Teledyne 300E Instruction Manual page 172

THEORY OF OPERATION
Phase Lock Warning
In order to detect critical fault conditions such as a failure of either the Segment
Sensor or the GFC Wheel motor, the Synch/Demod Board also performs a simple
check of the above signal synchronization to make sure everything is operation.
The PLD divides the X10 Clock signal by ten and sends this signal back to the PLL
circuit which compares it to the original Segment Sensor Reference signal.
If these two signals match, the PLL sends a status level to the PLD that the Phase
Lock is OK. If for some reason the two signals do not match, the PLL alerts the PLD
that Phase Lock has been lost and the PLD issues a Phase Lock Warning to the CPU.
Should this occur, A SYNC Warning will appear on the analyzer's front panel display
(see Section 11.1.1 for more information).
Sync/Demod Status LED's
The following two status LED's located on the Synch/Demod Board provide
additional diagnostic tools for checking the GFC Wheel rotation.
LED
D1 M/R Sensor Status
D2 Segment Sensor
See Section 11.1.3 for more information.
Photo-Detector Temperature Control
The Synch/Demod Board also contains circuitry that controls the IR Photo-
Detector's thermoelectric coolers. A drive voltage, PHT DRIVE, is supplied to the
coolers by the Synch/Demod Board which is adjusted by the Synch/Demod Board
based on a return signal called TEC Control which alerts informs the Synch/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.
Dark Calibration Switch
This switch initiates the Dark Calibration procedure. When initiated by the user
(see Section 6.6.5 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 Synch/Demod Board circuitry.
172
Function
Status
Model 300E Carbon Monoxide Analyzer
Status OK
LED flashes approximately
2/second
LED flashes approximately
6/second
Instruction Manual
Fault Status
LED is stuck
ON or OFF
LED is stuck
ON or OFF
P/N 04288 Rev: A