DC interruption detection circuit for telephone line - senses sign changes in difference between slowly and rapidly reacting current sensor outputs

摘要

A circuit for detecting an open circuit in a d.c. line contains a detector unit (3a) connected into the line (9) via two connectors (4, 5). The detector unit produces one output voltage (Ua) varying rapidly with the current in the line and another (Uk) varying slowly with the current. In normal operation the difference between the voltages is essentially proportional to the curent in the line. If the current in the line falls rapidly, the sign of the voltage difference changes in a time independent of the initial current level. USE/ADVANTAGE - Reliable detection of open circuit in d.c. conductor independently of current level and without delay.