On Wed, 2011-09-28 at 15:28 -0700, Cliff Blackburn wrote: > > On 9/28/2011 2:55 PM, Bruce Klawiter wrote: > > I was looking at this encoder, > > http://www.usdigital.com/products/e2#description > > It says: > > Tracks from 0 to 100,000 cycles/sec > > 32 to 1250 cycles per revolution (CPR) > > 128 to 5000 pulses per revolution (PPR) > > > > I don't understand the difference between CPR and PPR, I am thinking it has > > something to do with the A and B channel being 90 degrees out of phase. If > > that is the case why is the PPR 4 time higher and not only twice as high. > You can monitor the rising and falling edges of both a and b channels > giving you 4 times the resolution. > > Also does any one have a recommendation for an encoder, what is a good > > reliable brand, what CPR or PPR should I get. The high the line count the > > better I would assume. > I think the rule of thumb is to make sure you have at least 10 times > more counts than the smallest resolution you want to maintain. More > never hurts, but if you have too many the frequency at rapid speed is > going to be high causing noise and monitoring issues.
The rule I've heard is counts 5X better than the position accuracy you want to maintain. This came from a Boeing engineer. Velocity control is another matter and there more is probably better; it takes an awful lot of counts to overflow the counter in a few servo cycles. Time stamping may relieve some of the constraints. > > I have had good luck with dynapar encoders, there not cheap tho. I've been using the Koyo encoders that are just dust sealed which means one should go to some trouble to install them in housing that protects from all the nasties around a milling machine. Their price is about $90 from Automation Direct. I use the 2500 cpr differential ones. :-) Dave > > > > > Read about my conversion here: > > https://sites.google.com/site/bmklawt/home > > > > Regards, > > Bruce > > > > ------------------------------------------------------------------------------ > > All the data continuously generated in your IT infrastructure contains a > > definitive record of customers, application performance, security > > threats, fraudulent activity and more. Splunk takes this data and makes > > sense of it. Business sense. IT sense. Common sense. > > http://p.sf.net/sfu/splunk-d2dcopy1 > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ All the data continuously generated in your IT infrastructure contains a definitive record of customers, application performance, security threats, fraudulent activity and more. Splunk takes this data and makes sense of it. Business sense. IT sense. Common sense. http://p.sf.net/sfu/splunk-d2dcopy1 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
