How to set Spectrogram parameters

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Théo 2023-5-9

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https://ww2.mathworks.cn/matlabcentral/answers/1960209-how-to-set-spectrogram-parameters

评论： Mathieu NOE 2023-5-11

Run 1.xlsx

在 MATLAB Online 中打开

Hello Everyone,

I would like to print the spectrogram of a curve, in order to observe variations. But I don't really understand how to set the parameters of the function "spectrogram" even with the Matlab help.

For now I have this :

But I can't observe any variation. Is it possible to obtain something more like that :

There is my code and the attached file to get all the datas :

clear all;
clc ;
close all;
Valeurs = xlsread('C:\Users\tlam\Desktop\Run 80.xlsx',"Data1");
Temps = Valeurs(:,1);
Accelero = Valeurs(:,2);
Moteur_rpm = Valeurs(:,3);
BV_rpm = Valeurs(:,4);
Delta = Moteur_rpm - BV_rpm;
M_temps = max(Temps);
Moteur_Hz = Moteur_rpm * 0.016667;
BV_Hz = BV_rpm * 0.016667 ;
Delta_Hz = Delta * 0.016667;
%%
 F = figure( 'Position', [50 50 1600 900]) ; % Visible 'off' pour ne pas afficher
    t = tiledlayout(3,3,'TileSpacing','Compact','Padding','Compact');
    title(t,"Spectro FULL ")
      % Mot_rpm(t) et BV_rpm(t) Run 1
    nexttile([1 2])
    plot(Temps,Moteur_rpm,'red',Temps,BV_rpm,'green')
    xlim ([0 M_temps])
    ylabel('Moteur & BV [rpm]')
    legend ('Moteur','Boite de Vitesse')
    grid on
    Fs = 50000; %Hz
    % Spectrogramme Run 1
    nexttile([2 1])
    spectrogram(Accelero,100,99,100,Fs,'yaxis','power')
    hold on 
    plot(Temps,Moteur_Hz,'r',Temps,BV_Hz,'g',Temps,Delta_Hz,'b')
    colormap('jet')
    % Delta(t) Run 1
    nexttile([1 2])
    plot(Temps,Delta,'blue')
    xlim ([0 M_temps])
    ylabel('Delta [rpm]')
    grid on
    
    % Accelero(t) Run 1
    nexttile([1 2])
    plot(Temps,Accelero,'magenta')
    xlabel('temps [s]')
    xlim ([0 M_temps])
    ylabel('acceleromètre [V]')
    grid on

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Mathieu NOE 2023-5-9

在 MATLAB Online 中打开

Hello

I played a bit with your code and data and tried to make a better spectrogram rendering

I added some high pass filetring on your accel data, otherwise the spectrogram has a very strong output at DC 'not very interesting !)

now you can play with NFFT and OVERLAP if you want to have different frequency and time resolution

also I noticed that inside your code you hardcoded Fs = 5000, whereas from the dat file it's 50 Hz, what is the correct value ?

I could not find any visual correlation between your accel spectrogram and the other signals (converted to Hz) but I wonder if it's correct to compare this way as it assumes that you are only looking at the first engine order (when you convert from RPM to Hz).

For an IC engine, the vibration are higher at multiple engine orders (2nd and above typically)

code a bit tweaked :

clear all;
clc ;
close all;
% Valeurs = xlsread('C:\Users\tlam\Desktop\Run 80.xlsx',"Data1");
Valeurs = xlsread('Run 1.xlsx',"Data1");
Temps = Valeurs(:,1);
dt = mean(diff(Temps));
Fs = 1/dt;
Accelero = Valeurs(:,2);
Moteur_rpm = Valeurs(:,3);
BV_rpm = Valeurs(:,4);
Delta = Moteur_rpm - BV_rpm;
M_temps = max(Temps);
Moteur_Hz = Moteur_rpm /60;
BV_Hz = BV_rpm /60 ;
Delta_Hz = Delta /60;
% high pass filtering of accel signal
f_high = 1; % Hz
order = 3
[b,a] = butter(3,2/Fs*f_high,'high');
Accelero_filtered = filtfilt(b,a,Accelero);
    
%%
%  F = figure( 'Position', [50 50 1600 900]) ; % Visible 'off' pour ne pas afficher
 F = figure() ; % Visible 'off' pour ne pas afficher
    t = tiledlayout(3,3,'TileSpacing','Compact','Padding','Compact');
    title(t,"Spectro FULL ")
      % Mot_rpm(t) et BV_rpm(t) Run 1
    nexttile([1 2])
    plot(Temps,Moteur_rpm,'red',Temps,BV_rpm,'green')
    xlim ([0 M_temps])
    ylabel('Moteur & BV [rpm]')
    legend ('Moteur','Boite de Vitesse')
    grid on
    %Fs = 50000; %Hz ???
    % Spectrogramme Run 1
    nexttile([2 1])
    NFFT =200;
    NOVERLAP = round(0.95*NFFT);
    spectrogram(Accelero_filtered,hanning(NFFT),NOVERLAP,NFFT,Fs,'yaxis','power','MinThreshold',-80)
    hold on 
    plot(Temps,Moteur_Hz,'r',Temps,BV_Hz,'g',Temps,Delta_Hz,'b')
    colormap('jet')
    % Delta(t) Run 1
    nexttile([1 2])
    plot(Temps,Delta,'blue')
    xlim ([0 M_temps])
    ylabel('Delta [rpm]')
    grid on
    
    % Accelero(t) Run 1
    nexttile([1 2])
    plot(Temps,Accelero,'magenta')
    xlabel('temps [s]')
    xlim ([0 M_temps])
    ylabel('acceleromètre [V]')
    grid on

Théo 2023-5-10

在 MATLAB Online 中打开

Run 80bis.xlsx

Yea sure :

clear all;
clc ;
close all;
Valeurs = xlsread('C:\Users\tlam\Desktop\Run 80bis.xlsx',"Data1");
Temps = Valeurs(:,1);
Accelero = Valeurs(:,2);
Moteur_rpm = Valeurs(:,3);
BV_rpm = Valeurs(:,4);
Delta = Moteur_rpm - BV_rpm;
M_temps = max(Temps);
Moteur_Hz = Moteur_rpm /60;
BV_Hz = BV_rpm /60 ;
Delta_Hz = Delta /60;
dt = mean(diff(Temps));
Fs = 1/dt; %Hz
% high pass filtering of accel signal
f_high = 1000; % Hz
order = 3;
[b,a] = butter(3,2/Fs*f_high,'high');
Accelero_filtered = filtfilt(b,a,Accelero);
%%
 F = figure( 'Position', [50 50 1600 900]) ; % Visible 'off' pour ne pas afficher
    t = tiledlayout(3,3,'TileSpacing','Compact','Padding','Compact');
    title(t,"Spectro FULL ")
      % Mot_rpm(t) et BV_rpm(t) Run 1
    nexttile([1 2])
    plot(Temps,Moteur_rpm,'red',Temps,BV_rpm,'green')
    xlim ([0 M_temps])
    ylabel('Moteur & BV [rpm]')
    legend ('Moteur','Boite de Vitesse')
    grid on
 
    nexttile([2 1])
    NFFT =200;
    NOVERLAP = round(0.95*NFFT);
    spectrogram(Accelero_filtered,hanning(NFFT),NOVERLAP,NFFT,Fs,'yaxis','power','MinThreshold',-80)
    hold on
    plot(Temps,Moteur_Hz,'r',Temps,BV_Hz,'g',Temps,Delta_Hz,'b')
    colormap('jet')
    % Delta(t) Run 1
    nexttile([1 2])
    plot(Temps,Delta,'blue')
    xlim ([0 M_temps])
    ylabel('Delta [rpm]')
    grid on
    
    % Accelero(t) Run 1
    nexttile([1 2])
    plot(Temps,Accelero,'magenta')
    xlabel('temps [s]')
    xlim ([0 M_temps])
    ylabel('acceleromètre [V]')
    grid on

I linked a file with the first values at 50 kHz rate.

Thanks again Mathieu, taking time to help me that's realy kind :)

Mathieu NOE 2023-5-10

在 MATLAB Online 中打开

hello

try this new code

I let you discover the new spectrogram (with frequency axis in log scale to have good rendering both low and high freqs)

now the engine frequency trace is to be seen

by again I see no special event that coincide with the engine freq line

clear all;
clc ;
close all;
Valeurs = xlsread('Run 80bis.xlsx',"Data1");
Temps = Valeurs(:,1);
Accelero = Valeurs(:,2);
Moteur_rpm = Valeurs(:,3);
BV_rpm = Valeurs(:,4);
Delta = Moteur_rpm - BV_rpm;
M_temps = max(Temps);
Moteur_Hz = Moteur_rpm /60;
BV_Hz = BV_rpm /60 ;
Delta_Hz = Delta /60;
dt = mean(diff(Temps));
Fs = 1/dt; %Hz
% high pass filtering of accel signal
f_high = 5; % Hz
order = 2;
[b,a] = butter(3,2/Fs*f_high,'high');
Accelero_filtered = filtfilt(b,a,Accelero);
%%
 F = figure( 'Position', [50 50 1600 900]) ; % Visible 'off' pour ne pas afficher
    t = tiledlayout(3,3,'TileSpacing','Compact','Padding','Compact');
    title(t,"Spectro FULL ")
      % Mot_rpm(t) et BV_rpm(t) Run 1
    nexttile([1 2])
    plot(Temps,Moteur_rpm,'red',Temps,BV_rpm,'green')
    xlim ([0 M_temps])
    ylabel('Moteur & BV [rpm]')
    legend ('Moteur','Boite de Vitesse')
    grid on
 
    nexttile([2 1])
    NFFT =20000;
    NOVERLAP = round(0.95*NFFT);
    [S,F,T] = spectrogram(Accelero_filtered,hanning(NFFT),NOVERLAP,NFFT,Fs,'yaxis','power');
    idf = (F>0); % remove zero (dc) freq
    F = F(idf);
    S = S(idf,:);
   
    SdB = 20*log10(abs(S)); % convert S in dB
    SdBmax = max(SdB,[],'all');
    SdB_range = 80; % range in dB to display
    SdB(SdB<SdBmax-SdB_range) = NaN; % remove data below threshold (corresponding to max value - SdB_range)
    imagesc(T,F,SdB);
    set(gca, 'YDir','normal'); % to have the y = 0 at the bottom and not at the top
    set(gca, 'YScale','log'); % 
    
    colorbar('vert');
    xlabel('temps [s]')
    xlim ([0 M_temps])
    ylabel('Freq (Hz)')
    hold on
    plot(Temps,Moteur_Hz,'r',Temps,BV_Hz,'g',Temps,Delta_Hz,'b')
    colormap('jet')
    % Delta(t) Run 1
    nexttile([1 2])
    plot(Temps,Delta,'blue')
    xlim ([0 M_temps])
    ylabel('Delta [rpm]')
    grid on
    
    % Accelero(t) Run 1
    nexttile([1 2])
    plot(Temps,Accelero,'magenta')
    xlabel('temps [s]')
    xlim ([0 M_temps])
    ylabel('acceleromètre [V]')
    grid on