Xylem Expert 800-900 - Manual (Page 4)

Manual
GB Manual Expert Log 800-900.doc
4
Installation of Expert 900 Logger
General information
Fluid levels or fluctuations of a liquid can be determined by measuring the prevailing pressure at a
lower depth and comparing it with the pressure at the surface. This enables an approximate
calculation based on the density of the liquid. For example, in the case of water:
100mbar
Η
100cm water column (WC).
Measuring is always realized in relation to the ambient pressure (the pressure on the surface) in the
case of open systems or classical filling level measurement. This is achieved in conventional water
level sensors through a reference tube integrated in the sensor cable, which determines the
relationship to the ambient pressure. Measurement of air pressure fluctuations is thus independent.
An alternative option exists in intelligent systems, involving the realization of an absolute pressure
measurement and calculation of the air pressure correction using an additional barometer. This
means that the special cable (with the reference tube) need not be utilized.
Measuring methods
Relative measurement (Expert 900)
The Expert 900 is based on the classical level measuring method. The
instrument is equipped with a relative pressure sensor. The air pressure is
conveyed through the reference tube integrated in the sensor cable at the
rear of the sensor. The cable should therefore not be bent or crushed! The
upper end of the reference tube is fitted with a GORE-TEX® membrane.
This prevents dirt or liquid entering the instrument, while still ensuring the air
exchange.