JPS6252433A - Method for monitoring penetration of water in connection part of cable and optical fiber water penetration sensor - Google Patents

Abstract

PURPOSE:To make it possible to simply and economically detect the water penetration area of a cable connection point without receiving the effect of electromagnetic induction, by forming a bent part on an optical fiber by the volumetric expansion force of an absorbent due to the penetration of water. CONSTITUTION:When water is penetrated in the connection point of a cable, a water guiding cloth tape 6 guides water to an absorbent 4 by a capillary phenomenon to allow the absorbent to generate volumetric expansion. An engag ing plate 3 is moved by the volumetric expansion force at this time and the uneven parts 2a, 2b, 3a, 3b of engaging plates 2, 3 are mutually engaged so as to hold an optical fiber A therebetween and, therefore, the optical fiber A is brought to a state bent in a wavy form. Therefore, one end of the optical fiber A is connected to a light source while the other end thereof to a level meter in a central monitor unit and the monitoring of optical output is always performed by the level meter and, when there was loss variation, back scattering light is measured from one end of the optical fiber A by a pulse tester to make it possible to detect a water penetration area.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for simply and logically detecting a flooded location at a cable connection point, and an optical fiber flood sensor used in the method.

(Prior technology) Optical fiber cables have come to be used as communication cables, but if damage or defects occur in the cable parts or connections of underground cables, underground water or accumulated water in manholes can flood into the cables. However, it is known that the mechanical properties and transmission properties of optical fiber cables deteriorate (Reference: vA Ei et al., "Estimation of hydrogen generation m in flooded cables, 1984 National Conference on Materials and Materials of the Institute of Electronics and Communication Engineers 50γ, 1984.
Year).

For this reason, it is necessary to detect abnormalities when water has entered the cable and its connection parts.

Conventional methods for detecting flooding include the gas pressure monitoring method, in which gas is sealed in the cable and the gas pressure is remotely monitored using a gas pressure sensor, and the electric method, in which non-gas cables output a signal with a unique frequency at each connection point, is used. A method is used to detect the location of flooding from the oscillation signal during flooding.

(Problems to be Solved by the Invention) However, all of these detection methods require electrical components and metal core wires. For this reason, in areas where lightning strikes or induction occurs, there is a risk that large currents may flow through this metal core wire, and it is necessary to take induction countermeasures such as installing arresters. This has the disadvantage that the characteristic of optical fibers, which is that they are not subject to electromagnetic induction, is greatly impaired. In addition, since electrical parts are used, the number of parts that can be installed is limited due to current capacity and frequency distribution, making it difficult to respond flexibly to changes in the number of connection points due to various types of maintenance work.

(Objective of the Invention) An object of the present invention is to provide a method for remotely centrally monitoring all connection points of an optical cable at once using a water immersion sensor that is not affected by electromagnetic induction, and a sensor used in the method. .

(Means for Solving the Problems) In order to achieve the above object, the first invention arranges an optical fiber in the gap between a pair of fitting plates, each of which has a concavo-convex portion formed on the opposing surface so that they can fit into each other. An optical fiber water immersion sensor is used, in which at least one of a pair of fitting plates is arranged so that it can be moved to the other side by the volumetric expansion force of a water-absorbing agent, and the optical fiber water immersion sensor is installed at each connection point of the cable. All of the optical fiber immersion sensors are connected in series using the optical fibers in the cable, and the whole is arranged as one loop, so that the optical signal is input from one end of the optical fiber and the output is constantly monitored from the other end. I made it.

In order to achieve the above object, the second invention arranges an optical fiber in the gap between a pair of mating plates, each of which has a concavo-convex portion formed on opposing surfaces so as to be able to fit into each other, and absorbs water into at least one of the pair of mating plates. It was arranged so that it could move to the other side by the volumetric expansion force of the agent.

(Function) According to the first invention, since a bent portion is formed in the optical fiber due to the volumetric expansion force of the water absorbing agent due to water immersion, a change occurs in the transmission characteristics of the optical fiber, and water immersion is detected from this change. Can be done.

According to the second invention, when water enters, the water absorbing agent expands in volume and one fitting plate approaches the other fitting plate, so that a bent portion can be formed in the optical fiber by the uneven portion of the plate.

(Example) Figures 1 and 2 show an example of an optical fiber immersion sensor used in the method of the present invention, where A is an optical fiber, 1 is a case body with an open top, and 2 and 3 are A pair of fitting plates having a plurality of uneven parts 2a, 2b, 3a, 3b,
The convex part 2a or concave part 2b of one fitting plate 2 is arranged so that the four parts 3b or convex part 3a of the other fitting plate 3 fit together, and the other fitting plate 3 is placed toward the one fitting plate 2 side. It is now accessible. 4 is a water-absorbing agent, 5 is an introduction hole for the cloth tape, and 6 is a water-conducting cloth tape whose one end is in contact with the water-absorbing agent 4 through the introduction hole 5. The optical fiber A is inserted through the introduction groove 1a of the case body 1! : Disposed between the fitting plates 2 and 3.

In the sensor configured as described above, when water enters the connection point, the water-conducting cloth tape 6 guides water into the water-absorbing agent 4 by capillary action, causing the water-absorbing agent 4 to expand in volume. The fitting plate 3 is moved by the volumetric expansion force at this time, and the uneven portion 2a of the fitting plate 2.3 is moved with the optical fiber 1 in between.

2b, 3a, and 3b fit together, so the optical fiber A
is bent into a waveform as shown in FIG.

Because of this structure, if the sensor is installed within the cable connection point as shown in Figure 4, if water enters the connection point, the optical fiber 1 will be bent and optical loss will increase. , flooding can be detected from this optical loss.

Although it differs depending on the radius of the bending part of the fitting plate and the pressure applied, it was confirmed in experiments that a loss of 2 dB/force point or more occurred and that it could be used as a water immersion sensor.

The optical fiber has a core diameter of 50 μm and a glass outer diameter of 125 μm1.
It is a graded index type with a coating outer diameter of 0.9 mm and a relative refractive index difference of 1%, and the measurement light source is an LE with a wavelength of 1.3 μm.
It is D. A powdered super absorbent resin was used as the water absorbing agent.

FIG. 3 shows an embodiment of a remote flood monitoring method in which an optical fiber flood sensor of the present invention is installed and connected to each connection point of a cable. A is an optical fiber, and one of the cables 7 is used. 9a to 9j are respective connection points, 10a to 10j are optical fiber immersion sensors disposed at each connection point, 11 is a light source disposed at one end of the optical fiber A, 12 is a level meter similarly disposed at the other end, 13 is a central monitoring center, and the light source 11
and level meters are installed. Optical fiber A connects optical fiber immersion sensors 10a to 10 at each connection point 9a to 9j.
It is connected to J, and is formed into one loop via each connection point.

To carry out this method, one end of the optical fiber A is connected to the light source 11 in the central monitoring center 13, and the other end is connected to the level meter 12.
are connected to each other, and the level meter 12 constantly monitors the optical output, and if there is a change in loss, an alarm is issued. If an alarm occurs, optical fiber A
It is possible to detect abnormalities (water intrusion) by measuring backscattered light from one end or the other using a pulse tester. The experimental results confirmed that detection was possible even at a distance of 10 km or more from one end with a loss of 2 dB.

(Effects of the Invention) As explained above, according to the method of the present invention, since a sensor that does not require an electric circuit or metal wire is used, it is possible to detect lightning strikes and floods easily and economically without the need for induction countermeasures. It has the advantage of becoming

Furthermore, since the water immersion sensors are connected in series and the whole system has a loop configuration, it has the advantage that even if the number of connection points increases or decreases due to various maintenance works, it can be easily changed.

In addition, there are the following advantages.

(1) Replacement can be easily done by replacing the water absorbing agent.

(2) The insertion loss of the water immersion sensor is low.

(3) All connection points can be centrally monitored simultaneously from a remote location.

(4) Maintenance and operation costs are low.

Further, the sensor of the present invention does not require an electric circuit or metal wire, has a simple structure and is inexpensive, and has the advantage that the above-described method of the present invention can be carried out accurately.

[Brief explanation of drawings]

1 and 2 show an embodiment of the optical fiber immersion sensor of the present invention, FIG. 1 is a plan view, FIG. 2 is a perspective view of the operating state, and FIG. 3 is a immersion sensor of the present invention. A connection diagram of an optical fiber and an optical fiber immersion sensor showing a monitoring method, FIG. 4 is an explanatory diagram of a state in which an optical fiber immersion sensor is set at a connection point.

Claims (2)

[Claims] (1) An optical fiber is placed in the gap between a pair of mating plates that have concavities and convexities formed on opposing surfaces so that they can fit together, and at least one of the pair of mating plates is moved to the other side by the volumetric expansion force of the water-absorbing agent. The optical fiber immersion sensors are installed at each connection point of the cable, and all the optical fiber immersion sensors are connected in series using the optical fiber cores in the same cable. A method for monitoring flooding at a cable connection point, characterized in that the entire optical fiber is arranged in one loop, an optical signal is input from one end of the optical fiber, and the output is constantly monitored from the other end. (2) An optical fiber is placed in the gap between a pair of mating plates that have concavities and convexities formed on opposing surfaces so that they can fit together, and at least one of the pair of mating plates is moved to the other side by the volumetric expansion force of the water-absorbing agent. An optical fiber immersion sensor characterized by being arranged in such a way that it can