Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1988-01-07
1989-04-11
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
340516, 340572, G08B 1324, G08B 1314, G08B 2900
Patent
active
048210234
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.
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Bernat Louis
Del Norte Technology, Inc.
Mullen Jr. Thomas J.
Swann III Glen R.
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