Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 19)

1.6.3 Site Means
The TGA100’s site means sampling mode is similar to the flux gradient mode in that it controls switching valves and
calculates mean concentrations for each intake. The difference between the two sampling modes is that the gradient
mode considers the sample intakes in pairs, switching several times between an upper and lower intake before moving
to another site, but the site means mode considers all of the intakes as one group. It cycles through all of the intakes in
sequence (up to 18 sites are supported). Applications for the site means mode include concentration profile
measurements and trace gas flux measurements using the mass balance technique.
Figure 1-7
Figure 1-7. Example Profile Application
illustrates an eight-level vertical profile using the TGA100 site means mode. The eight intake assemblies are
arranged vertically on a single measurement tower. These intake assemblies include a filter to remove particulates and a
critical flow orifice to set the sample flow (typically less than 1 slpm). A separate tube connects each intake assembly to
the site selection system, which selects one of the intakes at a time. All of the unselected intakes are connected through
the bypass tube to the sample pump suction hose, keeping air flow at all times in all intake tubes. The flow from the
selected intake goes through a sample air dryer to the TGA100 analyzer. A second dryer is used to provide dry air to
purge the sample dryer.
Purge Dryer
Sample Dryer
Site Selection
Sampling
System
Digital Control Cable
Sample
Bypass
Dryer Purge
Sample
Sample
Intakes
19