On Friday 07 December 2007, John Kasunich wrote:
>Gene Heskett wrote:
>> I possibly didn't word that as precisely as I could. But at zero speed,
>> there truly is no signal to condition. Only if its moving can it generate
>> a signal.
>
>Not true. Hall and MR sensors are DC sensitive devices. From 1984 to
>1991 I worked at a company that makes MR based encoders. I designed the
>signal processing for one such encoder, which used an MR sensor and bias
>magnet to sense gear teeth. According to info on their website
>( http://www.avtron.com/tachs.htm ) it looks like they've gone away from
>the gear approach and now use a disk with the magnetic pattern directly
>imprinted on it.
>
>> Not for watching a 50 tooth gear on a headstock spindle turning 3k rpms.
>> That would be a 150 kilohertz signal, so this particular device then would
>> at the end of its range at 200 rpm in that scenario and it still wouldn't
>> have but a 7.2 degree resolution. That to me is not a very useful upper
>> speed limit, nor truly usable resolution for high precision threading.
>
>Shaft speed is in RPM, not Hz. A 50 tooth gear at 3000 RPM = 150,000
>counts per minute, which is only 2,500 Hz.
>
>Regards,
>
>John Kasunich
>
Can I plead that the real error = -ENOTENOUGHCOFFEE guys? :-)
Ok, so it can handle that scenario. But at 7.2 degrees per tooth, that
doesn't seem like enough resolution even for good thread cutting. What sort
of resolution are your machines using for that?
--
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)
The best diplomat I know is a fully activated phaser bank.
-- Scotty
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