Peak/valley detection problem

Hi,
How can i detect the maximum peak to valley on the graph attached. It is not the difference between the maximum and minimum all the whole data set that i require, I want to know the maximum value of the higher frequency peaks and valleys ignoring the small 'blips' within the data.
The X-axis is controlled by time and the number of samples between each peak varies between data sets. I have considered using a moving average to smooth the data but cannot do this due variation of samples between peaks.
Using the peak/valley detection VI would work great but due to the small 'blips' in the data set a true maximum value cannot be found.
Can anyone help?
Tom
Attachments:
graph.JPG ‏20 KB

Hi Tom,
I have been looking into your issue in an attempt to find you a solution. My initial thoughts are that you should apply some form of smoothing to the waveform before subjecting it to the the Peak Detector sub VI to detect the amplitude of the peaks and the troughs. These amplitudes could then be subtracted form each other thereby arriving at the values you are looking for. Can I confirm that this would solve your problem.
I have been looking into a methodology for smoothing your waveform and I found the following example which uses a moving average technique, which I think could be useful. Take a look and let me know what you think.
Best Regards,
Christian Hartshorne
Applications Engineer
National Instruments UK
Attachments:
Moving_Average-1.vi ‏15 KB

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Why no valley detected

Hi
Something seemingly simple I can not get to work...
Please see the attached VI which contains an array constant (which represents a typical set of acquired data points) on which I perform a peak/valley detection.
I would like to find the valley(s) but no matter what 'width' is used it never finds any valleys.
Any ideas as to why this may be or suggestions on how else to determin the valley location?
Many thanks for your help!
Jack
Solved!
Go to Solution.
Attachments:
Valley Detect.vi ‏14 KB

Hi there,
You need to wire in a value for the 'Threshold' input. This input tells the VI to ignore any valleys below the threshold value. As there are no valleys in your data set below 0, you will not detect any if you don't wire in this input.
Should you set the threshold value to '800' you will detect one valley. If you set the threshold value to '1200', you will detect three valleys.
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For surface analysis of a sample, I did signal processing and peak detection using inbuilt peak detector .vi . But the problem is in shown peak/valley location... I have attached the screenshot of one run. See there are some peaks(valleys) which are fairly away from the actual graph. I am confused. What might be the reason of this fault? Any idea?
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I have used the peak detection function in several application. The peak detections will sometimes be inaccurate in amplitude. The reason for this is as I think covered by Kolan and Alain S. I have found the that the locations is more accurate than the amplitudes parameter. So use the locations parameter to pick values from your wave data. This will improve your accuracy
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I have 2 waveforms coming in and I would like to detect the peaks and valleys(with the location, or ) and write them to a spreadsheet file.
In a pattern like this
peak #1(waveform 1)            peak #1(waveform 2)                  Location of peak#1(waveform 1)    Location of peak #1(waveform 2)
valley #1(waveform 1)           valley #1(waveform 2)                Location of valley#1(waveform 1)             Locationo of valley#1(waveform 2)
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valley #2(waveform 1)           valley#2(waveform 2)                  Location of valley#2(waveform 1)            Location of valley #2(waveform 2)
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If you search the forums for peak detect, you will find a number of hits. Also, here is a recent thread discussin peak detection without setting a pulse width.
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Hello There,
I am having trouble detecting multiple valleys within a bell curve type shape (see pic). The valleys are moving horizontally and I need to detect each of their positions in real time. The other issue is that the dips increase and decrease in magnitude thus making it difficult to use the dip detect function as it keeps jumping from one to the other.
any help would be greatly appreciated,
thanks.
Attachments:
multiple valley detect.jpg ‏51 KB

Hi TriboBoy,
Have you tried setting the threshold level above your data so that the algorithm used within the Peak Detection and Display VI considers all of the valleys occurring below it?
Below is a screen shot of the resulting graph using the Peak Detection and Display VI example in Example Finder:
The blue threshold line corresponds to the valley data points being considered and has been set to a value higher than any expected data points.
It is also worth noting that the width used should be as low as possible (limited to a value of 3) so that the maximum number of data points are considered.
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Hello!
I am using a software to predict the values of a parameter as a function of time. The result is output in an excel file with the time on first column and the parameter values on the second column of a worksheet. When I represent the parameter values versus time in an XY chart it looks similar to a signal or waveform with no noise.
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Hi RPJ,
Thanks for your post and I hope your well today.
I great VI in vi.lib I would recommend using is the Peak Detector:
Its outputs include,
Locations - the sample number
Amplitudes - the value at the peak/valley
2nd Derivatives - which you can use to test how abruptly/sharp the peaks/valleys are.
Its inputs include,
Theshold - they amplitude theshold
Width - how many samples above the theshold the peak/valley should be to be classed
Peak/Valley - type
You could use the 1st Derivative to find locations of flat zones (or use the 2nd derivative ..2nd Derivatives gives measurements of the second derivative of
the amplitude at each of the peaks or valleys found in the current block of
data. 2nd Derivatives gives an approximate measure of the
sharpness of each peak or valley. If you are detecting peaks, these values are
all negative. If you are detecting valleys, the values are all positive.)
I hope this helps, please let me know what you think,
Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
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Quote
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Quote
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