Measuring current in conductor

摘要

The current to be measured (Ip) flows in a conductor (1) which passes through a magnetic torus (2). Measurement is achieved by determining (5) a compensating current (Ic+Irf) flowing in a winding on the torus which makes the net magnetic field in the torus zero. The adverse effects of remanent magnetism on the measurement are overcome by superimposing (6a) a radio frequency current (Irf) on the compensating current (Ic) and using the absence of second harmonics (6b) as an indication of the null point. A single winding (3) on the magnetic torus is used to apply the compensating current and to determine the null point.