Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Patent
1995-10-17
1998-05-19
Snow, Walter E.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
324 67, G01V 311, G01V 3165, G01R 1900, H04B 102
Patent
active
057540497
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to apparatus for, and a method of, locating buried conductors or other sources of varying magnetic flux. It is particularly concerned with finding buried long conductors where there may be several close together.
BACKGROUND ART
It is known that long metal lines buried in the ground (pipes and cables) are cut by alternating magnetic fluxes, from various sources, and that electric currents consequently flow in them. It is also known that their positions may be found by detecting where general, uniformly-distributed fluxes (originating from distant sources) are disturbed by the conductors' nearby subsequent fluxes, and may easily be distinguished from them by antenna arrangements that are only sensitive to local flux variation. But where there are several local sources of flux these arrangements eliminate only the general flux and respond to the sum of the local fluxes.
Known systems make use of the fact that the signal output of a coil in response to the currents flowing in a nearby long, straight conductor is proportional to the reciprocal of the distance between the closest points on their axes, and the cosine of the angle between their axes. Thus the sign, or phase, of the induced flux changes as that angle changes between <90 to >90 degrees.
All reported existing systems except that of GB-A-1,509,380 need the detecting instrument to be traversed (i.e. moved from one side of the conductor to the other) so it can find a maximum (or minimum) resultant flux intensity to determine a conductor's position. This may be measured at a single frequency using a tuned receiver, or at many frequencies using a "wide-band" receiver. That is; the detector's operator decides the position of maximum (or, with coils of vertical axis, minimum) received energy. With either horizontally or vertically oriented coil axes, the instrument detects the coils' rapidly alternating voltage amplitude levels, over very many cycles, varying as they traverse regions of changing alternating magnetic flux. These are then rectified to drive a DC component through a meter or sound-producing transducer.
GB-A-1,509,380 discloses the detection of buried conductors by means of an array of three (or more) vertically extending aerial coils whose axes define the corners of a polygon on the ground. A buried conductor carrying an alternating current induces signals in the coils some of which are of different phases if the conductor is beneath the polygon. FIG. 1 shows such an apparatus, having a yes
o meter 4 for indicating coil phase differences coupled to three coil aerials 1, 2, 3 mounted vertically to define a triangle 5 by means of a support structure having telescopic legs.
It is also known that where two buried conductors carrying currents of similar spectral content lie near to each other, their combined fluxes somewhat resemble that of a single conductor lying between them. Thus a false result is shown by an existing type of instrument using either a vertically or horizontally oriented axis coil array.
DISCLOSURE OF THE INVENTION
I have now appreciated that it will generally be the case that each conductor carries spectral components that are dissimilar to those of the others, and that tuning to those discrete components will enable a detector to discriminate between the two conductors.
But such disparate spectral components may be very small in amplitude compared with other components common to both conductors, so seeking to discriminate them using wide-band detectors may fail. Use of narrow-band detectors may also fail, since the different frequencies of the currents will not be known.
Usually, a buried elongate conductor is subject to alternating magnetic fluxes of many frequencies along its length. A plurality of conductors are unlikely to be uniformly oriented throughout their lengths. Thus they will not pick up signals of equal amplitudes and frequencies from the widespread sources of radio and other energies; nor will they always pass equally closely to local sources of alterna
REFERENCES:
patent: 5361029 (1994-11-01), Rider et al.
LandOfFree
Method and apparatus for locating buried conductors in the prese does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for locating buried conductors in the prese, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for locating buried conductors in the prese will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1856154