> -----Original Message----- > From: Nicklas Karlsson [mailto:nicklas.karlsso...@gmail.com] > Sent: May-05-20 9:13 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Fluctuating RPM using CUI ATM 10 encoder > > > Do you have a dual trace 'scope? Spin the spindle and look at the input > > and output of the opto-isolator. See if there really is a lag. If you > > have a new scope would you have it capture the screen and post it. I'm > > really skeptical that those isolators are THAT bad. > > > > Here is the datasheet for the opto. > > https://www.mouser.com/datasheet/2/143/EL817-G-26528.pdf > > They claim an 18 uS rise and fall time. A 1KHz square wave will have a > > 1000 uS period and a 500 uS pulse width at 2 KHz the pulse width is still > > more than 10X the raise time of the opto. But maybe the opto is a fake > > counterfeit part with very poor performance. > > Opto couplers are rather slow. With a high resolution encoder frequency could > be maybe up to a few hundred kHz, > 2000*period/revolution*3600rpm=120000period/second=120kHz, 200PPR will be > 12kHz at 3600rpm, 1/(2*18µs) = about 27778Hz = > about a little bit below 28kHz if mad no misstake. >
I think your math is out. Most of the hi res encoders are running 2500 lines per rev. Many are less. But we're only looking at one encoder channel and that works out to twice the number of edges but the actual frequency is still lines per rev per second. So how many revs per second is that? You have to divide RPM by 60 to get revs per second so 3600 RPM is 60 RPS. Now you have 60 * 2500 Hz = 150kHz. Still way too high for that opto-isolator. Now if you do like Sam did for his hex milling you update the encoder. But initially he was milling with about 60 teeth and Linux is more than fine for that when power tapping etc. So 60 * 60 is 3600 Hz and the opto would be fine for that. Even 200 lines at 60 rps (3600 RPM) is 12,000 hz. Don't understand how you got 27778Hz John > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
