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What is Coating Thickness Testing?

What is Coating Thickness Testing?

The thickness of coatings or layers on a metalic substrate kan be measured and gauged by simple means when the coating and underlying substrate has different magnetic or electrical properties.
The thickness of non-ferromagnetic coatings on top of a ferromagnetic substrate is measured easily with instruments based on magnetic or electromagnetic principles.


The magnetic methods are mainly used for measuring coating thickness of paint, plastic and non-magnetic metal coatings on 'soft' steel, i.e steel with a hardness up to 550-600 HV.
More accurate and easily reproducible measurements is achieved with electromagnetic inductive methods.
The non-ferromagnetic layer forms a gap in the magnetic circuit between the base material and measuring probe. The inductance in an iron-core spool or in a transformer-core varies relative to the size of the gap.


This change in the inductance is then turned into a measurement for the coating thickness, which can be easily read out on the display in the handheld device such as the Phynix POCKET-SURFIX FN  or the Phynix Paintcheck.


History of Coating Thickness Testing:

Corrosion protection or decorative coatings has always had minimum requirements for their thickness to fulfill their purpose. There was a need for a device to measure this in a fast, easy and relative accurate manner.

With steel as the main construction material, it was only natural to study the magnetic attraction force that greatly decreases in correlation with distance to the magnet. The springloaded magnet as a thickness gauge was obvious and almost invented itself in the beginning.

Unfortunately the accuracy of this device was not very impressive. As the semiconductor technique gained traction, new lightweight and stable amplifiers that could register minute changes in electromagnetic circuits, new and improved equipments was invented that utilised the magnetic inductive principles.

By the 1960's they already had equipment on par with todays, although they were fairly klunky and not exactly cheap like modern devices.
Development has since focused mainly on user friendliness.