Ground piercing metal detector method for detecting the location of a buried metal object

• US 20020017904A1
• Filed: 09/06/2001
• Published: 02/14/2002
• Est. Priority Date: 08/04/1999
• Status: Active Grant

• Current Assignee: Ellen Ott, James H. Ott
• Original Assignee: Ellen Ott, James H. Ott
• Inventors: Ott, Ellen, Ott, James H.
• Granted Patent: US 6,452,397 B2
• Time in Patent Office: Days
• US Class Current: 324/327
• CPC Class Codes: G01V 3/15 specially adapted for use during transport, e.g. by a person, vehicle or boat

Abstract

A hand tool has a handgrip attached to a groundpiercing probe, which is manually insertable in the soil. The probe has a chamber in which at least one inductor is positioned and connected to metal detection circuitry. The preferred circuitry has a pulse generator applying current pulses to an inductor for inducing eddy currents in a buried target object. After the pulse terminates, the decaying coil voltage is sampled at different times to detect both the presence and range of the object, as well as the type of metal in the object. An asymmetric magnetic field pattern about the probe is aligned with a direction pointing indicium on the handgrip and provides directional sensitivity. The coil voltage samples are applied to signaling circuitry, which provides an audible signal which is a series of bursts of an audio tone. The pitch of the audio tone signals the presence, range and bearing of the buried metal object, while the pulse rate of the bursts signals the metal type.

Claims

1. An improved hand tool for detecting buried objects, the tool having a hand grip attached to a ground piercing probe which is manually insertable into soil to displace the soil radially outwardly from the probe, wherein the improvement comprises:

the probe having a chamber and at least one inductor positioned in the chamber and connected to a metal detection circuit.

2. A tool in accordance with claim 1 wherein the inductor is asymmetrically shaped to provide a radially asymmetric field pattern about the probe, the field pattern having a major lobe to provide angular sensitivity.

3. A tool in accordance with claim 1 wherein the inductor is positioned radially asymmetrically in the chamber to provide a radially asymmetric field pattern about the probe, the field pattern having a major lobe to provide angular sensitivity.

4. A tool in accordance with claim 1 wherein the circuit is a pulse induction metal detection circuit.

5. A tool in accordance with claim 4 wherein the inductor is a coil having a ferrite core.

6. A tool in accordance with claim 5 wherein the ferrite core is asymmetric about a central axis of the coil for distorting a time changing magnetic field generated by the coil into a field pattern which is radially asymmetric about the probe, said pattern having a major lobe to provide angular sensitivity.

7. A tool in accordance with claim 1 or claim 2 or claim 3 wherein the circuit is an induction balance detection circuit.

8. A tool in accordance with claim 1 wherein the probe comprises a nonferromagnetic, high resistivity metal.

9. A tool in accordance with claim 8 wherein the probe is stainless steel.

10. A tool in accordance with claim 9 wherein the probe is #304 stainless steel.

11. A tool in accordance with claim 1 wherein a portion of the probe laterally adjacent the inductor is a dielectric material and a resistance is connected in shunt across the inductor.

12. A tool in accordance with claim 11 wherein the dielectric material is a ceramic.

13. A tool in accordance with claim 12 wherein the ceramic is a zirconia probe tip.

14. A tool in accordance with claim 11 wherein the dielectric material is a metal oxide.

15. A tool in accordance with claim 14 wherein the metal oxide is sapphire.

16. A tool in accordance with claim 11 wherein the dielectric material is a glass.

17. A tool in accordance with claim 1 wherein the hand grip extends in opposite directions from an end of the probe to provide a T-shaped hand tool.

18. A tool in accordance with claim 1 wherein length graduations are formed along the probe.

19. A tool in accordance with claim 1 wherein the metal detection circuit includes a wireless communication link including a transmitter mounted to the hand tool and a sound transducer connected to a receiver.

20. A tool in accordance with claim 1 and further comprising a ferromagnetic body mounted to the probe for distorting a time changing magnetic field generated by the inductor into a field pattern which is radially asymmetric about the probe, said pattern having a major lobe to provide angular sensitivity.

21. A tool in accordance with claim 20 wherein a direction pointing indicium is formed on the handgrip indicating the direction of said major lobe.

22. A tool in accordance with claim 1 wherein the circuit is a pulse induction metal detection circuit, the inductor is a coil having a ferrite core and the probe is stainless steel.

23. A tool in accordance with claim 1 wherein the circuit is a pulse induction metal detection circuit, the inductor is a coil having a ferrite core and the probe tip is titanium.

24. A tool in accordance with claim 1 wherein the circuit is a pulse induction metal detection circuit, the inductor is a coil having a ferrite core and a resistance connected in shunt across the coil and the probe laterally adjacent to the coil is a dielectric material.

25. A tool in accordance with claim 22 or 23 or 24 wherein the ferrite core is asymmetric about a central axis of the coil for distorting a time changing magnetic field generated by the coil into a field pattern which is radially asymmetric about the probe, said pattern having a major lobe to provide angular sensitivity.

26. A tool in accordance with claim 25 wherein a direction pointing indicium is formed on the handgrip indicating the direction of said major lobe.

27. A tool in accordance with claim 26 wherein the metal detection circuit includes a wireless communication link including a transmitter mounted to the hand tool and a sound transducer connected to a receiver.

28. A tool in accordance with claim 27 wherein length graduations are formed along the probe.

29. A tool in accordance with claim 28 wherein the hand grip extends in opposite directions from an end of the probe to provide a T-shaped hand tool.

30. A tool in accordance with claim 1 wherein the tool further comprises a double throw switch and a headset connector connected to an output of the switch, the switch having an input connected to said metal detection circuit and an input connected to a second connector for connection to a second, above ground metal detector, the switch alternatively connecting the headset to the hand tool metal detection circuit and the second metal detector.

31. A tool in accordance with claim 1 wherein the probe has a diameter less than ⅜

inch.

32. A tool in accordance with claim 31 wherein the coil has a diameter not exceeding substantially ¼

inch.

33. A hand tool in accordance with claim 1 and further comprising:

(a) an inductance detector connected to the inductor for detecting a signal which varies as a function of changes in the apparent inductance of the inductor; and

(b) a signaling circuit connected to the inductance detector for signaling the direction and magnitude of change in the apparent inductance of the inductor as the probe is moved.

35. A method in accordance with claim 34 wherein the magnetic field is generated from and the current is detected through the same coil, the coil being energized by a pulse and connected to a detector circuit.

36. A method in accordance with claim 34 further comprising generating said magnetic field asymmetrically about the longitudinal axis of the probe, the field having a major lobe to provide directional sensitivity, and wherein the probe is rotated about the axis to detect the angular direction of the target object.

37. A method in accordance with claim 36 further comprising vertically adjusting the probe position in the soil to a metal detecting signal maximum for detecting the depth of the target object and the probe is rotated to a signal maximum for detecting the angular direction of the target object.

38. A method in accordance with claim 34 wherein the magnetic field is generated by a first coil in the chamber and the eddy current in the target object is detected at a second coil in the chamber.

40. A metal detection circuit in accordance with claim 39 wherein the signaling circuit is a voltage controlled oscillator.

41. A metal detection circuit in accordance with claim 39 wherein the transmitting coil connected to the pulse generator and the receiving coil are the same coil.

42. A metal detection circuit in accordance with claim 39 wherein the damper is a resistance connected across the transmitting coil.

43. A metal detection circuit in accordance with claim 39 wherein the damper is a non-ferromagnetic, high resistivity probe having the coil mounted in a chamber formed in the probe.

44. A metal detection circuit in accordance with claim 39 wherein the sampling circuit includes a first timing circuit having an input connected to the pulse generator and having timing components for sampling within said time interval for detecting a metal type sample representing the type of metal in the metal target object and a second timing circuit having an input connected to the pulse generator and having timing components and a sampling circuit for sampling the signal after said time interval for detecting a range sample representing the range of the metal target object.

45. A metal detection circuit in accordance with claim 44 and further comprising a second signaling circuit connected to the sampling circuit for receiving the range sample and signaling variations in the range sample.

47. A method in accordance with claim 46 wherein the first sampling time is substantially at the time at which the induced coil current in the absence of a metal target object decays to a magnitude which is substantially equal to the magnitude to which the induced coil current decays in the presence of a jewelry gold alloy metal target object.

48. A method in accordance with claim 46 and further comprising alternating the first sampling time between a spaced time interval before and a spaced time interval after the time at which the induced coil current in the absence of a metal target object decays to a magnitude which is substantially equal to the magnitude to which the induced coil current decays in the presence of a jewelry gold alloy metal target object.

49. A method in accordance with claim 46 wherein each coil is mounted in a chamber formed in a ground piercing probe and the method further comprises plunging the probe a distance into the soil to displace the soil outwardly from the probe and position the chamber below the surface of the soil.

50. A method in accordance with claim 46 and further comprising detecting the current induced in the coil at a second sample time after the time interval and monitoring changes in the current detected at the second sample time.

51. A method in accordance with claim 50 and further comprising varying the frequency of an audio signal as a function of the magnitude of the samples taken at one of said sample times and alternately switching the audio signal on and off at a switching rate which is a function of the magnitude of the samples taken at the other of said sample times.

52. A method in accordance with claim 51 wherein the audio frequency is varied as an increasing function of the magnitude of the samples taken at said second sample time and the audio signal is switched on and off at a switching rate which is an increasing function of the magnitude of the samples taken at said first sampling time.

34. A method for detecting the location of a metal target object buried below the surface of a soil, the method comprising:

(a) plunging a probe, having a chamber, a distance into the soil to displace the soil outwardly from the probe and position the chamber below the surface of the soil;

(b) inducing eddy currents in the target object by generating a time changing magnetic field from a coil located in the chamber; and

(c) detecting the current induced in a coil in the chamber by the eddy currents.

39. A metal detection circuit for detecting the metal type of a metal target object, the circuit comprising:

(a) a pulse generator;

(b) a transmitting coil connected to the pulse generator for generating a time changing magnetic field in response to electrical pulses applied to the coil;

(c) a resistive energy damper coupled to a receiving coil for attenuating the energy in the magnetic field;

(d) a sampling and storing circuit connected to the receiving coil for sampling a signal representing the magnitude of the coil current at a sampling time within a time interval beginning after termination of a pulse and ending before the time at which inductor current in the presence of a high conductivity metal target object decays to a current which exceeds the current to which the inductor current decays in the absence of a metal target object; and

(e) a signaling circuit connected to the sampling and storing circuit for signaling changes in the detected coil current at the sampling time as the coil is moved.

46. A method for detecting the metal type of a metal target object buried below the surface of a soil, the method comprising:

(a) attempting to induce eddy currents in the target object by applying a current pulse to a coil magnetically coupled to a damping load;

(b) detecting current induced in a coil by the eddy currents at a first sampling time within a time interval beginning after termination of the current pulse and ending before the time at which the induced coil current in the presence of a high conductivity metal target object decays to a current which exceeds the current to which the induced coil current decays in the absence of a metal target object; and

(c) monitoring and signaling changes in the detected coil current as the probe is moved.

53. A method for detecting the metal type of a metal target object buried below the surface of a soil, the method comprising:

(a) attempting to induce eddy currents in the target object by generating a time changing magnetic field about an inductor spaced from the target object;

(b) detecting a signal which is a function of coil apparent inductance resulting from mutual coupling with the eddy currents; and

(c) signaling the direction and magnitude of change in the apparent inductance of the inductor as the probe is moved.