| 摘要 |
Anti-theft device detecting the passage of a self-induction coil by modification of field lines. The invention relates to an electronic protection device detecting the non-authorised passage of articles in a protected passage. It is constituted by a frame 1 made of aluminium in the shape of an eight. The electronic board 2 generates currents at variable frequencies which are transformed by the frame 1 into electromagnetic fields at variable frequencies. The upper loop of the frame 1a transmits field lines and the lower loop 1b closes the latter. The field lines are distributed equally on each side of the faces of the frame 1. A screened cable 7 connects the frame 1 to the feed/detection/control/power unit 8, which provides the power supply of the assembly and the alarm controls. The circuit, modifying the field lines and thus allowing the detection of the latter during the passage in front of the frame, is constituted by a self-induction coil 16a comprising a winding of enamelled wire 17 tuned by a capacitor 18 to the resonant frequency of the frame 1. <IMAGE>
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