LI-COR LI-7500, Инструкция по эксплуатации

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Section 2
Theory of Operation 2-3
Measuring Absorptance
Given a source with radiant power
Φ
, and a detector some distance away, in the absence of
reflection, absorptance by gas i can be determined from
α τ
i i
i
o
= − = −
1 1
Φ
Φ
2-5
where
τ
i
is transmittance through gas i,
Φ
i
is transmitted radiant power in the absorption band
with some concentration of gas i present, and
Φ
o
is the transmitted radiant power in the
absorption band with zero concentration of i present. The LI-7500 approximates absorptance
by
α
i
i
io
A
A
= −

 

1
2-6
where A
i
is the power received from the source in an absorbing wavelength for gas i, and A
io
is the power received from the source in a reference wavelength that does not absorb gas i.
The LI-7500 measures A
i
and A
io
alternately 152 times per second.
If we combine Equations (2-6) and (2-3), we can write the full equation for computing molar
density from absorptance.