I have a problem in performing a loop calculation

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ABDALLA AL KHALEDI 2023-9-22

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评论： Star Strider 2023-9-24

I have this code which reads data from several excel files and extracts them into an array and performs a calculation on them then presents the results in a table, the problem now is that I need this calculation to be performed for for every 2000 data points (from 0.005 to 10 sec, note that the time vector in the excel file is from 0.005 to 81.92 with a step of 0.005). However, from my basic understanding, MATLAB uses double precision and there is a floating point so maybe using machine eps is a good approach instead of logical statements, the issue is that I have multiple files and I need the code to loop through each file and perform the below calculation plus and extra interval-by-interval calculation (the same calculation but for each interval instead of the total set of data) and store the results for the total and the intervals then presnt them in a table (so loop the files, then loop the vectors in the array to establish the intervals). I have had some AI sugeestions but I was not abble to determine how correct were they. Help is appreciated. I attached 3 data files for reference but I have like 400 files.

%Prompt the user to select a folder
folder_path = uigetdir('', 'Select the folder');
%Get a list of files in the folder
file_list = dir(fullfile(folder_path, '*.xlsx'));
%Initialize the output table
output_table = {};
%Loop through each file
for i = 1:numel(file_list)
    % Get the file name
    file_name = file_list(i).name;
    
    %Total Torque RMS Calculation
    
    %Load the data
    tq = readmatrix(fullfile(folder_path, file_name));
    %TRUE if values change (down to machine eps)
    d = [true; diff(tq(:, 2)) ~= 0];
    %Torque values at change points
    TQ = tq(d, 2);
    %Location of changes in logical vector
    ix = find([d(:); true]);
    %Difference in locations (number of occurrences)
    N = diff(ix);
    %Calculating the torque rms by groups weighted by time
    %Removing roundoff in dt calculation to get the overall dt
    dt = mean(diff(tq(:, 1)));
    %Total Time
    t_tot = dt * (size(tq, 1));
    %Calculate the total tq_rms
    tq_rms = sqrt(sum(TQ.^2 .* (N - 1) * dt) / t_tot);
    newRow = {tq_rms};
    %Add the newRow to the output_table
    output_table = [output_table; newRow];
    
end
column_name = {'TQ_RMS'};
%Convert the output table to a table
output_table = cell2table(output_table, 'VariableNames', column_name);
%Display the results table
disp(output_table);

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Answer 1

Star Strider 2023-9-22

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I cannot understand exactly what you want to do or what the logic vector ‘d’ does. If you simply want to get the RMS value of the torque signal every 10 seconds, that is actually straightforward.

Try this —

% Files = dir(pwd)

Files = dir('*.xlsx');

Files.name

ans = 'H5T06Z010RPM.xlsx'

ans = 'H5T06Z020RPM.xlsx'

ans = 'H5T06Z510RPM.xlsx'

for k = 1:numel(Files)

T1 = readtable(Files(k).name, 'VariableNamingRule','preserve');

VN = T1.Properties.VariableNames;

t = T1{:,1};

t_bfr = buffer(t, 2000);

tq = T1{:,2};

tq_bfr = buffer(tq, 2000);

tq_rms = rms(tq_bfr);

figure

yyaxis left

plot(T1{:,1}, T1{:,2})

hold on

plot(t_bfr, (ones(2000,1)*tq_rms))

hold off

ylabel(VN{2})

yyaxis right

plot(T1{:,1}, T1{:,end})

ylabel(VN{3})

grid

xlabel(VN{1})

xlim([min(t) max(t)])

title(Files(k).name)

timeseg = [t_bfr(1,:); t_bfr(end,:)].';

DisplayTable = table(timeseg(:,1), timeseg(:,2), tq_rms(:), 'VariableNames',{'Start Time','End Time','Torque RMS'})

Results{k,:} = DisplayTable;

end

DisplayTable = 9×3 table

Start Time End Time Torque RMS ___________ ________ __________ 0.005 10 0.36623 10.005 20 0.41522 20.005 30 0.38779 30.005 40 0.38848 40.005 50 0.41168 50.005 60 0.38471 60.005 70 0.38019 70.005 80 0.41781 80.005 0 0.14823

DisplayTable = 9×3 table

Start Time End Time Torque RMS ___________ ________ __________ 0.005 10 0.51982 10.005 20 0.47605 20.005 30 0.5089 30.005 40 0.48032 40.005 50 0.50803 50.005 60 0.51684 60.005 70 0.5473 70.005 80 0.48055 80.005 0 0.25016

DisplayTable = 9×3 table

Start Time End Time Torque RMS ___________ ________ __________ 0.005 10 0.2419 10.005 20 0.3432 20.005 30 0.32467 30.005 40 0.30427 40.005 50 0.32322 50.005 60 0.32414 60.005 70 0.27453 70.005 80 0.265 80.005 0 0.11693

.

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Star Strider 2023-9-23

I do not understand what you are doing, and the code does not really enlighten me in that respect. I do not see anything that could be considered a ‘change point’ in the torque values. They are quite noisy (with what I expect would be a low signal-to-noise ratio were we to calculate it) that appears to be due to the relatively low resolution of the ADC with a signal of quite small amplitude.

With respect to RMS, it is calculated as the square root of the mean of the square of the signal in a given segment of the signal or the entire signal, depending on what is desired. In my code, I use the Signal Processing Toolbox buffer function to divide the torque signal up into columns of 2000 samples (10 seconds) each, and then take the RMS value of each segment. I believe that this is what you want to do, and this way is significantly more efficient. (I did the same buffer operation with the time vector, both to plot the RMS values of the signal and to create the start and end times for tthe ‘Results’ table.)

The torque vectors are plotted in blue in these plots, with the RMS value being the interrupted blue line near the top of each plot, referenced to the left yyaxis. (The plot algorithm chooses the line style for each segment.)

ABDALLA AL KHALEDI 2023-9-24

编辑：ABDALLA AL KHALEDI 2023-9-24

@Star Strider thank you for your input, don't worry about the data. I am trying to improve and your input was helpful.

Star Strider 2023-9-24

As always, my pleasure!

Thank you!

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