Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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4-32 Display Setup Menu
SR785 Dynamic Signal Analyzer
Capture
The capture buffer stores sequential time domain data in memory. See ‘Capture’ in
Chapter 2 for more details. The capture measurement displays the contents of the capture
buffer. FFT measurements can use this stored data as input data by choosing Playback as
the Input Source in the [Input] menu.
The capture buffer often stores many time records. To graphically expand a region of the
display, use the Pan and Zoom functions in the [Display Setup] menu. The capture buffer
display will automatically pan as the capture fill and playback progress through the
buffer. During capture fill, if the capture buffer contains more points than can be
displayed, points are skipped. This speeds up the display update so that it keeps up with
the real time capture 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.
To measure from a region of the buffer, set the Playback Start and Length in the [Input]<
menu.
The capture data is filtered and down-sampled according to the capture Sample Rate.
Only baseband data (data bandwidth starts at DC) are captured. The capture buffer
resembles a digital oscilloscope display. Signals at frequencies above 1/2.56 times the
sample rate have been filtered out.
The capture buffer is not a continuous representation of the input signal. The data is
sampled and has a time resolution of 1/(sample rate). High frequency signals will appear
distorted in the time record. However, ALL of the spectral information (up to 1/2.56
times the Sample Rate) is preserved by the Nyquist theorem as long as the value of each
sample is accurate.
Amplitude calibration is performed in the frequency domain. Hence, the captured time
data amplitudes are not calibrated.
User Functions
A User Function displays the results of a user defined math function. User Functions
defined within the Correlation Measurement Group may include correlation
measurement results. Use the [User Math] menu to define a function.
A User Function may not be selected as the measurement if it uses a Trace which is
empty or which contains data taken in a different Measurement Group.
See ‘User Math Functions’ in Chapter 2 for more.
Measurement (Octave Analysis)
Select the Measurement of the active display when the Measurement Group is Octave
Analysis.
Each Measurement has an associated View. Changing the Measurement changes the
View to the View last used with the new Measurement.