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M102E/M501 TRS THEORY OF OPERATION
(Addendum to M101E Manual - P/N 04740 Rev A)
9. THEORY OF OPERATION
The M102E is a modified M101E which, when used in conjunction with a M501-TRS determines the
concentration of total reduced sulfur (TRS), in a sample gas drawn through the instrument In
most ways the theory of operation of the M102E & M501-TRS system is identical to the M101E
theory of operation as described in Chapter 10 of the M101E Manual - P/N 04740 Rev A.
This section describes those areas where differences between the M102E and the M101E exist as
well as updated information made available since the publication date of the M101E Manual - P/N
04740 Rev A.
9.1. Measurement Principle
This section supercedes Section 10.1 of the M101E Manual - P/N 04740 Rev A
9.1.1. TRS Conversion
The M102E TRS analyzer is basically an SO
2
analyzer with a TRS Æ SO
2
converter (the M501-
TRS) inserted into the gas stream before the sample gas enters the sample chamber.
The M501-TRS, receives sample gas from the M102E after it has been passed through a
particulate filter and has been scrubbed of hydrocarbon interferents. Once inside the M501-TRS
the sample gas is scrubbed of all naturally occurring SO
2
, then passed through a special quartz
converter which heats the gas to a very high temperature causing it to react with the O
2
present
in the sample gas creating SO
2
in the following manner .
TRS + O
2
Æ SO
2
(Equation 9-1)
The converter is most efficient when it operates at 1000°C, converting >95% of the TRS into SO
2
.
Converter temperature is viewable via the front panel of the M501-TRS
When the converter is operating at peak efficiency there is a nearly 1:1 relationship between the
amount of TRS entering the converter and the amount of SO
2
leaving it. Therefore, by measuring
the amount of SO
2
in the gas after it leaves the converter, the amount of TRS originally present
on the sample gas can be directly inferred.
9.1.2. SO
2
Ultraviolet Fluorescence
The physical principle upon which the M102E’s measurement method is based is the fluorescence
that occurs when sulfur dioxide (SO
2
) is excited by ultraviolet light with wavelengths in the range
of 190 nm-230 nm. This reaction is a two-step process.
The first stage (Equation 9-2) occurs when SO
2
molecules are struck by photons of the
appropriate ultraviolet wavelength. In the case of the Model 102E, a band pass filter between the
source of the UV light and the affected gas limits the wavelength of the light to approximately 214
05514 Rev A1 43