Measurement Principle of Coating Thickness Tester

Linshang coating thickness tester has the characteristics of small measurement error, high reliability, good stability and easy operation. It is an indispensable coating thickness measuring instrument for controlling and ensuring product quality. It is widely used in manufacturing, metal processing industry, chemical industrial, commercial inspection and other inspection fields.

1. Measuring principle of magnetic attraction coating thickness tester

The suction force between the permanent magnet (probe) and the magnetically conductive steel is proportional to the distance between the two. This distance is the coating thickness. As long as the difference between the magnetic permeability of the coating and the substrate is large enough, the measurement can be performed. In view of the fact that most industrial products are stamped and formed from structural steel and hot-rolled and cold-rolled steel plates. Magnetic coating thickness testers are the most widely used. The basic structure of the coating thickness tester is composed of magnetic steel, relay spring, scale and self-stop mechanism. After the magnetic steel is engaged with the measured object, the measuring spring is gradually elongated afterwards. The tensile force is gradually increased. When the pulling force is just greater than the suction force, the coating thickness can be obtained by recording the magnitude of the pulling force at the moment when the magnetic steel is detached. New products can automate this recording process. Different models have different ranges and applicable occasions. This coating thickness tester is characterized by easy operation and low price, which is suitable for on-site quality control in the workshop.

2. Measuring principle of magnetic induction coating thickness tester

When using the principle of magnetic induction, the coating thickness is measured by the magnitude of the magnetic flux flowing from the probe through the non-ferromagnetic coating into the ferromagnetic substrate. The coating thickness can also be measured by measuring the magnitude of the corresponding magnetic resistance. The thicker the coating, the greater the magnetic resistance and the smaller the magnetic flux. Coating thickness testers use the principle of magnetic induction can measure non-magnetically conductive coating thickness on the magnetically conductive substrate. Generally, the magnetic permeability of the substrate is above 500 microns. If the coating material is also magnetic, the difference between the magnetic permeability of the substrate and the base material is required to be large enough (such as nickel plating on steel). When the probe around the coil on the soft core is placed on the sample to be tested, the instrument automatically outputs the test current or test signal. Earlier products used a pointer meter to measure the magnitude of the induced electromotive force. The coating thickness tester amplified the signal and then indicated the coating thickness. In recent years, circuit design has introduced new technologies such as frequency stabilization. It also adopts a patented integrated circuit and introduces a microcomputer, which greatly improves the measurement accuracy and reproducibility (almost an order of magnitude). The modern magnetic induction coating thickness tester has a resolution of 0.1um, an allowable error of 1%, and a measuring range of 10mm.
       Linshang magnetic principle coating thickness tester can be applied to accurately measure the paint layer on the surface of steel, porcelain, enamel protective layer, plastic, rubber coating, various non-ferrous metal plating including nickel and chromium and various types of chemical oil anti-corrosion coating.

3. Measuring principle of eddy current coating thickness tester

High-frequency AC signals generate an electromagnetic field in the probe coil. When the probe is close to the conductor, an eddy current is formed in it. The closer the probe is to the conductive substrate, the greater the eddy current and the reflected impedance.
       This feedback function characterizes the distance between the probe and the conductive substrate, that is, the thickness of the non-conductive coating on the conductive substrate. This type of probe specifically measures the coating thickness on a non-ferromagnetic metal substrate, it is often called a non-magnetic probe. Non-magnetic probes use 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 differences are different probes, different signal frequencies and different signal and scale relationships. Like the magnetic induction coating thickness tester, the eddy current thickness gauge also achieves a high level of resolution of 0.1um, an allowable error of 1% and a range of 10mm.
       Coating thickness tester use the principle of eddy current and can measure the non-conductor coating on all conductors, such as paint, plastic coating anodized film. The cladding material has a certain conductivity, which can also be measured by calibration, but the conductivity ratio between the two is at least 3-5 times different (such as chrome plating on copper). Although the steel substrate is also a conductor, it is more appropriate to use magnetic coating thickness tester for such tasks.