Verifi Cation Of Calibration - Decagon Devices AquaLab 4TE Operator's Manual

AquaLab
7. Verifi cation and Calibration

Verifi cation of Calibration

When to Verify for Linear Off set
Linear off set should be checked against two known verifi cation
standards daily, either once per shift or before each use. Linear off set
should never be verifi ed solely against distilled water, since it does
not give an accurate representation of the linear off set. For batch pro-
cessing, the instrument should be checked regularly against a known
standard of similar water activity. It is also a good idea to check
the off set with a standard of similar water activity when the general
water activity range of your sample is changing. Checking the water
activity of a standard solution will alert you to the possibility of unit
contamination or shifts in the linear off set from other causes.
NOTE: Th e verifi cation process is the same for both the dewpoint and
capacitance sensors in TEV models except that the accuracy for the ca-
pacitance sensor is ± 0.015 a . Also, if using the 1.000 a or 0.984 a
w w w
verifi cation standards, you must wait an hour before testing other stan-
dards or samples in capacitance mode.
Verifi cation
To verify for linear off set of your AquaLab do the following:
(refer to the fl owchart at the end of this section)
1. Choose a verifi cation standard that is close to the water activity of
the sample you are measuring. Note: Th e AquaLab needs to warm
up for approximately 15 minutes to make accurate readings.
2. Empty a vial of solution into a sample cup and place it in the
AquaLab's testing chamber. Make sure that your standard is as close
to the instrument temperature as possible.
Note: Make sure the rim and outside of the sample cup are clean.
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