VEGA VEGAPULS 45 VBUS - Manual (Page 19)

VEGAPULS 42, 44 and 45 – VBUS 19
Mounting and installation
Extended bypass tube on a vessel with intense
product movements
75 %
0 %
100 %
> 300 mm
100 %
0 %
> 300 mm
300 ... 800 mm
Bypass tube with tube stub
Type label
For products with small dielectric constants
(< 4), a bypass tube longer than that re-
quired by the lower tube connection should
be used. Products with small dielectric con-
stants are partly penetrated by the radar
signals, so that the tube bottom delivers a
stronger echo than the product (when the
bypass tube is nearly empty). As a result of
the extension of the lower tube end, sufficient
liquid will remain even when the vessel is
emptied.
With a liquid quantity of 300 … 800 mm in the
blind lower end of the tube, the portion of the
signal that penetrates the liquid and reflects
from the tube bottom is sufficiently damped -
the sensor can then easily distinguish it from
the echo of the liquid surface. If not enough
liquid remains, a deflection plate located at
the bottom of a vertical pipe can provide the
same function. It deflects the signal reflected
from the tube end sideways into the standard
tube opening.
Connections to the bypass tube
The connections to the bypass tubes must
be fashioned in such a way that only minimal
reflections are caused by the walls of the
connecting tubes. This is especially important
for the breather connection in the upper part
of the tube. Observe the following points:
• Use small openings for the connection.
• The diameter of the connecting tubes
should not exceed 1/3 of the bypass diam-
eter.
• The tube connections must not protrude
into the bypass.
• Large welding beads in the tubes should
be avoided.
• Additional connections to the bypass tube
are more suitable if they lie on the same
plane as the upper and lower vessel con-
nection (superimposed or displaced by
180°).
Optimum connection to the bypass tube