Transmitter-receiver loop buried metal object locator with switch controlled reference voltage

• US 4,348,639 A
• Filed: 05/18/1979
• Issued: 09/07/1982
• Est. Priority Date: 05/18/1979
• Status: Expired due to Term

• Current Assignee: Discovery Electronics Incorporated
• Original Assignee: Triple DEE Electronics Incorporated
• Inventors: Karbowski, James P.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US06/040,399
• Time in Patent Office: 1,208 Days
• Field of Search: 324/326, 324/329, 324/334, 324/233
• US Class Current: 324/329
• CPC Class Codes: G01V 3/108 the emitter and the receiver coils or loops being uncoupled by positioning them perpendicularly to each other

Abstract

Apparatus and method are provided for locating the position, depth, and run of a longitudinal metal object. Specifically, apparatus and method are provided for the tracing of a longitudinal subterranean metal object such as pipes or cables. The apparatus is capable of energizing a subterranean metal object and thereafter detecting the electromagnetic field produced by the metal object with a search loop. The magnitude of a current produced in the search loop is precisely measured whereby the location of the pipe or cable is precisely established. Circuitry is provided to provide high noise immunity to the detection of electromagnetic fields not originating with the metal object. Means are provided to maintain the system sensitivity without relying upon tedious mechanical adjustments.

Claims

1. An electronic subterranean longitudinal metal object locator comprising:

(a) first and second closed rectangular loops, said first loop being oriented in a vertical plane and said second loop being oriented in a horizontal plane perpendicular to said first loop and spaced apart therefrom;

(b) means for energizing said first loop with an alternating electrical current whereby a varying electromagnetic field is produced;

(c) means for positioning said first loop in a plane perpendicular to said longitudinal metal object and said second loop in a plane parallel thereto, whereby a current is produced in said metal object from said first loop which produces a varying electromagnetic field for inducing a receive current in said second loop the magnitude of said received current being controlled by the relative position of said loops with respect to said metal object;

(d) an amplifier for providing a voltage proportional to a current induced in said second loop;

(e) a phase detector having a first input for receiving a voltage from said amplifier and a second input coupled to a source of a phase reference signal, said phase reference signal desensitizing said phase detector to ground signals;

(f) a comparator for providing an output voltage proportional to the difference between a reference voltage and the output voltage provided by said phase detector, said comparator output voltage being proportional to said received current;

(g) means for indicating the relative output voltage of said comparator, whereby changes in the relative level of said received current may be monitored; and

(h) means for manually varying the level of said reference voltage to alter said comparator output voltage in response to monitored increases in the magnitude of the received current in said second loop, said means including a switch connected to receive said comparator output voltage, said means providing a voltage related to said received current for restoring said comparator output voltage to a predetermined level in response to a momentary closure of said switch, whereby the relative magnitude of said current is monitored for accurately positioning said second loop with respect to said longitudinal metal object, the position of said second loop determining the position of said metal object.

2. The apparatus of claim 1, further comprising means for varying the phase of said reference signal.

3. The apparatus of claim 1, wherein said means for indicating provides an audible acoustic signal having a magnitude proportional to the output voltage of said comparator.

4. The apparatus of claim 2, wherein said reference signal has a frequency substantially equal to the frequency of said alternating electric signal.

5. A receiver for detecting an electromagnetic field produced by a subterranean metal object carrying an alternating current comprising:

(a) a rectangular closed loop for producing a signal current in response to said electromagnetic field;

(b) an amplifier operatively coupled to said loop for producing an output signal in response to said signal current;

(c) phase detector for providing a voltage having an amplitude proportional to the difference in phase between said amplifier output signal and a reference signal;

(d) means for supplying a reference signal to said phase detector, said reference signal having a phase in fixed relationship with the phase of said alternating current;

(e) a comparator means for providing an output voltage proportional to the difference between said phase detector output voltage and a reference voltage;

(f) a switch;

(g) a manually variable reference voltage generator connected to supply said reference voltage to said comparator means for establishing the output voltage of said comparator means at a predetermined level for different levels of said voltage from said phase detector, said switch connecting said reference voltage generator to receive said comparator means output voltage whereby said reference voltage is established and maintained in response to a momentary closing of said switch; and

(h) means for monitoring relative difference between said comparator output voltage and said predetermined level during positioning of said rectangular loop, whereby the optimum position of said loop for inducing a current in said rectangular loop may be precisely determined, said position being directly related to the location of said metal object.

6. An apparatus for determining the position of a longitudinal metallic object comprising:

(a) means for inducing an alternating current in said object having a predetermined frequency whereby an alternating field is produced;

(b) a rectangular loop for detecting said magnetic field, said loop producing a loop current having a frequency identical to said alternating current frequency;

(c) amplifier means operatively coupled to said rectangular loop for producing a voltage in response to the loop current;

(d) a peak detector connected to said amplifier for providing a voltage proportional to the peak voltage produced by said amplifier;

(e) a comparator having an output for providing a voltage proportional to the difference between the peak detector output voltage and a reference voltage;

(f) a switch;

(g) a manually selectable reference voltage source operatively connected to said comparator, said voltage source providing an input voltage to said comparator in response to the momentary closure of said switch, said switch connected between said comparator output and said reference voltage source, whereby the output voltage of said comparator is selected to be a predetermined level; and

(h) means for indicating changes in said comparator output voltage from said predetermined level, whereby an operator may reestablish said predetermined level as the difference between said peak detector output voltage and said reference voltage increases.

7. An apparatus for locating a buried metal object comprising:

first and second rectangular loops, said loops being spaced apart and lying in perpendicular planes;

means for energizing one of said loops with an alternating current;

means for detecting a current induced in the remaining of said loops, said means providing a signal proportional to the magnitude of said induced current;

means for comparing the phase of said induced current with the phase of said alternating current in said means for energizing, said means for comparing providing an output signal when said alternating current and said induced current have a predetermined phase relationship;

detector means for monitoring the level of a signal from said phase comparator comprising;

a differential amplifier having a first input connected to receive a signal from said means for comparing, a second input, and an output;

a momentary switch;

means for establishing a fixed voltage on said second input for reducing a voltage at said output to a predetermined level in response to a momentary closure of said switch, said switch connected between said means for establishing and said differential amplifier output;

means for maintaining said fixed voltage on said second input after said switch is opened;

means for providing an audible signal having a magnitude proportional to the magnitude of a singal from said first differential amplifier output;

whereby the proximity of said metal object is detected when said audible signal increases, and activating said momentary switch reestablishes a new fixed voltage decreasing said audible signal level permitting further positioning of said loops to increase said audible signal, further defining the location of said object.

8. An apparatus for locating a buried metal object comprising:

first and second rectangular loops, said loops being spaced apart and lying in perpendicular planes;

means for energizing said first loop with an alternating current;

means for detecting a signal induced in said second loop in response to an electromagnetic field generated by said metal object when in the presence of said first loop;

comparator means for detecting the difference between the magnitude of a signal induced in said second loop and the magnitude of a reference signal and providing at an output thereof a voltage indicating said difference;

means connected to said comparator means output for supplying a reference signal having a selectable magnitude to said comparator means, said means including a switch, said means providing in response to the momentary closure of said switch a reference signal voltage for establishing the comparator means output voltage to a predetermined level; and

means for monitoring said difference during the positioning of said first and second loops whereby increases in said difference resulting from the proximity of said second loop with respect to said metal object may be reduced by successive increases in the magnitude of said reference signal until said loops are optimally positioned with respect to said metal object.