Transmiter 9135 – pH/redox measurement
Page 65
7. Impedance measurement
Electrode impedance : electrode integrity index
A method generally used to detect an electrode default
is to calibrate a pH measurement system in pH
standards solutions. If the slope or the zero
(asymmetry) characteristics are out of the programmed
limits., one of the electrodes is considered to be
damaged.
An other method consists of the manual measurement
of both electrode impedance. This method is easy to
use with the reference electrode, but intricate with the
glass electrode which has a high impedance.
Besides, for both methods the electrodes need to be
withdrawn from the process.
Electrode defaults usually met are as follows :
• A crack of the glass membrane which shows a low
impedance between the sample and the
electrode.
• A contaminated electrode (deposit) which shows a
weaker measurement sensibility and an electrode
high impedance.
• A lack of electrolyte in the reference electrode
which shows a very important impedance.
a poisoned reference electrode by sulphides which
precipitate with silver ions and may clogged the
electrolytic junction. This poisoning shows a high
increase of the impedance .
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