On Thursday 06 December 2007, Kirk Wallace wrote: >Thanks for the lead Tony. > >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.
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. >This has gotten me to thinking about magnetism. My first guess with flag >sensors was that a ferrous flag would bridge the magnetic gap between a >magnet and a Hall sensor, so I set up a magnet and a 103SR such that the >magnet was just out of range to the sensor. When I placed a small screw >driver in between, I expected to trigger the sensor, but it didn't. Then >I placed the magnet in range, triggering the sensor, replaced the >screwdriver, which deactivated the sensor. So the flag seems to block or >perturb the magnetic field instead of conducting it. Which also makes >sense, but is not what I would have guessed. This magnetism is weird >stuff. The screwdrivers steel was a more easily magnetized medium than the air it displaced, so it effectively short circuited the field, reducing the field on the Hall or GMR device. Placed on the far side of the device, it may have drawn enough of the field lines across it to cause a trigger. I'm still puzzled by the 10 kilohertz response listed for this device. WTH? Its a GMR device, and GMR is now being used as the read head in modern hard drives, with data rates recovered from it at what is effectively a 3 gigahertz rate, so why is this device so darned slow? If I wanted to use it, I'd sure be calling their applications engineers to get the skinny on why their device is several thousand times slower. I have done that many times in the past, and at National Semi in particular, have found their people very knowledgeable. AMD was at one time similarly helpfull with a memory problem, and I would expect any semi house to be so if they wanted to win the design-ins. -- 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) You will be the last person to buy a Chrysler. ------------------------------------------------------------------------- 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
