JP4485235B2 - Fiber optic sensor - Google Patents

Description

  The present invention relates to a sensor capable of selectively detecting a liquid such as water and a liquid such as gasoline, kerosene and light oil.

  Japanese Patent Publication No. 59-47256 (Patent Document 1) is a sensor that detects a leakage of oil or gasoline in an oil pipeline, an oil storage tank, or a gasoline storage tank of a gas station. ) Has been proposed. According to the technique disclosed in Patent Document 1, leakage of water or gasoline can be selectively detected using an electrical signal using a continuous porous PTFE (polytetrafluoroethylene) material containing a conductive substance. .

  However, such oil pipelines, oil storage tanks or gasoline storage tanks of gas stations that handle dangerous materials such as oil and gasoline are required to be explosion-proof to prevent fires and explosion accidents. The proposal of Japanese Examined Patent Publication No. 59-47256 using an electrical signal was not preferable from the viewpoint of explosion prevention.

  On the other hand, the applicant of the present application has a core that is stretched after molding a melt made of crystalline perfluoro resin as a sensor that does not use an electrical signal, and a water-repellent porous layer is provided so as to surround the core. Japanese Patent Application No. 2003-066602 proposes to use a plastic optical fiber as a sensor. (Patent Document 2)

  However, in the sensor proposed in Patent Document 2, a porous layer having water repellency with respect to water is provided around the core in order to detect a liquid to be detected other than water. Thus, this sensor does not detect liquids such as water or pure water through a water-repellent porous layer, so it does not detect, while it detects liquids to be detected, such as gasoline, that pass through this porous layer. As a result, the liquid to be detected such as gasoline can be selectively detected. Therefore, in the above-mentioned Japanese Patent Application No. 2003-066032, in order to selectively detect water or gasoline, a water-repellent porous layer must be provided around the core, and the number of members constituting the sensor increases. There is a problem that it is troublesome to provide it around.

Japanese Patent Publication No.59-47256 Japanese Patent Application No. 2003-066032

  The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a liquid such as water and a liquid such as gasoline, kerosene and light oil without providing an explosion-proof and water-repellent porous layer. It is an object of the present invention to provide a sensor that can selectively detect.

The object of the present invention is achieved by the plastic optical fiber sensor of the present invention. That is, plastic optical fiber sensor of the present invention, by stretching the monofilament made of crystalline fluorine-containing resin in 3-10 times, forms a light permeable core having a refractive index of 1.38 to 1.40, the A plastic optical fiber sensor characterized in that leakage of a liquid to be detected having a refractive index larger than that of a core is detected .

  That is, the present invention is a plastic optical fiber sensor characterized in that a monofilament made of a crystalline fluorine-containing resin is stretched so that light can be transmitted and its refractive index is made smaller than that of the liquid to be detected. The mold can selectively detect liquids such as water and liquids such as gasoline.

A preferred embodiment of a leak sensor according to the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a schematic explanatory diagram of a preferred embodiment of a leak detection apparatus including a leak sensor according to the present invention.

Referring to FIG. 1, a leak detection device 10 is shown. The leak detection device 10 includes a leak sensor 1. A light source that inputs light to the leak sensor 1 is provided at one end of the leak sensor 1. 2 is provided, and on the other end side of the leakage sensor 1, a light receiving unit 3 that receives light from the light source 2 via the leakage sensor 1 is provided. Further, an output from the light receiving unit 3 is provided. An input light measuring device 4 is provided.
The leak sensor 1 includes a core capable of transmitting light by extruding a polyvinylidene fluoride melt into a monofilament shape and then stretching the film in the longitudinal direction about 5.5 times in the atmosphere at 150 ° C. And has a refractive index of 1.40.
Note that this core corresponds to the core in the sensor described in Patent Document 2. However, as is apparent from the description of the problem to be solved by the present invention around this core, Patent Document 2 Unlike the sensor in the prior art described in 1), a water-repellent porous material is not provided. In the above examples, the draw ratio was about 5.5 times. However, this draw ratio is preferably in the range of 3 to 10 times, and when the draw ratio is 3 times or less, it is transparent for transmitting light. Therefore, when the draw ratio is 10 times or more, mechanical properties such as crack resistance of the monofilament are remarkably lowered, which is not preferable as a leakage sensor. Here, the refractive index of the leakage sensor 1 when the stretch ratio is 3 to 10 is in the range of 1.38 to 1.42.
In addition to the above-mentioned polyvinylidene fluoride, a resin such as ethylene tetrafluoroethylene copolymer and polychlorotrifluoroethylene can be used as the material of the leakage sensor 1, but any stretching depending on the material used. The magnification can be set, and the refractive index after stretching needs to be in the range of 1.38 to 1.42.

Now, when the leak detection apparatus 10 configured as described above is in operation, the leak sensor 1 of the leak detection apparatus 10 is covered with, for example, gasoline leaked from a gasoline storage tank or the like (refractive index 1.40 to 1.42). When the detection liquid arrives at and adheres to the leak sensor 1 to form the adhering portion 5, the refractive index of the liquid to be detected has a refractive index of 1.40 or more of the leak sensor 1, that is, from the refractive index of the sensor , that is, the core. Since the light from the light source 2 is emitted from the attachment portion 5 of the leakage sensor 1 to the outside of the leakage sensor 1, the amount of light received by the light receiving portion 3 is reduced. The amount of light is displayed on the light meter 4. The decrease in the amount of light can detect the arrival of the liquid to be detected, that is, the leakage. In this embodiment, in the optical measuring device 4, it is set that the liquid to be detected has arrived when the decrease in the light quantity is reduced by 70.0% or more from the light quantity before detection. The setting of the light amount reduction for determining the arrival of the liquid can be arbitrarily set as necessary.

  Next, even if water or the like having a refractive index smaller than that of the leak sensor 1 arrives and adheres, the light from the light source 2 is not emitted from the adhering portion to the outside of the leak sensor 1, and as a result, the amount of light decreases. The light measuring device 4 does not detect water because the decrease in the amount of light is less than the detection set value.

Polycrystalline vinylidene fluoride (PVdF) (KF polymer (registered trademark) # 1100: manufactured by Kureha Chemical Co., Ltd.) as a crystalline fluororesin is extruded from an extruder at a die temperature of 300 ° C. and immediately cooled to 0 ° C. with a refrigerant. A monofilament having a diameter of 1.1 mm was produced.
Next, at 150 ° C. in the atmosphere, the monofilament is fed out at a speed of 0.18 m / min and tension is applied at a take-up speed of 1.0 m / min, and stretched to 5.5 times the original length, and the diameter is 0.46 mm. A stretched material was obtained.
Next, the tensioned state was maintained, and heat setting was performed in the atmosphere at 140 ° C. for 2 minutes to obtain a plastic optical fiber sensor having a refractive index of 1.40.

  The obtained plastic optical fiber sensor is cut to 60 mm, one end thereof is connected to a light source (MG9001A: manufactured by Anritsu), and the other end is connected to a light receiving unit (AQ-1966 SENSOR: manufactured by Ando Electric Co., Ltd.). The amount of light received by the optical unit is displayed on an optical measuring instrument (Optical Power Meter AQ1135E: manufactured by Ando Electric Co., Ltd.). Table 1 shows. The liquid used is a fluorine-based inert liquid, water, gasoline, kerosene, and light oil. In Table 1, the amount of incident light from the light source to the plastic optical fiber sensor is the amount of light before detection, and when the liquid to be detected is in contact with the optical fiber sensor, it enters the light receiving section via the optical fiber sensor. The amount of light received was measured, and it was determined whether leakage could be detected by the change in the amount of light.

  As shown in Table 1, when a liquid whose refractive index is greater than 1.40 is to be detected, i.e., a liquid to be detected, that is, a liquid to be detected, this liquid contacts the optical fiber sensor due to leakage or the like. At that time, the amount of light suddenly decreased in a short time from the amount of light before detection, so it was determined that the light was refracted from the liquid contact portion and emitted to the outside of the optical fiber sensor, and leakage detection was enabled. In addition, when the liquid to be detected is water such as rainwater (refractive index 1.33), when the water comes into contact with the optical fiber sensor, the amount of light is less decreased, so that the liquid is a liquid other than the liquid to be detected. It was judged that the leak was impossible. Even when a fluorine-based inert liquid having a different property from water is measured in the same manner, the amount of light decreases and falls below a predetermined value from the amount of light before detection. It was determined that the liquid was not refracted, and it was determined that the liquid was a liquid other than the liquid to be detected. Thus, the liquid to be detected and other liquids can be selectively detected.

In the above-described embodiments, liquids having a refractive index of 1.40 to 1.47 such as gasoline, kerosene, and light oil have been described as the liquids to be detected, but other refractive indexes such as benzene and toluene. A liquid having a refractive index of 1.47 to 1.52 may be used as a liquid to be detected. In short, a liquid having a refractive index higher than the refractive index of 1.38 to 1.42 of the optical fiber sensor is used as a liquid to be detected. Can do.

It is a schematic explanatory drawing of preferable embodiment of the leak detection apparatus provided with the leak sensor by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Leak sensor 2 Light source 3 Light-receiving part 4 Optical measuring device 5 Adhering part 10 Leak inspection apparatus 1010

Claims (1)

A monofilament made of a crystalline fluorine-containing resin is stretched 3 to 10 times to form a light transmissive core having a refractive index of 1.38 to 1.40, and has a refractive index larger than the refractive index of the core. A plastic optical fiber sensor , wherein leakage of a liquid to be detected is detected .

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