Campbell Scientific TGA200 Trace Gas Analyzer Overview - Manual (Page 12)

TGA200 Trace Gas Analyzer Overview
4. Multiple Ramp Mode
The TGA200 can be configured to measure two or three gases simultaneously
by alternating the spectral scan wavelength between nearby absorption lines.
This technique requires that the absorption lines be very close together (within
about 1 cm
-1 ), so it can be used only in very specific cases. The multiple ramp
mode is used to measure isotope ratios in carbon dioxide by tuning each ramp
to a different isotopolog.
The multiple ramp mode may also be used to measure some other pairs of
gases, such as nitrous oxide and carbon dioxide or nitrous oxide and methane,
but the measurement noise will generally be higher than if a single gas is
measured. For measurements of a single gas, the laser wavelength is chosen
for the strongest absorption lines of that gas. Choosing a laser that can
measure two gases simultaneously involves a compromise. Weaker absorption
lines must be used in order to find a line for each gas within the laser’s narrow
tuning range.
5. User Interface
The TGA200 includes TGA Windows software. Illustrated in Figure 5-1, TGA
Windows displays data in real time, allows modification of control parameters,
and saves data to the hard disk.
FIGURE 5-1. Real-time graphics screen
6