Detector circuit for current measurements

A detector circuit to be used in current measurements, comprising:

• two toroidal transformers which are wound substantially identically, in which a primary current induces first magneto-motive forces, which first magneto-motive forces are neutralized by other magneto-motive forces induced therein by a secondary current;
• an external current source which produces a sensing current;
• two cores;
• two sensing windings wound on each said core, at least one of said sensing windings carrying said sensing current from said external current source,
• rectifier means responsive to said sensing current for producing a d.c. control signal which is used as said secondary current;
• wherein said two sensing windings are wound on said two cores in a way to magnetize each winding to have mutually opposite magnetic senses when said sensing current is passed therethrough,
• each of said two sensing windings further being divided into two equal subwindings in such a manner that a number of ampere-turns of all four subwindings are substantially equal, said subwindings further being connected to each other,
• a plurality of switching means, coupled to said external current source and said subwindings, for selectively applying said sensing current to different ones of said subwindings;
• and
• means for controlling said switching means in a way such that odd-harmonic components of said sensing currents passing through said subwindings are outbalanced and even-harmonic components thereof are added.