Service and maintenance
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4 Service and maintenance
4.1 Refilling
To assure a rapid and reliable measurement of the soil water
tension, the cup must be filled possibly bubble-free with degassed
water. After dry periods or periods with a large number of wet and
drying out successions, Tensiometers must be refilled.
Refilling is the easiest with the refilling tools included in the T5-set or
T5-case. A readout device, for example the INFIELD7, is always
needed to control the signal.
4.1.1 When do Tensiometers need to be refilled?
Tensi
ometers need to be refilled:
the curve of the readings apparently gets flatter (for example a
rain event has no sharp peak but is round),
the maximum of -85 kPa is not reached anymore.
Refilling is only reasonable if the soil is moister than -90 kPa.
If the soil gets dryer than -85 kPa, the readings will remain constant
at the vapour pressure of water (i. e. for example 92,7 kPa at 20°C
and atmospheric pressure of 95 kPa). By diffusion and slight leakage
the reading will slowly drop within months.
If the soil dries out and reaches the bubble point (-200 kPa for T5;
-500 kPa forT5x), the tension will decrease rapidly as air will enter
the cup.
4.1.2 Refilling T5 in lab and field
This chapte
r describes the refilling of T5 or T5x using the T5-set.
The procedure has 5 steps:
1. Check the T5 Tensiometer
2. Degas cup and shaft
3. Degas sensor
4. Reassemble
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