SCHALTUNGSANORDNUNG ZUR AUSWERTUNG DER AUSGANGSSIGNALE VON STROMFLUSSDETEKTOREN IN FERNMELDEANLAGEN.

摘要

Current flow detectors are connected to the subscriber line (L) to which ringing current (IW) is delivered by an AC tone generator (RG). Two opto-isolators (SD1,SD2) are arranged in inverse-parallel across a resistance (R) and their outputs (AS1,AS2) are monitored by an evaluation circuit whereby if ringing current is superimposed on the feed current (IG) from a 05!source!(SQ),!the!zero!crossing!of!the!ringing!AC!is!detected. To improve the security of evaluation and to distinguish ringing tone from stray interference, the duration of both positive and negative half-cycles of the loop current is measured, and values are ascertained from comparison of the amt. and ratio of these measurements with predeterminable thresholds.