Identification of time-varying resistance during welding

The time-variation of resistance across the workpieces (weldment) during a weld, provides a nondestructive indication of weld quality. However, inductive noise, power factor, time-varying parameters and random noise complicate the measurement of resistance. Existing measurement methods have focused on the noise and bias problem, approximating the time variation by a single resistance value for each half cycle (8.33 msec). The goal of this paper is to present a method to identify time-varying resistance (and mutual inductance), with finer resolution and accuracy than existing methods. Sampled voltage and current measurements are used with a single-input (current), single-output (voltage), continuous, time-varying model