Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 18)

1.6.2 Flux Gradient
The TGA100 also supports the measurement of trace gas fluxes by the gradient method. The TGA100 automatically
controls gradient switching valves and computes the mean concentration at each of the two intake heights. Timing
parameters are entered by the user to control the gradient valves, typically switching between intakes every 5 to 20 s.
The results are displayed on the TGA100 PC in real-time and stored on the hard disk.
Figure 1-6
Figure 1-6. Example Gradient Flux Application
illustrates a typical gradient application. Two intake assemblies are mounted at different heights on the
measurement mast. Tubing connects each intake assembly to a gradient valve assembly that selects one of the intakes at
a time. The air sample from the selected intake flows through the PD1000 sample air dryer, which filters and dries the
air sample. A needle valve at the outlet of the PD1000 sets the sample flow rate, typically 5 to 10 slpm. Tubing
connects the outlet of the dryer to the TGA100 analyzer, which may be located 200 m (650 ft) or more away. The
TGA100 PC requires shelter from the environment, and can be located up to 500 m (1650 ft) away from the TGA100
analyzer, connected by fiber optic cable. However, for gradient applications the analyzer is normally positioned away
from the intake mast, and the PC is placed near the analyzer for convenience. The sample pump requires minimal
shelter and can be located up to 90 m (300 ft) away from the analyzer, connected by 1” ID suction hose.
This example shows a gradient flux measurement at a single site. However, the TGA100 can also support flux gradient
measurements at multiple sites by installing intake assemblies, a gradient valve assembly, and a sample dryer at each
site, and a site selection system near the analyzer. The site selection system connects one site at a time to the analyzer.
The TGA100 controls the site selection system using timing parameters supplied by the user. Normally each site is
measured for 15 to 30 min before switching to the next site.
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