Apparatus for locating buried conductors using phase-shifted signals
First Claim
1. An apparatus for detecting a test signal radiating from an obscured conductor carrying an alternating current, comprising:
- first means for sensing the test signal and creating a first electrical signal based thereon;
second means for sensing the test signal and creating a second electrical signal based thereon, said second sensing means being spatially displaced from said first sensing means, each of said first and second sensing means being parallel;
means for shifting the phase of said first electrical signal relative to said second electrical signal, resulting in a phase-shifted signal;
means for subtractively comparing said phase-shifted signal to said second electrical signal, yielding an electrical output signal; and
means for providing an indication of the amplitude of said output signal.
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Accused Products
Abstract
An apparatus for locating obscured conduits, such as buried cables, employs a novel signal processing technique to increase the sensitivity of the apparatus, particularly in congested areas. The cable locating apparatus is similar to prior art dual-peak detection devices which compare signals from two parallel induction coils, but a phase shift is introduced into one of the signals prior to the comparison. This phase shift serves to minimize the effects of side minima in the response curve of prior art dual-peak devices. This effect is enhanced by adding a gain mismatch to the two detected signals. The locator preferably operates with analog signals to reduce expense.
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Citations
18 Claims
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1. An apparatus for detecting a test signal radiating from an obscured conductor carrying an alternating current, comprising:
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first means for sensing the test signal and creating a first electrical signal based thereon; second means for sensing the test signal and creating a second electrical signal based thereon, said second sensing means being spatially displaced from said first sensing means, each of said first and second sensing means being parallel; means for shifting the phase of said first electrical signal relative to said second electrical signal, resulting in a phase-shifted signal; means for subtractively comparing said phase-shifted signal to said second electrical signal, yielding an electrical output signal; and means for providing an indication of the amplitude of said output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An apparatus for detecting a test signal radiating from an obscured conductor carrying an alternating current, the apparatus including first means for sensing the test signal and creating a first electrical signal based thereon, second means for sensing the test signal and creating a second electrical signal based thereon, said second sensing means being spatially displaced from said first sensing means, means for subtractively comparing said first and second signals, yielding an electrical output signal, and means for providing an indication of the amplitude of said output signal, wherein the improvement comprises:
means for shifting the phase of said first electrical signal relative to said second electrical signal. - View Dependent Claims (14, 15)
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16. A system for locating a buried or otherwise obscured conduit carrying an alternating current, comprising transmitter means for sending an alternating current along said conduit at a known frequency, and receiver means for detecting the electromagnetic signal, said receiving means including:
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a housing; a first induction coil having an axis, attached to said housing; a second induction coil having an axis, attached to said housing, said axes of said first and second coils being parallel; a first preamplifier connected to said first induction coil, having an output connected in series with a resistor imparting a change in the gain of a signal received by said first coil relative to the gain of a signal received by said second coil; a second preamplifier connected to said second induction coil, having an output; a variable gain amplifier having a first input connected to said series resistor, a second input connected to said output of said second preamplifier, and an output; a plurality of RC circuits each connected to said first input of said variable gain amplifier and each being switchably connected to ground, said RC circuits being tuned to shift the phase of signals at different frequencies, respectively; programmable bandpass filter means for selectively passing a signal at said different frequencies, said bandpass filter having an input connected to said output of said variable gain amplifier, and having an output; logic means for selecting one of said different frequencies; keypad means for manually controlling said logic means; and means for providing an indication of the amplitude of an output signal at said output of said bandpass filter.
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17. A method of determining the location of an obscured conduit carrying an alternating current, comprising the steps of applying an alternating current along said conduit at a known frequency, and detecting the relative strength of the electromagnetic signal radiated along the path of the conduit by:
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obtaining first and second electrical signals, respectively, from first and second means for sensing the radiated electromagnetic signal; shifting the phase of said first signal relative to said second signal; subtractively comparing said first phase-shifted signal with said second signal, yielding an output signal; and examining the strength of the output signal. - View Dependent Claims (18)
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Specification