Stanford Research Systems SR785, Руководство по эксплуатации и программированию

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Octave Measurements 2-43
SR785 Dynamic Signal Analyzer
distorted in the time record. However, ALL of the spectral information is preserved by
the Nyquist sampling theorem as long as the value of each sample is accurate.
Amplitude calibration is performed in the frequency domain. Hence, the captured time
data amplitudes are not calibrated.
User Function
User Function displays the results of a user defined math function. User Functions
defined within the Octave Analysis Measurement Group may include octave
measurement results. Use the [User Math] menu to define a math function.
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.
The number of Octave Channels limits the measurement choices of both displays. If 1
Octave Channel is selected, then only one input may be analyzed. If both displays are
making an octave measurement, they must both use the same input. Changing the input
of the active display will change the measurement or input of the other display if
necessary. User Functions which use both inputs may not be measured. Choosing 1
Octave Channel may change the current measurements so that both displays use the same
input.
See ‘User Math’ later in this section for more.
Octave Averaging
All octave measurements are averaged. There are four types of averaging - Linear Time,
Exponential Time, Equal Confidence and Peak Hold.
Linear Time
The band filter outputs are equally weighted and averaged for an Integration Time.
While Linear averaging is in progress, the integration time completed is shown in the
Horizontal Scale Bar below the graph. When the Integration Time has been completed,
the measurement stops and ‘Done’ is displayed below the graph.
If Waterfall Storage is On, the waterfall buffer only stores the completed linear averages,
not each individual measurement. Each time the linear average is done, the result is
stored in the waterfall buffer and the average is reset and started over (instead of
stopping). Each completed average counts as a single waterfall record.
Exponential Time
New filtered data is weighted more than older data. The exponential ‘time constant’ is
the Integration Time. Averaging continues indefinitely.
While Exponential averaging is in progress, the completed integration time is shown in
the Horizontal Scale Bar below the graph. The displayed time stops incrementing at the
Integration Time while the averaging continues.
Exponential weighting reaches a steady state after approximately an integration time.
Once in steady state, further changes in the average are detected only if they last for a