THEORY OF OPERATION Model 360E Instruction Manual
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
This emitter/detector assembly that produces a signal that 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
Light from this emitter/detector pair shines through a portion of the mask that is divided into the same number of
segments as the IR detector ring. It is used by the synchronous / demodulation circuitry of the analyzer to latch
onto the most stable part of each measurement and reference IR pulse.
174 05232 Rev B3