WP
4
PotentiaMeter
Calibration and Verification Standards
25
5. Calibration and
Ve r i f i c a t i o n
Verification
WP4 uses the chilled mirror dewpoint technique for
measuring water potential. Due to the nature of this
technique, periodic calibration is essential for the
instrument to perform properly. The calibration
slope is fixed during factory calibration. The user
just resets the zero offset. Usually any changes in
performance requiring recalibration are the result of
chamber contamination. When this occurs, it
changes the accuracy of your readings. In final test-
ing at Decagon, the slope of the instrument is fixed.
However, due to the reasons noted above, some
drift is expected over time. This is compensated for
by verification of the WP4’s calibration before use.
Calibration can be done with any solution of known
water potential. We recommend checking the cali-
bration by measuring a fresh sample of 0.5 molal
KCl and adjusting for any drift.
Verification Standards
Verification standards are specially prepared salt
solutions that have a specific molality and water
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