VEGA Capacitive electrodes EL … - Manual (Page 27)

Capacitive electrodes EL … 27
Mounting
Fig. 2.4 Humidity
Humidity from outside
Turn the cable entries of horizontally mounted
instruments after installation to the bottom to
avoid humidity ingress. The instrument housing
can be hence rotated by approx. 330
°
. For
vertically installed electrodes loop the
connection line to the electrode housing to the
bottom so that rain and 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 seal 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
4 mm up to 12 mm.
Two Pg-seal rings are attached to the
instrument:
- for cable diameter of 4 … 9 mm
- for cable diameter of 5 … 12 mm.
Use the smallest possible seal ring.
Aluminium vessel
In Aluminium vessels use an electrode with
steel mounting thread. Combination Aluminium
on Aluminium should be avoided as the thread
"seizes“ and can no more be removed after
some time without damage.
Metal vessel
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 covering 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 rod 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 mediums.