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Page 49
20.2 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 18.
•
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. Sensor is empty.
5. Sensor is faulty.
Replace membrane and refill
sensor.
Gently pump the pressure
compensation diaphragm to
re-flush the membrane.
Membrane should be
smooth and convex with no
wrinkles. Re-fit membrane if
necessary.
Replace membrane and re-
fill sensor.
Return sensor to factory for
repair or replacement
Blackened Silver
anode wire
Sensor has been exposed to
sulphides or other chemical
poisoning.
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
OVR
ppM
or
OVR%
.
1. Sensor has not yet
polarised.
2. Sensor is faulty
Wait for 2-3 minutes for the
sensor to polarise after the
WP-91
is switched on.
Return sensor to factory for
repair or replacement.