Decagon Devices AquaLab 4TE Operator's Manual page 46

AquaLab
7. Verifi cation and Calibration
3. Carefully close the lid and move the lever to the READ position.
4. Take two readings. Th e water activity readings should be within
± 0.003 a of the given value for the verifi cation standard. See Ap-
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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 of the verifi cation
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standard, chose a second verifi 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 )standard for your fi rst veri-
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fi cation and the 8.57M LiCl (0.50a ) for the second verifi cation.
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6. Prepare a sample cup of the second verifi cation standard and
make two readings. Th e second water activity reading for the second
verifi cation standard should be within ±0.003 a .
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7. If either of the verifi 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 verifi cation from step
two.
8. If you are consistently getting readings outside the water activity of
your fi rst verifi cation standard by more than ±0.003 a , a linear off set
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has probably occurred. In this case, adjust the reading to match the
verifi cation standard's correct value as outlined in the next section.
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