General - Keller DCX Series Operating Instructions Manual

General information
Fluctuations in the groundwater level (or the levels of other fluids) can be determined
and located precisely by measuring the prevailing (hydrostatic) pressure at a defined
depth below the surface of the water. To convert the pressure [bar] into the water
column level [mWS], it is only necessary to know the density of the fluid.
Example pure water (H2O): 100 mbar ≈ 1,02 mWS
h =
p = hydrostatic pressure (0,1 bar = 10,000 N/m
ρ = density (kg/m )
3
g = gravitational acceleration (m/s
h = height of water column (m)
Level measurement
In open systems, i.e. with the classical method of measuring
the filling level, the difference between the pressure acting
on the level sensor (total pressure) and the ambient pressure
acting on the water (air/atmospheric pressure in most cases) is
always measured. The pressure difference determined in this
way corresponds to the hydrostatic water pressure.
As a result of this measurement method, the level measurement becomes independent
of weather-induced fluctuations in air pressure that act on the surface of the fluid. The
following methods of compensating for air pressure are available:
Relative measurement method (VG)
In the relative measurement method, the sensor cable has an integrated capillary tube
which provides the reference to the ambient air pressure directly on the level sensor.
The sensor pressure measured in this way is therefore physically compensated for air
pressure.
Advantage: high accuracy and resolution
Disadvantage: high ambient humidity at the measuring point may disrupt or interrupt
compensation for air pressure and, in extreme cases, may even damage
the level sensor (→ use moisture absorber cartridges)
p N/m
2
=
ρ * g kg/m * m/s
3 2
)
2
 6 
= mWS
)
2
Ambient pressure (Air pressure)
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Hydrostatic pressure
of the water
Total pressure