Principle of magnetic attraction measurement and thickness gauge
The suction force between the magnet (probe) and the magnetizing steel is proportional to the distance between the two, which is the thickness of the coating. Using this principle to make a thickness gauge, as long as the difference in permeability between the coating and the substrate is large enough, it can be measured. Given that most industrial products are formed by stamping structural steel and hot-rolled and cold-rolled steel plates, magnetic thickness gauges are widely used. The basic structure of the thickness gauge consists of magnetic steel, relay spring, ruler, and self stopping mechanism. After the magnetic steel is attracted to the measured object, the measuring spring is gradually stretched and the tension gradually increases. When the tensile force is just greater than the suction force, the thickness of the coating can be obtained by recording the magnitude of the tensile force at the moment when the magnetic steel detaches. The new product can automatically complete this recording process. Different models have different ranges and applicable scenarios.
The characteristics of this instrument are easy to operate, sturdy and durable, no need for power supply, no need for calibration before measurement, and low price. It is very suitable for on-site quality control in the workshop.
Magnetic induction measurement
When using the principle of magnetic induction, the thickness of the coating is measured by the magnitude of the magnetic flux flowing into the ferromagnetic substrate through the non ferromagnetic coating from the measuring head. The corresponding magnetic resistance can also be measured to indicate its coating thickness. The thicker the coating, the greater the magnetic resistance and the smaller the magnetic flux. A thickness gauge using the principle of magnetic induction can, in principle, have a non magnetic coating thickness on a magnetic substrate. It is generally required that the substrate permeability be above 500. If the coating material also has magnetism, it is required that the difference in permeability between it and the substrate is large enough (such as nickel plating on steel). When the probe wrapped around 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 pointer type meters to measure the magnitude of induced electromotive force, and the instrument amplified the signal to indicate the thickness of the coating. In recent years, new technologies such as frequency stabilization, phase locking, and temperature compensation have been introduced in circuit design, utilizing magnetic resistance to modulate measurement signals. We also adopted designed integrated circuits and introduced microcomputers, which greatly improved the measurement accuracy and reproducibility (almost reaching an order of magnitude). Modern magnetic induction thickness gauges have a resolution of 0.1um, an allowable error rate of 1%, and a measurement range of 10mm.
The magnetic principle thickness gauge can be applied to measure the paint layer, porcelain and enamel protective layer, plastic and rubber coating on the surface of steel, various non-ferrous metal electroplating coatings including nickel chromium, as well as various anti-corrosion coatings for chemical and petroleum industries.
