Tophit H CPS471/CPS471D
4
Hauser
• Isothermic curves
– The Nernst equation defines the dependence of the measuring voltage on the hydrogen ion content (pH
value) and the temperature. It is the basis of pH measuring technology and for ISFET sensors too. A
temperature-dependent value for the potential change per pH value can be worked out from this equation
(isothermic curve, potential change per pH value at a defined temperature).
– The isothermic curves of the ISFET sensor are very close to the theoretical values (
4). This is further
proof for the high pH measurement precision of the sensor.
a0003868-de
Fig. 4:
Isothermic curves
a
Isothermic curve at 8 °C (46 °F), slope –55.8 mV/pH
b
Isothermic curve at 37 °C (99 °F), slope –61.5 mV/pH
c
Isothermic curve at 61 °C (142 °F), slope –66.3 mV/pH
500
300
100
-100
-300
-500
0
2
4
6
8
10
12
14
pH
mV
a
b
c
