Zeroflux Current Transducers
A zero flux transducer uses the flux gate principle. The current to be measured generates a magnetic flux that is counteracted by the flux generated by a secondary winding.
In general terms, the flux gate principle is to use an excited magnetic material coil as a probe. Thanks to a saturation/desaturation cycle and signal processing, this coil is able to measure the magnetic field proportionally. From that multiple options are possible to design a current transducer. It can simply replace a Hall effect probe in the air gap or the coil could have the shape of a tore.
The magnetic field in the toroid generated by the primary current (Ip) is counteracted by the compensating secondary current (Is) generated by the integrator.
The flux gate detects magnetic fields in the toroid from DC to less than 100 Hz at sub ppm levels and tells the integrator to compensate them out.
At higher frequencies, the feedback winding (Nfb) detects magnetic fields in the toroid at ppm levels and tells the integrator to compensate them out as well. The secondary current (Is) is therefore proportional to the primary current (Ip) with the ratio Np:Ns.