Apparatus for and methods of electromagnetic surveying of elongated underground conductors
First Claim
1. Apparatus for surveying an underground pipeline or other elongated element which carries, or can be made to carry, AC, the pipeline or element then forming a conductor around which there is a substantially cylindrical electromagnetic field, the apparatus comprising a coil array including a first pair of axially parallel coils arrangeable, in use, one above the other with their axes horizontal and transverse to the conductor;
- a phase comparator and indicator circuit for distinguishing from the outputs of a selection of coils of said array (such outputs being related to their position and attitude and the electromagnetic field) on which side of the conductor the array lies, a depth correction circuit including means responsive to the combined output of the first pair of coils to provide a correction factor dependent on the depth of the conductor, and a variable gain amplifier whose inputs are the correction factor and the output of one of said first pair of coils, and whose output is that coil output modified by the correction factor in such manner that variations in depth alone of the conductor leaves said output substantially unaffected although it will change according to variations of the electromagnetic field, a discontinuity in that field as the apparatus is progressed along the element corresponding to a fault; and
indicator or recording means responsive to said variable gain amplifier output by which any such discontinuities can be determined.
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Accused Products
Abstract
Apparatus for detecting underground conductors carrying AC, such as cables or pipelines, has two receiver coils with horizontal axes one above the other, and other coils. By making phase comparisons from a selection of these the apparatus is located directly above the conductor. Then using the two horizontal coils there is derived a signal corresponding to the depth of the conductor, which can be visually indicated. Also, this depth signal, which is continuously available as the conductor is followed, is used to modify an output from one of the coils so that as the depth varies that output remains constant provided there are no discontinuities or faults in the cable.
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Citations
11 Claims
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1. Apparatus for surveying an underground pipeline or other elongated element which carries, or can be made to carry, AC, the pipeline or element then forming a conductor around which there is a substantially cylindrical electromagnetic field, the apparatus comprising a coil array including a first pair of axially parallel coils arrangeable, in use, one above the other with their axes horizontal and transverse to the conductor;
- a phase comparator and indicator circuit for distinguishing from the outputs of a selection of coils of said array (such outputs being related to their position and attitude and the electromagnetic field) on which side of the conductor the array lies, a depth correction circuit including means responsive to the combined output of the first pair of coils to provide a correction factor dependent on the depth of the conductor, and a variable gain amplifier whose inputs are the correction factor and the output of one of said first pair of coils, and whose output is that coil output modified by the correction factor in such manner that variations in depth alone of the conductor leaves said output substantially unaffected although it will change according to variations of the electromagnetic field, a discontinuity in that field as the apparatus is progressed along the element corresponding to a fault; and
indicator or recording means responsive to said variable gain amplifier output by which any such discontinuities can be determined. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- a phase comparator and indicator circuit for distinguishing from the outputs of a selection of coils of said array (such outputs being related to their position and attitude and the electromagnetic field) on which side of the conductor the array lies, a depth correction circuit including means responsive to the combined output of the first pair of coils to provide a correction factor dependent on the depth of the conductor, and a variable gain amplifier whose inputs are the correction factor and the output of one of said first pair of coils, and whose output is that coil output modified by the correction factor in such manner that variations in depth alone of the conductor leaves said output substantially unaffected although it will change according to variations of the electromagnetic field, a discontinuity in that field as the apparatus is progressed along the element corresponding to a fault; and
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10. A method of surveying an underground pipeline or other element which carries, or is made to carry, AC, the pipeline or element then forming a conductor around which there is a substantially cylindrical electromagnetic field, the method comprising the steps of:
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(a) traversing a coil array across the line of a suspected conductor, (b) comparing the phases of signals induced in a selection of coils to determine on which side of the conductor the array lies, (c) locating the array over the conductor, (d) deriving from the combined output of two axially parallel coils of the array, one above the other with their axes horizontal and transverse to the conductor, a signal directly related to the depth of the conductor, (e) employing this depth signal to modify an output of one of said two axially parallel coils in such manner that variations in depth alone of the conductor leaves said output substantially unaffected, although it will change according to variations of the electromagnetic field, a discontinuity in that field as the coils are progressed along the conductor corresponding to a fault, (f) indicating or recording the modified output, and (g) repeating steps (a) to (f) along the conductor. - View Dependent Claims (11)
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Specification