Mettler Toledo InPro 6850 i 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 con-
figuration is very important. In particular, the thick-
ness 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, 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
© 04 / 13 Mettler-Toledo AG
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