Campbell Scientific AP200 CO2/H2O Atmospheric Profile System - Manual (Page 75)

Appendix B. AP200 Diagnostics
If the pump pressure is too low, check pump_control and pump_speed.
When the pressure falls below the setpoint, the AP200 will respond by
reducing pump_control. This should reduce pump_speed and allow
pump_press to rise to the setpoint. If pump_control = 0 but the pump is still
running, contact Campbell Scientific.
If the pump speed is oscillating, check the value of BuffDepth. This variable
is found in the Status table (see the CR1000 User Manual at
www.campbellsci.com for more information). The AP200 CRBasic program
runs in Pipeline mode, which allows measurements to stay on schedule even
when processing tasks fall behind. BuffDepth indicates how far processing
has fallen behind measurements (number of scans). If processing falls too far
behind, the delay between measuring the pump pressure and adjusting the
pump speed can cause the pump speed to oscillate. Normally, BuffDepth will
be 2 or less. If the value is higher than 2, contact Campbell Scientific.
Bit 5 : Sample flow is outside its normal range
If bit 5 of diag_AP200 is set, this indicates the sample flow is outside the
normal range. To confirm this error, check the value of sample_flow which is
measured by a mass-flow sensor mounted on the outlet of the valve manifold.
The sensor measures the flow to the IRGA. The normal range for the sample
flow is 100 to 350 ml/min. If the sample flow is outside this range, see the
appropriate section below.
Profile Inlets
The sample flow for profile inlets is set by an orifice in the intake assembly.
See Section 4.2.1, Intake Assemblies, for details.
If the flow goes too high at a valve switch but comes into the normal range
within a few seconds, this is normal. It is caused by a different pressure drop
through the valve manifold depending on whether the inlet is selected or
bypassed. The combined flow from the bypassed inlets causes slightly more
pressure drop than for the inlet selected to go to the IRGA. Consequently, the
pressure in the intake tubes and mixing volumes increases slightly when they
are bypassed. When a bypassed inlet is selected, the pressure equalizes by
pushing slightly higher flow than normal through the IRGA. This is acceptable
as long as the sample flow is within the normal range by the time the data are
included in the average.
If the flow for one or more of the inlets stabilizes at a high flow, this may
indicate a leak in a tube or connection. See Section 7.1, Plumbing Leaks, for
leak-checking suggestions.
If the flow is too low for one or more inlets, this is most likely caused by a
filter that is plugged with particulates. This normally happens over a span of
weeks or months. It may happen more quickly in dirty conditions. Try
replacing the filter (see Section 4.1.6, Replacement Parts). If this does not
resolve the problem, the orifice may be plugged, and Campbell Scientific
should be contacted.
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