Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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4-26 Display Setup Menu
SR785 Dynamic Signal Analyzer
The choice of Measurement Group changes the [Frequency], [Average] and [Source]
menus.
Command: MGRP(?) d {, i}
Measurement (FFT)
Select the Measurement of the active display when the Measurement Group is FFT.
Each Measurement has an associated View. Changing the Measurement changes the
View to the View last used with the new Measurement.
The two displays generally have different Measurements. This entry field can be linked
to both displays using the [Link] key.
Measurements which are listed as '2 channel' may only be selected if <Analyzer Config>
is set to 'Dual Channel.'
Command: MEAS(?) d {, i}
The following Measurements are available in the FFT Measurement Group:
FFT (Linear Spectrum)
The FFT spectrum is the basic measurement of an FFT analyzer. It is simply the FFT of a
time record. The spectrum is a complex quantity (it contains phase as well as amplitude
information). This is sometimes referred to as the linear spectrum.
The phase of the spectrum is meaningful only if the time record is triggered with a fixed
relationship to the input signal. If the signal is periodic as well (the signal and trigger
repeat), then vector averaging can be used to reduce the noise level of the spectrum. The
vector averaged spectrum is still a complex quantity
The precise definition of the FFT1 measurement for all averaging modes is as follows:
No Average
FFT 1 = FFT1
Vector Average
FFT 1 = <FFT1>
RMS Average
FFT 1 =
√
<FFT1*• FFT1>
Peak Hold Average
FFT 1 =
√
MAX(FFT1*• FFT1)
Power Spectrum
The Power Spectrum is derived from the FFT spectrum by multiplying the spectrum by
its complex conjugate. The averaged power spectrum is a good approximation to the rms