There are various methods for measuring the film thickness.
We will introduce general film thickness measurement methods (electromagnetic type, eddy current type, electrolytic test method, fluorescent X-ray type).
Film thickness measurement method
Electromagnetic type (electromagnetic induction type film thickness meter)
The base must be magnetic.
When a magnetic material is brought close to the tip of a probe containing a low-frequency AC electromagnet, a reaction (electromagnetic induction) occurs when the magnet attracts the magnetic material, and the secondary coil responds to a slight change in the distance between the two. The voltage of is changed. This change is used to measure the thickness of the film. The electromagnetic type can be used only when the base is a magnetic metal such as iron. If the base is non-ferrous metal (non-magnetic metal), use an eddy current phase film thickness meter that uses eddy current.
Measurement target: Non-magnetic film (plating, paint, resin film, etc.) on magnetic material (iron, copper, ferritic stainless steel, etc.)
(Note) The condition is that the base is a magnetic material. Since the distance from the probe to the magnetic substrate is measured, the degree of adhesion of the probe and the roughness of the film surface affect the measurement. To avoid this, we recommend the virtually non-contact eddy current phase equation and the beta ray equation for measuring mass. In addition, even if it is a contact type, it is possible to achieve averaging by using a type that has two sensors in the probe or an object with a large probe contact surface.
Eddy current type (eddy current type film thickness meter) -DIN EN ISO 2360, ASTM B244 compliant method-
The base must be a conductive / non-magnetic metal.
DIN EN ISO 2360, ASTM B244 compliant method. The heat of the insulating film on the metal is measured by using the electrical correlation between the magnitude of the eddy current induced on the surface of the non-magnetic metal by the high-frequency electric field and the distance between the magnetic field and the metal surface (film thickness). ..
When a probe containing a coil that generates an alternating magnetic field by high-frequency alternating current (2MHz or more) is brought close to the surface of a conductive non-magnetic metal, a vortex-shaped current is generated on the metal surface by the high-frequency alternating current. Since the eddy current flows in the direction that cancels the magnetic field, the current from the transmitter receives resistance. Since its size correlates with the characteristics of the base material and the distance (film thickness) from the probe, it is converted to film thickness.
Measurement target: Measurement of insulating film (coating film, resin film, alumite, etc.) and non-magnetic film thickness on conductive non-magnetic metal (aluminum, copper, austenitic stainless steel, etc.)
(Note) It is necessary that the base is a conductive / non-magnetic metal and an eddy current can be generated. Since the distance from the probe to the magnetic substrate is measured, the degree of adhesion of the probe and the roughness of the film surface affect the measurement.
Electrolytic test method (destructive test)
A method in which electrolysis is performed using the measurement surface as the anode and the cell in which the electrolytic solution is placed as the cathode. The time required to dissolve a certain area in the anode by constant current electrolysis with an electrolytic solution suitable for various metals. This is a test method for measuring the plating thickness by applying that is proportional to the thickness.
This test method belongs to the destructive test that damages the film, but the thickness of each film can also be measured for single-layer plating and multi-layer plating.
[Fluorescent X-ray type]
When a substance is irradiated with X-rays, the fluorescent X-ray thickness measuring device emits X-rays specific to the elements contained in the substance, and by comparing the fluorescent X-ray dose with a sample having a known plating thickness. Measure the plating thickness.
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