Transmitter 9135 - pH/redox measurement
Page 66
In our system, the electrode impedance measurement
results from the measurement system without addition
of commutation circuits.
Measurement principle
A non-oxidising electrode permits to set the liquid
potential to the zero measured. A very stable voltage
(equal to E) is applied to the electrode. Two capacities
are loaded through the electrode impedance. After a
certain time (which depends on the impedanc e
measured), the system measures the potential
variation on each electrode.
The process temperature is measured to compensate
the impedance measurement of the glass electrode.
The impedance measurement drift of the glass
electrode according to the temperature is represented
by the curve below :
0
200
400
600
800
1000
0
5
10
15
20
25
30
35
40
45
50
Temperature (°C)
impedance (T°C)
impedance (25°C)
Impedance measurement 8404_b
( Mohms )
