1. A TIME VARYING SIGNAL RATE OF CHARGE TRIP CIRCUIT COMPRISING: (A) A MAGNETIC CORE HAVING A FIRST PRIMARY WINDING, A SECOND OPPOSING PRIMARY WINDING, A BIAS WINDING AND A SECONDARY WINDING, (B) MEANS FOR COUPLING SAID TIME VARYING SIGNAL TO SAID FIRST PRIMARY WINDING, (C) MEANS COUPLED TO SAID SECONDARY PRIMARY WINDING FOR INDUCING A GREATER OPPOSING MAGNETOMOTIVE FORCE IN SAID CORE THAN SAID FIRST PRIMARY WINDING, A GIVEN PERIOD OF TIME AFTER SAID SIGNAL REACHES A PREDETERMINED LEVEL, (D) MEANS FOR APPLYING AN ADJUSTABLE BIAS CURRENT TO SAID BIAS WINDING, AND (E) MEANS COUPLED TO SAID SECONDARY WINDING FOR INDICATING A PREDETERMINED MAGNETOMOTIVE FORCE CONDITION OF SAID CORE WHEN SAID SIGNAL EXCEEDS A GIVEN RATE OF CHARGE.