54
16.2 Dissolved Oxygen Troubleshooting
Symptom
Possible Causes
Remedy
Unit fails to calibrate, even
with new sensor.
Calibration settings outside of
allowable limits due to previous
failed calibration.
Initialise the unit. See section 12.
•
Zero calibration fails
(Zero is greater than
7.0%)
•
Air calibration fails (Span
is less than 70% or greater
than 135%).
•
Unstable or inaccurate
readings.
1.
Membrane is leaking or
broken.
2.
Gap between membrane and
gold cathode is dry.
3.
Incorrectly fitted membrane.
4.
Electrode is empty.
5.
Electrode is faulty.
Replace membrane and refill electrode.
Gently pump the pressure compensation
diaphragm several times.
Membrane should be smooth and convex
with no wrinkles. Re-fit membrane if
necessary.
Replace membrane and re-fill electrode.
Return electrode to factory for repair or
replacement
Blackened Silver anode.
Electrode has been exposed to
sulphides or other chemical
poisoning.
Remove pressure compensation diaphragm
and membrane, then soak in 5% Ammonia
solution for 10 minutes.
If cleaning is unsuccessful, return the
sensor to the TPS factory for cleaning and
service.
Tarnished or scratched Gold
cathode.
Electrode has been chemically
poisoned or physically damaged.
Return to the TPS factory for cleaning and
service.
Dissolved Oxygen reading
flashes in ppM mode.
Conductivity/TDS reading is in
excess of 82mS/cm or 50ppK.
Dissolved Oxygen readings are still valid
and accurate, but no longer salinity-
compensated, as the Conductivity/ TDS has
exceeded the limit for accurate calculations.
Meter displays
OVR ppM
or
OVR%
instead of
Dissolved Oxygen data.
1.
Electrode has not yet
polarised.
2.
Electrode is faulty
Wait for 2-3 minutes for the electrode to
polarise after the
90-FL
is switched on.
Return electrode to factory for repair or
replacement.