39
AQUALAB TDL/TDL 2
6. The readings may lead to one of three outcomes.
a. If the AQUALAB TDL reads within ±0.005 a
w
of the first verification standard, take
two readings of the second verification standard. The second water activity reading
for the second verification standard should be within ±0.005 a
w
.
b. If either verification standard is not correct, it is probably due to contamination
of the sensor chamber. Clean and air out the chamber (Section4.2) and repeat
verification from step2.
c. If readings are consistently outside the water activity of the first verification
standard by more than ±0.005 a
w
, a linear offset can be applied. Adjust the reading
to match the correct verification standard value (Section4.1.2).
Measure verification standard
Clean sample
chamber
Reread first
standard
Go to offset
procedure
Go to sampling
procedure
Read second
standard
Clean sample
chamber
Repeat process
Figure47 Verification standard flowchart. A check indicates AQUALAB TDL verified the standard
within specification; a cross indicates AQUALAB TDL did not verify the standard within specifications.
4.1.2 LINEAR OFFSET
After verification and cleaning the instrument, an offset may be necessary.
NOTE: A linear offset does not adjust the calibration for all water activity levels and should only be used if measuring
water activity in a very small range.
1. Navigate to the Configuration tab.
2. Select Calibration.
3. Select Water Activity.
4. Select Start (Figure48).