Telephone line seizure detection device using two optocouplers connected in series to telephone line and including negative feedback circuit to decreases influence of their transfer coefficients

摘要

The device measures the voltage (UL) of the telephone line across two optocouplers (OC1, OC2) connected in series to the telephone line. The first optocoupler discharges a capacitor (C) connected to the telephone line, the second optocoupler converts the discharge current (ID) into an image current (ID') in a measurement circuit (S). A negative feedback circuit is included between the two optocouplers. An Independent claim is included for an apparatus.