Instruction Manual
Model MicroCEM
In the
The pneumatic detector compares and evaluates the radiation from the measuring and reference sides of the analysis cell and converts them into voltage signals proportional to their respective inten- sity.
The pneumatic detector consists of a gas- filled absorption chamber and a compensation chamber which are connected by a flow channel in which a Microflow filament sensor is mounted. This is shown in Figure
In principle the detector is filled with the infrared active gas to be measured and is only sensitive to this distinct gas with its characteristic absorption spectrum. The absorption chamber is sealed with a window which is transparent for infrared ra- diation. The window is usually Calcium Fluoride (CaF2).
Absorption chamber
Flow channel with 
Microflow sensor
When the infrared radiation passes through the reference side of the analysis cell into the detector, no
When the infrared radiation passes through the open measurement side of the analysis cell into the detector, a part of it is absorbed depending on the gas concentration. The gas in the absorption chamber is, therefore, heated less than in the case of radiation coming from the reference side. Absorption chamber gas becomes cooler, gas pressure in the absorption chamber is reduced and some gas from the compensation chamber passes through the flow channel into the absorption chamber.
The flow channel geometry is designed in such a way that it hardly impedes the gas flow by restriction. Due to the radiation of the chopper wheel, the different radiation intensities lead to periodically repeated flow pulses within the detector.
The Microflow sensor evaluates these flow pulses and converts them into electrical pulses which are processed into the corresponding analyzer output.
CaF2 Window
Compensation chamber
Figure
Description and Specifications | Rosemount Analytical Inc. A Division of Emerson Process Management |