Electrolysis Device SGM5EL Functional description
9
Based on the assumption that the total pressures of the gases are almost
the same at both electrodes (in this case the volume concentrations may
be used in the calculation instead of the partial pressures) and replacing
the parameters by numbers in equation (
I
) the following equation applies:
ϕ
O
2
=
20.64 · e
(-46,42 ·
)
(III)
U - potential difference in mV
T - measuring temperature in K
20.64 -
oxygen concentration in air with a relative humidity
of 50% in vol%.
ϕ
O2
-
oxygen concentration in the measured gas in vol%
4.2 Measuring conditions
4.2.1 General recommendations
The oxygen may be in free or bound form inside the measuring gas
1
.
Thereby, the following dependencies are valid:
– for free oxygen
– for bound oxygen
The equation
(III)
for calculating the oxygen concentration is valid for
measured gases with free oxygen as well as for reducing gas mixtures in
which oxygen only exists in bound form (e.g. in H
2
/H
2
O- or CO/CO
2
-
mixtures).
In reducing gas mixtures, the oxygen partial pressure is inversely
proportional to the temperature. For converting the measured value at the
measuring temperature into other temperatures special thermodynamic
equations are required.
Reducing gas
mixtures
1
D
ifferent conditions of oxygen in the measuring gas must be distinguished:
Free oxygen:
Oxygen molecules in the gas are independent without a bond to other gas components (inert gases
such as N
2
or Ar).
Bound oxygen:
Free oxygen molecules do not exist in the gas, only in bound form e.g. as water vapor. Higher
temperatures cause a dissociation and oxygen molecules are available. Since the dissociation degree increases
with the temperature, the measurement result depends on
the
temperature.
Possibly, free oxygen can react with potential burnable gases at the hot platinum electrode. The result can be a
reducing gas.
U
T
U
T
~
U
T
~
1