Additional notes
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True pressure in heights over sea level at an atmospheric
pressure related to sea level as published by meteorological
services
Height over sea
level (meter)
Atmospheric
pressure (kPa)
Max. measuring
range at 20°C (kPa)
0
101.3
-99.0
500
95.5
-93.2
1000
89.9
- 87.6
1500
84.6
- 82.3
2000
79.5
-77.2
2500
74.5
-72.2
3000
70.1
-67.8
10.1.3 Boiling retardation:
Water needs a nucleation site to boil. As our Tensiometers have
polished surfaces and a gas-free filling the so called boiling
retardation occurs – the Tensiometer keeps on measuring beyond
the boiling point. To achieve this shafts and sensor unit must have
an absolutely bubble free filling.
Some Tensiometer cups can go down to -250 kPa before they run
dry, occasionally even a range of -450 kPa is achievable. As this is
exceptional there is no guarantee for this measuring range.
For HYPROP measurements this means that a measuring campaign
should be continued as long as the Tensiometers keep on
functioning (unless the 8.8 bar range is irrelevant).
It is possible to get further information from the known bubble point
which is 8.8 bar for the HYPROP cups. The moment the tension
reading rapidly drops to zero the soil has a tension of -880 kPa (+/-
20 kPa). Therefore, it is recommendable to continue with the
measurement until the tension reading is 0 kPa. (see publication: U.
Schindler, JPNSS, The evaporation method - Extended
measurement range of soil hydraulic properties using the air-entry
pressure of the ceramic cup).
