LI-COR LI-8100A - Page 78

User Calibration
5-7
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
100 1000 10000 100000
CO
2
Absorptance
CO
2
(ppm)
LI-8100A Optical Bench
0.1
0.1
0.1
Figure 5-1. CO
2
absorptance differences for typical LI-8100A optical bench.
For CO
2
, the difference in absorptance between 200 and 1000 ppm is typically
about 0.1. There is also a 0.1 absorptance difference between 3500 and 7000
ppm, and between 15,000 and 40,000 ppm. For H
2
O, it is a little harder to get a
0.1 absorptance difference. If you want to do a secondary span at room
temperature, the two span values would need to be 5 °C or less, and 22 °C, for
example, as shown below.
0
0.1
0.2
0.3
0.4
-30 -20 -10 0 10 20 30 40
H
2
O Absorptance
Dew Point Temp (°C)
Typical LI-8100A
0.1
You can perform multiple secondary spans after a normal span. For example, span
at 200, then do a secondary span at 3000 ppm. Then, if you don’t like the result,