| 摘要 |
Unit 6 plugged permanently into the video-output (8, Fig. 2) of data-processing unit 2 maintains video-signal supply to monitor 3 only while a radio signal, sent by a badge or card 14 worn by an operator, continues to be received by loop-antenna 12 (e.g. incorporated in a mouse mat 13). The signal, possibly encoded, is transmitted from card 14 by a transponder (15, Fig. 2) in response to reception of a radio-frequency, possibly encoded, signal transmitted from antenna 12. When the card-signal is no longer detected, i.e. the operator moves out of range of the antenna 12, a switching circuit (9, Fig. 2) in the unit 6 is deactivated to block the video-signal supply to monitor 2. The video-signal supply is restored when the card-signal is detected again. The unit can also be arranged to interrupt the supply of signals to and from the processing unit 2, e.g. to/from the keyboard, mouse, printer (Fig. 3). The screen 4 can be left blank during interruption, or driven by an auxiliary video-signal source (36, Fig. 4) to provide a message/pattern display.
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