ZIROX SGM7.2, Руководство пользователя

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Oxygen Monitor SGM7.2 4 Functional Description
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
is valid:
Equation
for Oxygen
Concentrati
on
ϕ
O
2
= 20,64 · e
(-46,42 · U
T
)
(II)
ϕ
O2
– oxygen concentration in the measured gas in vol.-%
U – potential difference in mV
T – measuring temperature in K
20,64 – oxygen concentration in air with a relative
humidity of 50% in vol.-%.
4.1.1 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 U T ~
U
T
~
1
– for bound oxygen
The equation (II) 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.
1
It has to be distinguished between different conditions of the oxygen in the measuring gas:
Free oxygen: There are the oxygen molecules in the gas independently without every relationship
relation to the other gas components (inert gases such as N
2
or Ar)
Bound oxygen: There aren't any free oxygen molecules, but only in bound form e.g. as steam in
the gas. At higher temperatures a dissociation is carried out and oxygen molecules then are
availably. Since the dissociation degree increases with the temperature, the measurement result is
also dependent on
the
temperature.
Circumstances permitting free oxygen can react with perhaps available burning gasses at the hot
platinum electrode, a reducing gas then can be also in the result through what.
HB_SGM72_Rehm_eng.DOC
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