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3-13
Instruction Manual
HASAxE-IM-HS
05/2006
Emerson Process Management GmbH & Co. OHG
3 Principles
3-2 Oxygen Measurement
3-2-3 Special Hints on Oxygen Sensors
Paramagnetic Sensor
The table below shows how accompanying
gases interfere the paramagnetical oxygen
measurement.
If the concentration of such gases is already
given at time of enquiry this interference may
be taken into account during factory startup and
thus minimized (option).
Table 3-3: Paramagnetic Oxygen Measurement,
cross interference by accompanying gases
Electrochemical Sensor
Due to the measuring principle the electro-
chemical oxygen cell requires a minimum
internal consumption of oxygen (residual
humidity avoids drying of the cell). Supplying
cells continuously with dry sample gas of low
grade oxygen concentration or with sample
Gas Concentration Interference
Level
Carbon monoxide 0-100% no effect
Carbon dioxide 0-100% no effect
Nitric monoxide 0-1% no effect
Nitrogen dioxide 0-1% no effect
Sulfur dioxide 0-3% 3%
Hydrogen sulfide 0-3% no effect
Ammonia 0-3% 1%
Hydrogen 0-100% no effect
Hydrogen chloride 0-3% 1%
Benzene 0-100ppm 1%
Methane 0-100% no effect
Table 3-4: Electrochemical Oxygen Measurement,
cross interference by accompanying gases
This sensor is not suitable for anorganic gases
containing chlorene or flourene!
In addition is not suitable for sample gases
containing ozone, H
2
S (> 100 ppm) or
NH
3
(> 20 ppm).
For a number of other interfering gases see
table 4-3 below:
gas free of oxygen could result in a reversible
detuning of O
2
sensitivity. The output signal will
become unstable, but response time remains
constant.
For correct measurement the cell needs contin-
uously to be supplied with concentrations of at
least 0.1 Vol.-% O
2
. We recommend to use
the cells if need be in alternating mode, means
to purge cells with conditioned (not dried, but
dust removed) ambient air when measurement
pauses.
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 (N
2
) for less
than 1 h (e.g. for analyzer zeroing purpose) has
no influence on measuring characteristics.