Hall Effect Gear Tooth Sensor

[MTN-KAT]

[Bohdan snidely speaks...] 
-Huh?  Magnetization of gear teeth for "proper polarity"?  You guys better
-read up on the Hall Effect.  All that is required is something which will
-block/unblock a magnetic field (i.e., something that is ferromagnetic).

-Sze's SEMICONDUCTOR DEVICE PHYSICS is a good starting place...and it's readable,
-too!

-Bohdan

Thanks for the info, I'll check this book out.

[Jim explains...] 
-The following bizarre ASCII-gram shows the way the sensors are usually
-used.  A magnet (MM) is slapped right on the face of the sensor (HH)
-and a ferrous metal clip ("|+-") is routed from the other face of the
-magnet to make a gap in the vicinity of the other side of the sensor.
-As the ferrous teeth (Fe) of the gear pass by the gap they "complete"
-the magnetic circuit which increases the flux through the sensor.  A
-similar arrangement is used for distributor sensors.

-                   FeFe
-                 FeFeFe
-       +-----  FeFeFeFe
-       |MMHH-    FeFeFe
-                   FeFe
-                     Fe
-                   FeFe
-                 FeFeFe
-               FeFeFeFe
-                 FeFeFe

-Jim

I dug out both of my college Physics texts in a vain attempt to correct my
interpretation of the texts explanation of the Hall Effect. I can see how the 
sensor described above would work. Its 'amazing' how much better one can
understand text materials when the ideas are actually put to use. ;)
I also looked at the booklet that I had ordered with my Panasonic Hall Effect
sensors, every application description shows the sensor in a stand-alone 
design. They are all merely simple magnetic switches without anything even
vaguely resembling the above diagram. Maybe they don't understand either? :):)
This new information changes my engine position sensor design significantly!!!

Thank You very much Jim for spending the time to explain this to me and 
anyone else who had a somewhat limited knowledge of Hall Effect sensor 
applications.

Millam