Method and apparatus for detecting and distinguishing leaks using reflectometry and conductivity tests

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now the drawing, with particular attention to FIG.
1, there is illustrated a preferred embodiment of the system for detecting the presence of fluids and distinguishing between conductive and non-conductive fluids according to the invention generally designated by the reference numeral 8.
The system according to the invention preferably utilizes a fluid detecting cable 10 having a pair of conductors 14 and 46 and a pair of outer conductors 20 and 40 forming a shield.
One of the central conductors 14 is insulated, while the conductor 46 is not.
Also, one of the outer conductor 40 is not insulated while the others are.
A specific embodiment of the cable 10 will be discussed in conjunction with FIG.
2 below.
An isolation circuit 31 is connected to a pair insulated conductors 14 and 20 of the cable 10 and couples pulses from a time domain reflectometry (TDR) leak detector 32 to the insulated conductors of the cable 10 and returns reflections from the cable 10 to the time domain reflectometry leak detector 32.
An example of a time domain reflectometry leak detector particularly useable with the present invention is the one disclosed in the previously mentioned U.
S.
Pat.
No.
4,797,621, incorporated herein by reference.
A resistance measuring device 34 is connected to a pair of uninsulated wires 40 and 46 inside the cable 10.
The resistance measuring device 34 measures the resistance between the uninsulated wires 40 and 46 upon receiving an appropriate signal from a control and memory circuit 36.
The control and memory circuit receives signals from the resistance measuring circuit 34 and from the TDR leak detector 32 and stores the results in a memory as reference values and for display on a display 38 when a leak is detected.
Normally, the reference resistance between the conductors will be relatively high for a dry cable.
Also, although FIG.
1 shows four separate wires connected to the resistance measuring circuitry and the TDR circuitry, in practice, the conductors 14 and 16 and the conductors 20 and 40 would most likely be connected together at the connector connecting the cable 10 to the measurement circuitry and the cable switched between the TDR circuitry and the resistance measuring circuitry depending on the measurement desired