How to use the coating thickness gauge, points for attention
Coating thickness gauge generally has the following five types according to the measurement principle:
1. Magnetic thickness measurement method: It is suitable for measuring the thickness of the non-magnetic layer on the magnetically conductive material. The magnetically conductive material is generally: steel\iron\silver\nickel. This method has high measurement accuracy
2. Eddy current thickness measurement method: suitable for measuring the thickness of non-conductive layers on conductive metals. This method is less accurate than magnetic thickness measurement method
3. Ultrasonic thickness measurement method: At present, there is no such method in China to measure the thickness of the coating. Some foreign manufacturers have such instruments, which are suitable for the measurement of the thickness of multi-layer coatings or the occasions where the above two methods cannot be measured. But it is generally expensive and the measurement accuracy is not high.
4. Electrolytic thickness measurement method: This method is different from the above three methods. It does not belong to non-destructive testing and needs to destroy the coating. The general accuracy is not high. It is more troublesome to measure than other types
5. Radiation thickness measurement method: this kind of instrument is very expensive), suitable for some special occasions.
Measuring principle of magnetic induction
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, the difference in permeability from the base material is required to be sufficiently large (such as 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. Also adopt the designed integrated circuit and introduce the microcomputer, 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 accurately 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 petroleum. coating.
