JPH0128441Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber suitable for detecting oil leaks.

2. Description of the Related Art Conventionally, an optical fiber as shown in FIG. 1 has been used to detect oils such as gasoline, kerosene, and heavy oil leaking from oil storage equipment, piping, and the like. This optical fiber A is composed of a core a made of quartz glass or multi-component glass, and a clad b made of plastic such as silicone rubber or epoxy acrylate. A light emitting element C is attached to this optical fiber A.
The incident light is reflected from the boundary surface of the cladding b, passes through the core a, and reaches the light-receiving element d. In this case, when oil B adheres to optical fiber A, plastic clad b swells, its refractive index changes, and light leaks out from that part or is absorbed, reducing the amount of light reaching light receiving element d. do. By monitoring this change in the amount of light, it is possible to detect the presence or absence of oil leakage.

However, in order for the plastic cladding to swell with oil and have a sufficiently large change in its refractive index in a short period of time, the thickness of the cladding layer b must be several tens of micrometers or less, and if the cladding layer b is thus thin, the fiber It has the disadvantage that it is easily damaged during manufacturing and installation, and its strength is extremely low.

The present invention provides an optical fiber that overcomes these difficulties. Below, this optical fiber is
Detailed information is provided based on the diagram. 1 is core, 2 is clad,
3 is an optical fiber composed of a core and a cladding, and 4 is a primary coat layer formed during spinning. In the present invention, a coated optical fiber 6 is formed by providing a lateral pressure resistant coating layer 5 whose lateral pressure resistance is reduced by oil on the outer periphery of the primary coat layer 4.
It is made by applying lateral pressure to this coated fiber 6.

The primary coat layer 4 is made of silicone rubber, urethane acrylate, epoxy acrylate, or the like.

The lateral pressure-resistant coating layer 5 is made of hard plastic to prevent the stress from directly acting on the optical fiber 3 and micro-bending the optical fiber 3 even if non-uniform lateral pressure is applied from the outside. The Young's modulus of the lateral pressure-resistant coating layer 5 is 20 at room temperature, although it depends on the coating thickness.
Kg/mm ² or more is preferable from the viewpoint of lateral pressure resistance.

Further, the lateral pressure-resistant coating layer 5 preferably has the property of swelling and softening in a short time when it comes into contact with oil. Suitable materials include polystyrene, ABS, and AS.

In order to apply lateral pressure to the coated optical fiber 6 shown in FIG. 2, for example, as shown in FIG. 3, the optical fiber 6 may be stretched vertically around a copper wire or other similar tensile strength material 7, or may be wound spirally. Both 6 and 7 may be bound together by wrapping tape 8 around the outer periphery of both 6 and 7 while applying strong tension.

In this case, it is desirable that the tension applied to the tape 8 be such that winding the tape 8 slightly increases the transmission loss of the optical fiber 3. The tape 8 may be made of plastic or metal. Further, the cross-sectional shape and dimensions of the tape 8 are not particularly limited. Therefore, it is not necessarily a tape, but may be other materials.

As described above, in the present invention, the lateral pressure-resistant coating layer 5 is provided on the outer periphery of the optical fiber 3, and lateral pressure is applied to the coating layer 5. Therefore, when oil adheres to the lateral pressure-resistant coating layer 5, the coating layer 5 is It swells and softens in a short period of time, and the lateral pressure resistance of that part is significantly reduced, and the residual tension of the tape 8 causes microbends in the optical fiber 3, reducing transmission loss. Therefore, oil leakage can be detected sensitively, and the cladding 2 is not exposed to the outside, resulting in excellent strength and transmission characteristics.

As an experimental example of the present invention, a quartz-based step-index optical fiber with a core diameter of 50 μm and a cladding diameter of 125 μm was coated with silicone rubber to an outer diameter of 350 μm, and then polystyrene with a Young's modulus of 300 Kg/mm ² was coated around the outer circumference with an outer diameter of 800 μm. The coated optical fiber was then placed vertically on a copper wire with an outer diameter of 1 mm, and a Mylar tape with a width of 10 mm was applied at a tension of 1 kg.
Wrapped with. When one drop of heavy oil A was dropped while passing light through this optical fiber, a decrease in the amount of light received was immediately observed.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a conventional oil leakage detection method using an optical fiber, Fig. 2 is a front view showing an example of a coated optical fiber according to the present invention, and Fig. 3 is a diagram showing a method of applying lateral pressure to the optical fiber of Fig. 2. It is an explanatory diagram. 3 is an optical fiber, 5 is a lateral pressure-resistant coating layer, 7 is a tensile strength member, and 8 is a tape.

Claims (1)

[Scope of utility model registration request] A lateral pressure resistant coating layer whose lateral pressure resistance is reduced by contact with oil is formed on the outer periphery of the optical fiber, and a member that applies uneven lateral pressure in the longitudinal direction is arranged on the outer periphery of this coated optical fiber. An optical fiber for detecting oil, etc., characterized by: