User`s guide

1 Data Processing
Note You can plot several data sets with the same input and output channel
names. The plot displays data for all channels that have the same name. To
view a d if ferent in p ut- ou tpu t channel pair, select it from the Channel menu.
For more information about selecting different input and output pairs, see
“Selecting Measured and Noise Channels in Plots” on page 12-18.
The following table summarizes options that are specifictotimeplots,which
you can select from the plot window menus. For general information about
working with System Identification To olbo x plots, see “Working with Plots in
the System Identification Tool GUI” on page 12-15.
Time Plot Options
Action
Command
Toggle input display between
piece-wise continuous (zero-order
hold) an d linear interpo lation
(first-order h old) betw ee n samples.
Note This option only affects the
display and not the intersample
behavior specified when importing
the data.
Select Style > Staircase input for
zero-order hold or Style > Regular
input for first-order hold.
Working with a Data Spectra Plot
The Data spectra plot shows a periodogram or a spectral estimate of data1
and data3fd.
The periodogram is computed by taking the absolute squares of the Fourier
transforms of the data, dividing by the number of data points, and multiplying
by the sampling interval. The spectral estimate for time-domain data is a
smoothed spectrum calculated u sing
spa. For frequency-domain data, the
Data spectra plot shows the absolute value of the square of the a ctual data.
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