LINEARIZED PEAK HEIGHT MEASUREMENT
Linearized Peak Height (HL)
Two grades of Testex™
Press-O-Film™ replica tape, “Coarse” and "X-Coarse", are available to span the primary range of surface profiles for the coatings and linings industry –– 20 to 115 µm / 0.8 to 4.5 mils.
An unfortunate characteristic of replica tape is that conventional spring micrometer measurements are most accurate near the middle of each grade's range and least accurate at the outer ends of each grade's range. That is why two other grades, Coarse Minus (< 20 µm / 0.8 mils) and X-Coarse Plus (> 115 µm / 4.5 mils), are used to check and, if necessary, adjust measurements at the upper and lower ends of the primary range.
Inside the primary range, Coarse and X-Coarse tape share a 38 - 64 μm (1.5 - 2.5 mils) "overlap" region. Measurements with conventional micrometers require a complicated and time consuming procedure of averaging one reading using Coarse grade and one reading using X-Coarse grade to achieve reasonable accuracy.
With a single measurement, the PosiTector RTR produces a more accurate peak-to-valley height measurement HL from Coarse or X-Coarse tapes that has been adjusted for their non-linearity. There is no need to average two or more replicas from different grades of tape AND there is no need to subtract the 50.8 μm / 2 mils of incompressible polyester film. The advantages are a reduction in measurement uncertainty, inspector workload, likelihood of error, and the number of replicas needed by inspectors to assure accuracy.
The PosiTector RTR can also display a height value (H) that is comparable to what conventional analog spring micrometers would display after the 50.8 μm / 2 mils of incompressible polyester film has been subtracted.
Linearization of Roughness Measurements
by Robert Stachnik
(Scientific Director, Testex)