On Monday 03 December 2007, John Kasunich wrote: >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 > Not to mention John, that hall effect devices are poisoned and rendered useless, often in just a day or so by even the hint of a petroleum based lubricant that might get splattered on them. And they are commonly built on a ceramic substrate that is a bit porous. I believe moreso than the epoxy B covering the top of the device. I once lost a very fine character generator keyboard for over a week cuz it got a lot of grit in its keys after several years service and gave it a good washout with WD-40. Three days later, and 9 dead keys, I called the maker and while ordering the keyswitches at about $12 ea, I was instructed to run, not walk, to the corporate kitchens dishwasher and run it thru at least 2 cycles, once with the usual dishwasher powdered soap, and once more to rinse it well. In the top rack. That stopped the keyswitch failures after about 2 more.
So the short message is: Keep your hall effect devices scrupulously clean. And not with solvents, good old soap and water. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The day after tomorrow is the third day of the rest of your life. ------------------------------------------------------------------------- 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
