Detector for Calculating the Distortion of an Electromagnetic Field Produced by a Buried Current Carrying Conductor
First Claim
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1. A detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor, the detector comprising:
- a first antenna;
a second antenna having its axis parallel to an axis of the first antenna and spaced a distance s from the first antenna;
a third antenna having its 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 second 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.
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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.
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Citations
20 Claims
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1. A detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor, the detector comprising:
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a first antenna; a second antenna having its axis parallel to an axis of the first antenna and spaced a distance s from the first antenna; a third antenna having its 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 second 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.
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2. A detector as claimed in claim 1, wherein the magnetic fields at the first and second antennas and the magnetic fields at the second and third antennas are compared using the relationship:
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wherein BB is the electromagnetic field at the first antenna, BM is the electromagnetic field at the second antenna and BT is the electromagnetic field at the third antenna, wherein the first means for calculating the depth is arranged to calculate the depth d of said conductor below the first antenna using the relationship; wherein the second means for calculating the depth is arranged to calculate the depth d of said conductor below the first antenna using the relationship;
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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%.
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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.
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5. A detector as claimed in claim 4, further comprising means for amplifying the field strength signals.
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6. A detector as claimed in claim 5, further comprising:
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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.
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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.
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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.
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9. A method of calculating the distortion of an electromagnetic field produced by a buried current carrying conductor, the method comprising:
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providing a first antenna; providing a second antenna having its axis parallel to an axis of the first antenna and spaced a distance s from the first antenna; providing a third antenna having its 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; comparing magnetic fields at the first and second antennas to produce a first compared value; comparing magnetic fields at the second and third antennas to produce a second compared value; 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.
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10. A method as claimed in claim 9, wherein the magnetic fields at the first and second antennas and the magnetic fields at the second and third antennas are compared using the relationship:
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wherein BB is the electromagnetic field at the first antenna, BM is the electromagnetic field at the second antenna, and BT is the electromagnetic field at the third antenna, wherein the depth d of said conductor below the first antenna is first calculated using the relationship; wherein the depth d of said conductor below the first antenna is second calculated using the relationship;
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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%.
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12. A carrier medium carrying computer readable code for controlling a microprocessor to carry out the method of claim 9.
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13. A detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor, the detector comprising:
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a first antenna; a second antenna having its axis parallel to an axis of the first antenna and spaced a distance s from the first antenna; a third antenna having its 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 second 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.
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14. A detector as claimed in claim 13, wherein the magnetic fields at the first and second antennas and the magnetic fields at the second and third antennas are compared using the relationship:
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wherein BB is the electromagnetic field at the first antenna, BM is the electromagnetic field at the second antenna, and BT is the electromagnetic field at the third antenna, wherein the first depth d of said conductor below the first antenna is calculated using the relationship; wherein the second depth d of said conductor below the first antenna is calculated using the relationship;
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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%.
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16. A detector as claimed in claim 13, wherein each antenna outputs a field strength signal representative of the electromagnetic field at the antenna.
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17. A detector as claimed in claim 16, further comprising amplifiers arranged to amplify the field strength signals.
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18. A detector as claimed in claim 17, further comprising:
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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.
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19. A detector as claimed in claim 18, wherein the analogue to digital converter is a delta-sigma stereo CODEC.
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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.
Specification