JPS6156453B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber for liquid detection that can detect liquid leakage with high reliability.

BACKGROUND ART In liquid storage, pipe transportation, etc., early detection of liquid leakage accidents is important, as well as maintenance of storage tanks, transport pipes, etc. used in the storage and pipe transportation.

Particularly in the storage and transportation of oil, where risks such as fire and environmental pollution are major issues, as storage tanks become larger and transport pipes are laid over longer areas, oil leakage monitoring must be carried out over a wide area. .

Optical fiber is attracting attention as a means of monitoring oil leaks to cope with this increase in size.This optical fiber has the characteristics of being lightweight, inexpensive, and highly flexible when installing over a wide area. , has begun to be used as a detection element for this type of oil leak monitoring, but the following problems have been pointed out when using this optical fiber as a detection element.

In other words, the optical fiber itself has been developed and improved to improve its optical transmission characteristics, and technical considerations have been made to ensure that the transmission characteristics do not deteriorate even when a coating is provided on the fiber.

When such an optical fiber is used as a detection element, the coating may be melted by leaked oil and the resulting drop in the received light level can be detected, or the light attenuation rate may be reduced by leaked oil that has penetrated into the coating. Measures have been taken to increase the size and detect this on the light receiving side.

However, the above-mentioned deterioration in characteristics is not a phenomenon that occurs only due to oil leakage accidents, but also occurs due to failures such as breakage of the optical fiber itself. Even if the problem is caused by oil leakage or optical fiber failure, it becomes impossible to determine whether the problem is due to oil leakage or optical fiber failure.

In view of the above-mentioned problems, the present invention aims to provide an optical fiber for liquid detection that can clearly distinguish between an oil leakage accident and an optical fiber system accident. .

FIG. 1 shows a cross-sectional view of an optical fiber according to the present invention, in which 1 is an optical fiber strand consisting of a core and a cladding, 2 is a primary coat provided on the outer periphery, and 3 is the outer periphery. 4 is a liquid sensitive layer provided on the outer periphery of the buffer layer.

In the above, the optical fiber 1 has a core/cladding ratio larger than that of a commonly used communication optical fiber (for example, the core diameter
60μm, cladding diameter 150μm).

The optical fiber wire 1 is mainly made of quartz glass, but may also be made of multi-component glass, or may be made of plastic as long as it has liquid resistance to the detection target (oil, chemical liquid, etc.).

Primary coat 2 is urethane, Kynar,
It is formed by coating resin such as modified silicone with a thickness of about 5 to 20 μm, and is provided to directly protect the optical fiber 1.

It is desirable that this primary coat 2 is also made of a material that does not undergo deterioration or deterioration due to liquids such as oil.

The buffer layer 3 is normally formed for the purpose of alleviating lateral pressure when optical fibers are twisted into a cable, but here, the buffer layer 3 is formed to a desired thickness for the purpose of adjusting the coating pressure (lateral pressure, etc.) from the liquid sensitive layer 4, which will be described later. When the coating pressure from the liquid sensitive layer 4 is increased,
This buffer layer 3 may be omitted.

This buffer layer 3 is made of, for example, silicone rubber.

The liquid sensitive layer 4 is made of a material that swells or cracks due to the liquid to be detected (for example, oil), and when such a phenomenon occurs, the coating pressure of the sensitive layer 4 on the optical fiber 1 decreases. (lateral pressure) decreases.

In a normal optical fiber, each coating layer is provided to prevent the above-mentioned lateral pressure (a cause of microbending = deterioration of optical transmission characteristics), but in the case of this liquid sensitive layer 4, the optical fiber strand 1 is coated with coating layers. A coating condition is adopted in which microbending occurs, that is, the optical transmission characteristics are degraded.

Therefore, when the liquid sensitive layer 4 is wetted or impregnated with a liquid, the coating pressure on the optical fiber 1 (the cause of microbending) decreases, thereby improving the optical transmission characteristics of the optical fiber 1. It becomes like this.

The liquid sensitive layer 4 is suitably made of polystyrene or the like, and is formed by extrusion coating.

In addition, other styrene resins, SAN,
ABS, high-impact polystyrene may also be used as the material for the layer 4.

In the first aspect of the present invention, FIGS.
It is used for liquid detection in the manner shown in the figure.

First, in the case of Fig. 2, the optical fiber having the above configuration is used in a straight form, and this state is installed at a desired detection location such as a storage tank containing oil or an oil transport pipe. An optical signal is passed from one end of the optical fiber to the other end, and a monitoring arrangement is taken at the light receiving end.

If a liquid leakage accident such as an oil leak occurs during this inspection, the leaked liquid will wet or impregnate the liquid sensitive layer 4, and the liquid sensitive layer 4 will swell and cover the optical fiber 1. The pressure (lateral pressure) begins to ease.

This lateral pressure relaxation improves the optical transmission characteristics of the optical fiber 1 and also increases the output at the light receiving end.

Therefore, if the level of light received at the light-receiving end side of the optical fiber under monitoring increases, this indicates that liquid leakage has occurred, and this level increase indicates a leakage accident.

If an accident occurs such as the optical fiber 1 being broken for some reason, the optical signal will be significantly attenuated and the level of light received at the light receiving end will drop. It also becomes clear that there was an accident with Faiba itself.

Moreover, since a liquid leakage accident is revealed in different states due to an increase in the received light level, and an optical fiber accident is determined in different states due to a decrease in the received light level, there is no possibility of misunderstanding or inability to distinguish between the two accidents.

FIG. 3 shows another embodiment of the first invention, and the optical fiber of FIG. 3 is also used in the same manner as described above.

In this embodiment, the optical fiber is in a spirally bent state, and in this case, a buffering effect is obtained when unreasonable tension is applied to the optical fiber, and it is also possible to install it in a meandering manner or attach it to a curved surface. Layout installation can now be performed with a greater degree of freedom.

Next, a second aspect of the present invention will be explained with reference to FIGS. 4 to 6.

In each of the embodiments of the second invention, the optical fiber of the first invention described above and the elongated member 5 which is a support thereof are relatively combined. Fig. 5 shows an optical fiber wound around the outer periphery of the elongated member 5, and Fig. 6 shows an optical fiber wrapped around the outer periphery of the elongated member 5. Two long members 5, 5 are shown attached in the longitudinal direction of the outer periphery.

The elongated member 5 mentioned above may be made of any material such as soft, semi-hard, or hard, and may be flexible.

Specifically, metals, plastics, fiber lumber,
Alternatively, a suitable material such as a composite material of these materials can be used for the elongated member 5, and the cross-sectional shape thereof can also be freely adopted, such as circular or square.

A combination of the optical fiber and the elongated member 5 as described above can also be used for liquid detection in the same manner as described above, but in this case, the twisted state, wrapped state, and relative pressure of the two should be adjusted as appropriate. As a result, the degraded transmission characteristics and recovery characteristics of the optical fiber 1 can be freely set, and since the elongated member 5 reinforces the fragile optical fiber, it is practical under harsh usage conditions. can be secured and its versatility increases.

In addition, in FIGS. 4 to 6, the optical fiber and the elongated member 5 are in direct contact with each other, but there is an inclusion between the optical fiber and the elongated member 5 that may form a space between them. may be partially mediated,
In this way, the effective sensing surface area of the optical fiber can be increased.

As explained above, the optical fiber for liquid detection according to the first aspect of the present invention is provided with a liquid-sensitive layer on the outer periphery of the optical fiber, the coating pressure of which decreases due to liquid wetting, liquid impregnation, etc. In the relative relationship between the wire and the liquid-sensitive layer, the optical fiber wire is characterized by being coated with the liquid-sensitive layer under a coating pressure that causes microbends, so that accidents of the optical fiber wire can be avoided. This makes it possible to detect liquid leaks by distinguishing between

Further, in the optical fiber for liquid detection according to the second aspect of the present invention, a liquid sensitive layer whose coating pressure changes due to liquid wetting, liquid co-immersion, etc. is provided on the outer periphery of the optical fiber wire, and these optical fiber wires In relation to the liquid-sensitive layer, the optical fiber strands are
The optical fiber is coated with a liquid-sensitive layer under a coating pressure that causes microbending, and the optical fiber having the liquid-sensitive layer and the elongated member are combined in direct or indirect contact with each other. As a result, the reduced transmission characteristics (when no leakage is detected) and the recovery characteristics (when leakage is detected) of the optical fiber can be set more freely, and it also ensures practicality under harsh usage conditions. become.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one example of an optical fiber according to the present invention, FIGS. 2 and 3 are perspective views showing various embodiments of the first invention, and FIGS. 4, 5, and 6 The figures are perspective views showing various embodiments of the second invention. 1... Optical fiber wire, 4... Liquid sensitive layer, 5
...Long member.

Claims (1)

[Claims] 1. A liquid-sensitive layer whose coating pressure is reduced by liquid wetting, liquid impregnation, etc. is provided around the outer periphery of the optical fiber, and in the relative relationship between the optical fiber and the liquid-sensitive layer, the light An optical fiber for liquid detection, characterized in that the fiber wire is coated with a liquid sensitive layer under a coating pressure that causes microbending. 2. A liquid-sensitive layer whose coating pressure changes due to liquid wetting, liquid impregnation, etc. is provided on the outer periphery of the optical fiber wire, and in the relative relationship between the optical fiber wire and the liquid-sensitive layer, the optical fiber wire is The optical fiber is coated with a sensitive layer under a coating pressure that causes microbending, and the optical fiber having a liquid sensitive layer and a long member are combined in direct or indirect contact with each other. Optical fiber for liquid detection. 3. The optical fiber for liquid detection according to claim 2, wherein an optical fiber having a liquid sensitive layer and an elongated member are twisted together and combined. 4. A patent claim in which an optical fiber strand having a liquid-sensitive layer is wound in the longitudinal direction of the outer periphery of a long member, and the liquid-sensitive layer-attached optical fiber strand and the long member are mutually twisted and combined. Optical fiber for liquid detection according to scope 2. 5. An elongated member is attached to the outer circumferential longitudinal direction of the optical fiber strand having a liquid-sensitive layer, and the optical fiber strand with the liquid-sensitive layer and the elongated member are mutually twisted and combined. Optical fiber for liquid detection according to scope 2.