Specifications

DETECTOR METHODOLOGIES
2.1.3 Overall NDIR Method
In the case of dual-channel analyzers, the broadband emission from two infrared
sources pass through the chopper wheel. In the case of the Interference Filter
Correlation (IFC) method, the infrared radiation then passes through combinations of
interference filters. In the case of the opto-pneumatic method, the infrared radiation
passes through an optical filter depending on the application and need for reduction of
influences. Then the infrared radiation enters the analysis cells from which it is focused
by filter cells onto the corresponding detector. The preamplifier detector output signal is
then converted into the analytical results expressed directly in the appropriate physical
concentration units such as percent volume, ppm, mg/Nm
3
, etc. This is shown in Figure
2-3 below.
Figure 2-3. Overall NDIR Method
MOTOR
Duplex filter disc
Chopper
blade
Chopper
blade
Preamplifier
Preamplifier
Gas detector
Filter cell
Analysis cell
reference side
Analysis cell
measurin
g
side
Filter cell
Adapter cell
(
hi
g
h measurin
g
ran
g
e
)
Analysis cell
(
undivided
)
Pyroelectric detector
(
solid-state detector
)
Light source
Rosemount Analytical µCEM Continuous Analyzer Transmitter 2–4