Section 4
4-10
Calibration
Box 3
Box 4
Setting the Span
Make sure you have done a one or two point
match first.
1.
Flow reference gas through A, and the
span gas through B.
The concentrations must be different.
2.
Set CO
2
(or H
2
O) action to "Make cell
B read..."
You'll be prompted for the cell B target
value.
3.
Wait for stability, then press "DoCO2"
(or "DoH2O").
After about 5 seconds, the cell B reading
should be on target.
Calibrate Cell A
This procedure is necessary periodically while
in REM (Reference Estimation Mode)
operations.
1.
Flow a known gas through cell A.
Any concentration (including 0) is fine.
2.
Pick "Make cell A read..." for CO
2
(or
H
2
O).
You will be prompted for the
concentration.
3.
Press "DoCO2" (or "DoH2O").
After 5 or 6 seconds, cell A should be
reading the target value.
User Calibration
Example
Example 1. Reference Estimation Mode (REM) for both CO
2
and H
2
O.
REM is used when precise differential concentrations are required and
where absolute accuracies are less important. In this example a tank of
gas of 370 µmol/mol CO
2
in dry air is used for the CO
2
calibration. The
LI-610 is used to provide an airstream with known dew point to Cell A
for the H
2
O calibration. A periodic user calibration procedure for
operating the LI-7000 in REM is given below.
1.
Flow the calibration gas through both cells of the LI-7000 optical
bench.
2.
Press
Shift + 1
to display the calibration group labels.
3.
Press the
SetRef
key (f1). The Reference Cell Options are displayed.
Press
Edit
(f1) to edit the CO
2
options. Choose
Estimated
. Press
OK
. Repeat for H
2
O, and edit the H
2
O units box to display the
desired units (°C).
