Galvanic Applied Sciences 943-TGX-CE, Operation Manual

Page: 85 / 151

Revision 4 85 April 2020
When the analyzer is in back purge mode, the absorbance spectrum should be a horizontal
line at an absorbance of 0 AU. If it is not, and the analyzer is NOT in a fault condition, first
confirm that the current transmission spectrum in back purge is largely similar to the factory
reference spectrum, then immediately carry out a new zero calibration cycle OR use the New
Reference function on the Spectrum panel. After the zero-calibration cycle is complete,
confirm that the absorbance spectrum does become a horizontal line at 0 AU.
The shape of the absorbance spectrum when sampling depends primarily on the
concentrations of H
2
S and SO
2
in the sample. Other components are generally not present
in high enough concentrations to be visibly recognizable on the absorbance spectrum.
Figures 55 and 56 show the typical appearance of absorbance spectra for H
2
S only and SO
2
only.
Figure 55: Absorbance Spectrum for H
2
S
Figure 56: Absorbance Spectrum for SO
2
In most typical operating conditions, the tail gas stream will not contain only H
2
S or only SO
2
,
so typically the displayed absorbance spectrum will appear as a combination of the H
2
S
spectrum and the SO
2
spectrum. The exact magnitude of the absorbance for a given species
will depend on the concentration of that species as well as the measurement cell length. For
a given analyzer, however, the higher the concentration of the measured species is, the
higher the absorbance (i.e. peak height) will be for that species.
The concentrations shown below the absorbance spectrum are calculated by using a
calibration matrix
specific to the analyzer’s spectrometer to mathematically convert the