# How to measure the steady state amplitude of a control system output

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Michael Sohnen il 7 Mar 2021
Commentato: Michael Sohnen il 9 Mar 2021
Hello. I have included below an image concerning my problem
Here I have a sinusoidal weaveform that has an initial transient then settles to a steady state amplitude. It looks odd ebcause the plot is so dense, but the data is all sinsoidal with a transient offset. The data is represented as an array of time points and an array of ampltiude points. (tout and Y). How can I write an algorithm to detect when the transient is complete and return the final steady state amplitude? Technically, this is not only a MATLAB question, but a solution written in MATLAB code is preffered.
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Pat Gipper il 8 Mar 2021
The frequency of the injected signal is under control of the app. If that is not the case then you would need to use some form of a spectrum analyzer.
Michael Sohnen il 9 Mar 2021
@Paul Dear Paul, thank you for your comment. Thank you to other commenters as well. I need to be able to analyuze the data WITHOUT ACCESS TO THE INPUT SIGNAL, and WITHOUT ACCESS TO THE SIMULINK MODEL. I need to find a statistical approach. I am basically looking for an algorithm that can seperate the transient from the steady state component in ANY signal, knowing that the steady state is some sinusoid of a singe frequency.
I basically want to high pass filter my signal, then measure the amplitude using (max(data)-min(data))/2. How can I do a high pass filter on a signal in MATLAB given only data?

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### Risposta accettata

Michael Sohnen il 9 Mar 2021
I figured it out. If you have some idea of what frequencies will be present in the signal, just use the highpass command. In my problem, I know the exact sampling rate, so it works. I highpass the data with a lower cutoff of 1 hertz and then measure the amplitude using max and min.
Thanks all.
Best,
Mike
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Paul il 9 Mar 2021
If your system is "far from LTI" then there is no guarantee, in general, that the steady state output is a single sinusoid. So you have to have some idea about what's going on inside the system and what the output should be.
Good luck. Go Panthers!
Michael Sohnen il 9 Mar 2021
Good luck to you too!

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### Più risposte (1)

Pat Gipper il 8 Mar 2021
Try using this app. It injects a sine wave and measures the gain and phase after a number of cycles that you specify.
https://www.mathworks.com/matlabcentral/fileexchange/85448-frequency-response-analyzer
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Michael Sohnen il 8 Mar 2021
I was looking for something that worked exclusively on the output data, in the time domain.

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