Campbell Scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 41)

EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
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 imperative 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 the 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).
To check and then set the EC155 zero and span, follow the steps below:
a. Connect the EC100 to a PC with the EC100 USB cable (pn 26563), 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.
b. Check the differential pressure and replace the intake filter as needed (see
Section 9.2, Intake Filter Replacement).
c. Check the signal strengths and clean the windows as needed (see Section
9.3, Cleaning Analyzer Windows).
d. 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.
e. If the EC155 is configured with the heated intake assembly, 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 heated 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.
If the EC155 is configured with a sample inlet fitting to connect to the
user’s own intake assembly, there are two options for connecting the zero-
and-span gas:
NOTE
31