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Page 43
20.3 pH and mV/ORP 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.
1 Point calibration
fails (Asymmetry
is greater than +/-
1.00 pH).
1. Reference junction
blocked.
2. Reference sensor
contaminated.
Clean reference junction, as
per instructions supplied with
the sensor.
Flush with distilled water and
replace sensor.
2 Point calibration
fails (Slope is less
than 85.0%).
1. Incorrect primary buffer.
2. Glass bulb not clean.
3. Sensor is aged.
4. Connector is damp.
5. Buffers are inaccurate.
Ensure that you are using
the primary pH buffer for
which the
WP-81
has been
set (see section 17).
Clean glass bulb as per
instructions supplied with the
sensor.
Attempt rejuvenation, as per
instructions supplied with the
sensor. If not successful,
replace sensor.
Dry in a warm place.
Replace buffers.
Unstable
readings.
1. Sensor chamber needs
to be refilled.
2. Reference junction
blocked.
3. Glass bulb not clean.
4. Bubble in glass bulb.
5. Faulty connection to
meter.
6. Reference junction not
immersed.
7. KCl crystals around
reference junction, inside
the electrolyte chamber.
Refill with saturated KCl
filling solution.
Clean reference junction, as
per instructions supplied with
the sensor.
Clean glass bulb as per
instructions supplied with the
sensor.
Flick the sensor to remove
bubble.
Check connectors. Replace
if necessary.
Ensure that the bulb AND
the reference junction are
fully immersed.
Rinse electrolyte chamber
with warm distilled water until
dissolved. Replace
electrolyte.
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