VEGA Capacitive electrodes EL … - Manual (Page 42)

42 Capacitive electrodes EL …
Diagnosis
Contact 4 against middle pin (1)
The resistance must be 1 M
Ω
.
If the resistance is less, this means humidity in the housing or a failure in
the electrode isolation. A possible reason could be a not isolated
electrode which is used in conductive (humid) product.
If the resistance 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 the electrode must be repaired at 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 contact 4
and the vessel.
• Shortcircuit (0 … 3
Ω
), optimum connection
• Resistance > 3
Ω
- 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 coated flanges must be in any case connected via the earth
terminal to the vessel.
Contact 7 against middle pin (1)
The resistance must be infinite (>10 M
Ω
).
If the resistance is less, humidity penetrated or the compensation
capacitor is defect.
Contact 3 against 4
On electrodes without screen the resistance is infinite (>10 M
Ω
). On EL 26
the resistance must be 1 M
Ω
. In case of lower values, the electrode
isolation is defect or humidity penetrated into the instrument housing.
In case of higher values, a bonding failure in the adapter place is the case
or the resistor is defect.
Contact 4 against 6
In case of older sensors and EL 29 the resistance is infinite, with new
electrodes <3
Ω
. In case of values between 3
Ω
and 10 M
Ω
there is a
defect.
When you cannot find a failure on the electrode, replace the oscillator
against a similar replacement type (if available) or send the electrode for
repair to VEGA.
If the failure does not disappear after inserting of a replacement
electronics, the adjustment on the signal conditioning instrument should be
repeated as the oscillators have certain tolerances.