Campbell CPEC300, Product Manual, Page: 95 / 175

CPEC300/306/310 Closed-Path Eddy-Covariance Systems
86
TABLE 7-2. Site Sequence and Timing in the Auto Zero and Span Cycle
Step in
Auto
Zero/Span
Cycle
Description
Site
Name
Timing (seconds)
Omit Status (seconds of
measurements that are
ommitted from
statistics or stored data)
9
The system prepares to
resume operation in normal
EC field measurement
mode. All valves to zero
and span gases are closed.
The pump is turned on, and
ambient air is pulled
through sample cell.
equilib 30 30
1/ Because it is difficult to have an autonomous field H
2
O span gas source, the constants CHECK_H2OSPN and
SET_H2OSPN (see TABLE 6-1 ,
Program Constants
) are typically set to FALSE, and these steps in the auto zero/span
sequence are skipped.
7.1.2 CPEC310 Manual H
2
O Span
If the CPEC310 automatic zero/span cycle does not include an H
2
O span, a
manual H
2
O span may be setup and initiated as follows.
The user must first connect tubing from an H
2
O span gas source (e.g., dewpoint
generator) to the
H
2
O Span
port on the CPEC310 system enclosure. Turn on
the dewpoint generator and allow H
2
O span gas to flow. Even though the valve
module is not yet allowing H
2
O span gas to flow to the analyzer, back pressure
is not an issue as the CPEC310 system enclosure is designed to vent excess
H
2
O span gas flow.
Next, navigate to the Prfrm Field H2O Span menu found under the
Attendant Zero/Span menu. Within this menu, verify the value of H2O Span
TDP matches the dewpoint setting of the H
2
O span gas source/generator. If this
value needs to be edited, highlight it, press Enter , type in the new value, and
press Enter again to save. Next, highlight Pick SPN_H2O , press Enter , select
SPN_H2O , and press Enter . This will initiate an automatic sequence that is a
subset of the auto zero/span cycle shown in TABLE 7-2 ; specifically, it will
progress only through steps 1, 6, 7, and 8 of the steps shown in TABLE 7-2 .
Progress of the H
2
O span may be monitored by viewing the variables Site and
Sec on Site . While Site reads chk H2O , monitor the real-time readings of H
2
O
in the sample cell and ensure they have reached equilibrium (i.e. are not
changing) before Site switches to set H2O . If equilibrium was not reached, the
constant TIME_ZRO_SPN needs to be increased (see Section 6.2 , Set
Constants
(p. 36)
).
Upon completion of the H
2
O span, the value of Pick SPN_H2O will return to
FLD_MEA , indicating that the system’s measurement mode has returned to
normal EC field sampling, and Site will return to fld smp , indicating all
zero/span valves are closed and ambient air is being pulled into the sample cell.
TABLE 7-1 includes descriptions of varaibles in the the menus related to zero
and span.