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Del Norte Technology, Inc.

Eg&g Astrophysics Research Corporation

Stephen I Parks

Bennett A Parks

A coil for a metal detector is constructed from a ribbon cable having a plurality of spaced parallel conductors. The ribbon is formed into a loop where its opposing ends confront each other. The conductors are joined in an off-set manner at the end of the cable to form a single conductor into a loop. Various configurations of coil placement are shown to compensate for various external disturbances such as nearby metal objects, for example.

Metal detector coil

A pulsed-field walk-through metal detector contains circuitry to reduce several different types of external noise, or interference due to external stationary or moving metal, and signals due to small objects, such as jewelry. A self-test fixture monitors system performance. The detector has digitally controlled timing means operated at an odd half-multiple of the power mains frequency. A gated integrator is active for periods equal to a multiple of the TV retrace frequency. A switched-capacitor FIR filter removes signals due to steady power line hum, and a subtractive means removes signals due to stationary metal, prior to averaging or lowpass filtering. A peak limiter controls transient noise bursts. A voting circuit reduces the likelihood of false alarm triggering. A simple self-test circuit, consisting of a wire loop and a switch, tests the entire signal path and has no moving parts.

Walk-through metal detector

Method and apparatus for field evaluation of interrelated variables derived from event count per unit time. The method comprises simultaneously integrating selected multiple powers of the event count per unit time and registering only the resultant values. The apparatus is a self-contained portable electronic instrument which is employed in connection with an event count input device such as a digital anemometer which includes a plurality of digital rate multipliers and associated integrators coupled in a chain. It further includes power saving circuitry to turn off the apparatus when data retrieval conditions are not of interest. The method and apparatus are particularly useful for wind prospecting at remote sites where wind energy and optimum wind design speed are sought to be determined. The method and apparatus may also be employed for monitoring water flow, air and water pollution, traffic flow and any other phenomenon where an event count per unit time can be related to the phenomenon.

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Derwood, MD, United States of America

Stephen I Parks