Campbell Scientific AP200 CO2/H2O Atmospheric Profile System - Manual (Page 97)

Appendix F. Valve Sequence Timing
Example 2: LEVELS_USED = 5, STARTsequence set to True at 9:00:20.
As shown in TABLE F-1, the cycle time for 5 levels is 90 s. To synchronize
with the real-time clock, the sequence must start at multiples of 90 s, (for
example, 9:00:00, 9:01:30, 9:03:00, etc.) Valve 1 will be selected as soon as
STARTsequence is set = True (9:00:20), but the sequence will not actually
start until 9:01:30. Data will be included in the average for level 1 from
9:01:42 to 9:01:48, when the valve will switch to level 2. Data will be
included in the average for level 2 from 9:02:00 to 9:02:06, when the valve will
switch to level 3, and so on.
Calibration Sequence
The calibration (zero/span) sequence timing depends on the number of levels
used and also on whether the zero/span is merely to be checked or if the IRGA
is to set its internal zero and span coefficients. In either case the zero/span
sequence cycle time is chosen to replace an integer multiple of profile
sequences. This allows a seamless transition back and forth between the
profile sequence and the calibration sequence.
The zero/span behavior is determined by two of the system configuration
variables as shown in TABLE F-2.
TABLE F-2. System Configuration Variables of Zero/Span
MEASURE_TANKS AUTO_ZEROSPAN
False False
Do not measure cylinders. Run
profile sequence all the time True
True False Measure cylinders but do not
set the zero or span
True Measure cylinders and set the
zero and span
Without Setting Zero and Span
If the AP200 is configured with MEASURE_TANKS = True and
AUTO_ZEROSPAN = False, it will check the zero and CO
2
span, but it will
not command the IRGA to set them. This section gives timing details for this
case. The AP200 zero/span sequence will:
• Select inlet 10 (CO
2
Span), omit at least 20 s for equilibration, and
include 10 s in the average.
• Select inlet 9 (Zero), omit at least 30 s for equilibration, and include
10 s in the average.
• Select inlet 1 for at least 10 s. This allows the humidity in the tubing
and IRGA to equilibrate before restarting the profile sequence.
As shown in TABLE F-3, this minimum timing adds up to 80 s for the
zero/span sequence. The time for one or more of the steps is increased as
needed to equal the profile sequence cycle time (or a multiple of the cycle
F-3