| 摘要 |
The telecommunications test terminal (TEL) has a command circuit (CM) which is able to control the switching (IB) of a loop connection to a telephone line (L1,L2). This is used for testing purposes. A circuit (CD) measures whether the telephone line is occupied or not, by monitoring the signal appearing on the line (SL). This is done using a high impedance circuit arrangement (L4). If the signal level exceeds a predetermined threshold, then the circuit prevents the trial line from being switched.
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