Abbott Laboratories Corporation

White's Electronics, Inc.

Teknetics, Inc.

Richard Edward Hirschi

James L Tiefenthal

Ronald M Isaac

James P Karbowski

George C Payne

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 synchronous demodulator subsystem produces a ground balance pulse and a discriminate pulse each time a detector head housing the receive coil and an associated transmit coil passes over a metallic object (e.g., a target) buried in the ground. In one form, a pair of synchronous demodulators produce V.sub.X and V.sub.R signals, each of which includes a pulse each time the detector head passes over a target. The V.sub.X and V.sub.R signals are combined to produce the ground balance and discriminate pulses. Alternatively, a pair of synchronous demodulators are used to directly produce the ground balance and discriminate pulses. The polarity of the discriminate pulse is dependent upon on whether the target is a desirable or an undesirable target. Contrariwise, the polarity of the ground balance pulse is always the same. Further the ground balance pulse signal contains very little ground mineralization information whereas the discriminate pulse signal may contain a significant amount of ground mineralization information when the target is buried in mineralized ground. The ground balance and discriminate pulses are filtered to remove ground mineralization information and converted into in-phase or 180 degrees out-of-phase ringing signals. The ground balance ringing signal is modulated in a triangle modulator and the result divided into the discriminate ringing signal. The result of the division is a series of pulses on one or the other of two lines depending upon whether the target is a desirable or undesirable target. The division pulses control the polarity and magnitude of a DC voltage produced by an integrator, which in turn controls a corresponding increase or decrease in the level of an audio signal.

Metal detector system with undesirable target and mineralized ground

An induction balance metal detector is described which is capable of discriminating between different types of metal objects, such as bottle caps and coins, by amplitude discrimination of their corresponding receive signals. In addition, the detector is provided with a tuning control which is used to eliminate the effect of ferrous mineral soil on the output signal of the receive coil. The discriminate control changes the phase of the residual output signal of the receive coil to set the quiescent operating point of the metal detector to a selected angle between about zero and -90.degree. relative to the component of the receive coil signal produced by the presence of magnetic mineral soil, and the tuning control adjusts the amplitude of the residual signal to an audio threshold level. As a result, the desired coins or other high conductivity metal objects reduce the amplitude of the received signal below the audio threshold level so that they tend to produce no sound output or a negative indication while all other objects increase the amplitude of such signal above the audio threshold level so they tend to produce a sound output. This inverse discrimination is provided with a positive indication by means of a comparator having one input connected to an audio pulse generator synchronized to the oscillator and its other input connected to the demodulated audio frequency output of the receive coil. The comparator compares the amplitude of the input signals and produces a positive indication signal an audio output only when the received signal is less than the amplitude of the standard audio pulses. The detector may be provided with a transmit coil whose annular loop shaped windings are provided with a re-entrant portion forming a feedback coil so that current flows in opposite directions through such transmit coil and feedback coil.

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Sweet Home, OR, United States of America

Richard Edward Hirschi