Magnetic Field Sensor?

Question

I'm looking for a sensor that can detect large magnetic fields. Basically, I want a 1 when the field is greater than 75 Gauss, and a 0 when it's less than 75 Gauss.

I believed (EDIT: Wrongly!) Hall Effect sensors rely on moving through a magnetic field. Unfortunately, my application does not permit me to move through the field, and the field is not changing. It's since been pointed out that the Hall Effect does not rely on a change in the magnetic field. However, I still do not have any control over the orientation of the field.

Does anyone have any suggestions on how to detect such a magnetic field?

Answer 1

The Allegro A1301 is a cheap analogue hall effect sensor. It's a 3 pin device: 5V GND and OUT. It outputs 2.5mV per Gauss detected.

It's very easy to use, here's a project I used it in.

Answer 2

The Hall effect doesn't depend on variations in the magnetic field (i.e., motion relative to the field or time-varying field), as far as I know, it only depends on the strength of the field, and the orientation relative to the sensor.

Alternately you could look into 'magnetic reed switches'.

Answer 3

A hall effect sensor can detect large magnetic fields relatively easily. This is done by measuring the variance in resistance. You allow a DC current to pass, the Magnetic field will deflect electrons, increasing the DC resistance.

This gives you a magnetic field dependent resistor. These will be able to measure the current in 2 planes, the path of the current will be unaffected by a magnetic field in it's direction.

If you need to measure in 3 directions, I would suggest 2 to detect magnitude of field, and a general idea of direction. With 3 you can get a rather precise idea of direction.

There is no motion of the sensor required.

Answer 4

Are you sure that you want it to both turn off and on at 75 Gauss? Magnetic fields are variable, and you might get a lot of noise at that edge. Most Hall effect switches are designed with Hysteresis, or a Schmitt Trigger, for this reason.

With this knowledge, you can start looking at Digikey's selection of magnetic sensors.

The Allegro A3295 is an example of such a device. It turns on at 75 Gauss, and turns off once the field decays to 5 Gauss.

Answer 5

If you dont need high speed, look at reed contacts.

Answer 6

LOL 75 Gauss means never having to say your circuit failed; the electrons in there aren't going in any loop the magnet didn't pick first! Pick an optical sensor (e.g. a mineral anvil or mirror, or more easily a simple F/O loop) and remotely detect changes in light transmission and polarization to confirm the field characteristics. Are you making bets with http://www.magnet.fsu.edu/ , installing your first maglev train, or just in charge of field cleaning COTS naval artillery? I knew One Piece was popular, but not maglev trains....