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Model T101 Instruction Manual Principles Of Operation
243
10. PRINCIPLES OF OPERATION
The T101 UV Fluorescence H
2
S Analyzer is a microprocessor controlled analyzer that
determines the concentration of hydrogen sulfide (H
2
S), in a sample gas drawn through
the instrument It requires that sample and calibration gases be supplied at ambient
atmospheric pressure in order to establish a constant gas flow through the sample
chamber where the H
2
S in the sample gas is converted into SO
2
which is then exposed to
ultraviolet light causing the SO
2
molecules to change to an excited state (SO
2
*). As these
SO
2
* molecules decay back into SO
2
, they fluoresce. The instrument measures the
amount of fluorescence to determine the amount of SO
2
is present in the sample chamber
and by inference therefore the amount of H
2
S present in the sample gas.
Calibration of the instrument is performed in software and usually does not require
physical adjustments to the instrument. During calibration, the microprocessor measures
the sensor output signal when gases with known amounts of H
2
S at various
concentrations are supplied and stores these measurements in memory. The
microprocessor uses these calibration values along with other performance parameters
such as the PMT dark offset, UV lamp ratio and the amount of stray light present and
measurements of the temperature and pressure of the sample gas to compute the final
H
2
S concentration.
This concentration value and the original information from which it was calculated are
stored in the unit’s internal data acquisition system and reported to the user through a
vacuum fluorescent display or as electronic data via several communication ports.
This concentration value and the original information from which it was calculated are
stored in the unit’s internal data acquisition system (DAS Section 4.8) and reported to
the user through a vacuum
fluorescent display or several communication ports.
10.1. MEASUREMENT PRINCIPLE
10.1.1. H
2
S CONVERSION
The T101 H
2
S analyzer is basically a SO
2
analyzer with a H
2
S SO
2
conversion stage
inserted into the gas stream before the sample gas enters the sample chamber.
The H
2
S to SO
2
converter receives sample gas from which the SO
2
has been removed by
a scrubber. Once the naturally occurring SO
2
is removed from the sample gas, the
special converter changes the H
2
S in the sample stream to SO
2
using a high-temperature
catalytic oxidation.
07266B DCN6485