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6. Troubleshooting
6.1 pH and mV Troubleshooting
Symptom Possible
Causes
Remedy
Meter displays
“
-1.
" as a
reading.
pH reading is over-ranged.
pH sensor not connected or
faulty. Replace sensor if
necessary.
Asymmetry
calibration with
Calibrate
control
in pH6.88 or
pH7.00 buffer fails.
(Asymmetry is
greater than +/-1.00
pH.)
1.
Reference junction blocked.
(See section 7.3)
2.
Reference electrolyte
contaminated.
Clean reference by immersing
the probe in hot water (60
°
C)
for a few minutes. Proteins can
be cleaned off using a pepsin
solution.
Replace electrolyte if using a
refillable sensor.
Slope calibration
with
Slope
control
in low or high
buffer fails. (Slope
is less than 85.0%.)
1.
Glass bulb not clean.
2.
Sensor is aged.
3.
Connector is damp.
4.
Buffers are inaccurate.
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.
Inaccurate readings,
even when
calibration is
successful.
Reference junction blocked.
(See section 7.3)
Clean reference junction by
immersing the probe in hot
water (60
°
C) for a few minutes.
Displays around
pH7.00 for all
solutions.
Electrical short in connector.
1.
Check connector. Replace if
necessary.
2.
Replace sensor.
Displays 4-5 pH for
all solutions.
Glass bulb or internal stem
cracked.
Replace sensor.
