autocorrelation with labview

[esra]

Hello

I have tried to match the second half of the graph to exponential . Im using dynamic light scattering to find the particle size of nanoparticles. from the exponential fit I found the decay rate too low so that gave me huge particles not nanoparticles. so the exponential decay rate should be high so that teh calculation makes sense. in some articles I saw people are doing FFT after autocorrelation but I thought autocorrelation itself should be enough to correlate the scattering inetnsity. any more suggestions? thanx again

[DSPmchen]

Hi esra,

When you change to linear scale, you see the autocorrelation as a triangle. That means the second half decays linearly, not exponentially. So you will not get a high decay rate when you perform exponential fit on it.

Michael

[07824487940]

hi esra

I am trying out feasibility of setting up dynamic light scattering experiment. I would like to know about the kind of oscilloscope that you had used for the experiment. What was the bandwidth of the oscilloscope?  how successful was your attempt and whats the range of particle size you could determine? please do enlighten me to proceed further with the experiment.

deepa 

[esra]

Hello deepa

I was using Lecroy 9304A oscilloscope. my particles were in range 20-100 nm. I saw signal with this particles designed the set up. but I could never get autocorrelation function work in labview. Let me know if you have any suggestions about doing autocorrelation using labview.

thanx 

[07824487940]

Hi esra, Thank you for your reply. I havent started with the set up but planning to do so soon. I will try doing autocorrelation in LabVIEW and will surely let you the know the outcome.

Deepa 

[ay7973]

esra

I am trying to do a similar experiment as you and I am running into the same problem.  Did you every find a solution?

thanks

[George_P_Burdell]

Ay7973-

Are you using the AutoCorrelation.vi in LabVIEW?  This will probably be helpful for your application and here is a link to the Help for this VI.  It can help explain what this VI does.   

[ay7973]

Hey Mike S.

I am using the autocorrelation VI in labview, however, the help screen is not very helpful for me.  I know i need to modify the data some how, but i am not sure what steps i need to take in order to get the appropriate function.  It should come out as a sigmoidal decay when the x axis is in the log scale and the y axis is linear, but i am getting a triangle. If you have any ideas please let me know.  

Thanks

ay7973 

[George_P_Burdell]

ay7973-

What exactly are you looking to do?  This particular VI doesn’t require any data modification to the input before you use it.  Looking over this help, it appears the x and y axis are not in log scale.  Please provide more information on what exactly you are looking to accomplish in your application.

[ay7973]

To Mike S. and anyone else who knows anything about this:

Here is the whole story (the relevant part anyway).   Currently I have the NI Diadem software, I am not sure if u are familiar with it, but it is a data analysis software.  It includes an autocorrelation function.  When I put identical data into the diadem autocorrelation function  and the labview autocorrelation function VI I get different output curves.  I have no idea why this is. I have attached the data i am using in an ASCII file and ii have also attached the two curves i am getting with the data in the respective programs.  

In labiew, all I have done was connect a read file VI to the autocorrelation VI to a waveform indicator.  

I need any help I can get at this point.