Teledyne API – Model T300/T300M CO Analyzer
Theory of Operation
297
12.4.3.3.
PHOTO-DETECTOR TEMPERATURE CONTROL
The sync/demod board also contains circuitry that controls the IR photo-detector’s
Thermal Electric Coolers (TEC). A drive voltage,
PHT DRIVE
, is supplied to the
coolers by the sync/demod board which is adjusted by the sync/demod board based on a
return signal called TEC control which alerts the sync/demod board of the detector’s
temperature. The warmer the detector, the harder the coolers are driven.
PHT DRIVE
is one of the Test Functions viewable by the user via the form panel.
Press
<TST
or
TST>
until it appears on the display.
12.4.3.4.
DARK CALIBRATION SWITCH
This switch initiates the Dark Calibration procedure. When initiated by the user (See
Section 9.6.1 for more details), the dark calibration process opens this switch,
interrupting the signal from the IR photo-detector. This allows the analyzer to measure
any offset caused by the sync/demod board circuitry.
12.4.3.5.
ELECTRIC TEST SWITCH
When active, this circuit generates a specific waveform intended to simulate the function
of the IR photo-detector but with a known set of value which is substituted for the
detector’s actual signal via the dark switch. It may also be initiated by the user (See
Section 5.4 for more details).
12.4.4.
RELAY BOARD
By actuating various switches and relays located on this board, the CPU controls the
status of other key components. The relay board receives instructions in the form of
digital signals over the I
2
C bus, interprets these digital instructions and activates its
various switches and relays appropriately.
12.4.4.1.
HEATER CONTROL
The two heaters attached to the sample chamber housing and the GFC Wheel motor are
controlled by solid state relays located on the relay board.
The GFC Wheel heater is simply turned on or off, however control of the bench heater
also includes circuitry that selects which one of its two separate heating elements is
activated depending on whether the instrument is running on 100 VAC, 115 VAC or 230
VAC line power.
12.4.4.2.
GFC WHEEL MOTOR CONTROL
The GFC Wheel operates from a AC voltage supplied by a multi-input transformer
located on the relay board. The step-down ratio of this transformer is controlled by
factory-installed jumpers to adjust for 100 VAC, 115 VAC or 230 VAC line power.
Other circuitry slightly alters the phase of the AC power supplied to the motor during
start up based on whether line power is 50Hz or 60 Hz.
Normally, the GFC Wheel Motor is always turning while the analyzer is on. A physical
switch located on the relay board can be used to turn the motor off for certain diagnostic
procedures.
06864D DCN7562
Summary of Contents for T300
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