Hanna Instruments HI 9321 - Manual (Page 22)

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Since the resistance of the pH electrode is in the 200 Mohm range,
the current across the membrane is in the pico Ampere range. Large
currents can disturb the calibration of the electrode for many hours.
For these reasons high humidity environments, short circuits
and static discharges are detrimental for a stable pH reading.
The life of a conventional glass-body pH electrode also depends on the
temperature. If constantly used at high temperatures, the electrode
life is drastically reduced.
The resistance of glass electrodes partially depends on the tempera-
ture. The lower the temperature, the higher the resistance. It takes
longer for the reading to stabilize if the resistance is higher. In
addition, the response time will suffer to a greater degree at
temperatures below 10°C.
TEMPERATURE-RESISTANCE CORRELATION
FOR HANNA pH SENSITIVE GLASS
Typical Life of a Glass Electrode
Ambient Temperature 1- 3 years
80-90°C Less than 4 months
100-120°C Less than 1 month