Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 222)

Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 204
The four sample and hold circuits are:
DESIGNATION ACTIVE WHEN:
IR BEAM PASSING THROUGH SEGMENT SENSOR PULSE IS:
Measure Gate MEASUREMENT cell of GFC Wheel HIGH
Measure Dark Gate MEASUREMENT cell of GFC Wheel LOW
Reference Gate REFERENCE cell of GFC Wheel HIGH
Reference Dark Gate REFERENCE cell of GFC Wheel LOW
Timing for activating the Sample and Hold circuits is provided by a phase lock loop circuit (PLL). Using
the segment sensor output as a reference signal the PLL generates clock signal at ten times that
frequency. This faster clock signal is used by the PLD to make the sample and hold circuits capture the
signal during the center portions of the detected waveform, ignore the rising and falling edges of the
detector signal.
Sample & Hold
Active
Detector
Output
Sample & Hold
Inactive
Figure 9-14: Sample & Hold Timing
9.3.4.3. 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.
Table 9-1: Sync/Demod Status LED Activity
LED FUNCTION STATUS OK FAULT STATUS
D1 M/R Sensor Status LED flashes approximately
2/second
LED is stuck
ON or OFF
D2 Segment Sensor
Status
LED flashes approximately
6/second
LED is stuck
ON or OFF
See Section 11.1.4 for more information.