Chemiluminescence Detection In The T200 Reaction Cell; Nox - Teledyne T200 Operation Manual

Teledyne API – T200 NO/NO

13.1.2. CHEMILUMINESCENCE DETECTION IN THE T200 REACTION CELL

13.1.2.1. THE PHOTO MULTIPLIER TUBE (PMT)
13.1.2.2. OPTICAL FILTER
06858E DCN7057
/NO Analyzer Operation Manual
2 X
The T200 uses a special kind of vacuum tube, called a photo-multiplier tube (PMT), to
detect the amount of light created by the NO and O
Photons enter the PMT and strike a negatively charged photo cathode causing it to emit
electrons. These electrons are accelerated by an applied high voltage and multiplied
through a sequence of similar acceleration steps (dynodes) until a useable current signal
is generated (see Section 13.5 for a more detailed description). The more light present
(in this case photons given off by the chemiluminescent reaction described above), the
more current is produced. Therefore the more NO present in the reaction cell the more
current is produced by the PMT.
The current produced by the PMT is converted to a voltage and amplified by the
preamplifier board and then communicated to the T200‟s CPU via the A D converter
circuitry on the analyzer.
A high pass optical filter, only transparent to wavelengths of light above 645nm, placed
between the reaction cell and the PMT (see Figure 13-1) in conjunction with the
response characteristics of the PMT creates a very narrow window of wavelengths of
light to which the T200 will respond.
NO
Optical
Filter
PMT HOUSING
Figure 13-1: Reaction Cell with PMT Tube and Optical Filter
The narrowness of this band of sensitivity allows the T200 to ignore extraneous light
and radiation that might interfere with the T200‟s measurement. For instance, some
oxides of sulfur can also be chemiluminescent emitters when in contact with O
off light at much shorter wavelengths (usually around 260nm to 480nm).
O
3
NO+O
3
PMT
Principles of Operation
reaction in the reaction cell.
3
Reaction
Cell
but give
3
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