Useful notes
6.3 Temperature influences during measurements
If the sensor is not powered continuously the voltage should be
switched on 10 seconds before a measurement. In this case, the self
heating is negligible.
The correlation of water tension to water content is temperature
dependent. The influence is low at tensions of 0 to 10 kPa 0 …
0,6 kPa/K, but high for tensions over 100 kPa:
oM
TR
ln
= Water tension R = Gas constant (8,31J/mol K)
M = Molecular weight p = Vapour pressure
p
o
= Saturation vapour pressure at soil temperature
(from Scheffler/Straub, Grigull)
6.4 Vapour pressure influence on pF/WC
If the temperature of a soil with a constant water content rises from
20°C to 25°C the soil water tension is reduced for about 0,85 kPa
due to the increased vapour pressure which antagonizes the water
tension.
Temperature
in °C
4 10 16 20 25 30 50 70
Pressure
change per
Kelvin in [hPa]
0,6 0,9 1,2 1,5 1,9 2,5 7,2 14
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