Service And Maintenance; Refilling; When Do Tensiometers Need To Be Refilled - UMS T8 User Manual

Service and maintenance

5 Service and maintenance

5.1 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, the T8 must be refilled.
The following items are required for all refilling methods:
 Syringe with valve (one supplied with each order)
Degassed, de-ionized or distilled water

 Measuring device for checking the pressure signal
Simple method to degas water:
The best way to degas water is by using a syringe.
 Draw up water into the syringe until it is 2/3 filled. Close the valve
or block the syringe with your finger.
 Now draw up the syringe as far as possible to create a vacuum
inside. Rotate the syringe to create one big bubble.
 Take of your finger or open the valve and squeeze out the
bubble.
Repeat this procedure a few times.

5.1.1 When do Tensiometers need to be refilled?

Tensiometers need to be refilled:
 when the IR indicator will light up (for Tensiometers installed
"downwardly"),
 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 or
if a lower level installed Tensiometer shows wetter readings
again
If the soil gets dryer than -85 kPa, the readings will remain constant
at the vapor 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.
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