Method of and apparatus for tracing faults in electrical conductors
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United States of America Patent
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-
Jan 23, 1990
Grant Date -
N/A
app pub date -
Oct 24, 1988
filing date -
Oct 24, 1987
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A high frequency and two low frequency electromagnetic signals are generated (1), the low ones being coherent with the second being a sub-harmonic of the first. The high frequency is modulated (4) by the second low frequency and applied (7,9) as a composite signal to an underground conductor, while the first low frequency is applied (9,10) additively. A receiver traversed over the line has aerials (12,21) or ground probes (24,25) for picking up these signals in separate channels. The high frequency is demodulated (18) to provide a reference signal for a synchronous detector (20) to which the first low frequency is fed. That suffers a phase reversal if there is a fault, and the output of the synchronous detector is arranged to indicate that.
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