CHAPTER 1
INTRODUCTION
The Model 48C Gas Filter Correlation (GFC) CO Analyzer measures ambient level CO
concentrations. The Model 48C combines proven detection technology, easy to use
menu-driven software, and advanced diagnostics to offer unsurpassed flexibility and
reliability. The Model 48C has the following features:
Multi-line alphanumeric display
Menu-driven software
Field programmable ranges
Dual range mode
Auto range mode
Multiple analog outputs
High sensitivity
Fast response time
Linearity through all ranges
Highly specific to CO
Self-aligning optics
Automatic temperature and pressure correction
EPA approved
Thermo Environmental Instruments is pleased to supply this CO analyzer. We are
committed to the manufacture of instruments exhibiting high standards of quality,
performance, and workmanship. TEI service personnel are available for assistance with
any questions or problems that may arise in the use of this analyzer.
PRINCIPLE OF OPERATION
The Model 48C is based on the principle that carbon monoxide (CO) absorbs infrared
radiation at a wavelength of 4.6 microns. Because infrared absorption is a non-linear
measurement technique, it is necessary for the instrument electronics to transform the
basic analyzer signal into a linear output. The Model 48C uses an exact calibration curve
to accurately linearize the instrument output over any range up to a concentration of
10,000 ppm.
The sample is drawn into the Model 48C through the
SAMPLE
bulkhead, as shown in
Figure 1-1. The sample flows through the optical bench. Radiation from an infrared
source is chopped and then passed through a gas filter alternating between CO and N
2
.
The radiation then passes through a narrow bandpass interference filter and enters the
optical bench where absorption by the sample gas occurs. The infrared radiation then
exits the optical bench and falls on an infrared detector.
1-1
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