Hi All,

I have a logic problem I am having trouble solving with MATLAB. My objective is to select and count peaks in a dataset. However, findpeaks and peakseek function will not work.

My dataset consist mostly of electronic noise, with intermittent high frequency oscillations generated by a sensor responding to pressure impacts. When there is no pressure impacting the sensor, the dataset consist only of electronic noise (<0.00007). When the sensor is activated, the signal peaks 2-4 order of magnitude above the noise level (0.001> x >0.1). The first or second peak is the highest peak in the oscillation and the oscillation decreases at a constant rate for the next 10 to 20 observations (as the sensor returns to its equilibrium represented in the dataset as electronic noise level).

I can select out the peaks for single pressure impacts and count them. However, the PROBLEM IS counting MULTIPLE PRESSURE IMPACTS WITHIN 10-20 OBSERVATIONS...i.e. the signal peaks, then begins to decrease and a constant rate, and then another peak occurs before it reaches electronic noise.

So the problem is: how do you separate and count double peaks within a dataset that has single and double pressure impacts?

This is the code that I have written thus far, but I get error messages. The error message is a line 5: peakCount = r(1,1). . Anyone have any ideas?

function [xx] = reducetopeak (xx)
xx(xx(:,:) <=(2*std(xx)), :) = 0;

r = find(xx);
peakCount = r(1,1);
count = peakCount + 1;test

while (count < length(xx))
while (xx(count, 1) <= 0.50*xx(peakCount, 1))
xx(count, 1) = 0;
count = count + 1;
if count > length(xx)
break
end
end
peakCount = count;
count = peakCount + 1;

end

Some code comments would be useful.

TTFN
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function [xx] = reducetopeak (xx)
xx(xx(:,:) <=(2*std(xx)), :) = 0; %brings noise level down to zero

r = find(xx); % find the first nonzero element...so finding the first peak
peakCount = r(1,1); %specifying the first peak for while loop to begin
count = peakCount + 1; %defining the next variable for comparison of peak values

while (count < length(xx))
while (xx(count, 1) <= 0.50*xx(peakCount, 1)); %this compares adjacent peaks, if the next peak %is
xx(count, 1) = 0;
count = count + 1;
if count > length(xx)
break
end
end
peakCount = count;
count = peakCount + 1;

end

function [xx] = reducetopeak (xx)
xx(xx(:,:) <=(2*std(xx)), :) = 0; %brings noise level down to zero

r = find(xx); % find the first nonzero element...so finding the first peak
peakCount = r(1,1); %specifying the first peak for while loop to begin
count = peakCount + 1; %defining the next variable for comparison of peak values

while (count < length(xx))
while (xx(count, 1) <= 0.50*xx(peakCount, 1)); %this compares adjacent peaks, if the next peak is 50% less than the previous peak, then make that peak zero
xx(count, 1) = 0;
count = count + 1;
if count > length(xx)
break
end
end
peakCount = count;
count = peakCount + 1;

end

Thanks for checking this out.

just counting raw data is going to be tough, have you considered autocorrelation or time series analysis methods to better characterize you data

So you need to identify the sequence of amplitude peaks

9 10 9 8 7 6 5 4 3 2 1

and

10 9 8 7 6 5 4 3 2 1

as single peaks

and

7 6 5 10 9 8 7 6 5 4 3 2 1

as a double?

If so that seems rather a banal piece of programming.

Cheers

Greg Locock


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