Thermo Scientific 43iQ, Instruction Manual

Page: 230 / 284

System Description
Optical Bench DMC
8-2 43iQ Instruction Manual Thermo Scientific
●
Firmware
The Optical Bench DMC contains the key components of the optical
measurement that eventually results in SO
2
concentration. In the reaction
chamber pulsating light from the flash lamp excites the SO
2
molecules. A
condenser lens collects and focuses light from fluorescing SO
2
molecules
onto the PMT assembly.
The heated hydrocarbon kicker removes hydrocarbons from the gas stream
while leaving the SO
2
concentration unaffected. It operates on a selective
permeation principle using differential pressure to force hydrocarbon
molecules to pass through the tube wall. The differential pressure is created
across the tube wall as sample gas passes through a capillary tube which
reduces its pressure. The sample gas is then fed to the shell side of the
hydrocarbon kicker. The heated kicker operates at the same temperature as
the optical bench and requires no additional power.
The optics section provides the light source for the fluorescence reaction
and optimizes the reaction with a system of lenses and mirrors. It includes a
flash lamp, condensing lens, bandpass mirror assembly and light baffle.
The condensing lens focuses light from the flash lamp into the mirror
assembly.
A set of four mirrors selectively reflects only those wavelengths used in
exciting SO
2
molecules. This reflective filtering causes the radiation
reaching the detection chamber to be more intense and more stable
throughout the lifetime of the instrument.
The circular baffle helps keep stray light from entering the detection
volume.
The bandpass filter restricts the light reaching the photomultiplier tube to
the SO
2
fluorescence wavelengths.
Optical Bench
DMC
Heated Hydrocarbon
Kicker
Optical Bench
Hardware
Condensing Lens
Mirror Assembly
Light Baffle
Bandpass Filter