AC/DC current detecting method

Claim 1

An AC/DC current detecting method utilizing a single annular iron core made of a high permeability material having a symmetrical rectangular-type hysteresis curve of magnetization and a smaller coercive force than a soft magnetic core, a single coil wound on the annular iron core, excited by an excitation circuit produced by a high frequency electric source, an excitation circuit connected between the excitation coil and the high frequency electric source, a detection resistor connected to the excitation circuit, and a conductor passing through a center hole of the annular iron core, the method comprising the steps of: subjecting the single annular iron core having the single excitation coil to an excitation in a positive region and in a negative region, driving the magnetization of the annular iron core into saturation evenly in both regions where the magnetic flux density is substantially constant; moving a range of the magnetization of the hysteresis curve to cause a change in a value of the excitation current corresponding to the coercive force value of the excitation in response to an impression of a magnetic field induced by a detected current flowing in the conductor; obtaining the change in the value of the high frequency excitation current as one of a voltage change across the detection resistor and a voltage change across the single excitation coil; and calculating the detected current by a difference between absolute values of the voltage changes obtained in the obtaining step.