hbg6@QIS1.mcdphx.mot.com (John Schuch) (06/20/91)
After reading the construction article "Build A Solid State Compass" ( June 91, Radio Electronics ) I thought of a different application of the thing but have a question for the net. I understand Hall Effect Sensors produce a voltage when magnetic lines of flux pass through their body at a right angle. Does the output vary depending on the polarity of the magnetism? That is, is the output different depending on whether you place the North end or South end of a bar magnet next to the device? Also; Has anyone out there built one of these? Anyone know who sells HES in low quantities? (Sprague UGN3503U) Anyone interested in how mine turns out :-) Thanks, John ..................................................................... Send mail to hbg6@QIS1.mcdphx.mot.com ..................................................................... John Schuch - Motorola Inc., Computer Systems Division (602)438-3008 All opinions expressed are mine and not Motorolas, their loss. .....................................................................
neufeld@aurora.physics.utoronto.ca (Christopher Neufeld) (06/21/91)
In article <12536@qisoff.phx.mcd.mot.com> hbg6@QIS1.mcdphx.mot.com (John Schuch) writes: > >I understand Hall Effect Sensors produce a voltage when magnetic lines >of flux pass through their body at a right angle. Does the output vary >depending on the polarity of the magnetism? That is, is the output >different depending on whether you place the North end or South end >of a bar magnet next to the device? > The Hall effect is pretty easy to understand once you hear the details of operation. It's a four terminal measurement. Say you have a square piece of metal, with leads at the middles of the four faces. A steady current is fed across the face of the square through two of the leads. If a magnetic field is threading the face of the square then the charge carriers will experience a Lorentz force tending to push them up against one side of the square. The other two wires are held at a voltage so that no net current flows through them. This is the Hall voltage, the voltage which is set up at right angles to both the magnetic field lines and the current density vector. If the magnetic field lines change direction, so that they go through the conductor in the other direction, then the Hall voltage does change polarity. The measurement is only sensitive to the perpendicular component of the magnetic field, though I wonder if a six terminal device mightn't also work to measure the fields in both directions at right angles to the current density vector. Note that the Hall effect is felt by the "carriers" in the metal. This has interesting effects, among them that two different metals can have Hall resistances of opposite signs because the carriers can be hole-type. Dredging up old memories of undergrad courses I believe that aluminum is an example of a metal that exhibits a Hall effect indicative of positive charge carriers. I've used one of these before. We calibrated it first with a rotating coil gaussmetre and used it to measure fields of up to a couple of Tesla in a water-cooled magnet. -- 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" |