Newsgroups: sci.electronics
Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!aurora.physics.utoronto.ca!neufeld
From: neufeld@aurora.physics.utoronto.ca (Christopher Neufeld)
Subject: Re: Hall Effect Sensor
Message-ID: <1991Jun24.232559.3004@helios.physics.utoronto.ca>
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Organization: University of Toronto Physics/Astronomy/CITA
Date: Mon, 24 Jun 1991 23:25:59 GMT


keving@cheetah.inmos.co.uk  (Kevin Cameron) writes:

Followup-To: Hall Effect Sensor

This really fouled up my machine, it refused to post off-site, so I'm
restarting the thread manually.

>I always wanted to build a Hall-effect compass - but never got round to it.
>  [ goes on to discuss nulling field coil and Hall effect probe ]

   This is not the way to go. The Hall effect is not strong enough to
pick up gauss-sized fields easily. It's usually used to measure fields
some ten thousand times larger. At such low fields you'll have real
problems with thermally induced voltages when you try to measure the
voltage across the sample. Further, the errors will be large enough to
make bearing readings (from knowledge of the component in two different
directions) essentially useless.
   Now, a clever scheme which ought to be workable is a fluxgate
magnetometer. I won't go into details of the construction, you can find
them in any IEEE proceedings on magnetism. You need a signal generator
and a way to extract harmonics of the input frequency, then some nulling
and sensing coils, with a material chosen to saturate magnetically in
the regime of interest. You can buy packaged fluxgate magnetometers the
size of a 35mm film case, tri-axial, with analog outputs proportional to
the magnetic field strength along each axis, for about $3000. That
package contains everything, including the multiplexing hardware,
frequency generator and analyzer, and three fluxgates. It just takes
regulated supply voltages in. I offer this as an example that the thing
is possible for not exorbitant amounts of money, and in a small case.

>Kevin Cameron         INMOS, 1000 Aztec West, Almondsbury, Bristol BS12 4SQ, UK
>kevin@inmos.co.uk     Tel: (UK) 0454 616 616 x364, Fax: 617 910


-- 
 Christopher Neufeld....Just a graduate student  | If ignorance is bliss
 neufeld@aurora.physics.utoronto.ca    Ad astra  | why aren't there more
 cneufeld@{pnet91,pro-cco}.cts.com               | happy people?
 "Don't edit reality for the sake of simplicity" |