Advertisement
Introduction
Principle of Operation
Principle of
Operation
1-2
Model 48i Trace Level-Enhanced Instruction Manual
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 Chapter 7 "Servicing".
The Model 48i Trace Level-Enhanced 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 48i Trace Level-Enhanced uses an internally stored
calibration curve to accurately linearize the instrument output over any
range up to a concentration of 1000 ppm.
The sample is drawn into the Model 48i Trace Level-Enhanced 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
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
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 measurement beams equally. Thus, the GFC system responds
specifically to CO.
The Model 48i Trace Level-Enhanced outputs the CO concentration to
the front panel display, the analog outputs, and also makes the data
available over the serial or Ethernet connection.
. The radiation
2
side of the filter wheel is
2
Thermo Fisher Scientific
Advertisement
Troubleshooting
