Eddy current measurement principle of coating thickness gauge
The high-frequency AC signal generates an electromagnetic field in the probe coil, and when the probe is close to the conductor, eddy currents are formed in it. The closer the probe is to the conductive substrate, the greater the eddy current and the greater the reflection impedance. This amount of feedback characterizes the distance between the probe and the conductive substrate, that is, the thickness of the non-conductive coating on the conductive substrate. Since these probes specialize in measuring the thickness of coatings on non-ferromagnetic metal substrates, they are often referred to as non-magnetic probes. Non-magnetic probes use high-frequency materials as coil cores, such as platinum-nickel alloys or other new materials. Compared with the principle of magnetic induction, the main difference is that the probe is different, the frequency of the signal is different, the size and scale relationship of the signal are different. Like the magnetic induction thickness gauge, the eddy current thickness gauge has also reached a high level of resolution of 0.1um, allowable error of 1%, and range of 10mm.
The thickness gauge using the principle of eddy current can in principle measure the non-conductive coating on all electrical conductors, such as the surface of aerospace vehicles, vehicles, household appliances, aluminum alloy doors and windows and other aluminum products surface paint, plastic coating and Anodized film. The cladding material has a certain conductivity, which can also be measured by calibration, but the ratio of the two conductivity is required to be at least 3-5 times different (such as chrome plating on copper). Although steel substrates are also electrical conductors, magnetic principles are more suitable for this type of task.
