Campbell Scientific TGA100A Overview - Manual (Page 6)

TGA100A Trace Gas Analyzer Overview
OV4. Multiple Scan Mode
The TGA100A can be configured to measure two or three gases
simultaneously by alternating the spectral scan wavelength between two or
three absorption lines. This technique requires that the absorption lines be
close together (within about 1 cm
-1 ), so it can be used only in very specific
cases. The multiple scan mode is used to measure δ 13 C and δ 18 O isotope ratios
in carbon dioxide or δ 18 O and δD isotope ratios in water vapor by tuning each
scan to a different isotopologue.
The multiple scan mode may also be used to measure some other pairs of
gases, such as carbon monoxide and nitrous oxide, or nitrous oxide and
methane, but the measurement noise will be higher than if a single gas is
measured. For measurements of a single gas, the laser wavelength is chosen for
one of 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.
OV5. User Interface Software
The TGA100A user interface software runs on the user's PC. It displays the
data in real time and allows the user to modify control parameters. Normally
the trace gas concentration data are recorded by a datalogger, and the PC is
required only for setting up the TGA100A. However, the trace gas
concentration data can also be saved to the PC's hard disk, making the
datalogger unnecessary in some applications.
The real time graphics screen is presented in Figure OV5-1. In the upper left
corner is a box which displays the TGA software version, the laser and
detector temperatures, and the time. Beneath the time and temperature display
is a blank area used for information and error message display. The rest of the
top of the screen has five menu columns: run mode, dynamic parameters,
detector video, special function enable/disable, and graph selections.
OV-6