Sin Fit

[slucas]

this is all too excellent.  i do have labview v8.20.  and i believe my eyes have spied the tones vi.  also the FFT phase vi.  i have already implemented a "short" linear fit and the 3rd order polynomial.  i think i am going to code the former two and write a master vi to process and analyze the data from all four methods.  i will post the sucesses when my study is complete.  is that fair?  thanx again for all of your help, guidance, and suggestions.  lucas

[johnsold]

Yes, it is fair. It is always nice when someone posts the solutions they have developed with help from the forum. Then someone else who may have a similar problem can benefit from your sharing.

Lynn

[cmahendr]

Hi Lynn,

Can you help me out to understand what you have said before, if i fit part of sine wave with the polynomial equation (3rd order), how do i find the changes in the polynomial co-efficients for the rest of the curve?? please reply me as soon as possible.id is xs2mahendran at gmail.

thanks

mahe

[johnsold]

I will be busy this morning and possibly all day, but I will get back to you within a day or two.

Lynn

[johnsold]

mahe,

First note that this tread is five years old and some of the persons involved may not be on the Forums any longer.

Next, please tell us exactly what you are trying to do. Your question about "coefficients for the rest of the curve" is not clear.  The coefficients from the fitting completely define the polynomial for any value of x.  My suggestion for a cubic equation would only be valid for a segment of the sine wave with one zero crossing and probably no more than one peak (or valley).  It was a suggestion for finding a zero crossing location.

Lynn

[cmahendr]

Hi Lynn,

Thanks heaps for your reply. Have a look at the spreadsheet, was developed by my seniors. They have taken three points from the curve (halft of the curve) and did the curve fitting (3rd order) (Highlighted in yellow).after that they have extrapolated the coefficients (guess by Fourier transform). I am really not able to guess what they have done to calculated the C1,C2, C3 (which is in red color). as well a0 ( cell C34). Let me know if you can explain me about it.

Thanks

mahe

[johnsold]

mahe,

1. What does this have to do with LabVIEW?  You have an Excel worksheet but have not mentioned LV.

2. The graphs in the worksheet do not look anything like a sine wave.  What are you trying to fit to the data?  What is the underlying physical model for this process?

3. The formulas are in the spreadsheet. No need to guess.

Lynn

[RavensFan]

Don't attach a file that looks like it is an xlsx file, but actually turns out to be a zip file.

[Darin.K]

Actually all xslx files are zip files.

[RavensFan]

For some reason, when dowloading that file, it treats it as a zip file and opens it in Winzip rather than treating it as an xlsx file and opening it in Excel.

When you do a "Save target as" on the link, it wants to save it as a .zip extension rather than an .xlsx extension.

The link is lying to you about what the file actually is named.  Just like when people claim the have a .jpg attachment (and it looks like it on the link), but the underlying file is actually a .bmp and downloads as such.