Phase Sensitive Eddy Current

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This is how Phase Sensitive Eddy Current measuring works.

The phase-sensitive eddy current probes consist of a ferrite core around which two coils are wound. A current generates a high-frequency magnetic field (kHz-MHz range) in the exciter coil, which produces eddy currents in the sample.

By means of the second coil – the measuring coil – the AC resistance (impedance) of the probe is measured. This probe impedance is modified by the eddy currents in the sample and is out of phase (phase angle φ) compared to the excitation current (probe without sample).

The phase angle φ depends on the layer thickness and the electrical conductivity of the material. If the conductivity is known, the phase angle is compared in the instrument with a stored characteristic curve and converted into a coating thickness value.

Where is this process used?

Coating thickness measurement on electroplated surfaces and printed circuit boards, e.g.
- Ni on Fe
- Zn or Cu on Fe
- Cu on brass or bronze
- Thermally sprayed aluminum coatings (TSA) on Fe
- Cu on printed circuit boards
- Cu in holes in printed circuit boards

Applicable Standards

DIN EN ISO 21968

The conductivity of the coating and the base material determine the density of the induced eddy currents and thus have a direct influence on the coating thickness measurement. Therefore, the instrument must be calibrated with the correct combination of base material and coating, namely with the materials on which real measurements are to be made later. Cu in holes in printed circuit boards

Thickness of Test Piece ?

With metallic samples, eddy currents are generated not only in the coating material, but also in the base material. If the base material is very thin (such as flat sheet metal), care must be taken to ensure that the measurement frequency and material-dependent minimum thickness is guaranteed.