Campbell Scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 43)

EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
i. 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).
j. With the zero air still flowing and measurements stabilized, click on the
Zero CO
2
and H
2
O button in the Zero/Span window. This will cause the
analyzer to adjust the values of its CO
2
Zero and H
2
O Zero parameters,
forcing the CO
2
and H
2
O concentrations to read zero. Verify the CO
2
and
H
2
O concentrations now read zero.
k. Now, remove the zero air source and replace it with the CO
2
span gas.
Allow the gas to flow through the sample cell. Watch for readings to
stabilize.
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