Method and apparatus for determining direction to and position of an underground conductor

• US 5,093,622 A
• Filed: 03/17/1989
• Issued: 03/03/1992
• Est. Priority Date: 03/17/1989
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Balkman, William D.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): EDMONDS, WARREN
• Application Number:
  US07/325,153
• Time in Patent Office: 1,082 Days
• Field of Search: 324/67, 324/326, 324/327, 324/328, 324/329, 324/243, 324/260-262, 324/226, 324/228, 324/234
• US Class Current: 324/326
• CPC Class Codes: G01V 3/06 using ac

Abstract

An apparatus for determining the direction to and position of a buried conductor carrying an AC signal. The apparatus employs a unique antenna unit having upper and lower sensors, each sensor having two orthogonal solenoid coils. The signals from these coils, which are representative of the magnetic flux therethrough, are processed to yield corresponding digital values. The numbers are combined in a novel formula to yield a value which has been empirically found to be indicative of lateral postion. An appropriate display is controlled by the microprocessor according to the sign and magnitude of the positional value.

Claims

1. An apparatus for determining the lateral direction to a current-carrying conductor, comprising:

first sensor means for generating first and second analog signals associated with magnetic flux proximate said first sensor means;

second sensor means in fixed spatial relationship to said first sensor means for generating third and fourth analog signals associated with magnetic flux proximate said second sensor means;

processor means for computing the difference of (a) the product of said first and fourth signals, and (b) the product of said second and third signals, said difference being indicative of the lateral position of the conductor; and

display means responsive to said difference for indicating lateral position of the conductor with respect to said first and second sensor means.

2. The apparatus of claim 1 wherein:

said first sensor means comprises first and second coils which generate said first and second analog signals, respectively; and

said second sensor means comprises third and fourth coils which generate said third and fourth analog signals, respectively.

3. The apparatus of claim 2 wherein:

said first and second coils are generally perpendicular to one another;

said third and fourth coils are generally perpendicular to one another; and

said second and fourth coils essentially lie on a common axis.

9. The apparatus of claim 2 wherein the current-carrying conductor is buried, further comprising means for determining the depth of the buried conductor.

4. The apparatus of claim 4 wherein said processor means includes:

multiplexer means for sequentially sampling said first, second, third and fourth analog signals;

filter/amplifier means connected to said multiplexer means for amplifying each of said analog signals;

converter means connected to said filter/amplifier means for transforming each of said analog signals into digital values; and

a microprocessor for receiving said digital values and computing said difference.

5. The apparatus of claim 4 wherein said filter/amplifier means comprises:

a bandpass filter; and

an automatic gain controlled amplifier.

6. The apparatus of claim 4 wherein said filter/amplifier means comprises dual conversion receiver means for outputting an amplified signal at a predetermined frequency regardless of the input frequency of said first, second, third and fourth analog signals.

7. The apparatus of claim 6 further comprising keyboard means for directing said microprocessor, said microprocessor regulating said dual conversion receiver means.

8. The apparatus of claim 7 further comprising audible signal means for indicating proximity of the conductor, said audible signal means being activated by said microprocessor when said difference is approximately zero.

10. An apparatus for determining the lateral direction to a buried conductor carrying an AC signal, comprising:

first and second orthogonally disposed coils for generating first and second analog signals representative of magnetic flux passing therethrough, said magnetic flux being associated with the AC signal;

third and fourth orthogonally disposed coils for generating third and fourth analog signals representative of magnetic flux passing therethrough, said third and fourth coils being in a fixed spatial relationship with said first and second coils, and said second and fourth coils further essentially having a common axis;

processor means for computing the difference of (a) the product of said first and fourth signals, and (b) the product of said second and third signals, said difference being indicative of the lateral position of the buried conductor when said common axis is essentially vertical; and

display means responsive to said processor means for indicating lateral position of the conductor based on the sign and magnitude of said difference.

11. The apparatus of claim 10 wherein said processor means comprises:

an analog multiplexer for sequentially sampling said first, second, third and fourth analog signals;

filter/amplifier means connected to said multiplexer for amplifying each of said analog signals;

an analog-to-digital converter connected to said filter/amplifier means for transforming each of said analog signals into digital values;

a microprocessor for receiving said digital values and computing said difference; and

power supply means for providing electricity to said microprocessor.

12. The apparatus of claim 11 wherein said filter/amplifier means comprises a dual conversion receiver for outputting an amplified signal at a predetermined frequency regardless of the input frequency of said first, second, third and fourth analog signals, and further comprising keyboard means for directing said microprocessor, said microprocessor regulating said dual conversion receiver and controlling the sampling time of said multiplexer.

13. The apparatus of claim 10 further comprising:

housing means for accommodating said processor means; and

sheath means for enclosing each of said coils, said sheath means being detachable from said housing means, and connected thereto by cable means.

14. The apparatus of claim 10 wherein said display means includes:

a left-right indicator responsive to said sign of said difference; and

a proximity indicator responsive to the reciprocal of said magnitude of said difference.

15. The apparatus of claim 10 further comprising audible signal means for indicating proximity of the conductor, said audible signal means being activated by said processor means when said difference is approximately zero.

16. The apparatus of claim 10 further comprising means for determining the depth of the buried conductor.

17. A locating apparatus for determining the lateral position of a conductor carrying an AC signal, the conductor being obscured by a surface, comprising:

first and second orthogonally disposed solenoid coils having ferrite cores for generating first and second analog signals whose amplitudes are proportional to the magnetic flux passing therethrough, said magnetic flux being associated with the AC signal;

third and fourth orthogonally disposed solenoid coils having ferrite cores for generating third and fourth analog signals whose amplitudes are proportional to the magnetic flux passing therethrough, said third and fourth coils being in a fixed spatial relationship with said first and second coils, and said second and fourth coils further essentially having a common axis;

an analog multiplexer connected to each of said solenoid coils for sequentially sampling said first, second, third and fourth analog signals;

a dual conversion receiver connected to said analog multiplexer for outputting amplified signals at a predetermined frequency regardless of the input frequency of said first, second, third and fourth analog signals;

an analog-to-digital converter connected to said dual conversion receiver for transforming said first, second, third and fourth analog signals into first, second, third and fourth digital values, corresponding to said amplitudes of said analog signals, respectively;

a microprocessor for receiving said digital values and computing the difference of (a) the product of said first and fourth digital values, and (b) the product of said second and third digital values, said difference being indicative of the lateral position of the conductor with respect to the obscuring surface when said common axis is essentially normal to the obscuring surface;

power supply means for providing electricity to said microprocessor;

keyboard means for directing said microprocessor, said microprocessor further regulating said dual conversion receiver and controlling the sampling time of said multiplexer;

display means responsive to said microprocessor for indicating lateral position of the conductor based on the sign and magnitude of said difference, said display means including;

a left-right indicator responsive to said sign of said difference; and

a proximity indicator responsive to the reciprocal of said magnitude of said difference;

a speaker connected to said microprocessor for indicating proximity of the conductor, said speaker being activated by said microprocessor when said difference is approximately zero;

a housing for accommodating said multiplexer, dual conversion receiver, analog-to-digital converter, microprocessor, power supply means, keyboard means, display means, and speaker; and

sheath means for enclosing each of said coils, said sheath means being detachable from said housing means, and connected thereto by cable means.

18. A method of determining the direction to and position of a buried conductor carrying an AC signal, comprising the steps of:

(a) positioning an antenna unit above the ground in the vicinity of the conductor, said antenna unit comprising;

first and second orthogonally disposed coils for generating first and second analog signals representative of magnetic flux passing therethrough, said magnetic flux being associated with the AC signal; and

third and fourth orthogonally disposed coils for generating third and fourth analog signals representative of magnetic flux passing therethrough, said third and fourth coils being located below said first and second coils, and said second and fourth coils further having a common, essentially vertical, axis;

(b) computing the difference of (i) the product of said first and fourth signals, and (ii) the product of said second and third signals, the sign and magnitude of said difference being indicative of the lateral position of the buried conductor common axis is essentially vertical; and

moving the antenna unit the lateral direction indicated by said sign of said difference, while repeating step (b), until said magnitude of said difference is approximately zero.

19. The method of claim 18 wherein said computing step is carried out by processor means, said computing step further comprising the sub-steps of:

sequentially sampling said first, second, third and fourth analog signals to yield four consecutive analog signals;

amplifying each of said consecutive analog signals;

converting each of said consecutive analog signals into consecutive digital values;

storing said consecutive digital values until four such values are stored, corresponding to said first, second, third and fourth analog signals; and

calculating said difference based on said consecutive digital values.

20. The method of claim 18 further comprising the steps of:

calculating the reciprocal value of said difference; and

displaying said reciprocal value on display means, thereby providing a numeric indicator of lateral proximity to the conductor.