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
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 |