WP
4
PotentiaMeter
Sample Preparation
33
example, if you were measuring a dry sample and
the following screen appeared:
this screen indicates that the last water potential
reading the WP4 measured on this sample was
-301.8 Megapascals. Therefore, the actual water
potential of the sample is higher than the instru-
ment’s components can measure.
Samples and Temperature
Samples that are 4 degrees colder or warmer than
the instrument (chamber) temperature will need to
be close to the WP4’s temperature before a fast,
accurate reading can be made. Rapid changes in
temperature over short periods of time will cause
the water potential readings to rise or fall until the
temperature stabilizes. If you have a WP4-T, you
can set the chamber temperature to eliminate this
problem. If you have a standard WP4, when the
temperature stabilizes within one or two degrees of
the chamber temperature, you can proceed with
normal measurements. This is why the sample tem-
perature screen is available for you to access (see
chapter 4) before you read a sample:
Sample too dry
< -301.8 MPa
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