Elcometer 280 S, User Manual, Page: 10 / 112

9 SELECTING A VOLTAGE (continued)
5 A confirmation screen will now display the
selected test standard, dry film thickness
and calculated test voltage,
i Press OK to set the instrument voltage
to the calculated value,
or
ii Press ESC to return to the reading
screen without making changes.
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10 MANUALLY CALCULATING THE TEST VOLTAGE
When setting the voltage manually please follow the guidelines below
which describe how a safe, but effective, test voltage may be
determined.
Overview
For effective testing, the test voltage must lie between two limits - the
upper and lower limits.
The upper voltage limit is that at which the coating itself would
breakdown and be damaged at the thickness applied.
The lower limit is the voltage required to break down the thickness of
air equivalent to the coating thickness. If the output voltage is not
greater than this value, then a flaw will not be detected.
These two limits can be determined and a voltage approximately half
way between them selected as the test voltage.
Dielectric Strength
Whatever the material, if a high enough voltage is applied, it will
conduct electricity. For insulators such as paint, however, the level of
voltage required to achieve a current flow usually results in
irreversible material damage.