Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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4-34 Display Setup Menu
SR785 Dynamic Signal Analyzer
See ‘User Math Functions’ in Chapter 2 for more.
Measurement (Swept Sine)
Select the Measurement of the active display when the Measurement Group is Swept
Sine.
Each Measurement has an associated View. Changing the Measurement changes the
View to the View last used with the new Measurement.
Command: MEAS(?) d {, i}
The following Measurements are available in the Swept Sine Measurement Group:
Spectrum
The swept sine spectrum is simply the measurement of a single channel over a sweep.
The spectrum is complex (it contains phase and amplitude information). The phase is
relative to the source and is stable but arbitrary. Single channel phase is not generally
meaningful.
The spectrum measures the actual signal level at the inputs. If source auto level is On,
then the spectrum will tend to be constant. Use Frequency Response to remove the
effects of a changing source level.
Normalized Variance
Normalized variance is a measure of the signal to noise ratio of a swept sine
measurement after the signal has been integrated for a specified time, or a specified
number of cycles. Variance values near 1 indicate that the final signal to noise ratio is
high, while values near zero indicate that the final signal to noise ratio is poor.
Cross Spectrum
The swept sine cross spectrum is a two channel measurement defined as
Cross Spectrum = conj( Spec1 ) • Spec2
The cross spectrum contains both magnitude and phase information. The phase is the
relative phase (at each frequency) between the two channels.
The magnitude is simply the product of the magnitudes of each spectrum. Frequencies
where signal is present in both spectra will have large components in the cross spectrum.
Frequency Response
The swept sine Frequency Response (sometimes called frequency response) is a two
channel measurement defined as
Frequency Response = Spec2 / Spec1
The Frequency Response contains both magnitude and phase information. The phase is
the relative phase (at each frequency) between the two channels.