On Wednesday, August 04, 2010 12:21:10 pm Don Stanley did opine:
> Hi Gene:
> I considered saying the Sum of the 3 phase currents is zero, except for
> harmonic distortion and voltage difference, I decided not to complicate
> the message.
>
> On Sat, Jul 31, 2010 at 12:28 PM, Gene Heskett
<[email protected]>wrote:
> > that 3 phase 440 hz drive to the
> > headwheel motors was actually 3 separate oscillators whose feedback to
> > maintain the phase angles between them was mixed with the detected
> > time base errors in order to speed up the feedback loop and make it
> > stable, each oscillator then seeing the applied error in real time.
>
> Having watched the world of electronics got from all analog to all
> digital. I am curious where these drives were in the transition. Do you
> remember the basics of the circuit to synchronize the phases? No big
> deal, just curious.
Gee, that goes way back. I _think_ it was a 3 stage j-k of some sort, with
a common clock a (nominally, it was the clock being controlled for the
sync) running at 1200hz, which controlled the pace, and they were
interlocked to force the correct rotation sequence at startup, a ripple
counter in other words. That 400 hz square wave was then filtered to
something resembling a sine wave and fed to the transistorized power
amplifiers. Most assuredly NOT how I'd do it today for small motors, today
I would see if the Ramsey Electronics class D audio amplifier could be
harnessed as its very very efficient, capable to making 25 to 40 watts of
speaker driving output in a TO-5 can without any heat sinking. And, with
the carrier being largely filtered from the output, no reason many of them
couldn't be paralleled to get almost any reasonable level of servo power.
> > Here in Weston, WV, we have
> > one of those ma & pa ancient mary (AM) radio stations that does an
> > excellent job of keeping us up to date on such goings on.
>
> I also live on a single feed thirty miles off the power grid in South
> West VA.
A 2.5 hour drive maybe. ;-)
> We usually get 17.5 flickers before the outage. I run the system
> computer and
> electronics through a UPS and hope the joint following errors shut the
> system
> off before damage. The spindle and axis servo are direct to the AC power
> with
> linear power supplies; which can maintain voltage through small
> flickers. The shop radio tells me when flickers start (snicker).
That's a full blown chuckle. ;-) But how long did it take to arrive at
that 17.5 (average I assume) figure? Here, its 3 recycles of the
substation switch before it gives up after some drunk takes down a power
pole. ;-)
And obviously I'm dead on the first one even if the cpu does have a UPS.
But I've been lucky, the only broken bits have been my own stupidity. :(
--
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)
management, n.:
The art of getting other people to do all the work.
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