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From: neufeld@aurora.physics.utoronto.ca (Christopher Neufeld)
Subject: Re: Hall Effect Sensor
Message-ID: <1991Jun25.161850.11815@helios.physics.utoronto.ca>
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Organization: University of Toronto Physics/Astronomy/CITA
References: <1991Jun24.232559.3004@helios.physics.utoronto.ca> <16869@ganymede.inmos.co.uk>
Date: Tue, 25 Jun 1991 16:18:50 GMT

In article <16869@ganymede.inmos.co.uk> kevin@cheetah.inmos.co.uk (Kevin Cameron) writes:
>|> keving@cheetah.inmos.co.uk  (Kevin Cameron) writes:
>|> >I always wanted to build a Hall-effect compass - but never got round to it.
>|> 
>|>    This is not the way to go. The Hall effect is not strong enough to
>      ^^^^^^^^^^^^^^^^^^^^^^^^^^
>|>the regime of interest. You can buy packaged fluxgate magnetometers the
>|> the magnetic field strength along each axis, for about $3000. That
>                                                          ^^^^^
>|>  Christopher Neufeld....Just a graduate student  | If ignorance is bliss
>
>I'm sure you're right about it working, but $3000 seems a bit expensive
>compared to an ordinary magnetic compass. You could probably buy a global
>positioning system for that price (Inmos have developed a pocket one based
>on transputers).
>
   Well, that one is more sophisticated than it has to be for your
purposes. Potted in epoxy, intensities measured to high precision, you
could probably use it to detect submarines. A cobbled-together fluxgate
magnetometer shouldn't run $3000. I just gave that as an example. A
similar Hall effect sensor would contain a variable current power
supply, a precision variable voltage source and meter, and some logic to
calculate the field given current and voltage values. That stuff isn't
cheap if bought as commercial products.

>It only needs to be accurate to ~1 degree to be competitive with a
>magnetic compass on performance, but it would need to cost nearer $100
>in total to be worth buying instead.
>
>How strong is the Earth's magnetic field anyway?
>
   About 0.5 to 1.0 Gauss, or under 1e-4 Tesla. Hall effect sensors
which I've used have been for fields in the neighbourhood of 0.5 to 2.0
Tesla. You've got a factor of 10000 to recover there.

>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" |