LI-COR LI-820 - Page 64

Section 4
4-6 Theory of Operation
Z and S are zero and span parameters, where span is itself a linear function of absorptance,
SS
W
W
ZS
o
o
=+−
⎛
⎝
⎜
⎞
⎠
⎟
1
1
4-2
so,
α
c
o
o
o
W
W
ZS
W
W
ZS= −
⎛
⎝
⎜
⎞
⎠
⎟
+ −
⎛
⎝
⎜
⎞
⎠
⎟
11
2
1
4-3
The absorptance

pc
that is reported by the LI-820 is pressure corrected.

pc
= 
c
g
c
( 
c
,P) 4-4
Where g
c
( 
c
,P) is an empirically-determined pressure correction function (Figure 4-2).
gP
X
X
cc
(,) α =
⎛
⎝
⎜
⎜
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
⎟
⎟
for P < P
for P = P
for P > P
o
o
o
1
1
4-5
Where P
o
= 99.0 kPa,