>But if I hook up my 10 MHz clock and count the time between pulses, my
>accuracy is +1/-0 count out of 1,250,000 counts. That's a whole lot
>more accurate.
This is the key thing that misses the entire point. It's not the accuracy of
the time measurement that's the issue. It is the uncertainty of when position
transitions are crossed. With either electromagnetic or optical sensors, that
uncertainty is 1/8th of a revolution with an 8 ppr transducer. The fact that
you can measure the time between "pulses" accurately is not disputed. The
issue is that the rotational distance (hence velocity) 8 pulses represents is
known only to +/- 12.5%.
Again, no practical matter since no one would try to measure wind speed with
such a small sample and expect high accuracy. Nor can I think of a reason why
you would need to in this application.
Al
AB2ZY
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