Continuous-depth-indicating underground pipe and cable locator

• US 6,140,819 A
• Filed: 05/26/1998
• Issued: 10/31/2000
• Est. Priority Date: 05/26/1998
• Status: Expired due to Term

• Current Assignee: Heath Consultants, Inc.
• Original Assignee: Heath Consultants, Inc.
• Inventors: Peterman, David L., Peterman, Earl J.
• Primary Examiner(s): SNOW, WALTER E
• Application Number:
  US09/084,839
• Time in Patent Office: 889 Days
• Field of Search: 324/67, 324/207.11, 324/207.17, 324/207.19, 324/207.22, 324/207.26, 324/237, 324/243, 324/326, 324/327, 324/328, 324/329
• US Class Current: 324/326
• CPC Class Codes: G01V 3/15 specially adapted for use during transport, e.g. by a person, vehicle or boat

Abstract

An underground pipe and cable locator for continuous depth readings comprises a top and bottom receiver antenna sensor each connected to respective amplifier channels. A separate transmitter is used to stimulate electromagnetic radiations from a buried pipe, cable, or other electrical conductor. The bottom receiver antenna sensor is sampled and used to synchronize a phase locked loop controlled oscillator. The exceedingly faint and noise-riddled signals obtained from the top and bottom receiver antenna sensors are full-wave rectified without the use of rectifiers or diodes that can introduce distortions and offsets. Such signals are full-wave rectified by synchronously switching between inverted and non-inverted copies with an analog switch such that only the positive cycles of each are output in one pulse train. A continuous output is therefore obtainable from the top and bottom receiver antenna sensors, and this, in turn, permits a continuous display of the depth estimate of the buried conductor.

Claims

1. A locator for the continuous measurement of the depths of underground objects from the surface, comprising:

an antenna array that can be positioned at a point near a surface overlying an underground object that is radiating an electromagnetic wave;

a top and a bottom antenna included in the antenna array and having a known separation distance between them, and respectively providing for a first and a second received alternating current (AC) electrical signal that are each representative of a first field strength and a second field strength of said electromagnetic wave at corresponding points in space;

a phase-locked loop (PLL) for synthesizing a local oscillator frequency from either said first or second received AC electrical signal, wherein a gating signal is produced that is synchronized to a harmonic frequency of said first or second received AC electrical signal;

a first network for connecting said first received AC electrical signal to produce a first inverted and a first non-inverted AC signal representative of said electromagnetic wave at said top antenna;

a second network for connecting said second received AC electrical signal to produce a second inverted and a second non-inverted AC signal representative of said electromagnetic wave at said bottom antenna;

a first analog signal switch connected to said gating signal and providing for alternatively switching between said first inverted and said first non-inverted AC signals to produce a first full-wave rectified direct current (DC) signal;

a second analog signal switch connected to said gating signal and providing for alternatively switching between said second inverted and said second non-inverted AC signals to produce a second full-wave rectified DC signal in parallel with and independent from said first full-wave rectified direct current (DC) signal; and

a computer providing for a continuous and real-time estimate of said depth of said underground object to a user by equating a first field strength associated with said top antenna to an electrical magnitude of said first full-wave rectified DC signal, and equating a second field strength associated with said bottom antenna to an electrical magnitude of said second full-wave rectified DC signal, wherein a continuous real-time comparison is made between said first field strength to said second field strength to estimate a depth of said underground object from which said electromagnetic wave is radiating.

2. A locator for measuring the depths of underground objects from the surface, comprising:

an antenna array that can be positioned at a point near a surface overlying an underground object that is radiating an electromagnetic wave;

a top and a bottom antenna included in the antenna array and having a known separation distance between them, and respectively providing for a first and a second received alternating current (AC) electrical signal that are each representative of a first field strength and a second field strength of said electromagnetic wave at corresponding points;

a phase-locked loop (PLL) for synthesizing a local oscillator frequency from either said first or second received AC electrical signal, wherein a gating signal is produced that is synchronized to the frequency of said first or second received AC electrical signal;

a first network for connecting said first received AC electrical signal to produce a first inverted and a first non-inverted AC signal representative of said electromagnetic wave at said top antenna;

a second network for connecting said second received AC electrical signal to produce a second inverted and a second non-inverted AC signal representative of said electromagnetic wave at said bottom antenna;

a first analog signal switch connected to said gating signal and providing for synchronously switching between said first inverted and said first non-inverted AC signals to produce a first full-wave rectified direct current (DC) signal;

a second analog signal switch connected to said gating signal and providing for synchronously switching between said second inverted and said second non-inverted AC signals to produce a second full-wave rectified DC signal; and

a computer for equating a first field strength associated with said top antenna to an electrical magnitude of said first full-wave rectified DC signal, and further for equating a second field strength associated with said bottom antenna to an electrical magnitude of said second full-wave rectified DC signal, and wherein a comparison is made between said first field strength to said second field strength to estimate a depth of said underground object from which said electromagnetic wave is radiating.

3. The locator of claim 2, wherein:

the computer provides a continuous and real-time estimate of said depth of said underground object to a user.

4. The locator of claim 2, wherein:

said first and second full-wave rectified DC signals are produced in parallel and periodically converted by an analog-to-digital converter with an input multiplexer for input to the computer as digital values.

5. The locator of claim 2, wherein:

the computer includes a memory in which are stored calibration values and a program for using said calibration values during operation to reduce any gain and offset errors caused by said first and second full-wave rectified DC signals having been received and processed by different antennas and electronic circuits in parallel.

6. The locator of claim 2, further comprising:

a plumb-level sensor for indicating to the computer when the top and bottom antenna are plumb to one another.

7. A method for measuring a power level of an exceedingly faint electrical signal, comprising:

synthesizing a local oscillator frequency from an exceedingly faint alternating current (AC) electrical signal obtained from an input port, wherein a gating signal is produced that is synchronized to the frequency of said sample;

connecting said input port to produce an inverted and a non-inverted alternating current (AC) signal representative of said sample;

using said gating signal to synchronously switch between said inverted and said non-inverted AC signals to produce a full-wave rectified direct current (DC) signal; and

equating a signal strength measurement to an electrical magnitude of said full-wave rectified DC signal.

8. A method for determining the field strength of an electromagnetic wave at two different points in space, comprising:

positioning a first antenna to receive an electromagnetic wave at a first point in space;

positioning a second antenna to receive said electromagnetic wave at a second point in space;

synthesizing a local oscillator frequency from said electromagnetic wave obtained from said first or second antenna wherein a gating signal is produced that is synchronized to said electromagnetic wave;

connecting said first antenna to produce a first inverted and a first non-inverted alternating current (AC) signal representative of said electromagnetic wave at said first point in space;

connecting said second antenna to produce a second inverted and a second non-inverted AC signal representative of said electromagnetic wave at said second point in space;

using said gating signal to alternately switch between said first inverted and said first non-inverted AC signals to produce a first full-wave rectified direct current (DC) signal;

using said gating signal to alternately switch between said second inverted and said second non-inverted AC signals to produce a second full-wave rectified DC signal;

equating a first field strength associated with said first point in space to an electrical magnitude of said first full-wave rectified DC signal; and

equating a second field strength associated with said second point in space to an electrical magnitude of said second full-wave rectified DC signal.

9. The method of claim 8, further comprising:

comparing said first field strength to said second field strength to estimate a third point or line in space from which said electromagnetic wave is radiating.

10. The method of claim 8, wherein:

the steps of using gating signal to alternatively switch between inverted and non-inverted AC signals includes the use of an analog signal multiplexer.

11. The method of claim 8, wherein:

the step of synthesizing a local oscillator frequency includes the use of a phase-locked loop and outputting a "LOCK" signal to indicate to a microcomputer that said electromagnetic wave is being received and tracked.