Mettler Toledo InPro 6850i Bedienungsanleitung Seite 33

InPro 6850 i / 6900 i / 6950 i O
The membrane electrode according to Clark is today
most widely used. As compared to the electrode
without 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
configuration 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
InPro 6800 for medium and high oxygen concentra-
tions. Cathode and anode / reference. Anode and ref-
erence are united in a silver / silver chloride electrode.
The following equilibration reaction takes place at
the anode resp. reference:
Reaction: 4 Ag + 4 Cl
Measurement
liquid or gas
Type B, 3-electrodes system, InPro 6850 i
InPro 6850 i 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. Af-
ter polarization there is a stable equilibrium between
electrode surface and electrolyte. No net-reaction
takes place.
Reference reaction in equilibrium:
Reaction: No current
© 02 / 17 Mettler-Toledo GmbH
Printed in Switzerland
Sensor 12 / 25 mm
2
–
$
O O
2 2
O
2
O + 4 e –
$
2
4 AgCl + 4 e
2 O + 4 OH
2
InPro 6850 i / 6900 i / 6950 i
33
–
Polarization
voltage
Reference / Anode
Cathode
Electrolyte
Glass insulator
NTC 22 k
Membrane
–
52 206 349