VEGA VEGAPULS 51K…54K Profibus PA - Manual (Page 17)

VEGAPULS 51P … 54P 17
24890-EN-041227
Mounting and installation
Extended bypass tube on a vessel with turbulent
product movements
75 %
0 %
100 %
> 500 mm
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).
With measuring set-ups in surge or bypass
tubes, the max. measuring range is de-
creased by 5 … 20 % because of the shift in
running time of the radar signal (e.g. DN 50:
16 m instead of 20 m and DN 100 only 19 m
instead of 20 m).
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 sensor on a bypass tube
(e.g. on a previous floating or displacer unit),
the radar sensor should be placed approx.
500 mm or more from the max. level.
100 %
0 %
> 500 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 %
> 500 mm
Tube flange system as bypass tube
Type label