256 AO2000 CONTINUOUS GAS ANALYZERS | OI/AO2000-EN REV. B
Magnos28: Single-point calibration
Single-point calibration
The long-term sensitivity drift of the Magnos28 analyzer module is less than
0.15 % of measured value per three months (at least 0.03 vol.% O
2
per three
months) for measurement ranges up to 25 vol.% O
2
. Thus a regular offset
correction is sufficient. This so-called single-point calibration can be con-
ducted at each point on the characteristic curve since a parallel shift of this
curve results. Depending on the measurement task, however, we also rec-
ommend that an end-point calibration is carried out once a year.
Note: The short-term sensitivity drift can amount to 1 % of the measured
value per week.
Test gas
A test gas with any concentration of O
2
can be used for single point calibra-
tion as long as it lies within one of the measurement ranges in the analyzer
module.
Environmental air can also be used as the test gas.
The test gas must have the same moisture content as the process gas.
CAUTION!
In order to avoid accumulations of explosive gas mixtures, do not use air
as a test gas for single-point calibration when measuring flammable gas-
es!
Suppressed measuring range
The single-point calibration can also be carried out in a measuring range
with a suppressed zero point, provided that the suppression ratio is ≤ 1:5. In
this case as well, the O
2
concentration of the test gas must be within the
measurement range.
The drift at 100 vol.% of O
2
is smaller than 0.24 vol.% of O
2
per year.
Air pressure
The current air pressure must be considered for the single-point calibration.
This is done automatically if a pressure sensor is incorporated in the analyz-
er module.
Calibration method
If the analyzer module has one sample component the single-point calibra-
tion is carried out as common calibration only at the zero point.
If the analyzer module has more than one sample component the sin-
gle-point calibration is carried out as a substitute gas calibration only at the
zero point (see page 223).
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