Hanna Instruments HI 8614 - Manual (Page 12)

23 22
TEMPERATURE-RESISTANCE
CORRELATION FOR HANNA
pH SENSITIVE GLASS
The resistance of glass electrodes partially
depends on the temperature. The lower the
temperature, the higher the resistance. It takes
longer time for the reading to stabilize if the
resistance is higher. In addition, the response
time will suffer to a greater degree at tem-
peratures below 10°C.
Since the resistance of the pH electrode is in
the range of 200 Mohm, 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 environ-
ments, short circuits and static discharges
are detrimental for a stable pH reading.
The pH electrode's life also depends on the
temperature. If constantly used at high tem-
peratures, the electrode life is drastically re-
duced.
TROUBLESHOOTING
Evaluate your electrode performance based
on the following.
• Noise (Readings fluctuate up and down)
could be due to:
- Clogged/Dirty Junction: refer to the
Cleaning Procedure above.
- Loss of shielding due to low electrolyte
level (in refillable electrodes only): HI 7071
for single junction or HI 7082 for double
junction electrodes.
• Dry Membrane/Junction: soak in
HI 70300 storage solution for at least one
hour.
• Drifting: soak the electrode tip in warm
Hanna solution HI 7082 for one hour and
rinse the tip with distilled water. Refill with
fresh HI 7071 for single junction electrodes
and HI 7082 for double junction electrodes.
• Low Slope: refer to the Cleaning Proce-
dure above.
• No Slope: check the electrode for cracks
in glass stem or bulb and replace the
electrode.
• Slow Response/Excessive Drift: soak the
tip in Hanna HI 7061 cleaning solution for
30 minutes, rinse thoroughly in distilled
water and then follow the Cleaning Proce-
dure above.
-20 -20
-10
0 +10+20 +30+40 +50+60+70 +80+90 °C
-10
-10
Ω
-10
-10
-10
-10
2x10 9
1x10 9
2x10 8
1x10 8
2x10 7
1x10 7