Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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2-34 Capture Buffer
SR785 Dynamic Signal Analyzer
capture with the most recently acquired data stored in the buffer. Continuous Capture
Mode is not available in the Order measurement group.
While capture is in progress, the displays do not update unless the measurement is a
Capture buffer. Use Zoom and Pan to inspect a portion of the buffer. The capture buffer
display can automatically pan as the capture progresses through the buffer. During
capture, if the capture buffer accumulates points faster than can be displayed, some
points are not displayed. This speeds up the display update so that it keeps up with the
real time capture data but allows visual aliasing to occur. Once capture is complete, the
display is redrawn showing the envelope of all points, eliminating any visual aliasing
effects.
Capture Playback
Captured data can only be played back in a measurement with the same maximum
sampling rate. Data digitized at 262.1 kHz can only be played back in FFT Group with
the Base Frequency set to 102.4 kHz. Data digitized at 256 kHz can be played back in
both Octave and FFT Group as long as the FFT Base Frequency set to 100.0 kHz.
Data that is to be played back in the Order group must be captured in Order group. This
is because the order group capture must also capture the tachometer data as well as the
signal input.
Choose Playback as the Input Source in any Measurement Group except Swept Sine. Set
the Playback Start point within the capture buffer and the Playback Length. When
playing back in FFT Group, it is best to set the Playback Length to a multiple of the FFT
time record (Acquisition Time).
The Capture Progress indicator shows the playback progress through the buffer (relative
to Playback Length).
The capture buffer itself can be displayed as a measurement. Use Zoom and Pan to
inspect a portion of the buffer. During playback, the capture buffer display can
automatically pan as the playback progresses through the buffer. During playback, a
marker at the bottom of the graph indicates the current time record position within the
buffer.
The capture data represents a frequency span from 0 Hz to the sampling rate/2.56. The
playback measurement cannot exceed this measurement bandwidth. In the Frequency
menu, this places a limitation on the maximum FFT span and stop frequency or highest
Octave band during playback. The Average, Window and Waterfall menus all operate
normally during playback.
The Playback Mode can be either 1-Shot (once through the buffer) or Circular (repeat
over and over). In 1-Shot playback, the buffer is played a single time. The playback halts
when the end of the buffer is reached. In Circular playback, the playback starts over
when the end of the buffer is reached. There is often a discontinuity in the playback
measurement when the playback jumps from the end to the start of the buffer. In either
mode, press [Start/Reset] to restart playback at the start again.