Flywheel/Encoder patterns

[Mazda Ebrahimi]

RABBITT_Andrew at mv8.orbeng.com.au wrote:
> 
> >can you explain your thinking on the 60 tooth wheel.  I know
> >Electromotive uses both the 60 tooth design and the 120 tooth design.
> 
> We're looking at a 60 tooth wheel (over a 36 tooth) to improve our
> timing accuracy when we use missing tooth reference markers.
> 
> We use the industry standard practice of measuring time interval
> between edges and using this time to extrapolate the position over the
> next interval.  Usually clocks with a 250ns to 1us time resolution are
> used to drive the counters.
> 
> There are a couple of other issues driving this too, which are
> specific to our design and not applicable to MPI systems.
> 
> Andrew Rabbitt

Hi Andrew,
This is exactly what I was thinking about when I decided to use 180 
teeth.  I figured if I use a lower resolution, I would have to calculate 
RPM (which I have to do anyway), then calculate time elapsed per degree 
of rotation (which is estimated), and load my counter.  By going to 180 
teeth, I've eliminated the last two steps, and all events happen once 
per degree based on an actual signal, not an estimated value.  I realize 
that this approach also generates more interrupts per revolution, but it 
seems easier to work with.

Best Regards, Mazda