Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1989-12-08
1991-02-19
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
307119, G08B 1314
Patent
active
049947931
ABSTRACT:
A device for detecting intrusion for security or inventory control purposes includes a mat having loosely superposed metallic foil sheets separated by a sheet of paper or plastic foil dielectric to form a capacitor, and circuitry connected to provide a voltage differential to the capacitor and to detect a change in capacitance caused by weight applied to or removed from the mat. The circuit includes a voltage regulator to regulate the applied voltage differential, a unity gain amplifier to isolate the mat capacitor from change signal amplifier circuitry, a comparator to compare the amplified change signal with user settable thresholds, and a one-shot multivibrator for initiating an alarm signal pulse when one of the thresholds is exceeded. The sheets are preferably aluminum foil backed with plastic film and, in one form, are wrapped one around the other.
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Franz Warren L.
Swann III Glen R.
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