In order to tell if there are accelerations/decelerations in the rotation
rate, use a rotary encoder as described below, and run the pulse stream into a
frequency/voltage converter.  At constant speed, the outout will be a DC
voltage.  Variations in speed show up as shifts in DC level.  

Jon




On Thu, 17 May 2007 22:56:24 -0700, Lee Jones wrote
> > What are good methods for measuring rotation rate?
> >
> > I have a rotating device.  Currently I measure how fast it rotates
> > using a one-pulse-per-revolution optical sensor, and then assume
> > that it rotates at a fairly constant rate between pulses.
> >
> > Lately I wonder -- is it really rotating at a constant rate?
> > Or are there significant angular accelerations and decelerations
> > between pulses?
> >
> > I suppose some sort of rotary encoder (along with accurately timing
> > the width of each pulse) could possibly work.
> 
> > It would be more convenient if I could bolt something to the outside,
> > with a pattern ring about a foot in diameter glued to the stationary
> > part and a sensor bolted to the rotating part. (Or vice versa).
> > (Perhaps replacing, the one-pulse-per-revolution sensor I have now).
> 
> Construct a flat disk with identical evenly spaces slots around
> the outside edge.  Install disk on shaft, hopefully with little
> wobble or runout.  Put an LED on one side of disk, shining through
> slots.  Put a photo diode on other side of disk.  As shaft rotates,
> photo diode output is train of pulses.
> 
> Non contact, so limiting factors are response speed of photo diode
> and computational ability of microprocessor (at some speed, it will
> start to miss pulses -- upper bound determined by number of slots,
> shaft speed, any hardware buffering, CPU speed, quality of software,
> species of dead fish(*), etc).
> 
> (*) I hadn't seen it mentioned on PIClist in a while, so ... :-)
> 
> 						Lee Jones
> 
> old PIClist 
> output is train of pulses 
> of
> 
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