| 摘要 |
A passive radio-frequency monitoring system for moving objects in a control region consists of transmitting and receiving means and switching means assigned to the latter for triggering the alarm and of safeguarding devices assigned to the objects, in the form of a label, pendant or the like, which contain resonant circuits (tuned circuits). The safeguarding device has a circuit which consists of two tuned circuits (1, 2; 6, 7) which, when interconnected, form a resonant circuit having a first frequency (f2), while a single tuned circuit (2; 6) forms a resonant circuit having a second frequency (f1). At selected places in the control region (K) there are transceivers (S/E2) tuned to the first frequency (f2) and at its exits there are transceivers (S/E1) tuned to the second frequency (f1). The tuned circuits are simple parallel resonant circuits, one of which can be opened or interrupted. If the attempt is made to remove or destroy the safeguarding device without authorisation, the interconnection is opened. In accordance with this system, monitoring is possible both inside the control region and at its exits. <IMAGE>
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