VEGA VEGAPULS 43 4 … 20 mA; HART compact sensor - Manual (Page 19)

VEGAPULS 43 – 4 … 20 mA 19
26626-EN-041227
Guidelines for standpipe construction
The radar sensors with a DN 50 flange only
form a functioning measuring system in con-
junction with a measuring tube.
The measuring pipe must be smooth inside
(average roughness Rz
≤ 30). Use stainless
steel tubing (drawn or welded lengthwise) for
construction of the measuring pipe. Extend
the measuring pipe to the required length
with weld-on flanges or with connecting
sleeves. Make sure that no shoulders or
projections are created during welding. Be-
fore welding, join pipe and flange with their
inner surfaces flush and exactly fitting.
Avoid welding through the pipe wall. The pipe
must remain smooth inside. Roughness or
welding beads on the inner surfaces must be
carefully removed and burnished, as they
cause false echoes and encourage product
adhesion.
If the vessel contains agitated products,
fasten the measuring pipe to the vessel bot-
tom. Provide additional fastenings for longer
measuring pipes.
In products with lower dielectric values (< 4),
a part of the radar signal penetrates the
medium. If the vessel is nearly empty, echoes
are generated by both the product and the
vessel bottom. The echo from the vessel
bottom can in some cases be stronger than
the echo from the product surface. If a de-
flector is installed below the open end of the
measuring tube, the radar signals are scat-
tered and prevented from reaching the ves-
sel bottom. This ensures that, in nearly empty
vessels or with products of low dielectric
value, the product delivers a more distinct
echo than the vessel bottom.
Due to the deflector, the useful echo (and
thus the measured value) remains clearly
detectable in a nearly empty vessel, and the
0 % level can be reliably measured.
ø50
> 300 mm
Tube antenna system with ball valve cutoff in measur-
ing tube
Ball valve
Vent hole
Deflector
Mounting and installation
ø 5...15
Row of holes in one axis with the type label
Type label
Surge pipe with ball valve
If a ball valve is mounted in the surge pipe,
maintenance and servicing can be carried
out without opening the vessel (e.g. if it con-
tains liquid gas or toxic products).
A prerequisite for trouble-free operation is a
ball valve throat that corresponds to the pipe
diameter and provides a flush surface with
the pipe inner wall. The valve must not have
any rough edges or constrictions in its chan-
nel. The distance to the sensor flange should
be at least 300 mm.