US Patent 7525300 Current measuring device and method

A current measuring device measures the current flowing through each conductor which connects a power supply with a motor. Coreless current sensors are arranged between pairs of the conductors. Coefficients which represent a relationship between a fixed standard current flowing through a conductor and the output signal from coreless current sensors for the fixed standard current are obtained in advance from known measurements. A calculator then determines the current flowing through each conductor based upon the corresponding output signals from the coreless current sensors, the measured coefficients and formula Iu+Iv+Iw=0.