signal processing of real time signal

i m doing signal processing of real time signal i have written code for it but i dont known weather it is correct or not ? i had velocity data and i coverted that into the displacement.please check.

clc;
clear;
close all;
%%Time Domain Plot
vib1=readtimetable("sing2.txt","SampleRate",1);
tiledlayout(4,1)
nexttile
plot(vib1.Time,vib1.Sing1)
L=length(vib1.Sing1);
N= 2^nextpow2(L);
xlabel("Time(s)")
ylabel("Ampl(mm/s^2)")
%%Envolop analysis
nexttile
yh=hilbert(vib1.Sing1,N);
yz=abs(yh);
plot(vib1.Time,yz)
% % FFt
fs=1;%Sampling Frequency
delt=seconds(1/fs); %time step
Totaltime=(length(yz)-1);
my_fft=2/N*(fft(yz));%FFT of Signal normaization
abs_fft=abs(my_fft); %Absolute value of fft
delf=1/Totaltime; %Frequency Resolution
n2=0:1:N/2-1; %fft results are plotted for N/2 data points
fk=delf*n2;% frequency values
abs_fft(1:N/2);
nexttile
plot(fk,abs_fft(1:N/2))
[v,p]=findpeaks(abs_fft(1:N/2),fk,'MinPeakHeight',0.01);
findpeaks(abs_fft(1:N/2),fk,'MinPeakHeight',0.01)
xlabel("Frequency (Hz)")
ylabel("Ampl(mm/s^2)")
% Spectral density
nexttile
pspectrum(yz,vib1.Time,"spectrogram","FrequencyLimits",[.1005 .2976])

[Mathieu NOE]

hello

your code does envelope and fft analysis but there is nothing related to conversion from velocity to displacement conversion. Did you mean to do it in the frequency domain and in the time domain ? (fyi, use cumtrapz for that)

[GOURANG UPADHYAY]

i have done that also but in diffrent code.

so yes i have converted my data into displacement.but i just want to know approch is correct or not

Answer 1

[Mathieu NOE]

hello again !!

FYI this is simple code for time domain acceleration to velocity / displacement integration (data file attached)

in your case you would only need one (and not two) stage of integration.

be smart and use the FFT spectrum of the input data to fine tune the high pass filter (if needed ! it can be useful for dynamic signals where we need to keep all signals zero mean - even after integration; if this does not apply to your case then remove the detrend and the high pass filter and keep only the integration with cumtrapz)

clc
clearvars
data = readmatrix('Earthquake.xlsx');
t = data(:,1);
dt = mean(diff(t));       % Average dt
fs = 1/dt;                  % sampling rate

% Acceleration data
acc = data(:,2)*9.81;         % Add gravity factor ( g to m/s²)
acc = detrend(acc);     % baseline correction

% some additionnal high pass filtering     % baseline correction
N = 2;
fc = 0.25; % Hz
[B,A] = butter(N,2*fc/fs,'high');
acc = filter(B,A,acc);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
velocity = cumtrapz(dt,acc);
velocity = detrend(velocity);    % baseline correction

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
disp     = cumtrapz(dt,velocity);
disp = detrend(disp);    % baseline correction

%
figure(1)
subplot(311),plot(t,acc);
title('accel'); ylabel('m/s²');xlabel('time (s)');
subplot(312),plot(t,velocity);
title('velocity'); ylabel('m/s');xlabel('time (s)');
subplot(313),plot(t,disp);
title('disp'); ylabel('m');xlabel('time (s)');


%%fft
nfft = length(acc);
fft_spectrum = abs(fft(disp,nfft));

% one sidded fft spectrum  % Select first half 
    if rem(nfft,2)    % nfft odd
        select = (1:(nfft+1)/2)';
    else
        select = (1:nfft/2+1)';
    end
fft_spectrum = fft_spectrum(select,:);
freq_vector = (select - 1)*fs/nfft;

figure(2)
plot(freq_vector,fft_spectrum);
title('disp'); ylabel('m');xlabel('Frequency (Hz)');

xlim([0 10]);

[GOURANG UPADHYAY]

check this

clc;
clear;
close all;
%%Time Domain Plot
vib1=readtimetable("Final_cant.csv","SampleRate",1);
tiledlayout(4,1)
nexttile
plot(vib1.Time,vib1.Signal2)
L=length(vib1.Signal2);
N= 2^nextpow2(L);
xlabel("Time(s)")
ylabel("Ampl(mm/s)")
title("Velocity Time domain analysis")
A=readmatrix("Final_cant.csv");
x=A(:,1);
y=A(:,2);
z=cumtrapz(x,y);
nexttile
plot(A(:,1),z)
xlabel("Time(s)")
ylabel("Ampl(mm)")
title("Displacment Time domain analysis")
fs=1;%Sampling Frequency
delt=seconds(1/fs); %time step
Totaltime=(length(x)-1);
my_fft=2/N*(fft(z));%FFT of Signal
abs_fft=abs(my_fft); %Absolute value of fft
delf=1/Totaltime; %Frequency Resolution
n2=0:1:N/2-1; %fft results are plotted for N/2 data points
fk=delf*n2;% frequency values
abs_fft(1:N/2);
nexttile
plot(fk,abs_fft(1:N/2))
[v,p]=findpeaks(abs_fft(1:N/2),fk,'MinPeakHeight',0.01);
findpeaks(abs_fft(1:N/2),fk,'MinPeakHeight',0.01)
xlabel("Frequency (Hz)")
ylabel("Ampl(mm)")
title('Frequency domain analysis')

[Mathieu NOE]

file "Final_cant.csv" is missing

use the paperclip button

[GOURANG UPADHYAY]

now attached

[Mathieu NOE]

Code is correct - I just "cleaned" it up a bit as you were loading the data file twice

clc;
clearvars;
close all;
%%Time Domain Plot
A=readmatrix("Final_cant.csv");
x=A(:,1);
y=A(:,2);
tiledlayout(3,1)
nexttile
plot(x,y)
L=length(x);
N= 2^nextpow2(L);
xlabel("Time(s)")
ylabel("Ampl(mm/s)")
title("Velocity Time domain analysis")
z=cumtrapz(x,y);
nexttile
plot(x,z)
xlabel("Time(s)")
ylabel("Ampl(mm)")
title("Displacment Time domain analysis")
fs=1;%Sampling Frequency
delt=seconds(1/fs); %time step
Totaltime=(length(x)-1);
my_fft=2/N*(fft(z));%FFT of Signal
abs_fft=abs(my_fft); %Absolute value of fft
delf=1/Totaltime; %Frequency Resolution
n2=0:1:N/2-1; %fft results are plotted for N/2 data points
fk=delf*n2;% frequency values
abs_fft(1:N/2);
nexttile
plot(fk,abs_fft(1:N/2))
[v,p]=findpeaks(abs_fft(1:N/2),fk,'MinPeakHeight',0.01);
findpeaks(abs_fft(1:N/2),fk,'MinPeakHeight',0.01)
xlabel("Frequency (Hz)")
ylabel("Ampl(mm)")
title('Frequency domain analysis')

[GOURANG UPADHYAY]

Thanks.i have one doubt in fft like how to decide number of data point in fft for good analysis?

[Mathieu NOE]

hello again

what do you mean by "good analysis" ? what are your expectations ?

there are plenty of tutorials / publications available on the internet regarding fft

[GOURANG UPADHYAY]

i am looking for demodulation of signal by using hilbert hung transform.

thanks for your reply.

[Mathieu NOE]

My pleasure !