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Principles Of Operation Model T101 Instruction Manual
266
be adjusted through a potentiometer. These adjustments should only be performed when
encountering problems with the software calibration that cannot be rectified otherwise.
See Section 9.6.4 for this hardware calibration.
To
Motherboard
PMT Preamp PCA
Low Pass
Noise
Filter
Electrical Test Control
From CPU
MUX
Amp to
Voltage
Converter/
Amplifier
D-A
Converter
PMT Coarse
Gain Set
(Rotary
Switch)
PMT Fine
Gain Set
(Rotary
Switch)
PMT
Signal
Offset
Electrical Test
Generator
Optical Test
Generator
Optical Test Control
From CPU
PMT Temp
Sensor
PMT
Temperature
Feedback
Circuit
TEC Control
PCA
PMT Output
PMT HVPS
Drive Voltage
PMT Temp Analog Signal
to Motherboard
PMT Output Signal
(PMT) to Motherboard
Optical Test LED
Figure 10-16. PMT Preamp Block Diagram
The PMT temperature control loop maintains the PMT temperature around 7° C and can
be viewed as test function PMT TEMP on the front panel.
The electrical test (ETEST) circuit generates a constant, electronic signal intended to
simulate the output of the PMT (after conversion from current to voltage). By bypassing
the detector’s actual signal, it is possible to test most of the signal handling and
conditioning circuitry on the PMT preamplifier board. See Section 4.6.5 for instructions
on perform
ing this test.
The optical test (OT
EST) feature causes an LED inside the PMT cold block to create a
light signal that can be measured with the PMT. If zero air is supplied to the analyzer,
the entire measurement capability of the sensor module can be tested including the PMT
and the current to voltage conversion circuit on the PMT preamplifier board. See
Section 4.6.4 for instructions on performing this test.
07266B DCN6485