Introduction
Principle of Operation
1-2
Model 15
i
Instruction Manual
Thermo Fisher Scientific
Thermo Fisher Scientific is pleased to supply this HCl 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 15
i
operates on the principle that HCl absorbs infrared
radiation. Because infrared absorption is a non-linear measurement
technique, it is necessary to transform the basic analyzer signal into a linear
output. The Model 15
i
uses an internally stored calibration curve to
accurately linearize the instrument output over any range up to a
concentration of 5000 ppm.
The sample is drawn into the Model 15
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 HCl 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 HCl gas filter acts to produce a reference beam which cannot be
further attenuated by HCl 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 HCl 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 HCl 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 HCl.
The Model 15
i
outputs the HCl concentration to the front panel display,
the analog outputs, and also makes the data available over the serial or
Ethernet connection.
Principle of Operation
