Gene Heskett wrote: > On Monday 03 December 2007, Kirk Wallace wrote: >> Has anyone tried using a magnetic sensor such as a crankshaft position >> sensor for a spindle encoder? I would not have to protect this >> arrangement nearly so well as an optical system against oil and dirt. >> >> Initially, I found this part - AKL001-12E: >> >> http://www.nve.com/Downloads/gtsensor_catalog.pdf >> >> The "gear" and bias magnet would be easy to make and mount. I guess the >> tricky part is in dealing with the analog nature of the sensor, which >> means more than one or two components to wire, but no big deal. > > I'd think it would be an ideal solution. The response goes down to DC, and > obviously GMR is high speed too as its now being used in the new terrabyte > sized disk drives as the read head. > > There might be a physical problem with the bias fields when attempting to > develop an index pulse from an adjacent device, requiring more separation > than the usual opto thingy's need though. >
> > Here is a thought, cannibalize a 5 volt reed relay coil as the bias source, > you may be able to use one end of it for the gear teeth, and the other for > the index pulse detecting a piece of bailing or even picture hanger wire > going by for the index pulse. > Neat idea... at a former employer I worked on "pulse tachs" (really encoders, dunno why they called them tachs) that used hall effect sensors and a gear. Not suitable for very high resolution, but fine for a spindle. But we always used permanent magnets for bias, and I was assuming that Kirk would do the same. Using an electro-magnet has the disadvantage of needing a little power, but the advantage that whenever you turn the machine off, any metal chips that had been attracted to it would fall off or be easy to wipe away. Chips and permanent magnets are not a good combination, seems impossible to keep clean. Regards, John Kasunich ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
