VEGA VEGAPULS 51K…54K Profibus PA - Manual (Page 14)

14 VEGAPULS 51P … 54P
24890-EN-041227
When the sensors are mounted on vessels
with dished or rounded tops, the antenna
must protrude at least 10 mm on the longer
side of the socket.
Mounting on a dished vessel top
> 10 mm
3.2 Measurement of liquids
Horn antenna
Horn antenna on DIN socket piece
Radar sensors are usually mounted on short
DIN socket pieces. The lower side of the
instrument flange is the reference plane for
the measuring range. The antenna must
always protrude out of the flange pipe.
With longer DIN sockets, make sure the horn
antenna protrudes at least 10 mm out of the
socket.
Emission cone and false echoes
The radar signals are focused by the an-
tenna system. The signals leave the antenna
in a conical path similar to the beam pattern
of a spotlight. This emission cone depends
on the antenna used.
Any object in this beam cone will reflect the
radar signals. Within the first few meters of
the beam cone, tubes, struts or other installa-
tions can interfere with the measurement. At a
distance of 6 m, the false echo of a strut has
an amplitude nine times greater than at a
distance of 18 m.
At greater distances, the energy of the radar
signal distributes itself over a larger area,
thus causing weaker echoes from obstruct-
ing surfaces. The interfering signals are
therefore less critical than those at close
range.
Align the sensor axis as perpendicular as
possible to the product surface and keep
vessel installations (e.g. pipes and struts) out
of the 100% emission cone whenever possi-
ble.
The illustrations of the emission cones are
simplified and represent only the main beam
- a number of weaker beams also exist. Un-
der difficult measuring conditions, the an-
tenna alignment must be chosen with the
objective of reducing false echoes. Only
giving attention to the size of the useful echo
is not adequate when measuring conditions
are unfavourable.
In a difficult measuring environment, search-
ing for a mounting location with the lowest
possible false echo intensity will bring the
best results. In most cases, the useful echo
will then be present with sufficient strength.
With the adjustment software PACT
ware TM on
the PC, you can have a look at the echo im-
age and optimise the mounting location.
Mounting and installation
If possible, provide a "clear view“ to the
product inside the emission cone and avoid
vessel installations in the first third of the
emission cone.
Optimum measuring conditions exist when
the emission cone reaches the measured
product perpendicularly and when the emis-
sion cone is free from obstructions.
Mounting on DIN socket piece
> 10 mm
Reference
plane