VEGA VEGAPULS 41 4 … 20 mA; HART compact sensor - Manual (Page 17)

VEGAPULS 41 – 4 … 20 mA 17
26620-EN-041227
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Openings in a surge pipe for mixing of inhomogene-
ous products
slightly inhomogeneous
liquids
inhomogeneous liquids
homogeneous
liquids
Standpipe measurement of inhomoge-
neous products Seals on tube connections and tube ex-
tensions
Microwaves are very sensitive to gaps in
flange connections. If connections are made
without proper care, distinct false echoes as
well as increased signal noise can result.
Observe the following points:
• The applied seal should correspond to the
tube inner diameter.
• If possible, conductive seals such as con-
ductive PTFE or graphite should be used.
• There should be as few seal positions as
possible in the guide tube.
Flange connections on bypass tubes
Adhesive products
In non-adhesive or slightly adhesive prod-
ucts, use a surge pipe with a nominal width of
e.g. 50 mm. VEGAPULS 41 radar sensors
with 26 GHz technology are for the most part
insensitive to buildup in the measuring tube.
However, buildup should not block the meas-
uring tube.
For products with heavier buildup, the use of
a DN 80 to max. DN 100 standpipe or surge
pipe can make the measurement possible
despite buildup. With products that are ex-
tremely adhesive, measurement in a stand-
pipe is not possible at all.
Mounting and installation
If you want to measure inhomogeneous or
stratified products in a surge pipe, it must
have holes, elongated holes or slots. These
openings ensure that the liquid is mixed and
corresponds to the liquid in the vessel.
The more inhomogeneous the measured
product, the closer the openings should be
spaced.
Due to radar signal polarisation, the holes or
slots must be positioned in two rows offset
by 180°. The radar sensor must then be
mounted so that the type label of the sensor
is aligned with the rows of holes.
Every wider slot causes a false echo. The
slots should therefore not exceed a width of
10 mm in order to keep the signal-to-noise
level at a minimum. Round slot ends are bet-
ter than rectangular ones.