DeFelsko PosiTector 100 v.4.0 - Manual (Page 32)

Page 32 100 Series
Gates A & B
Each probe has a measuring range as shown in the chart on page 41. For
example, the C probe can measure polymer coatings in the range of
approximately 2 to 175 mils (50 to 4500 microns). However, there are times
when it is not desired to inspect this full range of thickness.
Gates are used to narrow the range of thickness that the Gage examines. Gate A
sets the minimum thickness limit and Gate B the maximum. These values are
adjusted to:
•
increase the resolution of the graphical display
•
make the Gage ignore echoes from other sources such as surface echoes and
echoes from within the substrate
•
improve the resolution of the displayed measurement results
•
reduce the likelihood of the Gage registering other than what the user
intended to measure
There are two ways to adjust the Gates. If the Graphics display is visible, use the
Setup q
q Gate/Zoom Control menu item to change the scale of the
display. If the Graphics display is OFF, use the
Setup q
q Application
Setup menu item to simply adjust their values.
When measuring, the Gage looks for a distinct interface within the two Gate
settings. If the actual thickness is outside this range, incorrect or dashed readings
occur.
Gate A should be high enough to prevent the Gage from reading surface
roughness. Unusually thin readings indicate that the Gate A value may be set too
low.
Gate B should be low enough to prevent total thickness measurements of both
the coating and substrate. If results are twice the expected thickness, lower the
value of Gate B.
Here are some typical setups...
Expected paint thickness Gate A Gate B
20 mils (500µm) on concrete 5 mils 150µm 40 mils 1000µm
2 mils (50µm) on wood 0.5 mils 13µm 10 mils 250µm