Sources Of Error In Gage Profile Measurement
A human hair is about 2 mils (50 microns) thick and individual bacteria are 0.1 mil (2.5 microns) in size. Field profile measurements to accuracies in this range will be influenced by subtle effects.
The four major sources of error in determining the profile of a blasted surface using replica tape and a micrometer gage are:
1) Inherent variation in point-to-point profile over the surface being measured,
SSPC - The Society for Protective Coatings - is currently (2010) developing standardized guidance on number of measurements per unit area.
2) Presence of particles of dirt on either the replica tape or gage,
Reasonable care should be taken to keep the gage anvils free of dirt or grit. Questionable measurements should be double checked.
3) Gage accuracy,
Suitable micrometric thickness gages commonly cite an accuracy of ±0.2 mil (5 microns). In addition to gear errors of this magnitude, we have observed that they commonly read approximately 0.1 mil high at room temperature and 0.1 mil low at freezing. Only gages specifically designed for use with replica tape will have the correct accuracy, closing force, anvil/contact point dimensions and parallelism specifications.
4) Rubbing technique,
Including excessive or inadequate burnishing force.
See "Step 7 " of Instructions.