MR8740、MR8741_user_manual_eng_20191016H.pdf - 第263页

12.3 Setting FFT Analysis Conditio ns 251 11 Chapter 12 FFT Function 12 About the frequency range a nd number of analysis point s ___________________ • The settings for the frequency r ange and number of ana lysis points…

12.3 Setting FFT Analysis Conditions

250

Select the data to be used for FFT analysis.

There are two analysis methods: analysis using new measurements and analysis of data measured

using the memory function.

12.3.2 Selecting the Data Source for Analysis

Select the input data source.

Move the flashing cursor to the

[Reference] item.

Select

When finished making settings, click [START].

For the [New Data] case

Measurement starts to acquire data for the number of analysis points

specified as the [Sampling Point], and FFT analysis is performed.

For the [From Memory] case

Analysis is performed on the number of specified points from data

previously recorded in memory (Memory function data) .

The analysis starting point can also be specified.

See: "12.7.1 Analyzing after Specifying an Analysis Starting Point" (p.273)

The frequency range is selected automatically.

See: "Relationship Between Frequency Range, Resolution and Number of

Analysis Points" (p.252)

New Data Acquire a new waveform for analysis.

From Memory

Calculates data measured using the memory function.

Procedure

To open the screen: Right-click and select [STATUS]  [Status] sheet

See: To set from the Waveform screen (p.265)

When the input data [Reference] is

[From Memory]

Analysis is performed until the specified

number of FFT analysis points have been

processed, then the data is shifted by that

amount and analysis repeats until all of the

previously acquired data has been pro-

cessed. (If the amount of data is less than

the specified number of FFT analysis

points, no analysis occurs.)

When no trace is displayed after start-

ing measurement

Analysis is impossible if [From Memory]

is selected as the input data source and

no recorded data exists in the instrument's

memory.

Either select [New Data] as the input data

source, or load the data to be analyzed

before clicking [START] again.

When the [Reference] is set to [From Memory], the frequency is automatically

set.

The setting cannot be changed.

12.3 Setting FFT Analysis Conditions

251

Chapter 12 FFT Function

About the frequency range and number of analysis points ___________________

• The settings for the frequency range and number of analysis points determine

the input signal acquisition time and frequency resolution.

• The frequency range setting for the FFT function corresponds to the timebase

setting of the Memory function. Changing the frequency range also changes

the data sampling period.

See: "Relationship Between Frequency Range, Resolution and Number of Analysis

Points" (p.252)

• The cut-off frequency of the anti-aliasing filter is the same as the frequency

range setting.

See: "Relationship Between Frequency Range, Resolution and Number of Analysis

Points" (p.252)

• The set number of analysis points specifies the amount of data to be analyzed

with each measurement. Increasing the number of analysis points increases

the frequency resolution, but also increases the time required for calculations.

See: "Number of Analysis Points" (p.A15)

12.3.3 Setting the Frequency Range and Number of

Analysis Points

When the [Reference] is [From Memory], the frequency is automatically

set.

The setting cannot be changed.

To control sampling by an external signal,

select [External]

When the input data [Reference] is

[From Memory]

The frequency range is set automatically

when analysis is started.

Set the number of FFT analysis points.

Move the flashing cursor to the [Sampling Point] item.

Select

See: "Number of Analysis Points" (p.A15)

Select the frequency range.

Move the flashing cursor to the [Frequency Range] item.

Select

See: "Relationship Between Frequency Range, Resolution and Number of

Analysis Points" (p.252)

1000 (default setting), 2000, 5000, 10000

8 MHz(default setting), 4 MHz, 2 MHz, 800 kHz, 400 kHz, 200 kHz, 80

kHz, 40 kHz, 20 kHz, 8 kHz, 4 kHz , 2 kHz, 800 Hz, 400 Hz, 200 Hz, 80

Hz, 40 Hz, 20 Hz, 8 Hz, 4 Hz, 1.33 Hz, 800 mHz, 667 mHz, 400 mHz, 333

mHz, 133 mHz, External

Procedure

To open the screen: Right-click and select [STATUS]  [Status] sheet

See: To set from the Waveform screen (p.265)

Frequency Resolution

(during acquisition)

The resolution is affected by settings of

frequency range and the number of

analysis points. Not displayed for exter-

nal sampling.

12.3 Setting FFT Analysis Conditions

252

Relationship Between Frequency Range, Resolution and Number of

Analysis Points

Range

[Hz]

Sampling

frequency

[Hz]

Timebase

[/div]

(MEM)

Sampling

period

Number of FFT Analysis Points

1,000 2,000 5,000 10,000

Resolu-

tion [Hz]

Acquisi-

tion

interval

Resolu-

tion [Hz]

Acquisi-

tion

interval

Resolu-

tion [Hz]

Acquisi-

tion

interval

Resolu-

tion [Hz]

Acquisi-

tion

interval

8 M *

20 M 5 s 50 ns 20 k 50 s 10 k 100 s 4 k 250 s 2 k 500 s

4 M *

10 M 10 s 100 ns 10 k 100 s5 k200 s 2 k 500 s1 k1 ms

2 M *

5 M 20 s 200 ns 5 k 200 s 2.5 k 400 s 1 k 1 ms 500 2 ms

800 k *

2 M 50 s 500 ns 2 k 500 s 1 k 1 ms 400 2.5 ms 200 5 ms

400 k *

1 M 100 s1 s 1 k 1 ms 500 2 ms 200 5 ms 100 10 ms

200 k *

500 k 200 s2 s 500 2 ms 250 4 ms 100 10 ms 50 20 ms

80 k *

200 k 500 s5 s 200 5 ms 100 10 ms 40 25 ms 20 50 ms

40 k

100 k 1 ms 10

s 100 10 ms 50 20 ms 20 50 ms 10 100 ms

20 k

50 k 2 ms 20

s 50 20 ms 25 50 ms 10 100 ms 5 200 ms

8 k

20 k 5 ms 50

s 20 50 ms 10 100 ms 4 250 ms 2 500 ms

4 k

10 k 10 ms 100

s 10 100 ms 5 200 ms 2 500 ms 1 1 s

2 k

5 k 20 ms 200 s 5 200 ms 2.5 400 ms 1 250 ms 500 m 2 s

800

2 k 50 ms 500 s 2 500 ms 1 1 s 400 m 2.5 s 200 m 5 s

400

1 k 100 ms 1 ms 1 1 s 500 m 2 s 200 m 5 s 100 m 10 s

200

500 200 ms 2 ms 500 m 2 s 250 m 4 s 100 m 10 s 50 m 20 s

200 500 ms 5 ms 200 m 5 s 100 m 10 s 40 m 25 s 20 m 50 s

100 1 s 10 ms 100 m 10 s 50 m 20 s 20 m 50 s 10 m 100 s

50 2 s 20 ms 50 m 20 s 25 m 40 s 10 m 100 s 5 m 200 s

8 *

20 5 s 50 ms 20 m 50 s 10 m 100 s 4 m 250 s 2 m 500s

4 *

10 10 s 100 ms 10 m 100 s 5 m 200s 2 m 500 s 1 m 1 ks

1.33 *

3.33 30 s 300 ms 3.33 m 300 s 1.66 m 600s 666  1.5 ks 333  3 ks

800 m *

2 50 s 500 ms 2 m 500 s 1 m 1 ks 400  2.5 ks 200  5 ks

667 m *

1.67 60 s 600 ms 1.66 m 600 s 833  1.2 ks 333  3 ks 166  6 ks

400 m *

1 100 s 1 s 1 m 1 ks 500  2 ks 200  5 ks 100  10 ks

333 m *

833 m 120 s 1.2 s 833  1.2 ks 416  2.4 ks 166  6 ks 83.3  12 ks

133 m *

333 m 300 s 3 s 333  3 ks 166  6 ks 66.6  15 ks 33.3  30 ks

The cut-off frequency of the anti-aliasing filter is the same as the frequency range.

*1. The anti-aliasing filter is turned off.

*2. Cut-off frequency is 20 Hz.