Campbell Scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 28)

EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
7.2 Details
This section gives an explanation for each setting.
7.2.1 SDM Address
This parameter must be set to use SDM output from the EC100. See Section
8.1, SDM Output for details on using SDM output.
Each SDM device on the SDM bus must have a unique address. The EC155
has a factory default SDM address of 1, but may be changed to any integer
value between 0 and 14. The value 15 is reserved as an SDM group trigger.
7.2.2 Bandwidth
The EC100 has a user-selectable low-pass filter to select the bandwith (5, 10,
12.5, 20, or 25 Hz). Setting the bandwith to a lower value will reduce noise.
However, it must be set high enough to retain the high-frequency fluctuations
in the CO
2
and H
2
O, or 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 bandwith settings may be used for higher
measurement heights, which inherently have lower frequency content. Refer to
Appendix A 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.
7.2.3 Unprompted Output
If the EC100 is to output data in one of the unprompted modes (USB or RS-
485, see Section 8.2, USB or RS-485 Output), this setting must be set
accordingly. The factory default is to disable the unprompted output, assuming
data will be logged via SDM (see Section 8.1, SDM Output).
Only one unprompted output type (i.e., USB, RS-485) may be selected at a
given time. The rate at which the EC100 outputs these data is determined by
the Unprompted Output Rate setting.
7.2.4 Unprompted Output Rate
This setting determines the output rate for unprompted output (USB or RS-485,
see Section 8.2, USB or RS-485 Output). If the unprompted output is disabled,
this parameter is not used. The factory default output rate is 10 Hz, but it may
be set to 10, 25, or 50 Hz.
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