Re: Analog encoder

OK Arne,
You are getting it now! Basically all shaft or linear encoders are linear devices. Many has built in electronics to convert
the analog output signal to a digital signal. Some high end ones leaves the conversion to the CNC system. Remember the A-D
converter I mentioned earlier.

It is easy to realize that it must be analog. Think about the slots being blocked and no light comes thorough. Now move or
turn it just a little bit, just a fraction of a slot. A little light will leak trough. Turn it a hair more and you get still
more. That will continue until you reach a maximum of light coming through and then it will start to fall. The light coming
through is measured with a photocell-transistor-diode and the output will be an analog electrical signal. If properly designed,
it will look like a reasonable sine wave.

And you are correct about the shaft encoder that you disassembled. It is hard to decipher your graphics but the stationary
grating is what you apparently saw.

The key to understanding the principle is to not count "slots" you must count light pulses. Of course, there will be one light
pulse for each equivalent turn/movement .

Bertho Boman
==================================

"Arne Chr. Jorgensen" wrote:

> From: "Arne Chr. Jorgensen" <instel@...>
>
> Hi again,
>
> Bertho Boman:
>
> I must have lost track of something. Do you mean that these dual
> gratings would produce a usable sine wave ?
>
> Here is a few notes:
>
> Back in the mid 80's, I studied a broken encoder from BEI
> electronics. If was some electronics inside it, because the outputs
> were differential, - I think. The disk was made of glass, - and had
> cracked.
>
> The disc had segments, or lines about 1/2" long. Underneath was a
> stationary glass plate with similar lines, but these were offset a
> bit :
>
> I will try to draw one. O !!!!!!!!!!!""""""----____!
>
> The "O" is the center hole. The active area is between the "!" and
> instead of a straight line or grating, - the lines was offset about
> 1/3 of line width.
> Behind the stationary glass plate, - looking as I have drawn it,
> was an ordinary light bulb. The sensors was large and above the
> rotating disk.
>
> I newer quite understood why the stationary pattern was made like
> this, but thought it some how had to make a sine wave. But the
> output was shaped as a square wave. I guess the electronic circuits
> had done that. The more I think of it, - the more I start to
> understand this - I think. What made me confused was the fact that
> I believed it would just read one line at any one time, not as you
> say - looking at many "slots" at the same time. This would also make
> some sense to the use of a light bulb instead of LED's.
>
> Do you think I am right or wrong here ?
>
> Note: I remember the earlier note from Ian, but I didn't understand
> what he meant. Sorry.
>
> //ARNE
>