andy pugh wrote: > On 10 December 2012 04:10, Jon Elson <[email protected]> wrote: > > >> I have a $13K box (Schlumberger dynamic signal analyzer) that is >> supposed to acquire the data for Bode plots. I tried to use it on my >> home-made analog servo amplifiers. I cut the servo loop and >> added a 100 Ohm resistor, and connected the drive/sense >> terminals across that. It excited the system with a sine wave, and at >> the lowest frequencies, I could see the table rock a small amount. >> But, the data I got made no sense at all, and may not have been >> repeatable, either. >> > > Is a sine-wave the correct input signal? > When I spent my working day creating frequency response curves we > typically used white-noise excitation. > If you have a way to extract the frequency+phase information from the encoder, that's fine. Due to the time sampling PLUS the distance quantization, I think the result from the encoder is SO noisy, this would be impossible. Also, the injection of a stimulus signal with a 1 KHz sample rate would further complicate the measurement. I think it would be possible to get amplitude plus phase from a single-tone excitation without great difficulty. I think it would be pretty hopeless to make it work with white noise, but I'd be glad to be proven wrong.
On the other hand, taking one long sample with white noise would be much better than taking a hundred (or more) short samples at single frequencies. I'm just concerned that a very noisy data block which also has timing jitter would make for very poor data via FFT. Jon ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
