Appendix f. valve sequence timing, Ee appendix f – Campbell Scientific AP200 CO2/H2O Atmospheric Profile System User Manual
Page 95
Appendix F. Valve Sequence Timing
The AP200 has two valve sequences: the profile sequence and the calibration
(zero/span) sequence. The AP200 will run the majority of the time in the
profile sequence, cycling through the profile inlets in order from one to the
number of levels selected (4 to 8). If configured for automatic zero/span, then
the AP200 will periodically run the calibration sequence before returning to the
profile sequence. The timing of the valve switching depends on settings of the
following system configuration variables (see Section 5.4.1, System
Configuration Variables, for details on the system configuration variables):
LEVELS_USED
MEASURE_TANKS
AUTO_ZEROSPAN
CAL_INTERVAL
CAL_TIMEOFFSET
Profile Sequence
The profile sequence cycles through the profile inlets in order, starting at 1, and
ending at the value of
LEVELS_USED. This cycle repeats until it is
interrupted for an automated calibration sequence (if this feature is enabled) or
until the sequence is stopped by the user.
The AP200 has pre-programmed parameters that determine the timing of the
profile sequence. These timing parameters allow for at least 15 s on each level,
with 10 s omitted to allow the CO
2
and H
2
O concentrations to equilibrate, and
5 s included in the average. In addition to these constraints, the timing
parameters depend on the number of levels used (
LEVELS_USED) to give an
integer number of complete cycles in each half-hour averaging period. As
shown in TABLE F-1, the timing for 4, 6, or 8 levels simply use these
minimum values, giving 15, 20, or 30 cycles per half hour. The times are
extended slightly for 5 or 7 levels to give integer number of cycles per half
hour.
TABLE F-1. Profile Sequence-timing Variables
Number
of Levels
Time on
Level (s)
Omitted
Time (s)
Averaged
Time (s)
Cycle
Time (s)
Cycles/
Half Hour
4
15
10
5
60
30
5
18
12
6
90
20
6
15
10
5
90
20
7
18/17*
12/11*
6
120
15
8
15
10
5
120
15
*18 s on level 1 with 12 s omitted; 17 s with 11 s omitted for the rest of the levels
F-1