mcsman:
Curious how a Hall effect sensor works. The few data sheets I have looked at don't answer my basic question of what happens when the magnet is removed? I am thinking of the sensor usually mounted somewhere on a modern auto engine that times the injection/ignition system.Is there a sensor that detects when the magnet goes by the sensor?
Yes there are hall effect sensor switches that will create a pulse as the magnetic field approaches and leaves leaves the sensor's head. There are also analog hall effect sensors that generate a variable DC output voltage proportional to how strong a magnetic field it is sensing. Some hall-effect sensor switches latch on when say a 'north pole' of sufficient strength is sensed and will only unlatch when a reversed 'south pole' field is sensed. One has to study a specific hall-effect sensor's datasheet to be sure they are getting one that works for the applications at hand.
That is, reacts to the magnet, then relaxes when the magnet passes? How does it work on the systems that have "teeth" around the perimeter of the wheel, but missing one tooth to indicate TDC?
A hall effect sensor won't work just 'looking' at the face of a gear wheel, as the teeth have no magnetic field. Variable reluctance speed sensors are one kind of sensor that is often used with gear wheels, and they are not based on hall effect devices, at least not the ones I worked on in a oil refinery used on large compressors, turbines, and other rotating equipment.
I think I need to look at a lot more data sheets to figure this out
Datasheets are always your best friend when learning and selecting sensors and trying to match them to your application.
LeftyDave