CS IRGASON, Instruction Manual

Page: 28 / 74

IRGASON
®
Integrated CO
2
/H
2
O Open-Path Gas Analyzer and 3D Sonic Anemometer
16
7.1 Factory Defaults
TABLE 7-1 shows the default value for each setting described in the following
sections.
TABLE 7-1. Factory Default Settings
Bandwidth 20 Hz
SDM Address 1
Unprompted Output disabled
RS-485 baud rate 115200 bps
Unprompted Output Rate 10 Hz
Analog Output disabled
ECMon Update Rate 10 Hz
Temperature Sensor Auto-Select (IRGASON Temp Sensor)
Pressure Sensor EC100 Basic or EC100 Enhanced (depending on
order)
Pressure Differential
Enable
Auto-Select (Disabled for IRGASON)
Heater Control
Disabled
7.2 Bandwidth
The EC100 has a user-selectable low-pass filter to select the bandwidth (5, 10,
12.5, 20, or 25 Hz). Setting the bandwidth to a lower value will reduce noise.
However, it must be set high enough to retain the high-frequency fluctuations
in CO
2
and H
2
O, or else the high frequency contributions to the flux will be
lost. The factory default bandwidth of the EC100 is 20 Hz, which is sufficient
for most flux applications. Lower bandwidth settings may be used for higher
measurement heights, which inherently have lower-frequency content. Refer to
Appendix A , Filter Bandwidth and Time Delay
(p. A-1)
, for more information on
the digital filter options.
If a spectral analysis is being done to evaluate the experimental setup, the
bandwidth should be set to the Nyquist frequency, which is half the datalogger
sample rate (for SDM output) or half the unprompted output rate (for USB and
RS-485 output). This ensures that the data will not be under-sampled and that
higher-frequency variations will not be aliased to lower frequencies. Note that
if too small a bandwidth is selected, high-frequency fluxes may be under-
measured.
7.3 SDM Address
This parameter must be set to use SDM output from the EC100. See Section
8.1 , SDM Output
(p. 22)
, for details on using SDM output.
Each SDM device on the SDM bus must have a unique address. The
IRGASON has a factory default SDM address of 1, but it may be changed to