Microphone User Manual

28
TEMPERATURE-RESISTANCE
CORRELATION
The resistance of glass electrodes partially depends on the tempera-
ture. 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 tempera-
tures 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 environments, 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 temperatures, the electrode life is drastically reduced.
Typical Electrode Life
Ambient Temperature 1- 3 years
90 °C Less than 4 months
120°C Less than 1 month
-2
0
-2
0
-10
0
+1
0
+2
0
+
30
+4
0
+
50
+
60
+7
0
+
80
+
90
°
C
-10
-10
Ω
-10
-10
-10
-10
Ω
2x10
9
1x10
9
2x10
8
1x10
8
2x10
7
1x10
7
-40 -20 0 +10 +20 +30 +40+50 +60 +70 +80 +90 °C