Basic knowledge explanation of coating thickness gauge
Coating thickness gauge, also known as overlay thickness gauge, operates on the following principle:
Principle of magnetic thickness measurement: When the measuring head comes into contact with the coating, Hall discovers that the potential difference UH is proportional to the current intensity IH. The measuring head and the magnetic metal substrate form a closed magnetic circuit. Due to the presence of the non-magnetic coating, the magnetic resistance of the magnetic circuit changes, which is proportional to the magnetic induction intensity B. When the measuring head comes into contact with the coating, eddy currents are generated on the metal substrate, which are inversely proportional to the thickness d of the thin film. By measuring its changes, the thickness of the covering layer can be calculated.
Principle of eddy current thickness measurement: using high-frequency alternating current to generate an electromagnetic field in the coil, magnetic thickness measurement method
It is used for non-destructive measurement of the thickness of non-magnetic coatings on magnetic metals. There is now a new type of coating thickness gauge, namely the coating thickness gauge, which uses the latest magnetic sensing technology. That is to say, the Hall effect, which was discovered by Hall in 1879. The eddy current method can non destructively measure the thickness of non-conductive layers on magnetic metal substrates. By studying the relationship between Hall voltage and working current, measuring the magnetic permeability of electromagnets, and studying the relationship between Hall voltage and magnetic field, coating thickness gauges, also known as coating thickness gauges, film gauges, and coating thickness gauges, adopt the principles of magnetic thickness measurement and eddy current thickness measurement.
There are generally five types of coating thickness gauges based on measurement principles:
1. Magnetic thickness measurement method: suitable for measuring the thickness of non-magnetic layers on magnetic materials Magnetic materials are generally steel, iron, silver, and 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: Currently, there is no such method used in China to measure the thickness of coating layers. Some foreign manufacturers have such instruments, which are suitable for measuring the thickness of multi-layer coating layers or situations where neither of the above methods can measure it But generally, the price is expensive, such as the 200 type ultrasonic coating thickness gauge, which is specifically designed to measure coatings on non-metallic substrates.
4. Electrolytic thickness measurement method: This method is different from the above three methods and does not belong to non-destructive testing. It requires the destruction of the coating layer The general accuracy is also not high Measuring is more complicated than other methods
5. Radiation thickness gauge: This type of instrument is very expensive and suitable for some special occasions.
