SWT4 User Manual v3.1
Useful notes
37
Interpretation Messwerte bis über 15 bar nahe der
Bodenoberfläche
1
10
100
1000
10000
100000
0
2
4
6
8
10
12
14
16
18
20
Zeit
W
a
s
s
e
rs
pa
nn
un
g
Bodenwasserspannung
Tensiometermesswert
6 Useful notes
6.1 Maximum measuring range and data
interpretation
The measuring range of Tensiometers is limited by the boiling point of
water. At a temperature of 20°C the boiling point is at 23 hPa over
vacuum. So with 20°C and an atmospheric pressure of 950 hPa the
Tensiometer cannot measure a tension below -927 hPa, even if the
soils gets drier than that. The readings remain at a constant value (Fig.
6.1, between day 10 and 16).
Fig. 6.1: Tensiometer readings with tensions beyond -15,000 hPa
If the soil dries to -15,000 hPa
, the ceramic’s bubble point is reached.
The water in the ceramic cup will run out quickly and the reading of the
air-filled cup will go to zero (Fig. 6.1, day 16 to 19).
Soil
wa
ter t
en
sio
n (
hPa)
Soil water tension
Tensiometer reading
Time
Day
Typical behaviour of tensiometer readings when
tension exceeds -15,000 hPa close to the surface
