Detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor

• US 8,566,043 B2
• Filed: 03/02/2009
• Issued: 10/22/2013
• Est. Priority Date: 03/03/2008
• Status: Active Grant

• Current Assignee: Radiodetection Limited
• Original Assignee: Radiodetection Limited
• Inventors: Royle, John Mark, Pearson, Richard David
• Primary Examiner(s): Thompson, Timothy
• Assistant Examiner(s): Alonzo Miller, Rhadames J
• Application Number:
  US12/396,413
• Publication Number:
  US 20100004880A1
• Time in Patent Office: 1,695 Days
• Field of Search: 702/57, 324/67, 324/326
• US Class Current: 702/57
• CPC Class Codes: G01V 3/081 the magnetic field is produced by the objects or geological structures characterised by the method of magnetic field measurement G01R33/00

Abstract

A detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor comprises three antennas B, M, T. Outputs of two pairs of antennas are compared and the depth of the buried conductor is calculated using two different methods. If there is a significant difference in the two calculated depths then it is deemed that the electromagnetic field produced by the buried current carrying conductor is significantly distorted by the material in which the conductor is buried.

Claims

1. A detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor, the detector comprising:

a first antenna having an axis;

a second antenna having an axis parallel to the axis of the first antenna and spaced a distance s from the first antenna;

a third antenna having an axis parallel to the axes of the first and second antennas and spaced a distance 2s from the first antenna and a distance s from the second antenna;

means for comparing magnetic fields at the first and second antennas to produce a first compared value;

means for comparing magnetic fields at the first and third antennas to produce a second compared value;

first means for calculating the depth of said buried conductor based on the first and second compared values;

second means for calculating the depth of said buried conductor based on the magnetic field at a pair of the first, second and third antennas; and

means for comparing the depth calculation of the first means for calculating depth and the second means for calculating depth to calculate the distortion of the electromagnetic field produced by said buried current carrying conductor.

2. A detector as claimed in claim 1, wherein the magnetic fields at the first and second antennas and the magnetic fields at the first and third antennas are compared using the relationship:

E

3. A detector as claimed in claim 2, further comprising means for alerting an operator when the distortion of the electromagnetic field produced by said buried current carrying conductor ≧

10%.

4. A detector as claimed in claim 1, wherein each antenna outputs an analogue field strength signal representative of the electromagnetic field at the antenna.

5. A detector as claimed in claim 4, further comprising means for amplifying the field strength signals.

6. A detector as claimed in claim 5, further comprising:

means for converting the analogue field strength signals into digital signals; and

means for processing the digital signals to isolate signals of predetermined frequency bands.

7. A detector as claimed in claim 6, wherein the means for converting the analogue field strength signals into digital signals is a delta-sigma stereo CODEC.

8. A detector as claimed in claim 1, wherein each pair of first and second antennas and second and third antennas is calibrated to an accuracy of at least 1 part in 600,000.

9. A microprocessor-based method of calculating the distortion of an electromagnetic field produced by a buried current carrying conductor, the method comprising:

comparing magnetic fields at a first antenna and a second antenna to produce a first compared value, the first antenna having an axis parallel to an axis of the second antenna and spaced a distance s from the second antenna;

comparing magnetic fields at the first antenna and a third antenna to produce a second compared value, the third antenna having an axis parallel to the axes of the first and second antennas and spaced a distance 2s from the first antenna and a distance s from the second antenna;

calculating the depth of said buried conductor based on the first and second compared values;

calculating the depth of said buried conductor based on the magnetic field at a pair of the first, second and third antennas; and

comparing results of the depth calculations and calculating the distortion of the electromagnetic field produced by said buried current carrying conductor.

10. A method as claimed in claim 9, wherein the magnetic fields at the first and second antennas and the magnetic fields at the first and third antennas are compared using the relationship:

11. A method as claimed in claim 10, further comprising alerting an operator when the distortion of the electromagnetic field produced by said buried current carrying conductor ≧

10%.

12. A non-transient carrier medium carrying computer readable code for controlling a microprocessor to carry out the method of claim 9.

13. A detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor, the detector comprising:

a first antenna having an axis;

a second antenna having an axis parallel to the axis of the first antenna and spaced a distance s from the first antenna;

a third antenna having an axis parallel to the axes of the first and second antennas and spaced a distance 2s from the first antenna and a distance s from the second antenna; and

a microprocessor, configured to;

compare magnetic fields at the first and second antennas to produce a first compared value;

compare magnetic fields at the first and third antennas to produce a second compared value;

calculate a first depth of said buried conductor based on the first and second compared values;

calculate a second depth of said buried conductor based on the magnetic field at a pair of the first, second and third antennas; and

compare the first and second depth calculations to calculate the distortion of the electromagnetic field produced by said buried current carrying conductor.

14. A detector as claimed in claim 13, wherein the magnetic fields at the first and second antennas and the magnetic fields at the first and third antennas are compared using the relationship:

15. A detector as claimed in claim 14, further comprising a user interface for alerting an operator when the distortion of the electromagnetic field produced by said buried current carrying conductor ≧

10%

16. A detector as claimed in claim 13, wherein each antenna outputs a field strength signal representative of the electromagnetic field at the antenna.

17. A detector as claimed in claim 16, further comprising amplifiers arranged to amplify the field strength signals.

18. A detector as claimed in claim 17, further comprising:

analogue to digital converters to convert the field strength signals into digital signals; and

a digital signal processor arranged to process the digital signals and to isolate signals of predetermined frequency bands.

19. A detector as claimed in claim 18, wherein the analogue to digital converter is a delta-sigma stereo CODEC.

20. A detector as claimed in claim 13, wherein each pair of first and second antennas and second and third antennas is calibrated to an accuracy of at least 1 part in 600,000.