VEGA Capacitive electrodes EK … with signal conditioning instrument - Manual (Page 20)

20 Capacitive electrodes EK with signal conditioning instrument
Mounting
Fig. 2.4 Humidity
Humidity from outside
After installation turn the cable entries of
horizontally mounted instruments to the bot-
tom to avoid humidity ingress. The instrument
housing is rotational by approx. 330°. In case
of vertically installed electrodes, loop the
connection line to the electrode housing to the
bottom so that rain or condensation water
can drain off.
This is mainly valid for mounting outside, in
areas where humidity must be expected
(e.g. by cleaning processes) or on cooled or
heated vessels (see fig. 2.4).
Cable entries
When mounting outside, on cooled vessels or
in humid areas where cleaning is made e.g.
with steam or high pressure, the sealing of
the cable entry is very important.
Use cable with a round cross-section area of
conductor and tighten the cable entry. The
cable entry is suitable for cable diameters of
5 mm to 9 mm.
Aluminium vessels
Use for Aluminium vessels an electrode with
steel thread. The combination Aluminium on
Aluminium should be avoided, as the thread
"seizes“ when being screwed and cannot be
loosened after some time without being dam-
aged.
Metal vessels
Note that the mechanical connection of the
electrode is electrically conductive connected
with the vessel to ensure sufficient earth.
Use conductive seals such as e.g. copper,
lead etc. Isolating measures such as cover-
ing the thread with Teflon tape can interrupt
the necessary electrical connection. In this
case use the earth terminal on the housing to
connect the electrode to the vessel wall.
Non-conductive vessels
In non-conductive vessels, e.g. plastic tanks,
the second pole of the capacitor must be
provided separately, e.g. by a concentric
tube or the use of a double rod electrode.
When using a standard electrode, a suitable
earth plate is necessary. Hence provide a
possibly large earth plate, e.g. wire braiding
laminated into the vessel wall or metal foil
which is glued to the vessel. Connect the
earth plate with the earth terminal on the
housing.
Rod electrode
Mount the electrode such that the electrode
protrudes into the vessel. When mounting in
a tube or a socket, build-up can be caused
which can influence the measurement. This is
particularly the case with viscous or adhesive
products.
(see fig. 2.5)