Electromagnetic arrangement for measuring electrical current

Claim 1

An arrangement for measuring an electrical line current flowing in a line circuit comprising: (A) two separate magnetic paths having essentially matching 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 two paths so that a particular amplitude and polarity of line current causes in the two paths corresponding essentially equal finite amounts of the same 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 control current flows in the control circuit; (E) means electromagnetically coupling the control circuit to the two paths so that each control current pulse causes in the two paths coresponding changes of control H where the changes of control H are of essentially equal finite amounts of the opposite polarity; (F) each change of control H in the two paths being such as to cause the magnetic inductions B in the two paths to undergo corresponding changes of opposite polarity where the amounts and polarities of the changes of B are determined by the combined amount and polarity of line H and control H in the two paths; (G) means including the control circuit coupling means controlled by each control signal and by the corresponding changes of B in the two paths to produce a corresponding voltage pulse the amplitude and duration and polarity of which are a measure of any algebraic difference between the amounts of the corresponding changes of B in the two paths; (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 including the control circuit coupling means controlled by the output voltage to cause in the two paths essentially equal amounts 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 each of the two paths 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.