Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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Display Setup Menu 4-37
SR785 Dynamic Signal Analyzer
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 (Time/Histogram)
Histogram
This is the basic measurement in the Time/Histogram group. The display shows a
histogram of the number of samples found in some length of the input signal versus the
amplitude of the sample. The amplitude covers the entire input range of the analyzer.
PDF
The PDF, or probability density function, is a normalized version of the histogram.. The
value of the PDF for a given voltage V multiplied by a small voltage interval,
∆
V, is the
probability that a sample of the signal will fall between V and V+
∆
V.
CDF
The CDF, or cumulative density function, is the integral of the probability density
function. The CDF at a given voltage is the probability that a sample of the input signal
will be below that voltage.
Time
The time record in the time/histogram measurement group shows the value of the input
signal sampled at intervals specified by <Sample Time> softkey. Unlike the FFT time
record, the histogram time record is not filtered as the sampling frequency is decreased
and may contain aliased signals. While this is important for the frequency domain
measurements in the FFT measurement group, it is not a consideration in time/histogram
group where the goal is to represent the original signal as closely as possible.
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. Time/Histogram 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.
User Functions
A User Function displays the results of a user defined math function. User Functions
defined within the Histogram Measurement Group may include histogram measurement
results. Use the [User Math] menu to define a function.