Analytical Functions
6-11
8 equals 4.10, so the minimum acceptable cut-off wavelength is 5 µm. The scan length must equal the
cut-off wavelength, so the maximum cutoff length is 2000. Therefore, you must select a cut-off value
between 5 and 2000 µm.
As shown in
, you set the filter cutoff values in the
Roughness and Waviness Filters
dialog box, which provides the following three separate cut-off filters for selecting the wavelength
bypass frequency.
Short (High) Pass Filter
This filter calculates
roughness
data, filtering out low frequency waviness signals and allowing high
frequency roughness data to pass through.
Long (Low) Pass Filters
This filter calculates
waviness
data, filtering out high frequency roughness signals and allowing low
frequency waviness data to pass through.
Band Pass Filter
When you select the band pass filter, both the short pass and long pass filters are enabled to calculate
the roughness data, creating a band that filters out high frequency signals above the band and low
frequency signals below the band.
ACTIVATING THE CUTOFF FILTERS
To obtain accurate roughness measurements, activate the short pass filter.
1
Select
Analysis
>
Cutoff Filters
from the
Data Plot
window menu bar to display a dialog box for setting
the roughness and waviness filters.
Figure 6-10: Roughness and Waviness Filters Dialog Box
2
Enter a value of
200
in the
Short Pass Filter Cutoff
field.
3
Enter a value of
200
in the
Long Pass Filter Cutoff
field.
4
Click
OK
to replot the profile trace with three separate scan traces, as shown in
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