Instruction manual

NGA 2000 MLT Hardware
CHECK AND REPLACEMENT OF ELECTROCHEMICAL OXYGEN SENSOR
18 - 2
Emerson Process Management GmbH & Co. OHG
Instruction Manual
90002929
07/2006
EO
2
-SENSOR
18.1 EO
2
-Sensor
Through measuring principle the oxygen sensor will have only a limited life time.
The life time of the oxygen sensor is dependent 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 sensor with a response time of about 12 s
The sensors will have the following life time at approx. 21 % Oxygen and 20 °C :
approx. 42.857 hours (approx. 5 years) for sensor with a response time of about 12 s
Note !
The given values are for reference only! The expected lifetime is greatly affected by the
temperature of the environment in which the sensor is used or stored. Increases or decreases in
atmospheric pressure have the same effect as that by increases or decreases in Oxygen
concentration. (Operation at 40 °C halves lifetime). .
Note !
Depending on measuring principle the electrochemical EO
2
cell needs a minimum internal
consumption of oxygen (residual humidity avoids drying of the cell). Admit cells continuously with
sample gas of low grade oxygen concentration or with oxygenfree sample gas could result a
reversible detuning of O
2
sensitivity. The output signal will become instabil.
For correct measurement the cells have to admit with a O
2
concentration of at least 0.1 Vol.-%.
We recommend to use the cells in intervall measurement [purge cells with conditioned (dust
removal but no drying) ambient air at measurement breaks].
If it is necessary to interrupt oxygen supply for several hours or days, the cell have to regenerate
(supply cell for about one day with ambient air). Temporary flushing with nitrogen (N
2
) for less than
1 h (e.g. analyzer zeroing) will have no influence to measuring value.
All analyzers with electrochemical EO
2
cell have to be purged with conditioned ambient air prior
to disconnect the gas lines ! Then the gas line fittings have to be closed for transport or depositing
analyzer.
sensor time (hours)
O
2
concentration (%)