Coating thickness gauges

The coating thickness measurment process

Like on other surface measurements, there are various procedures to measuring coating thickness.
The magneto-inductive method is an electro-magnetic process of non-destructive material testing.
Only magneticly neutral coatings (paints, plastic, chrome, copper, zinc, enamel, etc.) are used on magnetic basic metal surfaces (iron, steel). The heart of the probe is a transformer which is set with two windings. The prime winding is connected to the supply generator, the second one is connected to a measuring amplifier. During measurment, the material in subject becomes part of the transformer's core, with the layer on the material acting like a barrier now, splitting the new core in half (Graphic 1). Depending on the thickness of the coating layer, the magnetic resisitance of the transformer and the second winding changes. The amplitude of this tension has a non-linear decreases with increase of layer-thickness (Graphic 2). This effect is processed by a coating-thickness-measuring device that sends signals and converts them to thickness-measuring units. Since theses signals adapt to the surface, a zeroing process should be done prior to measuring.

Graphic 1

1 = Probe          2 = Layer          3 = Base material

Graphic 2

U = Voltage          D = Coating thickness 

The eddy current testing method is an electric and non-destructive method of material testing. It is used on non electric conducting layers (glass, paper, plastics, lacquers, enamels, rubber, etc.) layering non magnetic, electric conducting metals (aluminium, zinc, copper or brass). Using this method there appears an alternating magnetic field when a constant alternating current flows through a coil. The frequency of the created magnetic field equals the current and pushes through the tested material. If the material is non conducting, the magnetic field will still stay as it is. However, in the coated base material, eddy currents are being generated, and through Lenz's Law, create a opposing field that affects the overall impedance of the coil. The smaller the distance between the material and the coil, the larger the change in impedance (Graphic 3). The change in impedance is transmitted by a coating thickness gauge to determine the corresponding layer thickness.

Coating thickness gauges by SaluTron^©

The SaluTron ComBi-D3 combines, with integrated Fe and NFe probes, the coating measurments on Iron and non iron metals in one single gauge. If the combination is not wished, we offer two separate cheaper options as well. The SaluTron-D4 (integrated Fe probe) or the SaluTron (integrated NFe probe). Another combination device that is also cheaper would be the SaluTron^© ComBi D1000 for measuring on Steel/Iron as well as, non-magnetic substrate.

The D1, D2X and D6 gauges can find, with external cabel-probes, their individual application fields.

Graphic 3

1 = Coil                    2 = Eddy currents

3 = Base material      4 = Resulting current value