166 Keysight InfiniiVision HD3-Series Oscilloscopes User's Guide
12 Acquisition Control
For example, when storing 500 ms of data in 50,000,000 points of memory, the
actual sample rate is 100 MSa/s.
Likewise, when storing 50 ms of data in 50,000,000 points of memory, the actual
sample rate is 1 GSa/s.
The actual sample rate is displayed in the sample rate and memory depth
(Acquire) badge at the top of the display.
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 Open the Acquire dialog box by selecting the sample rate and memory depth
(Acquire) badge or by choosing Setup > Acquire... from the main menu.
2 In the Acquire dialog box, from the Acq Mode drop-down list, select the
acquisition mode:
• Normal — at slower time/div settings, normal decimation occurs, and there is
no averaging. Use this mode for most waveforms. See
"Normal Acquisition
Mode"
on page 167.
• Peak Detect — at slower time/div settings, the maximum and minimum
samples in the effective sample period are stored. Use this mode for
displaying narrow pulses that occur infrequently. See
"Peak Detect
Acquisition Mode"
on page 167.
• Averaging — at all time/div settings, the specified number of triggers are
averaged together. Use this mode for reducing noise and increasing
resolution of periodic signals without bandwidth or rise time degradation.
See "Averaging Acquisition Mode" on page 169.
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