Campbell Scientific CPEC200 Closed-Path Eddy-Covariance System - Manual (Page 49)

CPEC200 Closed-Path Eddy-Covariance System
The keyboard display has menus to facilitate manual zero control for users that
are onsite. Navigate:
Manual zero/span → Manual Control → H2O Span
Set valve_number = H2Ospan. If onsite, look at the LEDs on the valve
module to confirm the selected valve is now active. Verify valve_status
reports Valve flow is OK. If not, check the value of valve_flow and
troubleshoot as needed.
When the H2Ospan valve is selected, the CPEC200 does not
control the flow. It opens the control valve completely to minimize
pressure drop. The dewpoint generator determines the flow that it
pushes to the EC155. The variable valve_flow_OK = True for
any flow between 0.2 and 2.0.
Make sure the value in H2OSpanDewPt matches the setting of the dewpoint
generator.
Verify cpec_status reports CPEC is OK. If not, troubleshoot as needed.
There is no automatic error checking in manual zero/span mode,
so diagnostics must be checked manually.
Watch the values of H2O, Td_cell, and Td_ambient. All of these report the
measured humidity. H2O is the raw H
2
O concentration, in mmol mol -1 .
Td_cell is the dewpoint temperature calculated by the CPEC200 system for the
air in the sample cell (at the sample cell pressure). Td_ambient is similar to
Td_cell, but it is calculated for ambient pressure. Td ambient and Td_cell
should be very similar. If not, make sure the sample cell pressure is close to
ambient pressure ( diff_press is close to zero).
When Td_cell stabilizes, set DO_H2O_span = True. The IRGA will set the
H
2
O span to make the measured dewpoint Td_cell match H2OSpanDewPt.
Verify that these two values now match.
Set valve_number = None (0) to stop the flow of H
2
O span gas.
6.3.2.5 Returning to Normal EC Mode
When checking and setting are completed, turn the pump on by setting
pump_ON = True. This will make sure the valves are turned off and restart
the pump.
Disable temperature control of the valve module to conserve power (this is not
done automatically in full manual control).
7. Maintenance and Troubleshooting
Most of the basic diagnostic and troubleshooting issues for the CPEC200 are
covered in Appendix A, CPEC200 Diagnostics. The section that follows
provides additional detail on some issues that may arise with hardware
components.
NOTE
NOTE
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