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10-21
IM 701210-06E
Waveform Computation
10
Measurement Range: Start Point/End Point
Computation is performed on up to 800 kW of data when there is one equation, up to
400 kW when there are two equations, up to 200 kW when there is three or four
equations, and up to 100 kW when there are five to eight equations.
By default, the measurement range is
±
5 divisions of the display frame on the time axis.
You can limit this range.
The concept of the computation range is analogous to the concept of the selectable
range of cursor display position in cursor measurement.
For details, see section 11.5, “Selectable Range of Cursor Position.”
Setting the Digital Filter
The following three types of filters are available.
Type
Bandwidth
Gaussian
LowPass
Sharp
LowPass/BandPass/HighPass
IIR (Butterworth)
LowPass/BandPass/HighPass
Selectable range of cutoff frequencies: 2.0% to 30.0% of the sample rate (in 0.2% steps)
Setting Average and Peak Computation
Averaging and peak computation can be performed on the computed data. Four types of
operations are available: linear, exponential, cycle, and peak.
For linear averaging, set the average count (acquisition count, 2 to 128, in 2
n
steps). For
exponential averaging, set the attenuation constant (2 to 256, in 2
n
steps).
Make sure to specify which waveform, time axis waveform or frequency waveform, to
take the average. Specifying a wrong waveform will give a meaningless result.
For cycle averaging, set the number of data points of one cycle (Cycle Count) in the
range, 10 to 1800. This number is applied to the data from the start to the end of the
computed data, but the remaining data that cannot be divided by the Cycle Count are
ignored. Cycle average cannot be performed on an FFT waveform.
For peak computation, the maximum value at each point of the computed data is
determined and the waveform is displayed. For each computation, the new computed
value is compared with the past value and the larger value is kept.
• Example of Cycle Averaging
When the record length is 10 k, the Cycle Count is 720, the start point of computation
is –5.000 divisions, and the end point is +5.000 divisions
10k/720 = 13.88
13 cycles will be averaged.
13
×
720 = 9360
Data between the start point to the 9360
th
point will be cycle
averaged.
• Notes When Computing Average and Peak Computation
• Normally auto scaling is defined for the 1st computed waveform. If you wish to
obtain a computed waveform whose amplitude varies significantly after averaging
(e.g. Coherent function ), use manual scaling.
• If averaging is performed, the computation is not performed again after the
measurement is stopped. However, if the number of data points for the cycle
average is changed, computation is performed again.
• If the averaged waveform is measured using auto scaling and you change to
manual scaling after the measurement is stopped, the new setting is not applied.
The new setting is applied from the next measurement.
• Averaging cannot be performed on pulse width computation.
• If the computation condition is changed while averaging is in progress, the
computed data is cleared at that point, and averaging starts over.
10.5 User-Defined Computation (Optional)