Campbell Scientific CPEC200 Closed-Path Eddy-Covariance System - Manual (Page 68)

Appendix A. CPEC200 Diagnostics
generator and the Valve Module inlet. Make sure there is no tee in
this connection (see Section 5.2.2, Zero/Span). Finally, check the
flow setting of the dewpoint generator.
3. If the Zero Air valve (1) is selected and a scrub module is used, the
flow is controlled by the scrub module. The scrub module has a pump
to push the zero air through the valve module to the IRGA. The
CPEC200 fully opens the flow control valve by setting valveControl
= 1. The acceptable range for valve_flow is between 0.5 and 3.0
LPM. If the CPEC200 is accessible, check the indicator lights on the
valve module as described above. Also check the tubing connection
between the scrub module and the valve module inlet. Listen for the
sound of the scrub module pump to make sure it is running. Check
the scrub module pressure scrub_press. This pressure is measured at
the outlet of the scrub pump. This pressure is normally 3 to 20 kPa. If
the pressure is very high, it might indicate the Zero Air valve or the
proportion control valve is not open. If the pressure is very low, it
might indicate the pump is not running.
Bit 2: Valve Temperature
If the remainder of diag_cpec (after subtracting the numeric value for higher
bits that are set) is greater than 1, this means that bit 2 of diag_cpec is set. To
decode other diagnostic bits, subtract 2 from diag_cpec and compare the
remainder to the bit values below.
Bit 2 of diag_cpec indicates the valve module temperature is outside its
operating range. This check is performed only if the CPEC200 program is
configured to use a valve module, in which case the check is performed
continuously and Boolean variable valve_tmprOK is set accordingly.
However, the valve module temperature is ignored in EC mode (bit 2 of
diag_cpec is set only if it is relevant). If the valve module is outside its
operating range the zero/span sequence cannot be run, and the valves cannot be
selected manually. This protects the valves from possible damage.
To confirm the problem, verify that public variable valve_tmprOK = False.
This variable is set to T rue if the valve module temperature is within its
operating range (0°C to 60°C) and is set to False if it is outside this range.
The variable valve_tmprOK is not available for diagnosing a problem using
data saved in the output tables ( Flux or Zero_Span). Instead, check the value
of ValveTmprOK_Avg. This is a floating point number that represents the
fraction of time (from 0 to 1) that valve_tmprOK is true during the averaging
period. A value of 1 indicates no problem with the valve-module temperature
at any time during the averaging period. A value of 0 indicates a valve module
temperature problem during the entire time.
To continue troubleshooting a problem with the valve module temperature,
check the measured temperature, valve_tmpr. If it is NAN, this indicates a
problem with the temperature measurement. Make sure the valve module cable
is connected to the side of the valve module.
Next, compare valve_tmpr to the operating range (0°C to 60°C). The valve
module will be disabled if it is too cold. The valve module has a heater that
turns on if valve_tmpr falls below 2°C. If the valve module temperature is too
low, check the operation of the heater which is controlled by public variable
valve_heat_ON. For diagnosing a problem using data saved in the output
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