Campbell Scientific AP200 CO2/H2O Atmospheric Profile System - Manual (Page 52)

AP200 CO
2
/H
2
O Atmospheric Profile System
6. Infrared Gas Analyzer (IRGA) Zero and Span
The IRGA should be zeroed and spanned periodically to maintain its accuracy.
There are three ways to accomplish this:
1. The IRGA can be removed from the AP200 system and zeroed and
spanned per the manufacturer’s recommendation. See Section 7.4.1,
Installing and Removing the IRGA, for instructions on installing and
removing the IRGA, and see the LI-840A IRGA user manual for
details on performing the zero and span outside the AP200 system.
2. The IRGA zero and span may be performed manually without
removing the IRGA from the AP200. Further details for this option
are given in Section 6.2, Manual Zero and Span.
3. The IRGA zero and CO
2
span may be performed automatically by the
AP200 system. This option can zero both CO
2
and H
2
O, but it can
span only CO
2
. It is not practical to automatically span H
2
O because
of the difficulty in providing an online H
2
O span gas (dewpoint
generator) in the field. Further details for this option are given in
Section 6.1, Automatic Zero and Span.
See Sections 5.2.2, Zero and CO
2
Span, and 5.2.3, H
2
O Span, for details on
plumbing connections to zero and span the IRGA while installed in the AP200.
The following sections give details on configuring the AP200 for automatic or
manual zero and span.
6.1 Automatic Zero and Span
This section describes how to configure the AP200 for periodic, automated
zero (CO
2
and H
2
O) and CO
2
span of the IRGA. Five public variables are used
to configure the AP200 for automatic zero and span. These variables may be
edited with keyboard display, either at the Configure System menu, or through
the normal Public Table. They may also be edited using LoggerNet.
These variables are stored in the sys_conf_var.dat file, so their
values will be saved if the program is recompiled. See Section
5.4, Configure the Program, for more details.
MEASURE_TANKS: Set this variable to True to periodically switch to the
zero and CO
2
span cylinders.
AUTO_ZEROSPAN: This variable can be set to either True or False. True
will command the IRGA to perform the zero and span. False will command
the IRGA to measure the cylinders but not perform the zero and span. The
recommended default is to set this variable to True.
CAL_INTERVAL: This variable determines how often the calibration
(zero/span) cylinders are measured. The recommended default is 1,440 min
(once per day).
CAL_TIMEOFFSET: This variable determines when the zero/span is
performed within the CAL_INTERVAL time. The recommended default is
720 min to start the calibration (zero/span) sequence at noon.
CO2_SPAN_PPM: Enter the concentration of the CO
2
span tank in ppm.
NOTE
40