Smoothing a roughly sinusoidal signal

[llrjt100]

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:
<https://octave.1599824.n4.nabble.com/file/t373550/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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