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Method and apparatus including spaced antennas for determining the trace and depth of underground metallic conductors

  • US 4,691,165 A
  • Filed: 03/09/1984
  • Issued: 09/01/1987
  • Est. Priority Date: 07/09/1982
  • Status: Expired due to Fees
First Claim
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1. A method for determining the horizontal position and depth of an underground metallic conductor in which there exists an alternating current of a basic frequency which generates a corresponding electromagnetic field having horizontal and vertical components, said method comprising:

  • (a) detecting the electromagnetic field by ferrite antennas at an upper and a lower level, at least one of which is rotatable in a vertical plane, wherein the ferrite antennas are inductive elements of first and second band pass filter circuits, respectively, the capacitance of such circuits being selected such that each of the circuits has a resonant frequency equal to the Nth upper harmonic of the basic frequency when a separate generator is not used to generate the alternating current in the conductor, and each of the circuits has a resonant frequency equal to the Mth upper harmonic of the basic frequency when a separate generator is used to generate the alternating current in the conductor, wherein (i) N is equal to (CP±

    1) or (2C±

    1), (ii) M is equal to CP or 2C, (iii) C is a properly selected integer greater than 1, (iv) P is 1, 2, 3, or 6, and (v) the product CP is an even number;

    (b) determining the horizontal position of the conductor from sensing the vertical component of the magnetic field at either one of the upper and the lower levels, sensing the horizontal component of the magnetic field at the other of the levels, and forming the ratio of the two sensed components; and

    (c) determining the depth of the conductor from sensing the horizontal component of the magnetic field at both the upper and lower levels.

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