Verification And Calibration; Verification Standards - Decagon Devices pawkit Operator's Manual

Pawkit User Manual

6. Verification and Calibration

6. Verification and Calibration
As mentioned earlier, the Pawkit takes water activity mea-
surements by measuring the change in electrical properties
of a special polymer held between two electrodes. Due to
the nature of the capacitance humidity sensor, there may be
times when you may need to adjust the calibration. This sec-
tion explains how to do so. Calibrations should be verified
frequently with salt standards and adjusted as needed.

Verification Standards

The Pawkit uses 3 calibration standards: 6.0 molal NaCl
a
a
(0.760 ), 13.41 molal LiCl (0.250 ), and 2.33 molal
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w
a
NaCl (.920 ). You received a small supply of these stan-
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dards with your instrument. These standards are specially
prepared salt solutions at specific concentrations for con-
stant and accurate water activity measurements. They have
been produced under a strict quality assurance regime, and
their accuracy is verified by an independent third party
instrument. They are very accurate, easy to use, and readily
available from Decagon Devices. Most importantly, they
greatly reduce preparation errors. Because of these reasons,
we recommend using these standards for the most accurate
calibration of your Pawkit. The verification standards are
shelf-stable for one year.
If these standards are not available you can make a saturated
Sodium Chloride (NaCl) slurry with a water activity value
a
of 0.75 . To make a salt slurry of NaCl add water until the
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