Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 86)

Two parameters must be set for proper master/slave operation. First, each TGA100 must be identified as the master or
as slave 1 to 4. This is done by entering the Miscellaneous Valve Control menu and setting the Master/Slave
designation parameter as appropriate (0 for the master, 1 for slave #1, 2 for slave #2, etc.) This parameter must be set in
each TGA100. If there are no slaves attached (standalone operation), set this parameter to 0.
Second, set the Number of slaves attached to this TGA parameter. This parameter determines which slave data are to be
stored in the data files. If there are no slaves attached (standalone operation), set this parameter to 0 to avoid cluttering
data files with undefined "slave" data. For master/slave operation, in the master TGA set this parameter to the number
of slaves attached. On the slave TGA100s, this parameter should be set to 0.
5.3.2 Master/Slave Operation
To begin Master/slave operation, make each of the TGA100s operational, as discussed in section 2.3.1. Then start the
site means or gradient mode on the master TGA100. The master TGA will begin to control the valves and calculate
statistics as it normally does for site means or gradient mode. Additionally, every time the master TGA measures
concentration (10 Hz), it will put its concentration data and the valve control status into a master/slave information
packet and send it to slave 1. Slave 1 will add its own concentration data to the packet, and send it on to slave 2, etc.
until the last slave sends the completed packet back to the master TGA.
The 10 Hz concentration data from any slave may be displayed in the master’s real time graphs. The master TGA will
calculate the site means or gradient values for each slave, and save these results to its file.
The vertical lines that mark the valve switching times, the end of the shift samples, and the end of the omit samples will
be displayed in graph 1 and graph 2 of each slave. Gradient or site means intermediate results will also be displayed on
each slave TGA above graph 1.
5.3.3 Shift and Omit Samples
The master TGA calculates the mean concentration, etc. using the same shift samples and omit samples for all of the
TGAs. Depending on the design of the sampling system, a few extra samples may need to be omitted so that only valid
samples are included in the calculations for all of the TGAs.
6 EDDY COVARIANCE MEASUREMENTS
6.1 Overview
The TGA100's sample rate, frequency response, sensitivity and selectivity are optimized for measuring trace gas fluxes
using the eddy covariance (EC) method. It is designed to collect three-dimensional wind data from a CSAT3 sonic
anemometer while synchronously measuring trace gas concentration. Figure 6-1 illustrates a typical EC application.
The sonic anemometer and air sample intake are mounted on the measurement mast. Tubing connects the air sample
intake to the inlet of a 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 to approximately 15 slpm. The TGA100 analyzer is located near the
base of the measurement mast to minimize the length of sample tubing. This avoids the attenuation of high frequencies
in the concentration data that can be caused by excessive tubing length. The TGA100 PC requires shelter from the
environment, but can be located up to 500 m (1650 ft) away from the TGA100 analyzer, connected by fiber optic cable.
The sample pump requires minimal shelter and can be located up to 90 m (300 ft) away from the analyzer, connected
by the suction hose. The CSAT3 connects to the TGA analyzer by way of a TL925 serial interface module, which can
be mounted inside the analyzer enclosure for protection from the environment.
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