Chapter 1
DaqPRO
23
Note:
Sampling at a rate slower than the expected rate can cause
frequency aliasing
. In such a case,
the graph will show a frequency much lower than expected. In Figure 6 below, the higher frequency sine
wave was sampled at 1/3 of its frequency. Connecting the sampled points yielded a graph with a lower,
incorrect frequency.
Figure 6: Frequency Aliasing
Manual sampling
Use this mode for:
•
Recordings or measurements that are not related to time.
•
Situations in which you have to stop recording data after each sample obtained,
in order to change your location, or any other logging parameter
Note:
During recording
NO CHANGES
can be made to the
DaqPRO
’
s
configuration).
To start a recording using manual data logging, set the
RATE
to manual and press the
Enter
button
once to start the data recording, then press the
Enter
button each time you want to collect a
sample.
2. Sampling Points
After you have chosen the sampling rate, choosing the number of points will determine the logging
period: Samples / Rate = Logging time. You can also choose the duration of a run first, and then
calculate the number of samples: Samples = Logging time
×
Rate.
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