Introduction
Principle of Operation
1-2
Model 48
i
Instruction Manual
Thermo Fisher Scientific
Thermo Fisher Scientific is pleased to supply this CO analyzer. We are
committed to the manufacture of instruments exhibiting high standards of
quality, performance, and workmanship. Service personnel are available for
assistance with any questions or problems that may arise in the use of this
analyzer. For more information on servicing, see the “
Servicing
” chapter
starting on page
7-1
.
The Model 48
i
operates 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 to
transform the basic analyzer signal into a linear output. The Model 48
i
uses
an internally stored 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 48
i
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.
The CO gas filter acts to produce a reference beam, which cannot be
further attenuated by CO in the sample cell. The N
2
side of the filter wheel
is transparent to the infrared radiation and therefore produces a
measurement beam, which can be absorbed by CO in the cell. The
chopped detector signal is modulated by the alternation between the two
gas filters with an amplitude related to the concentration of CO in the
sample cell. Other gases do not cause modulation of the detector signal
since they absorb the reference and measure beams equally. Thus, the GFC
system responds specifically to CO.
The Model 48
i
outputs the CO concentration to the front panel display,
the analog outputs, and also makes the data available over the serial or
Ethernet connection.
Principle of
Operation
