Teledyne GFC-7001T - Trace CO Analyzer - Manual (Page 290)

Theory of Operation Teledyne API – Model T300/T300M CO Analyzer
Teledyne Analytical Instruments 290
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
GFC7001T/GFC7001TM, Carbon Monoxide (CO).
α
is the absorption coefficient that tells how well CO absorbs light at the specific
wavelength of interest.
13.2. MEASUREMENT FUNDAMENTALS
In the most basic terms, the GFC7001T/GFC7001TM 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 a number of times (see Figure 13-1).
The total length that the reflected light travels is directly related to the intended
sensitivity of the instrument. The lower the concentration that the instrument is
designed to detect, the longer the light path must be in order to create detectable levels
of attenuation.
Lengthening the absorption path is accomplished partly by making the physical
dimension of the reaction cell longer, but primarily by adding extra passes back and
forth along the length of the chamber.
Table 13-1: Absorption Path Lengths for GFC7001T and GFC7001TM
MODEL
TOTAL NUMBER OF
REFLECTIVE PASSES
DISTANCE BETWEEN MIRRORS
TOTAL
ABSORPTION LIGHT
PATH
GFC7001T 32 437.5 mm 14 Meters
GFC7001TM 8 312.5 mm 2.5 Meters