Campbell Scientific CSAT3B CSAT3B Three-Dimensional Sonic Anemometer - Page 61

Datalogger Programming using SDM or CPI

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CSAT3B Three-Dimensional Sonic Anemometer when the measurement actually took place, whereas the CSAT3B data will be delayed by 100 ms. Before covariances are calculated, the fine-wire thermocouple data should be lagged by one scan interval (100 ms) so that all data are aligned in time. This lagging of the data can be done online with the datalogger, or it is often done offline using PC software. TABLE 8-4 shows the measurement lags that should be applied to analog measurements or measurements with no delay in order to align them with CSAT3B data. The lags shown for Modes 2 and 4, indicate the number of output scans that the analog measurements should be delayed. For example, in Mode 2 where data is being filtered and then output is prompted by a datalogger, if the datalogger has a 10 Hz scan rate and the CSAT3B has been set to use a 5 Hz bandwidth filter, the analog measurements should be delayed by 8 datalogger scans (8·100ms/scan = 800 ms). TABLE 8-4 also indicates the preferred settings for flux measurements and spectral analysis. As discussed previously, for spectral analysis, the bandwidth should be selected as half the output rate. For flux applications, the output rate or sampling frequency need not be greater than 10 or 20 Hz in order to reduce unwieldy data sets, and the bandwidth may be left fairly wide open (for example, 20 Hz) to ensure high frequency fluxes are retained in the signal. TABLE 8-4. Measurement Lags for Analog Measurements or Measurements with No Delay Mode 11 Measurement Lag (in output samples), Ndelay 1 datalogger scan 3 Unprompted output rate/100 (lag in seconds) Output rate (fscan) 10 Hz 20 Hz 50 Hz 100 Hz Bandwidth (BW) 2 and 4 5 Hz 83 16 40 80 10 Hz 4 83 20 40 20 Hz 22 42 10 20 25 Hz - - 83 16 1 Best for flux applications 2 Good for flux applications 3 Recommended for spectral analysis 8.4 Datalogger Programming using SDM or CPI The CSAT3B() CRBasic instructions control and retrieve data from the CSAT3B. These instructions are available on the CR6, CR800/850, CR1000, and CR3000 dataloggers. 51

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CSAT3B Three-Dimensional Sonic Anemometer
when the measurement actually took place, whereas the CSAT3B data will be
delayed by 100 ms.
Before covariances are calculated, the fine-wire
thermocouple data should be lagged by one scan interval (100 ms) so that all
data are aligned in time.
This lagging of the data can be done online with the
datalogger, or it is often done offline using PC software.
TABLE 8-4 shows the measurement lags that should be applied to analog
measurements or measurements with no delay in order to align them with
CSAT3B data.
The lags shown for Modes 2 and 4, indicate the number of
output scans that the analog measurements should be delayed.
For example, in Mode 2 where data is being filtered and then output is
prompted by a datalogger, if the datalogger has a 10 Hz scan rate and the
CSAT3B has been set to use a 5 Hz bandwidth filter, the analog measurements
should be delayed by 8 datalogger scans (8ยท100ms/scan = 800 ms).
TABLE
8-4 also indicates the preferred settings for flux measurements and spectral
analysis.
As discussed previously, for spectral analysis, the bandwidth should
be selected as half the output rate.
For flux applications, the output rate or
sampling frequency need not be greater than 10 or 20 Hz in order to reduce
unwieldy data sets, and the bandwidth may be left fairly wide open (for
example, 20 Hz) to ensure high frequency fluxes are retained in the signal.
TABLE 8-4.
Measurement Lags for Analog Measurements or
Measurements with No Delay
Mode
Measurement Lag (in output samples), N
delay
1
1
1 datalogger scan
3
Unprompted output rate/100 (lag in seconds)
2 and 4
Output rate (f
scan
)
10 Hz
20 Hz
50 Hz
100 Hz
Bandwidth
(BW)
5 Hz
8
3
16
40
80
10 Hz
4
8
3
20
40
20 Hz
2
2
4
2
10
20
25 Hz
-
-
8
3
16
1
Best for flux applications
2
Good for flux applications
3
Recommended for spectral analysis
8.4
Datalogger Programming using SDM or CPI
The
CSAT3B() CRBasic
instructions control and retrieve data from the
CSAT3B.
These instructions are available on the CR6, CR800/850, CR1000,
and CR3000 dataloggers.
51