Abstract: Detection of liquid leaks and other changes in variables is disclosed. The event causes two elongate conductors to become electrically connected at a location which is determined by the event, thus creating a system in which the connection point can be located by measuring the potential drop from one end of one of the conductors (called the locating member) to the connection point. The system comprises a balancing component so that its sensitivity is not dependent on the location of the event along an elongate path. A fixed current flows through the connection, so that the result is independent of the resistance of the connection. The locating member can be a continuous resistive wire, coated with a conductive polymer; such a locating member can form part of a sensor cable in which the elongate components of the circuit are in a wrapped configuration. Alternatively the locating member comprises a plurality of discrete resistors.

Abstract: An elongate sensor for detecting and locating presence of a liquid, e.g. water or a hydrocarbon. The sensor includes first and second elongate members which are spaced apart from each other and each of which is a metal conductor covered by a conductive polymer; a third, insulated elongate conductor; and an elongate insulating core. At least one of the elongate members is helically wrapped around the core. Presence of the liquid at any point along the length of the sensor causes the first and second members to be electrically connected at that point, creating a system in which the potential drop down one of the members can be measured and the location of the connection determined.