All coating thickness gages are influenced to some degree by substrate roughness. It is generally accepted that coating thickness should be measured from the highest ‘peaks’ in the rough surface thus ensuring they are covered by the protective coating. However, coating thickness gages will instead measure the coating thickness from the effective magnetic surface, which is located somewhere between the highest peaks and deepest valleys of the profile.

To compensate for the influence of substrate conditions (including roughness), measure the uncoated substrate/part at a number of spots to obtain a representative average value. This average value is called the “base metal reading” or “BMR”. Subtract the BMR from subsequent coating thickness measurements to obtain the thickness of the coating over the ‘peaks’ of the rough surface.

Yes, but it depends upon the particular type of nickel coating that has been applied to the steel.vWhen nickel plating is deposited by a process of electrolysis (employing an electric current in the nickel bath), the resultant coating – commonly called “e-nickel” – is always conductive and magnetic to some degree and cannot be accurately measured by our gages when applied to ferrous or non-ferrous metals.

Electroless nickel coatings are deposited by an autocatalytic process which does not involve the addition of an electric current. If the nickel bath in this process contains a minimum concentration of ~8% phosphorus, the resulting nickel plating is effectively non-magnetic and its thickness can be accurately measured on ferrous steel with a magnetic principle coating thickness gage such as the PosiPen.