Campbell Scientific EC150 CO2 and H2O Open-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer User Manual
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Appendix B. Filter Bandwidth and Time Delay
provides a constant time delay for all spectral components within each filter’s
pass band.
TABLE B-1. Filter Time Delays for Various Bandwidths
Bandwidth (Hz)
Time Delay (ms)
5
800
10
400
12.5
320
20
200
25
160
The following examples show how to use TABLE B-1. To synchronize EC100
data to other datalogger measurements when the datalogger scan rate is 25 Hz
and the EC100 bandwidth is set to 20 Hz (a 200-msec time delay from TABLE
B-1), delay the non-EC100 data by five datalogger scans. Similarly, for a 10-
Hz datalogger scan rate and the same 20-Hz EC100 bandwidth, delay the non-
EC100 data by two datalogger scans to match the EC100 data. For the best
synchronicity, choose a datalogger scan interval that is an integer multiple of
the EC100 filter delay.
The EC100 measures the gas and wind data at 150 Hz, and the 150-Hz data are
down-sampled to the datalogger’s scan rate through SDM communications (see
Section 4.6.2, EC100 Outputs). This process synchronizes the EC100 gas and
wind data with other signals measured by the datalogger to within ±3.33 ms
(plus or minus one-half of the inverse of 150 Hz).
Alternately, when sending data to a data acquisition system that is not
manufactured by Campbell Scientific, the EC100 down-samples its USB and
RS-485 outputs to a user-selectable rate of 10, 25, or 50 Hz. Although the gas
and wind data from the EC100 remain synchronized with one another, the user
must consider the down-sampled output interval when synchronizing the
EC100 data with other measurements in their system. These slower output
intervals will increase the asynchronicity of EC100 data with other system
measurements.
B-3