Campbell Scientific CSIM11 pH and ORP Sensors - Manual (Page 23)

CSIM11 pH and ORP Probes
sensor in 3.5 molar KCl, or water if KCl is not available, and heat to
approximately 60 °C for 15 minutes; retest.
SYMPTOM: Slow response and/or noisy, erratic readings.
POSSIBLE REASON: Slow response is caused by a very high impedance in
either glass or reference electrode.
CHECK:
1. Visually inspect pH bulb and reference junction for coating or clogging. If
coated, clean as described in Section 9.2, Electrode Cleaning.
2. Allowing a pH electrode to dry out raises the impedance dramatically.
Soaking the electrode in 0.1 normal HCl for 1/2 hour and rinsing with
distilled water should speed response (always keep electrodes wet).
3. Chemical degradation of pH glass can occur rapidly in a high temperature
or high pH environment. This also increases impedance yielding sluggish
response.
4. Low temperature environments also increase impedance, with impedance
doubling every 8 °C temperature drop from 25 °C.
5. Test wiring for intermittent connections by moving wires at the connector
on the datalogger wiring panel. Tighten as necessary. This is a common
source of erratic signals.
SYMPTOM: No response to pH change.
POSSIBLE REASON: A cracked glass bulb.
CHECK:
If electrode reads between 5.8 and 6.2 pH in all solutions, visually inspect glass
bulb for cracks. Discard probe if it is cracked.
POSSIBLE REASON: Short circuit.
CHECK:
If electrode reads 7.0 pH or 0.0 mV when connected to the datalogger, visually
inspect cable for damage. If there is no visible damage, test electrode in 4.0
buffer.
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