Hioki 3390 - Measurement Channel and Window Function Settings

4.6 Viewing Noise Measurement Values (FFT Function)
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Select the measurement channels and Window function for noise analysis calculations.
Measurement Ch Select the measurement channel for noise analysis calculations.
Window type Select a Window type.
4.6.4 Measurement Channel and Window Function
Settings
Select with the F keys
Display the [Calc] page
Select [Analysis CH] or
[Window type]
What is a Window type?
Noise analysis is performed by applying FFT calculations to a specific interval of a waveform
defined by the specified number of points at the specified sampling rate. The processing of an
extracted interval of a waveform is called "Window processing." The FFT calculation of the
specified waveform interval is supposed to be repeated periodically.
On this instrument, the displayed waveform is shown with the defined window.
When the number of points specified for FFT calculation does not coincide with the measure-
ment waveform period, the edges of the waveform within the window become discontinuous
(called "leakage errors"), and non-existent noise is detected.
The Window type provide means of suppressing leakage errors by smoothly connecting the
edges of the waveforms.
Original Time Waveform
Supposed Waveform for FFT
Time Waveform
Set No. of Points
Set No. of PointsTime Waveform
CH1, CH2, CH3, CH4
Rectangular
This type of window function is effective when the measurement wave-
form period is an integer multiple of the FFT calculation interval.
Hann
This type of window function is effective when the rectangular window is
not, and when frequency resolution is the primary concern.
Flat-Top
This type of window function is effective when the rectangular window is
not, and when amplitude resolution is the primary concern.