VEGA Capacitive electrodes EL Profibus PA - Manual (Page 18)

18 Capacitive electrodes EL - Profibus PA
Cable electrode in solids
Mounting
Fixing
weight
Continuous electrodes
L
Non-conductive vessels
In non-conductive vessels, e.g. plastic tanks,
the second pole of the capacitor must be
provided separately, e.g. in the form of a
concentric tube.
When using a standard instrument, a suitable
grounding surface is necessary. Provide
therefore the largest possible grounding
surface, e.g. wire braiding laminated into the
vessel wall or metal foil glued to the vessel.
Connect the grounding surface to the ground
terminal on the housing.
Rod electrode
Mount the rod electrode such that the elec-
trode protrudes into the vessel. When mount-
ing in a tube or a socket, material buildup that
deters the measurement can form. This is
particularly the case with viscous or adhesive
mediums.
Cable electrode in solids
Depending on the type of solid, the filling
method and its location, the cable electrode
may "float" inspite of the gravity weight. The
electrode (cable) is pushed by the solid
against the vessel wall or to the surface, thus
causing incorrect measured values. This
should be avoided during continuous meas-
urement.
If this happens, use a fixing weight or insula-
tor to secure the cable electrode.
When securing the cable electrode, avoid
high tensile forces. An appropriate fixing
spring which prevents cable overload can be
found in our price list.
Lateral mounting
With measuring probes that deliver continu-
ous measured values, the electrode must be
installed vertically. If installation from the top
is not possible, the electrodes can also be
mounted laterally.
Under accessories in our price list, you can
find a screening tube and a closing cone or
an angled rod electrode with which the instru-
ment can also be laterally mounted. Deter-
mine a screening tube length (L) that will not
allow product bridges to form between cable
and vessel wall, and that will not allow the
electrode cable to touch the vessel wall
through movements. Use a fixing weight or
fixing insulator.