Theft detection method and apparatus in which the decay of a resonant circuit is detected
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United States of America Patent
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Oct 9, 1984
Grant Date -
N/A
app pub date -
Oct 23, 1981
filing date -
Oct 23, 1981
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
In an electronic theft detection apparatus the passage of a resonant circuit wafer 16 through an interrogation zone formed by transmitter and receiving antennas (30, 90) (32, 92) is detected by generating sharp pulses of electromagnetic energy to cause the resonant circuit wafer to resonate for a duration following each pulse. A receiver is provided with a switch (54), signal accumulators or filters (56 and 58) and a comparator (60) to sense the decay of the signal from the resonating wafer and to activate an alarm (36) when that decay occurs at a predetermined value.
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