Magnetic attraction measurement principle and coating thickness gauge
The suction force between the probe and the magnetic steel is proportional to the distance between the two. This distance is the thickness of the coating. According to this principle, a coating thickness gauge can be made, as long as the permeability between the coating and the substrate is sufficiently large, coating measurement can be carried out. Given that most industrial products are formed by stamping structural steel and hot-rolled cold-rolled steel plates, magnetic thickness gauges are widely used. The basic structure of the coating thickness gauge consists of magnetic steel, relay spring, ruler, and automatic stop mechanism. After the magnetic steel is attracted to the object being measured, the measuring spring gradually elongates behind it, and the tension gradually increases. When the tensile force is just greater than the attractive force, the coating thickness can be obtained by recording the magnitude of the tensile force at the moment when the magnetic steel separates. The characteristics of this instrument are easy operation, sturdy and durable, no need for power supply, no need for calibration before measurement, relatively low price, and it is very suitable for on-site quality control in workshops.
The principle of measuring coatings using magnetic induction method
When measuring coatings using the principle of magnetic induction, the thickness of the coating is determined by measuring the magnitude of the magnetic flux flowing into the ferromagnetic substrate through the non ferromagnetic coating using a probe. The corresponding magnetic resistance can also be measured to indicate the coating thickness. The thicker the coating, the greater the magnetic resistance and the smaller the magnetic flux. The coating thickness gauge using magnetic induction can, in principle, measure the thickness of non-magnetic coatings on magnetic substrates. Generally, it is required that the magnetic permeability of the substrate be above 500. If the coating material also has magnetism, it is required that the difference between its magnetic permeability and that of the substrate is large enough (such as nickel plating on steel). When the probe with a coil wound around the soft core is placed on the tested sample, the coating thickness gauge automatically outputs a test current or test signal. Early products used pointer type gauges to measure the magnitude of induced electromotive force, and coating thickness gauges amplified this signal to indicate coating thickness. In recent years, professionally designed integrated circuits have been adopted, single-chip microcomputers have been introduced, and advanced tools have been added, resulting in significant improvements in measurement accuracy and reproducibility. The magnetic principle coating thickness gauge can be applied to measure the thickness of paint layers, ceramic and enamel protective layers, plastic and rubber coatings, as well as various anti-corrosion coatings in the chemical and petroleum industries on steel surfaces.
