Campbell Scientific AP200 CO2/H2O Atmospheric Profile System - Manual (Page 96)

Appendix F. Valve Sequence Timing
The profile sequence timing parameters are implemented in the AP200
CRBasic program as a set of three arrays. These arrays have eight locations to
accommodate up to eight levels. These arrays are not accessible in the Public
table, but they are output to the TimeInfo table as a record of the system
configuration. See Appendix D, Output Tables, for details on this table. As
the AP200 program steps through the profile sequence, variable
sequence_index cycles from 1 to LEVELS_USED to access the values stored
in the corresponding location in these arrays.
Array ProfileSequence() contains the valve number for each step in the
profile sequence. The values in this array increment from 1 to
LEVELS_USED. If the intake assemblies are installed according to normal
convention, the lowest intake will be designated level 1 and will connect to
inlet 1 on the AP200 system enclosure. This gives a one-to-one correspondence
between public variables valve_number and sequence_index, as well as the
terms level and step. (The intake assembly at the bottom of the tower (level 1)
connects to inlet 1 on the AP200 system enclosure, which is controlled by
valve number 1. This valve is selected during step one of the profile sequence,
defined by seq_index = 1). Array locations beyond LEVELS_USED are
filled with zero.
Array ProfileOnCounts() contains the time (number of scans) for each step in
the profile sequence. This is similar to the Time on Level given in TABLE
F-1, except it is multiplied by two to account for the datalogger scan rate (2
scans/s). For most cases, the same value is used for each step in the sequence.
However, for seven levels, one extra second is allocated for level 1 to achieve
an integer number of cycles per half hour. Array locations beyond
LEVELS_USED are filled with zero.
ProfileOmitCounts() is the time (number of scans) to wait after a valve switch
before including data in the average. This is the Omitted Time given in
TABLE F-1, multiplied by two to account for the datalogger scan rate (2
scans/s). For most cases, the same value is used for each step in the sequence.
For seven levels, an extra second is allocated for level 1 to achieve an integer
number of cycles per half hour. Array locations beyond LEVELS_USED are
filled with zero.
Synchronization to the Real-time Clock
When the AP200 program starts or when the user restarts the sequence (see
Section 5.5, Stopping and Starting the Sequence), the AP200 will delay the
actual profile sequence start by up to two minutes to synchronize the sequence
to the datalogger real-time clock. The following examples illustrate this
synchronization:
Example 1: LEVELS_USED = 8, STARTsequence set to True at 9:15:25:
As shown in TABLE F-1, the cycle time for 8 levels is 120 s (2 min). To
synchronize with the real time clock, the sequence must start at a multiple of 2
min, (for example, 9:00:00, 9:02:00, 9:04:00, etc.) Valve 1 will be selected as
soon as STARTsequence is set = True (9:15:25), but the sequence will not
actually start until 9:16:00 (the earliest multiple of 2 min). Data will be
included in the average for level 1 from 9:16:10 to 9:16:15, when the valve will
switch to level 2. Data will be included in the average for level 2 from 9:16:25
to 9:16:30, when the valve will switch to level 3, and so on.
F-2