Performing FFT from three different Excel input data

Hi I have 3 different excel sheets i am reading data from and trying to perform FFT. the first colum in each file has time data, while the second colum has voltage data. I am able to perform FFT with one excel file, however i am stuck reading from three different files.

If anyone can help I would really apreciate it. I have attached test data files and code I am currently using here

%INITIALISATION
% % % % % % % % % % % % % % % % % % % % % % % % % % % %                                               
Ts = 0.00005;                                               % Sampling Interval (seconds)
Fs = 1/Ts;                                                  % Sampling Frequency (Hz)
Fn = Fs/2; 


path = genpath('C:\Users\Power User\Desktop\');  

x31 = csvread('test data1.csv',2);           %read data

x32 = csvread('test data1.csv', 2);

x33 = csvread('test data1.csv', 2);
       
Details =  (strsplit(path,'\'));                      %extract details for plot titles from path name
Details = char(Details(2));


    Signal = {x31;x32;x33};                      %Load all SC current signals into cell array
    
    
%PLOT TIME SERIES DATA
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
figure
plot(t, v);                                                 % plot time domain signal
grid
xlabel('Time')
ylabel('Voltage')
                                                 % Nyquist Frequency (Hz) half of the sampling rate of a discrete signal processing system

%PERFOM FFT
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
N = length(Signal);
meanSignal = mean(Signal);                                  % ‘Signal’ Mean
FTSignal = fft(Signal-meanSignal)/N;                        % Normalised Fourier Transform Of Baseline-Corrected ‘Signal’.
                                                            
                                                            
                                                            
                                                            
Fv = linspace(0, 1, fix(numel(FTSignal)/2)+1)*Fn;           % Frequency Vector
Iv = 1:numel(Fv);                                           % Index Vector
% % % % % % % % % % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%Plotting FFT
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
[pks,locs] = findpeaks(abs(FTSignal(Iv))*2, 'MinPeakHeight',0.044);
figure
plot(Fv, abs(FTSignal(Iv))*2)
grid
xlabel('Frequency(Hz)')
ylabel('Amplitude')
plotIdx = 1:Iv(max(locs));
figure
plot(Fv(plotIdx), abs(FTSignal(Iv(plotIdx)))*2)
hold on
plot(Fv(plotIdx(locs)), pks, '^r', 'MarkerFaceColor','r')
title('FFT for Power Analysis')
xlabel('Frequency (Hz)')
ylabel('Amplitude')
xlswrite('myfile.xls',Fv')
xlswrite('myfile2.xls',abs(FTSignal(Iv))*2')
hold off

Answer 1

[Geoff Hayes]

Jmv - if you just want to perform the FFT on each file, then wouldn't your code look something more like

%INITIALISATION
% % % % % % % % % % % % % % % % % % % % % % % % % % % %                                               
Ts = 0.00005;                                               % Sampling Interval (seconds)
Fs = 1/Ts;                                                  % Sampling Frequency (Hz)
Fn = Fs/2; 
path = genpath('C:\Users\Power User\Desktop\');  
x31 = csvread('test data1.csv',2);           %read data
x32 = csvread('test data1.csv', 2);
x33 = csvread('test data1.csv', 2);
       
Details =  (strsplit(path,'\'));                      %extract details for plot titles from path name
Details = char(Details(2));
Signal = {x31;x32;x33};

for k = 1:length(Signal)            % <------- iterate over each file
    %PERFROM FFT
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    N = length(Signal{k}(:,2));
    meanSignal = mean(Signal{k}(:,2));                                % kSignal(:,2) Mean
    FTSignal = fft(Signal{k}(:,2) - meanSignal)/N;                     % Normalised Fourier Transform Of Baseline-Corrected {Signalk.
    % etc.
end

The above code iterates over each dataset stored in Signal. On each iteration, we consider the dataset at Signal{k}.

[Jmv]

Hi Goff. Thanks very much for help with this. Yes what i am trying to do is perform FFT on each file. I added the iteration part of the code however I am not getting the right FFT plot. the below plot is what I should be getting. i intentionally used test data1.csv file only for the three signal to check if I would get the below plot.

i Don't know where I am going wrong as I am not getting any error when i implement the code in your comment above.

Thanks for any more help you can provide.

[Geoff Hayes]

Jmv - I don't know enough about your data to understand what may be going wrong. Why do you subtract the mean?

[Jmv]

Hi Geoff. Thanks again. I substracted mean to remove DC Component.