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Basic Principles and Standards of Eddy Current Digital Coating Thickness Gauge Technology


Ⅰ. The basic principle of eddy current digital coating thickness gauge technology


Eddy current digital coating thickness measuring instrument is a high-tech crystallization, using single-chip technology, featuring high precision, digital display, low power consumption, simple operation, no need to calibrate, small size, lightweight and It also has the characteristics of storage and low voltage reminder.


Eddy current digital coating thickness gauge is widely used in machinery, automobile, shipbuilding, petroleum, chemical industry, electroplating, plastic spraying, enamel, plastic, and other industries.


The basic principle of eddy current digital coating thickness gauge is: the principle of eddy current is adopted. When the coil core in the probe is energized, a high-frequency magnetic field is formed. The probe and the metal substrate of the coating to be tested will be in contact, and the size of the eddy current passing through the metal between the two can reflect the distance between the probe and the substrate. The closer the gauge head is to the metal substrate, the larger the eddy current, and the farther it is, the smaller the eddy current.


Based on this principle, the proportional relationship between the size of the eddy current and the size of the spacer can be found, and the spacer, which is the thickness of the coating, can be obtained.


Ⅱ. The measuring standards of the eddy current digital coating thickness gauge


In the international standard ISO 2360-1982, the standard and operation of the eddy current digital coating thickness gauge, the factors affecting the measurement accuracy, and the points for attention are described in detail. The factors affecting the measurement accuracy mainly include:


1. When the thickness of the overburden is greater than 25μm, the error is approximately proportional to the overburden thickness.


2. The conductivity of the base metal influences the measurement, which is related to the material composition of the base metal and the heat treatment method.


3. The eddy-current digital coating thickness gauge has an edge effect on the sample measurement, that is, the measurement near the edge or inside corner of the sample is not reliable.


4. Any coating thickness gauge requires a critical thickness of the base metal above which the measurement is not affected by the base metal thickness.


5. The curvature of the specimen affects the measurement, and the effect will increase obviously with the decrease of the radius of curvature.


6. The roughness of substrate metal and cover layer affects the measuring accuracy of thickness gauge, and the influence increases with the increase of roughness.


7. The eddy current digital coating thickness gauge is sensitive to the adhesion material that prevents the probe from contacting closely with the cover surface, so the dirt on the probe and cover surface should be removed before measurement. When the coating thickness gauge is measured, the probe should maintain constant pressure vertical contact with the test surface.


The scope of use of a single eddy current thickness gauge meter is not very wide, so the market gradually appeared at the same time using two principles of coating thickness gauge, this instrument at the same time using eddy current thickness measuring method and magnetic thickness measuring method can cover the measuring range of eddy current digital coating thickness measuring instrument and magnetic coating thickness measuring instrument.


The common non-magnetic metal is aluminum, and the common magnetic metal is iron, so this dual-principle instrument is what we call the iron and aluminum dual-purpose coating thickness gauge. The appearance of these thickness gauges also makes the thickness measurement of coating more simple and efficient.


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