BODY_CAPACITANCE_ALARM

Published:2009/7/16 6:03:00 Author:Jessie | From:SeekIC

Detects intruder by sensing body capacitance. Oscillator Q1 feeds 20 kc to capacitance bridge that contains C1, which is capacitance to ground of protected cabinet. When unbalanced, bridge feeds 20-kc signal to amplifier Q2, whose output goes to phase-sensitive detector D1-D2, which converts unbalance signal into d-c voltage for amplification by Q3. At balance, Q4 and Q5 send about I ma through relay K1 to keep it energized. When intruder approaches protected cabinet, output of phase-sensitive detector becomes more negative, causing K1 to drop out and sound an alarm.-S. M. Bagno, Sensitive Capacitance Intruder Alarm, Electronics, 33:38, p 65-67.



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