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Teledyne API M100E Analyzer Operation Manual Theory Of Operation
241
11.4.5. PMT PREAMPLIFIER
The PMT preamplifier board amplifies the PMT signal into a useable analog voltage that can be processed by
the motherboard into a digital signal to be used by the CPU to calculate the SO
2
concentration of the gas in the
sample chamber.
The output signal of the PMT is controlled by two different adjustments. First, the voltage across the electron
multiplier array of the PMT is adjusted with a set of two hexadecimal switches. Adjusting this voltage directly
affects the HVPS voltage and, hence, the signal from the PMT. Secondly, the gain of the amplified signal can
further be adjusted through a potentiometer. These adjustments should only be performed when encountering
problems with the software calibration that cannot be rectified otherwise. Refer to Section 12.7.2.8 for this
hard
w
are calibration.
COOLER (Closed Loop)
To
Motherboar
PMT Preamp PCA
E Test Control
From CPU
D-A
Converter
PMT
Coarse
Gain Set
(Rotary
PMT Fine
Gain Set
(Rotary
Switch)
PMT
Signal
Offset
E-Test
Generator
O-Test
Generator
O Test Control
From CPU
PMT Temp
Sensor
PMT
Temperature
Feedback
Circuit
TEC Control
PCA
PMT Out
p
ut
PMT HVPS
Drive Voltage
PMT Temp Analog Signal
to Motherboard
PMT Output Signal
(PMT) to Motherboard
O Test
LED
Amp to
Voltage
Converter/
Amplifier
Low Pass
Noise
Filter
MUX
Figure 11-17: PMT Preamp Block Diagram
04515F DCN6048