Basic knowledge of coating thickness gauge
The principle of magnetic thickness measurement: when the measuring head is in contact with the coating, Hall finds that the potential difference UH is proportional to the current intensity IH, and the measuring head and the magnetic metal substrate form a closed magnetic circuit. Due to the existence of the non-magnetic coating, the magnetic The reluctance of the circuit changes, which is proportional to the magnetic induction intensity B. When the probe is in contact with the covering layer, an eddy current is generated on the metal substrate, which is inversely proportional to the thickness d of the sheet. The thickness of the covering layer can be calculated by measuring its change.
The principle of eddy current thickness measurement: using high-frequency alternating current to generate an electromagnetic field in the coil, the magnetic thickness measurement method is used to non-destructively measure the thickness of the non-magnetic coating on the magnetic metal. Now there is a new type of coating thickness gauge, namely Coating thickness gauge, which uses the latest magnetic sensing technology. This is what we know as the Hall effect, discovered by Hall in 1879. The eddy current method can non-destructively measure the thickness of non-conductive layers on non-magnetic metal substrates. By studying the relationship between the Hall voltage and the working current, measuring the magnetic permeability of the electromagnet, and studying the relationship between the Hall voltage and the magnetic field, the coating thickness gauge is also called a coating thickness gauge, a film measuring instrument, and a coating and coating instrument. It adopts the principle of magnetic thickness measurement and eddy current method.
Coating thickness gauge generally has the following five types of methods according to the measurement principle:
1. Magnetic thickness measurement method: It is suitable for measuring the thickness of the non-magnetic layer on the magnetically conductive material. The magnetically conductive material is generally: steel\\iron\\silver\\nickel. This method has high measurement accuracy
2. Eddy current thickness measurement method: suitable for measuring the thickness of non-conductive layers on conductive metals.
3. Ultrasonic thickness measurement method: At present, there is no such method in China to measure the thickness of the coating. Some foreign manufacturers have such instruments, which are suitable for the measurement of the thickness of multi-layer coatings or the occasions where the above two methods cannot be measured. But generally expensive, such as the 200-type ultrasonic coating thickness gauge is dedicated to measuring coatings on non-metallic substrates.
4. Electrolytic thickness measurement method: This method is different from the above three methods. It does not belong to non-destructive testing and needs to destroy the coating. The general accuracy is not high. It is more troublesome to measure than other types
5. Radiation thickness gauge: This kind of instrument is very expensive (generally above 100,000 RMB), and is suitable for some special occasions.
