Introduction to the Magnetic Induction Principle of Coating Thickness Gauges
The principle of magnetic induction is to measure the thickness of the coating by measuring the magnetic flux flowing into the iron substrate through a non ferromagnetic coating. The thicker the coating, the smaller the magnetic flux. As an electronic instrument, it is easy to calibrate and can achieve multiple functions, expand the range, and improve accuracy. Due to the reduced testing conditions, it has a wider range of applications than magnetic attraction.
When the probe with a coil wound around a soft iron core is placed on the object being measured, the instrument automatically outputs a test current. The magnitude of the magnetic flux affects the magnitude of the induced electromotive force, and the instrument amplifies the signal to indicate the thickness of the coating. Early products used header indicators, which had poor accuracy and repeatability. Later, digital display was developed, and circuit design became increasingly sophisticated. In recent years, the introduction of microprocessor technology and new technologies such as electronic switches and frequency stabilization has led to the emergence of various products with greatly improved accuracy, reaching 1% and a resolution of 0.1 μ m. The measuring head of the magnetic induction thickness gauge mostly uses soft steel as the magnetic core, and the frequency of the coil current is not high to reduce the influence of eddy current effects. The measuring head has temperature compensation function. Due to the intelligence of the instrument, it can identify different probes, cooperate with different software, and automatically change the probe current and frequency. One instrument can be used with multiple probes, or the same instrument can be used. It can be said that instruments suitable for industrial production and scientific research have reached a very practical stage.
The thickness gauge developed using electromagnetic principles is generally applicable for measuring all non-magnetic coatings, and generally requires a basic magnetic permeability of 500 or above. If the coating material is also magnetic, it is required to have a sufficiently large difference in magnetic permeability with the substrate (such as nickel plating on steel). The magnetic principle thickness gauge can be applied to measure paint coatings on steel surfaces, ceramic and enamel protective layers, plastic and rubber coatings, various non-ferrous metal electroplating layers including nickel chromium, and various anti-corrosion coatings in the chemical and petroleum industries. For the production industry of photosensitive film, capacitor paper, plastic, polyester and other films, measuring platforms or rollers (made of steel) can also be used to achieve measurement of any point over a large area.
