Using a Hall Effect sensor IC for high fields

[snarfherder]

I'm trying to use IC hall effect sensors for a school project *not homework, rather an ungraded research project*. Basically, we are trying to measure the magnetic field gradient inside of an experiment chamber. The chamber is surrounded by two huge copper coils that have about 1000A running through them - the magnitude of the B field is ~900 gauss max.

Problem is, the only hall effect sensors i can find max out at around 800 gauss. The sensors we are trying to use now are made by optek (3150), and are easy to use but have too high of a sensitivity. Is anyone familiar with a way we can extend the range of fields we can measure? I thought about using magnetic shielding (wrapping the sensors in mu metal or something similar), but this is problematic and I was hoping for a more accurate solution. Any suggestions?

 

[vk6kro]

1000 amps in a school project? Are you sure?


Hall probes are sensitive to fields at right angles to the front surface, so you could possibly have a greater field at, say, 45 degrees to this surface?

So, if you located the direction of the field and rotated the probe by some fixed angle, maybe you could calibrate it that way for the actual field.

Shielding materials may become projectiles at high magnetic fields.

 

[Bob S]

Digikey (www.digikey.com) has these Alegro Micro linear analog Hall Effect sensors in stock for about $3.99 ea (unit price). Their sensitivity is about 0.7 to 1.4 mV per volt. See
http://www.allegromicro.com/en/Products/Part_Numbers/1360/1360.pdf

Bob S.

 

[snarfherder]

thanks for the suggestion. Only problem is, we don't know the exact field strength (900 gauss is the field at which cyclotron resonance occurs, but the field may be much higher in areas) and I'm worried that the sensors will still saturate even at a 45 degree angle. I also had someone suggest that we try decreasing the temperature of the sensors using liquid nitrogen to decrease the sensitivity of the sensors, but that introduces uncertainties...

1000 amps in a school project? Are you sure?

yup. I'm trying to make level curves of the field strength in an electron cyclotron resonance (ECR) machine, which we use for plasma processing of semiconductor wafers. The magnetic field is generated by two huge axial toroidal copper coils; the field resembles a magnetic bottle, if you want to visualize it.

 

[snarfherder]

Digikey (www.digikey.com) has these Alegro Micro linear analog Hall Effect sensors in stock for about $3.99 ea (unit price). Their sensitivity is about 0.7 to 1.4 mV per volt. See
http://www.allegromicro.com/en/Products/Part_Numbers/1360/1360.pdf

Bob S.

Beautiful. .7mv/Gauss is exactly what I need, thanks.

 

[Mike_In_Plano]

At the extremes, you can build a coil around the sensor and drive towards / at null. I don't know how reasonable this is off hand due to the power dissipation of the coil, but I seem to recall driving one to 550 Gauss / Oersted once without too much fuss.

In any case, if your coil gets hot, you can always take short readings.

- Mike

PS Beware hall sensors bearing magnetic materials inside...

 

[Bob S]

PS Beware hall sensors bearing magnetic materials inside...

Some nonlinear bipolar switch Hall Effect sensors may have some magnetic material in it, but the linear analog sensors don't.

For a complete list of Allegro Hall Effect devices, see

http://www.allegromicro.com/en/Products/Categories/Sensors/index.asp

Bob S