Endress+Hauser SS2000XP, Руководство по эксплуатации

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BA02183C SS500XP/SS2000XP Gas Analyzer
Hauser 1
–
5
analyzers, sample gas flows continuously through the sample cell ensuring that
the sample is always representative of the flow in the main pipe.
Due to their inherent structure, the molecules in the sample gas each have
characteristic natural frequencies (or resonances). When the output of the
laser is tuned to one of those natural frequencies, the molecules with that
particular resonance will absorb energy from the incident beam. That is, as the
beam of incident intensity, I
0
(  ) , passes through the sample, attenuation occurs
via absorption by the trace gas with absorption cross section

(

). According
to the Beer-Lambert absorption law, the intensity remaining, I (  ), as measured
by the detector at the end of the beam path of length I (cell length x number
of passes), is given by
, (1)
where N represents the species concentration. Thus, the ratio of the absorption
measured when the laser is tuned on-resonance versus off-resonance is
directly proportional to the number of molecules of that particular species in
the beam path, or
. (2)
0.8 m Measurement Cell
Figure 1–1 Schematic of a typical laser
diode absorption spectrometer
FAR MIRROR
OUTLET
TEMPERATURE
SENSOR
PRESSURE
SENSOR
WINDOW
DETECTOR
OPTICAL HEAD
TEC
LASER
INLET
I    I
0
   exp     lN –   =
N
1 –
    l
--------------
I   
I
0
  
-------------
ln =