MR8740、MR8741_user_manual_eng_20191016H.pdf - 第274页

12.3 Setting FFT Analysis Conditio ns 262  Octave Filter Setting Filter features ar e based on JIS C1 513-2002 class 1, class 2 (IEC61260 ). After determ ining the entire power spectrum, the instrument performs octave a…

12.3 Setting FFT Analysis Conditions

261

Chapter 12 FFT Function

When [Parameter] setting contents are displayed

Set the parameter.

Move the flashing cursor to the

[Parameter] column of the Anal-

ysis No. to set.

Select

Select the channel for analysis.

Move the flashing cursor to the [Ch1] item.

Select which channel number to use. However, the channel of

MR8990 Digital Voltmeter Unit cannot be set.

Set the horizontal and vertical axes displaying the calcu-

lation results.

Move the flashing cursor to the

[X Axis] or [Y Axis].

Set the contents of the calculation results to be displayed on

the horizontal and vertical axes.

(Selectable display contents vary by analysis mode.)

See: "Analysis Modes and X/Y Axis Display" (p.262)

Y-axis display

X-axis display

Analyze Parameter Setting Contents

1/1 Octave,

1/3 Octave

Filter: Normal

nables the octave filter.

See: "Octave Filter Setting" (p.262)

Filter: Sharp

Phase Spectrum

1ch FFT Calculates the phase of [Ch1].

2ch FFT Calculates the phase difference between [Ch1] and

[Ch2].

LPC (dencity)

Order :2 to 64 Larger numerical values make finer spectrum compo-

nents visible.

Lin-Mag Analysis results are displayed as amplitude values.

Log-Mag Analysis results are displayed as dB values.

The dB reference is 1 eu. (As a voltage example, 1 V is

0 dB.)

Lin-Real The real-number component of analysis results are dis-

played.

Lin-Imag The imaginary component of analysis results are dis-

played.

Linear Frequency-axis is displayed linearly.

Log Frequency-axis is displayed logarithmically.

This is convenient when the data of interest is at the lower end

of the frequency range, such as for sound and vibration.

Analysis channel setting

For any of the following analysis modes,

set both channels 1 and 2.

Transfer Function, Impulse Response,

Cross-correlation Function, Cross Power

Spectrum, Coherence Function, Phase

Spectrum (2ch FFT)

To analyze using external sampling

The horizontal axis ( x-axis) displays the

number of data points.

How do I copy settings to other calculation No.?

See: "7.8 Copying settings to other channels (calculation No.) (Copy function)" (p.160)

12.3 Setting FFT Analysis Conditions

262

 Octave Filter Setting

Filter features are based on JIS C1513-2002 class 1, class 2 (IEC61260).

After determining the entire power spectrum, the instrument performs octave analysis defined by the

above filter characteristics.

See:"Octave Filter Characteristics" (p.A25)

 Analysis Modes and X/Y Axis Display

Normal

Filter characteristics approximate those

of an analog filter.

Sharp

Only those spectral component within the

octave band are used for analysis. Spec-

tral components outside of the octave

band are totally ignored.

: Settable, ×: Unsettable

Analysis Mode

X axis Y axis

Nyquist

display

Linear Log Lin-Mag Log-Mag Lin-Real Lin-Imag

OFF

×××××× ×

Storage Waveform



××× ×

Histogram



××× ×

Linear Spectrum

 

RMS Spectrum



Power Spectrum



×× ×

Power Spectrum Density



×× ×

LPC analysis (Power Spectrum

Density)



×× ×

Transfer Function

 

Cross Power Spectrum

 

Impulse Response



××× ×

Coherence Function



××× ×

Phase Spectrum



××× ×

Auto-correlation Function



××× ×

Cross-correlation Function



××× ×

1/1 Octave



×× ×

1/3 Octave



×× ×

The x/y axes cannot be set when Nyquist Display is selected.

12.3 Setting FFT Analysis Conditions

263

Chapter 12 FFT Function

 Total harmonic distortion (THD)

When the analysis mode is one of the following, the cursor appears and the distortion rate is calculated.

(Linear spectrum, RMS spectrum, power spectrum)

The distortion rate calculates the cursor position as the fundamental wave. When 2 cursors appear, the A

cursor becomes the fundamental wave.

When calculation results cannot be obtained, [---%] is displayed.

Note that distortion rate values may become higher depending on the window function settings.

THD

 f



---------------

100=

=fundamental wave

= n next higher harmonic

[%]