VEGA VEGAPULS 45 Profibus PA - Manual (Page 25)

VEGAPULS 42, 44 and 45 – Profibus PA 25
24908-EN-041227
3.4 False echoes
The radar sensor must be installed at a loca-
tion where no installations or inflowing material
cross the radar pulses. The following exam-
ples and instructions show the most frequent
measuring problems and how to avoid them.
Vessel protrusions
Vessel forms with flat protrusions can make
measurement very difficult due to their strong
false echoes. Baffles mounted above these
flat protrusions scatter the false echoes and
guarantee a reliable measurement.
Intake pipes, e.g. for the mixing of materials -
with a flat surface directed towards the sen-
sor - should be covered with an angled baffle
that scatters false echoes.
Vessel protrusions (ledge)
Vessel protrusions (intake pipe)
Correct Incorrect
Correct Incorrect
Mounting and installation
0 %
0 %
Quadrant pipe on the bypass tube end
Quadrant pipe on the standpipe end
In products with lower dielectric values (< 4),
a part of the radar signal penetrates the
medium. If the vessel is nearly empty, echoes
are generated by both the product and the
vessel bottom. The echo from the vessel
bottom can in some cases be stronger than
the echo from the product surface. If a de-
flector is installed below the open end of the
measuring tube, the radar signals are scat-
tered and prevented from reaching the ves-
sel bottom. This ensures that, in nearly empty
vessels or with products of low dielectric
value, the product delivers a more distinct
echo than the vessel bottom.
Due to the deflector, the useful echo (and
thus the measured value) remains clearly
detectable in a nearly empty vessel - the 0 %
level can thus be reliably measured.
Instead of a deflector, the standpipe or surge
pipe can be equipped with a quadrant pipe
at the end. The quadrant pipe reflects the
radar signals that penetrate the medium
diffusely to the side and diminishes strong
echoes from the tube end or the vessel bot-
tom.