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frest.createStep

Package: frest

Create step input signal

Description

A step input signal has an initial value of 0 and transitions to a specified step size value after a specified step time. When performing frequency response estimation, step inputs are quick to simulate and can be useful as a first try when you do not have much knowledge about the system you are trying to estimate. However, the amplitude of the excitation decreases rapidly with increasing frequency. Therefore, step signals are best used to identify low-order plants where the slowest poles are dominant. Step inputs are not recommended for estimation across a wide range of frequencies.

When you use a step input signal for estimation, the frequencies returned in the estimated frd model depend on the length and sampling time of the signal. They are the frequencies obtained in the fast Fourier transform of the input signal (see the Algorithm section of frestimate).

For more information on input signals for frequency response estimation, see Estimation Input Signals.

example

input = frest.createStep(Name,Value) creates a step input signal for frequency response estimation using options specified using one or more name-value pair arguments.

Examples

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Create a step input signal with a default sample time and the following properties:

  • Step time of 5 seconds

  • Step size of 0.1

  • Total duration of 15 seconds

input = frest.createStep('StepTime',5,'StepSize',0.1,'FinalTime',15)
  timeseries

  Common Properties:
            Name: 'Created with frest.createStep utility'
            Time: [15001x1 double]
        TimeInfo: tsdata.timemetadata
            Data: [15001x1 double]
        DataInfo: tsdata.datametadata

Plot the step signal.

plot(input)

Input Arguments

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Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'Ts',0.01 sets the input signal sample time to 0.01

Sample time of the input signal in seconds, specified as the comma-separated pair 'Ts', followed by a positive scalar.

Step time when the input signal transitions from 0 to StepSize, specified as the comma-separated pair 'StepTime' followed by a positive scalar.

StepTime must be less than FinalTime

Step size, specified as the comma-separated pair 'StepSize' followed by a nonzero scalar. The input signal has value StepSize after StepTime seconds.

Input signal duration in seconds, specified as the comma-separated pair 'FinalTime' followed by a positive scalar.

FinalTime must be greater than StepTime

Output Arguments

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Step input signal for frequency response estimation, returned as a timeseries object.

To view a plot of your input signal, type plot(input).

Introduced in R2009b