Filter
Top Products
2.6 Acquisition Modes
The USBscope50 can acquire waveforms in two different ways. The
mode and sample interval (i.e. the time between each data point) is
displayed on the main panel
2.6.1 Single Shot
In this mode, the ADC is clocked at up to 50MegaSamples/sec.
Each sample is placed into the buffer and then the buffer is painted
on the screen.
This mode is the one to use for non-repetitive signals i.e. single
pulses, irregular bus events etc. It can also be used for repetitive
waveforms.
For practical purposes the maximum frequency sine wave you can
resolve is about 10MHz in this mode, giving just 5 sample points per
cycle: expect to see a very “jagged” and “triangular” looking
waveform when observing a 10MHz input! Drop the input
frequency down to say 1MHz and you will see a nice smooth
waveform.
In single shot mode the timebase can be set from 200ns/div all the
way up to 4s/div. The time to acquire the waveform gets noticeably
slower when rates above 40ms/div are selected: the total acquisition
time is approximately “30 x timebase” so at 4s/div, the display will
update once every 120s, or 2 minutes !
As with all digital storage scopes, be careful not to view a high
frequency waveform on too low a timebase. You may see a
waveform that looks correct but drifts or fluctuates over time, and
that has the wrong frequency…this is called aliasing and is quite
normal. To avoid this effect, always pick the fastest single shot
timebase consistent with being able to view the waveform in
question.
Elan Digital Systems Ltd. 18 USBscope50 USER’S GUIDE Iss5