On Wednesday 12 June 2013 11:07:52 Peter C. Wallace did opine: > On Wed, 12 Jun 2013, Gene Heskett wrote: > > Date: Wed, 12 Jun 2013 07:05:56 -0400 > > From: Gene Heskett <[email protected]> > > Reply-To: "Enhanced Machine Controller (EMC)" > > > > <[email protected]> > > > > To: [email protected] > > Subject: Re: [Emc-users] looking for a non-linearity in spindle speed > > control. > > > > On Wednesday 12 June 2013 06:28:33 Steve Blackmore did opine: > >> On Tue, 11 Jun 2013 18:12:16 -0400, you wrote: > >>> Someone mentioned there being an RMS conversion as part of the > >>> existing PWM to analog conversion methods but don't recall who now, > >>> can someone suggest a link for reading that might get me some > >>> insight on this? > >> > >> I mentioned the problem was to do with RMS in the pulsed signal, or > >> so I recall in discussions on converting PWM to an analogue voltage. > >> I think it's more to do with the Time constant on RC circuits like > >> the one used on a lot of breakout boards. They do not give a linear > >> response. Short of a look up comparison table I don't think you'll > >> ever get it linear. Near enough should do anyway :) > >> > >> > >> Steve Blackmore > > > > Thanks steve. > > > > Andy had mentioned lincurve.9 as a possible solution, but the version > > I save installed on this machine so I can run sims, doesn't have that > > module available. So I can't play what if using halrun. :( > > > > Problem is that I can type s60 thru s360 and pretty much get what was > > asked. From s400 on up, there is a huge positive curve. > > > > I have the tach set to display 1200 max at full scale. > > > > Entering s600 (gets about 770 revs, to pinning the tach at 1200 is > > around an s841 entry, a very large 'gain'. The new motors > > countershaft has a 3/1 stepdown, plus the gearing in the head, means > > that at 1200 indicated, the motor is about tapped out, about 6 grand. > > Thats a hell of a lot of well balanced cast iron flywheel, 6" in > > diameter, to be spinning that sort of rpms. > > > > And I'm looking at a storm headed my way they are saying we'll need to > > drag out our generators for. I've been trying to get a whole house, > > 18kw NG fired, but locally all they have is generac, junk. I want a > > kohler, better warranty, but no registered service people locally. > > So its not happening. One of the neighbors has a new generac, plenty > > big enough, but I drove past it during the last outage, and his > > overhead lights looked like they were running on 85 volts. My little > > 6kw, clipped onto the open main breaker isn't big enough to run the > > whole house AC, but the lights (100% ccfl) were fine. I wasn't > > impressed with the difference. > > > > Cheers, Gene > > > > ---------------------------------------------------------------------- > > -------- This SF.net email is sponsored by Windows: > > > > Build for Windows Store. > > > > http://p.sf.net/sfu/windows-dev2dev > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > Getting a highly linear analog output vs duty cycle from a PWM source is > trivial, it requires: > > 1. Equal high and low drive impedance from PWM source to the RC filter > (hint: swamp output impedance of PWM source with resistor)
Much easier said than done where dealing with one of Arturo's products. He does not supply schematics, and I have only reverse drawn perhaps 10% of the C41. I get the impression there is more layers than what can be seen to his boards. Its for sure that the opto device is an on-off only device, needing the help of an 74LS240 buffer chip that is now an 74HCT240, and which we both know does not have equal src and sink abilities even in our wildest dreams. > 2. Minimal delays (pulse width distortion) in the PWM signal Thats good here. Rise & fall times are well under 100ns when looked at by my 100mhz dual trace. > 3. Buffering the RC filter from load On that point, I'd need to trace the output stage again, but I think the load is hanging directly across an LM358, which is ATM buffering the filtering capacitor with a gain of about 1.25 that I installed in order to get closer to the plus rail. As I switched its 12 volts up to 15.5, those two resistors could likely be removed. IOW it sure looks buffered by the LM358. Another item I found while dickin around with the OEM 250 watt controller, was that its pot arm "input" _was_ the summing junction, and that a 10k resistor in series with the 'arm of the pot" input connection made an amazing difference in the linearity of the control, and did it with an un- measurable amount of voltage drop, un-measurable to a 10 meg input digital meter. And its something I have not tried here yet with this much bigger controller, and probably should. The effect I am seeing certainly walks like a brother to that particular duck. That would be a relatively easy item to restore amidst the stuff I have pasted on the bottom of that board now to make that gain of 1.25. But I also have a storm coming that is predicted to make us drag out our generators, and a jungle up to 10" tall to mow before it gets here this evening. Thanks Peter. > Peter Wallace > Mesa Electronics 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! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> travel, n.: Something that makes you feel like you're getting somewhere. A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
