Sensor Description; Design; Body And Shaft; Pressure Transducer - UMS T5 User Manual

Sensor description

2 Sensor description

2.1 Design

2.1.1

Body and shaft

The sensor body is made of acrylic glass and incorporates the
pressure transducer and all electronic parts. The corpus is backfilled
with resin to hermetically seal the electronics and make the body
watertight.
2.1.2

Pressure transducer

The piezoelectric pressure sensor measures the soil water tension
against the atmospheric pressure. The atmospheric pressure is
conducted through a watertight diaphragm (the white, 2 cm long tube
on the cable) and through the cable to the reference side of the
pressure sensor.
The non destructive maximum pressure is 3 bar (300 kPa).
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.
2.1.3

Reference air pressure

The reference atmospheric air pressure is conducted to the pressure
transducer via the air permeable (white) Teflon membrane and
through the cable. The membrane does not absorb water. Water will
not pass through the membrane into the cable, but moisture inside
the cable will leave the cable through the membrane.
The white membrane on the cable must always have contact to air
during a measurement and should never be submersed into water.
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