Principle of Eddy Current Measurement for Coating Thickness Gauge
High frequency AC signals generate electromagnetic fields in the probe coil, and when the probe is close to the conductor, eddy currents are formed within it. The closer the eddy current thickness gauge head is to the conductive substrate, the greater the eddy current and the greater the reflection impedance. This feedback action represents the distance between the probe and the conductive substrate, which is the thickness of the non-conductive coating on the conductive substrate. Due to the fact that this type of eddy current thickness gauge head is specifically designed to measure the thickness of the coating on non ferromagnetic metal substrates, it is commonly referred to as a non magnetic gauge head. The non magnetic measuring head of the eddy current thickness gauge uses high-frequency materials as the coil core, such as platinum nickel alloy 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, and the size and scale relationship of the signal are different. Like the magnetic induction thickness gauge, the eddy current thickness gauge also achieves a resolution of 0.1um, an allowable error of 1%, and a high level range of 10mm.
A coating thickness gauge using the principle of eddy current can measure non conductive coatings on all conductive materials, such as paint, plastic coatings, and anodic oxide films on the surfaces of aerospace aircraft, vehicles, household appliances, aluminum alloy doors and windows, and other aluminum products. The coating material has a certain degree of conductivity, which can also be measured through calibration, but the ratio of conductivity between the two is required to be at least 3-5 times different (such as chromium plating on copper). Although the steel substrate is also a conductive material, it is still more appropriate to use magnetic principles for such tasks.
Application and classification of coating thickness gauges
The coating thickness gauge can be divided into
Magnetic thickness gauge and non magnetic thickness gauge (i.e. eddy current coating thickness gauge)
The magnetic thickness measurement method can measure the thickness of all non magnetic metals and all non conductive layers on iron and steel magnetic metals, such as copper, zinc, chromium, gold, silver, etc. coated on iron, as well as paint, plastic, rubber, phosphating film, fiberglass, etc.
Eddy current layer thickness gauge can measure the thickness of non-conductive coatings on non magnetic conductive metals, such as paint layers, oxide films, phosphating films, fiberglass, rubber, and other coatings on stainless steel, copper, and aluminum metals.
