Current intensity transformer device for measuring a variable electric current

Claim 1

A current measuring device for measuring a variable electric current, comprising a current transformer with a magnetic circuit having at least one air-gap provided with a Hall effect device having an input supply terminal for connection to an energizing current generator and an output supply terminal, and having first and second measuring terminals, said output supply terminal of the Hall effect device being connected to an output terminal of an operational amplifier having first and second inputs, said first input being connected to a reference potential, and said second input being connected to said first measuring terminal of the Hall effect device, so that said first measuring terminal is maintained at said reference potential and the measuring voltage provided by the Hall effect device appears at said second measuring terminal with respect to said reference potential, said magnetic circuit being arranged so that it can be magnetically coupled with a primary conductor for the current to be measured, and bearing at least one secondary winding magnetically coupled with said magnetic circuit, said device further comprising an electric measuring circuit arranged for adding together the measuring voltage provided by the Hall effect device and a measuring voltage appearing at the terminals of a measuring resistor connected in series with said secondary winding, to provide an output voltage representing a measure of the current in the primary conductor.