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Coating Thickness Measurement
Technical Note

Rough-Surface Measurement Using
the “Set Range” feature on a PosiTector 200 B1 (Standard model)

To eliminate surface roughness interference, the PosiTector 200’s menu is used to alter the default “Set Range” settings. The following article provides step by step instructions.

 

See also: PosiTector 200 Instruction Video - Typical Rough-Surface Measurement Set-up

 



A plywood coating with surface roughness.

 

The first measurement taken on the rough plywood (left) is 1.3 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.

To eliminate surface roughness interference, the PosiTector 200’s menu is used to alter the default “Set Range” settings.

Set Range narrows the range of thickness that the gage examines. Lo sets the minimum thickness limit and Hi the maximum. The gage will only report thickness values (echoes) between these two Range values.


Fig.1


Fig.2


The measurement range was 0.5 to 30 mils (see Fig. 1). Using the “+” button, Lo is changed from 0.5 up to 1.5 mils (see Fig.2). Since the 1.3 measurement result is no longer inside the Range, the gage recalculates thickness using the next-loudest echo. The thickness result immediately changes to 7.9 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 7.9 to 8.6 mils.

To obtain meaningful thickness measurements on rough surfaces, the memory mode of the PosiTector 200 is used to calculate a running average.

With memory turned ON, the PosiTector 200 calculates and displays the number of readings taken (8), the average of those readings (5.11 mils), the standard deviation of those readings (0.29), and the highest (5.8 mils) and lowest (4.9 mils) readings.

The meaningful thickness measurement for this rough surface application is 5 mils.

Those 8 individual measurements can be viewed on the LCD or downloaded to a PC using the optional PosiSoft software.


 

 


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