When the principle of magnetic induction is adopted, the thickness of the coating is determined by the magnetic flux flowing from the probe into the ferromagnetic matrix through the non-ferromagnetic coating. The corresponding magnetoresistance can also be measured to indicate the coating thickness. The thicker the coating, the greater the magnetic resistance and the smaller the magnetic flux. In principle, the thickness gauge based on magnetic induction principle can have the thickness of non-magnetic coating on magnetic substrate. Generally speaking, the magnetic permeability of the substrate is required to be above 500. If the coating material is also magnetic, it is required that the difference between the permeability and the substrate is large enough (such as nickel plating on steel). When the probe wound on the coil on the soft core is placed on the tested sample, the instrument automatically outputs the test current or test signal. Early products used a pointer instrument to measure the induced electromotive force, and the instrument amplified the signal to indicate the coating thickness. Some circuit designs introduce new technologies such as frequency stabilization, phase locking and temperature compensation, and use magnetoresistance to modulate the measurement signal. Patented integrated circuits and microcomputers are also adopted, which greatly improves the measurement accuracy and reproducibility (almost an order of magnitude). The resolution of modern magnetic induction thickness gauge is 0.65438 0 micron, the allowable error is 65438 0%, and the measuring range is 65438 0 mm.
Magnetic principle thickness gauge can be used to accurately measure paint layer, enamel protective layer, plastic and rubber coating, electroplating layer of various non-ferrous metals including nickel and chromium, and various anti-corrosion coatings in chemical and petroleum industries.