Methods and apparatus employing permanent magnets for marking, locating, tracing and identifying hidden objects such as burried fiber optic cables

• US 5,006,806 A
• Filed: 10/30/1989
• Issued: 04/09/1991
• Est. Priority Date: 03/15/1989
• Status: Expired due to Fees

• Current Assignee: Schonstedt Instrument Co. LLC (SPX Corporation)
• Original Assignee: Schonstedt Instrument Company
• Inventors: Rippingale, John B., Schonstedt, Erick O., Osman, Bradley L., Upton, Charles R.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US07/428,757
• Time in Patent Office: 526 Days
• Field of Search: 324/67, 324/200, 324/207.11, 324/207.22, 324/207.26, 324/226, 324/260, 324/326-329, 324/345, 116/209, 116/DIG. 14, 138/104, 138/133, 138/174, 138/177, 138/178, 174/37, 335/285, 335/303, 335/306, 405/157, 405/160, 405/175, 405/176, 350/96.1, 350/96.23, 180/167, 180/168, 340/905
• US Class Current: 324/326
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• CPC Class Codes: G02B 6/562 locatable, e.g. using magnetic means

Abstract

In order to locate, trace, and identify hidden elongated objects, such as buried fiber optic cables, the objects are provided with elongated permanent magnet identifier devices having magnetic fields that may be detected at a distance from the objects. In one embodiment the identifier device comprises an elongated strip magnetized in the direction of its width and formed into a long-pitch helix, producing a characteristic "magnetic field signature" that enhances detection and identification of the object, as by a portable gradiometer that is moved over the surface of the earth along a line generally parallel to the length of the object. This embodiment may provide a magnetic field that diminishes as the square of the distance from the identifier device (rather than the usual cube of the distance), thereby enabling detection at substantial distances. In a second embodiment distinctive magnetic field signatures are produced by arrays of spaced permanent magnets, the fields of which add and subtract to provide resultant magnetic fields with peaks and valleys along a line generally parallel to the length of the object.

Claims

1. A method of locating, tracing, and identifying a hidden elongated object, comprising providing on said object a series of permanent magnets, said series extending along the length of said object, said permanent magnets being constructed and disposed so that magnetic fields of successive magnets add or subtract so as to produce a resultant magnetic field having a predetermined magnetic field signature including a series of peaks and valleys at points along a line substantially parallel to the length of said object, said series of magnets including a plurality of pairs of successive magnets in which the magnets of each pair are constructed and disposed so that the magnetic fields thereof are additive to produce at a point along said line a peak or valley of greater magnitude than would be produced by the individual magnets of the pair;

and locating, tracing, and identifying said object by moving a magnet field detector along said line and producing an output from said detector corresponding to said peaks and valleys.

2. A method in accordance with claim 1, wherein the output produced from said detector is of the type having opposite polarity indications corresponding to said peaks and valleys, respectively.

3. A method in accordance with claim 1, wherein said magnets are constructed by incorporating magnetic material in said object and by magnetizing said material at spaced locations along the length of said object and in a direction to produce magnets having magnetic axes parallel to the length of said object.

4. A method in accordance with claim 3, wherein said magnetic material is incorporated in said object by dispersing said magnetic material within said object.

5. A method in accordance with claim 1, wherein after said object is provided with said series of permanent magnets, said object is buried under ground and wherein said magnetic field detector is moved along said line above ground.

6. A method in accordance with claim 5, wherein said magnets are spaced apart along said object a distance of the order of one to two times the depth at which said object is buried.

7. A method in accordance with claim 1, wherein said magnet field detector is a gradiometer that detects a component of said resultant magnetic field at different positions along said line.

8. In combination with an elongated non-magnetic object to be magnetically detected, a series of spaced permanent magnets on said object and extending along the length of said object, said magnets having magnetic axes parallel to the length of said object and being constructed and disposed so that magnetic fields of successive mangets add or subtract to produce a resultant magnetic field having a predetermined magnetic field signature including a series of peaks and valleys at points along a line substantially parallel to the length of said object, said series of permanent mangets including a plurality of pairs of successive magnets in which the magnets of each pair are constructed and disposed so that the magnetic fields thereof are additive to produce at a point along said line a peak or valley of greater magnitude than would be produced by the individual magnets of the pair, whereby a magnetic field detector moved along said line produces an output corresponding to said peaks and valleys in order to locate, trace and identify said object.

9. A combination in accordance with claim 8, wherein said series includes successive magnets that have the same polarity as well as successive magnets that have opposite polarities.

10. A combination in accordance with claim 8, wherein said object is tubular and said permanent magnets comprise tubular segments coaxial with said object.

11. A combination in accordance with claim 10, wherein said segments are supported on an inner or outer surface of said object.

12. A combination in accordance with claim 10, wherein said segments are incorporated into said object.

13. A combination in accordance with claim 8, wherein said magnets are constituted by magnetic material in said object that is magnetized at spaced locations along the length of said object.

14. A combination in accordance with claim 13, wherein said magnetic material is dispersed within said object.

15. A method of locating, tracing, and identifying a plurality of hidden elongated objects comprising providing on each of said objects a corresponding series of permanent magnets extending along the length of the object, the permanent magnets of each series being constructed and disposed so that magnetic fields of successive mangets add or subtract to produce a resultant magnetic field having a predetermined magnetic field signature including a series of peaks and valleys at points along a line substantially parallel to the length of the object, said series of magnets including a plurality of pairs of successive magnets in which the magnets of each pair are constructed and disposed so that the magnetic fields thereof are additive to produce at a point along said line a peak or valley of greater magnitude than would be produced by the individual magnets of the pair, each series of permanent magnets differing from each of the other series so that the magnetic field signature of each series differs from the magnetic field signature of each of the other series;

and moving a magnetic field detector along each of said lines and producing an output from said detector corresponding to said peaks and valleys.