Magnetic surveillance system with odd-even harmonic and phase discrimination
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United States of America Patent
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-
Jan 5, 1982
Grant Date -
N/A
app pub date -
Oct 2, 1980
filing date -
Oct 2, 1980
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
Apparatus for detecting the presence within a surveillance zone of a body of high permeability material creates a surveillance field varying sinusoidally at a fundamental frequency. Parallel filter channels select the second and third harmonic components of the perturbations created by said material when present in the field and the phase of the second harmonic relative to a reference signal is compared. The signal level of each of the second and third harmonic components as well as the aforesaid phase congruency cooperatively control an alarm circuit. Rhomboid shaped transmitter coils surrounding figure '8' receiver coils improve coupling to the high permeability body.
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