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90002929(6) NGA-MLT e 30.10.99
Rosemount Analytical
CALIBRATION
7.2 Calibration
To insure correct measurement results, zeroing and spanning should be carried out once a
week.
The zero level must always first be set before any other calibrations are attempted.
For the calibration procedure the required test gases have to be fed to the analyzer through
the respective gas inlets (cf. section 5.3) with a no - back - pressure gas flow rate of about 1
l/min (the same as with sample gas) !
7.2.1 Calibration (Test) Gases
a) Zero Gas
For zeroing, the analyzer has to be purged with nitrogen (N
2
) or adequate zero gas [e. g. synth.
air or conditioned air (not as a standard for O
2
measurement)].
.
b) Span Gas
The calibration of all another analyzers should be done with pure span gases in order to prevent
interferences between the gases (e. g., CO
2
and CO) measured by the analyzer. Test gas
mixtures are also possible depending on the mixed components (c.f. or test gas supplier).
The concentration range of the span gas has to be in a range of 80 - 110 % of the full scale
range of the respective measuring channel. For lower span gas concentrations the measuring
accuracy could be lower for sample gas concentrations, which are higher than the span gas
concentration! For test gas concentration see certification of the test gas bottles.
Spanning for oxygen measurement can be done using conditioned ambient air as span gas,
if the oxygen concentration is known and constant.
To calibrate a H
2
O channel (0 - 3(4) Vol.-%), use water vapor saturated N
2
according to
saturation characteristic (Item 22.) as span gas. Purge N
2
through a gas-blubber bottle, filled
with distilled water and in a little bit higher ambient temperature as necessary. Connect a
second vessel into a kyrostat (to hold ambient temperature constant) in series to get defined
dew point.