Abstract: A system for tracing routes of conductors is disclosed. An alternating signal is applied to the object to be traced (12), and the field produced by this signal is detected remotely from the object. In order to distinguish between signals produced by the object being traced and those produced by nearby conductors (14) due to capacitive coupling, the alternating signal has first and second components, related in frequency and phase, and the field is detected at a plurality of positions. The phase relationship of the detected signals is investigated to determine unambiguously the position of the object concerned. In one embodiment, the second frequency component is a harmonic of the other. In another embodiment the frequency of the second component is the frequency of the first, plus or minus a sub-harmonic of the first.

Abstract: In order to detect if there is a fault in a cable (6), three signals are applied to the cable (6) by a suitable transmitter (FIG. 1). Two of the signals are of high frequency and the other signal is of low frequency equal to an integer multiple of the difference between the frequencies of the high frequency signals. Aerials (10a, 10b) of a receiver (FIG. 2) detect the high frequency signals and the receiver processes those high frequency signals to determine a frequency signal. This is then compared in a comparison circuit (31) with the low frequency signal detected by ground probes (22,23) of the receiver (FIG. 2). At a fault in the cable (6), e.g. where the outer insulation is damaged, the conductor of the cable (6) is shorted to ground and this causes a change in a phase between the signals. Thus by moving the receiver along the cable (6), there will be a change in place at or adjacent the fault which will be detected by the receiver (FIG. 2) allowing the fault to be located.