Andreas Strecker wrote: > Hello > The only way i know to get rid of the Problem is to measure the Timepoint > when an edge is created. This can be done by a Software Interrupt and if > this is too slow one needs a so called Timer Capture Input which stores the > timer value when the edge occurs in a Hardware Register. By comparing the > last edge before the Controlloop with the last edge from the previous > Controlloop one gets the exact speed. v=s/t. s is a discrete natural number, > so to get exact measurements the time has to be exactly measured. > Hopes this helps. > Not sure exactly what you are commenting about. But, if it is about my comments on the accuracy of sample time, then software recording of the time of a sampled edge doesn't help, as there can be a time gap between any two instructions due to interrupts or other CPU disturbances, like DMA. Yes, v=s/t, but if there is significant jitter in the t, then accuracy is lost. You only have to look at these things in real life to see HOW BAD it can get! Take a case where there are 1500 encoder counts/second, and it is being sampled at 1000 times/second. On alternate sample intervals you get one or two counts. Is the instantaneous velocity changing by 50%? Of course not. Using a time stamp and a higher sampling rate, you can smooth out these variations a bit, but you still get some jitter that can't be reduced. It is good enough to make a servo loop work. I have serious doubts you can extract gain vs. phase info over a wide range of frequencies with a white noise stimulus to create a Bode plot in one measurement.
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 Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
