AquaLab
7. Veri cation and Calibration
40
3. Carefully close the lid and move the lever to the READ position.
4. Take two readings. e water activity readings should be within
± 0.003 a
w
of the given value for the veri cation standard. See Ap-
pendix B for the correct water activity value of Decagon’s standards
at temperatures other than 25°C.
5. If your AquaLab is reading within ±0.003 a
w
of the veri cation
standard, chose a second veri cation standard that would border the
range of water activity you plan to test. For example, if you plan
to test for water activity readings ranging between 0.713 and 0.621
you should use the 6.0M, NaCl (0.76a
w
)standard for your rst veri-
cation and the 8.57M LiCl (0.50a
w
) for the second veri cation.
6. Prepare a sample cup of the second veri cation standard and
make two readings. e second water activity reading for the second
veri cation standard should be within ±0.003 a
w
.
7. If either of the veri cation standards is not correct, it is probably
due to contamination of the sensor chamber. For cleaning instruc-
tions, see Chapter 6. After cleaning, repeat veri cation from step
two.
8. If you are consistently getting readings outside the water activity of
your rst veri cation standard by more than ±0.003 a
w
, a linear o set
has probably occurred. In this case, adjust the reading to match the
veri cation standard’s correct value as outlined in the next section.
To Next Page
Loading...
