JP2000283882A - Optical fiber liquid sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable sensor with high sensitivity by drastically reducing the pinching by an inclusion tape as compared with a conventional one with an angle exceeding 45 degrees and eliminating the dependence of the detection sensitivity on the position in the longitudinal direction of the sensor. SOLUTION: The optical fiber liquid sensor consists of a slot 1 where a groove 2 is formed at an outer periphery in a longitudinal direction, an inflation material 3 that is arranged in the groove 2 and is inflated by the contact of liquid to be detected, an inclusion tape 4 that sags in the groove 2 and is arranged to cover the groove 2, an optical fiber 5 that is arranged on the inclusion tape 4 with the sag, and a linear restriction material 6 that is arranged so that it covers the groove 2. The inclusion tape 4 is arranged so that it has a sag of 45 degrees or less in terms of an angle formed by a tangent line in contact with the surface of the inclusion tape 4 and both ends of the groove 2 when being observed from the direction of the cross section of the groove 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber liquid sensor for detecting liquid leakage from a storage tank, a transportation pipeline, etc. of oil and chemicals.

[0002]

2. Description of the Related Art Conventionally, in storage and transportation facilities for oil and chemicals, there has been a problem of leakage of stored liquid due to factors such as deterioration of facilities and accidents. Leakage of oil, chemicals, and the like, which are stored liquids, is uneconomical and has important problems such as pollution of the environment and induction of disasters, and early detection of the leak is desired.

In order to meet these needs, Japanese Patent Application No. 9-217330 has proposed an optical fiber liquid sensor having a structure shown in FIG. In FIG. 4, 1 is a slot in which a groove 2 is formed on the outer periphery in the longitudinal direction, 3 is disposed in the groove 2,
A swelling material that swells due to contact with the liquid to be detected,
An interposition tape 5 having a slack therein and disposed so as to cover the groove 2 is an optical fiber disposed on the interposition tape 4 having a slack, and 5 is a line disposed so as to cover the groove 2. Constraint material, 6 is a linear constraint material, 7 is a braided body, 8
Is a tension member. In the optical fiber liquid sensor having such a configuration, when the liquid to be detected enters the groove 2, the swelling material 3 expands, and the optical fiber 5 is sandwiched between the interposition tape 4 and the restraining material 6 and receives a stress. The optical transmission loss of the optical fiber 5 increases due to the bending of the optical fiber 5.
By measuring the loss at the end of the optical fiber 5, the presence of the liquid can be known at a remote location.

This sensor has the following excellent features. -Any liquid that can be absorbed and swelled by the swelling material 3 regardless of the refractive index of the liquid can be detected. The optical fiber 5 is in a free state in the groove 2 and usually has a structure that is not directly restrained by the restraining member 6. Therefore, even if this sensor (having a cable shape) is bent by laying or the like, bending (bend) does not occur due to the restraining member 6. The built-in swelling material 3 at the bottom of the groove 2 of the slot 1 allows the generated force to effectively act upward (outward of the slot). An intervening tape 4 between the swelling material 3 and the optical fiber 5
Is inserted, it is possible to more effectively apply a generating force for generating the swelling material 3 to the optical fiber 5. -Since the bending loss generating portion has a structure in which the linear restricting member 6 is wound around the outer periphery of the slot 1, the bending loss generating portion can be easily formed. Further, the detection sensitivity can be easily adjusted by the diameter and the winding pitch of the restraint member 6, and it is possible to quickly respond to a wide range of needs.

[0005]

However, the sensor having the structure shown in FIG. 4 has a problem in detection reproducibility. That is, when a long sensor cable is prototyped, the sensor sensitivity (the loss caused when oil is applied per unit length) may differ at each location in the length direction. If the sensor sensitivity differs depending on the location as described above, a loss value (threshold value) for judging oil leakage when a sensor system is constructed cannot be strictly determined, and the reliability of the system is reduced. (The probability of malfunction increases)

The cause of the variation in the sensor sensitivity in the longitudinal direction is that the optical fiber 5 is pinched by the interposed tape 4 inserted between the swelling material 3 and the optical fiber 5 generated at the time of liquid sensing. I know that. (See FIG. 5) In the case of the type shown in FIG. 5 (1) (θ1 and θ2 are 45 ° or more), the optical fiber 5 does not come into contact with the bending portion formed of the restraining member 6, and as a result, No loss occurs. When the optical fiber 5 is pinched in the state shown in FIG.
Since the interposed tape 4 exists between the optical fiber 5 and the bending portion formed by the restraining member 6, the bending of the optical fiber 5 is hindered, and the amount of loss is reduced.

It is considered that the cause of the entrapment is related to the manner in which the force generated by the swelling material 3 is transmitted to the interposed tape 4 and the manner in which the interposed tape 4 is deformed. In the case of FIG. 5A, the direction of the force generated from the swelling material 3 is mainly from the bottom of the groove 2 of the slot 1 to its opening direction (y-axis direction in the figure). Since the angle of the interposed tape 4 receiving this force is larger than 45 °, the interposed tape 4 is dominated by the force in the x-axis direction, and the interposed tape 4 is
Is deformed in the direction of pinching.

In the case of FIG. 5 (2), the force generated by the swelling material 3 is applied to the bottom surface of the concave-shaped interposition tape 4. In this case, the most ideal deformation is that the concave side surface is deformed as shown in FIG. 6 (2). However, at present, if the applied force to the bottom surface of the interposition tape 4 is biased or the concave shape of the interposition tape 4 is distorted as shown in FIG. It may be like 5 (2). The shape of the interposed tape 4 as shown in FIG. 6 (3) is obtained when the interposed tape 4 is formed into a recess, when the slot 1 is dropped into the groove 2, and when the restraining member 6 is wound around the slot 1. It is likely to occur at times.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a slot having a groove formed on the outer periphery in the longitudinal direction, and a swelling material which is arranged in the groove and swells by contact with the liquid to be detected. An interposition tape having a slack in the groove and arranged to cover the groove, an optical fiber arranged on the interposition tape having the slack, and a linear fiber arranged to cover the groove. The optical fiber liquid is configured so that the liquid to be detected enters the groove, the swelling material expands, and the optical fiber is sandwiched between the intervening tape and the restricting material to receive stress. In the sensor, the interposed tape is disposed with a slack such that an angle between a tangent line in contact with the surface of the interposed tape and a straight line formed by both edges of the groove is 45 degrees or less when observed from the cross-sectional direction of the groove. Characteristic A.

[0010]

1 to 3 show different embodiments of the present invention. In these figures, 1
Numerals 8 to 8 are the same as those in the conventional case shown in FIG.

In the case of the shape of the interposition tape 4 shown in FIG. 1, by setting both the angles θ1 and θ2 to 45 ° or less, the force component in the y-axis direction becomes larger than that in the x-axis direction. 5 is reduced.
At this time, in the formation of the shape of the interposition tape 4, the generation of the pinching is further reduced by not making the crease of the interposition tape 4 strong. When the swelling material 3 is deformed due to swelling of the swelling material 3, the strong fold of the interposition tape 4 becomes a starting point of the deformation, and the degree of freedom of the deformation is lost.

Even in the case of the shape of the interposition tape 4 shown in FIG. 2, it is desirable that the fold of the interposition tape 4 in forming the shape is weak. In the case of the shape of the interposition tape 4 shown in FIG.
Since there is no fold to be the starting point of deformation and the interposed tape 4 is at 45 ° or less at any applied position with respect to the applied force, the occurrence of pinching is extremely small. It is desirable that the point B is on a straight line connecting the two tension members in the groove 2 from the viewpoint of protection of the optical fiber 5.

[0013]

EXAMPLE An oil-swelling resin was used as a swelling material, and a restraining wire was used as a restraining material. For the details, those having the basic configuration shown in Table 1 were adopted, and four types of oil leakage detection sensor cables were prototyped, each 20 m long. The difference between the four types is the shape of the interposed tape.
Numeral 2 is the shape of the interposition tape 4 shown in FIG. 1 and θ1 and θ2 were set to about 50 ° and 30 °, respectively. Type 3 is a concave shape with a clear strong fold, and type 4 is a shape shown in FIG. In addition, here, considering the detection characteristics of a more practical sensor cable structure, evaluation was performed using a cable coated with a braid for protecting the cable.

[0014]

[Table 1]

In the evaluation, the sensor sensitivities were measured at five arbitrary points in the length direction of each sensor cable and compared. The sensor sensitivity was measured by measuring the change in transmitted light intensity of the sensor cable. Kerosene was used for the evaluation. The sensor sensitivity is defined as a loss generated in a state where sufficient oil is dropped on the cable 30 cm and 30 minutes have passed since the dropping. Table 2 shows the evaluation results.

[0016]

[Table 2]

[0017]

According to the present invention, as described above, the angle between the tangent line in contact with the surface of the interposed tape and the straight line formed by both edges of the groove when observed from the cross-sectional direction of the slot is 45 degrees or less. , An interposition tape is disposed with a slack in the groove. As a result, in the present invention, as compared with the conventional angle having an angle exceeding 45 degrees, the pinching by the interposed tape is extremely reduced, and the detection sensitivity does not differ at the position in the longitudinal direction of the sensor. High sensitivity and stable characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is an essential part cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view of a main part showing a second embodiment of the present invention.

FIG. 3 is an essential part cross-sectional view showing a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an example of the related art.

FIG. 5 is a sectional view of an essential part for explaining the operation of the conventional example.

FIG. 6 is a sectional view of a main part for explaining an operation of a conventional example.

[Explanation of symbols]

 1 is a slot 2 is a groove 3 is a swelling material 4 is an interposition tape 5 is an optical fiber 6 is a restraining material 7 is a braided body 8 is a tension member

Claims (2)

[Claims] 1. A slot having a groove formed on the outer periphery in the longitudinal direction, a swelling material disposed in the groove and swelling by contact with a liquid to be detected, and a swelling material disposed in the groove so as to cover the groove. Interposed tape, an optical fiber disposed on the interposed tape with the slack, and a linear restraining member disposed so as to cover the groove, and the liquid to be detected enters the groove. By invading, the swelling material expands,
In an optical fiber liquid sensor configured such that an optical fiber is stressed by being sandwiched between an interposing tape and a restraining member, the interposing tape has both a tangent line and a groove that come into contact with the surface of the interposing tape when observed from a cross-sectional direction of the groove. An optical fiber liquid sensor having a slack so that an angle between a straight line formed by an edge and a straight line is 45 degrees or less. 2. The optical fiber liquid sensor according to claim 1, wherein the shape of the slack is formed so as to be a polygon of a triangle or more.