Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1991-09-30
1993-10-19
Mullen, Thomas
Communications: electrical
Condition responsive indicating system
Specific condition
340551, G08B 1314
Patent
active
052549747
ABSTRACT:
This invention relates to a deactivating device for deactivating shoplifting detection labels of an electronic shoplifting detection system. These labels comprise a resonant circuit with a coil and a capacitor and the deactivating device comprises an antenna circuit comprising an antenna coil tuned with at least one capacitor to the resonant frequency of the resonant circuit. By means of this arrangement, sufficient energy can be induced in a resonant circuit of a label to effect electrical breakdown in the capacitor thereof. According to the invention, the antenna coil of the deactivating device is coupled, on the one hand, to a supply source and, on the other, to earth via a switch. Circuitry is provided for supplying at intervals control pulses to the switch in order to bring the switch into the conductive state. The duration of each control pulse is chosen such that at the end of a control pulse, when the switch returns to the blocking state, the energy necessary for deactivation is stored as magnetic energy in the antenna coil. This energy is subsequently converted into an electromagnetic oscillation when the switch is in the blocking state.
REFERENCES:
patent: 4498076 (1985-02-01), Lichtblau
patent: 4567473 (1986-01-01), Lichtblau
patent: 4728938 (1988-03-01), Kaltner
patent: 4906974 (1990-03-01), Rehder
patent: 5008649 (1991-04-01), Klein
patent: 5153562 (1992-10-01), van Breemen
Fockens Tallienco W. H.
Rebers Paulus
Mullen Thomas
N.V. Nederlandsche Apparatenfabriek Nedap
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