Figure 7-6. Ftir Flow Schematic - Thermo Scientific Omni FTIR Multi Gas CEMS Instruction Manual

System Component Description
FTIR
7-8 Omni FTIR Multi Gas CEMS Instruction Manual
When both mirrors are the same distance from the beamsplitter, the two
reflected beams pass at exactly the same path length and, consequently, all
wavelengths of light are totally in phase. The resulting signal intensity is at
its maximum, a point called the Zero Path Distance (ZPD).
The modulated beam is reflected from the interferometer's mirrors and
lenses to the sample, where selective absorption takes place. From the
sample, the beam travels on to the detector, which translates the beam into
an electrical signal.
Infrared
Source
FT
Single-beam spectrum
Figure 7–6. FTIR Flow Schematic
The cosine waves produced by the source and modulated by the
interferometer appear to the detector as an interferogram, a signature of
intensity versus mirror position. The interferogram is a summation of all
the IR light frequencies and for all practical purposes; it cannot be
interpreted in its original form.
The detector sends the interferogram to the analog-to-digital converter or
ADC, which converts the interferogram into a form that can be used by a
computer, where it is transformed by the software into an IR spectrum
through a mathematical function called Fourier Transform or FT. The
function calculates the amplitude of each of the component signals. The
amplitude gives the intensity at the corresponding wavelength of light. A
Interferometer
Interferogram
Detector
ADC
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