Sensor Description; Parts; Body And Shaft; Pressure Sensor - Delta-T Devices SWT5 User Manual

2 Sensor Description

2.1 Parts

2.1.1 Body and shaft

The sensor body is made of transparent acrylic plastic and
incorporates the pressure transducer and all electronic parts. The body
is backfilled with resin to hermetically seal the electronics and make
the body watertight.

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 condensed water inside the
cable can leave the cable through the membrane.
The white membrane on the cable must always be in contact with air
during a measurement and should never be submersed under
water.
SWT5 User Manual v2
Sensor Description  13