Principle of operation of the eddy current coating thickness gauge
The working principle of an eddy current coating thickness gauge is that when the measuring head comes into contact with the tested sample, the high-frequency electromagnetic field generated by the measuring head device causes eddy currents in the metal conductor placed under the measuring head. The amplitude and phase of the eddy currents are functions of the non-conductive coating thickness between the conductor and the measuring head The alternating electromagnetic field generated by the eddy current will change the parameters of the measuring head, and the magnitude of the variable parameters of the measuring head can be converted and processed to obtain the thickness of the coating to be measured
Reasons that affect measurement accuracy
(1) When the thickness of the covering layer is greater than 25 µ m, the error is approximately proportional to the thickness of the covering layer;
(2) The conductivity of the base metal has an impact on the measurement, which is related to the composition of the base metal material and the heat treatment method;
(3) Any thickness gauge requires a critical thickness of the base metal. Only when the thickness is greater than this, the measurement will not be affected by the thickness of the base metal;
(4) Eddy current thickness gauges have edge effects on pattern measurement, which means that measurements near the edge or inner corner of the pattern are unreliable
(5) The curvature of the sample has an impact on the measurement, which will significantly increase with the decrease of curvature radius;
(6) The surface roughness of the base metal and covering layer affects the accuracy of measurement, and as the roughness increases, the impact increases;
(7) Eddy current thickness gauges are sensitive to adhering substances that hinder close contact between the measuring head and the surface of the covering layer. Therefore, before measurement, the dirt on the measuring head and the surface of the covering layer should be removed; During measurement, the probe should maintain a constant pressure vertical contact with the test surface
