VEGA VEGAPULS 45 4 … 20 mA; HART compact sensor - Manual (Page 26)

26 VEGAPULS 42, 44 and 45 – 4 … 20 mA
Pipe antenna: The surge pipe open to the bottom
must have a ventilation or equalisation hole at the
upper end
Correct Incorrect
VEGAPULS 44 on the surge pipe: The sensor type
plate must be aligned with the rows of holes
Type label
Correct Incorrect
Standpipe installation mistakes
Pipe antenna without ventilation hole
Pipe antenna systems must be provided with
a ventilation hole on the upper end of the
surge pipe. If this hole is absent, incorrect
measurements will result.
Wrong polarisation direction
When measuring in a surge pipe, especially if
there are holes or slots for mixing in the tube,
it is important that the radar sensor is aligned
with the rows of holes.
The two rows of holes (displaced by 180°) of
the measuring tube must be in one plane with
the polarisation direction of the radar signals.
The polarisation direction is always in the
same plane as the type label.
Mounting and installation
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.
Foam generation
Conductive
foam
Liquid
Provide preventative measures against foam
or measure in a bypass tube. Check, if nec-
essary, the possibility of using a different
measuring technology, e.g. capacitive elec-
trodes or hydrostatic pressure transmitters.
In many cases, VEGAPULS 54 radar sensors
with 5.8 GHz operating frequency achieve
considerably better and more reliable meas-
uring results in foam applications than series
40 sensors with 26 GHz technology.