Method of and apparatus for tracing faults in electrical conductors
First Claim
1. A method of tracing faults in an at least partially hidden or inaccessible electrical conductor, whose path is known or which can be assumed, comprising generating first and second low frequency phase coherent electromagnetic signals and a high frequency electromagnetic signal, modulating the high frequency signal by the second low frequency signal, additively coupling the modulated high frequency signal and the first low frequency signal to the conductor, traversing an electromagnetic signal receiver over the assumed or known path of the conductor, separately detecting from the receiver the low and high frequencies, deriving from the received high frequencies the second low frequency modulation of the high frequency signal and deriving from the received low frequencies a first low frequency gradient signal, comparing the second low frequency with the gradient signal and repeating such comparison at different positions of the traverse, substantial changes in result indicating the location of a fault.
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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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Citations
13 Claims
- 1. A method of tracing faults in an at least partially hidden or inaccessible electrical conductor, whose path is known or which can be assumed, comprising generating first and second low frequency phase coherent electromagnetic signals and a high frequency electromagnetic signal, modulating the high frequency signal by the second low frequency signal, additively coupling the modulated high frequency signal and the first low frequency signal to the conductor, traversing an electromagnetic signal receiver over the assumed or known path of the conductor, separately detecting from the receiver the low and high frequencies, deriving from the received high frequencies the second low frequency modulation of the high frequency signal and deriving from the received low frequencies a first low frequency gradient signal, comparing the second low frequency with the gradient signal and repeating such comparison at different positions of the traverse, substantial changes in result indicating the location of a fault.
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9. Apparatus for tracing faults in an at least partially hidden or inaccessible electrical conductor, whose path is known or which can be assumed, comprising means for generating first and second low frequency phase coherent electromagnetic signals and a high frequency signal, means for modulating the high frequency signal by the second low frequency signal, and means for additively coupling the modulated high frequency signal and the first low frequency signal to the conductor;
- and further comprising a receiver traversable over the assumed or known path of the conductor, the receiver including means for separately detecting the low and high frequencies, means for demodulating the high frequency to obtain the second low frequency, means for producing a first low frequency gradient signal, means for comparing the second low frequency with the gradient signal, and means for indicating the result of that comparison.
- View Dependent Claims (10, 11, 12, 13)
Specification