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Lab #4: Using Peak Detect Acquisition Mode
All DSOs and MSOs have a fixed amount of acquisition memory. This is
the number of samples that the oscilloscope can digitize for each
acquisition cycle. If the scope's timebase is set to a relatively fast time/div
setting, such as 20 ns/div, then the scope will always have a sufficient
amount of memory to capture a waveform at that setting using the scope's
maximum specified sample rate. For example, if a scope's maximum
specified sample rate is 4 GSa/s (250 ps between samples), and if the
scope's timebase is set to 20 ns/div, then an acquisition memory depth of
800 points is all that is required to capture and display a complete
waveform. At 20 ns/div, a complete waveform across the scope's screen
would consist of 200 ns of time (20 ns/div x 10 horizontal divisions). The
required memory depth to fill this time while still sampling at 4 GSa/s is
then just 800 points (200ns/250ps = 800).
If you set the scope's timebase to a much slower time/div setting in order
to capture slower waveforms and longer time, then the scope may need to
automatically reduce its sampling rate in order to fill the required
waveform time. All DSOs and MSOs do this. For example, let's assume that
you want to capture a relatively slow signal and need to set the scope's
timebase to 10 ms/div (100 ms across screen). If the scope's maximum
memory depth is 2 M points, then the scope will need to reduce its
sample rate to 20 MSa/s (100 ms/2 M = 50 ns sample period).
Although in most cases this is not a problem, because capturing slower
waveforms doesn't require fast sample rates, what if the input signal
consisted of a combination of low- speed and high- speed characteristics?
For example, what if the input signal that you want to capture is a 30 Hz
sine wave with very narrow glitches riding on it? Capturing the 30 Hz sine
wave doesn't require a fast sample rate, but capturing the narrow glitches
may require a very fast sample rate. Let's set up a test to capture a signal
such as this.
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2000 X-Series Oscilloscopes Advanced Training Guide
Connect the channel- 1 probe to the Demo 1 terminal and ground.
Press [Default Setup] on the scope's front panel.
Press [Help]; then press the Training Signals softkey.
Using the Entry knob, select the Sine with Glitch signal; then press the
Output softkey to turn it on.
Set channel- 1's V/div setting to 500.0 mV/div.
Set the scope's timebase to 50.00 ms/div.
Press the [Intensity] button (under the Entry knob); then set the
waveform trace intensity to 100% using the Entry knob.
Oscilloscope Familiarization Labs
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