Manual Version 19 / 01-2019 II Page 15 of 44
SF2 ECCR OPERATION MANUAL
3.2 Influence of pressure
Oxygen sensors usually measure the partial pressure of oxygen and not the percent.
The ambient air pressure therefore has a significant influence on the measurement
and calibration. At sea level there is an oxygen partial pressure of 0.209 bar. A
calibrated oxygen analyzer would show 20.9% accordingly. If the sensor were now
exposed to a pressure of 2 bar, it would display 41.8% (corresponding to 0.418 bar),
although the air composition has not changed.
In 5000 m, however, it would only show 10.45% (0.1045 bar). As a result, if the sea
level changes or if there are strong weather fluctuations, it must be recalibrated. Air
pressure fluctuations of 30 mbar due to changes in the weather lead to a
measurement error of around 3% (1 mbar pressure change corresponds to an error
of 0.1%). This means that the measurement of the oxygen content must always take
place under the same conditions as was previously calibrated. Most newer oxygen
analyzers, however, have
meanwhile a pressure sensor / barometer has been integrated so that the analyzer
corrects pressure fluctuations by itself.
Pressure fluctuations of this magnitude can also occur if the sensor is held directly
on a bottle valve or a mouthpiece for measurement. If the gas flow is too high (or if
gas flows directly onto the membrane), more gas flows onto the membrane than gas
can escape. This causes you "Back pressure" on the membrane, which is registered
by the sensor as an increased partial pressure. As a result, this leads to incorrect
measured values and can also lead to the destruction of the membrane.
A flow rate of 0.1-5 l / min neither affects the measurement accuracy nor does it
destroy the sensor membrane.
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