Decagon Devices AquaLab 4TE - When to Verify for Linear Offset; Verification Steps

AquaLab
7. Veri cation and Calibration
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Veri cation of Calibration
When to Verify for Linear O set
Linear o set should be checked against two known veri cation
standards daily, either once per shift or before each use. Linear o set
should never be veri ed solely against distilled water, since it does
not give an accurate representation of the linear o 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 o 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 o set from other causes.
NOTE:  e veri 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
w
. Also, if using the 1.000 a
w
or 0.984 a
w
veri cation standards, you must wait an hour before testing other stan-
dards or samples in capacitance mode.
Veri cation
To verify for linear o set of your AquaLab do the following:
(refer to the  owchart at the end of this section)
1. Choose a veri cation standard that is close to the water activity of
the sample you are measuring. Note:  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.