Re: [CAD_CAM_EDM_DRO] Hall Effect

In a message dated 18-March-00 07:02:32 Central Standard Time,
wotisname@... writes:

<< 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. >>

First, even the most-expensive/finest-accuracy balls would surely have an
"accumulative" error which would be worse than the "thousandts of inch per
foot" error than even a cheap purpose-made linear scale. And surely the
linear-total would vary wildly with every tiny change in ambient temperature!
Perhaps even more importantly, good "digital" or "snap-action" Hall-sensors
exhibit hysteresis. You admit to being a "novice at electronics...", so,
forgive if I define that for this pupose: That means it'd "switch on" as the
sensor passed in one direction, but it'd "stay on" if the direction of
movement was reversed for a tad, and not "switch off" until PAST the point it
had switched-on. This detail would be "OK" if you read in only one
direction, but no good if you reverse table-direction, which is routine, of
course!

This design of linear-encoder would be roughly like measuring with a
yard-stick and marking with chalk! P.S: I am not a "professional" machinist
nor electronic technician. I just "do that" to keep out of trouble with...
Nevermind.