Electromagnetic arrangement for measuring electrical current

Claim 1

An arrangement for measuring an electrical line current flowing in a line circuit comprising: (A) a single magnetic path having magnetic characteristics such that the slope of the hysteresis characteristic changes substantially as the magnetizing intensity H changes between a zero amount of H and a finite amount of H; (B) means electromagnetically coupling the line circuit to the path so that a particular amplitude and polarity of line current causes in the path a corresponding finite amount and polarity of line H; (C) means for supplying a succession of control signals; (D) a control circuit controlled by each control signal so that a corresponding pulse of particular amplitude and duration and polarity of electrical control current flows in the control circuit; (E) means electromagnetically coupling the control circuit to the path so that successive control current pulses cause in the path successive corresponding changes of control H where the successive changes of control H are of essentially equal finite amounts of the opposite polarity; (F) the successive changes of control H being such as to cause the magnetic induction B in the path to undergo successive corresponding changes of opposite polarity where the amounts of the changes of B are determined by the combined amount and polarity of line H and control H; (G) means controlled by each control signal and by the corresponding change of B to produce a corresponding voltage pulse the amplitude and duration and polarity of which are a measure of the amount and polarity of line H in the path; (H) means controlled by a plurality of successive voltage pulses (1) to perform cumulative algebraic integration of the successive voltage pulses (2) and to provide a changing output voltage the amplitude and polarity of which are a measure of the cumulative integration; (I) and, means controlled by the output voltage to cause in the path an amount of feedback H where (1) the amount of feedback H is according to the amplitude of the output voltage (2) and the polarity of the feedback H is opposite to the polarity of any line H; (J) whereby (1) the amplitude of the output voltage becomes essentially constant when in the path the amount of feedback H essentially equals the amount of line H (2) and the amplitude and polarity of the constant output voltage are a measure of the amplitude and polarity of the line current.