Extech Instruments CG204 User Manual page 10

Calibrating for Shot-blasted surfaces
The physical nature of shot-blasted surfaces results in higher than normal coating
thickness readings. The mean thickness over the peaks can be determined as follows:
1. The meter should be calibrated according to the calibration instructions. Use a smooth
calibration sample with the same curvature radius and the same substrate as the
device to be tested.
2. Take approx. 10 readings on the uncoated, shot-blasted sample to produce the mean
value Xo.
3. Take an additional 10 readings on the coated, shot blasted test sample to produce the
mean value Xm
4. The difference between the two mean values is the mean coating thickness Xeff over
the peaks. The greater standard deviation 'S' of the two values Xm and Xo should also
be taken into consideration: Xeff = (Xm - Xo) ±S
NOTE: For coatings thicker than 300 μm, the influence of roughness generally is of no
importance and therefore it is not necessary to apply the above calibration methods.
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10 CG204-EU-EN V2.1 3/11