ZIROX SGM7.2, Руководство пользователя

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Oxygen Monitor SGM7.2 4 Functional Description
4 Functional Description
4.1 Measuring principle
In industry and laboratories the measurement of the oxygen
concentration in gases is often required. Mostly, it is measured in
gases which have a remarkable temperature independent oxygen
concentration.
The NERNST-equation is used as a basis for determining the
oxygen concentration in gases with the oxygen monitor SGM7.2. NERNST-
Equation
U
RT
F
p
p
O air
O meas gas
=
4
2
2
ln
,
, .
(I)
U – cell voltage in V
R – molar gas constant, R = 8,314 J/(mol · K)
T – measuring temperature in K
F – Faraday-constant, F = 9,648 · 10
4
C/mol
p
O2,air
– partial pressure of the oxygen at the reference electrode
in dry air in Pa
p
O2,meas.gas
– partial pressure of the oxygen at the measuring electrode
in the measured gas in Pa.
The sensor of the SGM7.2 is based on the conductivity of
oxide ions in a special ceramic substance (zirconium
dioxide) with stabilising additives. The conductivity of these
oxide ions increases exponentially with the temperature and
it is sufficiently high for temperatures above 600°C.
The gas to be measured passes through the ceramic oxide
ion conductor which is a gas-tight pipe. The ceramic pipe is
situated axially symmetric in a thermally well-insulated
heater. The electrodes of the galvanic sensor are made from
platinum. The electrode on the outside of the pipe,
surrounded by dry air, is used as a reference electrode with
a constant, known electrode potential.
HB_SGM72_Rehm_eng.DOC
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