Three electronic thickness gauges used for metallic coatings

Three types of instruments for measuring the thickness of electrodeposited coatings have recently been developed by the National Bureau of Standards (NBS). While all three instruments depend upon the difference in electric conductivity between the plating and the basis metal, each makes use of different methods for sensing specimen resistance. Two of the instruments, the “Dermitron” and the phase-angle thickness meter, utilize electromagnetic coupling to the specimen, making use of the reflected field from eddy currents induced in the specimen. A third, a waveguide inspection tool, employs direct conductivity measurement with point electrodes. All three devices permit simple nondestructive determination of plating thickness of sample thickness for homogeneous metals. When appropriately calibrated, they can be used for measurement of magnetic as well as nonmagnetic materials.