JPS6186630A - Method for detecting water intrusion in communication cable using optical fiber - Google Patents

Abstract

PURPOSE:To make it possible to detect the intrusion of water into communication cable readily, by twisting a linear body, which is dissolved or softened by the water, and optical fiber, arranging said product in the communication cable as a sensor, and measuring the optical transmission loss of the optical fiber. CONSTITUTION:A sensor 15 in communication cable 14 is taken out to the outside through a connecting part 18. One end of optical fiber 16 in the sensor 15 is connected to a light pulse tester 19. When a light pulse signal is inputted to the fiber 16 from the tester 19, the light pulse is transmitted in the reverse direction in the fiber 16 with back scattering light being generated. The change in detected light on the time axis is measured, and the distribution of the transmission loss in the longitudinal direction of the fiber 16 is measured. When a hole is opened in the outer coating of the cable 14 and the water comes in, dissolving fiber 17 is dissolved or softened. As a result, the twisting of the fiber 16 is returned and the curvature becomes zero. The transmission loss is reduced. The change in transmission loss is detected, and the intrusion of the water in the cable can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a communication cable water intrusion detection method for detecting water intrusion into a communication cable.

"Conventional technology" Conventionally, methods for detecting water intrusion in communication cables include:
A method that utilizes the fact that two perforated coated copper wires are placed inside a communication cable and the insulation between these two copper wires deteriorates due to water entering the cable, and two PEF coated copper wires. There is a method that utilizes the fact that the electrostatic capacitance between these PEF1ffl copper wires is changed by the infiltration of water by disposing the PEF in a communication cable. Both of these methods do not have good detection sensitivity, and the former has the disadvantage that it is not possible to determine the location of flooding. Furthermore, these water intrusion detection methods using copper wires have the disadvantage of causing problems such as dielectric breakdown due to induction when used in areas with frequent lightning or near high-voltage power transmission lines.

An object of the present invention is to provide a water intrusion detection method for communications that can detect water intrusion with relatively high sensitivity without using copper wires.

``Child role for determining the question points'' According to this invention, a string fiber IF: (glandular tree) that melts or softens with water and an optical fiber are twisted 9 together to elastically deform at least the optical fiber, It is placed inside a communication cable and transmits an optical signal (by propagating it to the optical fiber).
Changes in transmission loss are measured, and water intrusion into the re-trusted cable is detected from the measurement results.

This 1ull determination of change in transmission loss is achieved by injecting a light signal into one end of an optical fiber and measuring the level of the optical signal output from the curved end of the optical fiber.Alternatively, by injecting an optical pulse signal into one end of the optical fiber. This is done by detecting the backscattered light that enters the optical fiber, is generated in the optical fiber by the light pulse signal, and returns to the light pulse input end, and detects the level change of the backscattered light on the time axis.In this case, i:iT also detects flooded locations
Becomes Noh.

``Example'' The method for detecting water intrusion using ζ according to the present invention will be described below with reference to the drawings.
Make amends. FIG. 1 shows an example of a communication cable. A plurality of optical fibers 12 are arranged around the outer periphery of the tensile strength member 11, and these are housed within a common cable outside 'fJ113' to constitute a 1-meter reliable cable 14.

In this invention, a sensor 15 using an optical fiber is disposed within the I... trust cable 14. For example, as shown in FIG. 2, the sensor 15 is made by twisting together an optical fiber 16 and a string-like fiber 17 that is water-soluble or softens with water.
6 is given a spiral bend by elastic deformation. In FIG. 1, such a sensor 15 has the same thickness as the optical fiber 12, and one or more sensors 15 are disposed in the communication cable 14 in the optical fiber 120 9. When a plurality of 7/s 15 are arranged, they are placed at equal angular intervals on the axis of the cable 14. Examples of the fibers 17 that melt or soften with water include carboxymethyl cellulose and polyvinyl alcohol tape.

As shown in FIG. 3, the sensor 1 in the 1m trust cable 14
5' is led out to the outside through the connection part 18, and one end of the optical fiber 16 in the sensor 15 is connected to the optical pulse tester 19. The output of this optical pulse tester 19 is the data processing device 2.
1, and the processing results are output to the output device 22.

A narrow optical pulse signal is input from the optical pulse tester 19 to one end of the optical fiber 16 . The optical pulse signal propagates within the optical fiber 16 within the communication cable 14 while generating backscattered light that travels in the opposite direction within the optical fiber 16. By detecting this backscattered light at the optical pulse signal input end of the optical fiber 16 and measuring the change in the detected light on the time axis, the distribution of one transmission loss in the longitudinal direction of the optical fiber 16 is measured.

The twist of the optical fiber 16 at the center 15
:I':J The pinch of the spiral is p, the radius of the spiral is r
Then, it becomes (2π)2r p 2 + (2πr)2. It is known that when music 9 is added to one optical fiber 16 in this way, the optical transmission loss of the optical signal transmitted through one optical fiber 16 is increased. This is for example the sentence: 'r 下, MarCIJSe, 'CLIrVatLjre 1
oss formula for optical fi
bers”, J, Qpt, Soc, Am,
55 (3).

216 (1976).

Therefore, when a hole is made in the outer cable wave 13 of the communication cable 14 and water infiltrates into the cable 14, the fibers 17 in the water-infiltrated part melt or become soft. As a result, the optical fiber 16
When the twist is restored, the curvature ρ becomes 0 and the transmission loss becomes very small. By detecting this change in one transmission loss, it is possible to detect whether the communication cable 14 is submerged in water. In other words, the third
The measurement thread shown in the figure monitors the change in transmission loss of the optical fiber 16, appropriately detects water intrusion in the communication cable,
Maintenance can be carried out. For example, as shown in FIG. 4, when the optical loss per unit length of the optical fiber 16 is measured and plotted against the distance of the optical fiber 16 from the tester 19, the number 23 at the submersion point is shown. It is detected that the location of the water inundation is 50 m in this example, because the optical loss is very small.

In addition, water-soluble or water-softened fibers r+1
The optical fiber 16 that is combined with the optical fiber 117 is coated with a layer or multiple layers of plastic to prevent its strength from deteriorating.
Skin: Summer is 9JH so it's very dry.

Alternatively, the string-like fibers 17 may be a twisted body of folded fibers 17 around which the optical fibers 16 are wound in a straight folded manner.

``Effects of the Invention'' As explained above, this invention consists of twisting linear bodies and optical fibers that become soft with water into a cable as a temporary tescenosa. 1 by measuring the transmission loss of light 1 of the optical fiber at t.
The flooding of the Yushin River 7-pull can be easily detected by +Qt. By configuring the optical pulse tester to measure the transmission loss using backscattered light, it is possible to know the 1st receiving water level, making it easier to maintain and monitor the 1st trust cable. What effect does it have in advance?

4 Simplification of drawings 11 Figure 1 (Oil level 1 showing an example of a 1m reliable cable with optical fiber sections arranged to apply the method of the present invention)
Figures 1 and 12 are perspective views showing an example of a sensor 15 using a special fiber used in the method of this invention, Figure 3 is a configuration diagram showing an example of a measurement system in the method of this invention, and Figure 4. is a diagram showing an example of the measurement.

11: Tensile strength body, 12: Optical fiber core wire, 13: Cable external wave, 14:! Heavy duty cable, 15: Cable using optical fiber, 16: Optical fiber, 17: Water-soluble fiber or linear body softened by water, 19: Optical pulse test gL21
: Data processing device decoration, 22: Output device.

Patent applicant Takuo Kusano, representative of Japan Telecommunications Telephone Corporation 1
Figure 3 Figure 4 Figure distance order (m)

Claims (2)

[Claims] (1) Transmission loss change of optical signal propagating through the optical fiber by twisting string-like fibers and optical fibers that melt or soften with water in a communication cable, and arranging the optical fibers so that at least the optical fibers are elastically deformed. A communication cable water intrusion detection method that uses optical fiber to measure water intrusion into the communication cable. (2) To measure the change in optical transmission loss, an optical pulse signal is input from one end of an optical fiber, and the backscattered light generated within the optical fiber by the optical pulse signal and returned to the optical pulse input end is measured on the time axis. A method for detecting water intrusion in a communication cable using an optical fiber according to claim 1, wherein the detection method is carried out by detecting water intrusion in a communication cable using an optical fiber.