The Danisense current sensor technology is based on a closed loop system, powered by a flux gate as the magnetic field detector.
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 magnetics 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