easily calculating FWHM from the result of Peak Detector.vi

[jazhu]

I am submitting this request based on a recent suggestion from a customer.

After doing a peak detect, the customer wants to find full width at half maximum(FWHM) of those peaks. 

However, in order to calculate FWHM, information of quadratic fit used to find the peaks is needed. However, we cannot get the equation from Peak Detector.vi. This means, the user needs to do an additional quadratic fit, and then calcualte FWHM after that.

It would be very nice if we can get FWHM from the Peak Detector.vi.

[X.]

There must be some misunderstanding as to what the Peak Detector.vi does.

As its description states, it fits a quadratic function to points above or below a threshold (below for a valley fit).

What do you think is the asymptotic value of that function as x (the argument) tends to +/- infinity?

Right, infinity (+ or -).

So how would your user define the FWHM based on the quadratic fit?

Take all points above the threshold and find which one corresponds to the fit function minus threshold equals one half of the peak minus threshold value?

But is that really the width you would be interested, say, if your threshold has been selected very conservatively?

In other words, there is no natural way of extracting a FWHM from a quadratic fit to a peak.

There would if the fit was Gaussian (and included the baseline), so what your user may want to do is fit the detected peak with a Gaussian (or a Lorentzian, or whatever is the theoretical shape of the response).

If I were working at NI, I would reject this request as nonsensical.

[DSPmchen]

Hi jazhu,

Thanks for submitting this idea. 

However, quadratic fit in the pead detector VI will not help you find the FWHM.  This requires you provide additional information to define 'half maximum'.  And it would be better to use Gaussian fit to calculate the FWHM. 

Thanks,

Michael

[Darren]

 Declined for reasons listed here: http://forums.ni.com/t5/LabVIEW-Idea-Exchange/easily-calculating-FWHM-from-the-result-of-Peak-Detect...