Techniques for measureing shaft speed

[frustrated]

We have been given a project request, with more restrictions than goals, and need to find a way of measuring shaft speed or position. A 5v digital pulse needs to occur at each 1/3rd degree of rotation. There is no physical reference that an encoder can be mounted to, but an optical reference can be used. So my question is what are the various methods we could use to either measure shaft speed or shaft position. Thanks for the help mates.

 

[nbucska]

Do you have to measure the position when stopped or only
while spinning ? What is the spin range ? Position error ? <nbucska@pcperipherals.com>

 

[frustrated]

The position only has to be measured while spinning 247.3RPM to 1236.6RPM. Position has to be accurate to 1/3rd of a degree. Hope that helped.

 

[dgallagher]

This application note may help for position measurement:

http://www.reliabilitydirect.com/appnotes/eccentricity.html

Any of these tach sensors can accomodate your speed readings:

http://www.reliabilitydirect.com/selfpoweredsensorproducts/selfpoweredsensors.htm

Cheers,
Dave G.

 

[frustrated]

Thanks again,
That really helped.

 

[nbucska]

This is about .1 % accuracy. You need to add some kind of
sensor preferrably an optical tachometer with e.g. 1000
lines/rev. Use a phase lock loop to filter it out.

If the inertia is large relative to the forces -- i.e. the
acceleration is minuscule -- you may get by with less
samples per rev.
<nbucska@pcperipherals.com>