| 摘要 |
1322216 Automatic exchange systems WESTERN ELECTRIC CO Inc 4 Aug 1970 [5 Aug 1969] 37465/70 Heading H4K A loop detector which is insensitive to longitudinal currents and leakage currents and which presents such a high impedance to line that it may be left permanently connected thereto, comprises a differential amplifier 24 connected between taps on potential dividers 16, 19 that are cross-coupled across the feed resistors 15, 12. A bias resistor 26 ensures that under on-hook conditions the voltage across b<SP>1</SP> a<SP>1</SP> is approximately plus 600 mvolts whereas under off-hook conditions it is minus 610 mvolts, the impedances being chosen and the amplifier adjusted such that 10 mvolts is allowed as a contribution by leakage currents. Lighting etc. surges have no effect on the detector. Resistors 14, 11 serve to increase the input impedance of the detector. |
