Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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Curve Fitting and Synthesis 2-77
SR785 Dynamic Signal Analyzer
Weighting
Because the quality of the measured frequency response function is not uniform over the
entire region to be fit, it is sometimes necessary to weight the input data when
performing the fit.
The analyzer can weight the fit in one of three ways. Uniform weighting weights all parts
of the fit region uniformly. Coherence weighting uses the calculated coherence function
(or normalized variance in the case of swept sine measurements) to weight the data.
Coherence is a measure of the signal to noise ratio of the measured frequency response
function. In regions of high signal to noise, the value of the coherence function will be
near 1. In regions of low signal to noise, the coherence function will be less than 1.
Coherence weighting is not available for Off-Line displays.
User weighting allows the user to specify the weighting function. The analyzer uses
whatever data is found in the real part of the specified weighting trace to determine the
weighting.
Curve Synthesis
The curve table is synthesized when the user presses the Synthesize Table 1 or
Synthesize Table 2 softkeys. The analyzer first looks at the active display to determine
the frequency range over which the synthesis occurs. Then the SR785 calculates the
complex frequency response function corresponding the curve parameters, frequency
scale, delay and gain settings contained in the curve table. These values are placed in the
trace corresponding to the synthesized curve table. Finally, the active display is taken
Off-Line, and the synthesized trace is displayed on the active display.
Synthesis is only allowed when the active display is in the FFT or Swept Sine
measurement group.