On Friday 07 December 2007, Tony Bussan wrote: >> >I cruised some of the Honeywell sensor pages and the Digikey catalog >> >page with the 1GP4001 on it. I had studied the previous Digikey page >> >because I was interested in the Honeywell 103SR13A-1 which are installed >> >on my Hardinge lathe. I am guessing that for rigid tapping that the >> >sensor will need the zero speed feature. It did not seem obvious to me >> >which sensors where zero speed capable. What should I look for that >> >would indicate this? >> >> First rule of magnetics is that a coil as and inductance is a velocity >> sensitive device, so there is a minimum speed below which it doesn't work. > >Zero speed capability has to do with the signal conditioning circuit. Some >sensors use an edge detect, some use a level comparator with hysterisis, and >some actually have an A/D and digital processing to constantly calculate >switch points. There are probably more that I am not thinking of right now. > 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.
>> As far as I know, all Hall and GMR devices are amplitude sensitive, not >> velicity. Even a reed switch fits this category if one doesn't mind the >> mechanical lag which could be in the milliseconds range. > >Be careful analyzing Magneto-resistive, it is amplitude sensitive until >saturated, and it is sensitive to the angle of the flux vector. It could be that the internal steering of the field to get maximum gain is a ferrous material, in which case its inductance will slow things down. That would be one possible explanation for the speed loss. 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. 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. >> 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. -- 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) Unix is a Registered Bell of AT&T Trademark Laboratories. -- Donn Seeley ------------------------------------------------------------------------- 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