WOLFRAM SYSTEMMODELER

RealFFT

Sampling and FFT of input u

Wolfram Language

In[1]:=
SystemModel["Modelica.Blocks.Math.RealFFT"]
Out[1]:=

Information

This information is part of the Modelica Standard Library maintained by the Modelica Association.

This block samples the input signal, calculates the Fast Fourier Transform by function Math.realFFT, and (when simulation terminates) writes the output to result file resultFileName by function Math.realFFTwriteToFile.

The number of sampling points as well as the samplePeriod is calculated from desired maximum frequency f_max and frequency resolution f_res.

Note

The user has to take care that enough points can be sampled before the simulation ends: startTime + (ns - 1)*samplePeriod <= stopTime.

The result file is written as mat, first column = frequency, second column = amplitudes, third column = phases. The frequency points are separated by rows with amplitude and phase = 0, so one can plot the result directly as frequency lines.

Parameters (7)

samplePeriod

Value: 1 / (2 * f_res * div(ns, 2))

Type: Time (s)

Description: Sample period of component

startTime

Value: 0

Type: Time (s)

Description: First sample time instant

f_max

Value:

Type: Frequency (Hz)

Description: Maximum frequency of interest

f_res

Value:

Type: Frequency (Hz)

Description: Frequency resolution

ns

Value: Modelica.Math.FastFourierTransform.realFFTsamplePoints(f_max, f_res, f_max_factor = 5)

Type: Integer

Description: Number of samples

nf

Value: max(1, min(integer(ceil(f_max / f_res)) + 1, div(ns, 2)))

Type: Integer

Description: Number of frequency points

resultFileName

Value: "realFFT.mat"

Type: String

Description: Result file: f, abs, arg

Outputs (3)

sampleTrigger

Type: Boolean

Description: True, if sample time instant

firstTrigger

Type: Boolean

Description: Rising edge signals first sample instant

info

Type: Integer

Description: Information flag from FFT computation

Connectors (1)

u

Type: RealInput

Used in Examples (2)

Rectifier6pulseFFT

Modelica.Blocks.Examples

Example of FFT block

Rectifier12pulseFFT

Modelica.Blocks.Examples

Example of FFT block