JP3196979B2 - Optical fiber sensor for fluid detection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The optical fiber sensor for detecting a fluid according to the present invention is used for detecting a liquid such as an oil leak or a chemical leak or a so-called gas, and particularly, for detecting a seabed over a long distance of several tens km. It is suitable for use in detecting oil leaks from oil-immersed paper insulated electric power cables (OF cables) wired in, or detecting leaks of crude oil from an oil tank.

[0002]

2. Description of the Related Art Optical fiber sensors capable of detecting gases such as various liquids and gases including oils and chemicals have been known. FIG. 6 shows an example of the optical fiber sensor 1 for detecting oil leakage. In this, the core 12 is disposed at an eccentric position in the clad 11, and a soft inner layer (oil-absorbing resin: refractive index ncl <nl) 13 is provided on the outer periphery of the clad 11,
A hard outer layer (oil-soluble resin: refractive index nc2 <
nl) 14 are provided. When the optical fiber sensor 1 detects an oil leak, the transmission loss locally increases or changes, and the scattered light and the reflected light change according to the detected amount. It is also known that a gas such as methane gas can be detected by an eccentric core fiber according to the same principle.

[0003] The optical fiber sensor 1 for detecting oil leakage or gas is provided with a soft inner layer 1 outside a clad 11.
3. Although a hard outer layer 14 is provided on the outer periphery thereof, there is a problem that the outer layer 14 is easily damaged when an external force or tension is applied during transportation or installation.

Conventionally, in order to solve the above problem, the optical fiber sensor 1 is housed in a reinforcing pipe 5 such as a metal pipe or a hard plastic pipe as shown in FIG. In some cases, a through hole 6 was provided.

[0005]

The reinforced optical fiber sensor shown in FIG. 7 has the following problems. . Since the through hole 6 for fluid intrusion is sparse, if there is a fluid leak at a position distant from the through hole 6, the fluid cannot enter the through hole 6 and does not contact the optical fiber sensor 1 inside. Actually, there is a problem that it cannot be detected despite the presence of a fluid leak. . Although the reinforcing pipe 5 is hard, the strength is improved, but on the other hand, since it is poor in flexibility, it is difficult to handle at the time of transportation, laying, etc., and it takes up space for storage.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber for detecting a fluid which has excellent strength, is highly flexible, and can be easily handled during transportation, installation and the like.

[0007]

As shown in FIG. 1, the optical fiber sensor for detecting a fluid according to the present invention comprises an optical fiber 1 capable of detecting a fluid such as a liquid or a gas and a gap 2 through which a fluid can enter. in the spiral tube 3 formed spirally provided, the spiral sleeve 3
A gap is formed between the inner peripheral surface of the optical fiber and the outer peripheral surface of the optical fiber 1.
It is stored in such a way that

[0008]

In the optical fiber sensor for detecting fluid of the present invention, since the gap 2 of the spiral tube 3 is continuously continuous in the longitudinal direction of the spiral tube 3, fluid leakage occurs at any position in the longitudinal direction of the spiral tube 3. However, the leaked fluid surely enters through the gap 2. Further, since the spiral cylinder 3 has the gap 2 formed therein and is spiral, it is rich in flexibility even when formed of a hard material, and can be easily handled during transportation, installation and the like.

[0009]

Embodiment 1 An optical fiber sensor for detecting fluid according to the present invention will be described in detail based on the embodiment of FIG. This embodiment is for liquid detection. In FIG. 1, 1 is an optical fiber sensor, 3 is a spiral cylinder, and 2 is a gap formed in the spiral cylinder at appropriate intervals.

As the optical fiber sensor 1 shown in FIG. 1, various types are used in accordance with applications such as oil leak detection, chemical leak detection, and gas leak detection. For example, an existing optical fiber sensor 1 for detecting oil leakage shown in FIG. 6 is used.

The spiral cylinder 3 shown in FIG. 1 is formed by spirally winding a metal plate 4 with a gap 2 therebetween. The inner diameter of the spiral tube 3 is appropriately selected according to the outer diameter of the optical fiber sensor 1. For example, when the outer diameter of the optical fiber sensor 1 is 1 mm, 3 mm
The degree is suitable. In this case, for example, a metal plate 4 having a plate thickness of 0.2 mm and a plate width of 10 mm is formed with an inner diameter of 3 mm and a helical pitch of 3 m.
A spiral tube 3 is formed by spirally winding a tube having a width of 1 mm and a gap 2 m.

The optical fiber sensor 10 for detecting fluid of the present invention shown in FIG. 1 can be used as it is laid or wired in the fluid detecting area as it is. For example, the optical fiber sensor 10 is used for detecting oil leakage of an optical composite submarine OF cable. In this case, as shown in FIG. 2, the optical composite submarine OF cable 20 can be incorporated.
In this case, it is preferable to dispose it between the lead sheath (insulator shielding layer) 27 and the anticorrosion layer 21 of the optical composite submarine OF cable.

By the way, in the optical composite submarine OF cable 20 shown in FIG. 2, 23 is a hollow oil passage, 24 is a galvanized steel strip spiral, 25 is a conductor, 26 is insulating paper, 27 is a lead sheath,
28 is a seating layer, 29 is a reinforcing layer, 30 is a hollow iron wire optical fiber unit for transmitting an optical signal, 31 is an iron wire, and 32 is an armored yarn.

[0014]

EXAMPLE 1 To detect an oil leak over a long distance (for example, 10 km or more) using the optical fiber sensor for fluid detection of the present invention, as shown in FIG. FIG. 3 shows an optical transmission line 34 in which the fluid of the present invention connects the detection optical fiber sensor 10 in series with an optical transmission fiber (for example, a single mode fiber) 33 having a small transmission loss. Wiring a large number of wires to the detection area for detecting liquid leakage,
One end of the optical pulse test device (OTDR: Optical
Time Domain Reflectometer) Connect to 35. In this case, the array position of the optical fiber sensors 10 for detecting fluid in the plurality of optical transmission lines 34 is regularly and sequentially shifted from the upper one in the axial direction of the optical transmission line 34 so that the number of optical fiber sensors 10 for detecting fluid in The entire optical fiber sensor 10 can cover (detect) the entire detection area.

In FIG. 3, when the fluid detecting optical fiber sensor 10 detects the liquid and the optical signal transmitted by the fluid detecting optical fiber sensor 10 changes, the change is transmitted to the OTDR 35 and the liquid is detected. The presence / absence, type, amount, etc. are analyzed.

[0016]

[Application Example 2] Optical fiber sensor 10 for detecting fluid of the present invention
In the case where is used, it may be as shown in FIG. This is an optical fiber sensor 1 for detecting a fluid in a plurality of optical transmission lines 34.
The array position of 0 is not regularly shifted from the top in the axial direction of the light detection path 34 but is shifted irregularly. However, even in this case, the entire length of the detection area is covered by the entirety of the optical fiber sensors 10 for detecting fluid in the plurality of optical transmission paths 34.

[0017]

EXAMPLE 3 FIG. 5 shows a case where a large number of the optical fiber sensors for fluid detection of the present invention are arranged and used as shown in FIGS.
The channel selector 3 before the OTDR 35 as shown in
6 is connected thereto, and the optical transmission fiber 33 of the optical transmission line 34 is connected thereto. When the optical transmission line 34 is switched and selected by the channel selector 36, the selected optical transmission line 3
The change of the optical signal of No. 4 is preferably analyzed by the OTDR 35. In addition, 37 in FIG. 3 is a personal computer.

[0018]

The optical fiber sensor for detecting fluid of the present invention has the following effects. . Since the gap 2 is spirally formed in the spiral tube 3, the gap 2 is continuous in the longitudinal direction of the spiral tube 3. Therefore, no matter where the liquid leaks in the longitudinal direction of the spiral cylinder 3, the leaked liquid always enters the gap 2 and the liquid leak is reliably detected. . Since the spiral cylinder 3 has a spiral shape and is spirally formed with the gap 2, the spiral cylinder 3 is rich in flexibility even when formed of a hard material, and is easy to handle during transportation, laying, and the like. is there. . Since the optical fiber sensor 1 is protected by the spiral tube 3, the mechanical strength is improved, and the optical fiber sensor 1 is strong against external force and tension.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of an optical fiber sensor for detecting fluid according to the present invention.

FIG. 2 is an explanatory view showing a state in which the fluid detection optical fiber sensor is incorporated in an OF cable.

FIG. 3 is an explanatory diagram showing a first usage example of the fluid detection optical fiber sensor.

FIG. 4 is an explanatory view showing a second usage example of the fluid detection optical fiber sensor.

FIG. 5 is an explanatory view showing a third usage example of the fluid detection optical fiber sensor.

FIG. 6 is an explanatory diagram of a conventional optical fiber sensor.

FIG. 7 is an explanatory view of a conventional reinforced optical fiber sensor.

[Explanation of symbols]

 Reference Signs List 1 optical fiber 2 gap 3 spiral tube

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01M 3/38 G02B 6/00

Claims (1)

(57) [Claims] An optical fiber 1 capable of detecting a fluid such as a liquid or a gas is provided inside a spiral tube 3 having a gap 2 through which the fluid can enter, and an inner peripheral surface of the spiral tube 3. And optical fiber
An optical fiber sensor for detecting a fluid, wherein the optical fiber sensor is housed in such a manner that a gap is formed between the optical fiber sensor and the outer peripheral surface of the optical fiber sensor.