Magnetic locating and tracing system and method using dual-antenna transmitter to distinguish between concealed adjacent objects

• US 4,818,944 A
• Filed: 05/06/1987
• Issued: 04/04/1989
• Est. Priority Date: 05/06/1987
• Status: Expired due to Term

• Current Assignee: Schonstedt Instrument Company
• Original Assignee: Schonstedt Instrument Company
• Inventors: Rippingale, John B.
• Primary Examiner(s): Eizenzopf, Reinhard J.
• Assistant Examiner(s): Snow, Walter E.
• Application Number:
  US07/046,463
• Time in Patent Office: 699 Days
• Field of Search: 324/66, 324/67, 324/326-329
• US Class Current: 324/326
• CPC Class Codes: G01V 3/06 using ac

Abstract

Locating and tracing of a concealed, elongated, conductive object, such as a buried pipe or cable, is enhanced, when a second such object is adjacent to the first, by employing a transmitter having a pair of antennae that induce distinguishable currents in the respective objects. A receiver movable with respect to the transmitter and with respect to the objects produces an output signal dependent upon the sensing of fields associated with both currents. The position of the transmitter relative to the objects is adjusted to optimize the output signal.

Claims

1. A system for locating at least one of a pair of concealed, elongated, conductive, adjacent objects, comprising, in combination, a transmitter and a receiver, said transmitter having means including a pair of spaced antennae for generating electromagnetic fields coupled to said objects for inducing a pair of distinguishable alternating currents in said objects, respectively said receiver being movable relative to said transmitter and to said objects, having means for sensing magnetic fields associated with said currents, respectively, and having means for producing an output signal dependent upon the sensing of both of said fields associated with said currents.

2. A system in accordance with claim 1, wherein said currents have different carrier frequencies.

3. A system in accordance with claim 1, wherein said currents are pulsed at different pulsation rates.

4. A system in accordance with claim 1, wherein said currents have the same carrier frequency but different modulation frequencies.

5. A system in accordance with claim 1, wherein said output signal producing means comprises means for producing a beat frequency signal related to said currents.

6. A system in accordance with claim 1, wherein said antennae are separated horizontally by about 3-5 feet.

7. A system in accordance with claim 1, wherein said sensing means comprises a coil for sensing both of said magnetic fields associated with said currents and for producing a combined signal, and wherein said output signal producing means produces said output signal only when said combined signal is present.

8. A system in accordance with claim 7, wherein said currents have different carrier frequencies and said combined signal has components corresponding to said different carrier frequencies, respectively, and wherein said output signal producing means produces a beat frequency signal from said components.

9. A system in accordance with claim 7, wherein said currents have different pulsation rates and said combined signal has components corresponding to said different pulsation rates, respectively, and wherein said output signal producing means produces a beat frequency signal from said components.

10. A system in accordance with claim 7, wherein said currents have different modulation frequencies and said combined signal has components corresponding to said different modulation frequencies, respectively, and wherein said output signal producing means produces a beat frequency signal from said components.

11. A system in accordance with claim 1, wherein said output signal producing means produces said output signal only upon the sensing of both of said fields associated with said currents.

12. A method of locating at least one of a pair of concealed, elongated, conductive, adjacent objects, comprising, producing in said objects a pair of distinguishable alternating currents, respectively, moving with respect to said objects a receiver sensitive to a pair of magnetic fields associated with said currents, respectively, and producing an output signal from said receiver dependent upon the sensing by said receiver of both of said fields, and only when both of said fields are present.

13. A method in accordance with claim 12, wherein said output signal is produced in response to a beat frequency signal generated by the sensing of both of said magnetic fields.

14. A method in accordance with claim 12 wherein said currents are induced in said objects by a pair of antennae.

15. A method in accordance with claim 12, wherein said currents have different carrier frequencies.

16. A method in accordance with claim 12 wherein said currents are pulsed at different pulsation rates.

17. A method in accordance with claim 12 wherein said currents have the same carrier frequency modulated at different frequencies.

18. A method in accordance with claim 12 wherein said receiver is moved back and forth transversely of said objects and is also moved longitudinally of said objects.

19. A method in accordance with claim 18, wherein said output signal from said receiver is produced by sensing said magnetic fields in a sensor coil, producing a combined signal from said coil that includes components corresponding to said magnetic fields, and producing a beat frequency signal from said components.

20. A method in accordance with claim 19, wherein said components have different carrier frequencies.

21. A method in accordance with claim 19, wherein said components have different pulsation rates.

22. A method in accordance with claim 19 wherein said components have different modulation frequencies.

23. A method of locating at least one of a pair of concealed, elongated, conductive, adjacent objects, comprising, producing in said objects a pair of distinguishable alternating currents, respectively, moving with respect to said objects as receiver sensitive to a pair of magnetic fields associated with said currents, respectively, and producing an output signal from said receiver dependent upon the sensing by said receiver of both of said fields, said currents being inducted in said objects by a transmitter that is positioned over said objects and that is provided with a pair of spaced antennae and said receiver being moved relative to said transmitter.

24. A method in accordance with claim 23, wherein the position of said transmitter relative to said objects is adjusted to optimize the sensing of said fields by said receiver.