Vega VEGABAR 87 Operating Instructions Manual page 37

Linearisation
Current output
Current output (mode)
Current output (min./
max.)
VEGABAR 87 • 4 ... 20 mA/HART
The default setting is a damping of 0 s.
A linearization is necessary for all vessels in which the vessel volume
does not increase linearly with the level - e.g. a horizontal cylindri-
cal or spherical tank - and the indication or output of the volume is
required. Corresponding linearization curves are preprogrammed for
these vessels. They represent the correlation between the level per-
centage and vessel volume. The linearization applies to the measured
value indication and the current output.
With flow measurement and selection " Linear" display and output
(percentage/current) are linear to " Differential pressure". This can
be used, for example, to feed a flow computer.
With flow measurement and selection " Extraction by root"display and
output (percentage/current) are linear to " Flow".
With flow in two directions (bidirectional) a negative differential pres-
sure is also possible. This must already be taken into account in menu
item " Min. adjustment flow".
Caution:
Note the following, if the respective sensor is used as part of an over-
fill protection system according to WHG:
If a linearisation curve is selected, the measuring signal is no longer
necessarily linear to the filling height. This must be considered by the
user especially when setting the switching point on the limit signal
transmitter.
In the menu items " Current output" you determine the properties of
the current output.
On instruments with integrated additional current output, the proper-
ties for each current output are adjusted individually. The following
descriptions apply to both current outputs.
In the menu item " Current output mode" you determine the output
characteristics and reaction of the current output in case of fault.
The default setting is output characteristics 4 ... 20 mA, fault mode
< 3.6 mA.
In the menu item " Current output Min./Max.", you determine the reac-
tion of the current output during operation.
The device assumes an approximately constant temperature and static
1)
pressure and converts the differential pressure into the flow rate via the
characteristic curve extracted by root.
6 Set up with the display and adjustment module
1)
37