Re: [CAD_CAM_EDM_DRO] Hall Effect

james owens wrote:

> From: "james owens" <wotisname@...>
>
> Hi,
>
> Being a novice at electronics maybe there is someone on the list that
> could explaine why the following cannot be done.
>
> Take a 1/4" internal diameter tube of aluminum and mill a 3/16" slot
> down it then fill itwith high grade ball-bearings. You have just made
> a very accurate scale. If you then move a Hall-Effect device alone it
> lenth what kind of signel do you get, is it analog or digital. If the
> former could the signel then be feed into an analog/digital converter
> the rest is easy.

If the hall effect devices are digital, then the output will be
digital. If you had 2 sensors and 2 magnets
spaced, say, 3/8" apart for quadrature, you would get a quadrature
encoder like signal, with a cycle
of 4/inch. By counting every transition, you would have an encoder with
resolution of 1/16".
Hmmm, not very useful.

By using analog hall sensors, you'd get sinals that could be
interpolated, but it sounds VERY
tricky to get decent resolution with this. There's no need to slot the
tube, it could be used
as is. One other problem is 'high grade' ball bearings are
non-magnetic. You'd need steel
balls that are magnetic. The commercial units use an AC signal, and
sense the balls by
induction. Yes, there are scales built just exactly this way, Matt
Shaver mentioned the
name just a few days ago. There are competing ads in the magazines that
seem to imply
that if you get so much as a magetized screwdriver near one of these
scales, you have to have
the manufacturer come out and demagnetize and recalibrate the scale for
you.

Jon