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[DPRG] PWM Frequency and torque

Subject: [DPRG] PWM Frequency and torque
From: Ed Paradis legomaniac at gmail.com
Date: Tue Feb 27 06:54:24 CST 2007

Just something to watch out for:

My function generator's "Duty" knob changes the frequency as well as
the duty.  It really seems to control the "length of the off period"
of the squarewave.  Its some Tektronix model.

Most people assume constant frequency and variable duty, so this might
account for some of your observations.

Also my model can only produce 0-50% or 50%-100% duty cyles.  You have
to use the "invert" button to reach the other range.  So if you're
just looking at "how much the knob is turned," you may be estimating
the produced PWM incorrectly.

I've found that my function generator was pretty much useless until I
got a scope and could see what waveforms it was actually producing.


On 2/27/07, Vimal Shankar <vimalsshankar at yahoo.com> wrote:
> Hmm.. now I think this is an interesting issue that
> lot of people are getting interested in.
> My biggest problem is I see so many PWM based
> questions surfacing here and there sporadically.. and
> almost noone seems to agree with each other and many
> don' understand what's going on...
> Why is PWM so hard to understand and apply in
> practise...
> But I am seriously starting to get worried..
> I am feeling a negative energy around me.. :)
> It seems like people are really not "in tune" (pun
> unintended) with me using 250Hz to drive my motors..
> At any higher freq there is a HUGE drop is torque..
> But I will get my scope and see what's going on..
> > I have to believe that there is probably
> > a 50 line program you
> > could put into one of the 8 bit PICs or AVRs to do
> > exactly this.
> Wow.. is it possible that you have a sample ?
> Is the 50 lines ASM or HLL code ?
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