On Saturday 16 June 2018 14:06:51 Chris Albertson wrote: > On Sat, Jun 16, 2018 at 1:23 AM Gene Heskett <ghesk...@shentel.net> wrote: > > On Friday 15 June 2018 23:53:03 Chris Albertson wrote: > > > > > > By using pdm/pwm in the pwmgens. At 50 kilohertz, then integrating > > that to get your analog voltage. But no not pass the raw signal thru > > an opto-isolator, the control linearity will be destroyed. > > Why is that? Let's assume you have onto-isolater that are fast enough > for the signals. It seems that at most they would introduce a delay. > Except the on delay is not the same as the off delay. Based on running the pwd at a high enough frequency to get smooth control in the first place. Even a 1 kilohertz pwm is fast enough to demo the effect, and at 1 kilohertz by the time its been smoothed to the analog equ, control bandwidth is in the toilet. Take the opto's out of the circuit, and run the pwm at 50 kilohertz, and you've then got control bandwidth to throw away. At 50 kilohertz, a .01% duty cycle gets you 15 to 20 revs at the motor shaft. With the lag of the opto's added, running at 1 kilohertz, it may take 5% duty cycle just to wake up the motor. Haveing the opto's confusing the issue you don't need.
> I do agree that you don't need an opto-isolator for an optical > encoder. That depends on the encoders resolution and how fast its spinning. Take the opto's out, and bingo, linear encoder response to 100 kilohertz or more. With the opto's the signals got lost at 240 rpms at the spindle, and the spindle went wide open. Now I can request 20 rpm in high gear, and I cannot stop the spindle by grabbing it. Burn up my hand maybe. -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
