Aten't there anenometers that work like this? With a oversize cup and a reference marker they can determine wind direction from the velocity variations. RP On 18/05/07, Russell McMahon wrote: > > 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 > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist