VEGA VEGAPULS 43 Profibus PA - Manual (Page 18)

18 VEGAPULS 43 – Profibus PA
100 %
0 %
> 300 mm
300 ... 800 mm
Tube flange system as bypass tube
Type label
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 on the same axis as the type
label lies on one axis with the tube holes or
the tube connection openings. The polarisa-
tion of the radar signals enables a consider-
ably stabler measurement with this alignment.
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.
Mounting and installation
If enough liquid (300 … 800 mm) remains in
the blind lower end of the tube, the portion of
the signal that penetrates the liquid and re-
flects from the tube bottom is sufficiently
damped - the sensor can then easily distin-
guish it from the echo of the liquid surface. In
cases where there is not enough liquid at the
bottom of the tube, a deflector situated there
will carry out the same function. It deflects
signals that reach the tube bottom into the
standard connection opening.
When mounting a VEGAPULS 43 on a by-
pass 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.