VEGA VEGAPULS 66 (≥ 2.0.0 - ≤ 3.8) enamel 4 … 20 mA_HART four-wire - Manual (Page 18)

Fig. 11: Agitators
T hrough the action of filling, stirring and other processes in the vessel,
dense foams which considerably damp the emitted signals may form
on the product surface.
I f foams are causing measurement errors, the biggest possible radar
antenna should be used.
A s an alternative, sensors with guided microwave can be used. These
are unaffected by foam generation and are best suited for such
applications.
B y using a standpipe, the influence of vessel installations and
turbulence can be excluded. Under these prerequisites, the meas-
urement of products with low dielectric values (from DK value 1.6) is
possible.
S urge or bypass tubes must extend all the way down to the requested
min. level, as measurement is only possible within the tube.
Surge pipe
M
ake sure you provide the necessary upper vent hole in the surge
pipe. The hole must be aligned so that it and the polarisation marking
on the sensor flange are in the same plane (see illustration: "Pipe
antenna system in a tank").
Foam generation
Measurement in the
standpipe (surge or by-
pass tube)
18 VEGAPULS 66 enamel • 4 … 20 mA/HART four-wire
4 M ounting
31954
-EN
-090305