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
> --
> "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>
> A penny saved is a penny taxed.
> A pen in the hand of this president is far more
> dangerous than 200 million guns in the hands of
> law-abiding citizens.
>
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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)
2. Minimal delays (pulse width distortion) in the PWM signal
3. Buffering the RC filter from load
Peter Wallace
Mesa Electronics
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