Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1992-10-13
1994-08-09
Swann, Glen
Communications: electrical
Condition responsive indicating system
Specific condition
340551, G08B 1324
Patent
active
053370406
ABSTRACT:
An apparatus for the detection of labels (21) used for preventing the shoplifting of articles (20) and which are provided with an electrical resonant circuit having a resonant frequency in the MHz range, comprises several pairs of transmitting and receiving antennas (8 to 13), which in each case bound passages (5 to 7) to be monitored. The transmitting antennas (8, 10, 12) of the pairs in each case radiate electromagnetic waves, whose frequency is wobbled in wobble cycles over the predetermined resonant frequency of the labels. The wobble cycles of all the pairs are synchronized with one another. To the receiving antenna (9, 11, 13) of each pair is connected a receiving circuit (17 to 19) detecting the presence of a label. For simplifying the installation, the invention proposes that the h.f.-oscillations radiated as electromagnetic waves by means of the transmitting antennas are generated by decentralized h.f.-generators (14 to 16) individually associated with the transmitting antennas and that the wobble cycles are synchronized with one another using a synchronization signal with at least one frequency in the LW-range generated in a central unit (22) and supplied to the h.f.-generators.
REFERENCES:
patent: 4309697 (1982-01-01), Weaver
patent: 4623877 (1986-11-01), Buckens
patent: 4797659 (1989-01-01), Larsen
patent: 4870391 (1989-09-01), Cooper
patent: 5153562 (1992-10-01), van Breemen
Actron Entwicklungs AG
Swann Glen
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