VEGA VEGAPULS 43 Profibus PA - Manual (Page 26)

26 VEGAPULS 43 – Profibus PA
Foam generation
Conductive
foam
Liquid
Mounting and installation
Unfavourable
Mounting on a vessel with parabolic tank top
Correct
Unfavourable
Parabolic effects on dished or arched
vessel tops
Round or parabolic tank tops act on the ra-
dar signals like a parabolic mirror. If the radar
sensor is placed at the focal point of such a
parabolic tank top, the sensor receives am-
plified false echoes. The optimum mounting
location is generally in the range of half the
vessel radius from the centre.
Sensor too close to the vessel wall
If the radar sensor is mounted too close to
the vessel wall, strong false echoes can be
caused. Buildup, rivets, screws or weld joints
superimpose their echoes onto the product
i.e. useful echo. Please ensure a sufficient
distance from the sensor to the vessel wall.
If there are good reflection conditions (liquid
medium, no vessel installations), we recom-
mend locating the sensor where there is no
vessel wall within the inner emission cone. For
products in less favourable reflection envi-
ronments, it is a good idea to also keep the
outer emission cone free of interfering instal-
lations. Note chapter "3.1 General installation
instructions“.
Foam generation
Conductive foam is penetrated to different
depths by the radar signals and generates a
number of individual (bubble) echoes. At the
same time, the signals are damped in foam,
similar to the way heat radiation is damped
by Styrofoam. Thick, dense, creamy and
conductive foam can cause incorrect meas-
urements.
Provide preventative measures against foam
or measure in a bypass tube. Check, if nec-
essary, the possibility of using a different
measurement technology, e.g. capacitive
electrodes or hydrostatic pressure transmit-
ters.