Measurement Method; Beer's Law; Measurement Fundamentals - Teledyne 300E Instruction Manual

THEORY OF OPERATION

10.1. Measurement Method

10.1.1. Beer's Law

The basic principle by which the analyzer works is called Beer's Law. It defines the
how light of a specific wavelength is absorbed by a particular gas molecule over a
certain distance. The mathematical relationship between these three parameters
is:
I = I
Where:
I
o is the intensity of the light if there was no absorption.
I
is the intensity with absorption.
L
is the absorption path, or the distance the light travels as it is being absorbed.
C
is the concentration of the absorbing gas. In the case of the Model 300E, carbon
monoxide (CO).
α
is the absorption coefficient that tells how well CO absorbs light at the specific wavelength
of interest.

10.1.2. Measurement Fundamentals

In the most basic terms, the Model 300E uses a high energy heated element to
generate a beam of broad-band IR light with a known intensity (measured during
Instrument calibration. This beam is directed through multi-pass cell filled with
sample gas. The sample cell uses mirrors at each end to reflect the IR beam back
and forth through the sample gas to generate a 14 meter absorption path (see
Figure 10–1). This length was chosen to give the analyzer maximum sensitivity to
fluctuations in CO density.
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Model 300E Carbon Monoxide Analyzer
Instruction Manual
P/N 04288 Rev: A