.Modelica_Requirements.ChecksInFixedWindow_withFFT.WithinRelativeDomain

Information

Syntax

property = WithinRelativeFFTdomain(condition=..., u=..., f_max=..., f_resolution=..., f_base=...., maxAmplitude=...).y;

Description

Whenever the Boolean input condition has a rising edge, the Real input u is sampled and stored in a buffer. Once enough values of u are stored in the buffer (depending on parameters f_max and f_resolution) a Fast Fourier Transform (FFT) of the buffer u-values is computed. The amplitudes and frequencies of the computed FFT are stored on file and displayed in the icon. The amplitudes must be below the polygon defined by parameter maxAmplitude (maxAmplitude[fi,Ai] defines the maximum amplitude Ai in [% of amplitude at base frequency] at frequency point fi in [Hz]. fi ≥ 0 required). The amplitude of the base frequency is defined to be the largest amplitude of the computed FFT around the frequency:

   f_base - df ≤ f ≤ f_base + df

and the frequency difference df is computed from the advanced parameter searchInterfal (default = 5 %) as:

   df = f_base*searchInterval/100

The check is performed in the range: 0 ≤ f ≤ min(f_max, maxAmplitude[end,1]) and the maxAmplitude values are linearly interpolated for this check.

For more details, see the description of package ChecksInFixedWindow_withFFT.

Example

This block is demonstrated with the following first example:

The amplitutes of the FFT are dynamically displayed in the icon of the block (in black), as well as the maximume amplitudes maxAmplitude (in red). The computed amplitude of the base frequency is shown in green (so this amplitude is 100 %)

Simulating this examples results in

	simulation result

As can be seen, the simulation is terminate (via instance terminate1 of block FallingEdgeTerminate) once the FFT has been computed (signaled via the falling edge of FFT_computation). Since all FFT amplitudes between 0 ≤ f ≤ min(f_max, maxAmplitude[end,1]) are below the maximally allowed limit, the block returns Property.Satisfied.

A plot of the FFT result file is shown in the next figure:

This block can be also used to compute several FFTs along a simulation as demonstrated with the following second example:

The amplitutes of the FFT are dynamically displayed in the icon of the block (in black), as well as the maximume amplitudes maxAmplitude (in red). At the end of the simulation, one of the amplitudes is larger as allowed:

Simulating this examples results in

	simulation result

As can be seen, the first FFT fulfills the check (scaledDistance = 0), whereas the second FFT has amplitudes that are larger as allowed (scaledDistance = -0.1).

Revisions