Teledyne GFC-7000E - Trace CO2 Analyzer - Manual (Page 175)

Model GFC7000E Instruction Manual THEORY OF OPERATION
04584 Rev A1 164
10.3.3.2. IR Source
The light used to detect CO
2
in the sample chamber is generated by a element heated to
approximately 1100 o C producing infrared radiation across a broad band. This radiation is optically
filtered after it has passed through the GFC Wheel and the sample chamber and just before it
reaches the photo-detector to eliminate all black body radiation and other extraneous IR emitted
by the various components of those components.
10.3.3.3. GFC Wheel
A synchronous AC motor turns the GFC wheel motor. For analyzers operating on 60Hz line power
this motor turns at 1800 rpm. For those operating on 50Hz line power the spin rate is 1500 rpm.
The actual spin rate is unimportant within a large rate since a phase lock loop circuit is used to
generate timing pulses for signal processing.
In order to accurately interpret the fluctuations of the IR beam after it has passed through the
sample gas, the GFC wheel several other timing signals are produced by other photo
emitters/detectors. These devices consist of a combination LED and detector mounted so that the
light emitted by the LED shines through the same mask on the GFC wheel that chops the IR
beam.
IR Detection Ring
Segment Sensor Ring
M/R Sensor Ring
KEY:
Detection Beam shining
through MEASUREMENT
side of GFC Wheel
Detection Beam shining
through REFERENCE
side of GFC Wheel
Figure 10-10: GFC Light Mask
M/R Sensor
The emitter/detector assembly that produces this signal shines through a portion of the mask that
allows light to pass for half of a full revolution of the wheel. The resulting light signal tells the
analyzer whether the IR beam is shining through the measurement or the reference side of the
GFC wheel.
Segment Sensor
This emitter/detector shines through a portion of the mask that is divided into the same number
of segments as the portion of the mask through which the IR beam passes. It is used by the