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The Offset function provides a method for adjusting an existing
calibration to obtain higher precision when it is not practical to
perform a new calibration.
A calibration is performed using the specific materials found in
the test samples. A new calibration ensures that the gauge will
obtain the highest precision possible. Perform an offset only as
an intermediate measure and if the materials vary slightly.
The Model 3241 Series offers three different types of offset
adjustments: slope, relative, and slope/intercept. The calibration
curve will be adjusted according to the offset selected.
Slope Offset
If the asphalt source changes and recalibration is not possible, a
slope offset can be performed (Figure 4). This offset uses a
selected calibration and a new offset sample of known %AC to
recalculate the slope of the calibration curve. A slope offset will
produce accurate results if the unknown samples are within
0.5%AC of the offset sample.
Relative Offset (%AC Shift)
This offset can be used to correlate gauge readings and
extraction results. A relative offset adds or subtracts the offset to
adjust the calculated value (Figure 5).
Relative Offset (Intercept)
If the aggregate moisture changes from the time the original
calibration was performed, the intercept relative offset can be
used. An offset sample of known %AC must be prepared and
measured to provide the information relevant to this offset (see
page 4-3).
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