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Smoothing a roughly sinusoidal signal

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Richard Taylor
Richard Taylor on 7 Nov 2019
Commented: Richard Taylor on 10 Nov 2019
Hi,
I have position data coming from a high resolution angular position sensor and I need to improve the accuracy of the data by removing a regular sinusoid from it.
The below graph shows three plots of angular position error against time:
MatLab Forum.JPG
  1. The brown plot is the position error which needs to be corrected (ideal is a zero error horizontal line).
  2. The blue plot is the position error of a very high accuracy reference angular position sensor (for testing only and not present in the deployed application).
  3. The green plot is the difference between the brown and blue plots.
Common to both the brown and blue plot is a fast in phase ~2 sec error which can be ignored.
In the brown plot there's a ~24 sec error which I need to remove (the green difference plot more clearly shows this as it removes the faster ~2 sec error). The solution algorithm eventually needs to be deployed to run in realtime on a 32 bit microcontroller.
The dataset is in .csv format which I can post for analysis.
I've Googled various examples which lead me to believe a solution to this problem should be possible. The issue is I don't have sufficient signal processing experience to know how to implement a solution and would be very grateful for any help in solving this problem.
Best wishes,
Richard

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Answers (1)

Daniel M
Daniel M on 8 Nov 2019
So are you saying you want to remove the frequency of the blue signal from the brown signal? Fairly easy, just use a notch/bandstop filter. You can find examples on these pages

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Richard Taylor
Richard Taylor on 9 Nov 2019
It's real-time - I guess I should have mentioned that earlier!
Daniel M
Daniel M on 9 Nov 2019
Are you using the DSP System toolbox? They have real time filters that you can do on individual samples at a time. But you'll have to look more into it, because I'm not too familiar.
Richard Taylor
Richard Taylor on 10 Nov 2019
I think I installed the DSP System Toolbox, but I've got no idea what I need to use, and how to use it. I'm hoping someone can point me in the right direction, then I can get productively stuck into the task.

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