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Model T101 Instruction Manual Principles Of Operation
263
10.4.4. PHOTO MULTIPLIER TUBE (PMT)
The T101 uses a photo multiplier tube (PMT) to detect the amount of fluorescence
created by the SO
2
and UV light reaction in the sample chamber.
PMT Input
Signal
Connector
Optical Test
LED
PMT
High Voltage
Power Supply
Insulator
Cold Block
PMT Temperature
Sensor
Heat Sink
PMT Output
Signal
Connector
TEC located
between Cold Block
and Heat
Sink
Light from Reaction
Chamber shines
throu
g
h hole is side
of Cold Block
Figure 10-13. PMT Assembly
A typical PMT is a vacuum tube containing a variety of specially designed electrodes.
Photons from the reaction are filtered by an optical high-pass filter, enter the PMT and
strike a negatively charged photo cathode causing it to emit electrons. A high voltage
potential across these focusing electrodes directs the electrons toward an array of high
voltage dynodes. The dynodes in this electron multiplier array are designed so that each
stage multiplies the number of emitted electrons by emitting multiple, new electrons.
The greatly increased number of electrons emitted from one end of electron multiplier
are collected by a positively charged anode at the other end, which creates a useable
current signal. This current signal is amplified by the preamplifier board and then
reported to the motherboard.
07266B DCN6485