waterfall plot
waterfall plot
(OP)
I neeed to know the mathematics behind the generation of waterfall plots. I have the time domain data (say some 2^n points gathered every 1 second thru the running speed range of the machine) and would like to convert that to the frequency domain and construct the waterfall plot from it.
Any books/answers will be very helpful.
Thanks
Any books/answers will be very helpful.
Thanks





RE: waterfall plot
Rather more important is what the plots are. You get from time series data to spectra by using FFTs, typically. Most usually you do a waterfall of power spectra, or the modulus of the spectrum(Z), against time or speed(Y), against frequency (X).
Here is an excellent on-line introduction that will get you going.
http://cp.literature.agilent.com/litweb/pdf/5952-8898E.pdf
Here's one with more details about FFTs
http://www.science.unitn.it/~bassi/Signal/NInotes/an041.pdf
Here is an excellent introduction to the philosophical details of FFTs. Ignore the details of wavelets, the stuff on Fourier is worth the price of admission
http://engineering.rowan.edu/~polikar/WAVELETS/WTtutorial.html
Excel has a built in FFT analysis, in one of the toolpaks. It is a bit hard to get right, but it does work. With a bit of cunning Excel will plot waterfalls as well.
Cheers
Greg Locock
RE: waterfall plot
M
RE: waterfall plot
Thanks for the post. Ive read those application notes atleast 10 times each. Let me state my question clearer. Say that I have the time domain data for every second as I stated before. I convert this to the freq domain with an FFT function. We now have the signature of the machine at various speeds. If I now need to plot the waterfall, is it just a matter of display (or visual representation )concerned with the particular software that I am using(say excel or mathcad..)or is there any Math involved there?
The reason is if I use mathcad I cant use one of those 3D graphs. And if I use a 2D graph, I have one "X" value for which there are many "Y" values..
Thanks
RE: waterfall plot
If you already have the data, there is no more math involved. Each FFT is assigned to its time slot and you then plot the 3-D data.
TTFN
RE: waterfall plot
Hope this helps. It really depends on how sophisticated your display program is. Most of the canned programs that come in vibration analysis software packages have some nice features but also have room for improvement.
Skip Hartman
http://www.machinerywatch.com
RE: waterfall plot
Cheers
Greg Locock
RE: waterfall plot