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System Description
Optical Bench DMC
Figure 8–1. 48iQ Flow Schematic with Filter Wheel Purge
Calibration Note The stability of the purge gas is very important. Since
this gas is in the same optical path as the sample, changes in the
composition of the purge gas can change the calibration of the instrument.
Therefore, either zero air or a non-toxic dry inert gas, such as nitrogen, is
required as the purge gas.
A constant purge flow of approximately 140 cc/min is recommended for
optimum performance. This is produced by feeding a purge gas to the rear
panel bulkhead at a constant pressure of 10 psig. A fitting with a 0.010-
inch laser drilled orifice delivers the required 140 cc/min purge flow. Flows
greater than this are not recommended due to unstable cooling effects on
the IR source. Lower flows are acceptable as long as the purge housing is
adequately purged for the application.
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Detector Preamp
The detector/preamplifier assembly converts infrared light, carrying
modulation and CO sample absorption, into an amplified electrical signal
that undergoes processing.
Infrared Source
The infrared light source is a special wire-wound resistor operated at high
temperature to generate broadband infrared radiation.
Optical Bench DMC
A single PCBA with microprocessor provides active controls for the above
elements, performs preliminary data processing, and generates registers that
Board
interact with the higher level system controls.
Thermo Scientific
48iQ Instruction Manual
8-3
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