Campbell Scientific EC150 CO2 and H2O Open-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 36)

EC150 CO
2
/H
2
O Open-Path Gas Analyzer
FIGURE 7-2. ECMon zero-and-span window
15. Remove the CO
2
span gas from the inlet of the shroud and replace it with
H
2
O span gas from a dew-point generator or another standard reference.
As water molecules can adsorb to inside of the tubing and the shroud, it
may take 30 minutes or more for the H
2
O concentration to stabilize. The
user may increase the flow rate for the first several minutes to more
quickly stabilize the system before returning it to between 0.2 and 0.4
LPM to make the H
2
O measurement. Record the reported H
2
O
concentration. If a stable reading is not achieved within 45 to 60 minutes,
troubleshooting steps should be undertaken.
16. Remove the H
2
O span gas, and connect a zero air source (no CO
2
or H
2
O)
to the inlet tube of the shroud. As described in step 11, use a pressure
regulator and flow controller so that zero air flows through the shroud
between 0.2 and 0.4 LPM. Wait for the measurement readings to stabilize
and record the reported values for CO
2
and H
2
O concentrations. If the
readings remain erratic, ensure that flow of the zero air is sufficient and
the shroud is correctly seated on the snouts.
If the quality of a zero gas is unknown or suspect, a desiccant and
CO
2
scrubber should be added between the zero gas tank and the
shroud to confirm that the gas being sampled during the zero
procedure is actually a zero air source.
17. Along with recording the CO
2
and H
2
O zero and span values, also record
the date and time, and temperature. With this information the user can
examine zero/span drift with time and temperature.
NOTE
26