SENSORCABLE

Abstract: An elongate cable, that may be employed as a sensor, for example of moisture, comprises two conductive polymer coated conductors (12, 14), for sensing, an insulating member (16) which comprises two water impermeable films which are bonded to each other at the centre and which physically separate the conductors (12, 14), and a support member (18) bonded to one of the films. The cable construction provides quick restoration of the sensor to an operating condition after sensing an occurrence.

Description: Description Cable That May Be Employed As A Sensor This invention relates to the detection of leaks from liquid-containing members. It is known, in order to detect leaks from a liquid-containing member, e.g a pipe or a storage container, to make use of an elongate sensor which is secured to the exterior of the member and which undergoes a detectable change when it is contacted by the liquid. The sensor can be capable of undergoing the change at any point along its length or only at selected points. Particularly useful systems for detecting and locating leaks are described in European Patent Publication Nos. 84304502.2, 84308260.3 and 85302559.1. We have found that, in the use of such elongate sensors, false alarms may result from moisture or "nuisance" wetting of the sensor due to capillary action. At the same time, it is desirable after a true alarm, to quickly and conveniently "clear" the sensor of residual moisture or nuisance wetting so that the sensor can be restored to an original operating condition and the detection of leaks can begin anew. The present invention substantially mitigates the problems of false alarms due to moisture or nuisance wetting and assists in providing quick restoration of a sensor to its original operating condition, e.g. in less than 1 minute. In one aspect, the invention provides a sensor cable for detecting the presence of an electrically conductive liquid, which cable comprises two elongate conductors, each conductor having an exposed surface which, when the cable is immersed in the liquid, is contacted by the liquid, and an insulating member which contacts each of the conductors and physically separates them in such a way that, when the cable is immersed in the liquid, the conductors become electrically connected by the liquid along a path which is not a straight line. In a second aspect, the invention provides a sensor cable for detecting the presence of an electrically conductive liquid, which cable comprises: two elongate conductors, each conductor having an exposed surface which, when the cable is immersed in the liquid, is contacted by the liquid, and a concave insulating member which contacts the conductors and physically separates them in such a way that the conductors become electri cally connected by the liquid when the concavity is filled. In a third aspect, the invention comprises a method for detecting the presence of an electrically conductive liquid, which method comprises the step of: placing a sensor cable in an environment which may contain the liquid, the cable comprising: two elongate conductors, each conductor having an exposed surface which, when the cable is immersed in the liquid, is contacted by the liquid, and an insulating member which contacts each of the conductors and physically separates them in such a way that the conductors become electrically connected by the liquid along a path which is not a straight line. In a fourth aspect, the invention comprises a method for detecting the presence of an electrically conductive liquid, which method comprises the step of: placing a sensor cable in an environment which may contain the liquid, the cable comprising: two elongate conductors, each conductor having an exposed surface which, when the cable is immersed in the liquid, is contacted by the liquid, and a concave insulating member which contacts the conductors and physically separates them in such a way that the conductors become electrically connected by the liquid when the concavity is filled. Preferably the conductors cannot be mutually wetted by capillary draw across the insulating member. In some embodiments the conductors are metal conductors coated with a conductive polymer. Preferably, the direction of the path leaving one electrode is at an angle of at least 300, preferably at least 900, especially at least 1600, to the direction of the path leaving the other electrode. The invention can be used to detect leaks from liquid-containing members e.g. a pipe or storage container which contains conductive liquid, for example, water. Accordingly, the insulating member preferably is composed of a water-impermeable film, for example, a polymeric film, e.g. a polyester film. The insulating member may comprise two polymeric films which are joined along a central portion and between which the conductors are sandwiched along respective edge portions. Preferably, in order to accommodate expansions and/or contractions of the cable, the insulating member may be provided with pockets, which pockets secure the conductors to the insulating member, the pockets comprising perforations for enabling the conductors to contact the liquid. The sensor cable can in addition comprise one or more insulated conductors so that it is suitable for use in the detection systems described in the European patent applications referenced above. Preferably, the insulated conductors are bonded to the insulating member, and preferably the conductors run substantially parallel to each other. The sensor cable can in addition comprise a support member. The support member can be of any material, but preferably it is composed of an organic polymer or some other insulator. The invention is illustrated in the accompanying drawing, in which Figure 1 is a schematic of a two conductor cable 10. The cable 10 includes conductive-polymer-coated-conductors 12 and 14, an insulating member 16 which comprises two waterimpermeable films which are bonded to each other at the center and which physically separate the conductors 12 and 14, and a support member 18 bonded to the film 16. Figure 2 is a schematic of a cable 20 that includes insulated conductors 22 and 24 and conductive-polymer-coated conductors 26 and 28. The four conductors are bonded to an insulating member 30 that comprises a water-impermeable film. In this arrangement, the conductors need be separated by no more than 5 mils. Figures 3A and 3B show alternative conductorinsulator configurations. In particular, Figure 3A shows conductors 32 and 34 that are located on opposite sides and ends of an insulating member 36, and Figure 3B shows conductors 38 and 40 that are located directly over each other, but on opposite sides of an insulating member 42. Figures 3C and 3D show perspective and plan views respectively of an insulating member 44 that is provided with pockets, which pockets secure conductors 46 and 48 to the insulating member 44. The pockets comprise perforations for enabling the conductors 46 and 48 to contact an electrically conductive liquid. Figure 3E shows a concave insulating member 50 which contacts conductors 52 and 54 and physically separates them in such a way that the conductors become electrically connected by the liquid when the concavity is filled.

Claims: Claims 1. A sensor cable for detecting the presence of an electrically conductive liquid, which comprises: two elongate conductors, each conductor having an exposed surface which, when the cable is immersed in the liquid, is contacted by the liquid, and an insulating member which contacts the conductors and physically separates them in such a way that, when the cable is immersed in the liquid, the conductors become electri cally connected by the liquid along a path which is not a straight line. 2. A cable according to claim 1, wherein the direction of the path leaving one electrode is at an angle of at least 300 to the direction of the path leaving the other electrode. 3. A sensor cable for detecting the presence of an electrically conductive liquid, which comprises: two elongate conductors, each conductor having an exposed surface which, when the cable is immersed in the liquid, is contacted by the liquid, and a concave insulating member which contacts the conductors and physically separates them in such a way that the conductors become electrically connected by the liquid when the concavity is filled. 4. A cable according to any one of the preceding claims, wherein, when the cable is removed from the liquid, the cable's original operating capability is restored within less than 1 minute. 5. A cable according to any one of the preceding claims, wherein the insulating member is composed of a water-impermeable film. 6. A cable according to any one of the preceding claims, wherein the insulating member comprises pockets which secure the conductors to the insulating member and which comprise perforations for enabling the conductors to contact the liquid. 7. A cable according to any one of the preceding claims, wherein each of the conductors comprises a metal conductor coated with a conductive polymer. 8. A method for detecting the presence of an electrically conductive liquid, which method comprises the step of: placing a sensor cable in an environment which may contain the liquid, the cable comprising: two elongate conductors, each conductor having an exposed surface which, when the cable is immersed in the liquid, is contacted by the liquid, and an insulating member which contacts each of the conductors and physically separates them in such a way that the conductors become electrically connected by the liquid along a path which is not a straight line. 9. A method for detecting the presence of an electrically conductive liquid, which method comprises the step of: placing a sensor cable in an environment which may contain the liquid, the cable comprising: two elongate conductors, each conductor having an exposed surface which, when the cable is immersed in the liquid, is contacted by the liquid, and a concave insulating member which contacts the conductors and physically separates them in such a way that the conductors become electrically connected by the liquid when the concavity is filled.

Inventors: HAUPTLY, PAUL D., MCCOY, KENNETH F.
Applicants: RAYCHEM CORPORATION (A DELAWARE CORPORATION)
Application year: 1986
Main classification: G01M3
IPC codes: G01N27, H01H35, G01M3