LI-COR LI-830 - Page 39

100 1000 10000 100000
Approximate CO Concentration (ppm)
Bandbroadening Coefficient for HO
1.5
1.4
1.3
1.2
1.1
1.0
Figure A-1. The typical relationship between h(α'
c
) and CO
2
concentration.
Note: We formulated equation A-19 with 0.64b
w
– 0.64 instead of the simple
equivalent (0.29) because this allows band broadening corrections to be turned
off by setting b
w
to 1. When b
w
=1, h( α
c
) = 1 everywhere. Also, to avoid com-
putational problems (underflows, overflows, and division by zero) we constrain
the argument α
c
when computing h( α
c
) to be 0.1 < α
c
≤ z. α
c
- 0.1 is typically
equivalent to about 600 ppm.
Calibration Equations
The following equations describe the implementation of zero and span calibrations.
Zeroing H
2
O (LI-850 only)
When the command for zeroing water is received, the LI-850 computes the water
zero from equation A-20, where and are averaged for 5 seconds.
A-20
Zeroing CO
2
When the command for zeroing CO
2
is received, the instrument computes the
CO
2
zero term from equation A-21, where , , , and are averaged for
5 seconds.
Appendix A. Equation Summary
A-5Appendix A. Equation Summary