Instruction Manual

748332-F April 2003

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.

INFRARED

CHOPPER

SOURCE

 

SAMPLE IN

REFERENCE

 

SAMPLE

CELL

 

CELL

 

SAMPLE OUT

 

DIAPHRAGM,

DETECTOR

DISTENDED

 

 

STATIONARY

 

COMPONENT OF INTEREST

PLATE

 

DIAPHRAGM,

NON-INTERFERING COMPOUNDS

 

 

DARK STATE

 

Figure 1-1. NDIR Technology

1-2 Description and Specifications

Rosemount Analytical Inc. A Division of Emerson Process Management