PN 9000-280-VE, Rev B
The voltage of the Cell depends on temperature, and so the Cell is maintained
at a constant temperature. The oxygen content is then determined from the
Nernst equation:
E = In
RT
4F
O
1
O
2
where
R
and
F
are constants,
T
is absolute temperature, and
O
1
and
O
2
are the
oxygen partial pressures on either side of the Cell.
Measuring Non-Combustible Gases
For measuring oxygen in non-combustibles gases, the calibration of an ana-
lyzer is obtained using the formula:
AT = 48.0 at 680°C
E = A*T*Log
20.9%
O
2
Unk%
Where
A
is a constant,
T
is the Cell temperature on an absolute scale (°C +273)
and
O
2
Unk%
is the unknown oxygen concentration of the gas to be analyzed,
and which is calculated by the analyzer.
The Cell produces zero voltage when the same amount of oxygen is on both
sides. Voltage increases as the oxygen concentration of the sample decreas-
es. The voltage created by the difference in the sample gas and the reference
air is transmitted to the microprocessor control unit and linearized to an
output signal.
Hydrocarbons in the Gas Sample
When hydrocarbons are present in a gas sample, a combustion process occurs
when the sample is exposed to the high temperature of the Zirconia Cell. If the
oxygen reading is lower than expected, it may be an indication that hydrocar-
bons are present.
The amount of oxygen reduction is dependent on the type of hydro-
carbons present in the sample gas.
Overview
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