| 摘要 |
<p>A telephone line loop detector is used to determine the status of a user line connected to an exchange or switchboard. A detector has a transformer (3) connected to the lines (A, B) and the telephone network. The detector also has a resistor bridge circuit (15-20) also connected to the transformer (3), a comparator (C) comprising a differential amplifier, a capacitor (C2) and a meter (30) connected by an optical device (PC). The bridge circuit (15-20) is connected either to a battery (+0, -Vo) or to a call circuit (8) by means of contacts (S1, S2) of a relay (14). The detector can detect use or non-use of a user line and numbering pulses from the user dial.</p> |
