Product description
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3.2.3 Tensiometers
.2.3 Tensiometers
Tensiometers measure the soil water tension or the matric potential.
These Tensiometers have a measuring range of +100 kPa
(water pressure) to -85 kPa (water tension). With proper
filling the Tensiometers may work beyond the conventional
tension measuring range. If the soil gets too dry the
Tensiometer needs to be refilled (see chapter “Refilling”).
Tensiometers measure the soil water tension or the matric potential.
These Tensiometers have a measuring range of +100 kPa
(water pressure) to -85 kPa (water tension). With proper
filling the Tensiometers may work beyond the conventional
tension measuring range. If the soil gets too dry the
Tensiometer needs to be refilled (see chapter “Refilling”).
The soil water tension is conducted via the porous ceramic
tip to the water inside the shaft and measured as an
analogue signal by the pressure transducer.
The soil water tension is conducted via the porous ceramic
tip to the water inside the shaft and measured as an
analogue signal by the pressure transducer.
The Tensiometer shafts are screwed into the transducer
openings in the sensor unit. Standard sampling rings can
easily be placed on the sensor unit so the Tensiometer
ceramic tips are positioned inside the soil sample. There is one short
and one long shaft to pick up the tension at two depths.
The Tensiometer shafts are screwed into the transducer
openings in the sensor unit. Standard sampling rings can
easily be placed on the sensor unit so the Tensiometer
ceramic tips are positioned inside the soil sample. There is one short
and one long shaft to pick up the tension at two depths.
Fig. 4
The Tensiometer shafts are one of the most sensitive parts of the
system. Always handle them with care.
To transfer the soil water tension as a negative pressure into the
Tensiometer, a semi-permeable diaphragm is required. This must
have good mechanical stability and water-permeability, but also have
gas impermeability.
The Tensiometer tip consists of porous ceramic Al
2
O
3
sintered
material. The special manufacturing process guarantees
homogeneous porosity with good water conductivity and very high
firmness. Compared to conventional porous ceramics the tip is much
more durable.
The bubble point of a Tensiometer ceramic is about 800 kPa. If the
soil gets dryer than the bubble point, air passes through. Thus, the
negative pressure inside the cup decreases and the readings go
down to 0 kPa.
With these characteristics this material has outstanding suitability to
work as the semi permeable diaphragm for Tensiometers.
Be aware that the ceramic will dry out when it is exposed to air
uncovered. Always put on the rubber cap filled with some water.
