VEGA VEGAPULS 51K…54K 4 … 20 mA; HART compact sensor - Manual (Page 17)

VEGAPULS 51K … 54K 17
21750-EN-031222
Mounting and installation
Guide tube in existing surge or bypass tube
Extended guide tube
Guide tube
Use of guide tubes
In case of very rough inner surfaces in exist-
ing bypass tubes (e.g. due to corrosion),
large connection openings as well as bypass
tubes with more than 100 mm inner diameter,
the use of a guide tube inside the existing
bypass tube is recommended. This reduces
the noise level and increases reliability con-
siderably. The flange of the guide tube can
be easily mounted as a sandwich flange
between vessel and sensor flange.
To increase the min. distance, the guide tube
can project out of the surge or bypass tube.
For this purpose, a plain flange can be
welded at the required position on the out-
side of the extended guide tube. In both
cases, a breather hole must be provided.
Seals on tube connections and tube ex-
tensions
Pipe antennas with DN 50, DN 80, DN 100 and
DN 150
DN 150 DN 50
ш 50 ш 150
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 seal used should correspond to the
tube inner diameter
• If possible, conductive seal made of mate-
rials such as conductive PTFE or graphite
should be used
• There should be as few seal positions as
possible in the guide tube.