A plywood coating with surface roughness.
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The first measurement taken on the
rough plywood (left) is 1 mil, a low result caused by surface
roughness.
This thickness result is roughly equivalent
to distance #2 below.
Couplant fills the voids between the probe
and the coating. |
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To eliminate surface roughness
interference, the PosiTector 200’s menu is
used to alter the default “Gate” settings.
Gates narrow the range of thickness that the gage examines. Gate
A sets the minimum thickness limit and Gate
B the maximum. The gage will only report thickness
values (echoes) between these two Gate values. |
Fig.1
Fig.2
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The
measurement range was 0.5 to 30 mils (see Fig.
1). Using the “+” button, Gate
A is changed from 0.5 up to 1.5 mils (see
Fig.2). Since the 1.0 measurement result is no
longer inside the Gates, the gage recalculates
thickness using the next-loudest echo. The thickness
result immediately changes to 4.7 mils. |
Now the gage accurately measures
the thickness of the wood finish. However, as expected,
roughness causes measurements to vary depending
upon the severity of the surface profile. In this
case, two measurements taken in close proximity
to each other vary from 4.7 to 5.6 mils. |
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To obtain meaningful thickness measurements on rough
surfaces, the memory mode of
the PosiTector 200 is used to calculate a running average.
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With memory turned ON, the PosiTector
200 calculates and displays the number of readings
taken (8), the average of those readings (5.00
mils), the standard deviation of those readings
(0.36), and the highest (5.7 mils) and lowest (4.7
mils) readings.
The meaningful thickness measurement for this
rough surface application is 5 mils. |
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Those 8 individual measurements can be viewed on the
LCD or downloaded to a PC using the optional PosiSoft software. |
