JPH0618357A - Liquid detecting sensor - Google Patents

Abstract

PURPOSE:To provide the sensor in which the detection sensitive to liquid is high and detection speed is high and the winding of a restraining member is easy. CONSTITUTION:On the peripheral part of a swelling member 15 constituting an optical fiber unit 12, an restraining member 13 is spirally wound with a fixed pitch. The unit 12 is provided with a sensor body 16 comprising an optical fiber 17, and the swelling member 15 covering the body 16. The swelling member 15 is made of a material expanding when absorbing a liquid. The sectional form of the arresting member 13 is flat, and the member 13 is wound so that the even surface 20 along the longitudinal direction of the section is opposed to the peripheral surface of the fiber unit 12. The secondary moment of section of the restraining member 13 is put a quarter or less of the secondary moment of a circle section having the same diameter as the size in the width direction of the section of the restraining member 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid detection sensor suitable for, for example, 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
For example, as seen in JP-A-2-25731,
A swelling member containing an optical fiber, in which a restraining member is wound around the outer periphery of the swelling member, or the optical fiber is embedded at an eccentric position inside the swelling member as shown in Japanese Patent Laid-Open No. 64-1934. In addition, a swelling member and a restraining member wound around the swelling member are known. The cross-sectional shape of the conventional restraint member used for such an application is circular.

In the above sensor, when a liquid leak occurs, the swelling member absorbs the liquid to be detected 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, whereby the Bending deformation (microbend) is caused in the 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]

In the above sensor,
A fairly thick restraint member is required to reliably suppress expansion of the swelling member by the restraint member. However, if the cross-sectional area of the restraint member is increased, it becomes difficult to wind the restraint member around the swelling member, and the tightening force varies greatly. If the restraint member is wound too tightly around the swelling member, the tightening force of the restraint member acts even if liquid leakage does not occur, and thus power loss at a level harmful to detection may occur in the optical fiber.

On the contrary, if the winding force of the restraint member is weak, a gap may occur between the restraint member and the swelling member.
There is a considerable delay between the time when the liquid leaks, that is, the start of the expansion of the swelling member and the occurrence of the microbend. Therefore, it takes time to detect the liquid leakage.

Therefore, an object of the present invention is to provide a liquid detection sensor which can wind the restraining member in a preferable state, and which has a short time from the absorption of the liquid by the swelling member to the occurrence of microbend and a high detection sensitivity. To provide.

[0007]

SUMMARY OF THE INVENTION The present invention, which has been developed to achieve the above object, provides an optical fiber unit including a swelling member that swells by absorbing liquid, and an optical fiber along the swelling member, and the optical fiber unit. And a restraint member provided in a spiral shape on the outer periphery of the restraint member, wherein the restraint member has a flat cross section and a surface along the longitudinal direction of the cross section faces the outer circumferential portion of the swelling member. The restraint member is wound around the optical fiber unit.

[0008]

When the liquid to be detected is absorbed by the swelling member, the swelling member expands in the radial direction and the longitudinal direction. Since the restraint member is spirally wound on 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 along the swelling member causes a microbend. Since the microbend causes a transmission loss in the optical fiber, the presence of the liquid and the location of the liquid leakage are detected by detecting the power loss of the transmission light and the time of the loss by the OTDR or the like.

Since the restraint member of the present invention has a flat cross section, it is easy to bend when it is wound around the optical fiber unit, the winding work is easy, and it fits well to the outer peripheral portion of the swelling member. It is also useful in eliminating the gap between the and the restraint member. Since this restraint member exerts a large strength against a tensile force, it exerts an effective restraint force to generate a microbend when the swelling member expands.

[0010]

Embodiments of the present invention will be described below with reference to FIGS. The liquid leak detection system 1 shown in FIG. 3 includes a liquid detection sensor 10 and an optical pulse tester 11.
And is configured. The liquid detection sensor 10 is arranged along a pipe (not shown) for detecting liquid leakage, and includes an optical fiber unit 12 and a restraining member 13 having the following structures.

As shown in FIG. 1, the optical fiber unit 12 is composed of a cylindrical swelling member 15 that causes a volume expansion due to absorption of liquid, and a sensor body 16 embedded in the swelling member 15. There is. Sensor body 1
6 is composed of at least one optical fiber 17 and at least one tension member 18, and passes through substantially the central portion of the swelling member 15 along the axial direction of the swelling member 15. The tension member 18 is made of a metal wire such as a steel wire or a material having high tensile strength such as FRP (fiber reinforced plastic).

The swelling member 15 may be provided continuously over substantially the entire length of the sensor main body 16, or the swelling member 15 may be locally provided at a position where it is necessary to detect a liquid leak. . 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.

When the liquid to be detected is oil such as petroleum, the material of the swelling member 15 is rubber, plastic, elastomer or the like that efficiently absorbs oil. Swelling member 15
Materials recommended as 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 restraint member 13 is made of, for example, a metal wire such as stainless steel, and is helically wound around the outer periphery of the optical fiber unit 12 at a predetermined pitch P. As shown in FIG. 2, the restraint member 13 has a flat cross section, and has a symmetrical shape with a neutral axis N along the longitudinal direction of the cross section as a boundary. That is, the flat surfaces 20, 2 along the longitudinal direction (width direction) of the cross section
1 and arcuate side surface portions 22 and 23 along the thickness direction of the cross section
Has a flat shape. In this case, the dimension B along the longitudinal direction of the cross section is 2 mm and the thickness h is 1 mm. Therefore,
The flatness is h = 0.5B.

The restraint member 13 is processed into the above-mentioned shape by crushing a metal wire having a perfect circular cross section in a radial direction by a rolling roller. The constraint member 13 having such a shape needs to satisfy h ≦ 0.6B in order to achieve the object of the present invention.

The restraint member 13 has a surface 2 along the neutral axis N.
It is wound around the optical fiber unit 12 so that 0 is in contact with the outer peripheral surface of the swelling member 15. Therefore, the restraint member 1
3 bends in a direction in which a portion on the side of one surface 20 is compressed and a portion on the side of the other surface 21 extends in a direction of extending with the neutral axis N as a boundary.

An example of the optical pulse tester 11 shown in FIG.
TDR, which is connected to one end side of the optical fiber 17 so that the power loss generated in the optical fiber 17 can be detected. The optical pulse tester 11 of the illustrated example is an optical fiber 1
Pulse light source 25 for sending an optical pulse to 7, a photodetector 26 having an optical / electrical conversion function, and an optical directional coupler 2 for guiding the backscattered light generated in the optical fiber 17 to the photodetector 26.
7, a signal processing device 28, a display device 29, and the like.

The operation of the liquid leak detection system 1 is as follows. The optical pulse emitted from the pulse light source 25 enters the optical fiber 17 via the optical directional coupler 27. This incident optical pulse propagates in the optical fiber 17, but due to scattering occurring in the optical fiber 17, the transmission power of the optical pulse is attenuated as the reaching distance becomes longer. At that time, part of the light scattered in the optical fiber 17 reaches the photodetector 26 through the optical directional coupler 27 as backscattered light. In FIG. 4, the vertical axis represents the power of the backscattered light that reaches the photodetector 26, and the photodetector 26 exits after the pulse light source 25 exits.
It is a diagram with the horizontal axis representing the time taken to reach.

Here, when a part of the light incident on the optical fiber 17 is emitted to the outside of the optical fiber 17 due to the bending deformation (microbend) of the optical fiber 17,
Since the power of the light pulse decreases at that point, the power loss of the backscattered light reaching the photodetector 26 changes as illustrated in FIG. In this case, the light pulse is the pulse light source 2
From the elapsed time T after exiting 5 and the speed of light traveling in the optical fiber 17, the location where the microbend is generated can be obtained.

FIG. 6 shows the sensor 10 of the above embodiment (which uses the restraint member 13 having a flat cross section shown in FIG. 2) and the conventional product (which uses a restraint member having a circular cross section of 2 mm in diameter). It is an experimental result which investigated the relationship between the immersion time of a liquid and the power loss of transmitted light.

As can be seen from FIG. 6, the sensor 10 of the present embodiment has a time period from the start of the liquid leakage to the detection of the liquid leakage, that is, a threshold value of a certain level, as compared with the conventional product. The time has been greatly reduced. It is judged that the conventional product is not suitable for practical use because it takes too long to reach the threshold value. It is considered that the reason why the delay time t occurred immediately after the start of the immersion in this conventional product was that there was a gap between the restraining member and the swelling member.

Since the flat-shaped restraint member 13 of this embodiment is highly flexible, the restraint member 13 is swollen in the step of winding the restraint member 13 around the optical fiber unit 12 when manufacturing the sensor 10. It becomes easy to wind the member 15 with an appropriate tightening force, and it is possible to prevent a gap from being formed between the restraining member 13 and the swelling member 15.

In carrying out the present invention, the restraint member 13a having a rectangular cross section (rectangular shape) shown in FIG. 7 may be used. Further, as shown in FIG. 8, chamfered portions (so-called C chamfers) of 45 ° are provided at the four corners of the rectangular cross section.
And a restraint member 1b provided with an arcuate chamfered portion (so-called R chamfer) 36 as shown in FIG.
It may be 3c. Alternatively, an oval restraint member 13d shown in FIG. 10 or an elliptical restraint member 13e shown in FIG. 11 may be employed.

In the case of the restraint member 13a having a rectangular cross section in FIG.
h is set to 0.6 B or less. Also in the case of the restraint members 13b, 13c, 13d shown in FIGS. 8 to 10, the h and B values are set so that h ≦ 0.6B. In the case of the restraint member 13e having the elliptical cross section shown in FIG. 11, r and R are set so that the relationship between the major axis R and the minor axis r is r ≦ 0.7 R.

In any of the above cases, the liquid detection performance is improved by setting the dimension B along the neutral axis N to be 0.5 times or more the outer diameter D of the optical fiber unit 12. Also,
Bending rigidity (second moment of area) about the neutral axis N
The restraint member 13 (13a to 13e) is easily wound around the optical fiber unit 12 by making the restraint member 13 (13a to 13e) around 1/4 or less of the circular cross section having the same diameter as the widthwise dimension B of the restraint member. With the swelling member 15
There is no gap between and.

In carrying out the present invention, a hard synthetic resin may be used for the restraint member, or an FRP containing fibers along the axial direction of the restraint member may be used. Further, the number of restraint members is not limited to one, and for example, the first
It can also be applied to those in which the restraint member and the second restraint member are wound at equal pitches in opposite directions so as to intersect in an X shape.

[0027]

According to the present invention, the restraint member can be wound around the optical fiber unit in a preferable state, and the microbend can be generated quickly and surely when the swelling member is swollen, so that liquid leakage occurs. The detection sensitivity is high and the time required for detection is short. Further, the work of winding the restraint member around the optical fiber unit at the time of manufacturing the sensor is easy. Moreover, since the sensor of the present invention itself is easily bent, there is no risk of giving an erroneous signal even if the sensor is installed in a bent portion such as a curved portion of piping.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of a restraint member used in the sensor shown in FIG.

3 is a schematic diagram of a liquid leakage detection system using the sensor shown in FIG.

4 is a diagram showing the relationship between the power of backscattered light of a light pulse detected by the liquid leak detection system shown in FIG. 3 and time.

5 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.

FIG. 6 is a diagram showing the relationship between the immersion time of the swelling member and the power loss increase amount.

FIG. 7 is a cross-sectional view showing a modified example of the restraint member.

FIG. 8 is a cross-sectional view showing another modified example of the restraint member.

FIG. 9 is a cross-sectional view showing still another modified example of the restraint member.

FIG. 10 is a cross-sectional view showing still another modified example of the restraint member.

FIG. 11 is a cross-sectional view showing still another modified example of the restraint member.

[Explanation of symbols]

1 ... Liquid leak detection system, 10 ... Liquid detection sensor, 11
... Optical pulse tester, 12 ... Optical fiber unit, 13 ...
Restraint members, 13a to 13e ... Restraint members, 15 ... Swelling member, 17 ... Optical fiber, 20, 21 ... Surfaces along the longitudinal direction of the cross section.

Claims (2)

[Claims] 1. A liquid detection sensor comprising an optical fiber unit including a swelling member that swells due to absorption of a liquid and an optical fiber along the swelling member, and a restraining member spirally provided on the outer peripheral portion of the optical fiber unit. Wherein the constraining member has a flat cross section and the constraining member is wound around the optical fiber unit so that the surface along the longitudinal direction of the cross section faces the outer peripheral portion of the swelling member. Detection sensor. 2. The second moment of area about the neutral axis along the longitudinal direction of the cross section of the restraint member is not more than ¼ of the circular cross section having the same diameter as the widthwise dimension of the restraint member. The liquid detection sensor according to claim 1, wherein the widthwise dimension and the thickness of the cross section of the restraint member are set.