On Wednesday 12 December 2012 22:02:40 John figie did opine: > What is the sample rate of the halscope and what is the motor rpm? Maybe > the halscope is aliasing. > I did some math before I made this encoder wheel, which said that with 39 slots, it should track ok to about 11,000 rpm.
24 u-secs base thread, or nominally 1 ms servo thread, plus whatever multiplier is set in that subscreen that selects that, but one must be careful with that as a 5 to 9 settind there makes halscope take 20 seconds or more to present an updated view. The motor, in low range gear, runs about 1250 rpms when wide open. I can look at the a & b signals and they do not seem to have any missing pulses, either on the halscope screen, or on my 100mhz dual trace hitachi service scope. But a change in spindle speed, as measured by the period of the index pulse, from 60 rpms, 1 Z per second, to 600 rpms, 1 Z every 100 ms, while it may show as 60 rpms by adjusting the encoder.position-scale at the low speed, only shows as about 250 rpms at an actual 600 as verified by an index pulse every 100ms, 10 rps times 60 secs = 600 rpms. Crank it till the motor is wide open, and the velocity output says only 407 to 409 rpms, where it should be showing 1200 and change in low gear, or 2500 in high gear. Very non-linear, but without an obvious breaking point which I believe if it was aliasing, should be present somewhere in that range. Another thing is (and I don't believe its related to the real problem here) that if I slow the pwmgen's prr below about 1350 hz, the encoders velocity output gets quite noisy, both in the signal and to my ears, its hunting like crazy, but doesn't seem to effect the long term average, its just slapping the nominally 5 degrees of play in the pulley keyways and timing belt slop. Yet we've been told that a lower prr enhances the step level smoothness by making it more base thread times wider, where adding a base period to the length is a smaller percentage change. > On Dec 12, 2012 6:22 PM, "Gene Heskett" <[email protected]> wrote: > > Greetings all; > > > > My encoder wheel has 39 slots detected in A/B quadrature, plus of > > course the index, Z. > > > > Running in rpms mode (as opposed to rps), then it seems to me that I'd > > need > > > to multiply that by 1.5384615384615384615 in oder to convert that to > > the unit of measurement, in this case a single revolution. > > > > I've also tried the reciprocal or .65, but neither of the resultant > > figures > > > actually gets me a displayed halmeter velocity that corresponds to the > > actual speed. > > > > Its rather hard to make sense too, of the halscope timebase. Looking > > at the same signals with my Hitachi, the halscope displayed graticle > > is off > > by > > > at least a factor of 3. > > > > How can I adjust this? Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! First pull up, then pull down. I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ 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-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
