🚀 go-pugleaf

On Wed, 18 Jun 2003 11:53:17 +0200, "Iman Habib"
<imanhabibREMOVETHIS@eml.cc> wrote:

<snip>
>
>After some thinking I came to the conclusion that capacitors would be
>an excellent choice. The idea was mostly due to the digital calipers
>I have. It has an accuracy of 0.01 mm and I read somewhere that
>the sensor is essentially a linear capacitor strip running inside the
>calipers slider. And I thought the actual electronics shouldn't be that
>expensive as the caliper itself costs about 30$.
>

Don't your calipers have a long rack and pinion gear like the old
dial calipers?  I assumed the digital encoding was strictly rotary.
If it uses capacitors, it is probably in the same way that you would
use a slotted disk with photo-optical methods:  strictly for counting.
That will give you best accuracy and linearity.

If you want to avoid gearing, tehn all you need is a linear grating
of some sort.  If you want to get really fancy, you can interpolate
between the teeth to get better resolution.  With an optical
system, you have 2 sensors with a slight offset, so that one is
being uncovered while the other is being covered by a tooth.
Similar idea will work with a capacitive system, where you are
looking at the capacitive coupling between the rotor tooth and
two sensor plates.   More excitiation passes through to the
sensor closest.



Bob Masta
tech(AT)daqarta(DOT)com
 
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