Inductive TDR Measurement of Thickness of Conductive Plating on Wire

A pulsed eddy current technique is described that is suitable for plating thickness measurements of low-permeability metals such as Au or Ag on high-permeability wire in the 3-80 mg/ in' range. Equipment costs, speed, and accuracy are such as to make this technique a strong contender not only for laboratory measurements but also for production line testing. The method is usable for plating thickness measurements whenever the ratio of relative permeability to electrical conductivity for the plating material differs substantially from that for the substrate, with the added condition that at least the plating is electrically conductive.