demo2

DEMO2
Initialize Variable
Load Data
Time Plot
Amplitude Probability Density
Frame Statistics
Power Spectral Density
Plot All Results

DEMO2

Demonstration script for various analyses of a time signal from a tracked vehicle. The script produces one window with four plots, with

Compressed time data
Amplitude probability density function (APD)
Frame statistics of RMS as a function of frame (for stationarity check)
Power spectral density (PSD)

% Copyright (c) 2003-2006, Axiom EduTech AB, Ljusterö, Sweden. All rights reserved.
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Initialize Variable

FontSize=8;

Load Data

First, load the data

load demo2data;

Time Plot

In the first quadrant of a four-quadrant window, plot the time signal. The command sigtrunc ensures that the data is correcly visualized on the limited screen resolution

fs = round(1/headdx(Header));
x = sigtrunc(Data,fs,0,72);
[xp,tp] = signpack(x,fs,20);
%

Amplitude Probability Density

Next, compute the statistical probability density, and plot it together with a theoretical normal (Gaussian) distribution. (Indeed, the current data are not from a stationary random process. Actually, they are from a periodic signal from a tracked vehicle.)

[a,n,ax] = apdnorm(x,101,-300,300);
%

Frame Statistics

Before computing a PSD of the signal, we should check the stationarity, so we compute frame statistics of the standard deviation

[s,ts] = framstat(x,fs,'std',4000,1000);
%

Power Spectral Density

Finally, we compute a PSD of our signal using a block size of 8192 samples, 50% overlap processing, and Hanning window (the latter two settings are not needed to input to the command).

[P,f] = psdnorm(x,fs,8192);

Plot All Results

figure(1);clf;%fullscrn
subplot(2,2,1);
plot(tp,xp,'k')
axis([0 70 -300 300])
xlabel('Time [s]','FontSize',FontSize);
ylabel('Acceleration [m/s^2]','FontSize',FontSize)
title('Time History','FontSize',FontSize)

subplot(2,2,2)
semilogy(ax,a,'k')
hold on
semilogy(ax,n,'r')
axis([-300 300 1.e-6 0.02])
xlabel('Amplitude [m/s^2]','FontSize',FontSize)
ylabel('Probability Density [s^2/m]','FontSize',FontSize)
title('Amplitude Probability Density Compared with Normal','FontSize',FontSize)

subplot(2,2,3)
plot(ts,s,'k')
axis([0 70 0 80])
xlabel('Time [s]','FontSize',FontSize)
ylabel('[m/s^2]','FontSize',FontSize)
title('Running RMS in 1 Second Intervals','FontSize',FontSize)

subplot(2,2,4)
loglog(f,P,'k')
axis([1 1000 0.001 100])
xlabel('Frequency [Hz]','FontSize',FontSize)
ylabel('PSD [(m/s^2)^2/Hz]','FontSize',FontSize)
title('Power Spectral Density','FontSize',FontSize)

drawnow

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