Teledyne Signal Synchronization and Demodulation, GFC 7001E/EM Sync/Demod Block Diagram

Theory of Operation Model GFC7001E Carbon Dioxide Analyzer

56V Bias

			Variable	Sample &	CO MEAS
Photo-	Pre Amp	Dark			Signal
		Switch	Gain Amp	Hold
detector
					Conditioner
				Circuits
	TEC Control
	PHT DRIVE	E-Test
		Generator			CO Reference
				(x4)	Signal
					Amplifiers
					Conditioner

Thermo-Electric

Cooler

Control Circuit

			E Test A Gate
			E Test B Gate
			Dark Test Gate
	Compact		Measure Gate
	Programmable		Measure Dark Gate
	Logic Device		Reference Gate
			Reference Dark Gate
M/R Sensor					Phase Lock Warning
	From GFC
Segment	Wheel
Sensor			Segment Clock
E Test Control			X1 Reference		Phase
				x10
	From CPU
					Lock
		10
Dark Switch	via Mother		X10 Clock
Control	Board				Loop	Segment
					M/R
			Phase Lock		Status LED	Status LED
	Figure 11-12:		GFC 7001E/EM Sync/Demod Block Diagram

11.5.4.2.Signal Synchronization and Demodulation

The signal emitted by the IR photo-detector goes through several stages of amplification before it can be accurately demodulated. The first is a pre-amplification stage that raises the signal to levels readable by the rest of the sync/demod board circuitry. The second is a variable amplification stage that is adjusted at the factory to compensate for performance variations of mirrors, detectors, and other components of the optical bench from instrument to instrument.

The workhorses of the sync/demod board are the four sample-and-hold circuits that capture various voltage levels found in the amplified detector signal needed to determine the value of CO MEAS and CO REF. They are activated by logic signals under the control of a compact Programmable Logic Device (PLD), which in turn responds to the output of the Segment Sensor and M/R Sensor as shown in Figure 11-9.

The four sample and hold circuits are:

Table 11-2: Sync DEMOD Sample and Hold Circuits

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
	Teledyne Analytical Instruments		243