Endress+Hauser SpectraSensors SS2100r, Hardware Manual

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SS2100r H
2
S Analyzer
1
–
4 4900002189 rev. D 3-7-18
resonance is directly proportional to the number of molecules of that particular
species in the beam path, or
. (2)
Figure 1–2 shows the typical raw data (in arbitrary units [u.a.]) from a laser
absorption spectrometer scan including the incident laser intensity,
I
0
(  )
,
and
the transmitted intensity,
I
(  ), for a clean system and one with contaminated
mirrors (shown to illustrate the system’s relative intensity to mirror
contamination). The positive slope of raw data results from ramping the current
to tune the laser, which not only increases the wavelength with current, but
also causes the corresponding output power to increase. By normalizing the
signal by the incident intensity, any laser output fluctuations are canceled, and
a typical, yet more pronounced, absorption profile results. Refer to Figure 1–3.
OPTICAL HEAD
DETECTOR
WINDOW
OUTLET
FAR MIRROR
TEC
LASER
INLET
PRESSURE
SENSOR
Figure 1–1 Schematic of a typical
tunable diode laser absorption spectrometer
8/28 m Measurement Cell
N
1 –
   
l
--------------
I
  
I
0
  
-------------- ln =