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20.2 Slope of a pH Sensor
As mentioned above, a pH sensor produces 0 mV output at around 7.00 pH. As
the pH goes up, an “ideal” pH sensor produces -59mV/pH unit at 25
o
C As the pH
goes down, an ideal pH sensor pr59mV/pH unit. In practice, pH sensors
usually produce slightly less than this. The output of a pH sensor is expressed as a
percentage of an ideal sensor. For example, an ideal sensor that produces
59mV/pH unit has “100% Slope”. An sensor that produces 50.15mV/pH unit has
“85% Slope” (see Figure 20-2).
-600
-400
-200
0
200
400
600
0
7
14
Millivolts
85% Slope at 25 oC
(50.15mV/pH)
100% Slope at 25 oC
(59mV/pH)
Response of pH Electrode, as a Function of Slope
pH
Figure 20-2