VEGA Capacitive electrodes EL Profibus PA - Manual (Page 32)

32 Capacitive electrodes EL - Profibus PA
Setup
Application:
- highly conductive products
- adhesive, conductive products
- solids with fluctuating moisture content
For use in conductive, viscous liquids, a
suitable electrode of type EL 24 or EL 24
should be used.
2. Adjustment
Under the menu item " Adjustment", you inform
the sensor of the meas. span it should oper-
ate in.
The following criteria apply to the conductiv-
ity:
Mode 1 (90°) Mode 2 (PSA 45°)
with conc. tube > 50 µS/cm > 150 µS/cm
w.o conc. tube > 100 µS/cm > 300 µS/cm
Adjustment in
First of all, choose the unit you want to carry
out the adjustment in. Possible are pF, m or ft.
Offset correction
Carry out the offset correction with
unimmersed electrode.
This is necessary in order to save the initial
capacitance in the electronics. The electrode
must be mounted in the vessel and it must be
completely uncovered by the medium.
For electrodes with concentric tube, this
function is already carried out at VEGA, as
the vessel does not influence the measure-
ment. The offset correction must only be
repeated if the oscillator is exchanged.
Conductivity
If you have selected adjustment in m or ft,
you have to enter whether the medium is
conductive or non-conductive. If the medium
is non-conductive, you also have to enter the
dielectric constant in the next menu item.
The above table shows you the criteria that
apply to conductivity in capacitive measure-
ment.
Adjustment with medium
Fill the vessel e.g. to 10 %, enter in the menu
"
Min. adjustment" with the "+" and "–" keys 10
% and confirm with the "OK" key. Then fill the
vessel e.g. to 80 % or 100 %, enter in the
menu "
Max. adjustment" with the "+" and "–"
keys 80 % or 100 % and confirm with the
"OK" key.
You can carry out the adjustment with me-
dium or without. Generally, you will carry out
the adjustment with medium, because the
electrode can then adapt to the conditions in
the vessel.
Adjustment without medium
If you want to carry out the adjustment with-
out medium, your measurement loop must
meet certain requirements.
In conductive medium
- electrode is fully insulated
In non-conductive medium
- concentric tube electrode
- you know the DK value of the medium
Max.
Min.
100 % corresponds to 1200 l
Span
0 % corresponds to 456 l