Re: That encoder stuff.

Re: Encoder output.
The exact shape of the analog output depends on may variables and as you said, straight parallel gratings will not necessary
give a perfect sine wave, it would be closer to a triangular wave. There are many reasons for not being a perfect sine wave,
there is light leakage because of not zero spacing between gratings, misalignment and sensor non-linearity for example.

The two important things are:

1: The output does not change shape regardless of SPEED as long as your electronics is fast enough and you do not exceed the
speed of light.

2: The output is an analog signal that is later converted to digital.


Re: Digital Tach.
All the digital tachs that I have seen has used a digital input from a regular encoder and then calculated the speed from pulse
timing.

On a high resolution system with an A-D converter it does not have to be a sine wave. A triangular wave would be more desirable
anyhow. As long as the system knows the shape, it can calculate the position.
Bertho
========================================

> "Arne Chr. Jorgensen" <instel@...> wrote:
> -------------> snip
> All I know is that it is difficult to get a sine wave that keep it's shape independent of the angular velocity.
>
> The L290 chip from SGS is a 14 pin dip package that will give you a
> tacho signal from an encoder, but in order to have it linear, you
> have to use encoders with a perfect sine wave. I have not been able
> to get it correct with the encoders I have.
> --------------- > snip