WO2006086178A1

WO2006086178A1 - Liquid leakage sensor

Info

Publication number: WO2006086178A1
Application number: PCT/US2006/003277
Authority: WO
Inventors: Shigeru Suzuki
Original assignee: 3M Innovative Properties Company
Priority date: 2005-02-10
Filing date: 2006-01-31
Publication date: 2006-08-17
Also published as: TWI403710B; JP4780970B2; JP2006220537A; TW200636222A

Abstract

A liquid leakage sensor is used for a leakage detection system. The liquid leakage senor includes an electrically insulating linear core member, and a pair of conductive wires individually helically wound on the surface of the core member. The conductive wires are arranged on the surface of the core member separate from each other. The conductive wires function as an electrode of the liquid leakage sensor. At the time when the liquid leakage sensor detects no liquid, the conductive wires are electrically insulated from each other on the surface of the core member. The liquid leakage sensor senses the existence of liquid by detecting an electric current flowing in both the conductive wires via the liquid when the conductive wires are electrically bridged while the liquid is being interposed between both of the conductive wires.

Description

LIQUID LEAKAGE SENSOR

FIELD OF THE INVENTION

[0001] The present invention relates to a liquid leakage sensor used for a leakage detecting system.

BACKGROUND

[0002] As one of the countermeasures for preventing disasters in residences , hospitals , warehouses and so forth, various leakage detecting systems are provided which immediately sense the occurrence of an accidental leakage and submersion so that the accident can be quickly notified to the residents and j anitors . In general , the leakage detecting system includes : a liquid leakage sensor for sensing the existence of liquid by using a medium such as electricity, sound or light ; and a leakage detector for performing a notifying action such as an alarm generation according to a signal of detecting liquid by the liquid leakage sensor . In this case , the electric type liquid leakage sensor senses the existence of water (leakage or submersion) by the passive electrical conduction between a pair of electrodes which are arranged being separate from each other. In the electric type liquid leakage sensor, the electric resistance of the liquid leakage sensor itself , which changes corresponding to an increase and decrease in a quantity of the liquid existing between the electrodes , is detected and processed by the leakage detector as a liquid sensing signal . Accordingly, in the leakage water detecting system into which the electric type leakage water sensor is incorporated, it is a precondition that the liquid to be sensed is electrically conductive .

[0003] The liquid sensing capacity (the sensitivity) of the electric type liquid leakage sensor in the leakage detecting system is determined mainly by the constitution of the electrodes . Conventionally, a liquid leakage sensor, the sensitivity of which corresponds to the application (the environment in which the leakage detecting system is laid, the obj ective liquid to be sensed and so forth) of the leakage detecting system, has been used being appropriately selected . For example , a high sensitivity type liquid leakage sensor is used for detecting the leakage of liquid such as pure water, the resistance of which is relatively high, and a low sensitivity type liquid leakage sensor is used for detecting the leakage of liquid such as town water, the resistance of which is relatively low.

SUMMARY OF THE INVENTION

[0004] An obj ect of the present invention is to provide an electric type highly sensitive liquid leakage sensor used for a leakage detection system characterized in that the occurrence of erroneous operation caused by not leaking or submerging water but a very small quantity of liquid can be prevented and further the liquid can be very easily removed at the time of recovery .

[0005] In order to accomplish the above obj ect , embodiments of the invention, for example, advantageously provide a liquid leakage sensor including a plurality of electrodes spaced from each other and sensing an electrical conduction between certain electrodes as an existence of liquid, the liquid leakage sensor comprising a linear core member having an electrical insulation property; and a plurality of conductive wires individually positioned on a surface of the core member in a helical fashion and arranged to be spaced from each other on the surface, the conductive wires respectively functioning as the electrodes .

[0006] Embodiments of the invention, for example , also advantageously provide a liquid leakage sensor, wherein the core member includes a plurality of grooves individually recessed along the surface in a helical fashion, each of the plurality of conductive wires being fixedly received in each of the grooves .

[0007] The Embodiments of the invention, for example, also advantageously provide a liquid leakage sensor, wherein each of the plurality of conductive wires includes an exposed surface part continuously exposed on the surface of the core member over substantially an entire length of a predetermined sensing region of the liquid leakage sensor .

[0008] Embodiments of the invention, for example, also advantageously provide a liquid leakage sensor, wherein the plurality of conductive wires are evenly spaced on the surface of the core member over substantially entire lengths of a predetermined sensing region of the liquid leakage sensor .

[0009] Embodiments of the invention, for example, also advantageously provide a liquid leakage sensor, wherein the surface of the core member comprises substantially a cylindrical surface .

[0010] Embodiments of the invention, for example , also advantageously provide a liquid leakage sensor, further comprising a net member having an electrical insulation property and a liquid permeability, the net member being arranged to cover the core member and the plurality of conductive wires .

[0011] Embodiments of the invention, for example , also advantageously provide a liquid leakage sensor, wherein the net member comprises a plurality of fibrous elements individually wound along the surface of the core member to surround the plurality of conductive wires . [0012] For example, since a plurality of conductive wires respectively functioning as an electrode are helically positioned on a surface of the core member, the minimum interval of these conductive wires on the core member surface is prescribed as a distance in the substantially circumferential direction of the core member . Accordingly, when the thickness of the core member is several mm, which is relatively thin, the minimum interval of these conductive wires can be several mm . Accordingly, it is possible to obtain a highly sensitive type liquid leakage sensor capable of sensing a relatively small quantity of liquid. On the other hand, for example , in the case where a very small quantity of liquid such as dew concentration water, which is not the leaking or submerging water, exists on a face on which the liquid leakage sensor is laid, an interval of the conductive wires for sensing the liquid is a distance in the longitudinal direction of the core member, irrespective of the thickness of the core member. When a plurality of conductive wires are arranged in the longitudinal direction of the core member being sufficiently separated from each other, for example , it becomes difficult to sense a very small quantity of liquid generated on the face on which the liquid leakage sensor is laid. As a result , it becomes possible to obtain a liquid leakage sensor which is seldom erroneously operated. When the liquid leakage sensor is recovered to the initial state after the leaking water has been sensed, liquid attaching to the core member and conductive wires can be easily and quickly removed .

[0013 ] Also, for example, each groove is previously formed into a helical shape corresponding to the shape required for each conductive wire so that the conductive wire can be used as an electrode . Due to the foregoing, the plurality of conductive wires can be easily arranged into a predetermined helical winding form along the core member surface .

[0014] Also, for example, it is possible to sense a local existence of liquid anywhere in the sensing region of the leakage water sensor . Further, the liquid, which bridges the conductive wires to each other, attaches onto the core member surface while the liquid is automatically spreading along the conductive wires by the action of surface tension. Therefore, an electric current can easily flow in the liquid. Accordingly, even in the case of pure water, the resistance of which is relatively high, its existence can be positively sensed.

[0015] Also, for example , the substantially uniform sensitivity can be ensured in the sensing region of the liquid leakage sensor . In the liquid leakage sensor, when an interval of arranging the plurality of conductive wires is appropriately selected, the sensitivity can be easily adjusted .

[0016] Also, for example, the individual conductive wires can be easily, accurately wound on the core member surface into a helical shape .

[0017] Also, for example , the liquid leakage sensor can be directly laid on a conductive surface of a pipe as it is .

[0018] Also, for example, a net member, the density of which is predetermined, can be relatively easily obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Fig . 1 shows a perspective view schematically showing a liquid leakage sensor according to one embodiment of the present invention. [0020] Fig . 2 shows a sectional view of the liquid leakage sensor shown in Fig . 1 , taken along a line II - II .

[0021] Fig . 3 shows a perspective view schematically showing a liquid leakage sensor according to another embodiment of the present invention.

[0022] Fig . 4 shows a sectional view of the liquid leakage sensor shown in Fig. 3 , taken along a line IV - IV.

DETAILED DESCRIPTION

[0023] Referring to the accompanying drawings , embodiments of the present invention will be explained in detail below. Like reference characters are used to indicate like parts in all the drawings .

[0024] Referring to the drawings , Fig . 1 is a perspective view showing an outline of the liquid leakage sensor 10 of an embodiment of the present invention . Fig . 2 is a sectional view of the liquid leakage sensor 10. The liquid leakage sensor 10 , for example , includes a pair or plurality of electrodes which are separate from each other, and the existence of liquid (the existence of leaking or submerging water) between the electrodes can be sensed by the electric electrical conduction between these electrodes , that is , the liquid leakage sensor 10 is of the electric type .

[0025] As shown in the drawing, the liquid leakage sensor 10 can include, for example, an electrically insulating linear core member 12 ; and a pair of conductive wires 14 , 16 individually, helically positioned on the surface 12a of the core member 12 and arranged on the surface 12a being separate from each other . These conductive wires 14 , 16 respectively function as an electrode of the liquid leakage sensor 10. At the time of not detecting operation, the conductive wires 14 , 16 are electrically insulated from each other on the surface 12a of the core member 12.

[0026] The pair of conductive wires 14 , 16 of the liquid leakage sensor 10 , for example, are connected to the leakage detector 18 composing the leakage detecting system in cooperation with the liquid leakage sensor 10. Due to the foregoing, the detecting circuit is composed. Voltage is impressed upon these conductive wires 14 , 16 by the leakage detector 18. When liquid is interposed between both the conductive wires 14 , 16 and these conductive wires 14 , 16 are electrically bridged to each other, an electric current flows in both conductive wires 14 , 16 via the liquid, so that the existence of the liquid can be sensed . The leakage detector 18 detects an electric resistance value of the detection circuit , which changes according to an increase and decrease in the quantity of the liquid that bridges both the conductive wires 14 , 16 of the liquid leakage sensor 10 , as a liquid sensing signal of the liquid leakage sensor 10. Then, for example , the leakage detector 18 performs a notifying action such as an alarm generation.

[0027] In embodiments of the liquid leakage sensor 10 having the above structure , for example , a pair of conductive wires 14 , 16 which function as electrodes , the polarities of which are different from each other, are respectively wound on the surface 12a of the core member 12. Therefore , the minimum distance between the conductive wires 14 , 16 , measured along the surface 12a, may be defined by a distance along the circumferential direction of the core member 12. Accordingly, for example, when the thickness of the core member 12 is relatively thin (e . g . several mm) , the minimum interval of both the conductive wires 14 , 16 can be relatively thin (e . g . several mm) . Accordingly, for example , it is possible to obtain a highly sensitive liquid leakage sensor 10 capable of detecting a relatively small quantity of liquid .

[0028] On the other hand, for example , when a very small quantity of liquid such as dew concentration water, which is not the leaking or submerging water, exists on a face on which the liquid leakage sensor 10 is laid, an interval of both the conductive wires 14 , 16 for sensing the liquid is a distance in the longitudinal direction of the core member 12 , irrespective of the thickness of the core member 12. When the pair of conductive wires 14 , 16 are arranged being separate from each other in the longitudinal direction of the core member 12 , for example, by 10 mm, it becomes difficult to sense a very small quantity of liquid such as dew concentration water generated on the face on which the liquid leakage sensor is laid. As a result , for example , it becomes possible to obtain a liquid leakage sensor 10 in which the erroneous operation is seldom caused .

[0029] Further, embodiments of the structure of this liquid leakage sensor 10 can include a plurality of conductive wires 14 , 16 that are only wound around the electrically insulating core member 12. Therefore, for example, when the liquid leakage sensor 10 is recovered to the initial state after leaking water has been sensed, the liquid attaching to the core member 12 and conductive wires 14 , 16 can be easily and quickly removed . As described above, for example , the liquid leakage sensor 10 is highly sensitive and further it is possible to prevent the occurrence of erroneous operation cause'd by a very small quantity of liquid which is not the leaking or submerging water . Furthermore , the attaching liquid can be very easily removed at the time of recovery .

[0030] In the above liquid leakage sensor 10 , for example, from the viewpoint of making the recovery work easy, it is advantageous that the core member 12 is made of insulating resin, the coefficient of water absorption of which is low, such as polyvinyl chloride . For example, the conductive wires 14 , 16 can be made of a good conductor, the anti-corrosion property of which is high, such as stainless steel . In order to ensure the mechanical strength and make it easy to handle the conductive wires , the conductive wires can be composed of stranded wires . Further, for example, the core member 12 and the conductive wires 14 , 16 can be flexible so that they can be freely curved and laid on various faces on which the liquid leakage sensor 10 is laid .

[0031] As shown in Fig . 2 , for example, the core member 12 can include a pair of grooves 20 , 22 individually, helically formed on the surface 12a of the core member 12 , and each of the pair of conductive wires 14 , 16 , for example , can be received in each of the grooves 20 , 22 being fixed into it . Due to the above structure, when each groove 20 , 22 is previously formed into a helical shape corresponding to the shape required for each conductive wire 14 , 16 so that the conductive wire can be used as an electrode , both the conductive wires 14 , 16 can be easily arranged into a predetermined helical winding form along the surface 12a of the core member 12. In this connection, for example , this liquid leakage sensor 10 can be made by an extrusion forming machine in such a manner that the material of the core member 12 and the pair of conductive wires 14 , 16 are simultaneously inserted into an extrusion die and appropriately twisted.

[0032] As shown in Fig . 1 , for example , it is advantageous that the pair of conductive wires 14 , 16 respectively have the exposed surface parts 14a, 16a continuously exposed on the surface 12a of the core member 12 over substantially the entire length of a predetermined sensing region ( i . e . , a predetermined length area) of the liquid leakage sensor 10. According to the structure of this embodiment , a local existence of liquid can be sensed at any position in the sensing region of the liquid leakage sensor 10. Further, since the liquid is attached to the core member surface 12a while the liquid bridging the pair of conductive wires 14 , 16 is automatically spreading along both the conductive wires 14 , 16 by the action of surface tension, an electric current easily flows in the liquid . Accordingly, for example, even pure water, the resistance of which is relatively high, can be positively sensed. In this case , for example, it is preferable that about 50% of the surfaces of the conductive wires 14 , 16 in the cross section shown in Fig . 2 are exposed surface parts 14a, 16a (of course , any desired amount of exposure more or less than 50% may be used) .

[0033] As shown in Fig . 1 , for example, it is advantageous that the pair of conductive wires 14 , 16 are arranged on the surface 12a of the core member 12 at regular intervals , over substantially the entire length of the predetermined sensing region of the liquid leakage sensor 10. According to the structure of this embodiment , it is possible to ensure a substantially uniform sensitivity in the sensing region of the liquid leakage sensor 10. When the winding pitch P ( shown in Fig . 1) of one conductive wire 14 (16 ) is set in the range of , for example, about 10 mm < P < 100 mm, preferably in the range of about 20 ram < P < 50 mm, and when the pair of conductive wires 14 , 16 are arranged on the opposite side (A difference in the phase is 180°) to each other on the core member surface 12a, the pair of conductive wires 14 , 16 can be arranged at regular intervals as described above . In this case, when the winding pitch P of each conductive wire 14 , 16 is shorter than 10 mm, there is a tendency that the sensitivity becomes too high and the erroneous operation is caused by dew concentration water . When the winding pitch P of each conductive wire 14 , 16 exceeds 100 mm, the sensitivity- becomes too low, and it becomes impossible to meet the demand of ensuring the high sensitivity . In the liquid leakage sensor 10 , when the winding pitch P of each conductive wire 14 , 16 is appropriately determined in the above range , the sensitivity can be easily adjusted .

[0034] The surface 12a of the core member 12 can be substantially cylindrical, for example, as shown in Fig . 2. According to the structure of this embodiment, each conductive wire 14 , 16 can be easily, accurately wound on the core member surface 12a into a helical shape . However, the surface 12a of the core member 12 may not be limited to the above specific structure . In the cross section shown in Fig . 2 , for example, it is possible to adopt various shapes of the surface 12a of the core member 12 such as an ellipse , polygon and so forth. In this connection, in the case of forming the core member 12 by means of extrusion, as described before, when the pair of conductive wires 14 , 16 are wound on the core member surface 12a before the core member 12 is solidified, the conductive wires 14 , 16 can be fixed to the core member 12 in accordance with the solidification of the core member 12. Alternatively, the conductive wires 14 , 16 can be fixed into the grooves 20 , 22 of the core member 12 by adhesive .

[0035] Figs . 3 and 4 are views showing a liquid leakage sensor 30 of another embodiment of the present invention. The liquid leakage sensor 30 is composed in such a manner that an appropriate net member 32 is added to the liquid leakage sensor 10 described before . Other points of the structure of the liquid leakage sensor 30 can be substantially the same as those of the liquid leakage sensor 10. Therefore , like reference characters are used to indicate like parts and the explanations are omitted here . [0036] The liquid leakage sensor 30 can further include , for example , an electrically insulating net member 32 having a liquid passing property which is arranged while covering the net member 32. The net member 32 is arranged at least in a predetermined sensing region of the liquid leakage sensor 30 in such a manner that the net member 32 covers the pair of conductive wires 14 , 16 over the entire length from the outside . Due to this structure , the liquid leakage sensor 30 can be directly laid on a conductive surface of a pipe as it is .

[0037] The density of the net member 32 of the liquid leakage sensor 30 is low, for example, the mesh of the net member 32 is rough, so that the liquid leakage sensor 30 can not exhibit a water holding function by itself . The reason why is that the sensitivity of the liquid leakage sensor 10 is sufficiently high even when the liquid leakage sensor 10 has no net member 32 and no contribution of the net member 32 to the sensitivity is required. As a result , although the liquid leakage sensor 30 includes the net member 32 , the erroneous operation of the liquid leakage sensor 30 can be prevented in the same manner as the liquid leakage sensor 10 , and the liquid can be very easily removed at the time of the recovery work .

[0038] It is advantageous that the net member 32 is made of insulating resin material , the coefficient of water absorption of which is low and the mechanical strength of which is high, such as polypropylene , polyethylene terephthalate and polyester . Due to the foregoing, the net member 32 can exhibit an auxiliary fixing function of fixing the pair of conductive wires 14 , 16 onto the surface 12a of the core member 12 and also exhibit a mechanically protecting function of protecting both the conductive wires 14 , 16. [0039] The net member 32 may, for example , include a plurality of fibrous elements 34 which are individually wound round the pair of conductive wires 14 , 16 along the surface 12a of the core member 12. In the embodiment shown in the drawing, when eight fibrous elements 34 which are individually wound along the surface 12a of the core member 12 , the net member 32 is composed. More specifically, four counterclockwise fibrous elements 34a and four clockwise fibrous elements 34b (shown in Fig . 4) are arranged on the core member surface 12a over the entire length at regular intervals at least in a predetermined sensing region of the liquid leakage sensor 30. Due to the foregoing, the net member 32 , the density of which is uniform in the entire body, can be composed. When the winding pitch of one fibrous element 34a (34b) is set in the range from abo.ut 10 mm to 100 mm, preferably in the range from, for example, about 20 mm to 50 mm which is the same as the winding pitch P of the leakage wires 14 , 16 described before , the net member 32 , the density of which is sufficiently high to exhibit the operational effect described before , can be relatively easily obtained . In this connection, the diameter of the fibrous element 34 can be 0.1 mm to 0.6 mm.

[0041] The liquid sensing capacity of the above liquid leakage sensor 30 was measured for city water, the electric conductivity of which was 140 μS/cm, and pure water, the electric conductivity of which was 0.7 μS/cm. In the experiment , the liquid leakage sensor 30 was laid on an acrylic board. While a pulse voltage of DC 9V was being impressed upon between a pair of conductive wires 14 , 16 , town water and pure water were directly dripped from a syringe to the liquid leakage sensor 30 , and a change in the resistance of the detection circuit was measured . As a comparative example , the same experiments were made for the conventional low sensitivity type liquid leakage sensor (B- 3P manufactured by 3M Corporation) and the conventional high sensitivity type liquid leakage sensor (S-IF manufactured by 3M Corporation) .

[0042] As a result of the experiments , with respect to town water, the liquid leakage sensor 30 generated no sensing signals when a quantity of dripping liquid was not more than 1 milliliter, that is , the liquid leakage sensor 30 showed the same stable sensitivity as that of the conventional low sensitivity type liquid leakage sensor (B- 3P) so that the erroneous operation could be seldom caused . In the case of the conventional high sensitivity type liquid leakage sensor (S-IF) , the above small quantity of town water was sensed . Accordingly, there was a possibility that the erroneous operation was caused by dew concentration water . With respect to pure water, the liquid leakage sensor 30 generates a sensing signal when a quantity of dripping liquid exceeded 4 milliliter, that is , the same excellent sensitivity as that of the conventional high sensitivity type liquid leakage sensor (S-IF) was shown . It was difficult for the conventional low sensitivity type liquid leakage sensor (B-3P) to sense the existence of pure water irrespective of a quantity of the pure water . Further, in the case of the liquid leakage sensor 30 , it was easy to wipe off the attached liquid . Therefore , it was proved that the liquid leakage sensor 30 could be easily recovered to the initial state .

[0043] It should be noted that the present invention is not limited to the above specific embodiments shown in the drawings , and variations may be made by those skilled in that art without departing from the scope of the claim of the invention. For example , the number of the conductive wires to be used as the electrodes of the liquid leakage sensor is not limited to the pair of conductive wires . It is possible to adopt the structure in which three or more conductive wires are provided. In this case , for example, one conductive wire can be used for specifying a position of leakage in the sensing region of the liquid leakage sensor .

Claims

That Claimed is :

1. A liquid leakage sensor including a plurality of electrodes spaced from each other and sensing an electrical conduction between the electrodes as an existence of liquid, the liquid leakage sensor comprising : a linear core member having an electrical insulation property; and a plurality of conductive wires individually positioned on a surface of said core member in a helical fashion and arranged to be spaced from each other on said surface, said conductive wires respectively functioning as said electrodes .

2. A liquid leakage sensor according to claim 1 , wherein said core member includes a plurality of grooves individually recessed along said surface in a helical fashion, each of said plurality of conductive wires being fixedly received in each of said grooves .

3. A liquid leakage sensor according to claim 1 or 2 , wherein each of said plurality of conductive wires includes an exposed surface part continuously exposed on said surface of said core member over substantially an entire length of a predetermined sensing region.

4. A liquid leakage sensor according to any one of claims 1 to 3 , wherein said plurality of conductive wires are evenly spaced on said surface of said core member over substantially entire lengths of a predetermined sensing region.

5. A liquid leakage sensor according to any one of claims

1 to 4 , wherein said surface of said core member comprises a substantially cylindrical surface .

6. A liquid leakage sensor according to any one of claims 1 to 5 , further comprising a net member having an electrical insulation property and a liquid permeability, said net member being arranged to cover said core member and said plurality of conductive wires .

7. A liquid leakage sensor according to claim 6 , wherein said net member comprises a plurality of fibrous elements individually wound along said surface of said core member to surround said plurality of conductive wires .