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CHECKING AND REPLACING AN ELECTROCHEMICAL OXYGEN SENSOR
25 - 1
ETC00781(4) Series 100 e 02/2004
25. Checking / Replacing an Electrochemical Oxygen Sensor
On account of the measuring principle the oxygen sensor has a limited life time.
The life time of the oxygen sensor depends on the sensor itself and on the measured oxygen
concentration and is calculated as follows:
life time =
The so-called “sensor time” (operation without oxygen at 20 °C ) is
approx. 900.000 hours for sensors with a response time of about 12 s
approx. 450.000 hours for sensors with a response time of about 6 s
The sensors have the following life time at approx. 21 % Oxygen and 20 °C :
approx. 42.857 hours (approx. 5 years) for sensors with a response time of about 12 s
approx. 21.428 hours (approx. 2.5 years) for sensors with a response time of about 6 s
Note !
The values given above are presented as guidelines only. The actual values are depending on
operation temperatures (the result of higher temperatures, for example 40 °C, could be the half
life time) and measured concentrations.
Note !
On account of the measuring principle the electrochemical O2 cell needs a minimum internal
consumption of oxygen (residual humidity avoids the cell running dry). Continuously supplying cells
with dry sample gas of low grade oxygen concentration or with oxygen-free sample gas could result
a reversible change of O2 sensitivity. The output signal will become unstable.
For correct measurement the cells have to be supplied with O2 concentrations of at least 0.1 Vol.-%.
We recommend to use the cells in intervall measurement (purge cells with conditioned (removal of dust
but no drying) ambient air during measurement breaks).
If it is necessary to interrupt oxygen supply for several hours or days, the cell has to regenerate (supply
cell for about one day with ambient air). Temporary flushing with nitrogen (N2) for less than 1 h (e.g.
analyzer zeroing) does not influence the measuring quality.
For analyzers with electrochemical O
2
cell purge all analyzer gas lines with conditioned ambient air
before closing the gas line fittings for transport or depositing the analyzer.
sensor time (hours)
O
2
- concentration (%)