In my work I will be acquiring light scattering data, so I will be measuring the intensity of the light as a function of time (my time intervals will generally be 5ms). One of the things I then want to do with my data is to run an intensity autocorrelation function on it; we want to be able to access the initial slope of the autocorrelation function.
So I found that there was an autocorrelation vi in labview. I put together my vi and ran it and worked out how to add my time intervals (ie after running the autocorrelation function). It was then that I realized that something seemed to be wrong. What I realized was that the number of data points I was getting back from the autocorrelation function was nearly double the number of data points of my data; for example my data is 100,000 points, I was getting back something like 199999 points. Given that I need to be able to equate my delay times with the corresponding autocorrelation data this left me with a problem. So I went back and read the help files with regards to this vi and realized why I was getting so many data points, the output sequence is 2N-1 and thus t=0 is the Nth element of the output sequence.
So given that I want to have access to the initial slope of the autocorrelation function (ie on the right hand of the x-axis relative to where t=0 would be), and I would prefer not to have to actually write out my own autocorrelation vi (that I have found is not as easy as it looks), I have been trying to work out how to extract the data from the Nth element onwards. So far I have been unsuccessful in doing this.
Note that from what I have gathered when an autocorrelation is done on dynamic light scattering data you essentially get an exponential curve and when I do eventually get some proper data to play with I would expect something similar (the data I have attached is some random noise I have generated so that I can work with my vi’s at the moment).
So any help in working out how to extract the relevant data would be appreciated. I have attached my original autocorrelation vi and the one I have modified. This was the final modification and it wasn’t able to extract the data I am after. I have also included one of the ‘data’ files I have been working with (ie the noise data).
I am using LV 8.6 and thanks for any help that can be provided, or suggestions as to alternative approaches as well.
