Method and apparatus for determining the presence of or absence of an underground body
First Claim
1. An instrument for determining the presence or absence of an underground body capable of radiating an electromagnetic field, such as a buried pipe or cable, comprising an array of at least three generally similarly oriented receiver antenna coils, means for mounting such coils so that their extended axes define the corners of a polygonal area on the ground, a receiver including means coupled to said coils for comparing the phases of signals produced in all the coils, and means coupled to said comparing means for giving a warning signal only when any two of the first-mentioned signals are in antiphase thereby to indicate that at least one pair of said extended axes are straddling an underground body.
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Accused Products
Abstract
An instrument for detecting the presence or absence of a buried pipe or cable employs three or more generally vertical coil aerials which define a triangular or polygonal area on the ground. The natural or induced electromagnetic radiation from any underground pipe or cable cutting that area gives rise to phase differences at the aerials which can be discriminated. The aerial array may be adjustable, and the discrimination may be direct or involve mixing the received signals. Facility for listening to various frequencies, perhaps simultaneously, can be provided.
25 Citations
13 Claims
- 1. An instrument for determining the presence or absence of an underground body capable of radiating an electromagnetic field, such as a buried pipe or cable, comprising an array of at least three generally similarly oriented receiver antenna coils, means for mounting such coils so that their extended axes define the corners of a polygonal area on the ground, a receiver including means coupled to said coils for comparing the phases of signals produced in all the coils, and means coupled to said comparing means for giving a warning signal only when any two of the first-mentioned signals are in antiphase thereby to indicate that at least one pair of said extended axes are straddling an underground body.
- 12. A method of determining the presence or absence of an underground body capable of radiating an electromagnetic field, such as a buried pipe or cable, comprising arranging at least three generally similarly oriented receiver antenna coils so that their extended axes define the corners of a polygonal area on the ground, comparing the phases of signals produced in all the coils, thereby to determine whether any two of said signals are in antiphase, and providing a warning signal only when any two first-mentioned said signals are in antiphase, representative of the presence of a said body directly below said polygonal area.
Specification