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Sensor Description
SWT4 User Manual v3.1
2 Sensor Description
2.1 Parts
2.1.1 Body and shaft
The pressure transducer is integrated in the sensor body. The
electronics are completely sealed and thus well protected against
moisture. The shaft is made of transparent blue acrylic plastic and has
a very high durability and impact resistance.
2.1.2 Pressure sensor
The piezoelectric pressure sensor measures the soil water tension
against the atmospheric pressure. Atmospheric pressure is conducted
via a white air-permeable membrane on the cable, through the cable,
to the reference side of the pressure sensor.
The maximum permissible, i.e. non-destructive, pressure is 3 bar
(300 kPa, 3000 hPa). Higher pressure will damage the sensor and
absolutely must be avoided! High pressures can appear for
example when cup and sensor are reassembled, when inserted in
wet, clayey soils, or in tri-axial vessels used for measuring shear
forces.
2.1.3 Reference air pressure
The reference atmospheric air pressure is conducted to the pressure
transducer via the air permeable (white) Teflon membrane in-line in
the cable. The membrane does not absorb water. Water will not pass
through the membrane into the cable, but condenation inside the cable
can leave the cable through the membrane.
The white membrane on the cable must always have contact to air
and should never be submersed under water.
