Polarization Voltage; Temperature; Dependence On Flow - Mettler Toledo InPro 6950 Série Instructions D'utilisation

InPro 6950 Series O

10.4 Polarization voltage

The voltage between the anode and the cathode is so
selected that the oxygen is fully (> A, see polarogram)
reduced while other gases are unaffected (< D). The
ideal voltage for the Pt/Ag/AgCl or Pt/Pt/Ag/AgCl sys-
tem is between –500 and –750 mV.
100
90
80
70
60
50
40
30
20
10
0
The polarization voltage should remain as constant
as possible. Besides a constant source of voltage the
following prerequisites must be met: The electrical re-
sistance of electrolyte film must not exceed a particu-
lar value so as to avoid a voltage drop.
The anode must have a large surface so as to prevent
polarization of the anode by the electrode current.

10.5 Temperature

The temperature dependence of the current passing
through an oxygen electrode when referred to a con-
stant O
properties of the gas-permeable membrane.

10.6 Dependence on flow

With most oxygen electrodes the electrode current is
smaller in stagnant solutions than in agitated ones.
The consumption of oxygen by the electrode results
in extraction of oxygen from the solution in the close
vicinity of the cathode outside the membrane. The
oxygen is replaced by diffusion. If the electrode cur-
rent is strong, the solution cannot fully restore the
oxygen by diffusion. This results in an electrode cur-
rent weaker than would correspond to conditions in
the solution. In agitated solutions the oxygen is con-
veyed to the surface of the membrane not only by dif-
fusion but additionally by the flow (convection). In
that case no oxygen impoverishment occurs at the
membrane surface.
A high degree of flow dependence occurs mainly with
large cathodes, thin and highly permeable mem-
branes, i.e. where electrode currents are large.
© 02 / 17 Mettler-Toledo GmbH
Printed in Switzerland
Sensor 12 mm
2
Typical current voltage
curves in agitated
0.1 mol/l KCl
No. 1 Nitrogen
No. 2 21% Oxygen
No. 3 100% Oxygen
«A»
0.2 0.4
partial pressure is determined mainly by the
2
No. 3
No. 2
«D»
0.6 0.8 1.0
No. 1
1.2 – E (Volts)
InPro 6950
52 206 137
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