Calibration of Unipolar High Current Impulses for Resistance Spot Welding

Requirement from practice is the need for quality and precise measurement of unipolar high current impulses, which are applied in resistance spot welding. The reason is the high dependence of weld quality on the shape and energy of applied current impulses. A new calibration method for this current impulses without disconnecting the current circuit of a resistance welding machine is required. Review and selection of suitable noninvasive current sensing devices have been made. Frequency analysis of typical unipolar current welding impulses was performed as well. The following measurements of chosen sensing devices with Hall sensors and special magnetoresistance sensor verified the necessary frequency bandwidth of the sensors. Verification measurements of unipolar current impulses were carried out as well. Finally, the uncertainty of the calibration method with a noninvasive current sensing device has been determined.