DeFelsko PosiTector 100 v.4.0 - Manual (Page 26)

Page 26 100 Series
C ALIBRATION I NTERVAL
Start with a recommended interval of one year and adjust that interval according
to your individual usage and environment.
Optimization
Thickness measurement error is minimized by ensuring that the Gage has the
correct velocity value for the particular coating system being measured. This is
done by following a 2-step procedure:
1. S
ELECT A C ATEGORY
2. O PTIMIZE TO A
K
NOWN
T
HICKNESS
Since actual sound velocity in materials often varies significantly from the
values found in published tables, optimization of the Model 100 for velocity is
made by measuring a known thickness of the particular material being measured
and adjusting the displayed result to the actual, known thickness. If a known
thickness is not available, factory settings alone can be used.
The need to optimize is dependant upon a number of factors, not the least of
which is the level of accuracy required. To measure thin coatings for which a
high degree of accuracy is required, such as lacquer on wood with a B probe, for
example, the user may decide that optimization is needed. To measure thick,
rough coatings for which fine accuracy is not critical such as epoxy on concrete
with a C probe, the user may decide that only Step 1 (selection of a category) is
needed. To measure paint on plastic with a B probe and have traceability to a
standard, Steps 1 and 2 must both be performed.
When an adjustment is made to the sound velocity constant, the upper and lower
measuring limits of the probe change. A fast velocity value, such as for metal,
raises both the thinnest and thickest measuring limits of the probe. A slower
velocity value, such as for rubber, lowers both the thinnest and thickest
measuring limits of the probe. Table 4 on page 41 gives some examples.
S
TEP
1: S
ELECT A
“C
ATEGORY
”
Probes for the Model 100 come pre-adjusted for a variety of coating and
substrate types, or categories.
When a coating category is selected from the Coating
List, a typical sound velocity constant for that
material is used by the Gage. The number of coating
categories available to choose from depends upon the
type of probe that is attached. B probes have only one
category, polymer. The C and D probes have several
categories including polymer, rubber, glass and
metal.