Teledyne T100, Instruction Manual, Page: 221 / 404

Teledyne ML - T100 UV Fluorescence SO2 Analyzer Theory Of Operation
06807A(DCNxxxx) 221
9.
THEORY OF OPERATION
This section describes the theory of operation for the T100 SO
2
analzyer (Section 9.1),
for the optional O
2
sensor (Section 9.2) and for the optional CO
2
sensor (Section 9.3). It
also describes the theory of operation for pneumatics (Section 9.4), electronics (Section
9.5), communication interfaces (9.6) and software (9.7).
9.1. SULFUR DIOXIDE (SO
2
) SENSOR THEORY OF OPERATION
The T100 UV Fluorescence SO
2
Analyzer is a microprocessor controlled analyzer that
determines the concentration of sulfur dioxide (SO
2
), 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 sample gas is exposed to ultraviolet light; this exposure causes the
SO
2
molecules to change to an excited state (SO
2
*). As these SO
2
* molecules decay into
SO
2
they fluoresce. The instrument measures the amount of fluorescence to determine
the amount of SO
2
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 SO
2
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
SO
2
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 (refer to Section 5.2) and reported to
the user through a vacuum fluorescent display or several communication ports.
9.1.1. SO
2
ULTRAVIOLET FLUORESCENCE MEASUREMENT PRINCIPLE
The physical principle upon which the T100’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 9-1) occurs when SO
2
molecules are struck by photons of the
appropriate ultraviolet wavelength. In the case of the T100, a band pass filter between the