Thermo Scientific 410iQ, Instruction Manual

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System Description
Optical Bench DMC
8-2 410iQ Instruction Manual Thermo Scientific
●
Oxygen Sensor (optional)
The Optical Bench DMC contains the key components of the optical
measurement that eventually results in CO
2
concentration.
The optical bench is an airtight bench that contains the sample gas. Heaters
are used to maintain the optical bench at a constant temperature.
A bandpass filter limits the light entering the optical bench to a narrow
band of the infrared within which CO
2
absorbs.
A gas filter wheel contains samples of CO
2
and N
2
gas with a chopper disk.
The wheel is rotated so that infrared light is periodically interrupted to
produce a modulated signal upon detection. Differentiating the light
through the CO
2
and N
2
components of the wheel, in the presence of CO
2
in the optical bench, allow the determination of sample CO
2
absorption
and concentration.
The chopper motor rotates the filter wheel and chopper disk at a uniform
speed.
A separate optical switch assembly detects the position of the filter wheel
for synchronizing the modulated signal and for checking the chopper
motor speed.
The filter wheel purge includes a housing attached between the optical
bench and the motor plate. It surrounds the gas correlation wheel and
allows purging the area around the gas correlation wheel with instrument
air or a gas other than that present in the local atmosphere. This increases
the reliability of the measurement by removing contaminants in the vicinity
of the wheel that would interfere with the analytical process.
Figure 8–1
and Figure 8–2 shows how the filter wheel purge is configured within the
instrument for an external purge gas supply. The instrument’s default
configuration allows for active flow of in instrument air through the filter
wheel purge.
Optical Bench
DMC
Optical Bench
Hardware
Filter Wheel Motor
Filter Wheel Purge