The zero-flux DC current transformer: a high precision bipolar wide- band measuring device

A current-carrying conductor is surrounded by a pair of ring cores. A sense winding on one core provides flux rate feedback to a power amplifier which drives the ampere-turn compensating current through a common compensating winding. The other core serves as a second- harmonic modulator to establish zero-flux operation and thus to ensure a perfect, temperature-independent current balance. A specially- developed burden resistor converts the compensating current into a voltage signal, which is amplified to give an 10 V output signal at the nominal value of the current to be measured. A substantial number of devices, ranging from 50 to 25000 Amperes is now operational in the beam transfer and extraction power supplies to the CERN SPS. (4 refs).