A gauge can only deliver correct results if it has been scrupulously calibrated. Here, we answer some questions about what you should consider when calibrating tactile gauges.
During calibration, the reading of a measuring device is compared with the actual property of the measured object (usually a standard with known values). Layer thickness is one such property. If the just-measured value deviates from the known value, the device must be adjusted. For all of Fischer’s tactile coating thickness gauges, these two functions are combined under the “Calibration ” menu item.
The same conditions should prevail during calibration as would later, during the actual measurement. If the thickness of a coating is to be measured, the device should be calibrated on an uncoated original part. For calibration, use the same location on the uncoated workpiece as you will when measuring the coated part.
In general, the instruments should be recalibrated whenever the measuring conditions change. For example, if the composition of the substrate changes, or if you go from a flat part to a curved one, it may be necessary to recalibrate, depending on the measuring method used.
On most devices, you can choose between a fast, single-point calibration and a comprehensive, multi-point calibration. The quick variant will usually suffice if the values you want to measure are very close. For example, if the thickness of the coating varies between 10 and 15 μm, it is enough to calibrate the device with a single 13 μm standard. If the range of thicknesses is larger, a multi-point calibration is recommended; the target values should bookend the expected range of coating thicknesses.
Common factors that can affect the results of a measurement. If one of these factors changes significantly, the device should be recalibrated:
- Curvature of the measuring surface
- For thin specimens: thickness of the base material
- For small specimens: dimensions of the piece
- Composition and magnetizability of the substrate or coating materials
- For conductivity measurements: temperature