VEGA VEGAPULS 45 4 … 20 mA; HART compact sensor - Manual (Page 16)

16 VEGAPULS 42, 44 and 45 – 4 … 20 mA
Extended bypass tube on a vessel with turbulent
product movements
75 %
0 %
100 %
> 300 mm
100 %
0 %
> 300 mm
300 ... 800 mm
Tube flange system as bypass tube
Type label
For products with small dielectric constants
(< 4), the bypass tube should have a length
greater than would normally be required for
the lower tube connection. Products with
small dielectric constants are partly pen-
etrated by the radar signals, allowing the
tube bottom to produce a stronger echo than
the product (when the bypass tube is nearly
empty). By extending the tube downward,
some liquid remains at the bottom even when
the vessel is completely empty.
100 %
0 %
> 300 mm
Tube flange system as bypass tube
Type label
Make sure the required upper vent hole in
the surge pipe is aligned with the sensor
type label.
As an alternative to a surge pipe in the ves-
sel, a pipe antenna system outside the ves-
sel in a bypass tube is also possible.
The surge and bypass tubes must generally
be made of metal. For plastic tubes, a
closed, conductive jacket is always required.
When using a metal tube with plastic inner
coating, make sure that the thickness of the
coating is minimal (approx. 2 … 4 mm).
Align the sensor so that the type label lies on
the same axis as the tube holes or the tube
connection openings. The polarisation of the
radar signals enables a considerably stabler
measurement with this alignment.
When mounting a VEGAPULS 42 or 44 sen-
sor on a bypass tube (e.g. on a previous
floating or displacer unit), the radar sensor
should be placed approx. 300 mm or more
from the max. level.
Mounting and installation