Non-contact ammeter

Claim 1

An ammeter for measuring the magnitude of direct current, alternating current, or a combination thereof in a conductor, said ammeter comprising: a single core capable of carrying a changeable magnetic flux, said core being in operative association with the conductor so that the conductor may serve as a primary winding for said core; second winding means operatively associated with said core for being inductively coupled to the conductor through the flux in the core so that the current in said second winding means may bear a relationship to the current in the conductor; means for sensing the magnetic flux condition of the core; voltage establishing means coupled to said second winding means for establishing the polarity of a voltage on said second winding means and the direction of flux change in said core, said voltage establishing means being responsive to said flux condition sensing means for periodically reversing the polarity of the voltage on said second winding means to reverse the direction of flux change in said core to maintain the inductive coupling between said second winding means and the conductor, said voltage establishing means including electrical power supply means coupled to said second winding means, said voltage establishing means providing a current flow path for the current in said second winding means in which said second winding means functions as an electrical source for said power supply means, as a load, and a given polarity of voltage is established in said second winding means and providing a current flow path for the current in said second winding means in which said second winding means functions as a load for the said power supply means, as an electrical source, and the polarity of the voltage on said second winding means is reversed; and means coupled to said second winding means and responsive to the instantaneous current in said second winding means for indicating the magnitude of the current in the conductor.