LI-COR LI7200RS, Инструкция по эксплуатации

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Section 4. User Calibration
l
Temperature:
A 10 °C change will typically change the H
2
O span by 1 to 2%.
For CO
2
at ambient concentrations, the span is very insensitive to temperature.
l
Pressure:
A large pressure change (40 kPa) will affect the CO
2
and H
2
O spans
by <1%, for ambient CO
2
concentrations (
≈
400 ppm) and high humidities (20
mmol/mol). So, diurnal pressure variations should not be a concern.
l
Chemicals:
Reduced internal chemical effectiveness will affect the span, but the
effect on the zero will be much more pronounced. In summary, span stability is
mostly a concern with H
2
O, when there are large temperature changes.
Note: Read the technical note called "Using CO
2
and H
2
O Scrubbers with
LI-COR Gas Analyzers" for information about the interactions between scrub
chemicals and the air.
See https://www.licor.com/documents/7i418s3uhd2uamoxfmjd.
Checking the Zero
Flow a dry CO
2
-free air through the optical path and check the analyzer reading in
the software dashboard. A suitable source of air for setting the zero can be gen-
erated with chemical scrubbers (such as soda lime for removing CO
2
and mag-
nesium perchlorate or Drierite® for removing water), or obtained from a cylinder
of zero-grade gas.
When using chemical scrubbers, make sure that the chemicals are fresh and that
air goes through the chemicals in the right order: Soda lime first, desiccant last (if
the desiccant is Drierite®, allow time for the CO
2
to "wash out" of it). Use a small
pump to push the air through the gas analyzer.
CO
2
Scrubber H
2
O Scrubber Particulate Filter
To Air In
When using a cylinder, make sure that the air in the cylinder really is CO
2
-free
since a typical cylinder of standard grade nitrogen might have as much as 20 ppm
of CO
2
in it. Compressed cylinders may be at pressures of several thousand pounds
per square inch; before using them for calibration, they should be fitted with a reg-
ulator to reduce the pressure down to a range of around thirty pounds per square
inch. Set the flow rate from 0.5 to 1.0 lpm.
4-2 LI-7200RS Enclosed CO₂/H₂O Analyzer