The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 11, 1989
Filed:
Jan. 07, 1988
Stephen I Parks, Derwood, MD (US);
Del Norte Technology, Inc., Euless, TX (US);
Abstract
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.