Introduction to magnetic induction principle thickness gauge
The principle of magnetic induction is to use the magnetic flux of the probe passing through a non ferromagnetic coating and flowing into the iron substrate to determine the thickness of the coating. The thicker the coating, the smaller the magnetic flux. Due to being an electronic instrument, it is easy to calibrate and can perform multiple functions, expand the range, improve accuracy. Due to the reduced testing conditions, it has a wider range of applications than magnetic suction.
When the measuring head wrapped around the coil on the soft iron core is placed on the tested object, the instrument automatically outputs the test current, and the magnitude of the magnetic flux affects the magnitude of the induced electromotive force. The instrument amplifies this signal to indicate the thickness of the coating. Early products used meter heads for indication, which resulted in poor accuracy and repeatability. Later, digital display was developed, and circuit design became increasingly sophisticated. In recent years, new technologies such as microprocessors, electronic switches, and frequency stabilization have been introduced, and various successful products have been introduced. The accuracy has been greatly improved, reaching 1%, and the resolution has reached 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 effect. 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 current and frequency of the probes. A single 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.
A thickness gauge developed using electromagnetic principles is generally suitable for all non magnetic coating measurements, with a basic magnetic permeability of over 500. If the coating material is also magnetic, it is required to have a sufficiently large difference in magnetic permeability compared to the substrate (such as nickel plating on steel). The magnetic principle thickness gauge can be applied to measuring paint coatings on steel surfaces, protective layers of porcelain and enamel, plastic and rubber coatings, various non-ferrous metal electroplating coatings 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 thin films, the use of measurement platforms or rollers (made of steel) can also be used to measure any point on a large area.
