Current meter

Abstract

A variable electrical current in a first winding on a magnetizable core produces a magnetomotive force in the core. A second core winding produces an opposing magnetomotive force digitally adjustable periodically by a third core winding, a pair of switches and a flip-flop coupled to a center tap for alternately closing such switches when triggered to opposite states. The flip-flop is triggered between opposite states when the third winding current reaches a particular magnitude. In each cycle, the time differences for producing the particular magnitudes and the opposite polarities are dependent upon the remanent core flux. Such time differences are counted digitally upwardly and downwardly for opposite polarities. The second winding current is adjusted digitally in each cycle in a direction to minimize such count. The magnitudes of successive adjustments may be compared periodically by adaptive tracking techniques to control the magnitudes of subsequent adjustments. With large magnitudes of the variable current, the first winding on the core may receive a stepped-down current from a first winding on a second core having a second winding to receive the variable current. Windings on the first and second cores may be connected in a closed loop, or windings on a third core produce in the first core a magnetomotive force aiding the magnetomotive force from the current in the second winding on the second core to compensate for energy losses as a result of such current. The second core may be notched to prevent core becoming saturation.