Measuring Principle; Ir Measurement - Emerson ROSEMOUNT Analytical NGA 2000 Instruction Manual

Instruction Manual
90002929
07/2006
2.

Measuring Principle

Depending on analyzer model different measuring methods will be used.
2.1

IR Measurement

The measuring effect devided from absorption of infrared radiation is due to the gas being
measured. The gas - specific wavelengths of the absorption bands characterize the type of gas
while the strength of the absorption gives a measure of the concentration of the component
measured. Due to a rotation chopper wheel, the radiation intensities coming from measuring and
reference side of the analysis cell produce periodically changing signals within the detector.
The detector signal amplitude thus alternates between concentration dependent and concentra-
tion independent values. The difference between the two is a reliable measure of the concentration
of the absorbing gas component.
The principle photometer assembly is shown in Fig. 2-1.
Emerson Process Management GmbH & Co. OHG
NGA 2000 MLT Hardware
MEASURING PRINCIPLE
IR MEASUREMENT
2 - 1