IRGASON Integrated CO
2
/H
2
O Open-Path Gas Analyzer and 3D Sonic Anemometer
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 optical instrumentation, the IRGASON gas analyzer may
drift slightly with exposure to natural elements, so a zero-and-span procedure
should be performed occasionally—on the order of weeks or months. As a
starting point, after cleaning the analyzer windows (Section 9.3, Gas Analyzer
Window Cleaning), perform the zero-and-span procedure. After the first
several zero-and-span procedures, the rate of drift in gain and offset (explained
later in this section) should be analyzed to better determine how frequently the
analyzer should be zeroed and spanned. If the IRGASON is employed at a site
with large seasonal changes in ambient conditions, the zero-and-span
procedure should be done at least seasonally.
The first part of the following procedure simply measures the CO
2
and H
2
O
zero and span, without making adjustments. This allows the CO
2
and H
2
O gain
factors to be calculated. These gain factors quantify the state of the analyzer
before the zero-and- span procedure, and in theory could be used to correct
recent measurements for drift. The last part of the zero-and-span procedure
adjusts internal processing parameters to correct subsequent measurements.
If the zero-and-span procedure is being performed off-site (e.g., in a lab), be
sure to mount the IRGASON on the lab stand (p/n 27278). This will ensure the
analyzer is in the correct upright orientation and has the correct optical
alignment.
It is imperative that the zero-and-span procedure be done correctly and not
rushed; allocate plenty of time for the procedure (at least an hour).
Resting the analyzer on its side during the zero-and-span
procedure may result in measurement inaccuracy.
CAUTION
To check and then set the IRGASON zero and span, follow the steps below:
1. Remove power from the EC100.
2. If not already done, clean the windows and snouts with alcohol and a non-
scratching tissue or cloth.
Make sure the alcohol and any residual water completely
evaporate from the analyzer before proceeding with the
zero-and-span procedure.
CAUTION
3. As shown in Figure 9-3, position the IRGASON zero-and-span shroud (p/n
26390) over the upper and lower snouts. To do this, twist the two ends of
the shroud together to minimize the length of the shroud. Make sure the
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