> Lately I wonder -- is it really rotating at a constant rate?
> Or are there significant angular accelerations and decelerations 
> between pulses?

What they said.
ie as others have suggested, a brute force and easy method is a multi 
pulse per turn sensor.
Many possibilities - slotted disk, optically striped track, multipole 
magnet, ... .
You could even have a semicontinuous method by having a sinusoidally 
(or other) modulated sensor and measure the rate of change of signal.

BUT, can it in fact alter significantly in a single turn?
If you know moment of inertia and energy sources / sinks then you can 
determine the maximum possible range of speed changes within a single 
cycle. That will then tell you whether you need to know more 
accurately.

Knowing what it is that you are measuring would help us comment.




        Russell


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