MATLAB: How to find time interval of peak value in a timeseries

peak loadthresholdtimeseries

i have a load profile data set.. Time vs Load Demand as a timeseries object. If I have a threshold for peak as 800KW How do I find at what time my value goes above 800 kW ? The time series object is for every 30 mins interval over 24 hrs.

I need to find the highlighted time interval in the picture. Any idea?

Best Answer

If you want to interpolate to find the ‘exact’ time, this works:

t = 0 : 30 : 1440;
LD = 500 + 400*sin(2*pi*t/2880);
zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);                    % Returns Approximate Zero-Crossing Indices Of Argument Vector
X800_idx = zci(LD - 800);                                               % Subtract 800, Find Approximate Zero-Crossing
LD800_Rng = LD(X800_idx-1 : X800_idx+1)';                               % Define Range For Interpolation

t800_Rng = t(X800_idx-1 : X800_idx+1)';                                 % Define Range For Interpolation
t800 = interp1(LD800_Rng, t800_Rng, 800, 'linear', 'extrap');           % Find ‘Exact’ Time (Minutes)
figure(1)
plot(t, LD)
hold on
plot(t800, 800, '*r')
hold off
grid

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The code

Fs=200;
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should be used either in the body of the function or outside of the function (where you need to define the input parameter t).

MATLAB: Zero-crossing of every column of a matrix

If you want the maximum and minimum amplitudes (and you have R2017b or later releases), use the islocalmax and islocalmin funcitons. Also, if you have the Signal Processing Toolbox, you can use findpeaks on the original and negative (to find the minima) versions of your signal, however it requires a loop for matrices because it only handles vectors.

There is no need to find the zero-crossings then. (However if you still need to find them, doing so is relatively straightforward.)

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