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Figure 14 The Peak Detect acquisition mode reliably captures the narrow glitches riding
The height of the glitches should now appear much more stable as shown
in
rather than sampling waveforms at a reduced rate, the scope intelligently
decimates acquired data at a higher sample rate. For example, let's assume
that the scope needs to run at a sample rate that is 1/100th of its
maximum sample rate. This would be equivalent to running the scope at
its maximum sample rate, but only storing every 1/100th point, which is
"unintelligent" decimation. In the Peak Detect mode, the scope would
analyze a group of 200 consecutive samples in real- time (sampled at a
high rate), and then store just the maximum and minimum digitized values
for this group of 200 points, which is just 2 points. This would be a
decimation factor of 100.
So you may ask why not always use the Peak Detect mode? There are some
tradeoffs when using this mode of acquisition. First of all, the scope's
absolute maximum sample rate is reduced. Secondly, stored points will
NOT be evenly spaced. And this is an important criterion of the Nyquist
Sampling theorem. So for this particular measurement application, using
the Peak Detect mode is a good choice. But for other measurement
applications, Peak Detect may not be the appropriate acquisition mode.
To learn more about oscilloscope real- time sampling, refer to Agilent's
Application Note titled, "Evaluating Oscilloscope Sample Rates vs
Sampling Fidelity" listed in
2000 X-Series Oscilloscopes Advanced Training Guide
on the slow sine wave.
Figure
14. When the Peak Detect acquisition mode has been selected,
Oscilloscope Familiarization Labs
"Related Agilent Literature"
2
on page 101.
29
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