White's Electronics, Inc.

Abbott Laboratories Corporation

Triple Dee Electronics Inc.

James P Karbowski

James L Tiefenthal

Ronald M Isaac

Richard Edward Hirschi

Mark W Rohde

A system for detecting the position of an object within a body of biological tissue includes a resonant circuit attached to the object and a probe including a receiver/transmitter that operates at the resonant frequency of the object. The resonant circuit rings in response to pulses transmitted from the probe thereby activating receiver circuits which control a visual display indicating the direction the probe should be moved to center it over the object. When the object is centered a second visual display provides confirmation.

Tube placement verifier system

A walk-through metal detector comprising an array module supporting transmit and receive coil arrays. Surrounding the array module, yet not touching it, is an outer shell protecting the array module from contact. A passageway tube passes through the opening in the array module, and is supported by the outer shell, further isolating the array module from mechanical vibration. The array module has a relatively high resonant frequency; thus, vibration induced signals are higher in frequency than actual target signals and are disregarded by the detection circuitry. The metal detector also includes a bypass chute, mechanically isolated from the array module, in which metallic objects may be placed and transported to the exit of the passageway without setting any alarms. The array module supports a balanced transmit and receive coil array for insensitivity to external electromagnetic interference. Alternate coil configurations may be selected by the operator to reduce the detector's sensitivity at predetermined portions of the passageway. The detection circuitry of the metal detector includes quadrature phase demodulators for separating target signals into components caused by eddy currents and by permeability changes. The detection circuitry looks for permeability changes only when detected eddy currents indicate a person is within the passageway. A small target detection circuit watches for metal only when the person is centered within the passageway. A large target detection circuit with less sensitivity detects quantities of metal that overload the small target detection circuit.

Walk-through metal detector

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.

Transmitter-receiver loop buried metal object locator with switch

An apparatus is described for detecting the presence of metal objects which may be subterranean. The apparatus comprises an amplifier equipped with a feedback network for forcing the amplifier into oscillation. The amplifier is critically biased such that the minimum gain necessary to maintain oscillation at the frequency of resonance is achieved. The presence of metal near the search coil which forms the tuned circuit of the amplifier loads the output circuit of the amplifier to a degree which suppresses oscillation. An indicator is provided to indicate when the oscillation has decreased in amplitude, whereby a metal object may be located.

Oscillator type metal detector with switch controlled fixed biasing

A transmit-receive type buried metal detector is described employing wide gating pulses to transmit a portion of the received signal through a gate means to an averaging means for reducing any noise in the signal. The gating pulses are centered on the received signal waveform at a centering position where a background signal component of such received signal is of minimum amplitude. As a result, equal positive and negative polarity portions of the background signal component are transmitted through the gate means during each pulse and are averaged to zero in order to eliminate such background signal from the output voltage of the averaging means. The background signal component may be produced by mineralized soil or by undesired metal objects located near the metal object sought to be detected. As a result, the mineral soil signal component or the background signal component of the undesired metal objects is eliminated from the output voltage of the averaging capacitor. This enables detection of the desired metal object in mineral soil or enables such desired metal object to be discriminated from undesired objects. A wide gating pulse greater than about 1/3 cycle and preferably equal to approximately 1/2 cycle of the oscillator signal, is used for improved noise rejection including random noise of high frequency and harmonics of 60 hertz power line frequency which are close to harmonics of the oscillator signal.

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Philomath, OR, United States of America

James P Karbowski