Keysight Technologies InfiniiVision 3000 X Series, User Manual

Page: 189 / 432

Acquisition Control
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Keysight InfiniiVision 3000 X-Series Oscilloscopes User's Guide 189
Memory Depth and Sample Rate
The number of points of oscilloscope memory is fixed, and there is a maximum
sample rate associated with oscilloscope's analog-to-digital converter; however,
the actual sample rate is determined by the time of the acquisition (which is set
according to the oscilloscope's horizontal time/div scale).
sample rate = number of samples / time of acquisition
For example, when storing 50 µs of data in 50,000 points of memory, the actual
sample rate is 1 GSa/s.
Likewise, when storing 50 ms of data in 50,000 points of memory, the actual
sample rate is 1 MSa/s.
The actual sample rate is displayed in the right-side information area.
The oscilloscope achieves the actual sample rate by throwing away (decimating)
unneeded samples.
Selecting the Acquisition Mode
When selecting the oscilloscope acquisition mode, keep in mind that samples are
normally decimated at slower time/div settings.
At slower time/div settings, the effective sample rate drops (and the effective
sample period increases) because the acquisition time increases and the
oscilloscope's digitizer is sampling faster than is required to fill memory.
For example, suppose an oscilloscope's digitizer has a sample period of 1 ns
(maximum sample rate of 1 GSa/s) and a 1 M memory depth. At that rate, memory
is filled in 1 ms. If the acquisition time is 100 ms (10 ms/div), only 1 of every 100
samples is needed to fill memory.
To select the acquisition mode:
1 Press the [Acquire] key on the front panel.
2 In the Acquire Menu, press the Acq Mode softkey; then, turn the Entry knob to
select the acquisition mode.
The InfiniiVision oscilloscopes have the following acquisition modes: