Coating Thickness Gauge Magnetic Induction Measuring Principle
When the principle of magnetic induction is used, the thickness of the coating is measured by the magnitude of the magnetic flux flowing from the probe through the non-ferromagnetic coating into the ferromagnetic substrate. The size of the corresponding magnetoresistance can also be measured to indicate the thickness of the coating. The thicker the coating, the greater the reluctance and the smaller the flux. The thickness gauge using the principle of magnetic induction can in principle have the thickness of the non-magnetic coating on the magnetic substrate. Generally, the magnetic permeability of the substrate is required to be above 500. If the cladding material is also magnetic, a sufficiently large difference in permeability from the base material is required (eg nickel plating on steel). When the probe with the coil wound on the soft core is placed on the sample to be tested, the instrument will automatically output the test current or test signal. Early products used a pointer gauge to measure the magnitude of the induced electromotive force, and the instrument amplified the signal to indicate the coating thickness. In recent years, circuit design has introduced new technologies such as frequency stabilization, phase locking, and temperature compensation, and uses magnetic resistance to modulate measurement signals. The designed integrated circuit is also used, and the microcomputer is introduced, so that the measurement accuracy and reproducibility have been greatly improved (almost an order of magnitude). The modern magnetic induction thickness gauge has a resolution of up to 0.1um, an allowable error of 1%, and a range of 10mm.
The magnetic principle thickness gauge can be used to measure the paint layer on the steel surface, porcelain, enamel protective layer, plastic, rubber coating, various non-ferrous metal plating layers including nickel and chromium, and various anti-corrosion coatings for chemical oil industry .
