Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 90)

7 AUXILIARY INPUTS AND OUTPUTS
The TGA100 has three options for digital communication with other devices: sending concentration data to a CR9000
data logger, reading data from a CSAT3 sonic anemometer, and reading data from a CR9000 data logger. It also has
four analog inputs and a 5V excitation output inside the analyzer enclosure. The optional 7996 Input/Output Board can
be installed in the PC to provide eight additional analog inputs, two analog outputs, and sixteen digital outputs. All I/O
channels are updated at 10 Hz, and are synchronized with the TGA100 concentration measurements.
Additional surge protection is recommended for all of the auxiliary inputs and outputs if a cable longer than 3 m is
attached. The SVP48 Surge Voltage Protector is available from Campbell Scientific for this purpose.
7.1 Reading Data from a CSAT3 Sonic Anemometer
For an eddy covariance measurement involving only a TGA100 and a CSAT3 sonic anemometer, the CSAT3 may be
connected directly to the TGA100, avoiding the additional complexity and expense of using a data logger. This requires
the use of the optional TL925 CR9000 COMPUTER TO SERIAL INTERFACE module to connect the CSAT3 to the
TGA100.
To read data from a CSAT3 Sonic Anemometer, complete the following steps:
1) Set the data rate of the TL925 to 9600 baud by removing the cover from the TL925 and setting the jumpers on the
board as indicated by the label on the inside of the cover.
2) Connect the TLINK RJ45 CABLE (CSI P/N 7954, supplied with the TL925) from the RS422 Link connector on
the TGA 9030 CPU card to the ‘CR9000/RS422’ port on the TL925.
3) Connect the RS232 output cable (CSAT3CBL2-L, supplied with the CSAT3) from the CSAT3 to the
‘Computer/RS232’ port on the TL925, using a null modem and a gender changer.
4) Apply 12 Vdc power to the CSAT3.
5) Start the TGA program and from the Main Menu, select the Parameter Change Menu and then the File Format
screen.
6) Set the Output conc data to additional device? parameter to 0.
7) Set the Read data from additional device? parameter to 1.
Every 0.1 sec the TGA100 will request and receive data from the CSAT3. The CSAT3 measures the wind velocity
when the TGA100 issues the request for data. In this way the CSAT3’s measurements are synchronized with the
TGA100’s concentration measurements, to minimize errors in the EC flux caused by random timing jitter between the
wind and concentration measurements. The data received from the CSAT3 include the three-dimensional wind velocity
(u
x
, u
y
, and u
z
), the speed of sound c, and the diagnostic word w. The TGA software scales the wind velocity data to m/s
using the range codes in the diagnostic word. It scales the speed of sound to m/s, and then converts it to sonic
temperature, T
s
, in °C, using:
15 . 273
2
− =
d d
s R
c
T
γ
where 4 . 1 =
d
γ
and JK 04 . 287 =
d
R -1 kg -1 . The TGA software then masks the range codes from the diagnostic
word. Refer to the CSAT3 user manual for details.
Any of the five CSAT3 data values can be displayed on the real time screen in graph 1, 2, or 3, by choosing it from the
graph selection menus. These data will be written to the 10 Hz data file if selected for file output on the File Output
Selection screen.
7.2 Reading Data from a CR9000
Some applications may require other measurements to be synchronized with the TGA100 concentration measurement.
For example, an eddy covariance experiment may include one or more CSAT3 sonic anemometers, KH20 Krypton
hygrometers, fine-wire thermocouples, etc., as well as the TGA100. It is important for all of the measurements to be
controlled by a single clock, to avoid timing jitter that would cause flux to be underestimated. A CR9000 datalogger
may be used for the additional measurements, with all data to be archived on the TGA100 hard disk. This option is used
in applications requiring 15 or fewer data fields from the CR9000.
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