logic problem of selecting mutliple peaks

[birdswords]

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?

 

[birdswords]

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

 

[IRstuff]

Some code comments would be useful.

TTFN
faq731-376

 

[birdswords]

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

 

[birdswords]

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.

 

[hacksaw]

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

 

[GregLocock]

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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