Mettler Toledo InPro 6000G Serie Instructions D'utilisation page 35

InPro 6800 G / 6850i G / 6900i G / 6950i G O
– Electrodes with gas-permeable membrane
(Clark Principle)
The membrane electrode according to Clark is today
most widely used. As compared to the electrode with-
out membrane it possesses the following advan-
tages:
– Oxygen measurement in gases and solutions
– No mutual contamination of electrode and solu-
tion
– No or little dependency on flow
In the case of the Clark electrode, geometrical config-
uration is very important. In particular, the thickness
of the electrolyte film between the cathode and the
membrane must be within narrow tolerances so as to
ensure good linearity and a low zero current (current
in a nitrogen atmosphere).
METTLER TOLEDO oxygen sensors are available in
different designs:
Type A, 2-electrodes system, InPro 6800 G
InPro 6800 G for medium and high oxygen concen-
trations. Cathode and anode /reference. Anode and
reference are united in a silver / silver chloride elec-
trode.
The following equilibration reaction takes place at the
anode resp. reference:
Reaction: 4 Ag + 4 Cl
Measurement
liquid or gas
Type B, 3-electrodes, InPro 6850i G
InPro 6850i G for medium and high oxygen concen-
trations. The reference corresponds the conventional
silver /silver chloride anode. The anode is a platine
electrode and separated from the reference.
The following reaction takes place at the anode:
Reaction: 4 H
The reference is a silver /silver chloride electrode.
After polarization there is a stable equilibrium be-
tween electrode surface and electrolyte. No net-reac-
tion takes place.
© 09 / 09 Mettler-Toledo AG
Printed in Switzerland
–
→
O O
2 2
O
2
–
O + 4 e
→
2
12 mm
2
4 AgCl + 4 e
2 O + 4 OH
2
InPro 6000 G – Series
35
–
Polarization
voltage
Reference / Anode
Cathode
Electrolyte
Glass insulator
NTC 22 k
Membrane
–
52 206 477