JP3560404B2 - Leak detection wire - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid leakage detection electric wire that electrically detects liquid leakage from a pipe or the like with a single detection line, and in particular, can reliably detect leakage at any position, The present invention relates to a liquid leakage detection wire capable of selectively detecting only leakage due to a failure in a piping system without being affected by temporary wetting.
[0002]
[Prior art]
Many attempts have been made to detect leaks from pipes and the like using electric wire-shaped sensors. As a typical example, two conductors are arranged in parallel at regular intervals, and the detection target is detected in the meantime. When the liquid infiltrates, the conductors conduct to each other to detect liquid leakage. For example, a liquid-permeable conductor and a liquid-permeable insulator as disclosed in Japanese Patent Publication No. 3-500822 are used. A method of detecting a liquid leak by measuring a change in electrical characteristics when a liquid to be detected enters these conductors and insulators by a TDR method (time domain reflection metrology) or the like. and so on.
[0003]
In addition, as another attempt, there has been known an apparatus using a swelling member that expands by absorbing a liquid to be detected. For example, Japanese Patent Application Laid-Open No. 6-249743 discloses an optical fiber comprising a stress applying member using a swelling member made of a polymer and an optical fiber.
[0004]
[Problems to be solved by the invention]
However, first, the method of detecting liquid leakage using a sensor having a configuration in which two conductors are arranged in parallel is liable to malfunction due to the effects of adhesion of dirt, dew condensation, etc. Irreversible changes such as dielectric breakdown may occur. To solve this problem, for example, Japanese Patent Application Laid-Open No. Hei 5-187555 discloses the use of a corrosion-resistant conductor, but has not reached any essential solution. Further, in the case of a method of detecting a liquid leak using the TDR method as disclosed in Japanese Patent Publication No. 3-500822, the use of an optical fiber is necessary, so that an electric circuit for processing the sensor output is expensive. There is a disadvantage that it becomes costly.
[0006]
[Means for Solving the Problems]
As a result of intensive studies based on such points, the present invention has succeeded in developing a detection wire that has less malfunction, has excellent durability, and has a simple and inexpensive electric circuit for processing the output. In addition, the response time of the sensing wire is longer than before, and by further providing a means to adjust it, it is not affected by temporary wetting due to condensation or rainfall, etc. It has also been found that it is possible to selectively detect only continuous wetting.
[0007]
[Means for Solving the Problems]
That is, the leak detecting wire according to the present invention is a leak detecting wire in which a spacer formed of an insulating material , an inner conductor, an expanding polymer layer expanded by a leak detection target liquid, and an outer diameter holding means are sequentially formed on a central conductor. In the detection wire, the inner conductor is in close contact with the expanded polymer layer, and in a state where the expanded polymer layer is not expanded, the inner conductor and the center conductor are kept in a spatially insulated state by the spacer attached on the center conductor. However, when the expanded polymer layer comes into contact with the leak detection target liquid and expands by a predetermined amount, the inner conductor and the center conductor are electrically contacted by the expansion pressure inward. is there. At this time, it is conceivable to further provide a polymer composition layer for controlling the invasion speed of the liquid to be leak-detected between the expanded polymer layer and the outer diameter holding means.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, as the center conductor, copper, copper alloy, nickel, iron, aluminum, stainless steel, nickel-chromium alloy, or a thin metal wire made of a material obtained by subjecting these metals to surface treatment such as tin, silver, and nickel Ordinary conductors such as single wires and stranded wires or resistance wires are used.
[0009]
The spacer is made of an insulating material. For example, an extruded string made of a conventionally known rubber material or resin material and having a predetermined cross-sectional shape, a conventionally known twisted fiber thread, or the like can be used. These are mounted on the center conductor by cascading, braiding or weaving, but it is necessary that the spacers do not completely cover the center conductor. Preferably, a design is made such that a portion of 50% or more and 95% or less of the conductor surface is exposed. If the exposed portion of the central conductor is less than 50%, even if the expanded polymer layer comes into contact with the leak detection target liquid and expands, it may not be possible to obtain a sufficient electrical contact state with the internal conductor. On the other hand, if the exposed portion of the center conductor exceeds 95%, the ability of the spacer to maintain the spatial insulation is reduced.
[0010]
The inner conductor is made of a metal material such as a metal film and a metal linear body. When using a metal film, it is preferable to adhere to the expanded polymer layer through a polymer adhesive layer, and when using a metal linear body, with or without an adhesive layer on the expanded polymer layer. Embedding is preferred. It is preferable that the internal conductor has a sufficiently low resistance as compared with the expanded polymer layer swollen by absorbing the liquid to be leak-detected, in order to detect the leak position. Therefore, as the metal material, a material made of copper, tin-plated copper, nickel-plated copper, silver-plated copper, and a copper alloy containing a small amount of the second component is preferably used.
[0011]
The expandable polymer layer that expands upon contact with the leak detection target liquid may have a property that the polymer itself expands, or may be a mixture of particles that expand in the polymer. Various types of such polymer materials have been known in the art, and they may be used. For example, when the liquid to be leak-detected is water, the polymer itself has a property of expanding, for example, a crosslinked polyvinyl alcohol-based material, and in particular, a commercially available product that can be extruded. Examples of the material containing expanding particles include various rubbers and plastics containing dry particles of acrylic acid-based hydrogel. If the leak detection target liquid is other fuel substances (for example, hydrocarbons) or chemicals, cross-linked polymers soluble in each substance are used alone or as a mixture, or are processed into powder. After that, it is used in a form mixed with any polymer.
[0012]
The thickness and type of the expandable polymer layer and the degree of saturation expansion of the leak detection target liquid are arbitrarily set in consideration of the structure, sensitivity, quick recovery and the like of the leak detection wire obtained by the present invention. For example, when the space insulation distance between the center conductor and the inner conductor is large and a quick detection is required, it is preferable to set the expanded polymer layer to be thick and the saturation expansion to be large. In the opposite case, it is preferable to set the expanded polymer layer to be thin and the degree of saturation expansion to be small.
[0013]
An outer diameter holding means is provided on the expanded polymer layer in a state of being close to the expanded polymer layer. The outer diameter holding means is for expanding the expanding polymer layer, which normally expands outward, toward the inside, and protecting the expanding polymer layer from external damage or the like. The constituent material is not particularly limited as long as it has a property of transmitting the liquid to be detected. For example, a braid made of a high-strength wire such as a metal, or a horizontal braid of a high tensile strength band made of a metal or the like may be used.
[0014]
In the present invention, in order to easily adjust the sensitivity, a polymer composition layer for controlling the intrusion speed of the leakage detection target liquid may be further provided between the expanded polymer layer and the outer diameter holding means. . The constituent material is appropriately selected from conventionally known polymer materials having a small expansion but having a property of easily transmitting the liquid to be detected. For example, when the leak detection target liquid is water, preferably, an aliphatic polyamide resin such as polyamide 6, polyamide 66, or the like is selected, and is continuously formed on the expanded polymer layer. When the leak detection target liquid is a petroleum-based liquid, preferably, a polyolefin-based resin such as polyethylene or polypropylene is selected, and is continuously formed on the expanded polymer layer.
[0015]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples.
[0016]
Example 1
First, an extruded string made of a polyester elastomer having a semicircular cross section with a diameter of 1 mm as a spacer is exposed on the periphery of a center conductor made of a nickel-plated soft copper wire having a cross-sectional area of 0.5 mm ^{2 so that} the surface of the center conductor is exposed by about 75%. , And heat-treated at the same time to give a spiral habit to the extruded string, thereby integrating the two. Next, when extruding a 1 mm thick expanded polymer layer formed by mixing 15 parts by weight of finely divided vinyl alcohol-acrylic acid copolymer gel with 100 parts by weight of a commercially available soft vinyl chloride compound, An internal conductor made of a 15 mm wide composite film (polyester film 25 μm, nickel-plated copper foil 20 μm) coated with an adhesive for vinyl chloride is vertically attached with the nickel-plated copper foil layer inside, and the internal conductor and the expanded polymer layer Was formed at the same time. Finally, four SUS304 strands having a diameter of 0.2 mm were aligned and braided using a 20-stroke braider to form an outer diameter holding means.
[0017]
One end of the liquid leakage detection wire thus manufactured was treated to draw out the center conductor and the inner conductor, and the resistance was measured between the two under the following conditions to evaluate the characteristics. First, as a test for temporary wetting, the detection wire was immersed in a water tank for 10 minutes, then pulled up, and the progress of the resistance value for 8 hours was observed. After 8 hours, the resistance value remained infinite, and no detection was performed. Next, as a test for continuous wetting, the progress of the resistance value was observed while continuously immersing the detection wire in the water tank. When 4 hours had passed, the resistance value was 21Ω, and the presence of water was detected.
[0018]
Example 2
In Example 1, after forming the expanded polymer layer, polyamide 6 was continuously extruded to a thickness of 0.15 mm to form a polymer composition layer. Next, an outer diameter holding means was formed in the same manner as in Example 1 to obtain a liquid leakage detection wire. The leak detection wire thus obtained was evaluated in the same manner as in Example 1. As a result, in the test for temporary wetting, the resistance value remained infinite, but in the test for continuous wetting, the resistance value was 21Ω after 10 hours, 6 hours later than the detection wire of Example 1. And the presence of water was detected.
[0019]
In this embodiment, further evaluation was performed on the detection wire of the first embodiment and the detection wire of the second embodiment. Both are buried in moist soil, and in one test, water is not supplied so that the soil gradually dries, and in the other test, water is appropriately supplied so that the moist condition is maintained. The situation was observed for a total of three days. As a result, in the former test, the detection wire of Example 1 operated after 6 hours, but the detection wire of Example 2 did not operate at all during the period. In the latter test, the detection wire of Example 1 operated after 6 hours, and the detection wire of Example 2 operated after 14 hours.
[0020]
From these test results, it is understood that the sensitivity can be easily adjusted by further providing the polymer composition layer as in Example 2 so as to prevent malfunction of the detection wire due to temporary wetting due to condensation, rainfall, and the like.
[0021]
The present invention is not limited to the above embodiment. In the above embodiment, since the liquid to be leak-detected was water, a composition of vinyl chloride and hydrogel was used as a constituent material of the expanded polymer layer. When the above-mentioned chemicals are used, the same effects as in the above embodiment can be obtained by appropriately selecting and using a material which expands upon contact with them.
[0022]
【The invention's effect】
As described above in detail, according to the present invention, a local leak can be reliably detected, and a conventional detection wire (for example, electrically detecting the presence of a liquid between two conductors) can be used. In this case, a leak detection wire capable of performing slow detection, which was not possible with the configuration described above, was obtained. With a sensing wire having such a characteristic remarkable effect, temporary leakage and continuous leakage can be reliably distinguished, so that malfunction does not occur and extremely high reliability is obtained. It will be. Therefore, for example, by installing in parallel with water and sewer pipes buried in the soil and water and sewer pipes built in the building, it does not react to temporary rainfall or moisture adhesion due to condensation In addition, it is possible to selectively detect only a local and continuous leak as in the case of a leak due to a pipe failure.
[0022]
Even if we take only water and sewage pipes, the loss of water supply due to leakage every year is enormous. It was impossible to detect and repair all leaks in the piping. Sewage also has problems such as accelerated deterioration of buildings due to liquid leakage, which has led to significant costs for management.
[0023]
However, the use of the detection wire of the present invention makes it extremely easy to control the entire length of the pipe, and thus it is considered that a great economic effect can be obtained. Also, if the conventional detection wire and the leak detection wire of the present invention capable of detecting both temporary leak and continuous leak are laid in parallel, even if the leak occurs at any position, This is more useful because it can be reliably detected.

Claims (2)

In a leak detection wire in which a spacer molded from an insulating material , an inner conductor, an inflatable polymer layer expanded by a leak detection target liquid, and an outer diameter holding means are sequentially formed on a center conductor, the inner conductor is an inflatable polymer layer. When the expanded polymer layer is not expanded, the inner conductor and the center conductor are kept in a spatially insulated state by the spacer attached on the center conductor, but the expanded polymer layer detects leakage. A leak detection wire wherein the inner conductor and the center conductor are electrically contacted by an inward expansion pressure when in contact with the target liquid and expanded by a predetermined amount. 2. The leak detecting wire according to claim 1, further comprising a polymer composition layer for controlling the intrusion speed of the leak detection target liquid between the expanding polymer layer and the outer diameter holding means.