Under and above ground, radio frequency driven element, metal locating system

• US 6,541,976 B1
• Filed: 12/11/2000
• Issued: 04/01/2003
• Est. Priority Date: 12/17/1999
• Status: Expired due to Fees

• Current Assignee: Geometrics Group, Inc.
• Original Assignee: Geometrics Group, Inc.
• Inventors: Dorren, Louis
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US09/734,963
• Time in Patent Office: 841 Days
• Field of Search: 324/326, 324/67
• US Class Current: 324/326
• CPC Class Codes: G01V 3/06 using ac

Abstract

A metal locating system includes a first transmitter unit and a second receiver detector unit for locating an under and above ground radio frequency driven element such as a pipe. The first unit is a radio frequency transmitter operating at radio frequencies and coupled to the driven element as a loss line antenna. The receiver second unit is a switched diversity antenna connected to a radio FM receiver and a differential phase detection system. When the first unit is driven by the driven element, the second unit is able to detect and trace the position of the driven element relative to the switched diversity antenna.

Claims

1. A metal detection system comprising

a signal generator for generating an electrical signal at a first frequency,

an impedance matching network for coupling the electrical signal to a metal object,

first and second spaced receiver antennas for receiving signals at the first frequency radiated by the metal object,

an FM demodulator receiver,

a switch driven by a switch signal at a second frequency for alternately applying signals from the first and second spaced antennas to the FM demodulator receiver, the FM demodulator receiver producing a signal at the second frequency,

an amplitude detector for detecting the amplitude of the signal produced by the FM demodulator receiver, and

a phase indicator for comparing the phase of the signal produced by the FM demodulator receiver and the phase of the switch signal,

whereby the amplitude and phase of the signal produced by the FM demodulator receiver indicates position of the metal object with respect to the antennas.

2. The metal detection system as defined by claim 1 and further including

a band pass filter for applying the signal from the FM demodulator receiver to the amplitude detector and to the phase indicator.

3. The metal detection system as defined by claim 2 wherein the FM demodulator receiver receives a signal at the first frequency for demodulating the signals from the antennas.

4. The metal detection system as defined by claim 2 wherein the first frequency is from VLF to UHF.

5. The metal detection system as defined by claim 1 wherein the FM demodulator receiver receives a signal at the first frequency for demodulating the signals from the antennas.

6. The metal detection system as defined by claim 1 wherein the metal object is an underground pipe.

7. A method of detecting the location of a metal object comprising the steps of

a) applying an electrical signal to the metal object for transmission at a transmission frequency,

b) receiving the transmitted signal from the metal object with a pair of spaced antennas,

c) applying the received signals from the antennas through a switch to an FM demodulator, the switch alternately connecting the antennas at a switch frequency and thereby frequency modulating the received transmitted signal and whereby the FM demodulator produces a phase variable signal at the switch frequency depending on position of the spaced antennas with respect to the metal object,

d) detecting the amplitude of the phase variable signal whereby a null indicates that the antennas are equidistant from the metal object, and

e) detecting the phase of the phase variable signal whereby the phase indicates relative positioning of the antennas with respect to the metal object.

8. In an underground and above ground, metal and pipe locating system, means for generating a radio frequency signal, means for coupling the radio frequency signal to the underground or above ground metal or pipe, means for electrically driving the metal or pipe as a loss transmission line radiator, and means for locating the underground or above ground metal or pipe by receiving the signal radiated by the metal or pipe with two identical antennas being switched in response to a switch signal, FM demodulating the switched received signals to obtain a demodulated signal, and comparing the phase of the demodulated signal with the switch signal as a reference to indicate relative position of the antennas with respect to the metal or pipe.

9. The metal and pipe locating system of claim 8 and further including a switch for rapidly switching the output of the two identical antennas at a synchronized rate with a phase detection system whereby the switch phase modulates the composite signal from the two antennas.

10. The metal and pipe locating system of claim 8 and including a signal amplitude detector for indicating an amplitude null of the demodulated signal when the two antennas are equidistant from the group metal or pipe.