Campbell EC155, Руководство по эксплуатации продукта

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EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
43
9.4 Zero and Span
As is the case with optical instrumentation, the EC155 may drift slightly with
exposure to natural elements. Thus, a zero-and-span procedure should be
performed occasionally. The first part of the procedure listed below simply
measures the CO
2
and H
2
O span and zero, without making any adjustments.
This allows the CO
2
and H
2
O gain factors to be calculated. These gain factors
quantify the state of the analyzer before the zero-and-span procedure, and in
theory could be used to correct recent measurements for drift. The last part of
the zero-and-span procedure adjusts internal processing parameters to correct
subsequent measurements.
If the EC155 was purchased as part of a CPEC200 closed-path
eddy covariance system, consult the CPEC200 manual. The
CPEC200 system has an optional valve module to allow the
datalogger to automate the zero-and-span procedure.
It is essential that the zero-and-span procedure be done correctly and not
rushed; allocate plenty of time for the procedure. During a normal zero-and-
span procedure a PC running ECMon software is used to monitor and control
the EC155. However, the zero-and-span procedure can also be performed using
either the Device Configuration Utility software or a datalogger running the
EC100Configure() instruction (see Section 10.2 ,
EC100Configure()
Instruction
(p. 53)
).
To check and then set the EC155 zero and span, follow the steps below:
1. Connect the EC100 to a PC with the EC100 USB cable, and launch
ECMon
on the PC. Select the appropriate USB port, and press Connect .
The main screen should now be reporting real-time CO
2
and H
2
O
concentrations.
2. Check the differential pressure and signal strengths and service the intake
as needed (see Section 9.2 ,
Intake Cleaning and Filter Replacement
(p. 35)
).
3. Check the signal strengths and clean the windows as needed (see Section
9.3 , Cleaning Analyzer Windows
(p. 40)
).
4. Verify that the Gas LED status light on the EC100 panel is green. Also
make sure the analyzer is resting right-side-up. If the zero-and-span
procedure is being performed on-site, this should already be the case.
5. Connect the zero-and-span gas to the Zero/Span inlet at the back of the
analyzer. The zero-and-span gas will be pushed backwards through the
EC155 sample cell and exhausted through the intake assembly. If the
sample pump is the CPEC200 pump module, it may be left connected and
simply shut off. A fraction of the zero-and-span gas will be pushed
through the pump, but not enough to affect the equilibration time.
Alternatively, the sample pump may be disconnected and the Pump
connection plugged.
6. Click on the Zero/Span button on the main screen of ECMon . A real-time
graph at the bottom of the window will appear that displays concentrations
of CO
2
and H
2
O (see FIGURE 9-10 ).
NOTE