Introduction
Hardware Installation and Maintenance Manual 1
–9
is at twice the modulation frequency (2f). Refer to Figure 1–4. below. This
phase-sensitive detection enables the filtering of low-frequency noise caused
by turbulence in the sample gas, temperature and/or pressure fluctuations,
low-frequency noise in the laser beam or thermal noise in the detector.
With the resulting low-noise signal and use of fast post-processing algorithms,
reliable parts per million (ppm) or parts per billion (ppb) detection levels are
possible (depending on target and background species) at real-time response
rates (on the order of 1 second).
All SpectraSensors TDL gas analyzers employ the same design and hardware
platform. Measuring different trace gases in various mixed hydrocarbon
background streams is accomplished by selecting a different optimum diode
laser wavelength between 700 nm to 3000 nm, which provides the least
amount of sensitivity to background stream variations.
Getting to Know the Analyzer
Figure 1–5 on page 1–10 shows a 2-Pack analyzer from the front view. The
analyzer is comprised of three main enclosures; the two analyzer electronics
enclosures at the top (Analyzer A on the left and Analyzer B on the right) and
the SCS at the bottom. The keypad and LCD on the front panel of the analyzer
electronics, serve as the user interface to the analyzer. Some systems may also
have a keypad cover. The analyzer control electronics drive the laser, collect the
signal, analyze the spectra and provide measurement output signals.
Normalized
2f Signal
Wavelength [a.u.]
Signal [a.u.]
Figure 1–4 Typical normalized 2f signal; species
concentration is proportional to peak height
Peak
Height
2f Peak
Height
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