VEGA Capacitive electrodes EK … with signal conditioning instrument - Manual (Page 34)

34 Capacitive electrodes EK with signal conditioning instrument
Diagnosis
Contact 4 against middle pin (1)
The resistor must be 1 M
W.
If the resistor is less, this means humidity in the housing or a failure in
the electrode isolation. A possible reason could be a not isolated elec-
trode used in a conductive (humid) medium.
If the resistor is higher or if the connection is interrupted, the reason is
mainly a bonding failure in the adapter plate or a defect resistor due to
strong electrostatic discharge.
In both cases return the electrode for repair to VEGA.
Contact 4 against vessel
The connection between contact 4 and the metal vessel (not instrument
hexagon or electrode flange) should be as good as possible. Measure
with an ohmmeter (range very low) the resistance value between con-
tact 4 and the vessel.
• Short-circuit (0 … 3
W), optimum connection
• Resistance > 3
W
- corrosion on the mounting boss or flange
- probably the mounting boss was covered with Teflon tape or
similar
Check the connection to the vessel. If there is no connection, you can
connect a line from the earth terminal outside to the vessel.
Note that covered flanges must be in any case connected via the earth
terminal to the vessel.
Contact 7 against middle pin (1)
The resistor must be infinite (>10 M
W).
If the resistor is less, humidity penetrated or the compensation capaci-
tor is defect.
Contact 3 against 4
In case of electrodes without screen, the resistor is infinite (>10 M
W).
With EK 26 the resistor should be 1 M
W. In case of lower values, the
electrode isolation is defect or humidity penetrated into the instrument
housing.
In case of higher values there is a bonding failure in the adapter plate
or the resistor is defect.
Contact 4 against 6
With older sensors the resistor is infinite, with newer electrodes <3
W. In
case of values between 3
W and 10 MW there is a defect.
When you cannot find a failure in the electrode, then replace the oscilla-
tor by a similar type (if available) or send the electrode for repair to
VEGA.
If the failure disappears after insertion of the new replacement electron-
ics, the adjustment on the signal conditioning instrument should be
repeated as the oscillators have different characteristics.