Coulometric coating thickness measurement according to DIN EN ISO 2177.
The COULOSCOPE instrument series operates according to the coulometric test method as per DIN EN ISO 2177. This involves dissolving a metal coating off of its metallic or non-metallic substrate by means of an electrolyte under controlled electric current, i.e. reversing the electroplating process (de-plating). The current required for de-plating is directly proportional to the mass of the metal to be removed. A clear correlation between the de-plating time and the coating thickness arises when the test current and area are both kept constant.
The following formula applies for determining coating thickness via the coulometric de-plating process: De-plating takes place in a measuring cell – a kind of miniature electrolytic bath. The measuring area is defined by a plastic gasket attached to the measuring cell. The electrolytes used are formulated for the various coating materials such that de-plating does not start until current flows. The de-plating process is initiated by the instrument’s electronics. A pump circulates the liquid within the measuring cell, continually refreshing the electrolyte in contact with the de-plating area, thereby ensuring uniform de-plating. Depending on the size of the area to be measured, gaskets with various diameters are available for the measuring cell.