To Next Page

To Previous Page

11-11

IM WT3001E-51EN

FFT (Option)

Index

• Selecting the Time Window

Press the FFT Window soft key to display the FFT Window menu.

Press the Rect, Hanning, or FlatTop soft key to select the time window.

Explanation

• Setting the Number of Computed Points

You can select 200 k (200000 points) or 20 k (20000 points). The frequency resolution

varies depending on the number of computed points as follows:

Number of Computed Points Frequency Resolution Measurement Period for the FFT

200 k 1 Hz 1 s

20 k 10 Hz 100 ms

Note

If the number of computed points is set to 200 k, FFT takes approximately 10 s. The display

update interval is determined by the longer of the two values, the data update interval and (the

measurement period of the FFT + FFT computing time). Thus, it may take more than 10 s for

the display to be updated.

• Selecting the Time Window

Select from the three types listed below. For details on the time window, see section

11.1.

• Rect (Rectangular)

This window is effective on repetitive waveform of AC signals whose period is equal

to an integer multiple of the FFT measurement period. For example, the rectangular

window is effective on 50-Hz or 60-Hz signal with repetitive waveform.

• Hanning

This window is effective on waveforms that do not meet the conditions for the

rectangular window. The frequency resolution of the Hanning window is high

compared to the flattop window.

• FlatTop

This window is effective on waveforms that do not meet the conditions for the

rectangular window. The flattop window has a higher level of accuracy than the

Hanning window.

11.5 Setting the Number of Computed Points and Time Window

YOKOGAWA WT3002E User Manual

Questions and Answers: