Useful Notes; Maximum Measuring Range And Data Interpretation - Delta-T Devices SWT5 User Manual

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).
Typical behaviour of tensiometer readings when tension
Interpretation Messwerte bis über 15 bar nahe der
100000
10000
1000
100
10
1
0 2
Fig. 6.1: Tensiometer readings with tensions to -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).
36  Useful notes
exceeds -15,000 hPa close to the surface
Bodenoberfläche
4 6 8
Bodenwasserspannung
Soil water tension
Tensiometer reading
Tensiometermesswert
10 12 14
Time
Time
Zeit
SWT5 User Manual v2
16 18 20