Forwarded: Re: Flywheel encoder patterns

[Stephen Dubovsky]

At 11:25 AM 12/9/96 est, you wrote:
>
>one of the problems you will run into with a hall-effect sensor is 
>the tooth width.  Most sensor will switch low several mm before the 
>centre of the sensor and the tooth edge coincide, and switch high 
>again several mm afterwards.  This will limit your tooth width and 
>hence your resolution for a given diameter.  We find that at about 220 
>mm dia (flywheel size), the best H-E sensor we can get will allow us 
>60 teeth without resorting to teeth that look like feeler gauges.
>
>Andrew Rabbitt
>

This is simply a function of the hall effect sensor you are using, the
magnetic field, and the geometry of the configuration. (I assume you have
the standard setup, a magnet and sensor placed around the gear so that a
gear tooth 'closes' the loop.)  You can either go find a less sensitive
detector (or use an analog one w/ a different trip point) or reduce the
magnetic field. (either move it farther from the wheel, get a smaller one,
or 'short-circuit' some of its field w/ ferrous material).
SMD
--
Stephen Dubovsky
dubovsky at vt.edu

95 Yamaha FZR600
83 Porsche 911SC
84 Jeep Cherokee