Dr. A. Kuntze PH-T Podręcznik - Strona 9

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Interpretation of the mV signals of pH sensors
The following table shows the mV values an ideal sensor would give in various buffer
solutions:
pH
0
mV ideal
406
pH
7
mV ideal
0
If your sensor does not show exactly those values, don´t worry - it simply means that
your sensor does not have a slope of 58mV/pH and/or that its zero point is not exactly
pH 7. For evaluation, determine its characteristics: the slope and the zero point error.
The zero point error is the mV value found in pH 7. For new sensors it should not be
greater than +/-15mV, for used sensors up to +/-55mV are tolerated.
The slope is the signal change in mV per pH. If you are working with buffers pH 7 and
pH 4, than the mV difference between them is 3 times the slope. The following table
gives a rough overview:
mV(pH4) - mV(pH7) 150
Slope / mV/pH
A new sensor should show a slope between 57 and 59 mV/pH, for used sensors
values between 50 and 60 mV/pH are tolerated.
NOTE
All those values are based on a temperature of 25°C. At higher
temperatures, slopes will be higher.
1
2
3
4
348
290
232
174
8
9
10
11
-58
-116
-174
-232
155
160
165
50
52
53
55
5
6
7
116
58
0
12
13
14
-290
-348
-406
170
175
180
56
58
60
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