Service And Maintenance; Refilling; When Do Tensiometers Need To Be Refilled; Refilling T5 In Lab And Field - UMS T5 User Manual

Service and maintenance

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?

Tensiometers 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 chapter 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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