JPH06109577A - Sensor cable for liquid detection - Google Patents

Abstract

PURPOSE:To obtain a sensor cable for liquid detection with high detection performance capable of protecting a sensor body part. CONSTITUTION:A sensor cable 10 for liquid detection is provided with a sensor body part 12 and a protection structure body 13. The sensor body part 12 is provided with an optical fiber unit 15 including a swelling member 20 and an optical fiber 21 and constraint members 16, 17 spirally wound on the outer circumferential part of the optical fiber unit 15. The protection structure body 13 is equipped with a coil 30 having an inner diameter of 1.2 times or more of an outer diameter of the optical fiber unit 15, a knitted pipe 31 covering the outside of the coil 30 and having a clearance allowing liquid to flow, a tension member 32 inserted in the inside of the knitted pipe 31 and receiving tension force applied in the direction of length of the optical fiber device 15 and a support member 33 arranged on a plurality of parts at proper intervals in the direction of the length of the optical fiber unit 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid detecting sensor cable suitable for a system for detecting a liquid leak in a pipe for transferring a liquid.

[0002]

2. Description of the Related Art An optical fiber and a backscattering light measuring device (OTDR) are used as means for detecting oil leaks in oil pipes and the like.
An optical detection system using the above is proposed. The conventional liquid detection sensor used in this type of detection system is
It is known that a constraining member is wound in a coil shape on the outer peripheral portion of a swelling member including an optical fiber.

In this type of liquid detection sensor, when a liquid leak occurs, the liquid to be detected is absorbed by the swelling member to cause the swelling member to expand in volume, and the movement of the swelling member due to the expansion is restricted by the restraining member. This causes bending deformation (microbend) in the optical fiber. When a microbend occurs, the power loss of the transmitted light sent to the optical fiber increases at the deformed part of the optical fiber. Therefore, by detecting the power loss and the time of loss occurrence with a measuring instrument such as OTDR, the liquid leakage occurs. I try to identify the point.

[0004]

However, the above liquid detection sensor is weak against the tensile force applied in the axial direction and the lateral force applied in the radial direction, and is easily caught by an obstacle when the sensor is installed, so that the installation work is difficult. The optical fiber and the swelling member inside the sensor may be damaged during the process. Further, even after installation, the optical fiber may be damaged or deformed due to the influence of the wind, the contact of scattered matter due to the wind, the contact of animals and plants, or the like. Therefore, there has been a demand for the development of a sensor cable capable of protecting the sensor main body portion including an optical fiber and a swelling member.

Further, as seen in Japanese Utility Model Laid-Open No. 2-14054, when a protective structure in which a coil is closely adhered to an optical fiber unit is adopted, the swelling member is removed by contacting the liquid to be detected with the swelling member. At the time of swelling, the contact between the coil and the swelling member hinders the generation of microbends, which causes deterioration of the detection performance. Moreover, in the case of the above-mentioned prior art, it is not easy to closely wind the coil without exerting an external force on the optical fiber, and it is difficult to stably manufacture a long liquid detection sensor.

Therefore, an object of the present invention is to provide a sensor cable for liquid detection which can protect the sensor main body portion by the protective structure and which does not deteriorate the detection performance even when covered with the protective structure.

[0007]

SUMMARY OF THE INVENTION The present invention, which was developed to achieve the above object, provides an optical fiber unit including an optical fiber in a swelling member that swells by absorbing a liquid to be detected, and an outer peripheral portion of the optical fiber unit. A sensor cable for liquid detection, comprising: a sensor main body including a helically wound restraint member; and a protective structure covering the outside of the sensor main body, wherein the protective structure is the optical fiber unit. A coil having an inner diameter 1.2 times or more the outer diameter before swelling and arranged outside the optical fiber unit so as to surround the optical fiber unit, and a gap that covers the outer side of the coil and allows the liquid to be detected to flow therethrough. And a tension member that is inserted through the inside of the knitting tube and that receives a tensile force applied in the length direction of the optical fiber unit, It is characterized in that it is provided with a supporting member arranged at a plurality of positions at appropriate intervals in the length direction of the optical fiber unit between the optical fiber units.

[0008]

The sensor main body of the present invention is covered with the protective structure, and the knitting tube and the tension member receive the tensile force in the longitudinal direction. The sensor body is protected by a braided tube or a coil against lateral force applied in the radial direction. Since the liquid to be detected can freely pass through the knitting tube, the liquid to be detected comes into immediate contact with the swelling member when liquid leakage occurs.

The swelling member that has absorbed the liquid to be detected expands in the radial direction and the longitudinal direction. Since the restraint member is wound around the outside of the swelling member, the movement of the swelling member due to the expansion is restricted by the restraint member, so that the optical fiber causes microbending. In the optical fiber unit including the swelling member, an appropriate gap is secured between the coil and the braided tube, and the supporting members are also arranged at appropriate intervals, so that the movement that causes the microbend is not hindered. . Since the microbend causes a transmission loss in the optical fiber, the liquid leakage occurrence point can be detected by detecting the power loss of the transmission light and the time point of the loss by the OTDR or the like.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The liquid leakage detection system 1 shown in FIG. 7 includes a liquid detection sensor cable 10 and an optical pulse tester 11. The liquid detection sensor cable 10 is arranged along a pipe (not shown) for detecting liquid leakage, and has a sensor main body 12 having the following structure and a protective structure 1 covering the outside of the sensor main body 12.
3 and 3.

As shown in FIGS. 1 to 3, the sensor body 12 includes an optical fiber unit 15 and a pair of restraining members 1 wound around the outer periphery of the optical fiber unit 15.
6, 17 and. The optical fiber unit 15 includes a cylindrical swelling member 20 that causes volume expansion due to absorption of a liquid to be detected, a plurality of optical fibers 21 enclosed in the swelling member 20, and an internal tension member 22.
And an auxiliary tension member 23 and the like. As the material for the tension members 22 and 23, a metal wire such as a steel wire or a material having high tensile strength such as aramid fiber is used.

As shown in FIG. 4 and the like, the first restraint member 16 and the second restraint member 17 are the same as those of the optical fiber unit 15.
Are spirally wound in opposite directions to each other at equal pitches so as to intersect each other in an X shape. The restraint members 16 and 17 are an assembly of a large number of flexible thin wires, each of which has a flat band shape. Restraint member 1
An example of the thin wire used in Nos. 6 and 17 is an organic synthetic fiber, but an inorganic fiber such as a metal fiber or a glass fiber, or a fiber reinforced plastic using these continuous fibers may be preferable in some cases.

As the material of the swelling member 20, when the liquid to be detected is oil such as petroleum, rubber, plastic, elastomer or the like which efficiently absorbs oil is used. Swelling member 2
Materials recommended as 0 are, for example, ethylene / olefin compounds such as ethylene propylene rubber, styrene / ethylene / butylene / styrene compounds, ethylene / ethyl acrylate, and ethylene / vinyl acetate.
When the liquid to be detected is water, it is preferable to use a rubber-like material obtained by mixing and vulcanizing a water-swelling resin and chloroprene rubber.

The swelling member 20 may be provided continuously over substantially the entire length of the optical fiber unit 15, or
Alternatively, the swelling member 20 may be locally provided at a location where it is necessary to detect liquid leakage. Further, it is possible to detect only a specific type of liquid by using a material that swells only in a specific liquid to be detected. The swelling member 20 swells as shown in FIG. 5 when it comes into contact with the liquid to be detected, and generates microbends in the optical fiber 21 inside.

The protective structure 13 comprises a coil 30, a braided tube 31, an external tension member 32, a support member 33 and the like. The prototype of the coil 30 is a stainless steel wire with a wire diameter of φ0.8 mm molded into an inner diameter of φ7.0 mm and a pitch of 5 mm, and is provided so as to surround the sensor body 12. The inner diameter of the coil 30 is 1.2 times or more the outer diameter of the optical fiber unit 15 before swelling so as not to prevent the microbend generation of the optical fiber 21 when the swelling member 20 swells.

As an example, the braided tube 31 has a wire diameter of 0.3 mm.
24 bundles of 5 stainless steel wires 31a are arranged in a plane. The braided tube 31 has a gap through which the liquid to be detected can freely pass so as not to prevent the liquid to be detected from entering the optical fiber unit 15.
By providing the braided tube 31 at the outermost peripheral portion of the sensor cable 10, slippage when laying the sensor cable 10 is improved, catching on an obstacle is prevented, and the coil 30 is reinforced.

As the external tension member 32, for example, a stainless steel wire having a wire diameter of φ1.0 mm is used. The tension member 32 is continuous over the entire length of the optical fiber unit 15 in the longitudinal direction, and receives the tensile force applied in the longitudinal direction of the sensor cable 10. The tension member 32 may be a single wire, or may be a plurality of wires in some cases.

The supporting member 33 is made of rubber or synthetic resin, and a plurality of supporting members 33 are provided between the inner peripheral surface of the knitting tube 31 and the outer peripheral surface of the optical fiber unit 15 with an appropriate interval in the length direction of the optical fiber unit 15. It is located in the place.
As shown in FIG. 6, a hole 34 penetrating in the axial direction and a spiral groove 35 are provided inside the support member 33.

The spiral groove 35 is a portion fitted into the coil 30. Therefore, the inner diameter D1 and pitch of the spiral groove 35 are
Each of the dimensions corresponds to the outer diameter and the pitch of the coil 30. The support member 33 is fitted into the coil 30 so as to wrap a part of the coil 30. The inner diameter D2 of the hole 34 is equal to or smaller than the outer diameter of the optical fiber unit 15. The support member 33 is provided with a cut 36 (see FIG. 1) that reaches the hole 34 in a part of the support member 33 in the circumferential direction so that the support member 33 can be attached from the outside of the optical fiber unit 15.

The prototype of the support member 33 is made of a soft nitrile butadiene rubber having a hardness of 60, and is adhered to the sensor main body 12 so that the sensor main body 12 and the coil 30, or the sensor main body 12 and the protection structure 13 are entirely longitudinal to each other. In addition to preventing the positional displacement from occurring in the direction, the restraining members 16 and 17 are pressed against the optical fiber unit 15.

Therefore, even if the restraint members 16 and 17 should be cut off on the way, the restraint members 16 and 17 can be broken.
The support member 33 can prevent the separation of the optical fiber from the optical fiber unit 15. The arrangement interval (pitch) of the support members 33 is selected from several tens of cm to about 10 m, but the narrower the arrangement interval is, the restraining members 16, 1 are.
Since the slack of 7 is reduced, it is convenient for increasing the liquid leakage detection sensitivity.

The force applied to the sensor cable 10 is mainly a tensile force applied in the longitudinal direction and a lateral force applied in the radial direction. The external tension member 32 mainly receives the pulling force. When it is necessary to pull the sensor cable 10 to lay the sensor cable 10,
The external tension member 32 is pulled.

The outer tension member 32 is sandwiched between the coil 30 and the braided tube 31, and the coil 30, the braided tube 31, and the outer tension member 32 are not connected to each other, but the sensor cable 10 is stretched. When attempting to do so, the diameter of the knitting tube 31 is inevitably narrowed due to the tension, and the coil 30 and the tension member 32 are tightened. Therefore, even if the tension member 32 is pulled, it does not come out alone. .

The coil 30 mainly receives a load against the lateral force. When a lateral force is applied in the direction of shearing the coil 30 or when a force is obliquely applied to the coil 30, the coil 30 may not be able to withstand it. Can deal with
Further, by providing the braided tube 31, the sensor cable 10
It was possible to prevent the cable 10 from being caught by an obstacle on the way even if the cable 10 was pulled when the cable was laid.

An example of the optical pulse tester 11 shown in FIG. 7 is an OTDR, which is connected to one end of the optical fiber 21 so that the power loss generated in the optical fiber 21 can be detected. The optical pulse tester 11 in the illustrated example uses a pulse light source 40 for sending an optical pulse to the optical fiber 21, a photodetector 41 having an optical / electrical conversion function, and a backscattered light generated in the optical fiber 21 for optical detection. The optical directional coupler 42 leading to the container 41, the signal processing device 43, the display device 44, and the like.

The operation of the liquid leak detection system 1 is as follows. The light pulse emitted from the pulse light source 40 enters the optical fiber 21 via the optical directional coupler 42. This incident optical pulse propagates in the optical fiber 21, but due to scattering occurring in the optical fiber 21, the transmission power of the optical pulse is attenuated as the reaching distance becomes longer. At that time, a part of the light scattered in the optical fiber 21 reaches the photodetector 41 through the optical directional coupler 42 as backscattered light.

Here, when a part of the light incident on the optical fiber 21 is emitted to the outside of the optical fiber 21 due to the bending deformation (microbend) of the optical fiber 21,
Since the power of the light pulse decreases at that point, the power loss of the backscattered light changes as illustrated in FIG. In this case, the location where the microbend is generated can be obtained from the elapsed time T after the light pulse exits the pulse light source 40 and the speed of the light traveling in the optical fiber 21.

When the swelling member 20 absorbs liquid and expands in volume, the swelling member 20 expands in the radial direction and the longitudinal direction, respectively, as shown in FIG. However, the restraint member 16,
Since the movement of the swelling member 20 is restricted by 17, the optical fiber 21 meanders and causes microbending,
Power loss of transmitted light occurs in the optical fiber 21.

The sensor cable 10 according to the present embodiment is designed so that the tensile force or lateral force applied to the sensor cable 10
The sensor structure 12 can be protected by the protective structure 13. In the case of this embodiment, the tensile force is 1
00kgf or more, for lateral force 3 per 1m of cable length
Even if a distributed load of 00 kgf or more was applied, the detection performance of the sensor body 12 was not affected.

Although the sensor main body 12 of this embodiment is covered with the protective structure 13, the liquid to be detected can freely pass through the knitting tube 31, and the sensor main body 12 is also provided.
Is in contact with the support member 33 provided at an appropriate interval.
Only. Therefore, even if the protective structure 13 is provided outside the sensor body 12, the liquid to be detected is swollen by the swelling member 2.
It does not take a long time to come into contact with 0, and the generation of microbends of the optical fiber 21 is not disturbed when the swelling member 20 swells. Therefore, the detection performance does not deteriorate even when compared with the sensor body 12 alone.

[0031]

According to the present invention, the sensor main body can be protected against the pulling force and the lateral force applied to the sensor cable, and the obstacle is not caught when the cable is laid. Further, even if the sensor body is covered with the protective structure, no force is exerted detrimentally on the optical fiber, and the reaction to liquid leakage is quick.

[Brief description of drawings]

FIG. 1 is a perspective view of a part of a liquid detection sensor cable showing an embodiment of the present invention.

FIG. 2 is a side view showing a part of the sensor cable shown in FIG. 1 in section.

FIG. 3 is a sectional view taken along the line III-III in FIG.

FIG. 4 is a plan view of a sensor body used in the sensor cable shown in FIG.

FIG. 5 is a side view of the sensor main body, showing how the swelling member swells.

6 is a cross-sectional view of a support member used in the sensor cable shown in FIG.

7 is a schematic view of a liquid leak detection system using the sensor cable shown in FIG.

8 is a diagram showing the relationship between the power of backscattered light and time when a liquid leak occurs in the liquid leak detection system shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid leak detection system, 10 ... Liquid detection sensor cable, 11 ... Optical pulse tester, 12 ... Sensor main body part, 1
3 ... Protective structure, 15 ... Optical fiber unit, 16, 1
7 ... Restraint member, 20 ... Swelling member, 21 ... Optical fiber, 3
0 ... coil, 31 ... braided tube, 32 ... tension member,
33 ... Support member.

Claims (1)

[Claims] 1. A sensor main body including an optical fiber unit in which an optical fiber is included in a swelling member that swells due to absorption of a liquid to be detected, and a restraining member spirally wound around an outer peripheral portion of the optical fiber unit, and the sensor. A sensor cable for liquid detection, comprising a protective structure covering the outside of the main body, wherein the protective structure has an inner diameter 1.2 times or more the outer diameter of the optical fiber unit before swelling, and A coil disposed outside the optical fiber unit so as to surround the fiber unit, a knitting tube that covers the outside of the coil and has a gap through which the liquid to be detected can flow, and the knitting tube that is inserted inside the knitting tube and A tension member that receives a tensile force applied in the length direction of the optical fiber unit, and a space between the braided tube and the optical fiber unit in the length direction of the optical fiber unit. Liquid detecting sensor cable, characterized by comprising a support member disposed at a plurality of locations spaced those intervals.