Page 20
9.2 Dissolved Oxygen Troubleshooting
Symptom
Possible Causes
Remedy
•
Zero calibration
fails (Zero is
greater than 10%)
•
Air calibration
fails (Span is less
than 70% or
greater than
130%).
•
Unstable or
inaccurate
readings.
1. Membrane is leaking or
broken.
2. Gap between membrane
and gold cathode is dry.
3. Incorrectly fitted
membrane.
4. Sensor is empty.
5. Sensor is faulty.
Replace membrane and refill
sensor.
ED1M: Undo the barrel 3
turns, then re-tighten to re-
flush the filling solution.
EDYSI: Gently pump the
pressure compensation
diaphragm to re-flush the
filling solution.
Membrane should be smooth
and convex with no wrinkles.
Re-fit membrane if necessary.
Replace membrane and re-fill
electrode.
Return sensor to factory for
repair or replacement
Blackened Silver
anode wire
Electrode has been exposed to
sulphides or other chemical
poisoning.
See section 10.4 for the sensor
cleaning procedure. If no
improvement, return to the TPS
factory for cleaning and service.
Tarnished or
scratched Gold
cathode.
Sensor has been chemically
poisoned or physically
damaged.
Return to the TPS factory for
cleaning and service.
Meter reads “
1.
”
(over-range
reading).
1. Sensor has not yet
polarised.
2. Electrode is faulty
Wait for 2-3 minutes for the
electrode to polarise after the
mini
CHEM
-DO
2
is switched
on.
Return electrode to factory for
repair or replacement.
