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Instruction Manual
748332-F
April 2003
1-2 Description and Specifications Rosemount Analytical Inc. A Division of Emerson Process Management
Model NGA2000 NDIR
During analysis, a portion of the infrared
radiation is absorbed by the component of
interest in the sample. The quantity of infrared
radiation that is absorbed is proportional to the
component concentration.
The detector is a "gas microphone" based on
the Luft principle. The detector is generally
filled with the same gas being analyzed. The
infrared energy is therefore absorbed at the
same wavelengths in the detector as that in the
sample cell, making the detector specific for the
analyzed component. The detector converts the
difference in energy between sample and
reference cells to a capacitance change. This
change, which is proportional to component
concentration, is processed and expressed as
the primary variable on the network.
Other modules comprising the NGA2000 unit
then use this variable for a variety of purposes
(e.g., expressing the gas concentration on the
Front Panel Display or sending it to external
data acquisition devices).
For a general understanding of the electrical
interconnections in the NDIR Analyzer Module,
see Figure 2-4 on page 2-5.
Figure 1-1. NDIR Technology
SAMPLE IN
SAMPLE OUT
COMPONENT OF INTEREST
NON-INTERFERING COMPOUNDS
INFRARED
SOURCE
DETECTOR
REFERENCE
CELL
STATIONARY
PLATE
CHOPPER
SAMPLE
CELL
DIAPHRAGM,
DISTENDED
DIAPHRAGM,
DARK STATE