Influencing Factors and Working Principle of Coating Thickness Gauge
Coating thickness gauge is also called film thickness gauge and paint thickness gauge. The coating thickness gauge can non-destructively measure the non-conductive coating thickness on the magnetic metal substrate and is convenient to carry. It is often applied in some chemical plants and metal manufacturing industry inspection fields. Although the coating thickness gauge has the characteristics of small measurement error, high reliability, good stability and easy operation. There are still some people who have doubts about the product price, selection method and troubleshooting method when using it.
The price of coating thickness gauges can range from thousands of RMB to tens of thousands of RMB. The huge price differences are mostly caused by the thickness measurement method in use. The selection of coating thickness gauges is generally divided into two types: dual-use and conventional. The former combines the characteristics of eddy current thickness gauges and magnetic thickness gauges. The latter has the characteristics of fast detection speed, which can make extensive testing of economical work.
1. The factors affecting the coating thickness gauge
(1) Base metal magnetic
During the heat treatment and cold processing, the magnetic properties of some base metals will change. Before testing, the instrument should be calibrated with a standard board with the same properties as the test piece base metal; The uncoated test piece can also be used for calibration.
(2) Electrical properties of base metal
During the heat treatment process, the conductivity of different base metals will change differently, so that the electrical properties of the base metal will change. Before testing, the instrument should be calibrated with a standard board with the same properties as the test piece base metal.
(3) Base metal thickness
Each instrument has a critical thickness of the base metal. Above this thickness, the measurement is not affected by the base metal thickness. (For the testing thickness of our company's instrument, please refer to the attached table two)
(4) Edge effects
When measuring the base metal with a non-smooth surface, the instrument will sensitively change the sharpness of the metal surface. Therefore, the data obtained from the measurement of the turning or uneven surface of the base metal is not reliable.
(5) Surface roughness
The metal looks smooth, but the upper surface is rough. The greater the roughness of the metal surface, the greater the error will be. In order to reduce the error, the same position can be repeatedly measured to reduce the error. Or after the cover layer is dissolved and removed with a solution that does not corrode the base metal.And then check the zero point of the instrument.
(6) Attached substances
When the measuring probe and the metal surface of the base body hinder the measurement, the measurement result will be effected. Therefore, the attached substances must be removed.
2. Working principle of coating thickness gauge
The working principle of the coating thickness gauge includes magnetic induction measurement principle, magnetic suction measurement principle and eddy current measurement principle.
The magnetic induction thickness gauge mainly use the pointer type meter to measure the magnitude of the base metal induced electromotive force. After receiving the instrument, the signal is amplified to indicate the coating thickness. In recent years, due to some new technological breakthroughs in circuit design, patented integrated circuits can be used. The introduction of microcomputers has reduced the error range. It is often used to measure the paint layer on steel surfaces and the anticorrosive layer in the chemical and petroleum industries.
Compared with the other two principles, the magnetic force measurement principle is simpler and the product price is lower. The principle mainly uses the suction force between the permanent magnet (probe) and the magnetically permeable steel to be proportional to the distance between the two. This distance is used to reflect the coating thickness.
The principle of eddy current measurement is to use a high-frequency AC signal to generate an electromagnetic field in the probe coil. When the probe is close to a conductor, eddy current is formed in it. The closer the probe is to the conductive substrate, the larger the eddy current and the reflection impedance. However, when using the principle of eddy current measurement, it is necessary to pay attention to a very important condition. The conductivity difference between the covering material and the conductivity of the base metal are more than three times
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