Gene Heskett wrote: > I possibly didn't word that as precisely as I could. But at zero speed, there > truly is no signal to condition. Only if its moving can it generate a > signal. > A Hall effect device is sensitive to a stationary magnetic field, unlike a coil of wire, which requires a moving field to sense anything. > Also, I believe here is a difference between Magneto-Resistive and the > so-called GMR, which takes place on a physical scale in the disk heads that > is in the sub-micron range. GMR was only discovered maybe 15 years ago, and > its taken all this time to get it into disk drives, in a head that flies > maybe 2 microns above the disk surface. IBM pioneered GMR heads probably 15 years ago, and had them in their proprietary drives a few years after that. High-end PC-class drives have had them since the late 90's. Part of that time was in developing > a write head that put the magnetic domains on the disk so they were > vertically aligned, which raised the data density per square inch by a factor > of about 100 compared to longitudinal recording methods used previously. > No, the vertical recording has nothing to do with GMR, but a GMR head is required to read the signal. Essentially ALL hard drives have been using GMR since before 2000, but only the 500 GB up drives are using vertical recording. > >>>I'm still puzzled by the 10 kilohertz response listed for this device. >>>WTH? >> >>The upper limit on frequency is most likely due to the signal processing >>circuit. I would bet that it has a low pass filter for noise immunity. You >>really don't want the sensor that sensitive to mechanical, magnetic or >>electrical noise. 10 kHz is pretty fast in mechanical terms. > > > Not for watching a 50 tooth gear on a headstock spindle turning 3k rpms. > That > would be a 150 kilohertz signal, so this particular device then would at the > end of its range at 200 rpm in that scenario and it still wouldn't have but a > 7.2 degree resolution. That to me is not a very useful upper speed limit, > nor truly usable resolution for high precision threading. > No, there are 60 seconds in a minute. 3000 PRM * 50 teeth / 60 secs/min = 2500 Hz. Your 150,000 is cycles/MINUTE.
Jon ------------------------------------------------------------------------- SF.Net email is sponsored by: Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
