Campbell Scientific IRGASON IRGASON Integrated CO2/H2O Open-Path Gas Analyzer - Page 42

Replacing Desiccant and Scrubber Bottles, Replacing Desiccant and, Scrubber Bottles

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IRGASON® Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer NOTE 11. Examine the measurements that were written down for span CO2, span H2O, and zero air. Compute the drift in instrument gain using the following equation: gain = spanactual spanmeas − zeromeas where, • spanactual = known concentration of the span gas • spanmeas = measured concentration of the span gas • zeromeas = measured concentration in zero gas. Note that in the zero-and- span window of ECMon, spanactual is reported to the right of the box where the user enters the span dew-point temperature. The software calculates spanactual by taking into account the dew-point temperature and current ambient temperature and pressure. The equations used for this calculation may be found in Appendix B. If drift (offset or gain) for CO2 or H2O is excessive, it may be time to replace the desiccant and CO2 scrubber bottles (see Section 9.5, Replacing Desiccant and Scrubber Bottles). 12. With zero air still flowing and measurements stabilized, click on the Zero CO2 and H2O button in the ECMon zero-and-span window. Air flow into the shroud should be close to the recommended rate. If the flow is too low, the shroud will not be properly flushed; if it is too high, the air pressure within the shroud will be too high, and the analyzer will not be zeroed and spanned properly. 13. Remove the zero air source and replace it with the CO2 span gas. Allow the gas to flow through the shroud, maintaining a flow between 0.4 and 0.6 l/min. Wait for readings to stabilize. 14. In the zero-and-span window, enter the known concentration of CO2 (in ppm) in the box labeled Span Concentration (dry) and press Span. 15. Replace the CO2 span gas with an H2O span gas of known dew point. Allow the gas to flow through the shroud; higher flows may be desired for a couple of minutes to more quickly establish equilibrium before resuming a flow between 0.4 and 0.6 l/min. Wait for the readings to stabilize. 16. Enter the known dew point (in C°) in the box labeled Span Dew Point and press Span. 17. The zero-and-span procedure is now complete. Remove the shroud, reconnect the IRGASON® temperature probe, and prepare the site for normal operation. 9.5 Replacing Desiccant and Scrubber Bottles If more than two years have passed since replacing the desiccant / scrubber bottles within the IRGASON, or if the zero-and-span readings have drifted 32

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IRGASON
®
Integrated CO
2
/H
2
O Open-Path Gas Analyzer and 3D Sonic Anemometer
11.
Examine the measurements that were written down for span CO
2
, span
H
2
O, and zero air.
Compute the drift in instrument gain using the
following equation:
meas
meas
actual
zero
span
span
gain
−
=
where,
•
span
actual
= known concentration of the span gas
•
span
meas
= measured concentration of the span gas
•
zero
meas
= measured concentration in zero gas.
Note that in the zero-and- span window of ECMon, span
actual
is reported to
the right of the box where the user enters the span dew-point temperature.
The software calculates span
actual
by taking into account the dew-point
temperature and current ambient temperature and pressure.
The equations
used for this calculation may be found in Appendix B.
If drift (offset or
gain) for CO
2
or H
2
O is excessive, it may be time to replace the desiccant
and CO
2
scrubber bottles (see Section 9.5,
Replacing Desiccant and
Scrubber Bottles
).
12.
With zero air still flowing and measurements stabilized, click on the
Zero
CO
2
and H
2
O
button in the ECMon zero-and-span window.
Air flow into the shroud should be close to the recommended rate.
If the flow is too low, the shroud will not be properly flushed; if it
is too high, the air pressure within the shroud will be too high, and
the analyzer will not be zeroed and spanned properly.
13.
Remove the zero air source and replace it with the CO
2
span gas.
Allow
the gas to flow through the shroud, maintaining a flow between 0.4 and 0.6
l/min.
Wait for readings to stabilize.
14.
In the zero-and-span window, enter the known concentration of CO
2
(in
ppm) in the box labeled
Span Concentration (dry)
and press
Span
.
15.
Replace the CO
2
span gas with an H
2
O span gas of known dew point.
Allow the gas to flow through the shroud; higher flows may be desired for
a couple of minutes to more quickly establish equilibrium before resuming
a flow between 0.4 and 0.6 l/min.
Wait for the readings to stabilize.
16.
Enter the known dew point (in C°) in the box labeled
Span Dew Point
and
press
Span
.
17.
The zero-and-span procedure is now complete.
Remove the shroud,
reconnect the IRGASON
®
temperature probe, and prepare the site for
normal operation.
9.5
Replacing Desiccant and Scrubber Bottles
If more than two years have passed since replacing the desiccant / scrubber
bottles within the IRGASON, or if the zero-and-span readings have drifted
NOTE
32