? on Mr Hall Effect

Tue Nov 10 18:48:48 GMT 1998

 No dis-respect intended (absolutely no flame) but I can't let this one slide...
I work with transistors every day-  never heard of a bipolar one with a "gate"
and certainly never heard of any transistor getting turned on by a magnetic
field (at least not one of practical magnitude).

OK--  thyristors (SCR's and Triacs)  may be considered bipolar devices and do
have terminals labeled "gate"---   I wouldn't call these things bipolar
transistors though.

Many electronic devices can be activated by an *electric* field and most
certainly by light... (as is the case with the phototransistor (or any
transistor))

Here is what "Physics"  second Edition by Tipler says:
-----------------------
"The force exerted by a magnetic field on a current-carrying wire is actually
exerted directly on the charge carriers in the wire, the electrons.  The force
is transferred to the wire by the forces which bind the electrons to the wire
at the surface.  Since the charge carriers themselves experience the magnetic
force when a current-carrying wire is in a magnetic field, the carriers are
accelerated toward one side of the wire.  This phenomenon, called the Hall
Effect, allows us to determine  the sign of the charge on the carrier......  It
also provides a convenient method for measuring magnetic fields.  "
-----------------------
The section goes on to discuss how you can measure this Hall effect (the higher
density of electrons at one edge of the conductor)  by measuring the voltage
difference across the end of a flat bar carrying current in a magnetic field.

Note that there is no transient behavior here-   only a presence of a magnetic
field and a current carrying conductor.

Just in case anyone else was interested...

comments invited.

________________________________________________
  Kevin Vannorsdel     IBM Arm Electronics Development
    408-256-6492                Tie 276-6492     kv at us.ibm.com

owner-diy_efi at efi332.eng.ohio-state.edu on 11/10/98 10:16:12 AM
Please respond to diy_efi at efi332.eng.ohio-state.edu
To: diy_efi at efi332.eng.ohio-state.edu
cc:
Subject: RE: ? on Mr Hall Effect

What  I recall of Hall Effect devices:

A bipolar transister
Gate can be turned on by the presence of a magnetic field.
The hardwired gate connection can be biased to alter the magnetic "turn-on"
threshold.

Similar to a photo-transistor in operating theory.

Regards,
Tom Butler

> -----Original Message-----
> From: Kevin Vannorsdel [SMTP:kv at us.ibm.com]
> Sent: Tuesday, November 10, 1998 12:43 PM
> To: diy_efi at efi332.eng.ohio-state.edu
> Subject: Re: ? on Mr Hall Effect
>
>
>  I have no knowledge of this particular sensor but correct me if I am
> wrong....
> The Hall Effect (proper) is not a transient thing right?  My recollection
> is
> that the Hall Effect occurs in the presence of a magnetic material... not
> only
> in the "passing" of it.
>
> Time to dig out my Physics 203 book!
>
> ________________________________________________
>   Kevin Vannorsdel     IBM Arm Electronics Development
>     408-256-6492                Tie 276-6492     kv at us.ibm.com
>
>
>
> owner-diy_efi at efi332.eng.ohio-state.edu on 11/10/98 08:35:25 AM
> Please respond to diy_efi at efi332.eng.ohio-state.edu
> To: diy_efi at efi332.eng.ohio-state.edu
> cc: diy_efi at esl.eng.ohio-state.edu
> Subject: Re: ? on Mr Hall Effect
>
>
>
>
> I think the teeth improve the magnetic coupling between the powered
> coil and the signal coil.   I would almost guess that the powered coil
> was powered by something other than a DC signal.  Basically the power
> coil to the signal coil is a transformer and putting the metal near it
> changes how the transformer acts and that is what is detected.
>
> I do not think a DVM would be able to detect the signal good enough.
> There would be only one change when you moved it in closer, and that
> would pass by the DVM way too fast to catch.
>
> All of those devices work on transients that are probably too fast to
> catch with a DVM.  If you have it, you may try feeding it into a sound
> card and see what the wave really looks like.  Also if you where
> spinning the disk past the sensor you would be able to detect the
> level out the output signal (average level) changing, but would owuld
> not be able to detect any of the waveforms themselves.  You might in
> the case be able to put the DVM on HZ (if yours had this) and count
> the number of teeth.
>
>    Roger
>
>  On Tue, 10 Nov 1998, Bruce Plecan wrote:
>
> > In the past, I done some trouble shooting with Hall Effect Devises.
> > Now, for the first time I hooked a meter to one with it sitting on the
> > table.  The one I'm starring at is a Toyota, it has a red lead, a white
> > lead, and a sheilded cable with ground.
> >   So being the Cone Shaped Hat Wearer that I am, I did the following.
> Using
> > a 9v battery, I grounded it to the shell of the sensor
> > applied + to the read lead, grounded the meter (DVM on V),
> > hooked the meter's lead to the white wire, and then tested it.
> > The test being held a gm crank disc near the tip of the toyota
> > sensor.  The meter just flickers as I expose it to the metal?.
> > I thought it would open and close as the metal came close to it?,
> > yes/no?..
> >   In various gm training references they show a pattern like
> >
> >        ___       ___       ___       ___
> > ___I      I___I     I___I      I___I      I
> >
> > Can someone splain this to me, or refer me to an online source for
> > accurate info?.
> > Thanks
> > Bruce
> >
> >
>