Communications: electrical – Systems – Call station
Patent
1975-01-14
1976-09-28
Swann, III, Glen R.
Communications: electrical
Systems
Call station
340258C, 3171575R, G08B 1322
Patent
active
039835529
ABSTRACT:
In a pilferage detection system employing apparatus for generating a magnetic field of alternating polarity and predetermined fundamental frequency through which articles subject to pilferage must pass to leave a protected area and a magnetic marker associated with each article in the protected area, markers are provided which generate both odd and even harmonics of the fundamental frequency in response to the alternating magnetic field when the marker is active (i.e., a control element of the marker is magnetized) and which generate only odd harmonics of the fundamental frequency when the marker is inactive. The presence of an active marker in the alternating magnetic field is therefore detected by detecting a predetermined even harmonic of the fundamental frequency. Apparatus is also provided for demagnetizing the control element of the marker associated with an article authorized for removal from the protected area to permit that article to pass through the alternating magnetic field undetected.
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Armstrong Albert L.
Bakeman, Jr. Paul E.
American District Telegraph Company
Jackson Robert R.
Smith Charles B.
Swann III Glen R.
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