in advance to a radius of curvature at which the optical fiber 2 is likely to cause an increase in loss, even if a single mode optical fiber is used, the transmission loss due to bending can be reduced. Controllability can be improved.

The reason for this will be explained based on FIG. FIG. 3 is a diagram for explaining an example of bending loss of a single mode optical fiber, and the horizontal axis of the diagram is the bending radius (mm) of the optical fiber;
The vertical axis represents the bending loss (dB) on a logarithmic scale. The single mode optical fiber used has a mode field diameter of 10 μm and a cladding outer diameter of 125 μm.
, refractive index difference (Δ) −0.3%, effective cutoff wavelength (λ
ce) = 1.15 μm, and the measurement wavelength (
λ) was set to 1.3 μm.

As is clear from this figure, as the bending radius of the optical fiber is reduced, the bending loss increases exponentially. In addition, in this figure, when estimating how much the bending loss changes with a slight change in the bending radius on the horizontal axis, for example, if the bending radius of the optical fiber is 17 mm, a ±1 mm change in the bending radius If the bending radius of the optical fiber is 10 mm, and the bending radius changes by ±1 mm, the bending loss will change by about 1 dB/m. It begins to show change. Therefore, if a single mode optical fiber is used, by bending the single mode optical fiber in advance so that the transmission loss is about 0.1 dB, and configuring the optical fiber to increase the bending when water is absorbed. Even the increase in transmission loss can be sufficiently identified.

FIG. 4 is a diagram showing a second embodiment of the present invention, and reference numeral 14 indicates a sensor. In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals, and their explanations will be omitted.

The difference between the sensor 14 of this example and the sensor 1 of the first embodiment is that a water absorption tube 4 is attached to an optical fiber 2, and a string 5 is wound around the outer circumference of the water absorption tube 4, and a plurality of mandrels 15... - By pressing the optical fiber 2 against the surface, a portion is formed by bending the optical fiber 2 with a predetermined radius of curvature r, and this portion is used as the water immersion sensor portion 16.

In this sensor 14, when a flooding accident occurs, moisture permeates into the water immersion sensor part 16, and the water absorption tube 4 absorbs this moisture, causing volumetric expansion, and the string 5 wound around the outer circumference of the water absorption tube 4. By suppressing this volumetric expansion, the water immersion sensor section I6 is deformed, and the radius of curvature of the optical fiber 2 becomes partially smaller than the initial setting value, so that the water immersion sensor section 16
transmission loss is increasing.

Therefore, in this sensor 14, by detecting the increase in the loss of transmitted light due to the bending that occurs in the optical fiber 2 using the above-mentioned water intrusion detection device 6, etc., it is possible to accurately and quickly detect the location where water intrusion occurs. , it is possible to obtain substantially the same effects as in the first embodiment.

FIG. 5 is a diagram showing a third embodiment of the present invention, and reference numeral 17 indicates a sensor. In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals, and their explanations will be omitted. The sensor 17 of this example has an optical fiber 2 wound in a ring shape to have a predetermined radius of curvature r to form a bent part, and this bent part is covered with two water-absorbing sheets made of the above-mentioned water-absorbing resin. 18, and then this water absorbing sheet 18 with 2
A water immersion sensor section 20 is formed by sandwiching the two expansion suppressing plates 19, and the water immersion sensor section 20 is attached to one or two locations on the optical fiber 2.
It is formed by forming more than one part.

The two expansion suppressing plates 19 have uneven surfaces on which concave and convex portions are formed, and in addition to turning each of these uneven surfaces toward the inner side, each expansion suppressing plate 19 or the optical fiber 2 when water is not absorbed is It is fixed with a slight gap so that the bent part will not be pushed or bent.

In this sensor 17, when a water flooding accident occurs, water leakage penetrates into the water absorbing sheet 18 in the water flooding sensor section 20, and the water absorbing sort 18 causes volumetric expansion, so that the bent portion of the optical fiber 2 has a curvature smaller than the radius r. It is designed to cause bending.

Therefore, with this sensor 17, by detecting the transmission loss of the optical fiber 2 that has increased due to the bending that has occurred, using the above-mentioned water immersion detection device 6 or the like, it is possible to accurately and quickly detect the location where water has occurred, etc. In addition to being able to obtain almost the same effects as in the first embodiment, the expansion suppressing plate 19.
Since the uneven surface 19 can generate a complicated bend in the bent portion of the optical fiber 2, the sensitivity of the water immersion sensor can be improved.

FIG. 6 is a diagram showing a fourth embodiment of the present invention, in which reference numeral 2I represents a sensor. In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals, and their explanations will be omitted. .

In the sensor 1 of the first embodiment described above, the water absorption tube 4 is attached to the optical fiber 2, and the outer periphery of this water absorption tube 4 is wound with a string 5. Furthermore, the water absorption tube 4 is attached by winding the part several turns to avoid immersion in water. In the sensor 21 of this embodiment, the optical fiber 2 is wound around the outer periphery of the round water-absorbing resin rod 22 so that the radius of curvature is about 10 to 100 mm. The optical fiber 2 is configured to have a water immersion sensor section 23 whose outer periphery is wrapped with a string 5 at one or more locations. The water-absorbing resin rod 22 has glass fiber <4fi
It is constructed by coating a core wire 24 made of a curved conical material such as reinforced plastic (PRP) with a water-absorbing resin.

In the sensor 21 of this embodiment, when a water-immersion accident occurs, water leaks into the water-absorbing resin rod 22 and causes volumetric expansion, and a force is generated in that portion to spread the optical fiber 2 outward. On the other hand, since the string 5 is wound around the outside of the optical fiber 2, the optical fiber 2, which has been expanded by the expansion of the water-absorbing resin rod 22, is pushed and bent by the string 5.

Therefore, this sensor 2! Embodiment 2 is almost the same as the first embodiment, in that by detecting the increase in the loss of light transmitted through the optical fiber 2 using the water intrusion detection device 6, etc., the location where water intrusion occurs can be detected accurately and quickly. You can get the effect.

Hereinafter, the effects of this invention will be clarified by showing experimental examples.

(Experiment example l) Mode field diameter 10μm1 Cladding outer diameter 125μ
Using a quartz-based single mode fiber core with a thermosetting silicon (secondary coating) diameter of 400 μm, a nylon (secondary coating) diameter of 0.9 mm, a refractive index difference of 0°3%, and an effective cutoff wavelength of 1.15 μm. This optical fiber is made of a water-absorbing resin made of a mixture of a thermoplastic elastomer and a polyacrylate-based water-absorbing material, and has an outer diameter of 1.0 mm and a length of 500 mm.
Attach a water absorption tube, wrap a plastic thread around the outer circumference of this water absorption tube at a pitch of 50 mm, and wrap the water absorption tube portion 4 turns with a radius of curvature of 13 mm to form a water immersion sensor section, similar to that shown in Figure 1. I created a sensor with the following configuration. Note that the water absorbent resin exhibited a volumetric expansion of about 100 times after absorbing water. Further, the initial loss value of this sensor was approximately 0.1 dB.

Next, the sensor was activated by immersing it in water for 24 hours, and then the flooded area was detected using a water immersion detection device having the same configuration as that shown in FIG.

As a result, an increase in loss of approximately 0.5 dB was detected at the location where the water immersion sensor portion was formed.

(Experimental Example 2) Using the same optical fiber, water-absorbing dupe, and string as used in Experimental Example 1, a water-absorbing tube was attached to the optical fiber, and the string was wound around the outer circumference of the water-absorbing tube at a pitch of 50 mm. Five mandrels each having a diameter of 25 mm are arranged as shown in Fig. 4, and the water absorption tube part is pressed against these mandrels to form a water immersion sensor part, and a sensor having the same structure as that shown in Fig. 4 is obtained. It was created. The number of wrappings was adjusted so that the initial loss value of the sensor was O, IdB.

Next, the sensor was activated by immersing the water immersion sensor section in water for 24 hours, and then the water immersion detection device was used to detect the location of the water immersion. As a result, an increase in loss of 0.5 dB was detected at the location where the water immersion sensor portion was formed.

(Experiment Example 3) Using the same optical fiber as used in Experiment Example 1,
As shown in Fig. 5, this optical fiber has a radius of curvature of 13 m.
Bend it so that it becomes m, sandwich this part between two water-absorbing sheets with a thickness of 2 mm, and then sandwich and fix this water-absorbing sheet between two expansion suppressing plates of the same shape as the one shown in Figure 5. A sensor having the same structure as the one shown in FIG. 5 was constructed by constructing a water immersion sensor section.

The above water absorption sheet is an experimental example! A material with the same composition as the water-absorbing resin used in was used.

Next, the sensor was activated by immersing the water immersion sensor section in water for 24 hours, and then the water immersion detection device was used to detect the location of the water immersion. As a result, an increase in loss of 0.5 dB was detected at the location where the water immersion sensor portion was formed.

(Experimental Example 4) Using the same optical fiber and string as the optical fiber used in Experimental Example 1, this optical fiber had a diameter of 0°4 mm and a length of 5 mm.
A 00mm FRP core wire is coated with a water-absorbing resin having the same composition as that used in Experimental Example 1 to an outer diameter of 1.8mm, and then wound at a pitch of 10mm around the outer circumference of a water-absorbing resin rod. Then, the string was wound in the opposite direction at a pitch of 30 mm to form a water immersion sensor section, and a sensor having the same structure as that shown in FIG. 6 was created.

Next, the sensor was activated by immersing the water immersion sensor section in water for 24 hours, and then the water immersion detection device was used to detect the location of the water immersion. As a result, an increase in loss of 0.5 dB was detected at the location where the water immersion sensor portion was formed.

"Effects of the Invention" As explained above, the optical fiber water immersion detection sensor according to the present invention forms a bent part in at least one part of a single mode optical fiber by applying bending stress to the optical fiber in advance, and A water immersion sensor section comprising a water-absorbing resin that expands in volume when absorbing water at a bent part, and an expansion suppressing material that suppresses expansion of the water-absorbing resin outside the bent part and the water-absorbing resin. In the event of a flooding accident, the water-absorbing resin absorbs the moisture that has penetrated into the water-absorbing sensor section and its volume expands, while the expansion suppressing material suppresses the volumetric expansion of the water-absorbing resin and causing the water-absorbing resin to expand. A bend is caused in the optical fiber, and the increased loss of transmitted light due to the bend in the optical fiber is detected by measuring reflected light such as backscattered light of the light incident from the input end of the optical fiber. and its occurrence location can be detected accurately and quickly.

In addition, the water intrusion detection method is based on the fact that the water-absorbing resin expands due to the penetration of moisture, causing bending in the optical fiber and increasing the transmission loss of the optical fiber, compared to conventional water intrusion detectors using metal conductors. It enables long-distance installation and can also be applied to areas where electromagnetic induction exists.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention, and is a perspective view of the sensor, FIG. 2 is a schematic configuration diagram illustrating an example of a water immersion detection system using the sensor of the present invention, and FIG. FIG. 4 is a graph for explaining an example of the relationship between the bending of an optical fiber and transmission loss, and FIG. 4 is a diagram showing a second embodiment of the present invention, and a side view of the sensor. FIG. 6 is a diagram showing a fourth embodiment of the present invention, and is a perspective view of a sensor. 1, +4.17.21...Sensor, 2...Optical fiber, 3. + 6.20.23...Flood sensor section,
4゜14...Water absorption tube (water absorbent resin), +8
... Water-absorbing notebook (water-absorbing resin), 22... Water-absorbing resin rod (water-absorbing resin), 5... String (swelling suppressing material),
+9...Expansion suppression plate.

Claims (1)

[Claims] A bent part is formed in at least one part of the single mode optical fiber by applying bending stress to the optical fiber in advance, and a water-absorbing resin that causes volumetric expansion when water is absorbed is added to the bent part of the optical fiber, and this bent part An optical fiber water immersion detection sensor comprising: a water immersion sensor portion formed by disposing an expansion suppressing material for suppressing expansion of the water absorbent resin on the outside of the water absorbent resin.