How do I find Peaks in Plotted data?

I have plotted some data for a simply damped object which has been displaced and is allowed to oscillate freely. The data plotted shows a sinusoidal behaviour.

I would like to find the peaks and have tried all of the recommended codes on Mathworks.

I have used [pks,locs]=findpeaks[Time, Displacement] I have also tried this in various different ways but have had no joy.

Hope you can help !

filename='Test_Results_19.xls'
ColumnA= xlsread(filename,'A2:A2088')
ColumnB= xlsread(filename,'B2:B2088')
B=ColumnB
A=ColumnA

%%Logarithmic Decrement Method
Time=ColumnA
Displacement=ColumnB
plot(Time,Displacement,'g'),grid on
findpeaks(Time,Displacement)
<</matlabcentral/answers/uploaded_files/93569/peaks.JPG>>

Answer 1

[Star Strider]

Using findpeaks is the correct approach. You need to reverse the arguments to get the result you want.

Try this:

[PkAmp, PkTime] = findpeaks(Displacement,Time);

The peak amplitudes are in the ‘PkAmp’ vector, and the corresponding times in the ‘PkTime’ vector.

[Serena Solanki]

Thank you for your suggestion. I have tried running the code you have given, it worked however, it does not identify the actual peaks or produce any other information apart from the graph.

Have I missed something?

%%Logarithmic Decrement Method
Time=ColumnA
Displacement=ColumnB
plot(Time,Displacement,'g'),grid on
[PKAmp,PKTime]=findpeaks(Displacement,Time);

[Star Strider]

My pleasure.

The order of the statements are important.

Try this:

Time=ColumnA
Displacement=ColumnB
[PKAmp,PKTime]=findpeaks(Displacement,Time);

figure(1)
plot(Time,Displacement,'g')
hold on
plot(PkTime, PkAmp, '^r', 'MarkerFaceColor','r')
hold off
grid on

That should plot red upward-pointing triangles at every peak.

NOTE — Since I don’t have your data, this is UNTESTED CODE. It should work.

[Serena Solanki]

This has worked perfectly! Thank you very much !

[Star Strider]

As always, my pleasure!

If my Answer helped you solve your problem, please Accept it!