Campbell Scientific IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer - Manual (Page 38)

IRGASON ® Integrated CO
2
/H
2
O Open-Path Gas Analyzer and 3D Sonic Anemometer
FIGURE 9-3. Proper location of the gas analyzer top wick (left) and
bottom wick (right)
9.3 Gas-Analyzer Window Cleaning
The windows of the analyzer should be cleaned if the signal strength for CO
2
or H
2
O drops below 0.7 or 70% of the original value. These values may be
monitored in the output data, or they can be viewed with ECMon. To clean the
windows, use isopropyl alcohol (2-propanol / isopropanol) and a cotton swab
or a non-scratching tissue or cloth. Verify that following cleaning the signal
strengths are restored to values close to 1.0.
9.4 Zero and Span
As is the case with all optical instruments, the IRGASON’s gas analyzer
measurements may drift slightly with exposure to natural elements. Therefore,
routine maintenance requires a periodic zero-and-span procedure. The
frequency with which this should be done is heavily dependent on the
environmental conditions in which the instrument is making measurements.
Campbell Scientific recommends that a new instrument, or an instrument that
has been moved to a new location, should have a monthly zero and span
procedure performed. Additionally, it is recommended to always zero and
span the analyzer after cleaning the windows (see Section 9.3, Gas-Analyzer
Window Cleaning). After the first several zero-and-span procedures, the rate of
drift in gain and offset (explained later in this section) will be better understood
for the existing environmental conditions. A regimented protocol for zero and
span of the instrument initially, will allow the user to assess the appropriate
time interval between zero and span procedures. However, if the IRGASON is
being used at a site with large seasonal changes in ambient conditions, the
zero-and-span procedure should be done at least seasonally.
In situations in which spanning the instrument is extremely difficult (for
example, in below freezing temperature conditions or in very remote sites),
performing a monthly zero will help mitigate the drift in the analyzer’s
measurements.
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