28
3000 X-Series Oscilloscopes Advanced Training Guide
2
Oscilloscope Familiarization Labs
At this point, you should see a sine wave similar to
look closely you should also see some glitches (narrow pulses) near the
peaks of this sine wave. And the amplitude of these glitches may appear
to vary (bouncing up and down). The amplitude of these glitches is
actually very stable. The problem is that the scope has reduced its sample
rate (note the sample rate shown under the Agilent logo on the scope’s
display) and the scope is now intermittently capturing the narrow glitches.
The scope is under- sampling the narrow glitches. Sometimes the scope
captures a single point on the peak of a glitch. Sometimes it captures a
point on a transition of the glitch. And sometimes it captures nothing at
all on the glitch (the glitch width is narrower than the sample interval).
This scope has a special acquisition mode called “Peak Detect” that will
resolve this problem. Let’s turn it on.
8
Press the
[Acquire]
front panel key (below the Cursors knob).
9
Press the
Acq Mode
softkey; then turn the Entry knob to select
Peak
Detect
.
Figure 13 The scope’s automatically-reduced sample rate under-samples the repetitive
glitch.