Model T101 Instruction Manual Principles Of Operation
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10. PRINCIPLES OF OPERATION
The T101 UV Fluorescence H2S Analyzer is a microprocessor controlled analyzer that
determines the concentration of hydrogen sulfide (H2S), 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 H2S in the sample gas is converted into SO2 which is then exposed to
ultraviolet light causing the SO2 molecules to change to an excited state (SO2*). As these
SO2* molecules decay back into SO2, they fluoresce. The instrument measures the
amount of fluorescence to determine the amount of SO2 is present in the sample chamber
and by inference therefore the amount of H2S 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 H2S 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
H2S 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. H2S CONVERSION
The T101 H2S analyzer is basically a SO2 analyzer with a H2S SO2 conversion stage
inserted into the gas stream before the sample gas enters the sample chamber.
The H2S to SO2 converter receives sample gas from which the SO2 has been removed by
a scrubber. Once the naturally occurring SO2 is removed from the sample gas, the
special converter changes the H2S in the sample stream to SO2 using a high-temperature
catalytic oxidation.
07266B DCN6485