Film thickness test method - eddy current method

The eddy current Thickness Gauge uses a probe with a high-frequency coil to generate a high-frequency magnetic field, so that eddy currents are generated in the sample to be tested under the probe. The amplitude and phase of this eddy current is a function of the thickness of the non-conductive coating between the probe and the sample under test . Coating thickness can be read directly from the measuring instrument.

This method can measure the thickness of non-conductive coatings on non-magnetic metal substrates (such as the thickness measurement of aluminum anodized film), single-layer metal coatings on non-conductors, and the thickness of plating (coating) layers with large conductivity differences between non-magnetic substrates and coatings. . The factors affecting the measurement accuracy are similar to those of the magnetic method. Eddy current thickness measurement is not only affected by the conductivity of the substrate, the thickness of the substrate, and the thickness of the coating, but also by the curvature of the sample, surface roughness, edge effects, and the pressure on the probe. The test error is within 10% . The measurement accuracy of coatings with thickness less than 3 μm is low.