Campbell CSAT3B, Инструкция по эксплуатации, Страница: 56 / 88

CSAT3B Three-Dimensional Sonic Anemometer
TABLE 8-1. Overview of CSAT3B Operating Modes.
Mode
Measurement Trigger Filters Output Prompt
Source Rate Enabled Bandwidth (Hz) Source Rate
1 Datalogger 1 to 100 Hz
1
No - Datalogger 1 to 100 Hz
*
2 CSAT3B 100 Hz Yes 5, 10, 20, 25 Datalogger 1 to 100 Hz
*
3 CSAT3B 100 Hz No - CSAT3B 10, 20, 50, 100 Hz
4 CSAT3B 100 Hz Yes 5, 10, 20, 25 CSAT3B 10, 20, 50, 100 Hz
1
The exact rate is determined by the scan interval set in the CRBasic program of the
datalogger.
The options for datalogger-prompted output require use of SDM
or CPI communications, while the options for unprompted output
to a PC require use of RS-485 or USB communications.
8.2.1 Measurement Trigger
A measurement trigger is the actual command to initiate a sonic measurement
and can be driven by either a datalogger or the CSAT3B internal timer. If the
trigger is given by a datalogger as in Mode 1, then no data filtering is done
(bandwidth is wide open) since each trigger will initiate a single new
measurement (single-measurement regime). The datalogger can trigger
measurements at rates from 1 to 100 Hz. If the trigger is given by the internal
CSAT3B timer as in Modes 2 ˗ 4 , the measurements will be self-triggered at a
rate of 100 Hz. This results in an oversampled measurement regime where the
100 Hz samples may be optionally processed through a filter before being
downsampled or decimated and output.
If a datalogger fails to provide a trigger and the CSAT3B has not
been configured for unprompted output, the CSAT3B will enter
into a lost-trigger state where it will output measurements at 1 Hz
based on its internal timer. If the CSAT3B is in a lost-trigger state
while connected with Device Configuration Utility , real-time
anemometer data will flash on the screen at one second intervals.
This is an indication that the settings should be checked. It does
not indicate a problem with the CSAT3B hardware. Once a
trigger is received by the CSAT3B, or once unprompted output is
enabled, normal operation will ensue.
8.2.2 Data Filter
The optional data filter (Modes 2 and 4) takes the 100 Hz sample points that
were self-triggered by the CSAT3B and runs them through a low-pass (high-
cut) filter, resulting in a new filtered output at the same 100 Hz rate. The
degree to which the data are filtered is determined by the user-selected filter
bandwidth. This is selected from the Device Configuration Utility in the
Measurement Settings tab.
The bandwidth is the frequency at which a signal is filtered to (1-1/e) of its
original power. In cases where unaliased spectra from the CSAT3B are to be
NOTE
NOTE
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