Supervisory circuit for telephone subscriber's line

Claim 1

A SUPERVISORY CIRCUIT FOR DETERMINING CHANGES-OFCONDITION IN A SUBSCRIBER SUBSET LOOP COMPRISING FIRST AND SECOND SUBSTANTIALLY IDENTICAL MAGNETIC CORES DISPLAYING A SUBSTANTIALLY RECTANGULAR HYSTERESIS CHARACTERISTIC, EACH OF SAID CORES HAVING SET AND RESET STATES OF REMANENT MAGNETIZATION AND SATURATION STATES, CURRENT BIASING MEANS COUPLED TO SAID FIRST CORE FOR NORMALLY MAINTAINING SAID FIRST CORE IN A RESET SATURATION STATE, SAID SECOND CORE BEING NORMALLY IN SAID REMANENT RESET STATE, MEANS COUPLING EACH OF SAID CORES TO SAID SUBSET LOOP FOR ENABLING DIRECT CURRENT IN SAID LOOP TO MAINTAIN SAID SECOND CORE IN A SET SATURATION STATE AND SAID FIRST CORE IN ONE OF SAID STATES OF REMANENT MAGNETIZATION, AN INTERROGATING MEANS COUPLED TO EACH OF SAID CORES FOR SWITCHING SAID FIRST CORE FROM SAID REMANENT RESET STATE TO SAID REMANENT SET STATE WHEN DIRECT CURRENT FLOWS IN SAID SUBSET LOOP AND FOR SWITCHING SAID SECOND CORE FROM SAID REMANENT SET STATE TO SAID REMANENT RESET STATE IN THE ABSENCE OF DIRECT CURRENT IN SAID SUBSET LOOP, AND UTILIZATION MEANS COUPLED TO EACH OF SAID CORES FOR DETECTING CHANGES IN FLUX DIRECTION IN SAID CORES.